• Structural Engineering and Mechanics
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• 제75권4호
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• pp.435-444
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• 2020

Ultrasonic guided wave testing is a very promising non-destructive testing method for rails, which is of great significance for ensuring the safe operation of railways. On the basis of the semi-analytical finite element (SAFE) method, a analytical model of 59R2 grooved rail was proposed, which is commonly used in the ballastless track of modern tram. The dispersion curves of ultrasonic guided waves in free rail and supported rail were obtained. Sensitivity analysis was then undertaken to evaluate the effect of rail elastic modulus on the phase velocity and group velocity dispersion curves of ultrasonic guided waves. The optimal guided wave mode, optimal excitation point and excitation direction suitable for detecting rail integrity were identified by analyzing the frequency, number of modes, and mode shapes. A sinusoidal signal modulated by a Hanning window with a center frequency of 25 kHz was used as the excitation source, and the propagation characteristics of high-frequency ultrasonic guided waves in the rail were obtained. The results show that the rail pad has a relatively little influence on the dispersion curves of ultrasonic guided waves in the high frequency band, and has a relatively large influence on the dispersion curves of ultrasonic guided waves in the low frequency band below 4 kHz. The rail elastic modulus has significant influence on the phase velocity in the high frequency band, while the group velocity is greatly affected by the rail elastic modulus in the low frequency band.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2002년도 유체기계 연구개발 발표회 논문집
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• pp.370-377
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• 2002

Generally, the system of calculation for the multi-path ultrasonic flow meters can be divided into two methods by how to get the mean velocity, namely, weighting and direct method. Weighting-method derive the mean velocity through modeling in theoretical velocity profile. Direct-method derive the mean velocity though actual flow distribution. The system of calculation varies with maker's transducer configuration and integration method. Each system has merits and demerits. This paper describes the system of integration that calculates line velocity over cross-section of the circular pipe. Flow rate mr discussed in this paper is a difference between theoretical flow rate and integrated flow rate according to values of Reynolds number in symmetric flow field or theoretical flow rate and integrated flow rate according to rotated model in asymmetric flow field.

• 콘크리트학회논문집
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• 제11권4호
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• pp.157-167
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• 1999

Among several non-destructive testing methods, ultrasonic pulse velocity method and rebound index method have been widely used for the evaluation of concrete strength. However, such methods might not provide accurate estimated results since factors influencing the relationship between strength and either ultrasonic pulse velocity or rebound index are not considered. In this paper, the evaluation method of concrete strength using rod-wave velocity measured by impact-resonance method is proposed. A basic equation is obtained by the linear regression of velocity vs, strength data at specific age and then, aging factor is employed in the equation to consider the difference of the increasing rate between wave velocity and strength. Strengths predicted by the proposed equation agree well with test results. Furthermore, the combined method of rod-wave velocity and rebound index is proposed.

• Macromolecular Research
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• 제12권6호
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• pp.559-563
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• 2004

Both the ultrasonic velocity at 3 MHz and the absorption coefficient in the frequency range from 0.2 to 2 MHz were measured for aqueous solutions of poly(sodium 4-styrenesulfonate) over the concentration range from 5 to $25\%$ (by weight). The pulse echo overlap method was employed to measure the ultrasonic velocity over the temperature range from 10 to $90^{\circ}C;$ the high-Q ultrasonic resonator method was used for the measurement of the absorption coefficient at $20^{\circ}C.$ The velocities exhibited their maximum values at ca. 55, 59, 63, 67, and $71^{\circ}C.$ for the 25, 20, 15, 10, and $5\%$ solutions, respectively. The velocity increased with respect to the poly(sodium 4-styrene-sulfonate) concentration at a given temperature. A study of the concentration dependence of the both the relaxation frequency and amplitude indicated that the relaxation at ca. 200 kHz is related to structural fluctuations of the polymer molecules, such as the segmental motions of the polymer chains and that the relaxation at ca. 1 MHz resulted from the proton transfer reactions of the oxygen sites of $SO_3.$ Both the absorption and the shear viscosity increase upon increasing the polymer concentration, but they decrease upon increasing the temperature.

• 한국지반환경공학회 논문집
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• 제7권2호
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• pp.33-42
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• 2006

표준화된 일축압축강도시험에 의해 구한 암석의 일축압축강도를 간편법에 의해 평가할 수 있는 관계를 구하기 위하여 18개의 안동 흑운모화강암과 27개의 여수 부근의 화성암(섬록암, 화강암, 안산암, 유문암) 암석이 실험에 이용되었다. 각 시험 결과의 타당성은 변동계수를 구하여 평가하였다. 그 결과 일축압축강도와 점하중시험, 슈미트해머시험 및 초음파속도시험 값들 사이에 압축강도를 평가할 수 있는 관계식을 구하였다. 각각 다른 방법으로 구한 예측된 압축강도 관계식은 신뢰할 수 있는 범위에 있었으며, 초음파 속도시험은 암석의 일축압축강도를 추정에 신뢰성 있는 관계식을 제공하고 있다.

