Dissertations / Theses: 'Wall models'

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Lamarche, Louis. "Reduction of wall interference for three dimensional models with two dimensional wall adaptation." Doctoral thesis, Universite Libre de Bruxelles, 1986. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/213544.

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Issa, Camille Amine. "Nonlinear earthquake analysis of wall pier bridges." Diss., Virginia Polytechnic Institute and State University, 1985. http://hdl.handle.net/10919/54297.

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Accurately predicting the response of complex bridge structures to strong earthquake ground motion requires the use of sophisticated nonlinear dynamic analysis computer programs not generally available to the bridge design engineer. The analytical tools that have been developed are generally applicable to bridges whose substructures can be idealized as beam-columns. Bridges with wall piers do not belong to this category The major objective of this study is to develop an analysis tool capable of simulating the effects of earthquakes on monolithic concrete wall pier bridges. Thus, after surveying the literature, a mathematical model is developed for the geometrically nonlinear earthquake analysis of wall pier bridges. Mixed plate elements are used to model the wall pier. The plate element has eight nodes and the degrees of freedom per node are three displacements and three moments. Beam elements are used to model the bridge deck. The beam element accounts for shear deformation and it has two nodes with three displacements and three rotations as degrees of freedom per node. A transitional element is used to join the beam elements to the plate elements. The equation of dynamic equilibrium is solved using the Newmark method with modified Newton-Raphson type iteration at each time step. The mixed plate element is used to model two plate structures and the results are compared with analytical and other finite element solutions. A two span wall pier bridge is modeled using the structural elements developed in this study. The digitized time history for the N-S component of the El Centro Earthquake of May 18, 1940, is used to seismically excite the bridge model.
Ph. D.

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SACCO, FRANCESCO. "Mathematical models and analysis of turbulent, wall-bounded, complex flows." Doctoral thesis, Gran Sasso Science Institute, 2020. http://hdl.handle.net/20.500.12571/15321.

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In the classical wall bounded turbulent flow a fundamental statement is the existence of a layer, called overlap layer, in which every flow behaves the same and the mean streamwise velocity of each system can be described with only the wall normal coordinate with a logarithmic profile, characterized by the von Kármán constant. This law has been at first derived on data on parallel flows and boundary layer, that are model flows for wall turbulence, but indeed have a much simpler flow than complex shape geometries. The formulation of Millikan has much more general requirement on the flow and it is based on the asymptotic expansion of the velocity field; this theory of the logarithmic behavior of the overlap layer is an asymptotic approximation, and so holds for very high Reynolds numbers, Re_τ → ∞. For this reason much of the research effort has been directed at increasing the Reynolds number. However, due to the limits in resources, and so in the possibility of reaching the highest possible value, every similarity theory is still incomplete; but like all asymptotic approximations, it can be improved with the addition of higher-order terms. We develop a correction of the classical von Kármán logarithmic law for a turbulent Taylor-Couette (TC) flow, the fluid flow developing between two coaxial, independently rotating cylinders, when the curvature of the system is small, i.e. with an inner to outer radius ratio η = r_i /r_o ≥ 0.9, when both the cylinder rotates with the same magnitude but in opposite directions. While in straight geometries like channel or pipe, the deviation from the law can be ascribed to the effect of pressure gradient, in small gap TC flow this effect can be accounted to the conserved transverse current of azimuthal motion. We show that, when the correction is applied, the logarithmic law is restored even when varying the curvature, and that the parameters founded here for TC flow converge to the ones founded in [P. Luchini. European Journal of Mechanics B Fluids, 71, 2018.] for plane Couette flow, in the limit of vanishing curvature η → 1.
In many shear- and pressure-driven wall-bounded turbulent flows secondary motions spontaneously develop and their interaction with the main flow alters the overall large-scale features and transfer properties. Taylor–Couette flow, the fluid motion developing in the gap between two concentric cylinders rotating at different angular velocities, is not an exception, and toroidal Taylor rolls have been observed from the early development of the flow up to the fully turbulent regime. In this manuscript we show that under the generic name of ‘Taylor rolls’ there is a wide variety of structures that differ in the vorticity distribution within the cores, the way they are driven and their effects on the mean flow. We relate the rolls at high Reynolds numbers not to centrifugal instabilities, but to a combination of shear and anti-cyclonic rotation, showing that they are preserved in the limit of vanishing curvature and can be better understood as a pinned cycle which shows similar characteristics as the self-sustained process of shear flows. By analysing the effect of the computational domain size, we show that this pinning is not a product of numerics, and that the position of the rolls is governed by a random process with the space and time variations depending on domain size.
We use experiments and direct numerical simulations to probe the phase space of low-curvature Taylor–Couette flow in the vicinity of the ultimate regime. The cylinder radius ratio is fixed at η = r_i /r_o = 0.91, where r_i (r_o ) is the inner (outer) cylinder radius. Non-dimensional shear drivings (Taylor numbers Ta) in the range 10^7 ≤ Ta ≤ 10^11 are explored for both co- and counter-rotating configurations. In the Ta range 10^8 ≤ Ta ≤ 10^10 , we observe two local maxima of the angular momentum transport as a function of the cylinder rotation ratio, which can be described as either ‘co-’ or ‘counter-rotating’ due to their location or as ‘broad’ or ‘narrow’ due to their shape. We confirm that the broad peak is accompanied by the strengthening of the large-scale structures, and that the narrow peak appears once the driving (Ta) is strong enough. As first evidenced in numerical simulations by Brauckmann et al. (J. Fluid Mech., vol. 790, 2016, pp. 419–452), the broad peak is produced by centrifugal instabilities and that the narrow peak is a consequence of shear instabilities. We describe how the peaks change with Ta as the flow becomes more turbulent. Close to the transition to the ultimate regime when the boundary layers (BLs) become turbulent, the usual structure of counter-rotating Taylor vortex pairs breaks down and stable unpaired rolls appear locally. We attribute this state to changes in the underlying roll characteristics during the transition to the ultimate regime. Further changes in the flow structure around Ta ≈ 10^10 cause the broad peak to disappear completely and the narrow peak to move. This second transition is caused when the regions inside the BLs which are locally smooth regions disappear and the whole boundary layer becomes active.
Large scale structures have been observed in many turbulent wall bounded flows, such as pipe, Couette or square duct flows. Many efforts have been made in order to capture such structures to understand and model them. However, commonly used methods have their limitations, such as arbitrariness in parameter choice or specificity to certain setups. In this manuscript we attempt to overcome these limitations by using two variants of Dynamic Mode Decomposition (DMD). We apply these methods to (rotating) Plane Couette flow, and verify that DMD-based methods are adequate to detect the coherent structures and to extract the distinct properties arising from different control parameters. In particular, these DMD variants are able to capture the influence of rotation on large-scale structures by coupling velocity components. We also show how high-order DMD methods are able to capture some complex temporal dynamics of the large-scale structures. These results show that DMD-based methods are a promising way of filtering and analysing wall bounded flows.

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Diaz, Ricardo H. "Critical evaluation and development of one-equation near-wall turbulence models." College Park, Md. : University of Maryland, 2003. http://hdl.handle.net/1903/2170.

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Thesis (Ph. D.) -- University of Maryland, College Park, 2003
Thesis research directed by: Aerospace Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.

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Prinsloo, Wilma. "Computational models for conformations of cell wall mycolates from Mycobacterium tuberculosis." Diss., Pretoria : [s.n.], 2009. http://upetd.up.ac.za/thesis/available/etd-06122009-114802/.

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Gunawan, Leonardus. "Numerical models to simulate the thermal performance of LSF wall panels." Thesis, Queensland University of Technology, 2011. https://eprints.qut.edu.au/49856/1/Leonardus_Gunawan_Thesis.pdf.

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Fire safety of buildings has been recognised as very important by the building industry and the community at large. Gypsum plasterboards are widely used to protect light gauge steel frame (LSF) walls all over the world. Gypsum contains free and chemically bound water in its crystal structure. Plasterboard also contains gypsum (CaSO4.2H2O) and calcium carbonate (CaCO3). The dehydration of gypsum and the decomposition of calcium carbonate absorb heat, and thus are able to protect LSF walls from fires. Kolarkar and Mahendran (2008) developed an innovative composite wall panel system, where the insulation was sandwiched between two plasterboards to improve the thermal and structural performance of LSF wall panels under fire conditions. In order to understand the performance of gypsum plasterboards and LSF wall panels under standard fire conditions, many experiments were conducted in the Fire Research Laboratory of Queensland University of Technology (Kolarkar, 2010). Fire tests were conducted on single, double and triple layers of Type X gypsum plasterboards and load bearing LSF wall panels under standard fire conditions. However, suitable numerical models have not been developed to investigate the thermal performance of LSF walls using the innovative composite panels under standard fire conditions. Continued reliance on expensive and time consuming fire tests is not acceptable. Therefore this research developed suitable numerical models to investigate the thermal performance of both plasterboard assemblies and load bearing LSF wall panels. SAFIR, a finite element program, was used to investigate the thermal performance of gypsum plasterboard assemblies and LSF wall panels under standard fire conditions. Appropriate values of important thermal properties were proposed for plasterboards and insulations based on laboratory tests, literature review and comparisons of finite element analysis results of small scale plasterboard assemblies from this research and corresponding experimental results from Kolarkar (2010). The important thermal properties (thermal conductivity, specific heat capacity and density) of gypsum plasterboard and insulation materials were proposed as functions of temperature and used in the numerical models of load bearing LSF wall panels. Using these thermal properties, the developed finite element models were able to accurately predict the time temperature profiles of plasterboard assemblies while they predicted them reasonably well for load bearing LSF wall systems despite the many complexities that are present in these LSF wall systems under fires. This thesis presents the details of the finite element models of plasterboard assemblies and load bearing LSF wall panels including those with the composite panels developed by Kolarkar and Mahendran (2008). It examines and compares the thermal performance of composite panels developed based on different insulating materials of varying densities and thicknesses based on 11 small scale tests, and makes suitable recommendations for improved fire performance of stud wall panels protected by these composite panels. It also presents the thermal performance data of LSF wall systems and demonstrates the superior performance of LSF wall systems using the composite panels. Using the developed finite element of models of LSF walls, this thesis has proposed new LSF wall systems with increased fire rating. The developed finite element models are particularly useful in comparing the thermal performance of different wall panel systems without time consuming and expensive fire tests.

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Visonà, Nicolò. "Study of plasma-wall interaction by fast cameras and numerical models." Doctoral thesis, Università degli studi di Padova, 2016. http://hdl.handle.net/11577/3427219.

