Naoki Niwa

Forced vibration test of a building with semi-active damper system

The authors developed a semi-active hydraulic damper (SHD) and installed it in an actual building in 1998. This was the first application of a semi-active structural control system that can control a buildings response in a large earthquake by continuously changing the devices damping coefficient. A forced vibration test was carried out by an exciter with a maximum force of 100 kN to investigate the buildings vibration characteristics and to determine the systems performance. As a result, the primary resonance frequency and the damping ratio of a building that the SHDs were not jointed to, decreased as the exciting force increased due to the influence of non-linear members such as PC curtain walls. The equivalent damping ratio was estimated by approximating the resonance curves using the steady-state response of the SDOF bilinear hysteretic system. After the eight SHDs were jointed to the building, the systems performance was identified by a response control test for steady-state vibration. The elements that composed the semi-active damper system demonstrated the specified performance and the whole system operated well. Copyright

Dynamic analysis of structures with Maxwell model

A numerical method has been developed for the dynamic analysis of a tall building structure with viscous dampers. Viscous dampers are installed between the top of an inverted V-shaped brace and the upper beam on each storey to reduce vibrations during strong disturbances like earthquakes. Analytically, it is modelled as a multi-degree-of freedom (MDOF) system with the Maxwell models. First, the computational method is formulated in the time domain by introducing a finite element of the Maxwell model into the equation of motion in the discrete-time system, which is based on the direct numerical integration. Next, analyses for numerical stability and accuracy of the proposed method are discussed. The results show its numerical stability. Finally, the proposed method is applied to the numerical analysis of a realistic building structure to demonstrate its practical validity.

Dynamic loading test and simulation analysis of full-scale semi-active hydraulic damper for structural control

A semi-active hydraulic damper (SHD) for a semi-active damper system, which is useful for practical structural control especially for large earthquakes, has been developed. Its maximum damping force is set to 1 or 2 MN, and it is controlled by only 70 W of electric power. An SHD with a maximum damping force of 1 MN was applied to an actual building in 1998. This paper first presents the results of a dynamic loading test to confirm the control performance of the SHD. Next, an analytical model of SHDs (SHD model) is constructed with the same concept for two kinds of SHDs based on the test results. Through simulation analyses of the test results using the proposed SHD model, the dynamic characteristics of the SHD can be well represented within practical conditions. Simulation analyses are also carried out using a simple structure model with the SHD model. It is shown that this SHD model can be used to precisely evaluate the control effect of the semi-active damper system and is useful in practical SHD design under the applied conditions. Copyright

New application of microwave power transmission for wireless power distribution system in buildings

A wireless power distribution system (WPDS) in buildings is proposed as the application of a microwave power transmission (MPT). Problems against a commercial MPT system, which are frequency regulation and shortage of technically and economically effective application, can be solved with the WPDS in buildings. The microwave propagates in the deck plate waveguide. Total cost of the building can be reduced and the benefit of use of electricity with the WPDS is increased.

Active response control of buildings for large earthquakes - seismic response control system with variable structural characteristics

This paper presents two types of active seismic-response control systems with variable structural characteristics, developed with the objective of ensuring that the safety and function of buildings are not impaired by large earthquakes. The systems are characterized by the active seismic-response control of large-scale civil engineering structures during large earthquakes, using only nominal amounts of energy. One system is the non-resonant active variable stiffness (AVS) system. The results of applying this system to an actual building and confirming its effectiveness through seismic observation are given. Additionally, the results from a simulation analysis evaluating the effectiveness of the system if applied to a high-rise building are also included. Then a brief outline is given of the other system, the active variable damping (AVD) system.

S-Parameter Analysis of GaN Schottky Diodes for Microwave Power Rectification

A gallium nitride (GaN) Schottky diode on semi-insulating SiC has been developed for microwave power rectification. A 2 μm x 100 μm finger type diode shows ON resistance of 8.2 Ω and depletion capacitance of 0.36 pF at 0 V with breakdown voltage of 90 V. S-parameter analysis separated the ON resistance into the intrinsic part and the access region part, which will benefit device optimization. With a 10-finger diode, RF/DC conversion efficiency of 74.4% is obtained at input power of 5 W and frequency of 2.45 GHz.