Improvement in output power of vibration generators based on piezoelectric elements by using internal capacitor cancel control rectifier

Recently, energy harvesting has attracted increasing attention. The present study focuses on vibration generators based on piezoelectric elements by proposing an internal capacitor cancel control (ICCC) rectifier to improve the output power. The proposed rectifier cancels the internal capacitor to improve the output power while retaining the maximum output power. Accordingly, this paper experimentally demonstrates the improvement in output power by using the ICCC rectifier compared to conventional circuits and the previous proposed circuit.     

Parallel computing for incompressible flow using a Nodal-Based method

In this paper, the development of a seamless system for parallel flow analysis using the “free-mesh method”, which is a kind of meshless method, is described. The system consists of two main parts: the computation of the global mass, advection, diffusion, gradient, and divergence matrices, and the time integration by the decoupled method with respect to velocity and pressure. This system is quite compatible with the parallel environment because the matrices are independently computed node-by-node without any node-element connectivity information, and furthermore because the fractional step method, with the interpolation functions for velocity and pressure being of equal order, is used with the conjugate gradient solver for the time integration. A parallel efficiency of approximately 83 was achieved for a large-scale problem with 480,000 degrees of freedom using 16 processors.     

A parallel triangular decomposition algorithm on a workstation network with application to structural vibration analysis

This paper presents a parallel triangular decomposition algorithm for banded symmetric matrices and its application to structural vibration analysis, which gives high rates of parallel efficiency on a workstation network. In case of decomposition of a matrix with halfbandwidth 822, the working efficiency rate was 84% using a network of six workstations (SUN SparcStation 20s). The algorithm provides a high rate of working efficiency in parallel environment with local memory, even if the communication time is considerably longer than the operation time. As an application of the algorithm, a finite element (FE) system for structural vibration analysis with the parallel decomposition algorithm was developed on the above workstation network and a model with more than 100,000 degrees of freedom (DOFs) was successfully analyzed by the system. The computation time for the model with 10,752 DOFs and halfbandwidth 822 was 3,661 sec by the present parallel system, whereas the computation time by a single workstation was 14,335 sec.     

Direct analysis method for probabilistic fracture mechanics

A new method for solving problems of probabilistic fracture mechanics (PFM) is proposed. A process of crack growth is reduced into an iterative integration equation with respect to the probabilistic distribution functions of crack geometry using approximate independence, which we have introduced. The integration equation which has a form of Stieltjes integral is solved by a numerical method. Some PFM problems are solved using the present method, and the results are compared with those by the MC method. Failure probabilities obtained from both calculations agree well. Execution time of the present method is shown to be remarkably short.     

The influences of mesh subdivision on nonlinear fracture analysis for surface cracked structures

The leak-before-break (LBB) concept can be expected to be applied not only to safety assessment, but also to the rationalization of nuclear power plants. The development of the method to evaluate fracture characteristics is required to establish this concept. The finite element method (FEM) is one of the most useful tools for this evaluation. However, the influences of various factors on the solution are not well understood and reliability has not been verified enough. In this study, elastic-plastic 3D analyses are performed for two kinds of surface cracked structure, and the influences of mesh design are discussed. The first problem is for surface crack growth in a carbon steel plate subjected to tension loading. A crack extension analysis is performed under the generation phase simulation using the crack release technique. The numerical instability of the J-integral solution is observed when the number of elements in the thickness direction of the ligament is reduced to three. The influence of mesh design in the ligament on the solution is discussed. The second problem is for a circumferential part-through crack in a carbon steel pipe subjected to a bending moment. Two kinds of mesh design are employed, and a comparison between two sets of results shows that the number of elements on the crack surface also affects solution as well as the number of elements in the ligament.     

On the dynamic fracture toughness and crack tip strain behavior of nuclear pressure vessel steel: Application of electromagnetic force

This paper is concerned with the application of the electromagnetic force to the determination of the dynamic fracture toughness of materials. Taken is an edge-cracked specimen which carries a transient electric current I and is simply supported in a steady magnetic field B. As a result of their interaction, the dynamic electromagnetic force occurs in the whole body of the specimen, which is then deformed to fracture in the opening mode of cracking.Using the electric potential and the J - R curve methods to determine the dynamic crack initiation point in the experiment, together with the finite element method to calculate the extended J-integral with the effects of the electromagnetic force and inertia, the dynamic fracture toughness values of nuclear pressure vessel steel A508 class 3 are evaluated over a wide temperature range from lower to upper shelves.The strain distribution near the crack tip in the dynamic process of fracture is also obtained by applying a computer picture processing.     

Probabilistic fracture mechanics analysis based on three-dimensional J-integral database

The development is described of a novel Probabilistic Fracture Mechanics (PFM) code based on the three-dimensional J-integral database, giving so-called fully plastic solutions. An efficient technique for the evaluation of leak and break probabilities is also utilized, based on the Stratified sampling Monte Carlo simulation (SMC).

The outline of the present PFM code is described, and the J-integral database and the numerical technique are presented. Nonlinear effects of materials on failure probabilities are discussed through the analysis of a surface cracked structure subjected to cyclic tension.     

A large-scale three-dimensional finite element analysis of incompressible viscous fluid flow

An efficient finite element scheme for large-scale three-dimensional flow analysis is proposed. Focus of attention is placed on the time integration algorithm and some techniques for the reduction of the storage requirement, including the one-point quadrature technique and an iterative matrix solver. Application to large-scale three-dimensional problems is given to demonstrate the feasibility of the proposed scheme.     

A round robin on numerical analyses for impact problems

In this paper, two types of numerical tests are performed using several general- and special-purpose computer codes to understand dynamic behaviors of CASK for nuclear fuel shipping under the impact onto rigid floor due to the accidental fall from the height of 9 m. Discussed are the efficiency and the validity of direct time integration schemes and the effects of material and geometric nonlinearities and contact conditions on the numerical data.     

Ductile fracture of edge-cracked beam under dynamic electromagnetic bending force

Dynamic and ductile fracture of edge-cracked beam made of Type 304 stainless steel under electromagnetic bending force is studied experimentally as well as theoretically. In the theoretical part, we calculate the extended J-integral with the effect of both electromagnetic force and thermal stress caused by the Joule heating concerning the fracture phenomena due to the electromagnetic force. In the experiments, the edge-cracked beam specimens of Type 304 stainless steel are fractured under the electromagnetic force, measuring the crack initiation time, the crack velocity etc. Finally, the theoretical and the experimental results are compared.