3. Sound waves

2018 ◽  
pp. 43-52
Author(s):  
Mike Goldsmith
Keyword(s):  
Pressure Wave ◽  
Red Light ◽  
Wave Spectrum ◽  
Sound Power ◽  
Sound Waves ◽  
Active Sonar ◽  
Sonar Systems ◽  
Audio Range ◽  
Deep Violet ◽  
Lower Frequencies

Sound is a small fraction of the pressure wave spectrum. In terms of wavelength, we can hear far more than we can see: while deep red light has waves about twice as long as those of deep violet, the lowest-pitched sound waves we can hear are about ten times longer than the highest. ‘Sound waves’ explains infrasound, the lower frequencies detectable by touch rather than hearing, and the audio range, describing the fundamental differences between sound power and loudness, and frequency and pitch. It also considers sound underwater. Sonar systems can be passive systems that simply detect sounds, while active sonar transmits sounds and detects those that are reflected.

Impact of strong direct blast on active sonar systems

2015 ◽  
Vol 51 (2) ◽  
pp. 894-909 ◽  
Author(s):  
Luzhou Xu ◽  
Jian Li ◽  
Akshay Jain
Keyword(s):  
Active Sonar ◽  
Sonar Systems

Performance comparison of target localization for active sonar systems

2008 ◽  
Vol 44 (4) ◽  
pp. 1371-1380 ◽  
Author(s):  
Suhwan Kim ◽  
Bonhwa Ku ◽  
Wooyoung Hong ◽  
Hanseok Ko
Keyword(s):  
Performance Comparison ◽  
Target Localization ◽  
Active Sonar ◽  
Sonar Systems

scholarly journals An Improved Velocity Estimation Method for Wideband Multi-Highlight Target Echoes in Active Sonar Systems

Sensors ◽  
2018 ◽  
Vol 18 (9) ◽  
pp. 2794 ◽  
Author(s):  
Shuxia Huang ◽  
Shiliang Fang ◽  
Ning Han
Keyword(s):  
Matched Filter ◽  
Estimation Method ◽  
Velocity Estimation ◽  
Filter Method ◽  
Improved Method ◽  
Matching Algorithm ◽  
Active Sonar ◽  
Estimation Performance ◽  
Effective Performance ◽  
Sonar Systems

In active sonar systems, the target echoes are usually equivalent to a superposition of the Doppler-scaled reflections from multiple highlights. The reflections overlap with each other both in the time and frequency domain, which results in a decreased velocity estimation performance. Recently, the hyperbolic-frequency modulated signal has been widely employed in sonar systems for moving targets due to its Doppler tolerance, while the precise velocity estimation becomes a great challenge under such conditions. In this paper, the echo c is modeled onsidering a target with a constant velocity and multi-highlights. The velocity estimation performance is analyzed though the signal’s matched filter and the wideband ambiguity function. An improved method based on the sliding window matching algorithm is proposed to improve the performance. The method controls the energy of environmental noise and interference by focusing on the dominant target highlight, and applying a designed window which utilizes the Doppler characteristics of hyperbolic-frequency modulated signals. Simulations and lake experiment allow us to compare between the improved method and the conventional matched filter method. The results verify the influence of the multi-highlights in velocity estimation and indicate that the improved method has more effective performance.

Analysis on Signal Transmission Methods for Rapid Searching in Active SONAR Systems

2018 ◽  
Vol 55 (8) ◽  
pp. 83-93
Author(s):  
Woo-Sung Son ◽  
Young Kwang Seo ◽  
Wan-Jin Kim ◽  
Hyoung-Nam Kim
Keyword(s):  
Signal Transmission ◽  
Active Sonar ◽  
Sonar Systems

Paper 11: Variation of Hydraulic Pressure in Annular Space between Guide Vanes and Impeller of a Francis Turbine

1966 ◽  
Vol 181 (1) ◽  
pp. 109-118
Author(s):  
E. Lund
Keyword(s):  
Wave Propagation ◽  
Sound Wave ◽  
Pressure Wave ◽  
Resonance Phenomenon ◽  
Francis Turbine ◽  
Laboratory Model ◽  
Hydraulic Pressure ◽  
Sound Waves ◽  
Annular Space ◽  
Guide Vanes

One of the main sources of vibration in Francis turbines is thought to be pressure-wave disturbances generated from the impeller and interference impulses between impeller vanes and guide vanes. A theory is developed which explains the occurrence of severe vibrations caused by the elasticity of the water as a resonance phenomenon between the disturbing impulses and normal modes of vibration in the space between the impeller and the guide wheel. The wave propagation in the fluid, which is assumed to be uniform with no steady flow, is thought to satisfy the well-known sound-wave differential equation without any damping effects. The natural frequencies for one- and two-dimensional pressure-wave oscillations are calculated. The calculations, based on prior knowledge of the velocity of sound-wave propagation, show that a simple theory of one-dimensional oscillations interpreted as rotating sound waves in the annular space is sufficient to predict critical speeds of the turbine. Measurements carried out on a laboratory model Francis turbine for a head of 4.5 m and a capacity of about 1.0 m3/s confirmed the presence of free oscillations and indicated the occurrence of a resonance phenomenon in the annular space.

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