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Tesi sul tema "Numerical computation"
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1
Lesage, Pierre-Yves. "Numerical computation and software design". Thesis, Cranfield University, 1999. http://dspace.lib.cranfield.ac.uk/handle/1826/11134.
Testo completoAbstract (sommario):
The development of simulation tools is becoming an important area in industry, recently fostered by the tremendous improvements in computer hardware. Many physical problems can be simulated by being modelled by mathematical equations which can then be solved numerically. This thesis is concerned with the development of a Finite Difference solver for time dependent partial differential equations. The development involves a number of challenging requirements that the solver must meet: to have the capacity of solving conservation and non-conservation laws (using several numerical techniques), to be robust, efficient and to have a modular and extendible design. Firstly, we focus on the architecture of the program and how an original design approach was used in order to carry out its development. A combination of Object- Oriented Design and Structured Design was adopted.
2
Lesage, P.-Y. "Numerical computation and software design". Thesis, Cranfield University, 1999. http://dspace.lib.cranfield.ac.uk/handle/1826/11134.
Testo completoAbstract (sommario):
The
development of simulation tools is becoming an important area in industry,
recently fostered by the tremendous improvements in computer hardware. Many
physical problems can be simulated by being modelled by mathematical equations
which can then be solved numerically.
This thesis is concerned with the development of a Finite Difference solver for time
dependent partial differential equations. The development involves a number of challenging
requirements that the solver must meet: to have the capacity of solving
conservation and non-conservation laws
(using several numerical techniques), to be
robust, efficient and to have a modular and extendible design.
Firstly, we focus on the architecture of the program and how an original design
approach was used in order to carry out its development. A combination of Object-
Oriented Design and Structured Design was adopted.
3
Nassiri, Masoud. "Numerical computation of shallow recirculating flow". Thesis, McGill University, 1994. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=68046.
Testo completoAbstract (sommario):
The recirculating flows behind a sudden expansion in an open channel are computed using three different turbulence models: (i) a standard single-length-scale $ kappa$-$ epsilon$ model, (ii) a two-length-scale $ kappa$-$ epsilon$, and (iii) a constant-eddy-viscosity model. The performance of these models is evaluated by comparing the numerical results with the experimental data obtained from the previous investigation.The flow simulation is characterized by two basic dimensionless parameters: a turbulent Reynolds number, $Re sb{T},$ which defines the level of eddy viscosity, and a bed-friction number, S, which represents the effect of bed friction. The study shows that in the limit of shallow water depth, that is S $>$ 0.10, the mean flow is quite successfully predicted by all employed models. However, in the limit of deep water depth, S $<$ 0.10, both $ kappa- epsilon$ models under-predict the length of the recirculating region due to the high level of computed eddy viscosity. On the other hand, the study indicates that the constant viscosity model gives quite acceptable results for most engineering applications.
Advantageously using the constant viscosity model's simple concept, an attempt is made to define a criterion for numerical stability of the computational procedure. The stability of the algorithm is assessed by varying the flow Reynolds number, the bed-friction number as well as the mesh size. The Courant number, a dimensionless parameter, is then introduced and correlated with the $Re sb{T}$ and S, thus providing the means to determine the stability of the numerical calculations.
As most of the recirculating flows observed in natural waterways are dominated by the bed-friction effect, accurate simulation of the mean flow field is possible even with an incorrect model for the lateral exchange process.
4
Zerroukat, Mohamed. "Numerical computation of moving boundary phenomena". Thesis, University of Glasgow, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.285256.
Testo completo
5
Romero, i. Sànchez David. "Numerical computation of invariant objects with wavelets". Doctoral thesis, Universitat Autònoma de Barcelona, 2015. http://hdl.handle.net/10803/395169.
Testo completo
6
Bohigas, Nadal Oriol. "Numerical computation and avoidance of manipulator singularities". Doctoral thesis, Universitat Politècnica de Catalunya, 2013. http://hdl.handle.net/10803/117535.
Testo completoAbstract (sommario):
This thesis develops general solutions to two open problems of robot kinematics: the exhaustive computation of the singularity set of a manipulator, and the synthesis of singularity-free paths between given configurations. Obtaining proper solutions to these problems is crucial, because singularities generally pose problems to the normal operation of a robot and, thus, they should be taken into account before the actual construction of a prototype. The ability to compute the whole singularity set also provides rich information on the global motion capabilities of a manipulator. The projections onto the task and joint spaces delimit the working regions in such spaces, may inform on the various assembly modes of the manipulator, and highlight areas where control or dexterity losses can arise, among other anomalous behaviour. These projections also supply a fair view of the feasible movements of the system, but do not reveal all possible singularity-free motions. Automatic motion planners allowing to circumvent problematic singularities should thus be devised to assist the design and programming stages of a manipulator.
The key role played by singular configurations has been thoroughly known for several years, but existing methods for singularity computation or avoidance still concentrate on specific classes of manipulators. The absence of methods able to tackle these problems on a sufficiently large class of manipulators is problematic because it hinders the analysis of more complex manipulators or the development of new robot topologies. A main reason for this absence has been the lack of computational tools suitable to the underlying mathematics that such problems conceal. However, recent advances in the field of numerical methods for polynomial system solving now permit to confront these issues with a very general intention in mind.
The purpose of this thesis is to take advantage of this progress and to propose general robust methods for the computation and avoidance of singularities on non-redundant manipulators of arbitrary architecture. Overall, the work seeks to contribute to the general understanding on how the motions of complex multibody systems can be predicted, planned, or controlled in an efficient and reliable way.Aquesta tesi desenvolupa solucions generals per dos problemes oberts de la cinemàtica de robots: el càlcul exhaustiu del conjunt singular d'un manipulador, i la síntesi de camins lliures de singularitats entre configuracions donades. Obtenir solucions adequades per aquests problemes és crucial, ja que les singularitats plantegen problemes al funcionament normal del robot i, per tant, haurien de ser completament identificades abans de la construcció d'un prototipus. La habilitat de computar tot el conjunt singular també proporciona informació rica sobre les capacitats globals de moviment d'un manipulador. Les projeccions cap a l'espai de tasques o d'articulacions delimiten les regions de treball en aquests espais, poden informar sobre les diferents maneres de muntar el manipulador, i remarquen les àrees on poden sorgir pèrdues de control o destresa, entre d'altres comportaments anòmals. Aquestes projeccions també proporcionen una imatge fidel dels moviments factibles del sistema, però no revelen tots els possibles moviments lliures de singularitats. Planificadors de moviment automàtics que permetin evitar les singularitats problemàtiques haurien de ser ideats per tal d'assistir les etapes de disseny i programació d'un manipulador. El paper clau que juguen les configuracions singulars ha estat àmpliament conegut durant anys, però els mètodes existents pel càlcul o evitació de singularitats encara es concentren en classes específiques de manipuladors. L'absència de mètodes capaços de tractar aquests problemes en una classe suficientment gran de manipuladors és problemàtica, ja que dificulta l'anàlisi de manipuladors més complexes o el desenvolupament de noves topologies de robots. Una raó principal d'aquesta absència ha estat la manca d'eines computacionals adequades a les matemàtiques subjacents que aquests problemes amaguen. No obstant, avenços recents en el camp de mètodes numèrics per la solució de sistemes polinòmics permeten ara enfrontar-se a aquests temes amb una intenció molt general en ment. El propòsit d'aquesta tesi és aprofitar aquest progrés i proposar mètodes robustos i generals pel càlcul i evitació de singularitats per manipuladors no redundants d'arquitectura arbitrària. En global, el treball busca contribuir a la comprensió general sobre com els moviments de sistemes multicos complexos es poden predir, planificar o controlar d'una manera eficient i segura
7
Lin, Hong-Chia. "Topics in Numerical Computation of Compressible Flow". Thesis, Cranfield University, 1990. http://dspace.lib.cranfield.ac.uk/handle/1826/4555.
