PSI - Issue 52

Muhammad Raihan Firdaus et al. / Procedia Structural Integrity 52 (2024) 309–322 M.R. Firdaus et al. / Structural Integrity Procedia 00 (2023) 000–000

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2. Proposed Numerical Method

In this research, the hydrodynamic impact between the float structure and the water domain was developed using ABAQUS finite element software. The finite element numerical simulation of hydrodynamic impact will be modeled using the Coupled Eulerian-Lagrangian (CEL) method. The structure is modeled as a Lagrangian mesh to comply with the deformation, while the fluid is modeled as an Eulerian mesh that is constructed using the Volume Fraction method.

2.1. Fluid-Structure Interaction

Water floating structures such as boats, ships, or even float structures of an amphibious aircraft are a ff ected by several types of dynamic loads including environmental actions, such as wind and waves, the latter being considered as the most important source of motions and structural responses in a seaway. The engineering analysis for the prediction of seaway-induced dynamic responses of such engineering systems could be based on a realistic formulation of the fluid-structure interaction (FSI) domain via integration of hydrodynamics, structural mechanics, and the use of novel modeling techniques. According to the degree of structural response, problem areas can be divided between those where the float structure can be treated as a rigid body and those for which its inherent flexibility significantly a ff ects the degree of dynamic response. The hydrodynamic impact is a derivation from the field of hydroelasticity that deals with inertial, hydrodynamic, and elastic forces. Here, generally, there are two existing states, namely the fluid and structural domains. In the structural domain, the areas of measurement and analysis of structural response under the influence of dynamic loading are divided into two conditions, either the structure is treated as a rigid body (using rigid body methods) or a flexible platform (using hydroelastic methods). In the early days, structural components were treated as rigid bodies and the prediction of the induced dynamic loads has been approached using hydrodynamic analysis and quasi-static structural safety assessment. The interaction between structural response and hydrodynamic loads will further define practical solutions for both the structural and fluid domains and thus provide knowledge regarding structural strength. Once a structural component is operated in a conjunction with another medium as one may refer as fluid (mainly water), the assessment of its structural response is critical. The interaction between the structural components with the fluids is called as fluid-structure interaction. Within this thesis, the Coupled Eulerian-Lagrangian (CEL) method is used to model the fluid-structure interaction during the numerical analysis. This method gives better analysis and results in simulating the structural strength of a body that is in contact through a fluid or Eulerian medium, such as water. Compared to the pure Eulerian analysis, CEL method maintains the geometry of a solid body being undisturbed by the fluid, instead the fluid flows around the body. Hence the true interpretation of its deformed shape can be obtained to furtherly being processed in acquiring its structural integrity. 2.2.1. Full Shell Modelling The geometry of float structure as a 3D shell model is used in both the static simulation and dynamic hydrodynamic impact simulation. The geometry model taken into the simulations is a section of a design of aircraft float structure, as displayed in Figure 2. The detail of dimensions of the model is given in Appendix A. The material properties assigned to the float structure are the isotropic material properties of Aluminum Alloy 7075-T6, as listed in Table. As a shell geometry model, the thickness value is given as an input during section creation. 2.2.2. Full Solid Modelling Similar to the shell float structure, the geometry of float structure as a 3D solid model is also used in both the static simulation and dynamic hydrodynamic impact simulation. This solid version of the float structure is a same section of aircraft float structure as the shell geometry. The Aluminum Alloy 7075-T6 properties are also assigned to this solid float structure part. The 3D model of this solid float structure geometry includes the physical appearance of the thickness, as given in Figure 3. 2.2. Finite Element Model