| The draft value of a ship is an indicator of its carrying capacity.At present,with the rapid development of shipping economy in the Yangtze River,the tonnage of ships is constantly increasing,and "over draft" accidents are becoming more and more common."Over draft" of ship is not only easy to lead to grounding and damage the channel,but also endanger the safety of crew.Therefore,the research of intelligent draft measurement system is of great significance to ensure navigation safety.At present,the commonly used draught measurement methods,such as image recognition,electronic draft,pressure sensing,laser scanning,head up scanning and so on,are not as suitable as the side scan draught measurement methods for "double floating platform".However,the traditional side scan draft measurement system relies on the fixed building as the detection platform,which can not deal with the attitude error caused by the floating of the "double floating platform".Moreover,in the summer when the temperature difference between day and night is large,the system is greatly affected by the temperature gradient of the "water temperature changing zone".In order to solve the above problems and improve the measurement accuracy of the side scan draft measurement system in the "double floating platform",firstly,through the field investigation,the ultrasonic transceiver and acoustic synchronization module,water temperature,water level and attitude measurement module,draft data processing module,ship two-dimensional display module and so on are built to form a perfect side scan draft measurement system.Then,the feasibility and effectiveness of the designed draught data processing method are verified by theoretical analysis,simulation,experimental test and real ship measurement.The main contents of this paper are as follows:(1)The pretreatment of draft data is completed.CRC algorithm is used to check the initial draft,interpolation algorithm is used to set the ship occlusion threshold,and dynamic median filtering algorithm is used to eliminate the random noise.(2)The attitude compensation algorithm of "double floating platform" is designed.Four attitude modes of horizontal tilt,vertical tilt,general tilt and dislocation are modeled respectively,and the corresponding attitude compensation coefficients are given to reduce the system attitude error caused by the "double floating platform".(3)In order to reduce the influence of ship "wake noise" on system measurement,a method based on grouping bubble sorting and LMS adaptive filtering is designed to complete the identification and filtering of ship "wake noise".The results show that the approximation degree of the wake curve after LMS filtering is 88.20%,which is better than the traditional median and mean filtering methods.(4)Finally,a compensation algorithm of draft value in variable temperature zone based on ultrasonic ray trajectory correction is proposed,and the expression of temperature compensation is given to reduce the influence of water temperature gradient change in "variable temperature zone in water" on draft measurement.In this paper,the effectiveness of attitude compensation and variable temperature compensation algorithm is verified by the simulated ship draft experiments in 25m constant temperature tank and 50m variable temperature tank of Dalian Maritime University.Furthermore,the accuracy and reliability of the system data processing method are verified in the channel 32m downstream of Xiangjiaba.The real ship measurement results show that the maximum measurement deviation of the system in Xiangjiaba 32m channel is 8cm,and the average measurement deviation is 5cm,which achieves the expected accuracy index of the project.At present,the measurement accuracy of the system has passed the measurement certification of China National Institute of metrology,and was officially completed and put into operation in Xiangjiaba Hydropower Plant in Yibin,Sichuan Province. |
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