Rozprawy doktorskie: „Octahedral shear stress model”

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Zhang, Xuesong, i n/a. "Punching Shear Failure Analysis of Reinforced Concrete Flat Plates Using Simplified Ust Failure Criterion". Griffith University. School of Engineering, 2003. http://www4.gu.edu.au:8080/adt-root/public/adt-QGU20051104.153239.

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Failure criteria play a vital role in the numerical analysis of reinforced concrete structures. The current failure criteria can be classified into two types, namely the empirical and theoretical failure criteria. Empirical failure criteria normally lack reasonable theoretical backgrounds, while theoretical ones either involve too many parameters or ignore the effects of intermediate principal stress on the concrete strength. Based on the octahedral shear stress model and the concrete tensile strength under the state of triaxial and uniaxial stress, a new failure criterion, that is, the simplified unified strength theory (UST), is developed by simplifiing the five-parameter UST for the analysis of reinforced concrete structures. According to the simplified UST failure criterion, the concrete strength is influenced by the maximum and intermediate principal shear stresses together with the corresponding normal stresses. Moreover, the effect of hydrostatic pressure on the concrete strength is also taken into account. The failure criterion involves three concrete strengths, namely the uniaxial tensile and compressive strengths and the equal biaxial compressive strength. In the numerical analysis, a degenerated shell element with the layered approach is adopted for the simulation of concrete structures. In the layered approach, concrete is divided into several layers over the thickness of the elements and reinforcing steel is smeared into the corresponding number of layers of equivalent thickness. In each concrete layer, three-dimensional stresses are calculated at the integration points. For the material modelling, concrete is treated as isotropic material until cracking occurs. Cracked concrete is treated as an orthotropic material incorporating tension stiffening and the reduction of cracked shear stiffness. Meanwhile, the smeared craclc model is employed. The bending reinforcements and the stirrups are simulated using a trilinear material model. To verify the correctness of the simplified UST failure criterion, comparisons are made with concrete triaxial empirical results as well as with the Kupfer and the Ottosen failure criteria. Finally, the proposed failure criterion is used for the flexural analysis of simply supported reinforced concrete beams. Also conducted are the punching shear analyses of single- and multi-column-slab connections and of half-scale flat plate models. In view of its accuracy and capabilities, the simplified UST failure criterion may be used to analyse beam- and slab-type reinforced concrete structures.

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Zhang, Xuesong. "Punching Shear Failure Analysis of Reinforced Concrete Flat Plates Using Simplified Ust Failure Criterion". Thesis, Griffith University, 2003. http://hdl.handle.net/10072/365777.

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Failure criteria play a vital role in the numerical analysis of reinforced concrete structures. The current failure criteria can be classified into two types, namely the empirical and theoretical failure criteria. Empirical failure criteria normally lack reasonable theoretical backgrounds, while theoretical ones either involve too many parameters or ignore the effects of intermediate principal stress on the concrete strength. Based on the octahedral shear stress model and the concrete tensile strength under the state of triaxial and uniaxial stress, a new failure criterion, that is, the simplified unified strength theory (UST), is developed by simplifiing the five-parameter UST for the analysis of reinforced concrete structures. According to the simplified UST failure criterion, the concrete strength is influenced by the maximum and intermediate principal shear stresses together with the corresponding normal stresses. Moreover, the effect of hydrostatic pressure on the concrete strength is also taken into account. The failure criterion involves three concrete strengths, namely the uniaxial tensile and compressive strengths and the equal biaxial compressive strength. In the numerical analysis, a degenerated shell element with the layered approach is adopted for the simulation of concrete structures. In the layered approach, concrete is divided into several layers over the thickness of the elements and reinforcing steel is smeared into the corresponding number of layers of equivalent thickness. In each concrete layer, three-dimensional stresses are calculated at the integration points. For the material modelling, concrete is treated as isotropic material until cracking occurs. Cracked concrete is treated as an orthotropic material incorporating tension stiffening and the reduction of cracked shear stiffness. Meanwhile, the smeared craclc model is employed. The bending reinforcements and the stirrups are simulated using a trilinear material model. To verify the correctness of the simplified UST failure criterion, comparisons are made with concrete triaxial empirical results as well as with the Kupfer and the Ottosen failure criteria. Finally, the proposed failure criterion is used for the flexural analysis of simply supported reinforced concrete beams. Also conducted are the punching shear analyses of single- and multi-column-slab connections and of half-scale flat plate models. In view of its accuracy and capabilities, the simplified UST failure criterion may be used to analyse beam- and slab-type reinforced concrete structures.
Thesis (Masters)
Master of Philosophy (MPhil)
School of Engineering
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Yadav, Priti. "Multiscale Modelling of Proximal Femur Growth : Importance of Geometry and Influence of Load". Doctoral thesis, KTH, Strukturmekanik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-209149.

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Longitudinal growth of long bone occurs at growth plates by a process called endochondral ossification. Endochondral ossification is affected by both biological and mechanical factors. This thesis focuses on the mechanical modulation of femoral bone growth occurring at the proximal growth plate, using mechanobiological theories reported in the literature. Finite element analysis was used to simulate bone growth. The first study analyzed the effect of subject-specific growth plate geometry over simplified growth plate geometry in numerical prediction of bone growth tendency. Subject-specific femur finite element model was constructed from magnetic resonance images of one able- bodied child. Gait kinematics and kinetics were acquired from motion analysis and analyzed further in musculoskeletal modelling to determine muscle and joint contact forces. These were used to determine loading on the femur in finite element analysis. The growth rate was computed based on a mechanobiological theory proposed by Carter and Wong, and a growth model in the principal stress direction was introduced. Our findings support the use of subject- specific geometry and of the principal stress growth direction in prediction of bone growth. The second study aimed to illustrate how different muscle groups’ activation during gait affects proximal femoral growth tendency in able-bodied children. Subject-specific femur models were used. Gait kinematics and kinetics were acquired for 3 able-bodied children, and muscle and joint contact forces were determined, similar to the first study. The contribution of different muscle groups to hip contact force was also determined. Finite element analysis was performed to compute the specific growth rate and growth direction due to individual muscle groups. The simulated growth model indicated that gait loading tends to reduce neck shaft angle and femoral anteversion during growth. The muscle groups that contributes most and least to growth rate were hip abductors and hip adductors, respectively. All muscle groups’ activation tended to reduce the neck shaft and femoral anteversion angles, except hip extensors and adductors which showed a tendency to increase the femoral anteversion. The third study’s aim was to understand the influence of different physical activities on proximal femoral growth tendency. Hip contact force orientation was varied to represent reported forces from a number of physical activities. The findings of this study showed that all studied physical activities tend to reduce the neck shaft angle and anteversion, which corresponds to the femur’s natural course during normal growth. The aim of the fourth study was to study the hypothesis that loading in the absence of physical activity, i.e. static loading, can have an adverse effect on bone growth. A subject-specific model was used and growth plate was modeled as a poroelastic material in finite element analysis. Prendergast’s indicators for bone growth was used to analyse the bone growth behavior. The results showed that tendency of bone growth rate decreases over a long duration of static loading. The study also showed that static sitting is less detrimental than static standing for predicted cartilage-to-bone differentiation likelihood, due to the lower magnitude of hip contact force. The prediction of growth using finite element analysis on experimental gait data and person- specific femur geometry, based on mechanobiological theories of bone growth, offers a biomechanical foundation for better understanding and prediction of bone growth-related deformity problems in growing children. It can ultimately help in treatment planning or physical activity guidelines in children at risk at developing a femur or hip deformity.

QC 20170616

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Rouleau, Léonie. "Endothelial cell response to shear stress in an asymmetric stenosis model". Thesis, McGill University, 2006. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=99535.

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Endothelial cell dysfunction has been linked to atherosclerosis through their response to hemodynamic forces. Flow in stenotic vessels creates complex spatial gradients in wall shear stress. In vitro studies examining the effect of shear stress on endothelial cells have used unrealistic and simplified models, which cannot reproduce physiological conditions. Endothelial cells were grown and exposed for different times to physiological steady flow in straight dynamic control and in idealized asymmetric stenosis models. Cells subjected to 1D flow aligned with flow direction and had a spindle-like shape when compared to static controls. Endothelial cell morphology differed in the spatial wall shear stress gradient regions, being randomly oriented and of cobblestone shape. No other study to date has described this morphology in the presence of a positive wall shear stress gradient or gradient of significant shear magnitude. This technique provides a more realistic model to study endothelial cell response to spatial and temporal shear stress gradients that are present in vivo and is an important advancement towards a better understanding of the mechanisms involved in coronary artery disease.

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Tucker, Russell P. "Validating a new in vitro model for dynamic fluid shear stress mechanobiology". Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:0ea8b159-5cb6-4bf0-9a60-4c580824016a.

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In vitro mechanotransduction studies, uncovering the basic science of the response of cells to mechanical forces, are essential for progress in tissue engineering and its clinical application. Many varying investigations have described a multitude of cell responses, however as the precise nature and magnitude of the stresses applied are infrequently reported and rarely validated, the experiments are often not comparable, limiting research progress. This thesis provides physical and biological validation of a widely available fluid stimulation device, a see-saw rocker, as an In vitro model for cyclic fluid shear stress mechanotransduction. This allows linkage between precisely characterised stimuli and cell monolayer response in a convenient six-well plate format. Computational fluid dynamic models of one well were analysed extensively to generate convergent, stable and consistent predictions of the cyclic fluid velocity vectors at a rocking frequency of 0.5 Hz, accounting for the free surface. Validation was provided by comparison with flow velocities measured experimentally using particle image velocimetry. Qualitative flow behaviour was matched and quantitative analysis showed good agreement at representative locations and time points. A maximum shear stress of 0.22Pa was estimated near the well edge, and time-average shear stress ranged between 0.029 and 0.068Pa, within the envelope of previous musculoskeletal In vitro fluid flow investigations. The CFD model was extended to explore changes in culture medium viscosity, rocking frequency and the robustness to position on the rocking platform. Shear stress magnitude was shown to increase almost linearly with an increase in the viscosity of culture medium. Compared with 0.5 Hz, models at 0.083 and 1:167 Hz, the operational limits of the see-saw rocker, indicated a change in shear stress patterns at the cell layer, and a reduction and increase in mean shear stress respectively. At the platform edge at 0.5 Hz, a 1.67-fold increase in time-average shear stress was identified. Extensive biological validations using human tenocytes underlined the versatility of the simple In vitro device. The application of fluid-induced shear stress at 0.5 Hz under varying regimes up to 0.714Pa caused a significant increase in secreted collagen (p < 0.05) compared to static controls. Tenocytes stimulated at a shear stress magnitude of 1.023Pa secreted significantly less collagen compared to static controls. The potential for a local maximum in the relationship between collagen secretion rate and shear stress was identified, indicating a change from anabolic to catabolic behaviour. Collagen biochemical assay results were echoed with antibody stains for proteins, where a co-localisation of connexin-32 with collagen type-I was also identified. A custom algorithm showed that four hours of fluid-induced shear stress of 0:033Pa intermittently applied to tenocytes encouraged alignment and elongation over an eight day period in comparison to static controls. Primary cilia were identified in human tenocyte cultures and bovine flexor tendon tissue; however primary cilium abrogation In vitro using chloral hydrate proved detrimental to cell viability. Collaborative investigations identified that ERK signalling and c-Fos transcription factor expression peaked after the application of 0.012Pa at 0.083 Hz for 20 minutes and anabolic collagen gene expression relative quantities increased after 48 hours of rocking at 0.083 Hz. In conclusion, validated shear stresses within a six-well plate, induced by cyclic flow from a see-saw rocker, provides an exceptional model for the In vitro study of dynamic fluid shear stress mechanobiology. Biological investigations have been linked to precise applied shear stress, creating a foundation for understanding the complex relationship between tenocytes and fluid-induced shear stress In vitro. Using this model, research is repeatable, comparable and accurately attributed to shear stress, accelerating the scientific advancement of musculoskeletal mechanobiology.

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Willett, Nick J. "Redox signaling in an in vivo flow model of low magnitude oscillatory wall shear stress". Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/33917.

