Monolithic Coupling of the Pressure and Rigid Body Motion Equations in Computational Marine Hydrodynamics

In Fluid Structure Interaction(FSI) problems encountered in marine hydrodynamics, the pressure field and the velocity of the rigid body are tightly coupled. This coupling is traditionally resolved in a partitioned manner by solving the rigid body motion equations once per nonlinear correction loop, updating the position of the body and solving the fluid flow equations in the new configuration. The partitioned approach requires a large number of nonlinear iteration loops per time–step. In order to enhance the coupling, a monolithic approach is proposed in Finite Volume(FV) framework,where the pressure equation and the rigid body motion equations are solved in a single linear system. The coupling is resolved by solving the rigid body motion equations once per linear solver iteration of the pressure equation, where updated pressure field is used to calculate new forces acting on the body, and by introducing the updated rigid body boundary velocity in to the pressure equation. In this paper the monolithic coupling is validated on a simple 2D heave decay case. Additionally, the method is compared to the traditional partitioned approach(i.e. "strongly coupled" approach) in terms of computational efficiency and accuracy. The comparison is performed on a seakeeping case in regular head waves, and it shows that the monolithic approach achieves similar accuracy with fewer nonlinear correctors per time–step. Hence, significant savings in computational time can be achieved while retaining the same level of accuracy.

A framework for efficient irregular wave simulations using Higher Order Spectral method coupled with viscous two phase model

In this paper a framework for efficient irregular wave simulations using Higher Order Spectral method coupled with fully nonlinear viscous,two-phase Computational Fluid Dynamics(CFD)model is presented.CFD model is based on solution decomposition via Spectral Wave Explicit Navier-Stokes Equation method,allowing efficient coupling with arbitrary potential flow solutions.Higher Order Spectrum is a pseudo-spectral,potential flow method for solving nonlinear free surface boundary conditions up to an arbitrary order of nonlinearity.It is capable of efficient long time nonlinear propagation of arbitrary input wave spectra,which can be used to obtain realistic extreme waves.To facilitate the coupling strategy,Higher Order Spectrum method is implemented in foam-extend alongside the CFD model.Validation of the Higher Order Spectrum method is performed on three test cases including monochromatic and irregular wave fields.Additionally,the coupling between Higher Order Spectrum and CFD is validated on three hour irregular wave propagation.Finally,a simulation of a 3D extreme wave encountering a full scale container ship is shown.