Breaking Wave Kinematics and Resulting Slamming Pressures on a Vertical Column

2012 ◽  
Author(s):  
Carl Trygve Stansberg ◽  
Kjetil Berget ◽  
Mateusz Graczyk ◽  
Chittiappa Muthanna ◽  
Csaba Pakozdi
Keyword(s):  
Breaking Waves ◽  
Full Scale ◽  
Breaking Wave ◽  
Offshore Platforms ◽  
Scaled Model ◽  
Vertical Column ◽  
Wave Kinematics ◽  
Annual Probability ◽  
Column Wall ◽  
Particle Velocities

A need has been identified to improve the knowledge about extreme slamming loads from breaking waves on vertical columns, such as offshore platforms and wind turbine foundations. Due to strongly nonlinear physical mechanisms and large statistical variability, more and improved experimental data are needed, as well as better qualified design procedures. In this paper, model test data and CFD simulations from a recent study with a fixed vertical column are compared and investigated in more detail. Selected individual extreme slamming events due to energetic breaking waves in 1:40 and 1:125 scaled model tests are presented and considered. Waves correspond approximately to extreme breaking wave occurrences in steep energetic sea states with 10-4 annual probability in the Norwegian sector. Slamming pressures on the column wall are measured in time and space by means of a 7 × 7 pressure sensor array covering 19m2 (full scale). Significant spatial variations are observed. When spatially averaged over the array, the observed highest pressures are typically in the range 1MPa–3MPa (full scale), while smaller measuring areas give higher values. This compares roughly to levels found from recent results in the literature; although exact comparison is difficult due to statistical uncertainty issues. Experiences obtained from parallel CFD and PIV activities are also compared to the experiments, from which free-surface particle velocities up to 25m/s (full scale) are estimated in the worst cases. Finally, a simple empirical formula for a slamming coefficient depending on the actual pressure integration area is suggested based on the results.

scholarly journals FIBER-OPTICAL MEASUREMENTS OF MECHANICALLY AND CHEMICALLY DISPERSED OIL IN WATER

1985 ◽  
Vol 1985 (1) ◽  
pp. 67-77
Author(s):  
Jan Nilsen
Keyword(s):  
Breaking Waves ◽  
Full Scale ◽  
Optical Measurements ◽  
Breaking Wave ◽  
Mean Values ◽  
Oil Emulsion ◽  
Dispersed Oil ◽  
Fiber Optical ◽  
Different Depths ◽  
Beam Transmittance

ABSTRACT A new fiber optical transmittance meter has been designed to measure oil concentrations in water. No electronic components are placed in the underwater sensor housings which are made relatively small to avoid influence on the surroundings. Both the light emitting diode and the receiver are synchroned demodulated. This together with AC-linked amplifiers in both the sender and receiver electronics give appropriate noise reduction. A transmittance meter was calibrated in a 1,0000:1 laboratory tank. Results from this calibration with mechanically dispersed Ekofisk crude oil and Reginol SAE 30 water-in-oil emulsion are presented. It was found that the beam attenuation increased almost exponentially up to a certain oil concentration which was a function of the particle size distribution and length of the waterpath of the light beam. The time changes in the concentration of dispersed oil under breaking waves in a wave tank in the laboratory have been measured at different depths below the surface. It was found that the oil concentrations decreased almost exponentially below the surface down to a depth approximately equal to the height of the breaking wave. During a full scale field experiment with oil in the North Sea in May 1982 the oil leakage under two different oil booms was measured with a beam transmittance meter at 1.5 m depth about 5 m behind the oil booms. Two-minute mean values of the beam transmittance were recorded. The measurements showed large variations in the oil concentrations behind the oil booms. Transmittance meter measurements also were carried out during offshore full scale tests with different chemical dispersants. The instruments have been towed at different depths from small boats passing through the slicks, measuring oil concentrations continuously at different levels simultaneously under the slicks. At Frigg in June 1984, the concentration of dispersed oil at 1, 2, and 3 m depth varied from (approximately) 0 to 60 ppm under one slick.

