Severe Wave-Body Interactions: a Potential-Flow HPC Method and its Strong Domain-Decomposition Coupling with a Level-Set Navier-Stokes Solver (original) (raw)
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European Journal of Mechanics B-fluids, 2022
To simulate the interaction of ocean waves with marine structures, coupling approaches between a potential flow model and a viscous model are investigated. The first model is a fully nonlinear potential flow (FNPF) model based on the Harmonic Polynomial Cell (HPC) method, which is highly accurate and best suited for representing long distance wave propagation. The second model is a CFD code, solving the Reynolds-Averaged Navier-Stokes (RANS) equations within the OpenFOAM R toolkit, more suited to represent viscous and turbulent effects at local scale in the body vicinity. Two one-way coupling strategies are developed and compared in two dimensions, considering fully submerged and fixed structures. A domain decomposition (DD) strategy is first considered, introducing a refined mesh in the body vicinity on which the RANS equations are solved. Boundary conditions and interpolation operators from the FNPF results are developed in order to enforce values at its outer boundary. The second coupling strategy considers a decomposition of variables (functional decomposition, FD) on the local grid. As the FNPF simulation provides fields of variables satisfying the irrotational Euler equations, complementary velocity and pressure components are introduced as the difference between the total flow variables and the potential ones. Those complementary variables are solutions of modified RANS equations. Extensive comparisons are presented for nonlinear waves interacting with a horizontal cylinder of rectangular cross-section. The loads exerted on the body computed from the four simulation methods (standalone FNPF, standalone CFD, DD and FD coupling schemes) are compared with experimental data. It is shown that both coupling approaches produce an accurate representation of the loads and associated hydrodynamic coefficients (inertia and drag) over a large range of incident wave steepness and Keulegan-Carpenter number, for a small fraction of the computational time needed by the complete CFD simulation.
2021
To simulate the propagation of ocean waves and their interaction with marine structures, coupling approaches between a potential flow model and a viscous model are investigated. The aim is to apply each model at the scale where it is most appropriate and to optimize the computational resources. This first model is a fully nonlinear potential flow (FNPF) model based on the Harmonic Polynomial Cell (HPC) method, which is highly accurate for representing long distance wave propagation and diffraction effects due to the presence of the structure. The second model is a viscous CFD code, solving the Reynolds-Averaged Navier-Stokes (RANS) equations within the OpenFOAM® toolkit, more suited to represent viscous and turbulent effects in the body’s vicinity. Two one-way coupling strategies are developed and compared. A domain decomposition (DD) strategy is first considered, introducing a refined mesh in the body vicinity on which the RANS equations are solved. Boundary conditions and interpol...
Combination of Potential & Viscous Flow Models for Wave Interaction with a Submerged Square Body
Coastal Engineering 2002 - Solving Coastal Conundrums - Proceedings of the 28th International Conference, 2003
This paper is devoted to the numerical simulation of water diffraction in viscous flow. An original approach using a diffracted flow defined as the difference between total and incident flows is followed. The incident flow is defined explicitly using nonlinear potential flow theory; Navier-Stokes equations and nonlinear free surface boundary conditions are solved for the diffracted flow only. This procedure, which is very efficient in terms of computing time and accuracy, was primarily developed by Ferrant (1996) for 3D non linear wave-body interactions in potential theory.
Ocean Engineering, 2021
A fully nonlinear two-dimensional numerical method based on potential-flow theory for water waves and their interaction with surface-piercing rigid bodies is presented. The harmonic polynomial cell (HPC) method is used to solve the Laplace equation for the velocity potential and its time derivative. The HPC method, which is a high-order method using analytical expressions (harmonic polynomials) to represent the solution inside overlapping cells, has previously been shown accurate and efficient. Supplementary research has shown that, in order to maximally benefit from the method's accuracy, it is a requirement that square or close-to-square cells are used. Here, we use an immersed boundary method to model non-stationary boundaries such as the free surface or the surface of a rigid body, and overlapping, body-fixed grids that are locally Cartesian to refine the solution near moving bodies. Combining these two modelling concepts with the HPC method represents the main novel contribution in the present work. With this combined method, denoted as an immersed-boundary overlapping grid method (IBOGM), the challenge of generating boundary-fitted grids for complex boundaries is avoided. Moreover, square cells can be used throughout the domain and the solution can be refined locally without increasing the number of unknowns unnecessarily. The method is systematically validated and verified against analytical, experimental and numerical reference results. The cases studied include propagation of steep waves, forced heave motions of a semi-submerged circular cylinder and a fixed and freely floating ship section in beam-sea waves. For the freely floating ship section, the present method is compared in detail with results from a dedicated study performed with a fully nonlinear boundary element method for cases with roll motions up to 30 •. The present results are generally in good agreement with reference results, even for the most challenging wave-body interaction cases considered. Based on this, we later intend to use the method to examine in depth the importance of nonlinear effects in the interaction between waves and rigid bodies.
