Preliminary Studies About General Design Of Very Large Floating Structure At Sea

Ocean has become the importance of the comprehensive national power competitionbetween countries all over the world since the21st century. International marine engineeringin recent years launched a study of very large floating structures (VLFS-Very LargeFloating Structure referred to VLFS) of the boom.For the conditions of our country, ourcountry has begun a series of proof of concept on VLFS.Firstly, the research status and trend of domestic and foreign VLFS has been fullyinvestigated in this paper. The idea of single module civil VLFS has been put forward inorder to accommodate the present situation of the south China sea. The parameters andstructure form have been determined and the general arrangement design has been finishedthrough the interactive design process. The functions of VLFS designed in this paper havealso been obtained which will provide logistics base for oil and gas resources exploration,mining, Marine survey, fishermen break, etc. Meanwhile, the power supply problems ofVLFS on the sea that have been existing for a long time will be solved with the new powergeneration technology thanks to the usage of solar energy, wind energy, wave energy andother renewable energy power.Secondly, the basic calculation theory about the seakeeping motion response of VLFShas been introduced briefly, which include the calculation of hydrodynamic parameters inthe frequency domain and the analysis of the coupling principles in the time domain. Theresponses of VLFS designed in this paper have been calculated and analyzed with theSESAM software developed by DNV. The expected region is the South China Sea, theworking depth of which is up to1000m. under the wind、wave and current at0°and90°marine environment, so we can confirm that VLFS can stand the extreme sea conditions inthe south China seaThirdly, buoyancy and stability of VLFS has been studied and the CCS "Rules forMobile Offshore"(2012) was chosen as the stability specification. The hydrostatic curvesincluding the displacement curve, center of buoyancy curve, floating center of water planecurve, tons of per immersion curve and curve of metacentric height have been obtained byNAPA software. Then, characteristics of buoyant were analyzed. The initial stability withthe impact of free face as well as the stability at large angle under the most dangerouscondition has been checked. Conclusion was drawn that the stability of the VLFS designed in this paper meets the requirements of the specification.Finally, the parameter sensitivity of the VLFS was analyzed. The selected parametersinclude the center of gravity height, spaces of columns and pontoons, cross sections ofcolumns and pontoons, draft and types of pontoon. It could lead to more comprehensiveunderstanding and more accurate prediction of stability and seakeeping characteristics ofsemi-submersible platforms. It is expected to be significant for promoting the developmentof offshore structures in deep sea areas in China.