Vibrational and acoustic power flow of an actively controlled thin plate

Abstract

This paper examines the characteristics of real vibrational power flow in a simply supported rectangular panel under the action of feedforward vibration control, induced by a control source input which is slightly sub-optimal such that the primary source is producing a slight amount of real vibrational power, and the control source is absorbing the same amount. It is found that the path of the power flow is a combination of translations and rotations, the rotations being induced by the interference of two modes which produces a ''vortex generating block.'' A qualitative formula for predicting the number of power flow vortices, as well as the discussion of the vortex period, is presented. Then, a quantitative formula for expressing the power flow vortices is discussed from the viewpoint of a stream function. A novel method to induce a vortex at an arbitrary location in 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 in the plate on the acoustic intensity distribution is investigated, showing that the rotational direction of the vortex in the plate is not always the same as that of the acoustic intensity in the near field. © 1996 Institute of Noise Control Engineering.

Numerical analysis and visualisation of energy flow by intensity vector method for a fluid-loaded structure

“…The change of sound vibration power is driven almost completely by the progressive wave characteristics in acoustic medium and the structural normal modes. 29 The sound power is close to the vibrational power of the stiffened plate at 709Hz corresponding to the structural nature frequencies in water, and the excitation point is at the peak of the mode shape, which makes the sound radiation power very large.…”

“…It is reported qualitatively that a pair of vibra- tion modes whose resonance frequencies that are very close to each other are necessary to produce the vibration intensity pattern; if these vibration modes are excited simultaneously, the vibration intensity pattern takes place due to the superposition of these vibration modes. 29 At the excitation frequency up to 709Hz, the higher order 26 th and 27 th modes make the energy flow more complex, as seen from Fig 11. The series of these pictures indicate the discrepancy in flow patterns of vibrational and acoustic intensity flows, both in air and water loading conditions. The sound radiated energy is determined by the contribution of each transverse vibration of the plate segment, while the characteristics of structural vibration intensity are related to the vibration distribution and level in the fluid-loaded structure.…”

On the use of energy based metrics in active structural acoustic control

“…Frequency (Hz) dB Attenuation (1,1) 27.52 17.01 (1,2) 52.93 17.01 (2,1) 84.68 17.14 (1,3) 95.27 17.14 (2,2) 110.09 17.12 (2,3) 152.43 17.23 (1,4) 154.54 17.00 (3,1) 179.95 17.02 (3,2) 205.35 16.99 (2,4) 211.70 17.12 (1,5) 230.76 17.05 (3,3) 247.69 17.17 (2,5) 287.92 17.12 (3,4) 306.97 17.00 (4,1) 313.32 17.13 (1,6) 323.91 17.12…”