To see the other types of publications on this topic, follow the link: Effect of boundary Conditions.
Dissertations / Theses on the topic 'Effect of boundary Conditions'
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 'Effect of boundary Conditions.'
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
Osth, Adam F. "Create or differentiate? Testing the boundary conditions of differentiation." The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1321390746.
Full text
2
Park, Kyeong M. "Boundary conditions of font size effects." Thesis, The University of Alabama in Huntsville, 2016. http://pqdtopen.proquest.com/#viewpdf?dispub=10130786.
Full textAbstract:
<p> Prior research has shown that people perceive items in a larger font size as being more memorable than items in a smaller font size. This perception leads to higher judgments of learning (JOLs; i.e., confidence ratings regarding the likelihood of recalling an item) for larger font size items than smaller font size items. Yet other research has shown that people recalled more when the information was presented in a smaller font than when it was presented in a larger font size. The present study examined if there are boundary conditions of font sizes affecting JOLs and actual recall performance. As we expected, the results show that JOLs increased as a function of the size category. The results also show that font size impacted recall performance such that items in the Smallest size category were recalled at a higher rate than items in the other three font size categories.</p>
3
Hilton, Kelsey. "The effect of boundary conditions and architecture on the response of cancellous bone." Master's thesis, University of Cape Town, 2018. http://hdl.handle.net/11427/29542.
Full textAbstract:
The investigation presented herein was performed to determine the effect of boundary conditions and architectural parameters on the mechanical properties of bovine cancellous bone. 124 cylindrical cancellous samples (7.5 mm height) were harvested from a total of 9 bovine humeri. Mechanical properties of these samples were determined using compression tests performed at three, quasi-static strain rates, namely: 10−3 , 10−2 and 10−1 s −1 .The specimen conditions investigated were standard specimens (with marrow, 10 mm diameter), defatted specimens (without marrow, 10 mm diameter), structurally confined specimens (with marrow and a confining collar, 10 mm diameter) and bone confined specimens (with marrow, 20 mm and 28 mm diameters). Each specimen was scanned using a µCT scanner (Phoenix, voxel size 80 µm, 70 kV, 350 µA, acquisition time of 500 ms per image). The images were used to determine the architectural parameters for each specimen, which were calculated using algorithms developed during the study. These algorithms were validated against existing software (BoneJ) which is available to calculate cancellous bone architectural parameters. The results of the compression testing showed little dependence of mechanical properties on strain rate. The results of the defatted and structurally confined specimens showed a decrease in scatter with the elimination and reduction, respectively, of flow of the marrow within the trabecular network. This suggests that although marrow does not strengthen bone at quasi-static strain rates, the flow of marrow disrupts the trabecular network. The bone confinement results showed significantly increased mechanical strength of the inner 10 mm core compared to the whole sample. Apparent modulus was found to be 58% and 60% higher in the central core of the sample for 20 mm and 28 mm samples respectively. This suggests that doubling the diameter effectively removes the edge effects, with any additional diameter increase having no effect. Inner core yield strength was 58% higher in the 20 mm samples, and roughly 96% higher in the 28 mm samples compared to full specimen yield strength. This suggested that post-yield behaviour requires a further increase in overall diameter to sufficiently remove the edge effects due to the boundary condition. University of Cape Town Department of Mechanical Engineering The results of the architectural parameters suggested a linear correlation between the mechanical properties and parameters bone volume versus total volume and trabecular number. An exponential relationship was found to exist between the mechanical properties and mean trabecular separation. No correlation was found between mechanical properties and mean trabecular thickness. It was also concluded that specimen condition affects the relationship between mechanical properties and architectural parameters. Therefore, to effectively predict the response of cancellous bone, specimen condition should be used in conjunction with at least two architectural parameters, preferably bone volume versus total volume and mean trabecular separation.
4
Jiang, Mingxiao. "Scale and boundary conditions effects in fiber-reinforced composites." Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/16373.
Full text
5
Pham, Thanh Tung. "Multiscale modelling and simulation of slip boundary conditions at fluid-solid interfaces." Phd thesis, Université Paris-Est, 2013. http://tel.archives-ouvertes.fr/tel-00980155.
Full textAbstract:
In most applications concerning a fluid flowing over a solid surface, the no-slip velocity condition was widely used because it is simple and produces the results in agreement with experiments. However, this dynamical boundary condition is not appropriate when the flow under consideration is at a micro or nano length scale.In order to model this effect at the macroscopic scale, the Navier boundary conditions have been introduced, with the slip length as a parameter. When the fluid is a gas, this length is related to the tangential momentum accommodation coefficient (TMAC) and the mean free path, according to the Maxwell model. The aim of this work is to systematically address this model using a multi-scale approach and to extend it by incorporating both the morphology and the anisotropy of a surface. The thesis consists of five chapters. In Chapter 1, the basics of the kinetic theory of gases, the Boltzmann equation and related solutions (Navier-Stokes-Fourier, Burnett, Grad, Direct Simulation Monte Carlo ...) are briefly presented. The models of gas-wall interaction and slip models introduced in the fluid mechanics are also recalled. The chapter ends with a description of the computational method used for the molecular dynamics simulations performed in this work. Chapter 2 is dedicated to the development of a simple technique to simulate the pressure driven flows. The principle is to rely on the atomistic formulas of the stress tensor (Irving Kirkwood, Method of Plane, Virial Stress) and to modify the periodic conditions by maintaining the difference between the kinetic energy of the ingoing and outgoing particles of the simulation domain. Several types of channels are studied with this technique. The results (temperature, velocity ...) are discussed and compared. Chapter 3 deals with the study of the gas-wall interaction potential by the ab-initio method. The code CRYSTAL 09 is used to obtain the potential between an atom of argon (Ar) and a surface of platinum (Pt) <111> as a function of distance. Then the gas-wall potential is decomposed into binary potential and approached by an analytic function. This function is then implemented in a MD code to simulate the gas-wall collisions and determine the TMAC coefficient. In Chapter 4, the effect of morphology is studied. The multi-body Quantum Sutton Chen (QSC) potential is used for Pt <100> solid and the binary potential proposed in the previous chapter for the Ar-Pt couple is employed. The QSC potential is needed to reproduce the surface effects that affect the final results. Different surfaces are treated : smooth, nanostructured surface and, random surface obtained by Chemical vapor deposition (CVD). The TMAC is determined using a generalized approach, i.e. depending on the angle of incident flux of gas atoms on the surface. The surface anisotropy and the scattering kernel are also examined. In Chapter 5, we propose a model of anisotropic slip for fluids based on accommodation tensor. The model is obtained by the analytical approximate calculations developed in the framework of the kinetic theory. We thus generalize Maxwell's equation by showing that the slip length tensor is directly related to the accommodation tensor. The model is in good agreement with the MD results. Thanks to our MD simulations, we develop a suitable technique for reproducing the anisotropy of the accommodation tensor. The thesis ends with a conclusion section in which we suggest some perspectives for a continuation of this work
6
Thomas, B. M. "The effect of boundary conditions on the failure of thin plates subjected to impulsive loading." Master's thesis, University of Cape Town, 1995. http://hdl.handle.net/11427/11618.
Full textAbstract:
Bibliography: leaves 64-65.<br>This report presents the results of an investigation into the effects of edge boundary conditions on the failure of thin plates subjected to impulsive loading. In previous investigations the discrepancy between experimental results and theoretical solutions and effects observed at the edges of deformed plates have brought the method of securing the plate into question. This investigation examines the effect of edge boundary conditions by comparing the results of previous experiments where the plates were secured by clamping - with experiments where the plates are built-in (integral) with their supports.
7
Cervantes, Michel. "Effects of boundary conditions and unsteadiness on draft tube flow." Doctoral thesis, Luleå tekniska universitet, Strömningslära och experimentell mekanik, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-16887.
