New Insights in Extreme Crest Height Distributions: A Summary of the ‘CresT’ JIP

2011 ◽  
Author(s):  
Bas Buchner ◽  
George Forristall ◽  
Kevin Ewans ◽  
Marios Christou ◽  
Janou Hennig
Keyword(s):  
Single Point ◽  
Field Measurements ◽  
Order Theory ◽  
Second Order ◽  
Wave Crest ◽  
Height Distribution ◽  
Extreme Waves ◽  
Wave Height Distribution ◽  
Floating Platforms ◽  
Crest Height

The objective of the CresT JIP was ‘to develop models for realistic extreme waves and a design methodology for the loading and response of floating platforms’. Within this objective the central question was: ‘What is the highest (most critical) wave crest that will be encountered by my platform in its lifetime?’ Based on the presented results for long and short-crested numerical, field and basin results in the paper, it can be concluded that the statistics of long-crested waves are different than those of short-crested waves. But also short-crested waves show a trend to reach crest heights above second order. This is in line with visual observations of the physics involved: crests are sharper than predicted by second order, waves are asymmetric (fronts are steeper) and waves are breaking. Although the development of extreme waves within short-crested sea states still needs further investigation (including the counteracting effect of breaking), at the end of the CresT project the following procedure for taking into account extreme waves in platform design is recommended: 1. For the wave height distribution, use the Forristall distribution (Forristall, 1978). 2. For the crest height distribution, use 2nd order distribution as basis. 3. Both the basin and field measurements show crest heights higher than predicted by second order theory for steeper sea states. It is therefore recommended to apply a correction to the second order distribution based on the basin results. 4. Account for the sampling variability at the tail of the distribution (and resulting remaining possibility of higher crests than given by the corrected second order distribution) in the reliability analysis. 5. Consider the fact that the maximum crest height under a complete platform deck can be considerably higher than the maximum crest at a single point.

Nonlinear Crest Height Distribution in Three-Dimensional Ocean Waves

2010 ◽  
Vol 132 (2) ◽  
Author(s):  
Felice Arena ◽  
Alfredo Ascanelli
Keyword(s):  
Water Depth ◽  
Three Dimensional ◽  
Ocean Waves ◽  
Order Theory ◽  
Second Order ◽  
Wave Crest ◽  
Height Distribution ◽  
Random Waves ◽  
Weakly Nonlinear ◽  
Wave Trough

The interest and studies on nonlinear waves are increased recently for their importance in the interaction with floating and fixed bodies. It is also well-known that nonlinearities influence wave crest and wave trough distributions, both deviating from the Rayleigh law. In this paper, a theoretical crest distribution is obtained, taking into account the extension of Boccotti’s quasideterminism theory (1982, “On Ocean Waves With High Crests,” Meccanica, 17, pp. 16–19), up to the second order for the case of three-dimensional waves in finite water depth. To this purpose, the Fedele and Arena (2005, “Weakly Nonlinear Statistics of High Random Waves,” Phys. Fluids, 17(026601), pp. 1–10) distribution is generalized to three-dimensional waves on an arbitrary water depth. The comparison with Forristall’s second order model (2000, “Wave Crest Distributions: Observations and Second-Order Theory,” J. Phys. Oceanogr., 30(8), pp. 1931–1943) shows the theoretical confirmation of his conclusion: The crest distribution in deep water for long-crested and short-crested waves are very close to each other; in shallow water the crest heights in three-dimensional waves are greater than values given by the long-crested model.

Wave Crest Sensor Intercomparison Study: An Overview of WACSIS

2002 ◽  
Author(s):  
George Z. Forristall ◽  
Stephen F. Barstow ◽  
Harald E. Krogstad ◽  
Marc Prevosto ◽  
Paul H. Taylor ◽  
...  
Keyword(s):  
Second Order ◽  
Wave Crest ◽  
Height Distribution ◽  
High Frequencies ◽  
Video Cameras ◽  
Period Distribution ◽  
Wave Sensors ◽  
Intercomparison Study ◽  
Crest Height ◽  
Made In

The Wave Crest Sensor Intercomparison Study (WACSIS) was designed as a thorough investigation of the statistical distribution of crest heights. Measurements were made in the southern North Sea during the winter of 1997–1998 from the Meetpost Noordwijk in 18 m water depth. The platform was outfitted with several popular wave sensors, including Saab and Marex radars, an EMI laser, a Baylor wave staff and a Vlissingen step gauge. Buoys were moored nearby to obtain directional spectra. Two video cameras viewed the ocean under the wave sensors and their signals were recorded digitally. The data analysis focused on comparisons of the crest height measurements from the various sensors and comparisons of the crest height distributions derived from the sensors and from theories. Some of the sensors had greater than expected energy at high frequencies. Once the measurements were filtered at 0.64 Hz, the Baylor, EMI and Vlissingen crest height distributions matched quite closely, while those from the other sensors were a few percent higher. The Baylor and EMI crest distributions agreed very well with the statistics from second order simulations, while previous parameterizations of the crest height distribution were generally too high. We conclude that crest height distributions derived from second order simulations can be used with confidence in engineering calculations. The data were also used in investigations of crest and trough shapes and the joint height/period distribution.

