A Coupled-Mode Model for the Transformation of Wave Systems Over Inhomogeneous Sea/Coastal Environment

2010 ◽  
Author(s):  
K. A. Belibassakis ◽  
Th. P. Gerosthathis ◽  
G. A. Athanassoulis
Keyword(s):  
Present Model ◽  
Bottom Topography ◽  
Wave Spectrum ◽  
Coastal Environment ◽  
Three Dimensions ◽  
Intermediate Water ◽  
Wave Energy Dissipation ◽  
Coupled Mode ◽  
Directional Wave ◽  
Ambient Currents

The transformation of the directional wave spectrum over an inhomogeneous sea/coastal environment is considered. Inhomogeneities include intermediate-water depth, strongly varying 3D bottom topography and ambient currents. The consistent coupled-mode model, developed by Athanassoulis and Belibassakis (1999), extended to three dimensions by Belibassakis et al. (2001) and applied to the transformation of wave systems over 3D bottom topography (Gerostathis et al 2008) is exploited for the calculation of the transfer function, connecting the incident wave with the wave conditions at each point in the field. This model is fully dispersive and takes into account reflection, refraction, and diffraction phenomena. In the present work, the coupled mode system is enhanced to account also for the effects of steady currents (Belibassakis et al, 2008), as well as, the effect of wave energy dissipation due to bottom friction and wave breaking. Numerical results obtained by the present model are compared with other models (as, e.g., Li et al 1993, Yoon et al 2004) and experimental measurements (Vincent and Briggs 1989), demonstrating the usefulness and practical applicability of the present method.

A Coupled-Mode, Phase-Resolving Model for the Transformation of Wave Spectrum Over Steep 3D Topography: Parallel-Architecture Implementation

2007 ◽  
Vol 130 (1) ◽  
Author(s):  
Th. P. Gerostathis ◽  
K. A. Belibassakis ◽  
G. A. Athanassoulis
Keyword(s):  
Incident Wave ◽  
Present Model ◽  
Parallel Implementation ◽  
Bottom Topography ◽  
Wave Spectrum ◽  
Present Approach ◽  
Wave System ◽  
Frequency Spectra ◽  
Intermediate Depth ◽  
Coupled Mode

The problem of transformation of the directional spectrum of an incident wave system over an intermediate-depth region of strongly varying 3D bottom topography is studied in the context of linear theory. The consistent coupled-mode model, developed by Athanassoulis and Belibassakis (J. Fluid Mech. 389, pp. 275–301 (1999)) and extended to three dimensions by Belibassakis et al. (Appl. Ocean Res. 23(6), pp. 319–336 (2001)) is exploited for the calculation of the linear transfer function, connecting the incident wave with the wave conditions at each point in the field. This model is fully dispersive and takes into account reflection, refraction, and diffraction phenomena, without any simplification apart the standard intermediate-depth linearization. The present approach permits the calculation of spectra of all interesting wave quantities (e.g., surface elevation, velocity, pressure) at every point in the liquid domain. The application of the present model to realistic geographical areas requires a vast amount of calculations, calling for the exploitation of advanced computational technologies. In this work, a parallel implementation of the model is developed, using the message passing programming paradigm on a commodity computer cluster. In that way, a direct numerical solution is made feasible for an area of 25km2 over Scripps and La Jolla submarine canyons in Southern California, where a large amount of wave measurements are available. A comparison of numerical results obtained by the present model with field measurements of free-surface frequency spectra transformation is presented, showing excellent agreement. The present approach can be extended to treat weakly nonlinear waves, and it can be further elaborated for studying wave propagation over random bottom topography.