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The present thesis is the product of three years of research in the field on magnetically confined nuclear fusion, that has the ultimate goal of demonstrating the possibility of obtaining clean energy from fusion of light nuclei. One of the current problems in this field deals with the interaction between the plasma and the wall of the containing device. Heat and particle fluxes impinging on the first wall can damage the machine structure and, on the other hand, particles expelled by plasma facing materials can degradate the performance and threat the very goal of reaching controlled fusion. The activity carried out during the Ph.D. concerned the study of plasma-wall interactions, focusing on three main topics. The first was a numerical study of advanced magnetic configurations to mitigate heat load and power density deposited on the divertor plates of FAST, a tokamak proposed as a satellite experiment for ITER. The following activity has ben done at RFX-mod, a Reversed-Field Pinch magnetic confinement experiment located in Padova, Italy. The plasma interaction with tungsten covered samples has been studied to investigate the properties of the material for its possible employment in a machine upgrade. As last activity, heat fluxes of the plasma edge have been measured through the instertion of graphite samples in limiter configuration, measuring the heat decay length for the first time in an RFP. The work is organized as follows. Chapter 1 gives a general introduction to fusion plasmas, magnetic confinement and main toroidal configurations studied. A short presentation of RFX-mod is given along with a quick glance to ITER. Chapter 2 gives a more detailed introduction to the topic of plasma edge, introducing concepts that are at the basis of the work presented later, as the divertor and the limiter configuration. Physical phenomena as recycling and superthermal electrons are also introduced here. Chapter 3 describes numerical simulations in the framework of preliminary studies for the proposed FAST tokamak. A quasi-snowflake divertor configuration has been studied and compared against a standard divertor using the EDGE2D/EIRENE code. Chapter 4 presents experimental measurements of surface properties of tungsten covered and full graphite samples. The activity was carried out at RFX-mod with a fast visible camera that measured the samples interactions with the plasma and a comparative analysis has been performed. Chapter 5 describes the investigation of heat flux properties of the plasma edge of the RFP through graphite samples inserted as limiters in the RFX-mod plasma. The measured temperature has been converted to heat flux with two software tools, that have been benchmarked. Heat fluxes and the measured heat decay length have been analyzed and correlated with plasma parameters. Conclusions are presented in the last chapter with an overview of possible future developments.
La tesi presentata è il risultato di tre anni di ricerca nel settore della fusione nucleare a confinamento magnetico, che ha come obiettivo di dimostrare la possibilità di ottenere energia pulita dalla fusione di atomi leggeri. Uno dei problemi attuali in questo campo riguarda l'interazione tra il plasma e la parete del dispositivo che lo contiene. Infatti i carichi termici e i flussi di particelle che incidono sulla prima parete possono danneggiare la struttura della macchina e, d'altra parte, le particelle rilasciate dai materiali che si affacciano al plasma possono influire negativamente sulle prestazioni e sul raggiungimento stesso dell'obiettivo della fusione controllata. L'attività svolta durante il periodo del dottorato di ricerca si è concentrata sullo studio dell'interazione plasma-parete, focalizzandosi su tre argomenti principali. Il primo è stato uno studio numerico di configurazioni magnetiche avanzate per ridurre sia l'intensità che la densità del flusso di calore incidente sul divertore di FAST, un tokamak proposto come esperimento satellite di ITER. Successivamente l'attività è stata svolta su RFX-mod, un'esperimento situato a Padova di confinamento magnetico in configurazione Reversed-Field Pinch. Si è studiata sperimentalmente l'interazione del plasma con dei provini ricoperti di tungsteno per analizzare le proprietà di questo materiale e valu-tarne il possibile impiego per future modifiche dell'esperimento. Come ultima attività sono stati misurati i flussi termici nel bordo del plasma tramite l'inserimento di campioni di grafite in configurazione limiter, misurando la lunghezza di decadimento del calore per la prima volta in un RFP. Il lavoro è presentato come segue. Il Capitolo 1 dà un'introduzione generale ai plasmi da fusione, al confinamento magnetico e alle principali configurazioni toroidali studiate. Viene fatta una breve introduzione a RFX-mod insieme ad uno sguardo a ITER. Il Capitolo 2 fornisce un'introduzione all'argomento del bordo plasma, introducendo concetti che sono alla base del lavoro presentato di seguito, come le configurazioni di divertore e limiter. Sono anche introdotti fenomeni fisici come il riciclaggio e gli elettroni sopratermici. Il Capitolo 3 descrive le simulazioni numeriche fatte nel contesto di studi preliminari per il tokamak proposto FAST. Una configurazione quasi-snowflake è stata studiata e confrontata a una di divertore standard usando il codice EDGE2D/EIRENE. Il Capitolo 4 presenta misure sperimentali di proprietà superficiali di provini ricoperti di tungsteno e di pura grafite. L'attività è stata svolta a RFX-mod con una telecamera veloce nel visibile che ha misurato le interazioni con il plasma ed è stata svolta un'analisi comparativa. Il Capitolo 5 descrive l'indagine sulle proprietà del flusso di calore del bordo del plasma di un RFP attraverso l'inserimento di campioni di grafite in configurazione limiter nel plasma di RFX-mod. La temperatura misurata è stata convertita in flusso termico da due software che sono stati standardizzati. I flussi termici e la lunghezza di decadimento del calore misurata sono stati analizzati e correlati con i parametri di plasma. Le Conclusioni sono presentate nell'ultimo capitolo insieme ad una panoramica sui possibili sviluppi futuri.

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Gupta, Vikrant. "Linear amplification analysis for extraction of coherent structures in wall-bounded turbulent flows." Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708610.

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Sánchez, Rocha Martín. "Wall-models for large eddy simulation based on a generic additive-filter formulation." Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/28086.

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Thesis (M. S.)--Aerospace Engineering, Georgia Institute of Technology, 2009.
Committee Chair: Menon, Suresh; Committee Member: Cvitanović, Predrag; Committee Member: Sankar, Lakshmi N.; Committee Member: Smith, Marilyn J.; Committee Member: Yeung, Pui-Kuen

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Chin, David 1982. "Wall shear patterns of a 50% asymmetric stenosis model using photochromic molecular flow visualization." Thesis, McGill University, 2008. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=111613.

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Photochromic Molecular Flow Visualization is an in vitro, experimental technique that uses high speed image acquisition combined with an ultraviolet laser to capture instantaneous flow profiles. It is particularly adept at measuring near wall velocities which are necessary for accurate wall shear rate measurements. This thesis describes the implementation and validation of the technique at McGill. The system was used to investigate the wall shear rate patterns in an idealized 50% asymmetric stenosis model under steady flow for Reynolds numbers 206, 99 and 50. A large recirculation zone with flow reattachment was seen downstream of the stenosis with maximum shear values occurring slightly upstream of peak stenosis for Reynolds number 206. This information is vital to ongoing dynamic cell culture experiments aimed at understanding the progression of atherosclerosis.

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Lau, Mei-wan, and 劉美雲. "On the early development of dispersion in flow through a tube with wall reactions." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2007. http://hub.hku.hk/bib/B38994859.

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Sánchez, Rocha Martín. "Wall-models for large eddy simulation based on a generic additive-filter formulation." Diss., Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/28086.

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In this work, the mathematical implications of merging two different turbulence modeling approaches are addressed by deriving the exact hybrid RANS/LES Navier-Stokes equations. These equations are derived by introducing an additive-filter, which linearly combines the RANS and LES operators with a blending function. The equations derived predict additional hybrid terms, which represent the interactions between RANS and LES formulations. Theoretically, the prediction of the hybrid terms demonstrates that the hybridization of the two approaches cannot be accomplished only by the turbulence model equations, as it is claimed in current hybrid RANS/LES models. The importance of the exact hybrid RANS/LES equations is demonstrated by conducting numerical calculations on a turbulent flat-plate boundary layer. Results indicate that the hybrid terms help to maintain an equilibrated model transition when the hybrid formulation switches from RANS to LES. Results also indicate, that when the hybrid terms are not included, the accuracy of the calculations strongly relies on the blending function implemented in the additive-filter. On the other hand, if the exact equations are resolved, results are only weakly affected by the characteristics of the blending function. Unfortunately, for practical applications the hybrid terms cannot be exactly computed. Consequently, a reconstruction procedure is proposed to approximate these terms. Results show, that the model proposed is able to mimic the exact hybrid terms, enhancing the accuracy of current hybrid RANS/LES approaches. In a second effort, the Two Level Simulation (TLS) approach is proposed as a near-wall model for LES. Here, TLS is first extended to compressible flows by deriving the small-scale equations required by the model. The full compressible TLS formulation and the hybrid TLS/LES approach is validated simulating the flow over a flat-plate turbulent boundary layer. Overall, results are found in reasonable agreement with experimental data and LES calculations.

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Kabiri, Ali. "Wall St. 1929 : Contemporary valuation models, money market arbitrage and liquidity Black Holes." Thesis, City University London, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.509120.

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Caillé, Jean. "New integral and differential computational procedures for incompressible wall-bounded turbulent flows." Diss., Virginia Tech, 1992. http://hdl.handle.net/10919/37425.

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Three new computational procedures are presented for the simulation of incompressible wall-bounded turbulent flows. First, an integral method based on the strip integral method has been developed for the solution of three-dimensional turbulent boundary-layer flows. The integral equations written in a general form using non-orthogonal streamline coordinates include the turbulent shear stress at the upper limit of an inner strip inside the boundary-layer. The shear stress components are modeled using the Boussinesq assumption, and the eddy viscosity is defined explicitly as in differential methods. The turbulence modeling is not hidden in opaque empirical correlations as in conventional integral methods. A practical four-parameter velocity profile has been established based on the Johnston Law of the Wall using a triangular model for the crosswise velocity. Two strips are used to solve for the four unknowns: skin friction coefficient, wall crossflow angle, boundary-layer thickness, and location of maximum crosswise velocity. The location of maximum crosswise velocity proves to be a natural and adequate parameter in the formulation, but it is numerically sensitive and has a strong influence on the wall crossflow angle. Good results were obtained when compared to predictions of other integral or differential methods. Secondly, two computational procedures solving the Reynolds Averaged Navier-Stokes equations for 20 and 3D flows respectively have also been developed using a new treatment of the near-wall region. The flow is solved down to the wall with a slip velocity based on Clauser's idea of a pseudolaminar velocity profile. The present idea is different from the wall-function methods and does not require a multi-layer eddy viscosity model. The solution of the equations of motion is obtained by the Finite Element Method using the wall shear stress as a boundary condition along solid surfaces, and using the Clauser outer region model for the eddy viscosity. The wall shear stress distribution is updated by solving integral equations obtained from the enforcement of conservation of mass and momentum over an inner strip in the near-wall region. The Navier-Stokes solution provides the necessary information to the inner strip integral formulation in order to evaluate the skin friction coefficient for 2D flows, or the skin friction coefficient and the wall crossflow angle for 3D flows. The procedures converge to the numerically "exact" solution in a few iterations depending on the accuracy of the initial guess for the wall shear stress. A small number of nodes is required in the boundary-layer to represent adequately the physics of the flow, which proves especially useful for 3D calculations. Excellent results were obtained for the 2D simulations with a simple eddy viscosity model. 3D calculations gave good results for the turbulent boundary-layer flows considered here. The present methods were validated using well-known experiments chosen for the STANFORD conferences and EUROVISC workshop. The 2D numerical predictions are compared with the experimental measurements obtained by Wieghardt-Tillmann, Samuel-Joubert, and Schubauer-Klebanoff. For the 3D analyses, the numerical predictions obtained by the strip-integral method and the Finite Element Navier-Stokes Integral Equation procedure are validated using the Van den Berg-Elsenaar and Müller-Krause experiments.
Ph. D.

