Structural Fatigue Analysis And Typical Local Details Optimization Research Of SWATH

Three common-used S-N curve methods, including rules'method by classification society, spectral fatigue analysis method and design wave approach are completed for the fatigue assessment of a SWATH. Structural optimization has been carried out so as to satisfy the requirement of fatigue strength. at the typical local details of this ship.The rules of CCS, DNV and ABS are refered in the simplified method. The CCS's guidelines give the formulae of design loads applied to the SWATH, while the others only give the formulae calculating the design loads adaptive for the high-speed or light craft. Therefore, in this paper, the CCS's formulae are chosen for calculating the fatigue loads. Usually, the rules'regulation for calculating cumulative damage is intended for the common-type ship which maybe not suitable for SWATH. As by different rules, the results of fatigue analysis can be different greatly with each other because of the different determination of the shape parameter of Weibull distribution and the choice of the S-N curve.A spectral fatigue analysis is also performed for better result. By contrast analysis, this paper gives the common principle for determination of the parameters applicable for SWATH in the simplified methods by different rules. And with the modified parameters, the results can be in accordance with each other.With the consideration that the design wave approach is more accurate than the rules'method and has less workload than the spectral fatigue analysis method, it is also carried out in this paper for the fatigue analysis of SWATH. By comparison with the results of former methods, the differences between them are in accepted range.A severe stress concentration at the intersection of the pillar and side platform can be noticed from the analysis, which result in a great excess of the allowance of the cumulative damage, a structural optimization is required therefor. Three kind of optimization methods such as size optimization, shape optimization and topology optimization are excuted in this paper, while local structural design is also modified to improve the fatigue strength . Finally, a recalculation of fatigue life afer structure optimization is performed, the result meet the rule's requirement perfectly.