• 대한기계학회논문집B
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• 제29권11호
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• pp.1248-1256
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• 2005

This study was undertaken to investigate the flow characteristics of emulsified fuel with the ultrasonic energy-adding system by using the chaotic method. Efffcts of water contents within emulsified fuel, flow rate and tube length with 5m in diameter from an emulsified chamber has been discussed on the strange attractor and power spectral density function. Five probe sensors were set up from 0.5 to 2.5m by length in 0.5m increments in the tube. In particular, the chaotic features of this system have been practically characterized in terms of chaotic statistics such as the power spectral density function and phase space portraits by resorting to the somewhat noble deterministic chaos theory. In the tube, the dominant frequency increased with increasing water contents and flow rate, but decreased a little with an increase in the length from the emulsified chamber.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2007년도 하계종합학술대회 논문집
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• pp.459-460
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• 2007

In this paper, we describe a development of ultrasonic nondestructive evaluation software to analyze steam generator of nuclear power plant. The developed software includes classical analysis method such as A, B, C and D-scan images. And it can analyze the size and the location of internal cracks using 2D image. To do such, we obtain raw data from specimens of real pipeline of power plants, and get the crack points using LPF and differential method from obtained ultrasonic 1-dimensional data. The results of applications showed that the developed software provided accurate images of cracks on various specimens.

• Journal of Periodontal and Implant Science
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• 제39권4호
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• pp.385-390
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• 2009

Purpose: In this study we evaluated the morphologic aspects of defects created by a piezoelectric ultrasonic scaler with scaler tip on casting gold alloy using scanning electron microscope (SEM) images and defect surface profiles. Methods: 54 blocks of type III casting gold alloy (Firmilay, Jellenko Inc, CA, USA) were scaled by a piezoelectric ultrasonic scaler (P-MAX, Satelec, France) with scaler tip (No. 1 tip) on a sledge device. 2-dimensional profiles of defects on all samples were investigated by a surface profilometer (a-Step 500, KLA-Tencor, CA, USA). The selected working parameters were lateral force (0.5 N, 1.0 N, 2.0 N), mode (P mode, S mode), and power setting (2, 4, 8). SEM images were obtained. Defect surface profiles were made on Microsoft Excel program using data obtained by a surface profilometer. Results: Among P mode samples, there were similarities on defect surface profiles and SEM images regardless of lateral force. The defects created in P mode were narrow and shallow although the depth and the width increased as power setting changed low (2) to high (8). In P mode samples, the defect depth was the greatest when lateral force of 0.5 N was applied. However all the depths were smaller than 1 m. SEM images of Lateral force of 0.5 N, S mode, power setting 2 and 4 were similar to that of P mode, but the other SEM images of S mode showed discernible changes. Defect depth of S mode samples was the greatest when lateral force of 1.0 N was applied. Conclusions: Within the limitations of this study, it can be concoluded that removing capability of piezoelectric scaler with scaler tip becomes maximized as power level becomes higher but the capability is restricted when excessive lateral force is applied on scaler tip.

• 비파괴검사학회지
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• 제24권4호
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• pp.331-340
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• 2004

기기 건전성의 온라인 검사 및 감시 기술은 기존의 원전의 가동 중 검사의 효율적 수행에 필요한 정보를 제공한다. 유도 초음파는 온라인 검사와 감시에 활용 가능성이 있는 기술 중의 하나로 알려져 있다. 본 연구에서는 온라인 검사 겐 감시 기술 개발의 일환으로 유도초음파를 이용하여 파이프의 건전성을 검사/감시하는 기술을 개발하고자 한다. 이를 위해 증기 발생기 세관을 실험 대상으로 하여 분산 선도 덴 특정 모드에 대응하는 초음파 입사각을 계산하였다. Short time Fourier transform을 이용한 시긴-주파수 분석을 통하여 유도초음파 모드를 확인하였으며, 유도 초음파가 증기발생기 세관의 곡관 부분을 통과할 때 모드 변환이 발생하지 않는 것을 실험적으로 확인하였다. 유도 초음파를 이용한 증기발생기 세관의 최적 검사 모드를 제안하고 실험에 의하여 이를 확인하였다.

• 한국기계가공학회지
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• 제2권1호
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• pp.15-21
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• 2003

The ultrasonic polishing machine was developed to get super finishing that consist of machine part that can rotate and travel the main shaft with power 1.5kW, ultrasonic generator with frequency 20kHz. By using this machine we were investigated the characteristics of ultrasonic polishing for three different ceramics, and so could be obtained following results. First, we could be obtained the excellent surface for hard-ta-difficult cutting materials. Second, the effect of surface roughness for the feed rate could be shown that the more the feed rate Increases, the more the value of surface roughness increases. Third, owing to the characteristics being progressed brittle fracture in $Al_2O_3$ polishing with this machine, the value of surface roughness is larger than other ceramics. Forth, because the ultrasonic polishing can be smoother than the existing grinding in discharging the chips, it could be possible to improve the surface roughness about up to 15%.

