Dissertations / Theses: 'Boundary Conditions'

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Ehrhardt, Matthias. "Discrete artificial boundary conditions." [S.l.] : [s.n.], 2001. http://deposit.ddb.de/cgi-bin/dokserv?idn=965232921.

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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.

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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.

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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.

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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.
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.

QC 20171122

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Gamlin, Samuel. "Boundary conditions in Abelian sandpiles." Thesis, University of Bath, 2016. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.687371.

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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 $\nu(E|I) − \nu(E)$.

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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.

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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]
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]

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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/.

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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.

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Schulze, Bert-Wolfgang, and Nikolai Tarkhanov. "Boundary value problems with Toeplitz conditions." Universität Potsdam, 2005. http://opus.kobv.de/ubp/volltexte/2009/2983/.

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We describe a new algebra of boundary value problems which contains Lopatinskii elliptic as well as Toeplitz type conditions. These latter are necessary, if an analogue of the Atiyah-Bott obstruction does not vanish. Every elliptic operator is proved to admit up to a stabilisation elliptic conditions of such a kind. Corresponding boundary value problems are then Fredholm in adequate scales of spaces. The crucial novelty consists of the new type of weighted Sobolev spaces which serve as domains of pseudodifferential operators and which fit well to the nature of operators.

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Stephenson, P. W. "Glueball spectra with twisted boundary conditions." Thesis, University of Oxford, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.276836.

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9

Deadman, Edvin. "Outer boundary conditions in numerical relativity." Thesis, University of Cambridge, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.608394.

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Park, Kyeong M. "Boundary conditions of font size effects." Thesis, The University of Alabama in Huntsville, 2016. http://pqdtopen.proquest.com/#viewpdf?dispub=10130786.

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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.

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Zacher, Rico. "Quasilinear parabolic problems with nonlinear boundary conditions." [S.l. : s.n.], 2003. http://deposit.ddb.de/cgi-bin/dokserv?idn=969321899.

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Stigner, Carl. "A classifying algebra for CFT boundary conditions." Licentiate thesis, Karlstad University, Faculty of Technology and Science, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-4890.

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Conformal field theories (CFT) constitute an interesting class of twodimensionalquantum field theories, with applications in string theoryas well as condensed matter physics. The symmetries of a CFT can beencoded in the mathematical structure of a conformal vertex algebra.The rational CFT’s are distinguished by the property that the categoryof representations of the vertex algebra is a modular tensor category.The solution of a rational CFT can be split off into two separate tasks, apurely complex analytic and a purely algebraic part.

The TFT-construction gives a solution to the second part of the problem.This construction gets its name from one of the crucial ingredients,a three-dimensional topological field theory (TFT). The correlators obtainedby the TFT-construction satisfy all consistency conditions of thetheory. Among them are the factorization constraints, whose implicationsfor boundary conditions are the main topic of this thesis.

The main result reviewed in this thesis is that the factorization constraintsgive rise to a semisimple commutative associative complex algebrawhose irreducible representations are the so-called reflection coefficients.The reflection coefficients capture essential information aboutboundary conditions, such as ground-state degeneracies and Ramond-Ramond charges of string compactifications. We also show that the annuluspartition function can be derived fromthis classifying algebra andits representation theory.

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Schulze, Bert-Wolfgang, and Y. Wei. "Edge-boundary problems with singular trace conditions." Universität Potsdam, 2008. http://opus.kobv.de/ubp/volltexte/2009/3031/.

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The ellipticity of boundary value problems on a smooth manifold with boundary relies on a two-component principal symbolic structure (σψ; σ∂), consisting of interior and boundary symbols. In the case of a smooth edge on manifolds with boundary we have a third symbolic component, namely the edge symbol σ∧, referring to extra conditions on the edge, analogously as boundary conditions. Apart from such conditions in integral form' there may exist singular trace conditions, investigated in [6] on closed' manifolds with edge. Here we concentrate on the phenomena in combination with boundary conditions and edge problem.

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Olsen, Robert. "Time-dependent boundary conditions for multiphase flow." Doctoral thesis, [Trondheim : Norges teknisk-naturvitenskapelige universitet, 2004. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-237.

