WAVE-PHASE RESOLVING SEDIMENT TRANSPORT DUE TO WAVE GROUPS AND IRREGULAR WAVES: COMPARISON OF FULL AND INTEGRATED APPROACHES

2015 ◽  
Author(s):  
KASPER KAERGAARD ◽  
SINA SAREMI ◽  
NILS DROENEN ◽  
ROLF DEIGAARD
Keyword(s):  
Sediment Transport ◽  
Irregular Waves ◽  
Wave Groups ◽  
Wave Phase ◽  
Integrated Approaches

CFD Analysis of Deck Impact in Irregular Waves: Wave Representation by Transient Wave Groups

2011 ◽  
Author(s):  
O̸ystein Lande ◽  
Thomas B. Johannessen
Keyword(s):  
Wave Field ◽  
Irregular Waves ◽  
Computational Domain ◽  
Cfd Analysis ◽  
Wave Group ◽  
Regular Waves ◽  
Transient Wave ◽  
Wave Groups ◽  
Wave Induced ◽  
Random Background

Analysis of wave structure interaction problems are increasingly handled by employing CFD methods such as the well known Volume-of-Fluid (VoF) method. In particular for the problem of deck impact on fixed structures with slender substructures, CFD methods have been used extensively in the last few years. For this case, the initial conditions have usually been treated as regular waves in an undisturbed wave field which may be given accurately as input. As CFD analyses become more widely available and are used for more complex problems it is also necessary to consider the problem of irregular waves in a CFD context. Irregular waves provide a closer description of the sea surface than regular waves and are also the chief source of statistical variability in the wave induced loading level. In general, it is not feasible to run a long simulation of an irregular seastate in a CFD analysis today since this would require very long simulation times and also a very large computational domain and sophisticated absorbing boundary conditions to avoid build-up of reflections in the domain. The present paper is concerned with the use of a single transient wave group to represent a large event in an irregular wave group. It is well known that the autocovariance function of the wave spectrum is proportional to the mean shape of a large wave in a Gaussian wave field. The transient nature of such a wave ensures that a relatively small wave is generated at the upwave boundary and dissipated at the downwave boundary compared with the wave in the centre of the domain. Furthermore, a transient wave may be embedded in a random background if it is believed that the random background is important for the load level. The present paper describes the method of generating transient wave groups in a CFD analysis of wave in deck impact. The evolution of transient wave groups is first studied and compared with experimental measurements in order to verify that nonlinear transient waves can be calculated accurately using the present CFD code. Vertical wave induced loads on a large deck is then investigated for different undisturbed wave velocities and deck inundations.

Interaction of Waves With a Moored Semisubmersible

1984 ◽  
Vol 106 (4) ◽  
pp. 419-425 ◽  
Author(s):  
S. K. Chakrabarti ◽  
D. C. Cotter
Keyword(s):  
Diffraction Theory ◽  
Nonlinear Damping ◽  
Irregular Waves ◽  
Test Results ◽  
Regular Waves ◽  
Mooring Lines ◽  
Wave Groups ◽  
First Order ◽  
Oscillating Motion ◽  
Theoretical Results

A semisubmersible moored in waves experiences a steady offset and two types of motion—a first-order motion at frequencies corresponding to the incident wave frequencies and a slowly oscillating motion near the natural frequency of the semisubmersible/mooring system. An extensive wave tank testing of a semisubmersible model was undertaken in which the motions of the semisubmersible and the loads in the mooring lines were measured. The semisubmersible was tested in the tank in a head sea as well as a beam sea heading in a series of regular waves, regular wave groups and irregular waves. The test results of the steady offset and first-order and slowly oscillating motions are presented for each heading and for each of these wave series as functions of the wave period. The experimental results are correlated with theoretical results based on a 3-D diffraction theory which takes into account the appropriate first and second-order terms. It is found that the nonlinear damping terms are quite important in explaining the behavior of the moored semisubmersible in waves and that the steady drift loads in wave groups can be determined from results based on regular waves.

Application of Focusing Wave Groups in Model Testing Practice

2014 ◽  
Author(s):  
Christian Schmittner ◽  
Joris Brouwer ◽  
Janou Hennig
Keyword(s):  
Hydrodynamic Model ◽  
Transfer Functions ◽  
Theoretical Description ◽  
Model Testing ◽  
Historical Background ◽  
Irregular Waves ◽  
Transient Wave ◽  
Wave Groups ◽  
Floating Structures

For hydrodynamic model testing different types of model waves are applied, where the most common ones are regular (monochromatic) and irregular (multichromatic) waves. In addition to these wave types the application of focusing wave groups, which are also often denoted as wave packages or transient wave packets, can give insight into aspects that cannot be assessed by the conventional model waves. This paper describes the different applications of focusing wave groups for hydrodynamic model testing. The paper starts with the historical background, followed by a theoretical description and the generation procedure. The main part of the paper is dedicated to the practical application of focusing wave groups in the basin. Items that will be described are a) the derivation of transfer functions for floating structures and for anti-roll tanks b) the determination of hydraulic and electrical transfer function of wave makers c) the verification of position and calibration of wave probes in the basin d) the generation of extreme wave events e) the assessment of reflection coefficient of beaches f) the investigation of non-linear aspects of transfer functions. Finally, characteristics of the analysis of focusing waves are introduced and compared to conventional methods based on regular and irregular waves.