Testo completoAbstract (sommario):
This thesis aims to assist the development of a multiblock
implicit Navier-Stokes code for hypersonic flow applications.
There are mainly three topics, which concern the understanding
of basic Riemann solvers, the implementing of implicit zonal
method, and grid adaption for viscous flow.
Three problems of Riemann solvers are investigated. The
post-shock oscillation problem of slowly moving shocks is
examined, especially for Roe's Riemann solver, and possible cures
are suggested for both first and second order schemes. The
carbuncle phenomenon associated with blunt body calculation is
cured by a formula based on pressure gradient, which will not
degrade the solutions for viscous calculations too much. The
grid-dependent characteristic of current upwind schemes is also
demonstrated.
Several issues associated with implicit zonal methods are
discussed. The effects of having different mesh sizes in
different zones when shock present are examined with first order
explicit scheme and such effects are shown to be unwanted
therefore big mesh size change should be avoided. Several
implicit schemes are tested for hypersonic flow. The
conservative DDADI scheme is found to be the most robust one. A
simple and robust implicit zonal method is demonstrated. A
proper treatment of the diagonal Jacobian and choosing the
updating method are found to be crucial.
The final topic concerns the calculation and grid adaption
of viscous flow. We study the linear advection-diffusion equation
thoroughly. The results are unfortunately not applicable to
Navier-Stokes equations directly. Nevertheless a suggestion on
the mesh size control for viscous flow is made and demonstrated.
An attempt to construct a cell-vertex TVD scheme is
described in the appendix.
8
Betcke, Timo. "Numerical computation of eigenfunctions of planar regions". Thesis, University of Oxford, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.426381.
Testo completo
9
Prosser, Robert. "Numerical methods for the computation of combustion". Thesis, University of Cambridge, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.340975.
Testo completo
10
Dougherty, Edward T. "Computation and Numerics in Neurostimulation". Diss., Virginia Tech, 2015. http://hdl.handle.net/10919/73350.
Testo completoAbstract (sommario):
Neurostimulation continues to demonstrate tremendous success as an intervention for neurodegenerative diseases, including Parkinson's disease, in addition to a range of other neurological and psychiatric disorders. In an effort to enhance the medical efficacy and comprehension of this form of brain therapy, modeling and computational simulation are regarded as valuable tools that enable in silico experiments for a range of neurostimulation research endeavours. To fully realize the capacities of neurostimulation simulations, several areas within computation and numerics need to be considered and addressed. Specifically, simulations of neurostimulation that incorporate (i) computational efficiency, (ii) application versatility, and (iii) characterizations of cellular-level electrophysiology would be highly propitious in supporting advancements in this medical treatment.
The focus of this dissertation is on these specific areas. First, preconditioners and iterative methods for solving the linear system of equations resulting from finite element discretizations of partial differential equation based transcranial electrical stimulation models are compared. Second, a software framework designed to efficiently support the range of clinical, biomedical, and numerical simulations utilized within the neurostimulation community is presented. Third, a multiscale model that couples transcranial direct current stimulation administrations to neuronal transmembrane voltage depolarization is presented. Fourth, numerical solvers for solving ordinary differential equation based ligand-gated neurotransmitter receptor models are analyzed.
A fundamental objective of this research has been to accurately emulate the unique medical characteristics of neurostimulation treatments, with minimal simplification, thereby providing optimal utility to the scientific research and medical communities. To accomplish this, numerical simulations incorporate high-resolution, MRI-derived three-dimensional head models, real-world electrode configurations and stimulation parameters, physiologically-based inhomogeneous and anisotropic tissue conductivities, and mathematical models accepted by the brain modeling community. It is my hope that this work facilitates advancements in neurostimulation simulation capabilities, and ultimately helps improve the understanding and treatment of brain disease.Ph. D.
11
Zhou, Jian Ming. "A multi-grid method for computation of film cooling". Thesis, University of British Columbia, 1990. http://hdl.handle.net/2429/29414.
Testo completoAbstract (sommario):
This thesis presents a multi-grid scheme applied to the solution of transport equations in turbulent flow associated with heat transfer. The multi-grid scheme is then applied to flow which occurs in the film cooling of turbine blades. The governing equations are discretized on a staggered grid with the hybrid differencing scheme. The momentum and continuity equations are solved by a nonlinear full multi-grid scheme with the SIMPLE algorithm as a relaxation smoother. The turbulence k — Є equations and the thermal energy equation are solved on each grid without multi-grid correction.
Observation shows that the multi-grid scheme has a faster convergence rate in solving the Navier-Stokes equations and that the rate is not sensitive to the number of mesh points or the Reynolds number. A significant acceleration of convergence is also produced for the k — Є and the thermal energy equations, even though the multi-grid correction is not applied to these equations. The multi-grid method provides a stable and efficient means for local mesh refinement with only little additional computational and.memory costs.
Driven cavity flows at high Reynolds numbers are computed on a number of fine meshes for both the multi-grid scheme and the local mesh-refinement scheme. Two-dimensional film cooling flow is studied using multi-grid processing and significant improvements
in the results are obtained. The non-uniformity of the flow at the slot exit and its influence on the film cooling are investigated with the fine grid resolution. A near-wall turbulence model is used. Film cooling results are presented for slot injection with different mass flow ratios.Science, Faculty of
Mathematics, Department of
Graduate
12
Eklund, David. "Topics in computation, numerical methods and algebraic geometry". Doctoral thesis, KTH, Matematik (Avd.), 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-25941.
