Spatial Evolution of an Extreme Sea State With an Embedded Rogue Wave

2008 ◽  
Author(s):  
Gu¨nther F. Clauss ◽  
Marco Klein ◽  
Daniel Testa
Keyword(s):  
Wave Propagation ◽  
Target Position ◽  
Spatial Development ◽  
Time Interval ◽  
Optimization Approach ◽  
Linear Wave ◽  
Wave Group ◽  
Extreme Wave ◽  
Sea State ◽  
Wave Forecast

In the last years the existence of freak waves has been affirmed by observations, registrations and severe accidents. Many publications investigated the occurrence of extreme waves, their characteristics and their impact on offshore structures, but their formation process is still under discussion. One of the famous real world registration is the so called “New Year Wave”, recorded in the North Sea at the Draupner jacket platform on January 1st, 1995. Since there is only a single point registration available, it is not possible to draw conclusions on the spatial development in front of and behind the measurement point which would be indispensable for a complete understanding of this phenomenon. This paper presents a spatial development of the “New Year Wave” being generated in a model basin (L = 120 m, W = 8 m, d = 1 m, scale 1:70). To transfer the recorded “New Year Wave” into the wave tank, an optimization approach for the experimental generation of wave sequences with predefined characteristics is applied. The method is utilized to generate scenarios with a single high wave superimposed to irregular seas. At the end of this optimization process, a control signal for a deterministic wave sequence is obtained. The generated sea state with the embedded “New Year Wave” is measured at different locations in the tank, in a range from 2163 m (full scale) ahead of to 1470 m behind the target position — altogether 520 registrations. The focus lies on a detailed description of a possible evolution of the “New Year Wave” over a large area and time interval. It is observed that the extreme wave at the target position develops mainly from a wave group of three smaller waves. In particular the group velocity, wave propagation and the energy flux of the wave group is analyzed. In addition, the WAVE FORECAST METHOD is applied. This method is based on linear wave propagation and provides a prediction of the wave train a few minutes in advance from a single surface elevation snap shot. The capability of the prediction of approaching extreme wave heights is shown.

The New Year Wave: Spatial Evolution of an Extreme Sea State

2009 ◽  
Vol 131 (4) ◽  
Author(s):  
Günther F. Clauss ◽  
Marco Klein
Keyword(s):  
Single Point ◽  
Target Position ◽  
Spatial Development ◽  
Offshore Structures ◽  
Time Interval ◽  
Optimization Approach ◽  
Wave Group ◽  
Large Area ◽  
Sea State ◽  
The North

In the past years the existence of freak waves has been affirmed by observations, registrations, and severe accidents. Many publications investigated the occurrence of extreme waves, their characteristics and their impact on offshore structures, but their formation process is still under discussion. One of the famous real world registrations is the so called “New Year wave,” recorded in the North Sea at the Draupner jacket platform on January 1st, 1995. Since there is only a single point registration available, it is not possible to draw conclusions on the spatial development in front of and behind the point of registration, which is indispensable for a complete understanding of this phenomenon. This paper presents the spatial development of the New Year wave generated in a model basin. To transfer the recorded New Year wave into the wave tank, an optimization approach for the experimental generation of wave sequences with predefined characteristics is applied. The extreme sea state obtained with this method is measured at different locations in the tank, in a range from 2163 m (full scale) ahead of to 1470 m behind the target position—520 registrations altogether. The focus lies on the detailed description of a possible evolution of the New Year wave over a large area and time interval. It is observed that the extreme wave at the target position develops mainly from a wave group of three smaller waves. The group velocity, wave propagation, and the energy flux of this wave group are analyzed, in particular.

The coastal refraction-diffraction wave propagation model

1995 ◽  
Vol 17 (4) ◽  
pp. 6-12
Author(s):  
Nguyen Tien Dat ◽  
Dinh Van Manh ◽  
Nguyen Minh Son
Keyword(s):  
Wave Propagation ◽  
Field Data ◽  
Surf Zone ◽  
Propagation Model ◽  
Wave Transformation ◽  
Diffraction Effect ◽  
Linear Wave ◽  
Diffraction Wave ◽  
Linear Wave Propagation ◽  
Wave Propagation Model

A mathematical model on linear wave propagation toward shore is chosen and corresponding software is built. The wave transformation outside and inside the surf zone is considered including the diffraction effect. The model is tested by laboratory and field data and gave reasonables results.

A CFD Study of Focused Extreme Wave Impact on Decks of Offshore Structures

2014 ◽  
Author(s):  
Xin Lu ◽  
Pankaj Kumar ◽  
Anand Bahuguni ◽  
Yanling Wu
Keyword(s):  
Real World ◽  
Offshore Structures ◽  
Air Gap ◽  
Irregular Waves ◽  
Linear Wave ◽  
Extreme Wave ◽  
Wave Impact ◽  
Loading Test ◽  
Wide Range ◽  
Wave Maker

