Dissertations / Theses on the topic 'Skin layers'
To see the other types of publications on this topic, follow the link: Skin layers.
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Skin layers.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Lakew, Wondwosen Ayelework. "Finite element based simulation of abrasion trauma." Thesis, IIT Delhi, 2018. http://eprint.iitd.ac.in:80//handle/2074/8036.
Full text
2
Hutchins, Nick. "An investigation of larger scale coherent structures in fully developed turbulent boundary layers." Thesis, University of Nottingham, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.289311.
Full text
3
Ozertugrul, Selin. "crys.tal.line_ a quest in realms of structure, skin and space." Thesis, Virginia Tech, 2000. http://hdl.handle.net/10919/33895.
Full textAbstract:
The articulation of frame and skin forms the space concertedly.
The project, stemming from this assertion, searches, explores and articulates the intricate relationship between structure, skin and space as prominent elements of architecture.Master of Architecture
4
Varano, Nathaniel David. "Fluid Dynamics and Surface Pressure Fluctuations of Turbulent Boundary Layers Over Sparse Roughness." Diss., Virginia Tech, 2010. http://hdl.handle.net/10919/26918.
Full textAbstract:
Turbulent boundary layers over rough surfaces are a common, yet often overlooked, problem of practical engineering importance. Development of correlations between boundary layer parameters that can be used in turbulence models and the surface geometry is the only practical option for solving these problems. Experiments have been performed on a two-dimensional zero pressure gradient turbulent boundary layer over sparsely spaced hemispherical roughness elements of 2 mm diameter. Laser Doppler velocimetry was used to measure all three components of velocity. The friction velocity was calculated using an integral momentum balance. Comparisons were made with various fitting methods that assume the von Kármán constant is appropriate for rough walls. Results indicate that this is not the case, and that the slope of the semi-logarithmic portion of the mean streamwise profile may be a function of the ratio of inner and outer length scales. Comparisons were also made between various correlations that relate the surface geometry to the behavior of the mean velocity profile. In general, the existing correlations achieved a reasonable agreement with the data within the estimated uncertainties.
A detailed study of the local turbulent structure around the roughness elements was performed. It was found that, in contrast to `sharper-edged' elements such as cylinders, an elevated region of TKE and Reynolds shear stress was found downstream of the element below the peak. This can be explained by the delay in separation of the flow coming over the top of the element due to the smooth curvature of the element.
Surface pressure fluctuation measurements were made as well using a dual microphone noise reduction technique. There have only been a few past experiments on the surface pressure fluctuations under rough wall boundary layers. However, it has been shown that the spectra of the wall fluctuations can be used to predict the far-field noise spectrum [1,2]. Therefore it is been the goal of this research to verify existing correlations between the surface pressure fluctuation spectrum and the surface geometry as well as develop new correlations that provide insight into the interactions between the turbulent motions in the flow surface pressure.Ph. D.
5
Yu, Fang. "Mathematical Modeling of the Disposition of Binary Solutions of Topically Applied Agents in the Stratum Corneum and Underlying Skin Layers." University of Cincinnati / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1627662280457926.
Full text
6
Hopkins, Andrew. "Fluid Dynamics and Surface Pressure Fluctuations of Two-Dimensional Turbulent Boundary Layers Over Densely Distributed Surface Roughness." Diss., Virginia Tech, 2010. http://hdl.handle.net/10919/26919.
Full textAbstract:
Measurements were made in two-dimensional zero pressure gradient turbulent boundary layers over 5 geometries of three-dimensional densely distributed surface roughness. A 3-velocity component laser Doppler velocimeter was used to measure instantaneous velocities. These measurements permitted an independent estimate of skin friction on the surfaces using a momentum balance approach, and the validity of the von Karman constant for rough walls was tested. Five roughness fetches were evaluated: three sandpaper roughness fetches of varying grit size and two cases of uniformly distributed hemispheres of different spacing. Optical surface profilometry was used to characterize the geometry of the sandgrain surfaces.
It was found that the smooth wall von Karman constant can not be assumed for densely distributed rough wall flows in order to determine the skin friction for these flows. This requires an independent measure of skin friction using more than a single boundary layer profile. Near wall flow structure measurements found that the hemispherical elements do not have high TKE or Reynolds shearing stress regions at the trailing edge of elements as had been shown for sparsely spaced cylindrical elements. This is likely due to the sharp trailing corner of the cylindrical elements, as opposed to an effect of spacing. Rather, hemispherical roughness has a periodically occurring high stress and TKE region located between two element centers in the stream-wise direction at a height of approximately 1.5 times the roughness element height. The periodic nature of the near wall flow extends to approximately 4 roughness element heights. The traditional roughness function f(λ) did not correlate well with λ or the modified Λ for the experimental data. However, it was found that the friction coefficient for the current dense roughness cases is a constant 0.004, within the experimental uncertainty. Traditional inner wall scalings, outer wall scalings, and roughness scalings were not able to collapse surface pressure fluctuation spectra for the various rough wall surfaces tested. However, the data do collapse for individual geometries based on Reynolds number. This gives rise to the ability to predict pressure fluctuation spectra at other Reynolds numbers.Ph. D.
7
Meira, Alianise da Silva. "Avaliação de condições experimentais de estudos in vitro de permeação / retenção cutânea empregando pele suína para creme comercial e nanoemulsão contendo penciclovir." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2013. http://hdl.handle.net/10183/143493.
Full textAbstract:
Estudos in vitro de absorção percutânea são uma importante ferramenta para avaliação de formulações semissólidas e transdérmicas. Embora haja um grande número de agências reguladoras preocupadas com a harmonização metodológica, em muitos parâmetros elas permanecem flexíveis e isto é possível verificar na ampla variedade e divergências encontradas na literatura. O objetivo do trabalho foi avaliar parâmetros ainda flexíveis a respeito dos estudos in vitro como modo de separação das camadas da pele, permeabilidade da pele congelada (tempo de armazenamento) e diferença de permeabilidade dos locais anatômicos. Os estudos foram conduzidos utilizando células de Franz, pele suína como membrana e formulações (comercializada e inovadora) contendo penciclovir. Inicialmente, nanoemulsões foram preparadas utilizando técnica de homogeneização a alta pressão, caracterizadas, incorporadas em gel de carbômero 940 e avaliadas quanto à liberação tópica em pele suína. Simultaneamente ao desenvolvimento da formulação foi desenvolvido e validado método analítico para quantificação do fármaco nas formulações e nas camadas da pele suína. As nanoemulsões apresentaram-se monodispersas com diâmetro de gotícula em torno de 180-200 nm, potencial zeta de -27 mV e teor de penciclovir de 98% mantendo sua estrutura após a incorporação em carbômero 940. A metodologia analítica demonstrou ter alta sensibilidade (LoQ 0,05 μg/mL), especificidade e uma adequada recuperação do fármaco a partir das matrizes biológicas (90 – 104%). Quanto aos estudos in vitro de comparação de metodologias, foi possível observar que, dependendo da solubilidade do fármaco em água e das características da formulação, o método clássico de separação das camadas da pele por imersão em água não é o mais indicado. Já para permeabilidade da pele suína congelada, os resultados obtidos indicam um aumento significativo na penetrabilidade e permeabilidade após um mês de congelamento. Dentre os locais anatômicos testados, não houve diferença entre abdômen e orelha suína desde que obtidos antes do procedimento de escaldo.In vitro percutaneous absorption studies are an important tool for evaluation of semisolid and transdermal formulations. Although there are a large number of official guides concerned with methodological harmonization in many parameters they remain flexible and it is possible to see the wide variety and differences reported in the literature. The aim of study was to evaluate some parameters regarding the in vitro studies as the mode of skin layers separation, skin frozen stability and permeability difference of anatomical sites. These studies were conducted with porcine skin and formulations (conventional and novel) using penciclovir as model drug. Initially, nanoemulsions were prepared using high pressure homogenization, characterized and incorporated into carbomer 940 gel and evaluated for topical delivery using porcine skin. Simultaneously with the development of the formulation, analytical method for quantification of the drug in the formulations and porcine skin layers was developed and validated. The nanoemulsions presented themselves monodisperse with droplet diameter of 180-200 nm, zeta potential of about -27 mV and penciclovir content of 98% maintaining their structure after incorporation into carbomer 940. The analytical methodology was shown to have high sensitivity (LOQ 0.05 μg/mL), specificity and adequate recovery of drug from the biological matrices (90-104%). Regarding the in vitro comparison methodologies, it was observed that, depending on the solubility of the drug in water and the characteristics of the formulation, the classical separation is not the most suitable for separation of the skin layers. For the stability of frozen porcine skin, the results indicate a significant increase in permeability and penetrability after one month of freezing. Within the anatomical sites tested, there was no difference between the abdomen and ear porcine skin since obtained before the scald procedure.
8
Alton, Borgelin Teresa. "Who I Am and Who You See." Thesis, Konstfack, Ädellab, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:konstfack:diva-7804.
Full textAbstract:
Now and then other people’s comments and/or behaviour reminds me that I look different and that my external features are connected to something beyond my Swedish identity. My black hair, dark brown eyes and my brownish skin color talk about something else. My appearance is connected to an identity, cultural identity and a country I have little knowledge of and a language I do not master. But still the way I look is a part of my heritage, a part of who I am and a part of me which I am proud of. It makes me wonder what actually makes up an identity and the power we all possess in deciding what or who another person is based on appearance. What do we become in the eyes of the beholder? Personal experiences from being Swedish, and adopted from another country, becomes the starting point for my investigation where the color of the skin leads to questions about norms, categorisations and the power of labelling another person. Living in the western world, my skin color automatically place me outside the norm. In a way that amazes me, that a single color can determine so much. As a jeweller maker in this degree project I make brooches. I use them as a method and as tools to both investigate the relationship between personal and social identity and to shed light on how structures in society and other peoples gazes push us into categories consciously and unconsciously. I use my objects as conversations pieces to reflect on history, present and future, from my perspective. There is always a beginning, but it is in the middle of the process it all comes alive. This is where I explore material, techniques and methods and where the brooches are born. They all have a history and part of it is public. At first sight you see the surface. But the brooches are like our bodies, they also have an inside/backside which creates an intimate relationship with the wearer. The brooches are more than ornamented pins, I want them to raise awareness of diversity, different perspectives, care and their ability to communicate as they move through various places attached in different ways to the body. My degree project, Who I am and who you see, touches upon questions and emotions about belonging, inclusion and exclusion and the state of being in-between. What makes up an identity? What different parts make up a whole? Which layers are added and which are peeled off? All these questions triggers my curiosity and search for more knowledge about the human being and being human.
9
Wedow, Jaret M. "A Flat Plate Skin Friction Correlation Including Transition." DigitalCommons@CalPoly, 2021. https://digitalcommons.calpoly.edu/theses/2299.
