We proposed an object-oriented approach for supporting parallel computational fluid dynamics(CFD), and designed a programming framework in order to realize the concept. The framework helps to write a code for parallel computing and improve the portability and reusability of it. Furthermore, taking an object for the data field as the core structure, pre and post processes are easily and seamlessly integrated. We explain the concept and design of the framework, and what it achieves. Examples of calculation and application systems are also shown in this paper.
A visual computing plays more important role to improve numerical methods, and real-time visualization system is helpful to analyze the flowfield, especially on a large scale and a parallel computations. Therefore, a computer environment that both flow and visualization systems exist together is ideal. However, in order to develop a flow analysis system efficiently, it is important for a visualization system to keep independence from a flow solver, because the flow solver influenced by visualization system restricts the operational computers and the visualization system adjusted by the solver cannot work on the various computational environments. In this paper, some visualization systems which are independent of the flow solver and coexist with it are considered. We will explain several frameworks to construct a new visualization system, and propose one solution using a concept of a class library.
This paper presents an applicability of the effective tangent modulus (Ef) method for evaluating the ultimate strength of super long-span cable-stayed bridges. Using the center span length 1000 m, 1200 m and 1400 m cable-stayed bridge models which are preliminary designed, the ultimate strength of them is calculated by the elasto-plastic finite displacement analysis and the Ef method. From this comparative study, the load factors (eigen-values) obtained by the Ef method showed good agreement in about 2.7%∼10.8% errors compared with those obtained by the elasto-plastic finite displacement analysis. So it is clear that Ef method is an effective procedure which evaluates the ultimate strength of overall cable-stayed bridges.
This paper describes the design of a WWW application system for a numerical simulation server development environment. The system is an infrastructure which supports to develop the numerical simulation programs and shearing the program resources on the Internet. In order to solve the scientific problems, program source and executable code are generated by using the Web browser interactively. The generated simulation program is running as an original “Web Server”. The server provides the Internet user with a specific numerical simulation environment. Visualized outputs are presented by contacting with the server through the browser interface. This system is composed of 5 object-servers, which are system management, program development, visualization, library management and the generated simulation-server. The details are proposed and discussed.
GeoFEM is a parallel finite element analysis system intended for multi-physics/multi-scale problems of solid earth field phenomena. At this stage, the very large linear elastic problem has been successfully completed by parallel computation with GeoFEM. At the next stage, the large-scale nonlinear problem is a target of research for GeoFEM. This paper shows an evaluation of iterative solver for linear system generated in elastic-plastic analysis and a possibility of large-scale parallel elastic-plastic analysis. Bi-CGSTAB method is better than ICCG method in terms of convergence rate, but stability of Bi-CGSTAB method is no good. Large-scale parallel elastic-plastic analysis is performed showing the good convergence of ICCG method.
The inverse analysis scheme based on equivalent inclusion method, which makes possible to obtain stress field from displacement field and boundary condition, even if its constitutive relationship is unknown, was developed. For the material control purpose, displacement can be measured remotely, however, it is difficult to obtain stress field especially if constitutive relationship is unknown, material is inhomogeneous, or inelastic. In this paper, the formulation and result for plain strain inelastic deformation, and the formulation for thin plate bending are shown. The new material control scheme, which is based on not only displacement field but also stress field, is also proposed.
The numerical solutions of nonlinear multiscale analyses based on the mathematical homogenization theory are studied in the context of the finite element method (FEM). Since the numerical solutions of the microscopic equilibrium problem are evaluated at each Gauss point in a finite element of the overall structure, the macroscopic mechanical behaviors are considered to depend on its spatial discretization. Such a mesh dependency may come from either the usual discretization errors in FE analyses or the mathematical modeling strategy inherent in the homogenization theory. After the motivation and the viewpoints in this study are explained, we shall carry out several numerical experiments in the framework of the homogenization for elastoplasticity. Together with appropriate error estimates, we examine the reliability of numerical solution of the multiple-scale nonlinear homogenization.
