Dynamic Analysis Of Undersea Cables And Its Application To Cable-Remotely Operated Vehicle System

Undersea cables are extensively used in the offshore industry, ranging from mooring systems of platforms to remotely operated vehicles (ROVs). In this thesis, the dynamic analysis of the undersea cables and its application to Cable-ROV system is presented as following order.First, taking the bending stiffness into consideration, the governing equations of undersea cables, which are based on the Euler-Bernoulli beam theory, are adopted and can satisfy many applications no matter what the magnitude of the cable tension is. Then the derived nonlinear coupled equations are solved by a popular central finite difference method which has second-order convergence accuracy and unconditional stability. The quadratically convergent Newton-Raphson iteration method is also applied to solve the differenced linear algebraic equations.Then, a towed array sonar system (TASS) problem is studied. The numerical solutions agree reasonably well with the experimental dates of Rispin (1980) and the simulated results of Ablow and Schechter (1983) and Milinazzo et al. (1987). The specified program of present thesis shows great robustness and efficiency. To better understand the transient dynamic behaviors of the free towed cable, several kinds of surrounding conditions, such as different towing speeds of surface vessel, different currents and waves with various frequencies and amplitudes, are exerted. Different mass of tow-body and different cable lengths are also investigated.Last, the dynamics of coupled Cable-ROV system is studied. The motion equation of the ROV, based on rigid body theory, is derived in the vertical plane with the coupled terms neglected. The relationships of the cable tension, shape, velocities and trajectory of the ROV versus time are presented.Besides, considering more and more ROV are operated in sea without a depressor by replacing it by some buoyancy balls attached on the cable, the influence of this phenomenon is also theoretically examined in present thesis. The results show that the ROV undergoes more stable motion while the cable tension doesn't show great difference with local buoyancy balls attached on the cable. But in this case, the ROV can go much higher and faster with the same time and thrust. In other words, it means the ROV can arrive at the same destination in a shorter time period. With the consideration of the vertical thruster is not applied when the ROV moves horizontally, we can conclude that the ROV shows a better maneuverability and can be easily controlled with local buoyancy balls attached on the cable.