Examining a Comprehensive Dataset Containing Thousands of Freak Wave Events: Part 2—Analysis and Findings

2011 ◽  
Author(s):  
Marios Christou ◽  
Kevin Ewans
Keyword(s):  
Environmental Conditions ◽  
Probability Distributions ◽  
Cooperative Research ◽  
Freak Waves ◽  
Freak Wave ◽  
Temporal Parameters ◽  
Wave Measurements ◽  
Insight Into

This paper concerns the analysis of a very large, quality-controlled dataset of raw wave measurements. It directly follows from paper 1, as part of work undertaken for the CresT (Cooperative Research on Extreme Seas and their impacT) Joint Industry Project (JIP), and describes the various analyses performed on the dataset. In particular numerous freak wave events are observed and various analyses are performed to gain an insight into conditions that are conducive to their formation. The examination of probability distributions, spectral and temporal parameters, degree of focusing and environmental conditions that lead to freak waves is performed and the findings are presented.

How Quartet Resonance Might or Might Not Amplify Large Waves Into Freak Waves

2011 ◽  
Author(s):  
Peter Tromans
Keyword(s):  
Spectral Response ◽  
Freak Waves ◽  
Freak Wave ◽  
Ocean Surface Waves ◽  
Surface Method ◽  
Random Seas ◽  
Time Marching ◽  
Physical Insight ◽  
The Difference ◽  
Insight Into

We have developed an approximate solution to Zakharov’s equations for the evolution of ocean surface waves. We have applied it with a spectral response surface method to estimate the probability of exceedance of crest elevation in random seas. The method avoids time-marching and allows probabilities to be estimated on practical time scales. The results indicate that quartet resonance can produce very large amplification of extreme crests in uni-directional seas. However, the effect is very much smaller in spread seas. Although the solution is approximate it provides a great deal of physical insight into the mechanisms by which a freak wave might develop and explains the difference in results between uni-directional and spread seas.

Examining a Comprehensive Dataset Containing Thousands of Freak Wave Events: Part 1—Description of the Data and Quality Control Procedure

2011 ◽  
Author(s):  
Marios Christou ◽  
Kevin Ewans
Keyword(s):  
Quality Control ◽  
Data Collection ◽  
Water Surface ◽  
Field Measurements ◽  
Surface Elevation ◽  
Control Procedure ◽  
Cooperative Research ◽  
Freak Wave ◽  
Quality Control Procedure ◽  
Wave Measurements

This paper concerns the description of the formation of a very large, quality-controlled dataset of raw wave measurements. As part of the CresT (Cooperative Research on Extreme Seas and their impacT) Joint Industry Project (JIP), the participants provided raw field measurements of water surface elevation from various installations across the globe. This paper will describe the data collection from the different installations, the strict quality control procedure employed to ensure a reliable dataset, and an overview of the occurrences of records containing freak wave events. Part 2 of this paper will then go on to describe the analysis performed on this dataset as well as the findings from the study.

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.

scholarly journals Damage of polyesters by the atmospheric free radical oxidant NO3 •: a product study involving model systems

2013 ◽  
Vol 9 ◽  
pp. 1907-1916 ◽  
Author(s):  
Catrin Goeschen ◽  
Uta Wille
Keyword(s):  
Free Radical ◽  
Environmental Conditions ◽  
Hot Spots ◽  
Polymer Materials ◽  
Model Systems ◽  
Night Time ◽  
High Performing ◽  
Work Model ◽  
Product Study ◽  
Insight Into

Manufactured polymer materials are used in increasingly demanding applications, but their lifetime is strongly influenced by environmental conditions. In particular, weathering and ageing leads to dramatic changes in the properties of the polymers, which results in decreased service life and limited usage. Despite the heavy reliance of our society on polymers, the mechanism of their degradation upon exposure to environmental oxidants is barely understood. In this work, model systems of important structural motifs in commercial high-performing polyesters were used to study the reaction with the night-time free radical oxidant NO3 • in the absence and presence of other radical and non-radical oxidants. Identification of the products revealed ‘hot spots’ in polyesters that are particularly vulnerable to attack by NO3 • and insight into the mechanism of oxidative damage by this environmentally important radical. It is suggested that both intermediates as well as products of these reactions are potentially capable of promoting further degradation processes in polyesters under environmental conditions.

