Control Signal Optimization for Non-Linear Wave Generation

2018 ◽  
Author(s):  
J. B. H. Hicks ◽  
H. B. Bingham ◽  
R. Read
Keyword(s):  
Water Waves ◽  
Numerical Optimization ◽  
Wave Generation ◽  
Linear Wave ◽  
Linear Potential ◽  
Numerical Work ◽  
Flow Solver ◽  
Control Signals ◽  
Correction Scheme ◽  
Non Linear

This paper investigates the use of optimization for numerical-physical wave generation in wave tanks. Control signals for a wedge-shaped plunger-type wave generator are developed to produce stable non-linear, deep-water waves in both numerical and physical wave tanks. A fully non-linear potential flow solver developed at DTU is used for the numerical work. Numerical optimization proceeds by a defect correction scheme, resulting in optimized control signals for wavelengths of 0.7–2 m (corresponding to non-dimensional wave numbers kh = 2–5.5) and steepnesses of 3–11%.

Applicability and limitations of highly non-linear potential flow solvers in the context of water waves

2017 ◽  
Vol 142 ◽  
pp. 233-244 ◽  
Author(s):  
Guillaume Ducrozet ◽  
Félicien Bonnefoy ◽  
Yves Perignon
Keyword(s):  
Potential Flow ◽  
Water Waves ◽  
Linear Potential ◽  
Non Linear

scholarly journals Relation between orbital velocities, pressure and surface elevation in non-linear nearshore water waves

2021 ◽  
Author(s):  
Kévin Martins ◽  
Philippe Bonneton ◽  
David Lannes ◽  
Hervé Michallet
Keyword(s):  
Free Surface ◽  
Surface Energy ◽  
Water Waves ◽  
Energy Levels ◽  
Sea Surface ◽  
Surface Elevation ◽  
Linear Wave ◽  
Free Surface Elevation ◽  
High Frequencies ◽  
Non Linear

AbstractThe inability of the linear wave dispersion relation to characterize the dispersive properties of non-linear shoaling and breaking waves in the nearshore has long been recognised. Yet, it remains widely used with linear wave theory to convert between sub-surface pressure, wave orbital velocities and the free surface elevation associated with non-linear nearshore waves. Here, we present a non-linear fully dispersive method for reconstructing the free surface elevation from sub-surface hydrodynamic measurements. This reconstruction requires knowledge of the dispersive properties of the wave field through the dominant wavenumbers magnitude κ, representative in an energy-averaged sense of a mixed sea-state composed of both free and forced components. The present approach is effective starting from intermediate water depths - where non-linear interactions between triads intensify - up to the surf zone, where most wave components are forced and travel approximately at the speed of non-dispersive shallow-water waves. In laboratory conditions, where measurements of κ are available, the non-linear fully dispersive method successfully reconstructs sea-surface energy levels at high frequencies in diverse non-linear and dispersive conditions. In the field, we investigate the potential of a reconstruction that uses a Boussinesq approximation of κ, since such measurements are generally lacking. Overall, the proposed approach offers great potential for collecting more accurate measurements under storm conditions, both in terms of sea-surface energy levels at high frequencies and wave-by-wave statistics (e.g. wave extrema). Through its control on the efficiency of non-linear energy transfers between triads, the spectral bandwidth is shown to greatly influence non-linear effects in the transfer functions between sub-surface hydrodynamics and the sea-surface elevation.

scholarly journals Non-linear wave generation and absorption using open boundaries within DualSPHysics

2019 ◽  
Vol 240 ◽  
pp. 46-59 ◽  
Author(s):  
Tim Verbrugghe ◽  
J.M. Domínguez ◽  
Corrado Altomare ◽  
Angelantonio Tafuni ◽  
Renato Vacondio ◽  
...  
Keyword(s):  
Wave Generation ◽  
Linear Wave ◽  
Open Boundaries ◽  
Non Linear

Non-linear wave-induced motions of cylindrical-shaped floaters of fish farms

2009 ◽  
Vol 223 (3) ◽  
pp. 361-375 ◽  
Author(s):  
D Kristiansen ◽  
O M Faltinsen
Keyword(s):  
Model Tests ◽  
Linear Wave ◽  
Linear Potential ◽  
Fish Farms ◽  
Non Linear ◽  
Computational Fluid Dynamics Cfd ◽  
Harmonic Components ◽  
Wave Induced ◽  
Hydrodynamic Effects ◽  
Sway Motion

This paper addresses the two-dimensional hydrodynamical problem of a floating circular cylinder in waves by means of model tests and numerical simulations. The problem is relevant for floaters of fish farms. Dedicated model tests and computational fluid dynamics (CFD)-simulations, using a presently developed numerical wave tank are presented. Large amplitude sway motion of the cylinder at a wave frequency equal to half the natural sway frequency was observed, both experimentally and numerically. This is argued to be associated with non-linear hydrodynamic effects and instabilities. Further, linear potential flow theory is shown to overpredict the sway motion at resonance of about 500 per cent compared with experiments and simulations. This discrepancy is explained to be mainly attributable to viscous damping caused by flow separation. Higher-order harmonic components of the hydrodynamic forces are significant and should be considered in fatigue life analyses of fish farms.

scholarly journals APPLICATION OF OPEN BOUNDARIES WITHIN A TWO-WAY COUPLED SPH MODEL TO SIMULATE NON-LINEAR WAVE-STRUCTURE INTERACTIONS

