• Journal of the Korean Society of Propulsion Engineers
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• v.16 no.6
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• pp.1-8
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• 2012

An experimental study has been conducted to scrutinize into the influence of ultrasonic standing wave on the propagating behavior and structural stabilization of propane/air premixed flame at various equivalence ratios in half-open rectangular duct. Evolutionary features of the flame fronts are caught by high-speed images, and the variation of flame structure and local flame velocities along the propagation are analyzed. It is revealed that the propagation velocity agitated by the ultrasonic standing wave is greater than that without the agitation: the velocity enhancement diminishes as the equivalence ratio approaches the stoichiometric. Influence of standing wave on the flame overwhelms that of the buoyancy which slants the flame front towards top of the duct, and thus the standing wave contributes to the structural stabilization of propane/air premixed flame.

• Journal of the Korea Society of Computer and Information
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• v.5 no.4
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• pp.62-68
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• 2000

It was designed a high-speed analog input card that is a important device of ultrasonic testing flaw detector in the middle of non-destructive testing in this Paper. The A/D Board is inquired high-speed sampling rate and fast data acquisition system. This pater shows a design that has a function of Peak- Detection for ultrasonic testing by ISA Bus type and a 50MHz of A/D converter in order to do sampling more than quadruple frequency of transducer frequency.

• Journal of the Korean Society for Nondestructive Testing
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• v.19 no.4
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• pp.259-269
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• 1999

Elastic wave velocity measurement technique such as impact-echo method and ultrasonic pulse velocity method has been successfully used to evaluate the moduli and strength of concrete. However, estimation results obtained by the NDT methods do not agree well with real things because longitudinal wave velocity is influenced by various factors. In this paper, among several factors influencing P-wave velocity, the influence of moisture content in concrete was investigated through the experiment. Test results show that longitudinal wave velocity is significantly affected by the moisture content of concrete, i.e., the lower moisture content. the lower velocity. Moisture content influences rod-wave velocity measured by impact-echo method stronger than ultrasonic pulse velocity measured by transmission method. During drying process with ages. the difference of increasing rate between longitudinal wave velocity and compressive strength of concrete is gradually increased. Therefore, to establish more accurate relationship between longitudinal wave velocity and strength, the difference of the increasing rate should be considered.

• Journal of the Korean Society for Nondestructive Testing
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• v.23 no.4
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• pp.334-341
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• 2003

When the pressure tubes(f are in contact with the calandria tube(CT) in the pressurized heavy water reactor(PHWR), the temperature difference between inner and outer wall of W results in a thermal diffusion of hydrogen (deuterium) and hydride blisters are formed on the outer surface of PT. Because the hydride blisters and zirconium matrix are acoustically continuous, it is not easy to distinguish the blisters from the matrix with conventional ultrasonic method. An ultrasonic velocity ratio method was developed to detect small hydride blisters on the zirconium pressure tube. Hydride blisters were grown in the PT specimen using a steady state thermal diffusion device. The flight times of longitudinal echo and reflected shear echo from the outer surface were measured accurately. The velocity ratio of the longitudinal wave to the shear wave was calculated and displayed using contour plot. Compared to the conventional flight time method of longitudinal wave, the velocity ratio method shows superior sensitivity to detect smaller blisters as well as better images for the blister shapes. Detectable limit of the outer shape of the hydride blisters was conservatively estimated as $500{\mu}m$, with the same specifications of ultrasonic transducer used in the actual PHWR pressure tube inspection.

• Journal of Conservation Science
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• v.34 no.2
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• pp.97-106
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• 2018

The lime-soil mixture on barrier (LSMB) tomb is a representative type of tomb from the Joseon Dynasty. It is an important reference for understanding the society and funeral culture of that time. The LSMB excavated at the Gungri site were classified with manufacturing type. The ultrasonic velocity and rebound hardness method were used to estimate the physical properties of the LSMB. The strength values on the tomb of layered wall were different depend on measuring method. The compressive strengths of the tomb with layered wall, which is calculated by ultrasonic velocity and rebound hardness ranged from 4.0 to 355 (mean 43.6) $kgf/cm^2$ and 18.8 to 538 (mean 245.2) $kgf/cm^2$ ranges. The damage to the tomb with integrated wall during excavation and removal of the corpse could be a reason for the difference in results obtained using ultrasonic velocity method. Compressive strengths of tombs with integrated wall, which is calculated by ultrasonic velocity and rebound hardness ranged from 5.7 to 793 (mean 281.6) $kgf/cm^2$ and 4.5 to 550.5 (mean 172.4) $kgf/cm^2$ values. Physical properties on the tombs of integrated wall had different in compressive strength value but showed similar tendency. Thus, evaluation of the physical properties has shown that measuring ultrasonic velocity and rebound hardness methods are more effective in the LSMB with integrated walls. Further, the strength values obtained through the rebound hardness method are more constant than those obtained through the ultrasonic method due to the small detection area required by the former.