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Cousins, William Bryan. "Boundary Conditions and Uncertainty Quantification for Hemodynamics." Thesis, North Carolina State University, 2013. http://pqdtopen.proquest.com/#viewpdf?dispub=3575896.

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We address outflow boundary conditions for blood flow modeling. In particular, we consider a variety of fundamental issues in the structured tree boundary condition. We provide a theoretical analysis of the numerical implementation of the structured tree, showing that it is sensible but must be performed with great care. We also perform analytical and numerical studies on the sensitivity of model output on the structured tree's defining geometrical parameters. The most important component of this dissertation is the derivation of the new, generalized structured tree boundary condition. Unlike the original structured tree condition, the generalized structured tree does not contain a temporal periodicity assumption and is thus applicable to a much broader class of blood flow simulations. We describe a numerical implementation of this new boundary condition and show that the original structured tree is in fact a rough approximation of the new, generalized condition.

We also investigate parameter selection for outflow boundary conditions, and attempt to determine a set of structured tree parameters that gives reasonable simulation results without requiring any calibration. We are successful in doing so for a simulation of the systemic arterial tree, but the same parameter set yields physiologically unreasonable results in simulations of the Circle of Willis. Finally, we investigate the extension of recently introduced PDF methods to smooth solutions of systems of hyperbolic balance laws subject to uncertain inputs. These methods, currently available only for scalar equations, would provide a powerful tool for quantifying uncertainty in predictions of blood flow and other phenomena governed by first order hyperbolic systems.

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Moore, Stuart Alex. "Lateral boundary conditions in numerical ocean models." Thesis, University of Reading, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.402199.

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Gunson, James Reginald. "Estimating open-ocean boundary conditions : sensitivity studies." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/53024.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1995.
Includes bibliographical references (leaves 145-149).
by James Reginald Gunson.
Ph.D.

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Savi, L. L. [UNESP]. "A geometric approach to cosmological boundary conditions." Universidade Estadual Paulista (UNESP), 2015. http://hdl.handle.net/11449/132136.

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Made available in DSpace on 2015-12-10T14:24:06Z (GMT). No. of bitstreams: 0 Previous issue date: 2015-06-09. Added 1 bitstream(s) on 2015-12-10T14:30:15Z : No. of bitstreams: 1 000852869.pdf: 540584 bytes, checksum: 876f75004ad5a8e7b7dbf74986332aea (MD5)
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A assimetria temporal observada na física macroscópica se deve à conﬁguração de entropia extremamente baixa do universo primordial. Apesar de a matéria estar muito quente e com uma temperatura uniforme naquele estágio, os graus de liberdade gravitacionais estavam em grande medida suprimidos, fato este que contribui para o baixo valor da entropia e está codiﬁcado no alto grau de simetria espacial (caráter aproximadamente Friedman-Lemaître-Robertson-Walker) da superfície de último espalhamento. Analisamos diferentes tentativas de explicar a origem de tal conﬁguração especial. O paradigma inﬂacionário é testado com respeito a esse problema, e é concluído que a baixa entropia inicial não pode ser explicada dentro dele. Conclusões similares são obtidas com respeito a formulações estatísticas (i.e. antrópicas). Por outro lado, o paradigma conhecido como cosmologia cíclica conforme (CCC) se apresenta como uma nova alternativa que ultrapassa muitas das diﬁculdades enfrentadas pelos seus rivais, apesar de levantar suas próprias questões em aberto. Introduzimos o modelo juntamente com a estrutura matemática das geometrias de Cartan como um meio possível de atingir um melhor entendimento das condições de contorno cosmológicas. Um elemento que é crucial nessa análise é a modelagem de uma estrutura geométrica de Cartan sobre o espaço de de Sitter SOe(4,1)/SOe(3,1) com um parâmetro de comprimento variável. A introdução de um parâmetro de comprimento na cinemática é favorecida pela observação de uma constante cosmológica positiva e também desejável por motivos oriundos da gravitação quântica, devido à escala natural determinada pelo comprimento de Planck
The observed T-asymmetry of macroscopic physics is traced back to the extremely low entropy conﬁguration of the early universe. Although matter was very hot and with a uniform temperature at that stage, the gravitational degrees of freedom were largely suppressed, which fact contributes to the lowness of the entropy and is encoded in the high level of spatial symmetry (nearly Friedman-Lemître-Robertson-Walker character) of the last scattering surface. I analyze diﬀerent attempts to explain the origin of such special conﬁguration. The inﬂation paradigm is probed with respect to this problem, and it is concluded that the initial low entropy cannot be accounted for within it. Similar conclusions are reached with respect to statistical (i.e. anthropic) reasonings. On the other hand, the paradigm known as conformal cyclic cosmology (CCC) presents itself as a new alternative which surpasses many of the diﬃculties faced by its rivals, although raising its own open questions. I introduce the model together with the mathematical structure of Cartan geometries as a possible means of achieving a better understanding of cosmological boundary conditions. One element which is crucial in this analysis is the modeling of the Cartan geometric structure over a de Sitter space SOe(4,1)/SOe(3,1) with varying length parameter. The introduction of a length parameter in the kinematics is favored by the observation of a positive cosmological constant and also desirable for quantum gravity reasons, due to the natural scale set by Planck's constant

