Time Domain Simulation of Jack-Up Platform in Second-Order Irregular Seas

2017 ◽  
Author(s):  
Michael Binsar Lubis ◽  
Sverre Haver ◽  
Jørgen Amdahl
Keyword(s):  
Wave Model ◽  
Second Order ◽  
Irregular Waves ◽  
Stokes Wave ◽  
Time Domain Simulation ◽  
Wave Load ◽  
Extreme Wave ◽  
Irregular Wave ◽  
Load Component ◽  
Jack Up

This paper reviews the significance of applying second-order irregular waves for assessing hydrodynamic loads on a jack-up platform. The study is based on a realistic jack-up model. The wave load is determined utilizing Morison equation. The study focuses on extreme wave elevations when the drag load component dominates and the magnitude of wave particle horizontal velocity is crucial. Both extreme surface elevation and wave particle kinematics are observed. For wave particle kinematic, two different stretching methods are compared. The static response of a pile structure using the second-order model and the 5th Stokes wave are compared. In the end, a dynamic analysis of the jack-up utilizing a second-order irregular wave model is performed.

Time-Domain Simulation of Second-Order Wave Diffraction in Irregular Wave

2012 ◽  
Author(s):  
Gang Xu ◽  
A. M. S. Hamouda
Keyword(s):  
Free Surface ◽  
Time Domain ◽  
Wave Diffraction ◽  
Second Order ◽  
Stokes Wave ◽  
Surface Boundary ◽  
Time Domain Simulation ◽  
Zone Method ◽  
Body Interaction ◽  
Irregular Wave

A time-domain second-order method is presented to simulate three-dimensional (3D) wave-body interaction. In the approach, Taylor series expansions are applied to the free surface boundary conditions, and Stokes perturbation procedure is then used to establish corresponding boundary value problem at first-order and second-order on the time-independent surfaces. A Boundary Element Method (BEM), based on Rankine source, is used to calculate wave field at each time step. Multi-Transmitting Formula coupled with Damping Zone method (MTF+DZ) is employed as radiation condition to minimize the wave reflection. A stable Integral form of Free surface Boundary Condition (IFBC) is used to update velocity potential on the free surface. The present method is applied to compute the second-order Stokes wave diffraction of bottom-mounted circular cylinder first, and then to compute the irregular second-order Stokes wave diffraction of truncated cylinder in infinite water depth with three wave components. It is shown that long time simulation can be done with stability, and the model can be used to time-domain simulation of nonlinear irregular wave-body interaction.

Influence of Multidirectional Irregular Wave Sampling to Second-Order Hydroelastic Responses of VLFS

2009 ◽  
Author(s):  
Xujun Chen ◽  
Torgeir Moan ◽  
Xuefeng Tang
Keyword(s):  
Computer Time ◽  
Second Order ◽  
Irregular Waves ◽  
Floating Structure ◽  
First Order ◽  
Fluid Forces ◽  
Irregular Wave ◽  
Very Large Floating Structure ◽  
Principal Coordinates ◽  
Hydroelastic Response

Hydroelasticity theory considering the second-order fluid forces induced by the coupling of first-order wave potentials is introduced briefly in this paper. Based on this theory, four types of multidirectional irregular wave samplings are introduced, the frequency steps Δω of the four samplings are 0.04, 0.04, 0.02 and 0.01 rad/s, and the corresponding numbers of wave components N are 17, 75, 147 and 285 respectively. The result of principal coordinates and displacements of a very large floating structure (VLFS) for the four types of sampling are presented and discussed. The influence of the sampling is analyzed. The conclusions show that the sampling of the multidirectional irregular waves influence the second-order hydroelastic response of the VLFS. The accuracy and the computer time of the calculating with sampling of frequency step Δω = 0.02 rad/s are acceptable.