Journal of Computational Physics, 2021
A fully nonlinear potential Numerical Wave Tank (NWT) is developed in two dimensions, using a combination of the Harmonic Polynomial Cell (HPC) method for solving the Laplace problem on the wave potential and the Immersed Boundary Method (IBM) for capturing the free surface motion. This NWT can consider fixed, submerged or wall-sided surface piercing, bodies. To compute the flow around the body and associated pressure field, a novel multi overlapping grid method is implemented. Each grid having its own free surface, a two-way communication is ensured between the problem in the body vicinity and the larger scale wave propagation problem. Pressure field and nonlinear loads on the structure are computed by solving a boundary value problem on the time derivative of the potential. The stability and convergence properties of the solver are studied basing on extensive tests with standing waves of large to extreme wave steepness, up to H/λ = 0.2 (H is the crest-to-trough wave height and λ the wavelength). Ranges of optimal time and spatial discretizations are determined and high-order convergence properties are verified, first without using any filter. For cases with either high level of nonlinearity or long simulation duration, the use of mild Savitzky-Golay filters is shown to extend the range of applicability of the model. Then, the NWT is tested against two wave flume experiments, analyzing forces on bodies in various wave conditions. First, nonlinear components of the vertical force acting on a small horizontal circular cylinder with low submergence below the mean water level are shown to be accurately simulated up to the third order in wave steepness. The second case is a dedicated experiment with a floating barge of rectangular cross-section. This very challenging case (body with sharp corners in large waves) allows to examine the behavior of the model in situations at and beyond the limits of its formal application domain. Though effects associated with viscosity and flow separation manifest experimentally, the NWT proves able to capture the main features of the wave-structure interaction and associated loads.
Simulation of wave-body interactions in viscous flow based on explicit wave models
2004
Introduction Today wave-body interaction problems can be solved numerically by using softwares based on Reynolds Averaged Navier-Stokes Equations (RANSE). So it is possible to take into account vorticity and viscosity effects which can influence hydrodynamic loads and structure of the flows. However numerical simulations under viscous flow theory still lead generally to large CPU times because of grid requirements to ensure a good propagation of incident waves in the meshed part of the fluid domain. Moreover successive wave reflections on the body and the outer boundaries can affect the incoming wave train and reduce the useable duration of the numerical simulation. To overcome these difficulties an original method consists in solving the diffracted flow only (Ferrant et al., 2003). Thus RANS Equations are modified by splitting all unknowns of the problem in a sum of an incident term and a diffracted term. The incident terms are explicitly described by fully non-linear wave models b...
Two-dimensional numerical simulation and experiment on strongly nonlinear wave–body interactions
Journal of Marine Science and Technology, 2009
A constrained interpolation profile (CIP)-based Cartesian grid method for strongly nonlinear wave-body interaction problems is presented and validated by a newly designed experiment, which is performed in a twodimensional wave channel. In the experiment, a floating body that has a rectangular section shape is used. A superstructure is installed on the deck and a small floatingbody freeboard is adopted in order to easily obtain wateron-deck phenomena. A forced oscillation test in heave and a wave-body interaction test are carried out. The numerical simulation is performed by the CIP-based Cartesian grid method, which is described in this paper. The CIP scheme is applied in the Cartesian grid-based flow solver. New improvements of the method include an interface-capturing method that applies the tangent of hyperbola for interface capturing (THINC) scheme and a virtual particle method for the floating body. The efficiency of the THINC scheme is shown by a dam-breaking computation. Numerical simulations on the experimental problem for both the forced oscillation test and the wave-body interaction test are carried out, and the results are compared to the measurements. All of the comparisons are reasonably good. It is shown, based on the numerical examples, that the present CIP-based Cartesian grid method is an accurate and efficient method for predicting strongly nonlinear wave-body interactions.
A comparison of methods in fully nonlinear boundary element numerical wave tank development
We present the development and validation of an efficient numerical wave tank (NWT) solving fully nonlinear potential flow (FNPF) equations. This approach is based on a variation of the 3D-MII (mid-interval interpolation) boundary element method (BEM), with mixed Eulerian-Lagrangian (MEL) explicit time integration, of Grilli et al., which has been successful at modeling many phenomena, including landslide-generated tsunami, rogue waves, and the initiation of wave breaking over slopes. The MEL time integration is based on a second-order Taylor series expansion, requiring to compute high order time and space derivatives. In order to solve wave-structure interaction problems with complex geometries, we reformulate the model to use a 3D unstructured triangular mesh, building on earlier work, but presently only working with linear elements. The added flexibility of arbitrary meshes is demonstrated by modeling the longitudinal forces on a truncated (surface-piercing) vertical cylinder, comparing to theory and experiment. In order to improve the computational efficiency of the BEM, we apply the fast multipole method (FMM), in the context of the new unstructured mesh. A detailed study of the resulting computational time shows both the efficiency of the earlier 3D-MII approach and the proposed one, and also what is necessary to scale such results up to larger grids.
2017
We report on recent progress and validation of a 3D hybrid model for naval hydrodynamics problems based on a perturbation method, in which both velocity and pressure are expressed as the sum of an inviscid flow with a viscous perturbation. The farto near-field inviscid flows can be solved with a Boundary Element Method (BEM), based on fully nonlinear potential flow theory, and the near-field perturbation flow is solved with a NS model based on a Lattice Boltzmann Method (LBM) with a Large Eddy Simulation (LES) of the turbulence. We summarize the hybrid model formulation and latest developments regarding the LES, and particularly a new wall model for the viscous/turbulent sub-layer near solid boundaries, that is generalized for an arbitrary geometry. The latter are validated by simulating turbulent flows over a flat plate for Re ∈ [3.7× 104;1.2× 10], for which the friction coefficient computed on the plate agrees well with experiments. We then simulate the flow past a NACA0012 foil u...
We present a comparison between two distinct numerical codes dedicated to the study of wave energy converters. Both are developed by the authors, using a boundary element method with linear triangular elements. One model applies fully nonlinear boundary conditions in a numerical wavetank environnment (and thus referred later as NWT), whereas the second relies on a weak-scatterer approach in open-domain and can be considered a weakly nonlinear potential code (referred later as WSC). For the purposes of comparison, we limit our study to the forces on a heaving submerged sphere. Additional results for more realistic problem geometries will be presented at the conference.