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Savi, L. L. (Lucas Lolli). "A geometric approach to cosmological boundary conditions /." São Paulo, 2015. http://hdl.handle.net/11449/132136.

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Orientador: José Geraldo Pereira
Banca: Bruto Max Pimentel Escobar
Banca: Roldão da Rocha Junior
Banca: Davi Cabral Rodrigues
Banca: José abdalla Helayel-Neto
Resumo: A assimetria temporal observada na física macroscópica se deve à conﬁguração de entropia extremamente baixa do universo primordial. Apesar de a matéria estar muito quente e com uma temperatura uniforme naquele estágio, os graus de liberdade gravitacionais estavam em grande medida suprimidos, fato este que contribui para o baixo valor da entropia e está codiﬁcado no alto grau de simetria espacial (caráter aproximadamente Friedman-Lemaître-Robertson-Walker) da superfície de último espalhamento. Analisamos diferentes tentativas de explicar a origem de tal conﬁguração especial. O paradigma inﬂacionário é testado com respeito a esse problema, e é concluído que a baixa entropia inicial não pode ser explicada dentro dele. Conclusões similares são obtidas com respeito a formulações estatísticas (i.e. antrópicas). Por outro lado, o paradigma conhecido como cosmologia cíclica conforme (CCC) se apresenta como uma nova alternativa que ultrapassa muitas das diﬁculdades enfrentadas pelos seus rivais, apesar de levantar suas próprias questões em aberto. Introduzimos o modelo juntamente com a estrutura matemática das geometrias de Cartan como um meio possível de atingir um melhor entendimento das condições de contorno cosmológicas. Um elemento que é crucial nessa análise é a modelagem de uma estrutura geométrica de Cartan sobre o espaço de de Sitter SOe(4,1)/SOe(3,1) com um parâmetro de comprimento variável. A introdução de um parâmetro de comprimento na cinemática é favorecida pela observação de uma constante cosmológica positiva e também desejável por motivos oriundos da gravitação quântica, devido à escala natural determinada pelo comprimento de Planck
Abstract:The observed T-asymmetry of macroscopic physics is traced back to the extremely low entropy conﬁguration of the early universe. Although matter was very hot and with a uniform temperature at that stage, the gravitational degrees of freedom were largely suppressed, which fact contributes to the lowness of the entropy and is encoded in the high level of spatial symmetry (nearly Friedman-Lemître-Robertson-Walker character) of the last scattering surface. I analyze diﬀerent attempts to explain the origin of such special conﬁguration. The inﬂation paradigm is probed with respect to this problem, and it is concluded that the initial low entropy cannot be accounted for within it. Similar conclusions are reached with respect to statistical (i.e. anthropic) reasonings. On the other hand, the paradigm known as conformal cyclic cosmology (CCC) presents itself as a new alternative which surpasses many of the diﬃculties faced by its rivals, although raising its own open questions. I introduce the model together with the mathematical structure of Cartan geometries as a possible means of achieving a better understanding of cosmological boundary conditions. One element which is crucial in this analysis is the modeling of the Cartan geometric structure over a de Sitter space SOe(4,1)/SOe(3,1) with varying length parameter. The introduction of a length parameter in the kinematics is favored by the observation of a positive cosmological constant and also desirable for quantum gravity reasons, due to the natural scale set by Planck's constant
Doutor

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Li, Hongwei. "Local absorbing boundary conditions for wave propagations." HKBU Institutional Repository, 2012. https://repository.hkbu.edu.hk/etd_ra/1434.

