Tomoyoshi Horie

A two-dimensional computational study on the fluid–structure interaction cause of wing pitch changes in dipteran flapping flight

SUMMARY In this study, the passive pitching due to wing torsional flexibility and its lift generation in dipteran flight were investigated using (a) the non-linear finite element method for the fluid–structure interaction, which analyzes the precise motions of the passive pitching of the wing interacting with the surrounding fluid flow, (b) the fluid–structure interaction similarity law, which characterizes insect flight, (c) the lumped torsional flexibility model as a simplified dipteran wing, and (d) the analytical wing model, which explains the characteristics of the passive pitching motion in the simulation. Given sinusoidal flapping with a frequency below the natural frequency of the wing torsion, the resulting passive pitching in the steady state, under fluid damping, is approximately sinusoidal with the advanced phase shift. We demonstrate that the generated lift can support the weight of some Diptera.

Passive maintenance of high angle of attack and its lift generation during flapping translation in crane fly wing.

SUMMARY We have studied the passive maintenance of high angle of attack and its lift generation during the crane flys flapping translation using a dynamically scaled model. Since the wing and the surrounding fluid interact with each other, the dynamic similarity between the model flight and actual insect flight was measured using not only the non-dimensional numbers for the fluid (the Reynolds and Strouhal numbers) but also those for the fluid—structure interaction (the mass and Cauchy numbers). A difference was observed between the mass number of the model and that of the actual insect because of the limitation of available solid materials. However, the dynamic similarity during the flapping translation was not much affected by the mass number since the inertial force during the flapping translation is not dominant because of the small acceleration. In our model flight, a high angle of attack of the wing was maintained passively during the flapping translation and the wing generated sufficient lift force to support the insect weight. The mechanism of the maintenance is the equilibrium between the elastic reaction force resulting from the wing torsion and the fluid dynamic pressure. Our model wing rotated quickly at the stroke reversal in spite of the reduced inertial effect of the wing mass compared with that of the actual insect. This result could be explained by the added mass from the surrounding fluid. Our results suggest that the pitching motion can be passive in the crane flys flapping flight.

Cracked beam under influence of dynamic electromagnetic force

Abstract This paper is concerned with both numerical analysis and experiment on the fracture phenomena related to the electromagnetic force, considering an edge-cracked beam which carries a transient current I and is placed in a uniform and steady magnetic field B 0 . As for the numerical study, isoparametric quarter point elements are used to treat the singularities at the crack tip both for the stress and the current density. Also some discussions are presented on the application of nonlinear fracture mechanics to the present problem, the temperature increase at the crack tip and the skin effect of the electric current.

Thermal shock tests on various materials of plasma facing components for FER/ITER

Development of plasma facing components and materials is a key element in the R&D program for the Fusion Experimental Reactor (FER), which has been designed at JAERI, and the International Thermonuclear Experimental Reactor (ITER), which has been designed under international collaboration. In these next-step tokamak devices, the plasma facing components and materials will be exposed to severe heat load and incident particle flux. The concern is especially acute that the extremely high thermal shock due to plasma disruption could cause material fracture. Efforts on developing the first wall and divertor have been energetically undertaken at JAERI. The present paper describes recent experimental and analytical results on thermal shock characteristics of various materials.

A simulated plasma disruption experiment using an electron beam as a heat source

An experimental study was made on the behavior of a solid surface subjected to an extremely high heat flux similar to that expected during a plasma disruption. An electron beam was used as the heat source to simulate the high heat flux. The beam was defocused in an attempt to give as much uniform heat flux as possible on the test surface. The 5-mm-diameter test pieces were made of 304 stainless steel, aluminum, and zinc. Heat fluxes from 10 to 110 MW/m2 were applied on the test pieces for durations of 90 to 180 msec. Special attention was paid to the measurement of the surface heat flux on the test surface. Comparison between experimental and analytical results on melt layer thickness and evaporation loss is made. An improved thermal analysis code (DAT-K) was developed for the analysis. Agreement between the experimental and analytical results on melt layer thickness is good. For evaporation loss, experimental and analytical results are in fair agreement. Features of the experiments and analysis that lead to the differences in the results are discussed.

