scholarly journals WAVE GROUP FORMATION AMONG STORM WAVES

1974 ◽  
Vol 1 (14) ◽  
pp. 7 ◽  
Author(s):  
H. Rye
Keyword(s):  
North Sea ◽  
Group Formation ◽  
Weather Conditions ◽  
Wave Group ◽  
Average Correlation ◽  
The North ◽  
Storm Waves ◽  
Stormy Weather ◽  
Wave Heights ◽  
The North Sea

Wave data obtained m the North Sea for stormy weather conditions are analyzed to determine the extent of wave group formation among large waves; i.e. the number of large waves succeeding each other in one single run. Three periods associated with the passage of high sea states are examined. The average correlation between succeeding wave heights is found to be +0.2H, which indicates that wave heights do have a "memory". Wave group formations are found to be more pronounced when the sea is growing than decaying. The average lengths of wave runs are calculated.

scholarly journals North Atlantic storm driving of extreme wave heights in the North Sea

2017 ◽  
Vol 122 (4) ◽  
pp. 3253-3268 ◽  
Author(s):  
R. J. Bell ◽  
S. L. Gray ◽  
O. P. Jones
Keyword(s):  
North Sea ◽  
North Atlantic ◽  
Extreme Wave ◽  
The North ◽  
Wave Heights ◽  
The North Sea

Using a Dacon Scoop to Recover a Loaded Liferaft at Sea

2013 ◽  
Author(s):  
Robert Brown ◽  
Kerri-Ann Evely ◽  
Graham Small ◽  
Scott MacKinnon
Keyword(s):  
North Sea ◽  
Human Factor ◽  
Effective Means ◽  
Field Trials ◽  
Safe Haven ◽  
Eastern Canada ◽  
The North ◽  
Wave Heights ◽  
The North Sea ◽  
Significant Wave Heights

Service and supply vessels that perform standby duties in the offshore sector are equipped with a variety of resources with which to perform rescue at sea. For light to moderate sea conditions, techniques currently understood and practiced tend to involve using a fast rescue craft (FRC) to rescue survivors and subsequently transfer them to a safe haven (often a standby vessel). Rescuing evacuees in higher, more challenging sea states, however, is difficult given that it can be unsafe to launch and recover FRCs in such conditions. For these cases, many standby vessels in Eastern Canada and the North Sea are equipped with a device called a Dacon Scoop. The Dacon Scoop is a 6 to 8m semi-rigid net that is deployed directly from the side of the standby vessel and designed to rescue people directly from the water. While not a conventional use, it has been suggested that the scoop could also be used to recover small rescue craft (life rafts, lifeboats and fast rescue craft) at sea. Although life rafts provide occupants with some protection from the elements, there are still issues that can make it less than desirable to remain inside for extended periods of time if an effective means of system recovery is available. This paper presents the findings of research carried-out to determine if it is safe to use a Dacon Scoop to recover a loaded liferaft. The research trials made use of a loaded inflatable 25 person davit launched life raft and two different standby vessels 75m in length. A total of 34 tests were carried out over three days in significant wave heights up to 3.7m. Recommendations are given in the context of a human factor assessment related to the procedures, equipment and field trials experiences.

scholarly journals STORM STATISTICS IN THE NORTH SEA

1988 ◽  
Vol 1 (21) ◽  
pp. 71
Author(s):  
B.A. Salih ◽  
R. Burrows ◽  
R.G. Tickell
Keyword(s):  
North Sea ◽  
Climate Model ◽  
Weather Conditions ◽  
Threshold Level ◽  
Storm Events ◽  
Directional Information ◽  
The North ◽  
Empirical Procedure ◽  
The North Sea ◽  
Lag Times

Effective planning of offshore activities requires statistical information detailing storm occurrences and durations (defined as exceedences of an Hs threshold). This information is often referred to as persistence. The frequency of storm events and the probability associated with a number of successive sea states being above (or below) a given threshold level is often required by engineers to estimate the potential work period and down-time as well as to incorporate the lead and lag times needed to stop and restart interrupted operations due to severe weather conditions. However, until recently, a lack of sufficiently long data bases has precluded any meaningful investigation of this nature. Unrepresentative or misleading results can follow from data records that were measured over only a limited number of years. Furthermore, significant distortions may be introduced if the data record is not continuous as data gaps interrupt the persistence pattern. As more recorded data have become available, concerted efforts have been ' made on this topic; most notably by Houmb and Vik who developed a probabilistic model describing the statistics of storm (and calm) durations and frequencies at varying levels of sea state intensity. The present study investigates the adequacy of the semi-empirical procedure proposed by Houmb and Vik and also discusses the development of two new modelling techniques. The performance of these models are examined against wave data measured at the BP Forties field in the North Sea. A number of new statistical descriptors relating to the profile and intensity of storms have also been developed. It is recognised that wave period (Tz) and directional information must ultimately be incorporated in a storm climate model. However, this is beyond the scope of the present discussion.