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FEVOLA, ELISA. "Boundary conditions estimation techniques for cardiovascular modeling." Doctoral thesis, Politecnico di Torino, 2022. http://hdl.handle.net/11583/2972100.

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Chamaillard, Mathieu. "Effective boundary conditions for thin periodic coatings." Electronic Thesis or Diss., Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLY001.

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Nous avons traité le cas de l'équation scalaire de Helmholtz. Nous allons tenter de traiter le cas des équations de Maxwell. On s'intéressera aux cas des méta-matériaux. Dans un premier cas la permittivité est négative dans la couche mince et dans le deuxième cas la perméabilité est en (1/delta)^2
We have dealt with the case of the scalar Helmholtz equation. We will try to handle the case of Maxwell's equation. We also will focus on the case of meta-materials. In a first case the permittivity is negative in the thin layer and in the second case is the permeability (1/delta) ^ 2

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Wintz, Nick. "Eigenvalue comparisons for an impulsive boundary value problem with Sturm-Liouville boundary conditions." Huntington, WV : [Marshall University Libraries], 2004. http://www.marshall.edu/etd/descript.asp?ref=414.

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Appelö, Daniel. "Non-reflecting Boundary Conditions for Wave Propagation Problems." Licentiate thesis, KTH, Numerical Analysis and Computer Science, NADA, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-1664.

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We consider two aspects of non-reflecting boundaryconditions for wave propagation problems. First we evaluate aproposed Perfectly Matched Layer (PML) method for thesimulation of advective acoustics. It is shown that theproposed PML becomes unstable for a certain combination ofparameters. A stabilizing procedure is proposed andimplemented. By numerical experiments the performance of thePML for a problem with nonuniform flow is investigated. Furtherthe performance for different types of waves, vorticity andsound waves, are investigated.

The second aspect concerns spurious waves, which areintroduced by any discretization procedure. We constructdiscrete boundary conditions, that are nonreflecting for bothphysical and spurious waves, when combined with a fourth orderaccurate explicit discretization of one-way wave equations. Theboundary condition is shown to be GKS-stable. The boundaryconditions are extended to hyperbolic systems in two spacedimensions, by combining exact continuous non-reflectingboundary conditions and the one dimensional discretelynon-reflecting boundary condition. The resulting boundarycondition is localized by the standard Pad´eapproximation.

Numerical experiments reveal that the resulting methodsuffers from boundary instabilities. Analysis of a relatedcontinuous problem suggests that the discrete boundarycondition can be stabilized by adding tangential viscosity atthe boundary. For the lowest order Pad´e approximation weare able to stabilize the discrete boundary condition.

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Schulze, Bert-Wolfgang, and Jörg Seiler. "Pseudodifferential boundary value problems with global projection conditions." Universität Potsdam, 2002. http://opus.kobv.de/ubp/volltexte/2008/2623/.

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Contents: Introduction 1 Operators with the transmission property 1.1 Operators on a manifold with boundary 1.2 Conditions with pseudodifferential projections 1.3 Projections and Fredholm families 2 Boundary value problems not requiring the transmission property 2.1 Interior operators 2.2 Edge amplitude functions 2.3 Boundary value problems 3 Operators with global projection conditions 3.1 Construction for boundary symbols 3.2 Ellipticity of boundary value problems with projection data 3.3 Operators of order zero

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Mossige, Endre Joachim. "Curved Boundary Conditions for the Lattice Boltzmann Method." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for energi- og prosessteknikk, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-14667.

