Systematically Varied Rogue Wave Sequences for the Experimental Investigation of Extreme Structure Behavior

2008 ◽  
Vol 130 (2) ◽  
Author(s):  
Günther F. Clauss ◽  
Christian E. Schmittner ◽  
Janou Hennig
Keyword(s):  
Wave Height ◽  
Rogue Wave ◽  
Wave Train ◽  
Weather Conditions ◽  
Offshore Structures ◽  
Severe Weather ◽  
Wave Profile ◽  
Bending Moments ◽  
Extreme Wave ◽  
Improved Design

For an improved design of ships and offshore structures with regard to their behavior under severe weather conditions, wave height and steepness as well as the shape of the wave profile have to be considered. In this paper, the extreme new year wave as documented in numerous publications is varied with respect to wave height and period. These varied wave sequences are realized and measured in a model tank and applied to the investigation of motions and bending moments of a floating production storage and offloading ship. The results are compared to the responses in the original wave train. An investigation of the riskiness of extreme wave sequences in comparison with existing rules concludes this paper.

Systematically Varied Rogue Wave Sequences for the Experimental Investigation of Extreme Structure Behavior

2006 ◽  
Author(s):  
Gu¨nther F. Clauss ◽  
Christian E. Schmittner ◽  
Janou Hennig
Keyword(s):  
Wave Height ◽  
Rogue Wave ◽  
Wave Train ◽  
Weather Conditions ◽  
Offshore Structures ◽  
Severe Weather ◽  
Wave Profile ◽  
Bending Moments ◽  
Extreme Wave ◽  
Improved Design

For an improved design of ships and offshore structures with regard to their behavior under severe weather conditions, wave height and steepness as well as the shape of the wave profile have to be considered. In this paper, the extreme New Year Wave as documented in numerous publications is varied with respect to wave height and period. These varied wave sequences are realized and measured in a model tank and applied to the investigation of motions and bending moments of an FPSO ship. The results are compared to the responses in the original wave train. An investigation of the riskiness of extreme wave sequences in comparison with existing rules concludes the paper.

scholarly journals Loads on a Point-Absorber Wave Energy Converter in Regular and Focused Extreme Wave Events

2020 ◽  
Author(s):  
Eirini Katsidoniotaki ◽  
Edward Ransley ◽  
Scott Brown ◽  
Johannes Palm ◽  
Jens Engström ◽  
...  
Keyword(s):  
Wave Energy ◽  
Wave Train ◽  
Offshore Structures ◽  
Wave Energy Converter ◽  
Extreme Waves ◽  
Extreme Wave ◽  
Energy Converter ◽  
Point Absorber ◽  
Wave Energy Converters ◽  
Extreme Loads

Abstract Accurate modeling and prediction of extreme loads for survivability is of crucial importance if wave energy is to become commercially viable. The fundamental differences in scale and dynamics from traditional offshore structures, as well as the fact that wave energy has not converged around one or a few technologies, implies that it is still an open question how the extreme loads should be modeled. In recent years, several methods to model wave energy converters in extreme waves have been developed, but it is not yet clear how the different methods compare. The purpose of this work is the comparison of two widely used approaches when studying the response of a point-absorber wave energy converter in extreme waves, using the open-source CFD software OpenFOAM. The equivalent design-waves are generated both as equivalent regular waves and as focused waves defined using NewWave theory. Our results show that the different extreme wave modeling methods produce different dynamics and extreme forces acting on the system. It is concluded that for the investigation of point-absorber response in extreme wave conditions, the wave train dynamics and the motion history of the buoy are of high importance for the resulting buoy response and mooring forces.

scholarly journals Assessment of reliability of extreme wave height prediction models