Full textAbstract:
Many existing boundary layer models treat transition as a rapid switch from laminar to turbulent flow, with correlations defining properties in each respective region. Natural transition, however, is not always a very spanwise uniform process, with the onset of transition varying somewhat between different streamwise paths of fluid flow. Thus, a spanwise average of natural transition can result in a more gradual, extended transition region than many existing models predict. Modern applications, such as aircraft wings and fuselages, are extremely streamlined and smooth, allowing for natural transition to occur rather than flow tripping to turbulent near the leading edge. Under these conditions, a skin friction model that takes this extended transition region into account provides a more accurate model compared to those which incorporate a rapid transition from laminar to turbulent flow. Lienhard’s recent publication 1 presents a new rationale for modeling the extent of the transition region on a smooth flat plate developed from re-analysis of existing heat transfer data. This correlation accounts for the extended natural transition region corresponding to a spanwise average of values. The primary objective of this thesis was to reinterpret Lienhard’s heat transfer correlation to solve for skin friction coefficient, then compare this correlation to available experimental data and higher order boundary layer models. After reinterpreting Lienhard’s correlation using the Reynolds analogy, it produced a gradual, extended transition region for skin friction coefficient. The reinterpreted correlation had excellent agreement with experimental data corresponding to a spanwise average of flow with natural transition. Tripped transitional values and data taken along a streamwise path of fluid resulted in a more rapid transition from laminar to turbulent flow. Both an integral boundary layer model and a Reynolds-averaged Navier-Stokes boundary layer model were used to validate the reinterpreted Lienhard correlation. Both of these models produced transition curves steeper than the reinterpreted Lienhard curve. These existing boundary layer models do not take into account the gradual transition region that natural transition may produce when looking at a spanwise average of values. With a focus on spanwise averaged values, such as overall drag over a streamlined surface, existing sophisticated boundary layer models may not accurately predict the behavior produced. The reinterpreted Lienhard correlation provides a new representation of skin friction coefficient throughout the boundary layer that takes into account the extended transition region that may occur when it is desired to model a spanwise average of fluid flow.
1Lienhard, J. Heat transfer in flat-plate boundary layers: A correlation for laminar, transitional, and turbulent flow. ASME Journal of Heat Transfer, 142, 2020.
10
Cherednychek, Mykyta [Verfasser]. "Different regimes of high harmonics generation in plasma skin layer / Mykyta Cherednychek." Düsseldorf : Universitäts- und Landesbibliothek der Heinrich-Heine-Universität Düsseldorf, 2016. http://d-nb.info/1118687876/34.
Full text
11
Estanbouli, Yasser. "A theoretical investigation of inversion layer transducers (ILT) for ultrasonic skin thickness measurement." Thesis, University of Strathclyde, 2004. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=24315.
Full textAbstract:
The human skin is the outermost organ of the body. The thickness of the skin can give useful clinical information on its condition. In this thesis the complicated structure of the skin was described and methods of skin thickness measurement critically reviewed. Ultrasound was identified as a non-invasive method having several advantages over the other methods, such as safety, ease of use and low cost. The existing ultrasonic systems have not been successful to quantify the skin structure properly, due to lack of high resolution transducers and the biology of the skin structure. The PZFlex Finite Element Method (FEM) package was used to model the skin, an ultrasonic thickness measurement system, and their interaction, in order to define the system structure and parameters. Initially, the skin was modelled as one planar layer of a linear isotropic material and 5MHz transducer was used to minimize computational effort. A nonplanar structure was then modelled and compared to the planar interface to see the effect of the additional complexity on the backscattered signal and to clarify the axial and lateral resolution requirements for skin thickness measurement. Different front face configurations of the transducer were also modelled to investigate the effect of the geometry on the backscattered signal as a starting point to introduce practical coupling. A more realistic skin structure was then modelled at 80 MHz, by super-imposing a FEM mesh on a micrograph of the skin and the backscattered ultrasound signal from the real skin interfaces compared to a signal from planar interfaces. An appraise of the existing technology was concluded and the requirements for an ideal skin thickness measurement system were then addressed. A monolithic LiNb0b3s transducer incorporating inversion layers (IL) was modelled using PZFlex to investigate the usefulness of these transducers for skin measurement. A novel mathematical 1-D linear systems model was developed for a transducer incorporating one front face inversion layer. This model gave a physical insight into, and more understanding of, the transducer behaviour. It was found that, although ILT's offer improved sensitivity and bandwidth for skin thickness measurement, they suffer from similar problems to conventional devices and a new transducer technology is needed for ultra high resolution applications on real skin surfaces. The new theory offers substantial base for the design of ILT' s, which will have significant applications in other areas, such as harmonic imaging and multi-frequency sonar.
12
Kinkade, Brittany Reanne. "Addition of a Stanton Gauge to the Boundary Layer Data System." DigitalCommons@CalPoly, 2014. https://digitalcommons.calpoly.edu/theses/1260.
Full textAbstract:
The Stanton gauge technique provides an indirect method for measurement of skin friction on a smooth aerodynamic surface in which a pressure tap is available. This thesis presents the design and evaluation of a new type of skin friction measurement gauge based on the Stanton gauge concept but not requiring a surface pressure tap. This new skin friction measurement gauge, called a "Flow Tab", can therefore be used on an aerodynamic model or aircraft surface without alteration of the surface. The Flow Tab is thus particularly well-suited to use with Cal Poly's Boundary Layer Data System (BLDS), a small, self-contained instrument that can be installed onto a model or aircraft surface without permanent alteration of the surface. A series of preliminary experiments conducted in a low-speed wind tunnel on a flat plate model with mild favorable pressure gradient, with both laminar and turbulent boundary layers, led to selection of three variants of the Flow Tab design. These Flow Tabs had edge heights of 0.002, 0.0035, and 0.005 inches, giving dimensionless heights h+ of 1.4 -16 over the streamwise Reynolds number range of about 0.7 to 2.2 million. Uncertainty analysis and test results demonstrated that better than 10% measurement uncertainty for the Flow Tab results could be achieved with edge heights of 0.0035 and 0.005 inches using the same calibration equations as published for the Stanton gauge. Further investigation of its performance over a wider range of Reynolds numbers, and in more complex conditions including those encountered on swept wings with a variety of pressure gradients, is recommended. Integration of the flow tab with BLDS for flight testing applications presents challenges related to its relatively small pressure signal that may require some special modifications to existing BLDS hardware and software.
13
MacLean, Matthew. "A Numerical Study of Internal Flow Effects on Skin Friction Gages." Diss., Virginia Tech, 2002. http://hdl.handle.net/10919/27114.
Full textAbstract:
This work examines the detailed flow characteristics of direct measuring skin friction gages with computational methods. This type of device uses a small movable head mounted flush to a wall such that the head is assumed to be exposed to the same shear stress from the flow as the surrounding wall. The force caused by the action of the shear stress on the head deflects a flexure system monitored by instruments such as strain gages mounted at the base of a beam.
The goal of the study was to develop an understanding of the effects that the geometric design and installation parameters of the sensor have on the surrounding flow and the ability of the sensor to reflect the undisturbed shear stress value. Disruption of the external flow due to poor design and/or improper installation of the sensor can take the form of intrusion into the flow, recession into the wall, and/or tilted alignment of the sensor such that the head is not flat in the plane of the wall, as well as flow into or out of the small gap surrounding the sensing head. Further, the performance of a direct measuring skin friction sensor in the presence of a pressure gradient has always been a concern. These effects are studied here with a three-dimensional, Navier-Stokes code based on a finite element method technique.
Numerical solutions for cases in which one or more design parameters were varied are shown for a variety of flow situations. These situations include: (a) a laminar fully-developed channel flow at a low Reynolds number, (b) a turbulent flat plate boundary layer flow at a high Reynolds number, and (c) strong favorable and adverse pressure gradient turbulent boundary layer flows created by converging and diverging channels at high Reynolds number. Reported results for all cases include detailed flow visualization and stress field imagery, and total surface forces on the sensing head and gage flexure. Under ideal circumstances, these total forces should reflect as accurately as possible the average value of undisturbed shear stress times the exposed sensing head area (the friction force). Any deviation from this value was considered an â errorâ in the simulated measurement.
The laminar channel flow case with a strong favorable pressure gradient showed the importance of proper alignment of the sensor. Protrusion or recession of the sensing head proved to be the dominant effect on resulting forces seen by the gage, changing the output by up to 15% for head protrusion and 10% for head recession for misalignments up to +/-1% of the head diameter. The thickness of the lip on the edge of the head also proved to have a significant effect on the output, with a smaller lip thickness generally showing better performance than a large one. Zero lip thickness indicated accuracy to within 1% of the desired wall shear result, since the pressure differences had little influence on the sensing head. Finally, the assumption of a linear pressure variation from the surface to the cavity along the lip as has been suggested in the past was investigated. The results indicate that the linear assumption works well only for large ratios of lip thickness to gap size, a fact which is correlated with previous experimental results.
For the turbulent external flat plate case, misalignment remained the dominant effect on the sensor response. Results indicated that, in general, protrusion is more costly than the same level of recession, and a protrusion of +1% of the head diameter was shown to cause in excess of 100% error in indicated wall shear output. Both protrusion and recession produced large variations in both force and moment on the sensing flexure, but the outcome was that for protrusion the errors caused by these two effects tended to sum together, while for recession they tended to partially cancel out.
The gap size played an increased role in the high Reynolds number boundary layer cases. Gap sizes of 1.67% up to 6.67% of the head diameter were studied and were shown to produce output errors between 4% and 22% (with larger errors corresponding to larger gap sizes), thus showing the importance of minimizing the gap for high Reynolds number flows. The lip was shown to have no significant effect for a flow without a pressure gradient.
Finally, the favorable and adverse pressure gradient flows showed reasonable performance of the skin friction gage. Errors in output were shown to be -6% for the favorable pressure gradient case and 17% for the adverse pressure gradient case. Only the baseline gage design was studied for these situations, but the results from the two cases indicate that further reducing the lip thickness may not improve the performance of the gage. The error in output was caused almost entirely by applied moment for the adverse pressure gradient, while the applied force and applied moment had a cancellation effect in the favorable pressure gradient case.
As a general result, the use of computational fluid dynamics has been shown to be an effective tool in the design and analysis of skin friction gages. Using a computational approach has the advantage of being able to resolve the small, confined gap regions of the gage, providing information that has been shown to be unavailable from previous experimental studies. This work has contributed to a much better understanding of the detailed flow over, in, and around skin friction gages. This will lead to improved gage design and reduced uncertainty in these important measurements.Ph. D.
14
DeTurris, Dianne Joan. "A technique for direct measurement of skin friction in supersonic combustion flow." Diss., Virginia Tech, 1992. http://hdl.handle.net/10919/39449.
Full text
15
Musgrave, Patrick Francis. "Turbulent Boundary Layer over a Piezoelectrically Excited Traveling Wave Surface." Diss., Virginia Tech, 2018. http://hdl.handle.net/10919/97011.
