The Experts below are selected from a list of 2367 Experts worldwide ranked by ideXlab platform

Paul Taylor - One of the best experts on this subject based on the ideXlab platform.

  • Non-linear evolution of large waves in deep water - The influence of Directional Spreading and spectral bandwidth
    2016
    Co-Authors: Thomas A. A. Adcock, Paul Taylor
    Abstract:

    As large waves form in the open ocean their dynamics are mod- ified from classic linear dispersion by non-linear physics. In this study we use a numerical model to study the evolution of isolated wave-groups in deep water. We find that the non-linear changes are rather sensitive to the initial conditions, with small changes in parameters such as Directional Spreading giving significantly different results. In all cases, although as aforementioned in dif- fering degrees, we find changes to the shape of the extreme wave- group – the wave-groups contracting in the mean wave direction, expanding laterally to increase the width of the extreme crest, and with the largest wave moving to the front of the groups. We find that significant extra elevation of the wave-group only occurs for cases which are close to uni-Directional.2

  • Estimating ocean wave Directional Spreading from an Eulerian surface elevation time history
    Proceedings of the Royal Society A: Mathematical Physical and Engineering Sciences, 2009
    Co-Authors: Thomas A. A. Adcock, Paul Taylor
    Abstract:

    The Directional Spreading of sea states is an important design parameter in offshore engineering. Wave Directionality affects the resulting wave kinematics, which affects the forces exerted on offshore structures. In this paper, we develop a method for estimating the amount of Spreading, when the only information available is the time history of free surface elevation at a single point in space. We do this by predicting the second-order bound waves that occur at the difference in frequency of two freely propagating waves. The magnitude of these second-order bound waves is a function of the angle between the interacting waves. Thus, it is possible to infer some information about Spreading from a single-point time history. We demonstrate that this approach works for wave groups in a fully nonlinear numerical wave tank. We create a synthetic random sea state and introduce noise into the analysis and thus show that our approach is robust and insensitive to noise, even with a signal-to-noise ratio of unity in the difference waves. This approach is also applied to random waves in a physical wave tank where Spreading was directly measured and also to a storm recorded in the North Sea. In all cases, we find our estimate of Spreading is in good agreement with other measurements.

  • Second-order wave forces and free-surface elevation around a moored ship in steep uni-Directional and spread waves
    2005
    Co-Authors: Jun Zang, Paul Taylor, Kang L. Wang, R. Eatock Taylor
    Abstract:

    Under the support from EU FR5, this paper presents a novel approach to extend the second-order wave diffraction simulation to Directionally spread sea. Results for wave interaction with an FPSO examined the effect of Directional Spreading in approaching waves on wave-structure interaction.

  • Non-linear interaction of Directionally spread waves with FPSO
    2005
    Co-Authors: Jun Zang, Paul Taylor, R. Eatock Taylor
    Abstract:

    As part of the FP5 REBASDO Programme, we are examining the effects of Directional wave Spreading on the non-linear hydrodynamic loads and the wave run-up in the region of the bow of a ship shaped FPSO. This paper presents a novel approach to deal with Directionally spread seas in the numerical simulation of non-linear wave interaction with the FPSO. Numerical solutions of the problem are obtained for various types of Directional Spreading. The results are compared with the corresponding results for a uniDirectional wave. From the comparison, it is shown that uni-Directional waves don’t always lead to the maximum wave forces on a ship-shaped FPSO, which contrasts to the effect of Spreading seas on a circular cylinder [2]. This finding indicates that the conventional calculation for uni-Directional waves may underestimate the wave forces on the vessel in a Directionally spread sea. Numerical approach

  • The Effect of Directional Spreading on Interaction of Focused Wave Groups With a Cylinder
    23rd International Conference on Offshore Mechanics and Arctic Engineering Volume 3, 2004
    Co-Authors: Eugeny Buldakov, Rodney Eatock Taylor, Paul Taylor
    Abstract:

    The problem of diffraction of a Directionally spread focused wave group by a bottom-seated circular cylinder is considered from the view point of second-order perturbation theory. After applying the time Fourier transform and separation of vertical variable the resulting two-dimensional non-homogeneous Helmholtz equations are solved numerically using finite differences. Numerical solutions of the problem are obtained for JONSWAP amplitude spectra for the incoming wave group with various types of Directional Spreading. The results are compared with the corresponding results for a uniDirectional wave group of the same amplitude spectrum. Finally we discuss the applicability of the averaged Spreading angle concept for practical applications.

