長嶋 利夫

The X-FEM in conjunction with the level set method can be used to simplify the modeling of continua containing several cracks and hence perform effective stress analyses related to fracture mechanics. This paper describes the two-dimensional stress analysis of structures containing cracks. Stress intensity factors having mixed modes coupled with mode-I and mode-II are evaluated by M_1-integral method. This method is examined in numerical examples of elastic analyses. The numerical results show that X-FEM is an effective method for performing stress analyses and evaluating stress intensity factors.

The modeling method using the volume data, which is produced by converting CAD data and CT data directly, has been utilized in various engineering analyses The analysis method based on the finite element method (FEM) in conjunction with "voxel" modeling can be performed to solve structural problems In such a voxel method however, the free surface having complex geometry does not always coincide with the surface of the voxel mesh in general Therefore an appropriate method to impose boundary conditions, which include both essential and natural boundary conditions is required to solve practical problems using the voxel method In this paper the procedure to enforce boundary conditions for the voxel method is described for the stress analysis based on FEM using structured hexahedral finite elements Moreover the numerical results by the structural FEM program, which can utilize the volume data structure of the volume CAD (V-CAD) developed in RIKEN and use the boundary condition treatment procedure stated in this paper, are also demonstrated

Recently, in order to improve thermal efficiency, the thickness of the compressor blade and vane has become thinner. Therefore, for the purpose of increasing reliability, the vane with a friction damper has been used. This paper presents the analysis method to predict damping characteristics of the compressor vane with a friction damper by applying the substructure synthesis method and the harmonic balance method. The excitation test of the damper vane is carried out to verify the validity of the analysis method proposed here. ln the excitation test, the newly developed magnetic exciter, which applies the feature of the resonant circuit, is used to experiment the vane with a large excitation force. Numerical results show good agreement with the experimental data and the damping characteristics of the damper vane is clarified.

The extended finite element method (X-FEM) proposed by Belytschko et al. (International Journal for Numerical Methods in Engineering 1999; 45:602; 1999; 46:131; 2001; 50:993) uses interpolation functions based on the concept of partition of unity, and considers the asymptotic solution and the discontinuity of displacement fields near a crack independently of the finite element mesh. This paper describes the application of X-FEM to stress analyses of structures containing interface cracks between dissimilar materials. In X-FEM, an interface crack can be modelled by locally changing an interpolation function in the element near a crack. The energy release rate should be separated into individual stress intensity factors, K-1 and K-2, because the stress field around the interface crack has mixed modes coupled with mode-I and mode-II. For this purpose, various evaluation methods used in conjunction with numerical methods such as FEM and BEM are reviewed. These methods are examined in numerical examples of elastostatic analyses of structures containing interface cracks using X-FEM. The numerical results show that X-FEM is an effective method for performing stress analyses and evaluating stress intensity factors in problems related to bi-material fractures. Copyright (C) 2003 John Wiley Sons, Ltd.

For the purpose of the reliability improvement, a friction damper is sometimes adopted in the vane of the gas turbine compressor. In order to verify the damping characteristic of the damper vane, the non-contact magnetic exciter was made and the excitation test of the damper vane was carried out. On the other hand, the analysis code was developed for predicting the damping characteristic of the damper vane. The frequency and damping of the damper vane measured by the excitation test was compared with the calculated results. The results of the test and the analysis showed that the damper vane has a excellent damping characteristic.

In order to study an impact damage accumulation problem in composite laminates, a special three-dimensional interface element is proposed to simulate the delamination propagation in laminates. The traction at the interface, which is a function of relative displacements of interface, can reduce to zero when the energy stored in element per unit area reaches critical total energy release rate. This element is incorporated in a commercially available finite element code and applied to the DCB and ENF fracture toughness test problems to demonstrate its validity. The solution converges smoothly and numerical results agree well with the theoretical ones when the element is sufficiently small compared to the significantly deformed area. Also, the present method is applied to damage accumulation problem of CFRP laminates subjected to transverse load and the results obtained are reasonable and interesting.

In most existing solid CAD systems, boundary representation methods, which express three dimensional geometry regions with surrounding surfaces and with their topological connections, are used. The boundary representation data structures give some difficulties to be used in CAE systems, and hardly import physical data from CAE systems. A new CAD system named Volume CAD (V-CAD) using volume data for geometry expression are developed for avoid these problems. V-CAD deals geometrical data with volume unit called cell defined all over the interested region, and each cell has physical data and simplified surface data. To use V-CAD data structure directly in the analysis, the extended finite element method (X-FEM), which can consider a free surface inside analysis element, are developed. In this paper, results of some example models models are compared to theoretical values, and show an ability of X-FEM to use V-CAD data structure directly.

The authors propose a node-by-node meshless method (NBNM), which discretizes the weak-formed governing equations of continuum mechanics using only distributed nodal data. This method uses the following three core methodologies: (i) interpolation using the moving least squares method (MLSM) (ii) estimation of stiffness by nodal integration with stabilization terms, and (iii) a node-by-node iterative solver. This paper discusses the effect of the stabilization term introduced to the NBNM and examines the convergence of the NBNM approximation. An error indicator for NBNM analysis is proposed, and the development of a prototype CAE system based on this method is outlined. Moreover, results of two-dimensional plane stress analysis with adaptation are shown. In conclusion, this paper will show that the NBNM is capable of utilizing CAD data easily and performing effective adaptation analyses, and therefore may be used as a convenient CAE tool. (C) 2000 Elsevier Science S.A. All rights reserved.

