| Fatigue damage is one of the main failure causes for naval architecture and ocean engineering structures.With the increasing demand for marine oil and gas resources such as oil and natural gas,the ocean nuclear power platform has attracted people's attention.As an organic combination of small nuclear reactors and ship engineering,the ocean nuclear power platform does not carry any power system itself.It is towed to working places by other ships during its operation,providing electricity,heat and fresh water resources for offshore natural gas and oil exploration platforms.The fatigue assessment of nuclear power platform is different from conventional ships in terms of wave load,structural characteristics,design fatigue life,and safety requirements.In this paper,the fatigue strength assessment methods and typical node optimization design of ocean nuclear power platform are studied,the main contents are listed as follows:(1)Using the CCS specification simplified calculation method to assess the fatigue strength of ocean nuclear power platforms.The fundamental principles of simplified calculation method of fatigue assessment are expounded in this paper.The contents and steps of simplified calculation are introduced in detail,including the calculation of fatigue load,the analysis of simplified stress,the selection of S-N curve,the calculation of fatigue cumulative damage and fatigue life.Three typical sections of the middle and 1/4 of the ship were selected,and the longitudinal bone nodes on the section were assessed for fatigue,the results of the fatigue simplified calculation are analyzed in detail.(2)Combined with the characteristics of ocean nuclear power platform and the fundamental principles and analysis procedures of the spectral analysis fatigue assessment method,a method for spectral analysis fatigue assessment of ocean nuclear power platform is proposed.The principle of spectral analysis is discussed in detail,including the transfer function of stress response,the response spectrum of stress,the short-term distribution of stress range,the long-term distribution of stress range,and the calculation of fatigue cumulative damage.Combined with the characteristics of ocean nuclear power platform,the specific operational problems are explained,such as finite element modeling and finite element refinement principle,corrosion allowance consideration,wave load calculation,hotspot location selection,PCL automatic loading technique,hotspot stress interpolation calculation and the extraction of stress,etc.,thus,a method for fatigue strength assessment of ocean nuclear power platform based on the spectral analysis is formed.(3)Combined with the structural characteristics of ocean nuclear power platform,the fatigue strength analysis is carried out for the single point mooring working state and the tugboat towing state using two different wave loads,the bow wave to the unequal probability distribution and the full wave to the equal probability distribution.According to the calculation results of spectral analysis,the fatigue damage caused by each wave direction is obtained,and the specific analysis is made of fatigue damage contributed by each wave direction,sea data,hotspot structure position,and whether the design fatigue life is satisfied.(4)The fundamental principles and operation procedures of three optimization methods:size optimization,shape optimization and topology optimization are expounded.Combined with the structural characteristics of the ocean nuclear power platform and the calculation results of the fatigue damage of the spectral analysis method,some typical nodes are selected for size optimization and shape optimization design.Through the optimization scheme,the stress level of the node structure is effectively reduced,the feasibility and rationality of the optimization method are verified,and the fatigue resistance of the node is improved,which can provide reference for the structural design of the ocean nuclear power platform. |
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