Spherical wave backscatter from straight cylinders: Thin-wire standard targets (original) (raw)
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Scattering and diffraction of acoustic waves by partially compliant cylinders
Journal of the Acoustical Society of America, 1981
SONAR equation. It is shown that in most cases the backscattering strength becomes range-independent beyond short distances. The backscattering strength therefore appears to be a useful parameterisation of regional and seasonal reverberation and may possibly be applied to determine the range dependence of transmission loss. 3:00 QQS. Scattering coefficients and Doppler spectra of specularly scatterS! sound from the sea surface. W. I. Roderick and W. G.
IEEE Transactions on Antennas and Propagation, 1986
A closed-form, high-frequency approximation is obtained for the diffracted-reflected-diffracted field contribution to the backscattered field resulting from the grazing illumination of a perfectly conducting, infinitely long, finned cylinder by a normally incident cylindrical transverse magnetic (TM) wave. The result, which is valid for any relative magnitudes of the cylinder radius and the fin w?idth provided both of them are electrically large, is derived by two different methods. One of them is the radiation integral method related to the physical theory of diffraction. The other is the complex rag tracing method related to the spectral theory of diffraction (STD). Relative merits and disadvantages of the two methods are pointed out.
Acoustic radiation and scattering from cylindrical bodies and analysis of transducer arrays
INFLIBNET, 2011
Front Cover: (Left) Far-field acoustic radiation from a phased array of cylindrical transducers (blue) and a rectangular piston (red); and (Right) the magnitude of the interior pressure field in an embedded fluid cylinder ensonified by a plane acoustic wave computed using ray theory iii THESIS CERTIFICATE This is to certify that the thesis entitled "Acoustic radiation and scattering from cylindrical bodies and analysis of transducer arrays" submitted by JASMINE MATHEW to the Cochin University of Science and Technology, Cochin for the award of degree of Doctor of Philosophy under the Faculty of Science is a bonafide record of research work carried out by her under my supervision. The contents of this thesis, in full or in parts, have not been submitted to any other institute or University for the award of any degree or diploma. The research work has been carried out
Sound scattering of an arbitrary wave incident on a simply-supported cylindrical shell
Journal of the Acoustical Society of Japan (E), 1995
Acoustic scattering of an arbitrary wave incident on a finite submerged cylindrical shell is studied theoretically and experimentally, where the term arbitrary wave is referred to non-plane, non-spherical wave-front emanating from an actual transducer driven by a single frequency. An analytical solution for the spherical wave incidence is extended by introducing the concepts of "insonified window" and "shape parameter."
Modelling and Measurement of Backscattering from Partially Water-Filled Cylindrical Shells
The backscattering from partially water-filled cylindrical shells has been studied using finite element (FE) analysis and experimental measurements for low to medium frequencies, corresponding to 2 < ka < 30 (where a is the shell outer radius). For a partially-filled shell, filled to three quarters of the inner diameter, backscattering has been investigated numerically as a function of the elevation angle of the incident wave, and in particular as the wave direction changes from horizontal to vertical. Comparisons with fully air-filled and fully water-filled shells indicate that the shell resembles the former when the wave is incident from above and the latter when the wave is incident horizontally. The experiments were performed in a reservoir, using horizontal incidence and wideband Ricker pulses generated by a parametric array. The short duration of the Ricker pulses made it possible to observe a number of returns after the specular return for a shell with a high filling fraction; these included contributions due to S 0 waves generated at the front and back walls of the shell, and the back wall return. Inversion of the FE model data enabled the expected waveforms to be predicted; the measurements were in very good agreement with the predictions.
Acoustic wave scattering from transversely isotropic cylinders
The Journal of the Acoustical Society of America, 1996
Mathematical expressions are derived for the far-field backscattering amplitude spectrum resulting from oblique insonification of an infinite, transversely isotropic elastic cylinder by a plane acoustic wave. The normal-mode solution is based on decoupling of the scalar potential representing the horizontally polarized shear wave from those of the compressional and vertically polarized waves. The solution degenerates to the well-known simple model for isotropic cylinders in the case of very weak anisotropy. The solution is used to study the influence of each element of the stiffness matrix on the various resonant modes of vibration. Perturbations of the elements c33 and c44, which characterize the cylinder along the axis, significantly affect resonant frequencies corresponding to axially guided waves. Perturbations of c11 and c12, which characterize the material on the transverse plane, predominantly affect the Rayleigh and Whispering Gallery resonance frequencies. Perturbations of ...