2016 ◽  
Author(s):  
Satish Samayam ◽  
Valentina Laface ◽  
Sannasiraj Sannasi Annamalaisamy ◽  
Felice Arena ◽  
Sundar Vallam ◽  
...  
Keyword(s):  
North America ◽  
Mediterranean Sea ◽  
Wave Height ◽  
Prediction Models ◽  
Offshore Structures ◽  
Coastal Hazards ◽  
Mitigation Measures ◽  
Extreme Wave ◽  
Indian Water ◽  
Buoy Data

Abstract. Extreme waves influence coastal engineering activities and have an immense geophysical implication. Therefore, their study, observation and extreme wave prediction are decisive for planning for mitigation measures against natural coastal hazards, ship routing, design of coastal and offshore structures. In this study, the estimates of design wave heights associated with return period of 30 and 100 years are dealt with in detail. The design wave height is estimated based on four different models to obtain a general and reliable model. Different locations are considered to perform the analysis: four sites in Indian waters, one in Mediterranean Sea and two in North America. For the Indian water domain European Centre for Medium-Range Weather Forecasts (ECMWF) global atmospheric reanalysis ERA-interim wave hind cast data covering a period of 36 years have been utilized for this purpose. For the locations in Mediterranean Sea and North America both ERA-interim wave hind cast and buoy data are considered. The reasons for the variation in return value estimates of the ERA-interim data and the buoy data using different estimation models are assessed in detail.

Study on Influence of Wave-Current Interaction on Prediction of Rogue Wave Taking Viscous Effect Into Account

2013 ◽  
Author(s):  
Bo Peng ◽  
Ning Ma ◽  
Xiechong Gu
Keyword(s):  
Numerical Model ◽  
Viscous Flow ◽  
Wave Height ◽  
Rogue Wave ◽  
Rogue Waves ◽  
Offshore Structures ◽  
Wave Generation ◽  
Group Method ◽  
Linear Wave ◽  
Current Interaction

Wave-current interaction is a common phenomenon in real sea and has significant influence on sea conditions, thus threatening the safety of offshore structures. Waves countering current is one of the main reasons for occurrence of rogue waves, which imperils offshore structures and is of much importance for research. Based on Computational Fluid Dynamics (CFD), the simulation of viscous flow for wave generation in a Circulating Water Channel (CWC) has been carried out. In the calculation model, the motion of an oscillating flap type wave maker is simulated to generate specified waves by controlling movement of dynamic mesh in numerical model. Smoothing and local refreshing of dynamic meshes have been done to adapt meshes. Then, viscous flow simulation of wave generation among current in numerical tank is accomplished by using Reynolds-Averaged-Navier-Stokes (RANS) equation, renormalization group method based (RNG-based) k-ε turbulence model and Volume of Fluid (VOF) method as treatment of free surface. Both waves propagating along and against current have been investigated. To validate the numerical model, a part of calculation results are compared with the experimental results in CWC for regular wave propagating along current. Furthermore, calculations based on linear wave theory and modified nonlinear Schrödinger Equation (mNLS) are also performed. For further investigation of occurrence of rogue wave in deep water, focusing technique is adopted by using transient water wave. Results show that wave height and group velocity of wave sequence would change notably when wave propagates along preexisting large-scale current. Wave height decreases as the velocity of uniform current increases and wave sequence arrives at given position earlier when propagating on faster current. On the other hand, on a counter current, waves are steepened and wave height increases dramatically. Based on the numerical results, several characteristics and principal values such as wave height and asymmetry have been discussed. The effects of viscous flow and wave-current interaction on prediction of rogue waves are analyzed and evaluated. Accordingly, some concluding remarks on improving of numerical model of rogue wave are given.

scholarly journals EXTREME WAVE CONDITIONS IN BRITISH AND ADJACENT WATERS

1972 ◽  
Vol 1 (13) ◽  
pp. 6 ◽  
Author(s):  
Laurence Draper
Keyword(s):  
Wave Height ◽  
Offshore Structures ◽  
Wave Period ◽  
The Other ◽  
Wind Data ◽  
Extreme Wave ◽  
Wave Measurements ◽  
Extreme Wind ◽  
Wave Conditions

Information on extreme wave conditions is needed in the design of offshore structures. This paper present the results of calculations of the parameters in the 50-year storm; the work has been based on extreme wind data and on instrumental wave measurements. The results are complementary, and are combined in two maps, one of extreme wave height and the other of the corresponding wave period.

