An Engineering-Model for Extreme Wave-Induced Loads on Monopile Foundations

2017 ◽  
Author(s):  
Hans Fabricius Hansen ◽  
Henrik Kofoed-Hansen
Keyword(s):  
Water Level ◽  
Stream Function ◽  
Wave Theory ◽  
Breaking Waves ◽  
Gradual Transition ◽  
Wave Load ◽  
Sea State ◽  
Load Model ◽  
Wave Basin ◽  
Wave Induced

An extension of the classical Wheeler’s method is here presented and validated. Just as the Wheeler’s method, it relies solely on the measurement of surface elevation in a point to make predictions of the wave induced loads. These measurements may be made in the field, but more often they will be generated in a laboratory wave basin. The classical Wheeler stretching plus Morison load model is augmented by a slamming load model for steep near-breaking and breaking waves, based on work published earlier by Nestegård et.al. (2004). The new model thereby spans the entire range from non-breaking waves to severely breaking overturning waves with a gradual transition. The model has been validated against surface elevations and wave loads measured in a laboratory wave tank and is found to reproduce wave load distributions over a range of sea state conditions well. Examples are given for typical design sea state conditions for offshore wind turbines at exposed locations in Northern Europe. The loads are compared to loads obtained using the stream function wave theory in combination with the Morison’s equation. The stream function wave theory loads are found to generally be lower than the loads predicted using the simple wave load model presented here. This is the case even for mildly non-linear non-breaking waves but becomes much more pronounced for steep near-breaking and breaking waves. Another striking feature of the comparison to regular wave theory is the different distribution of loads. The stream function loads below still water level are often higher than the loads from the simple model, but much lower than the simple load model loads above still water level.

Effects of Cnoidal Wave-Induced Seepage on Vertical Breakwater Resting on Permeable Elastic Seabed

2014 ◽  
Vol 716-717 ◽  
pp. 284-288
Author(s):  
Jian Kang Yang ◽  
Hua Huang ◽  
Lin Guo ◽  
Jing Rong Lin ◽  
Qing Yong Zhu ◽  
...  
Keyword(s):  
Shallow Water ◽  
Wave Theory ◽  
Cnoidal Wave ◽  
Load Prediction ◽  
Wave Load ◽  
Seepage Pressure ◽  
Theoretical Investigations ◽  
Nonlinearity Effect ◽  
Wave Nonlinearity ◽  
Wave Induced

Theoretical investigations on cnoidal waves interacting with breakwater resting on permeable elastic seabed are presented in this paper. Based on the shallow water reflected wave theory and Biot consolidation theory on wave-induced seepage pressure, the analytical solutions to first order cnoidal wave reflection and wave-induced seepage pressure are obtained by the eigenfunction expansion approach. Numerical results are presented to show the effects of depth of water, breakwater geometry on cnoidal wave-induced seepage uplift force and overturning moment. Compared with Airy wave theory, in certain shallow water conditions, the shallow water wave theory can more effectively illustrate wave nonlinearity effect in wave load prediction.

scholarly journals WAVE-INDUCED SHOCK PRESSURES UNDER REAL SEA STATE CONDITIONS

1988 ◽  
Vol 1 (21) ◽  
pp. 173 ◽  
Author(s):  
Joachim Grune
Keyword(s):  
Peak Pressure ◽  
Field Measurements ◽  
Breaking Waves ◽  
Sea State ◽  
Pressure Time ◽  
Time Histories ◽  
Wave Induced

This paper deals with a study on shock pressures, which occur on sloping seadykes and revetments due to breaking waves. Results from field measurements are presented with respect to peak pressure values as well as to characteristics of pressure-time histories.

scholarly journals SEA TESTS OF A SPREAD-MOORED LANDING CRAFT

1964 ◽  
Vol 1 (9) ◽  
pp. 47
Author(s):  
J.T. O'Brien ◽  
B.J. Muga
Keyword(s):  
Theoretical Prediction ◽  
Water Level ◽  
Regular Waves ◽  
Sea State ◽  
Amplitude Response ◽  
Initial Tension ◽  
Single Location ◽  
Water Level Variations ◽  
Wave Induced ◽  
Motion Amplitude

