Simulation On Testing Technique Of Active Truncated Mooring System

It is inevitable trend for the exploration of oil and gas to come into deep sea(≥500) and ultra deep sea(≥1500). As the water gets deeper and deeper, the performance of mooring system can become more important for the safety of the platform. For this reason, model tests for predicting the performance of platform play an important role in its design. Due to the limitation of depth and area of basin, it is difficult to put suitable sacled platform model with its mooring system into the basin. It needs a deeper, larger and more expensive ocean engineering basins. At present, testing technology called ‘passive truncated system’ are used in model test to study the performance of ocean platform with its mooring system in deep sea. However, passive trucated system can not simulate the dynamic behaviour of mooring system exactly and sometimes it is also difficult to simulate static characteristics of the platform. For solving the problem, technology called ‘active truncated system’, which can simulate the dynamic characteristics of mooring system was put forward and it will be a prospective testing technology in the future.The thesis studied on the active truncated system and the main work was as follow:(1) Study on static and dynamic characteristic of cable line. Solving program based on lumpedmass method was developed. For statics problem, a tension rope system was studied based on lumped-mass and catenary theory. For dynamic problem, lumped-mass model and General α method was used in solving program and its results were compared to the experiments..(2) Coupled motion analysis in time-domain of floters. In coupled motion analysis, numerical model of Semi-submerged platform and its mooring system operating in 320 m water depth was built. Hydrodynamic cofficients were calculated by AQWA which using 3D potential flow theory. Then coupled motion analysis was carried out by using AQWA and Orcaflex. Comparison between numerical calculation and experiments was also carried on.(3) Identification of motion model at truncated point. Base on work(2), transitive relationship model between motion of cable’s up point and truncated point gotten by using NARX network to identifies the motion model of cable at truncated point. With three different cases, NARX network was used to calculate the motion of truncated point and results were compared with that of lumpedmass method.(4) Construction of simulation platform. A simulation platform was built to simulate active truncated system. OrcaFlex and MATLAB were used to bulid up this platform and Python API was called for data exchange between two different softwares. Base on work(3), lumped-mass method was replaced by NARX network which will be used to calculate the motion of truncated point more efficiently. Comparison with results between full-depth system and truncated-depth system, it shown NARX network is feasible in active truncated system.