scholarly journals Surf Zone Turbulence and Suspended Sediment Dynamics—A Review

2021 ◽  
Vol 9 (11) ◽  
pp. 1300
Author(s):  
Troels Aagaard ◽  
Joost Brinkkemper ◽  
Drude F. Christensen ◽  
Michael G. Hughes ◽  
Gerben Ruessink
Keyword(s):  
Sediment Transport ◽  
Suspended Sediment ◽  
Suspended Sediment Concentration ◽  
Surf Zone ◽  
Sediment Concentration ◽  
Sandy Beaches ◽  
Suspended Sediment Transport ◽  
Velocity Signal ◽  
Wave Phase ◽  
Turbulence Production

The existence of sandy beaches relies on the onshore transport of sand by waves during post-storm conditions. Most operational sediment transport models employ wave-averaged terms, and/or the instantaneous cross-shore velocity signal, but the models often fail in predictions of the onshore-directed transport rates. An important reason is that they rarely consider the phase relationships between wave orbital velocity and the suspended sediment concentration. This relationship depends on the intra-wave structure of the bed shear stress and hence on the timing and magnitude of turbulence production in the water column. This paper provides an up-to-date review of recent experimental advances on intra-wave turbulence characteristics, sediment mobilization, and suspended sediment transport in laboratory and natural surf zones. Experimental results generally show that peaks in the suspended sediment concentration are shifted forward on the wave phase with increasing turbulence levels and instantaneous near-bed sediment concentration scales with instantaneous turbulent kinetic energy. The magnitude and intra-wave phase of turbulence production and sediment concentration are shown to depend on wave (breaker) type, seabed configuration, and relative wave height, which opens up the possibility of more robust predictions of transport rates for different wave and beach conditions.

scholarly journals Water wave diffraction by a cylinder array. Part 2. Irregular waves

2001 ◽  
Vol 442 ◽  
pp. 33-66 ◽  
Author(s):  
C. O. G. OHL ◽  
P. H. TAYLOR ◽  
R. EATOCK TAYLOR ◽  
A. G. L. BORTHWICK
Keyword(s):  
Incident Wave ◽  
Extreme Events ◽  
Diffraction Theory ◽  
Irregular Waves ◽  
Circular Cylinders ◽  
Random Wave ◽  
Wave Groups ◽  
Cylinder Array ◽  
Random Seas ◽  
Focused Wave

Diffraction of irregular waves, focused wave groups, and random seas by an array of vertical bottom-mounted circular cylinders is investigated using theoretical, computational and experimental methods. This is an extension of our study of such an array in regular waves, reported in Part 1. Linear focused wave group theory is reviewed as a method for predicting the probable shape of extreme events from random wave spectra. Measurements are presented of the free surface elevation distribution in the vicinity of a multi-column structure in an offshore basin when subjected to irregular waves having peak frequencies and significant wave heights in the range 0.449 < kpa < 0.555 and 0.114 < Hs < 0.124 respectively, where a is the cylinder radius. Analytical linear diffraction theory is extended for application to focused wave groups and random seas. Experimental irregular wave data are analysed for comparison with this theory. Linear diffraction theory for random seas is shown to give an excellent prediction of incident wave spectral diffraction, while linear diffraction theory for focused wave groups works well for linearized extreme events. Due to the phase shifting of incident wave spectral components, diffraction is shown to generate focused wave groups in the vicinity of the cylinder array.

scholarly journals PREDICTION OF SEDIMENT TRANSPORT DUE TO IRREGULAR WAVE MOTION

2012 ◽  
Vol 4 (2) ◽  
Author(s):  
Taufiqur Rachman ◽  
Suntoyo Suntoyo
Keyword(s):  
Shear Stress ◽  
Sediment Transport ◽  
Transport Rate ◽  
Irregular Waves ◽  
Bottom Shear Stress ◽  
Coastal Morphology ◽  
New Approach ◽  
Irregular Wave ◽  
Sediment Transport Rate ◽  
Rough Bed

<p>In general, waves in coastal environments are irregular and have a random shape with a height and period that was not constant. The accuracy of sediment transport rate prediction is the most important stages in the study of morphology and coastal marine environments. In addition, the predictive model of coastal morphology is more efficient to use the bottom shear stress calculation approach for practical purposes rather than a more complex approach to the modeling of two phases. In this paper, the calculation of sediment transport was based on the bottom shear stress modelling purposed with data validation from the experimental results in the turbulent bottom boundary layer over rough bed under irregular waves. The new approach to estimate the bottom shear stress was based on combining velocity and acceleration terms. Furthermore, a new approach of the bottom shear stress was applied to formulate the sheet flow sediment transport rate for irregular waves by using the experimental data from Dibadjnia and Watanabe (1998) and the empirical formula was found.</p> <p>Keywords: sediment transport, bottom shear stress, irregular waves</p>

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