Placing constrained layer damping patches using reactive shearing structural intensity measurements

The use of reactive shearing structural intensity to place small patches of constrained layer damping material in order to achieve the largest reduction in the radiated sound power of a cubic structure is described. The normal surface velocity of a square plate was measured using a laser vibrometer. The plate was measured with no damping and with various damping configurations. Reactive structural intensity was calculated for the undamped plate for velocity distributions at resonance frequencies of the first and third modes of the plate. A cube was simulated by placing various measured plate velocity distributions at these same two frequencies on one side of the cube while leaving the remaining five sides rigid. The sound power radiated by the cubic structure as a function of normal surface velocity was written using the boundary element method. Experimental results indicated that patches of constrained layer damping material placed over areas of high reactive structural intensity reduced the radiated sound power significantly more than patches of the same area placed over areas of low reactive structural intensity. Reductions as high as 10.25 dB were achieved for patches comprising only 6.4% of the area of one side of the cube by varying the number, size, shape, and placement of constrained layer damping patches to correspond to areas where the reactive shearing structural intensity magnitude was high. (C) 1997 Acoustical Society of America.