ASA 129th Meeting - Washington, DC - 1995 May 30 .. Jun 06

3aSA5. Vorticity characteristics of the vibration intensity field and the structure-borne sound.

Nobuo Tanaka

Vib. and Sound Div., Mech. Eng. Lab., 1-2 Namiki, Tsukuba Science City, Ibaraka 305, Japan

This paper deals with the characteristics of real vibrational power flow in a simply supported rectangular panel under the action of feedforward vibration control. It is found that the path of the power flow is a combination of translations and rotations, the rotations induced by the interference of two modes which products a ``vortex generating block.'' Particular emphasis is placed on the vortex power flow in the vibration intensity field. A qualitative formula for predicting the number of power flow vortices, as well as the discussion of the vortex period, is put forward. Then, by introducing an energy stream function, the generation mechanism of the vortex power flow is quantitatively discussed. The fundamental characteristics of the vortex power flow are further clarified by vortex function derived from the intensity field. A novel method to induce a vortex at an arbitrary location of the plate is also shown, which may have practical applications in controlling the path of vibrational power flow in systems of large extent. Moreover, the influence of the induced vortex power flow on the plate onto the acoustic intensity distribution is investigated, showing that the rotational direction of the vortex on the plate is not always the same with that of the acoustic intensity in the nearfield.