A Numerical Prediction on the Transient Response of a Spar-Type Floating Offshore Wind Turbine in Freak Waves

2020 ◽  
Vol 142 (6) ◽  
Author(s):  
Yan Li ◽  
Xiaoqi Qu ◽  
Liqin Liu ◽  
Peng Xie ◽  
Tianchang Yin ◽  
...  
Keyword(s):  
Dynamic Response ◽  
Wind Turbine ◽  
Offshore Wind ◽  
Numerical Code ◽  
Modulation Method ◽  
Offshore Wind Turbine ◽  
Freak Waves ◽  
Freak Wave ◽  
Floating Offshore Wind Turbine ◽  
The Impact

Abstract Simulations are conducted in time domain to investigate the dynamic response of a spar-type floating offshore wind turbine (FOWT) under the freak wave scenarios. Toward this end, a coupled aero-hydro-mooring in-house numerical code is adopted to perform the simulations. The methodology includes a blade-element-momentum (BEM) model for simulating the aerodynamic loads, a nonlinear model for simulating the hydrodynamic loads, a nonlinear restoring model of Spar buoy, and a nonlinear algorithm for simulating the mooring cables. The OC3 Hywind spar-type FOWT is adopted as an example to study the dynamic response under the freak wave conditions, meanwhile the time series of freak waves are generated using the random frequency components selection phase modulation method. The motion of platform, the tension applied on the mooring lines, and the power generation performance are documented in several cases. According to the simulations, it is indicated that when a freak wave acts on the FOWT, the transient motion of the FOWT is induced in all degrees-of-freedom, as well as the produced power decreases rapidly. Furthermore, the impact of freak wave parameters on the motion of FOWT is discussed.

Real-Time Monitoring of Dynamical State Changes in Staged Combustion

2002 ◽  
Author(s):  
C. S. Daw ◽  
C. E. A. Finney ◽  
R. T. Bailey ◽  
T. J. Flynn ◽  
T. A. Fuller
Keyword(s):  
Real Time ◽  
Probability Distributions ◽  
Real Time Monitoring ◽  
Temporal Asymmetry ◽  
Lifted Flames ◽  
Dynamical Features ◽  
State Changes ◽  
Utility Scale ◽  
Monitoring Software ◽  
Insight Into

We describe techniques for diagnosing the state of coal-fired utility burners using dynamic characteristics of the output of optical flame scanner signals. The analysis techniques are optimized for targeting dynamical features associated with nonlinear instabilities that develop as burner operating parameters are changed. Various specific instability indicators are used, including shifts in probability distributions, temporal asymmetry and coarsed-grained descriptions of unstable periodicities. We show that careful application of such methods can accurately characterize a range of different flame states. Specifically, transitions through bifurcation points between attached and lifted flames are targeted, giving insight into causes of instability such as stoichiometry or feed and flow variations. We demonstrate results from the application of these methods to utility-scale staged pulverized-coal burners in a real-time software package. The Flame Doctor™ burner-monitoring software is presently undergoing plant-implementation trials in a program sponsored by the Electric Power Research Institute and participating utilities. In a practical application, we show how real-time monitoring and intervention can significantly mitigate adverse combustion conditions.

Wave Measurements at Eastern Green Canyon During Hurricane Ike

2009 ◽  
Author(s):  
Oriol Rijken ◽  
Adam Bangs
Keyword(s):  
Wave Height ◽  
Wave Energy ◽  
Repetitive Sequences ◽  
Wave Crest ◽  
Hurricane Ike ◽  
Wave Trough ◽  
Wave Measurements ◽  
Wave Event ◽  
Measurement Location ◽  
Insight Into

Wave measurements were obtained at an Eastern Green Canyon location during hurricane Ike in September 2009. The eye of the hurricane passed approximately 68 nautical miles to the South West of the measurement location. The significant wave height was above 30 ft for about 20 hours and above 40 ft for about 5.5 hours. The wave time series provide an insight into the wave field as the storm approaches and leaves the location. One of the interesting features observed was that there were repetitive sequences, where each sequence consisted of a period of increased wave energy followed by periods of reduced wave energy. Each sequence lasted approximately one hour. Measured wave crest, wave trough and wave height distributions are discussed. One unique wave event was observed. This event was characterized by a predictably-sized crest followed by a very deep trough.

