EFFECTS OF UNDERWATER LOW-FREQUENCY SOUND PROPAGATION THROUGH CONTINENTAL BARRIER

Обнаружены и исследованы подводный и донный низкочастотные акустические сигналы (400 Гц) от подводного источника излучения, расположенного относительно приемной системы по другую сторону перешейка мыса Шульца. Приемная система состояла из трехкомпонентного донного геофона и приемной акустической комбинированной системы, расположенной в толще волновода на глубине 9 м. Кратчайшее расстояние между источником и приемником через материковый барьер составляет ~ 1000 м. Азимутальный угол прихода сигнала продольных волн совпадает с геометрической линией, соединяющей источник и приемник. Прием поперечной и продольной волн осуществляется по различным ортогональным осям координат геофона. Направление прихода продольной волны в точку измерения близко к горизонтальному. Наличие поперечной волны в донном грунте позволяет предположить, что дно волновода представляет собой твердую жесткую поверхность. The present work studies the underwater and sea bottom low-frequency signals (400 Hz) emitted by the underwater transducer and detected by the receiver system located on the other side of the Schultz cape neck relative to the transducer. The receiver system consisted of a three-component bottom geophone and composite acoustical system immersed 9 m down the water column of the waveguide. The shortest distance between transducer and receiver through the continental barrier was ~1000 m. The azimuth angle of signal arrival corresponds to a geometrical line connecting a pair transducer/receiver. The reception of longitudinal and transverse waves was performed alongside different orthogonal axes of geophone coordinates. The direction of the longitudinal wave arrival at the reception point was close to horizontal. The presence of the transverse wave in the bottom soil suggests that the bottom of the waveguide represents a solid rigid surface.

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Characteristics of Very Low Frequency Sound Propagation in Full Waveguides of Shallow Water

Sensors ◽

10.3390/s21010192 ◽

2020 ◽

Vol 21 (1) ◽

pp. 192

Author(s):

Nansong Li ◽

Hanhao Zhu ◽

Xiaohan Wang ◽

Rui Xiao ◽

Yangyang Xue ◽

...

Keyword(s):

Shallow Water ◽

Wave Speed ◽

Sound Propagation ◽

Sea Water ◽

Bottom Topography ◽

Low Frequency ◽

Acoustic Energy ◽

Propagation Characteristics ◽

Sea Bottom ◽

Proposed Model

This work is concerned with the characteristics of very low frequency sound propagation (VLF, ≤100 Hz) in the shallow marine environment. Under these conditions, the classical hypothesis of considering the sea bottom as a fluid environment is no longer appropriate, and the sound propagation characteristics at the sea bottom should be also considered. Hence, based on the finite element method (FEM), and setting the sea bottom as an elastic medium, a proposed model which unifies the sea water and sea bottom is established, and the propagation characteristics in full waveguides of shallow water can be synchronously discussed. Using this model, the effects of the sea bottom topography and the various geoacoustic parameters on VLF sound propagation and its corresponding mechanisms are investigated through numerical examples and acoustic theory. The simulation results demonstrate the adaptability of the proposed model to complex shallow water waveguides and the accuracy of the calculated acoustic field. For the sea bottom topography, the greater the inclination angle of an up-sloping sea bottom, the stronger the leak of acoustic energy to the sea bottom, and the more rapid the attenuation of the acoustic energy in sea water. The effect of a down-sloping sea bottom on acoustic energy is the opposite. Moreover, the greater the pressure wave (P-wave) speed in the sea bottom, the more acoustic energy remains in the water rather than leaking into the bottom; the influence laws of the density and the shear wave (S-wave) speed in the sea bottom are opposite.

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Sound Field Modeling with Bottom Reflective Parameters (P,Q) Based on Parabolic Equation

Journal of Theoretical and Computational Acoustics ◽

10.1142/s2591728520500292 ◽

2020 ◽

Vol 28 (04) ◽

pp. 2050029

Author(s):

C. J. Zhang ◽

J. R. WU ◽

Z. D. Zhao ◽

L. Ma ◽

E. C. Shang

Keyword(s):

Sound Propagation ◽

Transmission Loss ◽

Low Frequency ◽

Sound Field ◽

Propagation Models ◽

Acoustical Properties ◽

Sea Bottom ◽

Model Independent ◽

The Mean ◽

Parameter Coupling

Acoustical properties of the sea bottom can be described using geoacoustic (GA) models. Most existing propagation models use GA parameters as the bottom properties. It is difficult to obtain GA parameters for a layered bottom because of inter parameter coupling. These problems can be solved by inverting the model-independent reflective parameters P and Q. For a multilayered bottom, a sound field computation model, RamPQ, is developed using the mapping of GA and (P, Q) spaces. The mean square error of the transmission loss in numerical simulations and experimental data for low-frequency sound propagation are employed to validate RamPQ and demonstrate the performance of the model.

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Research and Fabrication of Broadband Ring Flextensional Underwater Transducer

Sensors ◽

10.3390/s21041548 ◽

2021 ◽

Vol 21 (4) ◽

pp. 1548

Author(s):

Jiuling Hu ◽

Lianjin Hong ◽

Lili Yin ◽

Yu Lan ◽

Hao Sun ◽

...

Keyword(s):

High Speed ◽

Structural Parameters ◽

Low Frequency ◽

Flexural Vibration ◽

Underwater Acoustic Communication ◽

Voltage Response ◽

Water Tank ◽

Spherical Cap ◽

Finite Element Software ◽

Underwater Transducer

At present, high-speed underwater acoustic communication requires underwater transducers with the characteristics of low frequency and broadband. The low-frequency transducers also are expected to be low-frequency directional for realization of point-to-point communication. In order to achieve the above targets, this paper proposes a new type of flextensional transducer which is constructed of double mosaic piezoelectric ceramic rings and spherical cap metal shells. The transducer realizes broadband transmission by means of the coupling between radial vibration of the piezoelectric rings and high-order flexural vibration of the spherical cap metal shells. The low-frequency directional transmission of the transducer is realized by using excitation signals with different amplitude and phase on two mosaic piezoelectric rings. The relationship between transmitting voltage response (TVR), resonance frequency and structural parameters of the transducer is analyzed by finite element software COMSOL. The broadband performance of the transducer is also optimized. On this basis, the low-frequency directivity of the transducer is further analyzed and the ratio of the excitation signals of the two piezoelectric rings is obtained. Finally, a prototype of the broadband ring flextensional underwater transducer is fabricated according to the results of simulation. The electroacoustic performance of the transducer is tested in an anechoic water tank. Experimental results show that the maximum TVR of the transducer is 147.2 dB and the operation bandwidth is 1.5–4 kHz, which means that the transducer has good low-frequency, broadband transmission capability. Meanwhile, cardioid directivity is obtained at 1.4 kHz and low-frequency directivity is realized.

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