Numerical Modeling Using CFD and Potential Wave Theory for Three-Hour Nonlinear Irregular Wave Simulations

2017 ◽  
Author(s):  
Aldric Baquet ◽  
Jang Kim ◽  
Zhenjia (Jerry) Huang
Keyword(s):  
Numerical Modeling ◽  
Potential Theory ◽  
Wave Spectrum ◽  
Nonlinear Effects ◽  
Wave Theory ◽  
Breaking Waves ◽  
Wave Crest ◽  
Fully Nonlinear ◽  
Irregular Wave ◽  
Stokes Waves

In this paper, we focus on the modeling of a fully-nonlinear, steep, irregular wave field of three-hour duration without structures in it. The fully-nonlinear effects are considered in the wave simulations using computational fluid dynamics (CFD), as well as potential theory. The overall approach for the numerical modeling is described in the paper. The Euler Overlay Method (EOM) is used to incorporate incoming waves, nonlinear effects, and CFD simulations in the numerical modeling. For computational efficiency, we also use potential theory to model the fully-nonlinear waves. Numerical damping was applied locally around the breaking region to enable simulations for large breaking waves. To compensate for energy loss in the numerical simulations, energy compensation factors of wave spectral frequency components are applied to the input wave spectrum. Results of convergence study, validation against high-order Stokes waves and fully-nonlinear irregular wave with prescribed target spectrum, as well as comparison between numerical wave crest distributions and those from multiple realizations of wave calibration tests are presented.

Irregular Wave Simulation and its Impact on Riser Extreme Response for a Production Semi

2020 ◽  
Author(s):  
Shaosong Zhang ◽  
Yongming Cheng ◽  
Yuanlang Cai ◽  
Ning He ◽  
Xiaolong Yang ◽  
...  
Keyword(s):  
Dynamic Response ◽  
Wave Spectrum ◽  
Irregular Waves ◽  
Wave Crest ◽  
Multiple Time ◽  
Irregular Wave ◽  
Wave Simulation ◽  
Extreme Response ◽  
Individual Wave ◽  
Wave Properties

Abstract Steel Catenary Risers (SCRs) are widely used in deepwater and ultra-deepwater field developments. The dynamic strength of SCRs is a concern in terms of the global performance. The analysis results are quite scattered in many cases due to the nature of the irregular wave stochastic properties. The widely accepted approach to predict the riser dynamic response in the irregular seas is to run the multiple time domain simulations based on different random seeds. This paper will address the impacts on the predicted riser dynamic response due to the random seeds selection. The discussion is based on the independent engineering verification work for a production Semi project in South China Sea. The site specific irregular waves are usually defined by not only the wave spectrum, but also the properties of individual waves, such as maximum wave height and minimum wave trough, which have big impacts on the riser extreme response. The code recommended approach for irregular wave simulation is based on the linear wave theory, which can ensure the match of the target wave spectrum, for example, Hs, Tp (or Tz), wave peakness for JONSWAP spectrum. But the variation of simulated individual wave properties to the specified value can be significant or there is no specified value to match. The simulated irregular waves based on linear theory is also a distortion to the real wave elevation time trace, such as the asymmetry of the wave crest and trough, especially for the tropical cyclone sea states. Some riser response, such as the compression load at riser touch down zone, can be significantly impacted by the nonlinear nature of the waves and the variation to the target individual wave properties. This paper will discuss the random wave simulation and its impacts on riser dynamic response. A SCR strength design case is presented for illustration in this paper. Key parameters are identified to show the correlation with the SCR dynamic response. The conclusion is finally drawn from the work presented in this paper.

