scholarly journals MNLS simulations of surface wave groups with directional spreading in deep and finite depth waters

2021 ◽  
Author(s):  
Dylan Barratt ◽  
Ton Stefan van den Bremer ◽  
Thomas Alan Adcock Adcock
Keyword(s):  
Potential Flow ◽  
Finite Depth ◽  
Spectral Peak ◽  
Wave Group ◽  
Carrier Wave ◽  
Linear Dispersion ◽  
Wave Groups ◽  
Fully Nonlinear ◽  
Nonlinear Potential ◽  
The Impact

AbstractWe simulate focusing surface gravity wave groups with directional spreading using the modified nonlinear Schrödinger (MNLS) equation and compare the results with a fully-nonlinear potential flow code, OceanWave3D. We alter the direction and characteristic wavenumber of the MNLS carrier wave, to assess the impact on the simulation results. Both a truncated (fifth-order) and exact version of the linear dispersion operator are used for the MNLS equation. The wave groups are based on the theory of quasi-determinism and a narrow-banded Gaussian spectrum. We find that the truncated and exact dispersion operators both perform well if: (1) the direction of the carrier wave aligns with the direction of wave group propagation; (2) the characteristic wavenumber of the carrier wave coincides with the initial spectral peak. However, the MNLS simulations based on the exact linear dispersion operator perform significantly better if the direction of the carrier wave does not align with the wave group direction or if the characteristic wavenumber does not coincide with the initial spectral peak. We also perform finite-depth simulations with the MNLS equation for dimensionless depths ($$k_{\text {p}}d$$ k p d ) between 1.36 and 5.59, incorporating depth into the boundary conditions as well as the dispersion operator, and compare the results with those of fully-nonlinear potential flow code to assess the finite-depth limitations of the MNLS.

scholarly journals Investigation of Focusing Wave Properties in a Numerical Wave Tank with a Fully Nonlinear Potential Flow Model

2019 ◽  
Vol 7 (10) ◽  
pp. 375 ◽  
Author(s):  
Weizhi Wang ◽  
Arun Kamath ◽  
Csaba Pakozdi ◽  
Hans Bihs
Keyword(s):  
Wave Height ◽  
Potential Flow ◽  
Wave Steepness ◽  
Numerical Wave Tank ◽  
Wave Groups ◽  
Wave Tank ◽  
Fully Nonlinear ◽  
Nonlinear Potential ◽  
Numerical Wave ◽  
Focused Wave

Nonlinear wave interactions and superpositions among the different wave components and wave groups in a random sea sometimes produce rogue waves with extremely large wave heights that appear unexpectedly. A good understanding of the generation and evolution of such extreme wave events is of great importance for the analysis of wave forces on marine structures. A fully nonlinear potential flow (FNPF) model is proposed in the presented paper to investigate the different factors that influence the wave focusing location, focusing time and focusing wave height in a numerical wave tank. Those factors include wave steepness, spectrum bandwidth, wave generation method, focused wave spectrum, and wave spreading functions. The proposed model solves the Laplace equation together with the boundary conditions on a σ -coordinate grid using high-order discretisation schemes on a fully parallel computational framework. The model is validated against the focused wave experiments and thereafter used to obtain insights into the effects of the different factors. It is found that the wave steepness contributes to changing the location and time of focus significantly. Spectrum bandwidth and directional spreading affect the focusing wave height and profile, for example, a wider bandwidth and a wider directional spread lead to a lower focusing wave height. A Neumann boundary condition represents the nonlinearity of the wave groups better than a relaxation method for wave generation.

Development of 3-Dimensional Fully Nonlinear Potential Flow Planar Wave Tank in Framework of OpenFOAM

2019 ◽  
Author(s):  
Zaibin Lin ◽  
Ling Qian ◽  
Wei Bai ◽  
Zhihua Ma ◽  
Hao Chen ◽  
...  
Keyword(s):  
Free Surface ◽  
Potential Flow ◽  
Wave Structure ◽  
Wave Model ◽  
Numerical Wave Tank ◽  
Wave Tank ◽  
Fully Nonlinear ◽  
3 Dimensional ◽  
Nonlinear Potential ◽  
Numerical Wave

Abstract A 3-Dimensional numerical wave tank based on the fully nonlinear potential flow theory has been developed in OpenFOAM, where the Laplace equation of velocity potential is discretized by Finite Volume Method. The water surface is tracked by the semi-Eulerian-Lagrangian method, where water particles on the free surface are allowed to move vertically only. The incident wave is generated by specifying velocity profiles at inlet boundary with a ramp function at the beginning of simulation to prevent initial transient disturbance. Additionally, an artificial damping zone is located at the end of wave tank to sufficiently absorb the outgoing waves before reaching downstream boundary. A five-point smoothing technique is applied at the free surface to eliminate the saw-tooth instability. The proposed wave model is validated against theoretical results and experimental data. The developed solver could be coupled with multiphase Navier-Stokes solvers in OpenFOAM in the future to establish an integrated versatile numerical wave tank for studying efficiently wave structure interaction problems.

