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

## 5aSA4. An approximation to the local acoustic impedance of a cylindrical
shell with hemispherical endcaps.

**Michael J. Utschig
**

**
Jan D. Achenbach
**

**
Takeru Igusa
**

**
**
*Dept. of Civil Eng., Northwestern Univ., Evanston, IL 60208
*

*
*
A method has been developed to approximate the local radiation impedance
of a cylindrical shell with hemispherical endcaps. This approximation greatly
reduces the effort required to calculate the acoustic impedance as compared to
an approach using a variational method. The approximate method uses the exact
acoustic impedances of several separable geometric shapes to approximate the
acoustic impedance of a complex structure that is a composite of those shapes.
The shell is broken into three components: two hemispheres and a finite
cylinder. These components are parts of regions that are separable in an
orthogonal coordinate system. It is assumed that the acoustic impedance of the
components is the same as the acoustic impedance calculated exactly for the
separable shapes. Furthermore, it is assumed that the local acoustic impedance
of the original complex shape is the same as that of corresponding points on
the simple components. The accuracy is improved when the interaction between
neighboring components is considered. The acoustic impedance and surface
pressure generated by a load applied in the center of the complex shape is
compared with that calculated using a variational formulation.