A Coupled-Mode, Phase-Resolving Model for the Transformation of Wave Spectrum Over Steep 3D Topography: A Parallel-Architecture Implementation

2005 ◽  
Author(s):  
Th. P. Gerosthathis ◽  
K. A. Belibassakis ◽  
G. A. Athanassoulis
Keyword(s):  
Incident Wave ◽  
Bottom Topography ◽  
Wave Spectrum ◽  
Three Dimensional ◽  
Parallel Architecture ◽  
Wave System ◽  
Directional Spectrum ◽  
Coupled Mode ◽  
Linear Waves ◽  
Velocity Pressure

The problem of transformation of the directional spectrum of an incident wave system over a region of strongly varying three-dimensional bottom topography is studied, in the context of linear theory. The Consistent Coupled-Mode Model (Athanassoulis and Belibassakis 1999, Belibassakis et al 2001) is exploited for the calculation of the linear transfer function, connecting the incident wave with the wave conditions at each point in the field. This model takes fully into account reflection, refraction and diffraction phenomena. The present approach permits the consistent transformation of any incident directional wave spectrum over a variable bathymetry region and the calculation of the spatial evolution of point spectra of all interesting wave quantities (free surface elevation, velocity, pressure), at every point in the domain. This approach can be extended to treat weakly non-linear waves.

scholarly journals OBSERVATION OF DIRECTIONAL WAVE SPECTRA AND REFLECTION COEFFICIENT OF BREAKWATER IN A HARBOR

1988 ◽  
Vol 1 (21) ◽  
pp. 3
Author(s):  
Tetsunori Ohshimo ◽  
Kosuke Kondo ◽  
Tsunehiro Sekimoto
Keyword(s):  
Reflection Coefficient ◽  
Wave Diffraction ◽  
Maximum Likelihood Method ◽  
Wave Spectrum ◽  
Field Investigation ◽  
Likelihood Method ◽  
Electromagnetic Current ◽  
Wave Spectra ◽  
Field Investigations ◽  
Directional Wave

Field investigations were performed in order to show the effect of wave diffraction by breakwaters through directional wave spectra measurements in a harbor, and to estimate the reflection coefficient by resolving the incident and reflected wave energy in front of a composite type breakwater. Combinations of an ultrasonic wave gage (USW) and an electromagnetic current meter (EMC) were used to measure the synchronized data of the water surface elevation and two horizontal velocities. The EMLM (Extended Maximum Likelihood Method) was applied for the calculation of the directional wave spectrum, and the modified EMLM for an incident and reflection wave field was applied for the estimation of the reflection coefficient. Through the estimated directional wave spectra, the effect of wave diffraction by breakwaters were discussed and the reflection coefficient was estimated at about 0.9. As a result, the applicability of the field investigation method and the modified EMLM were verified.

On the Estimation of Directional Wave Spectrum Based on Stationary Vessels 1st Order Motions: A New Set of Experimental Results

2008 ◽  
Author(s):  
Joa˜o V. Sparano ◽  
Eduardo A. Tannuri ◽  
Alexandre N. Simos ◽  
Vini´cius L. F. Matos
Keyword(s):  
Bayesian Inference ◽  
Wave Spectrum ◽  
Small Scale ◽  
Large Set ◽  
Wave Spectra ◽  
Inference Method ◽  
Peak Period ◽  
Wave Basin ◽  
Bayesian Inference Method ◽  
Directional Wave

The practicability of estimating directional wave spectra based on a vessel 1st order response has been recently addressed by several researchers. The interest is justified since on-board estimations would only require only a simple set of accelerometers and rate-gyros connected to an ordinary PC. The on-board wave inference based on 1st order motions is therefore an uncomplicated and inexpensive choice for wave estimation if compared to wave buoys and radar systems. The latest works in the field indicate that it is indeed possible to obtain accurate estimations and a Bayesian inference model seems to be the preferable method adopted for performing this task. Nevertheless, most of the previous analysis has been based exclusively on numerical simulations. At Polytechnic School, an extensive research program supported by Petrobras has been conducted since 2000, aiming to evaluate the possibility of estimating wave spectrum on-board offshore systems, like FPSO platforms. In this context, a series of small-scale tests has been performed at the LabOceano wave basin, comprising long and short crested seas. A possible candidate for on-board wave estimation has been recently studied: a crane barge (BGL) used for launching ducts offshore Brazil. The 1:48 model has been subjected to bow and quartering seas with different wave heights and periods and also different levels of directional spreading. A Bayesian inference method was adopted for evaluating the wave spectra based on the time-series of motions and the results were directly compared to the wave spectra measured in the basin by means of an array of wave probes. Very good estimations of the statistical parameters (significant wave height, peak period and mean wave direction) were obtained and, in most cases, even the directional spreading could be properly predicted. Inversion of the mean direction (180° shift), mentioned by some authors as a possible drawback of the Bayesian inference method, was not observed in any case. Sensitivity analysis on errors in the input parameters, such as the vessel inertial characteristics, has also been performed and attested that the method is robust enough to cope well with practical uncertainties. Overall results once again indicate a good performance of the inference method, providing an important additional validation supported by a large set of model tests.