Full textAbstract:
Recent studies have utilized spanwise traveling waves to alter the turbulent boundary layer with the aim of reducing skin friction drag. Spanwise traveling waves are a promising active drag reduction technique; however, the wave generation methods used in previous studies are bulky and could not be practically implemented. This research has developed an implementable traveling wave generation method and then fundamentally demonstrated how it changes the turbulent boundary layer, which is in a manner consistent with skin friction/shear stress reduction. Traveling waves were generated on a two-dimensional surface using low-profile piezoelectric actuators, in an open-loop fashion, and with minimal frequency limitations. The wave generation method was developed to generate tailored traveling wave patterns; thus, yielding control over the propagation direction, number of wave-fronts, and regions of the surface containing traveling waves. These tailored traveling waves have the capacity not just for affecting the boundary layer, but also for other applications such as propulsion.
The implementable traveling wave generation method was then tested in a low-speed wind tunnel and shown to alter the structure of the turbulent boundary layer. The boundary layer is pushed off the wall, and the viscous sublayer is thickened, indicating a reduction in shear stress. Analysis of the boundary layer at positions phase-locked to the wave oscillation suggests that the traveling waves induce a phase-lag effect in the flow. This phase-lag produces a stretching of the viscous sublayer and may contribute to the skin friction reduction. The effects of standing waves on the turbulent boundary layer were also investigated and compared with traveling waves. The results indicate that both wave types alter the boundary layer in the same manner. Standing waves are simpler to generate than traveling waves, suggesting that standing waves may be an effective skin friction reduction method. Before traveling or standing waves can be implemented, further research is necessary to investigate the interaction between the wave pattern and the turbulent phenomena and also to quantify the skin friction reduction and overall net energy usage.Ph. D.
16
Sinha, Roy Arijit. "Analysis and control of boundary layer transition on a NACA 0008 wing profile." Thesis, KTH, Mekanik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-239931.
Full textAbstract:
The main aim of this thesis was to understand the mechanism behind the classical transition scenario inside the boundary layer over an airfoil and eventually attempting to control this transition utilizing passive devices for transition delay. The initial objective of analyzing the transition phenomenon based on TS wave disturbance growth was conducted at 90 Hz using LDV and CTA measurement techniques at two different angles of attack. This was combined with the studies performed on two other frequencies of 100 and 110 Hz, in order to witness its impact on the neutral stability curve behavior. The challenges faced in the next phase of the thesis while trying to control the transition location, was to understand and encompass the effect of adverse pressure gradient before setting up the passive control devices, which in this case was miniature vortex generators. Consequently, several attempts were made to optimize the parameters of the miniature vortex generators depending upon the streak strength and stability. Finally, for 90 Hz a configuration of miniature vortex generators have been found to successfully stabilize the TS wave disturbances below a certain forcing amplitude, which also led to transition delay.
17
Sutardi. "Development of a turbulent boundary layer downstream of a transverse square groove." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0008/MQ36182.pdf.
Full text
18
Harion, Jean-Luc. "Influence de différences de densité importantes sur les propriétés de transfert d'une couche limite turbulente." Grenoble INPG, 1994. http://www.theses.fr/1994INPG0133.
Full textAbstract:
Les effets de differences de densite importantes sur les transferts turbulents en couche limite sont etudies experimentalement. L'installation principale est une soufflerie pressurisable. Les ecarts de densite au sein de la couche limite sont produits par injection tangentielle d'air ou d'helium dans un melange de ces deux constituants. Les mesures thermo-anemometriques portent sur les concentrations, vitesses et frottement parietal (valeurs moyennes, fluctuations) en aval de l'injection. Une sonde d'interference (fil+film) a ete mise au point avec de nouvelles conditions de surchauffes permettant l'acces a une gamme de vitesses plus etendues que les utilisations anterieures. Une sonde double ainsi qu'une nouvelle sonde aspirante parietales ont egalement ete developpees. Leur comportement physique a ete analyse. Les resultats montrent que pour un gaz donne, le developpement du jet parietal est principalement gouverne par le rapport des vitesses externe et d'injection. Pour des gaz differents, un bon regroupement des resultats est opere en tenant compte du nombre de reynolds d'injection et d'un terme base sur le rapport des densites. La couche limite turbulente obtenue est associee a un gradient de densite normal a la paroi. A vitesse d'injection donnee, les mesures mettent en evidence la conservation du frottement, et donc l'influence des differences de densite sur la vitesse de frottement. De plus, une forte correlation entre les variations de densite et de vitesse montrent l'influence marquee des structures coherentes sur les phenomenes de transfert
19
Bertolotti, Fabio P. "Temporal and spatial growth of subharmonic disturbances in Falkner-Skan flows." Thesis, Virginia Polytechnic Institute and State University, 1985. http://hdl.handle.net/10919/90912.
Full textAbstract:
The transition from laminar to turbulent flow in boundary-layers occurs in three stages: onset of two-dimensional TS waves, onset of three-dimensional secondary disturbances of fundamental or subharmonic type, and onset of the turbulent regime. In free flight conditions, subharmonic disturbances are the most amplified.
Recent modeling of the subharmonic disturbance as a parametric instability arising from the presence of a finite amplitude TS wave has given results in quantitative agreement with experiments conducted in a Blasius boundary-layer. The present work extends the analysis to the Falkner-Skan family of profiles, and develops a formulation for spatially growing disturbances to exactly match the experimental observations.
Results show that subharmonic disturbances in Falkner-Skan flows behave similarly to those in a Blasius flow. The most noticeable effect of the pressure gradient is a decrease (favorable) or an increase (adverse) of the disturbance's growth rate. Due to the lack of experimental data, a comparison of subharmonic growth rates from theory and experiment is limited to the Blasius boundary-layer. A comparison of results from the spatial formulation with those previously obtained from a temporal formulation shows the difference to be small. A connection between disturbance growth in a separating boundary-layer profile and a free shear layer is presented. A modification of Caster's transformation from temporal to spatial growth rates for secondary disturbances is given.M.S.
20
Hellon, C. S. "On the use of the boundary layer integral equations for the prediction of skin friction and heat transfer." Thesis, Cranfield University, 1986. http://hdl.handle.net/1826/3616.
Full textAbstract:
The usefulness of the energy equation integrated over the thickness of the
boundary layer, in predicing heat transfer rates to smooth body surfaces
in investigated. It is found that on assuming very simple closure
relations, similar to those often used with the momentum equation, highly
accurate predictions are made. It is shown further that the usefulness
of these predictions extend into areas where the momentum equation-skin
friction predictions, which have proved so popular, break down such as
regions of reverse flow and shock/boundary layer interactions. The
technique is has been tested in laminar transitional and turbulent flows
with both experiment and other more complex theories.
The technique is extended to three-dimensional laminar flows with the
inclusion of a crossflow model.
21
McClain, Stephen Taylor. "A discrete-element model for turbulent flow over randomly-rough surfaces." Diss., Mississippi State : Mississippi State University, 2002. http://library.msstate.edu/etd/show.asp?etd=etd-04032002-140007.
Full text
22
Silva, Paula Ventura da. "Emprego de redes neurais artificiais com skip-layer connections na mensura??o florestal." UFVJM, 2015. http://acervo.ufvjm.edu.br/jspui/handle/1/999.
Full textAbstract:
Submitted by M?rden L?les (marden.inacio@ufvjm.edu.br) on 2016-07-12T23:59:50Z
No. of bitstreams: 2
license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5)
paula_ventura_silva.pdf: 2872431 bytes, checksum: 13667045a80e3b80429055fd7e4a5e15 (MD5)Approved for entry into archive by Rodrigo Martins Cruz (rodrigo.cruz@ufvjm.edu.br) on 2016-07-18T14:50:22Z (GMT) No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) paula_ventura_silva.pdf: 2872431 bytes, checksum: 13667045a80e3b80429055fd7e4a5e15 (MD5)
Made available in DSpace on 2016-07-18T14:50:22Z (GMT). No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) paula_ventura_silva.pdf: 2872431 bytes, checksum: 13667045a80e3b80429055fd7e4a5e15 (MD5) Previous issue date: 2015
Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior (CAPES)
RESUMO SILVA, Paula Ventura da, M.Sc., Emprego de redes neurais artificiais com Skip-Layer Connections na mensura??o florestal. 2015. 46 f. Disserta??o (Mestrado em Ci?ncia Florestal) ? Universidade Federal dos Vales do Jequitinhonha e Mucuri, Diamantina, 2015. O objetivo principal deste estudo foi avaliar a aplica??o de Redes Neurais Artificiais (RNA) utilizando a t?cnica Skip-layer connections, com e sem recorr?ncia, para estima??o do volume individual e da altura total de ?rvores de eucalipto. Os objetivos espec?ficos foram testar e avaliar as redu??es no tamanho da base de dados do conjunto de ajuste (treinamento) para estima??o dessas vari?veis. Os dados utilizados foram provenientes de ?rvores abatidas para cubagem (estima??o do volume individual) e de medi??es de parcelas permanentes de invent?rios florestais cont?nuos (estima??o da altura total), em ?rea de povoamentos de eucalipto localizados no sul da Bahia, Brasil. Foram treinadas redes do tipo Multilayer Perceptron (MLP), utilizando a fun??o de ativa??o log?stica nas camadas intermedi?ria e de sa?da e oito neur?nios na camada oculta. O n?mero de neur?nios na camada de entrada variou conforme o n?mero e o tipo de vari?vel (qualitativa ou quantitativa) em cada estudo. Os crit?rios de parada foram o erro m?dio quadr?tico de 0,0001 ou 3.000 ciclos (?pocas). Em seguida, as RNA selecionadas foram aplicadas em parte dos dados separados, para generaliza??o (valida??o). O software utilizado para o treinamento e a generaliza??o das RNA foi o NeuroForest 3.3. Para compara??o dos resultados obtidos pelas RNA, foram ajustados os modelos tradicionais de regress?o tanto para volume, quanto para altura, e tamb?m foram treinadas e aplicadas RNA usando o algoritmo Resilient Propagation, comumente utilizado em aplica??es da mensura??o florestal. A avalia??o dos resultados gerados pelas RNA e pelos modelos de regress?o foi feita por meio do coeficiente de correla??o entre os valores observados e estimados, de gr?ficos de dispers?o e de histogramas de frequ?ncia percentual dos erros percentuais. As Redes Neurais Artificiais utilizando Skip-layer connections apresentaram resultados satisfat?rios para estima??o de volume e de altura de ?rvores de eucalipto, o que evidencia a possibilidade de aplicar a t?cnica em mensura??o e manejo florestal e uma expressiva redu??o das bases de dados para treinamento das RNA.
Disserta??o (Mestrado) ? Programa de P?s-Gradua??o em Ci?ncia Florestal, Universidade Federal dos Vales do Jequitinhonha e Mucuri, 2015.