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Barrows, Richard James. "Two Dimensional Finite Element Modeling of Swift Delta Soil Nail Wall by "ABAQUS"." PDXScholar, 1994. https://pdxscholar.library.pdx.edu/open_access_etds/4741.

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Soil nail walls are a form of mechanical earth stabilization for cut situations. They consist of the introduction of passive inclusions (nails) into soil cut lifts. These nailed lifts are then tied together with a structural facing (usually shotcrete) . The wall lifts are constructed incrementally from the top of cut down. Soil nail walls are being recognized as having potential for large cost savings over other alternatives. The increasing need to provide high capacity roadways in restricted rights of way under structures such as bridges will require increasing use of techniques such as combined soil nail and piling walls. The Swift Delta Soil Nail wall required installing nails between some of the existing pipe piling on the Oregon Slough Bridge. This raised questions of whether the piling would undergo internal stress changes due to the nail wall construction. Thus, it was considered necessary to understand the soil nail wall structure interaction in relation to the existing pile supported abutment. The purpose of this study was to investigate the Swift Delta Wall using finite element (FE) modeling techniques. Valuable data were available from the instrumentation of the swift Delta Wall. These data were compared with the results of the FE modeling. This study attempts to answer the following two questions: 1. Is there potential for the introduction of new bending stresses to the existing piling? 2. Is the soil nail wall system influenced by the presence of the piling? A general purpose FE code called ABAQUS was used to perform both linear and non-linear analyses. The analyses showed that the piling definitely underwent some stress changes. In addition they also indicated that piling influence resulted in lower nail stresses. Comparison of measured data to predicted behavior showed good agreement in wall face deflection but inconsistent agreement in nail stresses. This demonstrated the difficulty of modeling a soil nail due to the many variables resulting from nail installation.

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Blackwell, Neal Elwood. "Wall jet model for ceiling fan applications in broiler houses." Diss., Virginia Polytechnic Institute and State University, 1985. http://hdl.handle.net/10919/54187.

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A model was developed to predict velocity profiles of radial wall jets produced by ceiling fans and flowing over broiler chickens. Broilers were modeled by balloons with paper cylinders simulating the necks. Wall jet data was recorded for 91.5, 83.8 and 71.1 cm radius fans that were rated at 220, 160, and 108 W, respectively. Each fan was suspended 2.44 m above the floor and operated at four speeds. Applications of the model include 1) calculation of optimum design specifications for ceiling fan applications in broiler houses and 2) prediction of data for managerial decisions concerning existing ceiling fan applications. Model inputs are the fan radius and the characteristic velocity. The characteristic velocity was defined as the maximum air velocity 30 cm below the blades. The wall jet model was interfaced with a broiler growth model for heat stressed broilers to simulate summer conditions and to predict the additional weight gain due to the wall jet. Also, the wall jet was developed to predict the air velocity near the litter to aid litter management decisions. Ceiling fan applications in the southeast, used in conjunction with the summer model, have the potential of increasing summer broiler production by 10% and decreasing fan energy consumption by 8 to 12%. The model may be used to optimize the benefit to the producer.
Ph. D.

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Lam, Sze Yue. "Ground movements due to excavation in clay : physical and analytical models." Thesis, University of Cambridge, 2010. https://www.repository.cam.ac.uk/handle/1810/228701.

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In view of the recent catastrophes associated with deep excavations, there is an urgent need to provide vital guidelines on the design of the construction process. To develop a simple tool for predicting ground deformation around a deep excavation construction for preliminary design and decision-making purposes, small scale centrifuge models were made to observe the complicated mechanisms involved. A newly developed actuation system, with which the construction sequences ofpropping could be implemented, was developed, the new procedures were proven to give more realistic initial ground conditions before excavation with minimal development of pre-excavation bending moment and wall displacement. Incremental wall deformation profiles generally followed the O'Rourke cosine bulge equation and a new deformation mechanism was proposed with respect to wall toe fixity and excavation geometry. Validation of the conservation energy principle was carried out for the undrained excavation process. The total loss of potential energy was shown to be balanced by the total work done in shearing and the total elastic energy stored in structures with an error term of 30%. An improved mobilizable strength method (MSD) method using observed mechanistic deformation patterns was introduced to calculate the displacement profile of a multi-propped undrained excavation in soft clay. The incremental loss in potential energy associated with the formation of settlement toughs was balanced by the sum of incremental storage of elastic energy and the energy dissipation in shearing. A reasonable agreement was found between the prediction by the MSD method and the finite element results computed by an advanced MIT-E3 model for wall displacements, ground settlement, base heave and bending moment on fixed base walls. For cases of excavations supported by floating walls, the effect of embedded wall length, depth of the stiff layer, bending stiffness of wall and excavation geometry and over-consolidation ratio of soils were found to have a influence on the maximum wall deflection. In general, the predictions fell within 30% of the finite element computed results. A new chart Ψ versus normalized system stiffness was used to demonstrate that MSD could correctly capture the trend of wall displacements increasing with the ratio ofexcavation depth to depth of stiff layer, which could be controlled by increasing wall stiffness for very stiff wall system only. The incorporation of a simple parabolic curvequantifying small strain stiffness of soil was proven to be essential to good ground movement predictions. A new dimensionless group has been defined using the MSD concepts to analyze 110 cases of excavation. The new database can now be used to investigate the relationship between structural response ratio S and soil-structure stiffness ratio R where this is shown on log-log axes to capture the enormous range of wall stiffness between sheet-piles and thick diaphragm walls. Wall stiffness was found to have a negligible influence on the magnitude of the wall bulging displacements for deep excavation supported by fixed-based wall with stiffness ranging from sheet pile walls to ordinary reinforced concrete diaphragm walls, whereas excavations supported by floating walls were found to be influenced by wall stiffness due to the difference in deformation mechanisms.

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Hosseinpoor, Masoud. "Numerical simulation of fresh SCC flow in wall and beam elements using flow dynamics models." Thèse, Université de Sherbrooke, 2016. http://hdl.handle.net/11143/9808.

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Abstract : Recently, there is a great interest to study the flow characteristics of suspensions in different environmental and industrial applications, such as snow avalanches, debris flows, hydrotransport systems, and material casting processes. Regarding rheological aspects, the majority of these suspensions, such as fresh concrete, behave mostly as non-Newtonian fluids. Concrete is the most widely used construction material in the world. Due to the limitations that exist in terms of workability and formwork filling abilities of normal concrete, a new class of concrete that is able to flow under its own weight, especially through narrow gaps in the congested areas of the formwork was developed. Accordingly, self-consolidating concrete (SCC) is a novel construction material that is gaining market acceptance in various applications. Higher fluidity characteristics of SCC enable it to be used in a number of special applications, such as densely reinforced sections. However, higher flowability of SCC makes it more sensitive to segregation of coarse particles during flow (i.e., dynamic segregation) and thereafter at rest (i.e., static segregation). Dynamic segregation can increase when SCC flows over a long distance or in the presence of obstacles. Therefore, there is always a need to establish a trade-off between the flowability, passing ability, and stability properties of SCC suspensions. This should be taken into consideration to design the casting process and the mixture proportioning of SCC. This is called “workability design” of SCC. An efficient and non-expensive workability design approach consists of the prediction and optimization of the workability of the concrete mixtures for the selected construction processes, such as transportation, pumping, casting, compaction, and finishing. Indeed, the mixture proportioning of SCC should ensure the construction quality demands, such as demanded levels of flowability, passing ability, filling ability, and stability (dynamic and static). This is necessary to develop some theoretical tools to assess under what conditions the construction quality demands are satisfied. Accordingly, this thesis is dedicated to carry out analytical and numerical simulations to predict flow performance of SCC under different casting processes, such as pumping and tremie applications, or casting using buckets. The L-Box and T-Box set-ups can evaluate flow performance properties of SCC (e.g., flowability, passing ability, filling ability, shear-induced and gravitational dynamic segregation) in casting process of wall and beam elements. The specific objective of the study consists of relating numerical results of flow simulation of SCC in L-Box and T-Box test set-ups, reported in this thesis, to the flow performance properties of SCC during casting. Accordingly, the SCC is modeled as a heterogeneous material. Furthermore, an analytical model is proposed to predict flow performance of SCC in L-Box set-up using the Dam Break Theory. On the other hand, results of the numerical simulation of SCC casting in a reinforced beam are verified by experimental free surface profiles. The results of numerical simulations of SCC casting (modeled as a single homogeneous fluid), are used to determine the critical zones corresponding to the higher risks of segregation and blocking. The effects of rheological parameters, density, particle contents, distribution of reinforcing bars, and particle-bar interactions on flow performance of SCC are evaluated using CFD simulations of SCC flow in L-Box and T-box test set-ups (modeled as a heterogeneous material). Two new approaches are proposed to classify the SCC mixtures based on filling ability and performability properties, as a contribution of flowability, passing ability, and dynamic stability of SCC.
Résumé : Récemment, il y a un grand intérêt à étudier les caractéristiques d'écoulement des suspensions dans différentes applications environnementales et industrielles, telles que les avalanches des neiges, les coulées de débris, les systèmes de transport et les processus d’écoulement des matériaux. En ce qui concerne les aspects rhéologiques, la plupart des suspensions, comme le béton frais, se comportent comme un fluide non-Newtonien. Le béton est le matériau de construction le plus largement utilisé dans le monde. En raison de limites qui caractérisent le béton normal en termes de maniabilité et de capacité de remplissage de coffrage, il était nécessaire de développer une nouvelle classe de béton qui peut couler sous son propre poids, en particulier à travers les zones congestionnées du coffrage. Par conséquent, le béton autoplaçant (BAP) est un nouveau matériau de construction qui est de plus en plus utilisé dans les différentes applications. Étant donné sa fluidité élevée de BAP peut être utilisé dans certaines applications particulières, notamment dans la section densément renforcée. Cependant, la fluidité élevée rend le béton plus sensible à la ségrégation des gros granulats pendant l'écoulement (la ségrégation dynamique) et ensuite au repos (ségrégation statique). La ségrégation dynamique peut augmenter lorsque le BAP est coulé sur une longue distance ou en présence d'obstacles. Par conséquent, il est toujours nécessaire d'établir un compromis entre la fluidité, la capacité de passage, et la stabilité du BAP. Ceci doit être pris en considération afin de concevoir le processus de coulée et dosage des mélanges du BAP. Ceci est appelé la conception d'ouvrabilité du BAP. Une conception de maniabilité efficace et non coûteuse peut être achevée à travers la e prévision et l'optimisation de l'ouvrabilité des mélanges de béton pour les procédés de construction sélectionnés, notamment le transport, le pompage, la mise en place, le compactage, la finition, etc. En effet, les formulations de mélange doivent se confirmer à la qualité de la construction demandée, par exemple les niveaux exigés de fluidité, la capacité de passage, la capacité de remplissage, et la stabilité (statique et dynamique). Celui est nécessaire pour développer des outils théoriques afin d’évaluer dans quelles conditions les exigences de qualité de la construction sont satisfaites. Cette thèse est consacrée à la réaliser des simulations analytiques et numériques pour prédire la performance d'écoulement du BAP dans différents procédés de la mise en place du béton. L'objectif spécifique de cette étude consiste à simuler l'écoulement du BAP dans essais empiriques, notamment la boite en L et la boite en T pour évaluer la performance du BAP pendent la mise en place (la fluidité, la capacité de passage, la capacité de remplissage, et la ségrégation dynamique induite par cisaillement ou par gravité). Par conséquent, le BAP est modélisé comme matériau hétérogène. En outre, un modèle analytique est proposé pour prédire la performance à l'écoulement du BAP dans la boite en L en utilisant la théorie de Dam Break. D'autre part, les résultats des simulations numériques de l’écoulement du BAP dans une poutre renforcée sont comparés aux résultats expérimentaux par des profils de surface libres. Les résultats des simulations numériques de BAP coulée (modélisée comme un fluide homogène unique), sont utilisés pour déterminer les zones critiques correspondant à des risques plus élevés de ségrégation et de blocage. Les effets des paramètres rhéologiques, la masse volumique, le contenu des particules, la distribution de barres d'armature, et les interactions particule-barres sur les performances d'écoulement du BAP sont évaluées à l'aide de simulations MFN d’écoulement du BAP par les essais des L-Box et T-box (modélisée comme une matériau hétérogène). Deux nouvelles approches sont proposées pour classifier les mélanges du BAP sur la base de la capacité de remplissage, et les propriétés de performabilité, en fonction de la fluidité, la capacité de passage et de la stabilité dynamique du BAP.

