### ASA 130th Meeting - St. Louis, MO - 1995 Nov 27 .. Dec 01

## 2aSA7. Experimental measurements of vibrational energy and acoustic
radiation for a 3-D truss.

**Joseph E. Bondaryk
**

**
Ira Dyer
**

**
Leo Chiasson
**

**
J. Robert Fricke
**

**
**
*Dept. of Ocean Eng., MIT, 77 Massachusetts Ave., Rm. 5-435, Cambridge, MA
02139
*

*
*
The MIT Structural Acoustics Group is making experimental measurements to
determine the structural loss and radiation efficiency of an undamped,
three-dimensional truss structure, constructed of 0.5-in. aluminum tubing
connected by massive aluminum joints. The truss was excited with a shaker driven
by wideband white noise out to 20 kHz. The total vibrational energy in the truss
was calculated by spatially integrating the energy estimated from acceleration
measurements made over the entire truss. This value and the total input power,
as measured with an impedance head, allow estimation of the total loss factor
for the truss as a function of frequency. Total radiated sound power was
calculated by spatially integrating a set of average acoustic intensity
measurements made over a grid surrounding the truss. Since the total radiated
sound power is known, the total loss factor can easily be broken down into a
structural loss factor and a radiation loss factor. These measurements show that
the radiation loss is smaller than structural loss, but larger than radiation
from an equivalent length single strut would perdict. The additional radiation
is accounted for by a factor due to multipath in the truss. This factor is
frequency dependent and can be estimated from the data by comparing to theory.
[Research supported by ARPA and ONR.]