The Spatial Analysis of an Extreme Wave in a Model Basin

2007 ◽  
Author(s):  
Bas Buchner ◽  
Radboud van Dijk ◽  
Arjan Voogt
Keyword(s):  
Wave Propagation ◽  
Wave Spectrum ◽  
Normal Wave ◽  
Rayleigh Distribution ◽  
Order Theory ◽  
Second Order ◽  
Wave Crest ◽  
Extreme Waves ◽  
Extreme Wave ◽  
Linear Dispersion

As a pilot study into the understanding of the occurrence of extreme waves, the spatial development of an extreme wave (Ac/Hs = 1.59) in a model basin was investigated. This wave occurred in a wave spectrum that was not extremely steep and non-linear. It is observed that the extreme wave develops in less than half the wavelength from a relatively normal wave into an extreme crest. The wave crest stays high and constant over a large distance (almost 75m). Linear dispersion is not able to predict the wave propagation towards the observed extreme wave crest. Second order theory improves the prediction of the crest amplitude, but not enough. The crest amplitude is still underestimated. This is confirmed by the plots of the probability of extremes. The linear Rayleigh distribution underestimates the crest amplitudes. The second order distribution follows the measurements much better, but also in this case typically the highest 10 crests in a 3 hours storm are underestimated.

Wave Crest Sensor Intercomparison Study: An Overview of WACSIS

2004 ◽  
Vol 126 (1) ◽  
pp. 26-34 ◽  
Author(s):  
George Z. Forristall ◽  
Stephen F. Barstow ◽  
Harald E. Krogstad ◽  
Marc Prevosto ◽  
Paul H. Taylor ◽  
...  
Keyword(s):  
Second Order ◽  
Wave Crest ◽  
Height Distribution ◽  
High Frequencies ◽  
Video Cameras ◽  
Period Distribution ◽  
Wave Sensors ◽  
Intercomparison Study ◽  
Crest Height ◽  
Made In

The Wave Crest Sensor Intercomparison Study (WACSIS) was designed as a thorough investigation of the statistical distribution of crest heights. Measurements were made in the southern North Sea during the winter of 1997–1998 from the Meetpost Noordwijk in 18 m water depth. The platform was outfitted with several popular wave sensors, including Saab and Marex radars, an EMI laser, a Baylor wave staff and a Vlissingen step gauge. Buoys were moored nearby to obtain directional spectra. Two video cameras viewed the ocean under the wave sensors and their signals were recorded digitally. The data analysis focused on comparisons of the crest height measurements from the various sensors and comparisons of the crest height distributions derived from the sensors and from theories. Some of the sensors had greater than expected energy at high frequencies. Once the measurements were filtered at 0.64 Hz, the Baylor, EMI and Vlissingen crest height distributions matched quite closely, while those from the other sensors were a few percent higher. The Baylor and EMI crest distributions agreed very well with the statistics from second order simulations, while previous parameterizations of the crest height distribution were generally too high. We conclude that crest height distributions derived from second order simulations can be used with confidence in engineering calculations. The data were also used in investigations of crest and trough shapes and the joint height/period distribution.

Non-Gaussian Extreme Waves in the Central North Sea

1997 ◽  
Vol 119 (3) ◽  
pp. 146-150 ◽  
Author(s):  
J. Skourup ◽  
N.-E. O. Hansen ◽  
K. K. Andreasen
Keyword(s):  
Wave Height ◽  
North Sea ◽  
Upper Bound ◽  
Wave Crest ◽  
Extreme Waves ◽  
Freak Waves ◽  
Freak Wave ◽  
Wave Trains ◽  
Central North Sea ◽  
Crest Height

The area of the Central North Sea is notorious for the occurrence of very high waves in certain wave trains. The short-term distribution of these wave trains includes waves which are far steeper than predicted by the Rayleigh distribution. Such waves are often termed “extreme waves” or “freak waves.” An analysis of the extreme statistical properties of these waves has been made. The analysis is based on more than 12 yr of wave records from the Mærsk Olie og Gas AS operated Gorm Field which is located in the Danish sector of the Central North Sea. From the wave recordings more than 400 freak wave candidates were found. The ratio between the extreme crest height and the significant wave height (20-min value) has been found to be about 1.8, and the ratio between extreme crest height and extreme wave height has been found to be 0.69. The latter ratio is clearly outside the range of Gaussian waves, and it is higher than the maximum value for steep nonlinear long-crested waves, thus indicating that freak waves are not of a permanent form, and probably of short-crested nature. The extreme statistical distribution is represented by a Weibull distribution with an upper bound, where the upper bound is the value for a depth-limited breaking wave. Based on the measured data, a procedure for determining the freak wave crest height with a given return period is proposed. A sensitivity analysis of the extreme value of the crest height is also made.

