Development of CAD System for Control System of Autonomous Underwater Vehicle

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Underwater vehicles have been widely used for ocean measurements and developments. The vehicles could be classified into two groups, self-propulsive and towed vehicles. In the case of towed vehicle, the body shape should be streamlined in order to move fast for wide area survey of the ocean or sea bottom. From the view point of the motion control the quick response is not required in the case of a towed vehicle because its motion is constrained by the mother ship. On the other hand, in the case of self-propulsive vehicle, the blunt shape is generally adopted to make it unstable from the viewpoint of hydrodynamics, and it is supposed to be stabilized in order to realize good maneuverability as a control system. There is also another possibility to reduce a number of thrusters using multivariable control theory. Therefore, CACSD (Computer-Aided Control System Design) technology is expexted to play'a great role in balancing between function of controller (software), in order to achieve th … More e desired performance of the control system. In CACSD,a nonlinear simulator is necessary to evaluate the control system designed. So it is inevitable to model the controlled object mathematically. In particular, we must estimate hydrodynamic coefficients by carrying out forced oscillating tests on the vehicle in a water tank. Here a problem occurs on the accuracy we should achieve in the experiment. That is, we should answer whether or not the uncertainties of hydrodynamic coefficients could be allowed from the viewpoint of CACSD based on robust control theory. If the answer is "no" , we will be required achieve higher accuracy in the estimation of hydrodynamic coefficients.The present research has been carried out in order to establish a standard design method of the control system as following steps. At first general mathematical models for the motions of the underwater vehicle have been constructed, which describes 6-degree freedom motions of vehicles and 3-dimensional motions of a towing cable or umbilical cable.Secondly the model has strong non-linearity and it is linearized automatically by using computer software. Next adequate control systems are designed based on modem control theory. Through these procedure a standard design method for the control system of an underwater vehicle has been established. Less