Propagation of Steep and Breaking Short-Crested Waves: A Comparison of CFD Codes

2018 ◽  
Author(s):  
Øystein Lande ◽  
Thomas Berge Johannessen
Keyword(s):  
Wave Propagation ◽  
Wave Spectrum ◽  
Ocean Waves ◽  
Offshore Structures ◽  
Practical Reasons ◽  
Breaking Wave ◽  
Linear Wave ◽  
Wave Groups ◽  
Irregular Wave ◽  
Highly Nonlinear

Using the computational fluid domain for propagation of ocean waves have become an important tool for the calculation of highly nonlinear wave loading on offshore structures such as run-up, wave slamming and non-linear breaking wave kinematics. At present, there are many computational fluid dynamics (CFD) codes available which can be employed to calculate water wave propagation and wave induced loading on structures. For practical reasons, however, the use of these codes is often limited to the propagation of regular uni-directional waves initiated very close to the structure, or to investigating the properties and loading due to measured waves by fitting a numerical wave to a measured wave profile. The present paper focuses on the propagation of steep irregular and short crested wave groups up to the point of breaking. Indeed, this is challenging because of the highly nonlinear behavior of irregular wave groups as steepness increases and they approach the point of breaking. The complexity further increases with the introduction of short-crestedness requiring computation in a large 3-dimentional domain. Two CFD codes are used in this comparison study which are believed to be well conditioned for wave propagation, the commercial code ComFLOW (available through the ComFLOW JIP project) and the open-source code BASILISK. The primary objective of this paper to show the two CFD codes capability of recreating measured irregular wave groups, using the known linear wave components from the model test as input to fluid domain. Wave elevation is measured at several locations in the close vicinity of the focus point. The comparison is carried out for a selection of events with variation in steepness, wave spreading and wave spectrum.

Conditional Short-Crested Second Order Waves in Shallow Water and With Superimposed Current

2004 ◽  
Author(s):  
Jo̸rgen Juncher Jensen
Keyword(s):  
Shallow Water ◽  
Wave Spectrum ◽  
Ocean Waves ◽  
Offshore Structures ◽  
Second Order ◽  
Stokes Wave ◽  
Wave Crest ◽  
Wave Kinematics ◽  
Wave Approach ◽  
Non Linear

For bottom-supported offshore structures like oil drilling rigs and oil production platforms, a deterministic design wave approach is often applied using a regular non-linear Stokes’ wave. Thereby, the procedure accounts for non-linear effects in the wave loading but the randomness of the ocean waves is poorly represented, as the shape of the wave spectrum does not enter the wave kinematics. To overcome this problem and still keep the simplicity of a deterministic approach, Tromans, Anaturk and Hagemeijer (1991) suggested the use of a deterministic wave, defined as the expected linear Airy wave, given the value of the wave crest at a specific point in time or space. In the present paper a derivation of the expected second order short-crested wave riding on a uniform current is given. The analysis is based on the second order Sharma and Dean shallow water wave theory and the direction of the main wind direction can make any direction with the current. Numerical results showing the importance of the water depth, the directional spreading and the current on the conditional mean wave profile and the associated wave kinematics are presented. A discussion of the use of the conditional wave approach as design waves is given.

Prediction of the Damping-Controlled Response of Offshore Structures to Random Wave Excitation

1980 ◽  
Vol 20 (01) ◽  
pp. 5-14 ◽  
Author(s):  
Kim J. Vandiver
Keyword(s):  
Wave Spectrum ◽  
Wave Force ◽  
Ocean Waves ◽  
Radiation Damping ◽  
Explicit Calculation ◽  
Random Wave ◽  
Wave Forces ◽  
Linear Wave ◽  
Radiation Wave ◽  
Diffraction Effects