The design of offshore structures for extreme/abnormal waves assumes that there is sufficient air gap such that waves will not hit the platform deck. Due to inaccuracies in the predictions of extreme wave crests in addition to settlement or sea-level increases, the required air gap between the crest of the extreme wave and the deck is often inadequate in existing platforms and therefore wave-in-deck loads need to be considered when assessing the integrity of such platforms. The problem of wave-in-deck loading involves very complex physics and demands intensive study. In the Computational Fluid Mechanics (CFD) approach, two critical issues must be addressed, namely the efficient, realistic numerical wave maker and the accurate free surface capturing methodology. Most reported CFD research on wave-in-deck loads consider regular waves only, for instance the Stokes fifth-order waves. They are, however, recognized by designers as approximate approaches since “real world” sea states consist of random irregular waves. In our work, we report a recently developed focused extreme wave maker based on the NewWave theory. This model can better approximate the “real world” conditions, and is more efficient than conventional random wave makers. It is able to efficiently generate targeted waves at a prescribed time and location. The work is implemented and integrated with OpenFOAM, an open source platform that receives more and more attention in a wide range of industrial applications. We will describe the developed numerical method of predicting highly non-linear wave-in-deck loads in the time domain. The model’s capability is firstly demonstrated against 3D model testing experiments on a fixed block with various deck orientations under random waves. A detailed loading analysis is conducted and compared with available numerical and measurement data. It is then applied to an extreme wave loading test on a selected bridge with multiple under-deck girders. The waves are focused extreme irregular waves derived from NewWave theory and JONSWAP spectra.

Extreme Wave Condition at Doggerbank

2016 ◽  
Vol 138 (4) ◽  
Author(s):  
Espen Engebretsen ◽  
Sverre K. Haver ◽  
Dag Myrhaug
Keyword(s):  
Wind Turbines ◽  
Wind Farm ◽  
Offshore Wind ◽  
Extreme Condition ◽  
Exceedance Probability ◽  
Extreme Wave ◽  
Sea State ◽  
Wave Condition ◽  
The North ◽  
Wave Conditions

In design of offshore wind turbines, extreme wave conditions are of interest. Usually, the design wave condition is taken as the sea state corresponding to an annual exceedance probability of 2 × 10−2, i.e., a return period of 50 years. A possible location for a future wind farm, consisting of bottom fixed wind turbines, is the Doggerbank area. The water depth in this area varies from about 60 m in the north to about 20 m in the south. The hindcast database NORA10 provides sea state characteristics from 1957 to present over a domain covering Doggerbank. Regarding the deeper areas just north of Doggerbank, this hindcast model is found to be of good quality. Larger uncertainties are associated with the hindcast results as we approach shallower water further south. The purpose of the present study is to compare sea state evolution over Doggerbank as reflected by NORA10 with the results of the commonly used shallow water hindcast model SWAN. The adequacy of the default parameters of SWAN for reflecting changes in wave conditions over a sloping bottom is investigated by comparison with model test results. Extreme wave conditions for two locations 102.5 km apart in a north–south direction are established using NORA10. This is done using both, an all sea states approach and a peak over threshold (POT) approach. Assuming the extremes for the northern position to represent good estimates, the wave evolution southward is analyzed using SWAN. The extreme condition obtained from NORA10 in the northern position is used as input to SWAN and the results from the two hindcast models are compared in the southern position. SWAN seems to suggest a somewhat faster decay over Doggerbank compared to NORA10.

scholarly journals Storm Gloria: Sea State Evolution Based on in situ Measurements and Modeled Data and Its Impact on Extreme Values

2021 ◽  
Vol 8 ◽  
Author(s):  
Marta de Alfonso ◽  
Jue Lin-Ye ◽  
José M. García-Valdecasas ◽  
Susana Pérez-Rubio ◽  
M. Yolanda Luna ◽  
...  
Keyword(s):  
Extreme Values ◽  
Historical Context ◽  
Weather Forecast ◽  
Skill Score ◽  
Western Mediterranean ◽  
Special Focus ◽  
Atmospheric Conditions ◽  
Sea State ◽  
Wave Forecast

Storm Gloria, generated on January 17th, 2020 in the Eastern North Atlantic, crossed the Iberian Peninsula and impacted the Western Mediterranean during the following days. The event produced relevant damages on the coast and the infrastructures at the Catalan-Balearic Sea, due to extraordinary wind and wave fields, concomitant with anomalously intense rain and ocean currents. Puertos del Estado (the Spanish holding of harbors) has developed and operates a complex monitoring and forecasting system (PORTUS System), in collaboration with the Spanish Met Office (AEMET). The present work shows how Gloria was correctly forecasted by this system, alerts were properly issued (with special focus to the ports), and the buoys were able to monitor the sea state conditions during the event, measuring several new records of significant wave height and exceptional high mean wave periods. The paper describes, in detail, the dynamic evolution of the atmospheric conditions, and the sea state during the storm. It is by means of the study of both in situ and modeled PORTUS data, in combination with the AEMET weather forecast system results. The analysis also serves to place this storm in a historical context, showing the exceptional nature of the event, and to identify the specific reasons why its impact was particularly severe. The work also demonstrates the relevance of the PORTUS System to warn, in advance, the main Spanish Ports. It prevents accidents that could result in fatal casualties. To do so, the wave forecast warning performance is analyzed, making special focus on the skill score for the different horizons. Furthermore, it is demonstrated how a storm of this nature results in the need of changes on the extreme wave analysis for the area. It impacts all sorts of design activities at the coastline. The paper studies both how this storm fits into existing extreme analysis and how these should be modified in the light of this particular single event. This work is the first of a series of papers to be published on this issue. They analyze, in detail, other aspects of the event, including evolution of sea level and description of coastal damages.

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