Passive damping to attenuate snap loading on a ROV umbilical cable

Abstract

Summary form only given. Snap loading of the umbilical cable connecting a ship to a remotely operated vehicle (ROV) and its cage is a major problem when the ROV system is operating in rough sea conditions. Snap loading is the instantaneous, high magnitude, tensile loading of a cable. This loading arises when the amplitude and frequency of the ship motion is such that it causes parts of the cable to be subjected to compressive forces. Since cables are incapable of resisting such loads, slack can develop in a section of the cable where there is a compressive load. If the rate of retensioning is rapid, the cable will then experience snap loading. This paper describes the design of a passive damping system to attenuate snap loading in the ROV system. The mathematical model consists of the following sub-systems: 1) the boom and ship, 2) the cable, 3) the passive damper, and 4) the cage. The cable is modelled with discrete elements implemented using finite element theory. The total cable length is divided into a large number of elements, and the motion equations are written for each element, and a forcing function is applied to the top element.<>