Return Value Estimation of Significant Wave Heights With Maximum Entropy Distribution

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
S. Dong ◽  
W. Liu ◽  
L. Z. Zhang ◽  
C. Guedes Soares
Keyword(s):  
Maximum Entropy ◽  
North Sea ◽  
Significant Wave ◽  
The North ◽  
Compound Distribution ◽  
Wave Heights ◽  
The North Sea ◽  
Significant Wave Heights ◽  
Maximum Entropy Distribution ◽  
Return Value

The maximum entropy distribution is proposed to fit the long term and extreme distribution of significant wave heights from which return value estimates are derived. The maximum entropy distribution is applied to data from two sites of different characteristics, namely from Japan characterized by the occurrence of typhoons and from the North Sea with continuous variation of sea state intensity. The compound distribution, Poisson-maximum entropy distribution, is described and adopted to model the data from these two locations. It is shown that in the case of continuous data from the North Sea, this model does not bring any advantage over the direct application of the maximum entropy distribution to adjust the significant wave heights larger than different thresholds. For this case the maximum entropy distribution provides good fits.

scholarly journals Statistical downscaling for future extreme wave heights in the North Sea

2017 ◽  
Vol 11 (4) ◽  
pp. 2375-2403 ◽  
Author(s):  
Ross Towe ◽  
Emma Eastoe ◽  
Jonathan Tawn ◽  
Philip Jonathan
Keyword(s):  
North Sea ◽  
Statistical Downscaling ◽  
Extreme Wave ◽  
The North ◽  
Wave Heights ◽  
The North Sea

scholarly journals Associations of Synoptic Weather Conditions With Nocturnal Bird Migration Over the North Sea

2020 ◽  
Vol 8 ◽  
Author(s):  
Iris Manola ◽  
Maja Bradarić ◽  
Rob Groenland ◽  
Ruben Fijn ◽  
Willem Bouten ◽  
...  
Keyword(s):  
North Sea ◽  
Bird Migration ◽  
Weather Conditions ◽  
The North ◽  
Synoptic Weather ◽  
The North Sea ◽  
Nocturnal Bird Migration

scholarly journals HEIGHT DISTRIBUTION OF ESTUARINE WAVES

1982 ◽  
Vol 1 (18) ◽  
pp. 9
Author(s):  
V. Barthel
Keyword(s):  
North Sea ◽  
Rayleigh Distribution ◽  
Wave Climate ◽  
Field Investigation ◽  
Height Distribution ◽  
Empirical Distributions ◽  
The North ◽  
Wave Heights ◽  
The North Sea ◽  
Sea Wave

A field investigation program on waves was carried out in the Weser estuary, German Bight of the North Sea. Wave height and period distributions in this complicated wave climate can be approximated by a Rayleigh distribution. Empirical distributions of the wave heights characterise the different regions of the estuary. The presence of wave grouping as well as the group bounded long waves are shown in a few examples. The necessity of further investigations and analysis is highlighted.

scholarly journals Advanced Intelligent Control Strategy in Dynamic Positioning (DP) System Applied to a Semi-Submersible Drilling Platform in the North Sea

2021 ◽  
Author(s):  
Mohamad Alremeihi ◽  
Rosemary Norman ◽  
Kayvan Pazouki ◽  
Arun Dev ◽  
Musa Bashir
Keyword(s):  
North Sea ◽  
Oil And Gas ◽  
Weather Conditions ◽  
Dynamic Positioning ◽  
Gas Drilling ◽  
The North ◽  
Drilling Operations ◽  
The North Sea ◽  
And Performance ◽  
Wind Currents

Abstract Dynamic Positioning (DP) systems play a crucial role in oil and gas drilling and production floaters used globally for deep-water operations. Drilling operations need to maintain automatic positioning of the platform in the horizontal-plane within the safe zone. Operating DP systems typically require highly responsive control systems when encountering prevailing weather conditions. However, DP incident analysis demonstrates that control and thruster failures have been the leading causes of accidents for the past two decades, according to the International Marine Contractors Association (IMCA). In this paper, a Predictive Neural Network (PNN) strategy is proposed for thruster allocation on a platform; it has been developed by predicting the platform response and training the network to transform the required force commands from a nonlinear Proportional Integral Derivative (PID) motion controller for each thruster. The strategy is developed for increasing safety and zone keeping of DP-assisted-drilling operations in harsh weather. This is done by allowing the platform to recover the position more rapidly whilst decreasing the risk of losing the platform position and heading, which can lead to catastrophic damage. The operational performance of the DP system on a drilling platform subjected to the North Sea real environmental conditions of wind, currents and waves, is simulated with the model incorporating the PNN control algorithm, which deals with dynamic uncertainties, into the unstable conventional PID control system for a current drilling semi-submersible model. The simulation results demonstrate the improvement in DP accuracy and robustness for the semi-submersible drilling platform positioning and performance using the PNN strategy.

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