A study on the influence of cable tension on the movement of cable laying ship

Abstract

A cable laying ship is a deep-sea vessel designed and used to lay underwater cables for telecommunications, electricity, and such. Cable ships are distinguished by large cable sheaves for guiding cable over bow or stern or both. The movement of the cable and the influence of the cable tension on the movement of the cable laying ship are two key problems to be solved during the cable laying operation simulation. But in the process of cable mathematic model being established, too many factors bring great difficulties to the research of the cable modeling. It is necessary to reach a higher precision for the established model to ensure the cable tension in great practical value. Besides, a simplified model with less computing work and lower complexity is also needed to meet the requirement of computer real-time simulation. At first, it brings forward one easy and useful method to solve the problem of cable modeling. Linear and nonlinear methods are adopted separately to build up the underwater cable dynamic model. The analytical formula of the cable's shape is presented. The cable tension acting on the ship are also computed out under a given ship motion state. Then, a ship's model is established with a three degree-of-freedom including surge, heave and pitch, according to the cable laying operation based on some assumptions. And the cable ship mathematical models are established considering the cable tension on the relevant three degree-of-freedom. Further more, the cable model and the cable tension's influences on the ship movement are simulated in some computer test. Finally, through these simulation tests, the relations between the cable tension on the ship and ship speed, the cable tension and the cable laying velocity, the cable tension and the water depth are analyzed. Moreover, the concrete influences of the cable upon the ship at three degree-of-freedom motions are concluded. The modeling, simulation results and conclusions are in great value for engineering use, which provide effective theory basis for a cable ship's motion simulation and control research.