Discontinuous Galerkin Time Research Articles

Light scattering by randomly irregular dielectric particles larger than the wavelength

We present results of simulation of light scattering by randomly irregular particles that have dimensions larger than the wavelength of incident light. We apply the discontinuous Galerkin time domain method and compare the accurate solution with that obtained using an approximate geometric-optics model. A qualitative agreement is observed for scattering angle curves of intensity at the size parameter of X=60, whereas angular dependence of polarization appears to be more sensitive to the wave effects and requires larger sizes for application of geometrical optics.

High order space–time adaptive ADER-WENO finite volume schemes for non-conservative hyperbolic systems

We present a class of high order finite volume schemes for the solution of non-conservative hyperbolic systems that combines the one-step ADER-WENO finite volume approach with space–time adaptive mesh refinement (AMR). The resulting algorithm, which is particularly well suited for the treatment of material interfaces in compressible multi-phase flows, is based on: (i) high order of accuracy in space obtained through WENO reconstruction, (ii) a high order one-step time discretization via a local space–time discontinuous Galerkin predictor method, and (iii) the use of a path conservative scheme for handling the non-conservative terms of the equations. The AMR property with time accurate local time stepping, which has been treated according to a cell-by-cell strategy, strongly relies on the high order one-step time discretization, which naturally allows a high order accurate and consistent computation of the jump terms at interfaces between elements using different time steps. The new scheme has been successfully validated on some test problems for the Baer–Nunziato model of compressible multiphase flows.

High order non-conforming multi-element discontinuous Galerkin method for time domain electromagnetics

We study a high order Discontinuous Galerkin Time Domain (DGTD) method for solving the system of Maxwell equations. This method is formulated on a non-conforming multi-element mesh mixing an unstructured triangulation for the discretization of irregularly shaped objects with a structured (Cartesian) quadrangulation for the rest of the computational domain. Within each element, the electromagnetic field components are approximated by a high order nodal polynomial. The DG method proposed here makes use of a centered scheme for the definition of the numerical traces of the electric and magnetic fields at element interfaces, associated to a second order or fourth order leap-frog scheme for the time integration of the associated semi-discrete equations. We formulate this DGTD method in 3D and study its theoretical properties. In particular, an a priori convergence estimation is elaborated. Finally, we present numerical results for the application of the method to 2D test problems.

A time discontinuous Galerkin finite element method for generalized thermo-elastic wave analysis, considering non-Fourier effects

Generalized thermo-elastic theory, which is based on the non-Fourier theory, indicates that there is a time delay between the heat flux vector and the temperature gradient. At present, the traditional numerical method for solving the thermo-elastic problem subjected to high-frequency heat source generally fails to properly capture discontinuities of impulsive waves in space and produces spurious numerical oscillations in the simulation of high modes and sharp gradients. In the paper, a time discontinuous Galerkin finite element method (DGFEM) for the solution of generalized thermo-elastic coupled problems is presented on the basis of well-known Lord–Shulman theory. The essential feature of the DGFEM is that the general temperature-displacement vector and its temporal gradient are assumed to be discontinuous and interpolated individually at each time level in time domain, respectively. In order to filter out the spurious wave-front oscillations, an artificial damping scheme is implemented in the final finite element formula. Numerical results show that the present DGFEM shows good abilities and provides much more accurate solutions for generalized thermo-elastic coupled behavior. It can capture the discontinuities effectively at the wave front and filter out the effects of spurious numerical oscillation induced by a high-frequency thermal shock.

A multi-temporal scale approach to high cycle fatigue simulation

High cycle fatigue (HCF) is a failure mechanism that dominates the life of many engineering components and structures. Time scale associated with HCF loading is a main challenge for developing a simulation based life prediction framework using conventional FEM approach. Motivated by these challenges, the extended space---time method (XTFEM) based on the time discontinuous Galerkin formulation is proposed. For HCF life prediction, XTFEM is coupled with a two-scale continuum damage mechanics model for evaluating the fatigue damage accumulation. Direct numerical simulations of HCF are performed using the proposed methodology on a notched specimen of AISI 304L steel. It is shown the total fatigue life can be accurately predicted using the proposed simulation approach based on XTFEM. The presented computational framework can be extended for predicting the service and the residual life of structural components.

