System Design And Experiment Research On A Mini Autonomous Underwater Vehicle Used In Shallow Sea

A mini pre-programmed Autonomous Underwater Vehicle (AUV) for oceanography used in shallow sea is developed in this paper with regard to investigations including theoretical analysis, detailed structure design, prototype development, experimental research and systematic improvement. It is designed to meet requirements in specific sea area and its modular structure is found to be original. Through this research, not only an AUV has been developed to facilitate explorations and reconnaissance in ocean, but also a solid foundation has been laid for further investigation on multifunctional AUVs of novel style.Based on primary requirements of performance, a new type of AUV configuration has been made to enable measuring on the bottom of the sea as well as releasing the buoy. The blueprint of the overall design and development of updating prototype have been achieved after detailed systematic design. Methods for center of gravity and buoyancy of AUV with variant topology geometrical configuration are also introduced in the paper.Structural parameters of aluminum hull with enhancing structure, reliability of the releasing device, and means of AUV sinking have been studied and analyzed in particular. Structural parameters of aluminum hull are firstly optimized using minimal mass as the objective function. Effects of the two main manufacturing errors, cylindricity error and welding defect, on the bearing capacity of the shell are investigated using finite element analysis (FEA) in sequence. The results turn out to make guidance for setting reasonable machining precision of manufacturing errors for their impacts on bearing capacity of the shell. Finally, the effectiveness of the finite element model is verified through experiments. In addition, primary structural parameters of the releasing device are determined on the basis of theoretical analysis and experimental testing. The design of the releasing device is eventually proven reasonable and reliable by a series of field trials. In order to guarantee a stable and accurate landing of the AUV on the bottom of a specific sea area, three means of sinking have been fully understood through kinematics analysis and compared by the difficulties in realization. It is then decided that the body of the AUV will initially submerge and subsequently be in a state of free sinking. The effectiveness and reasonability of this way of sinking are verified by field trials.Based on Newton-Euler's equations, the general dynamic equations of the AUVare derived considering outside forces when it is sailing. Those dynamic equations are clearly expressed in the form of matrix. Since the general model is nonlinear, it is reasonably simplified using decoupling and method of small perturbation. The dynamic responses of the main body when floating in waves have been studied and analyzed. Using the second law of Newton, dynamic equations of the main body in free sinking and swaying are established with and without wave excitation. Calculation of the maximum roll angle and ratio of amplitudes of rising and sinking to the wave-amplitude will then become readily.According to the simplified dynamic model, four autopilot controllers are designed and simulated for forward speed, steering, pitch and depth control. The complete sailing process, composing modules and their functions are introduced, too. In this paper, Controller Area Net (CAN) is used in the AUV for the first time. A hybrid-distributed control architecture based on CAN has been developed to avoid the defects of previous controllers of the AUV.Experiments are carried out on the prototype of the AUV in several stages in order to test its performance such as waterproof, pressureproof and characteristics during navigation and the whole sailing process. Problems that appear in experiments will be settled after elaborate theoretical analysis and CFD calculation such that the prototype could be further improved. At last during a field trial in a lake, the AUV successfully accomplished a series of actions involving navigating, yawing, submergence, affusion, sinking to the bottom, releasing, and rising to the surface. The designs of the AUV and its control system are thus proven valid and feasible.