Ian R. Young - One of the best experts on this subject based on the ideXlab platform.

  • The form of the asymptotic depth-limited wind-wave spectrum part III: Directional Spreading
    Coastal Engineering, 2010
    Co-Authors: Ian R. Young
    Abstract:

    Abstract The Directional Spreading of both the wavenumber and frequency spectra of finite-depth wind generated waves at the asymptotic depth limit are examined. The analysis uses the Wavelet Directional Method, removing the need to assume a form for the dispersion relationship. The paper shows that both the wavenumber and frequency forms are narrowest at the spectral peak and broaden at wavenumbers (frequencies) both above and below the peak. The Directional Spreading of the wavenumber spectrum is bi-modal above the spectral peak. In contrast, the frequency spectrum is uni-modal. This difference is shown to be the result of energy in the wind direction being displaced from the linear dispersion shell. A full parametric relationship for the Directional Spreading of the wavenumber spectrum is developed. The analysis clearly shows that typical dispersion relationships are questionable at high frequencies and that such effects can be significant. This result supports greater attention being focussed on the routine recording of wavenumber spectra, rather than frequency spectra.

  • The growth of fetch limited waves in water of finite depth. Part 3. Directional spectra
    Coastal Engineering, 1996
    Co-Authors: Ian R. Young, L.a. Verhagen, Sk Khatri
    Abstract:

    Abstract The analysis of a comprehensive data set of fetch limited finite depth Directional wave spectra is presented. The data show that the spectra are narrowest at the frequency of the spectral peak and gradually broaden for frequencies both greater than and less than that of the peak. The Directional Spreading is found to be a function of f f p , where f is frequency and fp the frequency of the spectral peak. In addition, the present data reveal consistently broader Spreading than comparable deep water data. Hence, it is concluded that finite depth effects lead to an increase in the Directional Spreading of the spectrum. An analysis of the nonlinear coupling of wavenumber components within the spectrum indicates that such effects may lead to enhanced Directional Spreading of spectra as the water depth decreases, consistent with the present data set.

  • a note on the bimodal Directional Spreading of fetch limited wind waves
    Journal of Geophysical Research, 1995
    Co-Authors: Ian R. Young, L.a. Verhagen, Michael L. Banner
    Abstract:

    Measurements of the Directional spectra of fetch-limited wind waves are presented. The Directional Spreading functions for these spectra are unimodal and narrowest in the region of the spectral peak frequency. Consistent with previous measurements, the Spreading broadens for frequencies just above and below the spectral peak frequency. At frequencies of approximately twice the peak frequency, however, the unimodal Spreading becomes bimodal, and more wave energy propagates at an angle to the wind than in the wind direction. The bimodal sidelobes continue to separate with increasing frequency and become larger in magnitude. Results obtained with a numerical model with a full solution to the nonlinear terms indicate that the bimodal structure is maintained by Directional transfer of energy through nonlinear wave-wave interactions.

  • A note on the bimodal Directional Spreading of fetch‐limited wind waves
    Journal of Geophysical Research, 1995
    Co-Authors: Ian R. Young, L.a. Verhagen, Michael L. Banner
    Abstract:

    Measurements of the Directional spectra of fetch-limited wind waves are presented. The Directional Spreading functions for these spectra are unimodal and narrowest in the region of the spectral peak frequency. Consistent with previous measurements, the Spreading broadens for frequencies just above and below the spectral peak frequency. At frequencies of approximately twice the peak frequency, however, the unimodal Spreading becomes bimodal, and more wave energy propagates at an angle to the wind than in the wind direction. The bimodal sidelobes continue to separate with increasing frequency and become larger in magnitude. Results obtained with a numerical model with a full solution to the nonlinear terms indicate that the bimodal structure is maintained by Directional transfer of energy through nonlinear wave-wave interactions.

Yoshimi Goda - One of the best experts on this subject based on the ideXlab platform.