ABSTRACT SILVA, Paula Ventura da, M.Sc. Artificial neural networks with skip-layer connections in forest measurement. 2015. 46 f. Dissertation (Master in Forest Science) ? Universidade Federal dos Vales do Jequitinhonha e Mucuri, Diamantina, 2015. The aim of this study was to evaluate the application of Artificial Neural Networks (ANN) using the Skip-layer connections technique, with and without recurrence, to estimate the individual volume and total eucalyptus trees height. Its specific objectives were to test and evaluate reduction in the size of the adjustment assembly database (training) for estimating these variables. The data came from trees felled for scaling (estimation of individual volume) and measurements of permanent plots of continuous forest inventories (estimation of the total height), in eucalypt plantation area located in the south of Bahia, Brazil. Multilayer Perceptron (MLP) network type, using the logistic activation function in the intermediate and output layers and eight neurons in the hidden layer, were trained. The neurons number in the input layer varied according to the number and type of the variable (qualitative or quantitative) in each study. The stopping criteria were the root mean square error 0.0001 or 3,000 cycles (seasons). The software used for the RNA training and generalization was the NeuroForest 3.3. To compare the results obtained by RNA, traditional regression models were set for both the volume and the height, as well as RNA were trained and applied using the Resilient Propagation algorithm, commonly used in forest measurement applications. The evaluation of the results generated by the RNA and by the regression models was made via the correlation coefficient between observed and estimated values, scatter plots and histograms percentage frequency of the percentage errors. Artificial Neural Networks using Skip-layer connections showed satisfactory results for the estimation of volume and eucalyptus trees height, demonstrating the possibility of applying the technique in measuring and forest management and a significant reduction of databases for RNA training.
23
Kiani, Parnian [Verfasser], and Hartmut [Akademischer Betreuer] Schlüter. "Mass spectrometric investigation and determination of proteome composition of human skin tissues ablated using picosecond infrared laser (PIRL) in a ‘layer by layer’ approach / Parnian Kiani ; Betreuer: Hartmut Schlüter." Hamburg : Staats- und Universitätsbibliothek Hamburg, 2019. http://d-nb.info/1186891750/34.
Full text
24
DeMoss, Joshua Andrew. "Skin Friction and Cross-flow Separation on an Ellipsoidal Body During Constant Yaw Turns and a Pitch-up Maneuver with Roll Oscillation." Diss., Virginia Tech, 2010. http://hdl.handle.net/10919/29063.
Full textAbstract:
The skin friction and cross-flow separation location on a non-body-of-revolution (non-BOR) ellipsoidal model performing constant-yaw turns and a pitch-up maneuver, each with roll oscillation were studied for the first time. The detailed, low uncertainty, flow topology data provide an extensive experimental database on the flow over non-BOR hull shapes that does not exist anywhere else in the world and serves as a crucial tool for computational validation. The ellipsoidal model was mounted on a roll oscillation machine in the Virginia Tech Stability Wind Tunnel slotted wall test section. Hot-film sensors with constant temperature anemometers provided skin friction magnitudes on the body's surface for thirty-three steady flow model orientations and three unsteady maneuvers at a constant Reynolds number of 2.5 million. Cross-flow separation locations on the model were determined from span-wise minima in the skin friction magnitude for both the steady orientations and unsteady maneuvers. Steady hot-film data were obtained over roll angles between ±25° in 5° increments with the model mounted at 10° and 15° yaw and at 7° pitch with respect to the flow. The roll oscillation machine was used to create a near sinusoidal unsteady roll motion between ±26° at a rate of 3 Hz, which corresponded to a non-dimensional roll period of 5.4. Unsteady data were obtained with the ellipsoidal model mounted at 10° and 15° yaw and at 7° pitch during the rolling maneuver. Cross-flow separation was found to dominate the leeside flow of the model for all orientations. For the yaw cases, the separation location moved progressively more windward and inboard as the flow traveled downstream. Increasing the model roll or yaw angle increased the adverse pressure gradient on the leeward side, creating stronger cross-flow separation that began further upstream and migrated further windward on the model surface. For the pitch flow case, the cross-flow separation remained straight as the flow moved axially downstream. The strongest pitch cross-flow separation was observed at the most negative roll angle and dissipated, moving further downstream and inboard as the modelâ s roll angle was increased. The unsteady flow maneuvers exhibited the same flow topology observed in the quasi-steady conditions. However, the unsteady skin friction and separation locations lagged their quasi-steady counterparts at equivalent roll angles during the oscillation cycle. A first order time lag model and sinusoidal fit to the separation location data quantified the time lags that were observed.Ph. D.
25
Alabaster, C. M. "The Microwave properties of tissue and other lossy dielectrics." Thesis, Cranfield University, 2004. http://hdl.handle.net/1826/251.
Full textAbstract:
This thesis describes work on the theoretical modelling and experimental measurement
of the complex permittivity of dielectrics. The main focus of research has been into the
characterisation of permittivity of planar and layered samples within the millimetre
wave band. The measurement method is based on the free-space measurement of the
transmission and reflection coefficients of samples. A novel analytical method of
determining the transmission and reflection coefficients as functions of frequency
arising from a generalised structure of planar dielectric layers is also described and
validated. The analytical method is based on signal flow techniques. The measurement
and analytical techniques have been applied in two main areas: firstly, the acquisition of
new data on human skin in the band 57 to 100GHz and secondly, the detection and
location of defects in composite materials for which a band of 90 to 100GHz was used.
Measurements have been made on the complex permittivity of a single sample of
excised human skin fixed in formaldehyde. The experimental results have been
corrected to account for the fixing process in formaldehyde and are projected to body
temperature. This data is, to the best of the author’s knowledge, the first of its kind to be
published. Predicted skin permittivity based on various relaxation models varies widely
and only partially fits the measured data. The experimental results have been used to
determine the parameters of a Cole-Cole function which gives the best fit to the
measured data. The measured skin data has also been used to calculate power deposition
in skin exposed to millimetre wave radiation. This work concludes that a skin surface
temperature rise of only 0.20C results from a thirty second exposure to signals of
100W/m2.
Experimental work with fibreglass composite samples has shown that defects such as
delaminations, voids, matrix cracks and improper cure result in resolvable differences in
the dielectric properties of the samples at 90 – 100GHz. The measurement technique is
particularly sensitive to the detection of cracks and its spatial resolution is 20mm or
better. Whilst confirming the general conclusions of previously published work, the
specific findings of this study are novel.
26
Parkhe, Vineet. "A Parametric Study on Flow Over a Flat Plate with Microblowing." University of Akron / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=akron1258390482.
Full text
27
Alabaster, Clive M. "The microwave properties of tissue and other lossy dielectrics." Thesis, Cranfield University, 2004. http://dspace.lib.cranfield.ac.uk/handle/1826/251.
Full textAbstract:
This thesis describes work on the theoretical modelling and experimental measurement of the complex permittivity of dielectrics. The main focus of research has been into the characterisation of permittivity of planar and layered samples within the millimetre wave band. The measurement method is based on the free-space measurement of the transmission and reflection coefficients of samples. A novel analytical method of determining the transmission and reflection coefficients as functions of frequency arising from a generalised structure of planar dielectric layers is also described and validated. The analytical method is based on signal flow techniques. The measurement and analytical techniques have been applied in two main areas: firstly, the acquisition of new data on human skin in the band 57 to 100GHz and secondly, the detection and location of defects in composite materials for which a band of 90 to 100GHz was used. Measurements have been made on the complex permittivity of a single sample of excised human skin fixed in formaldehyde. The experimental results have been corrected to account for the fixing process in formaldehyde and are projected to body temperature. This data is, to the best of the author’s knowledge, the first of its kind to be published. Predicted skin permittivity based on various relaxation models varies widely and only partially fits the measured data. The experimental results have been used to determine the parameters of a Cole-Cole function which gives the best fit to the measured data. The measured skin data has also been used to calculate power deposition in skin exposed to millimetre wave radiation. This work concludes that a skin surface temperature rise of only 0.20C results from a thirty second exposure to signals of 100W/m2. Experimental work with fibreglass composite samples has shown that defects such as delaminations, voids, matrix cracks and improper cure result in resolvable differences in the dielectric properties of the samples at 90 – 100GHz. The measurement technique is particularly sensitive to the detection of cracks and its spatial resolution is 20mm or better. Whilst confirming the general conclusions of previously published work, the specific findings of this study are novel.
28
Riahi, Slimane. "Etude de l'écoulement turbulent dans un canal bidimensionnel à deux parois rugueuses, ou une paroi lisse et une paroi rugueuse." Valenciennes, 1987. https://ged.uphf.fr/nuxeo/site/esupversions/94fd57b2-e214-43f6-8da6-43775ac5edee.
Full textAbstract:
Étude expérimentale de l'influence des rugosités sur le développement de la couche limite. Mesures directes du frottement pariétal sur une paroi lisse et sur une paroi rugueuse à l'aide d'une balance à éléments flottants. A partir de la numérisation du signal anémométrique, on déduit le taux de turbulence, les facteurs de dissymétrie et d'aplatissement. Mise en évidence des zones de production, de transfert et de dissipation de l'énergie turbulente.
29
Brynjell-Rahkola, Mattias. "Global stability analysis of three-dimensional boundary layer flows." Licentiate thesis, KTH, Stabilitet, Transition, Kontroll, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-175353.
Full textAbstract:
This thesis considers the stability and transition of incompressible boundary layers. In particular, the Falkner–Skan–Cooke boundary layer subject to a cylindrical surface roughness, and the Blasius boundary layer with applied localized suction are investigated. These flows are of great importance within the aviation industry, feature complex transition scenarios, and are strongly three-dimensional in nature. Consequently, no assumptions regarding homogeneity in any of the spatial directions are possible, and the stability of the flow is governed by an extensive three-dimensional eigenvalue problem. The stability of these flows is addressed by high-order direct numerical simulations using the spectral element method, in combination with a Krylov subspace projection method. Such techniques target the long-term behavior of the flow and can provide lower limits beyond which transition is unavoidable. The origin of the instabilities, as well as the mechanisms leading to transition in the aforementioned cases are studied and the findings are reported. Additionally, a novel method for computing the optimal forcing of a dynamical system is developed. This type of analysis provides valuable information about the frequencies and structures that cause the largest energy amplification in the system. The method is based on the inverse power method, and is discussed in the context of the one-dimensional Ginzburg–Landau equation and a two-dimensional flow case governed by the Navier–Stokes equations.QC 20151015
30
Mello, Hilton Carlos de Miranda. "Estudo dos efeitos de um jato sintético simulado numericamente no atraso da separação de uma camada limite sobre um aerofólio hipotético." Universidade de São Paulo, 2005. http://www.teses.usp.br/teses/disponiveis/18/18135/tde-26022006-111816/.