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Atherosclerosis is a multifactoral inflammatory disease that occurs in predisposed locations in the vasculature where blood flow is disturbed. In vitro studies have implicated reactive oxygen species as mediators of mechanotransduction leading to inflammatory protein expression and ultimately atherogenesis. While these cell culture-based studies have provided enormous insight into the effects of WSS on endothelial biology, the applicability to the in vivo setting is questionable. We hypothesized that low magnitude oscillatory WSS acts through reactive oxygen species (ROS) to increase expression of inflammatory cell adhesion molecules leading to the development of atherosclerotic lesions. The overall objective for this thesis was to develop an in vivo flow model that produces low magnitude oscillatory WSS which could be used to investigate the in vivo molecular mechanisms of mechanotransduction. We created a novel aortic coarctation model using a shape memory nitinol clip. The clip reproducibly constricts the aorta creating a narrowing of the lumen resulting in a stenosis. This mechanical constraint produces a region of flow separation downstream from the coarctation. We have characterized the coarctation in terms of the efficacy, pressure loss, and fluid dynamics. We then measured the endothelial response of shear sensitive redox and inflammatory markers. Lastly, we utilized genetically modified mice and mice treated with pharmacological inhibitors to investigate the mechanisms involved in the expression of WSS induced inflammatory and redox markers. We found that inducing a coarctation of the aorta using a nitinol clip uniquely created a hemodynamic environment of low magnitude oscillatory WSS without a significant change in blood pressure. Using this model we found that the in vivo endothelial phenotype associated with acutely disturbed flow was characterized by increased production of superoxide and increased expression of select inflammatory proteins. In comparison, the phenotype associated with chronically disturbed flow was characterized by a more modest increase in superoxide and increased levels of multiple inflammatory proteins. We determined that in regions of acutely disturbed flow in vivo, VCAM-1 expression was not modulated by reactive oxygen species. Additionally, p47 phox-dependent NADPH Oxidase activity does not have a functional role in WSS induced superoxide generation in the endothelium. In summary, we have created a novel murine model of low magnitude oscillatory WSS that can be used to investigate the in vivo molecular mechanisms associated with atherogenesis. While previous data obtained in vitro indicated that depletion of an individual ROS was sufficient to inhibit flow-induced inflammatory protein expression, our findings, to the contrary, showed that antioxidant treatment in vivo does not inhibit shear-dependent inflammatory protein expression. Our results suggest that atherogenesis in the in vivo environment is significantly more complicated than the in vitro environment and that parallel pathways and compensatory mechanisms are likely activated in vivo in response to WSS. These results could have significant implications in the efficacy of antioxidant treatment of atherosclerosis and could explain the complexity of results observed in clinical trials.

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Vorobtsova, Natalya. "Computational model of coronary tortuosity". Thesis, Virginia Tech, 2015. http://hdl.handle.net/10919/51267.

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Coronary tortuosity is the abnormal curving and twisting of the coronary arteries. Although the phenomenon of coronary tortuosity is frequently encountered by cardiologists its clinical significance is unclear. It is known that coronary tortuosity has significant influence on the hemodynamics inside the coronary arteries, but it is difficult to draw definite conclusions due to the lack of patient-specific studies and an absence of a clear definition of tortuosity. In this work, in order to investigate a relation of coronary tortuosity to such diseases as atherosclerosis, ischemia, and angina, a numerical investigation of coronary tortuosity was performed. First, we studied a correlation between a degree of tortuosity and flow parameters in three simplified vessels with curvature and zero torsion. Next, a statistical analysis based on flow calculations of 23 patient-based real tortuous arteries was performed in order to investigate a correlation between tortuosity and flow parameters, such as pressure drop, wall shear stress distribution, and a strength of helical flow, represented by a helicity intensity, and concomitant risks. Results of both idealized and patient-specific studies indicate that a risk of perfusion defects grows with an increased degree of tortuosity due to an increased pressure drop downstream an artery. According to the results of the patient-specific study, a risk of atherosclerosis decreases in more tortuous arteries - a result different from an outcome of the idealized study of arteries with zero torsion. Consequently, a modeling of coronary tortuosity should take into account all aspects of tortuosity including a heart shape that introduces additional torsion to arteries. Moreover, strength of a helical flow was shown to depend strongly on a degree of tortuosity and affect flow alterations and accompanying risks of developing atherosclerosis and perfusion defects. A corresponding quantity, helicity intensity, might have a potential to be implemented in future studies as a universal single parameter to describe tortuosity and assess congruent impact on the health of a patient.
Master of Science

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Miller, Leigh Ann. "Wall shear stress distribution and the effects of branch angle on a human coronary artery model". Thesis, Georgia Institute of Technology, 1993. http://hdl.handle.net/1853/16088.

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Emmott, Alexander. "The effect of wall shear stress in a novel endothelial tissue culture model of arterial curvature". Thesis, McGill University, 2012. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=107873.

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Vessel wall shear stress (WSS) is hypothesized to cause focal endothelial cell (EC) dysfunction leading to a pro-inflammatory environment. Clinical observations of focal atherosclerosis have been documented in arterial bifurcations, branch points and in lesser arterial curvature. In both in vivo and in vitro experiments, it has been demonstrated that WSS can stimulate a cascade of biochemical interactions which activate the inflammatory pathway. The resultant functional changes include altered expression of inter- and vascular- cellular adhesion molecules (ICAM-1 and VCAM-1, respectively) on the luminal surface of the endothelium. This change in phenotype may indicate the early stages of lesion development by facilitating the adhesion of circulating leukocytes.We have created a three-dimensional tissue culture model using the non-dimensional Dean's number to model physiological hemodynamics in a curved artery (De=104). WSS within our tissue culture model is defined for the inner and outer walls using computational fluid dynamics to ensure well-defined stimuli. ECs cultured within the model are subjected to 24h perfusion experiments at an inlet WSS of 10 dynes/cm2. Regional changes in EC phenotype are evaluated using cell morphology (shape index), protein expression, and circulating leukocyte attachment. EC shape index suggests that ECs lining the inner wall exhibit an atheroprone phenotype relative to those seen lining the outer wall, with significance being observed throughout the entirety of the 180° curve. Similarly, leukocyte distribution favours the inner wall of the tissue culture model between 0°-90°. However, Western Blot analysis demonstrates a 54% decrease in endothelial ICAM-1 in the curve relative to the straight internal control. This study demonstrates that flow through a curved vessel results in significant regional variations in EC phenotype and preferential leukocyte adhesion in vitro, providing further insight into the role of localized hemodynamics in the early stages of atherosclerosis.
Il existe une hypothèse spéculant que les variations locales des forces hémodynamiques, particulièrement la contrainte de cisaillement à la paroi (CCP), mènent à un dérèglement important des cellules endothéliales (CEs) causant un environnement pro-inflammatoire. Les observations cliniques d'athérosclérose ont été documentées principalement dans: les bifurcations artérielles, les points de branchement et à la courbure artérielle. Des expériences in vivo et in vitro ont démontré que la CCP peut engendrer une cascade d'interactions biochimiques qui finissent par activer la voie inflammatoire. Les changements fonctionnels incluent : une expression modifiée des molécules d'adhésion inter-vasculaires et-cellulaire (ICAM-1 et VCAM-1, respectivement) de la surface luminale de l'endothélium. Ce changement de phénotype peuvent aider à identifier les premières phases du développement d'une lésion en facilitant l'adhérence des leucocytes en circulation dans le sang.Nous avons créé un modèle tridimensionnel de culture cellulaire en utilisant le nombre adimensionnel de Dean pour modéliser l'hémodynamique physiologique dans une artère courbée (De = 104). La CCP au sein de notre modèle de culture cellulaire est définie par les murs intérieurs et extérieurs en utilisant une méthode de dynamique des fluides computationnelle. Les CEs cultivées dans le modèle sont soumis à des expériences de perfusion pour une durée de 24h et à une CCP a l'entrée de 10 dynes/cm2. Les changements régionaux dans le phénotype des CEs sont évaluées en utilisant des indices de morphologie cellulaire (indice de forme par exemple), l'expression de certaines protéines et l'attachement des leucocytes circulants. L'indice de forme suggère que les CEs tapissant la paroi interne de notre modèle courbé présentent un phénotype atheroprone important par rapport à ceux vus tapissant le mur extérieur observée dans l'ensemble de la courbe de 180°. De même, la distribution des leucocytes favorise le mur interne du modèle de culture cellulaire entre 0°-90°. Cependant, l'analyse Western Blot montre une réduction de 54% en concentration de protéine endothéliale ICAM-1 dans la courbe relative au contrôle interne de droites. Cette étude démontre que le flux à travers un vaisseau courbé donne des résultats avec d'importantes variations locales dans le phénotype des CEs et préférentielles d'adhérence des leucocytes in vitro, donnant un aperçu futur sur le rôle de l'hémodynamique local dans les premiers stades de l'athérosclérose.

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Wang, Taige. "Mathematical Analysis on the PEC model for Thixotropic Fluids". Diss., Virginia Tech, 2016. http://hdl.handle.net/10919/70907.

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A lot of fluids are more complex than water: polymers, paints, gels, ketchup etc., because of big particles and their complicated microstructures, for instance, molecule entanglement. Due to this structure complexity, some material can display that it is still in yielded state when the imposed stress is released. This is referred to as thixotropy. This dissertation establishes mathematical analysis on a thixotropic yield stress fluid using a viscoelastic model under the limit that the ratio of retardation time versus relaxation time approaches zero. The differential equation model (the PEC model) describing the evolution of the conformation tensor is analyzed. We model the flow when simple shearing is imposed by prescribing a total stress. One part of this dissertation focuses on oscillatory shear stresses. In shear flow, different fluid states corresponding to yielded and unyielded phases occur. We use asymptotic analysis to study transition between these phases when slow oscillatory shearing is set up. Simulations will be used to illustrate and supplement the analysis. Another part of the dissertation focuses on planar Poiseuille flow. Since the flow is spatially inhomogeneous in this situation, shear bands are observed. The flow is driven by a homogeneous pressure gradient, leading to a variation of stress in the cross-stream direction. In this setting, the flow would yield in different time scales during the evolution. Formulas linking the yield locations, transition width, and yield time are obtained. When we introduce Korteweg stress in the transition, the yield location is shifted. An equal area rule is identified to fit the shifted locations.
Ph. D.

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11

Ibarra, Sandra. "A model of stress distribution and cracking in cohesive soils produced by simple tillage implements /". Thesis, McGill University, 2001. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=38205.

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The objective of this research was to further understand the behavior of the soil under the action of a tillage tool, with the purpose of finding a relation between the tool geometry and the resultant soil seed bed. Thus the problem consisted of understanding the mechanics of producing soil break up and to find a logical method of analyzing it.
The problem was solved using fundamental principles of soil mechanics and force equilibrium analyzis. As a result, a mathematical model was developed which describes three failure zones within the cut soil volume. The model can be programmed into a computer to generate maps of normal and shear stresses to visualize the three failure zones.
The failure zones are the shear failure zone, the tensile fracturing zone and the no failure zone. The tensile fracturing zone is delimited by the tensile stress reaching the tensile strength of the soil at the given soil moisture content and soil density. The tensile strength of the soil was measured using an apparatus and method designed in this research.
The mathematical model gives an explanation of the mechanics of crumbling and the shape of the failed volume, but it does not give information concerning soil aggregate quality and arrangement within the soil furrow. Then, a method of analyzing the formed aggregates was developed which considers some soil physical properties of aggregates.
The study concluded that the smaller tool width and the smaller tool rake angle, among the ones used in this research, produced the most efficient geometry in producing the largest amount of soil break up, the most uniform aggregate formation and the most stable aggregate arrangement. The same tool geometry requires less energy per unit volume of soil disturbed. The best performance is produced at the lowest soil water content among those tested.

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Shen, Yao. "A peierls model of dislocation transmission through coherent interfaces and embedded layers". Connect to this title online, 2004. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1092183192.

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Thesis (Ph. D.)--Ohio State University, 2004.
Title from first page of PDF file. Document formatted into pages; contains xv, 148 p.; also includes graphics Includes bibliographical references (p. 143-148).

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Rouleau, Léonie. "Endothelial cell response and leukocyte adhesion in an asymmetric stenosis model: role of fluid wall shear stress gradients". Thesis, McGill University, 2010. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=86519.