A New Nonslender Ringing Load Approach Verified Against Experiments

1998 ◽  
Vol 120 (1) ◽  
pp. 20-29 ◽  
Author(s):  
J. R. Krokstad ◽  
C. T. Stansberg ◽  
A. Nestega˚rd ◽  
T. Marthinsen
Keyword(s):  
Wave Model ◽  
Second Order ◽  
Wave Load ◽  
Peak Wavelength ◽  
Third Order ◽  
Load Model ◽  
Order Analysis ◽  
First Order ◽  
Load Effects ◽  
Vertical Cylinders

New results from the most recent work within the Norwegian Joint Industry Project (JIP) “Higher Order Wave Load Effects on Large Volume Structures” are presented. A nonslender theoretical model is validated from experiments for two fixed, vertical cylinders with different diameter/peak wavelength ratios. A combination of complete diffraction first-order simulations, sum and difference frequency second-order simulations, and third-order FNV (Faltinsen, Newman, and Vinje, nonlinear long wave model) is implemented in order to develop a simplified and robust ringing load model for a large range of cylinder diameter/peak wavelength ratios. Results from the full diffraction second-order analysis show a significant reduction of second-order loads compared to pure FNV in the wavelength range relevant for ringing loads. The results show improved correspondence with high-frequency experimental loads compared with the unmodified FNV. Results for different cylinder peak wavelength ratios are presented, including validation against experiments. In addition, a few simplified response simulations are carried out demonstrating significant improvements with the modified FNV model.

Numerical Reproduction of Extreme Wave Loads on a Gravity Wind Turbine Foundation

2006 ◽  
Author(s):  
H. Bredmose ◽  
J. Skourup ◽  
E. A. Hansen ◽  
E. D. Christensen ◽  
L. M. Pedersen ◽  
...  
Keyword(s):  
Wind Turbine ◽  
Wave Climate ◽  
Irregular Waves ◽  
Navier Stokes ◽  
Wave Loads ◽  
Load History ◽  
Wave Load ◽  
Extreme Wave ◽  
Run Up ◽  
A Current

A fully nonlinear 3D Navier Stokes solver with VOF (Volume of Fluid) treatment of the free surface is used to reproduce two extreme laboratory wave impacts on a gravity wind turbine foundation. The wave climate is irregular waves with a current. Numerical results for inline force, overturning moment and run-up are compared to measurements. The extreme wave loads for the two events are associated with slamming onto the under side of a horizontal platform placed 9.1m above the still water level. For such impacts, the computed wave loads are strongly sensitive to the shape of the incoming waves. A comparison with a Morison-type estimation of the wave loads shows that this much simpler approach can reproduce the overall trend of the wave load history, but not the extreme moment.

scholarly journals COUPLING STOKES AND CNOIDAL WAVE THEORIES IN A NONLINEAR REFRACTION MODEL

1988 ◽  
Vol 1 (21) ◽  
pp. 42
Author(s):  
Thomas A. Hardy ◽  
Nicholas C. Kraus
Keyword(s):  
Nonlinear Refraction ◽  
Wave Model ◽  
Wave Theory ◽  
Quantitative Agreement ◽  
Wave Mode ◽  
Finite Amplitude ◽  
Second Order ◽  
Stokes Wave ◽  
Linear Wave ◽  
Cnoidal Wave

An efficient numerical model is presented for calculating the refraction and shoaling of finite-amplitude waves over an irregular sea bottom. The model uses third-order Stokes wave theory in relatively deep water and second-order cnoidal wave theory in relatively shallow water. It can also be run using combinations of lower-order wave theories, including a pure linear wave mode. The problem of the connection of Stokes and cnoidal theories is investigated, and it is found that the use of second-order rather than first-order cnoidal theory greatly reduces the connection discontinuity. Calculations are compared with physical model measurements of the height and direction of waves passing over an elliptical shoal. The finite-amplitude wave model gives better qualitative and quantitative agreement with the measurements than the linear model.