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The lattice Boltzmann method is a modern method in computational fluid dynamics. Its primary use is the simulation of incompressible flows. It has computational advantages over conventional methods like the finite volume method. However, the implementation of boundary conditions is still an unsolved topic for this method. The method is defined on a Cartesian grid such that curved walls need special treatment as they are generally not aligned with the grid lines. We investigated a number of straight and curved boundary conditions and performed four different benchmark tests to verify these. Based on a formulation for curved walls with no-slip from the literature, we showed that this method could be extended to simulate flows with arbitrary velocity boundary conditions. Our scheme conserved the second order accuracy of the lattice Boltzmann method in time and space.

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Jung, Florian [Verfasser]. "Canonical group quantization and boundary conditions / Florian Jung." Mainz : Universitätsbibliothek Mainz, 2012. http://d-nb.info/1025490088/34.

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Burgess, N. A. "Stable boundary conditions for the shallow water equations." Thesis, University of Oxford, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.380000.

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Ilie, Alexandra. "Unethical Pro-Organizational Behaviors: Antecedents and Boundary Conditions." Scholar Commons, 2012. http://scholarcommons.usf.edu/etd/4085.

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The goals of the current study were to examine the antecedents and boundary conditions of a new construct called unethical pro-organizational behavior (UPB) defined as behaviors that are unethical but at the same time helping the organizations (e.g., giving a low performing employee a letter of recommendation to help him/her find a job in another organization). Drawing from social exchange theory, antecedents such as leader-member exchange, perceived organizational support, idiosyncratic deals, and leader-member exchange were hypothesized to be positively related to UPB Three moderators of the impact of the social exchange variables on UPB: were also investigated: moral identity, psychological entitlement, and supervisor's embodiment of the organization. Data was collected in a cross-sectional survey from 269 employees and 144 supervisors. The hypotheses were tested using correlations and moderated multiple regressions. The results indicate that none of the hypotheses were supported. However, there were some interesting unexpected findings as some social exchange variables were found to correlate negatively with UPB. Implications for future research and practice are discussed.

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Shepherd, Roger. "Coupled non-linear diffusion under periodic boundary conditions." Thesis, University of South Wales, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239985.

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Bélanger-Rioux, Rosalie. "Compressed absorbing boundary conditions for the Helmholtz equation." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/90179.

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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mathematics, 2014.
56
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 101-105).
Absorbing layers are sometimes required to be impractically thick in order to offer an accurate approximation of an absorbing boundary condition for the Helmholtz equation in a heterogeneous medium. It is always possible to reduce an absorbing layer to an operator at the boundary by layer-stripping elimination of the exterior unknowns, but the linear algebra involved is costly. We propose to bypass the elimination procedure, and directly fit the surface-to-surface operator in compressed form from a few exterior Helmholtz solves with random Dirichlet data. We obtain a concise description of the absorbing boundary condition, with a complexity that grows slowly (often, logarithmically) in the frequency parameter. We then obtain a fast (nearly linear in the dimension of the matrix) algorithm for the application of the absorbing boundary condition using partitioned low rank matrices. The result, modulo a precomputation, is a fast and memory-efficient compression scheme of an absorbing boundary condition for the Helmholtz equation.
by Rosalie Bélanger-Rioux.
Ph. D.

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Arbegard, Fredrik, and Håkan Jakobsson. "Evaluation of Boundary Conditions in Chassis Test Rig." Thesis, KTH, Hållfasthetslära (Inst.), 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-176497.

