DeCourcy Brendan

No Thumbnail Available
Last Name
First Name

Search Results

Now showing 1 - 7 of 7
  • Article
    Effects of front width on acoustic ducting by a continuous curved front over a sloping bottom
    (Acoustical Society of America, 2019-09-30) DeCourcy, Brendan ; Lin, Ying-Tsong ; Siegmann, William L.
    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.
  • Article
    Parameter dependence of acoustic mode quantities in an idealized model for shallow-water nonlinear internal wave ducts
    (Acoustical Society of America, 2019-09-30) Milone, Matthew A. ; DeCourcy, Brendan ; Lin, Ying-Tsong ; Siegmann, William L.
    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.
  • Article
    Approximate formulas and physical interpretations for horizontal acoustic modes in a shelf-slope front model
    (Acoustical Society of America, 2016-07-07) DeCourcy, Brendan ; Lin, Ying-Tsong ; Siegmann, William L.
    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.
  • Article
    Estimating the parameter sensitivity of acoustic mode quantities for an idealized shelf-slope front
    (Acoustical Society of America, 2018-02-06) DeCourcy, Brendan ; Lin, Ying-Tsong ; Siegmann, William L.
    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.
  • Article
    A coupled mode model for omnidirectional three-dimensional underwater sound propagation
    (Acoustical Society of America, 2020-07-07) DeCourcy, Brendan ; Duda, Timothy F.
    A fully three-dimensional (3D) omnidirectional numerical coupled mode model of acoustic propagation is detailed. A combination of normal mode and finite element computational methods is applied to produce the numerical results. The technique is tested in a strongly range-dependent ocean environment modeled after the Hudson Canyon. Modeled sound from three source locations selected over different bathymetric depths is examined to determine capabilities and difficulties associated with varying numbers of propagating vertical modes across the horizontal domain, and variable amounts of mode coupling. Model results are compared to those from a unidirectional Cartesian 3D parabolic equation simulation, and from adiabatic (uncoupled) simulations to illustrate the capabilities of the techniques to study the influences of coupling, strong refraction, and reflection.
  • Article
    Real-time joint ocean acoustics and circulation modeling in the 2021 New England Shelf Break Acoustics experiment (L)
    (Acoustical Society of America, 2022-11-10) DeCourcy, Brendan J. ; Lin, Ying-Tsong ; Zhang, Weifeng Gordon ; Ozanich, Emma Reeves ; Kukshtel, Natalie ; Siderius, Martin ; Gawarkiewicz, Glen ; Forsyth, Jacob
    During the spring of 2021, a coordinated multi-vessel effort was organized to study physical oceanography, marine geology and biology, and acoustics on the northeast United States continental shelf, as part of the New England Shelf Break Acoustics (NESBA) experiment. One scientific goal was to establish a real-time numerical model aboard the research vessel with high spatial and temporal resolution to predict the oceanography and sound propagation within the NESBA study area. The real-time forecast model performance and challenges are reported in this letter without adjustment or re-simulation after the cruise. Future research directions for post-experiment studies are also suggested.
  • Article
    Spatial and temporal variation of three-dimensional ship noise coherence in a submarine canyon
    (Acoustical Society of America, 2023-02-10) DeCourcy, Brendan J. ; Lin, Ying-Tsong
    Ship noise recorded by a vertical hydrophone array in the Mississippi Canyon region of the Gulf of Mexico is shown to contain the acoustic influence of bathymetric features, seabed properties, and water column sound speeds. Noise coherence is demonstrated to be an effective metric not just for identifying ship traffic in recorded data but also for “fingerprinting” the environment. A three-dimensional acoustics model adopting automatic identification system ship track information and realistic oceanographic conditions is used to compute noise coherence distributions across the canyon area and enables numerical study of the water column sound speed effects that can lead to temporal changes in noise coherence. The study shows the importance of including in situ sound speed measurements or constraints in passive ship noise localization from coherence measurements. Seasonal variability is also examined with models suggesting a strong influence of seasonal changes.