Research On The Control Of Submarines Near The Surface

With the development of technology and the rapid growth in the requirements energy, ocean gets more attention than ever before. Submarine, as one of the most important weapons and devices for the navy, has been studied in a deep-going way all over the world. The submarine is a complex system with highly nonlinear, strong coupling and time-variant parameters, the strong interference when steered near the surface increases the difficulty of control. With the above-mentioned characteristics of submarine, the sliding mode theory is applied to the research on the design of both course and depth autopilots.Some researches on the submarine control are just confined to horizontal or vertical plane, but ignore the coupling between the planes, so the controllers act poor performance in practical applications. The standard submarine equations, proposed by David Taylor Navy Ship Research and Development Center (DTNSRDC), is a form of Taylor series expansion. By ignoring the non-dominant hydrodynamic factor, a 6-DOD submarine model is established and simulated to verify its correctness. And the ocean forces, which can directly affect the motion of submarine, are also studied and simulated, then the first-order wave force on the value and the parameters'trends of second-order wave duration strength with depth and face angle are also given.By analyzing the basic theory of sliding mode, the relationship between switching function and the dynamic response of sliding mode control system can be pointed out. And the chattering phenomenon, widespread in the sliding mode control systems, is proved to be limit cycle in essence through the way of both theoretical analysis and graphic description. According to the theory above, a new method with fuzzy reaching law and approach angle-based saturation function for chattering reduction is proposed for the affine nonlinear systems. Fuzzy reaching law, which is mainly used in reaching stage, adjusts the appropriate approach speed according to the switching function and real switching function derivative to ensure the rapidity of the system and the low approach speed near the sliding mode surface. Saturation function based on approach angle, working through the way of changing the boundary layer thickness, makes the system states stabilized in the sliding surface rapidly.Course and depth autopilots for the spatial movement of submarine are designed respectively based on sliding mode theory and novel chattering reduction method, and simulated with and without the ocean disturbances. Compared with the traditional PID autopilot, sliding mode autopilot gets small overshoot, short settling time and good dynamic response, then eliminates the steady state error at late hour. When the disturbances exist, the sliding mode autopilot can consider more state variables to determine the final command rudder, conserving energy. As to vertical movement, the bow and stern joint autopilots effectively avoid the conflicts. Both depth keeping and changing the submarine can reach the command depth quickly and has static error-free.when the disturbances exist, the submarine also has a good dynamic response under the control of the joint autopilots, and maintains the value near the fixed depth. The amplitude decreases with the increases of the depth, which was fit to the theoretical expectation, the autopilots act good performance in both horizontal and vertical planes.