  • WAVE SETUP AND LONGSHORE CURRENTS INDUCED BY Directional SPECTRAL WAVES: PREDICTION FORMULAS BASED ON NUMERICAL COMPUTATION RESULTS
    Coastal Engineering Journal, 2008
    Co-Authors: Yoshimi Goda
    Abstract:

    Wave setup and longshore currents on planar beaches induced by Directional spectral waves have been computed for beach slopes ranging from 1/100 to 1/10, waves with deepwater wave steepness from 0.005 to 0.08 and offshore incident angles from 1° to 70°. The author's random wave breaking model PEGBIS (Parabolic Equation with Gradational Breaker Index for Spectral waves) is employed for the evaluation of wave attenuation by breaking. Prediction formulas are empirically derived for estimation of the wave setup at the shoreline and the cross-shore distribution of longshore currents on the basis of numerical computation results. Effects of spectral peakedness and Directional Spreading, surface roller, and turbulent eddy viscosity on wave setup and longshore currents are examined. The formulas have shown the capability to predict the wave setup and longshore currents observed in several field measurements fairly well.

  • STATISTICS OF WAVE CREST LENGTHS BASED ON Directional WAVE SIMULATIONS
    Journal of Offshore Mechanics and Arctic Engineering, 1994
    Co-Authors: Yoshimi Goda
    Abstract:

    Spatial surface elevations of Directional random waves have numerically been simulated for various Directional spectral conditions in deep water and finite uniform depth water. Individual wave crests are defined on the simulated surface data and the statistics of crest lengths are examined. The ratio of the mean crest length to the local wavelength is found to be governed by the Directional Spreading parameter. The average longitudinal profiles of high wave crests are presented for three typical values of Directional Spreading parameters.

Daniel Conley - One of the best experts on this subject based on the ideXlab platform.

  • An approximate solution for the wave energy shadow in the lee of an array of overtopping type wave energy converters
    Coastal Engineering, 2013
    Co-Authors: Kieran Monk, Qingping Zou, Daniel Conley
    Abstract:

    Abstract In this study we investigate how the wave energy deficit in the lee of an array of overtopping type wave energy converting devices (WECs), redistributes with distance from the array due to the natural variability of the wave climate and wave structure interactions. Wave Directional Spreading has previously been identified as the dominant mechanism that disperses the wave energy deficit, reducing the maximum wave height reduction with increasing distance from the array. In addition to this when waves pass by objects such as an overtopping type WEC device, diffracted waves re-distribute the incident wave energy and create a complex interference pattern. The effect of wave energy redistribution from diffraction on the wave energy shadow in the near and far field is less obvious. In this study, we present an approximate analytical solution that describes the diffracted and transmitted wave field about a single row array of overtopping type WECs, under random wave conditions. This is achieved with multiple superpositions of the analytical solutions for monochromatic uniDirectional waves about a semi-infinite breakwater, extended to account for partial reflection and transmission. The solution is used to investigate the sensitivity of the far field wave energy shadow to the array configuration, level of energy extraction, incident wave climate, and diffraction. Our results suggest that diffraction spreads part of the wave energy passing through the array, away from the direct shadow region of the array. This, in part, counteracts the dispersion of the wave energy deficit from Directional Spreading.

Alessandra Romolo - One of the best experts on this subject based on the ideXlab platform.

  • Three-dimensional nonlinear random wave groups in intermediate water depth
    Coastal Engineering, 2008
    Co-Authors: Felice Arena, Alfredo Ascanelli, Vincenzo Nava, Diego Pavone, Alessandra Romolo
    Abstract:

    Abstract High waves at ocean occur during a complex space–time evolution of wave groups. In this paper the nonlinear structure of three-dimensional sea wave groups at intermediate water depth is investigated. To this purpose, the Boccotti's Quasi-Determinism theory is firstly applied to describe the linear wave groups when a given exceptionally high crest occurs. Then, the second-order correction to the linear solution is derived for the general condition of three-dimensional wave groups, at a finite water depth. Several numerical applications, finally, have been carried out in order to show how both the spectral bandwidth and the Directional Spreading modify the nonlinear high waves at different water depth.