Approximate formulas and physical interpretations for horizontal acoustic modes in a shelf-slope front model

Author Posting. © Acoustical Society of America, 2016. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 140 (2016): EL20, doi:10.1121/1.4954881.The structure and behavior of horizontal acoustic modes for a three-dimensional idealized model of a shelf-slope front are examined analytically. The Wentzel–Kramers–Brillouin–Jeffreys (WKBJ) method is used to obtain convenient simple expressions and to provide physical insight into the structure and behavior of horizontal modes as trapped, leaky, or transition types. Validity regions for WKBJ expressions in terms of slope and frontal parameters are found, and outside the regions the asymptotic formulas for large order and large argument Hankel functions are used. These combined approximations have very good accuracy as shown by comparisons with numerical solutions for modal shapes and horizontal wavenumbers.This work has been supported by the Office of Naval Research through grants to Rensselaer Polytechnic Institute and to Woods Hole Oceanographic Institution

Estimating the parameter sensitivity of acoustic mode quantities for an idealized shelf-slope front

Author Posting. © Acoustical Society of America, 2018. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 143 (2018): 706-715, doi:10.1121/1.5022776.The acoustic modes of an idealized three-dimensional model for a curved shelf-slope ocean front [Lin and Lynch, J. Acoust. Soc. Am. 131, EL1–EL7 (2012)] is examined analytically and numerically. The goal is to quantify the influence of environmental and acoustic parameters on acoustic field metrics. This goal is achieved by using conserved quantities of the model, including the dispersion relation and a conservation of mode number. Analytic expressions for the horizontal wave numbers can be extracted by asymptotic approximations and perturbations, leading to accurate and convenient approximations for their parameter dependence. These equations provide the dependence on model parameter changes of both the real horizontal wavenumbers, leading to modal phase speeds and other metrics, and the imaginary parts, leading to modal attenuation coefficients. Further approximations for small parameter changes of these equations characterize the parameter sensitivities and produce assessments of environmental and acoustic influences.This work was supported by the Office of Naval Research under grants to Rensselaer Polytechnic Institute (Grant No. N00014-14-1-0372, which is a Special Research Award in Ocean Acoustics for the first author's Ph.D. degree, and also Grant No. N00014-17-1-2370), and to Woods Hole Oceanographic Institution (Grant No. N00014-11-1-0701), which is a Multidisciplinary University Research Initiative

Effects of front width on acoustic ducting by a continuous curved front over a sloping bottom

Author Posting. © Acoustical Society of America, 2019. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 146(3), (2019): 1923-1933, doi:10.1121/1.5125426.The behavior of sound near an ocean front in a region with wedge bathymetry is examined. The front is parameterized as a zone of variation with inshore and offshore boundaries parallel to a straight coastline. The importance of frontal width and frontal sound speed on the ducting of acoustic energy is examined. Previous analytical studies of sound propagation and parameter sensitivity in an idealized wedge environment use an unphysical but convenient single interface front representation, which is here replaced by a continuous sound speed profile. The continuous profile selected is convenient for analytical investigation, but encourages the use of asymptotic approximation methods which are also described. The analytical solution method is outlined, and numerical results are produced with an emphasis on comparing to the single interface front. These comparisons are made to highlight the strengths and weaknesses of the idealized model for capturing the horizontal ducting effects.The authors would like to thank Dr. T. F. Duda for his comments on this work. This work was supported by the Office of Naval Research under grants to Rensselaer Polytechnic Institute (Grant No. N00014-14-1-0372, which is a Special Research Award in Ocean Acoustics for the Ph.D. degree of B.J.D., and also Grant No. N00014-17-1-2370), and to Woods Hole Oceanographic Institution (Grant No. N00014-11-1-0701 which is a Multidisciplinary University Research Initiative, and Grant No. N00014-18-1-2172 which is a Postdoctoral Fellowship for B.J.D.).2020-03-3

Parameter dependence of acoustic mode quantities in an idealized model for shallow-water nonlinear internal wave ducts