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Furbo, Eric. "Evaluation of RANS turbulence models for flow problems with signigicant impact of boundary layers." Thesis, Uppsala universitet, Institutionen för informationsteknologi, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-138757.

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This master’s thesis was provided by the Swedish Defence Research Agency, FOI. The task is to test several RANS (Reynolds-averaged Navier-Stokes) models on two different case geometries and compare the results with LES and experimental data. The ﬁrst is two dimensional, constructed for flow separation at a sharp edge. The second is three dimensional and flow separation occurs at a smooth surface. The models tested are implemented in the open source CFD (Computational Fluid Dynamics) program, OpenFOAM. OpenFOAM uses the finite volume method and the SIMPLE algorithm as solution procedure. The main flow features evaluated is the shape, position and size of the flow separation. Most of the models tested have problems describing the complex dynamics of flow separation in these particular cases. In addition to the simulations, the RANS k-epsilon turbulence model is presented and the RANS equations and the equation for the turbulent kinetic energy are derived from the Navier-Stokes equations. The theory behind wall functions is described and these equations together with the equations in the k-epsilon model are compared with the equations implemented in OpenFOAM.

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Heazel, Thomas Edward. "Cell wall sulfur distribution in sulfonated southern pine latewood." Diss., Georgia Institute of Technology, 1988. http://hdl.handle.net/1853/5786.

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Biehler, Jonas [Verfasser], Wolfgang A. [Akademischer Betreuer] [Gutachter] Wall, and Phaedon-Stelios [Gutachter] Koutsourelakis. "Efficient Uncertainty Quantification for Large-Scale Biomechanical Models Using a Bayesian Multi-Fidelity Approach / Jonas Biehler ; Gutachter: Wolfgang A. Wall, Phaedon-Stelios Koutsourelakis ; Betreuer: Wolfgang A. Wall." München : Universitätsbibliothek der TU München, 2016. http://d-nb.info/1123729220/34.

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Perry, Logan Andrew. "Sensitivity Study on Modification of Vertical Distribution of Strength and Stiffness in Wood Shear Wall Building Models." Thesis, Virginia Tech, 2018. http://hdl.handle.net/10919/96023.

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This thesis presents a numerical study of the influence of varying story strength on the seismic performance of multi-story wood-frame shear wall buildings. In the prior FEMA P695 studies of these buildings, the non-simulated collapse limit-state was exceeded primarily in the first story. This observation raised interest in quantifying the influence of varying strength from story to story on seismic response. In this study, four distributions of strength are used as bounding cases. The Parabolic strength distribution (1) results from the ELF vertical force distribution method in ASCE 7 that assigns forces to each level based on weight and story height. The Triangular strength distribution (2) results from an assumed vertical force distribution that assigns lateral forces based on the seismic weight at each level. The Constant strength distribution (3) results from an assumed vertical force distribution that assigns a concentrated lateral force at the uppermost level based on the total seismic weight of all levels. The Baseline distribution (4) reflects a realistic vertical strength distribution resulting from the ELF vertical force distribution method. The FEMA P695 methodology, which quantifies seismic performance via adjusted collapse margin ratios, is employed in this study. The analytical models include P-Delta effects and utilize the 10-parameter hysteresis CASHEW model. It is observed that the Parabolic strength distribution allows for dissipation of energy over the height of the building, has less collapse risk than other strength distributions studied, and reduces occurrence of concentrated deformations in a single story from the onset of applied lateral force.
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Grill, Maximilian Josef [Verfasser], Wolfgang A. [Akademischer Betreuer] Wall, Wolfgang A. [Gutachter] Wall, and Philipp J. [Gutachter] Thurner. "Computational Models and Methods for Molecular Interactions of Deformable Fibers in Complex Biophysical Systems / Maximilian Josef Grill ; Gutachter: Wolfgang A. Wall, Philipp J. Thurner ; Betreuer: Wolfgang A. Wall." München : Universitätsbibliothek der TU München, 2020. http://d-nb.info/122267274X/34.

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Mumaw, James. "A comparison of analytical models and experimental results for the acoustic response in a non-rigid-wall enclosure." Thesis, This resource online, 1996. http://scholar.lib.vt.edu/theses/available/etd-10022008-063326/.

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25

Karolyi, Daniel Roberts. "Hemodynamic wall shear stress in models of atherosclerotic plaques using phase contrast magnetic resonance velocimetry and computational fluid dynamics." Diss., Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/20132.

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Tassotti, Luca. "Seismic analysis and design of innovative steel and concrete hybrid coupled wall systems." Doctoral thesis, Università Politecnica delle Marche, 2015. http://hdl.handle.net/11566/242920.

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L’applicazione del concetto di fusibile strutturale nei sistemi sismo-resistenti ha portato allo sviluppo di diverse soluzioni strutturali, tra queste sono compresi i promettenti sistemi ibridi acciaio calcestruzzo. Questi sistemi sono ottenuti tramite una combinazione in serie di elementi in acciaio e in calcestruzzo armato con l’obiettivo di sfruttare al loro meglio le potenzialità di ciascun materiale. In questo lavoro viene indagato il comportamento sismico del sistema innovativo ibrido a parete accoppiata (HCSW), sviluppato nel progetto di ricerca europeo INNO-HYCO (INNOvative HYbrid and COmposite steel-concrete structural solutions for building in seismic area). La soluzione sismo-resistente è composta da una parete in calcestruzzo armato accoppiata a colonne laterali di acciaio tramite link sostituibili con l’obiettivo di sfruttare sia la rigidezza della parete, necessaria a limitare il danneggiamento della costruzione sotto l’azione di terremoti di bassa intensità, che la duttilità dei link di acciaio, necessaria a dissipare l’energia dei sismi di medio-alta intensità. Il comportamento sismico del sistema viene valutato tramite analisi statiche non lineari (pushover) e analisi dinamiche non lineari incrementali (IDA). Per questi scopi, inizialmente è stato progettato un insieme di casi studio realistici, poi è stato sviluppato un modello agli elementi finiti a fibre, validato successivamente tramite confronti con risultati sperimentali comprendendo quantità di risposta locali e globali. Infine, viene mostrata una selezione dei risultati ottenuti, includendo parametri di risposta locale e globale, per mettere in luce le potenzialità dei sistemi innovativi proposti e la concreta possibilità di sviluppare un comportamento duttile nel quale le deformazioni plastiche nei link sono attese prima dello snervamento della parete. Inoltre, i risultati finali permettono di fornire un supporto per l’identificazione delle soluzioni ottimali che potrebbero risultare competitive rispetto a sistemi esistenti.
The concept of structural fuse applied to earthquake resistant systems has led to the development of several seismic-resistant structural solutions, including interesting steel and concrete hybrid systems. These systems are obtained through a combination in series of steel elements and reinforced concrete elements with the aim of exploiting at their best the potentialities of each material. In this work the seismic behaviour of an innovative hybrid coupled shear wall (HCSW) system, developed in the European research project INNO-HYCO (INNOvative HYbrid and COmposite steel-concrete structural solutions for building in seismic area), is investigated. The earthquake resistant solution is composed by a reinforced concrete wall coupled to steel side columns by means of easily replaceable steel links with the objective to exploit both the stiffness of reinforced concrete wall, necessary to limit building damage under low-intensity earthquakes, and the ductility of steel links, necessary to dissipate energy under medium- and high-intensity earthquakes. The seismic behaviour of the system is assessed through nonlinear static (pushover) analysis and multi-record nonlinear incremental dynamic analysis (IDA). For this purpose, firstly a set of realistic case studies is designed, then a finite element model is developed into the platform Opensees and validated through comparisons against experimental tests including local and global responses quantities. A selection of results including global and local response quantities is shown in order to highlight the potentialities of the proposed innovative HCSW systems and the actual possibility to develop a ductile behaviour where plastic deformation are attained in the steel links before yielding in the reinforced concrete wall. The final results permit to provide a support for the identification of optimal solutions that could be competitive against existing seismic resistant structural systems.

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Williams, Scott A. "Numerical Analysis of Reinforced Masonry Shear Walls Using the Nonlinear Truss Approach." Thesis, Virginia Tech, 2014. http://hdl.handle.net/10919/25219.

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Reinforced masonry (RM) shear walls are a common lateral load-resisting system for building structures. The seismic design guidelines for such systems are based on relatively limited experimental data. Given the restrictions imposed by the capabilities of available experimental equipment, analytical modeling is the only means to conduct systematic parametric studies for prototype RM wall systems and quantify the seismic safety offered by current design standards. A number of modeling approaches, with varying levels of complexity, have been used for the analysis of reinforced concrete (RC) and masonry wall structures. Among the various methods, the truss analogy is deemed attractive for its conceptual simplicity and excellent accuracy, as indicated by recent studies focusing on RC walls. This thesis uses an existing modeling method, based on nonlinear truss models, to simulate the behavior of fully grouted reinforced masonry shear walls. The modeling method, which was originally created and used for RC walls, is enhanced to capture the effect of localized sliding along the base of a wall, which may be the dominant mode of damage for several types of RM walls. The truss modeling approach is validated with the results of quasi-static cyclic tests on single-story isolated walls and dynamic tests on a multi-story, three-dimensional wall system. For the latter, the truss model is found to give similar results to those obtained using a much more refined, three-dimensional finite element model, while requiring a significantly smaller amount of time for the analysis. Finally, truss models are used for the nonlinear static analysis of prototype low-rise walls, which had been analyzed with nonlinear beam models during a previous research project. The comparison of the results obtained with the two modeling methods indicates that the previously employed beam models may significantly overestimate the ductility capacity of RM squat walls, due to their inability to accurately capture the shear-flexure interaction and the effect of shear damage on the strength of a wall.
Master of Science

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Palombo, Carlo Loris. "Development and validation of an improved wall-function boundary condition for computational aerodynamics." Thesis, KTH, Strömningsmekanik och Teknisk Akustik, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-293754.

