Steep Unidirectional Wave Groups: Fully Nonlinear Simulations vs Experiments

2015 ◽  
Author(s):  
Lev Shemer ◽  
Bernard K. Ee
Keyword(s):  
Surface Elevation ◽  
Computational Results ◽  
Local Surface ◽  
Qualitative Comparison ◽  
Wave Groups ◽  
Fully Nonlinear ◽  
Nonlinear Simulations ◽  
Velocity Of Propagation ◽  
Steep Waves

A method was developed to carry out detailed qualitative comparison of fully nonlinear computations with the measurements of unidirectional wave groups. Computational results on evolving wave groups were compared with the available experiments. The local surface elevation variation, evolution of envelope shapes, the velocity of propagation of the steepest crests in the group and their relation to the height of the crests were obtained numerically and experimentally. The results shed additional light on the mechanisms leading to the breaking of steep waves.

scholarly journals Steep unidirectional wave groups – fully nonlinear simulations vs. experiments

2015 ◽  
Vol 2 (4) ◽  
pp. 1159-1195 ◽  
Author(s):  
L. Shemer ◽  
B. K. Ee
Keyword(s):  
Wave Breaking ◽  
Surface Elevation ◽  
Computational Results ◽  
Local Surface ◽  
Qualitative Comparison ◽  
Wave Groups ◽  
Fully Nonlinear ◽  
Nonlinear Simulations ◽  
Velocity Of Propagation ◽  
Steep Waves

Abstract. A method was developed to carry out detailed qualitative comparison of fully nonlinear computations with the measurements of unidirectional wave groups. Computational results on evolving wave groups were compared with the available experiments. The local surface elevation variation, evolution of envelope shapes, the velocity of propagation of the steepest crests in the group and their relation to the height of the crests were obtained numerically and experimentally. Conditions corresponding to incipient wave breaking were investigated in greater detail. The results shed additional light on the limits of applicability of the computational results, as well as on mechanisms leading to the breaking of steep waves.

scholarly journals Steep unidirectional wave groups – fully nonlinear simulations vs. experiments

2015 ◽  
Vol 22 (6) ◽  
pp. 737-747 ◽  
Author(s):  
L. Shemer ◽  
B. K. Ee
Keyword(s):  
Wave Breaking ◽  
Initial Conditions ◽  
Crucial Importance ◽  
Local Surface ◽  
Exact Matching ◽  
Wave Groups ◽  
Fully Nonlinear ◽  
Nonlinear Simulations ◽  
Velocity Of Propagation ◽  
Steep Waves

Abstract. A detailed quantitative comparison of fully nonlinear computations with the measurements of unidirectional wave groups is presented. Computational results on evolving wave groups were compared with previous available experiments. The local surface elevation variation, the evolution of envelope shapes, the velocity of propagation of the steepest crests in the group and their relation to the height of the crests were obtained numerically and experimentally. Conditions corresponding to incipient wave breaking were investigated in greater detail. The results shed additional light on mechanisms leading to the breaking of steep waves, as well as on the crucial importance of exact matching between initial conditions in computations and experiments.

Forecast of Critical Wave Groups From Surface Elevation Snapshots

2007 ◽  
Author(s):  
Gu¨nther F. Clauss ◽  
Daniel Testa ◽  
Sascha Kosleck ◽  
Robert Stu¨ck
Keyword(s):  
Wave Train ◽  
Wave Length ◽  
Wave Spectrum ◽  
Amplitude Spectrum ◽  
Response Spectra ◽  
Phase Spectrum ◽  
Surface Elevation ◽  
Fast Fourier Transformation ◽  
Wave Groups ◽  
The Impact