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Trucks are constantly developed in order to achieve new goals in terms of demands from the customers and regulation. In order to develop the truck chassis to withstand the load, different tests are conducted and among those life time testing. At Scania, service life of frames and suspensions is tested using a purpose built test rig known as Ramriggen. The test rig subjects the frame to a quasi-static load created of measurements from a test track. The current rig for frame testing has boundary conditions that distribute the loads unevenly within the chassis, especially for trucks with added frame twisting. In the current rig, the front axle load is absorbed solely by the engine and the frame twisting is inserted by a cradle. With increased axle load the error in vertical loading is also increased and with the current configuration for frame twisting, unexpected cracks in the frame has been observed. In order to improve the emulation of a real truck the boundary conditions requires development. The purpose of this study is to compare different boundary conditions at the front of the truck. An investigation of how new boundary conditions at the front of truck can redistribute the loads has been conducted. This investigation utilized FEM as a tool and method to reach the end results. In order to compare different boundary conditions two synthetic load cases were defined from measurements conducted on a truck at a test track. The two load cases consisted of a vertical load and two cases of frame twisting. This investigation resulted in new boundary conditions for a concept test rig. The new boundary conditions consist of a cab mock-up that is able to absorb vertical load and induce frame twisting. The result of the investigation of the two load cases shows that the engine beam is overloaded at most 40% and the base mount with 150% with the current boundary conditions compared with the new suggested concept.
Lastbilar utvecklas ständigt för att uppnå nya krav och regelverk. När lastbilschassin optimeras för hållfasthet måste olika prover utföras bland annat livslängdsprov. Livslängdsprov på ramar och hjulupphängningar utförs på Scania i en speciell kvasistatisk rigg, Ramriggen. Riggen utsätter ramarna för en lasthistorik skapad utifrån provbanemätningar. Dagens rigg för provning av ramar har randvillkor som snedfördelar lasterna inom chassiet, speciellt för dragbilar med pålagd ramvridning. Dragbilens framaxeltyck tags enbart upp utav motorn och vridningen av ramen införs i basfästena via en krängningsvagga. Vid större axeltryck blir felet ifrån vertikallasten allt större och vid ramvridning så har oförutsedda utfall skett i framvagnen. För att förbättra Ramriggens förmåga att efterlikna en verklig lastbil behöver randvillkoren utvecklas. Syftet med undersökningen är att jämföra olika randvillkor i dragbilens framvagn. En undersökning om nya randvillkor för dragbilens framvagn i riggen kan omfördela lasterna har genomförts. I undersökningen användes FEM. För att jämföra olika randvillkor har två lastfall syntetiserats utifrån olika mätningar inmätta på dragbil. Ett lastfall för hög vertikallast och två lastfall med ramvridning. Genom undersökningen har nya randvillkorskoncept för riggen tagits fram. De nya randvillkoren innefattar en hyttattrapp som kan bidra med mothåll för vertikallaster samt inducera ramvridning. Resultatet av undersökningen av de två lastfallen visar att motorbalken överlastas med som mest 40% och basfästet 150% med de nuvarande randvillkoren jämfört med det föreslagna konceptet.

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33

Ahmed, Ashfaq. "Investigation of boundary conditions for hydrological design analysis." Thesis, University of Birmingham, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.396238.

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This study deals with the fundamental problems of hydrological design. Specifically, it explores the boundary conditions for design flood analysis. The problem of extrapolation of design relationships has been investigated by the systematic analysis of important design parameters namely unit hydrograph time to peak (tp), catchment antecedent conditions (CWI), runoff losses (PR) and the relationship between rainfall and flood return periods. In particular, this thesis investigates the combination of these variables representative of design analysis. A review of the hydrological design tools of response identification along with the physical evidence of catchment response is presented. The results of the investigation regarding time to peak (tp) show that it varies significantly between events, and the relationships developed between tp and flood magnitude (Qp) show the non-linear catchment behaviour which conform with most of the physical and field investigations. The relationships suggest that the unit hydrograph (UH) parameters derived from moderate events should be adjusted for extreme events and therefore a correction in UH tp has been developed which depends on the flood return period (Ashfaq and Webster, 2000a). The analysis of catchment wetness index (CWI) from a large number of observed events showed that antecedent conditions observed in the flood season are reasonably representative of the major events. This contrasts with the existing design recommendations which suggest consistently lower values. An alternative relationship of CWI therefore has been developed for design purposes (Webster and Ashfaq, submitted manuscript). The investigation showed that the percentage runoff (PR) characteristics of large events are consistently different than available from the existing design PR-method. The design method underestimates for the standardised conditions especially for large events because of its limited range of estimates for a wide range of return periods (e.g. 11% range in PR for 2 to 1000 year return periods). This problem is related with the PR-method itself for catchments having higher mean annual rainfall (SAAR> 800 mm) whereas for lower SAAR areas « 800 mm), it is related to the selection of design CWI values. The analysis of observed large events also revealed that a flood is generally associated with the storm of less return period than that of the flood. This contrasts with the suggested design rainfall-flood return periods relationship in the FSR (NERC, 1975; [H, 1999), but conforms with the curves presented by Webster (1998, 1999). This observation is further established by a detailed investigation of the characteristics of extreme events through a continuous model as well as the hydrological analysis of observed extreme floods of Easter-1998 (Ashfaq and Webster,2000b). The study demonstrates that the characteristics of extreme floods are different from those of small and moderate events. Relationships based on moderate events should be adjusted for the design of major events. The aggregated and integrated findings based on a comprehensive series of analysis led to the proposal of an alternative combination of design parameters. The performance of this combination showed improved flood estimates without any prior calibration in comparison to the FSR as well as FEH. A revised design methodology has therefore been proposed on the philosophy of 'independent treatment of input variables'. The application of this methodology on new catchments also provides encouraging estimates of flood quantiles. It is suggested that the methodology is equally applicable for both gauged and ungauged catchments especially where the observed data are limited or no data are available.

