Research On Seabed Interaction Of Deep Water Catenary Moorings

With the exhaustion of reserved petroleum in land and shallow water zone in the sea,theexploration and development of profound petroleum has become a new direction during the Marine industry.In order to explore and exploit the profound petroleum resource effectively,so many deepwater platforms have been installed in the world at present.These deepwater platform need to be in position by mooring system on the sea in general.The mooring line is an important part for the mooring system.If the mooring line lose efficacy,it will cause great economic loss and even endanger the personal safety.Under the function of wind,wave and flow,As the most commonly used deepwater catenary mooring line contacts and separate with seabed frequently.The chain point,as the first touching position between mooring lines and seabed,is the intersection point between the section of catenary and the bottom part of the mooring line.With the effect of environmental loads,the chain point is constantly changing.The chain point is very easy to generate alternated stress and even cause fatigue damage so that it will not only affect the dynamic response of the entire mooring system and endanger the safety of the whole deepwater platform.Due to the contact area involved in geometric nonlinearity,contact nonlinear and seabed parameters uncertainty,this area need to study as a key point the numerical analysis of mooring lines.Within the scope of time domain,this study is the deep analysis of the problem in fatigue properties between the mooring lines and the contact area of the seabed soil.The main study is as follows:1.In consider of the geometric nonlinearity of catenary mooring line and soil nonlinear among mooring line with soil,this study adopting great finite element software ANSYS,set up the interactional finite element model between mooring line and seabed soil.2.According to the hydrodynamic software AQWA,this study get the overall motion time response of the platform that is the top input conditions of mooring line so that calculate the contact stress between mooring line and seabed soil.3.For each short-term sea condition,respectively based on the rigid,flexible,DP elastic-plastic constitutive model of soil,the study focus on the influence of various models on contact stress respectively.4.Through the statistics of stress time curve of the contact area of mooring line,merging with the rain-flow counting method,this study gets the fatigue load spectrum.According to the theory of Miner linear cumulative damage,this study has been liner accumulation for fatigue damage for each short-term sea condition so that the fatigue damage of different contact area in sea condition for a long time.In conclusion,this study evaluates the fatigue property of mooring line.