• Journal of the Korean Society for Nondestructive Testing
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• v.25 no.2
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• pp.103-109
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• 2005

Fiber reinforced plastic material should be inspected in fabrication process in order to enhance quality by prevent defects such as delamination and void. Generally, ultrasonic technique is widely used to evaluate FRP. In conventional ultrasonic techniques, transducer should be contacted on FRP. However, conventional contacting method could not be applied in fabrication process and novel non-contact evaluating technique was required. Laser-based ultrasonic technique was tried to evaluate CFRP plate. Laser-based ultrasonic waves propagated on CFRP were received with various transducers such as accelerometer and AE sensor in order to evaluate the properties of waves due to the variation of frequency. Velocities of laser-based ultrasonic waves were evaluated for various fiber orientation. In addition, laser interferometry was used to receive ultrasonic wave in CFRP and frequency was analysed.

• Journal of the Korean Society for Nondestructive Testing
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• v.25 no.1
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• pp.20-26
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• 2005

Ultrasonic guided waves have been widely employed for long range inspection of structures such as plates, rods and pipes. There are numerous modes with different wave velocities, and the appropriate mode selection is one of key techniques in the application of guided waves. In the present work, phase tuning by an array transducer was applied to generate ultrasonic guided waves. For this purpose, 8-channel ultrasonic pulser/receiver and their controller which enables sequential activation of each channels with given time delay were developed. Eight transducers were fabricated in order to generate guided waves by using an array transducer. The selective tuning of wave mode can be achieved by changing the interval between elements of an array transducer.

• Journal of Welding and Joining
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• v.12 no.4
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• pp.21-34
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• 1994

컴퓨터의 발달과 아울러 High Technology분야에서 급속도로 발전되어 FULL DIGITAL 초음 탐상기도 제 3세대의 NoteBook타입 초음파 탐상기가 선보인 것이다. 휴대하기 간편하며, 다양한 기능을 갖추었으면서도 사용하기 아주 쉽게 된 것이 특징이다. 산업의 고도화 성장과 급속한 발전으로 인하여 다양한 재질, 다양한 형태, 다양한 적용범위가 폭 넓어지고 있기 때문에 여기에 가장 알맞는 기능을 가진 초음파 두께기의 탐상기를 고려하지 않으면 외화낭비, 시간낭비, 그 밖에 여러 가지 낭비가 되게된다. 따라서 이제부터 초음파 두께기분야와 초음파 탐상기분야에서 어떻게 변천되어왔고, 어떻게 산업에 응용할 수 있는지를 살펴보자.

• 전기의세계
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• v.28 no.1
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• pp.5-14
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• 1979

비파괴검사방법에는 여러가지가 있는데 과거에는 주로 방사건 유도시험이 주역을 이루어 왔다고 볼수 있다. 그런데 최근에는 초음파를 이용한 탐상장치의 성능이 향상하였고 초음파를 이용하지 않으면 검사할수 없는 대상물의 검사가 필요하게 되었다는 점에 의하여 초음파의 이용이 상당히 급속하게 확대되어 그 응용범위도 수도관에서 원자연료까지 이루게 되었다. 그러나 방사선 투과식 시험에서는 검출곤란한 균열을 검출할 수 있는 기술적 특성및 고가인 소모품이 필요치 않고 또한 검사속도도 빠르다는 경제성에 주목하여 방사투과시험이 가능한 대상물에 대해서도 이용하게끔 되었다. 초음파에 의한 비파괴시험을 이용목적에 따라 분류하면 탐상과 계측으로 대별할 수 있다. 이하 이들의 각종방법에 대하여 순차적으로 그 개요를 설명하겠다.

• Journal of the Speleological Society of Korea
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• no.81
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• pp.7-19
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• 2007

본 논문은 초음파센서와 적외선센서를 이용하여 그 신호를 받아 주 모터를 제어한 것으로, 센서를 이용한 선풍기의 풍향 및 풍속을 제어하였다. 풍향제어는 인체감지센서와 ATmega128, DC모터를 사용하였고, 기본적으로 WmAVR과 PonyProg를 사용하여 소스코딩 및 다운로딩을 하였으며, 모터 구동드라이버는 모터제어에 범용으로 쓰이는 L298 칩을 사용하였다. 풍속제어는 초음파센서와 ATmeBa16, DC모터를 사용하여 제작하였고, 풍향제어부와 마찬가지로 WinAVR과 PonyProg 및 L298 칩을 사용하여 소스코딩 및 다운로딩을 하였다. 풍향제어는 물체가 정면에 위치하면 회전을 멈추고, 좌우로 $100^{\circ}$ 반경이내에서 거리 1m내외의 물체를 감지하도록 설계하였다. 풍속제어는 물체까지의 거리를 최소 3cm 최대 3m 이내에서 물체를 감지하여 모터의 속도를 제어할 수 있도록 하였고, 모터속도는 DC모터를 PWM 방식으로 제어하여 속도를 조절하였다.