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The focal nature of atherosclerosis has been associated with complex geometries. The response of endothelial cells to hemodynamics is believed to be linked to atherosclerotic plaque development, progression and rupture. Great advances have been made in our ability to study cellular responses to mechanical forces. Unfortunately, the inability to recreate in vitro the realistic in vivo mechanical stimuli may be obscuring our understanding. In order to determine the mechanistic link between hemodynamics and plaque stability, three dimensional in vitro cell culture models were designed and biomolecular techniques were adapted to analyze endothelial cell function. Dextran was used as a supplement to increase the growth medium viscosity and its effects were characterized. Straight/tubular in vitro models were used to study the acute and long term response of endothelial cells to wall shear stress (WSS) of different magnitude. Anatomically realistic and asymmetric stenosis models were created in order to examine the morphological response of endothelial cells to complex hemodynamic forces. Within the stenosis models, the regional adhesive properties of neutrophils were tested as well as the localized expression of inflammatory molecules. Results show that appropriate time matched dextran containing static controls are required as this additive modified inflammatory marker cell expression both under static and flow conditions in a concentration and time dependent manner. Endothelial cells exposed to wall shear stress altered their morphology depending on the magnitude and duration of exposure. Morphological adaptation was sensitive to the spatial wall shear stress gradients present in both the asymmetric stenosis and the anatomically realistic models. Neutrophil adhesion and inflammatory marker expression differed in the spatial WSS gradient regions of the asymmetric stenosis models. This study highlights the possible role for spatial wall shear stress gradients in t
L'athérosclérose est une maladie qui se développe localement où le flux sanguin est perturbé. Les cellules endothéliales sont soumises en permanence à des contraintes mécaniques et leur réponse a été reliée au développement et à la progression de l'artériosclérose. Différentes chambres d'écoulement ont été développées in vitro afin d'étudier la réponse des cellules endothéliales aux forces de cisaillement et de grandes avancées ont été faites afin de mieux comprendre les réponses cellulaires à l'écoulement sanguin. Ces modèles ne peuvent reproduire adéquatement la complexité des conditions présentes in vivo. Ainsi, afin de déterminer le lien entre les forces hémodynamiques et la stabilité des plaques artérioscléreuses, des modèles tridimensionnels ont été développés ainsi que les techniques biomoléculaires nécessaire afin d'étudier la fonction des cellules à l'intérieur de ceux-ci. Du dextran a été utilisé comme supplément afin d'augmenter la viscosité du média de culture et son effet sur les cellules a été caractérisé. Des modèles tubulaires ont été utilisés afin d'étudier la réponse à court et à long terme des cellules endothéliales à des forces de cisaillement de diverses magnitudes. La réponse morphologique des cellules endothéliales, suite à l'exposition d'un débit constant, a été étudiée dans des modèles idéalisés de sténoses asymétriques et réalistes anatomiquement. L'expression régionale des cellules endothéliales et l'adhésion locale de neutrophiles dans les modèles sténosés ont été quantifiées en fonction de la durée et de la magnitude des forces de cisaillement. Les résultats obtenus démontrent que le dextran peut affecter la réponse des cellules et ainsi les contrôles appropriés doivent être utilisé. La morphologie des cellules endothéliales varie avec la durée et la force du cisaillement ainsi que dans les régions où des gradients sont présent

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Brooks, Zachary Edward. "Mechanical Stresses on Nasal Mucosa Using Nose-On-Chip Model". Wright State University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=wright1578492176817977.

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Altshuler, Angelina E. "Proteolytic receptor cleavage and attenuated endothelial cell response to fluid shear stress in a model for autodigestion in shock". Diss., [La Jolla] : University of California, San Diego, 2010. http://wwwlib.umi.com/cr/fullcit?p1477880.

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Thesis (M.S.)--University of California, San Diego, 2010.
Title from first page of PDF file (viewed July 10, 2010). Available via ProQuest Digital Dissertations. Includes bibliographical references (leaves 75-85).

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Wiesner, Theodore F. "A mathematical model of the dynamics of cytosolic free calcium in cultured vascular endothelial cells responding to shear stress". Diss., Georgia Institute of Technology, 1994. http://hdl.handle.net/1853/9374.

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Yamanaka, Kenya. "Olprinone Attenuates Excessive Shear Stress Through Up-Regulation of Endothelial Nitric Oxide Synthase in a Rat Excessive Hepatectomy Model". Kyoto University, 2012. http://hdl.handle.net/2433/157435.

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Abo, Abdulla. "A three-dimensional flow model for different cross-section high-velocity channels". Thesis, University of Plymouth, 2013. http://hdl.handle.net/10026.1/2852.

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High velocity channels are typically designed to discharge surplus water during severe flood events, and these types of flow are distinguished by high velocity, usually supercritical. A major challenge in high velocity channel design is to predict the free surface flow. Being able to predict the free surface flow profile beforehand can assist in selecting the best design for the channel as a whole. When the flow encounters a bridge pier, the streamline of the flow is separated and pressure may drop to a minimum; in contrast, velocity rises to its maximum value. As a result, cavitation damage may occur. The present study has used the computational fluid dynamics code ANSYS-CFX to investigate a full scale, three-dimensional engineering flow simulation of high velocity channels with different cross sections. The simulations were carried out on a high performance computing HPC cluster with 32 nodes. The code is based on the finite volume method and the Volume of Fluid (VOF) method was used to predict the position of the free surface profile. The impact of variation of the following parameters was investigated in terms of the free surface flow profile, both along the centreline and the wall of the channel: the minimum cavity index, and maximum shear stress on both bed and wall of the channel and on bridge pier; aspect ratio (channel bed width/flow depth), bed and side slopes of the channel, different discharges, which are represented by Froude numbers; the length and thickness of the bridge pier. First, the code sensitivity tools for convergence were examined. For this purpose, cases with different mesh sizes were examined and the best size chosen, depending on computation expense and convergence. Then, different turbulence models, such as the standard k-ε, RNG k-ε, and SST turbulence models were tested. The results show that the standard k-ε gives satisfactory results. Next, efforts were made to establish whether the flow achieved steady state conditions. This involved simulating two cases, one with steady state and the other with a transient state. Comparison of the two results shows that the flow properties do not change after three seconds and stay stable thereafter, so the flow can be considered as attaining a steady state. Finally, symmetry within the model geometry was tested, as this would allow a reduction in computation time, with only one side of the symmetrical model needing to be simulated. Two cases were investigated: firstly a simulation of only half of the channel geometry, and secondly a full geometry simulation. A comparison of the results of each case showed that the flow can be considered symmetrical along the centreline of the channel. Next, the code was validated against both numerical and experimental published results. For the free surface flow profile and velocity distribution the published experimental and numerical work of Stockstill (1996) was used; the ANSYS-CFX code results agree more closely with Stockstill’s experimental data than Stockstill’s numerical data. To test for shear stress distribution on the wall, uniform flow within a trapezoidal cross section channel was investigated and the results compared with those presented in the literature. The comparison shows good agreement between the ANSYS-CFX and published experimental works, for the predicted shear stress distributions on the walls and the bed of the channel. In total, sixty cases were simulated in order to investigate the impact of variations in the aforementioned parameters on maximum flow depth (both along the centreline and the wall of the channel) minimum cavity index, and maximum shear stress on both bed and wall of the channel and on bridge pier. Finally, non-dimensional curves are provided in addition to formulae derived from the data regression, which are intended to provide useful guidelines for designers.

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Kornuta, Jeffrey Alan. "Characterization of lymphatic pump function in response to mechanical loading". Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/52208.

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The lymphatic system is crucial for normal physiologic function, performing such basic functions as maintaining tissue fluid balance, trafficking immune cells, draining interstitial proteins, as well as transporting fat from the intestine to the blood. To perform these functions properly, downstream vessels (known as collecting lymphatics) actively pump like the heart to dynamically propel lymph from the interstitial spaces of the body to the blood vasculature. However, despite the fact that lymphatics are so important, there exists very little knowledge regarding the details of this active pumping. Specifically, it is known that external mechanical loading such as fluid shear stress and circumferential stress due to transmural pressure affect pumping response; however, anything other than simple, static relationships remain unknown. Because mechanical environment has been implicated in lymphatic diseases such as lymphedema, understanding these dynamic relationships between lymphatic pumping and mechanical loading during normal function are crucial to grasp before these pathologies can be unraveled. For this reason, this thesis describes several tools developed to study lymphatic function in response to the unique mechanical loads these vessels experience both in vitro and ex vivo. Moreover, this work investigates how shear stress sensitivity is affected by transmural pressure and how the presence of dynamic shear independently affects lymphatic contractile function.

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Nishii, Kenichiro. "MICRO-SCALE FLUID DYNAMICS AND ITS EFFECT ON HEPATIC PROGENITOR CELL REGENERATION ACTIVATION". Miami University / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=miami1461945701.

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Ricci, Giovanni. "Organic matter deposition/resuspension in a one-dimensional physical-biogeochemical model. A modelling study". Master's thesis, Alma Mater Studiorum - Università di Bologna, 2016. http://amslaurea.unibo.it/10595/.

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The shallow water configuration of the gulf of Trieste allows the propagation of the stress due to wind and waves along the whole water column down to the bottom. When the stress overcomes a particular threshold it produces resuspension processes of the benthic detritus. The benthic sediments in the North Adriatic are rich of organic matter, transported here by many rivers. This biological active particulate, when remaining in the water, can be transported in all the Adriatic basin by the basin-wide circulation. In this work is presented a first implementation of a resuspension/deposition submodel in the oceanographic coupled physical-biogeochemical 1-dimensional numerical model POM-BFM. At first has been considered the only climatological wind stress forcing, next has been introduced, on the surface, an annual cycle of wave motion and finally have been imposed some exceptional wave event in different periods of the year. The results show a strong relationship between the efficiency of the resuspension process and the stratification of the water column. During summer the strong stratification can contained a great quantity of suspended matter near to the bottom, while during winter even a low concentration of particulate can reach the surface and remains into the water for several months without settling and influencing the biogeochemical system. Looking at the biologic effects, the organic particulate, injected in the water column, allow a sudden growth of the pelagic bacteria which competes with the phytoplankton for nutrients strongly inhibiting its growth. This happen especially during summer when the suspended benthic detritus concentration is greater.

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Grytsan, Andrii. "Abdominal aortic aneurysm inception and evolution - A computational model". Doctoral thesis, KTH, Biomekanik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-197289.

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Abdominal aortic aneurysm (AAA) is characterized by a bulge in the abdominal aorta. AAA development is mostly asymptomatic, but such a bulge may suddenly rupture, which is associated with a high mortality rate. Unfortunately, there is no medication that can prevent AAA from expanding or rupturing. Therefore, patients with detected AAA are monitored until treatment indication, such as maximum AAA diameter of 55 mm or expansion rate of 1 cm/year. Models of AAA development may help to understand the disease progression and to inform decision-making on a patient-specific basis. AAA growth and remodeling (G&R) models are rather complex, and before the challenge is undertaken, sound clinical validation is required. In Paper A, an existing thick-walled model of growth and remodeling of one layer of an AAA slice has been extended to a two-layered model, which better reflects the layered structure of the vessel wall. A parameter study was performed to investigate the influence of mechanical properties and G&R parameters of such a model on the aneurysm growth. In Paper B, the model from Paper A was extended to an organ level model of AAA growth. Furthermore, the model was incorporated into a Fluid-Solid-Growth (FSG) framework. A patient-specific geometry of the abdominal aorta is used to illustrate the model capabilities. In Paper C, the evolution of the patient-specific biomechanical characteristics of the AAA was investigated. Four patients with five to eight Computed Tomography-Angiography (CT-A) scans at different time points were analyzed. Several non-trivial statistical correlations were found between the analyzed parameters. In Paper D, the effect of different growth kinematics on AAA growth was investigated. The transverse isotropic in-thickness growth was the most suitable AAA growth assumption, while fully isotropic growth and transverse isotropic in-plane growth produced unrealistic results. In addition, modeling of the tissue volume change improved the wall thickness prediction, but still overestimated thinning of the wall during aneurysm expansion.
Bukaortaaneurysm (AAA) kännetecknas av en utbuktning hos aortaväggen i buken. Tillväxt av en AAA är oftast asymtomatisk, men en sådan utbuktning kan plö̈tsligt brista, vilket har hög dödlighet. Tyvärr finns det inga mediciner som kan förhindra AAA från att expandera eller brista. Patienter med upptä̈ckt AAA hålls därför under uppsikt tills operationskrav är uppnådda, såsom maximal AAA-diameter på 55 mm eller expansionstakt på 1 cm/år. Modeller för AAA-tillväxt kan bidra till att öka förståelsen för sjukdomsförloppet och till att förbättra beslutsunderlaget på en patientspecifik basis. AAA modeller för tillväxt och strukturförändring (G&R) är ganska komplicerade och innan man tar sig an denna utmaning krävs de god klinisk validering. I Artikel A har en befintlig tjockväggig modell för tillväxt av ett skikt av en AAA-skiva utö̈kats till en två-skiktsmodell. Denna modell återspeglar bättre den skiktade strukturen hos kärlväggen. Genom en parameterstudie undersö̈ktes påverkan av mekaniska egenskaper och G&R-parametrar hos en sådan modell för AAA-tillväxt. I Artikel B utvidgades modellen från Artikel A till en organnivå-modell för AAA-tillväxt. Vidare inkorporerades modellen i ett “Fluid–Solid–Growth” (FSG) ramverk. En patientspecifik geometri hos bukaortan användes för att illustrera möjligheterna med modellen. I Artikel C undersöktes utvecklingen av patientspecifika biomekaniska egenskaper hos AAA. Fyra patienter som skannats fem till åtta gånger med “Computed Tomography-Angiography” (CT-A) vid olika tillfällen analyserades. Flera icke triviala statistiska samband konstaterades mellan de analyserade parametrarna. I Artikel D undersöktes effekten av olika tillväxt-kinematik för AAA tillväxt. En modell med transversellt-isotrop-i-tjockleken-tillväxt var den bäst lämpade för AAA tillväxt, medans antagandet om fullt-isotrop-tillväxt och transversellt-isotrop-i-planet-tillväxt producerade orimliga resultat. Dessutom gav modellering av vävnadsvolymsförändring ett förbättrat väggtjockleks resultat men en fortsatt överskattning av väggförtunningen under AAA-expansionen.

