Risk-based Analysis Of Structural Performance For Sphere-cylinder Combined Shell

Ship and ocean engineering structures suffer from a variety of sudden and accidentalfactors in the stage of construction, transportation, installation, operation and demolition,which makes the structure system face the risk of damage. Due to comprehensivelyconsideration on structural safety, it is needed to study on the risk-based structuralperformance analysis. As the pressure hull structure of mono-shell submarine, sphere-cylindercombined shells have the characteristics of super-long cabin and large subdivision. Theinteractions between cylindrical shell and spherical shell will influence the structureperformance of combined shell.Aiming at the above problems and using a combination of theoretical analysis andmodel test, this paper has carried out some researches, which include three aspects: thestructural mechanical performance of combined shell, structural system reliability, andrisk-based structure design. The main contents are as follows:(1) Considering the deformation coordination conditions at the joint of combined shell,structural mechanics model of sphere-cylinder combined shell is established. The influence ofstructural parameters to sphere-cylinder combined shell strength is analyzed. The law ofcombined shell structure performance is summarized. The edge effect is analyzed usingsimplified boundary model. For the structural stability of sphere-cylinder combined shell, thestructure displacement function which meeting the displacement coordination is established.The stability calculation formula of sphere-cylinder combined shell is deduced, while the totalpotential energy is divided into external work, thin film strain energy and bending strainenergy.(2) In order to validate the theory analysis results, three test models which have differentparameters were designed. The rule of stress distribution and the effects of structureparameters are analyzed by the measured strain of models. The edge effects of sphere-cylindercombined shells are verified through comparing with the results of theory analysis and modeltest.(3) The failure mode and distribution and statistics characteristic of random variable ofsphere-cylinder combined shells are determined through the analysis of uncertainty factors, and the reliability models are established. Joint failure probability calculation formula of tworelated failure modes is derived through2d joint probability density function and the fullprobability formula of tandem structure system of sphere-cylinder combined shells whichconsidering the correlation among failure modes is given. And then the correctness of systemreliability calculation is verified through Monte Carlo simulation. The reliability-basedoptimization design is carried out through multi-island genetic algorithm.(4) The concept of risk beyond the submerged depth is firstly put forward. The“cost-benefit” criteria of structure design is formulated through overall considering therequirements of society, environment, person and economy to risk beyond the submergeddepth. Through the extreme distribution function, the probability of risk beyond thesubmerged depth is described. Selecting the reliability of99%, the sphere-cylinder combinedshells are designed based on the reliability optimization under different submerged depth andthe structure security costs (structure weight) of each scheme are given. According to theprinciples of structure design, safety cost and occurrence probability of risk, the properdecisions is made. Finally, a framework of risk-based structure design is constructed.