Study On The Calculation Method Of Yield And Buckling Strength For Very Large SWATH Ships

Small water-plane area twin hull (SWATH) ships have attracted widespread attention for its larger deck area, better seakeeping ability and smaller wave resistance in high-speed navigation compared to conventional single ship. The design dimension of SWATH ships is increasing constantly, from the initial 26.8m ship length to nearly 100m nowadays. The applicability of the rules needs further verification with the increasing of ship size.Optimization studies related to structural strength problems, such as large openings, which are caused by increasing ship size,are necessary. In this paper,a comparative study of direct calculation and simplified standard calculation is carried out. In addition, improvement of the yielding and buckling strength criteria and optimization methods of structural issues are developed on basis of more mature standard, in order to provide reference to the structural design of large SWATH ships. The main work of the thesis is shown as below:(1) In the load calculation of SWATH ships, method and process of simplified load calculation and finite element loading method are presented according to the Guide of CCS,using design wave method. Furthermore,comparative studies of the results of real ship model calculation are performed, and load combination coefficients analysis is conducted.(2) In order to improve the yielding and buckling strength criteria, the coordinate system,model range, unit requirements, weight adjustment in FEM modeling, assessment section,criteria and refine of yield assessment,also the method and process of buckling strength assessment are elaborated, in reference to CCS guidelines and HCSR rules, etc.(3) In the study of the influence of slamming, the slamming impact on the local parts of the ship is calculated based on CCS and ABS guidelines. Then, the relative motion between the wave and the ship is calculated. Additionally, the calculation of the impact force at the moment when cross-section slamming occurs is performed according to LR rules etc. Finally,comparison of the results is made and the analysis of the influence of slamming on the strength is conducted.(4) In the structural optimization of the large SWATH ships, sub-model method is used to analyze the optimization effects of the sponson bottom and the arc circle at the brace connections to the structure. The strengthen effects of outer flitch plate and bulkhead plate to the structure are analyzed and computed in order to get the appropriate flitch dimensions.Besides, comparative analysis of different optimization methods’ strengthen effects at the deck of the superstructure and connections of trunk bulkhead is presented. Moreover, studies of the enhance effects of strengthen methods of large deck openings,as well as the optimized arrangement and dimension selection of the openings are performed.