Analysis of a fully discrete local discontinuous Galerkin method for time-fractional fourth-order problems

In this paper, we propose and analyze a fully discrete local discontinuous Galerkin (LDG) finite element method for time-fractional fourth-order problems. The method is based on a finite difference scheme in time and local discontinuous Galerkin methods in space. Stability is ensured by a careful choice of interface numerical fluxes. We prove that our scheme is unconditional stable and convergent. Numerical examples are shown to illustrate the efficiency and accuracy of our scheme.

A coupled lattice Boltzmann-finite element approach for two-dimensional fluid–structure interaction

In this paper, a systematic approach to couple the lattice Boltzmann and the finite element methods is presented for fluid–structure interaction problems. In particular, elastic structures and weakly compressible viscous fluids are considered. Three partitioned coupling strategies are proposed and the accuracy and convergence properties of the resultant algorithms are numerically investigated together with their computational efficiency. The corotational formulation is adopted to account for structure large displacements. The Time Discontinuous Galerkin method is used as time integration scheme for structure dynamics. The advantages over standard Newmark time integration schemes are discussed. In the lattice Boltzmann solver, an accurate curved boundary condition is implemented in order to properly define the structure position. In addition, moving boundaries are treated by an effective refill procedure.

Third order convergent time discretization for parabolic optimal control problems with control constraints

We consider a priori error analysis for a discretization of a linear quadratic parabolic optimal control problem with box constraints on the time-dependent control variable. For such problems one can show that a time-discrete solution with second order convergence can be obtained by a first order discontinuous Galerkin time discretization for the state variable and either the variational discretization approach or a post-processing strategy for the control variable. Here, by combining the two approaches for the control variable, we demonstrate that almost third order convergence with respect to the size of the time steps can be achieved.

A Novel Approach for Thermomechanical Analysis of Stationary Rolling Tires within an ALE–Kinematic Framework

ABSTRACT A new computational technique for the thermomechanical analysis of tires in stationary rolling contact is suggested. Different from the existing approaches, the proposed method uses the constitutive description of tire rubber components, such as large deformations, viscous hysteresis, dynamic stiffening, internal heating, and temperature dependency. A thermoviscoelastic constitutive model, which incorporates all the mentioned effects and their numerical aspects, is presented. An isentropic operator-split algorithm, which ensures numerical stability, was chosen for solving the coupled mechanical and energy balance equations. For the stationary rolling-contact analysis, the constitutive model presented and the operator-split algorithm are embedded into the Arbitrary Lagrangian Eulerian (ALE)–relative kinematic framework. The flow of material particles and their inelastic history within the spatially fixed mesh is described by using the recently developed numerical technique based on the Time Discontinuous Galerkin (TDG) method. For the efficient numerical solutions, a three-phase, staggered scheme is introduced. First, the nonlinear, mechanical subproblem is solved using inelastic constitutive equations. Next, deformations are transferred to the subsequent thermal phase for the solution of the heat equations concerning the internal dissipation as a source term. In the third step, the history of each material particle, i.e., each internal variable, is transported through the fixed mesh corresponding to the convective velocities. Finally, some numerical tests with an inelastic rubber wheel and a car tire model are presented.

Entropy stable shock capturing space–time discontinuous Galerkin schemes for systems of conservation laws

We present a streamline diffusion shock capturing spacetime discontinuous Galerkin (DG) method to approximate nonlinear systems of conservation laws in several space dimensions. The degrees of freedom are in terms of the entropy variables and the numerical flux functions are the entropy stable finite volume fluxes. We show entropy stability of the (formally) arbitrarily high order accurate method for a general system of conservation laws. Furthermore, we prove that the approximate solutions converge to the entropy measure valued solutions for nonlinear systems of conservation laws. Convergence to entropy solutions for scalar conservation laws and for linear symmetrizable systems is also shown. Numerical experiments are presented to illustrate the robustness of the proposed schemes.

Time discontinuous Galerkin space-time finite element method for nonlinear Sobolev equations

This article presents a complete discretization of a nonlinear Sobolev equation using space-time discontinuous Galerkin method that is discontinuous in time and continuous in space. The scheme is formulated by introducing the equivalent integral equation of the primal equation. The proposed scheme does not explicitly include the jump terms in time, which represent the discontinuity characteristics of approximate solution. And then the complexity of the theoretical analysis is reduced. The existence and uniqueness of the approximate solution and the stability of the scheme are proved. The optimalorder error estimates in L2(H1) and L2(L2) norms are derived. These estimates are valid under weak restrictions on the space-time mesh, namely, without the condition kn ⩾ ch2, which is necessary in traditional space-time discontinuous Galerkin methods. Numerical experiments are presented to verify the theoretical results.