On Modelling Kinematics of Steep Irregular Seaway and Freak Waves

2008 ◽  
Author(s):  
Gu¨nther F. Clauss ◽  
Florian Stempinski ◽  
Robert Stu¨ck
Keyword(s):  
Water Waves ◽  
Wave Train ◽  
Breaking Waves ◽  
Breaking Wave ◽  
Coupling Mechanism ◽  
Fast Method ◽  
Freak Waves ◽  
Irregular Wave ◽  
Wave Kinematics ◽  
Stokes Waves

The realistic modelling of velocity and pressure fields in steep, irregular seaways is still a challenging task, especially when extreme events such as freak waves are under investigation. Conventional wave theories provide fast and reliable results while CFD-codes based on RANSE or potential theory are gaining more acceptance for simulating water waves even though they are still considerably time consuming. This paper presents an approach to approximate irregular wave trains with known surface elevations by interacting Stokes waves of up to third order. This is a fast method to determine the wave potential of wind generated waves for long lasting wave registrations with arbitrary origin. The technique is applied to a steep breaking wave package as well as to a realization of a wave train in a wave tank (scale 1:120) which contain a measured extreme wave sequence. Here, special attention is paid to the distinction between the kinematics of the wave crests in extremely high waves and their surrounding irregular wave field. The predicted wave kinematics are validated by experiments employing particle velocity measurements (by Laser Doppler Velocimetry) as well as by pressure recordings. Kinematics of breaking waves are not covered by concurrent analytical wave theories. To address this deficiency a coupling mechanism between a conventionally determined velocity field with a RANSE/VoF-method is applied.

scholarly journals Preliminary Evaluation of the Effectiveness of Using Artificial Reefs to Reduce Breaking Wave Impact on Offshore Structures

2017 ◽  
Author(s):  
Charlotte Loedsen Andersen ◽  
Ida Skov Milthers ◽  
Julie Caroee Kristoffersen ◽  
Christos Thomas Georgakis ◽  
Longbin Tao
Keyword(s):  
Artificial Reef ◽  
Breaking Waves ◽  
Offshore Structures ◽  
Artificial Reefs ◽  
Breaking Wave ◽  
Preliminary Evaluation ◽  
Offshore Platforms ◽  
Wave Impact ◽  
Maximum Displacement ◽  
The People

Waves breaking on offshore platforms can have damaging consequences for the structure and for the safety of the people working on it. Recent unexpected extreme wave events have shown the effects that breaking waves have on offshore platforms. In this paper, the results from a scaled experimental investigation conducted the Newcastle University wind, wave and current tank, are presented. With these tests, the effectiveness of using artificial reefs to avoid or lessen the effects of breaking wave activity is examined. Four different types of artificial reefs are tested and their effects are compared to a reference test with no artificial reef. The comparison is based on the changes of the size and location of the maximum wave amplitude, the maximum displacement of a scaled platform and the artificial reef’s ability to dissipate wave energy. Overall, the results show that placing the rectangular reef in the tank produces the most promising results. However, it is also shown that placing any one of the artificial reefs in the tank will affect a change in the wave motion. Thus, this investigation shows that the use of an artificial reef could be a step in securing a higher level of protection for personnel and operations.

Comparison of Breaking Wave Kinematics From Numerical Simulations With PIV Measurements

2017 ◽  
Author(s):  
Bülent Düz ◽  
Rene Lindeboom ◽  
Jule Scharnke ◽  
Joop Helder ◽  
Henry Bandringa
Keyword(s):  
Numerical Simulations ◽  
Wave Model ◽  
Breaking Waves ◽  
Research Area ◽  
Breaking Wave ◽  
Strongly Nonlinear ◽  
Wave Kinematics ◽  
Image Velocimetry ◽  
Measurement Results ◽  
Spilling Breakers

Breaking waves have been a popular research area among scientists and engineers since they present a strongly nonlinear and turbulent phenomenon. When these waves encounter an offshore or coastal structure, they exert significant amount of loads and stresses, which may result in a catastrophic consequence. Therefore, it is of utmost importance to study breaking waves and associated phenomena. Inspired by this need, in a recent MARIN experiment kinematics of breaking waves were measured with Particle Image Velocimetry (PIV). Among different types of breaking waves, spilling breakers were selected in this initial campaign. First, a summary of the measurement results will be given. These results will then be used for validation of a Computational Fluid Dynamics (CFD) tool. In numerical simulations two methods were followed in order to reproduce the focused wave: in the first method, the CFD tool was coupled to a nonlinear wave model, and in the second method an iterative scheme was used with the CFD tool. Results from these methods were then compared with the measurements.

