Results 1  10
of
244
Functional Phonology  Formalizing the interactions between articulatory and perceptual drives
, 1998
"... ..."
Flows on Surfaces of Arbitrary Topology
, 2003
"... In this paper we introduce a method to simulate fluid flows on smooth surfaces of arbitrary topology: an effect never seen before. We achieve this by combining a twodimensional stable fluid solver with an atlas of parametrizations of a CatmullClark surface. The contributions of this paper are: (i) ..."
Abstract

Cited by 94 (0 self)
 Add to MetaCart
In this paper we introduce a method to simulate fluid flows on smooth surfaces of arbitrary topology: an effect never seen before. We achieve this by combining a twodimensional stable fluid solver with an atlas of parametrizations of a CatmullClark surface. The contributions of this paper are: (i) an extension of the Stable Fluids solver to arbitrary curvilinear coordinates, (ii) an elegant method to handle crosspatch boundary conditions and (iii) a set of new external forces custom tailored for surface flows. Our techniques can also be generalized to handle other types of processes on surfaces modeled by partial differential equations, such as reactiondiffusion. Some of our simulations allow a user to interactively place densities and apply forces to the surface, then watch their effects in realtime. We have also computed higher resolution animations of surface flows offline.
Stateoftheart of Vehicular Traffic Flow Modelling
 Delft University of Technology, Delft, The
, 2001
"... Nowadays traffic flow and congestion is one of the main societal and economical problems related to transportation in industrialised countries. In this respect, managing traffic in congested networks requires a clear understanding of traffic flow operations. That is, insights into what causes conge ..."
Abstract

Cited by 87 (1 self)
 Add to MetaCart
Nowadays traffic flow and congestion is one of the main societal and economical problems related to transportation in industrialised countries. In this respect, managing traffic in congested networks requires a clear understanding of traffic flow operations. That is, insights into what causes congestion, what determines the time and location of traffic breakdown, how does the congestion propagate through the network, etc., are essential. For this purpose, during the past fifty years, a wide range of traffic flow theories and models have been developed to answer these research questions. This paper presents a overview of some fifty years of modelling vehicular traffic flow. A rich variety of modelling approaches developed so far and in use today will be discussed and compared. The considered models are classified based on the levelofdetail with which the vehicular flow is described. For each of the categories, issues like modelling accuracy, applicability, generalisability, and model calibration and validation, are discussed.
Verification, validation and predictive capability in computational engineering and physics
 Hopkins University
, 2002
"... Computer simulations of physical processes are being relied on to an increasing degree for design, performance, reliability, and safety of engineered systems. Computational analyses have addressed the operation of systems at design conditions, offdesign conditions, and accident scenarios. For examp ..."
Abstract

Cited by 49 (3 self)
 Add to MetaCart
(Show Context)
Computer simulations of physical processes are being relied on to an increasing degree for design, performance, reliability, and safety of engineered systems. Computational analyses have addressed the operation of systems at design conditions, offdesign conditions, and accident scenarios. For example, the safety aspects of products or systems can represent an important, sometimes dominant, element of numerical simulations. The potential legal and liability costs of hardware failures can be staggering to a company, the environment, or the public. This consideration is especially crucial, given that we may be interested in highconsequence systems that cannot ever be physically tested, including the catastrophic failure of a fullscale containment building for a nuclear power plant, explosive damage to a highrise office building, ballistic missile defense systems, and a nuclear weapon involved in a transportation accident. Developers of computer codes, analysts who use the codes, and decision makers who rely on the results of the analyses face a critical question: How should confidence in modeling and simulation be critically assessed? Verification and validation (V&V) of computational simulations are the primary methods for building and quantifying this confidence. Briefly, verification is the assessment of the accuracy of the solution to a computational model. Validation is the assessment
Algebraic flux correction I. Scalar conservation laws. Chapter 6 in the first edition of this book
, 2005
"... Abstract This chapter is concerned with the design of highresolution finite element schemes satisfying the discrete maximum principle. The presented algebraic flux correction paradigm is a generalization of the fluxcorrected transport (FCT) methodology. Given the standard Galerkin discretization ..."
Abstract

Cited by 45 (23 self)
 Add to MetaCart
(Show Context)
Abstract This chapter is concerned with the design of highresolution finite element schemes satisfying the discrete maximum principle. The presented algebraic flux correction paradigm is a generalization of the fluxcorrected transport (FCT) methodology. Given the standard Galerkin discretization of a scalar transport equation, we decompose the antidiffusive part of the discrete operator into numerical fluxes and limit these fluxes in a conservative way. The purpose of this manipulation is to make the antidiffusive term local extremum diminishing. The available limiting techniques include a family of implicit FCT schemes and a new linearitypreserving limiter which provides a unified treatment of stationary and timedependent problems. The use of Anderson acceleration makes it possible to design a simple and efficient quasiNewton solver for the constrained Galerkin scheme. We also present a linearized FCT method for computations with small time steps. The numerical behavior of the proposed algorithms is illustrated by a grid convergence study for convectiondominated transport problems and anisotropic diffusion equations. 1
Globalized Newton–Krylov–Schwarz algorithms and software for parallel implicit CFD
 Int. J. High Perform. Comput. Appl
"... Implicit solution methods are important in applications modeled by PDEs with disparate temporal and spatial scales. Because such applications require high resolution with reasonable turnaround, parallelization is essential. The pseudotransient matrixfree NewtonKrylovSchwarz ( Y NKS) algorithmic ..."
Abstract