Rogue Waves: Results of the MaxWave Project

2008 ◽  
Vol 130 (2) ◽  
Author(s):  
W. Rosenthal ◽  
S. Lehner
Keyword(s):  
Weather Conditions ◽  
Rogue Waves ◽  
Offshore Structures ◽  
Severe Weather ◽  
Sea Surface ◽  
Extreme Waves ◽  
Synthetic Aperture Radar Data ◽  
European Project ◽  
Sea Surface Topography ◽  
The Impact

Safety of shipping is an ever growing concern. In a summary, Faulkner investigated the causes of shipping casualties (2002, “Shipping Safety: A Matter of Concern,” Ingenia, The Royal Academy of Engineering, Marine Matters, pp. 13–20) and concluded that the numbers of unexplained accidents are far too high in comparison to other means of transport. From various sources, including insurers data over 30% of the casualties are due to bad weather (a fact that ships should be able to cope with) and a further 25% remain completely unexplained. The European project MaxWave aimed at investigating ship and platform accidents due to severe weather conditions using different radars and in situ sensors and at suggesting improved design and new safety measures. Heavy sea states and severe weather conditions have caused the loss of more than 200 large cargo vessels within the 20years between 1981 and 2000 (Table 1 in Faulkner). In many cases, single “rogue waves” of abnormal height as well as groups of extreme waves have been reported by crew members of such ships. The European Project MaxWave deals with both theoretical aspects of extreme waves and new techniques to observe these waves using different remote sensing techniques. The final goal is to improve the understanding of the physical processes responsible for the generation of extreme waves and to identify geophysical conditions in which such waves are most likely to occur. Two-dimensional sea surface elevation fields are derived from marine radar and space borne synthetic aperture radar data. Individual wave parameters such as maximum to significant wave height ratios and wave steepness, are derived from the sea surface topography. Several ship and offshore platform accidents are analyzed and the impact on ship and offshore design is discussed. Tank experiments are performed to test the impact of designed extreme waves on ships and offshore structures. This article gives an overview of the different work packages on observation of rogue waves, explanations, and consequences for design.

The Taming of the Shrew: Tailoring Freak Wave Sequences for Seakeeping Tests

2008 ◽  
Vol 52 (03) ◽  
pp. 194-226
Author(s):  
Günther F. Clauss
Keyword(s):  
Wave Height ◽  
Wave Train ◽  
Random Phase ◽  
Offshore Structures ◽  
Green Water ◽  
Discrete Wavelet ◽  
Peak Period ◽  
Worst Case ◽  
Apparent Lack ◽  
Starting Point

If you want to build a ship, don't drum up people together to collect woodand don't assign them tasks and work but rather teach them to long for the endless immensity of the sea.___Antoine de Saint-Exupery (1900–1944)___The basic law of the seaway is the apparent lack of any law.___Lord Rayleigh___Based on the wave focusing technique for the generation of task-related wave packets, a new technique is proposed for the synthesization of tailored design wave sequences in extreme seas. The physical wave field is fitted to predetermined global and local target characteristics designed in terms of significant wave height, peak period, as well as wave height, crest height, and period of individual waves. The generation procedure is based on two steps: First, a linear approximation of the desired wave train is computed by a sequential quadratic programming method that optimizes an initially random phase spectrum for a given variance spectrum. The wave board motion derived from this initial guess serves as a starting point for directly fitting the physical wave train to the target parameters. The subplex method is applied to improve systematically a certain time frame of the wave board motion, which is responsible for the evolution of the response-related design wave sequence. The discrete wavelet transform is introduced to reduce significantly the number of free variables to be considered in the fitting process. Wavelet analysis allows the efficient localization of the relevant information on the electrical control signal of the wave maker in time and frequency domain. As the presented technique permits the deterministic generation of design rogue wave sequences in extreme seas, it is well suited for investigating the mechanism of arbitrary wave-structure interactions, including capsizing, slamming, and green water as well as other survivability design aspects. Even worst case wave sequences, such as the Draupner New Year wave, can be modeled in the wave tank to analyze the evolution of these events and to evaluate the response of offshore structures under abnormal conditions. This procedure is illustrated by investigations of an offshore lift operation, of the behavior of a semisubmersible and an FPSO in tailored freak waves as well as the analysis of ship capsizing in deterministic wave sequences at selected target positions.