scholarly journals EXPERIMENTAL RESULTS OF BREAKING WAVE IMPACT ON A VERTICAL WALL WITH AN OVERHANGING HORIZONTAL CANTILEVER SLAB

2011 ◽  
Vol 1 (32) ◽  
pp. 26
Author(s):  
Dogan Kisacik ◽  
Peter Troch ◽  
Philippe Van Bogaert
Keyword(s):  
Wave Height ◽  
Water Depth ◽  
Vertical Wall ◽  
Breaking Waves ◽  
Wave Period ◽  
Breaking Wave ◽  
Wave Impact ◽  
Scaled Model ◽  
Physical Experiments ◽  
Horizontal Part

Physical experiments (at a scale of 1/20) are carried out using a vertical wall with horizontal cantilevering slab. Tests are conducted for a range of values of water depth, wave period and wave height. A parametric analysis of measured forces (Fh and Fv) both on the vertical and horizontal part of the scaled model respectively is conducted. The highest impact pressure and forces are measured in the case of breaking waves with a small air trap. Maximum pressures are measured around SWL and at the corner of the scaled model. The horizontal part of the scaled model is more exposed to impact waves than the vertical part. Fh and Fv are very sensitive for the variation of water depth (hs) and wave height (H) while variation of wave period (T) has a rather limited effect.

scholarly journals Characteristics of Breaking Wave Forces on Piles over a Permeable Seabed

2021 ◽  
Vol 9 (5) ◽  
pp. 520
Author(s):  
Zhenyu Liu ◽  
Zhen Guo ◽  
Yuzhe Dou ◽  
Fanyu Zeng
Keyword(s):  
Wave Breaking ◽  
Stokes Equations ◽  
Slope Angle ◽  
Wave Force ◽  
Breaking Waves ◽  
Offshore Wind ◽  
Secondary Wave ◽  
Wave Forces ◽  
Breaking Wave ◽  
Breaking Wave Forces

Most offshore wind turbines are installed in shallow water and exposed to breaking waves. Previous numerical studies focusing on breaking wave forces generally ignored the seabed permeability. In this paper, a numerical model based on Volume-Averaged Reynolds Averaged Navier–Stokes equations (VARANS) is employed to reveal the process of a solitary wave interacting with a rigid pile over a permeable slope. Through applying the Forchheimer saturated drag equation, effects of seabed permeability on fluid motions are simulated. The reliability of the present model is verified by comparisons between experimentally obtained data and the numerical results. Further, 190 cases are simulated and the effects of different parameters on breaking wave forces on the pile are studied systematically. Results indicate that over a permeable seabed, the maximum breaking wave forces can occur not only when waves break just before the pile, but also when a “secondary wave wall” slams against the pile, after wave breaking. With the initial wave height increasing, breaking wave forces will increase, but the growth can decrease as the slope angle and permeability increase. For inclined piles around the wave breaking point, the maximum breaking wave force usually occurs with an inclination angle of α = −22.5° or 0°.

scholarly journals Influence of the Spatial Pressure Distribution of Breaking Wave Loading on the Dynamic Response of Wolf Rock Lighthouse

2021 ◽  
Vol 9 (1) ◽  
pp. 55
Author(s):  
Darshana T. Dassanayake ◽  
Alessandro Antonini ◽  
Athanasios Pappas ◽  
Alison Raby ◽  
James Mark William Brownjohn ◽  
...  
Keyword(s):  
Dynamic Response ◽  
Pressure Distribution ◽  
Distinct Element ◽  
Breaking Waves ◽  
Breaking Wave ◽  
Wave Loading ◽  
Wave Impact ◽  
Pressure Distributions ◽  
Impact Area ◽  
The Impact