QC 20161201

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23

Ramesh, Chandra D. S. "Turbulent Mixed Convection". Thesis, Indian Institute of Science, 2000. http://hdl.handle.net/2005/236.

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Turbulent mixed convection is a complicated flow where the buoyancy and shear forces compete with each other in affecting the flow dynamics. This thesis deals with the near wall dynamics in a turbulent mixed convection flow over an isothermal horizontal heated plate. We distinguish between two types of mixed convection ; low-speed mixed convection (LSM) and high-speed mixed convection (HSM). In LSM the entire boundary layer, including the near-wall region, is dominated by buoyancy; in HSM the near-wall region, is dominated by shear and the outer region by buoyancy. We show that the value of the parameter (* = ^ determines whether the flow is LSM or HSM. Here yr is the friction length scale and L is the Monin-Obukhov length scale. In the present thesis we proposed a model for the near-wall dynamics in LSM. We assume the coherent structure near-wall for low-speed mixed convection to be streamwise aligned periodic array of laminar plumes and give a 2d model for the near wall dynamics, Here the equation to solve for the streamwise velocity is linear with the vertical and spanwise velocities given by the free convection model of Theerthan and Arakeri [1]. We determine the profiles of streamwise velocity, Reynolds shear stress and RMS of the fluctuations of the three components of velocity. From the model we obtain the scaling for wall shear stress rw as rw oc (UooAT*), where Uoo is the free-stream velocity and AT is the temperature difference between the free-stream and the horizontal surface.A similar scaling for rw was obtained in the experiments of Ingersoll [5] and by Narasimha et al [11] in the atmospheric boundary layer under low wind speed conditions. We also derive a formula for boundary layer thickness 5(x) which predicts the boundary layer growth for the combination free-stream velocity Uoo and AT in the low-speed mixed convection regime.

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24

Shaarbaf, Ihsan Ali Saib. "Three-dimensional non-linear finite element analysis of reinforced concrete beams in torsion : reinforced concrete members under torsion and bending are analysed up to failure : a non-linear concrete model for general states of stress including compressive strength degradation due to cracking is described". Thesis, University of Bradford, 1990. http://hdl.handle.net/10454/3576.

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This thesis describes a non-linear finite element model suitable for the analysis of reinforced concrete, or steel, structures under general three-dimensional states of loading. The 20 noded isoparametric brick element has been used to model the concrete and reinforcing bars are idealised as axial members embedded within the concrete elements. The compressive behaviour of concrete is simulated by an elasto-plastic work hardening model followed by a perfectly plastic plateau which is terminated at the onset the . crushing. In tension, a smeared crack model with fixed orthogonal cracks has been used with the inclusion of models for the retained post-cracking stress and the reduced shear modulus. The non-linear equations of equilibrium have been solved using an incremental-iterative technique operating under load control. The solution algorithms used are the standard and the modified Newton-Raphson methods. Line searches have been implemented to accelerate convergence. The numerical integration has been generally carried out using 15 point Gaussian type rules. Results of a study to investigate the performance of these rules show that the 15 point rules are accurate and computationally efficient compared with the 27(3X3X3) point Gaussian rule. The three- dimensional finite element model has been used to investigate the problem of elasto-plastic torsion of homogeneous members. The accuracy of the finite element solutions obtained for beams of different cross-sections subjected to pure and warping torsion have been assessed by comparing them with the available exact or approximate analytical solutions. Because the present work is devoted towards the analysis of reinforced concrete members which fail in shear or torsional modes, the computer program incorporates three models to account for the degradation in the compressive strength of concrete due to presence of tensile straining of transverse reinforcement. The numerical solutions obtained for reinforced concrete panels under pure shear and beams in torsion and combined torsion and bending reveal that the inclusion of a model for reducing the compressive strength of cracked concrete can significantly improve the correlation of the predicted post-cracking stiffness and the computed ultimate loads with the experimental results. Parametric studies to investigate the effects of some important material and solution parameters have been carried out. It is concluded that in the presence of a compression strength reduction model, the tension-stiffening parameters required for reinforced concrete members under torsion should be similar to those used for members in which bending dominates.

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Jurášek, Lubomír. "Nelineární analýza stěnových železobetonových prvků". Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2012. http://www.nusl.cz/ntk/nusl-225628.

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Master thesis is based on a doctor thesis dealing with the behavior of reinforced concrete elements stressed shear by the author Ing. Stanislav Martinec, Ph.D. Author master thesis has the task create a spatial finally element model loading testing construction and researched the wall element. Defined finally elements model is mainly to provide proper interaction test device steel frame with the test wall element. Need for sufficiently detailed numerical analysis is necessary to define the non-linear concrete material model, that is researched element, using the extensions multiPlas for calculation software Ansys. The key output parameters, for comparison with the results of load tests, are total bevel and maximum level of applied force on the wall element. The goal is assess the effect of a steel frame, contained in finally element model, to output parameters for by non-linear numerical analysis.

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Johnson, Tiffany Lynn. "Endothelial Cell Function Using a Tissue Engineered Blood Vessel Model: A Case Study of Cell-Cell Communication". Diss., Available online, Georgia Institute of Technology, 2006, 2006. http://etd.gatech.edu/theses/available/etd-04032006-120602/.

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Thesis (Ph. D.)--Biomedical Engineering, Georgia Institute of Technology, 2006.
Pollman, Matthew, Committee Member ; Galis, Zorina, Committee Member ; McIntire, Larry, Committee Member ; Taylor, W Robert, Committee Member ; Jo, Hanjoong, Committee Member ; Nerem, Robert, Committee Chair.

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27

Hrabovský, Michal. "Návrh rekonstrukce balvanitého skluzu na toku Lomná v km 1,9". Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2017. http://www.nusl.cz/ntk/nusl-265698.

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The thesis deals the assessment of the resistance of the existing boulder chute in the river Lomná. At km 1,9 Boulder chute is located in the village Jablunkov. Surface resistance of boulder chute is assessed newly on the basis of non-dimensional shear stress for particle on arbitrarily sloped bed. The calculation of 2D flow was computed by HEC-RAS. On the assessment of resistance was proposed reconstruction of boulder chute.

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Shamu, John. "On the measurement and application of cement grout rheological properties". Licentiate thesis, KTH, Jord- och bergmekanik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-251745.

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The rheological properties of cement-based grouts play a key role in determining the final spread in grouted rock formations. Rheologically, cement grouts are known to be complex thixotropic fluids, but their steady flow behavior is often described by fitting the simple Bingham constitutive law to flow curve data. The resultant Bingham parameters are then used in grouting design of e.g. tunnels, to estimate the penetration length. Since cement grouts are thixotropic suspensions, the interpretation of their flow curves as obtained from flow sweeps in concentric cylinder rotational rheometers is often complicated by: the presence of wall slip, sedimentation and unstable flow at low shear rates. A systematic approach to study these effects within the constraints of the concentric cylinder geometry (Couette) and for different cement grout concentrations was carried out as part of the Licentiate research work. Of particular interest was the influence of geometry and flow sweep measurement interval on flow curves, including the characteristic unstable flow branch that appears at applied shear rates that are below the critical shear rate. The unstable flow branch observed below the critical shear rate has been described as a characteristic feature in the flow curves of thixotropic suspensions, e.g. cement grouts, laponite. From a practical standpoint, this information can then be readily used to improve rheological measurements of cement grouts. The existence of the critical shear rate below which no stable flow occurs, plus the complex wall slip phenomenon are then discussed by considering how they affect actual spread in rough and smooth rock fractures. Another major part of the research presented in this thesis relates to the measurement of model yield stress fluid (YSF), i.e. Carbopol, velocity profiles within the radial flow geometry. Radial flow between parallel plates, is an idealized fundamental flow configuration that is often used as a basis for grout spread estimation in planar rock fractures. Compared to other flow configurations with YSFs, e.g. channels, only a limited amount of work has presented analytical solutions, numerical models and especially experimental work for radial flow. Thus, as a first step towards more systematic studies of the plug flow region of YSFs in radial flow the current work presents the design, manufacture and for the first time velocity profile measurements that were conducted by using the pulsed Ultrasound Velocity Profiling (UVP) technique. The current observations for tests carried out with different disk spacings and flow rates show a distinct plug region, coupled with wall slip effects for the Carbopol model YSF fluid that was used. The theoretically predicted velocity profiles and the measured ones agree reasonably well, and the main discrepancies are discussed. Future studies, would then be targeted at improving the current experimental setup, for detailed measurements of the plug flow region along the radial length, which remains a challenging issue for studies on YSFs and engineering applications such as rock grouting design.
Cementbaserade injekteringsmedels reologiska egenskaper har en stor påverkan på strömning och inträngningslängd i sprickigt berg. Medlens reologi är komplex, inklusive tixotropi, men strömningen beskrivs ändå oftast med den enkla linjära Bingham modellen i injekteringssammanhang. De två parametrarna från denna modell, flytgräns och viskositet, används sedan inom injekteringsdesign, för t.ex. tunnlar och dammar, för att bedöma inträngningen. Eftersom cementbaserade medel är tixoptropa suspensioner försvåras utvärderingen vid mätning med konventionella rotationsviskometrar på grund av glidning vid fasta begränsningsytor, sedimentation/separation av partiklarna och instabila flöden vid låga deformationshastigheter. En systematisk mätprocedur för att studera ovanstående problem med rotationsviskometer och koncentriska cylindrar samt olika vanliga vattencementtal, har utförts inom ramen för detta licentiatarbete. Av särskilt intresse har varit att studera effekten av olika geometrier och tidsintervallet mellan mätningarna, inklusive den instabila delen av flödeskurvan då deformationshastigheten är lägre än ett kritiskt värde. Denna del av kurvan har i litteraturen beskrivits som karakteristisk för tixotropa suspensioner, som t.ex. cementbaserade injekteringsmedel. Praktiskt kan ovanstående kunskap användas för att förbättra mätningen av de reologiska egenskaperna. Existensen av en kritisk deformationshastighet under vilken det inte finns något stabilt flöde, i kombination med glidning vid fasta begränsningsytor, diskuteras särskilt med hänsyn till dess påverkan på faktisk inträngning i släta och råa bergsprickor. Ett annat fokus i licentiatarbetet har varit att studera icke-Newtonska modellvätskors (Carbopol) radiella strömning mellan parallella plattor. Denna typ av strömningsgeometri används ofta som en idealiserad konfiguration för strömning i bergsprickor. I jämförelse med andra enklare geometrier, finns endast en begränsad forskning utförd för denna geometri både då det gäller analytiska och numeriska beräkningar men framförallt då det gäller experiment. Som ett första steg inför en mer systematisk undersökning av icke-Newtonsk radiella strömning presenteras i detta arbete framtagandet av en fysisk laboratoriemodell där hastighetsprofilerna mellan plattorna för första gången visualiserats med hjälp av ultraljud. De utförda mätningarna med tre olika öppningar mellan plattorna sam tre olika värden på det konstanta flödet, visar på en distinkt plugg som är ett resultat av vätskans flytgräns samt glidning i gränsskiktet mellan vätskan och plattornas fasta begränsningsytor. En jämförelse mellan uppmätta hastighetsprofiler och analytiskt beräknade diskuteras där resultaten överensstämmer relativt väl, med beaktande av de långtgående förenklade antaganden som krävs för beräkningarna. Fortsatta studier kommer att fokuseras på att förbättra laboratoriemodellen för en mer detaljerad studie av icke-Newtonska vätskors strömning och hur pluggen utvecklas under den radiella inträngningen, vilket fortsättningsvis är av betydelse för design av injektering i bergsprickor.