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 BREAKING WAVE CRITERIA; A STUDY EMPLOYING A NUMERICAL WAVE THEORY

1968 ◽  
Vol 1 (11) ◽  
pp. 8 ◽  
Author(s):  
Robert G. Dean
Keyword(s):  
Stream Function ◽  
Nonlinear Wave ◽  
Wave Spectrum ◽  
Small Diameter ◽  
Wave Theory ◽  
Breaking Waves ◽  
Fundamental Period ◽  
Breaking Wave ◽  
Engineering Design Problems ◽  
Wide Range

Although it is well recognized that wave systems in nature are irregular, comprising a spectrum of fundamental periods, there is still a need for improving our understanding of near-breaking nonlinear wave systems which contain a single fundamental period. For example, most of the shallow water design situations and other cases including forces on small diameter structures in which drag forces predominate are more directly treated in terms of a "design wave" rather than a wave spectrum. This situation is contrasted to many important engineering design problems in which the dynamics of the system are paramount; for example, in the case of a moored drilling vessel. Finally, one may reasonably expect that accurate solutions to the problem of nonlinear wave systems with a single fundamental period will lend insight regarding productive approaches to the more realistic problem of a spectrum of nonlinear waves. This paper investigates the applicability of the stream function wave theory1 for the representation of breaking and near-breaking waves. This particular problem has received little attention, although considerable progress has occurred on two related problems: 1. The development of wave theories covering a wide range of relative water depths and wave heights, and 2. The development of wave theories which apply at breaking conditions. In general, although these theories may be applicable for the limiting wave conditions, their basis of derivation is such that they cannot be extended to non-breaking waves. The purpose of the present investigation, then, is to establish whether or not the stream function wave theory can be applied to span the range extending up to breaking conditions.

On Modelling Kinematics of Steep Irregular Seaway and Freak Waves

2008 ◽  
Author(s):  
Gu¨nther F. Clauss ◽  
Florian Stempinski ◽  
Robert Stu¨ck
Keyword(s):  
Water Waves ◽  
Wave Train ◽  
Breaking Waves ◽  
Breaking Wave ◽  
Coupling Mechanism ◽  
Fast Method ◽  
Freak Waves ◽  
Irregular Wave ◽  
Wave Kinematics ◽  
Stokes Waves

The realistic modelling of velocity and pressure fields in steep, irregular seaways is still a challenging task, especially when extreme events such as freak waves are under investigation. Conventional wave theories provide fast and reliable results while CFD-codes based on RANSE or potential theory are gaining more acceptance for simulating water waves even though they are still considerably time consuming. This paper presents an approach to approximate irregular wave trains with known surface elevations by interacting Stokes waves of up to third order. This is a fast method to determine the wave potential of wind generated waves for long lasting wave registrations with arbitrary origin. The technique is applied to a steep breaking wave package as well as to a realization of a wave train in a wave tank (scale 1:120) which contain a measured extreme wave sequence. Here, special attention is paid to the distinction between the kinematics of the wave crests in extremely high waves and their surrounding irregular wave field. The predicted wave kinematics are validated by experiments employing particle velocity measurements (by Laser Doppler Velocimetry) as well as by pressure recordings. Kinematics of breaking waves are not covered by concurrent analytical wave theories. To address this deficiency a coupling mechanism between a conventionally determined velocity field with a RANSE/VoF-method is applied.

scholarly journals Investigation of Focused Wave Impact on Floating Platform for Offshore Floating Wind Turbine: A CFD Study

2019 ◽  
Author(s):  
Yang Zhou ◽  
Qing Xiao ◽  
Yuanchuan Liu ◽  
Atilla Incecik ◽  
Christophe Peyrard
Keyword(s):  
Potential Theory ◽  
Wave Theory ◽  
Second Order ◽  
Floating Platform ◽  
Wave Impact ◽  
Pitch Motion ◽  
Irregular Wave ◽  
Wave Parameters ◽  
Motion Responses ◽  
Focused Wave

