Nonlinear Wave Group Impact on a Cylindrical Monopile

2013 ◽  
Author(s):  
Zhong Peng ◽  
Tim Raaijmakers ◽  
Peter Wellens
Keyword(s):  
Nonlinear Wave ◽  
Wave Height ◽  
Wave Period ◽  
Wave Crest ◽  
Vertical Force ◽  
Wave Group ◽  
Wave Loads ◽  
Wave Impact ◽  
Wave Groups ◽  
Individual Wave

The ComFLOW wave model has been employed to study the impact of nonlinear wave groups on cylindrical monopiles. Four nonlinear wave groups are selected from fully nonlinear waves generated by a 2D ComFLOW model, representing wave groups with the largest or the second largest crest heights, the largest wave height and a wave group consisting of consecutive large waves. These four wave groups are used to investigate the wave loads on the foundation and the platform in a 3D ComFLOW model. Model results show that the maximum wave loads on the foundation and the platform by nonlinear wave groups are determined by their individual wave crest height. This study presents a relationship between platform level and wave impact on the platform, as the vertical force on the platform is the combination of buoyancy force (if inundated) and wave impact force due to wave run-up. Results also show that wave loads on the foundation and wave impact on the platform decrease as the wave period increases from 13s to 16s (typical wave period at German Bight). A wave group can cause a larger wave load on the foundation and the platform than regular waves, considering a regular wave height equal to the maximum wave height, regardless of the associated wave period (period of individual wave or peak period).

Semi-Empirical Crest Distributions of Long-Crest Nonlinear Waves of Three-Hour Duration

2017 ◽  
Author(s):  
Zhenjia (Jerry) Huang ◽  
Qiuchen Guo
Keyword(s):  
Nonlinear Wave ◽  
Wave Height ◽  
Model Test ◽  
Significant Wave Height ◽  
Spectral Peak ◽  
Wave Crest ◽  
Empirical Formulas ◽  
Peak Period ◽  
Significant Wave ◽  
Semi Empirical

In wave basin model test of an offshore structure, waves that represent the given sea states have to be generated, qualified and accepted for the model test. For seakeeping and stationkeeping model tests, we normally accept waves in wave calibration tests if the significant wave height, spectral peak period and spectrum match the specified target values. However, for model tests where the responses depend highly on the local wave motions (wave elevation and kinematics) such as wave impact, green water impact on deck and air gap tests, additional qualification checks may be required. For instance, we may need to check wave crest probability distributions to avoid unrealistic wave crest in the test. To date, acceptance criteria of wave crest distribution calibration tests of large and steep waves of three-hour duration (full scale) have not been established. The purpose of the work presented in the paper is to provide a semi-empirical nonlinear wave crest distribution of three-hour duration for practical use, i.e. as an acceptance criterion for wave calibration tests. The semi-empirical formulas proposed in this paper were developed through regression analysis of a large number of fully nonlinear wave crest distributions. Wave time series from potential flow simulations, computational fluid dynamics (CFD) simulations and model test results were used to establish the probability distribution. The wave simulations were performed for three-hour duration assuming that they were long-crested. The sea states are assumed to be represented by JONSWAP spectrum, where a wide range of significant wave height, peak period, spectral peak parameter, and water depth were considered. Coefficients of the proposed semi-empirical formulas, comparisons among crest distributions from wave calibration tests, numerical simulations and the semi-empirical formulas are presented in this paper.