Sea tests of motion and mooring force were conducted on an LST (Landing Ship Tank) of about 44O0 long tons displacement. The LST was spread-moored by six 2-1/16 inch and one 1-1/4 inch (port breast) stud-link chains in simple catenary configuration in about 45 feet of water in the open Gulf of Mexico about 65 air miles south of New Orleans, Louisiana. Water-level variations at a single location, ship rotations and accelerations, mooring force, and wind were measured in sea states of 2 and 4. Three recordings of 38, 62, 67 minutes duration were analyzed, using timeseries techniques to provide apparent amplitude-response operators for all of the ship's motions and seven mooring chains. Theoretical prediction of the operators using long crested regular waves was made also. In longitudinal plane, theory predicts motions 1/3 to 4 times and chain tensions 1/4 to 9 times those measured. The most probable maximum-motion amplitude responses in sea state 4 are found to be 1.7, 1.1, and 1.7 feet, respectively, in surge, sway and heave, and 3.4 and 0.5 degrees, respectively in pitch and yaw. Roll was measured only in sea-state 2 with a corresponding maximum of 2.1 degrees. Maximum wave-induced chain tensions in kips were: 85.1 and 48.0 in port and starboard bow chains respectively; 10.6 (sea state 2) and 19.7 in port and starboard breast chains; 13.9 and 4.3 in port and starboard quarter chains (sea state 2) and 9.7 in stem chain. Total tension in port bow chain was 116.1 kips (85.1 plus initial tension of 31.0 kips). Chain response operators vary directly with initial tension, whicl complicates design. It is concluded that: (i) moor was unbalanced, i.e., port bow chain took most of load; (ii) chains loaded lightly, e.g., maximum wave induced tension was 116 kips compared to new proof load of 300 kips for the particular chain, the port bow; (iii) water level should be measured at more than one point; (iv) discouragement over differences is balanced by encouragement over agreements between measurements and theoretical prediction of motion and chain tension; (v) toward improvement: Theory needs extension to include short crested waves and barge types; (vi) initial tension unique to problem of mooring design; (vii) propulsion devices may be needed toward maintaining design initial tension, especially in storm; (viii) if directional spectra had been measured and if theory involving short crested waves had been available and used, then discrepancies between observation and theory likely would have been less.

scholarly journals BREAKING WAVE CRITERIA; A STUDY EMPLOYING A NUMERICAL WAVE THEORY

1968 ◽  
Vol 1 (11) ◽  
pp. 8 ◽  
Author(s):  
Robert G. Dean
Keyword(s):  
Stream Function ◽  
Nonlinear Wave ◽  
Wave Spectrum ◽  
Small Diameter ◽  
Wave Theory ◽  
Breaking Waves ◽  
Fundamental Period ◽  
Breaking Wave ◽  
Engineering Design Problems ◽  
Wide Range

Although it is well recognized that wave systems in nature are irregular, comprising a spectrum of fundamental periods, there is still a need for improving our understanding of near-breaking nonlinear wave systems which contain a single fundamental period. For example, most of the shallow water design situations and other cases including forces on small diameter structures in which drag forces predominate are more directly treated in terms of a "design wave" rather than a wave spectrum. This situation is contrasted to many important engineering design problems in which the dynamics of the system are paramount; for example, in the case of a moored drilling vessel. Finally, one may reasonably expect that accurate solutions to the problem of nonlinear wave systems with a single fundamental period will lend insight regarding productive approaches to the more realistic problem of a spectrum of nonlinear waves. This paper investigates the applicability of the stream function wave theory1 for the representation of breaking and near-breaking waves. This particular problem has received little attention, although considerable progress has occurred on two related problems: 1. The development of wave theories covering a wide range of relative water depths and wave heights, and 2. The development of wave theories which apply at breaking conditions. In general, although these theories may be applicable for the limiting wave conditions, their basis of derivation is such that they cannot be extended to non-breaking waves. The purpose of the present investigation, then, is to establish whether or not the stream function wave theory can be applied to span the range extending up to breaking conditions.

Wave-Deck-Load Analysis for a Jack-Up Platform

2009 ◽  
Author(s):  
Thomas E. Schellin ◽  
Milovan Peric´ ◽  
Ould el Moctar
Keyword(s):  
Stokes Equations ◽  
Volume Fraction ◽  
Wave Theory ◽  
Breaking Waves ◽  
Design Parameters ◽  
Wave Direction ◽  
Wave Load ◽  
Two Phase ◽  
Highly Nonlinear ◽  
Jack Up

The paper analyzes freak wave-in-deck load effects on a typical three-leg jack-up platform stationed in the North Sea. Considered were cases where the air gap is small and the hull is subject to impact-related wave-in-deck loads. Wave load predictions were based on the use of a validated CFD code that solves the Reynolds-averaged Navier-Stokes equations. The code relies on the interface-capturing technique of the volume-of-fluid type to account for highly nonlinear wave effects. It computes the two-phase flow of water and air to describe the physics associated with complex free-surface shapes with breaking waves and air trapping, hydrodynamic phenomena that had to be considered to yield reliable predictions. Stokes 5th order wave theory was used to initialize volume fraction of water and velocity distribution in the solution domain, as well as to prescribe time-dependent boundary conditions at inlet and outlet boundaries. It was demonstrated that CFD methods can be used to predict the load phenomena under extreme wave conditions and thus serve as a valuable tool for both initial design and subsequent assessment of safety aspects. In particular, we demonstrated that effects of different operating and design parameters on wave-in-deck loads, such as wave direction, wave height, wave period, and wind speed, can be evaluated with an affordable computing effort using personal computers.

