The paper presents the first 3D fully Lagrangian meshfree projection-based hydroelastic solver for fluid-structure interactions (FSI) encountered in ocean engineering. The fluid model is based on an enhanced version of a projection-based SPH, namely, Incompressible SPH or ISPH; the structure model is based on SPH approximations of conservations of linear and angular momenta. The fluid-structure coupling is achieved by incorporating a so-called FSA or Fluid-Structure Acceleration-based scheme to ensure satisfaction of fluid-structure interface boundary conditions. Validations are performed through both classical benchmark test cases as well as engineering ones. Stable and acceptable results are achieved without inclusion of any artificial numerical stabilizers that often require tuning.


Fluid-Structure Interaction (FSI) phenomena are involved in many branches of engineering fields. In the domains of ocean/coastal engineering, typical examples can be seen, for instance, in ocean wave loads on ship hulls, sloshing loads in liquid containers, slamming impact loads on offshore structures. For the reliable designs of ocean/coastal structures, precise evaluations of the highlyinteractive/ complex FSI systems are of considerable importance.

Considering the challenging features of ocean/coastal engineering FSI problems (e.g. violent free-surface flows, large structure deformations, large/abrupt impact pressure etc.), fully Lagrangian meshfree numerical methods (Gotoh and Khayyer, 2018), e.g. Smoothed Particle Hydrodynamics (SPH; Gingold and Monaghan, 1977), can be considered as one of the appropriate computational frameworks thanks to their major advantages in treating complex boundary conditions. In addition, the projection-based particle methods, e.g. Incompressible SPH (ISPH; Shao and Lo, 2003), are founded on a rigorous mathematical background, i.e. Helmholtz-Leray decomposition, and the refined version of ISPH, referred to as Enhanced ISPH, can provide reliable and robust estimation of pressure field including impact pressure.

With respect to the abovementioned reasons, considerable effort has been put into development of the so-called fully Lagrangian meshfree projection-based hydroelastic FSI solvers, which couple fully Lagrangian meshfree projection-based fluid model with particle-based structure models. Thanks to the common numerical frameworks in both fluid and structure domains, the FSI solvers can benefit from flexibility as well as consistency in fluid-structure coupling. Rafiee and Thiagarajan (2009) developed an Explicit Incompressible SPHSPH FSI solver. The solver was shown to well reproduce the interaction between incompressible fluid flow and hypoelastic structure interaction. Hwang et al. (2014) developed a fully Lagrangian meshfree projection-based FSI solver in the context of MPS (Moving Particle Semi-implicit; Koshizuka and Oka, 1996) method, referred to as MPS-MPS FSI solver. The performance of the MPS-MPS FSI solver was investigated through several benchmark tests. Later, in the works of Hwang et al. (2015) and Hwang et al. (2016), the developed solver was applied for slamming and sloshing simulations, indicating the potential applicability of the solver towards practical engineering problems. Khayyer et al. (2017a) also developed a refined MPS-MPS FSI solver, which incorporated a set of refined schemes, and applied the solver for slamming problems. The solver was further enhanced in terms of adaptivity by incorporating multiresolution MPS scheme (Khayyer et al., 2019). Furthermore, Khayyer et al. (2018a) proposed a FSI solver in the framework of SPH, namely Enhanced ISPH-SPH FSI solver. The solver was rigorously verified and validated by conducting a number of benchmark tests. In the work by Khayyer et al. (2018b), another mechanical framework, i.e. Hamiltonian mechanics, was utilized for configuration of energy conservative fully Lagrangian meshfree structure models, namely Hamiltonian MPS and Hamiltonian SPH (HMPS and HSPH)

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