Toshihiko Horiuchi

Real-time hybrid experimental system with actuator delay compensation and its application to a piping system with energy absorber

A real-time hybrid experimental method, in which output from an actuator-excited vibration experiment and response calculation are combined on-line and conducted simultaneously in real time, is being developed as a new seismic experimental method for structural systems. In real-time hybrid experiments, however, there is an inevitable actuator-response delay, which has an effect equivalent to negative damping. To solve this problem, a real-time hybrid experimental system (including an actuator-delay compensation method) was developed. And seismic experiments were conducted in order to demonstrate the advantages of this system. Experimental results obtained using the developed hybrid experimental system were compared with exact results obtained using shaking-table experiments, and it was found that the two experimental methods gave almost identical results. It can therefore be concluded that the structural response can be obtained precisely by using the developed hybrid experimental system. Comparison of these experiments showed the advantages of the hybrid experiments; that is, they are simple and economical. This is because the hybrid experiment requires only a small structure as the excitation model, while a shaking-table experiment must consider the whole structural system. Copyright

A new method for compensating actuator delay in real–time hybrid experiments

We developed an on–line experimental system for conducting hybrid experiments in real time. It combines a computer, which conducts vibration simulation and generates a control signal, and a hydraulic actuator, which conducts a vibration experiment driven by the control signal. This system compensates for actuator delay and thus enables experiments to be carried out in real time. We evaluated the stability of the experiments with respect to the mass of the structure under excitation, and we developed a new method for compensating actuator delay in order to increase the stability condition. In this method, the compensated control signal is generated from the simulation results by using not only displacement but also velocity and acceleration. This method provides a stability criterion (allowable ratio of mass of the structure under excitation to that of a numerical model) about three times larger than that from the current method.

Shaking-Table Control by Real-Time Compensation of the Reaction Force Caused by a Nonlinear Specimen

An improved shaking-table control method has been developed. This method compensates the reaction force caused by a nonlinear specimen in real time, and thus maintains a desired table acceleration. To do so, it identifies the difference between the desired and the actual transfer characteristics of the shaking table, then compensates for the difference. Because the required time for this combination of identification and compensation is less than one second, the method can compensate, in real time, for the disturbance caused by a nonlinear specimen. By means of a series of experiments, it is confirmed that the method can maintain a desired table acceleration even when a nonlinear specimen is under excitation.

Multiple degree of freedom vibration exciting apparatus and system

The testing performs a vibration excitation testing of a part of the structure, performs a numerical calculus of vibration response of the other parts of the structure, and calculates the vibration response of a whole of the structure by combining these two methods. Testing includes calculating a position of a point of exciting force on the basis of vibration exciting, and calculating a reaction force on the basis of a load detected and the position of the point of exciting force. Then, a displacement of a numerical model is computed by using the reaction force calculated and a known external force, and calculating a vibration exciting machine displacement command value on the basis of the displacement. A drive drives the vibration exciting on the basis of an output thereof. Vibration excitation is performed in the translational direction as well as the rotational direction.

Development of SAFA, a seismic analysis program for FBR core components

A computer program, SAFA (seismic analysis program for fuel assemblies) has been developed to analyze core component vibration in fast breeder reactors (FBRs) during seismic excitation. Since an FBR core is composed of as many as 1000 core subassemblies (fuel assemblies, blanket assemblies, neutron shield assemblies, etc.), which are immersed in a coolant fluid, seismic analysis of FBR cores must consider the vibrations generated in a system with a large number of degrees of freedom with impacts under fluid-structure interactions. SAFA models subassemblies as finite beam elements. Fluid interaction forces are considered as added mass and time integration is done using mode superposition and the Nigam method. The load pad impact is modeled using a gap, a linear spring and a linear damper. The program also uses a new method to determine the nonlinear impact force, making it unnecessary to use convergence iteration. Comparison with experimental results confirms that the program can closely predict the seismic response of FBR cores.

Visual and Versatile Hybrid Seismic Testing System Incorporated With Non-Linear Finite Element Analysis

Hybrid simulation/testing systems have been developed incorporating a non-linear finite element method with a pseudo-dynamic test. In order to ensure stability and efficiency for time integration, the incremental formulation of the α-OS method has been implemented on this system. Visualization system has also been integrated to recognize both numerical simulation for whole systems and laboratory testing for local parts. Numerical hybrid examinations of the soil structure interaction problem have been conducted on this system. By these results, validity and effectiveness of this system has been demonstrated.Copyright

Verification Test for Hybrid Seismic Experimental Method Using Nonlinear Finite Element Method

An improved substructure hybrid seismic experimental method has been developed. This method consists of numerical computations using a general-purpose nonlinear finite element analysis tool and a pseudo-dynamic vibration test. Therefore, it enables seismic testing of large-scale structures that cannot be loaded onto a shaking table. The method also visualizes both data measured by sensors placed on the specimen and the results of the numerical analysis, and it helps us to understand the behavior of an entire structure consisting of a specimen and a numerical model. We performed verification tests for a piping system, in which we used a numerical model including supports, valves, and a branch pipe, and a specimen including two elbows. As results of tests, we conclude that the developed system has enough accuracy to be used as a seismic testing method.Copyright

Vibration Experiment of a Piping System Supported by Elastoplastic damper Using Real-Time Hybrid Excitation.

Hybrid experimental method, in which a vibration experiment using an actuator and a vibration analysis using a computer are simultaneously conducted by exchanging information with each other, is being developed as a new seismic experimental method. We developed a real-time hybrid experimental system using a hydraulic actuator with large excitation capacity and used it in a seismic experiment of an energy absorber. This absorber is a new type of pipe-support absorbing vibration energy by elastoplastic deformation By comparing the results of the hybrid experiment with those of the shaking-table experiment, we showed that the results obtained by the two experimental methods were close to each other. Therefore reliability of the developed hybrid experimental system was verified.