Testo completoAbstract (sommario):
This thesis concerns computation and algebraic geometry. On the computational side we have focused on numerical homotopy methods. These procedures may be used to numerically solve systems of polynomial equations. The thesis contains four papers. In Paper I and Paper II we apply continuation techniques, as well as symbolic algorithms, to formulate methods to compute Chern classes of smooth algebraic varieties. More specifically, in Paper I we give an algorithm to compute the degrees of the Chern classes of smooth projective varieties and in Paper II we extend these ideas to cover also the degrees of intersections of Chern classes. In Paper III we formulate a numerical homotopy to compute the intersection of two complementary dimensional subvarieties of a smooth quadric hypersurface in projective space. If the two subvarieties intersect transversely, then the number of homotopy paths is optimal. As an application we give a new solution to the inverse kinematics problem of a six-revolute serial-link mechanism. Paper IV is a study of curves on certain special quartic surfaces in projective 3-space. The surfaces are invariant under the action of a finite group called the level (2,2) Heisenberg group. In the paper, we determine the Picard group of a very general member of this family of quartics. We have found that the general Heisenberg invariant quartic contains 320 smooth conics and we prove that in the very general case, this collection of conics generates the Picard group.QC 20101115
13
Stewart, Dawn L. "Numerical Methods for Accurate Computation of Design Sensitivities". Diss., Virginia Tech, 1998. http://hdl.handle.net/10919/30561.
Testo completoAbstract (sommario):
This work is concerned with the development of computational methods for
approximating sensitivities of solutions to boundary value problems.
We focus on the continuous sensitivity equation method and
investigate the application of adaptive meshing and smoothing
projection techniques to enhance the basic scheme. The fundamental
ideas are first developed for a one dimensional problem and then
extended to 2-D flow problems governed by the incompressible
Navier-Stokes equations. Numerical experiments are conducted to test the
algorithms and to investigate the benefits of adaptivity and smoothing.Ph. D.
14
Lu, Jiaqing. "Numerical Modeling and Computation of Radio Frequency Devices". The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1543457620064355.
Testo completo
15
Tomita, Yu. "Numerical and analytical studies of quantum error correction". Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/53468.
Testo completoAbstract (sommario):
A reliable large-scale quantum computer, if built, can solve many real-life problems exponentially faster than the existing digital devices. The biggest obstacle to building one is that they are extremely sensitive and error-prone regardless of the selection of physical implementation. Both data storage and data manipulation require careful implementation and precise control due to its quantum mechanical nature. For the development of a practical and scalable computer, it is essential to identify possible quantum errors and reduce them throughout every layer of the hierarchy of quantum computation.
In this dissertation, we present our investigation into new methods to reduce errors in quantum computers from three different directions: quantum memory, quantum control, and quantum error correcting codes. For quantum memory, we pursue the potential of the quantum equivalent of a magnetic hard drive using two-body-interaction structures in fractal dimensions. With regard to quantum control, we show that it is possible to arbitrarily reduce error when manipulating multiple quantum bits using a technique popular in nuclear magnetic resonance. Finally, we introduce an efficient tool to study quantum error correcting codes and present analysis of the codes' performance on model quantum architectures.
16
Li, Zhou, of Western Sydney Nepean University e of Mechatronic Computer and Electrical Engineering School. "Numerical computation of core losses in permanent magnet machines". THESIS_XXXX_MCEE_Li_Z.xml, 2000. http://handle.uws.edu.au:8081/1959.7/284.
Testo completoAbstract (sommario):
This thesis presents a study on core loss calculations in rotating electrical machines. The basic concepts concerning magnetic moments, ferromagnetism, magnetic domains and magnetic hysteresis are introduced. The three-term models for alternating and rotational core losses in electrical steel sheets are presented. Several core loss measurement techniques are reviewed and an experiment is carried out to measure the total core losses in an electrical sheet steel sample under alternating and rotational magnetic fields of various frequencies and amplitudes. The coefficients in the loss models for alternating and rotational core losses are obtained through curve fitting process. The theory of electromagnetic fields is presented through the Maxwell equations and field scalar equations. A detailed review on core loss models for rotating electrical machines is presented. A rotational core loss model is adopted to calculate the core losses in a PM motor. The total core loss in the PM motor is obtained by summing the element losses using a MATLAB program. An experiment is conducted to measure the total core loss in the PM motor. The calculated total core loss in the PM motor is compared with the experimental results. The calculated total core losses are about 19% lower than the tested results. Various possible causes for this discrepancy are discussedMaster of Engineering (Hons)
17
Peng, Hongxuan. "Numerical computation of multi-hull ship resistance and motion". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp05/NQ63482.pdf.
Testo completo
18
Lanzoni, J. "Numerical computation of resonances and pseudospectra in acoustic scattering". Thesis, University College London (University of London), 2016. http://discovery.ucl.ac.uk/1474317/.
Testo completoAbstract (sommario):
Acoustic scattering is a well-known physical phenomenon which arises in a wide range of fields: when acoustic waves propagating in a medium impinge on a localised non-uniformity, such as a density fluctuation or an external obstacle, their trajectories are deviated and scattered waves are generated. A key role in scattering theory is played by resonances; these are particular scatterer-dependent non-physical ‘complex’ frequencies at which acoustic scattering exhibits exceptional behaviour. The study of acoustic resonances for a particular scatterer provides an insight in the behaviour that the acoustic scattering assumes at the near physical ‘real’ frequencies, and it is a fundamental step in many applications. Yet, the numerical computation of resonances and pseudospectra - a mathematical tool which can be used to study the influence of resonances on physical frequencies - remains very expensive. With the present Thesis we want to address this particular problem, by proposing numerical algorithms based on the Boundary Element Method (BEM) for computing resonances and pseudospectra and by analysing their efficiency and performance. Finally, we apply such algorithms to half a dozen of physically relevant scatterer, inspired from different fields where acoustic scattering plays a relevant role.
19
Norton, Richard. "Numerical computation of band gaps in photonic crystal fibres". Thesis, University of Bath, 2008. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.501623.
