In this part, simulation and lake experiments have been conducted on WEILONG mini-AUV for many times to verify the feasibility and superiority of the mathmetical modelling and control method. The position errors of longitudinal control simulation are shown in Fig. 8. Reference inputs are 5m, the velocity of current is 0 m/s, and the voltage of thrusters is restricted by 2.5V. As can be seen, S surface control is feasible for the AUV motion control. For the figure on the left, k1 = 8.0 and k2 = 5.0 . Since the initial parameters are too big, there is certain overshoot and concussion aroud the object state in S surface control. However, the parameters are adjusted by self-learning in improved S surface control. The overshoot is reduced and the balance (? Do you mean steady state) is achieved rapidly. For the figure on the right, k1 = 3.0 and k2 = 5.0 . The initial parameters are too small, so the rate of convergence is too slow in S surface control. In improved S surface control, the rate of convergence is picked up and the performance is improved greatly.

Field experiments are conducted in the lake. The experiments use the impoved S surface control and the results are shown in Fig. 9 and Fig. 10. As there exits various disturbance (such as wave and current), the result curves are not smooth enough. In yaw control experiment, the action of the disturbances is greater than the acting force, so we can see some concussions in Fig. 9. It needs to be explained in the depth control that there is no response at the beginning of the experiment. The reason is the velocity of WEILONG mini-AUV is very low and the fin effect is too small. In the computer simulation, we don't use the fins until the velocity reaches certain value.

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