HF Radar Directional Spectra Validation With Buoy and Model Data

2008 ◽  
Author(s):  
L. R. Wyatt ◽  
J. J. Green ◽  
A. Middleditch ◽  
J. C. Waters
Keyword(s):  
Wave Spectrum ◽  
Hf Radar ◽  
Model Data ◽  
Work In Progress ◽  
Directional Wave Spectrum ◽  
Directional Wave ◽  
Good Agreement

Examples of the measurement of the directional wave spectrum using HF radars are presented. These are compared with both buoy and model data and good agreement is demonstrated. Work in progress on partitioning these spectra for more detailed comparisons and for assimilation into models is discussed.

Dynamic Selection of Ship Responses for Estimation of On-Site Directional Wave Spectra

2012 ◽  
Author(s):  
Ingrid Marie Vincent Andersen ◽  
Gaute Storhaug
Keyword(s):  
Transfer Functions ◽  
Response Spectrum ◽  
Wave Spectrum ◽  
Selection Procedure ◽  
Selection Method ◽  
Parametric Modelling ◽  
Dynamic Selection ◽  
Directional Wave Spectrum ◽  
Reliability Method ◽  
Directional Wave

Knowledge of the wave environment in which a ship is operating is crucial for most on-board decision support systems. Previous research has shown that the directional wave spectrum can be estimated by the use of measured global ship responses and a set of transfer functions determined for the specific ship. The approach can either be based on parametric or Bayesian (non-parametric) modelling, and in both cases a set of three ship responses usually provides the best estimation. The optimal response combination of three responses at any time depends on the environmental conditions and the operation of the ship. Since measurements of more than three responses are usually available, a quick, dynamic selection procedure of the three signals best suited for the wave spectrum estimation procedure is essential. In the present paper the concept of a selection method based on a simple pre-estimate of the wave spectrum is suggested. The selection method needs to be robust for what reason a parameterised uni-directional, two-parameter wave spectrum is treated. The parameters included are the zero up-crossing period, the significant wave height and the main wave direction relative to the ship’s heading. The procedure basically seeks to minimise the difference between a set of spectral moments derived from a measured response spectrum and the corresponding response spectrum calculated from the parameterised wave spectrum and the transfer function for any given response. Subsequently, the three responses with the best overall agreement are selected for the actual estimation of the directional wave spectrum. The transfer functions for the ship responses can be determined using different computational methods such as striptheory, 3D panel codes, closed form expressions or model tests. The uncertainty associated with transfer functions depends on the computational method used, relative heading, frequency and type of response. This uncertainty is conceptually taken into account in the selection procedure using the First Order Reliability Method (FORM). However, specific assessment of the uncertainties has not been carried out, but is subject to later studies.

Generalized vortex methods for free-surface flow problems

1982 ◽  
Vol 123 ◽  
pp. 477-501 ◽  
Author(s):  
Gregory R. Baker ◽  
Daniel I. Meiron ◽  
Steven A. Orszag
Keyword(s):  
Water Waves ◽  
Evolution Equations ◽  
Bottom Topography ◽  
Free Surface Flow ◽  
Surface Flow ◽  
Three Dimensions ◽  
Fredholm Integral Equations ◽  
Free Surfaces ◽  
Flow Problems ◽  
Dipole Vortex

The motion of free surfaces in incompressible, irrotational, inviscid layered flows is studied by evolution equations for the position of the free surfaces and appropriate dipole (vortex) and source strengths. The resulting Fredholm integral equations of the second kind may be solved efficiently in both storage and work by iteration in both two and three dimensions. Applications to breaking water waves over finite-bottom topography and interacting triads of surface and interfacial waves are given.

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