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1

Microphone Based Acoustic Vector Sensor for Direction Finding with Bias Removal

Wajid Mohd, Kumar Arun, Bahl Rajendar

Archives of Acoustics

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2022

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Vol. 47, No. 2

151--167

EN

The acoustic vector sensor (AVS) is used to measure the acoustic intensity, which gives the direction-of-arrival (DOA) of an acoustic source. However, while estimating the DOA from the measured acoustic intensity the finite microphone separation (d) in a practical AVS causes angular bias. Also, in the presence of noise there exists a trade off between the bias (strictly increasing function of d) and variance (strictly decreasing function of d) of the DOA estimate. In this paper, we propose a novel method for mitigating the angular bias caused due to finite microphone separation in an AVS. We have reduced the variance by increasing the microphone separation and then removed the bias with the proposed bias model. Our approach employs the finite element method (FEM) and curves fitting to model the angular bias in terms of microphone separations and frequency of a narrowband signal. Further, the bias correction algorithm based on the intensity spectrum has been proposed to improve the DOA estimation accuracy of a broadband signal. Simulation results demonstrate that the proposed bias correction scheme significantly reduces the angular bias and improves the root mean square angular error (RMSAE) in the presence of noise. Experiments have been performed in an acoustic full anechoic room to corroborate the effect of microphone separation on DOA estimation and the efficacy of the bias correction method.

2

Numerical Modelling of Detonation Reaction Zone of Nitromethane by EXPLO5 Code and Wood and Kirkwood Theory

Štimac Barbara, Chan Hay Yee Serene, Kunzel Martin, Suceska Muhamed

Central European Journal of Energetic Materials

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2020

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Vol. 17, no. 2

239--261

EN

The detonation reaction zone of nitromethane (NM) has been extensively studied both experimentally and theoretically. The measured particle velocity profile of NM shows the existence of a sharp spike followed by a rapid drop over the first 5-10 ns (fast reaction). The sharp spike is followed by a gradual decrease (slow reactions) which terminate after approximately 50-60 ns when the CJ condition is attained. Based on experimental data, the total reaction zone length is estimated to be around 300 μm. Some experimental observations, such as the reaction zone width and the diameter effect, can be satisfactorily reproduced by numerical modelling, provided an appropriate reaction rate model is known. Here we describe the model for numerical modelling of the steady state detonation of NM. The model is based on the coupling thermochemical code EXPLO5 with the Wood-Kirkwood detonation theory, supplemented with different reaction rate models. The constants in the rate models are calibrated based on experimentally measured particle velocity profiles and the detonation reaction zone width. It was found that the model can describe the experimentally measured total reaction time (width of reaction zone) and the particle velocitytime profile of NM. It was found also that the reaction rate model plays a key role on the shape of the shock wave front. In addition, the model can predict the detonation parameters (D, pCJ, TCJ, VCJ, etc.) and the effect of charge diameter on the detonation parameters.

3

Optimizing the seismic effects of blasting in quarries by timing

Baulovič Ján, Pandula Blažej, Kondela Julián, Prekopová Marta

Materiały Wysokoenergetyczne

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2019

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T. 11(2)

48--62

EN

Recently, negative effects of the blasting operations and quantification of the seismic safety are regarded as very important technical problem in quarries. The impact of blasting operations is accompanied by both positive and negative seismic effects. For example, vibrations generated by explosion create very positive effect − when help to break the rocks, but, on the other hand, also result in negative effect − when affect constructions and natural environment in the vicinity of a blasting works site. If the vibrations are large enough, then the nearby objects could be damaged or destroyed. This article highlights the results of the blasting operation monitoring in limestone Lopušné Pažite quarry on Slovakia, which based on the rule that the negative effects depend on their range and strength. This method is applied in all quarries in Slovakia, which are close to settlements.

PL

Współcześnie, niepożądane skutki prac strzałowych oraz ilościowa ocena bezpieczeństwa sejsmicznego są szczególnie ważnym tematem badawczym w górnictwie odkrywkowym. Prowadzeniu prac strzałowych towarzyszą zarówno pożądane, jak i niekorzystne efekty sejsmiczne, np. drgania generowane wybuchem powodują z jednej strony efekt pożądany, czyli pozwalają na kruszenie skał, jednak z drugiej strony zagrażają konstrukcjom i środowisku naturalnemu w otoczeniu miejsca prowadzenia prac strzałowych. Jeżeli drgania są wystarczająco silne, wtedy konstrukcja pobliskich obiektów może zostać uszkodzona, lub obiekty te mogą ulec całkowitemu zniszczeniu. W pracy przedstawiono wyniki monitoringu prac strzałowych wykonanych w kopalni odkrywkowej wapienia w Lopušné Pažite (Słowacja), które bazują na zasadzie, że skala oddziaływania efektów niepożądanych zależy od zasięgu ich oddziaływania i siły. Zaprezentowana metoda jest stosowana we wszystkich kamieniołomach na Słowacji, w pobliżu których znajdują się obszary zamieszkane.