To study and research the best algorithm for large-scaled parallel finite element method (FEM), we select two types of domain decomposition method (DDM) which are solving reduced boundary freedom by iterative method (method-A) and solving whole freedom by iterative solver (method-B). These methods are evaluated by benchmark problems of simple cubic model. Having the result of parametric analyses, method-B is superior than method-A in terms of low required memory and short elapsed time. The method, which is proved better, is being used by GeoFEM project to simulate solid earth behavior by parallel FEM.
An economical new structural system with the aerodynamic stability is necessary to achieve super long span suspension bridges. The dual cable suspension bridge using advanced composites aims to restrain increasing in the mass moment of inertia proportional to the cable self weight and complement decreasing in restoring force by the self weight with introducing the sub-cable prestress. In this paper, the numerical analysis by the direct flutter FEM method is executed to the dual cable suspension bridge of 3000m center span length, then the flutter characteristics and the economics are investigated and discussed in comparison with standard suspension bridge.
The 3 dimensional simulation model of golf swing is developed based on the multibody dynamics, which is reasonable compared to the traditional 2 dimensional model. The model consists of 7 rigid body and 1 elastic body, and 8 joints. The experiments using high speed camera are carried out to determine the driving force of the swing. The numerical simulation is compared with the experiments, and good agreement is observed. Finally, the optimal design of club is carried out. The design variables are taken as the thickness of the plate of the shaft and mass of the club head, and initial speed of the ball after impact is maximized. With the optimally designed club, it was shown that there is possibility that the initial ball speed increases about 10 %.
We are developing a program called GeoFEM, which is a parallel programming platform for the solid earth analysis and the program is intended to use on “Earth Simulator” which is promoted by Science and Technology Agency, Japan. For GeoFEM, many parallel analyzing programs have been developed and will be developed, but the input data format of these programs must be common in a sense. For this purpose, 1) the specification of data which is commonly used by the analyzers of GeoFEM is fixed, and 2) GeoFEM Data description Language (GDL) is provided for supporting of uncommon data items among analyzers. The data specification written in GDL is automatically converted to the “reader” program for the data which conforms to the defined specification. In this paper, these two techniques are described and the comparisons with the other data services, netCDF, HDF5, and CORBA externalization service are made.
The method of numerical iteration strategy for the elsto-plastic finite displacement analysis of long-span cable-stayed bridges is discussed in this paper. An improved method for stress integration in plastic zone is first proposed. As for the iterative analysis, some of arc-length and displacement incremental methods are considered and their efficiency is compared by analyzing a cable-stayed bridge model with the center span length of 1400m. The numerical result shows that the iterative method using displacement control condition is efficient for the elsto-plastic finite displacement analysis of the long-span cable-stayed bridge.
An automatic finite element procedure based on h method is presented for shell-solid structures. The geometry of the structure composed by beam, shell and solid parts is created by selecting necessary parts from parts library, giving dimensions to the parts and arranging them in the 3D space to get the required geometry of the structure. Physical conditions for the structural analysis are given directly on the geometry of the parts. By giving the total number of elements to create, the element mesh including beam, shell and solid elements is generated, constraint equations are created to combine beam, shell and solid elements on the surfaces between parts to be combined, and the initial analysis is made automatically. By giving only the allowable ratio of the finite element error, the adaptive mesh refinement is made and the detailed analysis is also carried out for the shell-solid structure automatically. A practical PC program based on the present method has been developed. Numerical examples are demonstrated to show the validity and effectiveness of the proposed method.
It has been problematic to develop simple and practical automatic mesh generation techniques that can minimize the amount of required input data and can generate a lot of nodes. The necessary data include the specification of external boundary of the given domain and an internal node density distribution. In particular, for the application of automatic mesh generation to stress concentration area, simple computer algorithms for managing input and output data are necessitated. In many cases, the difficulty of the finite element analysis lies in the mesh generation which is free from errors in the mesh formation. Customary meshing algorithms do not automatically generate optimal triangular meshes of the structure. The stress gradient of mesh refinement is based on the condition that the sum of element area by the stress at each elemet is constant. In order to satisfy these requirements, the Fuzzy reasoning is chosen here as an automatic mesh generation scheme which is applicable to the triangular element.