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Computational Fluid Dynamics is a powerful and widely used tool for developing projectsthat concern flow motion, in very different fields. Industrial CFD solvers are continuouslydeveloped with the aim of improving accuracy and reducing the computational cost of thesimulations. Turbulent wall-flow cases are particular demanding as the presence of a solidsurfaceinterface generates steep gradients in the proximity of the wall. Resolving suchgradients can be crucial to obtain a consistent solution but also very expensive in terms ofgrid refinement, and hence computational time. Wall functions are widely used and offersignificant computational savings when it comes to near-wall flow resolution. Previous wallfunction implemented in the M-Edge solver suffered by poor performances in complex flowscharacterized by strong pressure-gradient phenomena, such as separation. A new formulationhas been developed and validated for k − omega and Spalart-Allmaras turbulence models. Testsimulations started from simple and near-ideal cases (2D zero pressure gradient flat plate)and advanced to always more complex flow cases and geometries (full 3D general fighter).Every case has been run coupling the wall-function boundary condition with three differentturbulence models: the Menter SST, the Menter BSL with an EARSM and the Spalart-Allmaras one-equation model. Overall results showed the upgraded performance of new wallfunction in flow resolution together with more agile grid requirements, faster and deeperconvergence of the residuals and a general reduction in computational time.
Berör strömmande fluider inom mycket olika områden. Industriella CFD-lösare utvecklaskontinuerligt i syfte att förbättra noggrannheten och minska beräkningskostnaderna försimuleringarna. Turbulent strömning nära väggar är särskilt krävande eftersom närvaron avett fast ytgränssnitt genererar stora gradienter i närheten av väggen. Att lösa upp sådanagradienter kan vara avgörande för att få en konsistent lösning men också mycket beräkningskrävandepå grund av nödvändig nätförfining.Väggfunktioner används ofta och ger betydandereduktioner i beräkningstid när det gäller att lösa upp strömningen nära vägg. En tidigareväggfunktion implementerad i M-Edge-lösaren led av dåliga prestanda i komplexa flödenmed starka tryckgradienter, såsom separation. En ny formulering har utvecklats och valideratsför k − omega och Spalart-Allmaras turbulensmodeller. Den har testats för enkla generiska fall(2D-plan platta utan tryckgradient) och för mer avancerade och komplexa strömningsfall ochgeometrier (komplett 3D-stridsflygplan).Varje fall har körts med väggfunktionens randvillkorkopplat med tre olika turbulensmodeller: Menter SST, Menter BSL med EARSM och Spalart-Allmaras enekvationsmodell. De övergripande resultaten visar att nya väggfunktionen gerbetydande förbättringar i att beskriva strömningen tillsammans med reducerade krav pånätupplösning, snabbare och djupare konvergens av lösningen och en allmän minskning avberäkningstiden.

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Ranasinghe, Chathura P. "Development of combustion models for RANS and LES applications in SI engines." Thesis, Loughborough University, 2013. https://dspace.lboro.ac.uk/2134/12507.

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Prediction of flow and combustion in IC engines remains a challenging task. Traditional Reynolds Averaged Navier Stokes (RANS) methods and emerging Large Eddy Simulation (LES) techniques are being used as reliable mathematical tools for such predictions. However, RANS models have to be further refined to make them more predictive by eliminating or reducing the requirement for application based fine tuning. LES holds a great potential for more accurate predictions in engine related unsteady combustion and associated cycle-tocycle variations. Accordingly, in the present work, new advanced CFD based flow models were developed and validated for RANS and LES modelling of turbulent premixed combustion in SI engines. In the research undertaken for RANS modelling, theoretical and experimental based modifications have been investigated, such that the Bray-Moss-Libby (BML) model can be applied to wall-bounded combustion modelling, eliminating its inherent wall flame acceleration problem. Estimation of integral length scale of turbulence has been made dynamic providing allowances for spatial inhomogeneity of turbulence. A new dynamic formulation has been proposed to evaluate the mean flame wrinkling scale based on the Kolmogorov Pertovsky Piskunow (KPP) analysis and fractal geometry. In addition, a novel empirical correlation to quantify the quenching rates in the influenced zone of the quenching region near solid boundaries has been derived based on experimentally estimated flame image data. Moreover, to model the spark ignition and early stage of flame kernel formation, an improved version of the Discrete Particle Ignition Kernel (DPIK) model was developed, accounting for local bulk flow convection effects. These models were first verified against published benchmark test cases. Subsequently, full cycle combustion in a Ricardo E6 engine for different operating conditions was simulated. An experimental programme was conducted to obtain engine data and operating conditions of the Ricardo E6 engine and the formulated model was validated using the obtained experimental data. Results show that, the present improvements have been successful in eliminating the wall flame acceleration problem, while accurately predicting the in-cylinder pressure rise and flame propagation characteristics throughout the combustion period. In the LES work carried out in this research, the KIVA-4 RANS code was modified to incorporate the LES capability. Various turbulence models were implemented and validated in engine applications. The flame surface density approach was implemented to model the combustion process. A new ignition and flame kernel formation model was also developed to simulate the early stage of flame propagation in the context of LES. A dynamic procedure was formulated, where all model coefficients were locally evaluated using the resolved and test filtered flow properties during the fully turbulent phase of combustion. A test filtering technique was adopted to use in wall bounded systems. The developed methodology was then applied to simulate the combustion and associated unsteady effects in Ricardo E6 spark ignition engine at different operating conditions. Results show that, present LES model has been able to resolve the evolution of a large number of in-cylinder flow structures, which are more influential for engine performance. Predicted heat release rates, flame propagation characteristics, in-cylinder pressure rise and their cyclic variations are also in good agreement with measurements.

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Dick, Melissa. "The effect of statins on endothelial cell response to wall shear stress in three dimensional in vitro tissue culture models." Thesis, McGill University, 2012. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=107919.

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High blood cholesterol is a primary risk factor for cardiovascular diseases such as atherosclerosis. Atherosclerosis is a disease in which white blood cells, lipids (including cholesterol), and other cellular debris build up within the blood vessel walls to cause vessel inflammation and narrowing, ultimately leading to heart attack or stroke. Statin drugs, inhibitors of the enzyme 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, were designed to inhibit cholesterol synthesis by preventing the conversion of HMG-CoA to mevalonate within the cholesterol biosynthesis pathway. Although clinically effective at reducing circulating levels of cholesterol, statins have also been shown to have other beneficial effects, termed pleiotropic effects. Researchers believe that these pleiotropic effects are caused by the positive influence of statins on endothelial cells, the inner most layer of the vasculature that is constantly exposed to fluid wall shear stress.This work studied the cumulative effect of statin therapy and wall shear stress on endothelial cell structure and function using a three dimensional, in vitro tissue culture model. Endothelial cells were cultured within the model and exposed to 12.5 dynes/cm2 of wall shear stress and treated with the statin drug simvastatin for 24 hours. Endothelial cell morphology, F-actin cytoskeleton arrangement, and neutrophil adhesion to endothelial cells were analyzed.Statins caused endothelial cells to conform to a rounded, unhealthy phenotype, which was not reversed by the presence of wall shear stress. The F-actin cytoskeleton of the endothelial cells was disrupted by statin treatment, also non-reversible by wall shear stress. There was no conclusive evidence that statin therapy affected neutrophil adhesion, although wall shear stress significantly decreased adhesion. The addition of mevalonate reversed all statin effects, confirming statin regulation through the cholesterol biosynthesis pathway. Understanding how statin therapy affects endothelial cells in the presence of wall shear stress may allow for improved treatment options or more specific statin drugs in the future.
L'hypercholestérolémie est un facteur de risque des maladies cardiovasculaires comme l'athérosclérose. L'athérosclérose est une maladie dans laquelle les globules blancs, des lipides (y compris le cholestérol), et d'autres débris cellulaires s'accumulent dans les parois des vaisseaux sanguins ce qui provoque l'inflammation et le rétrécissement des vaisseaux, menant finalement à une crise cardiaque. Les statines, des inhibiteurs de l'enzyme 3-hydroxy-3-méthylglutaryl coenzyme A (HMG-CoA) réductase, ont été conçus pour inhiber la synthèse du cholestérol en empêchant la conversion de l'HMG-CoA en mévalonate dans la voie de biosynthèse du cholestérol. Bien que efficace pour réduire les taux de cholestérol, les statines démontrent d'autres effets bénéfiques. Les scientifiques pensent que ces effets sont causés par l'influence positive des statines sur les cellules endothéliales, la couche interne de la vascularisation qui est constamment exposée aux forces de cisaillement du fluide vasculaire.Ce travail étudie l'effet des statines et la contrainte de cisaillement sur la fonction et la structure des cellules endothéliales en utilisant un modèle tridimensionnel, in vitro de culture tissulaire. Les cellules ont été cultivées dans le modèle, exposées à une contrainte de cisaillement de 12,5 dynes/cm2, et traités avec la statine simvastatine pendant 24 heures. La morphologie des cellules endothéliale, l'arrangement du cytosquelette d'actine et l'adhésion des neutrophiles aux cellules endothéliales ont été analysés.Les statines ont causé l'arrondissement des cellules endothéliales, un phénotype malsain, qui n'a pas été renversé par la présence des forces de cisaillement. Le cytosquelette d'actine a été perturbé par le traitement aux statines, un effet qui n'a également pas été renversé par les forces de cisaillement. Il n'y avait pas de preuve que la thérapie aux statines affecte l'adhésion des neutrophiles, même si les forces de cisaillement ont diminué l'adhérence. L'ajout de mévalonate a inversé tous les effets des statines, ce qui confirme la réglementation statine par la voie de biosynthèse du cholestérol. Comprendre comment les statines affectent les cellules endothéliales en présence de forces de cisaillement pourrait permettre de meilleures options de traitement dans l'avenir.

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Guardigli, Sara. "Dynamic out-of-plane behaviour of Dutch cavity walls: validation of numerical models." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2017.

