scholarly journals Simulation and analysis on low-frequency scattering characteristics of the finite cylindrical shell in shallow water

2019 ◽  
Vol 283 ◽  
pp. 03007
Author(s):  
Jinyu Li ◽  
Dejiang Shang ◽  
Yan Xiao
Keyword(s):  
Cylindrical Shell ◽  
Free Space ◽  
Acoustic Scattering ◽  
Low Frequency ◽  
Target Strength ◽  
Wave Direction ◽  
Scattering Field ◽  
Simulation Results ◽  
Finite Cylindrical Shell ◽  
Target Locations

Low-frequency acoustic scatterings from a finite cylindrical shell are numerically analyzed by FEM. The simulation results show that the acoustic-scattering field in waveguide has lots of frequency-related sidelobes, while no sidelobes exist in free space at low frequencies. The simulation also indicates that the module value in waveguide can be almost 20 dB larger than that in free space at low frequency, which is caused by the ocean boundaries. We also demonstrate that when the incident wave direction is normal to the target at low frequency, the target strength will be maximum and the distribution of the acoustic-scattering field is axisymmetric about the incident waving direction. Meanwhile, the acoustic-scattering field is also related to the impedance of the seabed, and the change of the impedance makes just a little contribution to the scattering field. Finally, the influence of different target locations is analyzed, including the targets near the sea surface, seabed and the middle region of the ocean waveguide, respectively. From simulation results, it is evident that the distribution of the acoustic-scattering field at low frequency has a little difference, which is smaller than 0.5 dB with various target locations, and the change is frequency and boundary-related.

An acoustic metasurface with simultaneous phase modulation and energy attenuation

2018 ◽  
Vol 32 (23) ◽  
pp. 1850276 ◽  
Author(s):  
Baozhu Cheng ◽  
Hong Hou ◽  
Nansha Gao
Keyword(s):  
Phase Modulation ◽  
Low Frequency ◽  
Layered Media ◽  
Media Theory ◽  
Wave Direction ◽  
Medium Theory ◽  
Underwater Acoustic ◽  
Potential Applications ◽  
Simulation Results ◽  
Effective Phase

We introduced a rigid structure into the acoustic metasurface design, the proposed labyrinth structure is based on the equivalent medium theory and different media are replaced by curly labyrinth. Layered media theory and equivalent medium theory are combined to design the arbitrary acoustic metasurface structure. An acoustic metasurface studied in this paper realized simultaneous phase modulation and energy attenuation in the air, the effective phase modulation range covered from 30[Formula: see text] to 90[Formula: see text] and the energy attenuation is over 40%. According to layered media theory which could modulate the acoustic wave direction, the metasurface with same function can also be applied to underwater case. Corresponding simulation results are calculated by FEA. Finally, by introducing the curly labyrinth theory, the underwater acoustic metasurface with simultaneous phase modulation and energy attenuation is designed and verified. This paper has potential applications in rigid underwater acoustic metasurface designs with low frequency, adjustable direction and sound energy attenuation.

Acoustic Scattering Field Reconstruction Using Truncated Total Least Square Algorithm

2018 ◽  
Vol 27 (04) ◽  
pp. 1850055
Author(s):  
Haitao Yu ◽  
Yingmin Wang ◽  
Qi Wang
Keyword(s):  
Acoustic Scattering ◽  
Reconstruction Algorithm ◽  
Least Square ◽  
Modal Expansion ◽  
Field Reconstruction ◽  
Scattering Field ◽  
Wave Numbers ◽  
Total Least Square ◽  
Simulation Results ◽  
Expansion Coefficients

Acoustic scattering-field reconstruction of structures with arbitrary shape is the research basis of the scattering characteristics for underwater targets. Firstly, using boundary element method (BEM) and acoustic radiation modes (ARMs) solution in fluid domain, it is proved that the scattering pressures can be expressed by ARMs. Secondly, the acoustic field distribution modes (AFDMs) are constructed by ARMs and a new acoustic transfer matrix (ATM) which is acquired by the simplification of the traditional ATM. At the same time, the scattering pressures can be expressed as the product of the AFDMs and the modal expansion coefficients. Thus, the scattering reconstruction problem is converted into the exact solution problem of the modal expansion coefficients. Aiming at the existing noise of both the pressures at measuring point and AFDMs, the total least square (TLS) algorithm is introduced to acquire the accurate solution. Further, considering the ill-conditioned AFDMs matrix, the truncated total least square (TTLS) algorithm is introduced to solve the modal expansion coefficients. Simulation results show that the capability of resisting noise contamination is limited for the reconstruction algorithm based on TLS and that the reconstruction algorithm based on TTLS has a better denoising performance than the TLS one. At the same time, for smaller wave numbers, the modal orders for reconstruction at different noise levels are approximately equal and the reconstruction errors are small. The simulation results also demonstrate that the reconstruction algorithm based on TTLS has a better denoising performance at smaller wave numbers than at higher wave numbers. For the higher wave numbers, the modal orders for reconstruction decrease and the reconstruction errors increase with the decrease of the signal-to-noise ratio (SNR). For the backward reconstruction at smaller wave numbers, the influence to reconstruction results, which arises from structure complexity ascending and evanescent waves existing, should be considered when the reconstruction surfaces are near the structures.