In this paper, we discuss the dynamic stability problem of a flow conveying pipe with a lumped mass by using boundary element method for a regional division type. Our problem is nonconservative and reduces to flutter type instability depending on the internal damping, a lumped mass and mass ratio of the system. We demonstrate important effects on the parameters of the system on flutter insatability of the pipe through numerical results. Firstly, the effect of the internal damping on the stability for a big or small lumped mass is discussed. Secondly, we show the effects of on position of a lumped mass through the comparison of critical velocity for internal damping.
In the present study, acoustic wave propagation is simulated using Cellular Automata(CA) method. CA method has been attracted wide interest for modeling many physical processes which are described generally by partial differential equations, such as diffusion and wave propagation. CA is a discrete system which consists of finite state variables, arranged on a uniform grid (cell). CA dynamics is described by a local interaction rule, which is used for computation of new state of each cells from the present state at every time step. We report simulation results of wave propagation model using CA. Acoustic pipe was introduced as one dimentional model, and its pressure distribution was calculated. Furthermore, two dimentional wave propagation was simulated, where the acoustic field was driven by a point source. CA approach for such modeling is discussed, comparing with analytical solutions.
In flow visualization, methods of exploring a scalar field have been almost established. On the other hand, visualization of a vector field has not been settled yet. It seems that particle tracking methods are useful to visualize the vector field. The methods are efficient to show a large scale and a small scale structure in the field clearly. However, initial positions of the particles sometimes affect a visualized pattern. Also, when a particle lies on another one, it becomes difficult to display the particle and to recognize the pattern. In this paper, we consider an enhancement of particle tracking methods against those problems. First, we are attempt to reduce the dependency of the initial position. Second, a vector field is visualized by the line integral convolution method (LIC), and some drawbacks of LIC are found. Finally, a novel technique called as PEM (Pixel Exposure Method) is proposed.
This paper describes a simulation of purchase in a store by customers using Cellular Automata(CA). CA was developed by John von Neuman and Stanislaw Ulam in 1940s, and considered as a class of computer modeling techniques of Complex Systems in which the local interactions of components of the system emerge the whole phenomenon. In CA algorithm, the simulation space is devided into discrete areas called “cells”, and the whole phenomenon can be emerged just by the local neighbor interactions between each state variables defined on each cell. In contrast with the conventional approach to engineering problems, it is not necessary to set up the governing equation of the system to be considered. The behavior of purchase of customers in a store is a typical example of Complex Systems. In the present paper, the local neighbor rules are derived expressing the movement of customers in a store considering the degree of attraction of goods on the shelves in several cases of “planned purchase” and “unplanned purchase” of customers. The simulated results are quite similar to those in actual stores.
The overlaying mesh finite element method, which uses global and local mesh that overlies each other, is applied for 2 dimensional elastostatic problem and plate bending problem. The results are compared with the traditional zooming analysis, in which displacement or load boundary conditions obtained by global analysis are given to local analysis. It was shown that while the accuracy of zooming analysis greatly depends on the size of the global mesh, the overlying mesh analysis generally gives quite good results even when coarse mesh is used in global analysis. Also the method that repeat local and global analysis iteratively is proposed, which makes it possible to use general purpose FEM code in overlaying mesh method, and it was shown that using under relaxation the convergence speed increase.
This paper presents analytical evaluation of weakly singular integrals arising in the boundary element analysis of Helmholtz and modified Helmholtz equations. Expressions for these boundary integrals are presented in terms of elementary integrals for straight line elements of arbitrary order, which are applicable not only to the singular integrals but also to the regular integrals when the collocation point is collinear with the integration element. Closed form analytical expressions have been derived for the elementary integrals for both the problems. The proposed finite term analytical formulae involving Bessel and Struve functions are very efficient compared to specialized numerical quadrature or the analytical formulae in terms of infinite series of some elementary integrals available in the literature.
In the field of continuum mechanics, there is a need to hypothesize empirical rule such as the constitutive laws. If the discipline governing the dynamics at an atomic/molecular level is considered, it is believed that the physical properties, such as the stress intensity factor unique to the material, may be predicted. For obtaining such information from the computations, it is required to solve a system of massively clustered particles. To do this end, the authors have developed a parallel algorithm for computing the motion of particles, which is described by the pair potential. The developed program carries out the domain decomposition, which divides the domain into arbitrary number of sub-domains. PVM, or the parallel virtual machine, is implemented as the message passing library in the parallel environments. By using this program, apply to 2.56×107 particles problem.