Full textAbstract:
A realização deste trabalho tem como objetivo fundamental estudar os efeitos dos atuadores de jato sintético no escoamento de uma camada limite desenvolvida sobre uma placa plana e um aerofólio hipotético. A interação dos jatos sintéticos com um escoamento transversal pode conduzir a uma aparente modificação da forma aerodinâmica de corpos rombudos e, dessa forma, fornecer uma maneira de controle da separação na camada limite. Estudos recentes demonstram que tipos diferentes de escoamentos podem ser produzidos pelo atuador dependendo da oscilação da membrana. Um método numérico para solução das equações de Navier-Stokes incompressíveis bidimensionais na formulação vorticidade-velocidade é utilizado neste trabalho. As equações governantes são discretizadas utilizando-se métodos de diferenças finitas compactas de sexta ordem para as derivadas espaciais. A equação de Poisson para a componente da velocidade normal é resolvida por um método iterativo de sobre-relaxação em linhas sucessivas usando um esquema com malha composta para acelerar a convergência. Os resultados de simulações com diferentes valores de freqüência, amplitude e comprimento de fenda foram verificados através de uma análise de Fourier temporal. Através desta análise é verificado qual a melhor situação para se atrasar a separação da camada limiteThis work has as a fundamental objective the study of the effects of synthetic jet actuators on the boundary layer flow on a flat plate and on a hypothetical airfoil. The interaction of synthetic jets with transverse flow can lead to an apparent modification in the aerodynamic shape of blunt bodies and, in that way, supply a means of control of transition within the boundary layer. Recent studies demonstrate that different types of flow may be produced by the actuator, depending on the amplitude of oscillation of the membrane. A numerical method for the solution of two-dimensional incompressible Navier-Stokes equations written in vorticity-velocity formulation is used in this work. The spatial derivatives are discretized with a sixth order compact finite differences scheme. The Poisson equation for the normal velocity component is solved by an iterative line successive over relaxation method and uses a multigrid full approximation scheme to accelerate the convergence. The results of simulations with different values of frequency, amplitude and slot length were verified through a temporal Fourier analysis. By way of this analysis it is verified which are the better parameters for the controlled delay of boundary layer separation
31
Joseph, Laya. "Development of Ultra-Wide band 500 MHz – 20 GHz Heterogeneous Multi-Layered Phantom Comprises of Human Skin, Fat and Muscle Tissues for Various Microwaves Based Biomedical Application." Thesis, Uppsala universitet, Fasta tillståndets elektronik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-402458.
Full textAbstract:
In biomedical applications realistic phantoms are becoming more useful for validation and testing of precursor systems. These artificial phantoms require stable and flexible tissue-mimicking materials with realistic dielectric properties in order to properly model human tissues. We have fabricated a low-water-content, low cost, mechanically and electrically stable, good shelf life and multi-layered heterogeneous phantom consisting of skin, fat and muscle tissues. We have chosen semi-solid type phantom for each tissue layer. The size and thickness of the each layer is chosen based on the average thickness of human tissue. Altering the ingredient composition wisely we can alter its dielectric properties also. By reason of no osmosis occurrence, the tissues can be employed to construct heterogeneous phantoms or even anthropomorphic phantoms without causing any changes in geometry or electrical properties. The performance of the fabricated phantom is carried out using an open-ended coaxial slim probe system by Agilent Technologies. Nearly all previous studies were based on very high frequency( VHF), so we present ultra-wide band (UWB), 500MHz-20GHz multilayered phantoms. We have measured our phantom after 2 month time period and we got quite good results for the dielectric properties without having significant variations. Thus, our fabricated sets of ATE phantom have good long lasting properties with good physical and dielectric stability.
32
Bleesen, Christoph A. "Variotherme Spritzgießtechnologie zur Beeinflussung tribologischer Eigenschaften thermoplastischer Formteile." Doctoral thesis, Universitätsbibliothek Chemnitz, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-203353.
Full textAbstract:
Im Rahmen der vorliegenden Arbeit wurde ein Spritzgießwerkzeug mit einem neuartigen Mehrschichtverbundheizsystem zur dynamischen Temperierung entwickelt und umgesetzt. Dabei wurde das ausgewählte Heiz‐ und Kühlsystem unter theoretischen und praktischen Gesichtspunkten betrachtet und für den variothermen Fertigungsprozess verifiziert. Aus den ersten durchgeführten praktischen Versuchen zeigte sich, dass dieses Heizsystem zur dynamischen Temperierung von Formwerkzeugen geeignet ist. Anschließend wurden mit dem realisierten Spritzgießwerkzeug Versuchskörper mit spezieller Oberflächenstrukturierung und variierenden Werkzeugwandtemperaturen angefertigt und untersucht. Ziel war es, über diese Strukturierung eine Beeinflussung der Glasfaserverteilung im Formteilrandbereich zu erreichen und die tribologischen Eigenschaften bei Kunststoff‐Kunststoff‐Gleitpaarungen hinsichtlich Reibung und Verschleiß zu verbessern. Mit einer kleinen Auswahl an Strukturen und entsprechenden thermoplastischen Polymermaterialien wurden praktische Versuche zur tribologischen Prüfung durchgeführtIn the present work an injection mould was developed and implemented with a novel multilayer composite heating system for dynamic temperature control. Here the selected heating and cooling system was considered from a theoretical and practical point of view and verified for the variothermal manufacturing process. The first practical tests showed that this heating system is suitable for the dynamic temperature control of tools. Subsequently, with this injection mould, test specimens with a special surface structure and varying mould wall temperatures were produced and examined. The aim was to achieve through this structuring an impact on the distribution of glass fibres in the edge region of mouldings and improve the tribological properties of plastic‐plastic‐pairings in terms of friction and wear. With a small selection of structures and corresponding thermoplastic polymeric materials practical experiments for tribological testing were performed
33
Chevalier, Mattias. "Adjoint based control and optimization of aerodynamic flows." Licentiate thesis, KTH, Mechanics, 2002. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-1435.
Full text
34
Brynjell-Rahkola, Mattias. "Studies on instability and optimal forcing of incompressible flows." Doctoral thesis, KTH, Stabilitet, Transition, Kontroll, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-218172.
Full textAbstract:
This thesis considers the hydrodynamic instability and optimal forcing of a number of incompressible flow cases. In the first part, the instabilities of three problems that are of great interest in energy and aerospace applications are studied, namely a Blasius boundary layer subject to localized wall-suction, a Falkner–Skan–Cooke boundary layer with a localized surface roughness, and a pair of helical vortices. The two boundary layer flows are studied through spectral element simulations and eigenvalue computations, which enable their long-term behavior as well as the mechanisms causing transition to be determined. The emergence of transition in these cases is found to originate from a linear flow instability, but whereas the onset of this instability in the Blasius flow can be associated with a localized region in the vicinity of the suction orifice, the instability in the Falkner–Skan–Cooke flow involves the entire flow field. Due to this difference, the results of the eigenvalue analysis in the former case are found to be robust with respect to numerical parameters and domain size, whereas the results in the latter case exhibit an extreme sensitivity that prevents domain independent critical parameters from being determined. The instability of the two helices is primarily addressed through experiments and analytic theory. It is shown that the well known pairing instability of neighboring vortex filaments is responsible for transition, and careful measurements enable growth rates of the instabilities to be obtained that are in close agreement with theoretical predictions. Using the experimental baseflow data, a successful attempt is subsequently also made to reproduce this experiment numerically. In the second part of the thesis, a novel method for computing the optimal forcing of a dynamical system is developed. The method is based on an application of the inverse power method preconditioned by the Laplace preconditioner to the direct and adjoint resolvent operators. The method is analyzed for the Ginzburg–Landau equation and afterwards the Navier–Stokes equations, where it is implemented in the spectral element method and validated on the two-dimensional lid-driven cavity flow and the flow around a cylinder.QC 20171124
35
Bleesen, Christoph A. "Variotherme Spritzgießtechnologie zur Beeinflussung tribologischer Eigenschaften thermoplastischer Formteile." Doctoral thesis, Universitätsverlag der Technischen Universität Chemnitz, 2015. https://monarch.qucosa.de/id/qucosa%3A20459.
Full textAbstract:
Im Rahmen der vorliegenden Arbeit wurde ein Spritzgießwerkzeug mit einem neuartigen Mehrschichtverbundheizsystem zur dynamischen Temperierung entwickelt und umgesetzt. Dabei wurde das ausgewählte Heiz‐ und Kühlsystem unter theoretischen und praktischen Gesichtspunkten betrachtet und für den variothermen Fertigungsprozess verifiziert. Aus den ersten durchgeführten praktischen Versuchen zeigte sich, dass dieses Heizsystem zur dynamischen Temperierung von Formwerkzeugen geeignet ist.
Anschließend wurden mit dem realisierten Spritzgießwerkzeug Versuchskörper mit spezieller Oberflächenstrukturierung und variierenden Werkzeugwandtemperaturen angefertigt und untersucht. Ziel war es, über diese Strukturierung eine Beeinflussung der Glasfaserverteilung im Formteilrandbereich zu erreichen und die tribologischen Eigenschaften bei Kunststoff‐Kunststoff‐Gleitpaarungen hinsichtlich Reibung und Verschleiß
zu verbessern. Mit einer kleinen Auswahl an Strukturen und entsprechenden thermoplastischen Polymermaterialien wurden praktische Versuche zur tribologischen Prüfung durchgeführt.In the present work an injection mould was developed and implemented with a novel multilayer composite heating system for dynamic temperature control. Here the selected heating and cooling system was considered from a theoretical and practical point of view and verified for the variothermal manufacturing process. The first practical tests showed that this heating system is suitable for the dynamic temperature control of tools. Subsequently, with this injection mould, test specimens with a special surface structure and varying mould wall temperatures were produced and examined. The aim was to achieve through this structuring an impact on the distribution of glass fibres in the edge region of mouldings and improve the tribological properties of plastic‐plastic‐pairings in terms of friction and wear. With a small selection of structures and corresponding thermoplastic polymeric materials practical experiments for tribological testing were performed.
36
Štefan, David. "Struktura proudění a energetické přeměny v kolenové sací troubě." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2011. http://www.nusl.cz/ntk/nusl-229640.
Full textAbstract:
Draft tube is very important part of hydraulic turbines. Only optimum work together with turbine can bring highest performance of this machine set. Hence it is necessary to deal with character of flow in the draft tube for different operating conditions. Efficiency of the draft tube depends on many phenomena of flow. Observing these phenomena and finding their relation with energetic transformation in the draft tube is a suitable tool to judge quality of draft tube performance. Incorrect design of the draft tube can sometimes cause lower efficiency of whole machine set. The goal of this thesis is finding the main reasons causing draft tube efficiency drop for given operating conditions.
37
Pezzotti, Simone. "DFT-MD simulations and theoretical SFG spectroscopy to characterize H-Bonded networks at aqueous interfaces : from hydrophobic to hydrophilic environments Structural definition of the BIL and DL: a new universal methodology to rationalize non-linear χ(2)(ω) SFG signals at charged interfaces, including χ(3)(ω) contributions What the Diffuse Layer (DL) Reveals in Non-Linear SFG Spectroscopy 2D H-Bond Network as the Topmost Skin to the Air-Water Interface Combining ab-initio and classical molecular dynamics simulations to unravel the structure of the 2D-HB-network at the air-water interface 2D-HB-Network at the air-water interface: A structural and dynamical characterization by means of ab initio and classical molecular dynamics simulations Spectroscopic BIL-SFG Invariance Hides the Chaotropic Effect of Protons at the Air-Water Interface Molecular hydrophobicity at a macroscopically hydrophilic surface Graph theory for automatic structural recognition in molecular dynamics simulations DFT-MD of the (110)-Co3O4 cobalt oxide semiconductor in contact with liquid water, preliminary chemical and physical insights into the electrochemical environment." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLE008.