Full textAbstract:
The present research focuses on flow properties of the elbow draft tube. This element has a major function in low head turbines, since up to half of the losses may arise there at part load. The use of computational fluid dynamic (CFD) to redisign a draft tube necessitates detailed knowledged of the boundary conditions. They are generally not available and qualified guesses must be made. This applies in particular to the radial velocity at the inlet. A method to estimate this component in swirling flow from experimental values of the axial and tangential velocities is derived. The method uses a two dimensional non- viscous description of the flow, the Squire-Long formulation. It is tested against swirling flow in a diffuser and applied to the Turbine-99 draft tube flow. As several other boundary conditions are difficult to estimate and many input parameters are available to perform a simulation, the use of factorial design is proposed as an alternative to design simulations in a systematic, objective and quantitative way. The method allows the deternmination of the main and joint effects of input parameters on the numerical simulation. The input parameters may be experimental uncertainty on boundary conditions, unknown boundary conditions, grid and turbulence models. The method is applied to the Turbine-99 test case, where the radial velocity, the surface roughness, the turbulence length scale and the grid were the factors investigated. The inlet radial velocity is found to have a major effect on the pressure recovery. The flow in water turbines is highly unsteady due to the runner blade rotation, guide vanes and stay vanes. Unsteady pressure measurements on a Kaplan prototype point out unsteadiness in the high and low pressure regions of the turbine. Since model and prototype are not running in dynamically similar conditions, the influence of unsteadiness on the losses is of interest. The derivation of the variation of the mechanical energy for the mean, oscillating and turbulent fields point out the contribution of unsteadiness to the losses and the turbulent production. Application to turbulent channel flow reveals that the contribution is a function of the amplitude of the oscillation, the frequency and the friction velocity. Turbulent pulsating flow in a generic model of the rectangular diffuser found at the end of elbow draft tube is studied in detail with laser Doppler anemometry (LDA). Three frequencies, corresponding to the quasi-steady, relaxation and quasi-laminar regimes with an amplitude of about 10% are investigated. The results indicate no alteration of the mean flow by the excitation of a single frequency. Furthermore. the existence of the different regimes, as found in turbulent pulsating turbulent pipe and channel flows, is confirmed.<br>Godkänd; 2003; 20061108 (haneit)
8
Cervantes, Michel J. "Effects of boundary conditions and unsteadiness on draft tube flow /." Luleå, 2003. http://epubl.luth.se/1402-1544/2003/11/index.html.
Full text
9
Cherman, Aleksey, Srimoyee Sen, Michael L. Wagman, and Laurence G. Yaffe. "Exponential reduction of finite volume effects with twisted boundary conditions." AMER PHYSICAL SOC, 2017. http://hdl.handle.net/10150/624042.
Full textAbstract:
Flavor-twisted boundary conditions can be used for exponential reduction of finite volume artifacts in flavor-averaged observables in lattice QCD calculations with SU (N-f) light quark flavor symmetry. Finite volume artifact reduction arises from destructive interference effects in a manner closely related to the phase averaging which leads to large N-c volume independence. With a particular choice of flavor-twisted boundary conditions, finite volume artifacts for flavor-singlet observables in a hypercubic spacetime volume are reduced to the size of finite volume artifacts in a spacetime volume with periodic boundary conditions that is four times larger.
10
Gu, Lian Sheng. "Effects of boundary conditions on the propagation of quasi-detonation waves." Thesis, McGill University, 1987. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=63863.
Full text
11
Cote, Dominic. "Effect of Realistic Boundary Conditions on the Behaviour of Cross-Laminated Timber Elements Subjected to Simulated Blast Loads." Thesis, Université d'Ottawa / University of Ottawa, 2017. http://hdl.handle.net/10393/36993.
Full textAbstract:
Cross-laminated timber (CLT) is an emerging engineered wood product in North America. Past research effort to establish the behaviour of CLT under extreme loading conditions has focussed CLT slabs with idealized simply-supported boundary conditions. Connections between the wall and the floor systems above and below are critical to fully describing the overall behaviour of CLT structures when subjected to blast loads. The current study investigates the effects of “realistic” boundary conditions on the behaviour of cross-laminated timber walls when subjected to simulated out-of-plane blast loads.
The methodology followed in the current research consists of experimental and analytical components. The experimental component was conducted in the Blast Research Laboratory at the University of Ottawa, where shock waves were applied to the specimens. Configurations with seismic detailing were considered, in order to evaluate whether existing structures that have adequate capacities to resist high seismic loads would also be capable of resisting a blast load with reasonable damage. In addition, typical connections used in construction to resist gravity and lateral loads, as well as connections designed specifically to resist a given blast load were investigated.
The results indicate that the detailing of the connections appears to significantly affect the behaviour of the CLT slab. Typical detailing for platform construction where long screws connect the floor slab to the wall in end grain performed poorly and experienced brittle failure through splitting in the perpendicular to grain direction in the CLT. Bearing type connections generally behaved well and yielding in the fasteners and/or angles brackets meant that a significant portion of the energy was dissipated there reducing the energy imparted on the CLT slab significantly. Hence less displacement and thereby damage was observed in the slab. The study also concluded that using simplified tools such as single-degree-of-freedom (SDOF) models together with current available material models for CLT is not sufficient to adequately describe the behaviour and estimate the damage. More testing and development of models with higher fidelity are required in order to develop robust tools for the design of CLT element subjected to blast loading.
12
Das, Sumitesh. "The effect of boundary conditions and material data representation on the simulation of deformation during hot rolling." Thesis, University of Sheffield, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.269410.
Full text
13
Hedley, Mark. "The effects of lateral boundary conditions on a two-dimensional cloud model /." Thesis, McGill University, 1986. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=65503.
Full text
14
Li, Yao Hou. "Modelling of boundary conditions and their effects during hot forging and rolling." Thesis, University of Sheffield, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.245646.
Full text
15
Tourtit, Youness. "Effect of the Boundary Conditions Applied to the Liquid Bridge on the Liquid Transfer between Two Solid Surfaces." Doctoral thesis, Universite Libre de Bruxelles, 2021. https://dipot.ulb.ac.be/dspace/bitstream/2013/321652/5/contratYT.pdf.
Full textAbstract:
The trend towards miniaturization requires to handle even smaller micro-components: they must be picked, placed with high accuracy, and then released. This highly challenging process should take into account two aspects: the yield of successful placements and the minimized risk of damaging the manipulated micrometer-sized objects due to contact forces. Despite the advantages of the latest gripping technologies, including low complexity, high accuracy, and high reliability, the component is subjected to high contact forces that could damage it. As a consequence, there is a need of developing new and innovative ways to manipulate micro-sized components with respect to the requirements mentioned above. Gripping based on capillary bridges is a promising technique to handle components at the micrometric scale. This technique offers many advantages: flexibility and reliability, self-centering effect, the capability of grasping small and delicate components in a wide range of shapes and materials thanks to the “bumper” effect of the mediated liquid bridge. Nevertheless, the liquid residue on the component after breaking up the bridge is undesirable. As a consequence, there is a need to design a capillary gripping system that can retain all the liquid after the breakup of the bridge. Understanding the formation, the stretching, and the liquid distribution after the breakup of the liquid bridge is mandatory. In this thesis and in the first place, we studied the rupture of a liquid bridge confined between different geometries of the gripper and the substrate: plane/plane, cone/plane, and cavity/plane. We developed, based on the resolution of the Young-Laplace equation, an operational quasi-static criterion to predict the rupture gap of the bridge. We also investigated the effect of the geometry on the liquid distribution after the breakup. Optimal geometries are found to retain up to 90$%$ of the liquid after the breakup of the bridge. In the second place, we investigated the secretion dispensing in green dock beetles ( extit{Gastrophysa viridula}). Their ability to walk upside-down on any kind of surfaces rely on mediated secretion between their hairy pad and the surface they walk on. We studied the mechanism of the secretion dispensing from the source where it is produced to the contact zone. Experimental setups have been designed, with advancing 3D printing and micro-fabrication techniques. Models have been developed, discussed, and compared to experimental data.<br>Doctorat en Sciences de l'ingénieur et technologie<br>info:eu-repo/semantics/nonPublished
16
Turgut, Ozhan Hulusi. "Effects Of Extrapolation Boundary Conditions On Subsonic Mems Flows Over A Flat Plate." Master's thesis, METU, 2006. http://etd.lib.metu.edu.tr/upload/12606962/index.pdf.
Full textAbstract:
In this research, subsonic rarefied flows over a flat-plate at constant pressure are investigated using the direct simulation Monte Carlo (DSMC) technique. An infinitely thin plate (either finite or semi-infinite) with zero angle of attack is considered. Flows with a Mach number of 0.102 and 0.4 and a Reynolds number varying between 0.063 and 246 are considered covering most of the transitional regime between the free-molecule and the continuum limits. A two-dimensional DSMC code of G.A. Bird is used to simulate these flows, and the code is modified to examine the effects of various inflow and outflow boundary conditions. It is observed that simulations of the subsonic rarefied flows are sensitive to the applied boundary conditions. Several extrapolation techniques are considered for the evaluation of the flow properties at the inflow and outflow boundaries. Among various alternatives, four techniques are considered in which the solutions are found to be relatively less sensitive. In addition to the commonly used extrapolation techniques, in which the flow properties are taken from the neighboring boundary cells of the domain, a newly developed extrapolation scheme, based on tracking streamlines, is applied to the outflow boundaries, and the best results are obtained using the new extrapolation technique together with the Neumann boundary conditions. With the new technique, the flow is not distorted even when the computational domain is small. Simulations are performed for various freestream conditions and computational domain configurations, and excellent agreement is obtained with the available experimental data.
