Study On Modeling And Simulation Of 6-DOF Motion Of Water-jet Propelled Unmanned Surface Vehicle

Unmanned surface vehicle (USV) is a kind of unmanned surface ship with the capability of autonomous navigation, which has some technical advantages, such as high-intelligent, high-speed, long-range, high-flexibility and stealthy. In recent years, because of the plea of military, economic and research needs for the surrounding seas, many governments and research institutions have increased technology research and development efforts to the USV. However, due to some movement characteristics of the USV, includes nonlinear, randomness, higher-order, strong coupling and vulnerable to environmental impact, that make the R&D works more difficult and dangerous. So, in order to make researchers to better understand and predict the motion of the USV, the research works about the USV’s motion and the establishment of the USV motion mathematical model are both very important.Therefore, on the basis of previous research works no the motion of the USV and ship motion mathematical model, and the data of full-scale trials, this thesis tries to carry out a study on modeling and simulation of 6-DOF motion of the 9m water-jet propelled USV developed by a certain research institution. This thesis includes the following three parts.1. Kinematic and dynamic characteristics of the USV is analyzed, calculation methods and formulas of the forces and moments acted on the USV are discussed, and the 6-DOF motion mathematical model of the USV is derived by adopting the MMG (Ship Manoeuvring Mathematical Model Group) modeling method. Firstly, referring to the character of hydrodynamic forces acted on the USV, a stress analysis of the USV hull is carried on. According to results of the stress analysis, forces acted on the USV are divided into gravity, water-jet propulsive force, fluid hydrodynamic and environmental disturbance forces. Secondly, the fluid hydrodynamic acted on the USV is deeply studied and discussed, by combining the theoretical formulas and test data fitting, the calculation formulas of the fluid hydrodynamic model are given. Then, the water-jet propulsion’s structure and principles are described, according to kinetic energy theorem and momentum theorem, a water-jet propulsive force mathematical model is derived. Furthermore, a new method named "flow analysis" is proposed, that is used to calculate the interaction effect of the nozzle angel and the bucket angle to the water-jet propulsive force. Finally, on the basis of the MMG’s separated modeling theory, a complete mathematical model of 6-DOF motion of the water-jet propelled USV is built up by integrating all the dynamic sub-models.2. According to hull parameters of a certain USV, a simulation model of motion of the USV is established and implemented by Matlab/Simulink software tool, and then, in term of the data of full-scale trials, the simulation model is validated. Firstly, the hull structure of the USV is introduced, and detail hull parameters of the USV are listed. Then, based on the above motion mathematical model of the USV, the paper developed a simulation platform for the USV’s manipulation motion by Matlab/Simulink. According to test process of full-scale trials, the realistic simulations of the USV’s typical movement including direct sailing ability, accelerating/decelerating ability, turning ability are made. Finally, the results are satisfactory by comparing with the data of full-scale trials, hence, the model suggested by this paper is correct and effective.3. Based on the previous simulation tests, more numerical simulation tests of the simulation model are conducted, including direct sailing ability with variable velocity, active brake/astern ability, turning ability within full speed domain and motion ability in impact of environmental disturbance forces, and on the basis of Kinematic and dynamic theory of the USV, simulation results of 6-DOF motion of the simulation model are analyzed. By summary and analysis, simulation results are in good agreement with theory, and are reasonable and similar to the real situation. Hence, this model can be used for calculation and prediction of the USV’s maneuverability.