Abstract A method is presented for predicting the damping-controlled response of a structure at a known natural frequency to random wave forces. The principal advantage of the proposed method over those in current use proposed method over those in current use is that explicit calculation of wave forces is not required in the analysis. This is accomplished by application of the principle of reciprocity: that the linear wave force spectrum for a particular vibration mode is proportional to the radiation (wave-making) proportional to the radiation (wave-making) damping of that mode. Several example calculations are presented including the prediction of the heave response of a prediction of the heave response of a tension-leg platform. The directional distribution of the wave spectrum included in the analysis. Introduction This paper introduces a simple procedure for estimating the dynamic response of a structure at each of its natural frequencies to the random excitation of ocean waves. The principal advantage of the proposed method is that the explicit calculation of wave forces has been eliminated from the analysis. This is made possible by a direct applications of the reciprocity relations for ocean waves, originally established by Haskind and described by Newman, in a form that is easy to implement. Briefly stated, fore many structures it is possible to derive a simple expression for the wave force spectrum in terms of the radiation damping and the prescribed wave amplitude spectrum. In general, such a substitution is of little use because the radiation damping coefficient may be equally difficult to find. However, the substitution leads to a very useful result when the dynamically amplified response at a natural frequency is of concern. In such cases it is shown that, contrary to popular belief, the response is not inversely proportional to the total damping but is, in fact, proportional to the ratio of the radiation damping to the total damping. Therefore, in the absence of a reliable estimate of either the total damping or the ratio of the radiation component to the total, an upper bound estimate of the response still may be achieved because of the existence of this upper bound is one of the key contributions of this paper.Linear wave theory is assumed; therefore, excitation caused by drag forces is not considered. However, for many structures drag excitation is negligible except for very large wave events. In the design process extreme events are modeled deterministically process extreme events are modeled deterministically by means of a prescribed design wave and not stochastically as is done here. In many circumstances linear wave forces will dominate, and the results shown here will be applicable. Although drag-exciting forces are not included, damping resulting from hydrodynamic drag is included. Wave diffraction effects are extremely difficult to calculate. This analysis includes diffraction effects but never requires explicit evaluation of them.It has been recognized that directional spreading of the wave spectrum is an important consideration in the estimation of dynamic response. In this paper such effects are accounted for in closed-form expressions. The evaluation of the expressions requires knowledge of estimates of the variation of the modal exciting force with wave incidence angle. However, only the relative variation of the modal exciting force as a percent of that at an arbitrarily chosen reference angle is required. Evaluation of the wave force in absolute terms still is not required. SPEJ p. 5

Ocean Surface Modeling in Vary Wind Field

2011 ◽  
Vol 480-481 ◽  
pp. 1452-1456
Author(s):  
Li Bo ◽  
Zhong Yi Li ◽  
Yue Jin Zhang
Keyword(s):  
Wind Field ◽  
Wave Spectrum ◽  
Wave Model ◽  
Ocean Surface ◽  
Ocean Waves ◽  
Surface Modeling ◽  
Ocean Wave ◽  
Statistical Characteristics ◽  
Linear Wave ◽  
Wave Models

In ocean surface modeling a popular method of wave modeling is making use of ocean wave spectrum, which is a physical wave model and based on linear wave theories. The ocean waves produced in this way can reflect the statistical characteristics of the real ocean well. However, few investigations of ocean simulation have been focused on turbulent fluid under vary wind field in this way, while all ocean wave models are built with the same wind parameters. In order to resolve the problem of traditional method, we proposed a new method of dividing the ocean surface into regular grids and generating wave models with different parameters of wind in different location of view scope. The method not only preserves the fidelity of statistical characteristics, but also can be accelerated with the processing of GPU and widely used in VR applications.

Conditional Short-Crested Waves in Shallow Water and With Superimposed Current

2002 ◽  
Author(s):  
Jo̸rgen Juncher Jensen
Keyword(s):  
Shallow Water ◽  
Water Depth ◽  
Wave Spectrum ◽  
Wave Theory ◽  
Ocean Waves ◽  
Offshore Structures ◽  
Stokes Wave ◽  
Wave Crest ◽  
Non Linear ◽  
Drilling Rigs

For bottom-supported offshore structures like oil drilling rigs and oil production platforms, a deterministic design wave approach is often applied using a regular non-linear Stokes’ wave. Thereby, the procedure accounts for non-linear effects in the wave loading but the randomness of the ocean waves is poorly represented, as the shape of the wave spectrum does not enter the wave kinematics. To overcome this problem and still keep the simplicity of a deterministic approach, Tromans, Anaturk and Hagemeijer (1991) suggested the use of a deterministic wave, defined as the expected linear Airy wave, given the value of the wave crest at a specific point in time or space. In the present paper a derivation of the expected linear short-crested wave riding on a uniform current is given. The analysis is based on the conventional shallow water Airy wave theory and the direction of the main wind direction can make any direction with the current. A consistent derivation of the wave spectrum taking into account current and finite water depth is used. The numerical results show a significant effect of the water depth, the directional spreading and the current on the conditional mean wave profile. Extensions to higher order waves are finally discussed.