17
Thammavichai, Jackkrit. "Effects of compressor face boundary conditions on the dynamic behavior of supersonic inlets." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/47397.
Full text
18
Ryan, Desmond Michael. "Electronic states and optical properties of quantum well heterostructures with strain and electric field effects." Thesis, Durham University, 1997. http://etheses.dur.ac.uk/5058/.
Full textAbstract:
The aim of this work was to develop an envelope function method to calculate the electronic states and optical properties of complex quantum well heterostructures, and to demonstrate its effectiveness by application to some device structures of topical interest. In particular, structures have been considered which might form the basis of intensity modulators and polarization insensitive amplifier devices for light at a wavelength of 1.55 µm. The modulator structures considered all have the general form of two coupled quantum wells of different widths as the active region. The application of an electric field in the growth direction is intended to result in a shift in the energy and spatial localisation of the confined states and produce an increase in the absorption coefficient at longer wavelengths than the zero field absorption edge. The effectiveness of certain structures is examined in terms of field induced absorption increase at 1.55 µm. A system which shows a significant increase in absorption coefficient at this wavelength on application of a practical electric field has been identified as a possible candidate for an intensity modulator. In the case of the amplifier, the active region of the most promising structure considered consists of a stepped well which comprises two layers, one with tensile and one with compressive strain. It is known that the presence of the two oppositely strained layers can result in the TE and TM gain peaks appearing at similar photon energies. Our calculations show that a suitable choice of strain and layer widths can result in a small or zero difference between the TE and TM gains at 1.55 µm, which can be important for the polarization insensitive operation of devices in optical communications applications. In order to predict the optical properties of quantum well devices it is necessary to calculate the electron and hole states for a range of in-plane wavevectors. The calculations developed and carried out in this work are based on a multi-layer (eight band) k.p model including strain effects. The interfacial boundary conditions which result from approximations to Burt's exact envelope function theory are included in the model. The effect of an electric field is modelled by including a potential energy term in each layer Hamiltonian which is equal to the average energy shift across the layer in question due to the presence of the field. The model has been developed with flexibility in mind and has applications beyond the specific devices considered in this thesis.
19
Chythanya, Meghana. "Finite element analysis on the effect of fire for specified duration, on a reinforced concrete beam with varied boundary conditions." Tallahassee, Florida : Florida State University, 2009. http://etd.lib.fsu.edu/theses/available/etd-05082009-160338/.
Full textAbstract:
Thesis (M.S.)--Florida State University, 2009.<br>Advisor: Lisa K Spainhour, Florida State University, FAMU-FSU College of Engineering, Dept. of Civil and Environmental Engineering. Title and description from dissertation home page (viewed on Nov. 4, 2009). Document formatted into pages; contains xiii, 77 pages. Includes bibliographical references.
20
Ni, Qinglai. "Effects of particle properties and boundary conditions on soil shear behaviour : 3-D numerical simulations." Thesis, University of Southampton, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.398730.
Full text
21
Greif, Vladimir. "Study on the effects of various boundary conditions on the failure mechanism in natural rock slopes." 京都大学 (Kyoto University), 2003. http://hdl.handle.net/2433/149082.
Full text
22
Croënne, C., J. O. Vasseur, Matar O. Bou, et al. "Brillouin scattering-like effect and non-reciprocal propagation of elastic waves due to spatio-temporal modulation of electrical boundary conditions in piezoelectric media." AMER INST PHYSICS, 2017. http://hdl.handle.net/10150/623049.
Full textAbstract:
The properties of a one-dimensional phononic crystal made of identical piezoelectric elements separated by thin metallic electrodes connected to the ground are studied theoretically for cases where the locations of the electrical connections change as a function of time with a specific speed. This spatio-temporal modulation of the electrical boundary conditions results in significant non-linear effects that are evidenced numerically. The interaction between an incident harmonic longitudinal wave and the time-dependent phononic crystal is shown to lead to frequency splitting analogous to Brillouin scattering. Moreover, the boundaries of the Bragg bandgaps are strongly affected, and for some specific modulation speed, one-way wave propagation can be achieved. Published by AIP Publishing.
23
Tomezyk, Jérôme. "Résolution numérique de quelques problèmes du type Helmholtz avec conditions au bord d'impédance ou des couches absorbantes (PML)." Thesis, Valenciennes, 2019. http://www.theses.fr/2019VALE0017/document.
Full textAbstract:
Dans cette thèse, nous étudions la convergence de méthode de type éléments finis pour les équations de Maxwell en régime harmonique avec condition au bord d'impédance et l'équation de Helmholtz avec une couche parfaitement absorbante(PML). On étudie en premier, la formulation régularisée de l'équation de Maxwell en régime harmonique avec condition au bord d'impédance (qui consiste à ajouter le term ∇ div à l'équation originale pour avoir un problème elliptique) et on garde la condition d'impédance comme une condition au bord essentielle. Pour des domaines à bord régulier, le caractère bien posé de cette formulation est bien connu mais cela n'est pas le cas pour des domaines polyédraux convexes. On commence alors le premier chapitre par la preuve du caractère bien posé dans le cas du polyèdre convexe, qui est basé sur le fait que l'espace variationnel est inclus dans H¹. Dans le but d'avoir des estimations explicites en le nombre d'onde k de ce problème, il est obligatoire d'avoir des résultats de stabilité explicites en ce nombre d'onde. C'est aussi proposé, pour quelques situations particulières, dans ce chapitre. Dans le second chapitre on décrit les singularités d'arêtes et de coins pour notre problème. On peut alors déduire la régularité de la solution du problème original, ainsi que de son adjoint. On a tous les ingrédients pour proposer une analyse de convergence explicite en k pour une méthode d'éléments finis avec éléments de Lagrange. Dans le troisième chapitre, on considère une méthode d'éléments finis hp non conforme pour un domaine à bord régulier. Pour obtenir des estimations explicites en k, on introduit un résultat de décomposition, qui sépare la solution du problème original (ou de son adjoint) en une partie régulière mais fortement oscillante et une partie moins régulière mais peu oscillante. Ce résultat permet de montrer des estimations explicites en k. Le dernier chapitre est dédié à l'équation de Helmholtz avec une PML. L'équation de Helmholtz dans l'espace entier est souvent utilisée pour modéliser la diffraction d'onde acoustique (en régime harmonique), avec la condition de radiation à l'infini de Sommerfeld. L'ajout d'une PML est une façon pour passer d'un domaine infini à un domaine fini, elle correspond à l'ajout d'une couche autour du domaine de calcul qui absorbe très vite toutes les ondes sortantes. On propose en premier un résultat de stabilité explicite en k. On propose alors deux schémas numériques, une méthode d'éléments finis hp et une méthode multi- échelle basée sur un sous-espace local de correction. Le résultat de stabilité est utilisé pour mettre en relation de choix des paramètres des méthodes numériques considérées avec k. Nous montrons aussi des estimations d'erreur a priori. A la fin de ces chapitres, des tests numériques sont proposés pour confirmer nos résultats théoriques<br>In this thesis, we propose wavenumber explicit convergence analyses of some finite element methods for time-harmonic Maxwell's equations with impedance boundary condition and for the Helmholtz equation with Perfectly Matched Layer (PML). We first study the regularized formulation of time-harmonic Maxwell's equations with impedance boundary conditions (where we add a ∇ div-term to the original equation to have an elliptic problem) and keep the impedance boundary condition as an essential boundary condition. For a smooth domain, the wellposedness of this formulation is well-known. But the well-posedness for convex polyhedral domain has been not yet investigated. Hence, we start the first chapter with the proof of the well-posedness in this case, which is based on the fact that the variational space is embedded in H¹. In order to perform a wavenumber explicit error analysis of our problem, a wavenumber explicit stability estimate is mandatory. We then prove such an estimate for some particular configurations. In the second chapter, we describe the corner and edge singularities for such problem. Then we deduce the regularity of the solution of the original and the adjoint problem, thus we have all ingredients to propose a explicit wavenumber convergence analysis for h-FEM with Lagrange element. In the third chapter, we consider a non conforming hp-finite element approximation for domains with a smooth boundary. To perform a wavenumber explicit error analysis, we split the solution of the original problem (or its adjoint) into a regular but oscillating part and a rough component that behaves nicely for large frequencies. This result allows to prove convergence analysis for our FEM, again explicit in the wavenumber. The last chapter is dedicated to the Helmholtz equation with PML. The Helmholtz equation in full space is often used to model time harmonic acoustic scattering problems, with Sommerfeld radiation condition at infinity. Adding a PML is a way to reduce the infinite domain to a finite one. It corresponds to add an artificial absorbing layer surrounding a computational domain, in which scattered wave will decrease very quickly. We first propose a wavenumber explicit stability result for such problem. Then, we propose two numerical discretizations: an hp-FEM and a multiscale method based on local subspace correction. The stability result is used to relate the choice of the parameters in the numerical methods to the wavenumber. A priori error estimates are shown. At the end of each chapter, we perform numerical tests to confirm our theoritical results
24
Kaisarly, Dalia Adel Mahmoud [Verfasser], and Karl-Heinz [Akademischer Betreuer] Kunzelmann. "The effect of boundary conditions on the polymerization shrinkage vectors of light-cured dental resin composites / Dalia Adel Mahmoud Kaisarly. Betreuer: Karl-Heinz Kunzelmann." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2014. http://d-nb.info/108077288X/34.