Testo completoAbstract (sommario):
Photonic crystal fibres are capable of special light guiding properties that ordinary optical fibres do not possess, and efforts have been made to numerically model these properties. The plane wave expansion method is one of the numerical methods that has been used. Unfortunately, the function that describes the material in the fibre n(x) is discontinuous, and convergence of the plane wave expansion method is adversely affected by this. For this reason, the plane wave expansion method may not be every applied mathematician’s first choice method but we will show that it is comparable in implementation and convergence to the standard finite element method. In particular,an optimal preconditioner for the system matrix A can easily be obtained and matrixvector products with A can be computed in O(N logN) operations (where N is the size of A) using the Fast Fourier Transform. Although we are always interested in the efficiency of the method, the main contribution of this thesis is the development of convergence analysis for the plane wave expansion method applied to 4 different 2nd-order elliptic eigenvalue problems in R and R2 with discontinuous coefficients. To obtain the convergence analysis three issues must be confronted: regularity of the eigenfunctions; approximation error with respect to plane waves; and stability of the plane wave expansion method. We successfully tackle the regularity and approximation error issues but proving stability relies on showing that the plane wave expansion method is equivalent to a spectral Galerkin method, and not all of our problems allow this. However, stability is observed in all of our numerical computations. It has been proposed in [40], [53], [63] and [64] that replacing the discontinuous coefficients in the problem with smooth coefficients will improve the plane wave expansion method, despite the additional error. Our convergence analysis for the method in[63] and [64] shows that the overall rate of convergence is no faster than before. To define A we need the Fourier coefficients of n(x), and sometimes these must be approximated, thus adding an additional error. We analyse the errors for a method where n(x) is sampled on a uniform grid and the Fourier coefficients are computed with the Fast Fourier Transform. We then devise a strategy for setting the grid-spacing that will recover the convergence rate of the plane wave expansion method with exact Fourier coefficients.
20
Koyyapu, Naresh Kumar. "Numerical Computation of Transient Response of 2D Wedge Impact". ScholarWorks@UNO, 2016. http://scholarworks.uno.edu/td/2260.
Testo completoAbstract (sommario):
The diverse applications of advanced marine craft ascribed to their high speed and technological advancements has led to the use of stronger and lighter metals in such crafts. High speed, in effect also increases slamming loads as higher speed increases frequency of wave encounter while operating in waves. The present study is limited to wedge impact models. Fundamentally, the study is thus about two-dimensional (2D) wedge impact in water. In an attempt to predict the structural response to impact hydrodynamic force, a beam element based finite element (FE) computer program is written and the results of the code are presented in the thesis. A computational tool is developed to predict the transient elastic response of a 2D wedge under impact force using two different numerical methods. Both explicit and implicit numerical schemes have also been studied in order to apply to the present work. Explicit forth order Runge-Kutta (RK4) method and implicit Newmark-b (NB) method have been used in the present work. Coupling effects between excitation and response are ignored in the present numerical computations. Both the numerical schemes are validated using simple static solution and also modal expansion technique.
21
Li, Zhou. "Numerical computation of core losses in permanent magnet machines". Thesis, View thesis, 2000. http://handle.uws.edu.au:8081/1959.7/284.
Testo completoAbstract (sommario):
This thesis presents a study on core loss calculations in rotating electrical machines. The basic concepts concerning magnetic moments, ferromagnetism, magnetic domains and magnetic hysteresis are introduced. The three-term models for alternating and rotational core losses in electrical steel sheets are presented. Several core loss measurement techniques are reviewed and an experiment is carried out to measure the total core losses in an electrical sheet steel sample under alternating and rotational magnetic fields of various frequencies and amplitudes. The coefficients in the loss models for alternating and rotational core losses are obtained through curve fitting process. The theory of electromagnetic fields is presented through the Maxwell equations and field scalar equations. A detailed review on core loss models for rotating electrical machines is presented. A rotational core loss model is adopted to calculate the core losses in a PM motor. The total core loss in the PM motor is obtained by summing the element losses using a MATLAB program. An experiment is conducted to measure the total core loss in the PM motor. The calculated total core loss in the PM motor is compared with the experimental results. The calculated total core losses are about 19% lower than the tested results. Various possible causes for this discrepancy are discussed
22
Li, Zhou. "Numerical computation of core losses in permanent magnet machines /". View thesis, 2000. http://library.uws.edu.au/adt-NUWS/public/adt-NUWS20030901.113715/index.html.
Testo completoAbstract (sommario):
Thesis (M.Sc (Hons)) -- University of Western Sydney, Nepean, 2000."Submitted for the degree of Master of Engineering (Hons), School of Mechatronic, Computer & Electrical Engineering, University of Western Sydney, Nepean" Includes bibliographical references (leaves 107-114).
23
Dyson, Peter. "Numerical computation of fluid properties at nano/meso scales". Thesis, Swansea University, 2006. https://cronfa.swan.ac.uk/Record/cronfa42784.
Testo completoAbstract (sommario):
Engineering systems are increasingly being developed with dimensions within the micro to nano scale. Mature simulation schemes are available for large scale systems (> 0.5mum) in the form of continuum mechanics, and for small scale systems (< 50nn). However, there is to simulation scheme that covers the middle, meso scale, range between them. The work presented in this thesis focuses on the development of a computational framework focused on fluid systems on the nano- meso scale, with characteristic dimensions between 50nm and 500nm. Existing methods approach the meso scale either with approximated molecular behaviour from the 'top down', or directly modelling molecular physics from the 'bottom up'. Top down approaches have the disadvantage of only including known behaviour with some statistical variations to approximate chaotic behavior. Bottom up approaches model the fluid from a molecular physics model, but fail to capture bulk fluid behaviour and are computationally expensive. The approach developed in this thesis, covers the middle ground between continuum and molecular simulation scales. A molecular physics model is used to govern the behaviour of the fluid, and is surrounded by a set of meso scale boundary conditions, providing an accurate and efficient fluid model. Bulk fluid behaviour is extracted in the form of ensemble property distributions in a versatile grid-like implementation, allowing the fluid properties to be calculated from first principles accurately and efficiently. Each part of the developed method is validated separately. The physics model is compared with published results of simulations at molecular scales, as there is insufficient information for meso scale fluid systems. The bulk ensemble property collection scheme is fully explored by means of a parametric study. Case studies are presented to highlight how bulk fluid properties, such as velocity, temperature and pressure, can be examined as distributions in time and space over the flow field in channel flow systems. The approach developed in this thesis opens the door to accurate and efficient meso scale fluid simulation. This work has also identified the next step to widen and improve the abilities for meso scale fluids to be fully investigated.
24
Motamed, Mohammad. "Topics in Analysis and Computation of Linear Wave Propagation". Doctoral thesis, Stockhollm : Numerical Analysis, Kungliga tekniska högskolan, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4715.
Testo completo
25
Geçgel, Murat. "Parallel, navier-stokes computation of the flowfield of a hovering helicopter rotor". Ankara : METU, 2003. http://etd.lib.metu.edu.tr/upload/12604807/index.pdf.
Testo completoAbstract (sommario):
Thesis (M.S.)--Middle East Technical University, 2003.Keywords: Rotary wing, thin₆layer Navier₆Stokes equations, finite volume method, structured grid, parallel processing, MPI, blade₆vortex interactions, flat plate.
