Structure Strength Assessment And Optimum Design For The Bow Structure Of The Very Large Ore Carrier

With the development of large-scale ore carriers, structural designers need to focus more problems. Compared with other areas, the bow of the very large ore carrier is the key area where marine accidents such as yielding failure, buckling deformation and fatigue crack occur. This paper aims to optimize the bow structure according to the calculations which are done by studying the structural strength of the bow through the rule calculation and direct strength calculation. Therefore, this paper mainly discusses about the following several aspects:1. The method of calculating the bottom slamming pressure and flare slamming pressure is discussed. The slamming pressure and pressure distribution along the 3D ship body is calculated in time domain by integrating the ship motion theory with the empirical formula.2. Based on the rule design, it probes into the influence of the quantity and layout of opening platforms and the longitudinals in the bow on the weight of bow structure.This means setting four-layer, five-layer or six-layer opening platforms separately on the bow with the impact of construction technology included to qualitatively analyze the advantages and disadvantages of different number of layer and their weights as well. After setting the program for platform,it also calculates the impact of different longitudinals arrangement on the structural weight and welding workload in the bow area.3. It expounds the calculation and evaluation method of direct strength on the basis of specification of DNV which gives detailed illustration of several aspects such as establishment of the model, calculation of load and criterion of structural strength assessment. As to the area where its structure is prone to damage such as the connection between the longitudinal and web frame, fine mesh finite element analysis is carried out based on this connection. Rule design slamming pressure and transient loads data which was get from direct prediction are respectively set as the design loads applied on the FE model.4. The direct fatigue assessment, based on spectral analysis, is also studied. It makes a full probability fatigue strength analysis based on the spectral fatigue analysis in easily fatigue crack areas of the bow. It is dissussed for the fine mesh of finite element model, calculations of wave load that spectral analysis requires. And then Sesam/Stofat program is used to realize automatic loading, automatically submitting calculation and processing results as well as other short-term and highly efficient calculation of fatigue assessment method.