Objectives  In order to improve the efficiency of structural strength verification in finite element calculation, and reduce workloads for size optimization in iterative process, this paper is intended to propose a method for plate seam arrangement and size optimization of double bottom longitudinal girders of bulk carriers.

  Methods  First, based on the theoretical formula, the reliability of the sub-model technology is demonstrated and a multi-condition screening method for the optimization design of double bottom longitudinal girders is proposed. Then, a double bottom longitudinal girder of a real bulk carrier is taken as an example and divided into plate panels. The plate thickness is set as a variable and the permissible stress of the Harmonized Common Structural Rules (HCSR) is used as the optimization constraint in size optimization. The plate seam arrangement with the minimum weight is chosen as the optimized arrangement after using the exhaustive method to list all the seam arrangements and merge the plate thicknesses. Finally, considering the HCSR regulatory requirements about yield strength finite element calculation of hold section, the plate seam arrangement of the longitudinal girder strengthening area of interest is optimized, on this basis, the satisfactory structural sizes that meet the regulatory requirements are obtained using the proposed size optimization method.

  Results  The results show that this method for plate seam optimization and structural strengthening based on size optimization can reduce the weight of the optimized area by 4.9%.

  Conclusions  The method proposed herein can effectively reduce the randomness of finite element-based manual calculation of structural strengthening, optimize finite element design scheme and reduce the weight of strengthening.