Individual wave height and wave crest distributions based on field measurements from the northern North Sea

2018 ◽  
Vol 68 (12) ◽  
pp. 1727-1738 ◽  
Author(s):  
Børge Kvingedal ◽  
Kjersti Bruserud ◽  
Einar Nygaard
Keyword(s):  
Wave Height ◽  
North Sea ◽  
Field Measurements ◽  
Wave Crest ◽  
Individual Wave ◽  
Northern North Sea

Extreme Wave Loads

2008 ◽  
Author(s):  
Sofia Caires ◽  
Marcel R. A. van Gent
Keyword(s):  
Wave Height ◽  
Ad Hoc ◽  
Value Theory ◽  
Extreme Value ◽  
Wave Period ◽  
Extreme Value Analysis ◽  
Wave Loads ◽  
Extreme Wave ◽  
Value Analysis ◽  
Return Value

This paper compares three main methods for estimating extreme wave loads with a view towards determining the sensitivity of estimates to the particular approach chosen. The approaches considered include: a) The generally used ad-hoc procedure of performing an extreme value analysis of the Hs data, trying to find a relationship between wave height and period at the storm peaks and then, once the return values of extreme wave heights are estimated, estimating the associated return value of the wave period by means of the relationship found. b) The ‘structure variable method’ in which the pairs wave height and period observations are converted into univariate loads to which univariate extreme value theory is applied to estimate the return value of the structural load. c) The multivariate extreme value approach suggested by [1] in which a ‘multivariate return value’, namely the most probable value of the wave period conditional on a return value of the wave height, is estimated. Our study is based on a 44-yr long timeseries of wave conditions created using the shallow water wave model SWAN and calibrated ERA-40 data. The results suggest that the three approaches yield similar estimates. However, the ad-hoc procedure a gives the least conservative estimates. Approach c provides results that apply to any choice of load function and which to a certain extent are independent of the location in which the estimates are obtained, for which reason it may generally be the preferred one.

Gaussian Analysis of an Irregular Wave Impact on Deck

2010 ◽  
Vol 132 (4) ◽  
Author(s):  
Ravikiran S. Kota ◽  
Torgeir Moan
Keyword(s):  
Probability Density Function ◽  
Probability Density ◽  
Density Function ◽  
Joint Probability ◽  
Vertical Force ◽  
Wave Loads ◽  
Wave Impact ◽  
Irregular Wave ◽  
Wave Kinematics ◽  
Wetting Process

Level-crossing analysis of long-crested, Gaussian waves in space and time are studied in the context of wave loads on a fixed, horizontal deck-box above mean waterline. Vertical wave loads on decks due to insufficient airgap are a major concern for many in-service platforms. Reliable estimation of magnitude and duration of these loads is important in assessing structural and global response of an offshore platform. In the case of an irregular wave-impact on a flat deck of dimensions comparable to mean wavelength of the incident waves, both temporal and spatial variability of wave-kinematics need to be considered during the deck-wetting process. In the present study, we have used a multidimensional Gaussian formulation of incident wave-kinematics to derive a joint probability density function of deck-wetting (or exceedance) duration and its spatial extent. We have also derived a probability density function for initial slam force on deck. A numerical scheme for simulating wave-impact events on a two-dimensional deck is discussed, results from which are compared against corresponding analytical estimates. Vertical force on deck was estimated using the momentum method, which includes a von Kármán slamming model applied over the wetted-length determined from an undisturbed wave profile.

Statistics of Ocean Wave Groups

1973 ◽  
Vol 13 (03) ◽  
pp. 139-146 ◽  
Author(s):  
K.G. Nolte
Keyword(s):  
Energy Spectrum ◽  
Wave Height ◽  
Wave Amplitude ◽  
Ocean Waves ◽  
Theoretical Expression ◽  
Wave Group ◽  
Amplitude Envelope ◽  
Ocean Engineering ◽  
Wave Groups ◽  
The Individual

