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All figures (9)
TABLE II. Backscattered pressure amplitude relative to the incident pressure amplitude in units of 131026 for a 50-mm-diam spherical void immersed in sea water, calculated at 1000 m range for the analytical expressed solution and BEM, and scaled to 1000 m for the farfield Kirchhoff approximation. The effect o amplitude of the orientation of the subdivided icosahedron used to represent the void in the BEM and Kir approximation is expressed through the parenthetical quantity, which is the maximum percentage de from the mean observed over a wide range of axial orientations. Values in italics indicate that the mode nodal separation exceedingl/6 at the specified frequency.
FIG. 2. Frequency dependence of a spherical void of radius 25 mm mersed in water of density 1025 kg/m3 and sound speed 1470 m/s, as giv by the series solution, Kirchhoff integral through the closed-form expres in Eq. ~13!, numerical Kirchhoff approximation using a surface mesh w 642 nodes, and boundary-element method using the same 642-node s mesh.
TABLE IV. Back- and forward-scattered pressure amplitudes shown in Table III, but expressed in de relative to 1-m range and incident wave amplitude.
TABLE III. Back- and forward-scattered pressure amplitudes relative to the incident pressure amplitude i of 131026 for a 50-mm-diam spherical void at 1000-m range for the analytical series-expressed solutio BEM, and scaled to 1000 m for the farfield Kirchhoff approximation. A single, fixed orientation is assume the axis of the subdivided icosahedron used to represent the void in the BEM and Kirchhoff approximatio percentage deviation relative to the analytical solution is given.
TABLE I. Properties of the 15 specimens whose swimbladder surfaces have been remapped, based on the original mapping~Ref. 23! with ntri small triangular facets, bynelem curvilinear elements withnnodesnodes. The nodal separation distance such that 99% of neighboring separations are smaller and the m nodal separation are both specified.
FIG. 3. BEM and Kirchhoff-approximation-model computations of target strength as a function of tilt angle compared against direct measurem specimen No. 205. The functions are shown for both dorsal and ventral aspects at each of four frequencies.
FIG. 1. Boundary-element mesh of the swimbladder to specimen No. 20 Ref. 23, shown in both oblique and dorsal views. The model has 1 elements and 3181 nodes. The meshed swimbladder length is 141 mm
TABLE V. Regression coefficient for the target strength–fish length relationship based on computati measurements of each of 15 specimens in dorsal aspect when averaged over four distinct distribution angleu, characterized by the meanū and standard deviationsu , abbreviated s.d. The coefficientb is that shown in Eq. ~15!. The associated standard error of the regression, SE, is also shown.
TABLE VI. Regression coefficient for the target strength–fish length relationship based on computatio measurements of each of 15 specimens in ventral aspect when averaged over four distinct distribution angleu, characterized by the meanū and standard deviationsu , abbreviated s.d. The coefficientb is that shown in Eq. ~15!. The associated standard error of the regression, SE, is also shown.
Journal Article
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DOI
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Comparing Kirchhoff-approximation and boundary-element models for computing gadoid target strengths
[...]
Kenneth G. Foote
1
,
David T. I. Francis
•
Institutions (1)
Woods Hole Oceanographic Institution
1
03 Apr 2002
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Journal of the Acoustical Society of America