• Title/Summary/Keyword: 초음파 전파속도

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A Structural Behavior of the Propane/Air Premixed Flame Interacting with an Ultrasonic Standing-wave (정상초음파가 개재하는 프로판/공기 예혼합화염의 구조 거동)

  • Lee, Sang-Shin;Seo, Hang-Seok;Kim, Jeong-Soo;Lee, Do-Hyung
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2012.05a
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    • pp.294-299
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    • 2012
  • An investigation into the influence of ultrasonic standing wave on the structural behavior of propane/air premixed flame has been made to get a clue to the combustion reaction acceleration and combustion instability, as well. Visualization technique utilizing the Schlieren method was employed for the observation of structural variation of the premixed flame. The flame shape and propagation velocity were measured according to the variation of equivalence ratio. It was found that the standing wave distorted the flame front and expedited a transition to the flame with turbulent nature.

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A Basic Study on the Varying Thickness Detection of Steel Plate Using Ultrasonic Velocity Method (초음파 속도법을 활용한 강판의 두께 변화 탐지를 위한 기초연구)

  • Kim, WooSeok;Mun, Seongmo;Kim, Chulmin;Im, Seokbeen
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.24 no.6
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    • pp.146-152
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    • 2020
  • This study was initiated to develop an effective inspection method to detect defects such as corrosion in closed-cell steel members in steel-box girder bridges. The ultrasonic velocity method among various non-destructive method was selected as a rapid and effective method to derive the average propagation velocity in the medium by using the ultrasonic wave velocity method for specimens of different thickness. The regression analysis was performed based on the experimental results, and the results was interpolated to evaluate the prediction accuracy. If the material properties are identical, this ultrasonic velocity method can predict the thickness using the averaged transmitted velocity. In addition, a continuous scanning method moving at 200 mm/s was tested for scanning a wide area of a bridge. The results exhibited that the continuous scanning method was able to effectively scan the different thickness of a bridge.

Ultrasonic Velocity Measurements of Engineering Plastic Cores by Pulse-echo-overlap Method Using Cross-correlation (다중 반사파 중첩 자료의 상호상관을 이용한 엔지니어링 플라스틱 코어의 초음파속도 측정)

  • Lee, Sang Kyu;Lee, Tae Jong;Kim, Hyoung Chan
    • Geophysics and Geophysical Exploration
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    • v.16 no.3
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    • pp.171-179
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    • 2013
  • An automated ultrasonic velocity measurement system adopting pulse-echo-overlap (PEO) method has been constructed, which is known to be a precise and versatile method. It has been applied to velocity measurements for 5 kinds of engineering plastic cores and compared to first arrival picking (FAP) method. Because it needs multiple reflected waves and waves travel at least 4 times longer than FAP, PEO has basic restriction on sample length measurable. Velocities measured by PEO showed slightly lower than that by FAP, which comes from damping and diffusive characteristics of the samples as the wave travels longer distance in PEO. PEO, however, can measure velocities automatically by cross-correlating the first echo to the second or third echo, so that it can exclude the operator-oriented errors. Once measurable, PEO shows essentially higher repeatability and reproducibility than FAP. PEO system can diminish random noises by stacking multiple measurements. If it changes the experimental conditions such as temperature, saturation and so forth, the automated PEO system in this study can be applied to monitoring the velocity changes with respect to the parameter changes.

LSAW Velocity Measurement by Using a PVDF Line-Focus Ultrasonic Transducer (PVDF 직선집속 초음파 트랜스듀서에 의한 누설탄성표면파 속도 측정)

  • 윤혁준;하강열;김무준;윤종락
    • The Journal of the Acoustical Society of Korea
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    • v.20 no.1
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    • pp.62-67
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    • 2001
  • Velocities of leaky surface acoustic waves (LSAW/sub s/) were measured by using a line-focus polyvinylidene fluoride (PVDF) transducer and compared with theoretically calculated ones. Isotropic materials of Cu, Al, fused quartz, and anisotropic one of Z-cut α-quartz crystal were used as specimens. The velocities were obtained by the separation time between wave components reflected directly from the surface of specimen and LSAW components according to the defocusing distance. The measured velocities well agree with the theoretical results within 1% error, and it was shown that the leaky pseudo-surface acoustic wave (LPSAW) as well as the LSAW propagates with the typical 6-fold anisotropy on the (0,0,1) surface of α-quartz.

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Nondestructive Diagnosis of NPP Piping System Using Ultrasonic Wave Imaging Technique Based on a Pulsed Laser Scanning System (펄스 레이저 스캐닝 기반 초음파 영상화 기술을 활용한 원전 배관 비파괴 진단)

  • Kim, Hyun-Uk;Lee, Chang-Gil;Park, Seung-Hee
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.18 no.1
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    • pp.166-173
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    • 2014
  • A noncontact nondestructive testing (NDT) method is proposed to detect the damage of pipeline structures and to identify the location of the damage. To achieve this goal, a scanning laser source actuation technique is utilized to generate a guided wave and scans a specific area to find damage location more precisely. The ND: YAG pulsed laser is used to generate Lamb wave and a piezoelectric sensor is installed to measure the structural responses. The measured responses are analyzed using three dimensional Fourier transformation (3DFT). The damage-sensitive features are extracted by wavenumber filtering based on the 3D FT. Then, flaw imaging techniques of a pipeline structures is conducted using the damage-sensitive features. Finally, the pipes with notches are investigated to verify the effectiveness and the robustness of the proposed NDT approach.