Full text
25
Gloss, Kevin T. "A Photoelastic Investigation into the Effects of Cracks and Boundary Conditions on Stress Intensity Factors in Bonded Specimens." Thesis, Virginia Tech, 2000. http://hdl.handle.net/10919/32786.
Full textAbstract:
An investigation into the influence of cracks in bonded specimens is conducted.
Photoelastic specimens containing a bondline are subjected to a constant displacement
boundary condition created by bonded end grips. Specimens containing various crack
orientations are analyzed to determine stress intensity factors at the induced crack tips.
Specimens containing interface and sub-interface cracks were investigated. Two global
geometries were used in this investigation, square and rectangular. The constant
displacement boundary condition was induced on the specimen through dead weights
hung from bonded aluminum end grips. Stress intensity factors were determined using
photoelastic techniques. The stress intensity factors were examined to determine trends
in the results as a function of changes in geometry. The effects of the induced boundary
condition, the specimen geometry, and the bondline were investigated. The results from
this investigation were compared to known solutions with a similar specimen geometry.
These tests exhibited influences from the bondline, the boundary conditions, and the
specimen geometry. The bondline tended to decrease the stress intensity factor for
specimens with small crack lengths and tended to increase the stress intensity factor for
specimens containing long crack lengths. As the crack length increased so too did the
stress intensity factor. A reduction in the bondline to crack distance with sub-interface
crack specimens caused a reduction in the stress intensity factor. A reduction in the
global height of the specimen caused a reduction in the stress intensity factor also. The
results from this investigation will aid in the understanding of the influence of interface
and sub-interface cracks in bonded specimens.<br>Master of Science
26
Stolarz, Jacques. "Corrosion d'aciers inoxydables austénitiques au silicium dans les conditions tranpassives." Paris, ENMP, 1989. http://www.theses.fr/1989ENMP0133.
Full textAbstract:
Proposition d'un modèle électrochimique de dissolution intergranulaire dans les conditions transpassives. Essai potentiostatique de corrosion pour examiner la ségrégation du silicium dans les joints de flexion autour de 100 de l'acier inoxydable 17-13
27
Schuppler, Matthias Bernhard [Verfasser], Andreas [Akademischer Betreuer] [Gutachter] Bausch, and Matthias [Gutachter] Rief. "Effects of boundary conditions on cytoskeletal structure formation / Matthias Bernhard Schuppler ; Gutachter: Andreas Bausch, Matthias Rief ; Betreuer: Andreas Bausch." München : Universitätsbibliothek der TU München, 2017. http://d-nb.info/1125627034/34.
Full text
28
Powell, Mark E. "Natural convection from an array of rectangular protrusions in an enclosure filled with dielectric fluid: effects of boundary conditions." Thesis, Monterey, California. Naval Postgraduate School, 1989. http://hdl.handle.net/10945/27149.
Full text
29
Araujo, Vanilse da Silva. "Condições de Contorno mais Gerais no Espalhamento Aharonov-Bohm de uma Partícula de Dirac em Duas Dimensões: Conservação da Helicidade e da Simetria de Aharonov-Bohm." Universidade de São Paulo, 2000. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-28112013-105008/.
Full textAbstract:
Nessa tese, mostramos que a Hamiltoniana H e o operador helicidade de uma partícula de Dirac que se movimenta em duas dimensões na presença de um tubo de fluxo magnético infinitamente fino na origem admitem, cada um, uma família de quatro parâmetros de extensões auto-adjuntas. Para cada extensão correspondem condições de contorno a serem satisfeitas pelas auto-fuções na origem. Apesar dos operadores H e formalmente comutarem antes da especificação das condições de contorno, para garantirmos a conservação da helicidade, não é suficiente obtermos as mesmas condições de contorno para ambos os operadores, ou seja, não é suficiente a determinação de um domínio comum a ambos. Mostramos que, para certas relações entre os parâmetros das extensões satisfeitas, é possível a determinação dos domínios mais gerais onde ambos os operadores H e são auto-adjuntos e onde a helicidade é conservada, simultaneamente com a preservação da simetria de Aharonov-Bohm ( + 1), onde é o fluxo magnético em unidades naturais. Nossos resultados implicam que, nem a conservação da helicidade nem a simetria de Aharonov-Bohn, resolvem o problema da escolha da condição de contorno fisicamente correta.<br>We show that both the Hamiltonian H and the helicity operator of a Dirac particle moving in two dimension in the presence of an infinitely thin magnetic flux tube admit each a four- parameter family of self-adjoint extensions. Each extension is in one-to-one correspondence with the boundary conditions (BC\'s) to be satisfied by the eigenfunctions at the origin. Althou- gh the actions af these two operators commute before specification of boundary conditions, to ensure helicity conservation it is not sufficient to take the same BC\'s for both operators. We show that, given certain relations between the parameters of the extensions it is possible to write down the most general domain where both operators H and are self-adjoint with heli- city conservation and also Aharonov-Bohm symmetry ( + 1) preserved, where is the magnetic flux in natural units. The continuity of the dynamics is also obtained. Our results im- ply that neither helicity conservation nor Aharonov-Bohm symmetry by themselves solves the problem of choosing the \"physical \"boundary conditions for this system.
30
Lohrey, Sven. "The effects of servant leadership on follower performance and well-being : underlying mechanisms, boundary conditions, and the role of training." Thesis, Aston University, 2016. http://publications.aston.ac.uk/28629/.
Full textAbstract:
Based on a review of the servant leadership, well-being, and performance literatures, the first study develops a research model that examines how and under which conditions servant leadership is related to follower performance and well-being alike. Data was collected from 33 leaders and 86 of their followers working in six organizations. Multilevel moderated mediation analyses revealed that servant leadership was indeed related to eudaimonic well-being and lead-er-rated performance via followers’ positive psychological capital, but that the strength and di-rection of the examined relationships depended on organizational policies and practices promot-ing employee health, and in the case of follower performance on a developmental team climate, shedding light on the importance of the context in which servant leadership takes place. In addi-tion, two more research questions resulted from a review of the training literature, namely how and under which conditions servant leadership can be trained, and whether follower performance and well-being follow from servant leadership enhanced by training. We subsequently designed a servant leadership training and conducted a longitudinal field experiment to examine our sec-ond research question. Analyses were based on data from 38 leaders randomly assigned to a training or control condition, and 91 of their followers in 36 teams. Hierarchical linear modeling results showed that the training, which addressed the knowledge of, attitudes towards, and ability to apply servant leadership, positively affected leader and follower perceptions of servant leader-ship, but in the latter case only when leaders strongly identified with their team. These findings provide causal evidence as to how and when servant leadership can be effectively developed. Fi-nally, the research model of Study 1 was replicated in a third study based on 58 followers in 32 teams drawn from the same population used for Study 2, confirming that follower eudaimonic well-being and leader-rated performance follow from developing servant leadership via increases in psychological capital, and thus establishing the directionality of the examined relationships.
31
Avellaneda, Jean-Marc. "Thermodynamic optimization of solar receivers : analysis of entropy generation rates in anisothermal flows subjected to asymmetric thermal boundary conditions." Thesis, Perpignan, 2019. http://www.theses.fr/2019PERP0035.