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LaGrone, John. "Application and optimization of complete radiation boundary conditions." Thesis, Southern Methodist University, 2016. http://pqdtopen.proquest.com/#viewpdf?dispub=10144064.

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We describe the implementation of optimal local radiation boundary condition sequences for second order finite difference approximations to Maxwell's equations and the scalar wave equation using the double absorbing boundary formulation. Numerical experiments are presented which demonstrate that the design accuracy of the boundary conditions is achieved and exceeds that of perfectly matched layers for comparable effort.

We also describe the application of CRBC type boundary conditions for elastic waves in (an)isotropic media. The results show that we can optimize the CRBC problems for a subset of elastic media. Additionally, we propose a generalized CRBC type boundary conditions that may be more applicable to elastic wave equations and present some preliminary results.

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35

Mezzadri, Francesco. "Boundary conditions for torus maps and spectral statistics." Thesis, University of Bristol, 1999. http://hdl.handle.net/1983/dcba3276-00be-4bae-a89f-f864750e77ff.

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36

Massa, Kenneth L. "Control of Burgers' Equation With Mixed Boundary Conditions." Thesis, Virginia Tech, 1998. http://hdl.handle.net/10919/36681.

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We consider the problems of simulation and control for Burgers' equation with mixed boundary conditions. We first conduct numerical experiments to test the convergence and stability of two standard finite element schemes for various Robin boundary conditions and a variety of Reynolds numbers. These schemes are used to compute LQR feedback controllers for Burgers' equation with boundary control. Numerical studies of these feedback control laws are used to evaluate the performance and practicality of this approach to boundary control of non-linear systems.
Master of Science

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37

Berrabah, Nassif. "On High Order On-Surface Radiation Boundary Conditions." University of Akron / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=akron1415620836.

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38

Dade, William Brian. "Studies on boundary conditions for fine-sediment transport /." Thesis, Connect to this title online; UW restricted, 1992. http://hdl.handle.net/1773/11052.

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39

Padbidri, Jagan. "Minimal boundary conditions for simulations of disordered materials." WSU all campuses online access, 2003. http://www.dissertations.wsu.edu/Thesis/Fall2003/j%5Fpadbidri%5F121503.pdf.

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40

Kharche, Sanjay. "Stefan problems with two-dimensional, linearised perturbations in their boundary geometry or boundary conditions." Thesis, University of Hull, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.327179.

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41

Gilkey, Peter B., Klaus Kirsten, Dmitri V. Vassilevich, and vassil@itp uni-leipzig de. "Heat Trace Asymptotics with Transmittal Boundary Conditions and Quantum." Nucl. Phys. B 601 (2001) 125-148, 2001. ftp://ftp.esi.ac.at/pub/Preprints/esi982.ps.

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42

Teymur, Berrak. "The significance of boundary conditions in dynamic centrifuge modelling." Thesis, University of Cambridge, 2002. https://www.repository.cam.ac.uk/handle/1810/251828.

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43

Clipp, Rachel Betany. "Determination of Impedance Boundary Conditions for the Pulmonary Vasculature." NCSU, 2007. http://www.lib.ncsu.edu/theses/available/etd-03282007-001101/.