Analysis of a local discontinuous Galerkin method for time‐fractional advection‐diffusion equations

PurposeThe purpose of this paper is to develop a fully discrete local discontinuous Galerkin (LDG) finite element method for solving a time‐fractional advection‐diffusion equation.Design/methodology/approachThe method is based on a finite difference scheme in time and local discontinuous Galerkin methods in space.FindingsBy choosing the numerical fluxes carefully the authors' scheme is proved to be unconditionally stable and gets L2 error estimates of O(hk+1+(Δt)2+(Δt)α/2hk+(1/2)). Finally Numerical examples are performed to illustrate the effectiveness and the accuracy of the method.Originality/valueThe proposed method is different from the traditional LDG method, which discretes an equation in spatial direction and couples an ordinary differential equation (ODE) solver, such as Runger‐Kutta method. This fully discrete scheme is based on a finite difference method in time and local discontinuous Galerkin methods in space. Numerical examples prove that the authors' method is very effective. The present paper is the authors' first step towards an effective approach based on the discontinuous Galerkin method for the solution of fractional‐order problems.

A hybrid DGTD-TDIE method for solving complex electromagnetic problems

This paper presents a novel hybrid method that effectively combines two capable numerical methods – the discontinuous Galerkin time domain (DGTD) method and the time domain integral equation (TDIE) method. The hybrid DGTD-TDIE method is highly applicable to the interaction problem between arbitrarily shaped thin wires and dielectric structures with complex media compositions. The Huygens equivalence principle is employed to divide the original problem into two subproblems: (1) the region containing the thin wires, which is calculated by using the TDIE method, and (2) the dielectric region modeled by unstructured grids and analyzed by the DGTD method. A time-stepping scheme is used to match the different time steps between the DGTD and TDIE methods. To validate the hybrid method, several numerical results have been presented, which prove it a promising scheme to solve the complex coupling problems.

ADER-WENO finite volume schemes with space–time adaptive mesh refinement

We present the first high order one-step ADER-WENO finite volume scheme with adaptive mesh refinement (AMR) in multiple space dimensions. High order spatial accuracy is obtained through a WENO reconstruction, while a high order one-step time discretization is achieved using a local space–time discontinuous Galerkin predictor method. Due to the one-step nature of the underlying scheme, the resulting algorithm is particularly well suited for an AMR strategy on space–time adaptive meshes, i.e. with time-accurate local time stepping. The AMR property has been implemented ‘cell-by-cell’, with a standard tree-type algorithm, while the scheme has been parallelized via the message passing interface (MPI) paradigm. The new scheme has been tested over a wide range of examples for nonlinear systems of hyperbolic conservation laws, including the classical Euler equations of compressible gas dynamics and the equations of magnetohydrodynamics (MHD). High order in space and time have been confirmed via a numerical convergence study and a detailed analysis of the computational speed-up with respect to highly refined uniform meshes is also presented. We also show test problems where the presented high order AMR scheme behaves clearly better than traditional second order AMR methods. The proposed scheme that combines for the first time high order ADER methods with space–time adaptive grids in two and three space dimensions is likely to become a useful tool in several fields of computational physics, applied mathematics and mechanics.

Fully discrete local discontinuous Galerkin method for solving the fractional telegraph equation

This paper aims to develop a fully discrete local discontinuous Galerkin finite element method for numerical simulation of the time-fractional telegraph equation, where the fractional derivative is in the sense of Caputo. The method is based on a finite difference scheme in time and local discontinuous Galerkin methods in space. The stability and convergence of this discontinuous approach are discussed and theoretically proven. Finally numerical examples are performed to illustrate the effectiveness and the accuracy of the method.