Cnoidal Wave-Induced Seepage Forces on Large Porous Vertical Circular Cylinder Resting on Porous Elastic Seabed

2014 ◽  
Vol 501-504 ◽  
pp. 2060-2064
Author(s):  
Hua Huang ◽  
Rui Zhi Chen ◽  
Qi Li ◽  
Jie Min Zhang ◽  
Lin Guo
Keyword(s):  
Circular Cylinder ◽  
Shallow Water ◽  
Water Wave ◽  
Wave Theory ◽  
The Body ◽  
Cnoidal Wave ◽  
Wave Load ◽  
Seepage Pressure ◽  
Shallow Water Wave ◽  
Wave Induced

The influence of the porosity of the structure on the shallow water wave-Induced seepage force on the bottom of porous vertical circular cylinder resting on porous elastic seabed has been investigated. Based on the shallow water diffracted wave theory and Biot consolidation theory on wave-induced seepage pressure, the analytical solutions to first order cnoidal wave diffraction by porous vertical circular cylinder and wave-induced seepage pressure are obtained by the eigenfunction expansion approach. Numerical results show that cnoidal wave-induced uplift and moment may have same order of magnitude as the horizontal cnoidal wave force and moment , and the body porosity of the structure may lead to a reduction both in direct cnoidal wave forces and in the cnoidal wave induced seepage moment. Compared with Airy wave theory, in certain shallow water conditions, the shallow water wave theory can more effectively reflect wave nonlinearity effect in wave load prediction.

scholarly journals NON-BREAKING AND BREAKING WAVE LOADS ON A COOLING WATER OUTFALL

1978 ◽  
Vol 1 (16) ◽  
pp. 148
Author(s):  
G.R. Mogridge ◽  
W.W. Jamieson
Keyword(s):  
Water Level ◽  
Cooling Water ◽  
High Water ◽  
Breaking Waves ◽  
Irregular Waves ◽  
Scale Model ◽  
Breaking Wave ◽  
Wave Loads ◽  
Eastern Canada ◽  
Spilling Breakers

Cooling water from a power generating station in Eastern Canada is pumped to an outfall and distributed into the ocean through discharge ports in the sidewalls of a diffuser cap. The cap is essentially a shell-type structure consisting of a submerged circular cylinder 26.5 ft in diameter and 14 ft high. It is located in 25 ft of water at low water level and 54 ft at high water level. Horizontal forces, vertical forces and overturning moments exerted by waves on a 1:36 scale model of the diffuser cap were measured with and without cooling water discharging from the outfall. Tests were run with regular and irregular waves producing both non-breaking and breaking wave loads on the diffuser cap. The overturning moments measured on the diffuser cap were up to 150 percent greater than those on a solid submerged cylinder sealed to the seabed. Unlike sealed cylinders, all of the wave loads measured on the relatively open structure reached maximum values at approximately the same time. The largest wave loads were measured on the diffuser structure when it was subjected to spilling breakers at low water level. For a given wave height, the spilling breakers caused wave loads up to 100 percent greater than those due to non-breaking waves.

scholarly journals RUN-UP OF PERIODIC WAVES ON BEACHES OF NON-UNIFORM SLOPE

1984 ◽  
Vol 1 (19) ◽  
pp. 23 ◽  
Author(s):  
Yoshinobu Ogawa ◽  
Nobuo Shuto
Keyword(s):  
Experimental Data ◽  
Wave Theory ◽  
Breaking Waves ◽  
Lagrangian Description ◽  
Periodic Waves ◽  
Swash Zone ◽  
Slope Method ◽  
Long Wave ◽  
Run Up ◽  
Better Than

Run-up of periodic waves on gentle or non-uniform slopes is discussed. Breaking condition and run-up height of non-breaking waves are derived "by the use of the linear long wave theory in the Lagrangian description. As to the breaking waves, the width of swash zone and the run-up height are-obtained for relatively gentle slopes (less than 1/30), on dividing the transformation of waves into dissipation and swash processes. The formula obtained here agrees with experimental data better than Hunt's formula does. The same procedure is applied to non-uniform slopes and is found to give better results than Saville's composite slope method.

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.

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