Full textAbstract:
Ce travail de thèse s'inscrit dans le cadre des recherches visant à améliorer la performance des récepteurs de centrales solaires à concentration qui présentent des gradients de température importants et des conditions aux limites thermiques asymétriques. Il est nécessaire d'analyser les puissances utiles perdues du fait des irréversibilités thermiques et visqueuses : ceci est réalisé par l'étude de la puissance entropique générée au sein de l'écoulement en adoptant trois axes d'analyse différents qui apportent des éclairages complémentaires : (1) l'étude détaillée de la puissance entropique générée dans une couche limite laminaire en examinant en particulier l'effet du type de condition aux limites (température imposée vs densité de flux thermique imposé) (2) l'utilisation du calcul variationnel afin de déterminer quels champs de vitesse optimisent une fonctionnelle objectif reliée à la puissance entropique générée dans un écoulement en canal plan dont le tiers d'une des parois est à densité de flux imposée (3) l'étude de la puissance entropique générée dans un écoulement en canal plan, turbulent, quasi-compressible et pour un fluide dont les propriétés thermophysiques dépendent de la température<br>This thesis work is part of research aimed at improving the performance of concentrated solar power plant receivers with large temperature gradients and asymmetric thermal boundary conditions. It is necessary to analyze the power lost due to thermal and viscous irreversibility: this is achieved by studying the entropy generation rate within the flow and by adopting three different axis of analysis that provide complementary insights: (1) the detailed study of the entropy generation rate in a laminar boundary layer by examining in particular the effect of the thermal boundary condition type (imposed temperature vs. fixed heat flux density) (2) the use of the calculus of variations to determine which velocity fields optimize an objective functional related to the entropy generation rate in a flat plate channel flow, one-third of one of the walls being at imposed heat flux density (3) the study of the entropy generation rate in a flat plate channel flow, turbulent, quasi-compressible and for a fluid which thermo-physical properties depend on temperature
32
Warman, Craig S. "Understanding the spatial and temporal variation in anthropogenically induced channel response in the Irwin River catchment." University of Western Australia. School of Earth and Geographical Sciences, 2008. http://theses.library.uwa.edu.au/adt-WU2008.0214.
Full textAbstract:
The Irwin River catchment, located in the central western region of Western Australia, has been the scene of significant geomorphological change over both historical and geological timescales. This thesis focuses on the most recent of these changes, the anthropogenic imprint, through the development of a catchment-scale understanding of system behaviour. Analysis and modelling of changes in the hydrological behaviour of the system indicates that while the Irwin River has displayed a natural susceptibility to large flood events, these have been exacerbated by the widespread clearing of native vegetation throughout the catchment. As a result, when such events do occur, the catchment response is now larger, more direct and has a greater ability to cause erosion. However, the nature and detail of sediment yield processes and stream channel response varies markedly throughout the system. A series of representative channel reaches, as defined by their planform characteristics, geometry and architecture, are presented to illustrate spatial changes in stream channel behaviour. A distinct variation in river morphotypes is seen both downstream throughout the system as well as across the tributary sub-catchments of the Irwin River, Lockier River and Green Brook. This inter and intra sub-catchment variation in stream channel response can be attributed to changes in the boundary conditions and coupling mechanisms in operation throughout the Irwin River system. The pronounced spatial variability in response to human disturbance and the changing nature of catchment-scale connectivity seen in the Irwin River system differs markedly to that reported elsewhere in the literature. Appreciation of the variability in form, behaviour and evolutionary history throughout the Irwin River catchment not only provides the foundation for effective management but also contributes to a wider understanding of fluvial system behaviour. Unlike the majority of existing literature, which tends to identify and measure channel changes in a single catchment where historical variation to the sediment and discharge regime is well known, this study demonstrates the role of boundary conditions in determining the response of the fluvial system to changing environmental controls.
33
Schwenk, Johanna [Verfasser], and Verena [Akademischer Betreuer] Hüttl-Maack. "The impact of multilingual product information on consumer evaluations : an assessment of basic effects, boundary conditions, and drivers / Johanna Schwenk ; Betreuer: Verena Hüttl-Maack." Hohenheim : Kommunikations-, Informations- und Medienzentrum der Universität Hohenheim, 2021. http://d-nb.info/1236990625/34.
Full text
34
Ozturk, Burak. "Combined effects of Reynolds number, turbulence intensity and periodic unsteady wake flow conditions on boundary layer development and heat transfer of a low pressure turbine blade." [College Station, Tex. : Texas A&M University, 2006. http://hdl.handle.net/1969.1/ETD-TAMU-1150.
Full text
35
Andersson, Lucas. "Shadow effects in open cross-sections : An analysis of steel temperatures with COMSOL Multiphysics, TASEF and Eurocode." Thesis, Luleå tekniska universitet, Byggkonstruktion och brand, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-70086.
Full textAbstract:
Steel is a material commonly used in various constructions such as high-rise buildings, sport arenas, ships etc. Steel is a versatile building material due to its isotropic characteristics, e.g. both high tensile- and compressive strength. This allows steel to be formed into open section profiles which reduces material usage but simultaneously allows the tensile- and compressive stress resistance to be high in directions were loads are applied. Although steel has a high stress resistance its sensitivity to fire is larger than other building materials due to its high thermal conductivity. The strength of the material is reduced at higher temperatures and thereby makes the dimensioning of beams in fire cases vital in fire safety design of structural elements. An aspect to consider when dimensioning open section building elements in steel is the shadow effect. The shadow effect is the result of the open cross-section geometrical shape of beams and columns, e.g. H-profiles. The interior of the profile is screened from thermal radiation caused by fire which makes the characteristics of the thermal exposure different from closed cross-section profiles. A common way to estimate the temperatures of steel after a certain time of fire exposure is to use numerical calculations described in Eurocode. In these calculations the shadow effect is applied as a reduction of the total heat exchange, i.e. both convection and thermal radiation, from the fire exposure. A more realistic approach is to separate these boundary conditions and treat them as independent quantities. Wickström (2001) argues that a void is created within the flanges and that reduction factor thereby only should be applied to the radiative part of the total heat exchange, acting as a reduction of surface emissivity within the profile. This, since the convection is not affected by the shadow effect. Wickströms (2001) suggestion of application has been investigated in this thesis and has showed a better correlation than the approach suggested in Eurocode when compared to experimental tests. Shadow effects calculated on the premises of separated boundary conditions for the total heat exchange has of yet only been investigated in detail with TASEF+-simulations, but these simulations predicts steel temperatures with satisfactory results. It is possible to reproduce a similar setup in the program COMSOL Multiphysics in two-dimensional simulations, and further three-dimensional simulations. This possibility has been investigated in this thesis. COMSOL Multiphysics has proven to be an adequate tool when it comes to simulate fire exposure on slender steel beam with shadow effects considered. Both three- and two-dimensional models produced simulation results correlating well to simulations conducted in TASEF. Additionally, adequate correlations with experimental tests were obtained for COMSOL Multiphysics as well. Further work regarding fire simulations with the utilisation of COMSOL Multiphysics is thereby suggested.
36
Torres, Edgardo I. "Natural convection cooling of a 3 by 3 array of rectangular protrusions in an enclosure filled with dielectric liquid: effects of boundary conditions and component orientation." Thesis, Monterey, California. Naval Postgraduate School, 1988. http://hdl.handle.net/10945/23078.
Full text
37
Griffiths, Georgianne J. K. "The effect of field boundary type on the community structure, spatial distribution and physiological condition of overwintering arthropods, with special reference to Carabidae and Staphylinidae (Coleoptera)." Thesis, University of Plymouth, 2003. http://hdl.handle.net/10026.1/2366.
Full textAbstract:
The potential of different field boundary types in lowland farmland to contribute to arthropod biodiversity and sustainable agriculture was investigated. Field boundaries, categorised according to nationally applicable definitions, were found to represent ecologically differing habitats based on their woody abundance and the frequency of young and mature emergent trees. These habitat characteristics were determining factors in the community structure and composition of overwintering epigeal arthropods. Hedgerows supported the most species rich carabid and staphylinid assemblage. Degraded hedgerow boundaries supported the most equitable carabid community, and provided a refuge for carabid species with poor dispersal power to a greater extent that hedgerows or post and wire fences. The grassy and natural regeneration vegetation associated with post and wire boundaries supported high densities of all taxa particularly overwintering carabid and staphylinid polyphagous predators. A subset of all field boundary types was required for complete species representation, indicating that maximising the heterogeneity of field boundary habitats represented at the farm-scale will enhance arthropod biodiversity in farmland. Carabidae and Staphylinidae actively selected overwintering sites and the physiological condition of polyphagous predators was generally high. It was concluded that heterogeneous distributions in field boundaries were more likely to be the result of differential microhabitat selection rather than differential survival overwinter. This indicated that favourable overwintering microhabitats occurred in all field boundary types. Generally, overwintering survival did not appear to be a regulating factor in the population dynamics of polyphagous predators. Margins adjacent to pre-existing boundaries may contribute to enhanced densities and physiological condition of some polyphagous predators, both over winter and in early spring. The results were discussed in relation to field boundary management and agri-environment policy.