QC 20190521

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McKellar, Dougan Kelk. "A dislocation model of plasticity with particular application to fatigue crack closure". Thesis, University of Oxford, 2001. http://ora.ox.ac.uk/objects/uuid:45183b90-017f-4ac1-9550-94772a0ca88b.

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The ability to predict fatigue crack growth rates is essential in safety critical systems. The discovery of fatigue crack closure in 1970 caused a flourish of research in attempts to simulate this behaviour, which crucially affects crack growth rates. Historically, crack tip plasticity models have been based on one-dimensional rays of plasticity emanating from the crack tip, either co-linear with the crack (for the case of plane stress), or at a chosen angle in the plane of analysis (for plane strain). In this thesis, one such model for plane stress, developed to predict fatigue crack closure, has been refined. It is applied to a study of the relationship between the apparent stress intensity range (easily calculated using linear elastic fracture mechanics), and the true stress intensity range, which includes the effects of plasticity induced fatigue crack closure. Results are presented for all load cases for a finite crack in an infinite plane, and a method is demonstrated which allows the calculation of the true stress intensity range for a growing crack, based only on the apparent stress intensity range for a static crack. Although the yield criterion is satisfied along the plastic ray, these one-dimensional plasticity models violate the yield criterion in the area immediately surrounding the plasticity ray. An area plasticity model is therefore required in order to model the plasticity more accurately. This thesis develops such a model by distributing dislocations over an area. Use of the model reveals that current methods for incremental plasticity algorithms using distributed dislocations produce an over-constrained system, due to misleading assumptions concerning the normality condition. A method is presented which allows the system an extra degree of freedom; this requires the introduction of a parameter, derived using the Prandtl-Reuss flow rule, which relates the magnitude of slip on complementary shear planes. The method is applied to two problems, confirming its validity.

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Wu, Zexiang. "Modélisation du comportement des sables sous la condition de cisaillement simple et applications au calcul des pieux". Thesis, Ecole centrale de Nantes, 2017. http://www.theses.fr/2017ECDN0045/document.

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La thèse vise à étudier le comportement mécanique des sables sous la condition de cisaillement simple et à son application au calcul des pieux. Tout d'abord, un modèle de sable récemment développé (SIMSAND) prenant en compte l'état critique est introduit avec une procédure directe de détermination des paramètres. Le modèle est implanté dans un code de calcul aux éléments finis qui a fait l’objet de différentes validations. Ensuite, le modèle est amélioré en considérant l'anisotropie inhérente lors de la rotation des contraintes principales sous la condition de cisaillement simple et a été validé en utilisant les résultats des essais tri axiaux et de cisaillement simple sur le sable de Fontainebleau. Les essais de cisaillement simple sont analysés en imposant les conditions de sollicitations réelles tridimensionnelles appliquées par l’appareillage utilisé. L'inhomogénéité de l'échantillon avec l'effet de la taille de l'échantillon est également étudiée. Puis, des essais de cisaillement simple cycliques drainés et non-drainés sur le sable de Fontainebleau sont effectués pour étudier les caractéristiques sous charges cycliques, telles que la dégradation de la contrainte normale effective et l'accumulation de la déformation volumique, compte tenus de certains facteurs comme l’indice des vide initial, la contrainte normale appliquée, le rapport de contrainte de cisaillement cyclique et le rapport de contrainte de cisaillement moyenne. Sur la base de ces résultats, deux modèles analytiques sont proposés pour prédire la dégradation à long terme de la contrainte normale effective et l'accumulation des déformations volumiques en fonction du nombre de cycles. En outre, les essais cycliques de cisaillement simple sont simulés par le modèle SIMSAND amélioré en utilisant une technique d'inversion de contrainte. Enfin, on simule une série de pieux modèles sous charges monotone et cyclique pour laquelle la résistance en pointe du pieu est évaluée ainsi que la réponse du sol entourant le pieu
The thesis aims to study the mechanical behaviour of sand under simple shear condition and to apply the results to the numerical simulation of pile foundation. First, a recently developed critical state sand model (SIMSAND) is introduced with a straight forward procedure of parameters determination, implemented into a finite element code and then subjected to a series of validations. Then, the model is enhanced by considering the inherent anisotropy during the principal stress rotation under the simple shear condition and validated by using results of both triaxial tests and simple shear tests on Fontainebleau sand. Simple shear tests are analysed by simulating in three-dimensions the real conditions imposed by the simple shear apparatus. The inhomogeneity of the samples with the effect of sample size is also investigated. Furthermore, undrained and drained cyclic simple shear tests on Fontainebleau sand are conducted to investigate the cyclic responses, such as the effective normal stress degradation and the volumetric strain accumulation, respectively, considering some impact factors such as the initial void ratio, the normal stress, the cyclic shear stress ratio and the average shear stress ratio. Based on these results, two analytical models are proposed to predict the long-term degradation of the effective normal stress and the accumulation of the volumetric strain with the number of cycles. Moreover, the cyclic simple shear tests are simulated by the enhanced SIMSAND model by incorporating the stress reversal technique. Finally, a series of model pile tests under monotonic and cyclic loadings are simulated based on which the cone resistance of the piles is evaluated as well as the response of the soil surrounding the pile

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Duffrene, Lucas. "Comportement viscoélastique d'un verre silico-sodocalcique dans le domaine des températures intermédiaires : approche phénoménologique et modélisation en triaxialité". Paris, ENMP, 1994. http://www.theses.fr/1994ENMP0515.

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Les opérations de mise en forme ou de traitement thermique (trempe, recuisson) sont généralement effectuées à des températures intermédiaires (500-650c) et à des niveaux de contraintes modérés pour lesquels le comportement mécanique du verre peut être décrit par une loi viscoélastique linéaire. L'objectif de la thèse est de réaliser une démarche expérimentale complète afin de modéliser le comportement viscoélastique en triaxialité d'un verre silico-sodocalcique. Les modules d'élasticité du verre ont été mesures par diffusion Brillouin dans le domaine de la transition. Des essais statiques de relaxation des contraintes et de fluage-recouvrance en cisaillement et en sollicitation uniaxiale ont été réalisés autour de la transition vitreuse. Ils permettent en particulier de montrer la dualité fluage-relaxation. Des essais dynamiques en cisaillement ont été également réalisés afin de montrer la correspondance statique-dynamique. Un développement de la théorie de la viscoélasticite par l'introduction des moments des spectres de relaxation et de retard ainsi que des constantes viscoélastiques permet d'obtenir des relations fondamentales entre les sollicitations uniaxiale, de cisaillement et de pression hydrostatique. Ainsi, dans le cadre du modèle de Maxwell généralisé, la partie hydrostatique du comportement viscoélastique est déterminée à partir des essais en sollicitation uniaxiale et par la connaisance du comportement en cisaillement. On montre également que la fonction de Kohlraush et le modèle de Perez ne conviennent pas pour décrire d'une manière phénomenologique le comportement viscoélastique du verre silico-sodocalcique. Le modèle de Maxwell généralisé est validé en comparant les résultats d'un calcul de structure avec un essai présentant un état de contraintes triaxiales complexes. Le modèle viscoélastique déterminé peut être étendu à la thermoviscoélasticite pour simuler les procédés de formage, de trempe des vitrages automobiles en verre silico-sodocalcique

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Shabani, Behnam. "Wave-Associated Seabed Behaviour near Submarine Buried Pipelines". University of Sydney, 2008. http://hdl.handle.net/2123/3532.

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Master of Engineering (Research)
Soil surrounding a submarine buried pipeline consolidates as ocean waves propagate over the seabed surface. Conventional models for the analysis of soil behaviour near the pipeline assume a two-dimensional interaction problem between waves, the seabed soil, and the structure. In other words, it is often considered that water waves travel normal to the orientation of pipeline. However, the real ocean environment is three-dimensional and waves approach the structure from various directions. It is therefore the key objective of the present research to study the seabed behaviour in the vicinity of marine pipelines from a three-dimensional point of view. A three-dimensional numerical model is developed based on the Finite Element Method to analyse the so-called momentary behaviour of soil under the wave loading. In this model, the pipeline is assumed to be rigid and anchored within a rigid impervious trench. A non-slip condition is considered to exist between the pipe and the surrounding soil. Quasi-static soil consolidation equations are then solved with the aid of the proposed FE model. In this analysis, the seabed behaviour is assumed to be linear elastic with the soil strains remaining small. The influence of wave obliquity on seabed responses, i.e. the pore pressure and soil stresses, are then studied. It is revealed that three-dimensional characteristics systematically affect the distribution of soil response around the circumference of the underwater pipeline. Numerical results suggest that the effect of wave obliquity on soil responses can be explained through the following two mechanisms: (i) geometry-based three-dimensional influences, and (ii) the formation of inversion nodes. Further, a parametric study is carried out to investigate the influence of soil, wave and pipeline properties on wave-associated pore pressure as well as principal effective and shear stresses within the porous bed, with the aid of proposed three-dimensional model. There is strong evidence in the literature that the failure of marine pipelines often stems from the instability of seabed soil close to this structure, rather than from construction deficiencies. The wave-induced seabed instability is either associated with the soil shear failure or the seabed liquefaction. Therefore, the developed three-dimensional FE model is used in this thesis to further investigate the instability of seabed soil in the presence of a pipeline. The widely-accepted criterion, which links the soil liquefaction to the wave-induced excess pressure is used herein to justify the seabed liquefaction. It should be pointed out that although the present analysis is only concerned with the momentary liquefaction of seabed soil, this study forms the basis for the three-dimensional analysis of liquefaction due to the residual mechanisms. The latter can be an important subject for future investigations. At the same time, a new concept is developed in this thesis to apply the dynamic component of soil stress angle to address the phenomenon of wave-associated soil shear failure. At this point, the influence of three-dimensionality on the potentials for seabed liquefaction and shear failure around the pipeline is investigated. Numerical simulations reveal that the wave obliquity may not notably affect the risk of liquefaction near the underwater pipeline. But, it significantly influences the potential for soil shear failure. Finally, the thesis proceeds to a parametric study on effects of wave, soil and pipeline characteristics on excess pore pressure and stress angle in the vicinity of the structure.

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Zagzoule, Mokhtar. "Modelisation mathematique de la circulation sanguine cerebrale : aspects instationnaires et non-newtoniens". Toulouse 3, 1987. http://www.theses.fr/1987TOU30144.

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Desombre, Jonathan. "Modélisation vof de l’écoulement de jet de rive en surface et dans une plage perméable". Thesis, Pau, 2012. http://www.theses.fr/2012PAUU3038/document.

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Cette thèse propose une modélisation numérique 2D des écoulements en zone de jet de rive avec un code Volume-Of-Fluid. Dans un premier temps, le détail de la structure interne de l’écoulement de jet de rive généré par l’effondrement d’un front d’onde turbulent sur une plage imperméable lisse est étudié. Le modèle numérique est ensuite étendu à la simulation des écoulements en milieu poreux internes à la plage. L’utilisation d’une unique équation de quantité de mouvement (VARANS) et de la méthode 1-fluide, permet de résoudre simultanément les écoulements de l’eau et de l’air à la surface et dans une plage perméable. Ce modèle a été confronté à une série de cas tests analytiques et à de récentes mesures expérimentales. Les résultats numériques montrent l’aptitude du modèle VOF-VARANS à reproduire les écoulements en zone de jet de rive sur une plage imperméable fixe
A 2D numerical modeling of flows in the swash zone is proposed using a Volume-Of- Fluid code. The detailed flow structure of a bore-driven swash event over an impermeable beach is first studied. The numerical model is then developed to account for porous media flow within the beach. The unique VARANS momentum equation and 1-fluid method used allow to solve simultaneously both surface and subsurface flows of air and water phases in the swash zone. This model is validated against a series of analytical tests cases and confronted to recent experimental measurements. The numerical results highlight the ability of the VOF-VARANS model to reproduce swash flows over and within a permeable beach

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Sincos, Igor Rafael. "Determinação do impacto do oversizing da endoprótese sobre a aorta torácica. Estudo experimental em porcos". Universidade de São Paulo, 2012. http://www.teses.usp.br/teses/disponiveis/5/5132/tde-22012013-160615/.