scholarly journals IRREGULAR WAVE TRANSFORMATION IN A BOUSSINESO WAVE MODEL

1986 ◽  
Vol 1 (20) ◽  
pp. 205
Author(s):  
H.H. Pruser ◽  
H. Schaper ◽  
W. Zielke
Keyword(s):  
Water Waves ◽  
Wave Equations ◽  
Numerical Models ◽  
Wave Model ◽  
Wave Climate ◽  
Irregular Waves ◽  
Wave Transformation ◽  
Diffraction Reflection ◽  
Irregular Wave ◽  
Wave Models

Numerical wave models for shallow water waves are of particular importance for the calculation of the wave climate in harbours and coastal areas. Especially nonlinear time domain models, which are based on the Boussinesq-Wave- Equations, may be helpful in the future for simulating the interaction of currents with refraction, diffraction, reflection and for simulating shoaling..-of irregular waves in natural areas; a potential which has not yet been fully developed. During the last ten years numerical models, based on these equations, have been published; such as ABBOTT et. al. , HAUGUEL and SCHAPER / ZIELKE . Research on this topic is currently being carried on. Some efforts have been made to verify the capability of the models to describe the various physical phenomena. However, up to now, verification has been limited to regular waves. The aim of this paper therefore is, to consider questions concerning irregular, nonlinear waves.

High frequency resonant response of a monopile in irregular deep water waves

2018 ◽  
Vol 853 ◽  
pp. 564-586 ◽  
Author(s):  
Bjørn Hervold Riise ◽  
John Grue ◽  
Atle Jensen ◽  
Thomas B. Johannessen
Keyword(s):  
Resonance Frequency ◽  
Deep Water ◽  
Water Waves ◽  
Irregular Waves ◽  
Breaking Wave ◽  
Wave Load ◽  
Irregular Wave ◽  
The Third ◽  
Extreme Response ◽  
Wave Slope

Experiments with a weakly damped monopile, either fixed or free to oscillate, exposed to irregular waves in deep water, obtain the wave-exciting moment and motion response. The nonlinearity and peak wavenumber cover the ranges: $\unicode[STIX]{x1D716}_{P}\sim 0.10{-}0.14$ and $k_{P}r\sim 0.09{-}0.14$ where $\unicode[STIX]{x1D716}_{P}=0.5H_{S}k_{P}$ is an estimate of the spectral wave slope, $H_{S}$ the significant wave height, $k_{P}$ the peak wavenumber and $r$ the cylinder radius. The response and its statistics, expressed in terms of the exceedance probability, are discussed as a function of the resonance frequency, $\unicode[STIX]{x1D714}_{0}$ in the range $\unicode[STIX]{x1D714}_{0}\sim 3{-}5$ times the spectral peak frequency, $\unicode[STIX]{x1D714}_{P}$. For small wave slope, long waves and $\unicode[STIX]{x1D714}_{0}/\unicode[STIX]{x1D714}_{P}=3$, the nonlinear response deviates only very little from its linear counterpart. However, the nonlinearity becomes important for increasing wave slope, wavenumber and resonance frequency ratio. The extreme response events are found in a region where the Keulegan–Carpenter number exceeds $KC>5$, indicating the importance of possible flow separation effects. A similar region is also covered by a Froude number exceeding $Fr>0.4$, pointing to surface gravity wave effects at the scale of the cylinder diameter. Regarding contributions to the higher harmonic forces, different wave load mechanisms are identified, including: (i) wave-exciting inertia forces, a function of the fluid acceleration; (ii) wave slamming due to both non-breaking and breaking wave events; (iii) a secondary load cycle; and (iv) possible drag forces, a function of the fluid velocity. Also, history effects due to the inertia of the moving pile, contribute to the large response events. The ensemble means of the third, fourth and fifth harmonic wave-exciting force components extracted from the irregular wave results are compared to the third harmonic FNV (Faltinsen, Newman and Vinje) theory as well as other available experiments and calculations. The present irregular wave measurements generalize results obtained in deep water regular waves.

