## 1 Introduction
To evaluate the structural strength of the LNG CCS subjected to sloshing loads, it is necessary to make a reasonable evaluation that reflects the hydro-elasticity effect and apply it in a method appropriate to the structural strength evaluation through a sloshing fluid structure interaction (FSI) analysis method [15; 16]. FSI analysis is a method that can analyze the sloshing phenomenon by simultaneously analyzing fluid flow and structural deformation. However, it is difficult to obtain both solution convergence and result accuracy since the fluid flow analysis depends heavily on the numerical calculation method [13; 17]. Therefore, various studies have been conducted and published using FSI analysis to simulate fluid flow during sloshing impact. [PERSON] and [PERSON] analyzed nonlinear and viscous flow of sloshing in a rectangular tank using the finite difference method (FDM) [18]. The FDM was also used for sloshing flow in a 3D rectangular tank subjected to harmonic excitation [19]. [PERSON] numerically studied sloshing flows with impact loads in 2D and 3D liquid containers by FDM to analyze the characteristics of sloshing impact loads [10]. The finite element method was used to calculate the governing equation of fluid flow in a differential form assuming a fluid continuum model for analyzing the sloshing impact in a partially filled tank under irregular excitation [20]. However, most of the effort undertaken to assess sloshing fluid flow was focused on simple fluid models, such as continuous fluid or homogeneous multi-phase models, due to relatively low computational costs and excellent numerical stability [21; 22]. The compressibility and multiphase properties of fluids should be taken into account when modeling the sloshing flow, as fluid is mixed with gases and liquids in the event of a sloshing impact. [PERSON] et al. suggested that an inhomogeneous model is suitable as a multi-phase model of sloshing flow and compared a homogeneous and an inhomogeneous multi-phase model for sloshing flow in a rectangular tank subjected to harmonic excitation [23]. As a time-averaged equation of fluid flow motion, the Reynoldsaveraged Navier-Stokes (RANS) equation is widely used to simulate sloshing flows. The RANS equation can be applied with approximations based on information of the properties of sloshing flow and turbulence properties to provide approximate time-averaged solutions to the Navier-Stokes equations. This method is used to solve multi-phase fluid flows in most commercial CFD codes, ANSYS CFX, with various usage of volume of fluid (VOF) approaches [24]. The present study is designed to evaluate the effect of sloshing impact on structural strength. The method for evaluating structural strength is to apply the FSI analysis method and consider the hydro-elastic effect of the sloshing flow. For the FSI analysis method, a fluid impact model of LNG sloshing was created based on VOF approaches and the RANS. The CFD models are based on a Eulerian-Eulerian model using the control volume based finite element method (CVFEM). The inhomogeneous multiphase model included fluid flow and gas entrapment as well as momentum transfer between liquid and gas. To review the suggested multi-phase model and the application of fluid impact simulations, analysis results were compared with experimental results of dam breaking problems presented by [PERSON] and [PERSON], as well as a rectangular sloshing model test [25; 26]. The validated CFD model, combined with the FSI method, performed a structural strength evaluation of LNG CCS by sloshing impact on the Mark III type CCS model. Finally, we discussed the results of structural response analysis of Mark III type CCS reviewed in this study and investigated the effectiveness of the FSI model on structural response evaluation by the proposed sloshing simulation model.