RANDOM WAVE KINEMATICS AND COASTAL STRUCTURES.

1999 ◽  
Vol 136 (2) ◽  
pp. 93-104
Author(s):  
T O DONOGHUE ◽  
J SUTHERLAND
Keyword(s):  
Random Wave ◽  
Coastal Structures ◽  
Wave Kinematics

Green Sea and Water Impact on FPSO: Numerical Predictions Validated Against Model Tests

2002 ◽  
Author(s):  
C. T. Stansberg ◽  
O̸. Hellan ◽  
J. R. Hoff ◽  
V. Moe
Keyword(s):  
Structural Integrity ◽  
Design Method ◽  
Model Tests ◽  
Random Wave ◽  
Simplified Approach ◽  
Irregular Wave ◽  
Wave Kinematics ◽  
Numerical Predictions ◽  
Statistical Sense ◽  
Local Pressures

A recently developed numerical design method for analysis of green sea events and resulting impact loads on deck structures of FPSO’s, is validated against model test data. Steep irregular wave conditions are considered, and numerical time series reconstructions are made using the measured wave as input. A second-order numerical random wave description is combined with standard 3D wave diffraction and related vessel motions to predict the relative wave kinematics. A modified shallow water formulation is applied for the prediction of the propagation on deck, and resulting local pressures on the deck-house are estimated by a similarity solution. From this an analysis of the structural integrity can be made. Comparisons to the experiments are made for the relative wave amplitudes, water propagation on deck, and the resulting deck-house loads. A reasonably good agreement is observed for the reconstructions, in a statistical sense, but also for individual events. Thus selected green sea events are investigated in detail, and characteristics identified. The agreement with the model tests is promising especially on the background of the simplified approach used, as well as the expected statistical scatter.

scholarly journals ROUGHNESS FACTOR FOR MULTI-LAYER ARMOUR AS OVERTOPPING ESTIMATOR

2020 ◽  
pp. 25
Author(s):  
Leopoldo Franco ◽  
Yuri Pepi ◽  
Stefano de Finis ◽  
Verdiana Iorio ◽  
Giorgio Bellotti ◽  
...  
Keyword(s):  
Structural Characteristics ◽  
Storm Surges ◽  
Random Wave ◽  
Roughness Factor ◽  
Coastal Structures ◽  
Wave Overtopping ◽  
Wave Flume ◽  
Physical Model Tests ◽  
Rubble Mound ◽  
Rubble Mound Breakwaters

Nowadays one of the most challenging problem for engineers is to adapt existing coastal structures to climate changes. Wave overtopping is highly sensitive to the increasing extreme water depths due to higher storm surges coupled with sea level rise. One way to face these problems for rubble mound breakwaters is to add one or more layers to the existing armour. Prediction of wave overtopping of coastal structures is presently obtained from empirical formulae in EurOtop (2018). For the case of overtopping over multi-layer armour, no validated method exists, so prediction must be based upon assumptions and judgement, with related uncertainties. This study is focused on the effects of different types of armour, the number of layer and other structural characteristics on the roughness factor f. The main effects of porosity and roughness will be investigated. This paper analyzes the results of several new physical model tests of different rubble mound breakwaters reproduced at the new medium scale random wave flume of the Department of Engineering of Roma Tre University.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/8cOdqkqQ-9s

Aspects of Nonlinear Random Wave Kinematics

2002 ◽  
Author(s):  
Dag Myrhaug ◽  
Carl Trygve Stansberg ◽  
Hanne Therese Wist
Keyword(s):  
Free Surface ◽  
Second Order ◽  
Difference Frequency ◽  
Stokes Wave ◽  
Frequency Effect ◽  
Random Wave ◽  
Sum Frequency ◽  
Wave Kinematics ◽  
Nonlinear Random Wave ◽  
Nonlinear Free Surface

Statistics of the nonlinear free surface elevation as well as the nonlinear random wave kinematics in terms of the horizontal velocity component in arbitrary water depth are addressed. Two different methods are considered: a simplified analytical approach based on second-order Stokes wave theory including the sum-frequency effect only, and a second-order random wave model including both sum-frequency and difference-frequency effects. The paper compares results for the statistics of the nonlinear free surface, and the consequences of neglecting the difference-frequency effect in the first method are discussed.

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.

scholarly journals Comparison of Extreme Offshore Structural Response from Two Alterna-tive Stretching Techniques

2013 ◽  
Vol 7 (1) ◽  
pp. 273-281 ◽  
Author(s):  
N.I. Mohd Zaki ◽  
M.K. Abu Husain ◽  
G. Najafian
Keyword(s):  
Wave Theory ◽  
Surface Elevation ◽  
Random Wave ◽  
Surface Zone ◽  
Offshore Structure ◽  
Near Surface ◽  
Water Particle ◽  
Wave Kinematics ◽  
Water Particle Kinematics ◽  
Extreme Responses