Abstract Most existing research related to a semi-submersible offshore floating platform focuses on the wave-structure interaction under either a regular or irregular wave condition. In order to numerically model the irregular wave impact on a semi-submersible platform hydrodynamic response with a low computational cost, in this study, a focused wave is utilized. The platform under this consideration is the DeepCwind semi-submersible platform. A high fidelity CFD numerical solver based on solving Navier-Stokes equations is adopted to estimate the dynamic response and the hydrodynamic loading of the platform. The focused wave is firstly generated based on a first order irregular wave theory in a numerical wave tank and validated against the linear wave theory results. Next, for CFD coding validation, the surface elevation of a fixed FPSO model associated with a focused wave is calculated and compared with the benchmark results. At last, the dynamic responses of the platform are numerically simulated under various focused wave parameters, and the results are compared with those obtained from an in-house potential flow theory tool at Électricité de France (EDF). It is found that the predicted CFD surge motion responses are close to those achieved with the second order potential theory while differ from the results obtained using linear potential theory. As to the pitch motion, differences are observed between two results, due to the different methods used for second order loads and viscous effects calculation. Turning to the results under different wave parameters, the surge and heave motion responses increase as the wave period goes up. However, the pitch motion is not affected significantly by varying wave periods. It may be due to the fact that the low-frequency effects have limited impact on the pitch motion. The strong nonlinearity at extremely large wave amplitude will be the task in our near future study.

Computations of fully nonlinear three-dimensional wave–wave and wave–body interactions. Part 1. Dynamics of steep three-dimensional waves

2001 ◽  
Vol 438 ◽  
pp. 11-39 ◽  
Author(s):  
MING XUE ◽  
HONGBO XÜ ◽  
YUMING LIU ◽  
DICK K. P. YUE
Keyword(s):  
Three Dimensional ◽  
Breaking Waves ◽  
Stokes Wave ◽  
Two Dimensional ◽  
Wave Instability ◽  
Fully Nonlinear ◽  
Stokes Waves ◽  
Distinct Features ◽  
Wave Problems ◽  
Dimensional Wave

We develop an efficient high-order boundary-element method with the mixed-Eulerian–Lagrangian approach for the simulation of fully nonlinear three-dimensional wave–wave and wave–body interactions. For illustration, we apply this method to the study of two three-dimensional steep wave problems. (The application to wave–body interactions is addressed in an accompanying paper: Liu, Xue & Yue 2001.) In the first problem, we investigate the dynamics of three-dimensional overturning breaking waves. We obtain detailed kinematics and full quantification of three-dimensional effects upon wave plunging. Systematic simulations show that, compared to two-dimensional waves, three-dimensional waves generally break at higher surface elevations and greater maximum longitudinal accelerations, but with smaller tip velocities and less arched front faces. For the second problem, we study the generation mechanism of steep crescent waves. We show that the development of such waves is a result of three-dimensional (class II) Stokes wave instability. Starting with two-dimensional Stokes waves with small three-dimensional perturbations, we obtain direct simulations of the evolution of both L2 and L3 crescent waves. Our results compare quantitatively well with experimental measurements for all the distinct features and geometric properties of such waves.

Nonlinear Sloshing in Fixed and Vertically Excited Containers

2002 ◽  
Author(s):  
Jannette B. Frandsen ◽  
Alistair G. L. Borthwick
Keyword(s):  
Perturbation Theory ◽  
Free Surface ◽  
Small Perturbation ◽  
Numerical Solutions ◽  
Vertical Direction ◽  
Nonlinear Effects ◽  
Breaking Waves ◽  
Surface Flow ◽  
Nonlinear Behaviour ◽  
Computational Domain