4

Research on the milisecond delay blasting impact in order to minimize seismic effects in Kučín quarry surrounding

Baulovič J., Pandula B., Kondela J.

Materiały Wysokoenergetyczne

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2015

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T. 7

5--13

EN

The intensity of seismic waves’ vibrations is proportional to the weight of the applied explosive. If the vibrations are sufficientin energy, surrounding buildings can be damaged or destroyed. Evaluating the negative effects of the blasting operations and quantification of the seismic safety is nowadays very actual and a challenging problem. The article presents the results of the analysis as well as an evaluation on seismic safety of the objects during blasting in the quarry Kučín. The results the evaluation seismic effects blasting verified in a Kučín quarry are the methodological base for evaluating the seismic effects of blasting in all quarries in Slovakia.

5

Entropijny model rozkładu prędkości ziaren w pionowym klasyﬁkatorze grawitacyjnym

Otwinowski H.

Inżynieria i Aparatura Chemiczna

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2013

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Nr 3

222--223

PL

W artykule przedstawiono modelowanie rozkładu prędkości ziaren w kolumnie pionowego klasyﬁkatora grawitacyjnego przy wykorzystaniu zasady maksymalizacji entropii informacyjnej. Zagadnienie wariacyjne z dwoma warunkami dodatkowymi rozwiązano metodą mnożników Lagrange’a. Adekwatność modelu potwierdziły wyniki eksperymentalnej weryﬁkacji na podstawie pomiarów prędkości ziaren elektrokorundu w pionowej kolumnie układu z cyrkulacyjną warstwą ﬂuidalną.

EN

Modeling of particle velocity distribution in a vertical column of gravitational classifier using the maximum informational entropy principle is presented in the paper. Variational problem with two additional conditions was solved using the Lagrange multipliers method. Results of experimental verification confirmed the model adequacy. Verification was carried out by the measurement of velocity of electrocorundum particles in a vertical column with the circulating fluidized bed.

6

Statistics and characteristic scales for bed load in a channel flow with sidewall effects

Radice A., Ballio F., Nikora V.

Acta Geophysica

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2010

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Vol. 58, no. 6

1072-1093

EN

Results are presented for a long-duration sediment transport experiment with a plane bed. High-frequency time series of sediment concentration, sediment velocity and solid discharge per unit width were measured using image analysis of video records. A range of transport intensities from a single experiment has been analysed considering transport at different distances from the sidewalls as an independent variable. First and second order temporal statistics of the spatially-averaged values of the transport parameters are presented, which are in agreement with previous studies. A refined statistical analysis of the sediment concentration dynamics, reflecting bed load process, is also given. The characteristic scales of the sediment concentration dynamics are evaluated and analyzed in conjunction with those of the near-bed and bulk flow fields.

7

Anechoic measurements of particle-velocity probes compared to pressure gradient and pressure microphones

Woszczyk W., Iwaki M., Sugimoto T., Ono K., de Bree H. E.

Archives of Acoustics

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2007

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Vol. 32, No. 3

643--658

EN

The Microflown is an acoustic particle velocity sensor invented at the University of Twente in Holland in 1994 and commercialized in 1997 [1, 9]. The sensor directly measures particle velocity rather than pressure-gradient as do most unidirectional and bidirectional microphones. The sensor has several interesting operational characteristics however few measurements of the Microflown have been published until now making it difficult for a potential user to assess the merits of this transducer in comparison to high quality condenser microphones commonly used in music and speech recording. This paper offers some insight by presenting anechoic measurements of particle velocity probes compared to the measurements of pressuregradient and pressure microphones (of condenser type) made under identical acoustical conditions at varying distances from a point source having a wide frequency range. Detailed frequency response measurements show how the characteristics of these transducer types are dependent on their distance to the source, and highlight the need of transducer calibration with respect to distance. Very few microphone manufacturers publish frequency response data for more than one reference distance to the source although distance is often used to modify the applied response of the microphone. An additional goal for making these measurements is to establish the relationship between particle velocity and pressure gradient values using the same acoustical conditions. The measurements were made in the large anechoic chamber of the NHK Science and Technical Research Laboratories (STRL) in Tokyo during the April-May of 2006.