The Transient Character of the Near - Field Acoustic Radiation from Cylindrical Diaphragm Excited by Waterhammer Transients

1970 ◽  
Author(s):  
B.W. Davis ◽  
E.E. Weynand
Keyword(s):  
Acoustic Radiation ◽  
Near Field

Acoustic radiation simulation and pre-stress effect on compact acoustic levitation platform

2019 ◽  
Vol 33 (07) ◽  
pp. 1950080 ◽  
Author(s):  
Bin Wei ◽  
Yongyong He ◽  
Wei Wang
Keyword(s):  
Pressure Distribution ◽  
Acoustic Radiation ◽  
Near Field ◽  
Parameters Optimization ◽  
Squeeze Film ◽  
Acoustic Levitation ◽  
Stress Effect ◽  
Biological Engineering ◽  
Loop Control ◽  
Close Loop Control

In order to satisfy the requirements of precise components with tidiness, low power and high stability in the field of biological engineering, medical equipment and semiconductors etc. a pre-stress acoustic transport prototype without horn was proposed in this paper. The mechanism of levitation and transport which is driven by orthogonal waves was revealed by the analysis of waveform and squeeze film characteristics in high-frequency exciting condition; also, the electric, solid and acoustic coupled finite element method (FEM) was established to investigate the effect of pre-stress and acoustic pressure distribution in the near field. The levitation and driving capacity of near field acoustic levitation (NFAL) transport platform without horns can be proved in this experiment and further to achieve the goal of parameters optimization. The theoretical and experimental results indicate that the pre-stress has a significant effect on resonant frequency and levitating stability, the pre-stress are determined by the DC voltage offset which is related to the system working point so that we cannot increase the offset and exciting voltage unlimitedly to improve the stability. At the same time, the calculated pressure distribution of acoustic radiation can generally reflect the regional bearing capacity in near and far field for levitation. These achievements can partly solve the problem of accuracy design of prototype and thickness of gas film, supporting for accuracy close loop control of levitating height.

Effects of Quay Wall and Seabed Reflection on the AUV Acoustic Radiation Test Analysis

2014 ◽  
Vol 599-601 ◽  
pp. 922-926
Author(s):  
Guo Liang Xu ◽  
Qi Wei He ◽  
Shao Chun Ding ◽  
Hai Bo Wan
Keyword(s):  
Acoustic Field ◽  
Field Test ◽  
Sound Pressure ◽  
Acoustic Radiation ◽  
Near Field ◽  
Test Analysis ◽  
Complex Sound ◽  
Quay Wall ◽  
Radiation Test ◽  
Acoustical Holography

To analyze effects of quay environment on the AUV radiated acoustic field test, the PNAH (PNAH: planar near-field acoustical holography) was used to simulate acoustic field. By simulating the free and non-free acoustic field and comparing amplitudes and angles of complex sound pressure, Analyze effects of quay wall and seabed reflection on the AUV radiated acoustic field test to determine the standard of quay wall and seabed environment which meets testing. The work would provide a certain reference for the AUV radiated acoustic field test.

Noncontact Planar Stage Based on Near-Field Acoustic Transportation

2020 ◽  
Vol 8 (2) ◽  
Author(s):  
Yang Yang ◽  
Keyu Chen ◽  
Ping Guo
Keyword(s):  
Reynolds Equation ◽  
Closed Loop ◽  
Acoustic Radiation ◽  
Dimensional Space ◽  
Near Field ◽  
Radiation Force ◽  
Driving Mechanism ◽  
Two Dimensional ◽  
Closed Loop System ◽  
Novel Design

Abstract Acoustic radiation force in the near-field of a vibrating source can be utilized to lift and transport objects, which provides a noncontact driving technology in addition to maglev. This paper presents a novel design of a self-levitated planar stage based on near-field acoustic transportation. A closed-loop system is proposed to design a capacitance surface encoder to provide direct two-dimensional (2D) position feedback. A dynamic model based on the Reynolds equation is established to study its driving mechanism. A prototype including the levitation stage, encoder, and controller is implemented to demonstrate the potential of arbitrary trajectory tracking in two-dimensional space.

