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.

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.

scholarly journals Wave current interaction: Effect on force prediction for fixed offshore structures

2018 ◽  
Vol 203 ◽  
pp. 01011
Author(s):  
Mohamed Latheef ◽  
Nasir Abdulla ◽  
Mohd Faieez Mohd Jupri
Keyword(s):  
Vertical Structure ◽  
Offshore Structures ◽  
Base Shear ◽  
Sea State ◽  
Clear Trend ◽  
The North ◽  
Relative Water ◽  
The North Sea ◽  
Current Interaction ◽  
Typical Design

MetOcean conditions in the South China Sea (SCS) indicates that unlike other locations such as the North Sea, the magnitude of the currents can be relatively large. In addition, these currents are strongly sheared. The present study focused on the typical design problem of calculating the ultimate base shear and overturning moments for slender fixed structureswiththe inclusion of the interaction between the currents and the wave field. It has been found that the loads on average can be around 15% larger when this interaction is accounted for in the calculation of the loads, highlighting the importance. In addition, the level of these amplifications were found to be dependent on the sea state steepness and the relative water depth. While no clear trend was found (changed case by case) in the present work, incorporating the vertical structure of the current was found to change the pattern of the amplification of the loads.

scholarly journals Field Measurements of Rogue Water Waves

2014 ◽  
Vol 44 (9) ◽  
pp. 2317-2335 ◽  
Author(s):  
Marios Christou ◽  
Kevin Ewans
Keyword(s):  
Quality Control ◽  
Wave Height ◽  
Water Waves ◽  
Normal Population ◽  
Single Point ◽  
Field Measurements ◽  
Rogue Waves ◽  
Control Procedure ◽  
Sea State ◽  
The North

Abstract This paper concerns the collation, quality control, and analysis of single-point field measurements from fixed sensors mounted on offshore platforms. In total, the quality-controlled database contains 122 million individual waves, of which 3649 are rogue waves. Geographically, the majority of the field measurements were recorded in the North Sea, with supplementary data from the Gulf of Mexico, the South China Sea, and the North West shelf of Australia. The significant wave height ranged from 0.12 to 15.4 m, the peak period ranged from 1 to 24.7 s, the maximum crest height was 18.5 m, and the maximum recorded wave height was 25.5 m. This paper will describe the offshore installations, instrumentation, and the strict quality control procedure employed to ensure a reliable dataset. An examination of sea state parameters, environmental conditions, and local characteristics is performed to gain an insight into the behavior of rogue waves. Evidence is provided to demonstrate that rogue waves are not governed by sea state parameters. Rather, the results are consistent with rogue waves being merely extraordinary and rare events of the normal population caused by dispersive focusing.

scholarly journals The Expected Impact of Marine Energy Farms Operating in Island Environments with Mild Wave Energy Resources—A Case Study in the Mediterranean Sea

Inventions ◽  
2021 ◽  
Vol 6 (2) ◽  
pp. 33
Author(s):  
Liliana Rusu ◽  
Florin Onea ◽  
Eugen Rusu
Keyword(s):  
Mediterranean Sea ◽  
Wind Turbines ◽  
Electricity Production ◽  
Time Interval ◽  
Target Area ◽  
Sea State ◽  
The North ◽  
Marine Energy ◽  
The Mediterranean ◽  
The Impact

A particularity of island areas is that they are subjected to strong sea state conditions that can have a severe impact on the beach stability, while on the other hand, they rely mainly on diesel combustion for electricity production which in the long run is not a sustainable solution. The aim of this work is to tackle these two issues, by assessing the impact of a hybrid marine energy farm that may operate near the north-western part of Giglio Island in the Mediterranean Sea. As a first step, the most relevant environmental conditions (wind and waves) over a 27-year time interval (January 1992–December 2018) were identified considering data coming from both ERA5 and the European Space Agency Climate Change Initiative for Sea State. An overview of the electricity production was made by considering some offshore wind turbines, the results showing that even during the summertime when there is a peak demand (but low wind resources), the demand can be fully covered by five wind turbines defined each by a rated power of 6 MW. The main objective of this work is to assess the coastal impact induced by a marine energy farm, and for this reason, various layouts obtained by varying the number of lines (one or two) and the distance between the devices were proposed. The modelling system considered has been already calibrated in the target area for this type of study while the selected device is defined by a relatively low absorption property. The dynamics of various wave parameters has been analysed, including significant wave height, but also parameters related to the breaking mechanics, and longshore currents. It was noticed that although the target area is naturally protected by the dominant waves that are coming from the south-western sector, it is possible to occur extreme waves coming from the north-west during the wintertime that can be efficiently attenuated by the presence of the marine energy farm.

