Isoharu Nishiguchi

On the local force computation of deformable bodies in magnetic field

In order to examine the accuracy of the nodal force method, a comparative study of the FEM solution has been performed which includes the edge element and the nodal element formulations. The treatment when the Maxwell stress tensor becomes asymmetric has also been investigated.

Verification of Alternative Criteria for Shakedown Evaluation Using Flat Head Vessel

Alternative stress evaluation criteria suitable for Finite Element Analysis (FEA) proposed by Okamoto et al. [1] have been studied by the Committee on Three Dimensional Finite Element Stress Evaluation (C-TDF) in Japan. Thermal stress ratchet criteria in plastic FEA are now under consideration. Two criteria are proposed: evaluating variations in plastic strain increments and evaluating variations in the elastic core region. To verify the validity of these criteria, calculations were performed for several typical models in C-TDF [2]. This paper shows calculations and evaluation results of a Flat Head Vessel for shakedown. To study shakedown criteria for gross structural discontinuity, a flat head vessel is surveyed. The flat head vessel consists of a stiff flat head and a shell and is subjected internal pressure and thermal cycle. The elastic shakedown area and the plastic area are compared and plastic strain increments are surveyed. A shakedown evaluation method based on distribution of elastic-plastic strain range is proposed.© 2002 ASME

A comparative study of magnetostatics using three-field and conventional vector potential formulations

The three-field finite element formulation for electromagnetics was proposed as an alternative to the existing vector potential formulations. In the formulation, three fields, that is (i) the vector potential, (ii) the divergence of the vector potential and (iii) a scalar variable which is adjoint to (ii), are interpolated independently and the imposition of the gauge condition can be relaxed. A comparative study of magnetostatic problems is presented which includes the calculations by conventional vector potential formulations using second order nodal elements. It is shown that the three-field formulation gives better results than conventional vector potential formulations with and without gauging.

On the pressure buckling of rectangular bellows for fusion reactors

Bellows are planned for use in the torus vacuum vessel of ITER to absorb the relative displacements resulting from thermal expansion. Though both sides of the bellows are in vacuum during normal conditions, these bellows would be subjected to external or internal pressures of several MPa during accidents. Since the vacuum vessel forms the tritium boundary during postulated accidents, the prevention of bellow failure in these events is very important in the ITER design. For equipping the internal components, rectangular bellows are preferable to circular bellows in the ITER design. However, investigations concerning pressure buckling of rectangular bellows are few. Therefore, we investigated the buckling behavior of rectangular bellows and proposed a simplified evaluation method based on the half pitch model for bellows with a relatively high length-to-diameter ratio, where elastic column squirm is dominant. For bellows with a lower number of convolutions, however, inplane squirm buckling should be considered, therefore, we have investigated inplane squirm of rectangular bellows and compared it with that of circular bellows in this paper.

Seismic Study of High-Temperature Engineering Test Reactor Core Graphite Structures

The High-Temperature Engineering Test Reactor (HTTR) is a 30-MW(thermal) helium gas-cooled reactor with a core composed of prismatic graphite blocks piled on core support structures. Safety analyse...

Theoretical and Experimental Investigation of Pipe Wall Thinning Detection Using Guided Waves

A method to investigate pipe wall thinning using guided waves has been developed for pipes in thermal power generation facilities. In this paper, the reflection coefficient and the transmission coefficient are derived for the torsional waves which propagate along a pipe and a simplified method to predict the waveform is proposed. The predictions of the waveforms by the FEM and a simplified method based on the reflection of torsional waves are also examined by comparing with experimental data.Copyright

Application of Shell Elements to Collapse Load Analysis

Shell elements make it easy to generate FEA model, and reduce time and costs for the analysis. Those are useful for surveying shape of structure. In this paper, FEA with shell elements are performed for a clamped circular plate in order to survey influence of mesh types on the collapse load, as for the sizes, the number of integration points and the order of shape functions. Based on the results, collapse load analysis for a torispherical head vessel for 2-dimensional model with shell elements is performed and studied for applicability of shell elements to collapse load analysis.Copyright

Verification of Alternative Criteria for Shakedown Evaluation Using 2-Dimensional and 3-Dimensional Nozzle Models

Alternative stress evaluation criteria suitable for Finite Element Analysis (FEA) proposed by Okamoto et al. [1] have been studied by the Committee on Three Dimensional Finite Element Stress Evaluation (C-TDF) in Japan. Thermal stress ratchet criteria in plastic FEA are now under consideration. Two criteria are proposed: evaluating variations in plastic strain increments and evaluating variations in the elastic core region. To verify the validity of these criteria, calculations were performed for several typical models in C-TDF [2]. This paper shows calculations and evaluation results of 2-dimensional and 3-dimentinal nozzles for shakedown and Ke-factors, as defined by equation 2. Two models are used. One is a 2-dimensional (2D) axi-symmetric model of a typical nozzle. The other is a 3-dimantional (3D) model of the nozzle of which shell radius is half of 2-dimensional model. The primary and secondary stress, shakedown analyses using elastic-plastic FEA and Ke-factors which are directly calculated from elastic-plastic FE analyses are surveyed. The results show that the alternative criteria are applicable for those models. The analysis results of the 2D model show good relation to those of the 3D model.Copyright

Simulation of three-dimensional motion of a piano string using detailed and simplified computational models

It is well known that the decay curve of the piano sound is steep for the first few seconds and followed by slower decay at longer time. The causes of this double decay are also known: the effect of polarization of a string which is considered to be caused by the motion of the bridge which is connected to the string by two bridge pins and interaction among multiple strings for a note. As for the later, it is explained that multiple strings for a note tend to vibrate out of phase each other when they have slightly different frequencies and this suppresses the energy transferred to the soundboard through the bridge. However, to make quantitative evaluations of these causes, it is indispensable to develop a physical model of the piano in which contributions of each factor of these causes can be simulated with a necessary degree of accuracy. In this study, the finite element method and the mode superposition method are employed to simulate the three-dimensional motion of a piano string in which interaction wi...

Outline of the JSME Rules on Pipe Wall Thinning Management for Thermal Power Generation Facilities

In response to the pipe wall thinning damage experienced in power plants in 2004, the Japan Society of Mechanical Engineers (JSME) has started activities to develop technical standards on the pipe wall thinning management. The first edition of the JSME rules on pipe wall thinning management for thermal power generation facilities (JSME S TB1-2006 [1]) was issued in March 2006, and its latest edition will be issued in 2007, which describes the technical requirements to meet the JSME performance-based rules for pipe wall thinning management (JSME S CA-1 2005 [2]). Based on 24,774 inspection data obtained at the thermal power plants in Japan, the latest JSME rules will show the specific attention to the need for inspection of piping systems that are susceptible to the wall thinning damage. The JSME rules describe the selection of thickness measurement locations such as downstream of piping configurations that produce turbulence, downstream of orifices, downstream of control valves, and they describe the periodic inspections including the first inspection to be scheduled taking the wall thinning rate data at the equivalent locations into consideration. The JSME rules stipulate some available inspection methods such as ultrasonic scanning, radiographic profile, eddy current and potential drop technique. This paper presents outline of the JSME rules including basic philosophy, technical requirements on the inspection and testing practices and the relation with the regulations in Japan.Copyright