Massively parallel anisotropic mesh adaptation

Efficiency of parallel anisotropic mesh adaptation for the solution of the bidomain model in cardiac tissue

Parallel adaptive tetrahedral mesh generation by the advancing front technique

A parallel adaptive mesh method for the numerical simulation of multiphase flows

: A parallel tetrahedral mesh adaptation code is expanded to treat general, mixed-element unstructured meshes comprised of any combination of basic element types. Emphasis is placed on developing conforming mesh modification methods that are solver-independent. Specific developments include the implementation of a treatment for viscous, high aspect ratio near wall tetrahedra, and cell subdivision methods for prismatic, hexahedral, and pyramid cells. Rebalancing of the adapted grid, and particularly issues associated with processor assignment of parent/child cell sets, is addressed. Validations are performed for decomposed, mixed-element meshes using cell-vertex and cell-centered unstructured solvers. The resulting parallel adaptation package is a powerful, versatile tool for obtaining gridconverged, steady state results, and may readily be applied to other unstructured flow solvers.

Parallel hybrid mesh adaptation by refinement and coarsening

Radiative property investigation of dispersed particulate medium with the consideration of non-uniform particle size distribution and dependent scattering effects

In this paper, we introduce a novel, SPH-based(Smoothed Particle Hydrodynamics), parallel adaptive quadrilateral-dominated mesh generation method. Building upon particle-based mesh generation techniques, we propose an innovative Adaptive Smoothing Length Smoothed Particle Hydrodynamics (ASL-SPH) Method utilizing the L∞ norm metric to enhance particle relaxation. The core concept leverages the square characteristic of the L∞ norm's unit circle to facilitate the construction of high-quality quadrilateral meshes. The algorithm comprises three primary stages: (1) computation of the initial adaptive particle distribution based on target size and density fields; (2) GPU-accelerated particle relaxation guided by a direction field, employing the proposed ASL-SPH grounded in the L∞ norm metric; and (3) establishment of topological connections among particles to generate a quadrilateral-dominated mesh. Numerical experiments validate that the proposed method effectively generates high-quality quadrilateral-dominated meshes under complex boundary conditions. Furthermore, the integration of GPU parallel computing significantly enhances the algorithm's efficiency.

A discontinuous Galerkin finite element computational methodology is presented for the solution of the coupled phase-field and heat conduction equations for modeling microstructure evolution during solidification. The details of the discontinuous formulation and the solution procedures are given. A major difference between the current method and those used in the literatures is the application of higher-order localized formulation and unstructured mesh, which holds a great promise in both parallel computing and adaptive meshing. The accuracy of the discontinuous model is checked with the analytic solution for a simple 1-D solidification problem. Numerical simulations and selected results are given for more complex 2-D dendrite structures formed during solidification. The calculated results are consistent with those reported in literature.

A generic solver in a parallel Cartesian adaptive mesh refinement framework is extended to simulate detonations on three-dimensional structured curvilinear meshes. A second-order accurate finite volume method is used with grid-aligned Riemann solvers for thermally perfect gas mixtures. Detailed, multi-step chemical kinetic mechanisms are employed and numerically incorporated with a splitting approach. The adaptive mesh refinement technique is applied to a mapped mesh using modified prolongation and restriction operators. The flux along the coarse-fine interface is considered in a correction procedure to ensure the conservation of the solver. The numerical accuracy, conservation and robustness of the simulations are verified and validated with suitable benchmark tests. The new solver is then used to simulate detonation problems in non-Cartesian geometries. A simulation is conducted of the three-dimensional detonation propagation in a 90-degree pipe bend. A detonation in a round tube is also simulated in a Galilean frame of reference. Both a rectangular mode and a spinning mode are observed in the simulations. In addition, the fundamental problem of detonation wave/boundary layer interaction is studied. The results show that the new solver can simulate high-speed reactive flows efficiently by the combined use of a curvilinear mapping with mesh adaptation.

