Investigation of Shallow Water Kinematics and Local Loading Effects on Reliability of Minimum Structures

2001 ◽  
Vol 124 (1) ◽  
pp. 41-47
Author(s):  
Suhartodjo Tuty ◽  
Mark J. Cassidy ◽  
Beverley F. Ronalds
Keyword(s):  
Shallow Water ◽  
Stream Function ◽  
Function Theory ◽  
Strong Relationship ◽  
Wave Theory ◽  
Wave Crest ◽  
Linear Wave ◽  
North West ◽  
Wave Kinematics ◽  
The North

In shallow water, and specifically for minimum structures, the critical wave height exponent α has been shown to vary significantly with structural configuration. Because of the strong relationship to the wave kinematics, α is also sensitive to the wave theory chosen. The North West Shelf offshore Australia has numerous minimum structures located in relatively shallow water, which requires non-linear wave theory. In the near-breaking condition, estimation of the wave crest kinematics is difficult, with Stream Function theory being the most widely used. However, various other wave theories and nonlinear numerical techniques have been developed to predict wave kinematics for shallow water conditions. The following wave theories are compared: regular Stream Function theory, Cnoidal wave theory, Stokes’ theory, NewWave theory, and a second-order correction to NewWave theory. Kinematics, loads and α results are presented for a cylinder in three different water depths.

Experiments and Analysis of Laboratory Generated Steep Waves

2002 ◽  
Author(s):  
Subrata K. Chakrabarti
Keyword(s):  
Stream Function ◽  
Function Theory ◽  
Wave Theory ◽  
Higher Order ◽  
Random Waves ◽  
Design Guideline ◽  
Wave Tank ◽  
Wave Kinematics ◽  
Wave Profiles ◽  
Steep Waves

In many offshore locations, storm generated steep waves are common and the survival of offshore structures in their presence is an important design condition. The design environment in depth-limited waters often includes waves of breaking and near-breaking conditions, in which currents may be present. Experiments were carried out in a wave tank with simulated steep waves with and without steady in-line current in which the wave profiles and the corresponding kinematics were simultaneously measured. The waves included both regular and random waves and often approached the breaking wave height for the water depth. These waves were analyzed by higher-order wave theory. In particular, the regular waves were simulated by the regular and irregular stream function theory. Especially steep wave profiles within the random waves were computed using the irregular stream function theory. The theory allows inclusion of steady current in its formulation for computation of wave kinematics. The correlation of the measured wave kinematics with the higher-order stream function wave theory showed that the wave theory could predict the kinematics of these steep waves (with and without the presence of current) well. However, in breaking waves, the vertical water particle velocity was not predicted well, specially near the trough. The effect of breaking and near-breaking steep waves on a fixed vertical caisson was also studied. The forces measured on the vertical caisson from the wave tank testing were analyzed to determine the effect of these waves and currents on the forces. It was found that the measured forces (and overturning moments) on the caisson model matched fairly well by the proper choice of force coefficients from the design guideline and the nonlinear stream function theory of appropriate order.

Measurement and Analysis of Laboratory Generated Steep Waves

2003 ◽  
Vol 125 (1) ◽  
pp. 17-24
Author(s):  
Subrata K. Chakrabarti
Keyword(s):  
Stream Function ◽  
Function Theory ◽  
Wave Theory ◽  
Higher Order ◽  
Random Waves ◽  
Design Guideline ◽  
Wave Tank ◽  
Wave Kinematics ◽  
Wave Profiles ◽  
Steep Waves

In many offshore locations, storm generated steep waves are common and the survival of offshore structures in their presence is an important design condition. The design environment in depth-limited waters often includes waves of breaking and near-breaking conditions, in which currents may be present. Experiments were carried out in a wave tank with simulated steep waves with and without steady in-line current in which the wave profiles and the corresponding kinematics were simultaneously measured. The waves included both regular and random waves and often approached the breaking wave height for the water depth. These waves were analyzed by higher-order wave theory. In particular, the regular waves were simulated by the regular and irregular stream function theory. Especially steep wave profiles within the random waves were computed using the irregular stream function theory. The theory allows inclusion of steady current in its formulation for computation of wave kinematics. The correlation of the measured wave kinematics with the higher-order stream function wave theory showed that the wave theory could predict the kinematics of these steep waves (with and without the presence of current) well. However, in breaking waves, the vertical water particle velocity was not predicted well, especially near the trough. The effect of breaking and near-breaking steep waves on a fixed vertical caisson was also studied. The forces measured on the vertical caisson from the wave tank testing were analyzed to determine the effect of these waves and currents on the forces. It was found that the measured forces (and overturning moments) on the caisson model matched fairly well by the proper choice of force coefficients from the design guideline and the nonlinear stream function theory of appropriate order.