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Introdução: A utilização da técnica endovascular para tratar as diversas afecções da aorta têm suplantado as técnicas abertas tradicionais, sendo particularmente promissora no trauma 1. A ruptura traumática da aorta é a segunda causa de morte por acidente de trânsito 2,3; e o reparo endoluminal dessas lesões com endopróteses apresenta menor taxa de mortalidade e paraplegia quando comparada a cirurgia aberta, no entanto os resultados a longo prazo ainda não estão disponíveis2-7. As próteses aprovadas e comercialmente disponíveis, até o momento desse estudo, foram desenhadas para doença aneurismática, com diâmetro muito superior ao diâmetro da aorta de jovens (vítimas de trauma). Esse sobredimensionamento (oversizing) pode levar a alteração mecânica na interação da prótese com a parede aórtica, comprometendo a vascularização e aumento o risco de complicações relacionadas ao implante de endopróteses 8-12. Objetivos: Analisar, a partir de um modelo animal experimental, o efeito biomecânico e histopatológico de quatro níveis diferentes de sobredimensionamento de endopróteses sobre a aorta não aterosclerótica, semelhante às encontradas em pacientes jovens vítimas de trauma. Método: O diâmetro da aorta torácica suína é semelhante ao da aorta de jovens adultos (18-20 mm), desta forma 25 porcos foram randomizados em 5 grupos: 1 controle (sem stent) e 4 grupos de sobredimensionamento (A: 10% -19 %, B: 20% -29%, C: 30% -39%, e D: >40% de sobredimensionamento). Dois tipos de testes biomecânicos foram realizados em todas as aortas 4 semanas após a implantação da endoprótese: \" z\" endoprótese; e o teste de biomecânica propriamente dito dos fragmentos aórticos coletados. Os fragmentos foram, então, submetidos a uma análise histológica e imunohistoquímica. Resultados: Os resultados do teste de destacamento, que avaliou a força necessária para remover o stent da aorta, foram semelhantes nos quatro grupos (A: 42 N, B: 41 N, C: 46 N e D: 46 N, p= 0,881204). O segundo teste foi realizado em três segmentos da aorta. Força máxima, estresse máximo e tensão máxima suportada pela parede da aorta tiveram uma correlação negativa e linear com o oversizing, isto é, quanto maior o oversizing, menor a resistência do fragmento à ruptura. Houve diferenças significativas em todos os quatro grupos, quando comparados com o grupo controle. A deformação máxima e o Strain, que refletem as propriedades elásticas da parede da aorta, foram muito semelhantes em todos os quatro grupos de sobredimensionamento. Mas, uma diminuição significativa da elasticidade foi encontrada quando comparados cada um dos grupos com o grupo controle (p= 0,0000001). A análise histológica e imunohistoquímica demonstrou que a parede da aorta tem uma perda significativa de fibras musculares e ?-actina com o aumento do sobredimensionamento (p= 0,000198 e p= 0,002031, respectivamente). A quantidade de fibra elástica apresentou uma queda significativa independente do sobredimensionamento (p= 0,0000001). Conclusões: Os quatro níveis de sobredimensionamento estudados não demonstraram diferenças significativas no teste de destacamento. Os testes biomecânicos dos fragmentos da aorta mostraram uma diminuição na resistência da parede aórtica proporcional ao aumento do oversizing. A elasticidade da parede aórtica sofre alteração significativa independente do sobredimensionamento utilizado. Os exames histopatológicos e imunohistoquímicos comprovaram o desarranjo na estrutura da parede aórtica com a utilização de endopróteses, resultando na diminuição da quantidade de fibras elásticas e musculares
Introduction: The use of endovascular techniques to treat the various disorders of the aorta has supplanted traditional open techniques, and is particularly promising in trauma1. The traumatic rupture of the aorta is the second leading cause of death by traffic accident2, 3, and repair of these lesions with endoluminal stents has showed lower mortality and paraplegia when compared to open surgery, however the long-term results are not yet available2-7. The endoprosthesis approved and commercially available during this study were designed to aneurysmal disease, with a diameter greater than the diameter of the aorta of young people ( ) \" z \" prosthesis with the aortic wall, affecting the vascularization and raising the risk of complications related to stent-graft implantation8-12. Purpose: Analyze, from an experimental animal model, the biomechanical and histological effects of four different levels of stents-graft oversizing in non-atherosclerotic aortas; such as those aorta found in young individuals who undergo stent-graft repair for traumatic aortic injuries. Methods: The diameter of the porcine thoracic aorta is similar to the aorta of young adults (18-20 mm), so 25 pigs were randomized into 5 groups: 1 control (without stent-graft) and 4 oversizing groups (A: 10%-19%, B: 20%-29%, C: 30%-39%, and D: .40%). Two types of biomechanical tests were performed on all aortas 4 weeks after endoprosthesis deployment: The \"detachment\" of the stent, and the biomechanics test of aortic fragments collected. The fragments were submitted to a histological and an immunohistochemistry analysis. Results: The results of the detachment test, which analyzed the strength necessary to remove the stent-graft from the aorta, were similar in the 4 groups (A: 42 N, B: 41 N, C: 46 N e D: 46 N, p= 0,881204). The second test was performed in 3 aortic segments. Maximum strength, maximum stress, and maximum tension supported by the aortic wall had a negative and linear correlation with oversizing. There were significant differences in all 4 groups when compared with the control group. The maximum deformation and strain, which reflect the elastic properties of the aortic wall, were very similar in all 4 groups. But a significant decrease in elasticity was found when compared each group with the control group (p = 0.0000001). Histological and immunohistochemistry analysis supported that the aortic wall has a signifi-?-actin by increasing the oversize (p = 0.000198 p = 0.002031, respectively). The amount of elastic fiber showed a significant drop regardless of the oversizing (p = 0.0000001). Conclusion: The four levels of oversizing studied did not show significant differences in the detachment test. Biomechanical tests of the fragments of the aorta showed a decrease in resistance of the aortic wall with increase in oversize. The elasticity of the aortic wall undergoes significant change independent of the oversizing used. The histopathological and immunohistochemical examinations confirmed the breakdown in the structure of the aortic wall with the use of stents-graft, resulting in decreased amount of elastic and muscle fibers.

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Vlach, Jakub. "Porovnání návrhů monolitické konstrukce bez a se zohledněním postupu výstavby". Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2015. http://www.nusl.cz/ntk/nusl-227302.

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The aim of this thesis is to propose and evaluate static three-storey reinforced concrete structure. For static analysis supporting structure was used computer program based on FEM SCIA - Engineer 2013 - student version. In computing program have been two independent computational models and in 2D and 3D space. The results were compared and evaluated with each other. On the basis of the report is drafted drawings consisting of reinforcement drawing and drawing shape.

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Vouaillat, Guillaume. "Analyse de la fatigue de contact d'engrenages aéronautiques". Thesis, Lyon, 2020. http://www.theses.fr/2020LYSEI035.

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Le micro-écaillage est une défaillance en fatigue de contact qui intervient sur les composants de transmissions mécaniques tels que les roulements et les engrenages. Le plus souvent, il est le résultat d’un manque de lubrification ou d’un écart avec les spécifications d’état de surfaces. La conséquence est alors l’apparition de sur-contraintes dans le matériau qui évoluent vers des arrachements microscopiques de matière. Ces derniers sont appelés micro-écailles et peuvent éventuellement amener à des dysfonctionnements de la transmission dans laquelle les pièces impactées sont en jeu. La littérature a alors mené de nombreuses études à ce sujet mais manque de travaux liant dans la même analyse, la représentation de l’état de surface à l’origine de la défaillance d’une part et la simulation d’un état microstructural du matériau sollicité qui rentre en compte dans les mécanismes de création de la fatigue de contact, d’autre part. Les travaux de cette thèse présentent donc d’abord, un modèle regroupant ces deux caractéristiques, construit à partir des outils et théories de la littérature. Une étude paramétrique est alors conduite et permet d’estimer l’influence de plusieurs paramètres de contact (glissement, frottement, pressions, rugosité) sur les résultats de trois critères en fatigue de contact. La mise en place d’un critère complémentaire est alors nécessaire pour apporter des précisions là où les premiers critères semblent insuffisants. A partir de l’étude des contraintes de cisaillement au niveau des joints de grains du matériau, la prise en compte de l’historique complet de la sollicitation est possible. Elle permet notamment de proposer une durée de vie avant initiation des microfissures et d’identifier dans le cas du glissement, des cycles locaux complémentaires de sollicitation. Ces derniers résultent des passages répétés des pics rugueux en surface du matériau. Finalement, une comparaison avec une application expérimentale sur composant denture d’engrenages apporte des éléments d’identification des zones à risque vis-à-vis du micro-écaillage dans les applications concernées
Gears and rolling elements that are parts of transmissions are sometimes subjected to rolling contact fatigue failures as micro-pitting. It usually results from a lubrication loss or an uncontrolled surface finishing. First layers of the material are consequently overstressed. Microscopic material wrenching then occurs and is called micro-pitting. Such transmission parts failures may potentially lead to the whole system dysfunction. Several studies have already been performed in the literature concerning this topic. However, few of them take into account both surface roughness and material microstructure analyses which impact rolling contact fatigue mechanisms. Thus, a model with those characteristics is developed from literature theories and tools and presented in this thesis. A parametrical study is then conducted so as to estimate the influence of specific contact parameters (among sliding, friction, pressure and roughness) on three fatigue criteria results. However the use of an additional criterion is necessary in order to give more accurate conclusions. Intergranular shear stresses are subsequently studied and make the analysis of the complete stress history possible. Moreover, a life expectancy to micro-cracks nucleation is computed. An identification of sliding-linked local shear stress oscillations which result from successive rough peaks passing over the material surface is also made. Finally, numerical results are compared to an experimental investigation conducted on FZG-type gears. The most at risk areas regarding micropitting in the relevant applications are thus identified among the addendum, the dedendum and the pitch

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Andersson, Harald. "Numerical and experimental study of confluent jets supply device with variable airflow". Licentiate thesis, Högskolan i Gävle, Energisystem och byggnadsteknik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:hig:diva-29271.