scholarly journals Acoustic scattering from a stiffened finite cylindrical shell with external rings

2019 ◽  
Vol 283 ◽  
pp. 03002
Author(s):  
Fulin Zhou ◽  
Jun Fan ◽  
Bin Wang
Keyword(s):  
Cylindrical Shell ◽  
Acoustic Waves ◽  
Cylindrical Shells ◽  
Acoustic Scattering ◽  
Approximate Analytical Expression ◽  
Low Frequencies ◽  
Stiffened Cylindrical Shell ◽  
Layered Shells ◽  
Underwater Target ◽  
Finite Cylindrical Shell

Studying the interaction of sound with cylindrical shells immersed in water is essential and helpful to improving underwater target detection and classification algorithms. Elastic cylindrical shells often occur as part of double-layered shell and have been widely used in marine and aerospace area. Acoustic waves are easy to be transmitted through the outer shell to the interior especially at low frequencies, thus directly being scattered by the inner shell and the rings in water between double-layered shells. Therefore, the externally ring-stiffened cylindrical shell is investigated in this paper. An experiment was conducted that measured the acoustic scattering. A hybrid 2-D/3-D finite-element modelling technique is employed to numerically calculate the scattering characteristics. Good qualitative agreement is found between numerical calculations and experimental measurement. An approximate analytical expression is given explicitly to identify the Bragg wave trajectories in the frequency-angle spectrum. It also has been shown that the rings not only affect the dynamic response of shell and indirectly influence the exterior scattered field, but also become direct acoustic scatterers in water and increase the target cross section especially at oblique incidence.

Near-field target strength of finite cylindrical shell in water

2021 ◽  
Vol 182 ◽  
pp. 108233
Author(s):  
Keunhwa Lee ◽  
Yeon-Seong Choo ◽  
Giyung Choi ◽  
Youngmin Choo ◽  
Sung-Hoon Byun ◽  
...  
Keyword(s):  
Cylindrical Shell ◽  
Near Field ◽  
Target Strength ◽  
Finite Cylindrical Shell

Effect of internal inhomogeneities on acoustic scattering from finite cylindrical shell bounded by hemispherical endcaps

1999 ◽  
Vol 105 (2) ◽  
pp. 1088-1088
Author(s):  
Nicolas Touraine ◽  
Dominique Décultot ◽  
Gérard Maze ◽  
Aleksander Klauson ◽  
Jaan Metsaveer
Keyword(s):  
Cylindrical Shell ◽  
Acoustic Scattering ◽  
Finite Cylindrical Shell

scholarly journals Acoustic scattering by an arbitrarily shaped body: an application of the boundary-element method

2003 ◽  
Vol 60 (3) ◽  
pp. 563-570 ◽  
Author(s):  
Tsuyoshi Okumura ◽  
Toshikazu Masuya ◽  
Yoshimi Takao ◽  
Kouichi Sawada
Keyword(s):  
Boundary Element Method ◽  
Boundary Element ◽  
Excellent Agreement ◽  
Acoustic Scattering ◽  
Low Frequency ◽  
Prolate Spheroid ◽  
Target Strength ◽  
Extinction Cross Section ◽  
Quality Factor Q ◽  
Element Method

Abstract The boundary-element method (BEM) is applied to calculate target strength (TS) and extinction cross-section of a scatterer. The scattering amplitudes of four types of prolate spheroid, namely, the vacant, rigid, liquid-filled, and gas-filled, are calculated using the BEM. Comparison between the results of the BEM and the prolate-spheroid model (PSM), which is a numerical calculation using spheroidal-wave functions, shows excellent agreement for the vacant, rigid, and liquid-filled spheroids. The TS of a gas-filled prolate spheroid, calculated by the BEM, shows resonance at a low frequency. The lowest resonant frequency, the peak ratio, and the quality factor (Q) of this resonance are compared with those given by the T-matrix and an analytical solution. Again the results show excellent agreement.

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