26
Sakajo, Takashi. "Numerical Computation of three-dimensional vortex sheet with swirl flow". 京都大学 (Kyoto University), 1999. http://hdl.handle.net/2433/181452.
Testo completo
27
Al-Awadi, Huda. "Efficient numerical computation of the dynamics of a spherical bubble". Thesis, University of Brighton, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.341282.
Testo completo
28
Zhao, Shouqi. "Dependent risk modelling and ruin probability : numerical computation and applications". Thesis, City University London, 2014. http://openaccess.city.ac.uk/13702/.
Testo completoAbstract (sommario):
In this thesis, we are concerned with the finite-time ruin probabilities in two alternative dependent risk models, the insurance risk model and the dual risk model, including the numerical evaluation of the explicit expressions for these quantities and the application of the probabilistic results obtained. We first investigate the numerical properties of the formulas for the finite-time ruin probability derived by Ignatov and Kaishev (2000, 2004) and Ignatov et al. (2001) for a generalized insurance risk model allowing dependence. Efficient numerical algorithms are proposed for computing the ruin probability with a prescribed accuracy in order to facilitate the following studies. We then propose a new definition of alarm time in the insurance risk model, which generalizes that of Das and Kratz (2012), expressed in terms of the joint distribution of the time to ruin and the deficit at ruin. The alarm time is devised to warn that the future ruin probability within a finite-time window has reached a pre-specified critical level and capital injection is required. Due to our definition, the implementation of the alarm time highly relies on the computation of the finite-time ruin probability, which utilizes the previous results on computing the ruin probability with a prescribed accuracy. The results of the ruin probability and the alarm time are then transferred nicely to a generalized dual risk model, whose name stems from its duality to the insurance risk model, through an enlightening link established between the two risk models. Finally, based on the two alternative risk models, we introduce a framework for analyzing the risk of systems failure based on estimating the failure probability, and illustrate how the probabilistic models and results obtained can be applied as risk analytic tools in various practical risk assessment situations, such as systems reliability, inventory management, flood control via dam management, infection disease spread and financial insolvency.
29
Song, Weihong. "A real space approach to LEED computation with flexible local mesh refinement". Click to view the E-thesis via HKUTO, 2004. http://sunzi.lib.hku.hk/hkuto/record/B39849004.
Testo completo
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Song, Weihong, e 宋慰鴻. "A real space approach to LEED computation with flexible local mesh refinement". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2004. http://hub.hku.hk/bib/B39849004.
Testo completo
31
Onoufriou, Andros. "The numerical computation of wall shear stress with applications in stenosis". Thesis, University of Hertfordshire, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.485945.
Testo completoAbstract (sommario):
Numerical investigations have been carried out for steady flow through an idealised model of an arterial stenosis at physiological Reynolds numbers of500 and 2000 using the large-eddy simulation turbulence methodology and quantitative comparisons have been made with published experimental data. The results indicate that the largeeddy simulation, methodology is suitable for modelling arterial stenosis flows, which reinforces other published work that came to the same conclusion but from a purely qualitative perspective. Moreover, investigations into simpler, classical, problems in the field ofseparated flows, exhibiting similar behaviour to arterial stenosis flows, e.g. confined jet flow through a sudden expansion, have highlighted inaccuracies in an existing publication ofthe Journal ofFluid Mechanics. Our work has revealed that the experimental data, pertaining to the steady confined jet flow through a symmetric sudden expansion, contained in the aforementioned paper, is erroneous and should not be used for comparison with other experimental or numerical results. For over two decades this paper has never been challenged despite the inaccuracies contained therein. Furthermore, higher-order one-sided finite-difference formulae for the approximation ofvelocity gradients and therefore wall shear stresses have been developed for nonuniform grids. It is shown by application to plane-Poiseuille flow, that the 3-point formula yields greater accuracy than the, often used, 2-point formula.
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Austin, Anthony P. "Some new results on, and applications of, interpolation in numerical computation". Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:11c16937-4a59-494d-a06f-6d27b634e2f3.
Testo completoAbstract (sommario):
This thesis discusses several topics related to interpolation and how it is used in numerical analysis. It begins with an overview of the aspects of interpolation theory that are relevant to the discussion at hand before presenting three new contributions to the field. The first new result is a detailed error analysis of the barycentric formula for trigonometric interpolation in equally-spaced points. We show that, unlike the barycentric formula for polynomial interpolation in Chebyshev points (and contrary to the main view in the literature), this formula is not always stable. We demonstrate how to correct this instability via a rewriting of the formula and establish the forward stability of the resulting algorithm. Second, we consider the problem of trigonometric interpolation in grids that are perturbations of equally-spaced grids in which each point is allowed to move by at most a fixed fraction of the grid spacing. We prove that the Lebesgue constant for these grids grows at a rate that is at most algebraic in the number of points, thus answering questions put forth by Trefethen and Weideman about the robustness of numerical methods based on trigonometric interpolation in points that are uniformly distributed but not equally-spaced. We use this bound to derive theorems about the convergence rate of trigonometric interpolation in these grids and also discuss the related question of quadrature. Specifically, we prove that if a function has V ≥ 1 derivatives, the Vth of which is Hölder continuous (with a Hölder exponent that depends on the size of the maximum allowable perturbation), then the interpolants converge uniformly to the function at an algebraic rate; larger values of V lead to more rapid convergence. A similar statement holds for the corresponding quadrature rule. We also consider what analogue, if any, there is for trigonometric interpolation of the famous 1/4 theorem of Kadec from sampling theory that restricts the size of the perturbations one can make to the integers and still be guaranteed to have a set of stable sampling for the Paley-Wiener space. We present numerical evidence suggesting that in the discrete case, the 1/4 threshold takes the form of a threshold for the boundedness of a "2-norm Lebesgue constant" and does not appear to have much significance in practice. We believe that these are the first results regarding this problem to appear in the literature. While we do not believe the results we establish are the best possible quantitatively, they do (rigorously) capture the main features of trigonometric interpolation in perturbations of equally-spaced grids. We make several conjectures as to what the optimal results may be, backed by extensive numerical results. Finally, we consider a new application of interpolation to numerical linear algebra. We show that recently developed methods for computing the eigenvalues of a matrix by dis- cretizing contour integrals of its resolvent are equivalent to computing a rational interpolant to the resolvent and finding its poles. Using this observation as the foundation, we develop a method for computing the eigenvalues of real symmetric matrices that enjoys the same advantages as contour integral methods with respect to parallelism but employs only real arithmetic, thereby cutting the computational cost and storage requirements in half.
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Albaiz, Abdulaziz (Abdulaziz Mohammad). "MPI-based scalable computing platform for parallel numerical application". Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/95562.
Testo completoAbstract (sommario):
Thesis: S.M., Massachusetts Institute of Technology, Computation for Design and Optimization Program, 2014.Cataloged from PDF version of thesis.
