Hiroshi Takata

Analysis of steering shimmy accompanied by sprung mass vibration on light duty truck - fundamental mechanism

Steering shimmy phenomena are classified into two groups according to vehicle speeds. One is self-excited vibration at low vehicle speeds, and the other is forced vibration at high speeds. Shimmy on a light duty truck has been considered as that of self-excited vibration. However, it causes vibration not only on the steering system but also on the cabin, with a large amplitude at relatively high speeds. The phenomenon was analyzed by performing vehicle tests and numerical simulations using simplified models. As a result, the phenomenon was found to be self-excited vibration basically caused by two closed-loop vibration mechanisms.

The use of near‐field acoustical holography (NAH) and partial‐field decomposition to identify and quantify the sources of exterior noise radiated from a vehicle

Since power‐train noise sources are ‘‘hidden’’ within the engine compartment, it is difficult to use NAH to identify the sources and the associated partial radiation fields that create the exterior noise field radiated by a motor vehicle. Integrated near‐field acoustical holography (INAH) has been developed to address this concern. INAH represents a combination of NAH, reference microphone selection procedures, and coherence techniques. The procedure entails sensing the sources inside the engine compartment by using an array of reference microphones, and then calculating the associated partial sound fields by using NAH. A key factor in the success of this procedure is the selection of a good reference microphone subset. A selection procedure has been developed by combining condition number and coherence analyses. The partial field determination problem has been approached by using both partial coherence and singular value decompositon (SVD) procedures. It has been found that the partial coherence techniqu...

Research on Nearfield Acoustic Holography. Selection Strategies for Optimal Reference Sets Using Singular Value Decomposition.

It is not always possible to apply nearfield acoustic holography (NAH) for the acoustic field composed of multiple incoherent sources. To apply NAH properly it is necessary to select optimal reference sets and divide mutually incoherent acoustic fields. In this work a new selection technique for optimal reference sets using singular value decomposition is presented and tested by using two speakers.

Research on Nearfield Acoustic Holography. Selection Strategies for Optimal Reference Sets Using ARMA Model.

It is not always possible to apply Nearfield Acoustic Holography (NAH) for the acoustic field composed of multiple incoherent sources. To apply NAH properly it is necessary to select optimal reference sets and divide mutually incoherent acoustic fields. In this work a new selection technique for optimal reference sets using the ARMA model is presented and tested by using actual tire noise.