Zenzo Yamaguchi

Sound field radiated by an infinitely long elastic plate strip in contact with a vertical reflecting surface

Abstract For understanding the phenomenon nature of the elevated structure noise around motorways, theoretical studies concerning the main source are needed. Steel plate girders of elevated motorways are the main source of the elevated structure noise. Considering the real conditions, it is necessary to clarify the effect of a concrete slab on the radiated sound field from a steel plate girder. In the present study, a steel plate girder in contact with a concrete slab is modelled by an infinitely long elastic plate strip in contact with a vertical reflecting surface. The method of equivalent sources is used. The sound field radiated by the elastic plate strip is illustrated by numerical examples. The main effects of a slab on the sound field are discussed. Furthermore, the variation of the effects due to the varying height of a plate girder is demonstrated. It is shown that a concrete slab does not affect significantly the sound field radiated by a plate girder in the range of 500–1000 Hz at most receiving points, which is the frequency range of the main interest in the study on the elevated structure noise.

Reduction of radiated sound from a continuum using low‐damping vibration absorbers

When reducing the sound radiated from a resonant structure, it is necessary to ensure that the driving frequency does not correspond to any of the system resonance frequencies. In addition, it may be desirable to use dynamic vibration absorbers to reduce the response at the driving frequency. In this paper, a low‐damping vibration absorber is studied for solving noise radiation problems from a resonant, light‐gauge structure driven by a force whose frequency and amplitude are constant and whose frequency does not match any of the system natural frequencies. When the driving frequency and the structures natural frequency are different, the structure cannot be represented by as a SDOF system. Therefore, the conventional design method, based on equivalent mass, is inapplicable. In this paper, a design method based on the mobility of the structure is proposed. By means of the proposed method, the sound power radiated from a simply supported beam with an attached absorber is calculated and it leads to the fol...

Experimental identification of force radiation modes

The location of a vibration source within a machine is sometimes found to have a significant impact upon the machines radiated sound power. Radiation mode analysis is known to be a powerful tool for interpreting and predicting sound radiation from a vibrating object since radiation modes are independent of a structures surface vibration. However, knowledge of the radiation modes alone cannot be used directly to understand the relationship between vibration source location and sound power radiation. Previously, it was suggested that the radiation mode concept could be extended to understand the relationship between the sound power and the driving force distribution by combining a structures mobility matrix and its radiation modes to form force radiation modes (frad-modes). It was demonstrated by simulation that the radiated sound power can be reduced by choosing the driving force location to be at or near the nodes of the force radiation modes. Here, to further validate the usefulness of the force radiation mode concept, the acoustic transfer vectors and the mobility matrix of a thin steel strip mounted in a rigid baffle were first measured. Then, the force radiation modes were calculated by using the experimental data and it was confirmed that the force radiation modes can serve as a practical guide for choosing a vibration source location that minimizes the radiated sound power, especially at low frequencies.