| Large cage net(purse) is an important way for marine resource utilization, and sustainable development of marine fisheries. Net damage detecting is the base condition of cage culture. At present, there is no automated equipment to accomplish the net damage detecting work all over the world, and the main method is tested by divers in the sea. Based on the commonly used large cage structure in China, this paper develops a frametype AUV system with spiraling detection strategy for this problem. Based on the spiraling detection strategy, the paper carried out the mechanical structure design work of the function modules and parameter setting work of the system. Through the calculation of dynamic model of the frame-type AUV and the parameters of the large cages and water quality, design a dedicated controller to control the frame-type AUV cruise along the spiral way, and develop a complete frame-type AUV system. The system can get the realtime video data of the cage net back to base station, complete the net damage detecting work, which provides a stable foundation for large scale application.This main research content of this paper is as follows:(1) This paper elaborate the frame-type AUV work plan. According to the characteristics of large cage culture, put forward the spiraling detection strategy, and based on this, advances the frame-type AUV working mode and control requirements, and overall design the frame-type AUV system. Frame-type AUV mainly includes the underwater vehicle, the communication system and the receiving base station. This three parts are designed according to the modular design method, and the function modules of the three parts include framework, propulsion system, underwater camera system, energy supply system, communication system, etc. Considering the size of the large net and working environment, propose the key technical index of the frame-type AUV system, and according to the index, propose the design concept and design plan.(2) According to the general conception, design the mechanical structure and select the components of the frame-type AUV. Considering the reliability, security, and easy for operation, select the square frame structure. By comparing the characteristic from 5 kinds of materials, select the PVC plastics for processing. For the power system, select the appropriate motor according to the water resistance and design the reasonable structure for rudder blade. The selection of the multiple exposure and video controller chip of underwater cameras module mainly consider the adaptability of low illumination and high anti-noise property and design the dedicated seal structure for the underwater cameras. Through the analysis of the overall power consumption, chose 4 solar panel of power in 10 W cooperate with a 30 Ah lead-acid batteries to support the cost of energy for the system. According to the working environment, select microwave in 2.4 GHz band for the communication system, which has realized the real-time video data back to the base station.(3)For the control module, formulate the path of the frame-type AUV at first. According to the size of the cage and the experiment measured water visibility, on the premise of cage net video is clear and unabridged, the helix function of frame-type AUV is defined in the geodetic coordinate system, and the parameter of the function is calculated. Defining the local coordinate system whose center is coincident with barycenter of frame-type AUV, the matrix expressions of four main force and moment of the frame-type AUV by force analysis are obtained, and with this expressions, the dynamic model of frame-type AUV is acquired in both geodetic coordinate system and local coordinate system. Base on the dynamic model, design a controller with internal control loop and feedback loop, which simplifies the model for the controller decoupling of linear system. After the introduction of paranoia proportional differential control, calculate the two positive definite parameter matrix, and the AUV system control equation is obtained.(4)In order to test the reliability and practicability of frame-type AUV, a net damage detecting experiment for the large cage was conducted in Xiangshan Harbour. At first, scientifically measure the water flow velocity of the sea area of Xiangshan Harbour and induce the relationship among the water flow velocity, the tide and the visibility of the sea water, so that the best time for the work of the frame-type AUV can be found. In the period of the sea being calm, which is between duration of tide and duration of fall, carry out the resistance to the wave experiment and cage net identification experiment. When the water flow velocity is less than 0.4m/s, no matter the green big mesh cage or the black small mesh cage, the frame-type AUV can get the clear video of the cage net. But when the water flow velocity is more than 0.8m/s, the frame-type AUV fails to be controlled sometimes and can’t get the video. The experiment shows that the frame-type AUV can send back the clear real-time video of the whole cage net when the water flow velocity is less than 0.4m/s, and mesh size or color of the net can be identified. For the problem of control failure in the big water velocity flow field, the working time can be chosen when the sea is clam which can be judged by the tides. The experiment achieved the desired effect and proved the practicability and reliability of the frame-type AUV, which solved the key problem in popularize the large cage culture.Finally, the paper discusses the development prospect and problems need to be further solved of this system. |
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