Research On Design Of Shallow Water Mooring And Hydrodynamic Analysis Of Floating Marine Structures

With the implementation of the strong marine country strategy,the government has been increasingly devoted to ocean exploration and exploitation.It is well known that there are abundant resources in islands located in South China Sea.Meanwhile,due to the geopolitical position of the South China Sea,it is urgent to strengthen the development and utilization of island resources in the South China Sea for further steps.The near-island reef floating offshore platform has great advantages on developing islands and reefs resources comprehensively.However,due to the complex terrain near the islands and reefs,the design of mooring systems always suffered from a number of problems.Taking a floating offshore platform arranged in near-island reef shallow-water into consideration,the article includes two traditional catenary and taut symmetrical mooring systems for the specific marine environment where the platform is located.According to the research and analysis of the hydrodynamic performance of the offshore platform,and the project requirements,three mooring methods have been designed,such as a water drum mooring method,a pile anchor chain combined mooring method and a anchor chain with heavy block mooring method,which are in line with two traditional symmetrical systems.The numerical simulation results of the mooring system have been compared to obtain the movement characteristics of the platform and the variation law of the mooring line tension with the application of the mooring system.The feasibility and rationality of these three mooring methods have also been discussed.(1)Hydrodynamic analysis of shallow-water floating platforms in frequency domain.The software ANSYS-WORKBENCH based on finite element method has been used to establish the wet surface model of the shallow-water floating platform.The AQWA-LINE module has been applied to calculate the additional mass,radiation damping,motion response amplitude operator,first-order wave-excited force of the platform and steady drift force at different water depths and different wave direction angles under frequency domain analysis and they have been summarized as general rules.It lays a foundation for the following time domain coupling analysis.(2)Two traditional catenary and taut symmetrical mooring systems have been preliminarily designed based on ANSYSY-AQWA software.In order to verify the accuracy of numerical simulation,this paper verifies with a model test result,the results are in good agreement and within the allowable range of the error.At the same time,according to the JONSWAP wave spectrum theory,time-domain numerical calculations have been performed on shallow-water floating offshore platforms and mooring systems.The six-degree-offreedom motion responses of the platform at working sea conditions and the results of mooring cable tension have been obtained.In addition,the platform motion results and mooring line tension results have also been compared and analyzed.(3)According to the structural characteristics of the research-targeted platform and the marine environmental conditions in the layering area,a type of water drum mooring system and a type of pile anchor chain combined mooring system has been designed.The software was used to investigate the hydrodynamic performance of the floating offshore platform under the mooring system.By comparing the motion response and mooring tension of the floating offshore platform between the mooring systems and the traditional ones,the rationality and feasibility of two mooring systems has been verified preliminarily.(4)According to the research referred in the previous chapter,another type of anchor chain with heavy block mooring system have been designed.The software have also been applied to study the hydrodynamic performance of the floating offshore platform under the anchor chain with heavy block mooring system.The comparison results show that the floating offshore platform will obtain better hydrodynamic performance than that of others under the mooring system,which is a coupling of anchor chain with heavy block.