38
Gandomzadeh, Ali. "Dynamic soil-structure interaction : effect of nonlinear soil behavior." Phd thesis, Université Paris-Est, 2011. http://tel.archives-ouvertes.fr/tel-00648179.
Full textAbstract:
The interaction of the soil with the structure has been largely explored the assumption of material and geometrical linearity of the soil. Nevertheless, for moderate or strong seismic events, the maximum shear strain can easily reach the elastic limit of the soil behavior. Considering soil-structure interaction, the nonlinear effects may change the soil stiffness at the base of the structure and therefore energy dissipation into the soil. Consequently, ignoring the nonlinear characteristics of the dynamic soil-structure interaction (DSSI) this phenomenon could lead toerroneous predictions of structural response. The goal of this work is to implement a fully nonlinear constitutive model for soils into anumerical code in order to investigate the effect of soil nonlinearity on dynamic soil structureinteraction. Moreover, different issues are taken into account such as the effect of confining stress on the shear modulus of the soil, initial static condition, contact elements in the soil-structure interface, etc. During this work, a simple absorbing layer method based on a Rayleigh / Caughey damping formulation, which is often already available in existing. Finite Element softwares, is also presented. The stability conditions of the wave propagation problems are studied and it is shown that the linear and nonlinear behavior are very different when dealing with numerical dispersion. It is shown that the 10 points per wavelength rule, recommended in the literature for the elastic media is not sufficient for the nonlinear case. The implemented model is first numerically verified by comparing the results with other known numerical codes. Afterward, a parametric study is carried out for different types of structures and various soil profiles to characterize nonlinear effects. Different features of the DSSI are compared to the linear case : modification of the amplitude and frequency content of the waves propagated into the soil, fundamental frequency, energy dissipation in the soil and the response of the soil-structure system. Through these parametric studies we show that depending on the soil properties, frequency content of the soil response could change significantly due to the soil nonlinearity. The peaks of the transfer function between free field and outcropping responsesshift to lower frequencies and amplification happens at this frequency range. Amplificationreduction for the high frequencies and even deamplication may happen for high level inputmotions. These changes influence the structural response.We show that depending on the combination of the fundamental frequency of the structureand the the natural frequency of the soil, the effect of soil-structure interaction could be significant or negligible. However, the effect of structure weight and rocking of the superstructurecould change the results. Finally, the basin of Nice is used as an example of wave propagation ona heterogeneous nonlinear media and dynamic soil-structure interaction. The basin response isstrongly dependent on the combination of soil nonlinearity, topographic effects and impedancecontrast between soil layers. For the selected structures and soil profiles of this work, the performed numerical simulations show that the shift of the fundamental frequency is not a goodindex to discriminate linear from nonlinear soil behavior
39
Monti, Jonathan David. "Boundary condition effects on vibrating cantilever beams." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/96463.
Full textAbstract:
Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2014.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (pages 104-106).<br>Compliant mechanisms continue to see increased used in many areas of modem engineering. Their low cost, ease of production and manufacturing, and precision of motion have made them attractive solutions to many controlled motion systems such as nanopositioners or linear platforms. However, in some applications the stiffness requirements for the devices to function properly and the stiffness requirements for devices to survive outside effects such at vibration or impulse create a conflict which cannot be rectified with traditional engineering approaches. By utilizing boundary controls which acted only when a flexure reached a certain deflection, the original purpose of the device could be preserved while also reducing or eliminating the risk of failure from plastic deformation or brittle failure. By starting with the most basic of compliant mechanisms, the cantilever beam, and utilizing Buckingham Pi theory the dynamic behavior of the vibrating beams could be quantified and the associated variables used to tailor the design of a flexure and boundary control system. This research details the primary correlation between variables in a flexure system during natural frequency excitation and provides the mathematics necessary to implement boundary controls to prevent flexure failure. With this new information, cantilever style flexures can now be designed to operate in environments which previously would have put them at risk of catastrophic failure, and can allow for three to four times the increased range performance of a compliant mechanism in these environments without risk of failure. Furthermore, this research lays the foundation for the study of more complex flexures and multi degree-of-freedom systems.<br>by Jonathan David Monti.<br>S.M.
40
Zhang, Xiong. "Consolidation theories for saturated-unsaturated soils and numerical simulation of residential buildings on expansive soils." Texas A&M University, 2004. http://hdl.handle.net/1969.1/2747.
Full textAbstract:
The coupled and uncoupled consolidation theories for saturated-unsaturated soils have been discussed. A new method for constructing the constitutive surfaces for saturated-unsaturated soils has been proposed. The consolidation processes for saturated-unsaturated soils have been explained by thermodynamic analogue. One dimensional consolidation theory for saturated-unsaturated soils is presented and a new method is proposed to calculate the immediate settlement, total settlement and the time history of the consolidation settlement manually in the same way as what we have done for saturated soils with a higher accuracy. It makes the consolidation theory of unsaturated soils as applicable as that of saturated soils. This method can also be used to perform uncoupled two or three dimensional consolidation calculation for both expansive soils and collapsible soils. From the analysis, the equivalent effective stress and excessive pore water pressure can be easily calculated. At the same time, the physical meanings for the parameters in the constitutive laws for saturated-unsaturated are illustrated. A new set of the differential equations for the coupled two or three dimensional consolidation of saturated-unsaturated soils are proposed, together with the corresponding method to solve the differential equations. It is also proved numerically and analytically that during the consolidation process the Mandel-Cryer effect exists for unsaturated expansive soils and there is a ??reverse?? Mandel-Cryer effect for unsaturated collapsible soils. A new method is proposed to estimate the volume change of expansive soils.
A complete system is proposed for the numerical simulation of residential buildings on expansive soils. The strength of this method lies in its use of simple and readily available historic weather data such as daily temperature, solar radiation, relative humidity, wind speed and rainfall as input. Accurate three dimensional predictions are obtained by integrating a number of different analytical and numerical techniques: different simulation methods for different boundary conditions such as tree, grass, and bare soils, coupled hydro-mechanical stress analysis to describe deformation of saturated-unsaturated soils, jointed elements simulation of soil-structure interaction, analysis of structure stress moment by general shell elements, and to assess structural damage by the smeared cracking model. The real-time and dynamic simulation results are consistent with filed measurements.
41
Werning, Jan P. [Verfasser], Stefan [Gutachter] Spinler, and Carl Marcus [Gutachter] Wallenburg. "The transition from linear towards circular economy business models : theoretical and empirical study of boundary conditions and other effects on the value chain / Jan P. Werning ; Gutachter: Stefan Spinler, Carl Marcus Wallenburg." Vallendar : WHU - Otto Beisheim School of Management, 2021. http://d-nb.info/1231792108/34.
Full text
42
Věžník, Tomáš. "Vliv fyzikálních vlastností tekutiny na efektivitu tepelného přenosu turbulentní Rayleighovou-Bénardovou konvekcí." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2021. http://www.nusl.cz/ntk/nusl-443752.
Full text
43
Ehrhardt, Matthias. "Discrete artificial boundary conditions." [S.l.] : [s.n.], 2001. http://deposit.ddb.de/cgi-bin/dokserv?idn=965232921.
Full text
44
Nishio, Yoshiyuki. "Challenges in applying the PSPG/SUPG Finite element method to the atmosphéric boundary layer." Thesis, La Rochelle, 2021. http://www.theses.fr/2021LAROS017.