The Transient Character of the Near-Field Acoustic Radiation From a Cylindrical Diaphragm Excited by Water Hammer Transients

1971 ◽  
Vol 93 (4) ◽  
pp. 1216-1224
Author(s):  
B. W. Davis ◽  
E. E. Weynand
Keyword(s):  
Produced Water ◽  
Acoustic Radiation ◽  
Mechanical Design ◽  
Near Field ◽  
Experimental System ◽  
Wave Pattern ◽  
Water Hammer ◽  
Compressive Wave ◽  
Surrounding Water ◽  
Time Space

An investigation of the transient character of the near-field acoustic radiation from a water hammer excited, cylindrical diaphragm was conducted. The investigation was principally experimental and focused on relating the radiated waveforms to pressure transients within the pipe. The basic experimental system consisted of a length of rigid pipe extending from a flow source into a large sonar tank. The rigid pipe was interrupted by a cylindrical section of elastomeric tubing which served as a diaphragm and, thus, as an acoustic coupler between the water inside the pipe and water surrounding the pipe. A quick-closing valve downstream of the diaphragm produced water hammer transients which were coupled to the surrounding water through the diaphragm and were monitored in the near-field by hydrophones. The physical system geometry was varied to include data for a range of pipe sizes from 0.5 in. to 4.0 in. inside dia and from 10 ft to 34 ft in length. The experiments revealed that two distinct major waves could always be identified in each radiated wave pattern. One was found to originate from the primary water hammer compressive wave downstream of the diaphragm. The other major wave was attributed to a precursor wave which originated upstream of the diaphragm. The propagation paths of the two waves are identified and it is shown that their relation to one another in time space is a predictable function of geometry. It is estimated, by extrapolating from the experimental data, that an acoustic pressure in excess of 88 psi at one yard is possible from a system of realistic mechanical design.

scholarly journals Observation of photoacoustic Smith-Purcell radiation

2021 ◽  
Author(s):  
Dongyi Shen ◽  
Zhihao Zhou ◽  
Guolin Zhao ◽  
Xianfeng Chen ◽  
Wenjie Wan
Keyword(s):  
Shock Waves ◽  
Frequency Spectrum ◽  
Acoustic Radiation ◽  
Near Field ◽  
Critical Role ◽  
Universal Theory ◽  
Relativistic Electrons ◽  
Radiation Process ◽  
Constant Frequency ◽  
Acoustic Wave Generation

Abstract Relativistic electrons moving over a periodic metal grating can lead to an intriguing emission of light, known as Smith-Purcell radiation (SPR), the precursor of the free-electron laser. During the radiation process, the speed of light plays a critical role in determining the emitted angle and frequency spectrum. Inspired by the photonic SPR, here we experimentally demonstrate a photoacoustic version of the Smith-Purcell effect using laser-induced surface shock waves generation. We observe similar acoustic radiation pattern and their associated frequency spectrum in the far-field, perfectly predicted by a universal theory working for both the photonic and acoustic SPR. Moreover, our numerical studies reveal non-constant frequency components due to the supersonic traveling of the shock waves in the near field, greatly contrasting its photonic counterpart. This scheme extends the SPR into the acoustic domain by levitating the wave’s speed limit, paves the way towards coherent acoustic wave generation and microstructure metrology.

Near-field acoustic holography of acoustic radiation from structures

2012 ◽  
Vol 131 (4) ◽  
pp. 3258-3258
Author(s):  
Rongfu Mao ◽  
Zhimin Chen ◽  
Haichao Zhu
Keyword(s):  
Acoustic Radiation ◽  
Near Field ◽  
Acoustic Holography
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