• Title/Summary/Keyword: Propagation characteristics

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Flame Propagation Characteristics of Propane-Air Premixed Mixtures (프로판-공기 예혼합기의 화염전파 과정에 관한 연구)

  • Bae, Choong-Sik
    • Journal of the Korean Society of Combustion
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    • v.1 no.2
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    • pp.21-29
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    • 1996
  • Flame propagation characteristics of propane-air mixtures were experimentally investigated in constant-volume combustion chambers. Flame propagation process was observed as a function of mixture strength, initial mixture temperature and initial mixture pressure in quiescent mixtures. A cylindrical combustion chamber and a spherical combustion chamber contain a pair of parallel windows through which optical access into the chamber can be provided. Laser two beam deflection method was adopted to measure the local flame propagation, which gave information on the flame size and flame propagation speed. Pressure development was also measured by a piezoelectric pressure transducer to characterize combustion in quiescent mixtures. Burning velocity was calculated from flame propagation and pressure measurements. The effect of flow on flame propagation was also investigated under flowing mixture conditions. Laser two beam method was found to be feasible in measuring flame propagation of quiescent mixtures. Flame was observed to propagate faster with higher initial mixture temperature and lower initial pressure. Combustion duration was shortened in the highly turbulent flowing mixtures.

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An Enhanced Approach for a Prediction Method of the Propagation Characteristics in Korean Environments at 781 MHz

  • Jung, Myoung-Won;Kim, Jong Ho;Choi, Jae Ick;Kim, Joo Seok;Kim, Kyungseok;Pack, Jeong-Ki
    • ETRI Journal
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    • v.34 no.6
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    • pp.911-921
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    • 2012
  • In high-speed wireless communications, an analysis of the propagation characteristics is an important process. Information on the propagation characteristics suitable for each environment significantly helps in the design of mobile communications. This paper presents the analysis results of radio propagation characteristics in outdoor environments for a new mobile wireless system at 781 MHz. To avoid the interference of Korean DTV broadcasting, we measure the channel characteristics in urban, suburban, and rural areas on Jeju Island, Republic of Korea, using a channel sounder and $4{\times}4$ antenna. The path loss (PL) measurement results differ from those of existing propagation models by more than 10 dB. To analyze the frequency characteristics for Korean propagation environments, we derive various propagation characteristic parameters: PL, delay spread, angular spread, and K-factor. Finally, we verify the validity of the measurement results by comparing them with the actual measurement results and 3D ray-tracing simulation results.

Effects Analysis of Partial Discharge Signal Propagation Characteristics in Underground Transmission Cables Using EMTP (EMTP를 이용한 지중송전케이블의 부분방전 신호 전파특성 분석)

  • Jung, Chae-Kyun;Jang, Tai-In
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.63 no.5
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    • pp.629-635
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    • 2014
  • This paper describes propagation characteristics obtained by considering semiconducting screen and cross-bonding in underground transmission cables. The semiconducting screen of power cable has effect on propagation characteristics including attenuation, velocity and surge impedance. However, it is very difficult to apply the semiconduction screen for EMTP model because of the number of conductors limitation. Therefore, CIGRE WG 21-05 proposed advanced insulation structure and analysis technique of simplified approach including inner and outer semiconducting screen. In this paper, the various propagation characteristics analyse using this structure and technique for 154kV XLPE $2000mm^2$ cable. The frequency independent model of EMTP CABLE PARAMETER is used for just pattern analysis of propagation characteristics. For exact data analysis, the frequency dependent model of J-marti is used for EMTP modeling. From these result, various propagation characteristics of 154kV XLPE $2000mm^2$ cable according to semi conducting screen consideration, frequency range, cable length and pulse width are analysed. In addition, in this paper, the effects of cross-bonding are also variously discussed according to cross-bonding methods, direct connection and impedance of lead cable.

Stress wave propagation in clearance joints based on characteristics method

  • Tang, Ya-Qiong;Li, Tuan-Jie;Chen, Cong-Cong;Wang, Zuo-Wei
    • Structural Engineering and Mechanics
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    • v.62 no.6
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    • pp.781-788
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    • 2017
  • In this paper, a stress wave model is established to describe the three states (separate, contact and impact) of clearance joints. Based on this stress wave model, the propagation characteristics of stress wave generated in clearance joints is revealed. First, the stress wave model of clearance joints is established based on the viscoelastic theory. Then, the reflection and transmission characteristics of stress wave with different boundaries are studied, and the propagation of stress wave in viscoelastic rods is described by the characteristics method. Finally, the stress wave propagation in clearance joints with three states is analyzed to validate the proposed model and method. The results show the clearance sizes, initial axial speeds and material parameters have important influences on the stress wave propagation, and the new stress waves will generate when the clearance joint in contact and impact states, and there exist some high stress region near contact area of clearance joints when the incident waves are superposed with reflection waves, which may speed up the damage of joints.

A Study on Characteristics of Noise Propagation for Railway (철도차량 소음방사 특성에 관한 연구)

  • 구동회;김재철;박태원
    • Journal of the Korean Society for Railway
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    • v.5 no.1
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    • pp.26-31
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    • 2002
  • The more sophisticated patterns of propagation model is presented in this paper, which includes three different source characteristics (spherical, cosine and dipole). The spherical, cosine and dipole radiation characteristics compared, and sound event level and the maximum sound level are calculated by experiment and calculation. It is shown that patterns of propagation have dipole characteristics for low speed range (below about 150Km/h) at electric multiple system. We know that push-pull high speed system has cosine characteristics of noise propagation at low speed range (below about 200Km/h).