Offshore structures – why all offshore facilities should have a demanning requirement

2019 ◽  
Vol 59 (2) ◽  
pp. 789 ◽  
Author(s):  
Matt Keys
Keyword(s):  
Offshore Structures ◽  
Structure Design ◽  
Risk Level ◽  
Design Codes ◽  
Offshore Structure ◽  
Sea State ◽  
The North ◽  
Offshore Structure Design ◽  
Cost Implications ◽  
Level Of Risk

Most offshore structure design codes focus on setting appropriate safety factors to achieve an acceptable annual level of risk. Recent work by Atkins SNC-Lavalin, together with a large number of operators in Australian waters and the North Sea, has discovered that a large number of aging assets are implementing a demanning requirement to limit the risk of platform collapse to personnel, due to changes in loading or degradation of the structure. This work has shown there are two risk scenarios that should drive this requirement. The first scenario which is intended by the codes in limiting the overall annual risk. The second is to limit the collapse risk associated with a known forecast storm, as the level of risk from helicopter demanning is much lower. For all the older offshore fixed and permanently mooring floating structures assessed for a risk level considered acceptable for a forecast storm, this risk level would govern the sea-state demanning criteria. For recently installed facilities that are compliant with current standards, the findings were the same: that all facilities should have a demanning requirement. The level of this demanning sea-state limit has been shown to be lower than expected and is likely to occur only once in the asset’s life; therefore, the cost implications of implementing demanning procedures are minor. This paper presents the basis and range of findings for calculating the risks associated with an annual occurrence and an ‘in a forecast storm’ risk. Further, this paper proposes acceptable demanning limits for facilities designed to current and historical design codes.

Estimating ocean wave directional spreading from an Eulerian surface elevation time history

2009 ◽  
Vol 465 (2111) ◽  
pp. 3361-3381 ◽  
Author(s):  
T. A. A. Adcock ◽  
P. H. Taylor
Keyword(s):  
Signal To Noise Ratio ◽  
Single Point ◽  
Time History ◽  
Offshore Structures ◽  
Second Order ◽  
Surface Elevation ◽  
Random Waves ◽  
Wave Tank ◽  
The North ◽  
The Difference

The directional spreading of sea states is an important design parameter in offshore engineering. Wave directionality affects the resulting wave kinematics, which affects the forces exerted on offshore structures. In this paper, we develop a method for estimating the amount of spreading, when the only information available is the time history of free surface elevation at a single point in space. We do this by predicting the second-order bound waves that occur at the difference in frequency of two freely propagating waves. The magnitude of these second-order bound waves is a function of the angle between the interacting waves. Thus, it is possible to infer some information about spreading from a single-point time history. We demonstrate that this approach works for wave groups in a fully nonlinear numerical wave tank. We create a synthetic random sea state and introduce noise into the analysis and thus show that our approach is robust and insensitive to noise, even with a signal-to-noise ratio of unity in the difference waves. This approach is also applied to random waves in a physical wave tank where spreading was directly measured and also to a storm recorded in the North Sea. In all cases, we find our estimate of spreading is in good agreement with other measurements.

Direction-finding studies of large-scale ionospheric irregularities

1953 ◽  
Vol 220 (1140) ◽  
pp. 39-61 ◽  
Keyword(s):  
Negative Correlation ◽  
Oblique Incidence ◽  
Large Scale ◽  
Single Point ◽  
Ionospheric Irregularities ◽  
Time Interval ◽  
Time Intervals ◽  
Space Correlation ◽  
The North ◽  
Ionization Density

The paper describes the results of directional measurements on pulse signals reflected from the ionosphere, on various frequencies in the range 2 to 15 Mc/s. The measurements have been made at vertical and oblique incidence (distance 700 km), and the observed directional variations have been interpreted in terms of ionospheric tilts. At any instant the direction of the tilt may be regarded as random; the magnitude is found to be similar, on the average, in each of two orthogonal directions. The way in which the tilts change with time and distance have been studied, the latter by means of observations using either spaced receivers or transmitters. The tilts at a given point in region F are found to be uncorrelated at a time interval of about 5 min during the day and about 10 min during the night. At a given time they are uncorrelated at points separated horizontally by about 50 km. There is appreciable negative correlation at greater time intervals at a single point, and there may be a similar effect in the space-correlation. Observations are described which indicate large-scale horizontal movements in the iono­sphere. In the sporadic E layer these appear to be in the nature of drifting clouds of ioniza­tion, while in the F layer the effects are such as would be produced by horizontally travelling ripples in the surfaces of constant ionization density. These ripples have wave-lengths of 50 to 400 km and speeds up to 350 m/s. The direction of motion tends to be more often towards the east or west than towards the north or south, and evidence of a diurnal change has been obtained.

scholarly journals Palynological indications for Silurian – earliest Devonian age strata in the Netherlands