This document presents a description of the octree mesh-generation capabilities and of the parallel mesh adaptation kernel. As it is discussed in Section 1.3.2 of part B of the project proposal there are two parallel research lines aimed at developing scalable adaptive mesh refinement (AMR) algorithms and implementations. The first one is based on using octree-based mesh generation and adaptation for the whole simulation in combination with unfitted finite element methods (FEMs) and the use of algebraic constraints to deal with non-conformity of spaces. On the other hand the second strategy is based on the use of an initial octree mesh that, after make it conforming through the addition of templatebased tetrahedral refinements, is adapted anisotropically during the calculation. Regarding the first strategy the following items are included:

Transient flowfields appear in many applications of interest and present numerous challenges to current simulation methods. Such problems include shock propagation and reflection, bluff body wakes with periodic shedding, and pulsatile flows generated by flow control devices. Also of interest are cases where boundaries are in relative motion, as found in weapons separation from aircraft, valve and piston motion in internal combustion engines, and rotor/stator interactions. The task of providing a computational mesh that is adequate to capture evolving flow structures as they change in time is an important and difficult aspect of this class of simulations. In moving body applications, the problem is compounded by the need to accommodate topology changes in the mesh. The issue of spatial resolution in transient flows has been addressed by various researchers using adaptive mesh refinement. However to date such strategies have largely been ad hoc and problem-dependent. The simulation of bodies undergoing relative motion has typically been performed using overset grid methods, which require considerable expertise and can be significantly labor intensive, particularly when generating overlapping grids for realistic geometries. This work presents new approaches for performing unstructured mesh adaptation for transient flows with fixed or moving boundaries. Notable advances in parallel mesh adaptation methods are made to facilitate the integration of mesh coarsening and refinement within the iteration loop, operating directly on the decomposed domains used by the parallel flow solver. A novel method is developed which modifies the mesh automatically at variable intervals according to how rapidly the solution is changing, rather than relying on a predefined, constant frequency. The new approach is founded on the concept of projecting refinement of solution errors ahead of their current location, and subsequently monitoring their accumulation. For moving boundary problems, a formal mesh deformation matrix analysis is employed to direct where corrective coarsening and refinement are required. Automation of mesh corrections for such problems is based on the deformation history of the mesh. These advances are demonstrated on controlled, unit problems as well as more complex problems of interest involving stationary and moving geometries.

Laboratory modelling of the processes of interaction between the atmosphere and ocean in the boundary layers is one of the most interesting from the point of view of the features of the hydrophysical experiment. The main characteristics that need to be controlled in these experiments include, first of all, the air velocity field over the rough surface waves and the underwater flow, as well as the shape of the free surface. However especial features as spray of droplets, the bubbles in the water and foam generated during the breaking of waves should also be taken into account when modelling extreme weather conditions associated with strong winds. Thus, from the point of view of experimental hydrodynamics, we are dealing with a multiphase turbulent flow with a free boundary. For purpose of experimental study on the wind-wave flume, an integrated approach is required that allows simultaneous measurements of the velocity flow fields, the sizes of droplets and bubbles, the shape of waves and parameters of foam coverage. Contact methods often do not allow for universality. This review study describes developing approaches to the use of optical methods for performing these studies. Presented results were obtained in experiments carried out on several wind-wave flumes. To study the processes of fragmentation of the water surface leading to the formation of droplets an foam, high-speed multi-angle video taking is used in combination with the shadow imaging method.

The optimal management strategy of patients with concomitant anterior communicating artery aneurysm (ACoAA) and internal carotid artery (ICA) stenosis is unclear. This study aims to evaluate the impacts of unilateral ICA revascularization on hemodynamics factors associated with rupture in an ACoAA. In the present study, a multiscale computational model of ACoAA was developed by coupling zero-dimensional (0D) models of the cerebral vascular system with a three-dimensional (3D) patient-specific ACoAA model. Distributions of flow patterns, wall shear stress (WSS), relative residence time (RRT) and oscillating shear index (OSI) in the ACoAA under left ICA revascularization procedure were quantitatively assessed by using transient computational fluid dynamics (CFD) simulations. Our results showed that the revascularization procedures significantly changed the hemodynamic environments in the ACoAA. The flow disturbance in the ACoAA was enhanced by the resumed flow from the affected side. In addition, higher OSI (0.057 vs. 0.02), prolonged RRT (1.14 vs. 0.39) and larger low WSS area (66 vs. 50 mm2) in ACoAA were found in the non-stenotic case. These acute changes in hemodynamics after revascularization may elevate the rupture risk of ACoAA. The preliminary results validated the feasibility of predicting aneurismal hemodynamics characteristics in revascularization procedures by using multiscale CFD simulations, which would benefit the management of this group of patients.

Evaluation of nonlinear dynamic phenomena in the hysteretic behaviour of magnetorheological dampers

Optimal shape of thick blades for a hydraulic Savonius turbine