VM-WB-MECH-101

VM-WB-MECH-101
Natural Frequency of a Submerged Ring

Overview

Reference: Schroeder, E. A., & Marcus, M. S. (1975). Finite element solution of fluid structure interaction problems. In Shock and Vibration Symposium (pp. 1-10). San Diego, CA.
Solver(s):

Ansys Mechanical

Analysis Type(s): Modal Analysis
Element Type(s): Solid

Test Case

A steel ring is submerged in compressible fluid (water). Determine the lowest natural frequency for x-y plane bending modes of the fluid-structure system.

Figure 133: Problem Schematic

Problem Schematic

Material PropertiesGeometric Properties
Steel:
E = 30 x 106 PSI
= 0.3
= 0.0089 slugs per cubic inch (per reference)
Water:
C = 57480 in/sec (speed of sound in water)
= 0.001156 slugs per cubic inch (per reference)
a = 10 in
b = 30 in
t = 0.25 in

Analysis Assumptions and Modeling Notes

The acoustic media (water) is assumed to extend to a radius of 30 inches. An acoustic pressure of zero on the outer surface of the acoustic media is modeled with a negligible value of 1 x 10-6 PSI.

Results Comparison

ResultTargetMechanicalError (%)
Frequency, Hz (higher order)10.2010.3271.245
Frequency, Hz (lower order)10.2010.4042.0

Figure 134: Total Deformation of First Mode

Total Deformation of First Mode