Full textAbstract:
Améliorer notre connaissance de la structure de l'eau dans l'environnement spécial offert par une interface est essentiel pour la compréhension de nombreux phénomènes naturels et applications technologiques. Pour révéler cette structure interfaciale de l'eau, des techniques capables de fournir des informations microscopiques, de manière sélective, pour cette couche interfaciale (BIL) sont nécessaires. Dans le présent travail de thèse, nous avons donc étudié les interfaces aqueuses au niveau moléculaire, en couplant la modélisation théorique à partir de simulations DFT-MD avec les spectroscopies SFG et THz-IR. En développant de nouveaux protocoles/outils d'investigation associant simulations DFT-MD et spectroscopie SFG, en particulier pour la rationalisation plus complexe des interfaces chargées, nous avons fourni une compréhension globale de l'effet des conditions interfaciales d'hydrophilicité, de pH, de force ionique sur le réseau des liaisons-H formé dans la couche interfaciale BIL, sur ses signatures spectroscopiques et sur son impact sur les propriétés physico-chimiques. Nous avons montré pour la première fois que, dans des conditions suffisamment hydrophobes, l'eau interfaciale crée des réseaux des liaisons-H bidimensionnels, révélé expérimentalement par les spectres THz-IR. Le réseau-2D dicte la dynamique de l'eau interfaciale, le potentiel de surface, l'acidité de surface, la tension superficielle et la thermodynamique d'hydratation des solutés hydrophobes. Cet "ordre horizontal" aux interfaces hydrophobes est opposé à "l'ordre verticale" obtenu aux interfaces hydrophiles. Nous avons aussi révélé comment les ions et les conditions de pH modifient ces arrangements structurauxImproving our knowledge on water H-Bonded networks formed in the special environment offered by an interface is pivotal for our understanding of many natural phenomena and technological applications. To reveal the interfacial water arrangement, techniques able to provide detailed microscopic information selectively for the interfacial layer are required. In the present thesis work, we have hence investigated aqueous interfaces at the molecular level, by coupling theoretical modeling from DFT-MD simulations with SFG & THz-IR spectroscopies. By developing new investigation protocols/tools, coupling DFT-MD simulations and SFG spectroscopy, in particular for the more complex rationalization of charged interfaces, we have provided a global comprehension of the effect of various interfacial conditions (hydrophilicity, pH, ionic strength) on the HB-Network formed in the interfacial layer (BIL), on its spectroscopic signatures and on its impact on physico-chemical properties. We have shown for the first time that, in sufficiently hydrophobic conditions, BIL interfacial water creates special 2-Dimensional HB-Networks, experimentally revealed by one specific THz-IR marker band. Such 2D-network dictates HBs and orientational dynamics of interfacial water, surface potential, surface acidity, water surface tension and thermodynamics of hydration of hydrophobic solutes. Such "horizontal ordering” of water at hydrophobic interfaces is found opposite to the “vertical ordering” of water at hydrophilic interfaces, while coexistence of the two orders leads to disordered interfacial water in intermediate hydrophilic/hydrophobic conditions. Both DFT-MD and SFG further revealed how ions & pH conditions alter these BIL-water orders
38
Hoque, Mohammad Azizul. "Coupled consolidation model for negative skin friction on piles in clay layers." Thesis, 2006. http://spectrum.library.concordia.ca/8785/1/MR14247.pdf.
Full textAbstract:
Piles driven in clay are often subjected to indirect loading as a result of the surcharge applied on the surrounding area. During the drained period, both the pile and the soil undergo downward movements caused by the axial and the surcharge loading, respectively. Depending on the relative movement of the pile/soil system, positive and negative skin friction develop on the pile's shaft. Negative skin friction is the drag force that may be large enough to reduce the pile capacity and/or to overstress the pile's material causing fractures or perhaps structural failure or possibly pulling out the pile from the cap. A numerical model was developed to simulate the case of a single pile driven in soft clay layer overlying a deep deposit. Coupled consolidation method of analysis is adopted to predict time/settlement/skin friction distribution relationships. The model is an axisymmetric that uses the finite element technique combined with the soil responses according to Mohr-Coulomb criteria. The model was first tested against the results predicted by the classic theories for bearing capacity of pile foundations on clay. Furthermore, the model was validated with the results of three full scale field tests available in the literature
39
Ajit, Dixit Shivsai. "Structure Of Sink Flow Boundary Layers." Thesis, 2009. https://etd.iisc.ac.in/handle/2005/1098.
Full textAbstract:
The work reported in this thesis is an experimental and theoretical investigation of the so-called sink flow boundary layers. These are two-dimensional (in the mean), favourable-pressure-gradient (FPG) boundary layer flows where the boundary layers experience stream-wise acceleration inside a two-dimensional convergent channel with smooth and plane walls. The boundary layers studied are mainly turbulent with few cases that may be identified as reverse-transitional. The sink flow turbulent boundary layers (TBLs) are the only smooth-walled layers that are in ‘perfect equilibrium’ or ‘exact self-preservation’ in the sense of Townsend (1976) and Rotta (1962).
The present boundary layer experiments were conducted in an open-return low-speed wind tunnel. The sink flow conditions were established on the test-plate by using a contoured test-section ceiling for creating a convergent channel with smooth and plane walls. The strength of the streamwise FPG was varied by changing the freestream speed in the test-section. Few zero-pressure-gradient (ZPG) turbulent boundary layers were also measured in the same tunnel for which the contoured ceiling was replaced by a straight one. The velocity measurement techniques used include conventional Pitot-tubes for mean flow measurements and hotwire/crosswire probes for turbulence measurements. For measurement of skin friction in ZPG flows, Preston-tube was used while for the sink flows the so-called surface hotwire method was employed. Static pressures were measured on the test-surface using an alcohol-based projection manometer. Boundary layers were tripped at the beginning of the test-plate to ensure quick transition to turbulence.
The mean velocity scaling in sink flow TBLs in the presence of strong FPG has been studied systematically, especially in view of the apparent pressure-gradient-dependence of the logarithmic laws reported in the literature (Spalart & Leonard, 1986; Nickels, 2004; Chauhan et al., 2007). The experimental study of sink flow TBLs carried out over a wide range of streamwise FPGs has shown that the mean velocity profiles (in inner coordinates) exhibit systematic departures from the universal logarithmic law as the pressure gradient parameter ∆p is varied. Even so, each of these profiles exhibits a logarithmic region, albeit non-universal, whose constants are functions of the pressure gradient. Systematic dependence of these constants on the pressure gradient parameter ∆p is observed. Moreover, the wake region is uniformly absent in all these profiles. In other words, each profile looks like a ‘pure wall-flow’, in the sense of Coles (1957), only if it is viewed in relation to its own non-universal logarithmic law.
To support the experimental observation of the pressure-gradient-dependence of logarithmic laws in sink flow TBLs, a theory based on the method of matched asymptotic expansions has been applied to sink flow TBLs and this theory reveals a systematic dependence of inner and outer logarithmic laws on the pressure gradient parameter ∆p. This dependence is essentially a higher-order effect and therefore becomes significant only in the presence of relatively strong pressure gradients. Comparison of the theory with the experimental data demonstrates that the disappearance of the universal logarithmic law in strong FPG situations does not necessarily imply the absence of classical inner-outer overlap region. The overlap may still manifest itself as a logarithmic functional form with constants that are strongly influenced by the magnitude of the FPG.
An immediate use of the non-universal log laws is towards the estimation skin friction in strong-pressure-gradient equilibrium and near-equilibrium TBL flows and this issue has been studied in some detail. It is shown that the conventional Clauser-chart method for estimation of skin friction (which gives fairly accurate results for ZPG or mild-pressure-gradient flows), originally proposed by Clauser (1954), can be modified to deal with the situations involving strong streamwise pressure gradients, provided that the equilibrium or near-equilibrium TBL under consideration is not very close to relaminarization or separation. In such cases, the overlap layer manifests itself in the form of non-universal logarithmic laws that are dependent on the local strength of the pressure gradient. Using these non-universal log laws in conjunction with the measured pressure distribution (necessary for obtaining the acceleration parameter K) and a measured mean velocity profile, it is possible to obtain the local skin friction coefficient to an accuracy which is typical of skin friction measurements. This modified Clauser-chart method (MCCM) employs a two-fold iterative procedure (one iteration on Cf and the other on ∆p) in contrast to the conventional method that involves only one iteration (on Cf alone). As a by-product of this MCCM, one obtains the local pressure gradient parameter ∆p and the slope 1/κ and intercept C of the non-universal log law for that profile. It is also demonstrated that the arm´MCCM is quite robust to the changes in the universal values of K´arman constant κ0 and intercept C0 for the ZPG turbulent boundary layer.
Various aspects of the large-scale structure in turbulent and reverse-transitional sink flow boundary layers subjected to streamwise FPGs have also been investigated. The use of sink flow configuration allows systematic characterization of the large-scale structure with the strength of the FPG as a parameter where the characterization is not contaminated by the upstream history effects. The large-scale structure is identified by cross-correlating the wall-shear stress fluctuation with the streamwise velocity fluctuation. The structure orientation is found to be linear over a large wall-normal extent typically extending from y/δ of 0.1 to 0.6. Beyond y/δ =0.6, the correlation under consideration becomes very weak to allow any conclusive results. The average structure inclination angle αavg is found to decrease systematically with increase in the streamwise FPG. This result is important and has implications towards modeling of the near-wall region. Further it is found that the structure gets elongated considerably as the FPG is increased, i.e. the streamwise spatial extent of the structure increases. Taken together, it is observed that the structure becomes flatter and longer with the increase in FPG. Structural models are proposed for sink flow TBLs in the form of either the shape of individual hairpin vortices or the possible structural self-organization. These models are then discussed in the light of present experimental results. It is also shown that the process of relaminarization of a TBL by strong FPG may be better appreciated by appealing to these structural models.
The validity of Taylor’s hypothesis for structure angle measurements in the present study has been established experimentally. This exercise is important since the flows under consideration are highly accelerated and sometimes even reverse-transitional. In most of the previous work on the validity of Taylor’s hypothesis, at least for the measurements similar to the present work, the emphasis has been on ZPG turbulent boundary layers. The present exercise is therefore crucial for accelerating flows. Possible reasons for the observed validity of Taylor’s hypothesis have also been identified − specifically it is seen that the condition ∆xp/L << 1 needs to be met for Taylor’s hypothesis to be valid in pressure gradient flows.
Investigation of the structure convection velocity from the space-time correlations has revealed that the convection velocity of a typical structure in the present sink flow boundary layers is almost equal to the local mean velocity (more than 90%). This implies that the structure gets convected downstream almost along with the mean flow.
Near-wall ‘active’ and ‘inactive’ motions in sink flow TBLs have been studied, discussed and compared with the corresponding results for ZPG turbulent boundary layers from five different aspects: (i) turbulent diffusion of TKE, (ii) quadrant statistics, (iii) profiles of the streamwise turbulence intensity, (iv) event correlation length scales obtained from conditional sampling on the instantaneous flux signal and (v) profiles of the Townsend parameter Tp =(−uv) /u2.
