arXiv subjects

Abdolreza Amiri

Publications and source records attributed to Abdolreza Amiri.

5 recordsLinked to original sources

arXiv2026

A finite element method preserving the eigenvalue range of symmetric tensor fields

This paper presents a finite element method that preserves (at the degrees of freedom) the eigenvalue range of the solution of tensor-valued time-dependent convection--diffusion equations. Starting from a high-order spatial baseline discretisation (in this case, the CIP stabilised finite element method), our approach formulates the fully discrete problem as a variational inequality posed on a closed convex set of tensor-valued functions that respect the same eigenvalue bounds at their degrees of freedom. The numerical realisation of the scheme relies on the definition of a projection that, at each node, performs the diagonalisation of the tensor and then truncates the eigenvalues to lie within the prescribed bounds. The temporal discretisation is carried out using the implicit Euler method, and unconditional stability and optimal-order error estimates are proven for this choice. Numerical experiments confirm the theoretical findings and illustrate the method's ability to maintain eigenvalue constraints while accurately approximating solutions in the convection-dominated regime.

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arXiv2025

A nodally bound-preserving composite discontinuous Galerkin method on polytopic meshes

We introduce a nodally bound-preserving Galerkin method for second-order elliptic problems on general polygonal/polyhedral, henceforth collectively termed as \emph{polytopic}, meshes. Starting from an interior penalty discontinuous Galerkin (DG) formulation posed on a polytopic mesh, the method enforces preservation of \emph{a priori} prescribed upper and lower bounds for the numerical solution at an arbitrary number of user-defined points \emph{within} each polytopic element. This is achieved by employing a simplicial submesh and enforcing bound preservation at the submesh nodes via a nonlinear iteration. By construction, the submeshing procedure preserves the order of accuracy of the DG method, \emph{without} introducing any additional global numerical degrees of freedom compared to the baseline DG method, thereby, falling into the category of composite finite element approaches. A salient feature of the proposed method is that it automatically reverts to the standard DG method on polytopic meshes when no prescribed bound violation occurs. In particular, the choice of the discontinuity-penalisation parameter is independent of the submesh granularity. The resulting composite method combines the geometric flexibility of polytopic meshes with the accuracy and stability of discontinuous Galerkin discretisations, while rigorously guaranteeing bound preservation. The existence and uniqueness of the numerical solution is proven. A priori error bounds, assuming sufficient regularity of the exact solution are shown, employing a non-standard construction of discrete nodally bound-preserving interpolant. Numerical experiments confirm optimal convergence for smooth problems and demonstrate robustness in the presence of sharp gradients, such as boundary and interior layers.

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arXiv2025

Analysis of the application of a high order symplectic method in Shardlow's method for dissipative particle dynamics

This study investigates the efficiency and reliability of the modified Shardlow's (M-Shardlow) method for dissipative particle dynamics (DPD). We show that the M-Shardlow method in which for its construction, the second order velocity Verlet method in the Shardlows method to integrate the Hamiltonian part has been replaced by a symplectic fourth order method, improperly uses some parameters. %In other words, in this paper, it is shown that the initial M-Shardlow method employed some parameters improperly in the fourth order symplectic method that was used for the M-Shardlow method. By numerical experiments and computing, some important configurational quantities such as configurational temperature and radial distribution function (RDF), the M-Shardlow's method is compared with the Shardlow and ABOBA methods. These results indicate that the new method obtained in this way, even with the proper parameters is too costly in the sense of the CPU-time that is required per each step which makes it an inefficient DPD integrator. Besides, by a comparison of the radial distribution function of this method with Shardlow and ABOBA for large time increments, we can observe no considerable improvement in preserving the structure of the system by this new DPD solver.

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arXiv2025

A nodally bound-preserving finite element method for time-dependent convection-diffusion equations

This paper presents a new method to approximate the time-dependent convection-diffusion equations using conforming finite element methods, ensuring that the discrete solution respects the physical bounds imposed by the differential equation. The method is built by defining, at each time step, a convex set of admissible finite element functions (that is, the ones that satisfy the global bounds at their degrees of freedom) and seeks for a discrete solution in this admissible set. A family of $θ$-schemes is used as time integrators, and well-posedness of the discrete schemes is proven for the whole family, but stability and optimal-order error estimates are proven for the implicit Euler scheme. Nevertheless, our numerical experiments show that the method also provides stable and optimally-convergent solutions when the Crank-Nicolson method is used.

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arXiv2023

A nodally bound-preserving finite element method for reaction-convection-diffusion equations

This paper introduces a novel approach to approximate a broad range of reaction-convection-diffusion equations using conforming finite element methods while providing a discrete solution respecting the physical bounds given by the underlying differential equation. The main result of this work demonstrates that the numerical solution achieves accuracy of $O(h^k)$ in the energy norm, where $k$ represents the underlying polynomial degree. To validate the approach, a series of numerical experiments is conducted for various problem instances. Comparisons with the linear continuous interior penalty stabilised method, and the algebraic flux-correction scheme (for the piecewise linear finite element case) have been carried out, where we can observe the favourable performance of the current approach.

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