2018 ◽  
pp. 14 ◽  
Author(s):  
Tim Verbrugghe ◽  
José Manuel Dominguez ◽  
Corrado Altomare ◽  
Angelantonio Tafuni ◽  
Peter Troch ◽  
...  
Keyword(s):  
Coupled Model ◽  
Wave Structure ◽  
Surface Elevation ◽  
Open Boundary ◽  
Test Case ◽  
Linear Wave ◽  
Linear Potential ◽  
Original Solution ◽  
Non Linear ◽  
Sph Model

A two-way coupling between the fully non-linear potential flow (FNPF) solver OceanWave3D and the Smoothed Particle Hydrodynamics (SPH) solver DualSPHysics is presented. At the coupling interfaces within the SPH domain, an open boundary formulation is applied. An inlet and outlet zone are filled with bu er particles. At the inlet, horizontal orbital velocities and surface elevations calculated with OceanWave3D are imposed on the bu er particles. At the outlet, horizontal orbital velocities are imposed, but the surface elevation is extrapolated from the fluid domain. Velocity corrections are applied to avoid unwanted reflections in the fluid domain. The SPH surface elevation can be coupled back to OceanWave3D, where the original solution is overwritten. The coupling methodology is validated using a 2-D test case of a floating box. Additionally, a 3-D proof of concept is shown where overtopping waves are acting on a heaving cylinder. The 2-way coupled model proofs to be capable of simulating wave propagation and wave-structure interaction problems with an acceptable accuracy with RMSE values remaining below the smoothing length h.

scholarly journals On the Deterministic Prediction of Water Waves

Fluids ◽  
2020 ◽  
Vol 5 (1) ◽  
pp. 9 ◽  
Author(s):  
Marco Klein ◽  
Matthias Dudek ◽  
Günther F. Clauss ◽  
Sören Ehlers ◽  
Jasper Behrendt ◽  
...  
Keyword(s):  
Water Waves ◽  
Linear Wave ◽  
Wave Steepness ◽  
Forecast Horizon ◽  
Linear Dispersion ◽  
Similarity Parameter ◽  
Linear Solution ◽  
Basic Module ◽  
Wave Prediction ◽  
Non Linear

This paper discusses the potential of deterministic wave prediction as one basic module for decision support of offshore operations. Therefore, methods of different complexity—the linear wave solution, the non-linear Schrödinger equation (NLSE) of two different orders and the high-order spectral method (HOSM)—are presented in terms of applicability and limitations of use. For this purpose, irregular sea states with varying parameters are addressed by numerical simulations as well as model tests in the controlled environment of a seakeeping basin. The irregular sea state investigations focuses on JONSWAP spectra with varying wave steepness and enhancement factor. In addition, the influence of the propagation distance as well as the forecast horizon is discussed. For the evaluation of the accuracy of the prediction, the surface similarity parameter is used, allowing an exact, quantitative validation of the results. Based on the results, the pros and cons of the different deterministic wave prediction methods are discussed. In conclusion, this paper shows that the classical NLSE is not applicable for deterministic wave prediction of arbitrary irregular sea states compared to the linear solution. However, the application of the exact linear dispersion operator within the linear dispersive part of the NLSE increased the accuracy of the prediction for small wave steepness significantly. In addition, it is shown that non-linear deterministic wave prediction based on second-order NLSE as well as HOSM leads to a substantial improvement of the prediction quality for moderate and steep irregular wave trains in terms of individual waves and prediction distance, with the HOSM providing a high accuracy over a wider range of applications.

Comparing Numerical and Analytical Solutions of Solitary Water Waves Over Finite and Variable Depth

2021 ◽  
Author(s):  
Thiago S. Hallak ◽  
Hafizul Islam ◽  
Sarat Chandra Mohapatra ◽  
C. Guedes Soares
Keyword(s):  
Analytical Solutions ◽  
Potential Flow ◽  
Water Waves ◽  
Numerical Solutions ◽  
Turbulence Models ◽  
Boundary Element Methods ◽  
Linear Potential ◽  
Variable Depth ◽  
Viscous Effects ◽  
Non Linear

Abstract In this paper, three methods are used in order to obtain the solution for the propagation of water solitons over finite and variable depth. First, the exact analytical solitary wave solutions of the one-dimensional non-linear Boussinesq equations under shallow water condition are described for constant and variable depth. Second, the three-dimensional Fully Non-linear Potential Flow code OceanWave3D is used in order to obtain the numerical solutions for the solitary waves’ propagation over same depth ranges, providing robust solutions for the potential flow problem. Third, Computational Fluid Dynamics’ tool OpenFOAM is used in order to obtain the viscous solution for the same problem, however, without the accounts of turbulence models. The free-surface profiles are drawn and compared; and the stability of the numerical solutions are assessed. Since the approximations of Boussinesq-type equations depend mainly on the orders of magnitude of amplitude and depth, the numerical-analytical comparison will draw the limits for the validity of the analytical solutions. On the other hand, the comparison will provide the limits where viscous effects start playing an important role, whereas the CFD simulations predict the occurrence of wave breaking. These benchmark cases are compared with past references. After all, results regarding the same phenomena have been described in the literature according to, e.g. Fully Non-linear Boussinesq Models, and Fully Nonlinear Potential Flow schemes solved by Boundary Element Methods. Last but not least, the open source Fully Non-linear Potential Flow code is used in order to provide the potential flow solution for some extra cases of water soliton propagation, in order to capture the trends in weak shoaling scenarios.

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