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단일방향 탄소섬유복합재료 적층 판에서 전파 방향에 따른 램파 $S_o$ 모드의 군속도의 변화
김영환,이승석,김호철,이정기,Kim Young H.,Lee Seung Seok,Kim Ho Chul,Lee Jeong Ki 한국복합재료학회 2005 Composites research Vol.18 No.1
In this paper, the group velocity dispersion curves of the $S_o$ symmetric mode in unidirectional CFRP plate was calculated as varying the propagating direction. The group velocity curve was obtained with the group velocities of the $S_o$ symmetric mode corresponding to 0.2 MHz-mm under the first cut-off frequency in the dispersion curves, and corrected by introducing the slowness curve. The velocities of the $S_o$ symmetric mode in the unidirectional CFRP plate were measured as varying the propagating direction and compared with the col?rotted group velocity curve. The measured velocities were good agreement with the corrected group velocity curve except near the fiber direction which was called the cusp region. It implies that the direction of the group velocities incline toward the fiber direction of the unidirectional CFRP plates when the propagation direction is not accorded with the principal axis. It is supposed that this phenomenon rerults from the preferential propagating the energy toward the direction with the faster propagation velocity. 본 연구에서는 단일방향 탄소섬유강화복합재료 판에서 $S_o$ 대칭모드의 군속도 분선곡선을 전파 방향을 변화시키먼서 계산하였다. 그리고 속노 분산 곡선에서 첫 번째 단절주파수 이하인 0.2 MHz-mm에 해당하는 $S_o$ 대칭모드 군속도를 가지고서 위상속도 곡선을 얻고 slowness 곡선을 도입하여 군속도 곡선으로 교정하였다. 단일방향 섬유강화복합재료 판에서 $S_o$ 대칭모드의 속도를 전파 방향을 변화시키면서 측정하였고 교정된 군속도 곡선과 비교하였다. 측정된 속도는 섬유 방향 근처의 cusp 영역을 제외하고는 교정된 군속도 곡선과 잘 일치하였다. 이것은 단일방향 탄소섬유강화복합재료 판에서 속도가 빠른 방향으로 에너지를 더 잘 전파하기 때문에 전파 방향이 주축방향과 일치하지 않을 때 군속도 방향은 섬유 방향 쪽으로 기울어지는 결과로 나타난 것이다.
후방복사된 초음파를 이용한 터빈 블레이드 재료의 부식 열화특성 평가
송성진,김영환,배동호,정민호,권성덕,Song, Sung-Jin,Kim, Young-H.,Bae, Dong-Ho,Jung, Min-Ho,Kwon, Sung-Duk 대한기계학회 2002 大韓機械學會論文集A Vol.26 No.11
The corrosion degradation characteristics of the 12Cr alloy steel, which is widely used in fossil power plants as a turbine blade material, are evaluated nondestructively by use of the backward radiated Rayleigh surface wave. In order to evaluate corrosion degradation characteristics, we constructed automated system for the backward radiation, and the frequency dependency of the Rayleigh surface wave is investigated indirectly by measuring the angular dependency of the backward radiation of the incident ultrasonic wave in the specimens. The velocity of the surface wave decrease as the increase of the aging time in the backward radiation profile, which seems to result from the increase of the effective degrading layer thickness. And, amplitude of the surface wave increase as the aging time, which seems to result from the increase of the intergranular corrosion. The result observed in this study demonstrates high potential of the backward radiated ultrasound as a tool for the nondestructive evaluation of the corrosion degradation characteristics of the aged materials.
유도초음파를 활용한 열교환기 튜브 손상 진단 시스템 개발 연구
김정남(Jeongnam Kim),마리커브 카흐라몬 우글리 아자마트전(Malikov Azamatjon Kakhramon Ug),김영환(Young H. Kim),조윤호(Younho Cho),김형규(Hyung-Kyu Kim) 대한기계학회 2021 대한기계학회 춘추학술대회 Vol.2021 No.11
In this study, we design a guided wave inspection system that can be used to detect the failed tubes in a tube bundle structure (e.g., heat exchanger) where the gap between the tubes is considerably narrow. The gap between the tubes is set as 1.5 mm in the experiment. Thus, we design the thickness of the strip with a transducer to be 1 mm so that it can pass through the gap for the failure detection. As a result the propagation mode in the underwater environment is F mode. It is confirmed that the signal amplitude obtained from the water-filled tube specimen is smaller than that from the air-filled one. This shows a strong possibility of using the developed method for the purpose of the present study. It is expected that a reliable system for the failure detection of a tube bundle with a narrow gap can be built through further works such as and precise signal analysis.