Near-wall inactive motion is seen to be related to the strength of the large-eddy structure in the outer region of TBL flow. For APG flows the near-wall inactive motion is known to be more intense (Bradshaw, 1967b) than the ZPG flows, say at the same K´arman number δ+. This observation is consistent with a stronger large-eddy structure that may be perceived from the stronger wake component in the mean velocity variation and the larger mean entrainment in an APG turbulent boundary layer as compared to the ZPG flow at same δ+. In sink flow TBLs, the large-eddy structure is much weaker in comparison to the ZPG flow at same δ+ which is consistent with the absence of wake component in the mean velocity profile as well as the zero mean entrainment into the layer. A sink flow TBL represents, a state of weakest large-eddy structure and hence minimum intensity of inactive motion compared to any other equilibrium or near-equilibrium TBL flow having the same K´arman number δ+. All the analysis of the relevant experimental data seems to support this.
40
Ajit, Dixit Shivsai. "Structure Of Sink Flow Boundary Layers." Thesis, 2009. http://hdl.handle.net/2005/1098.
Full textAbstract:
The work reported in this thesis is an experimental and theoretical investigation of the so-called sink flow boundary layers. These are two-dimensional (in the mean), favourable-pressure-gradient (FPG) boundary layer flows where the boundary layers experience stream-wise acceleration inside a two-dimensional convergent channel with smooth and plane walls. The boundary layers studied are mainly turbulent with few cases that may be identified as reverse-transitional. The sink flow turbulent boundary layers (TBLs) are the only smooth-walled layers that are in ‘perfect equilibrium’ or ‘exact self-preservation’ in the sense of Townsend (1976) and Rotta (1962).
The present boundary layer experiments were conducted in an open-return low-speed wind tunnel. The sink flow conditions were established on the test-plate by using a contoured test-section ceiling for creating a convergent channel with smooth and plane walls. The strength of the streamwise FPG was varied by changing the freestream speed in the test-section. Few zero-pressure-gradient (ZPG) turbulent boundary layers were also measured in the same tunnel for which the contoured ceiling was replaced by a straight one. The velocity measurement techniques used include conventional Pitot-tubes for mean flow measurements and hotwire/crosswire probes for turbulence measurements. For measurement of skin friction in ZPG flows, Preston-tube was used while for the sink flows the so-called surface hotwire method was employed. Static pressures were measured on the test-surface using an alcohol-based projection manometer. Boundary layers were tripped at the beginning of the test-plate to ensure quick transition to turbulence.
The mean velocity scaling in sink flow TBLs in the presence of strong FPG has been studied systematically, especially in view of the apparent pressure-gradient-dependence of the logarithmic laws reported in the literature (Spalart & Leonard, 1986; Nickels, 2004; Chauhan et al., 2007). The experimental study of sink flow TBLs carried out over a wide range of streamwise FPGs has shown that the mean velocity profiles (in inner coordinates) exhibit systematic departures from the universal logarithmic law as the pressure gradient parameter ∆p is varied. Even so, each of these profiles exhibits a logarithmic region, albeit non-universal, whose constants are functions of the pressure gradient. Systematic dependence of these constants on the pressure gradient parameter ∆p is observed. Moreover, the wake region is uniformly absent in all these profiles. In other words, each profile looks like a ‘pure wall-flow’, in the sense of Coles (1957), only if it is viewed in relation to its own non-universal logarithmic law.
To support the experimental observation of the pressure-gradient-dependence of logarithmic laws in sink flow TBLs, a theory based on the method of matched asymptotic expansions has been applied to sink flow TBLs and this theory reveals a systematic dependence of inner and outer logarithmic laws on the pressure gradient parameter ∆p. This dependence is essentially a higher-order effect and therefore becomes significant only in the presence of relatively strong pressure gradients. Comparison of the theory with the experimental data demonstrates that the disappearance of the universal logarithmic law in strong FPG situations does not necessarily imply the absence of classical inner-outer overlap region. The overlap may still manifest itself as a logarithmic functional form with constants that are strongly influenced by the magnitude of the FPG.
An immediate use of the non-universal log laws is towards the estimation skin friction in strong-pressure-gradient equilibrium and near-equilibrium TBL flows and this issue has been studied in some detail. It is shown that the conventional Clauser-chart method for estimation of skin friction (which gives fairly accurate results for ZPG or mild-pressure-gradient flows), originally proposed by Clauser (1954), can be modified to deal with the situations involving strong streamwise pressure gradients, provided that the equilibrium or near-equilibrium TBL under consideration is not very close to relaminarization or separation. In such cases, the overlap layer manifests itself in the form of non-universal logarithmic laws that are dependent on the local strength of the pressure gradient. Using these non-universal log laws in conjunction with the measured pressure distribution (necessary for obtaining the acceleration parameter K) and a measured mean velocity profile, it is possible to obtain the local skin friction coefficient to an accuracy which is typical of skin friction measurements. This modified Clauser-chart method (MCCM) employs a two-fold iterative procedure (one iteration on Cf and the other on ∆p) in contrast to the conventional method that involves only one iteration (on Cf alone). As a by-product of this MCCM, one obtains the local pressure gradient parameter ∆p and the slope 1/κ and intercept C of the non-universal log law for that profile. It is also demonstrated that the arm´MCCM is quite robust to the changes in the universal values of K´arman constant κ0 and intercept C0 for the ZPG turbulent boundary layer.
Various aspects of the large-scale structure in turbulent and reverse-transitional sink flow boundary layers subjected to streamwise FPGs have also been investigated. The use of sink flow configuration allows systematic characterization of the large-scale structure with the strength of the FPG as a parameter where the characterization is not contaminated by the upstream history effects. The large-scale structure is identified by cross-correlating the wall-shear stress fluctuation with the streamwise velocity fluctuation. The structure orientation is found to be linear over a large wall-normal extent typically extending from y/δ of 0.1 to 0.6. Beyond y/δ =0.6, the correlation under consideration becomes very weak to allow any conclusive results. The average structure inclination angle αavg is found to decrease systematically with increase in the streamwise FPG. This result is important and has implications towards modeling of the near-wall region. Further it is found that the structure gets elongated considerably as the FPG is increased, i.e. the streamwise spatial extent of the structure increases. Taken together, it is observed that the structure becomes flatter and longer with the increase in FPG. Structural models are proposed for sink flow TBLs in the form of either the shape of individual hairpin vortices or the possible structural self-organization. These models are then discussed in the light of present experimental results. It is also shown that the process of relaminarization of a TBL by strong FPG may be better appreciated by appealing to these structural models.
The validity of Taylor’s hypothesis for structure angle measurements in the present study has been established experimentally. This exercise is important since the flows under consideration are highly accelerated and sometimes even reverse-transitional. In most of the previous work on the validity of Taylor’s hypothesis, at least for the measurements similar to the present work, the emphasis has been on ZPG turbulent boundary layers. The present exercise is therefore crucial for accelerating flows. Possible reasons for the observed validity of Taylor’s hypothesis have also been identified − specifically it is seen that the condition ∆xp/L << 1 needs to be met for Taylor’s hypothesis to be valid in pressure gradient flows.
Investigation of the structure convection velocity from the space-time correlations has revealed that the convection velocity of a typical structure in the present sink flow boundary layers is almost equal to the local mean velocity (more than 90%). This implies that the structure gets convected downstream almost along with the mean flow.
Near-wall ‘active’ and ‘inactive’ motions in sink flow TBLs have been studied, discussed and compared with the corresponding results for ZPG turbulent boundary layers from five different aspects: (i) turbulent diffusion of TKE, (ii) quadrant statistics, (iii) profiles of the streamwise turbulence intensity, (iv) event correlation length scales obtained from conditional sampling on the instantaneous flux signal and (v) profiles of the Townsend parameter Tp =(−uv) /u2.
Near-wall inactive motion is seen to be related to the strength of the large-eddy structure in the outer region of TBL flow. For APG flows the near-wall inactive motion is known to be more intense (Bradshaw, 1967b) than the ZPG flows, say at the same K´arman number δ+. This observation is consistent with a stronger large-eddy structure that may be perceived from the stronger wake component in the mean velocity variation and the larger mean entrainment in an APG turbulent boundary layer as compared to the ZPG flow at same δ+. In sink flow TBLs, the large-eddy structure is much weaker in comparison to the ZPG flow at same δ+ which is consistent with the absence of wake component in the mean velocity profile as well as the zero mean entrainment into the layer. A sink flow TBL represents, a state of weakest large-eddy structure and hence minimum intensity of inactive motion compared to any other equilibrium or near-equilibrium TBL flow having the same K´arman number δ+. All the analysis of the relevant experimental data seems to support this.
41
Andrewartha, JM. "The effect of freshwater biofilms on turbulent boundary layers and the implications for hydropower canals." Thesis, 2010. https://eprints.utas.edu.au/10691/1/01front.pdf.
Full textAbstract:
The majority of the electricity supplied in Tasmania, Australia, is produced by hydropower.
Hydro Tasmania, the power generation utility, operates 29 hydropower stations incorporating
170 km of open channels. These open channels are susceptible to extensive biofilm growth
dominated by the freshwater diatoms Gomphonema tarraleahae and Tabellaria flocculosa,
which form a gelatinous biofilm several millimetres thick and cause reductions in flow capacity
of up to 10%.
This thesis presents results of a multidisciplinary study on the effects of freshwater biofilms on
hydropower canal capacity and turbulent boundary layer structure. The extent to which the
surface roughness affects the structure of the turbulent boundary layer was critically examined,
in the context of the wall similarity hypothesis.
A recirculating water tunnel, equipped with a floating element force balance and a twodimensional
Laser Doppler Velocimetry system, was used to obtain detailed measurements on
test plates covered with flow-conditioned freshwater biofilms. Total drag measurements, mean
velocity profiles and turbulent Reynolds stresses were compared for smooth, sandgrain and
biofouled test plates. An artificial biofilm was developed to study the motion of algae streamers
under flow conditions. Each test surface was mapped using digital close-range photogrammetry
to provide a three-dimensional surface model. A logarithmic relationship was found between the
roughness function and the maximum peak-to-valley height from the photogrammetry
measurements for the low-form gelatinous biofilms.
Seven methods for determining the wall shear stress were investigated; however, none of the
methods examined were entirely satisfactory. A method which can be used for both smooth and
rough surfaces with reasonable measurement uncertainty is needed to allow objective
comparison of the structure of smooth and rough wall turbulent boundary layers.
The presence of biofouling caused a significant increase in the local skin friction coefficient and
overall drag coefficient with increases in skin friction of up to 210% measured over smooth plate
values. Results for low-form gelatinous biofilms provided support for the wall similarity
hypothesis. The biofilms modified the structure of the turbulent boundary layer in the near-wall
region. Velocity defect profiles, Reynolds stress profiles and quadrant analyses showed good
agreement for different test plate surfaces in the outer region of the boundary layer. The results
for an artificial filamentous biofilm were less conclusive, and may not support wall similarity.
42
Hsieh, Chia-Siou, and 謝嘉修. "Development of tri-layer cultured skin substitute." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/k6tkhy.