The meshless method is expected to become an effective procedure for realizing a CAD/CAE seamless system for analyses ranging from modelling to computation, because time-consuming mesh generation processes are not required. In the present study, a new meshless approach, referred to as the Node-By-Node Meshless method is proposed, in which only nodal data is utilized to discretize the governing equations, which are derived using either the principle of virtual work or the Galerkin method. In this method, three key methodologies are utilized: (i) nodal integration using stabilization terms, (ii) interpolation by the Moving Least-Squares Method, and (iii) a node-by-node iterative solver. This paper presents the formulation of the proposed method along with numerical results obtained for two-dimensional elastostatic and eigenvalue problems. Copyright (C) 1999 John Wiley & Sons, Ltd.

Recently, in order to improve power plant thermal efficiency, the turbine blade, which is the most important element of the power plant, has been used under severe conditions of high loading. Therefore, for the purpose of increasing plant reliability, the blade with friction dampers has been used. This paper presents the analysis method to predict damping characteristics of the seal pin type damper blades by applying the substructure synthesis method and the harmonic balance method to the bladed disk. The model test is carried out and the experimental data are compared with the numerical results in order to verify the validity of the analytical method proposed here. Numerical results show good agreement with the experimental data and it is shown that the damping characteristics of seal pin type damper blades can be controlled by altering the weight of pin and the grooveangie.

When calculating the resonant response of bladed turbine disks, it has proved useful to assume that all blades on a given disk are identical. This leads to the prediction that all blades experience the same amplitude of displacement and stress when excited by forces harmonically related to the rotor speed. However, it has been shown experimentally that significant variations in these amplitudes occur for different blades on the same disk. These variations arise due to the effects of mistuning, which refers to small differences in the blade characteristics. In this paper, vibrational characteristics of a bladed disk of mistuned grouped blades is studied using the substructure synthesis method and modal analysis. It is found that a bladed disk system of grouped blades is very sensitive to mistuning, and the fundamental vibrational characteristics of grouped blades with mistuning is shown.

The meshless method is expected to be an effective procedure for realizing a "CAD/CAE seamless" system from modeling to computation. In this study an effective meshless approach that uses node-by-node procedures to discretize the weak formed governing eguations derived by the principle of virtual work is proposed. To realize node-by-node procedures, three key methodologies are utilized. They are interpolation by MLSM, nodal integration and iterative solver using the stiffness at nodes. We describe the formulation and implementation, and investigate the applicability of the method in two-dimensional elastic problems.

Recently, in order to improve power plant thermal efficiency, the turbine blade, which is the most important element of the power plant, has been used under severe conditions of high loading. Therefore, for the purpose of increasing plant reliability, the blade with friction dampers has been used. This paper presents the analysis method to predict damping characteristics of the damper blades by applying the substructure synthesis method and the harmonic balance method to the bladed disk. In order to verify the validity of the analytical method proposed here, the calculated results by the harmonic balance method are compared with the results by the direct integration method. Also, the model test is carried out and the experimental data are compared with the numerical results. It is found that a large damping effect can be obtained by using the damper elements and the numerical results show good agreement with the experimental data.

Recently, in order to improve power plant thermal efficiency, the turbine blade, which is the most important element of the power plant, has been used under severe conditions of high loading. Therefore, for the purpose of increasing plant reliability, the blade with friction dampers has been used. This paper presents the analysis method to predict damping characteristics of the dampered blades by applying the harmonic balance method to the bladed disk. The numerical results show that a large damping effect can be obtained by using the damper elements. It is found that the peak frequencies of the dampered blades can be estimated by the linear finite-element method, if we choose the appropriate ratio of the friction force and the excitation force. Also, the validity of the method used in this paper is examined by comparing the calculated results with the experimental data.

When calculating the resonant response of bladed turbine disks, it has been expedient to assume that all blades on a given disk are identical. This leads to the prediction that all blades experience the same amplitude of displacement and stresses when excited by forces harmonically related to the rotor speed. However, it has been shown experimentally that significant variations in these amplitudes occur for different blades on the Same disk. These variations arise due to the effects of mistuning, wcich refers to small differences in blade characteristics. In this paper, effects of mistuning for free-standing blades and integral shroud blades are studied by using Monte Carlo simulation and the sensitivity analysis. It is found that weakly coupled systems with small damping are very sensitive to mistuning. Also, the validity of the lumped model used in this paper is examined by comparing the calculated results with experimental data.

As a fundamental research problem relating to the amplitude of Pogo oscillation of liquid propellant launch vehicles, an experimental study was conducted in which a cylindrical shell vertically hung and partially filled with liquid was longitudinally excited at the bottom in the authors' previous paper. The vibration of the shell wall was induced at the several specific ranges of exciting frequency by the mechanism of parametric excitation. To analyze this problem, a set of nonlinear equations of vibration is derived with the aid of the finite element method. Axial mode shapes of the axisymmetrical and circumferentially n-wave modes are calculated from the linear part of the set of nonlinear equations. Using these two modes, the set of nonlinear equations is reduced to the coupled equations of two degrees of freedom. The equations to calculate a stationary vibration, and its stability are derived. The range of the parametric excitation is obtained in the plane of exciting force amplitude and frequency.

As a fundamental research problem relating to the amplitude of Pogo oscillations of liquid propellant launch vehicles, an experimental study was conducted in which a vertical cylindrical shell partially filled with liquid was longitudinally excited. The vibration of the shell wall was induced at exciting frequencies close to the fundamental natural frequency of longitudinal vibration of the system. It was a phenomenon of parametric excitation, i.e. the longitudinal motion of the liquid excited the transverse wall vibration. A non-linear theoretical analysis has been carried out in order to model this phenomenon, including the study of existence and stability of this wall vibration. Good agreement was observed between the analytical and the experimental results. © 1987 Academic Press Limited.