Dependencies of phase velocities of ultrasonic guided waves on cortical thickness in soft tissue-bone mimicking phantoms (연조직-골 모사 팬텀에서 피질골 두께에 대한 유도초음파 위상속도의 의존성)

  • Lee, Kang Il
    • The Journal of the Acoustical Society of Korea
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    • v.40 no.6
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    • pp.587-592
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    • 2021
  • Change in the cortical thickness of long bones occurring with aging and osteoporosis is known to be a risk factor for fracture. The present study aims to investigate the dependencies of phase velocities of ultrasonic guided waves on the cortical thickness in 7 soft tissue-bone mimicking phantoms consisting of acrylic plates covered by a 2 mm-thick silicone rubber layer by using the axial transmission technique with a pair of transducers with a center frequency of 200 kHz and a diameter of 12.7 mm. Two distinct propagating waves with different velocities, the First Arriving Signal (FAS) and the Slow Guided Waved (SGW), were consistently observed for all the soft tissue-bone mimicking phantoms. The FAS velocity decreased slightly with increasing thickness, whereas the SGW velocity increased strongly with increasing thickness. The FAS and the SGW velocities were found to be closely consistent with the S0 and the A0 Lamb mode velocities for a free acrylic plate, respectively, suggesting that the presence of the soft tissue mimicking material (2 mm-thick silicone rubber layer) covering the acrylic plates does not influence significantly the velocity measurements.

Correlations of Phase Velocities of Guided Ultrasonic Waves with Cortical Thickness in Bovine Tibia (소의 경골에서 유도초음파의 위상속도와 피질골 두께 사이의 상관관계)

  • Lee, Kang-Il
    • The Journal of the Acoustical Society of Korea
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    • v.30 no.1
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    • pp.56-62
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    • 2011
  • In the present study, the phase velocities of guided ultrasonic waves such as the first arriving signal (FAS) and the slow guided wave (SGW) propagating along the long axis on the 12 tubular cortical bone samples in vitro were measured and their correlations with the cortical thickness were investigated. The phase velocities of the FAS and the SGW were measured by using the axial transmission method in air with a pair of unfocused ultrasonic transducers with a diameter of 12.7 mm and a center frequency of 200 kHz. The phase velocity of the FAS measured at 200 kHz exhibited a very high negative correlation with the cortical thickness and that of the SGW arriving after the FAS showed a high positive correlation with the cortical thickness. The simple and multiple linear regression models with the phase velocities of the FAS and the SGW as independent variables and the cortical thickness as a dependent variable revealed that the coefficient of determination of the multiple linear regression model was higher than those of the simple linear regression models. The phase velocities of the FAS and the SGW measured at 200 kHz on the 12 tubular cortical bone samples were, respectively, consistent with those of the S0 and the A0 Lamb modes calculated at 200 kHz on the cortical bone plate.

Improving Wave Propagation Performance of an Ultrasonic Waveguide for Heat Isolation (열 차단용 초음파 도파관의 전파성능 향상 연구)

  • 최인석;전한용;김인수;김진오
    • The Journal of the Acoustical Society of Korea
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    • v.22 no.7
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    • pp.545-553
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    • 2003
  • This paper is concerned with protecting piezoelectric transducers used in an ultrasonic flowmeter from the high temperature of hot fluid in a pipe by using a waveguide and with improving the propagation of ultrasonic longitudinal vibration in the waveguide. Waveguide material has been chosen for efficient insulation of heat transferred in the waveguide, and the minimum length of the waveguide for protecting piezoelectric transducer has been estimated. Forced response of the longitudinal vibration in a uniform circular rod has been obtained and the length of the waveguide has been selected for maximum amplitude. Longitudinal vibration response of a conically-tapered rod excited at a natural frequency has been obtained to confirm that wave motion is amplified as the cross-sectional size of the waveguide decreases along the axial direction. The fact that dispersion of a pulse wave in a waveguide is reduced as the cross-sectional radius is decreased has been examined theoretically and confirmed experimentally by using a single-rod waveguide. A bundle-type waveguide has proven to be a practical one through the evaluation of the wave propagation performance.

An Integrated Navigation System Combining INS and Ultrasonic-Speedometer to Overcome GPS-denied Area (GPS 음영 지역 극복을 위한 INS/초음파 속도계 결합 항법 시스템 설계)

  • Choi, Bu-Sung;Yoo, Won-Jae;Kim, La-Woo;Lee, Yu-Dam;Lee, Hyung-Keun
    • Journal of Advanced Navigation Technology
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    • v.23 no.3
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    • pp.228-236
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    • 2019
  • Recently, multi-sensor integration techniques have been actively studied to obtain reliable and accurate navigation solution in GPS (Global Positioning System)-denied harsh environments such as urban canyons, tunnels, and underground roads. In this paper, we propose a low-cost ultrasonic-speedometer utilizing the characteristics of the ultrasonic propagation. An efficient integrated INS (inertial navigation system)/ultrasonic-speedometer navigation system is also proposed to improve the accuracy of positioning in GPS-denied environments. To evaluate the proposed system, car experiments with field-collected measurements were performed. By the experiment results, it was confirmed that the proposed INS/ultrasonic-speedometer system bounds the positioning error growth effectively even though GPS signal is blocked more than 10 seconds and a low-cost MEMS IMU (micro electro mechanical systems inertial measurement unit) is utilized.

A Method for Non-invasive Diagnosis of bone by Measuring Phase Velocity (비침투적인 생체 경조직의 음향진단을 위한 기초실험)

  • Park, Mu-Hun
    • Journal of Biomedical Engineering Research
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    • v.20 no.1
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    • pp.91-97
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    • 1999
  • We propose a new method for measuring the frequency characteristics of phase velocity along a bone for bending vibration modes to diagnose its mechanical characteristics. By introducing a simple model of a distributed-constant-network, the phase velocity is determined for each frequency from the spatial distribution of velocity along a radius bone surface which is measured by the ultrasonic Doppler method.

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