• Title/Summary/Keyword: Attenuation

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Effects of Wave Attenuation on the Acoustic Emission Amplitude Distribution of Injection-Molded Fiber/Plastic Composites (섬유/플라스틱 사출성형 복합재료의 음향방출 진폭분포에 대한 감쇠효과)

  • Choi, N.S.;Takahashi, Kiyoshi
    • Journal of the Korean Society for Nondestructive Testing
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    • v.18 no.1
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    • pp.1-9
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    • 1998
  • The attenuation of acoustic emission (AE) waves was evaluated for injection-molded short-fiber-reinforced thermoplastic composites employing simulated AE waves. Values of attenuation coefficient (${\alpha}$) decreased more with increasing fiber volume fraction ($V_f$) than that expected from a simple linear relation between ${\alpha}$ and $V_f$. The effect of wave attenuation was taken into account in a quantitative analysis of the AE peak amplitude distribution which was obtained from each zone partitioned in a specimen gage portion. The amplitude distribution compensated for the measured attenuation loss was exhibited almost similar in every zone of the specimen. Consequently, it was, shown that the AE amplitudes obtained from fiber/plastic composites were considerably affected by the attenuation.

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Experimental Investigation for the Attenuation Coefficient of Ultrasonic Guided Wave (유도초음파의 감쇠계수에 대한 실험적 고찰)

  • Lee, Dong-Jin;Cho, Youn-Ho;Lee, Joon-Hyun;Shin, Dong-Chul
    • Journal of the Korean Society for Nondestructive Testing
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    • v.29 no.5
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    • pp.458-465
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    • 2009
  • In general, ultrasonic guided wave techniques that used for an evaluation of the internal defect have been applied without considering energy loss. It can be found out that the significant attenuation is observed in the signal of structure with defect by the scattering and absorption. Even in the signal acquired from defect-free structure, this attenuation can be also significant. Therefore, it is very essential to determine the Lamb wave propagation characteristics depending on modes because the dispersibility of Lamb wave can be easily influenced by the attenuation effect with frequency and thickness. For this reason, changing the propagation distance, attenuation coefficient of each Lamb wave mode needs to be investigated by the contact pitch-catch method with PZT(piezoelectric) sensors. In this paper, the experimental attenuation coefficient is measured by choosing the following three different variables; mode, thickness and plate materials. As a result, experimental attenuation coefficient is obtained as the function of variables.

Performance Simulation of ACM for Compensating Rain Attenuation in Satellite Link (위성시스템 강우 감쇠 보상을 위한 ACM 성능 시뮬레이션)

  • Zhang, Meixiang;Kim, Sooyoung;Pack, Jeong-Ki;Kim, Ihn-Kyum
    • Journal of Satellite, Information and Communications
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    • v.7 no.3
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    • pp.8-15
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    • 2012
  • Adaptive transmission technique is an effective means to counter-measure rain attenation that is one of the most significant factors degrading link quality in satellite communication systems. This paper introduces a simulator for adaptive transmission technique to compensate rain attenuation. In the simulator, a dynamic rain attenuation model is loaded, which was developed to synthesize Korean rain attenuation dynamics at a frequency band of Ka. It is a Markov chain model with rain attenuation parameters extracted from the rain attenuation data measured per second. In addition, various transmission schemes are embedded so that a user defined simulations can be performed. This paper demonstrates simulation results of adaptive schemes in comprison with fixed schemes, and show the efficiency of the adaptive schemes to compensate the rain attenuation.

Loss Estimation in Southeast Korea from a Scenario Earthquake using the Deterministic Method in HAZUS

  • Kim, Kwang-Hee;Kang, Su-Young
    • 한국방재학회:학술대회논문집
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    • 2009.02b
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    • pp.43-50
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    • 2009
  • Strong ground motion attenuation relationship represents a comprehensive trend of ground shakings at sites with distances from the source, geology, local soil conditions, and others. It is necessary to develop an attenuation relationship with careful considerations of characteristics of the target area for reliable seismic hazard/risk assessments. In the study, observed ground motions from the January 2007 magnitude 4.9 Odaesan earthquake and the events occurring in the Gyeongsang provinces are compared with the previously proposed ground attenuation relationships in the Korean Peninsula to select most appropriate one. In the meantime, a few strong ground motion attenuation relationships are proposed and introduced in HAZUS, which have been designed for the Western United States and the Central and Eastern United States. The selected relationship from the ones for the Korean Peninsula has been compared with attenuation relationships available in HAZUS. Then, the attenuation relation for the Western United States proposed by Sadigh et al. (1997) for the Site Class B has been selected for this study. Reliability of the assessment will be improved by using an appropriate attenuation relation. It has been used for the earthquake loss estimation of the Gyeongju area located in southeast Korea using the deterministic method in HAZUS with a scenario earthquake (M=6.7). Our preliminary estimates show 15.6% damage of houses, shelter needs for about three thousands residents, and 75 life losses in the study area for the scenario events occurring at 2 A.M. Approximately 96% of hospitals will be in normal operation in 24 hours from the proposed event. Losses related to houses will be more than 114 million US dollars. Application of the improved methodology for loss estimation in Korea will help decision makers for planning disaster responses and hazard mitigation.

