Experimental investigation on nonlinear dynamic response of towing cable under vessel motion

Abstract

Marine towing cable is a crucial equipment of the underwater towing system which can acquire the marine resources distribution in the sea. The marine towing cable will experience nonlinear dynamic problems due to the vortex shedding and vessel motion during the towing movement. In order to investigate the dynamic response characteristics of the towing cable during the working process, a set of experimental devices for towing cable is designed and a PPR (Polypropylene-Random) pipe with the aspect ratio of 150 is tested with coupled uniform towing and vessel motion. The characteristics of response amplitude and frequency under uniform towing are compared and analyzed comprehensively with different towing speeds and towing depths. The key characteristics of nonlinear dynamic response under vessel motion are then discussed. Some phenomena involving multi-modal participation, frequency transition and amplitude modulation are captured. The vessel motion will excite ωCT - ωT, ωCT + ωT, ωT frequency components in the CF (cross-flow) direction which may be caused by the parametric excitation, and wave frequency ωT dominates the IL (in-line) direction response. Some extreme motion conditions may enlarge the response displacement in the IL and CF direction. It is suggested that the vessel motion should be taken into account in the evaluation of the nonlinear dynamic analysis of marine towing cable.