Includes bibliographical references (page 61).
Developing parallel numerical applications, such as simulators and solvers, involves a variety of challenges in dealing with data partitioning, workload balancing, data dependencies, and synchronization. Many numerical applications share the need for an underlying parallel framework for parallelization on multi-core/multi-machine hardware. In this thesis, a computing platform for parallel numerical applications is designed and implemented. The platform performs parallelization by multiprocessing over MPI library, and serves as a layer of abstraction that hides the complexities in dealing with data distribution and inter-process communication. It also provides the essential functions that most numerical application use, such as handling data-dependency, workload-balancing, and overlapping communication and computation. The performance evaluation of the parallel platform shows that it is highly scalable for large problems.
by Abdulaziz Albaiz.
S.M.
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Xiao, Qinwen. "Optimizing beer distribution game order policy using numerical simulations". Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/55081.
Testo completoAbstract (sommario):
Thesis (S.M.)--Massachusetts Institute of Technology, Computation for Design and Optimization Program, 2009.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 63-64).
One of the major challenges in supply chain management is the level of information availability. It is very hard yet important to coordinate each stage in the supply chain when the information is not centralized and the demand is uncertain. In this thesis, I analyzed the bullwhip effect in supply chain management using the MIT Beer Distribution Game. I also proposed heuristics and models to optimize the MIT Beer Distribution Game order policy when the customer's demand is both known and unknown. The proposed model provides each player with an order policy based on how many weeks of inventory the player needs to keep ahead to minimize the global cost of the supply chain. The optimized order policy is robust, practical, and generated by numerical simulations. The model is applied in a number of experiments involving deterministic and random demand and lead time. The simulation results of my work are compared with two other artificial agent algorithms, and the improvements brought by my results are presented and analyzed.
by Qinwen Xiao.
S.M.
35
Alhubail, Maitham Makki (Maitham Makki Hussain). "A thread-based parallel programming library for numerical algorithms". Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/90080.
Testo completoAbstract (sommario):
Thesis: S.M., Massachusetts Institute of Technology, Computation for Design and Optimization Program, 2014.Cataloged from PDF version of thesis.
Includes bibliographical references (page 47).
This thesis presents a new simple lightweight C++ thread based parallelization library, intended for use in numerical algorithms. It provides simple multitasking and task synchronization functions. The library hides all internal system calls from the developer and utilizes thread pooling to provide better performance and utilization of system time and resources. The library is lightweight and platform independent, and has been tested on Linux, and Windows. Experiments were conducted to verify the proper functionality of the library and to show that parallelized algorithms on a single machine are more efficient than using the Message Passing Interface (MPI) using shared memory. In the opinion of several researchers who have used this library, the parallelized code is more easily understood and debugged than MPI. The results of initial experiments show that algorithms are as efficient or better than those using MPI.
by Maitham Makki Alhubail.
S.M.
36
Harb, Ammar. "Discrete Stability of DPG Methods". PDXScholar, 2016. http://pdxscholar.library.pdx.edu/open_access_etds/2916.
Testo completoAbstract (sommario):
This dissertation presents a duality theorem of the Aubin-Nitsche type for discontinuous Petrov Galerkin (DPG) methods. This explains the numerically observed higher convergence rates in weaker norms. Considering the specific example of the mild-weak (or primal) DPG method for the Laplace equation, two further results are obtained. First, for triangular meshes, the DPG method continues to be solvable even when the test space degree is reduced, provided it is odd. Second, a non-conforming method of analysis is developed to explain the numerically observed convergence rates for a test space of reduced degree. Finally, for rectangular meshes, the test space is reduced, yet the convergence is recovered regardless of parity.
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Hurley, Robert C. "Computation of monopole antenna currents using cylindrical harmonic expansions". Thesis, Monterey, California. Naval Postgraduate School, 1988. http://hdl.handle.net/10945/22966.
Testo completoAbstract (sommario):
Approved for public release; distribution is unlimitedThis thesis investigates the viability of a new method for numerically computing the input impedance and the currents on simple antenna structures. This technique considers the antenna between two ground planes and uses multiregion cylindrical harmonic expansions with tangential field continuity to obtain the surface currents and input impedance. The computed results are compared to the results obtained from the Numerical Electromagnetics Code for various physical parameters to assess computational accuracy.
http://archive.org/details/computationofmon00hurl
Lieutenant, United States Navy
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Beattie, Bridget Joan Healy. "The use of libraries for numerical computation in distributed memory MIMD systems". Thesis, University of Liverpool, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.266172.
Testo completo
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Xie, Lutao. "Numerical approaches to optimize dispatch on microgrids with energy storage". Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/104567.
Testo completoAbstract (sommario):
Thesis: S.M., Massachusetts Institute of Technology, Computation for Design and Optimization Program, 2016.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 49-50).
Microgrids and distributed generation are predicted to become extremely dominant in developing nations, and will be largely beneficial to both electricity suppliers and consumers. With the penetration of renewable energy into the electricity supply, to maintain a balance between power supply and demand is becoming more difficult. Nevertheless, it is quite feasible that large electrical storage systems such as batteries can efficiently mitigate problems caused by the intermittency of renewables, and thus enable stable adoption of such power sources. In order to understand how the energy capacity and power characteristics of batteries should be specified to optimize economic or socioeconomic benefits, an optimizing strategy for battery usage in microgrids energy scheduling was constructed. This strategy is based on the past power consumption, predictions of day-ahead power consumption, and historical trends of seasonal and daily trends, which gives a nonlinear, discontinuous and high dimensional objective function. Optimizing such an objective function is found to be very computational intensive and complex. In this paper, the nature of this large-scale optimization problem is studied. For real time dispatch, four optimization methods including active-set, interior-point method, sequential quadratic programming (SQP) and trust-region-reflective are discussed and compared to find the relatively fast and robust optimization algorithm. The computation was implemented by using the MATLAB nonlinear programming solver 'fmincon'. Three main objectives are carried out to improve the efficiency of solving this optimization problem: (1) determination of the mathematical& physical definitions of tolerances and discussion on convergence criteria with the corresponding tolerances; (2) Study and comparison on influences of the initial condition and the behavior of the objective function (highly related to peak demand charge); and (3) suggestions on modification of the model to achieve reduction of the computation time whilst maintain acceptable accuracy.
by Lutao Xie.
S.M.
40
Nikram, Elham. "Three essays on game theory and computation". Thesis, University of Exeter, 2016. http://hdl.handle.net/10871/28755.