An experimental and three-dimensional computational study on the aerodynamic contribution to the passive pitching motion of flapping wings in hovering flies.

The relative importance of the wings inertial and aerodynamic forces is the key to revealing how the kinematical characteristics of the passive pitching motion of insect flapping wings are generated, which is still unclear irrespective of its importance in the design of insect-like micro air vehicles. Therefore, we investigate three species of flies in order to reveal this, using a novel fluid-structure interaction analysis that consists of a dynamically scaled experiment and a three-dimensional finite element analysis. In the experiment, the dynamic similarity between the lumped torsional flexibility model as a first approximation of the dipteran wing and the actual insect is measured by the Reynolds number Re, the Strouhal number St, the mass ratio M, and the Cauchy number Ch. In the computation, the three-dimension is important in order to simulate the stable leading edge vortex and lift force in the present Re regime over 254. The drawback of the present experiment is the difficulty in satisfying the condition of M due to the limitation of available solid materials. The novelty of the present analysis is to complement this drawback using the computation. We analyze the following two cases: (a) The equilibrium between the wings elastic and fluid forces is dynamically similar to that of the actual insect, while the wings inertial force can be ignored. (b) All forces are dynamically similar to those of the actual insect. From the comparison between the results of cases (a) and (b), we evaluate the contributions of the equilibrium between the aerodynamic and the wings elastic forces and the wings inertial force to the passive pitching motion as 80-90% and 10-20%, respectively. It follows from these results that the dipteran passive pitching motion will be based on the equilibrium between the wings elastic and aerodynamic forces, while it will be enhanced by the wings inertial force.

Present status of JT-60 upgrade

In the JT-60 tokamak, the original outer single-null plasma containment vacuum vessel and poloidal field coils, will be exchanged with those of large D-shaped cross sections. The basic dimensions of the new vessel will allow plasmas of 6-MA current, 70 to 100 m/sup 3/ volume, and vertical elongations of 1.4 to 1.7. Installation of a large vessel is made possible at the cost of high toroidal ripple volume in the space occupied by the plasma and at the cost of high electromagnetic force acting on the coils and the vessel. A prime requirement for the modification is maximizing the plasma performance with minimum expense, while ensuring access to the plasma for heating and diagnostics. The plasma configuration is designed to allow the largest D-shape discharge with a lower single null, within the boundary of the original toroidal field coils. The D-shaped vessel is designed according to a new concept of Inconel 625 all-welded continuous chamber in a double skin construction. Rectangular tubes are sandwiched by three-dimensionally curved skins to form a totally everywhere rounded vacuum vessel. The gas is being changed to deuterium from hydrogen, which will allow neutral beams of 40 MW. The lower hybrid and ion-cyclotron systems will be provided with larger antennas.<<ETX>>

A computer program system for transient electromagnetic analysis on a tokamak device

A description is given of EDDYTOR, an eddy-current analysis and evaluation code system for tokamak reactors. The EDDYTOR system is able to calculate eddy currents, electromagnetic forces, stress and deformation, and plasma position and control properties. The program was designed to operate on an engineering work station utilizing a commercial CAE (computer-aided engineering) package. It has been shown to save on design time and to maintain overall design consistency, since a comprehensive design analysis can be performed within the same system. >

Lifetime analysis for fusion reactor first walls and divertor plates

Lifetime analysis of fusion reactor first walls and divertor plates is performed by (1) a one-dimensional analytical plate model, and (2) a two-dimensional elastic-plastic finite element method. Life-limiting mechanisms and the limits of applicability for these analysis methods are examined. Structural design criteria are also discussed.

Numerical instability of magnetic damping problem of elastic plate

Numerical instability occurs in an analysis of a vibration with magnetic damping, or an electromagnetic and structural coupled problem. In this paper, the numerical instability of the coupled analysis is examined by the finite element in time. It is confirmed that the simultaneous method is unconditionally stable even if the magnetic field and the time increment are large. For the staggered method, we obtain the conditions where the numerical instability occurs.