Paulo R. M. Lyra

GENERAL PURPOSE VERSUS SPECIAL ALGORITHMS FOR HIGH-SPEED FLOWS WITH SHOCKS

In this paper we compare the performance of a new general algorithm developed recently in application to problems of high Mach number flows with the performance of specialised algorithms applicable only to such flows. It appears that the results for most examples compare well, the biggest difference occurring in that of high Mach number compression corner.

An edge-based unstructured finite volume procedure for the numerical analysis of heat conduction applications

In recent years, there has been a significant level of research on the application of unstructured mesh methods to the simulation of a variety of engineering and scientific problems. Great progress has been achieved in such area and one of the most successful methodologies consists on the use of the Finite Volume Method (FVM). The unstructured FV formulation is very flexible to deal with any kind of control volume and therefore any kind of unstructured meshes, which are particularly important when complex geometries or automatic mesh adaptation are required. In this article, an unstructured finite volume vertex centered formulation, which was implemented using an edge-based data structure, is deduced and detailed for the solution of heat conduction problems. The numerical formulation is initially described considering a tri-dimensional model and latter particularized for bi-dimensional applications using triangular meshes. The presented procedure is very flexible and efficient to solve potential problems. It can also be extended to deal with a broader class of applications, such as models involving convection-diffusion-reaction terms, after considering the appropriate discretization of the convection-type term. In order to demonstrate the potentiality of the method, some model problems are investigated and the results are validated using analytical or other well-established numerical solutions.

An axisymmetric finite volume formulation for the solution of heat conduction problems using unstructured meshes

In this work, a finite volume formulation developed for two-dimensional models is extended to deal with axisymmetric models of heat conduction applications. This formulation uses a vertex centered finite volume method and it was implemented using an edge-based data structure. The time and domain discretization using triangular meshes is described in details, including the treatment of boundary conditions, source terms, and domains with multiple materials. The proposed formulation is validated and proves to be effective and flexible through the solution of simple model problems.

Development of a computational efficient tool for robust structural optimization

Purpose – Optimization under a deterministic approach generally leads to a final design in which the performance may degrade significantly and/or constraints can be violated because of perturbations arising from uncertainties. The purpose of this paper is to obtain a better strategy that would obtain an optimum design which is less sensitive to changes in uncertain parameters. The process of finding these optima is referred to as robust design optimization (RDO), in which improvement of the performance and reduction of its variability are sought, while maintaining the feasibility of the solution. This overall process is very time consuming, requiring a robust tool to conduct this optimum search efficiently. Design/methodology/approach – In this paper, the authors propose an integrated tool to efficiently obtain RDO solutions. The tool encompasses suitable multiobjective optimization (MO) techniques (encompassing: Normal-Boundary Intersection, Normalized Normal-Constraint, weighted sum method and min-max m...

A computational methodology for automatic two-dimensional anisotropic mesh generation and adaptation

This paper describes a versatile computational program for automatic two-dimensional mesh generation and remeshing adaptation of triangular, quadrilateral and mixed meshes. The system is flexible to be incorporated into an adaptive global or local remeshing procedure and for generating both, iso and anisotropic meshes. The main contribution of this work is to extend well established procedures for the generation and adaptation of both, iso and anisotropic triangular meshes, such as local and global remeshing as well as boundary layer mesh generation, to deal with iso and anisotropic quadrilateral and mixed meshes. Several examples are presented to illustrate the quality of the meshes produced, and the flexibilities of the computational system.

An edge-based unstructured mesh formulation for high speed tridimensional compressible flow simulation

Numerical simulation of realistic compressible flows is very important and requires accurate and flexible tridimensional formulations, which should furthermore be robust and efficient. In this work we describe the development of a computational tool for numerical simulation of inviscid compressible 3-D fluid flow problems. This tool uses as the main building block an edge-based Galerkin FEM (Finite Element Method) together with a MUSCL (Monotonic Upstream-centered Schemes for Conservations Laws) approach to get a higher-order scheme with LED (Local Extremum Diminishing) property. The code is particularly developed for the simulation of supersonic and hypersonic flow regimes and several important (sometimes unavoidable) numerical procedures incorporated to increase its robustness are described. Some aspects related to the adoption of an edge-based data structure and other implementation issues are also described. Finally, some numerical model problems are analyzed and compared with results found in the literature demonstrating the effectiveness of the developed tool.