Testo completoAbstract (sommario):
The results section of my thesis includes three chapters. The first two chapters are on theoretical game theory. In both chapters, by mathematical modelling and game theoretical tools, I am predicting the behaviour of the players in some real world issues. Hoteling-Downs model plays an important role in the modern political interpretations. The first chapter of this study investigates an extension of Hoteling-Downs model to have multi-dimensional strategy space and asymmetric candidates. Chapter 3 looks into the inspection game where the inspections are not the same in the series of sequential inspections. By modelling the game as a series of recursive zero-sum games I find the optimal strategy of the players in the equilibrium. The forth chapter investigates direct optimization methods for large scale problems. Using Matlab implementations of Genetic and Nelder-Mead algorithms, I compare the efficiency and accuracy of the most famous direct optimization methods for unconstraint optimization problems based on differing number of variables.
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Chan, Chun Tat. "Computation of flows by the finite volume method as applied to unstructured meshes". Thesis, Imperial College London, 1997. http://hdl.handle.net/10044/1/7653.
Testo completo
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Kedia, Kushal Sharad. "Numerical simulations of perforated plate stabilized premixed flames with detailed chemistry". Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/61793.
Testo completoAbstract (sommario):
Thesis (S.M.)--Massachusetts Institute of Technology, Computation for Design and Optimization Program, 2010.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (p. 83-86).
The objective of this work is to develop a high efficiency two-dimensional reactive flow solver to investigate perforated-plate stabilized laminar premixed flames. The developed code is used to examine the impact of the operating conditions and the perforated plate design on the steady flame characteristics. It is also used to numerically investigate the response of these flames to imposed inlet velocity perturbations. The two-dimensional simulations are performed using a reduced chemical kinetics mechanism for methane-air combustion, consisting of 20 species and 79 reactions. Heat exchange is allowed between the gas mixture and the solid plate. The physical model is based on a zero-Mach-number formulation of the axi-symmetric compressible conservation equations. The steady results suggest that the flame consumption speed, the flame structure, and the flame surface area depend significantly on the equivalence ratio, mean inlet velocity, the distance between the perforated plate holes and the plate thermal conductivity. In the case of an adiabatic plate, a conical flame is formed, anchored near the corner of the hole. When the heat exchange between the mixture and the plate is finite, the flame acquires a Gaussian shape stabilizing at a stand-off distance, that grows with the plate conductivity. The flame tip is negatively curved; i.e. concave with respect to the reactants. Downstream of the plate, the flame base is positively curved; i.e. convex with respect to the reactants, stabilizing above a stagnation region established between neighboring holes. As the plate's thermal conductivity increases, the heat flux to the plate decreases, lowering its top surface temperature. As the equivalence ratio increases, the flame moves closer to the plate, raising its temperature, and lowering the flame stand-off distance. As the mean inlet velocity increases, the flame stabilizes further downstream, the flame tip becomes sharper, hence raising the burning rate at that location. The curvature of the flame base depends on the distance between the neighboring holes; and the flame there is characterized by high concentration of intermediates, like carbon monoxide. To investigate flame dynamics, linear transfer functions, for low mean inlet velocity oscillations, are analyzed for different equivalence ratio, mean inlet velocity, plate thermal conductivity and distance between adjacent holes. The oscillations of the heat exchange rate at the top of the burner surface plays a critical role in driving the growth of the perturbations over a wide range of conditions, including resonance. The flame response to the perturbations at its base takes the form of consumption speed oscillations in this region. Flame stand-off distance increases/decreases when the flame-wall interaction strengthens/weakens, impacting the overall dynamics of the heat release. The convective lag between the perturbations and the flame base response govern the phase of heat release rate oscillations. There is an additional convective lag between the perturbations at the flame base and the flame tip which has a weaker impact on the heat release rate oscillations. At higher frequencies, the flame-wall interaction is weaker and the heat release oscillations are driven by the flame area oscillations. The response of the flame to higher amplitude oscillations are used to gain further insight into the mechanisms. Key words: Laminar premixed flames, perforated-plate stabilized flames, flame-wall interactions, flame consumption speed, stand-off distance.
by Kushal Sharad Kedia.
S.M.
43
Li, Zhen. "Numerical computation of an optimal control problem with homogenization in one-dimensional case". [Ames, Iowa : Iowa State University], 2008.
Cerca il testo completo
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Kropf, Everett. "Numerical computation of Schwarz-Christoffel transformations and slit maps for multiply connected domains". Diss., Wichita State University, 2012. http://hdl.handle.net/10057/5361.
Testo completoAbstract (sommario):
Two methods for the numerical conformal mapping of domains with m < ∞ separated
circular holes to domains with m polygonal holes are presented; bounded and unbounded
domains are both considered. The methods are based on extensions of the classical Schwarz-
Christo el transformation to nitely connected domains. The rst method uses a truncated
in nite product expressed in terms of re
ections through circles, and is found to have a
computational time which increases geometrically with the number of levels of re
ection
used. The second method uses the boundary behavior of the map to construct a linear system
which gives the coe cients of a Laurent series expansion for the map. The second method
has a computational time which is polynomial with the number of terms of the truncated
series. Both methods require the solution of a non-linear system of equations which gives the
correct parameters for the desired map. The solution to the non-linear system is achieved
by a numerical continuation (homotopy) method. An application is given. Maps from the
circle domains to the canonical slit domains are also computed using similar techniques.Thesis (Ph.D.)--Wichita State University, College of Liberal Arts and Sciences, Dept. of Mathematics, Statistics and Physics
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Liu, Yang, e Ziyu Wang. "The Numerical Computation Method of Physical Quantity of Dust Concentration Based on Matlab". Thesis, Högskolan i Gävle, Avdelningen för elektronik, matematik och naturvetenskap, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:hig:diva-19149.
Testo completoAbstract (sommario):
With the rapid development of the industry all over the world, the consumption of fossil fuel of human activities has reached an extremely high level which result in an incredible dust emission level nowadays. As one of the major environment challenges today, dust pollution has become a vital issue that the human beings have to face and resolve. To tackle the dust pollution problem, a reliable measurement of the dust concentration level is essential. In recent years, methods with different principles are used to detect the dust concentration have been developed. The methods developed based on the scattering principle and the extinction principle for dust concentration measurement have a series of virtues such as high measurement speed, excellent precision and can be useful for real time monitoring. This thesis reviewed the popular theories that are applied in the field which are light scattering (Mie theory) and light extinction (Lambert-beer theory). Matlab simulation is used to verify the possibility of the determined physical quantities related to the concentration measurement in the theory analysis. A new method using the ratio of scattering intensity and extinction intensity is discussed in this thesis providing a more accurate result eliminating the drawbacks of the scattering method and the extinction method.
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KASSAR, BRUNO DE BARROS MENDES. "NUMERICAL SIMULATION OF MULTIPHASE FLOWS WITH ENHANCED CURVATURE COMPUTATION BY POINT-CLOUD SAMPLING". PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2016. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=27512@1.