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Computational modeling can be used to achieve a better understanding of fluid analysis within the pulmonary circulation. Boundary conditions are used in fluid analysis to determine the pressure and flow profiles of the blood as it moves through the lung. Accurate boundary conditions are critical in providing accurate models of blood pressure and blood flow. An important consideration when determining boundary conditions for the pulmonary vasculature is the effect of respiration on the impedance of the pulmonary vasculature. An additional consideration for the pulmonary vasculature is the physiologic differences between the pulmonary circulation and that of the systemic circulation. This research determines impedance boundary conditions for the pulmonary vasculature that reflect the specific geometry of the lung and correspond to maximal inspiration and maximal expiration. The analysis was performed using an existing one-dimensional finite element analysis system. The boundary conditions were defined by a bifurcating structure tree with a number of variables that were used to change the resistance of the pulmonary vessels. The variables within the structure tree were altered to reflect the differences between the pulmonary circulation and the systemic circulation. These variables include the length to radius ratio of the vessels in the structure tree and the asymmetry as the branches. A respiration factor was used to scale the vessels of the structure tree to reflect the effects of respiration on the geometry of the lung. The compliance of the vessels was also changed to reflect the more distensible vessels found in the pulmonary system. The geometry of the lung was defined with the structured tree parameters at maximal inspiration and the respiration factor was used to scale the defined geometry and reflect maximal expiration. The parameters were determined by utilizing an optimization technique. The Levinberg-Marquardt least-squares non-linear optimization algorithm was used to find a set of non-unique optimal parameters. The computed data was validated using measured pressure and flow data collected in a previous study.

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44

Jiang, Mingxiao. "Scale and boundary conditions effects in fiber-reinforced composites." Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/16373.

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Mara, Gillian E. "Boundary conditions for the virtual testing of athletic footwear." Thesis, Loughborough University, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.510279.

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Agadjanov, Dimitri [Verfasser]. "Exploring exotic states with twisted boundary conditions / Dimitri Agadjanov." Bonn : Universitäts- und Landesbibliothek Bonn, 2017. http://d-nb.info/1149154004/34.

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Thompson, Katrina Alison. "An investigation into outflow boundary conditions for vortex flows." Thesis, Queen's University Belfast, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.287433.

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Brown, Mark Gregory. "The boundary conditions for quantum evaporation in liquid '4He." Thesis, University of Exeter, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.277101.

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Parham, Jonathan Brent. "Physically consistent boundary conditions for free-molecular satellite aerodynamics." Thesis, Boston University, 2014. https://hdl.handle.net/2144/21230.

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Thesis (M.Sc.Eng.)
To determine satellite trajectories in low earth orbit, engineers need to adequately estimate aerodynamic forces. But to this day, such a task su↵ers from inexact values of drag forces acting on complicated shapes that form modern spacecraft. While some of the complications arise from the uncertainty in the upper atmosphere, this work focuses on the problems in modeling the flow interaction with the satellite geometry. The only numerical approach that accurately captures e↵ects in this flow regime—like self-shadowing and multiple molecular reflections—is known as Test Particle Monte Carlo. This method executes a ray-tracing algorithm to follow particles that pass through a control volume containing the spacecraft and accumulates the momentum transfer to the body surfaces. Statistical fluctuations inherent in the approach demand particle numbers on the order of millions, often making this scheme too costly to be practical. This work presents a parallel Test Particle Monte Carlo method that takes advantage of both graphics processing units and multi-core central processing units. The speed at which this model can run with millions of particles enabled the exploration of regimes where a flaw was revealed in the model’s initial particle seeding. A new model introduces an analytical fix to this flaw—consisting of initial position distributions at the boundary of a spherical control volume and an integral for the correct number flux—which is used to seed the calculation. This thesis includes validation of the proposed model using analytical solutions for several simple geometries and demonstrates uses of the method for the aero-stabilization of the Phobos-Grunt Martian probe and pose-estimation for the ICESat mission.
2031-01-01

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Johnson, Francis 1974. "Thermal boundary conditions for heat pipe assisted crystal growth." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/85269.

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Dissertations / Theses on the topic 'Boundary Conditions'

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