Author Posting. © Acoustical Society of America, 2019. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 146(3), (2019): 1934-1945, doi:10.1121/1.5125261.Nonlinear internal waves in shallow water have significant acoustic impacts and cause three-dimensional ducting effects, for example, energy trapping in a duct between curved wavefronts that propagates over long distances. A normal mode approach applied to a three-dimensional idealized parametric model [Lin, McMahon, Lynch, and Siegmann, J. Acoust. Soc. Am. 133(1), 37–49 (2013)] determines the dependence of such effects on parameters of the features. Specifically, an extension of mode number conservation leads to convenient analytical formulas for along-duct (angular) acoustic wavenumbers. The radial modes are classified into five types depending on geometric characteristics, resulting in five distinct formulas to obtain wavenumber approximations. Examples of their dependence on wavefront curvature and duct width, along with benchmark comparisons, demonstrate approximation accuracy over a broad range of physical values, even including situations where transitions in mode types occur with parameter changes. Horizontal-mode transmission loss contours found from approximate and numerically exact wavenumbers agree well in structure and location of intensity features. Cross-sectional plots show only small differences between pattern phases and amplitudes of the two calculations. The efficiency and accuracy of acoustic wavenumber and field approximations, in combination with the mode-type classifications, suggest their application to determining parameter sensitivity and also to other feature models.This work was supported by the Office of Naval Research under grants to Rensselaer Polytechnic Institute (Grant Nos. N00014-14-1-0372 and N00014-17-1-2370) and to Woods Hole Oceanographic Institution (Grant Nos. N00014-11-1-0701 and N00014-17-1-2692). Additional funding was provided by Naval Undersea Warfare Center Division Newport through the SMART Scholarship for the first author's doctoral degree program. The authors also thank Dr. Timothy F. Duda of WHOI and Dr. David Wells of University of North Carolina at Chapel Hill for their assistance with this paper.2020-03-3

Analysis and modeling of broadband airgun data influenced by nonlinear internal waves

Author Posting. © Acoustical Society of America, 2004. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 116 (2004): 3404-3422, doi:10.1121/1.1819499.To investigate acoustic effects of nonlinear internal waves, the two southwest tracks of the SWARM 95 experiment are considered. An airgun source produced broadband acoustic signals while a packet of large nonlinear internal waves passed between the source and two vertical linear arrays. The broadband data and its frequency range (10–180 Hz) distinguish this study from previous work. Models are developed for the internal wave environment, the geoacoustic parameters, and the airgun source signature. Parabolic equation simulations demonstrate that observed variations in intensity and wavelet time–frequency plots can be attributed to nonlinear internal waves. Empirical tests are provided of the internal wave-acoustic resonance condition that is the apparent theoretical mechanism responsible for the variations. Peaks of the effective internal wave spectrum are shown to coincide with differences in dominant acoustic wavenumbers comprising the airgun signal. The robustness of these relationships is investigated by simulations for a variety of geoacoustic and nonlinear internal wave model parameters.This work was supported by an ONR Ocean Acoustics Graduate Traineeship Award and by ONR grants to Rensselaer, the University of Delaware, and Woods Hole Oceanographic Institution

Measurement and modeling of three-dimensional sound intensity variations due to shallow-water internal waves

Author Posting. © Acoustical Society of America, 2005. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 117 (2005): 613-625, doi:10.1121/1.1828571.Broadband acoustic data (30–160 Hz) from the SWARM'95 experiment are analyzed to investigate acoustic signal variability in the presence of ocean internal waves. Temporal variations in the intensity of the received signals were observed over periods of 10 to 15 min. These fluctuations are synchronous in depth and are dependent upon the water column variability. They can be explained by significant horizontal refraction taking place when the orientation of the acoustic track is nearly parallel to the fronts of the internal waves. Analyses based on the equations of vertical modes and horizontal rays and on a parabolic equation in the horizontal plane are carried out and show interesting frequency-dependent behavior of the intensity. Good agreement is obtained between theoretical calculations and experimental data.This work was supported by the Ocean Acoustics Program at the Office of Naval Research (ONR Grants N00014-01-1-0114 to U.D., and N00014-04-1-0016 to R.P.I.) and by the Russian Foundation For Basic Research (RFBR Grant 03-05-64568-a)

Experimental evidence of three-dimensional acoustic propagation caused by nonlinear internal waves

Author Posting. © Acoustical Society of America, 2005. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 118 (2005): 723-734, doi:10.1121/1.1942428.The 1995 SWARM experiment collected high quality environmental and acoustic data. One goal was to investigate nonlinear internal wave effects on acoustic signals. This study continues an investigation of broadband airgun data from the two southwest propagation tracks. One notable feature of the experiment is that a packet of nonlinear internal waves crossed these tracks at two different incidence angles. Observed variations for the lower angle track were modeled using two-dimensional parabolic equation calculations in a previous study. The higher incidence angle is close to critical for total internal reflection, suggesting that acoustic horizontal refraction occurs as nonlinear internal waves traverse this track. Three-dimensional adiabatic mode parabolic equation calculations reproduce principal features of observed acoustic intensity variations. The correspondence between data and simulation results provides strong evidence of the actual occurrence of horizontal refraction due to nonlinear internal waves.This work was supported by an ONR Ocean Acoustics Graduate Traineeship Award and by ONR grants to Rensselaer, the University of Delaware, and the Woods Hole Oceanographic Institution