Testo completoAbstract (sommario):
PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROCOORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
PROGRAMA DE EXCELENCIA ACADEMICA
Volume of Fluid (VOF) é um método amplamente empregado na predição de escoamentos multifásicos devido à sua simplicidade, boas características de conservação de massa e natural tratamento de interfaces topologicamente complexas. No entanto, para escoamentos dominados por tensão interfacial, a literatura tem mostrado que a precisão nas estimativas da tensão interfacial ainda é um problema em questão, que pode levar a correntes parasíticas e previsão imprecisa da condição de salto de pressão através das interfaces. Isto ocorre principalmente devido às variações abruptas do campo de fração volumétrica através das interfaces, que leva a imprecisão no cálculo das curvaturas interfaciais. Portanto, diferentes abordagens têm sido apresentadas para mitigar este problema, incluindo funções-altura, suavização da fração volumétrica, ajuste parabólico, entre outros. Este trabalho propõe uma nova abordagem para estimativa de curvatura em VOF, mas não limitado a este, que lança uma nova luz a este problema persistente. A ideia é amostrar a interface por nuvens de pontos e normais na isosuperfície de nível 0.5 do campo de fração volumétrica e calcular a curvatura para cada ponto da nuvem por uma técnica de Computação Gráfica (ajuste de normais). As curvaturas são, então, projetadas na malha Euleriana de maneira tal como no método Front-Tracking. O novo método foi implementado no código padrão de VOF do OpenFOAM (interFoam) resultando em melhorias nas estimativas de salto de pressão e em significativa redução das correntes espúrias. Simulações numéricas foram realizadas e resultados comparados a dados de referência demonstrando a viabilidade da ideia.
Volume of Fluid (VOF) is a widely employed method for multiphase flows prediction for its simplicity, good mass conservation characteristics and natural handling of topologically complex interfaces. For surface tension dominated flows, however, literature has shown that accuracy in surface tension estimations is still an issue, what may cause parasitic currents and inaccurate prediction of pressure jump condition across interfaces. It occurs mainly due to abrupt changes in the volume fraction field across the interfaces, which takes to inaccurate estimates of interfacial curvatures. Therefore, different approaches have been proposed to mitigate this problem including height-functions, volume fraction smoothing, parabolic fittings, among others. This work proposes a novel approach for curvature estimation in VOF, but not limited to it, that sheds a new light on this persistent problem. The idea is to sample the interfaces with clouds of points and normals at the 0.5 level isosurface of the volume fraction field and to compute the curvature for each point of the cloud by a Computer Graphics technique (normal fitting). The curvatures are then projected onto the Eulerian grid in a Front-Tracking fashion. The new method was implemented in the standard OpenFOAM VOF solver (interFoam) resulting in improvements on the pressure jump estimations and in significant reduction of spurious currents. Numerical simulations were performed and results compared to benchmark data showing the feasibility of the idea.
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Michel, Florence. "Transient numerical computation of the temperature of the electronic equipment in passengers cars". Valenciennes, 2009. http://ged.univ-valenciennes.fr/nuxeo/site/esupversions/0c0e0027-679d-4983-a115-263443a25c8a.
Testo completoAbstract (sommario):
Afin d’assurer la fiabilité des composants électroniques d’un véhicule, leur situation thermique est évaluée successivement à chaque phase du processus de développement. En particulier, il s’agit d’estimer la durée pendant laquelle le système électronique travaille dans son régime optimal de température, alors qu’il est soumis à des conditions de fonctionnement critiques. Pour le calcul de sa température dans des conditions de charge thermique instationnaires, différents modèles numériques et méthodes de simulation ont été développés et validés dans l’étude présente. Dans une première partie, deux stratégies innovatrices de couplage de codes pour le calcul des différents modes de transfert sont proposées, selon les conditions limites convectives, à partir d’une analyse de système. Pour réduire le temps de calcul dans le processus de développement, l’écoulement convectif est calculé avec une approche stationnaire. Dans la deuxième partie, plusieurs modèles numériques pour le calcul du mode de transfert convectif sont examinés sur des cas test, et vérifiés en comparaison avec la littérature, en particulier avec une analyse du maillage et des modèles de turbulence. Dans la troisième et dernière partie, les stratégies de co-simulation sont vérifiées pour deux systèmes électroniques complexes, d’une part une batterie au plomb assemblée dans une cavité de roue de secours, et d’autre part un amplificateur audio placé dans une cavité située entre le compartiment moteur et la cabine. Finalement, l’efficacité et la fiabilité de chacune des stratégies de co-simulation sont discutées en considérant l’implémentation dans le processus de développement digitalIn order to ensure a reliable operation of the electronic devices of a passenger car, its thermal situation is successively evaluated during each phase of the development process. Of particular interest is to predict the time period, during which the electronic system works within its optimal temperature range, while it is subjected to critical operating conditions. In order to compute its temperature under time-dependent thermal loads, different numerical models and computational methods have been developed and validated in the present study. In a first part, several innovative coupling codes strategies for the computation of the different heat transfer modes are proposed according to the convection boundary conditions and based on a system analysis. For reasonable computing times in the development process, a steady-state approach is used to solve the convective flow. In a second part, numerical models for the computation of the convective heat transfer mode are examined with test cases, in particular in view of mesh requirements and turbulence modeling, and verified in comparison with literature. In the third and last part, the co-simulation strategies are verified by means of two complex electronic systems, on the one hand a lead-acid battery situated in a spare-wheel cavity, on the other hand a sound amplifier assembled in cavity located between the engine compartment and the cabin. Finally, the efficiency and the reliability of both co-simulation strategies are discussed for implementation in the digital development process
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Michel, Florence. "Transient numerical computation of the temperature of the electronic equipment in passenger cars". Göttingen Cuvillier, 2009. http://d-nb.info/1000128997/04.
Testo completo
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Alvarez, Vicente. "A numerical computation of eigenfunctions for the Kusuoka Laplacian on the Sierpinski gasket". Diss., UC access only, 2009. http://proquest.umi.com/pqdweb?index=10&did=1874451711&SrchMode=1&sid=4&Fmt=2&VInst=PROD&VType=PQD&RQT=309&VName=PQD&TS=1270059102&clientId=48051.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--University of California, Riverside, 2009.Includes abstract. Includes bibliographical references (leaves 92-93). Issued in print and online. Available via ProQuest Digital Dissertations.
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Mangoubi, Claude. "Analytical and numerical problems in the computation of the flow of viscoelastic fluids". E-thesis Full text, 2008. http://shemer.mslib.huji.ac.il/dissertations/W/JMC/001491630.pdf.
Testo completo