Directional Wavenumber Spectra of Ocean Surface Waves

Abstract

REPORT DOCUMENTATION PAGEPublic reporting burden for this collection of information is estimated to average i hour per response, including the time for reviewing instructions, searching existing data sources gathering and maintaining the data needed, and completing and reviewing this collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports (0704-0188), 1215 Jefferson Dav,s Highway, Suite 1204, Arlington. VA 22202-4302 Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it do" not display a currently valid OMB control number. PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS REPORT DATE (DD-MM-YYYY)05 U. ABSTRACT ' ~ It has been accepted as a truth that under a steady wind forcing condition, the wind generated waves travel in the direction of the wind vector. Based on field measurements, the directional beamwidth is narrowest near the spectral peak, and increases toward both higher and lower frequency components. Over the last several decades, such scenario is the basis for the design of the directional distribution function of any spectral model for engineering and scientific applications. We present results from a spectral analysis of 3D topography of random surface waves generated by a quasi-steady wind field. The directional spectra display clear oimodal pattern in the wavenumber region just above the spectral peak. The generation mechanism f the bimodal directional distribution in the short wave region is identified to be nonlinear wave-wave interaction. After presentation or publication, pertinent publication/presentation data will be entered in the publications data base, in accordance with reference (a). , ."_ * , M It is the opinion of the author that the subject paper (is)4JsrBe$©tessified, in accordance with reference (b). This paper does not violate any disclosure of trade secrets or suggestions of outside individuals or concerns which have been communicated to the Laboratory in confidence. This paper (does)=£toe^-r4©t^ontain any military critical technology. This subject paper (has)<tjasneyer) been incorporated in an official NRL Report. Substantive changes made in this document after approval by Classification Review and Public Release invalidate these reviews. Classification Review Therefore, if any substantive changes are made by the author, Technical Information, or anyone else, the document must be (Initcii/Dsts) returned for another Classification Review and Public Release. INSTRUCTIONSAuthor completes and submits this form with the manuscript via line channels to the division head for review and approval according to the routing in Section 4. AbstractIt has been accepted as a truth that under a steady wind forcing condition, the wind generat...

Directional Breaking Kinematics Observations from 3D Stereo Reconstruction of Ocean Waves

“…'stereography' can be used to obtain 2D measurements with higher directional resolution (M. Banner et al, 1989;I. Young et al, 1995;Jasper et al, 2020;Hwang et al, 2000Hwang et al, , 2000Romero & Melville, 2010a;Benetazzo, 2006). One of the first applications of stereography in oceanographic research involved computing the directional spectra of ocean waves from 3D elevation maps measured off San Diego from an offshore tower (M. Banner et al, 1989).…”

“…Here we refer to F (k cos θ, k sin θ) as F (k, θ) following the convention used in certain studies (M. L. Banner, 1990;Hwang et al, 2000;Romero et al, 2012;Romero, 2019;Romero & Lubana, 2022). But note that the 'true' polar spectrum is defined as et al, 2009;Holthuijsen, 2010;Benetazzo et al, 2016;Peureux et al, 2018).…”

“…It is well established that F (k, θ) is unimodal at the spectral peak and becomes bimodal at lower and higher wavenumbers (I. Young et al, 1995;Ewans, 1998;Hwang et al, 2000;Romero & Melville, 2010a;Leckler et al, 2015;Peureux et al, 2018) with the lobe separation approaching ±90 o at higher wavenumbers . However, efforts to model the directional spectrum with the 'exact' computations of S nl systematically yielded narrower spectra and weak bimodality at high wavenumbers compared to observations (Romero & Melville, 2010b;Liu et al, 2019;Romero & Lubana, 2022).…”

A New Probabilistic Wave Breaking Model for Dominant Wind-sea Waves Based on the Gaussian Field Theory

“…A4)in which H h is the Heaviside step function, k c is the central wavenumber for a given wavenumber range, σ(k c ) = σ(k c ) θ(k c ) is the saturation spectrum normalized by the averaged directional spreading, p 1 = 0.0045 and p 2 = 33 are constants obtained from their observations. FollowingBanner et al (2002), the directional spreading angle is calculated according toHwang et al (2000) (their equation 19a):…”