Research On Method Of Hybrid Model Testing For FPSO Mooring System

With the increasing of the depth of the ocean development, more and more attention has been paid to the performance of the offshore platform. How to accurately forecast the performance of offshore platform and mooring system has become a major problem in recent research. This paper takes a multi-point mooring system for instance, which works in the depth of 1700m underwater in West Africa. Firstly, the passive hybrid model test is researched.Comparing with active hybrid model test, a new method of active hybrid model test will be proposed.Equivalent truncation designs are carried out on the mooring system, and the main consideration is the similar static loading between mooring lines in truncated depth and full depth. It can be better meet the different environment direction. It is very important for the representative mooring line's top tension and system horizontal restoring force. The design result shows that they are fitted well between the truncation depth and full depth. Specific truncation method is proposed to support the hybrid model test.Model tests on the turret FPSO mooring system and offloading system are carried out in the basin of Harbin Engineering University, which include free decay tests of FPSO, RAO tests under white noise wave, flow resistance tests, wind resistance tests, tests of FPSO global response under irregular. According to the test results, AQWA software is used to reconstruct and extrapolate the model test results to identify the key hydrodynamic parameters. The results will be used to forecast the actual FPSO's motion and mooring lines tension,and provide the necessary data support for the mooring line dynamic response.It analyzes the active hybrid model test technique, and gets the dynamic response of the mooring line bottom end points. It provides the related programs based on the software of MATLAB, and analysis the dynamic response for nonlinear mooring lines. The upper end point motion is obtained under the action of Ochi-Hubble spectrum, which is a single direction motion. To get the motion and force laws on the equivalent depth truncation points of mooring line, the lump mass method is used. Compared with the results of hybrid model test and its extrapolation, the errors of motion and tension response have been reached. As a result, a kind of active hybrid model test method is proposed.According to the results of the program calculation, a hydraulic six DOFs mechanism is designed to simulate the motion of the truncated point. The simulation and control of truncated points are analysis by the plug-in unit of SolidWorks Motion. The swing angle and free stroke of six telescopic rods are obtained, and the control system is analyzed. It will provide some technical support for the design of the active hybrid model test.