Irregular Wave Forces on Monopile Foundations: Effect of Full Nonlinearity and Bed Slope

2011 ◽  
Author(s):  
Signe Schlo̸er ◽  
Henrik Bredmose ◽  
Harry B. Bingham
Keyword(s):  
Stream Function ◽  
Function Theory ◽  
Wave Train ◽  
Wave Theory ◽  
Irregular Waves ◽  
Wave Forces ◽  
Linear Wave ◽  
Irregular Wave ◽  
Bed Slope ◽  
Force Profiles

Forces on a monopile from a nonlinear irregular unidirectional wave model are investigated. Two seabed profiles of different slopes are considered. Morison’s equation is used to investigate the forcing from fully nonlinear irregular waves and to compare the results with those obtained from linear wave theory and with stream function wave theory. The latter of these theories is only valid on a flat bed. The three predictions of wave forces are compared and the influence of the bed slope is investigated. Force-profiles of two selected waves from the irregular wave train are further compared with the corresponding force-profiles from stream function theory. The results suggest that the nonlinear irregular waves give rise to larger extreme wave forces than those predicted by linear theory and that a steeper bed slope increases the wave forces both for linear and nonlinear waves. It is further found that stream function theory in some cases underestimate the wave forces acting on the monopile.

scholarly journals The Sjælland Fjelde Formation: a new Ordovician formation from eastern North Greenland

1986 ◽  
Vol 132 ◽  
pp. 27-37
Author(s):  
J.R Ineson ◽  
J.S Peel ◽  
M.P Smith
Keyword(s):  
Shallow Water ◽  
North West ◽  
Middle Ordovician ◽  
The North ◽  
New Formation ◽  
North Greenland

The name Sjælland Fjelde Formation is introduced for a varied sequence of shallow-water platform dolomites and dolomitic limestones, about 105 m in thickness, in Kronprins Christian Land, eastern North Greenland. The new formation lies between the previously described Wandel Valley and Børglum River Formations. Conodont faunas indicate that the Sjælland Fjelde Formation is of Middle to earliest Late Whiterockian (early Middle Ordovician) age and that it can be eorrelated with the upper part of the Wandel Valley Formation of Peary Land to the north-west.

Conditional Short-Crested Second Order Waves in Shallow Water and With Superimposed Current

2004 ◽  
Author(s):  
Jo̸rgen Juncher Jensen
Keyword(s):  
Shallow Water ◽  
Wave Spectrum ◽  
Ocean Waves ◽  
Offshore Structures ◽  
Second Order ◽  
Stokes Wave ◽  
Wave Crest ◽  
Wave Kinematics ◽  
Wave Approach ◽  
Non Linear

For bottom-supported offshore structures like oil drilling rigs and oil production platforms, a deterministic design wave approach is often applied using a regular non-linear Stokes’ wave. Thereby, the procedure accounts for non-linear effects in the wave loading but the randomness of the ocean waves is poorly represented, as the shape of the wave spectrum does not enter the wave kinematics. To overcome this problem and still keep the simplicity of a deterministic approach, Tromans, Anaturk and Hagemeijer (1991) suggested the use of a deterministic wave, defined as the expected linear Airy wave, given the value of the wave crest at a specific point in time or space. In the present paper a derivation of the expected second order short-crested wave riding on a uniform current is given. The analysis is based on the second order Sharma and Dean shallow water wave theory and the direction of the main wind direction can make any direction with the current. Numerical results showing the importance of the water depth, the directional spreading and the current on the conditional mean wave profile and the associated wave kinematics are presented. A discussion of the use of the conditional wave approach as design waves is given.

The Interaction Between Strength and Fatigue Reliability for a Minimum Structure in Shallow Water

2003 ◽  
Vol 125 (4) ◽  
pp. 281-287 ◽  
Author(s):  
G. K. Cole ◽  
B. F. Ronalds ◽  
E. Fakas
Keyword(s):  
Shallow Water ◽  
Wave Climate ◽  
Offshore Structures ◽  
Life Extension ◽  
Fatigue Reliability ◽  
North West ◽  
The North ◽  
Local Wave ◽  
Structural Inspection ◽  
The Relationship

The relationship between strength and fatigue reliability of an offshore platform is an important aspect in the setting of appropriate structural inspection programs, as well as providing valuable information when considering the life extension of ageing offshore structures. This paper uses the example of a braced monopod to examine the interaction between strength and fatigue reliability for shallow-water platforms subjected to wave climates typical of the North West Shelf of Australia. The central role played by the local wave climate in both the strength and fatigue response of the structure is investigated. The probability of fatigue failure at the critical location was found to be approximately three orders of magnitude less than the overall probability of storm overload failure. This inequity between strength and fatigue reliability raises the possibility of redirecting inspection effort toward higher-risk threats such as accidental damage and corrosion. The potential for further optimizing the total life-cycle costs of new offshore structures is also briefly discussed.

scholarly journals DIRECTIONAL WAVE SPECTRA AND WAVE KINEMATICS IN HURRICANES CARMEN AND ELOISE