Numerical simulation of two dimensional compressible and incompressible flows

In this article, we make use of a stabilized Finite Element method to solve the complete set of Navier-Stokes equations. The methodology adopted is such that it allows for the use of different sets of variables, particularly the so called conservative and pressure variables. A space-time formulation using a simple augmented SUPG stabilizing term is proposed for the particular case of pressure variables. Comparison with data published in the available literature is done and a reasonably good agreement is obtained.

A hybrid parallel DEM approach with workload balancing based on HSFC

Purpose The purpose of this paper is to present a methodology of hybrid parallelization applied to the discrete element method that combines message-passing interface and OpenMP to improve computational performance. The scheme is based on mapping procedures based on Hilbert space-filling curves (HSFC). Design/methodology/approach The methodology uses domain decomposition strategies to distribute the computation of large-scale models in a cluster. It also partitions the workload of each subdomain among threads. This additional procedure aims to reach higher computational performance by adjusting the usage of message-passing artefacts and threads. The main objective is to reduce the communication among processes. The work division by threads employs HSFC in order to improve data locality and to avoid related overheads. Numerical simulations presented in this work permit to evaluate the proposed method in terms of parallel performance for models that contain up to 3.2 million particles. Findings Distinct partitioning algorithms were used in order to evaluate the local decomposition scheme, including the recursive coordinate bisection method and a topological scheme based on METIS. The results show that the hybrid implementations reach better computational performance than those based on message passing only, including a good control of load balancing among threads. Case studies present good scalability and parallel efficiencies. Originality/value The proposed approach defines a configurable execution environment for numerical models and introduces a combined scheme that improves data locality and iterative workload balancing.

A parallel DEM approach with memory access optimization using HSFC

Purpose The purpose of this paper is to present a methodology for parallel simulation that employs the discrete element method (DEM) and improves the cache performance using Hilbert space filling curves (HSFC). Design/methodology/approach The methodology is well suited for large-scale engineering simulations and considers modelling restrictions due to memory limitations related to the problem size. An algorithm based on mapping indexes, which does not use excessive additional memory, is adopted to enable the contact search procedure for highly scattered domains. The parallel solution strategy uses the recursive coordinate bisection method in the dynamical load balancing procedure. The proposed memory access control aims to improve the data locality of a dynamic set of particles. The numerical simulations presented here contain up to 7.8 millions of particles, considering a visco-elastic model of contact and a rolling friction assumption. Findings A real landslide is adopted as reference to evaluate the numerical approach. Three-dimensional simulations are compared in terms of the deposition pattern of the Shum Wan Road landslide. The results show that the methodology permits the simulation of models with a good control of load balancing and memory access. The improvement in cache performance significantly reduces the processing time for large-scale models. Originality/value The proposed approach allows the application of DEM in several practical engineering problems of large scale. It also introduces the use of HSFC in the optimization of memory access for DEM simulations.

Minimization of vortex induced vibrations using Surrogate Based Optimization

In this work we consider the application of optimization techniques in fluid-structure interaction (FSI) problems. An arbitrary Lagrangian Eulerian (ALE) finite element formulation, based on a Fractional Step Method is extended to deal with incompressible flow problems with moving interfaces. The vortex induced vibrations (VIV) phenomena are evaluated, and the reduction of such vibrations is attempted by using an acoustic excitation on the surface of the cylinder or by positioning a flat plate behind the cylinder, with the optima design parameters obtained through the minimization of the cylinder vibration. As the cost of FSI numerical simulation can be very high it is generally not feasible to couple the simulator directly to the optimizer. Therefore, a cheap surrogate model is used to capture the main trends of the objective and constraint functions. In this work we adopt Kriging data fitting approximation to build surrogate models to be used in the context of local optimization. The Sequential Approximate Optimization (SAO) strategy is used to solve the problem as a sequence of local problems. A trust region based framework is employed to adaptively update the design variable space for each local optimization. Sequential Quadratic Programming (SQP) is the algorithm of choice for the local problems. This optimizer will operate solely on the surrogates, which is smooth and also allows for the gradient computation. The integrated approach presented for optimization of FSI problems using surrogate models and the proposed strategy for sampling reuse leads to a robust and efficient tool, which were successful in solving the model problems analyzed. Also the proposed tool proved to be accurate and its performance confirms the efficient regularization of simulator numerical noise.