Experimental investigation of the effects of underwater exposure on the damping characteristics of bolted structural connections for plates and shells

Abstract

Recent studies have indicated that use of the bolted structural connection and the introduction of a viscoelastic material at the joint build-up can reduce the vibration response of a structure. Many potential applications utilizing this type of vibration reduction must operate in an underwater environment. A test structure consisting of two concentric circular shells connected by four vanes and assembled with bolts was tested to determine the effects of underwater exposure on the damping properties of a bolted structure. The effects of underwater exposure on system damping were examined for various structural bolt torques and for the application of a viscoelastic layer at the joint interfaces. With increasing underwater exposure time, the modal frequencies, damping and response amplitude remained constant. The changes in the frequency response of the structure with underwater exposure resulted from the effects of increased viscous fluid layer damping at the joint interfaces. As water replaced the air at the joint interfaces, with continued underwater exposure, the effects of viscous fluid layer damping increased