Abstract Statistical parameters are derived that describe the occurrence probability for the number and height of consecutive waves in as group, which are large compared with the average wave height. Such wave groups can create extreme forces in mooring lines of large vessels. All the parameters that describe the statistics of wave groups can be derived from the energy spectrum representing the sea state, if the energy spectrum is assumed to contain only a narrow band of wave frequencies. Good agreement was found between the theoretical expression derived in this paper and actual wave data. Introduction It has been shown by Hsu and Blenkarn that be long-period sway motion and peak mooring-line force observed in a model study of a barge resulted from the combined action of a sequence of consecutive high waves in the random wave train. Such a sequence of waves will be referred to as a wave group. Independent model-tank tests conducted by Remery and Hermans substantiated the findings presented in Ref. 1. it is anticipated that the presented in Ref. 1. it is anticipated that the action of wave groups may also be important in other types of ocean engineering systems that are subjected to horizontal motions with periods much longer than the period of individual waves. Such systems could include dynamically positioned vessels. In the analysis and design of such systems it would be prudent to check whether the action of wave groups could subject the systems to motions beyond those calculated on the basis of individual waves. As a basis to perform such a check, one can use either recorded wave groups measured in the sea, or wave groups generated in a model tank. There are also available electronic and numerical methods to simulate ocean waves. However, to make proper engineering decisions, one would need to know whether the occurrence of such wave groups is a common or a rare event. More specifically, one would require a probabilistic description of the basic characteristics of wave groups in order to assess whether a system is likely to survive. The purpose of this paper is to develop tools with which one can characterize the statistics of wave groups in terms of occurrence probabilities. No attempt is made here to illustrate how such statistical tools could be used in practical engineering. Rational procedures for utilizing such tools for specific problems can best be developed by individual users. THEORETICAL DERIVATIONS In this paper a wave group will be defined in terms of the envelopes of wave crests and troughs as shown in Fig. 1. The distance between the crest envelope and the trough envelope will be called the height envelope, whereas the distance between the crest envelope and the mean water surface will be called the amplitude envelope. The height envelope indicates the change of wave heights. Similarly, the amplitude envelope indicates the change of wave amplitude. In reality, ocean waves are not symmetrical as is implied by the term "amplitude". Measured from mean water level, the distance to the crest of a wave is generally greater than the distance to the trough. However, in order to use the theoretical methods developed by Rice, we shall assume that the wave amplitude is half the wave height. As one can see from Fig. 1, the height envelope has the characteristics of a wave with a much longer period than the individual waves. period than the individual waves. SPEJ P. 139

scholarly journals On Determining the Onset and Strength of Breaking for Deep Water Waves. Part I: Unforced Irrotational Wave Groups

2002 ◽  
Vol 32 (9) ◽  
pp. 2541-2558 ◽  
Author(s):  
Jin-Bao Song ◽  
Michael L. Banner
Keyword(s):  
Growth Rate ◽  
Nonlinear Wave ◽  
Deep Water ◽  
Water Waves ◽  
Wave Group ◽  
Two Dimensional ◽  
Wave Groups ◽  
Average Growth ◽  
Deep Water Waves

Abstract Finding a robust threshold variable that determines the onset of breaking for deep water waves has been an elusive problem for many decades. Recent numerical studies of the unforced evolution of two-dimensional nonlinear wave trains have highlighted the complex evolution to recurrence or breaking, together with the fundamental role played by nonlinear intrawave group dynamics. In Part I of this paper the scope of two-dimensional nonlinear wave group calculations is extended by using a wave-group-following approach applied to a wider class of initial wave group geometries, with the primary goal of identifying the differences between evolution to recurrence and to breaking onset. Part II examines the additional influences of wind forcing and background shear on these evolution processes. The present investigation focuses on the long-term evolution of the maximum of the local energy density along wave groups. It contributes a more complete picture, both long-term and short-term, of the approach to breaking and identifies a dimensionless local average growth rate parameter that is associated with the mean convergence of wave-coherent energy at the wave group maximum. This diagnostic growth rate appears to have a common threshold for all routes to breaking in deep water that have been examined and provides an earlier and more decisive indicator for the onset of breaking than previously proposed breaking thresholds. The authors suggest that this growth rate may also provide an indicative measure of the strength of wave breaking events.

scholarly journals EXPERIMENTAL RESULTS OF BREAKING WAVE IMPACT ON A VERTICAL WALL WITH AN OVERHANGING HORIZONTAL CANTILEVER SLAB