Horizontal ducting of sound by curved nonlinear internal gravity waves in the continental shelf areas

Author Posting. © Acoustical Society of America, 2013. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 133 (2013): 37-49, doi:10.1121/1.4770240.The acoustic ducting effect by curved nonlinear gravity waves in shallow water is studied through idealized models in this paper. The internal wave ducts are three-dimensional, bounded vertically by the sea surface and bottom, and horizontally by aligned wavefronts. Both normal mode and parabolic equation methods are taken to analyze the ducted sound field. Two types of horizontal acoustic modes can be found in the curved internal wave duct. One is a whispering-gallery type formed by the sound energy trapped along the outer and concave boundary of the duct, and the other is a fully bouncing type due to continual reflections from boundaries in the duct. The ducting condition depends on both internal-wave and acoustic-source parameters, and a parametric study is conducted to derive a general pattern. The parabolic equation method provides full-field modeling of the sound field, so it includes other acoustic effects caused by internal waves, such as mode coupling/scattering and horizontal Lloyd's mirror interference. Two examples are provided to present internal wave ducts with constant curvature and meandering wavefronts.This work was sponsored by the Office of Naval Research under grants N00014-10-1-0040 and N00014-11- 1-0701

Technological elites, the meritocracy, and postracial myths in Silicon Valley

Entre as modernas elites tecnológicas digitais, os mitos da meritocracia e da façanha intelectual são usados como marcadores de raça e gênero por uma supremacia branca masculina que consolida recursos de forma desproporcional em relação a pessoas não brancas, principalmente negros, latinos e indígenas. Os investimentos em mitos meritocráticos suprimem os questionamentos de racismo e discriminação, mesmo quando os produtos das elites digitais são infundidos com marcadores de raça, classe e gênero. As lutas históricas por inclusão social, política e econômica de negros, mulheres e outras classes desprotegidas têm implicado no reconhecimento da exclusão sistêmica, do trabalho forçado e da privação de direitos estruturais, além de compromissos com políticas públicas dos EUA, como as ações afirmativas, que foram igualmente fundamentais para reformas políticas voltadas para participação e oportunidades econômicas. A ascensão da tecnocracia digital tem sido, em muitos aspectos, antitética a esses esforços no sentido de reconhecer raça e gênero como fatores cruciais para inclusão e oportunidades tecnocráticas. Este artigo explora algumas das formas pelas quais os discursos das elites tecnocráticas do Vale do Silício reforçam os investimentos no pós racialismo como um pretexto para a re-consolidação do capital em oposição às políticas públicas que prometem acabar com práticas discriminatórias no mundo do trabalho. Por meio de uma análise cuidadosa do surgimento de empresas de tecnologias digitais e de uma discussão sobre como as elites tecnológicas trabalham para mascarar tudo, como inscrições algorítmicas e genéticas de raça incorporadas em seus produtos, mostramos como as elites digitais omitem a sua responsabilidade por suas reinscrições pós raciais de (in)visibilidades raciais. A partir do uso de análise histórica e crítica do discurso, o artigo revela como os mitos de uma meritocracia digital baseados em um “daltonismo racial” tecnocrático emergem como chave para a manutenção de exclusões de gênero e raça.Palavras-chave: Tecnologia. Raça. Gênero.Among modern digital technology elites, myths of meritocracy and intellectual prowess are used as racial and gender markers of white male supremacy that disproportionately consolidate resources away from people of color, particularly African Americans, Latino/as and Native Americans. Investments in meritocratic myths suppress interrogations of racism and discrimination even as the products of digital elites are infused with racial, class, and gender markers. Longstanding struggles for social, political, and economic inclusion for African Americans, women, and other legally protected classes have been predicated upon the recognition of systemic exclusion, forced labor, and structural disenfranchisement, and commitments to US public policies like affirmative action have, likewise, been fundamental to political reforms geared to economic opportunity and participation. The rise of the digital technocracy has, in many ways, been antithetical to these sustained efforts to recognize race and gender as salient factors structuring technocratic opportunity and inclusion. This paper explores some of the ways in which discourses of Silicon Valley technocratic elites bolster investments in post-racialism as a pretext for re-consolidations of capital, in opposition to public policy commitments to end discriminatory labor practices. Through a careful analysis of the rise of digital technology companies, and a discussion of how technology elites work to mask everything from algorithmic to genetic inscriptions of race embedded in their products, we show how digital elites elide responsibility for their post-racial re-inscriptions of racial visibilities (and invisibilities). Using historical and critical discourse analysis, the paper reveals how myths of a digital meritocracy premised on a technocratic colorblindness emerge key to perpetuating gender and racial exclusions.Keywords: Technology. Race. Gender