scholarly journals Phase-Resolved Reconstruction Algorithm and Deterministic Prediction of Nonlinear Ocean Waves From Spatio-Temporal Optical Measurements

2018 ◽  
Author(s):  
Nicolas Desmars ◽  
Yves Pérignon ◽  
Guillaume Ducrozet ◽  
Charles-Antoine Guérin ◽  
Stephan T. Grilli ◽  
...  
Keyword(s):  
Free Surface ◽  
Wave Model ◽  
Reconstruction Algorithm ◽  
Wave Theory ◽  
Ocean Waves ◽  
Optical Measurements ◽  
Linear Wave ◽  
Offshore Structure ◽  
Highly Nonlinear ◽  
Spatio Temporal

We investigate a nonlinear phase-resolved reconstruction algorithm and models for the deterministic prediction of ocean waves based on a large number of spatio-temporal optical measurements of surface elevations. We consider a single sensor (e.g., LIDAR, stereo-video, etc.) mounted on a fixed offshore structure and remotely measuring fields of free surface elevations. Assuming a uniform distribution of measurement points over the sensor aperture angles, the density of free surface observation points geometrically decreases with the distance from the sensor. Additionally, wave shadowing effects occur, which become more important at small viewing angles (i.e., grazing incidence on the surface). These effects result in observations of surface elevation that are sparsely distributed. Here, based on earlier work by [1], we present and discuss the characteristics of an algorithm, aimed at assimilating such sparse data and able to deterministically reconstruct and propagate ocean surface elevations for their prediction in time and space. This algorithm could assist in the automatic steering and control of a variety of surface vehicles. Specifically, we compare prediction results using linear wave theory and the weakly nonlinear Choppy Wave Model [2, 3], extended here to an “improved” second order formulation. The latter model is based on an efficient Lagrangian formulation of the free surface and was shown to be able to model wave properties that are important to the proper representation of nonlinear free surfaces, namely wave shape and celerity. Synthetic datasets from highly nonlinear High Order Spectral simulations are used as reference oceanic surfaces. Predicted results are analyzed over an area that evolves in time, using the theoretical amount of information assimilated during the reconstruction of the wave field. For typical horizons of prediction, we discuss the capabilities of our assimilation process for each wave model considered.

Breaking Wave on a Slender Cylinder: Comparison of Experimental Data and Numerical Results

2012 ◽  
Author(s):  
Jorge Ramirez ◽  
Peter Frigaard ◽  
Thomas Lykke Andersen ◽  
Erik Damgaard Christensen
Keyword(s):  
Target Location ◽  
Experimental Tests ◽  
Offshore Structures ◽  
Breaking Wave ◽  
Linear Wave ◽  
Wave Loads ◽  
Cfd Models ◽  
Focused Wave ◽  
Harmonic Components ◽  
Run Up

CFD models are promising in predicting non-linear wave loads on fixed and floating offshore structures. The NS3 model is described in this paper and it has been validated by means of model test such as wave run-up on monopiles in regular waves. The goal for the use of the NS3 model is to make a detailed investigation of the effect of 2D waves on the run-up height. The focused wave is designed by choosing the phases of the linear harmonic components such that they are in phase at a certain target location. The aim of this paper is the approach on the ability of NS3 model to reproduce these focused wave groups and compare with the results of the experimental tests carried out at Grossen WellenKanal (GWK).

The coastal refraction-diffraction wave propagation model

1995 ◽  
Vol 17 (4) ◽  
pp. 6-12
Author(s):  
Nguyen Tien Dat ◽  
Dinh Van Manh ◽  
Nguyen Minh Son
Keyword(s):  
Wave Propagation ◽  
Field Data ◽  
Surf Zone ◽  
Propagation Model ◽  
Wave Transformation ◽  
Diffraction Effect ◽  
Linear Wave ◽  
Diffraction Wave ◽  
Linear Wave Propagation ◽  
Wave Propagation Model

A mathematical model on linear wave propagation toward shore is chosen and corresponding software is built. The wave transformation outside and inside the surf zone is considered including the diffraction effect. The model is tested by laboratory and field data and gave reasonables results.