The survivability analysis of offshore rock lighthouses requires several assumptions of the pressure distribution due to the breaking wave loading (Raby et al. (2019), Antonini et al. (2019). Due to the peculiar bathymetries and topographies of rock pinnacles, there is no dedicated formula to properly quantify the loads induced by the breaking waves on offshore rock lighthouses. Wienke’s formula (Wienke and Oumeraci (2005) was used in this study to estimate the loads, even though it was not derived for breaking waves on offshore rock lighthouses, but rather for the breaking wave loading on offshore monopiles. However, a thorough sensitivity analysis of the effects of the assumed pressure distribution has never been performed. In this paper, by means of the Wolf Rock lighthouse distinct element model, we quantified the influence of the pressure distributions on the dynamic response of the lighthouse structure. Different pressure distributions were tested, while keeping the initial wave impact area and pressure integrated force unchanged, in order to quantify the effect of different pressure distribution patterns. The pressure distributions considered in this paper showed subtle differences in the overall dynamic structure responses; however, pressure distribution #3, based on published experimental data such as Tanimoto et al. (1986) and Zhou et al. (1991) gave the largest displacements. This scenario has a triangular pressure distribution with a peak at the centroid of the impact area, which then linearly decreases to zero at the top and bottom boundaries of the impact area. The azimuthal horizontal distribution was adopted from Wienke and Oumeraci’s work (2005). The main findings of this study will be of interest not only for the assessment of rock lighthouses but also for all the cylindrical structures built on rock pinnacles or rocky coastlines (with steep foreshore slopes) and exposed to harsh breaking wave loading.

Guidelines for CFD Simulations of Spar VIM

2013 ◽  
Author(s):  
Charles Lefevre ◽  
Yiannis Constantinides ◽  
Jang Whan Kim ◽  
Mike Henneke ◽  
Robert Gordon ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Test Data ◽  
Model Test ◽  
Model Tests ◽  
Full Scale ◽  
Mooring System ◽  
Time Step ◽  
Cfd Simulations ◽  
Scaled Model ◽  
Sway Motion

Vortex-Induced Motion (VIM), which occurs as a consequence of exposure to strong current such as Loop Current eddies in the Gulf of Mexico, is one of the critical factors in the design of the mooring and riser systems for deepwater offshore structures such as Spars and multi-column Deep Draft Floaters (DDFs). The VIM response can have a significant impact on the fatigue life of mooring and riser components. In particular, Steel Catenary Risers (SCRs) suspended from the floater can be sensitive to VIM-induced fatigue at their mudline touchdown points. Industry currently relies on scaled model testing to determine VIM for design. However, scaled model tests are limited in their ability to represent VIM for the full scale structure since they are generally not able to represent the full scale Reynolds number and also cannot fully represent waves effects, nonlinear mooring system behavior or sheared and unsteady currents. The use of Computational Fluid Dynamics (CFD) to simulate VIM can more realistically represent the full scale Reynolds number, waves effects, mooring system, and ocean currents than scaled physical model tests. This paper describes a set of VIM CFD simulations for a Spar hard tank with appurtenances and their comparison against a high quality scaled model test. The test data showed considerable sensitivity to heading angle relative to the incident flow as well as to reduced velocity. The simulated VIM-induced sway motion was compared against the model test data for different reduced velocities (Vm) and Spar headings. Agreement between CFD and model test VIM-induced sway motion was within 9% over the full range of Vm and headings. Use of the Improved Delayed Detached Eddy Simulation (IDDES, Shur et al 2008) turbulence model gives the best agreement with the model test measurements. Guidelines are provided for meshing and time step/solver setting selection.

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.

Microwave backscatter and acoustic radiation from breaking waves

1991 ◽  
Vol 224 ◽  
pp. 601-623 ◽  
Author(s):  
M. R. Loewen ◽  
W. K. Melville
Keyword(s):  
Microwave Power ◽  
Field Experiments ◽  
Acoustic Radiation ◽  
Mechanical Energy ◽  
Breaking Waves ◽  
Acoustic Energy ◽  
Breaking Wave ◽  
Mean Square ◽  
The Mean ◽  
Microwave Backscatter

An experimental study of the microwave backscatter and acoustic radiation from breaking waves is reported. It is found that the averaged microwave and acoustic measurements correlate with the dynamics of wave breaking. Both the mean-square acoustic pressure and the backscattered microwave power correlate with the wave slope and dissipation, for waves of moderate slope (S < 0.28). The backscattered power and the mean-square pressure are also found to correlate strongly with each other. As the slope and wavelength of the breaking wave packet is increased, both the backscattered power and the mean-square pressure increase. It is found that a large portion of the backscattered microwave power precedes the onset of sound production and visible breaking. This indicates that the unsteadiness of the breaking process is important and that the geometry of the wave prior to breaking may dominate the backscattering. It is observed that the amount of acoustic energy radiated by an individual breaking wave scaled with the amount of mechanical energy dissipated during breaking. These laboratory results are compared to the field experiments of Farmer & Vagle (1988), Crowther (1989) and Jessup et al. (1990).

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