Full textAbstract:
Suite à une requête de la Défense belge dans le cadre des applications CBRN (chimique, biologique, radiologique et nucléaire), l’objectif initial du travail était de simuler un cas CBRN réaliste a l’air libre (dispersion de particules après une explosion dans une ville), en appliquant la stabilisation Streamline-Upwind Petrov-Galerkin (SUPG) sur une méthode d’éléments finis (FEM), incluant une deuxième phase (particules). Pour cette simulation, les développements se font dans le code Coolfuid 3, un langage spécifique au domaine (DSL) écrit en C++. Cependant, les applications à l’air libre nécessitent de décrire correctement la couche limite atmosphérique (ABL). Cela n’a jamais été fait en utilisant des éléments finis stabilisés. Par conséquent, le défi de ce travail est de répondre à la question simple : Comment modéliser une ABL en s’appuyant sur la méthode de stabilisation SUPG. Afin de réduire le nombre d’éléments nécessaires pour une simulation résolvant toutes les échelles de turbulences jusqu’aux parois, l’ABL a été implémentée avec un modèle de paroi, puis vérifiée en 2D, tandis que quelques corrections (la résolution du maillage, la stabilité du profil de vitesse) ont également pu être menées. Néanmoins, l’implémentation 3D a révélé certaines oscillations parasites, laissant supposer à une origine numérique. Bien que la SUPG produise de la dissipation, cette dernière ne semble pas suffisante pour un écoulement à nombre de Reynolds aussi élevé. Par conséquent, pour ajouter de la dissipation, deux directions ont été suivies : Premièrement, une implémentation de l’évolution de la SUPG, la Méthode Variationnelle MultiScale (VMS), a été initiée. Cette dernière fournit un cadre combiné à la fois pour la stabilisation et la modélisation de la turbulence. Deuxièmement, deux formulations LES, connues pour leur comportement dissipatif, ont également été intégrées. Après avoir réduit les oscillations parasites, le profil de vitesse a été analysé. Finalement, pour permettre la comparaison avec un résultat DNS disponible, le nombre de Reynolds visqueux du domaine ABL a été réduit. Favorablement, et ceci également pour deux autres conditions, l’implémentation du modèle ABL a fourni des résultats se rapprochant le plus de la courbe DNS. En conclusion, nous avons déterminé deux méthodologies (LES et SUPG / VMS) qui ont le potentiel d’approcher l’écoulement ABL. La FEM stabilisée utilisant la SUPG a révélé qu’elle n’est actuellement pas encore suffisante pour éviter les oscillations parasites dans le cas d’un écoulement ABL. En revanche, la LES a fourni des résultats encourageants, ce qui prouve qu’un certain type de modèle de turbulence est indispensable. Cela souligne l’intérêt pour la méthode VMS, bien que celle-ci reste difficile à implémenter<br>In the context of a Chemical, Biological, Radiological, and Nuclear (CBRN) application for the Belgian Defense, the original objective of the work was to simulate a realistic open-air CBRN case (e.g. dispersion after an explosion of particles in a city), by applying the Streamline-Upwind Petrov-Galerkin (SUPG) stabilization on a nite element method (FEM), together with a second phase (i.e. particles). This would be done through the code Cool uid 3, a Domain Speci c Language (DSL) written in C++.However, open-air applications requires to describe the atmospheric bound-ary layer (ABL) correctly. This has never been done using stabilized FEM. Consequently, the challenge of this work is to answer the simple question: How to model an ABL taking advantage of the SUPG stabilization method.To reduce the number of elements produced by a wall-resolved simulation, the ABL was implemented with a wall model and veri ed in 2D, while a few corrections (e.g. grid scalability, stable velocity pro le) could also be adressed.However, the 3D implementation revealed spurious oscillations, suggesting a numerical origin. Although SUPG does provide dissipation, it seemed not su cient enough for such a high Reynolds ow. Consequently, two directions were followed to add numerical dissipation: Firstly, the implementation of an extended version of the SUPG, the Variational MultiScale method (VMS), was initiated. The latter provides a combined framework for stabilization and turbulence modeling. Secondly, two LES formulations, known for their dissipative behavior, were integrated.Having solved the spurious oscillations, the velocity pro le was analyzed. Eventually, the viscous Reynolds number for the ABL domain was reduced to enable the comparison with an available DNS result. Fortunately, rela-tive to the standard no-slip wall condition and to the friction velocity condi-tion, the wall model implementation provided the best result, although not matching.In conclusion, we ascertained two methodologies (LES and SUPG / VMS) that have the potential to approach the ABL ow. The stabilized FEM using SUPG revealed that it is currently not su cient to avoid spurious oscillations in the case of an ABL ow. In contrast, LES provided encouraging results for reduced Reynolds number, supporting that some kind of turbulence model is indispensable. This emphasizes that the implementation of VMS should be promising, although challenging
45
le, coupanec erwan. "Boundary conditions for the lattice Boltzmann method : Mass conserving boundary conditions for moving walls." Thesis, Norwegian University of Science and Technology, Department of Energy and Process Engineering, 2010. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-10154.
Full textAbstract:
<p>Based on the no-slip boundary condition for walls at rest for the lattice Boltzmann Bathnagar-Gross-Krook method by J.C.G. Verschaeve [Phys. Rev. 80,036703 (2009)], a no-slip boundary condition for walls with a tangential movement is derived. Numerical tests verify that the present boundary condition is second order accurate and stable for relaxation frequencies close to two.</p>
46
Boström, Erik. "Boundary Conditions for Spectral Simulations of Atmospheric Boundary Layers." Licentiate thesis, KTH, Stabilitet, Transition, Kontroll, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-218054.
Full textAbstract:
An atmospheric boundary layer (ABL) is generally a very high Reynolds number boundary layer over a fully rough surface that is influenced by different external forces. Numerical simulations of ABLs are typically demanding, particularly due to the high Reynolds numbers. Large eddy simulation (LES) where the grid filtered Navier--Stokes equations are solved together with a turbulence model for the subgrid-scale motions is the most accurate and widely used technique to date for ABLs. However, high Reynolds numbers, filtered equations and rough surfaces do not support the simple no-slip boundary conditions together with a feasible grid resolution. A paramount part for the performance of an ABL LES simulation therefore lies in the quality of approximate wall boundary conditions, so called wall models. The vast majority of LES codes used for ABL simulations rely on spatial discretization methods with low order finite difference approximations for the derivatives in the inhomogeneous wall normal direction. Furthermore, the wall boundary conditions are typically chosen in a mesh-dependent, non-local way, relying on the finite differences formulation. In this thesis we focus on solving the ABL LES equations with a fully (pseudo) spectral Fourier--Chebyshev code. We present how wall boundary conditions can be formulated through Robin boundary conditions and how to implement these in the normal-velocity normal-vorticity formulation that we solve. A new idea of specifying boundary conditions directly in Fourier space where also the turbulence intensity statistics can be controlled is presented and verified. The present results show that the Robin-type formulation is effective at least in near-equilibrium boundary layers. The code and boundary conditions were tested in both low and high Reynolds number (open and full) channel flows of neutral and stable stratification. Results were validated with both low to moderate Reynolds number DNS statistics as well as with the logarithmic law. Our results indicate great potential for both the the new boundary condition formulation and the specific code implementation. Further analysis of more complex flow situations will show whether the Robin-type formulation will give similarly good results.<br>Ett atmosfäriskt gränsskikt (ABL) är generellt sett ett gränsskikt med väldigt högt Reynolds-tal över en rand med ojämn yta och som är påverkad av yttre krafter. Numeriska simuleringar av ABLs är typiskt sett väldigt krävande, speciellt på grund av de höga Reynolds-talen. Large eddy simulation (LES) där de filtrerade Navier--Stokes ekvationerna är lösta tillsammans med en turbulensmodell för the oupplösta skalorna är den mest noggranna och mest använda tekniken för ABLs. Men, för höga Reynolds-tal, filtrerade ekvationer och ytojämnheter är inte ``no-slip'' randvillkor giltiga för en genomförbart hög nätupplösning. En viktig del för kvalitén hos en ABL LES simulering ligger därför i prestandan i approximativa randvillkor, så kallade väggmodeller. Majoriteten av alla LES koder som används för ABL simuleringar är baserade på en lågordnings finita-differens diskretisering för derivatorna i den inhomogena väggnormalriktningen. Dessutom så är vägg-randvillkoren typiskt valda nätberoende och icke-lokala och direkt beroende av finita-differens diskretiseringen. I den här avhandlingen så fokuserar vi i att lösa ABL LES ekvationerna med en fullt (pseudo) spektral Fourier--Chebyshev kod. Vi förklarar vidare hur väggrandvillkor kan formuleras genom Robin-randvillkor och hur man implementerar dessa i normalhastighet normalvorticitet formuleringen som vi löser. En ny idé i att specifiera randvillkor direkt i Fourier-rummet där statistiken för den turbulenta intensiteten kan kontrolleras är också presenterad och verifierad. Resultaten vi härmed presenterar visar att Robin-randvillkor formuleringen är effektiv åtminstone for gränsskikt i nära jämvikt. Den numeriska koden och randvillkoren var testade för kanalströmning (öppen och stängd) av både neutral och stabil stratifikation och för både låga och höga Reynolds-tal. Våra resultat visar på en god potential hos både den nya randvillkorsformuleringen och den nya kodimplementationen. Vidare analys i mer komplexa flödessituationer kommer att visa om Robin-randvillkor formuleringen ger lika goda resultat.<br><p>QC 20171122</p>
47
Gamlin, Samuel. "Boundary conditions in Abelian sandpiles." Thesis, University of Bath, 2016. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.687371.