Freak Wave Generation in a Wave Basin With HOSM-WG Method

2015 ◽  
Author(s):  
Hidetaka Houtani ◽  
Takuji Waseda ◽  
Wataru Fujimoto ◽  
Keiji Kiyomatsu ◽  
Katsuji Tanizawa
Keyword(s):  
Control Method ◽  
Irregular Waves ◽  
Frequency Bandwidth ◽  
Freak Waves ◽  
Freak Wave ◽  
Wave Basin ◽  
Wave Trains ◽  
Directional Wave ◽  
Wave Maker ◽  
The Difference

A method to produce freak waves with arbitrary spectrum in a fully directional wave basin is presented here. This is an extension of Waseda, Houtani and Tanizawa at OMAE 2013[1], which used “HOSM-WG” based on the higher-order spectral method (HOSM). We used the following three methods to improve the HOSM-WG in [1]: “separation of free waves from bound waves,” “using Biesel’s transfer function in wavenumber space” and “using Schaffer’s 2nd-order wave maker control method.” Modulational wave trains, freak waves in unidirectional irregular waves and freak waves in short-crested irregular waves were generated in a wave basin. The experimental results using the improved HOSM-WG were compared to the HOSM simulation, and good agreements were found. The effectiveness of the improved HOSM-WG was ascertained. We showed that the difference between HOSM-WG and HOSM simulations became larger as wave steepness, frequency bandwidth of the spectrum or directional spreading became larger.

Can swell increase the number of freak waves in a wind sea?

2010 ◽  
Vol 650 ◽  
pp. 57-79 ◽  
Author(s):  
ODIN GRAMSTAD ◽  
KARSTEN TRULSEN
Keyword(s):  
Nonlinear Evolution ◽  
Wind Waves ◽  
Short Wave ◽  
Freak Waves ◽  
Freak Wave ◽  
Short Waves ◽  
Term Evolution ◽  
Wind Sea ◽  
Modified Equation

The effect of a swell on the statistical distribution of a directional short-wave field is investigated. Starting from Zakharov's spectral formulation, we derive a new modified nonlinear Schrödinger equation appropriate for the nonlinear evolution of a narrow-banded spectrum of short waves influenced by a swell. The swell-modified equation is solved analytically to yield an extended version of the result of Longuet-Higgins & Stewart (J. Fluid Mech., vol. 8, no. 4, 1960, pp. 565–583) for the modulation of a short wave riding on a longer wave. Numerical Monte Carlo simulations of the long-term evolution of a spectrum of short waves in the presence of a monochromatic swell are employed to extract statistical distributions of freak waves among the short waves. We find evidence that a realistic short-crested wind sea can on average experience a small increase in freak wave probability because of a swell provided the swell is not orthogonal to the wind waves. For orthogonal swell and wind waves we find evidence that there is almost no significant change in the probability of freak waves in the wind sea. If the short waves are unrealistically long crested, such that the Benjamin–Feir index serves as indicator for freak waves (Gramstad & Trulsen, J. Fluid Mech., vol. 582, 2007, pp. 463–472), it appears that the swell has much smaller relative influence on the probability of freak waves than in the short-crested case.

scholarly journals Detecting damage events in concrete using diffuse ultrasound structural health monitoring during strong environmental variations

2017 ◽  
Vol 17 (2) ◽  
pp. 410-419 ◽  
Author(s):  
Patrik Fröjd ◽  
Peter Ulriksen
Keyword(s):  
Structural Health Monitoring ◽  
Health Monitoring ◽  
Environmental Conditions ◽  
Continuous Wave ◽  
Data Set ◽  
Phase Measurements ◽  
Structural Health ◽  
Wave Measurements ◽  
Environmental Variations ◽  
Window Approach

Diffuse ultrasonic wave measurements used in structural health monitoring applications can detect damage in concrete. However, the accuracy is very susceptible to environmental variations. In this study, a large concrete floor slab was monitored using diffuse wave fields that were generated by continuous-wave transmissions between ultrasonic transducers. The slab was monitored for several weeks while being subjected to changes in environmental conditions. Subsequently, it was damaged using impact hits, resulting in centimeter-scale cracking. The variations caused by the environment masked the effects of the damage in the measurements. To address this issue, the Mahalanobis distance was used to distinguish between the influence of the damage and the influence of the environmental variations. The Mahalanobis model uses amplitude and phase measurements of continuous waves at a set of different frequencies as inputs. A moving window approach was applied to the baseline data set to account for slow trends. This study shows that this technique greatly suppresses most of the variations caused by environmental conditions. All damage events in our data set have been detected.

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