Reports on damages of ships, cargo and structures during heavy seas have been increasing within the last years. The impact of single extreme waves or wave groups on marine structures and ships causes enormous forces often leading to critical situations or even loss of crew, ship and cargo. Dangerous situations can be predicted by a forecast of encountering wave trains and the identification of critical wave groups. The paper presents a method to calculate the wave train a ship will encounter from surface elevation snapshots of the surrounding sea, taken by the ship radar. The time-dependent surface elevation snapshot far ahead of the ship is transferred into frequency domain by the use of Fast Fourier Transformation (FFT). The resulting complex Fourier spectrum given over the inverse wave length 1/L is converted into an amplitude spectrum and a phase spectrum. By shifting the phase spectrum to the position of the cruising ship the encountering waves can in turn be calculated in advance — depending on speed. The permanent processing of incoming snapshots delivers a continuous prediction of the water surface elevation at the position of the cruising ship. Based on these data the expected ship motion behaviour can be calculated continuously in time domain. In addition the response spectra, resulting from the wave spectrum and the relevant RAOs, are also evaluated. As wave data far ahead of the ship are used, it allows a forward glance, and dangerous situations, particularly resonance and parametric resonance are detectable before the ship is encountering this wave train. Consequently, the procedure can be used by the master as an assistance support system.

CONVECTIVE PATTERNS IN LIQUID–VAPOR SYSTEMS WITH DIFFUSE INTERFACE

2006 ◽  
Vol 16 (09) ◽  
pp. 2705-2711 ◽  
Author(s):  
RODICA BORCIA ◽  
DOMNIC MERKT ◽  
MICHAEL BESTEHORN
Keyword(s):  
Phase Field ◽  
Compressible Fluid ◽  
Field Model ◽  
Marangoni Convection ◽  
Van Der Waals ◽  
Phase Field Model ◽  
Diffuse Interface ◽  
Fully Nonlinear ◽  
Nonlinear Simulations ◽  
Liquid Vapor

Recently, we have developed a phase field model to describe Marangoni convection with evaporation in a compressible fluid of van der Waals type away from criticality [Eur. Phys. J. B44 (2005)]. Using this model, we report now 2D fully nonlinear simulations where we emphasize the influence of evaporation on convective patterns.

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.

scholarly journals Fully nonlinear simulations of unidirectional extreme waves provoked by strong depth transitions: The effect of slope

2020 ◽  
Vol 5 (6) ◽  
Author(s):  
Yaokun Zheng ◽  
Zhiliang Lin ◽  
Yan Li ◽  
T. A. A. Adcock ◽  
Ye Li ◽  
...  
Keyword(s):  
Extreme Waves ◽  
Fully Nonlinear ◽  
Nonlinear Simulations

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.

Effect of Second-Order and Fully Nonlinear Wave Kinematics on a Tension-Leg-Platform Wind Turbine in Extreme Wave Conditions

2017 ◽  
Author(s):  
Antonio Pegalajar-Jurado ◽  
Michael Borg ◽  
Amy Robertson ◽  
Jason Jonkman ◽  
Henrik Bredmose
Keyword(s):  
Wind Turbine ◽  
Nonlinear Wave ◽  
Second Order ◽  
Surface Elevation ◽  
Tension Leg Platform ◽  
Fully Nonlinear ◽  
Wave Kinematics ◽  
Wave Basin ◽  
Definition Of ◽  
The Impact

In this study, we assess the impact of different wave kinematics models on the dynamic response of a tension-leg-platform wind turbine. Aero-hydro-elastic simulations of the floating wind turbine are carried out employing linear, second-order, and fully nonlinear kinematics using the Morison equation for the hydrodynamic forcing. The wave kinematics are computed from either theoretical or measured signals of free-surface elevation. The numerical results from each model are compared to results from wave basin tests on a scaled prototype. The comparison shows that sub and superharmonic responses can be introduced by second-order and fully nonlinear wave kinematics. The response at the wave frequency range is better reproduced when kinematics are generated from the measured surface elevation. In the future, the numerical response may be further improved by replacing the global, constant damping coefficients in the model by a more detailed, customizable definition of the user-defined numerical damping.

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