Nonlinear effects of standing wave motions in fixed and vertically excited tanks are numerically investigated. The present fully nonlinear model analyses two-dimensional waves in stable and unstable regions of the free-surface flow. Numerical solutions of the governing nonlinear potential flow equations are obtained using a finite-difference time-stepping scheme on adaptively mapped grids. A σ-transformation in the vertical direction that stretches directly between the free-surface and bed boundary is applied to map the moving free surface physical domain onto a fixed computational domain. A horizontal linear mapping is also applied, so that the resulting computational domain is rectangular, and consists of unit square cells. The small-amplitude free-surface predictions in the fixed and vertically excited tanks compare well with 2nd order small perturbation theory. For stable steep waves in the vertically excited tank, the free-surface exhibits nonlinear behaviour. Parametric resonance is evident in the instability zones, as the amplitudes grow exponentially, even for small forcing amplitudes. For steep initial amplitudes the predictions differ considerably from the small perturbation theory solution, demonstrating the importance of nonlinear effects. The present numerical model provides a simple way of simulating steep non-breaking waves. It is computationally quick and accurate, and there is no need for free surface smoothing because of the σ-transformation.

scholarly journals The nonlinear effects on the characteristics of gravity wave packets: dispersion and polarization relations

2000 ◽  
Vol 18 (10) ◽  
pp. 1316-1324 ◽  
Author(s):  
S.-D. Zhang ◽  
F. Yi ◽  
J.-F. Wang
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Middle Atmosphere ◽  
Wave Packets ◽  
Nonlinear Effects ◽  
Wave Theory ◽  
Nonlinear Propagation ◽  
Waves And Tides ◽  
Time Variations ◽  
Isothermal Atmosphere

Abstract. By analyzing the results of the numerical simulations of nonlinear propagation of three Gaussian gravity-wave packets in isothermal atmosphere individually, the nonlinear effects on the characteristics of gravity waves are studied quantitatively. The analyses show that during the nonlinear propagation of gravity wave packets the mean flows are accelerated and the vertical wavelengths show clear reduction due to nonlinearity. On the other hand, though nonlinear effects exist, the time variations of the frequencies of gravity wave packets are close to those derived from the dispersion relation and the amplitude and phase relations of wave-associated disturbance components are consistent with the predictions of the polarization relation of gravity waves. This indicates that the dispersion and polarization relations based on the linear gravity wave theory can be applied extensively in the nonlinear region.Key words: Meteorology and atmospheric dynamics (middle atmosphere dynamics; waves and tides)

The Effect of Pitch Gyradius on Added Resistance of Yacht Hulls

1991 ◽  
Author(s):  
James F. Moran
Keyword(s):  
Water Resistance ◽  
Wave Spectrum ◽  
Response Amplitude ◽  
Added Resistance ◽  
Regular Waves ◽  
Low Frequencies ◽  
Irregular Wave ◽  
Wave Data ◽  
The Difference ◽  
Response Amplitude Operators

The purpose of this investigation was to determine the effect of pitch gyradius on added resistance of yacht hulls. Tank testing of a model yacht in head seas was performed in the Webb Robinson Model Basin. The model was tested in regular waves at two speeds and five variations of gyradius. The model was also evaluated in irregular seas of the Pierson-Moskowitz spectrum at various speeds with two gyradii. Response Amplitude Operators were developed from the regular wave data and comparisons made. The irregular wave data were analyzed for the effect of speed on the difference in added resistance between the maximum and minimum gyradius settings. Several conclusions were arrived at after analyzing the data. The Response Amplitude Operaters shift as the gyradius changes. In regular waves, at low frequencies of encounter, a lower, gyradius resulted in less added frequencies of encounter in regular waves, this trend reverses itself and the higher gyradii result in reduced added resistance. However, at higher frequencies of encounter in regular waves, this trend reverses, reverses itself in reduced added resistance. The peaks of the RAO curves shift to higher frequencies at higher gyradii. It was also concluded that at the higher speed, Froude Number of 0.3, the added resistance was lower relative to the still-water resistance for each gyradius tested. The irregular wave testing revealed the effect of the lower frequencies dominating the irregular wave spectrum. The minimum gyradius, in irregular seas showed less added resistance than the maximum gyradius. In addition, the irregular wave testing verified, the reduction of added resistance, relative to still-water resistance, at increasing speeds for both the minimum and maximum gyradii.

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