József Bakosi

23033431600

Publications - 5

Robust 3D multi-material hydrodynamics using discontinuous Galerkin methods

József Bakosi Jacob Waltz Aditya Pandare Weizhao Li Hong Luo

Publication Name: International Journal for Numerical Methods in Fluids

Publication Date: 2025-02-01

Volume: 97

Issue: 2

Page Range: 188-209

Description:

A high-order discontinuous Galerkin (DG) method is presented for nonequilibrium multi-material ((Formula presented.)) flow with sharp interfaces. Material interfaces are reconstructed using the algebraic THINC approach, resulting in a sharp interface resolution. The system assumes stiff velocity relaxation and pressure nonequilibrium. The presented DG method uses Dubiner's orthogonal basis functions on tetrahedral elements. This results in a unique combination of sharp multimaterial interfaces and high-order accurate solutions in smooth single-material regions. A novel shock indicator based on the interface conservation condition is introduced to mark regions with discontinuities. Slope limiting techniques are applied only in these regions so that nonphysical oscillations are eliminated while maintaining high-order accuracy in smooth regions. A local projection is applied on the limited solution to ensure discrete closure law preservation. The effectiveness of this novel limiting strategy is demonstrated for complex three-dimensional multi-material problems, where robustness of the method is critical. The presented numerical problems demonstrate that more accurate and efficient multi-material solutions can be obtained by the DG method, as compared to second-order finite volume methods.

Open Access: Yes

DOI: 10.1002/fld.5340

Partition deactivation with load balancing for parallel flow simulations

József Bakosi

Publication Name: Journal of Computational Physics

Publication Date: 2024-12-15

Volume: 519

Issue: Unknown

Page Range: Unknown

Description:

An algorithm is presented to save CPU time by dynamically deactivating partitions of a decomposed computational mesh during parallel flow simulations. The procedure targets classes of problems where the propagation behavior, inherent in the equations solved, can be exploited, such as detonation or scalar transport. Combined with dynamic load balancing based on real-time CPU-measurement, available, e.g., by coding the solver using the Charm++ runtime system, yields considerable savings in solution times for both shared-, and distributed-memory calculations. The complete source code is available at https://xyst.cc.

Open Access: Yes

DOI: 10.1016/j.jcp.2024.113387

Open-source complex-geometry 3D fluid dynamics for applications with unpredictable heterogeneous dynamic high-performance-computing loads

József Bakosi

Publication Name: Computer Methods in Applied Mechanics and Engineering

Publication Date: 2024-01-05

Volume: 418

Issue: Unknown

Page Range: Unknown

Description:

We discuss the software implementation of a finite element method, intended for the simulation of complex-geometry 3D flows, using hardware resources effectively, including problems with a priori unknown, heterogeneous, and dynamic parallel computational load. Our fundamental choices of data structures, algorithm, and software design specifically target engineering resolution and accuracy requirements. Some of these choices are: unstructured grids (to explicitly resolve complex 3D geometries), tetrahedra-only computational elements (to enable automatic mesh generation), edge-based finite element scheme (to reduce indirect addressing for increased performance), distributed-memory parallel computing paradigm (to enable large problems), and Charm++ (https://charmplusplus.org) as the runtime system (to effectively use computing resources even in the presence of hardware heterogeneities and dynamic application requirements). We discuss aspects of the implementation that enable exercising unique features of the runtime system, e.g., the single Charm++ programming abstraction, overdecomposition, asynchronous execution, latency-hiding parallel communication and computation, task-parallelism, and dynamic load balancing via object migratability. Multiple test problems are used to verify and validate the numerical solutions and computational performance and scalability to high-performance computing environments are discussed. For maximum transparency and reproducibility, and to encourage future research, development, and use, the full source code, together with regression tests and documentation, is publicly available at https://xyst.cc.

Open Access: Yes

DOI: 10.1016/j.cma.2023.116586

On the design of stable, consistent, and conservative high-order methods for multi-material hydrodynamics

József Bakosi Jacob Waltz Aditya Pandare Weizhao Li Hong Luo

Publication Name: Journal of Computational Physics

Publication Date: 2023-10-01

Volume: 490

Issue: Unknown

Page Range: Unknown

Description:

Obtaining stable and high-order numerical solutions for multi-material hydrodynamics is an open challenge. Although slope limiters are widely used to maintain monotonicity near discontinuities, typical limiting procedures violate closure laws at the discrete level when applied to multi-material hydrodynamics equations. Due to this, the high-order expansions of quantities related by the closure laws are no longer consistent. The commonly observed symptom of this consistency-violation is that the numerical method fails to maintain constant pressure and velocity across material interfaces. This leads to sub-optimal convergence rates for smooth multi-material problems as well. Specialized limiting procedures that satisfy consistency while maintaining conservation need to be developed for such equations. A novel procedure that re-instates consistency into slope-limited high-order discretizations applied to the multi-material hydrodynamics equations is presented here. Using simple examples, it is demonstrated that the presented method satisfies closure laws at the discrete level, while maintaining conservative properties of the high-order method. Furthermore, this procedure involves a projection step which relies on the compact basis of the underlying spatial discretization, i.e. for discontinuous schemes (viz. DG and FV) the projection is local, and does not involve global matrix solves. Comparisons with conventional approaches emphasizes the necessity of the consistent closure-law preserving limiting approach, in order to maintain design order of accuracy for smooth multi-material problems.

Open Access: Yes

DOI: 10.1016/j.jcp.2023.112313

Complex-Geometry 3D Computational Fluid Dynamics with Automatic Load Balancing

József Bakosi L. Környei Marc Charest Jacob Waltz Aditya Pandare Mátyás Constans Paula Rutherford Ákos Kovács Zoltán Horváth

Publication Name: Fluids

Publication Date: 2023-05-01

Volume: 8

Issue: 5

Page Range: Unknown

Description:

We present an open-source code, Xyst, intended for the simulation of complex-geometry 3D compressible flows. The software implementation facilitates the effective use of the largest distributed-memory machines, combining data-, and task-parallelism on top of the Charm++ runtime system. Charm++’s execution model is asynchronous by default, allowing arbitrary overlap of computation and communication. Built-in automatic load balancing enables redistribution of arbitrarily heterogeneous computational load based on real-time CPU load measurement at negligible cost. The runtime system also features automatic checkpointing, fault tolerance, resilience against hardware failure, and supports power- and energy-aware computation. We verify and validate the numerical method and demonstrate the benefits of automatic load balancing for irregular workloads.

Open Access: Yes

DOI: 10.3390/fluids8050147