Time-discrete higher order ALE formulations: a priori error analysis

We derive optimal a priori error estimates for discontinuous Galerkin (dG) time discrete schemes of any order applied to an advection---diffusion model defined on moving domains and written in the Arbitrary Lagrangian Eulerian (ALE) framework. Our estimates hold without any restrictions on the time steps for dG with exact integration or Reynolds' quadrature. They involve a mild restriction on the time steps for the practical Runge---Kutta---Radau methods of any order. The key ingredients are the stability results shown earlier in Bonito et al. (Time-discrete higher order ALE formulations: stability, 2013) along with a novel ALE projection. Numerical experiments illustrate and complement our theoretical results.

Lattice Boltzmann Analysis of Fluid-Structure Interaction with Moving Boundaries

AbstractThis work is concerned with the modelling of the interaction of fluid flow with flexibly supported rigid bodies. The fluid flow is modelled by Lattice-Boltzmann Method, coupled to a set of ordinary differential equations describing the dynamics of the solid body in terms its elastic and damping properties. The time discretization of the body dynamics is performed via the Time Discontinuous Galerkin Method. Several numerical examples are presented and highlight the robustness and efficiency of the proposed methodology, by means of comparisons with previously published results. The examples show that the present fluid-structure method is able to capture vortex- induced oscillations of flexibly-supported rigid body.

Non-conformal and parallel discontinuous Galerkin time domain method for Maxwell’s equations: EM analysis of IC packages

In this article, we present an Interior Penalty discontinuous Galerkin Time Domain (IPDGTD) method on non-conformal meshes. The motivation for a non-conformal IPDGTD comes from the fact there are applications with very complicated geometries (for example, IC packages) where a conformal mesh may be very difficult to obtain. Therefore, the ability to handle non-conformal meshes really comes in handy. In the proposed approach, we first decompose the computational domain into non-overlapping subdomains. Afterward, each sub-domain is meshed independently resulting in non-conformal domain interfaces, but simultaneously providing great flexibility in the meshing process. The non-conformal triangulations at sub-domain interfaces can be naturally supported within the IPDGTD framework. Moreover, a MPI parallelization together with a local time-stepping strategy is applied to significantly increase the efficiency of the method. Furthermore, a general balancing strategy is described. Through a practical example with multi-scale features, it is shown that the proposed balancing strategy leads to better use of the available computational resources and reduces substantially the total simulation time. Finally, numerical results are included to validate the accuracy and demonstrate the flexibilities of the proposed non-conformal IPDGTD.

Space–time proper generalized decompositions for the resolution of transient elastodynamic models

In this paper, we investigate ability of proper generalized decomposition (PGD) to solve transient elastodynamic models in space–time domain. Classical methods use time integration schemes and an incremental resolution process. We propose here to use standard time integration methods in a non-incremental strategy. As a result, PGD gives a separated representation of the space–time solution as a sum of tensorial products of space and time vectors, that we interpret as space–time modes. Recent time integration schemes are based on multi-field formulations. In this case, separated representation can be constructed using state vectors in space and same vectors in time. However, we have experienced bad convergence order using this decomposition. Furthermore, temporal approximation must be the same for all fields. Thus, we propose an extension of classical separated representation for multi-field problems. This multi-field PGD (MF-PGD) uses space and time vectors that are different for each field. Calculation of decomposition is done using a monolithic approach in space and time, potentially allowing the use of different approximations in space and time. Finally, several simulations are performed with the transient elastodynamic problem with one dimension in space. Different approximations in time are investigated: Newmark scheme, single field time discontinuous Galerkin method and two fields time continuous and discontinuous Galerkin methods.

A space–time discontinuous Galerkin method for the incompressible Navier–Stokes equations

We introduce a space–time discontinuous Galerkin (DG) finite element method for the incompressible Navier–Stokes equations. Our formulation can be made arbitrarily high-order accurate in both space and time and can be directly applied to deforming domains. Different stabilizing approaches are discussed which ensure stability of the method. A numerical study is performed to compare the effect of the stabilizing approaches, to show the method’s robustness on deforming domains and to investigate the behavior of the convergence rates of the solution. Recently we introduced a space–time hybridizable DG (HDG) method for incompressible flows [S. Rhebergen, B. Cockburn, A space–time hybridizable discontinuous Galerkin method for incompressible flows on deforming domains, J. Comput. Phys. 231 (2012) 4185–4204]. We will compare numerical results of the space–time DG and space–time HDG methods. This constitutes the first comparison between DG and HDG methods.