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This paper proposes a fast multigrid algorithm to simulate the non-linear motion of ships in both intact and damaged conditions. The simulations of ship motions in waves are known to require much time to calculate due to the strong non-linear interactions between ship and waves. To improve the calculation efficiency while retaining the accuracy, a prediction-correction strategy was designed to accelerate the simulation through three sets of locally refined meshes. The flow field was first estimated in a coarse mesh and then mapped to a locally refine mesh for further higher-fidelity corrections. A partitioned radial basis function (PRBF) method is proposed to interpolate and reconstruct the flow field for the refined mesh. A new two-phase flow solver was developed with a fast multigrid algorithm based on the Reynolds-averaged Navier–Stokes equations (RANSE). The new solver was applied to study the non-linear behavior of a damaged ship in beam waves and the effect of damaged compartments on ship rolling motion. Validation against the solution with the original method of single set meshes and experimental data indicates that the proposed algorithm yields satisfactory results while saving 30–40% of the computational time.

Being a powerful strategy to preclude drag and achieve hydrodynamic invisibility, flow field manipulation is attracting widespread attention. In this investigation, we introduce a systematic set of arbitrary-space divide-and-conquer transformation strategies to design complex hydrodynamic cloaks. This theory removes the difficulties associated with the analytic description of complicated and irregular structures to construct hydrodynamic cloaks by adopting the divide-and-conquer algorithm and reconfiguring strategies. It also provides an approach for redistributing the flow field energy and guiding the fluid flow as desired. The proposed theory not only opens up new ideas for improving the speed and concealment of marine vehicles but also provides a new strategy for ensuring the safety of aquatic and underwater structure operations.

By design of the external and internal wave-current generators, the objective of this paper is to extend our efficient Navier-Stokes solver [T. Li, P. Troch, J. De Rouck, Wave overtopping over a sea dike, J. Comput. Phys. 198 (2004) 686-726] for modelling of interactions between breaking waves and a current over a cut-cell grid, based on a dynamic subgrid-scale (SGS) model. This solver is constructed by a novel VOF finite volume approach, coupled with surface tension. When studying waves following a positive current, our external generator creates the combined inflow motions of waves and a current, which is viewed as one type of wavy inflow conditions. For cases of waves against strong currents, our internal generator describes the opposing current, by incorporating the source function to the continuity and momentum equations as a net driving force, acting on the fluid elements lying within the finite thickness source region. The outgoing waves downstream are dissipated with a breaking-type wave absorber placed in the tank extremity. Five test cases recommended are of distinctly different applications of interest, characterized by overtopping of following waves over sloping and vertical structures. Under the grid refinement effects, the results in 2D and 3D are in close agreement with the experimental data available in terms of the surface wave. Additionally, the performance of convergence in computations is also investigated, including full discussion for waves on beaches between 2D and 3D. By visualization of the motions that describe the physics of turbulence, it has been shown that our solver can capture most of the significant features in wave-current interactions varying with three different current speeds (positive, zero, negative).

In this paper, coupled analysis of a parallel-connected FLNG and LNG carrier system is carried out in time domain method, taking into account of the hydrodynamic interaction between the two vessels, as well as the mechanical interaction between the vessels, moorings, hawsers and fenders. The allowable safe range of side-by-side offloading operation is derived by considering the check of two vessels' relative motions and hawsers and fenders' force condition together. Damaged and normal operating conditions are investigated for assessment of the safety in mooring, involving some major aspects, e.g., the relative motions, hawsers tension and fenders deflection during the LNG offloading process when subjected to two different loading conditions.

This paper describes a method for simulation of viscous flows with a free surface around realistic hull forms with a transom, which has been developed based on a FINFLO RANS solver with a moving mesh. A dry-transom model is proposed and implemented for the treatment of flows off the transom. The bulk RANS flow with the artificial compressibility is solved by a cell-centred finite volume multigrid scheme and the free surface deformed by wave motions is tracked by satisfying the kinematic and dynamic free-surface boundary conditions on the actual location of the surface. The effects of turbulence on flows are evaluated with the Baldwin–Lomax turbulence model without a wall function. A test case is modern container ship model with a transom, the Hamburg Test Case. The calculated results are validated and they agree well with the measured results in terms of the free-surface waves and the total resistance coefficient. Furthermore, the numerical solutions successfully captured many important features of the complicated interaction of the free surface with viscous flows around transom stern ships. In addition, the convergence performance and the grid refinement studies are also investigated. Copyright © 2001 John Wiley & Sons, Ltd.

The calculated results for the violent impact of water waves onto rigid stationary coastal structures are presented in this paper. The simulation is performed in a numerical wave flume using our recently developed in-house Navier-Stokes solver([4]) named LVOF. It is a VOF finite volume approach that incorporates the surface tension effects, coupled with a dynamic subgrid-scale (SGS) turbulence model. Test cases concern a combination of wave propagation, shoaling, reflection, diffraction, breaking and overtopping after impact. Additionally, the effects of a current on wave-structure interactions are investigated, including the study of the influence of viscosity on the wave boundary layer under breakwater and the 3D effects. Our results demonstrate that our solver can describe most of the significant features of motions induced by regular and irregular waves. In particular, the shape of the free surface agrees well with measurements under grid refinementscaptured and even during lengthy computations.

Publisher Summary This chapter explores the development of a FINFLO solver for simulation of a turbulent free-surface flow around a modem ship by resolving the RANS equations with the artificial compressibility that incorporates a treatment of the free-surface boundary conditions. Within a moving mesh system, a cell-centered finite volume multigrid scheme, and two turbulence models, the Baldwin–Lomax model and the Chien's low Reynolds number k–ɛ model, are implemented. A nonlinear free-surface boundary condition is satisfied on the exact location of the surface. Utilizing the method of FINFLO–RANS code with a moving mesh, the overall degree of accuracy is achieved for simulation of a turbulent free-surface flow around a modern ship. This is demonstrated with the benchmarks: the KCS model, the DTMB 5415 model, the tanker model, and the HTC model, using the B–L model and the k–ɛ model, respectively. They are in very good agreement with the experimental data available. The present chapter can provide the detailed and extensive information for analysis and design of a ship.