Full textAbstract:
碩士國立臺北科技大學
生物科技研究所
98
Skin is composed of epidermis, dermis, hypodermis, important glands, nerves and blood vessels. It is the most important defense line of our human body. It has the functions of thermoregulation, protects the internal organs, regulation of water evaporation to sustain life. When burn or scald occupies area of body surface to reach above 30% or damage to hypodermis occupies area of body surface above 10%, surgical method such as skin grafting must be performed to recover the protective barrier of skin. In general, there are three kinds of skin grafting surgeries, namely autograft, allograft and xenograft. Autograft may face the insufficient supply of oneself skin tissue. Allograft and xenograft will encounter the concern of graft rejection and the risks of zoonostic diseases transmitted from other living organisms. In order to resolve aforementioned problems encountered during grafting, cultured skin substitute has been developed. The existing cultured skin substitutes found in the market use collagen as a matrix for cell attachment and growth. In principle, collagen matrix is inoculated with fibroblast as dermis substitute and inoculated with keratinocyte as epidermis substitute. However the existing cultured skin substitutes have two drawbacks including (1) lack of mechanical strength resulted in easy degradation and shrinkage; (2) delayed vascularization due to ischemia that reduces graft bioactivity, leading to poor grafting efficacy. The present paper introduced a cultured skin substitute with vascularization capacity which can overcome the questions associated with current culture skin substitutes. With the advancement of collagen extraction technology, collagen matrix formation technique, skin cell separation and the mass cultured technology and endothelial cell isolation technique have successfully constructed a tri-layered artificial skin substitute. The anticipated vascularization system will increase not only the mechanical strength of the cultured skin substitute, but also significantly improve transplantation efficacy.
43
Mahjour, S. B., X. Fu, X. Yang, J. Fong, Farshid Sefat, and H. Wang. "Rapid creation of skin substitutes from human skin cells and biomimetic nanofibers for acute full-thickness wound repair." 2015. http://hdl.handle.net/10454/11151.
Full textAbstract:
yesCreation of functional skin substitutes within a clinically acceptable time window is essential for timely repair and management of large wounds such as extensive burns. The aim of this study was to investigate the possibility of fabricating skin substitutes via a bottom-up nanofiber-enabled cell assembly approach and using such substitutes for full-thickness wound repair in nude mice. Following a layer-by-layer (L-b-L) manner, human primary skin cells (fibroblasts and keratinocytes) were rapidly assembled together with electrospun polycaprolactone (PCL)/collagen (3:1 w/w, 8% w/v) nanofibers into 3D constructs, in which fibroblasts and keratinocytes were located in the bottom and upper portion respectively. Following culture, the constructs developed into a skin-like structure with expression of basal keratinocyte markers and deposition of new matrix while exhibited good mechanical strength (as high as 4.0 MPa by 14 days). Treatment of the full-thickness wounds created on the back of nude mice with various grafts (acellular nanofiber meshes, dermal substitutes, skin substitutes and autografts) revealed that 14-day-cultured skin substitutes facilitated a rapid wound closure with complete epithelialization comparable to autografts. Taken together, skin-like substitutes can be formed by L-b-L assembling human skin cells and biomimetic nanofibers and they are effective to heal acute full-thickness wounds in nude mice.
44
Chou, Yu-Te, and 周育德. "Formation of Skin Layer in Cake Filtration of Deformable Particles." Thesis, 1998. http://ndltd.ncl.edu.tw/handle/35168931860556207616.
Full textAbstract:
碩士淡江大學
化學工程學系研究所
86
The filtration of deformable particles occurs in many industrial practice, such as chemical industries, food processes, biochemical processes, etc. The basic filtration equations used for the design of a filter or for searching for the optimum operating condition are the conventional filtration theories which can only be employed for rigid particles. By using these equations for the filtration of deformable particles may result in a large deviation between predictions and experimental data. Although the filtration theory of deformable particles is very important, a few researchers pay attention to this subject, and rare efficient theory has been derived. Three kinds of deformable particles (Ca-alginate gel particles) with different elasticity are prepared and used to study the mechanism of formation of skin layer in cake filtration. The experiment data studied by Fischmeister(1978) is used to estimate the value of surface area of particles due to their area contact in a cake. A numerical program is design to simulate the variations of local cake porosity. The results show that the average properties of the filter cake calculated by Kelvin model agree well with the experiment data. Furthermore, the results of simulation of dynamic analysis compared with Kelvin model indicate that the skin layer has been formed at tf in the figure of v vs. t and its thickness ratio in a cake decreases with increasing the time of filtration.
45
Tseng, Po-Kai, and 曾柏凱. "Preparation of Pt3Ni(Pt-skin) thin layer modified Pd/C oxygen reaction electrocatalysts." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/2np3vc.
Full textAbstract:
碩士國立中興大學
化學系所
106
Bimetallic Pt-Ni with Pt on the outermost layer and an innermost layer enriched in Ni, referred to as (Pt3Ni(Pt-skin), is a promising configuration of electrocatalyst for the oxygen reduction reaction (ORR) in fuel cells. We prepare a core (Pd)/shell (Pt3Ni(Pt-skin)) catalyst (Pt3Ni(Pt-skin)/Pd/C) from Zn underpotential deposition (UPD) on a Ni UPD modified Pd/C catalyst, facilitating Pt atomic layer-by-layer growth on the Ni surface through the galvanic replacement process. The Pt3Ni(Pt-skin)/Pd/C shows the best ORR performance, with a Pt specific activity 16.7 mA cm-2 and Pt mass activity 14.2 A mgPt-1, which are 90- and 156- fold improvements over commercial Pt/C catalysts. The Pt3Ni(Pt-skin) structure effectively inhibits Ni leaching to improve the durability under the two accelerated durability test modes mimicking the catalyst lifetime and start-up/shut-down cycles.
46
Zhang, J. N., Z. F. Cui, R. Field, M. G. Moloney, Stephen Rimmer, and H. Ye. "Thermo-responsive microcarriers based on poly(N-isopropylacrylamide)." 2015. http://hdl.handle.net/10454/9425.
Full textAbstract:
NoMicrocarrier cell culture systems provide an attractive alternative to the conventional monolayer cell culture for cell amplification, due to their high surface area-to-volume ratio. Unlike enzymatic methods for removing cells from microcarriers after cell culture, which can lead to irreversible damage of the cells, microcarriers which release cells by temperature adjustment have been developed. This was achieved by grafting a temperature-responsive polymer, poly(N-isopropylacrylamide) (PNIPAAm), on the microcarrier surface. This review comprehensively presents various methods to prepare such thermo-responsive microcarriers based on PNIPAAm. These methods include the grafting-to technique, grafting-from technique, grafting-through technique, along with methods leading to PNIPAAm hydrogel beads, seeded polymerization, and non-covalent adsorption. The methods for controlling PNIPAAm grafting density, molecular weight and molecular architecture are also outlined. Further, the efficiency of cell attachment, proliferation and thermally-induced detachment of such thermo-responsive microcarriers is introduced and compared. (C) 2015 Elsevier Ltd. All rights reserved.
EPSRC
47
Shah, Mohammad Khalid. "Skin friction characteristics in smooth-wall, transitionally rough and fully rough turbulent boundary layer." 2004. http://hdl.handle.net/1993/15762.
Full text
48
Oguntala, G., V. Indramohan, S. Jeffery, and Raed A. Abd-Alhameed. "Triple-layer Tissue Prediction for Cutaneous Skin Burn Injury: Analytical Solution and Parametric Analysis." 2001. http://hdl.handle.net/10454/18487.
Full textAbstract:
NoThis paper demonstrates a non-Fourier prediction methodology of triple-layer human skin tissue for determining skin burn injury with non-ideal properties of tissue, metabolism and blood perfusion. The dual-phase lag (DPL) bioheat model is employed and solved using joint integral transform (JIT) through Laplace and Fourier transforms methods. Parametric studies on the effects of skin tissue properties, initial temperature, blood perfusion rate and heat transfer parameters for the thermal response and exposure time of the layers of the skin tissue are carried out. The study demonstrates that the initial tissue temperature, the thermal conductivity of the epidermis and dermis, relaxation time, thermalisation time and convective heat transfer coefficient are critical parameters to examine skin burn injury threshold. The study also shows that thermal conductivity and the blood perfusion rate exhibits negligible effects on the burn injury threshold. The objective of the present study is to support the accurate quantification and assessment of skin burn injury for reliable experimentation, design and optimisation of thermal therapy delivery.
49
Oguntala, George A., V. Indramohan, S. Jeffery, and Raed A. Abd-Alhameed. "Triple-layer Tissue Prediction for Cutaneous Skin Burn Injury: Analytical Solution and Parametric Analysis." 2021. http://hdl.handle.net/10454/18487.
Full textAbstract:
YesThis paper demonstrates a non-Fourier prediction methodology of triple-layer human skin tissue for determining skin burn injury with non-ideal properties of tissue, metabolism and blood perfusion. The dual-phase lag (DPL) bioheat model is employed and solved using joint integral transform (JIT) through Laplace and Fourier transforms methods. Parametric studies on the effects of skin tissue properties, initial temperature, blood perfusion rate and heat transfer parameters for the thermal response and exposure time of the layers of the skin tissue are carried out. The study demonstrates that the initial tissue temperature, the thermal conductivity of the epidermis and dermis, relaxation time, thermalisation time and convective heat transfer coefficient are critical parameters to examine skin burn injury threshold. The study also shows that thermal conductivity and the blood perfusion rate exhibits negligible effects on the burn injury threshold. The objective of the present study is to support the accurate quantification and assessment of skin burn injury for reliable experimentation, design and optimisation of thermal therapy delivery.
The full-text of this article will be released for public view at the end of the publisher embargo on 15th Apr 2022.
50
Wen-YungChung and 鍾文陽. "A Study of Sulfurization Cu(InGa)Se2 Skin Layer Used for Solar Cell Applications." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/28500285126764571657.
Full textAbstract:
碩士國立成功大學
微電子工程研究所碩博士班
100
In this thesis I used co-electroplating method, instead of traditional physical vapor deposition, to deposition Copper–Indium-Gallium precursors on the flexible stainless steel substrate , followed by a selenization process to form Cu(InGa)Se2 (CIGS) absorber layer and used surface sulfurization the skin layer of the CIGS film to passivate and/or repair the surface defects. The sulfurization process can replace some Se with S which can increase the open-circurt voltage of the solar cell. In this study, the influences of the compositions of the precursors, selenazation temperature and duration, method of sulfurization, and the degree of sulfurization on the CIGS film and on the device characteristics were investigated. A SEM was used to observe the film’s morphology, crystalline phase and orientation were determined by XRD and Raman analysis, and an EDS was used to analyze the compositions of the absorber layer. Finally, Cu(InGa)SeS (CIGSS) thin film solar cells were fabricated and tested.The best device has remarkable diode characteristics.The key parameters are: Voc(open-circuit voltage)=179 mV、Jsc(short-circuit current)=30.97 mA/cm2、F.F.(fill factor)=26%、η=1.46%.