2021 ◽  
Vol 100 ◽  
Author(s):  
Alexander J.P. Houben ◽  
Geert-Jan Vis
Keyword(s):  
The Netherlands ◽  
Core Material ◽  
Late Devonian ◽  
Time Interval ◽  
The South ◽  
Early Devonian ◽  
The North ◽  
Depositional Settings ◽  
Palynological Study ◽  
Devonian Age

Abstract Knowledge of the stratigraphic development of pre-Carboniferous strata in the subsurface of the Netherlands is very limited, leaving the lithostratigraphic nomenclature for this time interval informal. In two wells from the southwestern Netherlands, Silurian strata have repeatedly been reported, suggesting that these are the oldest ever recovered in the Netherlands. The hypothesised presence of Silurian-aged strata has not been tested by biostratigraphic analysis. A similar lack of biostratigraphic control applies to the overlying Devonian succession. We present the results of a palynological study of core material from wells KTG-01 and S05-01. Relatively low-diversity and poorly preserved miospore associations were recorded. These, nonetheless, provide new insights into the regional stratigraphic development of the pre-Carboniferous of the SW Netherlands. The lower two cores from well KTG-01 are of a late Silurian (Ludlow–Pridoli Epoch) to earliest Devonian (Lochkovian) age, confirming that these are the oldest sedimentary strata ever recovered in the Netherlands. The results from the upper cored section from the pre-Carboniferous succession in well KTG-01 and the cored sections from the pre-Carboniferous succession in well S05-01 are more ambiguous. This inferred Devonian succession is, in the current informal lithostratigraphy of the Netherlands, assigned to the Banjaard group and its subordinate Bollen Claystone formation, of presumed Frasnian (i.e. early Late Devonian) age. Age-indicative Middle to Late Devonian palynomorphs were, however, not recorded, and the overall character of the poorly preserved palynological associations in wells KTG-01 and S05-01 may also suggest an Early Devonian age. In terms of lithofacies, however, the cores in well S05-01 can be correlated to the upper Frasnian – lower Famennian Falisolle Formation in the Campine Basin in Belgium. Hence, it remains plausible that an unconformity separates Silurian to Lower Devonian strata from Upper Devonian (Frasnian–Famennian) strata in the SW Netherlands. In general, the abundance of miospore associations points to the presence of a vegetated hinterland and a relatively proximal yet relatively deep marine setting during late Silurian and Early Devonian times. This differs markedly from the open marine depositional settings reported from the Brabant Massif area to the south in present-day Belgium, suggesting a sediment source to the north. The episodic presence of reworked (marine) acritarchs of Ordovician age suggests the influx of sedimentary material from uplifted elements on the present-day Brabant Massif to the south, possibly in relation to the activation of a Brabant Arch system.

Technical Analysis of Ocean Towing Evolutions

2021 ◽  
Author(s):  
Bartley Eckhardt ◽  
Daniel Fridline ◽  
Richard Burke
Keyword(s):  
Failure Modes ◽  
Human Life ◽  
Single Point ◽  
Forensic Analysis ◽  
Sea State ◽  
Worst Case ◽  
Strain Monitoring ◽  
Load Limit ◽  
Offshore Oil

Ocean towing in general, and non-routine tows in particular, present unique technical challenges to towing vessel owners/operators, salvors, the offshore oil/gas and wind industries, and others. When such tows “go wrong”, the harm to human life, property and/or the environment can be significant. The authors have drawn from their work on the Towing Safety Advisory Committee’s investigation of the grounding of the MODU Kulluk to present methods and considerations in analyzing ocean towing evolutions, both “routine” and “non-routine”. (TASK 14-01) The methods and considerations presented should be employed in advance of a towing evolution, but can be used in accident reconstruction and forensic analysis when an evolution has failed. The methods presented are iterative, and consider 2 x 6 degree freedom of motion (of the towing vessel(s) and towed vessel respectively) and characteristics of the towline, and facilitate determination of: Worst Case Conditions. Extreme Towline Tension (ETT) as a function of sea state and speed. Limits of the Tow (Go-No Go Criteria). Recommended Catenary Length as a function of sea state and speed. Size and Selection of the Towing Vessel and Gear, including: Required Bollard Pull. Required Strength, Characteristics and Condition of the Towline. Limits and Set Points of the Towing Winch, Automatic or Manual. Required Strength and Characteristics of the Synthetic Emergency Towline and its methods of deployment and connection. Working Load Limit (WLL) of the Shackles, Delta Plate and Attachment Points. Required Strength and Characteristics of Bridles, Pendant and Surge Gear/Shock Lines. The authors further explore the implications of single point failure modes, redundancy in gear and towing vessel(s), high cycle fatigue, and strain monitoring.

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