Investigation On Hybrid Model Testing Based On The Complex Method For Discrete Variables

In the design of floating mooring system,the model test in the test basin is needed to make a reasonable prediction of the motion response of the floating body and the force of mooring cables.But it is difficult to meet the requirements of full depth model test,with the increasing depth of offshore resources development.The hybrid model test is an effective way to solve this problem,the method is as follows: In the model test,the mooring cable is truncated according to the depth and scale ratio of the pool,and the motion of the truncated point is simulated by a specific method.According to the simulation mode,the mixed model test can be divided into the active and the passive mixed model test.The passive mixed model test is widely applied because of its simple technology and low cost.The rational truncation design is very important in the passive hybrid model test.The aim is to make the mooring system have similar motion characteristics in the truncated water depth and the full water depth by adjusting the parameters such as length,stiffness and wet weight of mooring cables.In this paper,the general static characteristic analysis program of mooring system is written with Matlab.Then the discrete complex method is used to optimize the truncated mooring system,so that the truncated depth and the static characteristics of the mooring system are similar as far as possible.The main contents of this paper are as follows:First,based on the three-dimensional potential flow theory and the related environmental load calculation method,the FPSO in full depth is analyzed in frequency domain and time domain using hydrodynamic calculation software AQWA.The motion response of the floating body and the force of mooring cable under full water depth,different directions and sea conditions are obtained.Through static analysis,the displacement-restoring force characteristic of mooring system under static state is obtained,which provides reference for optimal design of truncated system and checking of static characteristic of mooring system program.Then,based on the catenary equation based on analytical method,static displacement-restoring force characteristic of single component with elastic mooring cable and multi component tensioner mooring cable is analyzed,and the general displacementrestoring force characteristic curve of mooring system is obtained.The general static analysis program of mooring system is compiled by Matlab,which is compared with the static analysis function of AQWA software.The rationality of the program is verified,and the discrete complex method is applied to the optimization design of truncated mooring system based on static similarity.Finally,the hull,mooring line and riser model are made according to the truncated design results and the test scaling factor.The FPSO’s irregular wave model test are carried out to get the motion response and mooring cable’s force under different angles and sea conditions.By numerical calculation and model test,the motion response of the floating body and the force of mooring cable are analyzed and compared in the existence and removal of the riser system.The influence of the existence of the riser system on the mooring system is predicted and quantifiedIn a word,the mooring system’s truncation design has a great impact on the model test.How to design the equivalent truncation of the mooring system and the riser system quickly and effectively is an important work in the mooring system model test.This article hopes to provide a certain reference for the similar research through the truncation design and model test of the FPSO mooring system and the riser system.