Eizaburo Tachibana

Application of shape memory alloys to compacting and element-quickly replaceable design in high-power density fusion reactors

Abstract Quick replacement has been accomplished by using a shape memory alloy (SMA) coupling in the conceptual design of a cassette compact toroid reactor (CCTR). Further, by using an SMA driving element, a compact large gate valve can be newly devised. This gate valve will enable in-situ handling without breaking vacuum, so that the baking of the vacuum boundary for every replacement becomes unnecessary, except the initial baking. In these applications of SMA, the compacting and quickly replaceable technology that are needed for dealing with the problems associated with very high neutron loading in a compact reactor become available by using presently available or promised materials rather than an assumed material.

Quick replacement of the fusion core parts in a cassette compact toroid reactor

A study of a conceptual design for a “cassette” compact toroid reactor, which emphasizes quick replacement, has been carried out. The quick replacement, accomplished by using a functional material, the SMA joint, is necessary to release the first wall from high neutron loading. The SMA joint permits the connection or disconnection of the joint part by means of a simple operation involving the control of the SMA temperature, without the need for an extremely intelligent robot. Pheripheral structural mechanisms have also been devised for the blanket and the shielding construction.

Effective location of active control devices for building vibrations caused by periodic excitation acting on intermediate storey

In order to investigate ways of reducing vibrations of building structures subjected to excitation acting on intermediate storey, active vibration controls are conducted with active control devices installed on different floors of the structure, and the effective location of control devices is also investigated. In this paper, we propose a new ‘Discrete-Optimizing Control Method’ for vibration control. The control forces are determined analytically which makes the ‘discrete-index function’ minimum. Through numerical simulation, the Discrete-Optimizing Control Method is proved to be an effective control method. The response reduction effects are best when the control devices are concentrated on the adjacent three floors of the vibration source. Copyright

Identification of seismic damage to structural buildings using the quasi-Newton method

In order to restore damaged buildings affected by earthquake excitations, it is important to identify damaged elements in terms of their dynamic properties; stiffness, mass and damping coefficients. In this paper, a simple method is proposed for identification of the damaged part. By considering all unknown dynamic properties of structure as variables of a target function f in nonlinear programming problem, the damage identification problem can be replaced by a typical unconstrained minimization problem. The target function is defined as f equals (Sigma) [ (yn,i) - (yn*) ]2 where (yn,i) is structural response at the time of t equals (Delta) X n derived from i-th trial variable (Xi), and (yn*) means observed response, respectively. In order to achieve quick convergence, quasi- Newton method and BFGS formulae are adopted for minimizing the target function. Two decision problems are discussed. One is the choice of structural response; displacement, velocity or acceleration. The second is the kind of external excitations that should be adopted. By observing three dimensional graphics. It appeared that good convergence can be achieved by adopting displacement response and sinusoidal excitation. Furthermore, it appeared that we should not evaluate the identified properties only from the response diagrams.

Effects of using hysteretic dampers for asymmetric frame structures on its earthquakes responses

In this paper, an emphasis is put on investigations for effectiveness of hysteretic dampers introduced to stiffness and strength asymmetric frame structures. To avoid large displacements caused by torsional responses at the flexible- edge of the structures, reductions of eccentricity are aimed on general designs of the asymmetric structures. The concepts of those structural design are based on what dynamic behaviors of building structures limited within elastic regions, so that, inelastic behaviors of stiffness and strength asymmetric frame structures are not considered sufficiently. To consider to inelastic behaviors of asymmetric frame structures by installing hysteretic dampers, numerical simulations are executed. As a result, it is assured that, by adequately locating of hysteretic dampers to the asymmetric frame structures, inelastic structural responses regarding to the maximum displacements can be reduced to the same level of those of symmetric frame structures.

Active response control using a rotor fin for wind-induced structural vibrations

Various types of active control systems have been proposed in order to reduce wind-induced structural vibrations. The objectives of this control are to keep structures safe from some distorting damages and to avoid sea sick of habitants. The typical type of those kinds of systems is so-called active mass damper system (AMD). This system aims to use controllable inertia forces of the AMD in order to reduce the structural vibrations. However, another problem may be arisen on the AMD systems. It is that dead loads of structures obviously increased by introducing this system. Moreover, the AMD system needs large electric power to shake its additional mass. In order to solve those problems, an active fin system(1,(2)) is proposed by authors as an effective technique of the active control for wind-induced structural vibrations. The concept of this system is based on an idea to use wind force itself as effective damping forces. By changing the angle of the fin according to both wind direction and structural vibration direction, wind resistant forces can be generated arbitrarily. Moreover, the active fin system requires comparatively less electric power than that of the AMD system. In this paper, the effectiveness of two different types of control devices of the active fin are investigated by experimental tests (a wind tunnel is used for this aim). One is a single-fin type and the other is a twin-fin type. Following three items are focused to investigate: (1) Composition of an effective control algorithm for the active fin system, (2) Comparisons of control effects in the case of using the single-fin type and in the case of using the twin-fins type, (3) Estimation for real wind resistance forces acting on the fins.

Finite Element Analysis of Tubular Connection Sealed with O-Ring and Shape Memory Alloy’s Coupler

Numerical Analysis method for SMA couplers is investigated. Reversible SMA couplers are chosen here. New basic rules for modeling the temperature-deformation curve under the stress field are reduced from experimental results. As for the example, numerical simulations for tubular connection sealed with o-ring and SMA coupler are presented. This example also involves geometrical-material nonlinear problems, thermo-anisotropy problem, constrained volume problem, and contact problems.

Finite Element Analysis for Shape Memory Alloy

The shape memory alloy (SMA) is used widely in structural engineerings. It can change its form about 8% by small force. But it is recovered to the original memorized shape when the temperature is raised to the phase transformation point. By making use of this peculiar nature, many types of thermo-mechanical tools were developed. But the numerical analysis method for the SMA has not been established because of its complicated behaviour. It concerns with large deformation problems, thermo-anisotropy problems and constrained volume problems. It may also concern with contact problems.