ABSTRACT:

An efficient method for computation of responses of cable - ROV system as a result of forces from waves and current and/or thrust of ROV is presented. Analyses are performed for the model consisting of series of links connected to each other by ball-and-socket joint representing the tethered cable and ROV, subjected to gravity and buoyancy and drag forces induced by the relative motion of the cable with wave and current. For the analysis, a computer program is developed. The program is capable of solving dynamic behavior of a nonlinear, three-dimensional, finite segment model of a submerged multi-component cable with ROV. Two different integration algorithms, i.e., Houbolt method and Newmark method are incorporated respectively, with the lumped mass method originally developed by Walton and Polachek in 1959 in the program. The time histories of dynamic tension and/or behavior of a tether cable under hydrodynamic loading, tension excitations caused by surface vessel and the thrust of ROV system are easily predicted. The present Finite Difference scheme is believed to have practical application potentials for engineers since the procedure is concise and computing time is relatively small comparing with Finite Element Method approach. For typical - ROV systems, the two methods are employed for the dynamic analysis and the results are compared. Also several examples are presented to show the reliable performance of the scheme with the comparison of experiments with relatively good agreement.

INTRODUCTION

ROV is the new technology equipment being made to replace manned systems, both manned submersibles and divers. Principal task of ROV is to freely travel and steadily approach to an object in aqua-space and transmit video information of it to water surface by using tether cable, since electro-magnetic wave cannot be utilized in water, although it is very powerful means on land and the aero-apace.

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