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In recent years, application of confluent jets for design of ventilation supply devices has been studied. Similarly, numerus studies have been made on the potential and application of variable air volume (VAV) in order to reduce the energy demand of ventilation systems. This study investigates the combination of supply devices based on confluent jets and VAV, both in terms of the nearfield flow behavior of the device and the impact on thermal comfort, indoor air quality and energy efficiency on a classroom-level space when the airflow rate is varied. The method used in this study is an experimental field study where the confluent jets-based supply devices were compared to the previously installed displacement ventilation. The field study evaluated the energy efficiency, thermal comfort and indoor air quality of the two systems. In the case of the confluent jets supply devices, airflow rate was varied in order to see what impact the variation had on the performance of the system for each airflow rate. Furthermore, the confluent jets supply devices were investigated both experimentally and numerically in a well insulated test room to get high resolution data on the particular flow characteristics for this type of supply device when the airflow rate is varied. The results from the field study show nearly uniform distribution of the local mean age of air in the occupied zone, even in the cases of relatively low airflow rates. The airflow rates have no significant effect on the degree of mixing. The thermal comfort in the classroom was increased when the airflow rate was adapted to the heat load compared to the displacement system. The results lead to the conclusion that the combination of supply devices based on confluent jets can reduce energy usage in the school while maintaining indoor air quality and increasing the thermal comfort in the occupied zone. The results from the experimental and numerical study show that the flow pattern and velocity in each nozzle is directly dependent on the total airflow rate. However, the flow pattern does not vary between the three different airflow rates. The numerical investigation shows that velocity profiles for each nozzle have the same pattern regardless of the airflow rate, but the magnitude of the velocity profile increases as the airflow increases. Thus, a supply device of this kind could be used for variable air volume and produce confluent jets for different airflow rates. The results from both studies show that the airflow rate does not affect the distribution of the airflow on both near-field and room level. The distribution of air is nearly uniform in the case of the near-field results and the room-level measurement shows a completely uniform degree of mixing and air quality in the occupied zone for each airflow rate. This means that there is potential for combining these two schemes for designing air distribution systems with high energy efficiency and high thermal comfort and indoor air quality.
Under senare tid har applikation av Confluent jets för design av tilluftsdon studerats. Många studier har även utförts över potentialen av att applicera variabelt luftflöde (VAV) för att minska energianvändningen i ventilationssystem. Denna studie undersöker möjligheten att kombinera Confluent jets-don med VAV, både med avseende på den lokala flödesbilden och dess påverkan på termisk komfort, luftkvalitet och energieffektivitet i en klassrumsmiljö där luftflödes varieras. Denna studie baseras dels på en experimentell fältstudie där tilluftsdon baserade på Confluents jets jämfördes med befintliga deplacerande tilluftsdon. Fältstudien utvärderade energieffektiviteten, den termiska komforten och luftkvaliteten för båda typerna av tillluftsdon. Confluent jets-donen testades under varierat luftflöde för att se påverkan av flödesvariationen på ventilationens prestation under de olika flödena. Utöver fältstudien testades Confluent jets-donen experimentellt och numeriskt i ett välisolerat test-rum för få den detaljerade flödeskarakteristiken för den här typen tilluftsdon vid varierat luftflöde. Resultaten från fältstudien visar på en jämn fördelning av den lokala luftsmedelåldern i vistelsezonen, även för fallen med relativt låga luftflöden. Luftflöden har ingen signifikant effekt på omblandningen. Den termiska komforten i klassrummet ökade när luftflödet anpassades efter värmelasten jämfört med de deplacerande donen. Slutsatsen från fältstudien är att kombinationen av VAV och Confluent jets-don kan användas för att minska energianvändningen på skolan och bevara luftkvaliteten och den termiska komforten i vistelsezonen. Resultaten från den experimental och numeriska studien visar luftflödet och lufthastigheten i varje enskild dysa är direkt beroende på det totala luftflödet genom donet. Dock är flödesfördelningen mellan dysorna oberoende av de tre olika luftflödena. Den numeriska undersökningen visar att flödesprofilen för varje dysa är konstant trots att flödet varieras, men amplituden för varje profil ökar med en höjning av luftflödet. Det betyder att tilluftsdon av den här typen kan användas med VAV för att producera Confluent jets för olika luftflöden. Resultaten från båda studierna visar att luftflöde inte påverkar fördelningen av luften vare sig längs luftdonen eller på rumsnivå. Fördelningen av luften är nästan helt jämn längs donen och på rumsnivå är omblandningen och luftkvalitet den samma för varje luftflöde. Det betyder att det finns potential för att kombinera det här två teknikerna för att designa luftdistribueringssystem med hög energieffektivitet och hög termisk komfort med god luftkvalitet.

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Chovet, Rogelio. "Caractérisation expérimentale et numérique du comportement rhéologique d'un fluide complexe : application à une mousse en écoulement dans un canal horizontal droit avec et sans singularités". Thesis, Valenciennes, 2015. http://www.theses.fr/2015VALE0021/document.

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Ce travail porte sur l’étude expérimentale et numérique de l’écoulement des mousses humides dans un canal horizontal droit de section carrée avec ou sans singularités. Il est consacré tout particulièrement à déterminer les paramètres pertinents de l’écoulement dont la chute de pression longitudinale, les champs de vitesse de l’écoulement de mousse en proche parois, les épaisseurs de films liquides minces et épais en paroi et l’évolution de la contrainte pariétale pour une mousse humide dont la fraction gazeuse varie de 55 à 85% et la vitesse débitante de la mousse est 2, 4 puis 6 cm/s. Une fois ces paramètres déterminés en conduite horizontale droite, nous avons ensuite effectué des mesures sur différentes géométries représentant un élargissement brusque, une chicane verticale et écoulement de mousse autour d’un cylindre, dont le but est d’étudier la réorganisation de l’écoulement en vue de déterminer le comportement rhéologique des mousses en écoulement à l’aval et à l’amont des singularités. Finalement, une étude de simulation numérique (CFD) en utilisant les lois de comportement de type Bingham, pour fluides non newtoniens, a été effectuée afin de tester sa capacité de représenter des écoulements type mousse humide dans une conduite horizontale avec ou sans singularités. Nous avons vérifié tout d’abord l’évolution longitudinale de la pression statique qui est linéaire à l’amont comme à l’aval loin des zones influencées par les singularités. La chute de pression singulière reste à peu près constante pour une vitesse débitante donnée de la mousse. À partir de la technique de Vélocimétrie par Image de Particule (PIV), nous avons déterminé les composantes de vitesse au voisinage immédiat des singularités. Ces mesures nous ont permis de mettre en évidence l’existence de différents régimes d’écoulement, et de déterminer la réorganisation et le comportement rhéologique de l’écoulement de mousse autour des géométries étudiées. L’analyse des mesures d’épaisseur de films liquides, obtenues par la méthode conductimétrique, indique que la paroi reste mouillée par un film liquide suffisamment épais pour qu’on puisse appliquer la méthode électrochimique. Les signaux polarographiques obtenus avec la mousse présentent alors de fortes fluctuations. La comparaison de celles-ci avec les contraintes pariétales déduites à partir des mesures de la chute de pression montre bien une bonne concordance. L’étude numérique (CFD), effectuée pour une fraction volumique de gaz égale à 70% et qui s’écoule avec une vitesse débitante de 2 cm/s, montre que le modèle rhéologique de Bingham pourrait être bien adapté à ce genre de mousse humide évoluant en écoulement en bloc
This work is an experimental and numerical study of aqueous foam flow inside a horizontal square duct, with and without flow disruption devices (fdd). It is especially devoted to determine the pertinent parameters of the flow: longitudinal pressure losses, velocity fields of foam flow near the walls, liquid film thickness (thick and thin), and the wall shear stress evolution, for an aqueous foam with a void fraction range between 55 and 85%, for a mean foam flow velocity of 2, 4 and 6 cm/s. Once they were determined, inside the horizontal channel, we carried out measurements over different geometries: half-sudden expansion, vertical fence and foam flow around a cylinder. The goal was to study the foam flow reorganization to well understand the rheological behavior of aqueous foam flow in the vicinities of different fdd. Finally, a numerical simulation (CFD), using the Bingham behavior model of non-Newtonian fluid, was undertaken to test its capacity to represent the aqueous foam flow inside the horizontal duct with flow disruption devices. First of all, we verified the static longitudinal pressure evolution, which varies linearly upstream and downstream far from the fdd. The singular pressure loss remains constant for a given mean foam velocity and a foam quality (void fraction). From the Particle Imaging Velocimetry (PIV) technique (2D), we determined the two velocity components in the immediate vicinities of the disruption devices. They allowed us to put into evidence the different foam flow regimes and to observe the foam flow reorganization and rheological behavior through the studied fdd. The slip-layer thickness analysis, obtained using the conductimetry method, shows that the wall presents a liquid film thick enough to apply an electrochemical technique (polarography). Thus, the polarographic signals, obtained for the foam flow, present important fluctuations. They were compared to the wall shear stress deducted from the measurement of pressure losses, showing a good similarity between them. The numerical study (CFD), carried out for aqueous foam flow with a void fraction of 70% and a mean foam flow velocity of 2 cm/s, shows that the Bingham rheological model can be adapted to this kind of aqueous foam flow which is flowing like a block

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Goudot, Guillaume. "Applications innovantes des ultrasons en pathologie vasculaire : utilisation de l'imagerie ultrarapide dans l'analyse de la rigidité artérielle et des ultrasons pulsés en thérapie Arterial stiffening assessed by ultrafast ultrasound imaging gives new insight into arterial phenotype of vascular Ehlers–Danlos mouse models Aortic wall elastic properties in case of bicuspid aortic valve Segmental aortic stiffness in bicuspid aortic valve patients compared to first-degree relatives Wall shear stress measurement by ultrafast vector flow imaging for atherosclerotic carotid stenosis Pulsed cavitational therapy using high-frequency ultrasound for the treatment of deep vein thrombosis in an in vitro model of human blood clot". Thesis, Sorbonne Paris Cité, 2018. https://wo.app.u-paris.fr/cgi-bin/WebObjects/TheseWeb.woa/wa/show?t=2215&f=13951.

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41

Baumgarten, Lars. "Gesteinsmechanische Versuche und petrophysikalische Untersuchungen – Laborergebnisse und numerische Simulationen". Doctoral thesis, Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2016. http://nbn-resolving.de/urn:nbn:de:bsz:105-qucosa-202612.

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Dreiaxiale Druckprüfungen können als Einstufenversuche, als Mehrstufenversuche oder als Versuche mit kontinuierlichen Bruchzuständen ausgeführt werden. Bei der Anwendung der Mehrstufentechnik ergeben sich insbesondere Fragestellungen hinsichtlich der richtigen Wahl des Umschaltpunktes und des optimalen Verlaufs des Spannungspfades zwischen den einzelnen Versuchsstufen. Fraglich beim Versuch mit kontinuierlichen Bruchzuständen bleibt, ob im Versuchsverlauf tatsächlich Spannungszustände erfasst werden, welche die Höchstfestigkeit des untersuchten Materials repräsentieren. Die Dissertation greift diese Fragestellungen auf, ermöglicht den Einstieg in die beschriebene Thematik und schafft die Voraussetzungen, die zur Lösung der aufgeführten Problemstellungen notwendig sind. Auf der Grundlage einer umfangreichen Datenbasis gesteinsmechanischer und petrophysikalischer Kennwerte wurde ein numerisches Modell entwickelt, welches das Spannungs-Verformungs-, Festigkeits- und Bruchverhalten eines Sandsteins im direkten Zug- und im einaxialen Druckversuch sowie in dreiaxialen Druckprüfungen zufriedenstellend wiedergibt. Das Festigkeitsverhalten des entwickelten Modells wurde in Mehrstufentests mit unterschiedlichen Spannungspfaden analysiert und mit den entsprechenden Laborbefunden verglichen.

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42

Tsai, Yu-Lin, i 蔡育霖. "Pulsatile Flows and Wall Shear Stress in Human Aortic Arch Model". Thesis, 2007. http://ndltd.ncl.edu.tw/handle/vzsswd.

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碩士
國立臺灣科技大學
機械工程系
95
Pulsatile flow characteristics and evolution processes in a model simulating the aortic arch of human being is diagnosed by using the particle tracking flow visualization method (PTFV) and the particle image velocimeter (PIV). The aortic arch model is made of transparent Plexiglas U-tube with three main branches (brachiocephalic artery, left common carotid artery, and left subclavian artery). Water is used as the working fluid. Pulsatile flows simulating the output of a human heart beat is supplied by a “pulsatile blood pump”. The results of this study are obtained using a 72 strokes/minute (1.2 Hz) stroke rate, a 75 ml/stroke (5.4 L/minute) stroke volume, and a 35%/65% systole/diastole ratio, all of which simulate the general conditions of the human cardiovascular system. The Womersley parameter, Dean number, and time-averaged Reynolds number are measured as 12.94, 2493, and 3697, respectively. The temporal/spatial evolution processes of the flow pattern, velocity distribution, and wall shear stress during systolic and diastolic phases are presented and discussed. It is found that the flows evolve complicatedly into three dimensional structures during the processes of acceleration, deceleration, and reversing. During the systole phase, the boundary layer on the inner wall separates from the area near the turning arch to the descending thoracic aorta. The induced reverse flow has low speed and would increase the probability of plaque deposition. During the diastolic phase, strong reverse flow is produced in the arch. Measured shear stresses show low values around the branch junctions and particularly high values around the outer wall of ascending aorta and descending thoracic aorta. These results correlate with the widely accepted clinic observation that the vessel segments that appear to be at the highest risk for development of atherosclerosis are around the junctions of the three branches and the aneurysms are tentatively found around the outer wall of ascending aorta and descending thoracic aorta. The oscillatory flow separation and shear stress distribution are apparently the primary causes leading to the atheroma and dissection/aneurysm.

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43

Wang, Teng, i 王騰. "Pulsatile Flows and Wall Shear Stress in Renal Arterial System Model". Thesis, 2009. http://ndltd.ncl.edu.tw/handle/98216540397202801179.

