The Analysis Of Motion Characteristics And Influence Factors Of Cargo Transfer Vessel

CTV(Cargo Transfer Vessel)is invented due to make the VLCC keep a safety distance with PFSO when delivering crude oil in deep water.It has functions of self-propulsion and dynamic positioning,so that it can tow the ordinary oil tankers that lack the ability of positioning to be motionless around the FPSO safely and effectively.In order to make sure the operation system of transfer can work as expected,the simulation of oscillating motions of CTV is carried out in this paper.The method of replacing dynamic positioning in time domain analysis is studied.Numerical simulation of the model test of low frequency drift force is carried out to select a proper method to measure the drift force.Comparing the results produced by different selection methods of the spring stiffness,this paper confirms that the restraint system's natural period should be one order of magnitude grater than the lowest wave period and model natural period.The motion characteristics and influencing factors of CTV are analyzed.Based on the three-dimensional potential theory,the motion characteristics of CTV in regular and irregular waves are calculated.The changes of the towline tension and minimum space between CTV and VLCC are analyzed in various sea conditions,the results show that when the cable length is more than 160 meters,and the changes of the tension of the towline the minimum space show stable trend,which means increasing the length of the towline can not improve the performance of the fishtailing motion and excess surge.So the length of the towline is 160 meters in this paper.The shadowing effect of FPSO on the motions of CTV is analyzed,and the calculation results show that the influence of shadowing effect of FPSO on CTV motions is very small,it can be ignored in the actual work.The results of the numerical simulation are compared with that of the model experiments.The results show that the simulation values are basically consistent with the experiments,which verifies the accuracy of numerical simulation.