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.

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.

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.

scholarly journals PERIODIC THEORY VELOCITY PREDICTION IN RANDOM WAVE

1978 ◽  
Vol 1 (16) ◽  
pp. 18
Author(s):  
John H. Nath ◽  
Koji Kobune
Keyword(s):  
Wave Theory ◽  
Ocean Waves ◽  
Periodic Wave ◽  
Random Wave ◽  
Random Waves ◽  
Wave Kinematics ◽  
Velocity Prediction ◽  
Water Particle Kinematics ◽  
Predictive Theory ◽  
Random Ocean Waves

Large waves in a series of random ocean waves are considered in the design of ocean structures. When random structural vibrations can be ignored, periodic wave theories are used to predict the water particle kinematics for a design wave even though the real wave is irregular. This paper presents the authors' first attempt to quantify the validity of using periodic wave theory for random waves. Measurements of maximum horizontal and vertical velocities were made in laboratory generated periodic and random waves. They compared favorably with predictions from periodic wave theories (even with Airy theory) particularly for the large waves in a series. Since the design wave concept is applied to the largest waves, the conclusion is that periodic wave theory may be adequate, providing an appropriate factor of safety is used to account for the differences between the actual maximum wave kinematics in nature and those in the predictive theory.

Effect of Applying 2nd Order Wave Theory on Pipeline Dynamic Response

2010 ◽  
Author(s):  
Hammam Zeitoun ◽  
Knut To̸rnes ◽  
Stuart Oldfield ◽  
Gary Cumming ◽  
Andrew Pearce ◽  
...  
Keyword(s):  
Dynamic Response ◽  
Wave Theory ◽  
Higher Order ◽  
Cost Driver ◽  
Design Solution ◽  
Linear Wave ◽  
Finite Elements Analysis ◽  
Linear Wave Theory ◽  
Wave Kinematics ◽  
Subsea Pipelines

Ensuring subsea pipelines on-bottom stability by determining the stabilisation requirements which will limit pipelines movement under extreme waves and currents is an essential aspect of subsea pipelines design. These requirements can be a major project cost driver in some locations around the world, where the designer is faced with severe metocean conditions. This is particularly the case when the selected design solution is associated with costly stabilisation requirements such as trenching, anchoring [14], rock dumping, or mattressing. An appreciation of the pipeline structural response, when exposed to waves and steady currents kinematics is fundamental to optimise the stabilisation solution. An advanced approach used to optimise stabilisation requirements is to use transient dynamic finite element analysis. The analysis is used to simulate the dynamic response of subsea pipelines exposed to near-seabed kinematics, due to a combination of steady currents and waves. Wave kinematics at the seabed are therefore an essential input to the analysis and will significantly affect both the hydrodynamic loads on the pipeline and the pipeline response. The typical method for generating the wave kinematics in a dynamic analysis has been based on calculating the near-bed velocities corresponding to a randomly generated seastate, using linear wave theory. It has been acknowledged that this calculation is likely to produce a conservative estimate of the positive wave velocities. An improved prediction of seabed kinematics can be achieved by using higher order wave theories. Application of higher order wave theories, results in changing the velocity magnitude under wave crests and troughs. This change in kinematics may result in a change of pipeline response. This paper investigates the effect of using 2nd order wave theory for predicting the kinematics on the pipeline dynamic response. Dynamic finite elements analysis is used for determining the pipeline response and to compare the pipeline response when using 2nd order wave theory and linear wave theory. The work presented in this paper was commissioned by Woodside and performed by J P Kenny Pty Ltd.

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 Comparison of Extreme Surface Elevation for Linear and Nonlinear Random Wave Theory for Offshore Structures

2018 ◽  
Vol 203 ◽  
pp. 01021
Author(s):  
Nurul 'Azizah Mukhlas ◽  
Noor Irza Mohd Zaki ◽  
Mohd Khairi Abu Husain ◽  
Gholamhossein Najafian
Keyword(s):  
Probabilistic Approach ◽  
Wave Theory ◽  
Offshore Structures ◽  
Random Wave ◽  
Linear Wave ◽  
Random Waves ◽  
Sea State ◽  
Higher Order Terms ◽  
Structural Responses ◽  
Nonlinear Random Wave

For offshore structural design, the load due to wind-generated random waves is usually the most important source of loading. While these structures can be designed by exposing them to extreme regular waves (100-year design wave), it is much more satisfactory to use a probabilistic approach to account for the inherent randomness of the wave loading. This method allows the statistical properties of the loads and structural responses to be determined, which is essential for the risk-based assessment of these structures. It has been recognized that the simplest wave generation is by using linear random wave theory. However, there is some limitation on its application as some of the nonlinearities cannot be explained when higher order terms are excluded and lead to underestimating of 100-year wave height. In this paper, the contribution of nonlinearities based on the second order wave theory was considered and being tested at a variety of sea state condition from low, moderate to high. Hence, it was proven that the contribution of nonlinearities gives significant impact the prediction of 100-year wave's design as it provides a higher prediction compared to linear wave theory.