Cited by 44 (17 self)
 Add to MetaCart
(Show Context)
Implicit solution methods are important in applications modeled by PDEs with disparate temporal and spatial scales. Because such applications require high resolution with reasonable turnaround, parallelization is essential. The pseudotransient matrixfree NewtonKrylovSchwarz ( Y NKS) algorithmic framework is presented as a widely applicable answer. This article shows that for the classical problem of threedimensional transonic Euler flow about an M6 wing, Y NKS can simultaneously deliver globalized, asymptotically rapid convergence through adaptive pseudotransient continuation and Newton’s method; reasonable parallelizability for an implicit method through deferred synchronization and favorable communicationtocomputation scaling in the Krylov linear solver; and high per processor performance through attention to distributed memory and cache locality, especially through the Schwarz preconditioner. Two discouraging features of Y NKS methods are their sensitivity to the coding of the underlying PDE discretization and the large number of parameters that must be selected to govern convergence. The authors therefore distill several recommendations from their experience and reading of the literature on various algorithmic components of Y NKS, and they describe a freely available MPIbased portable parallel software implementation of the solver employed here. 1
A Positive FiniteDifference Advection Scheme
 J. Comput. Phys
, 1995
"... . This paper examines a class of explicit finitedifference advection schemes derived along the method of lines. An important application field is largescale atmospheric transport. The paper therefore focuses on the demand of positivity. For the spatial discretization, attention is confined to cons ..."
Abstract

Cited by 34 (8 self)
 Add to MetaCart
(Show Context)
. This paper examines a class of explicit finitedifference advection schemes derived along the method of lines. An important application field is largescale atmospheric transport. The paper therefore focuses on the demand of positivity. For the spatial discretization, attention is confined to conservative schemes using 5 points per direction. The 4th order central scheme and the family of schemes, comprising the 2nd order central, the 2nd order upwind and the 3rd order upwind biased, are studied. Positivity is enforced through flux limiting. It is concluded that the limited 3rd order upwind discretization is the best candidate from the four examined. For the time integration attention is confined to a number of explicit RungeKutta methods of orders 2 up to 4. With regard to the demand of positivity, these integration methods turn out to behave almost equally and no best method could be identified. A Positive FiniteDifference Advection Scheme 3 1 Introduction The subject of...
A minimum overlap restricted additive Schwarz preconditioner and applications in 3D flow simulations
 Contemporary Mathematics
, 1998
"... Numerical simulations of unsteady threedimensional compressible flow problems require the solution of large, sparse, nonlinear systems of equations arising from the discretization of Euler or NavierStokes equations on unstructured, possibly dynamic, meshes. In this ..."
Abstract

Cited by 27 (2 self)
 Add to MetaCart
(Show Context)
Numerical simulations of unsteady threedimensional compressible flow problems require the solution of large, sparse, nonlinear systems of equations arising from the discretization of Euler or NavierStokes equations on unstructured, possibly dynamic, meshes. In this
An Isobaric Fix for the Overheating Problem in Multimaterial Compressible Flows
 J. Computational Physics
, 1999
"... In many problems of interest, solid objects are treated as rigid bodies in compressible flowfields. When these solid objects interact with certain features of the compressible flowfield, inaccurate solutions may develop. In particular, the well known "overheating effect" occurs when a shoc ..."
Abstract

Cited by 26 (13 self)
 Add to MetaCart
(Show Context)
In many problems of interest, solid objects are treated as rigid bodies in compressible flowfields. When these solid objects interact with certain features of the compressible flowfield, inaccurate solutions may develop. In particular, the well known "overheating effect" occurs when a shock reflects off of a stationary solid wall boundary causing overshoots in temperature and density, while pressure and velocity remain constant (see e.g. [3, 7, 13, 14]). This "overheating effect" is more dramatic when compressible flows are coupled to moving solid objects (e.g. moving pistons), where the nonphysical density and temperature overshoots can be cumulative and lead to negative values. We consider the general class of material interface problems where numerical methods can predict pressure and velocity adequately, but fail miserably in their prediction of density and temperature. Motivated by both total variation considerations and physical considerations, we have developed a simple but gene...
Multistage Schemes with Multigrid for the Euler and NavierStokes Equations
 Volume I: Components and Analysis, NASA TP3631
, 1997
"... ..."