Conservation form of Helbing's fluid dynamic traffic flow model

A standard conservation form is derived in this paper.The hyperbolicity of Helbing＇s fluid dynamic traffic flow model is proved,which is essential to the general analytical and numerical study of this model.On the basis of this conservation form,a local discontinuous Galerkin scheme is designed to solve the resulting system efficiently.The evolution of an unstable equilibrium traffic state leading to a stable stop-and-go traveling wave is simulated.This simulation also verifies that the model is truly improved by the introduction of the modified diffusion coefficients,and thus helps to protect vehicles from collisions and avoide the appearance of the extremely large density.

A UNIFORMLY CONVERGENT SECOND ORDER DIFFERENCE SCHEME FOR A SINGULARLY PERTURBED SELF-ADJOINT ORDINARY DIFFERENTIAL EQUATION IN CONSERVATION FORM

In this paper, based on the idea of El-Mistikawy and Werle[1] we construct a difference scheme for a singularly perturbed self-adjoint ordinary differential equation in conservation form. We prove that it is a uniformly convergent second order scheme.

A HIGH ACCURACY DIFFERENCE SCHEME FOR THE SINGULAR PERTURBATION PROBLEM OF THE SECOND-ORDER LINEAR ORDINARY DIFFERENTIAL EQUATION IN CONSERVATION FORM

In this paper, combining the idea of difference method and finite element method, we construct a difference scheme for a self-adjoint problem in conservation form. Its solution uniformly converges to that of the original differential equation problem with order h3.

High‑Order ADER Discontinuous Galerkin Schemes for a Symmetric Hyperbolic Model of Compressible Barotropic Two‑Fluid Flows

This paper presents a high-order discontinuous Galerkin(DG)finite-element method to solve the barotropic version of the conservative symmetric hyperbolic and thermodynamically compatible(SHTC)model of compressible two-phase flow,introduced by Romenski et al.in[59,62],in multiple space dimensions.In the absence of algebraic source terms,the model is endowed with a curl constraint on the relative velocity field.In this paper,the hyperbolicity of the system is studied for the first time in the multidimensional case,showing that the original model is only weakly hyperbolic in multiple space dimensions.To restore the strong hyperbolicity,two different methodologies are used:(i)the explicit symmetrization of the system,which can be achieved by adding terms that contain linear combinations of the curl involution,similar to the Godunov-Powell terms in the MHD equations;(ii)the use of the hyperbolic generalized Lagrangian multiplier(GLM)curl-cleaning approach forwarded.The PDE system is solved using a high-order ADER-DG method with a posteriori subcell finite-volume limiter to deal with shock waves and the steep gradients in the volume fraction commonly appearing in the solutions of this type of model.To illustrate the performance of the method,several different test cases and benchmark problems have been run,showing the high order of the scheme and the good agreement when compared to reference solutions computed with other well-known methods.

Higher-dimensional integrable deformations of the modified KdV equation

The derivation of nonlinear integrable evolution partial differential equations in higher dimensions has always been the holy grail in the field of integrability.The well-known modified Kd V equation is a prototypical example of an integrable evolution equation in one spatial dimension.Do there exist integrable analogs of the modified Kd V equation in higher spatial dimensions?In what follows,we present a positive answer to this question.In particular,rewriting the(1+1)-dimensional integrable modified Kd V equation in conservation forms and adding deformation mappings during the process allows one to construct higher-dimensional integrable equations.Further,we illustrate this idea with examples from the modified Kd V hierarchy and also present the Lax pairs of these higher-dimensional integrable evolution equations.

A MODIFIED SIMPLE ALGORITHM FOR 2-D FLOW IN OPEN CHANNEL

For two-dimensional wa ter flow in open channel, by discritizing hydrodynamic differential equation of conservative form, the corresponding algebraic equations were derived which invo lve the relationship between velocity and depth. Based on the relationship, this paper deduced a modified formula of velocity correction for SIMPLE algorithm. A s a test case, the flow in a prismatic channel with two different slopes was com puted and a good result was obtained.

The Unified Coordinate System in Computational Fluid Dynamics

A fundamental issue in CFD is the role of coordinates and,in particular,the search for“optimal”coordinates.This paper reviews and generalizes the recently developed unified coordinate system(UC).For one-dimensional flow,UC uses a material coordinate and thus coincides with Lagrangian system.For two-dimensional flow it uses a material coordinate,with the other coordinate determined so as to preserve mesh othorgonality(or the Jacobian),whereas for three-dimensional flow it uses two material coordinates,with the third one determined so as to preserve mesh skewness(or the Jacobian).The unified coordinate system combines the advantages of both Eulerian and the Lagrangian system and beyond.Specifically,the followings are shown in this paper.(a)For 1-D flow,Lagrangian system plus shock-adaptive Godunov scheme is superior to Eulerian system.(b)The governing equations in any moving multi-dimensional coordinates can be written as a system of closed conservation partial differential equations(PDE)by appending the time evolution equations–called geometric conservation laws–of the coefficients of the transformation(from Cartesian to the moving coordinates)to the physical conservation laws;consequently,effects of coordinate movement on the flow are fully accounted for.(c)The system of Lagrangian gas dynamics equations is written in conservation PDE form,thus providing a foundation for developing Lagrangian schemes as moving mesh schemes.(d)The Lagrangian system of gas dynamics equations in two-and three-dimension are shown to be only weakly hyperbolic,in direct contrast to the Eulerian system which is fully hyperbolic;hence the two systems are not equivalent to each other.(e)The unified coordinate system possesses the advantages of the Lagrangian system in that contact discontinuities(including material interfaces and free surfaces)are resolved sharply.(f)In using the UC,there is no need to generate a body-fitted mesh prior to computing flow past a body;the mesh is automatically generated by the flow.Numerical examples are given to confirm these properties.Relations of the UC approach with the Arbitrary-Lagrangian-Eulerian(ALE)approach and with various moving coordinates approaches are also clarified.