Analysis of Combustion and Flame Propagation Characteristics of LPG and Gasoline Fuels by Laser Deflection Method

  • Lee, Ki-Hyung;Lee, Chang-Sik;Ryu, Jea-Duk;Park, Gyung-Min
    • Journal of Mechanical Science and Technology
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    • v.16 no.7
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    • pp.935-941
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    • 2002
  • This work is to investigate the combustion characteristics and flame propagation of the LPG (liquified petroleum gas) and gasoline fuel. In order to characterize the combustion processes of the fuels, the flame propagation and combustion characteristics were investigated by using a constant volume combustion chamber The flame propagation of both LPG and gasoline fuels was investigated by the laser deflection method and the high-speed Schlieren photography. The result of laser deflection method show that the error of measured flame propagation speed by laser method is less than 5% compared with the result of high-speed camera. The flame propagation speed of the fuel is increased with the decrease of initial pressure and the increase of initial temperature in the constant volume chamber. The results also show that the equivalence ratio has a grate effect on the flame speed, combustion pressure and the combustion duration of the fuel-air mixture.

A study on characteristics of noise propagation for railway (철도차량의 소음방사 특성에 관한 연구)

  • Kim, Jae-Chul;Koo, Dong-Hoe;Moon, Kyeong-Ho
    • Proceedings of the KSME Conference
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    • pp.204-209
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    • 2001
  • The more sophisticated patterns of propagation model is presented in this paper, which includes three different source characteristics (spherical, cosine and dipole). The spherical, cosine and dipole radiation characteristics compared, and sound event level and the maximum sound level are calculated by experiment and calculation. It is shown that patterns of propagation have dipole characteristics for low speed range (below about 150Km/h) at electric multiple system. We know that push-pull high speed system has cosine characteristics of noise propagation at low speed range (below about 200Km/h).

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A Study on Propagation Characteristics of Acoustic Signals in Indoor Environments (실내 음향신호 경로감쇠 모형 및 분석)

  • Jeong, Sang-Hyo;Lee, Eui-Hyoung;Yoo, Seung-Soo;Kim, Sun-Yong
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.36 no.2C
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    • pp.119-125
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    • 2011
  • Start This paper analyzes the propagation characteristics of acoustic signals in indoor environments, which is applicable to indoor positioning system. Indoor stereo sound system is generally valid within $25m^2$. So it is not possible to apply prevalent sound propagation characteristic to indoor positioning system because the prevalent acoustic signals propagation characteristic is defined under free space condition. Therefore, in this paper, we present the propagation characteristics of acoustic signals in indoor environments considering the free space propagation characteristic as well as room characteristic such as humidity, temperature, absorption of atmosphere and so on. To verify the designed propagation model of indoor acoustic signals, this paper presents the propagation characteristics of decreasing sinusoidal signals whose frequencies ate from 1kHz to 20kHz in anechoic room. In addition, this paper also presents the propagation characteristics of decreasing sinusoidal signals which have multiple frequencies.

Characteristics of Propagating Tribrachial Flames in Counterflow (대향류 유동장에서 삼지 화염 전파 특성에 관한 연구)

  • Chung, Tae-Man;Ko, Young-Sung;Chung, Suk-Ho
    • Proceedings of the KSME Conference
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    • pp.422-427
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    • 2000
  • Propagation characteristics of tribrachial flames have been investigated experimentally in both two-dimensional and axisymmetric counterflows. Mixture fraction gradient at stoichiometric location is controlled by varying equivalence ratios at the two nozzles, one of which maintains rich while the other lean premixture. Tribrachial flames propagating through these mixtures are investigated. The propagation speed of tribrachial flames in two-dimensional counterflow decreases with fuel concentration gradient and has much higher speed than the maximum speed predicted previously in two-dimensional mixing layers. From an analogy with premixed flame propagation, this excessively large propagation speed can be attributed to the tribrachial flame propagating with respect to burnt gas. Corresponding maximum speed in the limit of small mixture fraction gradient is estimated and extrapolated experimental results substantiate this limiting speed. As mixture fraction gradient approaches zero, a transition in propagation characteristics occurs, such that the propagation speed of tribrachial flame approaches stoichiometric laminar burning velocity with respect to burnt gas. Similar behavior has been obtained for tribrachial flames propagating in axisymmetric counterflow.

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Structural Health Monitoring Based on Wave Propagation Characteristics (파동전파특성에 기초한 구조 건전도 모니터링)

  • Kim, Seung-Joon;Park, Jun-Hong
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • pp.311-314
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    • 2007
  • The experimental method of measuring dynamic properties of structures was presented. The method is based on the flexural wave propagation characteristics. Using the method, change in structural dynamic properties due to damage is measured. The crack has much more significant impact on the strain energy than the inertial effects. From this, the sensitivity of the dynamic stiffness on the crack location is estimated by calculating the strain energy. When the wave propagates, the strain and kinetic energies shows cyclic changed over space. The crack that occurred at locations where the wave energy is in the form of the potential energy affected most significantly the wave propagation characteristics. The effects of crack location on the wave propagation were used to determine the crack location.

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