Linear random wave theory (LRWT) has successfully explained most properties of real sea waves with the ex-ception of some nonlinear effects for surface elevation and water particle kinematics. Due to its simplicity, it is frequently used to simulate water particle kinematics at different nodes of an offshore structure from a reference surface elevation record; however, predicted water particle kinematics from LRWT suffer from unrealistically large high-frequency compo-nents in the vicinity of mean water level (MWL). To overcome this deficiency, a common industry practice for evaluation of wave kinematics in the free surface zone consists of using linear random wave theory in conjunction with empirical techniques (such as Wheeler and vertical stretching methods) to provide a more realistic representation of near-surface wave kinematics. It is well known that the predicted kinematics from these methods are different; however, no systematic study has been conducted to investigate the effect of this on the magnitude of extreme responses of an offshore structure. In this paper, probability distributions of extreme responses of an offshore structure from Wheeler and vertical stretching methods are compared. It is shown that the difference is significant; consequently, further research is required to deter-mine which method is more reliable.

scholarly journals Reflection Analysis of Impermeable Slopes under Bimodal Sea Conditions

2020 ◽  
Author(s):  
Stephen Orimoloye ◽  
Harshinie Karunarathna ◽  
Dominic Reeve
Keyword(s):  
Reflection Coefficient ◽  
Wave Reflection ◽  
Experimental Tests ◽  
Random Wave ◽  
Random Waves ◽  
Coastal Structures ◽  
Test Analysis ◽  
Relative Water ◽  
Analysis Of Results ◽  
Reflection Characteristics

Understanding of reflection characteristics of coastal seawalls is crucial for design. Wave reflection can cause difficulties to small vessel manoeuvring at the harbour entrance and constitute damaging scouring at the toe of coastal structures. Previous studies have considered reflection characteristics of coastal seawalls under wind-generated random waves without paying attention to the effects of wave bimodality created by the presence of swell waves. The present study focuses on the influence of random wave bimodality on reflective characteristics of coastal seawalls. More than eight hundred experimental tests have been conducted to examine the reflection performance of impermeable sloping seawalls under bimodal waves. Reflection coefficients were computed from each test. Analysis of results suggests that both unimodal and bimodal waves give similar reflection characteristics. However, the reflection coefficient in bimodal sea states seems to be more prolonged than in the unimodal sea states. It was found that the reflection coefficient of coastal seawalls is strongly influenced by the seawall slope, the wave steepness, relative water depth, and the surf similarity parameters. A new empirical reflection equation to describe the influence of wave bimodality on the reflection characteristics of coastal seawalls has been formulated based on this study.

scholarly journals Method of the Laboratory Wave Generation for Two Dimensional Hydraulic Model Experiment in the Coastal Engineering Fields: Case of Random Waves

2021 ◽  
Vol 33 (6) ◽  
pp. 383-390
Author(s):  
Jong-In Lee ◽  
Il Rho Bae ◽  
Young-Taek Kim
Keyword(s):  
Wave Generation ◽  
Hydraulic Model ◽  
Coastal Engineering ◽  
Experimental Results ◽  
Random Wave ◽  
Two Dimensional ◽  
Random Waves ◽  
Coastal Structures ◽  
Successful Execution ◽  
The Stability

The experiments in coastal engineering are very complex and a lot of components should be concerned. The experience has an important role in the successful execution. Hydraulic model experiments have been improved with the development of the wave generator and the advanced measuring apparatus. The hydraulic experiments have the advantage, that is, the stability of coastal structures and the hydraulic characteristics could be observed more intuitively rather than the numerical modelings. However, different experimental results can be drawn depending on the model scale, facilities, apparatus, and experimenters. In this study, two-dimensional hydraulic experiments were performed to suggest the guide of the test wave(random wave) generation, which is the most basic and important factor for the model test. The techniques for generating the random waves with frequency energy spectrum and the range for the incident wave height [(HS)M/(HS)T = 1~1.05] were suggested. The proposed guide for the test wave generation will contribute to enhancing the reliability of the experimental results in coastal engineering.

A Semi-Linear Method for Particle Kinematics Under Steep Random-Wave Crests

2008 ◽  
Author(s):  
Nwaka Chuks Ojieh ◽  
Nigel Barltrop
Keyword(s):  
Linear Method ◽  
Wave Interaction ◽  
New Method ◽  
Random Wave ◽  
Linear Extrapolation ◽  
Wave Kinematics ◽  
Horizontal Particle ◽  
Method Show ◽  
Good Agreement

The determination of random wave kinematics in high sea-states especially in the region above mean water surface has been a major challenge and most proposed methods are not robust. In this work, a method which is similar to stretching and extrapolation in its simplicity is developed based on a simplified form of wave-wave interaction which is robust to 2nd order. To check the usefulness of the new method, horizontal particle velocity results are compared with Zhang’s HWM, Wheeler stretching, linear extrapolation above MWL, experimental measurements and theoretical computations of Longridge et al (1996), Skjelbriea et al (1991) and Stansberg et al (2006). Results of the new method show good agreement with the results of Skjelbriea et al (1991) and are closer to experiment than 2nd order results of Stansberg et al (2006) while only showing a qualitative agreement with Longridge et al (1996). The poorer comparison with Longridge et al (1996) is probably because it was not possible to reproduce the exact time series used by Longridge et al as the exact amplitudes and phases were not available. The improved capability of the new method over existing methods has thus been demonstrated and its advantage over the HWM lies in being simpler to implement.

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