Bending Moments of an FPSO in Rogue Waves

2004 ◽  
Author(s):  
Gu¨nther F. Clauss ◽  
Christian E. Schmittner ◽  
Janou Hennig ◽  
Carlos Guedes Soares ◽  
Nuno Fonseca ◽  
...  
Keyword(s):  
Time Domain ◽  
Rogue Wave ◽  
Rogue Waves ◽  
Offshore Structures ◽  
Bending Moments ◽  
The North ◽  
Frequency Domain Methods ◽  
Local Wave ◽  
The Time Domain ◽  
Wave Induced

The increasing numbers of reported rogue waves with extreme crest and wave heights and unusual group pattern with the consequence of severe damages raise the question if such exceptional events have to be considered routinely for the design of ships and offshore structures. For the investigation of the effects of rogue wave impacts time domain simulation methods are required in addition to traditional frequency domain methods which may not be sufficient to consider these extreme events. In this paper the vertical bending moments at the midship section of an FPSO are investigated using state of the art numerical simulation tools in combination with experiments. For the seakeeping tests the extremely high New Year Wave (registered in the North Sea) is generated in the wave tank, and motions and structural forces are analyzed at model scale. For validation the results are evaluated deterministically and compared to numerical simulations. The time domain calculation allows to artificially change local wave characteristics. The steepness of the selected rogue wave is varied and the influence on wave induced loads is studied. A comparison with standard procedures of seakeeping analysis and classification rules closes the paper.

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.

scholarly journals EXTREME WAVE PRESSURES AND LOADS ON A PILE-SUPPORTED WHARF DECK - INFLUENCES OF AIR GAP AND WAVE DIRECTION

2018 ◽  
pp. 5
Author(s):  
Andrew Cornett
Keyword(s):  
Offshore Structures ◽  
Model Tests ◽  
Scale Model ◽  
Extreme Waves ◽  
Wave Direction ◽  
Coastal Structures ◽  
Extreme Wave ◽  
Wave Impact ◽  
The Past ◽  
Water Depths

Many deck-on-pile structures are located in shallow water depths at elevations low enough to be inundated by large waves during intense storms or tsunami. Many researchers have studied wave-in-deck loads over the past decade using a variety of theoretical, experimental, and numerical methods. Wave-in-deck loads on various pile supported coastal structures such as jetties, piers, wharves and bridges have been studied by Tirindelli et al. (2003), Cuomo et al. (2007, 2009), Murali et al. (2009), and Meng et al. (2010). All these authors analyzed data from scale model tests to investigate the pressures and loads on beam and deck elements subject to wave impact under various conditions. Wavein- deck loads on fixed offshore structures have been studied by Murray et al. (1997), Finnigan et al. (1997), Bea et al. (1999, 2001), Baarholm et al. (2004, 2009), and Raaij et al. (2007). These authors have studied both simplified and realistic deck structures using a mixture of theoretical analysis and model tests. Other researchers, including Kendon et al. (2010), Schellin et al. (2009), Lande et al. (2011) and Wemmenhove et al. (2011) have demonstrated that various CFD methods can be used to simulate the interaction of extreme waves with both simple and more realistic deck structures, and predict wave-in-deck pressures and loads.

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