Objectives  In response to the increasing depth of research and design on liquefied natural gas (LNG) ship structures, higher requirements are put forward for a reliability analysis method that can quickly and accurately evaluate uncertain factors. This paper proposes a method based on an improved random forest-Monte Carlo method (RF-MC) to solve the calculation of the failure probability of A-type independent liquid tank support structures.

  Methods  First, the MC method is used to generate a sample set according to the probability distribution of uncertain factors, then take the local outlier factor (LOF) as the criterion for filtering out sample points near the failure surface. After selecting the sample points, they are calculated using finite element software and added to the training set to train the random forest (RF) model. The generation, filtering and training process is repeated until the approximate model meets the accuracy requirements. Finally, the approximate model is used to determine whether the sample points are invalid, then combined with the MC method to calculate the failure probability of the structure.

  Results  Considering the accuracy, complexity and efficiency of the algorithm, and combined with Cases 1 and 2, it is found that the improved RF-MC method has better advantages than MC or biased probability (BP)-MC in analyzing reliability problems. The results of Case 3 show applicability of the method in reliability analysis of an A-type independent liquid tank support structure.

  Conclusions  This study provides a feasible technical solution for future optimization design of liquefied gas carriers.