The treatment of coupled phenomena involving liquids and solids in the finite element analysis is reported in this paper. The authors have developed and implemented a new methodology for adequately computing a structure/thermal fluid coupled problem. The reported methodology is based on the techniques of large-scale finite element analysis for solving incompressible viscous fluids, which were reported in the past by the authors. The new scheme allows the acquisition of the dynamic responses of the structures and fluids, at the same time. The developed program was implemented onto the CRAY-T3D and the various factors which influence the parallel efficiency were considered. As a sample numerical result, a problem involving the cooling of a LSI package is examined, to illustrate the effectiveness of this new methodology.
A step-by-step finite element approach has been developed for the simulation of curved crack growth, where a cracked domain is successively re-meshed by an automatic mesh generator. It is well known that the pre-processing is a cumbersome procedure in such a simulation, so that an efficient pre-processor has been developed by using an automatic quadrilateral mesh generator based on the paving method. In order to obtain a favorable mesh density distribution, improvements of the algorithms and implementation of a new conversion technique for quadrilateral elements are made for the paving method. An automatic boundary nodes generator with an embedded template-mesh around a crack tip is developed for the preprocessor of a crack analysis, which is applied to problems with single and multiple-crack tip. The accuracy and the effectiveness of the crack analysis are confirmed by a numerical example. Since the path of a curved crack may sometimes be influenced by the selection of the increment size of a crack, an appropriate numerical procedure including re-analysis is proposed. The validity of the method is then demonstrated by the simulation of wavy crack growth of thermally induced brittle cracking.
A new learning algorithm named whole learning algorithm is proposed for the feedforward neural network. Strictly speaking, the learning of the feedforward neural network is a kind of multi-objective optimization problem to minimize the errors of outputs for all the learning data sets with respect to the amount of weight modification. All the learning data sets are simultaneously taken into account to constitute the governing equation of the weight modification, which is formulated as linear simultaneous equations with rectangular matrix of coefficients in the proposed algorithm. The solution of the equation is determined by means of the Moore-Penrose generalized inverse to deal with the rectangular matrix. The efficiency of the proposed algorithm is demonstrated through the problem to learn the nolinear behavior described by the Ramberg-Osgood model. The applicability of the proposed algorithm is investigated in problem to learn the earthquake response of RC members.
This paper describes a framework for integration of CAE modules on a distributed computer environment. The framework can enhance the capability of solving complex problems such as multiphysics analysis. In this paper, we implemented CAE-Document Transition system as the first step of the whole framework. This supports universal access to Disk File Document(on Disk) as well as Network Document(on Memory). Owing to the Network Document, CAE-Document Transition system can be used as a way of network wide Inter Process Communication. Fundamental performances of the framework were demonstrated through the implementation of prototype system.
A new mesh generation algorithm for extremely large scale finite element analysis is proposed in this paper. In this algorithm, the analysis domain is decomposed spaciously to the so-called buckets and mesh generation process is performed on each bucket independently. Therefore this algorithm has the good feature of locality of data reference and is basically parallelizable. In each bucket, nodes are generated on grids according to the nodal density field, which is defined on each bucket, and the consistency on the boundary of each bucket is realized by simple mapping technique. Fundamental performances of this algorithm are also shown in this paper.
The element-free Galerkin method (EFGM) is one of the meshless method without node-element connectivity information. It is expected to reduce the work for creating the mesh. It has been tried to be applied to various problems. Another notable feature of the EFGM is that it has the continuity of the first derivative i.e. strain and stress for a structural analysis by selecting the weight function. Since the displacement, strain and stress can be obtained anywhere, it is more advantageous to calculate the fracture mechanics parameters for nonlinear fracture mechanics problems than the finite element method (FEM). We can set the arbitrary integral contour or the moving integral contour along the crack propagation when we calculate them. In the present paper, the EFGM is applied to two-dimensional stable crack growth analysis which is required to estimate J-integral and T*-integral, and we confirm that the EFGM is effective for stable crack growth analysis.