• 한국생산제조학회지
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• 제20권6호
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• pp.773-777
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• 2011

Conventional ultrasonic thickness measurement is to be considered as the assumption that the ultrasonic velocity is known. In actual applications the velocity is often not well known and access is often limited to one side. This paper aims at determining the ultrasonic velocity and thickness of plates with parallel or wedged surfaces using contact measurements made on one surface only. For wedged plates the thickness at one point and the wedge angle are determined. Equations are used for determining the ultrasonic velocity, thickness and wedge angle of the plate based on the times-of-flight measured by two contact transducers coupled to one surface. The time-of-flight of the obliquely reflected longitudinal wave echo was measured as a function of the separation between the two transducers. In addition, a simulation was made for comparing the experimental data and a FEM image. Experiments and simulations were performed on flat and wedged plates of aluminium materials; the calculated results for the unknown quantities are generally agreed with them to some degree.

• 한국압력기기공학회 논문집
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• 제7권4호
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• pp.26-30
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• 2011

In order to ship low & Intermediate level radioactive waste drums, which have been temporarily stored on site, to a disposal facility, their physical and chemical properties should be evaluated and proven to meet the acceptance guideline prior to their shipment. Ultrasonic velocity method, which has been used to estimate the strength of concrete, can be suggested to evaluate the compressive strength of solidified radioactive waste, which is one of the evaluated properties. The strength is estimated from acoustic velocity. However, a guided wave traveling along a drum is generated when applying ultrasonic method to the drum, and this makes it difficult to analyze the signal due to overlap between transmitted wave through the contents in drum and the guided wave. This paper reported feasibility of ultrasonic method to evaluate of the compressive strength of the solidified LLW. It is observed that the guide wave is greater than transmitted wave, and ultrasonic velocity could be estimated from transmitted wave signal arriving prior to the guided wave

• 한국구조물진단유지관리공학회 논문집
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• 제11권6호
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• pp.181-192
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• 2007

외부 강선의 긴장력 측정 기법은 국내의 경우, 거의 전무한 연구 실적을 가지고 있는 실정이다. 따라서 본연구의 목적은 강선의 긴장력을 유도 초음파법을 이용하여 측정하는 것으로 이를 위하여 시험용 웨지 및 측정 시스템을 설계 제작하여 강선에 가하여지는 긴장력 변화에 따른 초음파의 특성을 분석하여 그 상관관계를 도출하고, 이를 기반으로 초음파 특성 변화로부터 강선에 가하여지는 긴장력을 측정할 수 있는 기법을 개발하고자 한다. 이에 긴장력-속도변화의 관계식들을 구하여 제시하였으며, 제시된 식들의 오차는 약 3.92~8.77%로 나타나 현장적용이 가능할 것으로 판단된다.

• 한국농공학회지
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• 제45권3호
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• pp.59-64
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• 2003

Hwangto would be an environment-friendly material that can be readily used. The purpose of this study is to obtain the absorption ratio, ultrasonic pulse velocity and neutralization of the mortar with non-active Hwangto and stone dust. The absorption ratio and neutralization depth are increased with increase of non-active Hwangto. But, the ultrasonic pulse velocity is decreased with increase of non-active Hwangto. In results of SEM analysis, the crystals are increased with increase of non-active Hwangto.

• 한국가시화정보학회지
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• 제3권1호
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• pp.78-89
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• 2005

An experimental study was carried out to investigate the effect of local ultrasonic forcing on a turbulent boundary layer. Stereoscopic particle image velocimetry (SPIV) was used to probe the characteristics of the flow. A ultrasonic forcing system was made by adhering six ultrasonic transducers to the local flat plate. Cavitation which generates uncountable minute air-bubbles having fast wall normal velocity occurs when ultrasonic was projected into water. The SPIV results showed that the wall normal mean velocity is increased in a boundary layer dramatically and the streamwise mean velocity is reduced. The skin friction coefficient (C$_{f}$) decreases 60$\%$and gradually recovers at the downstream. The ultrasonic forcing reduces wall-region streamwise turbulent intensity, however, streamwise turbulent intensity is increased away from the wall. Wall-normal turbulent intensity is almost the same near the wall but it increases away from the wall. In the vicinity of the wall, Reynold shear stress, sweep strength and production of turbulent kinetic energy were decreased. This suggests that the streamwise vortical structures are lifted by ultrasonic forcing and then skin friction is reduced.