Simulation And Control Research Of Marine Towed Seismic System

The underwater towed system, as an effective tool, is extensively used for various oceanic applications, geographical measurements and military tasks etc., it provides an effective means for various marine activities, the study of towed system has become a focus of modern oceanic exploitation. Accurately predicting its performance and motion is of primary importance during the design and application processes of towed system, it has attracted the interest of many researchers. Because the towed system is a technology- intensive complicated system, which involves many sciences, although significant advances have been made in this field in the past half centenary, there still exist many problems concerning motion and control of towed system.The present thesis mainly concerns the modeling of towed seismic system and depth control of streamer, numerical method, as the researching means, is employed to study the steady-state and dynamic motion of towed system. In this thesis, a comprehensive mathematical model of towed system and its corresponding numerical schemes are developed, from the viewpoint of design, intensive research on the towed system has been carried out based on the former related research, then the depth control problem of streamer is introduced and studied tentatively. The research of this thesis may help to ensure towed system to work properly in the real sea surroundings, and provide theoretical support for the design and application of towed system. The main contents and conclusions of this thesis can be summarized as follows.Firstly, a comprehensive review of modern towed system is given, as well as various research methods, whose advantages, disadvantages and applicable ranges are also pointed out in detail; subsequently the author decide to employ (nested) bisection method and lumped mass method (lumped parameter method) to develop the numerical scheme for the steady-state motion and the mathematical model for the dynamic motion. While the research about the hydrodynamic force acting on the cable is summed up, which is presented as appendix for future reference.For various towed systems and towing types, numerical schemes are proposed to deal with the steady state problem of towed cable, the effect of non-uniform(sheared) current is also taken into consideration, which varies in magnitude and direction with depth. For most of towed systems, the steady state problem can be resolved into two-point boundary-value problem, or initial value problem in some special cases where the initial values are available directly. A new technique is proposed and attempted to solve the two-point boundary-value problem rather than the conventional Shooting Method due to its algorithm complexity and low efficiency. First, the boundary conditions are transformed into a set of nonlinear governing equations about the initial values, in which the initial values can be themselves, or serve as temporary functions of...