• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2003년도 봄 학술발표회 논문집
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• pp.757-762
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• 2003

This paper concerns the new equations for the compressive strength of existing concrete structures by ultrasonic pulse velocity test. The proposed equation are as follows; fc =5255.9 - 3365.8Vp + $548.4Vp^2$ (here, $r^2$=89.7%)

• 한국농공학회지
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• 제34권E호
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• pp.60-69
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• 1992

The research significance of the paper is to identify the major properties of synthetic lightweight concrete that are affected by ASR expansion and to determine the extent and magnitude of the loss in these properties. Emphasis is also given to the use of non-destructive testing techniques ; Such as dynamic modulus of elasticity and ultrasonic pulse velocity, to examine whether these methods could be used to identify the initiation of expansion and the internal structural damage caused by ASR.

• Journal of Mechanical Science and Technology
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• 제14권3호
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• pp.320-330
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• 2000

It is desirable to perform nondestructive evaluation (NDE) to assess material properties and part homogeneity because the manufacturing of carbon/carbon brake disks requires complicated and costly processes. In this work several ultrasonic techniques were applied to carbon/carbon brake disks (322mm ad, 135mm id) for the evaluation of spatial variations in material properties that are attributable to the manufacturing process. In a large carbon/carbon disk manufactured by chemical vapor infiltration (CYI) method, the spatial variation of ultrasonic velocity was measured and found to be consistent with the densification behavior in CYI process. Low frequency (e.g., 1-5MHz) through-transmission scans based on both amplitude and time-of-flight of the ultrasonic pulse were used for mapping out the material property inhomogeneity. Images based on both the amplitude and the time-of-flight of the transmitted ultrasonic pulse showed significant variation in the radial direction. The radial variations in ultrasonic velocity and attenuation were attributed to a density variation caused by the more efficient densification of pitch impregnation near the id and od and by the less efficient densification away from the exposed edged of the disk. Ultrasonic velocities in the edges of the disk. Ultrasonic velocities in the thickness direction were also measured as a function of location using dry-coupling transducers ; the results were consistent with the densification behavior. However, velocities in the in-plane directions (circumferential and radial) seemed to be affected more by the relative contents of fabric and chopped fiber, and less by the void content.

• 한국추진공학회지
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• 제16권3호
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• pp.16-23
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• 2012

정상초음파의 교반이 메탄/공기 예혼합화염의 동역학적 거동에 미치는 영향을 규명하는 실험 결과를 본 연구에서 제시한다. 슐리렌 기법을 이용하여 전파하는 화염을 가시화하였고, 이미지 후처리를 통해 정상초음파 유무에 따른 화염선단의 전파속도를 상세히 관찰하였다. 전파속도는 이론당량비에서 정상 초음파가 교반하는 경우에 크게 증가하였으며, 당량비가 연소 상한계 혹은 연소 하한계로 벗어남에 따라 교반의 효과는 감소하였다. 정상초음파장은 화염 구조의 왜곡을 동반하고, 그 변이 형상은 교반하는 초음파장의 특성에 전적으로 종속하였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.998-1003
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• 2003

Ultrasonic flow metering(UFM) technology is being received much attention from a variety of industrial fields to exactly measure the flow rate. The UFM has much advantage over other conventional flow meter systems, since it has no moving parts, and offers good accuracy and reliability without giving any disturbances to measure the flow rate, thereby not causing pressure losses in the flow fields. In the present study, 3-dimensional, unsteady, compressible Navier-Stokes equations are solved by a finite volume scheme, based upon the second order upwind scheme for spatial derivatives and the multi-stage Runge-Kutta integral method for time derivatives. In order to simulate multi-path ultrasonic flow meter, an excited pressure signal is applied to three different locations upstream, and the pressure signals are received at three different locations downstream. The mean flow velocities are calculated by the time difference between upstream and downstream propagating pressure signals. The obtained results show that the present CFD method simulates successfully ultrasonic meter gas flow and the mean velocity measured along the chord near the wall is considerably influenced by the boundary layers.