IEEE Transactions on Antennas and Propagation, 2001
The idea of using acoustically induced Doppler spectra as a means for target detection and identification is introduced. An analytical solution for the calculation of the bistatic scattered Doppler spectrum from an acoustically excited, vibrating metallic circular cylinder is presented. First the electromagnetic scattering solution of a slightly deformed circular cylinder is obtained using a perturbation method. Then, assuming the vibration frequency is much smaller than the frequency of the incident electromagnetic wave, a closed form expression for the time-frequency response of the bistatic scattered field is obtained which can be used directly for estimating the Doppler spectrum. The acoustic scattering solution for an incident acoustic plane wave upon a solid elastic cylinder is applied to give the displacement of the cylinder surface as a function of time. Results indicate that the scattered Doppler frequencies correspond to the mechanical vibration frequencies of the cylinder, and the sidelobe Doppler spectrum level is, to the first order, linearly proportional to the degree of deformation and is a function of bistatic angle. Moreover, the deformation in the cylinder, and thus the Doppler sidelobe level, only becomes sizeable near frequencies of normal modes of free vibration in the cylinder. Utilizing the information in the scattered Doppler spectrum could provide an effective means of buried object identification, where acoustic waves are used to excite the mechanical resonances of a buried object.
A revisit to the plane problem for low-frequency acoustic scattering by an elastic cylindrical shell
The proposed revisit to a classical problem in fluid-structure interaction is due to an interest in the analysis of the narrow resonances corresponding to a low-frequency fluid-borne wave, inspired by modeling and design of metamaterials. In this case, numerical implementations would greatly benefit from preliminary asymptotic predictions. The normal incidence of an acoustic wave is studied for a circular cylindrical shell governed by plane strain equations in elasticity. A novel highorder asymptotic procedure is established considering for the first time all the peculiarities of the low-frequency behavior of a thin fluid-loaded cylinder. The obtained results are exposed in the form suggested by the Resonance Scattering Theory. It is shown that the pressure scattered by rigid cylinder is the best choice for a background component. Simple explicit formulae for resonant frequencies, amplitudes, and widths are presented. They support various important observations, including comparison between widths and the error of the asymptotic expansion for frequencies.
Scattering of Electromagnetic Waves from a Deeply Buried Circular Cylinder
Journal of Electromagnetic Waves and Applications, 2000
Utilizing an approximate induced current distribution, the far-zone scattered fields from a perfectly conducting, circular cylinder, which is deeply buried in a dielectric half-space are evaluated. Interpretation of these scattered fields is presented in terms of ray optics. Important scattering parameters, i.e., far-zone field patterns, 3dB beamwidth, scattering width and total scattered power are evaluated. It is found that monostatic scattering width of circular cylinder, which is deeply buried in a dielectric half-space configuration, is related to monostatic scattering width of circular cylinder in a homogeneous medium via dielectric constant times the fourth power of Fresnel transmission coefficient. Behaviour of the total scattered power as a function of depth is found to be oscillatory around a mean value which is the total power scattered from a cylinder in homogeneous medium.
Physics of Fluids, 2022
For nonlinear wave–structure interactions, the high-frequency scattered waves can be identified within the drag-inertia regime, especially in steep incident waves where viscous effects are not negligible. According to previous studies, this unexpected phenomenon is highly associated with the local flow field, posing challenges to the existing harmonic-based diffraction solutions (mostly up to second-order). To overcome these shortcomings in potential flows, we establish a high-fidelity numerical wave tank to solve this two-phase free surface flow in the open source computational fluid dynamics framework OpenFOAM. We implement the ghost fluid method to eliminate the spurious velocities, mostly reported in two-phase volume of fluid solvers, in the vicinity of the free surface and preserve a sharp air–water interface. A modified generating–absorbing boundary condition is employed to achieve high computational efficiency without passive relaxation zones. Good agreement with experimental...