| The manned cabin is one of the pivotal components and key metal structure for security personnel,and to guarantee the service safety of the submersible it is of great concern to establish the reliability assessment method for the manned cabin.The fatigue life prediction methods of offshore structures are basically deterministic and can not assess the effect of the uncertainties on the fatigue life.This dissertation will introduce the reliability theories into fatigue analysis of manned cabins,and put forward a preliminary fatigue reliability assessment procedure for deep-sea manned cabins.This dissertation involves the following research issues and results:(1)Make a general summarization on the research development of fatigue prediction methods,and several common reliability analyses methods have been reviewed and compared.The analysis results provide fundamental theories for establishing fatigue reliability assessment procedure of manned cabin.(2)The comprehensive properties of alternative materials for full-ocean-depth manned cabin are analyzed.The service environment,structural properties and the loading history of the manned cabin are described.(3)The model reliability of the unified fatigue assessment methods as well as the crack growth rate models considering dwell and small crack effects is analyzed.It is found that the larger the standard deviations or coefficients of variances are,the more scatters will be drawn into the reliability index,and vice versa.(4)The load spectrum of deep manned submersibles is re-described mathematically.The manned submersible is subjected to the dwelling of maximum stress at its destination depth,and the fatigue-dwell behavior of the submersible under which therefore is relative to both normal fatigue and dwell.(5)The static analysis on PMMA viewport of the manned cabin is carried out using finite element methods(FEM)to find out the hot spots on the structure.Considering the creep properties of PMMA,the Damage Separation method is applied to calculate the fatigue-creep reliability of PMMA viewport along with analysis methods.(6)A procedure to analyze the fatigue reliability of full-ocean-depth manned submersibles is proposed,and the content is composed of the fatigue reliability assessment of the hull and that of the PMMA viewports.Taking a spherical hull made of titanium alloy,its stress concentration point is confirmed by means of FEM,where the fatigue growth simulation is performed.The stress intensity factor on the crack tip is calculated,and hereafter the fatigue reliability can be evaluated based on fatigue crack growth rate model.This dissertation combines the theories of fracture mechanics,reliability,finite element method,etc.The effects of materials,structures,loading and environment are considered together with the fatigue crack growth rate models to assess the fatigue-creep reliability of the manned cabin,which will provide foundation for the establishment of a relatively complete safety assessment methodology for full-ocean depth manned cabin. |
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