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Numerical Study on the Attenuation Effect of Water Mist on Thermal Radiation (미세물분무에 의한 열복사 감쇠 효과에 대한 수치해석 연구)

  • Ko, Gwon Hyun
    • Fire Science and Engineering
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    • v.34 no.4
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    • pp.7-12
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    • 2020
  • A numerical study was conducted to investigate the effects of the spray characteristics of water mist on the attenuation of thermal radiation. The attenuation process of the thermal radiation, generated from a hot surface panel, passing through the water mist was calculated via Fire Dynamics Simulator (FDS), and the effects of the flow rate, droplet mean diameter, and spray injecting angle of the water mist were analyzed. The results indicated that the increase in flowrate and decrease in droplet size led to an increase in the attenuation of thermal radiation. As the thermal radiation passed through the spray droplets, the effect of the spatial distribution of spray droplets was verified by calculating the thermal radiation attenuation at different spray injecting angles. The results indicated that the radiation attenuation increases as the spray angle increases. This implies that a wider distribution of spray droplets, irrespective of the droplet size and flowrate, increases the attenuation effect on thermal radiation.

Underwater E-plane Attenuation Model of Omnidirectional Antenna Using Half Power Beam Width (HPBW) (반전력빔폭을 이용한 전방향성 안테나의 수중 환경 수직 평면 감쇠 모델)

  • Kwak, Kyungmin;Park, Daegil;Kim, Younghyeon;Chung, Wan Kyun;Kim, Jinhyun
    • Journal of Institute of Control, Robotics and Systems
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    • v.21 no.11
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    • pp.1050-1056
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    • 2015
  • In this paper, we use the characteristics of electromagnetic waves underwater attenuation for estimating linear distance between a transmitting node and receiving node, and research underwater vertical plane attenuation model for constructing the underwater localization system. The underwater localization of 2 dimensional with the plane attenuation model in the horizontal plane (H-plane) was proposed previous research. But for the 3 dimensional underwater localization, the additional vertical plane (E-plane) model should be considered. Because the horizontal plane of omnidirectional antenna has the same attenuation tendency in x-y plane according to the distance, whereas in vertical plane shows an irregular pattern in x-z plane. For that reason, in the vertical plane environment, the attenuation should be changed by the position and inclination. Hence, in this paper the distance and angle between transmitting and receiving node are defined using spherical coordinate system and derive an antenna gain pattern using half power beam width (HPBW). The HPBW is called a term which defines antenna's performance between isotropic and other antennas. This paper derives omnidirectional antenna's maximum gain and attenuation pattern model and define vertical plane's gain pattern model using HPBW. Finally, experimental verifications for the proposed underwater vertical plane's attenuation model was executed.

DETECTION OF INTERFACIAL CRACK LENGTH BY USING ULTRASONIC ATTENUATION COEFFICIENTS ON ADHESIVELY BONDED JOINTS

  • Chung, N.Y.;Park, S.I.
    • International Journal of Automotive Technology
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    • v.5 no.4
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    • pp.303-309
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    • 2004
  • In this paper, an interfacial crack length has been detected by using the ultrasonic attenuation coefficient on the adhesively bonded double-cantilever beam (DCB) joints. The correlations between energy release rates which were investigated by experimental measurement, the boundary element method (BEM) and Ripling's equation are compared with each other. The experimental results show that the interfacial crack length for the ultrasonic attenuation coefficient and energy release rate increases proportionally. From the experimental results, we propose a method to detect the interfacial crack length by using the ultrasonic attenuation coefficient and discuss it.

Measurement of Rainfall Characteristics and Rain-Attenuation at 38 GHz in Worst Months Affected by El Nino Signal in 1998

  • Jang Won-Gyu;Choi Jae-Hoon
    • Journal of electromagnetic engineering and science
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    • v.5 no.4
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    • pp.189-192
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    • 2005
  • The measurement of unique rainfall phenomenon and rain attenuation on 38 GHz terrestrial links at South Korea in 1998 is presented. It was one of the most severe rainfall years at the measured region due to increased EI Nino signal. The rainfall rate exceeded at $0.01\%$ was 97.4 mm/h during a worst month and annual rate was 63.5 mm/h. Experimentally measured results have been compared with some models and found that the rain attenuation by system level was underestimated by the existing prediction models. As it was measured only three months, further study and measurement of rainfall and rain attenuation in this region are needed for stable millimeter-wave system operation at all times.

Attenuation of Fundamental Longitudinal Guided Wave Mode in Steel Pipes Embedded in Soil

  • Lee, Ju-Won;Shin, Sung-Woo;Na, Won-Bae
    • Journal of the Korean Society for Nondestructive Testing
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    • v.30 no.6
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    • pp.539-547
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    • 2010
  • In this study, characteristics of the fundamental longitudinal guided wave mode, L(0,1), which is a usual mode employed in the inspection of the above-ground pipe, of the buried pipe were numerically investigated considering property changes in the surrounding soil. Results showed that soil conditions are significantly affecting the attenuation of L(0,1) mode in the pipe embedded in soil. Especially, if the soil is partially saturated, the attenuation of L(0,1) mode is larger and is very similar regardless of the degree of water saturation in the surrounding soil. However, when the soil is fully saturated, the attenuation of L(0,1) mode is less and show different trend with its partially saturated counterparts.

Development of Medical Ultrasound Imaging Techniques for Tissue Characterization (The Correction Method of Diffraction Effect in Measurements of Attenuation Coefficient) (조직 정량화를 위한 의용 초음파 영상 기술 개발(감쇠계수 측정에서 회질 영향의 보정법))

  • 한성현;이강호;최종호;최종수
    • Journal of the Korean Institute of Telematics and Electronics
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    • v.27 no.12
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    • pp.1925-1932
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    • 1990
  • In this paper, we consider the effect of diffraction due to the finite-sized aperture and propose the new correction method of errors in measurements of attenuation coefficient owing to the diffraction effect. In the existing correction method, we obtained the attenuation coefficient after correct the spectrum at each depth. However, this paper obtain the attenuation coefficient using lg-spectral difference approach and then correct errors. As a proposed method is not correction for the spectrum at each depth but the difference spectrum, we reduce the calculation. Also the correction is performed through the total frequency range, the accurate attenuation coefficient in whole bandwidth is produced.

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