Dynamic Analysis Of A Modular Floating Structure Based On Tension-legs

As land resource becomes more and more precious,the very large floating structure(VLFS)has been paid more and more attention for its environmentally-friendly and cost effective characteristics,which has ambitious future applications.However,most VLFSs are pontoon-type or semi-submersible,the uneven vertical loads on different modules may have strong impact on the draft difference between the modules,which can result in considerable vertical loads on connectors.If the VLFS can be modularized by TLPs,the draft of different modules can keep steady due to the pretension force of tension legs.It can reduce the relative motion between the modules and vertical loads on the connectors,as well as improve the variable carrying capacity of different modules.In addition,ocean wave energy is considerable,if VLFS can be equipped with wave energy converters(WEC),the WECs can not only produce energy production,but also reduce the wave loads on the VLFS.Therefore,in the present work,a modular floating structure based on tension-legs(marked as MTLPW)has been proposed,which includes several TLP modules and WEC modules.The combined system can effectively relieve the pressure of land resource and energy,and serve as the guard of our maritime and island as well,which may enhance the power of our maritime military.The main investigation and corresponding results have been clarified as follows:(1)The preliminary conceptual design of the MTLPW system has been proposed,which includes two outermost rows of pitch-type WEC modules,several rows of inner TLP modules,three kinds of connectors and two kinds of auxiliary device(includes additional heave plates and additional 10 MW horizontal wind turbine).The hydrodynamic interaction effect and the mechanical coupling effect between the modules have been taken into consideration.The numerical model of the simplified three-module and seven-module MTLPW system have been established.(2)The effects of key design parameters of the WEC modules on the hydrodynamic characteristics of the three-module MTLPW system have been clarified.The results indicate that the outermost WEC modules can significantly reduce the surge response of the central TLP and produce considerable wave energy.(3)The effects of different connection types,pretension levels,additional heave plates and additional wind turbine on the hydrodynamic and generation performance of the MTLPW system have been further investigated,and the results indicate that both the outermost WEC modules and the additional heave plates can be available for improving the hydrodynamic performance of the MTLPW system,the central TLP module can suffer about 2000 t mass variation,the additional wind turbine can play a key role in the whole energy system and have little influence on the hydrodynamic response of the MTLPW system.(4)The comparision of the effects of five connection modes on the hydrodynamic responses of the seven-module MTLPW system has been proposed.The results show that the hydrodynamic responses of the MTLPW system are sensitive to the connection type of the outermost WECs.The extreme responses of the bending moment of connectors depend on the number of continuously fixed modules.By properly utilizing hinge-type connectors to optimize the connection mode for the MTLPW system,the effect of the number of inner TLP modules on the hydrodynamic responses of the MTLPW system can be limited.Therefore,the MTLPW system can be potentially expanded to a large degree.