Development of a dynamic analysis scheme of cable for ROV operation

Abstract

Remote Operated Vehicle, ROV is the new concept equipment being made to replace the manned systems, both manned submersibles and deep-sea divers. The performance of ROV is strongly dependent upon its tether cable that is subjected to hydrostatic and hydrodynamic forces in addition to the gravity and inertia forces. As the operational depth of ROV increases, the behavior of tether cable becomes more and more complicated and the dynamic analysis of the cable become important as well as expensive and complicated for the safety of ROV operations. In this paper, a dynamic analysis scheme as well as the relevant computer program that is efficient and relatively simple, for the prediction of the behaviors of the cable and attached ROV system is developed. The scheme is valid for the analysis of a single, nonlinear, three-dimensional and static/dynamic model of a submersible cable and attached system. The Jumped mass method with Houbolt integration algorithm and Newmark method are basically employed here. In this method, the continuous distribution of the mass of the cable is replaced by the discrete distributions of the lumped masses at the finite number of points on the cable, resulting in relatively simple and effective analysis. Consequently the external forces on the cable can be simplified and calculated only at the nodal points. The problem under consideration is the examination of the behavior of the tether cable under hydrodynamic loading, excitation caused by support vessel and the trust of the relevant vehicle. Numerical examples are presented to show the reliable performance of the method and the corresponding program and its applicability. Also several experiments are performed and the results are compared with theoretical ones to provide the precisions. The scheme developed here proved to be effective and reliable for the dynamic analysis of the cable and relevant ROV system.