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After the second world war, cavity walls became a widespread external wall type in the North Western Europe including the Netherlands. Cavity walls consist of two leaves separated by a hollow space (cavity). The leaves are commonly made by masonry bricks, blocks, and wall ties. Wall ties are used to connect the two leaves of a cavity wall and are installed during construction. The ties are meant to withstand wind pressure mostly. Recently in the north of the Netherlands induced earthquakes took place. As consequence, many cavity walls may fail due to the crisis of the ties subjected to seismic solicitations for which they were not designed. The present work investigate numerically the behaviour of cavity masonry wall systems with or without wall ties. The models were implemented taking into account the physical and geometric nonlinearities. Both nonlinear static and dynamic analyses have been performed by means of the �nite element software DIANA.

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Johnson, Kevin Robert. "In Vivo Coronary Wall Shear Stress Determination Using CT, MRI, and Computational Fluid Dynamics." Diss., Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/14482.

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Wall shear stress (WSS) has long been identified as a factor in the development of atherosclerotic lesions. Autopsy studies have revealed a strong tendency for lesion development at arterial branch sites and along the inner walls of curvature areas that, in theory, should experience low WSS. Calculations of coronary artery WSS have typically been based upon average models of coronary artery geometry with average flow conditions and then compared to average lesion distributions. With all the averaging involved, a more detailed knowledge of the correlation between WSS and atherosclerotic lesion development might be obscured. Recent advancements in hemodynamic modeling now enable the calculation of WSS in individual subjects. An image-based approach for patient-specific calculation of in vivo WSS using computational fluid dynamics (CFD) would allow a more direct study of this correlation. New state-of-the-art technologies in multi-detector computed tomography (CT) and 3.0 Tesla magnetic resonance imaging (MRI) offer potential improvements for the measurement of coronary artery geometry and blood flow. The overall objective of this research was to evaluate the quantitative accuracy of multi-detector CT and 3.0 Tesla MRI and incorporate those imaging modalities into a patient-specific CFD model of coronary artery WSS. Using a series of vessel motion phantoms, it has been shown that 64-detector CT can provide accurate measurements of coronary artery geometry for heart rates below 70 beats per minute. A flow phantom was used to validate the use of navigator-echo gated, phase contrast MRI at 3.0 Tesla to measure velocity of coronary blood flow. Patient-specific, time-resolved CFD models of coronary WSS were created for two subjects. Furthermore, it was determined that population-average velocity curves or steady state velocities can predict locations of high or low WSS with high degrees of accuracy compared to the use of patient-specific blood flow velocity measurements as CFD boundary conditions. This work is significant because it constitutes the first technique to non-invasively calculate in vivo coronary artery WSS using image-based, patient-specific modeling.

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33

Yanovskiy, Vadim. "Theoretical analysis of tokamak disruptions by simplified analytical models and numerical simulations." Doctoral thesis, Università degli studi di Padova, 2016. http://hdl.handle.net/11577/3427140.

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One of the main obstacle on the way to the commercial fusion reactor based on the tokamak configuration is disruptions, which are abrupt terminations of the plasma discharge. Being not mitigated they can cause severe damage to the machine. For future large devices, like ITER and DEMO, strong electromagnetic loads on the vacuum vessel during disruptions pose a threat to their structural integrity. Some estimates for ITER give alarming hundred MN, but the lack of the predictive theory including all the effects into account, raise a concern about the accuracy of these evaluations. The largest forces are observed when plasma touches the wall. Their amplitudes depend on the halo currents, which are the part of the plasma current flowing into the conducting structures and then returning back into the plasma. Uncertainties in the halo current distribution and dynamics are a challenge for the theoretical modelling. The first part of this thesis presents the calculations of the EM force acting on the vacuum vessel within single-mode cylindrical approximation and the analysis of the interplay between eddy currents, plasma surface currents and halo currents. The second part of the thesis is dedicated to the most dangerous instabilities that can lead to a disruption: the resistive wall mode RWM and the tearing mode. In the presence of the resistive wall both can be suppressed or partially mitigated by the plasma rotation. This effect is studied analytically for configurations with positive and negative magnetic shear. For the advance tokamak scenario with hollow equilibrium current profile the influence of the differential plasma rotation on the double tearing mode stability is analyzed. The double and triple wall assemblies with different parameters are considered with respect to the problem of the magnetic island locking. In particular, a simple analytical formula for the electromagnetic torque acting on the plasma is derived for the ITER wall arrangement with double vacuum vessel and blanket.
Uno dei principali ostacoli sulla via della realizzazione di un reattore a fusione commerciale che si basi sulla configurazione Tokamak è rappresentato dalle disruzioni, cioè dalle terminazioni veloci della scarica di plasma, che se non adeguatamente mitigate possono causare danni gravi al reattore. Per futuri grandi impianti come ITER o DEMO, i forti carichi elettromagnetici sul contenitore da vuoto (vessel) durante le disruzioni possono minacciarne l’integrità strutturale. Alcune stime per ITER prevedono forze di decine di MN, ma la mancanza di una teoria veramente predittiva e completa, che includa tutti gli effetti rilevanti, solleva anche preoccupazioni sull’accuratezza di queste previsioni. Le forze più elevate sono osservate sperimentalmente quando il plasma viene in contatto con la prima parete. L’ampiezza dipende dalle cosiddette correnti di halo, che rappresentano la parte di corrente di plasma che può fluire verso le strutture conduttive ed eventualmente richiudersi nuovamente sul plasma stesso. Incertezze sull’ampiezza e la distribuzione delle correnti di halo e sulla dinamica del processo rappresentano una sfida aperta ai modelli teorici. La prima parte del lavoro di tesi presenta il calcolo delle forze elettromagnetiche sul vessel esercitate da una perturbazione in approssimazione cilindrica e l’analisi e la relazione tra vari tipi di correnti: le correnti indotte (eddy), le correnti di superficie (surface) e le correnti di halo propriamente dette. La seconda parte della tesi è dedicate alle instabilità più pericolose che possono portare a disruzioni: I modi di parete detti Resistive Wall Modes (RWM) e i modi tearing o riconnettivi. In presenza di una parete resistiva entrambi possono essere soppressi o almeno mitigati dalla rotazione di plasma. Questo effetto viene studiato analiticamente per configurazioni con shear magnetico positive e negative. Si analizza l’effetto della rotazione nel caso specifico di uno scenario tokamak avanzato con profilo di corrente cavo. Rispetto al problema del frenamento di un’isola magnetica vengono considerati gli effetti di pareti resistive multiple (fino a 3) aventi diverse conducibilità elettriche. In particolare viene derivata una formula analitica semplice per il momento elettromagnetico esercitato dalla parete di ITER, comprendente vessel e blanket.

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Šliaužytė, Brigita. "Kompiuterinio automatizuoto projektavimo posistemė pastato sienoms su angomis formuoti." Master's thesis, Lithuanian Academic Libraries Network (LABT), 2006. http://vddb.library.lt/obj/LT-eLABa-0001:E.02~2006~D_20060605_094639-19992.

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Many architects is working with AutoCAD system. But it is very time consuming work when it is needed to do such a work like drawing 3D models of walls with openings. This can be solved because of AutoCAD open architecture. Advantages of this would be less of errors in drawings and more time for other work for architects. Created software is able from 2D draft of lines make 3D walls and, if was chossed, openings. The user describes dimensions of wall and / or opening and the program will change selected line by set of planes with the opening inside. There are a few aviable options for user choise: openings may have a form of triangle or rectangular, walls maybe be like surfaces or lines, it is possible to create a wall with an array of rectangular openings, and delete already created walls leaving primary lines. For software creation was choosen Visual Basic for Aplication programing language because of it is object – oriented and easy comunication with standart AutoCAD’s classes and graphical objects. User‘s dialog’s form was choosen nearly these, what apear in such software like Architectural Desktop because of its logical simplicity. Supposing created software will be developed further in these ways: o Adding more opening’s shapes o Creating library of opening’s o Supporting all standarts needed for professional.

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Ding, Yao. "Evaluation of New Seismic Performance Factors for Special Hybrid Coupled Core Wall Systems with Steel Coupling Beams." University of Cincinnati / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1573225104906633.

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PELA', Luca. "CONTINUUM DAMAGE MODEL FOR NONLINEAR ANALYSIS OF MASONRY STRUCTURES." Doctoral thesis, Università degli studi di Ferrara, 2009. http://hdl.handle.net/11392/2389195.

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The present work focuses on the formulation of a Continuum Damage Mechanics model for nonlinear analysis of masonry structural elements. The material is studied at the macro-level, i.e. it is modelled as a homogeneous orthotropic continuum. The orthotropic behaviour is simulated by means of an original methodology, which is based on nonlinear damage constitutive laws and on the concept of mapped tensors from the anisotropic real space to the isotropic fictitious one. It is based on establishing a one-to-one mapping relationship between the behaviour of an anisotropic real material and that of an isotropic fictitious one. Therefore, the problem is solved in the isotropic fictitious space and the results are transported to the real field. The application of this idea to strain-based Continuum Damage Models is rather innovative. The proposed theory is a generalization of classical theories and allows us to use the models and algorithms developed for isotropic materials. A first version of the model makes use of an isotropic scalar damage model. The adoption of such a simple constitutive model in the fictitious space, together with an appropriate definition of the mathematical transformation between the two spaces, provides a damage model for orthotropic materials able to reproduce the overall nonlinear behaviour, including stiffness degradation and strain-hardening/softening response. The relationship between the two spaces is expressed in terms of a transformation tensor which contains all the information concerning the real orthotropy of the material. A major advantage of this working strategy lies in the possibility of adjusting an arbitrary isotropic criterion to the particular behaviour of the orthotropic material. Moreover, orthotropic elastic and inelastic behaviours can be modelled in such a way that totally different mechanical responses can be predicted along the material axes. The aforementioned approach is then refined in order to account for different behaviours of masonry in tension and compression. The aim of studying a real material via an equivalent fictitious solid is achieved by means of the appropriate definitions of two transformation tensors related to tensile or compressive states, respectively. These important assumptions permit to consider two individual damage criteria, according to different failure mechanisms, i.e. cracking and crushing. The constitutive model adopted in the fictitious space makes use of two scalar variables, which monitor the local damage under tension and compression, respectively. Such a model, which is based on a stress tensor split into tensile and compressive contributions that allows the model to contemplate orthotropic induced damage, permits also to account for masonry unilateral effects. The orthotropic nature of the Tension-Compression Damage Model adopted in the fictitious space is demonstrated. This feature, both with the assumption of two distinct damage criteria for tension and compression, does not permit to term the fictitious space as “isotropic”. Therefore, the proposed formulation turns the original concept of “mapping the real space into an isotropic fictitious one” into the innovative and more general one of “mapping the real space into a favourable (or convenient) fictitious one”. Validation of the model is carried out by means of comparisons with experimental results on different types of orthotropic masonry. The model is fully formulated for the 2-dimensional case. However, it can be easily extended to the 3-dimensional case. It provides high algorithmic efficiency, a feature of primary importance when analyses of even large scale masonry structures are carried out. To account for this requisite it adopts a strain-driven formalism consistent with standard displacement-based finite element codes. The implementation in finite element programs is straightforward. Finally, a localized damage model for orthotropic materials is formulated. This is achieved by means of the implementation of a crack tracking algorithm, which forces the crack to develop along a single row of finite elements. Compared with the smeared cracking approach, such an approach shows a better capacity to predict realistic collapsing mechanisms. The resulting damage in the ultimate condition appears localized in individual cracks. Moreover, the results do not suffer from spurious mesh-size or mesh-bias dependence. The numerical tool is finally validated via a finite element analysis of an in-plane loaded masonry shear wall.