Wave crest height distribution during the tropical cyclone period

2020 ◽  
Vol 197 ◽  
pp. 106899 ◽  
Author(s):  
V. Sanil Kumar ◽  
S. Harikrishnan ◽  
Sourav Mandal
Keyword(s):  
Tropical Cyclone ◽  
Wave Crest ◽  
Height Distribution ◽  
Crest Height

Extreme Waves and Stochastic Wave Groups

2006 ◽  
Author(s):  
Francesco Fedele ◽  
M. Aziz Tayfun
Keyword(s):  
Numerical Results ◽  
Resonance Interaction ◽  
Experimental Results ◽  
Wave Crest ◽  
Extreme Waves ◽  
Zakharov Equation ◽  
Wave Groups ◽  
Probability Of Exceedance ◽  
Random Seas ◽  
Crest Height

We introduce the concept of stochastic wave groups to explain the occurrence of extreme waves in nonlinear random seas, according to the dynamics imposed by the Zakharov equation (Zakharov, 1999). As a corollary, a new probability of exceedance of the crest-to-trough height which takes in to account the quasi-resonance interaction is derived. Furthermore, a generalization of the Tayfun distribution (Tayfun, 1986) for the wave crest height is also proposed. The new analytical distributions explain qualitatively well the experimental results of Onorato et al. (2004, 2005) and the numerical results of Juglard et al. (2005).

Nonlinear Crest Height Distribution in Three-Dimensional Ocean Waves

2008 ◽  
Author(s):  
Felice Arena ◽  
Alfredo Ascanelli
Keyword(s):  
Water Depth ◽  
Three Dimensional ◽  
Ocean Waves ◽  
Second Order ◽  
Wave Crest ◽  
Height Distribution ◽  
Order Model ◽  
Rayleigh Law ◽  
Wave Trough ◽  
Finite Water Depth

The interest and the studies on nonlinear waves are increased recently for their importance in the interaction with floating and fixed bodies. It is also well known that nonlinearities influence wave crest and wave trough distributions, both deviating from Rayleigh law. In this paper a theoretical crest distribution is obtained taking into account the extension of Boccotti’s Quasi Determinism theory, up to the second order for the case of three-dimensional waves, in finite water depth. To this purpose the Fedele & Arena [2005] distribution is generalized to three-dimensional waves on an arbitrary water depth. The comparison with Forristall second order model shows the theoretical confirmation of his conclusion: the crest distribution in deep water for long-crested and short crested waves are very close to each other; in shallow water the crest heights in three dimensional waves are greater than values given by long-crested model.

Maximum Crest Heights Over an Area: Laboratory Measurements Compared to Theory

2015 ◽  
Author(s):  
George Z. Forristall
Keyword(s):  
Single Point ◽  
Ocean Waves ◽  
Wave Crest ◽  
Large Area ◽  
Array Measurements ◽  
Theoretical Predictions ◽  
Wave Heights ◽  
Significant Wave Heights ◽  
Model Platform ◽  
Crest Height

Platform decks cover a reasonably large area compared to the size of a wave crest. Ocean waves are dispersive and directionally spread. As they propagate, their crest heights change. A platform deck samples those waves at many different locations. The maximum crest height over the area of a deck during a storm will naturally be greater than the maximum at a single point. The principle is clear but measurements are needed to confirm quantitative theoretical predictions. Such measurements were made in Marin wave basins using an array of 100 wave probes. At prototype scale, they covered an area of 100 by 100 m. Random directionally spread waves with prototype significant wave heights from 12 to 15 m and peak periods from 12 to 15 sec were generated and run through the array. Measurements were also made with pressure gauges mounted underneath a model platform deck placed at 11.5 and 13.0 m above still water level. Numerical simulations are used to find the maximum linear crest height expected over these areas. The second order enhancement of crest is accounted for by factoring the Gaussian maximum. Empirical fits to the simulations were found that can be used for most practical problems.

Burial and Scour of Short Cylinders and Truncated Cones Due to Long-Crested and Short-Crested Nonlinear Random Waves Plus Currents

2018 ◽  
Vol 140 (3) ◽  
Author(s):  
Muk Chen Ong ◽  
Dag Myrhaug
Keyword(s):  
Narrow Band ◽  
Three Dimensional ◽  
Wave Crest ◽  
Height Distribution ◽  
Random Waves ◽  
Regular Waves ◽  
Nonlinear Random Waves ◽  
2D And 3D ◽  
The Waves ◽  
Crest Height

This paper provides a practical stochastic method by which the burial and scour depths of short cylinders and truncated cones exposed to long-crested (two-dimensional (2D)) and short-crested (three-dimensional (3D)) nonlinear random waves plus currents can be derived. The approach is based on assuming the waves to be a stationary narrow-band random process, adopting the Forristall second-order wave crest height distribution representing both 2D and 3D nonlinear random waves. Moreover, the formulas for the burial and the scour depths for regular waves plus currents presented by previous published work for short cylinders and truncated cones are used.

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