Wave Scattering Around a Vertical Cylinder: Fully Nonlinear Potential Flow Calculations Compared With Low Order Perturbation Results and Experiment

2002 ◽  
Author(s):  
Karsten Trulsen ◽  
Per Teigen
Keyword(s):  
Potential Flow ◽  
Wave Scattering ◽  
Vertical Cylinder ◽  
Wave Interaction ◽  
Perturbation Approach ◽  
Marine Structures ◽  
Fully Nonlinear ◽  
Nonlinear Potential ◽  
Specific Geometry ◽  
Truncated Cylinder

A detailed description of a fully nonlinear numerical method for computing wave interaction effects around arbitrary marine structures is presented. The paper highlights application to one specific geometry: A single, fixed vertical truncated cylinder. The fully nonlinear computations are compared with linear and second-order nonlinear results obtained with the perturbation approach, as well as with experiments.

scholarly journals High-Fidelity Representation of Three-Hour Offshore Short-Crested Wave Field in the Fully Nonlinear Potential Flow Model REEF3D::FNPF

2020 ◽  
Author(s):  
Weizhi Wang ◽  
Csaba Pakozdi ◽  
Arun Kamath ◽  
Hans Bihs
Keyword(s):  
Wave Field ◽  
Potential Flow ◽  
Flow Model ◽  
Offshore Structures ◽  
High Fidelity ◽  
Fully Nonlinear ◽  
Space And Time ◽  
Nonlinear Potential ◽  
Potential Flow Model ◽  
Wave Properties

Abstract Stochastic wave properties are crucial for the design of offshore structures. Short-crested seas are commonly seen at the sites of offshore structures, especially during storm events. A long time duration is required in order to obtain the statistical properties, which is challenging for numerical simulations because of the high demand of computational resources. In this scenario, a potential flow solver is ideal due to its computational efficiency. A procedure of producing accurate representation of short-crested sea states using the open-source fully nonlinear potential flow model REEF3D::FNPF is presented in the paper. The procedure examines the sensitivity of the resolutions in space and time as well as the arrangements of wave gauge arrays. A narrow band power spectrum and a mildly spreading directional spreading function are simulated, and an equal energy method is used to generate input waves to avoid phase-locking. REEF3D::FNPF solves the Laplace equation together with the boundary conditions using a finite difference method. A sigma grid is used in the vertical direction and the vertical grid clustering follows the principle of constant truncation error. High-order discretisation methods are implemented in space and time. Message passing interface is used for high performance computation using multiple processors. Three-hour simulations are performed in full-scale at a hypothetic offshore site with constant water depth. The significant wave height, peak period, kurtosis, skewness and ergodicity are examined in the numerically generated wave field. The stochastic wave properties in the numerical wave tank (NWT) using REEF3D::FNPF match the input wave conditions with high fidelity.

Steep Wave Loads From Irregular Waves on an Offshore Wind Turbine Foundation: Computation and Experiment

2013 ◽  
Author(s):  
Bo Terp Paulsen ◽  
Henrik Bredmose ◽  
Harry B. Bingham ◽  
Signe Schløer
Keyword(s):  
Free Surface ◽  
Potential Flow ◽  
Surface Elevation ◽  
Irregular Waves ◽  
Navier Stokes ◽  
Two Dimensional ◽  
Free Surface Elevation ◽  
Fully Nonlinear ◽  
Flow Solver ◽  
Nonlinear Potential

Two-dimensional irregular waves on a sloping bed and their impact on a bottom mounted circular cylinder is modeled by three different numerical methods and the results are validated against laboratory experiments. We here consider the performance of a linear-, a fully nonlinear potential flow solver and a fully nonlinear Navier-Stokes/VOF solver. The validation is carried out in terms of both the free surface elevation and the inline force. Special attention is paid to the ultimate load in case of a single wave event and the general ability of the numerical models to capture the higher harmonic forcing. The test case is representative for monopile foundations at intermediate water depths. The potential flow computations are carried out in a two-dimensional vertical plane and the inline force on the cylinder is evaluated by the Morison equation. The Navier-Stokes/VOF computations are carried out in three-dimensions and the force is obtained by spatial pressure integration over the wettet area of the cylinder. In terms of both the free surface elevation and the inline force, the linear potential flow model is shown to be of limited accuracy and large deviations are generally seen when compared to the experimental measurements. The fully nonlinear Navier-Stokes/VOF computations are accurately predicting both the free surface elevation and the inline force. However, the computational cost is high relative to the potential flow solvers. Despite the fact that the nonlinear potential flow model is carried out in two-dimensions it is shown to perform just as good as the three-dimensional Navier-Stokes/VOF solver. This is observed for both the free surface elevation and the inline force, where both the ultimate load and the higher harmonic forces are accurately predicted. This shows that for moderately steep irregular waves a Morison equation combined with a fully nonlinear two-dimensional potential flow solver can be a good approximation.

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