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Nguyen, Van Vinh. "Direct Strength Method for the Design of Cold-Formed Steel Sections Under Localised Loading." Thesis, The University of Sydney, 2017. http://hdl.handle.net/2123/17069.

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The main objective of the thesis is the development of the Direct Strength Method (DSM) for the design of cold-formed steel sections under general localised loading. In order to calibrate the DSM equations, it is necessary to have three main input variables which are the buckling load, the yield load and the experimental data. The first objective of this research is the development of the Finite Strip Method (FSM) theory for analysis of thin-walled sections under localised loading with general end boundary conditions to determine the buckling load as described in Chapters 3 and 4 of the thesis. The theory is included in Version 2.0 of the THIN-WALL-2 program which can be used for analysing structural members under generalised loading conditions as described in Chapter 5. The second objective is the formulation of plastic mechanism models to estimate the yield load of thin-walled sections subjected to localised loading. In order to establish these models, observations are performed from experiments to ascertain the failure modes of structural members under localised loading with different cross-sections, load cases and flange fastening conditions. From the data, new simple plastic mechanism models are built-up based on the concept of the balance between the internal energy of the structural member and the external energy of the applied loads to estimate the yield load as described in Chapter 6. The third objective is collating the experimental data of thin-walled sections under localised loading. The data is collected from previous literature for different types of cross-sections: un-lipped plain-C, lipped plain-C, SupaCee and Dimond Hi-Span channel (DHS) sections subjected to all load cases. In addition, both flange fastened and unfastened conditions are assembled in the experimental database as described in Chapter 6. From these three input variables, the DSM design equations are proposed for structural members under general localised loading. The method is a consistent and simplified model generalised for all localised load cases. It includes both an inelastic reserve component as observed in testing and a yield load component. Also, a reliability analysis calibration is performed to validate the accuracy of the DSM predictions with the collected experimental data as described in Chapter 7.

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Savio, Daniele. "Nanoscale phenomena in lubrication : From atomistic simulations to their integration into continuous models." Phd thesis, INSA de Lyon, 2013. http://tel.archives-ouvertes.fr/tel-00961197.

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The modern trends in lubrication aim at reducing the oil quantity in tribological applications. As a consequence, the film thickness in the contact zone decreases significantly and can reach the order of magnitude of a few nanometres. Hence, the surface separation is ensured by very few lubricant molecules. Atomistic simulations based on the Molecular Dynamics method are used to analyze the local behavior of these severely confined films. A particular attention is paid to the occurrence of wall slip: predictive models and analytical laws are formulated to quantify and predict this phenomenon as a function of the surface-lubricant pair or the local operating conditions in a contact interface. Then, the coupling between Molecular Dynamics simulations and macroscopic models is explored. The classical lubrication theory is modified to include slip effects characterized previously. This approach is employed to study an entire contact featuring a nano-confined lubricant in its center, showing a severe modification of the film thickness and friction. Finally, the lubricant quantity reduction is pushed to the limits up to the occurrence of local film breakdown and direct surface contact. In this scenario, atomistic simulations allow to understand the relationship between the configuration of the last fluid molecules in the contact and the local tribological behavior.

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Kheirkhah, Gildeh Hossein. "Numerical Modeling of Thermal/Saline Discharges in Coastal Waters." Thèse, Université d'Ottawa / University of Ottawa, 2013. http://hdl.handle.net/10393/24230.

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Liquid waste discharged from industrial outfalls is categorized into two major classes based on their density. One type is the effluent that has a higher density than that of the ambient water body. In this case, the discharged effluent has a tendency to sink as a negatively buoyant jet. The second type is the effluent that has a lower density than that of the ambient water body and is hence defined as a (positively) buoyant jet that causes the effluent to rise. Negatively/Positively buoyant jets are found in various civil and environmental engineering projects: discharges of desalination plants, discharges of cooling water from nuclear power plants turbines, mixing chambers, etc. This thesis investigated the mixing and dispersion characteristics of such jets numerically. In this thesis, mixing behavior of these jets is studied using a finite volume model (OpenFOAM). Various turbulence models have been applied in the numerical model to assess the accuracy of turbulence models in predicting the effluent discharges in submerged outfalls. Four Linear Eddy Viscosity Models (LEVMs) are used in the positively buoyant wall jet model for discharging of heated waste including: standard k-ε, RNG k-ε, realizable k-ε and SST k-ω turbulence models. It was found that RNG k-ε, and realizable k-ε turbulence models performed better among the four models chosen. Then, in the next step, numerical simulations of 30˚ and 45˚ inclined dense turbulent jets in stationary ambient water have been conducted. These two angles are examined in this study due to lower terminal rise height for 30˚ and 45˚, which is very important for discharges of effluent in shallow waters compared to higher angles. Five Reynolds-Averaged Navier-Stokes (RANS) turbulence models are applied to evaluate the accuracy of CFD predictions. These models include two LEVMs: RNG k-ε, and realizable k-ε; one Nonlinear Eddy Viscosity Model (NLEVM): Nonlinear k-ε; and two Reynolds Stress Models (RSMs): LRR and Launder-Gibson. It has been observed that the LRR turbulence model as well as the realizable k-ε model predict the flow more accurately among the various turbulence models studied herein.

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Vaa, Kristian Huustad. "Yttervägg av trä utan invändig diffusionsbarriär : En byggnadsfysikalisk studie av en stuga." Thesis, Mittuniversitetet, Avdelningen för ekoteknik och hållbart byggande, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:miun:diva-35526.

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Trä har byggnadsfysikaliska egenskaper som skiljer det från en del andra material som traditionellt har blivit använda som bärande delar vid byggen. Träets hygroskopiska egenskaper och låga egenvikt ger andra användningsområden än till exempel betong eller stål. Dess låga egenvikt ger också spännande konstruktionsmässiga möjligheter och kan göra det möjligt att bygga på platser som annars inte är tillgängliga utan användning av mer avancerande tekniker och transportmetoder. I denna rapport har en del av ytterväggen till en stuga undersökts med avsikt att bedöma huruvida det i väggkonstruktionen kommer uppstå problem med mögelangrepp. Den undersökta delen av väggen ligger tre meter under marknivå. Väggen är konstruerad med en ångspärr mot marken och med ett en meter tjockt lager cellglasgrus mot denna. Innanför cellglasgruset är det en geotextil, 2 x 100 mm träfiberisolering samt 93 mm vertikalt timrat limträtimmer vilket också utgör ytskiktet på invändig sida. Undersökningen utfördes som en analys av en simulering som blev genomförd med mjukvaran WUFI® Pro 6.1. Resultaten av analysen var kvantitativa data i form av grafer och diagram. Resultatet av simuleringen visade att det inte kommer uppstå problem med mögel i konstruktionen. Dock är träets fuktbuffrande egenskaper tydliga och det anses generellt viktigt att se till att material har en inbyggnadsfukthalt som är under det som är gynnsamt för växt av mögel.
Wood has physical properties that makes it different from most other materials that traditionally has been used as load bearing parts when constructing a building. The hygroscopic properties and low relative weight of wood makes room for a different field of application than what is the case with for instance concrete or steel. Its low relative weight also gives interesting constructional possibilities and can make it possible to build on sites otherwise inaccessible without advanced techniques and means of transport. In this report the lower part of an exterior wall in a mountain cabin has been studied. The purpose of the study has been to examine whether the cabin will have problems related to mould or fungus. The examined part of the wall lies three meters below ground level. It is constructed with a steam barrier towards the ground, and a one meter thick layer of foam glass fragments on the inside of this. Further towards the inside of the wall there is a geotextile, two layers of 100 mm wood fibre insulation and one layer of 93 mm thick laminated vertically timbered timber, which faces the inside of the cabin. The examination was performed as an analysis of a simulation made with the software WUFI® Pro 6.1. The results of the analysis were quantitative data in the form of graphs and diagrams that were easily assessed against relevant literature. The results from the simulation showed that the construction would not have any problems related mould or fungus. However, the moisture buffering properties of the wood are obvious, and it is generally considered important that materials have a built-in moisture that is below what is favourable for mould or fungus growth.

Betyg 2019-06-05

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41

Olander, Sahlén Simon. "Feature Analysis in Online Signature Verification on Digital Whiteboard : An analysis on the performance of handwritten signature authentication using local and global features with Hidden Markov models." Thesis, KTH, Skolan för datavetenskap och kommunikation (CSC), 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-224661.

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The usage of signatures for authentication is widely accepted, and remains one of the most familiar biometric in our society. Efforts to digitalise and automate the verification of these signatures are hot topics in the field of Machine Learning, and a plethora of different tools and methods have been developed and adapted for this purpose. The intention of this report is to study the authentication of handwritten signatures on digital whiteboards, and how to most effectively set up a dual verification system based on Hidden Markov models (HMMs) and global aggregate features such as average speed. The aim is to gauge which features are Suitable for determining that a signature is in fact genuine Suitable for rejecting forgeries Unsuitable for gauging the authenticity of a signature all together In addition, we take a look at the configuration of the HMMs themselves, in order to find good configurations for The number of components used in the model What type of covariance to use The best threshold to draw the line between a genuine signature and a forgery For the research, we collected a total of 200 signatures and 400 forgeries, gathered from 10 different people on digital whiteboards. We concluded that the best configurations of our HMMs had 11 components, used a full covariance model, and observed about five features, where pressure, angle and speed were the most important. Among the global features, we discarded 11 out of 35 due to either strong correlation with other features, or contained too little discriminatory information. The strongest global features were the ones pertaining to speed, acceleration, direction, and curvature. Using the combined verification we obtained an EER of 7 %, which is in the typical range of contemporary studies. We conclude that the best way to combine global feature verification with local HMM verification is to perform both separately, and only accept signatures that are admissible by both, with a tolerance level for the global and local verifications of 1.2 and 2.5 standard deviations, respectively.
Användandet av signaturer för autentisering är allmänt accepterat, och är fortfarande den mest använda biometriken i vårt samhälle. Arbetet med att digitalisera och automatisera verifieringen av dessa signaturer är ett populärt ämne inom maskininlärning, och en uppsjö av olika verktyg och metoder har utvecklats och anpassats för detta ändamål. Avsikten med denna studie är att bestämma hur man mest framgångsrikt kan inrätta ett verifikationssystem för handskrivna signatures på digitala whiteboards baserat på dolda Markovmodeller (HMMs) och globalt aggregerade attribut. Syftet är att bedöma vilka features som är Lämpliga för att bestämma huruvida en signatur är äkta Lämpliga för att avvisa förfalskningar Olämpliga för att mäta äktheten hos en signatur över huvud taget Utöver detta studerar vi HMM-konfigurationen själv, i syfte att hitta bra konfigurationer för Antalet komponenter som används i modellen Vilken typ av kovarians som ger bäst resultat Det bästa tröskelvärdet vid vilken att dra gränsen för huruvida en signatur är äkta eller förfalskad För forskningen samlade vi totalt in 200 signaturer och 400 förfalskningar från 10 olika personer med hjälp av digitala whiteboards. Vi drog slutsatsen att de bästa konfigurationerna hade 11 komponenter, använde komplett kovarians, och använde cirka fem features, där tryck, vinkel och hastighet var det viktigaste. Bland våra globala features kastade vi 11 av 35 på grund av att de antingen korrelerade för starkt med andra features, eller på grund av att de innehöll för lite information för att utröna huruvida en signatur var äkta eller ej. Våra bästa globala features var de som hänförde sig till hastighet, acceleration, riktning och krökning. Genom att använda den kombinerade verifieraren fick vi en EER på 7 %, vilket är i linje med liknande studier. Vi drog även slutsatsen att det bästa sättet att kombinera global verifiering med lokal HMM-verifiering är att utföra dem separat och endast acceptera signaturer som godkänns av bägge två. Den bästa toleransnivån för den globala och lokala verifieraren var 1,2 och 2,5 standardavvikelser, respektive.