1980 ◽  
Vol 1 (17) ◽  
pp. 34
Author(s):  
G.Z. Forristall ◽  
E.G. Ward ◽  
V.J. Cardone
Keyword(s):  
Wave Height ◽  
Local Equilibrium ◽  
Wave Theory ◽  
Electromagnetic Current ◽  
Linear Wave ◽  
Directional Spectrum ◽  
Wave Kinematics ◽  
Storm Waves ◽  
Velocity Probability ◽  
Realistic Description

A realistic description of the kinematics of hurricane waves requires that the directional spectrum of the sea be known. Models for hindcasting the directional spectrum have existed for some time, but there has been a dearth of data available for checking the directional characteristics of the hindcasts. Hurricane Carmen in 1974 and hurricane Eloise in 1975 passed reasonably close to platforms in the Gulf of Mexico which were instrumented with wave staffs and electromagnetic current meters. The maximum recorded significant wave height was 29 feet. The simultaneous measurements of wave height and water particle velocity permitted estimates of the directional spectra to be made. The estimated directional spectra are complicated and often bimodal in frequency and direction. Swell from the center of the storm can propagate in directions over 90 degrees away from the direction of the shorter waves which are in local equilibrium with the wind. The hindcast model reproduces these directional features remarkably well. The measurements of wave kinematics also permitted tests of the accuracy of wave theories in high and confused storm waves. All of the unidirectional theories tested showed a bias toward overpredicting the velocity under the highest waves. However, the kinetic energy in the velocity components and the velocity probability distribution could be found to within a ten percent scatter using directional spectral concepts and linear wave theory.

Crest-Height Distribution in Nonlinear Random Wave

2009 ◽  
Author(s):  
Cuilin Li ◽  
Dingyong Yu ◽  
Yangyang Gao ◽  
Junxian Yang
Keyword(s):  
Nonlinear Wave ◽  
Wave Theory ◽  
Distribution Functions ◽  
Theoretical Distribution ◽  
Distribution Model ◽  
Stokes Wave ◽  
Wave Crest ◽  
Linear Wave ◽  
Height Distribution ◽  
Crest Height

Many empirical and theoretical distribution functions for wave crest heights have been proposed, but there is a lack of agreement. With the development of ocean exploitation, waves crest heights represent a key point in the design of coastal structures, both fixed and floating, for shoreline protection and flood prevention. Waves crest height is the dominant parameter in assessing the likelihood of wave-in-deck impact and its resulting severe damage. Unlike wave heights, wave crests generally appear to be affected by nonlinearities; therefore, linear wave theory could not be satisfied to practical application. It is great significant to estimate a new nonlinear wave crest height distribution model correctly. This paper derives an approximation distribution formula based on Stokes wave theory. The resulting theoretical forms for nonlinear wave crest are compared with observed data and discussed in detail. The results are shown to be in good agreement. Furthermore, the results indicate that the new theoretical distribution has more accurate than other methods presented in this paper (e.g. Rayleigh distribution and Weibull distribution) and appears to have a greater range of applicability.

Shallow Water Muddy Sands of the North-West Atlantic Ocean

2019 ◽  
pp. 128-163
Author(s):  
Sarah A. Woodin ◽  
Susan S. Bell ◽  
Jon Grant ◽  
Paul V. R. Snelgrove ◽  
David S. Wethey
Keyword(s):  
Atlantic Ocean ◽  
Shallow Water ◽  
North West ◽  
The North

scholarly journals Characteristics of Positive Surges in a Rectangular Channel

Water ◽  
2018 ◽  
Vol 10 (10) ◽  
pp. 1473 ◽  
Author(s):  
Feidong Zheng ◽  
Yun Li ◽  
Guoxiang Xuan ◽  
Zhonghua Li ◽  
Long Zhu
Keyword(s):  
Rectangular Channel ◽  
Experimental Studies ◽  
Wave Theory ◽  
Progressive Increase ◽  
Wave Crest ◽  
Linear Wave ◽  
Sudden Increase ◽  
Initial Profile ◽  
Increasing Trend ◽  
Flow Motion

A positive surge is an unsteady open channel flow motion characterized by an increase of flow depth. In previous experimental studies, a positive surge was typically induced by either a sudden increase of discharge in a channel or by the rapid closure of a downstream sluice gate, thus leading to a steep initial profile. However, in many instances, the evolution of a positive surge is of a progressive manner (e.g., in the downstream navigation canal during the emptying operation of lock chambers). In the present work, the inception and development of a positive surge induced by a progressive increase of discharge was investigated in a rectangular channel with a smooth bed. Both undular and breaking surges were studied. The results demonstrate that the maximum wave height at the first wave crest of an undular surge is in very close agreement with the McCowan theory. Additionally, the wave amplitude essentially shows a linearly increasing trend with an increasing surge Froude number up to Fr0 = 1.26 to 1.28, whereas it tends to suggest a power law reduction for larger surge Froude numbers. Moreover, the dispersion of undular surges is consistent with the linear wave theory only for surge Froude numbers close to unity. Overall, the present study demonstrates the unique features of positive surges induced by a progressive increase of discharge.

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