Masaaki Okuma

Identification and Prediction of Frame Structure Dynamics by Spatial Matrix Identification Method

This paper presents the results of using an experimental spatial matrix identification method to predict the dynamics of a frame structure under various boundary conditions. The single-input-multiple-output frequency response functions (FRFs) of the test structure under the free-free boundary condition are measured by hammer testing. Using the FRFs, a set of spatial matrices is constructed in order to represent the structural dynamic characteristics of the system by the new method. Using the spatial matrices, the dynamic characteristics of the test structure under the boundary condition of clamping 4 points is predicted. The prediction is adequately accurate for practical application. The results of the prediction demonstrate that the spatial matrices identified by this method can be used for structural modification and substructure synthesis in the field of computer-aided mechanical engineering.

An Optimum Embossment of Rectangular Section in Panel to Minimize Noise Power

In this paper, the authors propose a new method for optimum design of embossed panel sections on vibrating panel-like structures to reduce noise. It is proposed in the method to use the mapping of sound pressure level on the vibrating panels surface for best positioning of an embossed panel section, which means a raised panel section, in other words, and to apply the particle swarm optimization algorithm for determining the best dimensions of the embossed panel section. The optimum design method is applied to a rectangular aluminum panel whose size is 0.45 m X 0.4 m with thickness 0.001 m under the boundary condition of clamping four edge lines. Then, according to the optimum design, an embossed section is actually made in each panel by embossing using a press machine, and experiments are carried out to the panels for verification. The application study is carried out for two cases of different positions of a point force excitation on the panels. The two applications demonstrate that the embossed panel sections designed by the optimization method can realize good reduction of sound power.

Correction of finite element models using experimental modal data for vibration analysis

Abstract A method is presented for correcting finite element models by referring their modal parameters to experimental modal data. The method is based upon both the sensitivity analysis and the least squares method, and gives a physically realistic solution of appropriate design variables. In this paper, the procedure of the method is first explained, and then two applications are presented. The first application is a correction of a beam structure, as a basic research study. The second is a correction of a practical structure, a “Centre-beam”, which is a structural component of an automotive body. The initial finite element models of both cases are successfully corrected to adjust their dynamic characteristics to experimental results. In particular, it is experimentally verified that the corrected finite element model of the “Centre-beam” is able to represent its dynamic characteristics well, even under different boundary conditions. The verification proves the physical validity and the practical availability of the corrected model.

Implementation of Single and Multiple Adaptive Step-Size Algorithm to ANC

The purpose of this paper is to investigate a modified adaptive step-size algorithm and implement an active noise control (ANC) system. It is well known that there is a tradeoff between steady state error and convergence rate depending on the step size. This study shows that the new algorithm can track changes in the dynamic characteristics of the ANC system as well as produce a low steady state error. Simulation results are presented to compare the performance of the new algorithm to the basic least mean square (LMS) algorithm. Although there have been several studies of adaptive step-size algorithms, no quantitative analysis has yet been reported for real time active noise control application as far as the authors know. Experimental results are presented for a duct system. The results indicate that the new algorithm provides better performance than the fixed step-size filtered-X least mean square (FXLMS) algorithm.

Repeatability of Stored Configuration of a Large Solar Sail with Non-negligible Thickness

Hiraku Sakamoto∗, Shogo Kadonishi, Yasutaka Satou, Hiroshi Furuya, Tokyo Institute of Technology, Tokyo 152-8552, Japan Yoji Shirasawa, Nobukatsu Okuizumi, Osamu Mori, Hirotaka Sawada, Japan Aerospace Exploration Agency, Kanagawa 252-5210, Japan Jun Matsumoto, University of Tokyo, Tokyo 113-8656, Japan M. C. Natori, Waseda University, Tokyo 169-8555, Japan Yasuyuki Miyazaki Nihon University, Chiba 274-8501, Japan and Masaaki Okuma Tokyo Institute of Technology, Tokyo 152-8552, Japan

Elimination of Bias Errors Due to Suspension Effects in FRF-Based Rigid Body Property Identification

The prediction of a mechanical structures rigid dynamic behavior requires knowledge of ten inertia parameters. In cases where no accurate models of the structures geometry and mass distribution are available, the ten inertia parameters must be determined experimentally. Experimental methods based on measurements of frequency response functions (FRFs) are subject to bias errors due to suspension effects. This paper proposes a method for eliminating these errors by using a single-wire suspension condition and modeling the suspensions effect on the FRFs. The suspension model depends only on the unknown rigid body properties and on three easy-to-measure parameters. The rigid body properties are determined by fitting FRFs derived from the suspension model and from the rigid body mass matrix directly to the experimental FRF data. Eliminating the suspension bias makes it possible to use low-frequency FRF data, which in turn justifies the assumption of rigid behavior. In this way, bias-free rigid body property identification can be achieved without modal curve fitting. Simulation and experimental results are presented showing the effectiveness of the approach.

Experimental study of reflector shape control under various thermal conditions

This study clarifies the effect of thermal deformation in the reconfigurable space reflector system, through a series of experiments in a thermostatic chamber using a prototype of reconfigurable space reflectors. This study then discusses possible countermeasures against precision degradation of such system due to the thermal deformation, exploiting a finiteelement model that is tuned to the experimental results. Though reconfigurable reflector systems inherently have the mismatch in the coefficients of thermal expansion among their structural members, the effect of the mismatch may be minimized by a proper combination of several materials. The prototype used in this study is designed as a preliminary model of a secondary mirror for future radio astronomy satellites.

Sound-Radiation Analysis for Boat Hull Based on Hammering Test and BEM

The accurate prediction of the sound power radiated from complicated structures, whose precise models are practically difficult to be made by the finite element method, is performed by an experimental-based approach combining impulse vibration testing and the boundary element method. This approach is applied to a small boat hull comprising of some panels with some longitudinal bending stiffeners and ribs as a basic research work in the series of a research for establishing an integrated analysis and optimization of mechanical systems to be assembled some components such as boat hulls and outer engines by means of using both experimental and theoretical modeling. It is verified that the predicted sound power level radiated from the hull is in a good agreement with an experiment. The parts of the hull radiating the noise dominantly can be identified.Copyright

Attenuation of tall flexible structures using longitudinal moving mass: Moving finite element method

For the foreseeable future, tall building structures will be built taller and more flexible, which means more vulnerable to excitations. As such, there is considerable interest in developing structural control methods to protect against harmful vibrations. However, challenges present themselves for conventional mass damper systems as these tend to primarily utilise lateral motion which becomes very limited as the height of structures increases. This article proposes a novel approach to reduce tall building’s long-period oscillations using mass damper motion in the much larger longitudinal direction. This motion induces Coriolis effect and if manoeuvred properly can be used to effectively reduce vibration of the primary structure. Numerical analysis was done using finite element method. The Shinjuku Mitsui Building was used as a benchmark for the primary structure, which was modelled as a vertical cantilever beam. The results showed the concept to be a viable approach for damping long-period vibrations of flexible structures. Enhancing this effect was also introduced and briefly discussed, using a multiple-degree-of-freedom damper and a constant positive velocity water-flow damper as examples. Further work continues for optimum design of the concept to make it a practical approach for tall buildings. Additionally, investigation into enhancing the damping effect is being done in more detail. This approach provides new possibilities for vibration control of any long-period structure.

A03 Construction of Thermal Analysis Model for Smart Reconfigurable Reflector

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