• 비파괴검사학회지
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• 제36권2호
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• pp.138-148
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• 2016

Measurement of elastic constants is crucial for engineering aspects of predicting the behavior of materials under load as well as structural health monitoring of material degradation. Ultrasonic velocity measurement for material properties has been broadly used as a nondestructive evaluation method for material characterization. In particular, pulse-echo method has been extensively utilized as it is not only simple but also effective when only one side of the inspected objects is accessible. However, the conventional technique in this approach measures longitudinal and shear waves individually to obtain their velocities. This produces a set of two data for each measurement. This paper proposes a simultaneous sensing system of longitudinal waves and shear waves for elastic constant measurement. The proposed system senses both these waves simultaneously as a single overlapped signal, which is then analyzed to calculate both the ultrasonic velocities for obtaining elastic constants. Therefore, this system requires just half the number of data to obtain elastic constants compared to the conventional individual measurement. The results of the proposed simultaneous measurement had smaller standard deviations than those in the individual measurement. These results validate that the proposed approach improves the efficiency and reliability of ultrasonic elastic constant measurement by reducing the complexity of the measurement system, its operating procedures, and the number of data.

• 한국해양공학회지
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• 제13권2호통권32호
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• pp.99-107
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• 1999

Boiler high-temperature pipelines such as main steam pipe, header and steam drum in fossil power plants are degraded by creep damage due to severe operationg conditions which are high temperature and high pressure for an extended period time. Such material degradation leads to various component failures causing serious accidents at the plants. Conventional measurement techniques such as replica method, electric resistance method, and hardness test method have such disadvantages as complex preparation and measurement procedures, too many control parameters, and therefore, low practicality and they were applied only to component surfaces with good accessibility. In this paper, artificial creep degradation test and ultrasonic measurement for their creep degraded specimens have been carried out for the purpose of evaluation for creep damage which can occur in high-temperature pipeline of fossil power plant. Absolute measuring method of quantitative ultrasonic measurement for material degradation was established, and long term creep degradationtests using life prediction formula were carried out. As a result of ultrasonic tests for crept specimens, we confirmed that the sound velocity decreased and the attenuation coefficient linearly increased in proportion to the increase of creep fractiin(${\phi}$c).

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2012년도 제38회 춘계학술대회논문집
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• pp.318-323
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• 2012

본 연구에서는 정상초음파와 교반하는 메탄/공기 예혼합화염의 동역학적 거동을 규명하기 위한 실험결과를 제시한다. 슐리렌 기법을 이용하여 전파하는 화염을 가시화하였고, 이미지 후처리를 통해 정상초음파 유무에 따른 화염선단의 형상 및 전파속도를 관찰하였다. 전파속도는 연소한계를 제외한 당량비에서 정상초음파장이 가진되는 경우에 더욱 증가하였으며, 화염선단의 찌그러지는 위치는 초음파 특성이 변하지 않는 한 일정하였다.

• Journal of the Korean Wood Science and Technology
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• 제32권4호
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• pp.74-81
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• 2004

비파괴 시험 방법 중 초음파 방법을 이용하여, 목재의 열화상태를 진단하였다. 기초 자료로서, 목재 내 온도변화에 따른 초음파 전송속도의 변화, 목재 내 함수율변화에 따른 초음파 전송속도 변화, 목재 강제부후에 의한 중량감소와 초음파 전송속도 변화를 검토하였다. 또한 원목의 비파괴 시험 등을 수행하고, 초음파 전송속도에 근거한 부후분포도를 작성하여 고목재의 열화 진단을 하였다. 일련의 시험들을 통하여 비파괴 방법에 의한 목재 열화진단을 위한 데이터를 축적하고, 이를 고목재에 적용하여 목재 내부의 부후분포도를 작성함으로써 금후 고목재의 비파괴 방법에 의한 부후탐지의 가능성을 검토하였다.

• Journal of Advanced Marine Engineering and Technology
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• 제25권6호
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• pp.1281-1290
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• 2001

A study on the fluid flow with ultrasonic forcing is carried out to obtain data for the turbulence enhancement. A large water tank is made of the transparent acrylic plates and a horizontal flow field is given by setting two acrylic tubes to face mutually on a horizontal line. A 2-dimensional PlV system which is composed of a continuous-output 4W Argon-ion laser, a high-speed video camera, a PC based by an image grabber and a high resolution monitor is used to investigate characteristics of the complex turbulence flow field. And a 2MHz ultrasonic transducer is used fur ultrasonic vibration forcing. Some experiments are carried out at Reynolds numbers of 2,000 and 4,000 and at 7 angles of ultrasonic incidence. In results, the flew velocity vector distribution, kinetic energy and turbulence intensity in both cases of with and without ultrasonic forcing are examined, compared and discussed by using PIV measurement. It is clarified that the ultrasonic forcing into flow field is valid to obtain the turbulence enhancement.