scholarly journals The acoustical impulse response of a line source of finite length above an absorbing plane

2020 ◽  
Vol 147 (5) ◽  
pp. 3691-3701
Author(s):  
Martin Ochmann
Keyword(s):  
Impulse Response ◽  
Finite Length ◽  
Line Source

Tilting at wave beams: a new perspective on the St. Andrew’s Cross

2017 ◽  
Vol 830 ◽  
pp. 660-680 ◽  
Author(s):  
T. Kataoka ◽  
S. J. Ghaemsaidi ◽  
N. Holzenberger ◽  
T. Peacock ◽  
T. R. Akylas
Keyword(s):  
Wave Field ◽  
Finite Length ◽  
Line Source ◽  
Cutoff Frequency ◽  
Three Dimensional ◽  
Resonance Phenomenon ◽  
Buoyancy Frequency ◽  
Reynolds Stresses ◽  
Mean Flow ◽  
Viscous Effects

The generation of internal gravity waves by a vertically oscillating cylinder that is tilted to the horizontal in a stratified Boussinesq fluid of constant buoyancy frequency, $N$, is investigated. This variant of the widely studied horizontal configuration – where a cylinder aligned with a plane of constant gravitational potential induces four wave beams that emanate from the cylinder, forming a cross pattern known as the ‘St. Andrew’s Cross’ – brings out certain unique features of radiated internal waves from a line source tilted to the horizontal. Specifically, simple kinematic considerations reveal that for a cylinder inclined by a given angle $\unicode[STIX]{x1D719}$ to the horizontal, there is a cutoff frequency, $N\sin \unicode[STIX]{x1D719}$, below which there is no longer a radiated wave field. Furthermore, three-dimensional effects due to the finite length of the cylinder, which are minor in the horizontal configuration, become a significant factor and eventually dominate the wave field as the cutoff frequency is approached; these results are confirmed by supporting laboratory experiments. The kinematic analysis, moreover, suggests a resonance phenomenon near the cutoff frequency as the group-velocity component perpendicular to the cylinder direction vanishes at cutoff; as a result, energy cannot be easily radiated away from the source, and nonlinear and viscous effects are likely to come into play. This scenario is examined by adapting the model for three-dimensional wave beams developed in Kataoka & Akylas (J. Fluid Mech., vol. 769, 2015, pp. 621–634) to the near-resonant wave field due to a tilted line source of large but finite length. According to this model, the combination of three-dimensional, nonlinear and viscous effects near cutoff triggers transfer of energy, through the action of Reynolds stresses, to a circulating horizontal mean flow. Experimental evidence of such an induced mean flow near cutoff is also presented.

Subsurface Electromagnetic Fields of a Grounded Cable of Finite Length

1973 ◽  
Vol 51 (14) ◽  
pp. 1534-1540 ◽  
Author(s):  
David A. Hill ◽  
James R. Wait
Keyword(s):  
Electromagnetic Fields ◽  
Finite Length ◽  
Line Source ◽  
Low Frequency ◽  
Frequency Limit ◽  
Special Cases ◽  
General Field ◽  
Finite Line ◽  
Radio Location ◽  
Finite Line Source

The subsurface fields of a finite line source or current-carrying cable are examined. Some special cases, such as the low-frequency limit, are treated analytically, and some simple working formulas are obtained. The general field expressions are reduced to single integrals with finite limits that are evaluated numerically. It is shown that if the source cable is sufficiently long, the fields are approximated by those for an infinite cable. The results have possible application to downlink communication and radio location of trapped miners.

scholarly journals The Effect of Car Free Day (CFD) on Pollutant Emissions at Alternative Roads (Case Study: RE Martadinata Street, Bogor City)

Agromet ◽  
2019 ◽  
Vol 33 (1) ◽  
pp. 8-19
Author(s):  
Rachmawati Aida ◽  
Fithriya Yulisiasih Rohmawati ◽  
Ana Turyanti
Keyword(s):  
Finite Length ◽  
Line Source ◽  
Vehicle Emissions ◽  
Ambient Air ◽  
Box Model ◽  
Pollutant Emissions ◽  
Estimate Dispersion ◽  
Short Time

Car Free Day (CFD) is a social campaign aimed to reduce the dependence of people on vehicle uses, which occurs once per week in Bogor. The idea intends to decrease the vehicle emissions. However, CFD is often to cause a new problem like the congestions, which are found on the nearby alternative roads, as happened in RE Martadinata Street, Bogor City. This study aims to compare the emission load and the concentrations of pollutants in ambient air during CFD (06.00-09.00 am) and non-CFD days in alternative road. We measured the following pollutants: CO, HC, NOx, PM10 and SO2. This research first applied Fixed-Box Model to estimate concentration of pollutants, then we used the Finite Length Line Source (FLLS) to estimate dispersion of pollutants. The results showed that there was no substantial difference in pollutant emissions between CFD and non-CFD days. But if we separate between weekdays and weekend, our analysis revealed that emissions during the weekend are bigger than that of weekdays. This was consistent with an increase of number of vehicles during the weekends by 17.2%. Based on our analysis, motorcycle contributes to an increased of CO, HC, PM10 pollutants, whereas SO2 and NOx pollutants were generated by cars. Our findings suggest that a short time of CFD does not contribute a lot to reduce the emissions.

Acoustic field radiated by an impulsively excited line source of finite length

1978 ◽  
Vol 64 (S1) ◽  
pp. S168-S168
Author(s):  
Anthony J. Rudgers ◽  
Ronald L. Spooner
Keyword(s):  
Acoustic Field ◽  
Finite Length ◽  
Line Source

scholarly journals A Method for Improving the Accuracy of Natural Frequency Measurement Using In-the-loop Computing

2021 ◽  
Vol 21 (4) ◽  
pp. 93-98
Author(s):  
Adam Kotowski
Keyword(s):  
Natural Frequency ◽  
Impulse Response ◽  
Finite Length ◽  
Spectral Resolution ◽  
Natural Frequencies ◽  
Reference Method ◽  
Frequency Measurement ◽  
Frequency Resolution ◽  
Zero Padding

Abstract The method presented in the paper is based on in-the-loop computing applied for impulse response to obtain a spectrum with a much higher frequency resolution than using FFT. Then, higher spectrum frequency resolution results in greater accuracy in estimation of natural frequencies. The frequency resolution of estimated spectrum in this method is completely independent of the length of impulse response and, by extension, the method eliminates the problem of spectral resolution limitation using FFT due to finite length of recorded signals. This fact is very useful and is the main advantage of the proposed method. The results of the method have been shown and compared in quantitative terms to natural frequencies estimated using classical FFT with zero-padding as reference method.

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