2011 ◽  
Vol 1 (32) ◽  
pp. 26
Author(s):  
Dogan Kisacik ◽  
Peter Troch ◽  
Philippe Van Bogaert
Keyword(s):  
Wave Height ◽  
Water Depth ◽  
Vertical Wall ◽  
Breaking Waves ◽  
Wave Period ◽  
Breaking Wave ◽  
Wave Impact ◽  
Scaled Model ◽  
Physical Experiments ◽  
Horizontal Part

Physical experiments (at a scale of 1/20) are carried out using a vertical wall with horizontal cantilevering slab. Tests are conducted for a range of values of water depth, wave period and wave height. A parametric analysis of measured forces (Fh and Fv) both on the vertical and horizontal part of the scaled model respectively is conducted. The highest impact pressure and forces are measured in the case of breaking waves with a small air trap. Maximum pressures are measured around SWL and at the corner of the scaled model. The horizontal part of the scaled model is more exposed to impact waves than the vertical part. Fh and Fv are very sensitive for the variation of water depth (hs) and wave height (H) while variation of wave period (T) has a rather limited effect.

UNDERWATER BARRED BEACH PROFILE TRANSFORMATION UNDER DIFFERENT WAVES CONDITIONS

2017 ◽  
Author(s):  
Olga Kuznetsova ◽  
Olga Kuznetsova ◽  
Yana Saprykina ◽  
Yana Saprykina ◽  
Boris Divinsky ◽  
...  
Keyword(s):  
Numerical Modelling ◽  
Coastal Zone ◽  
Wave Height ◽  
Wave Energy ◽  
Wave Period ◽  
Beach Profile ◽  
Infragravity Waves ◽  
Wave Parameters ◽  
Mean Wave Period

Based on numerical modelling evolution of beach under waves with height 1,0-1,5 m and period 7,5 and 10,6 sec as well as spectral wave parameters varying cross-shore analysed. The beach reformation of coastal zone relief is spatially uneven. It is established that upper part of underwater beach profile become terraced and width of the terrace is in direct pro-portion to wave height and period on the seaward boundary but inversely to angle of wave energy spreading. In addition it was ascertain that the greatest transfiguration of profile was accompanied by existence of bound infragravity waves, smaller part of its energy and shorter mean wave period as well as more significant roller energy.

scholarly journals Physical Modelling of the Effect on the Wave Field of the WaveCat Wave Energy Converter

2021 ◽  
Vol 9 (3) ◽  
pp. 309
Author(s):  
James Allen ◽  
Gregorio Iglesias ◽  
Deborah Greaves ◽  
Jon Miles
Keyword(s):  
Wave Height ◽  
Wave Energy ◽  
Significant Wave Height ◽  
Wedge Angle ◽  
Wave Energy Converter ◽  
Wave Period ◽  
Surface Elevation ◽  
Energy Converter ◽  
Significant Wave ◽  
Model Scale

The WaveCat is a moored Wave Energy Converter design which uses wave overtopping discharge into a variable v-shaped hull, to generate electricity through low head turbines. Physical model tests of WaveCat WEC were carried out to determine the device reflection, transmission, absorption and capture coefficients based on selected wave conditions. The model scale was 1:30, with hulls of 3 m in length, 0.4 m in height and a freeboard of 0.2 m. Wave gauges monitored the surface elevation at discrete points around the experimental area, and level sensors and flowmeters recorded the amount of water captured and released by the model. Random waves of significant wave height between 0.03 m and 0.12 m and peak wave periods of 0.91 s to 2.37 s at model scale were tested. The wedge angle of the device was set to 60°. A reflection analysis was carried out using a revised three probe method and spectral analysis of the surface elevation to determine the incident, reflected and transmitted energy. The results show that the reflection coefficient is highest (0.79) at low significant wave height and low peak wave period, the transmission coefficient is highest (0.98) at low significant wave height and high peak wave period, and absorption coefficient is highest (0.78) when significant wave height is high and peak wave period is low. The model also shows the highest Capture Width Ratio (0.015) at wavelengths on the order of model length. The results have particular implications for wave energy conversion prediction potential using this design of device.

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