OOFEM — an Object-oriented Simulation Tool for Advanced Modeling of Materials and Structures

The aim of this paper is to describe the object-oriented design of the finite element based simulation code. The overall, object-oriented structure is described, and the role of the fundamental classes is discussed. The paper discusses the advanced parallel, adaptive, and multiphysics capabilities of the OOFEM code, and illustrates them on the basis of selected examples

ON TUNING THE DYNAMIC LOAD BALANCING FEM FRAMEWORK

Developments in computer hardware are currently bringing new opportunities for numerical modelling. The current trend in technology is parallel processing making use of multiple processing units simultaneously to solve a given problem. This paper deals with exploring the parallel dynamic load balancing framework implemented in the finite element software. This framework is based on a domain decomposition paradigm for distributed memory model. The paper describes the improved technique to determine the actual processor weights related to performance of individual processing units. The load recovery consisting in mesh (re)partitioning is based on actual processor weights. The (re)partitioning process has to be performed during the simulation and whenever the load imbalance is significant. The performance of the proposed technique is tested on the benchmark problem and discussed

ON EVALUATION OF THE THREE-DIMENSIONAL ISOGEOMETRIC BEAM ELEMENT

The exact description of the arbitrarily curved geometries, including conic sections, is an undeniable advantage of isogeometric analysis (IGA) over standard finite element method (FEM). With B-spline/NURBS approximation functions used for both geometry and unknown approximations, IGA is able to exactly describe beams of various shapes and thus eliminate the geometry approximation errors. Moreover, naturally higher continuity than standard C0 can be provided along the entire computational domain. This paper evaluates the performance of the nonlinear spatial Bernoulli beam adapted from formulation of Bauer et al. [1]. The element formulation is presented and the comparison with standard FEM straight beam element and fully three-dimensional analysis is provided. Although the element is capable of geometrically nonlinear analysis, only geometrically linear cases are evaluated for the purposes of this study

OOFEM – An Object Oriented Framework for Finite Element Analysis

This paper presents the design principles and structure of the object-oriented finite element software OOFEM, which has been under active development for several years. The main advantages of the presented framework include modular design, extensibility, and robustness. The code itself is freely available and is distributed under GNU public license. It provides tools for linear and nonlinear analysis of mechanical and transport problems on sequential and parallel computers.

IMPLEMENTATION OF 3D VOF TRACKING ALGORITHM BASED ON BINARY SPACE-PARTITIONING

The paper focuses on modelling free surface flow. The interface is modelled using the Volume-Of-Fluid method, where the advection of volume fractions is treated by a purely geometrical method. The novelty of the work lies in the way that it incorporates Binary Space-Partitioning trees for computing the intersections of polyhedra. Volume-conserving properties and shape-preserving properties are presented on two benchmarks and on a simulation of the famous broken dam problem

FICTITIOUS DOMAIN METHOD FOR NUMERICAL SIMULATION OF INCOMPRESSIBLE VISCOUS FLOW AROUND RIGID BODIES

This article describes the method of efficient simulation of the flow around potentially many rigid obstacles. The finite element implementation is based on the incompressible Navier-Stokes equations using structured, regular, two dimensional triangular mesh. The fictitious domain method is introduced to account for the presence of rigid particles, representing obstacles to the flow. To enforce rigid body constraints in parts corresponding to rigid obstacles, Lagrange multipliers are used. For time discretization, an operator splitting technique is used. The model is validated using 2D channel flow simulations with circular obstacles. Different possibilities of enforcing rigid body constraints are compared to the fully resolved simulations and optimal strategy is recommended

PARALLELIZATION OF ASSEMBLY OPERATION IN FINITE ELEMENT METHOD

The efficient codes can take an advantage of multiple threads and/or processing nodes to partition a work that can be processed concurrently. This can reduce the overall run-time or make the solution of a large problem feasible. This paper deals with evaluation of different parallelization strategies of assembly operations for global vectors and matrices, which are one of the critical operations in any finite element software. Different assembly strategies for systems with a shared memory model are proposed and evaluated, using Open Multi-Processing (OpenMP), Portable Operating System Interface (POSIX), and C++11 Threads. The considered strategies are based on simple synchronization directives, various block locking algorithms and, finally, on smart locking free processing based on a colouring algorithm. The different strategies were implemented in a free finite element code with object-oriented architecture OOFEM [1]

PRE-PROCESSING OF ADDITIVE MANUFACTURING INPUT FILES FOR NUMERICAL SIMULATION

In this contribution, we present the concept of a 3D printer software emulator facilitating the creation of a spatial finite element mesh suitable for the printing process simulation. The concept is based on gradual processing of a native 3D printer input file (in a G-code format). This file contains a complete description of manufacturing process consisting of series of individual commands interpreted by a printer. The effect of each command needs to be precisely evaluated to obtain the position of the printer head and the volume of the deposited material in any given time. The calculation is performed in the same way as in the Marlin printer firmware using the trapezoidal motion curves and a command buffer. To represent a computational model, a discrete voxel model with variable edge length and time discretization is used. The volume of deposited material is calculated for each voxel as a function of time. The resulting model is suitable for numerical analysis of the printing process

ON COMPARISON OF 3D ISOGEOMETRIC TIMOSHENKO AND BERNOULLI BEAM FORMULATIONS

Application of isogeometric analysis (IGA) for curved beams is very convenient for its ability of exact representation of curved geometries. Several beam formulation has been presented since the introduction of IGA. In this paper, two different beam formulations are presented: Bernoulli beam formulation of A. M. Bauer et al. [1], and Timoshenko beam element introduced by G. Zhang et al. [2]. Both beam elements are implemented and their performance is documented on the fully threedimensionalexample of helicoidal spring