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碩士
國立臺灣科技大學
機械工程系
97
The pulsatile flow characteristics and evolution process in a model which simulate the renal artery of human being is diagnosed by using the particle tracking flow visualization method (PTFV) and the particle image velocimeter (PIV). The renal artery model is made of transparent plexiglas material which has different dimension with three tubes (abdominal artery, left renal artery and right renal artery). Mixture of glycerol and water at 37oC is used in the experiment as a working fluid to mimic the blood flow. To simulate the pulsating blood as it came out from the human heart, a “pulsatile blood pump” is used. A 72 strokes/minute (1.2Hz) stroke rate, with a volume flow rate of 4 L/min and a 45%/55% systole/diastole ratio is adopted in this study. The temporal/spatial evolution processes of the flow pattern, velocity distribution, and wall shear stress during systolic and diastolic phases are presented and discussed. During the systole stroke, the separation of boundary layer from the inner wall near the branch is shown in the PIV results. These characteristic flow structures induce reverse and low speed flows therefore would increase the probability of plaque deposition around the inner wall of the renal artery. The measured shear stresses around the branch junctions are low while the measured shear stresses at the outer wall of the renal artery are high. The high shear stress at the outer wall of the renal artery might crack the fibrolipid plaque and collagenous cap of atherosclerotic. This would induce rapid assembling of platelets on the exposed connective tissues which form the thrombosis. Furthermore it diminishes the transport of oxygen and metabolites supplied to the organ.

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44

Lai, Tzung-Chi, i 賴宗祺. "Prediction on Shear Stress-Strain Curve of Beam-Column Joint without Shear Reinforcement by Means of Softened Truss Model". Thesis, 2004. http://ndltd.ncl.edu.tw/handle/48637099010730042354.

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碩士
國立中央大學
土木工程研究所
92
This thesis comes from an idea of Hakuto’s shear degradation curve provided in 1990’s, proposing a rationally theoretical model verified basing on experimental data. The purpose of this study is to simulate the beam-column joint using a panel truss model via present concrete softened theories to find out the degradation curve of joint. Meanwhile, the analytical results of shear. Degradation on curves of beam-column joints can offer a tool for the seismic assessment of building structures. Results show, in order to predict the ultimate joint stress, the ratio of joint reinforcement have to properly reduce, restricting to the assumption of distributed joint reinforcement of the panel analysis. To obtain joint shear degradation curve, previous softened concrete models are adopted. According to data fitting, 1995’s Belarbi and Hsu softened model with Thorefeldt can simulate the behavior of beam-column joint well. However, it needs more experimental verification.

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45

Shih, Chien-Hung, i 施建宏. "The Plastic Model of Shear Energy Dissipation Device Using Low-yield-stress Steel". Thesis, 2006. http://ndltd.ncl.edu.tw/handle/04946621035025660204.

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碩士
中原大學
土木工程研究所
94
The low yield strength steel plate is materials developed newly in recent years, and it possesses large ductility, low yield strength, and small yield ratio. The researches of using shear energy dissipation device using low-yield-stress steel are very much in domestic and foreign. There are many models which can successful simulate disappears energy. It is necessary to find real response of the model can descript this material rightly. The studies is using isotropic-kinematic harden model with Ramberg-Osgood model in Nakashima【1,2】,and finds the model which has a good way of choseing parameters easily . The main purposes of this research are: (1) uses the model to simulate the disappear energy of shear energy dissipation device using low-yield-stress steel in the load tests, and finds five suitable parameters of model. They are the initial yield stress, the initial elastic stiffness, parameterα, parameterη, parameterβ. (2) simulates the capacity of disappear energy in different amplitude of load tests and discusses it.

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46

Gomez, Elizondo Carlos Arturo 1981. "Turbulence Modeling for Compressible Shear Flows". Thesis, 2012. http://hdl.handle.net/1969.1/148160.

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Compressibility profoundly affects many aspects of turbulence in high-speed flows - most notably stability characteristics, anisotropy, kinetic-potential energy interchange and spectral cascade rate. Many of the features observed in compressible flows are due to the changing nature of pressure. Whereas for incompressible flows pressure merely serves to enforce incompressibility, in compressible flows pressure becomes a thermodynamic variable that introduces a strong coupling between energy, state, and momentum equations. Closure models that attempt to address compressibility effects must begin their development from sound first-principles related to the changing nature of pressure as a flow goes from incompressible to compressible regime. In this thesis, a unified framework is developed for modeling pressure-related compressibility effects by characterizing the role and action of pressure at different speed regimes. Rapid distortion theory is used to examine the physical connection between the various compressibility effects leading to model form suggestions for the pressure-strain correlation, pressure-dilatation and dissipation evolution equation. The pressure-strain correlation closure coefficients are established using fixed point analysis by requiring consistency between model and direct numerical simulation asymptotic behavior in compressible homogeneous shear flow. The closure models are employed to compute high-speed mixing-layers and boundary layers in a differential Reynolds stress modeling solver. The self-similar mixing-layer profile, increased Reynolds stress anisotropy and diminished mixing-layer growth rates with increasing relative Mach number are all well captured. High-speed boundary layer results are also adequately replicated even without the use of advanced thermal-flux models or low Reynolds number corrections. To reduce the computational burden required for differential Reynolds stress calculations, the present compressible pressure-strain correlation model is incorporated into the algebraic modeling framework. The resulting closure is fully explicit, physically realizable, and is a function of mean flow strain rate, rotation rate, turbulent kinetic energy, dissipation rate, and gradient Mach number. The new algebraic model is validated with direct numerical simulations of homogeneous shear flow and experimental data of high-speed mixing-layers. Homogeneous shear flow calculations show that the model captures the asymptotic behavior of direct numerical simulations quite well. Calculations of plane supersonic mixing-layers are performed and comparison with experimental data shows good agreement. Therefore the algebraic model may serve as a surrogate for the more computationally expensive differential Reynolds stress model for flows that permit the weak-equilibrium simplification.

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47

Hung, Chien-Min, i 洪健閔. "Effects of Stent on Pulsatile Flows and Wall Shear Stress in Human Aortic Arch Model". Thesis, 2010. http://ndltd.ncl.edu.tw/handle/27520110313673929894.

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碩士
國立臺灣科技大學
機械工程系
98
The pulsatile flow characteristics in a human stent aortic arch has been studied experimentally using particle tracking flow visualization method (PTFV) and the particle image velocimeter (PIV). Such an aortic arch is modeled using transparent Plexiglas U-tube with three main branches (brachiocephalic artery, left common carotid artery, and left subclavian artery) while the working fluid used to mimic the blood is a mixture by water and glycerol. Pulsatile flows simulating the output of a human heart beat is supplied by a “pulsatile blood pump”. The results of this study are obtained using a 72 strokes/minute (1.2 Hz) stroke rate, a 70 ml/stroke (5 L/minute) stroke volume, and a 45% / 55% systole/diastole ratio. The temperature, Womersley parameter and time-averaged Reynolds number are set at 37oC, 16.28 and 1148 respectively. The temporal/spatial evolution processes of the flow pattern, velocity distribution, and wall shear stress during systolic and diastolic phases are presented and discussed. During the systole phase, the boundary layer at the inner wall separates from the area near the turning arch where the thoracic aorta descends. The induced reverse flow increases the probability of plaque deposition while the strong reverse flow during diastolic phase is produced in the arch. Measured shear stresses show low values around the branch junctions and particularly high values around the outer wall of ascending aorta and descending thoracic aorta. These results showed a potential risk of atherosclerosis around the junctions of the three branches and aneurysms at the outer wall of ascending aorta. The benefit of placing the stent at the descending thoracic aorta is the decrease of wall shear stress along the aortic arch and three main branches. Furthermore, shaking of wall shear stress decreases with time during systole and diastole cycle due to the present of stent. The present result would be useful for further improvements in placing of stent technology.

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48

Kun, Lan-Yi, i 藍益坤. "Effects of Fluid Influence of Atherosclerosis on Pulsatile Flows and Wall Shear-Stress in Human Aortic Arch Model". Thesis, 2008. http://ndltd.ncl.edu.tw/handle/67831041773328249451.

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碩士
國立臺灣科技大學
機械工程系
96
Pulsatile flow characteristics and evolution processes in a model simulating the aortic arch of human being is diagnosed by using the particle tracking flow visualization method (PTFV) and the particle image velocimeter (PIV). The aortic arch model is made of transparent Plexiglas U-tube which has different ratio with three main branches (brachiocephalic artery, left common carotid artery, and left subclavian artery). Working fluid is used as the mixture by water and glycerol. Pulsatile flows simulating the output of a human heart beat is supplied by a “pulsatile blood pump”. The results of this study are obtained using a 72 strokes/minute (1.2 Hz) stroke rate, a 70 ml/stroke (5 L/minute) stroke volume, and a 45%/55% systole/diastole ratio. The temperature, Womersley parameter and time-averaged Reynolds number are measured as 37℃, 17.31, 2869. During systole stroke, the boundary layer on the inner wall separates from the area near the turning arch to the descending thoracic aorta and three dimensional secondary flows are observed. These characteristic flow structures induce reverse and low speed flows and therefore would increase the probability of plaque deposition around the inner wall of the arch. When the stenosis increases, the separation point would be deferred a little to the downstream area and the timing for separation would be advanced. During the diastolic phase, strong reverse flow is produced in the arch. Measured shear stresses show low values around the branch junctions and particularly high values around the outer wall of ascending aorta and descending thoracic aorta. In the aortic arch model with the atherosclerotic, the maximum wall shear stress appears on the inner wall of the arch might crack fibrolipid plaque and collagenous cap of atherosclerotic plaque and therefore would induce rapid assembling of platelets on the exposed connective tissues, form the thrombosis, and therefore diminish the transport of oxygen and metabolites to the organs.

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49

Tait, Simon J., J. Heald, I. K. McEwan, M. Soressen, G. Cunningham, B. Willetts i D. Goring. "Probabilistic modelling of bed-load composition". 2009. http://hdl.handle.net/10454/2850.

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No
This paper proposes that the changes which occur in composition of the bed load during the transport of mixed-grain-size sediments are largely controlled by the distributions of critical entrainment shear stress for the various size fractions. This hypothesis is examined for a unimodal sediment mixture by calculating these distributions with a discrete particle model and using them in a probabilistic calculation of bed-load composition. The estimates of bed-load composition compare favorably with observations of fractional transport rates made in a laboratory flume for the same sediment, suggesting that the hypothesis is reasonable. The analysis provides additional insight, in terms of grain mechanics, into the processes that determine bed-load composition. These insights strongly suggest that better prediction methods will result from taking account of the variation of threshold within size fractions, something that most previous studies have neglected.

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50

Fiddes, Lindsey. "A Study of the Flow of Microgels in Patterned Microchannels". Thesis, 2011. http://hdl.handle.net/1807/29719.

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This work describes the results of experimental study of the flow of soft objects (microgels) through microchannels. This work was carried with the intention of building a fundamental biophysical model for the flow of neutrophil cells in microcirculatory system. In Chapter 1 we give a summary of the literature describing the flow of cells and “model cells” in microchannels. Paramount to this we developed methods to modify microchannels fabricated in poly(dimethyl siloxane) (PDMS). Originally, these microchannels could not be used to mimic biological microenvironments because they are hydrophobic and have rectangular cross-sections. We designed a method to create durable protein coatings in PDMS microchannels, as outlined in Chapter 3. Surface modification of the channels was accomplished by a two-step approach which included (i) the site-specific photografting of a layer of poly(acrylamide) (PAAm) to the PDMS surface and (ii) the bioconjugation of PAAm with the desired protein. This method is compatible with different channel geometries and it exhibits excellent longevity under shear stresses up to 1 dyn/cm. The modification was proven to be successful for various proteins of various molecular weights and does not affect protein activity. The microchannels were further modified by modifying the cross-sections in order to replicate cardiovascular flow conditions. In our work, we transformed the rectangular cross-sections into circular corss-sections. Microchannels were modified by polymerizing a liquid silicone oligomer around a gas stream coaxially introduced into the channel, as outlined in Chapter 3. We demonstrated the ability to control the diameter of circular cross-sections of microchannels. The flow behaviour of microgels in microchannels was studied in a series of experiments aimed at studying microgel flow (i) under electrostatic interactions (Chapter 4), (ii) binding of proteins attached to the microgel and the microchannel (Chapter 5) and (iii) under the conditions of varying channel geometry (Chapter 6). This work overall present’s new methods to study the flow of soft objects such as cells, in the confined geometries of microchannels. Using these methods, variables can be independently probed and analyzed.

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