Robust and Scalable Overset Grid Assembly for Partitioned Unstructured Meshes

Abstract

This paper presents a method to perform efficient and automated Overset Grid Assembly (OGA) on a system of overlapping unstructured meshes in a parallel computing environment where all meshes are partitioned into multiple mesh-blocks and processed on multiple cores. The main task of the overset grid assembler is to identify, in parallel, among all points in the overlapping mesh system, at which points the flow solution should be computed (field points), interpolated (receptor points), or not computed at all (hole points). Point containment search or donor search, an algorithm to efficiently determine the cell that contains a given point is the core procedure necessary for accomplishing this task. Donor search is particularly challenging for partitioned unstructured meshes because of the complex geometry that is often created at the boundaries of each mesh-block during partitioning. Another challenge arises because of the large variation in the type of mesh-block overlap and the resulting large load imbalance on multiple processors. Desirable traits for the grid assembly method are efficiency (requiring only a small fraction of the solver time), robustness (correct identification of all point types), and full automation (no user input required other than the mesh system). Additionally, the method should be scalable, which is an important challenge due to the inherent load imbalance. In this paper, two fully-automated grid assembly algorithms are described. One is based on the use of auxiliary grids and Exact Inverse Maps (EIM), and the other is based on the use of Alternating Digital Trees (ADT). The EIM method is demonstrated to be more efficient than the ADT method, while retaining robustness. An adaptive load re-balance algorithm is also designed and implemented, which considerably improves the scalability of the method.

Enabling the environmentally clean air transportation of the future: a vision of computational fluid dynamics in 2030

“…Focused research programmes in streamlined CAD access and interfacing, large-scale mesh generation and automated optimal adaptive meshing techniques are required. Efforts must concentrate on making mesh generation and adaptation less burdensome and, ultimately, invisible to the CFD process, while developing technologies that enable the Vision 2030 CFD capabilities, namely very large-scale parallel mesh generation, curved mesh elements for higher order methods [46,47], highly scalable dynamic structured and unstructured overset mesh technology [48,49] and in situ anisotropic adaptive methods for time-dependent problems. Advances in these areas will require incremental software development, combined with advances in fundamental areas such as computational geometry.…”

SOGA: Toward Developing and Application of an Intelligent Structured Chimera Grid Assembling Library for Moving Objectives

“…Therefore, the ADT method is selected in this paper as an efficient and robust algorithm for donor search. For detail, one can refer to [20].…”

“…It's known that the key for success in a Chimera grid approach is to identify the field points,the receptor points and the hole points in the overlapping grid system [20]. The field point (also often termed as active point) is point at which the governing flow equation should be solved.…”

“…The main task herein is that we have to identify all three different points in the composite overlapping grid system composed of different component grids, at which points the flow solution should be computed (the field points), interpolated (the receptor points), and not computed at all (the hole points). In generally, the procedure to identify these different points is graphically called the procedure for 'hole cutting', or hole profiling [20]. In Figure 2, a practical example consisting of five overlapping grids and a background grid for the five-cylinder case is shown to further to illustrate these terminologies.…”

An efficient and robust localization scheme on massively distributed systems

“…An improved method using kd‐tree based data structures was demonstrated for actuator blade source interpolation by Lynch et al . Roget and Sitaraman employ an alternating digital tree based data structure for overset interpolation stencil searches. Additionally, they explore subdividing the domain into blocks to help speed up the search procedure.…”