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42

Stocca, Valentina. "Development of a predictive LES model for the study of the pollutant dispersion in urban areas." Doctoral thesis, Università degli studi di Trieste, 2010. http://hdl.handle.net/10077/3512.

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2008/2009
In this thesis, a new large-eddy simulation solver, LES-AIR, has been developed, tested and applied to a practical situation of flow and pollutant dispersion in urban environments. The novelty of the present research resides in the application of a high resolution, accurate, CFD technique to the simulation of real-life flows. The code uses a body fitted curvilinear grid to account for the macro geometry such as terrain slopes, and is thus able to reproduce in detail the complex conditions typical of urban areas; by utilizing the technique of immersed boundaries, the code is also able to mimic the presence the micro complexities such as anthropic structures (i.e. buildings). The first part of the thesis presents a detailed description of the mathematical and numerical model on which the code is based. An extensive set of validation tests was performed in flow configurations having an increasing degree of complexity in terms of forcing and geometry. The numerical model thus validated is applied for obtaining flow and pollutant dispersion in the Servola-Valmaura suburban area of the city of Trieste in Italy. The pollutant was introduced into the domain from a line source near the ground, mimicking the emission from vehicular traffic. In spite of the idealizations inherent to the model, LES-AIR is able to predict the flow and dispersion patterns well, and has proven to be a reliable tool for adaptation in urban pollution studies.
Nella presente tesi è stato sviluppato, testato ed applicato ad un caso studio applicativo un nuovo solutore numerico, chiamato codice LES-AIR, capace di predire i campi di vento e la dispersione di nquinanti in ambienti urbani. La maggiore novità di questo lavoro risiede nell’utilizzo di una tecnica ﬂuidodinamica molto accurata e ad alta risoluzione per la simulazione di ﬂussi reali. Il codice LES-AIR è capace di riprodurre con grande dettaglio le geometrie complesse tipiche delle aree urbane tramite l’utilizzo congiunto di una griglia curvilinea, che si adatta all’ orograﬁa del terreno, e della tecnica dei corpi immersi, con la quale vengono riprodotti gli ostacoli antropici, quali gli ediﬁci. Nella prima parte della tesi viene fornita una descrizione dettagliata del modello matematico e numerico su cui si basa il codice. Il modello è stato validato per mezzo di un esteso set di casi test, aventi un grado crescente di complessit à in termini di forzanti e di conﬁgurazione geometriche. Il modello così validato è stato applicato alla riproduzione di un caso applicativo nel quale i campi di vento e la dispersione di un inquinante nella zona di Servola-Valmaura, situata nella periferia di Trieste, sono stati simulati. L’ inquinante è stato introdotto da una sorgente lineare posta in prosimità del terreno e rappresentante l’emissione derivante dal traﬃco cittadino. Nonostante le condizioni idealizzate di vento considerate, il codice LES-AIR si è dimostrato molto eﬃcace nella predizione del ﬂusso e della dispersione dell’inquinante e quindi si è attestato essere un valido strumento negli studi d’ inquinamento urbani.
XXII Ciclo
1981

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43

Dilip, Deepu. "Wall Modeled Large Eddy Simulation of Flow over a Wall Mounted Hump." Thesis, Virginia Tech, 2014. http://hdl.handle.net/10919/64356.

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Large Eddy Simulation (LES) is a relatively more accurate and reliable alternative to solution of Reynolds Averaged Navier Stokes (RANS) equations in simulating complex turbulent flows at a lesser computational cost than a direct numerical simulation (DNS). However, LES of wall-bounded flows still requires a very high grid resolution in the inner wall layer making its widespread use difficult. Different attempts have been made in the past time to overcome this problem by modeling the near wall turbulence instead of resolving it. One such approach is a two-layer wall model that solves for a reduced one-dimensional equation in the inner wall layer, while solving for the filtered Navier-Stokes equations in the outer layer. The use of such a model allows for a coarser grid resolution than a wall resolved LES. This work validates the performance of a two-layer wall model developed for an arbitrary body fitted non-orthogonal grid in the flow over a wall mounted hump at Reynolds number 9.36x105. The wall modeled large eddy simulation (WMLES) relaxes the grid requirement compared to a wall resolved LES (WRLES) by allowing the first off-wall grid point to be placed at a y+ of approximately 20-40. It is found that the WMLES results are general good agreement with WRLES and experiments. Surface pressure coefficient, skin friction, mean velocity profiles, and the reattachment location compare very well with experiment. The WMLES and WRLES exhibit some under prediction of the peak values in the turbulent quantities close to the reattachment location, with better agreement with the experiment in the separated region. In contrast, a simulation that did not employ the wall model on the grid used for WMLES failed to predict flow separation and showed large discrepancies with the experimental data. In addition to the relaxation of the grid requirement in the wall normal direction, it was also observed that the wall model allowed a reduction in the number of computational cells in the span-wise direction by half. However an LES calculation on a grid with reduced number of cells in span-wise direction turned unstable almost immediately, thereby highlighting the effectiveness of the wall model. Besides reducing the number of grid points in the spatial domain, the relaxed grid resolution for the WMLES also permitted the use of a larger time step. This resulted in an order of magnitude reduction in the total CPU time relative to WRLES.
Master of Science

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44

Yang, Jin Rong. "The Application of Fuzzy Logic and Virtual Reality in the Study of Ancient Methods and Materials Used for the Construction of the Great Wall of China in Jinshanling." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu152410262072719.

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45

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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Koudela, Pavel. "Stanovení hodnot vstupních parametrů pokročilých materiálových modelů s využitím optimalizačních metod." Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2018. http://www.nusl.cz/ntk/nusl-372248.

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Choice of the constitutive model and determination of input parameters are necessary for a successful application of numerical methods in geotechnical engineering. Higher complexity of modern constitutive models results in an increase of the number of input parameters and time requirements for their calibration. Optimization methods are a possible solution for this problem. An application in which metaheuristic optimization method Particle swarm optimization (PSO) is involved is presented in this thesis. Critical review and testing of various PSO alternatives was performed in the first part of this thesis. The most efective PSO alternatives were chosen. In the second part connection between PSO algorithm and finite element solver was prepared. Automatization of determination of constitutive models input parameters was performed on three boundary value problems: laboratory test (oedometer), in-situ test (pressuremeter) and geotechical construction (retaining wall). Three types of constitutive models are used. Linear elastic-perfectly plastic Mohr-Coulomb model, elastoplastic non-linear Hardening soil model and Hardening soil - small strain model.

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Wong, Thomas. "Enumeration problems in directed walk models." Thesis, University of British Columbia, 2015. http://hdl.handle.net/2429/54483.

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Self-avoiding walks appear ubiquitously in the study of linear polymers as it naturally captures their volume exclusion property. However, self-avoiding walks are very difficult to analyse with few rigourous results available. In 2008, Alvarez et al. determined numerical results for the forces induced by a self-avoiding walk in an interactive slit. These results resembled the exact results for a directed model in the same setting by Brak et al., suggesting the physical consistency of directed walks as polymer models. In the directed walk model, three phases were identified in the infinite slit limit as well as the regions of attractive and repulsive forces induced by the polymer on the walls. Via the kernel method, we extend the model to include two directed walks as a way to find exact enumerative results for studying the behaviour of ring polymers near an interactive wall, or walls. We first consider a ring polymer near an interactive surface via two friendly walks that begin and end together along a single wall. We find an exact solution and provide a full analysis of the phase diagram, which admits three phase transitions. The model is extended to include a second wall so that two friendly walks are confined in an interactive slit. We find and analyse the exact solution of two friendly walks tethered to different walls where single interactions are permitted. That is, each walk interacts with the wall it is tethered to. This model exhibits repulsive force only in the parameter space. While these results differ from the single polymer models, they are consistent with Alvarez et al. Finally, we consider the model with double interactions, where each walk interacts with both walls. We are unable to find exact solutions via the kernel method. Instead, we use transfer matrices to obtain numerical results to identify regions of attractive and repulsive forces. The results we obtain are qualitatively similar to those presented in Alvarez et al. Furthermore, we provide evidence that the zero force curve does not satisfy any simple polynomial equation.
Science, Faculty of
Mathematics, Department of
Graduate

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Mehta, A. "Scaling approaches to interacting walk models." Thesis, University of Oxford, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.370291.

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Thomson, D. J. "Random walk models of turbulent dispersion." Thesis, Brunel University, 1988. http://bura.brunel.ac.uk/handle/2438/5549.

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An understanding of the dispersion of contaminants in turbulent flows is important in many fields ranging from air pollution to chemical engineering, and random walk models provide one approach to understanding and calculating aspects of dispersion. Two types of random walk model are investigated in this thesis. The first type, so-called "one-particle models", are capable of predicting only mean concentrations while the second type, "two-particle models", are able to give some information on the fluctuations in concentration as well. Many different one-particle random walk models have been proposed previously and several criteria have emerged to distinguish good models from bad. In this thesis, the relationships between the various criteria are examined and it is shown that most of the criteria are equivalent. It is also shown how a model can be designed to (i) satisfy the criteria exactly and (ii) be consistent with inertial subrange theory. Some examples of models which obey the criteria are described. The theory developed for one-particle models is then extended to the two-particle case and used to design a two-particle model suitable for modelling dispersion in high Reynolds number isotropic turbulence. The properties of this model are investigated in detail and compared with previous models. In contrast to most previous models, the new model is three-dimensional and leads to a prediction for the particle separation probability density function which is in agreement with inertial subrange theory. The values of concentration variance from the new model are compared with experimental data and show encouraging agreement.

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Ball, Stephen. "Near wall flow characteristics in jet impingement heat transfer." Thesis, Nottingham Trent University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.388866.

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