| With the vigorous development of the LNG ship market,the research and development of its additional products has received increasing attention.Especially,LNG tanks,as storage containers for LNG fuel,occupy an important position in the entire system.The design of tanks,strength checketc.all need to be strictly controlled.In particular,there is necessary to have a special attention in the aspect of fatigue strength check and life estimation.According to statistics,most of the ship accidents are due to the fatigue of structure,so doing the best on structural fatigue is a guarantee of life.This article revolved around the topic of fatigue and did the following:(1)First,the author summarized the previouswork ofother researchers by reviewing relevant papers,and had a certain understanding of the entire research background.Subsequently,the article introduced the factors of affecting fatigue strength,including the effects of stress concentration,the influence of dimensions of components,the influence of surface conditions and loading conditions;Then there were some introduction of the normative development of fatigue problems at home and abroad,and a certain degree of certainty over the situation in the entire industry;And the method for estimating the fatigue life is generally described,including the S-N curve method and fracture mechanics,and made a detailed introduction about them;Finally,the type of fatigue damage theory was introduced,including linear theory,modified linear theory and other theories,as well as related factors.Therefore,there is a good academic foundation for the following research.(2)Through the calculation and analysis of the 100m3 low-temperature LNG fuel tank and the 30m3 cryogenic liquid tank,the influence to the structural fatigue damage with different layout directions of the LNG tank on the ship was explored.According to the latest revised edition of the “Rulesfor Natural Gas Fuelled Ships”,the finite element model is loaded and calculated by the acceleration ellipse method,and the appropriate working conditions are selected to calculate the structural fatigue damage value.Finally,it is concluded that the different arrangement of the LNG fuel tanks on the ship do have an effect on the structural strength,and it is safer for tanks in longitudinal arrangement.It is recommended to consider the acceleration of the ship in the project and,as far as conditions permit,try to arrange the tank longitudinally.(3)Because the ship's navigation in real ocean conditions is much more complicated,the simplified method of the specification may cause inaccuracy of the results.And the fatigue life assessment based on the spectrum analysis method,taking into account the actual wave spectrum,is more in line with the actual situation,and the related work is less of evaluating the fatigue life of LNG tanks based on the spectrum analysis method in the industry,so this paper based on this method analyzed the fatigue life of 100m3 low-temperature LNG fuel tank.Finally,the results based on the spectral analysis method are less than those based on the standard method,and indicate that the requirements of the specification are somewhat safe,and the selection of short-term sea conditions and wave spectrum will also have an impact on the final result.(4)Considering that LNG ships are always under a very low temperature environment during operation,it is necessary to study the influence of low temperature environment on the fatigue life of structures.The relevant low-temperature corrected S-N curves were used to compare the structural fatigue damage values at room temperature and at low temperature.Finally,it was concluded that low temperature will increase the fatigue strength of the material,and then increase the fatigue life of the structure,and the degree of impact will be greater.Consider the impactionin the projects. |
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