Finite Element Analysis of Guyed Offshore Monotower Subjected to Extreme Environment in Malaysian Water

2014 ◽  
Vol 711 ◽  
pp. 535-541
Author(s):  
Mohd Affiq Jamaluddin ◽  
Mohd Shahir Liew ◽  
Kurian V. John ◽  
Lee Hsiu Eik
Keyword(s):  
Finite Element ◽  
Extreme Environments ◽  
Wave Theory ◽  
Extreme Environment ◽  
Response Analysis ◽  
Environmental Load ◽  
Free Standing ◽  
Element Analysis ◽  
Wave Kinematics ◽  
Fifth Order

This paper presents the finite element structural sensitivity analysis of a cable guyed monotower known as the Tarpon Monopod when subjected to extreme environments in Malaysian waters. A hydrodynamic loading and static platform response analysis is performed in SACS v5.3 to gauge the structural robustness in extreme Malaysian metocean conditions. A Stokes Fifth Order Wave Theory was employed to obtain wave kinematics and dynamics for load computation. The Tarpon Monopod design is reviewed generically. An actual platform located in 60m water depth within Malaysian waters is modelled for analysis. Four different guying cable scenarios are considered which are the fully guyed condition (three guy cables pinned), two guy cables condition (one wire loss), one guy cable condition (two wire loss) and free standing condition (total loss of guy wires) are presented. The environmental load sets are simulated at different headings using 45 degree steps. The results suggest that the structural caisson contributes little to the lateral stiffness of the platform. The Tarpon Monopod has little structural redundancy and its integrity is highly dependent on guy wire condition and environmental load headings.

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.

Non-Rotational-Loosening Behavior of Bolted Joint Constructed From Steel Tube and Plates

2006 ◽  
Author(s):  
Yasuo Fujioka ◽  
Koichi Hara ◽  
Toshiyuki Sawa
Keyword(s):  
Carbon Steel ◽  
External Load ◽  
Cumulative Effect ◽  
Steel Tube ◽  
Steel Plates ◽  
Random Waves ◽  
Axial Tension ◽  
First Case ◽  
Wave Profiles ◽  
Number Of Cycles

The reduction in axial tension was investigated in bolted joints, which comprise two hot-rolled steel plates and a carbon steel tube sandwiched between the plates. After tightening the bolts, vibration tests were carried in the following two cases. In the first case, flat-faced steel tubes without having any serrations on both ends of the tube were used, and the effect of wave profiles of the external load was investigated. These wave profiles are those of random waves, quasi-random waves that are obtained by only eliminating random waves with small amplitudes, and 7-step programmed waves generated from random waves. In each test, the maximum and the minimum amplitudes are the same. In the other case, the effect of the convex height of the serrations, which are cut on the end face of a tube, was investigated. In addition to the flat faces, the end faces of the tubes were serrated with three different heights for the purpose of comparison. In this case, the vibrations were applied only by means of sinusoidal waves. The effect of the wave profile on the external load is as follows. During the period of low cyclic loading, the bolt axial tension was reduced in the following order: the reduction was the minimum for the 7-step programmed waves, followed by the quasi-random waves, and was maximum for the random waves. As the number of cycles increases, the scattering range of bolt axial tensions corresponding to three types of waves becomes smaller. Furthermore, a comparison of this result with a fatigue test on mild steels indicates that the vibrating wave affects the reduction in axial tension, this is evident from the wave profiles and frequency. With regard to the convex height of the serration, after 106 cycles, the data shows that the lower the convex height, smaller is the reduction in the axial tension. The value of relative micro-slippage of the contact surfaces between the carbon steel tube and the steel plates is small at the sharp serrations. Therefore, the reduction in the axial tension is assumed to be mainly due to the cumulative effect of the plastic deformations.

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