Wave propagation improvement in two-dimensional bond-based peridynamics model

2021 ◽  
pp. 095440622098555
Author(s):  
Reza Alebrahim ◽  
Pawel Packo ◽  
Mirco Zaccariotto ◽  
Ugo Galvanetto
Keyword(s):  
Wave Propagation ◽  
Dynamic Performance ◽  
Numerical Dispersion ◽  
Motion Modeling ◽  
Minimization Method ◽  
Irregular Wave ◽  
Point Collocation ◽  
Potential Applications ◽  
Non Local ◽  
Set Up

In this study, methods to mitigate anomalous wave propagation in 2-D Bond-Based Peridynamics (PD) are presented. Similarly to what happens in classical non-local models, an irregular wave transmission phenomenon occurs at high frequencies. This feature of the dynamic performance of PD, limits its potential applications. A minimization method based on the weighted residual point collocation is introduced to substantially extend the frequency range of wave motion modeling. The optimization problem, developed through inverse analysis, is set up by comparing exact and numerical dispersion curves and minimizing the error in the frequency-wavenumber domain. A significant improvement in the wave propagation simulation using Bond-Based PD is observed.

A CFD Study of Focused Extreme Wave Impact on Decks of Offshore Structures

2014 ◽  
Author(s):  
Xin Lu ◽  
Pankaj Kumar ◽  
Anand Bahuguni ◽  
Yanling Wu
Keyword(s):  
Real World ◽  
Offshore Structures ◽  
Air Gap ◽  
Irregular Waves ◽  
Linear Wave ◽  
Extreme Wave ◽  
Wave Impact ◽  
Loading Test ◽  
Wide Range ◽  
Wave Maker

The design of offshore structures for extreme/abnormal waves assumes that there is sufficient air gap such that waves will not hit the platform deck. Due to inaccuracies in the predictions of extreme wave crests in addition to settlement or sea-level increases, the required air gap between the crest of the extreme wave and the deck is often inadequate in existing platforms and therefore wave-in-deck loads need to be considered when assessing the integrity of such platforms. The problem of wave-in-deck loading involves very complex physics and demands intensive study. In the Computational Fluid Mechanics (CFD) approach, two critical issues must be addressed, namely the efficient, realistic numerical wave maker and the accurate free surface capturing methodology. Most reported CFD research on wave-in-deck loads consider regular waves only, for instance the Stokes fifth-order waves. They are, however, recognized by designers as approximate approaches since “real world” sea states consist of random irregular waves. In our work, we report a recently developed focused extreme wave maker based on the NewWave theory. This model can better approximate the “real world” conditions, and is more efficient than conventional random wave makers. It is able to efficiently generate targeted waves at a prescribed time and location. The work is implemented and integrated with OpenFOAM, an open source platform that receives more and more attention in a wide range of industrial applications. We will describe the developed numerical method of predicting highly non-linear wave-in-deck loads in the time domain. The model’s capability is firstly demonstrated against 3D model testing experiments on a fixed block with various deck orientations under random waves. A detailed loading analysis is conducted and compared with available numerical and measurement data. It is then applied to an extreme wave loading test on a selected bridge with multiple under-deck girders. The waves are focused extreme irregular waves derived from NewWave theory and JONSWAP spectra.

Sea State Estimation Based on Ship Motions Measurements and Data Fusion

2013 ◽  
Author(s):  
Céline Drouet ◽  
Nicolas Cellier ◽  
Jérémie Raymond ◽  
Denis Martigny
Keyword(s):  
Data Fusion ◽  
State Estimation ◽  
Wave Height ◽  
Significant Wave Height ◽  
Wave Spectrum ◽  
Ocean Waves ◽  
Ship Motions ◽  
Sea State ◽  
Significant Wave ◽  
X Band

In-service monitoring can help to increase safety of ships especially regarding the fatigue assessment. For this purpose, it is compulsory to know the environmental conditions encountered: wind, but also the full directional wave spectrum. During the EU TULCS project, a full scale measurements campaign has been conducted onboard the CMA-CGM 13200 TEU container ship Rigoletto. She has been instrumented to measure deformation of the ship as well as the sea state encountered during its trip. This paper will focus on the sea state estimation. Three systems have been installed to estimate the sea state encountered by the Rigoletto: An X-band radar from Ocean Waves with WAMOS® system and two altimetric wave radars from RADAC®. Nevertheless, the measured significant wave height can be disturbed by several external elements like bow waves, sprays, sea surface ripples, etc… Furthermore, ship motions are also measured and can provide another estimation of the significant wave height using a specific algorithm developed by DCNS Research for the TULCS project. As all those estimations are inherently different, it is necessary to make a fusion of those data to provide a single estimation (“best estimate”) of the significant wave height. This paper will present the data fusion process developed for TULCS and show some first validation results.

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