A pattern of cell death induced by 40 kHz ultrasound in yeast cell model
김지욱,공희정,김영환,강광일,Kim, Ji Wook,Kong, Hee Jeong,Kim, Young H.,Kang, Kwang Il The Acoustical Society of Korea 2017 韓國音響學會誌 Vol.36 No.3
초음파는 세포사멸을 포함하여 의학 및 생물학분야에 널리 응용되고 있으나 그 정확한 기작에 대해선 논쟁의 여지가 있다. 본 연구에서는 40 kH 초음파 조사시스템을 단세포 효모에 적합하게 개발하고 세포사멸 유도시 40 kH 초음파의 생물학적 현상을 살펴보았다. 아이오딘화 칼륨 선량 측정법을 이용하여 1.5 ml 실험튜브에 40 kH 초음파 조사 시스템의 최적 조건을 맞추어 세포사멸을 시간 의존적 방식으로 연구하였고 초음파 조사과정동안 온열효과와는 별개로 세포 사멸이 관찰되었다. 40 kH 초음파와 과산화수소의 동시 처리는 세포사멸에 상조적인 효과가 관찰되어 활성산소가 40 kH 초음파사멸에 관련이 있었다. 그러나 활성산소 저해제, NAC(N-acetyl-Lcysteine)는 초음파에 의한 세포사멸에 약한 영향만을 미쳤고 다른 세포사멸, 괴사억제제[글리실리진(glycyrrhizin) 또는 zVAD-fmk] 역시도 세포사멸을 완전히 억제하진 못하였다. 본 연구를 통하여 40 kH 초음파에 의한 세포사멸에는 온열효과나 활성산소만으로 사멸이 유도되지는 않는 것으로 보인다. Ultrasound has been widely used for biological and medical applications including induction of cell death, but a precise mechanism of induced cell death by ultrasound is controversial. In this study, an irradiation system with 40 kHz ultrasound was developed for a suitable cell death test of a representative unicellular organism, yeast, and used to study the biological effect of ultrasound on inducing cell death. Potassium Iodide (KI) dosimetry was used to devise an optimal system that successfully delivers 40 kHz ultrasound and produces reactive oxygen species in a 1.5 ml Eppendorf tube. Cell death was observed in an ultrasound transmission time-dependent fashion in this system. Thermal effect during irradiation was not observable in ultrasound induced cell death. Co-treatment of 40 kHz ultrasound and hydrogen peroxide showed a synergistic effect in inducing cell death. This finding suggests that 40 kHz ultrasound is related to reactive oxygen species formation. However, NAC (N-acetyl-L-cysteine) oxygen scavenger slightly inhibited the cell death by 40 kHz ultrasound. It was also found that 40 kHz ultrasound induced cell death was slightly inhibited by inhibitors of necrosis or apoptosis (glycyrrhizin or zVAD-fmk). This study suggests that cell death induced by 40 kHz ultrasound may not be exclusively related to reactive oxygen species formation and thermal effects in irradiated yeast cells.
베르누이 원리와 bolt-clamped Langevin type 초음파 진동자를 이용한 정상파 음파 공중부양의 탐구
박민철,박두재,김영환,Park, Mincheol,Park, Doojae,Kim, Young H. 한국음향학회 2018 韓國音響學會誌 Vol.37 No.6
본 연구에서는 소형 물체가 음파 정상파의 압력 마디 부근에 소형 물체가 부양하는 정상파 음파 공중부양(standing wave acoustic levitation) 현상에 대해 베르누이 원리를 이용하여 부양의 원인이 되는 음향 방사힘(acoustic radiation force)의 근원과 개형을 기존에 알려진 진동자에서 떨어진 거리에 따른 음향 방사힘의 그래프와 비교함을 통해 개념적으로 설명했다. 이러한 설명을 뒷받침하는 일련의 실험들을 BLT(Bolt-clamped Langevin Type) 초음파 진동자를 이용해서 수행하여, 물체들이 공기의 압력 마디 부근에 부양하고 있음을 확인했고, 물체가 부양하고 있는 상태에서 정상파가 형성되는 조건임을 확인했다. 더불어, 정상파 음파 공중부양 현상에서 부양하는 물체들이 수직하게 일렬로 정렬하는 현상 역시 설명할 수 있었다. The purpose of this study is to investigate the effect of acoustic radiation force on the standing wave acoustic levitation phenomenon, which is the levitation of small objects near the pressure node of the standing wave, using the Bernoulli principle. The source and scheme of the acoustic radiation force, which is the cause of the levitation, are conceptually explained through comparison with the graph of the acoustic radiation force versus the distance from the transducer. A series of experiments supporting this explanation was performed with a BLT(Bolt-clamped Langevin Type) ultrasonic transducer to confirm that the objects are floating near the pressure nodes and that it satisfies the condition for the standing wave formation when the object is levitating. Furthermore, the vertical alignment of floating objects, which is a characteristic of standing wave acoustic levitation phenomenon, could be explained.