Full textAbstract:
The focus of this thesis is to investigate the impact of the boundary conditions on configurations in the Abelian sandpile model. We have two main results to present in this thesis. Firstly we give a family of continuous, measure preserving, almost one-to-one mappings from the wired spanning forest to recurrent sandpiles. In the special case of $Z^d$, $d \geq 2$, we show how these bijections yield a power law upper bound on the rate of convergence to the sandpile measure along any exhaustion of $Z^d$. Secondly we consider the Abelian sandpile on ladder graphs. For the ladder sandpile measure, $\nu$, a recurrent configuration on the boundary, I, and a cylinder event, E, we provide an upper bound for $\nu(E|I) − \nu(E)$.
48
Roman, Svetlana. "Green's functions for boundary-value problems with nonlocal boundary conditions." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2011. http://vddb.laba.lt/obj/LT-eLABa-0001:E.02~2011~D_20111227_092148-01085.
Full textAbstract:
In the dissertation, second-order and higher-order differential and discrete equations with additional conditions which are described by linearly independent linear functionals are investigated. The solutions to these problems, formulae and the existence conditions of Green's functions are presented, if the general solution of a homogeneous equation is known. The relation between two Green's functions of two nonhomogeneous problems for the same equation but with different additional conditions is obtained. These results are applied to problems with nonlocal boundary conditions.
In the introduction the topicality of the problem is defined, the goals and tasks of the research are formulated, the scientific novelty of the dissertation, the methodology of research, the practical value and the significance of the results are presented.
m-order differential problem and its Green's function are investigated in the first chapter. The relation between two Green's functions and the existence condition of Green's function are obtained.
In the second chapter, the main definitions and results of the first chapter are formulated for the second-order differential equation with additional conditions. In the examples the application of the received results is analyzed for problems with nonlocal boundary conditions in detail.
In the third chapter, the second-order difference equation with two additional conditions is considered. The expression of Green's function and its existence... [to full text]<br>Disertacijoje tiriami antros ir aukštesnės eilės diferencialinis ir diskretusis uždaviniai su įvairiomis, tame tarpe ir nelokaliosiomis, sąlygomis, kurios yra aprašytos tiesiškai nepriklausomais tiesiniais funkcionalais. Pateikiamos šių uždavinių Gryno funkcijų išraiškos ir jų egzistavimo sąlygos, jei žinoma homogeninės lygties fundamentalioji sistema. Gautas dviejų Gryno funkcijų sąryšis uždaviniams su ta pačia lygtimi, bet su papildomomis sąlygomis. Rezultatai pritaikomi uždaviniams su nelokaliosiomis kraštinėmis sąlygomis.
Įvadiniame skyriuje aprašyta tiriamoji problema ir temos objektas, išanalizuotas temos aktualumas, išdėstyti darbo tikslai, uždaviniai, naudojama tyrimų metodika, mokslinis darbo naujumas ir gautų rezultatų reikšmė, pateikti ginamieji teiginiai ir darbo rezultatų aprobavimas.
m-tosios eilės diferencialinis uždavinys ir jo Gryno funkcija nagrinėjami pirmajame skyriuje. Surastas uždavinio sprendinys, išreikštas per Gryno funkciją. Pateikta Gryno funkcijos egzistavimo sąlyga.
Antrajame skyriuje pateikti pirmojo skyriaus pagrindiniai apibrėžimai ir rezultatai antros eilės diferencialinei lygčiai. Pavyzdžiuose išsamiai išanalizuotas gautų rezultatų pritaikymas uždaviniams su nelokaliosiomis kraštinėmis sąlygomis.
Trečiajame skyriuje nagrinėjama antros eilės diskrečioji lygtis su dviem sąlygomis. Surastos diskrečiosios Gryno funkcijos išraiška ir jos egzistavimo sąlyga. Taip pat pateiktas dviejų Gryno funkcijų sąryšis, kuris leidžia surasti diskrečiosios... [toliau žr. visą tekstą]
49
Onyango, Thomas Tonny Mboya. "Boundary element methods for solving inverse boundary conditions identification problems." Thesis, University of Leeds, 2008. http://etheses.whiterose.ac.uk/11283/.
Full textAbstract:
This thesis explores various features of the boundary element method (BEM) used in solving heat transfer boundary conditions identification problems. In particular, we present boundary integral equation (BIE) formulations and procedures of the numerical computation for the approximation of the boundary temperatures, heat fluxes and space, time or temperature dependent heat transfer coefficients. There are many practical heat transfer situations where such problems occur, for example in high temperature regions or hostile environments, such as in combustion chambers, steel cooling processes, etc., in which the actual method of heat transfer on the surface is unknown. In such situations the boundary condition relating the heat flux to the difference between the boundary temperature and that of the surrounding fluid is represented by an unknown function which may depend on space, time, or temperature. In these inverse heat conduction problems (IHCP), the BEM is formulated as a minimization of some functional that measures the discrepancy between the measured data, say the average temperature on a portion of the boundary or at an instant over the whole domain. The minimization provides solutions that are consistent with the data. This indicates that the BEM algorithms for the IRCP are robust, stable and predict reliable results. When the input data is noisy, we have used the truncated singular value decomposition and the Tikhonov regularisation methods to stabilise the solution of the IRCI' boundary conditions identification. Numerical approximations have been obtained and, where possible, the results obtained are compared to the analytical solutions.
50
Wang, Qingzhao. "Computational Investigations of Boundary Condition Effects on Simulations of Thermoacoustic Instabilities." Diss., Virginia Tech, 2016. http://hdl.handle.net/10919/78692.
Full textAbstract:
This dissertation presents a formulation of the Continuous Sensitivity Equation Method (CSEM) applied to the Computational Fluid Dynamics (CFD) simulation of thermoacoustic instability problems. The proposed sensitivity analysis approach only requires a single run of the CFD simulation. Moreover, the sensitivities of field variables, pressure, velocity and temperature to boundary-condition parameters are directly obtained from the solution to sensitivity equations. Thermoacoustic instability is predicted by the Rayleigh criterion. The sensitivity of the Rayleigh index is computed utilizing the sensitivities of field variables.
The application of the CSEM to thermoacoustic instability problems is demonstrated by two classic examples. The first example explores the effects of the heated wall temperature on the one-dimensional thermoacoustic convection. The sensitivity of the Rayleigh index, which is the indicator of thermoacoustic instabilities, is computed by the sensitivity of field variables. As the heat wall temperature increases, the sensitivity of the Rayleigh index decreases. The evolution from positive to negative sensitivity values suggests the transition from a destabilizing trend to stabilizing trend of the thermoacoustic system.
Thermoacoustic instabilities in a self-excited Rijke tube are investigated following the relatively simple thermoacoustic convection problem. The complexity of simulating the Rijke tube increases in both dimensions and mechanisms which incorporate the species transport process and chemical reactions. As a representative model of the large lean premixed combustor, Rijke tube has been extensively studied. Quantitative sensitivity analysis sets the present work apart from previous research on the prediction and control of thermoacoustic instabilities. The effects of two boundary-condition parameters, i.e. the inlet mass flow rate and the equivalence ratio, are tested respectively. Small variations in both parameters predict a rapid change in sensitivities of field variables in the early stage of the total time length of 1.2s. The sensitivity of the Rayleigh index "blows up" at a specific time point of the early stage. In addition, variations in the inlet mass flow rate and the equivalence ratio lead to opposite effects on the sensitivity of the Rayleigh index.
There exist some common findings on the application of the CSEM. For both thermoacoustic problems, the sensitivities of field variables and the Rayleigh index exhibit oscillatory nature, confirming that thermoacoustic instability is an overall effect of the coupling process between fluctuations of pressure and heat release rate. All the sensitivities of the Rayleigh index show rapid changes and "blow up" in the early stage. Although the numerical errors could influence the fidelity of computational results, it is believed that the rapid changes reflect the susceptibility to thermoacoustic instabilities in the studied systems. It should also be noted that the sensitivities are obtained for small variations in influential parameters. Therefore, the resulting sensitivities do not predict the occurrence of thermoacoustic instabilities under a condition that is far from the reference state determined by either CFD simulation results (employed in this dissertation) or experimental data.
The sensitivity solver developed for the present research has the feature of flexibility. Additional mechanisms and more complicated instability criteria could be easily incorporated into the solver. Moreover, the sensitivity equations formulated in this dissertation are derived from the full set of nonlinear governing equations. Therefore, it is possible to extend the use of the sensitivity solver to other CFD problems. The developed sensitivity solver needs to be optimized to gain better performance, which is considered to be the primary future work of this research.<br>Ph. D.