Amplification of Waves by a Concrete Gravity Sub-Structure: Linear Diffraction Analysis and Estimating the Extreme Crest Height

2004 ◽  
Author(s):  
E. J. van Iperen ◽  
G. Z. Forristall ◽  
J. A. Battjes ◽  
J. A. Pinkster
Keyword(s):  
Wave Model ◽  
Diffraction Theory ◽  
Peak Frequency ◽  
Model Tests ◽  
Second Order ◽  
Irregular Waves ◽  
Regular Wave ◽  
Experimental Surface ◽  
Elevation Data ◽  
Using Data

Diffraction of both regular and irregular waves by a Concrete Gravity Sub-structure (CGS) was investigated using experimental surface elevation data and computational results of the linear diffraction code DELFRAC. The influence of the box-shaped base that supports the four vertical columns was studied independently from the columns, using data from regular wave model tests of the Malampaya CGS. DELFRAC was shown to give accurate results for the focusing of waves over the submerged structure. Results from regular wave data analysis of model tests of the complete Sakhalin II project Lunskoye CGS were compared to the predictions by the linear diffraction code. For the wave cases tested, the first-order amplitudes were accurately predicted. Diffraction of irregular waves at the Lunskoye CGS was studied in a similar way and linear diffraction theory for random seas gave an excellent prediction of incident wave spectral diffraction, including the peaks in the diffracted spectrum near twice the peak frequency in the input spectrum. The results obtained for the Lunksoye CGS in the present study were consistent with results found in similar studies on less complex structures. An attempt to predict the extreme crest heights from the diffracted spectrum was made using a Weibull distribution, and a second-order expansion of the sea surface that captures the effects of wave steepness, water depth and directional spreading with no other approximation than the truncation of the expansion at second order. Depth induced breaking appeared to be an important phenomenon limiting the crest heights. The crest heights in a 100-year sea state at the Lunskoye CGS were accurately predicted.

Kinematics Under Extreme Waves

2008 ◽  
Vol 130 (2) ◽  
Author(s):  
Carl Trygve Stansberg ◽  
Ove T. Gudmestad ◽  
Sverre K. Haver
Keyword(s):  
Free Surface ◽  
Water Level ◽  
Deep Water ◽  
Wave Model ◽  
Second Order ◽  
Irregular Waves ◽  
Random Wave ◽  
Extreme Waves ◽  
Near Surface ◽  
Particle Velocities

Nonlinear contributions in near-surface particle velocities under extreme crests in random seas can be important in the prediction of wave loads. Four different prediction methods are compared in this paper. The purpose is to observe and evaluate differences in predicted particle velocities under high and extreme crests, and how well they agree with measurements. The study includes linear prediction, a second-order random wave model, Wheeler’s method [1970, “Method for Calculating Forces Produced by Irregular Waves,” JPT, J. Pet. Technol., pp. 359–367] and a new method proposed by Grue et al. [2003, “Kinematics of Extreme Waves in Deep Water,” Appl. Ocean Res., 25, pp. 355–366]. Comparison to laboratory data is also made. The whole wave-zone range from below still water level up to the free surface is considered. Large nonlinear contributions are identified in the near-surface velocities. The results are interpreted to be correlated with the local steepness kA. Some scatter between the different methods is observed in the results. The comparison to experiments shows that among the methods included, the second-order random wave model works best in the whole range under a steep crest in deep or almost deep water, and is therefore recommended. The method of Grue et al. works reasonably well for z>0, i.e., above the calm water level, while it overpredicts the velocities for z<0. Wheeler’s method, when used with a measured or a second-order input elevation record, predicts velocities fairly well at the free surface z=ηmax, but it underpredicts around z=0 and further below. The relative magnitude of this latter error is slightly smaller than the local steepness kA0 and can be quite significant in extreme waves. If Wheeler’s method is used with a linear input, the same error occurs in the whole range, i.e., also at the free surface.

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