Local Strength Analysis And Lightweight Optimization Of The Living Quarter On A Large Deep Water Semi-Submersible Drilling Platform

With the large consumption of petroleum and the rapid development of ocean engineering technology,people start to exploit the crude in the deep-sea so as to satisfy the need for production and living requirements.The dimension of the semi-submersible drilling platform,which is one of the most important oil exploit equipment,is becoming larger.The size of the living quarter which can provide space for living,entertaining and working,is upsizing as well.The large living quarter tends to cause two problems: one is that the living quarter starts to take part in total deformation which will cause stress concentration in the corner of living quarter;the other is that the weight of living quarter is increasing,which will raise the COG of the whole platform,which increases the possibility to seriously influence the comprehensive performance of the platform.To figure out a solution,the thesis mainly focuses on the living quarter and deals with the problems mentioned above.The main content of the work is as follows:(1)A FEA model is established for the whole deep water semi-submersible drilling platform,for calculating the design wave parameter with the random design wave method and then find out the most dangerous load case.Under this load case,bracket dimension and shape are regarded as design variate,the bracket strength is regarded as constraint condition,the maximum stress in the corner of living quarter and utilization ratio of the bracket are taken as the optimization objectives,a mathematical model with response surface method is adopted,and the model is solved with the help of NCGA.Finally,an optimal bracket is determined which takes both living quarter safety and utilization ratio of the bracket into consideration.Meanwhile,analysis of the change of bracket shape and dimension with weight ratio increasing is carried out.(2)The corner strength and the fatigue performance of living quarter after adopting the optimal bracket under the typical design wave are accessed.(3)With respect to the lightweight design,the much lighter carbon fiber-reinforced composite is used to replace the traditional steel material.A thin-wall plate structural combine with hat shape girder is adapted to substitute for traditional stiffened plate and T-shape girder.The plate and girder dimension are taken as design variate,deck strength and deformation are taken as constraint conditions,the structure weight is taken as the optimization objective,a mathematical model with response surface method is adopted,and the NCGA algorithm is used to solve the response surface.Finally,the optimal deck structure is determined and its strength under the typical design wave is verified.(4)The stress concentration problem is studied regarding the connections between the living quarter and main deck.An approach to strengthening connection is utilized to substitute the rigid connections with springs,the improvement effect of the stress concentration phenomenon when using different spring layout plans is compared.The adopted methods and completed work in this thesis can provide references for the local structure design and optimization of a semi-submersible drilling platform,as well as the composite living quarter optimization design.