• 한국조명전기설비학회지:조명전기설비
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• 제8권2호
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• pp.46-53
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• 1994

본 논문에서는 초음파 센서를 이용하여 부분방전에 의해 발생하는 기준준위 이상의 초음파 펄스수를 계수하여, 전력용 변압기의 부분방전 진전을 상시 감시할 수 있는 예방진단기술에 관하여 연구하였다. 실험결과, 초음파 발생장치 및 침-평판전극에 일정전압을 인가하여 일정한 초음파 및 부분방전을 발생시킬 경우에 측정한 초음파 펄스수의 경향은 일정하였으며, 침-평판전극에 인가전압을 상승시켜 부분방전을 임의로 크게 하거나, 침-평판전극에 절연지를 삽입하고 일정전압을 인가하여 부분방전을 진전시킬 경우의 초음파 펄스수는 부분방전의 진전과 더불어 증가함을 보여, 본 연구에서 제시한 진단장치를 이용하여 부분방전의 진전을 상시 감시할 수 있음을 확인하였다.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2009년 추계학술발표대회
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• pp.221-225
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• 2009

A solar thermal collector is a solar collector specifically intended to collect heat: that is, to absorb sunlight to provide heat. A flat plate is the most common type of solar thermal collector, and is usually used as a solar hot water panel to generate solar hot water. A flat plate collector consists basically of an insulated metal box with a glass or a plastic cover and a dark-colored copper absorber plate. Solar radiation is absorbed by the copper absorber plate and transferred to water that circulates through the collector in copper tubes. Ultrasonic welding is an industrial technique whereby high-frequency ultrasonic acoustic vibrations are locally applied to work pieces being held together under pressure to create a solid-state weld. In this study, we developed solar collector ultrasonic welding machine with digital controlled power supply and tested various welding conditions such as welding pressure, welding amplitude, welding speed. Welding speed was considered in 2~12m/min. The width of ultrasonic welds was increased with welding amplitude by 2.2~2.5mm. The fracture load of ultrasonic welds showed 20% higher than domestic products.

• 한국전자통신학회논문지
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• 제14권1호
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• pp.137-146
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• 2019

다수의 초음파 트랜스듀서를 이용한 초음파 위상 배열은 초점제어에 의해 인체 내 종양을 치료하는 목적 등으로 사용되고 있다. 초점제어에 의해 결정된 각 초음파 트랜스듀서 표면음압의 크기와 위상은 각 초음파 트랜스듀서에 인가되는 전압의 크기와 위상을 제어하여 구현 가능하다. 본 논문에서는 초음파 트랜스듀서의 인가전압과 표면음압 사이의 관계를 모델링하고, 요구되는 초음파 트랜스듀서의 표면음압을 생성하기 위한 인가전압을 PWM 기법으로 제어하는 방법을 제안한다. 제안한 방법의 타당성은 61개의 초음파 트랜스듀서로 구성된 초음파 위상배열의 초점제어를 예로 들어 시뮬레이션으로 검증하였다.

• 동력기계공학회지
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• 제20권6호
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• pp.58-63
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• 2016

A stainless steel has high corrosion resistance because of nickel in material, so it is used as materials for transportation and storage of hydrogen. In this study, TIG(tungsten ingot gas) welding was carried out on the stainless steel using the storage vessel of hydrogen. The microscopic structures at each region of TIG welded material such as HAZ, weld and base metals using optical microscope were observed. And the damage behavior of stainless steel that underwent the hydrogen charging using nondestructive evaluation was also studied. Ultrasonic test, which is the most generalized nondestructive technique, was applied to evaluate the relationship between the ultrasonic wave and mechanical properties at each zone of TIG welded stainless steel. The velocity and attenuation coefficients of ultrasonic wave didn't show a remarkable difference at each region of welded stainless steel. However, the attenuation coefficient was the highest at the weld zone when hydrogen charged stainless steel. In addition, acoustic emission test was also used to study the dynamic behavior of stainless steel experienced both hydrogen charging and weld. Lots of AE event at elastic region of stress-strain curve were occurred both the hydrogen charged specimen and the free specimen.

• Structural Engineering and Mechanics
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• 제69권4호
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• pp.407-416
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• 2019

This paper develops a wireless sensor for online fatigue crack detection and failure warning based on crack-induced nonlinear ultrasonic modulation. The wireless sensor consists of packaged piezoelectric (PZT) module, an excitation/sensing module, a data acquisition/processing module, a wireless communication module, and a power supply module. The packaged PZT and the excitation/sensing module generate ultrasonic waves on a structure and capture the response. Based on nonlinear ultrasonic modulation created by a crack, the data acquisition/processing module periodically performs fatigue crack diagnosis and provides failure warning if a component failure is imminent. The outcomes are transmitted to a base through the wireless communication module where two-levels duty cycling media access control (MAC) is implemented. The uniqueness of the paper lies in that 1) the proposed wireless sensor is developed specifically for online fatigue crack detection and failure warning, 2) failure warning as well as crack diagnosis are provided based on crack-induced nonlinear ultrasonic modulation, 3) event-driven operation of the sensor, considering rare extreme events such as earthquakes, is made possible with a power minimization strategy, and 4) the applicability of the wireless sensor to steel welded members is examined through field and laboratory tests. A fatigue crack on a steel welded specimen was successfully detected when the overall width of the crack was around $30{\mu}m$, and a failure warnings were provided when about 97.6% of the remaining useful fatigue lives were reached. Four wireless sensors were deployed on Yeongjong Grand Bridge in Souht Korea. The wireless sensor consumed 282.95 J for 3 weeks, and the processed results on the sensor were transmitted up to 20 m with over 90% success rate.