Modeling And Simulation Of Single-Boat Mid-Water Trawl System

With the development of modem fishery, fishing simulator will play a more and more important role in the fishery education and training, fishery maritime evaluation, assessment for preventing fishing ship accidents and fishing port planning, etc. To simulate the dynamic behaviors of single-boat mid-water trawl system in fishing simulator, a modeling method to establish the mathematical model of single-boat mid-water trawl system is proposed. Also, simulation software is developed and visualization of the system is realized, which lay a good foundation for the development of fishing simulator. The primary research and contributions of this dissertation summarized here are:1. A modeling method to establish the mathematical model of single-boat mid-water trawl system is proposed, and visualization of the system is realized by using scene management software OpenGVS (Open Generic Visual System) . The mathematical model of the system is divided into mathematical models of trawler, warp and fishing net, which are connected by boundary conditions reflecting the influence of each other. By using this modeling method, the dynamic simulation of the process of drawing in and giving out the fishing net is realized. The feasibility of proposed modeling method is verified by simulation results.2. Considering mooring line weight and non-linear elongation, the mathematical model for calculating mooring line tension is improved. When the line elongation obeys Hooke's law, the relationship between line's tension and original length is induced by using catenary equation and Hooke's law, and the line tension is obtained through trial. Otherwise, the line weight is neglected and the line tension is calculated by using the polynomial obtained through line stress-strain curve. Whether line tension exceeds safety load and line is broken or not is judged by calculatied line broken intensity. The correctness and practicability of the model are verified by computation instances. 3. A maneuvering mathematical model for Controllable-Pitch Propeller (CPP) ships with three degrees of freedom is established according to separate modeling theory. Based on Netherlands Ship Model Basin's open-water tests, CPP thrust coefficients and torque coefficients in four-quadrant with different pitch ratio of screw and different types of CPP are obtained by using Akima interpolation. Therefore, CPP thrusts and torques are obtained. With the influences of wind and current, the model can be used for maneuvering simulation of ships equipped with CPP in ordinary-speed and low-speed fields. Simulation results being similar to the sea-trial test shows that the model is reasonable and its precision can meet the requirement of full mission ship-handling simulator.4. A numerical calculation method for the mathematical model of fishing nets is proposed. Instituting variables of position of mass points of calculated positions to calculate connected mass points' elastic force, equations of mass point can be solely calculated. This method can avoid solving the huge nonlinear equations directly, and computing time can be reduced. Also, Newmark-βintegration method is used to calculate the equations of mass point, which can stably take large time steps.5. The dynamic model of warp is established by using finite difference method. The equilibrium equations under local coordinate are obtained through Euler angle transformation. In the modeling of warp, otter door is treated as the end node. The equilibrium equation of otter door is established through d'Alembert's principle. It provides the end boundary condition of the dynamic model of warp. By central difference in time and space and boundary conditions, equilibrium equations of warp are transformed into the definite equations and solved by Newton's iteration. The model also takes into account influences of uniform current and winch speed of warp, and can be used to simulate unsteady warp motions. Simulation computations of a model towed cable proposed in a paper have been done. Comparing the computation results with that given in the paper, the rationality of the model is verified.6. A hydrodynamic model of fishing net is established according to the lumped mass model, which divides fishing net into finite mass points connected with springs without mass. According to Newton's Second Law, equation of mass point is set up tak- ing the influence of uniform current into account. Dynamic behaviors of a panel net and a mid-water trawl are simulated. Comparing the computation results with that of flume experiments, the rationality of the model is verified.