Dynamic Simulation And Experimental Research Of Towed Low-tension Cable Based On Generalized α Method

As China is rich in the marine oil and gas resources, it has great significance to carry out the exploration of China's ocean oil and gas resources in solving the future energy needs of the national economy development. Marine seismic exploration is now the most popular and effective application of the geophysical techniques. In design and application of marine seismic streamer system, it becomes an important objective to accurately predict the attitude of the streamer. More attention has been paid, and more and more scholars and researcher are dedicated in research of this area.Firstly, this thesis reviews the current geophysical techniques and seismic towing cable system and its present development situation. And then study the 3D dynamic of low-tension cable and the towed cable dynamic equation in Lagrange coordinate system. Based on those, a more accurate 3D low-tension cable dynamic equation is established with micro element method, including bending stiffness. Based on the finite difference Box method commonly used in time domain on solving discrete nonlinear equation has the instability problem, the generalizedαmethod is used in time domain to solving the governing equation. Through being applied in simple nonlinear problem, the generalizedαmethod has been proved to have second order accuracy. Through comparison and analysis on the spectral radius of finite difference scheme, the generalizedαmethod trapezoidal algorithm box and backward difference algorithm, comparative analysis shows that the generalized-αmethod has better stability.The cable's 3D governing equation'solution at a time is a two-point boundary value problem. This thesis analyzes the relaxation method and shooting method's advantages and disadvantages in solving two-point boundary value problems, and suggests using relaxation method to solve the cable's dynamic equation. A computing process is given in the relaxation method to solve the three dimensional cable governing equation Applying this to the cable's nonlinear dynamic equation, this thesis retains the Box method's spatial discretization, but employs the generalizedαmethod for temporal discretization. Based on Matlab, we edit the calculation program of the low-tension cable. Compared with the backward difference, finite difference Box method, the generalizedαmethod not only has good precision, but has a shorter computation time.Finally, an experiment is carried out to in this thesis to study low-tension cable dynamic characteristic. In the experiment, the cable is towed in 0.5 m/s, 1.0 m/s, 1.5 m/s three velocities to study the dynamic response of the low-tension cable, and verifies the accuracy of the mathematical model of the low-tension cable and the efficiency of the generalizedαalgorithm and proves the existence of the vortex vibration, constant coefficient method and variable coefficient method are employed to transient behavior simulation to study the transient dynamic response, the simulation results show that the variable resistance coefficient is better than the constant coefficient method.