Correlation of experimental and finite element modal analysis of the PHALANX M61A1 Close-In Weapon System

Abstract

The M6 1 Al gatling gun is the principal component of the PHALANX close-In Weapons System (CIWS), which provides U.S. Navy surface ships with a final defense against anti-ship cruise missiles. The objectives of this study are to provide an experimental set of modal parameters and to validate a new finite-element model (FEM) of the gun. Swept sine frequency response measurements on an actual PHALANX gun were conducted in the laboratory to obtain a complete set of modal parameters (frequency, amplitude, mode shapes). The finite-element model was couelated using the experimental modal frequencies as a reference. This result was obtained by adjusting stiffnesses in the three bearing assemblies within the gun: ball-bearing, needle bearing and ball joint. The investigation was conducted with and without the production muzzle restraint currently used in the fleet. Good agreement between the measured and computed FEM modal parameters was found for the first three modes in both the horizontal and vertical directions for the 5 to 125 Hz frequency range of interest. With the production muzzle restraint installed, agreement between the experimental and finite-element results was poor. It is suspected that 'play' in the actual restraint mounting system is present, which is not modeled by the FEM. Recommendations are made for follow-on studies. (MM)