• Geomechanics and Engineering
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• 제31권4호
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• pp.365-373
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• 2022

In order to investigate the damage evolution law of rock specimens under cyclic loading, cyclic loading tests under constant loads with different amplitudes were carried out on limestone specimens with high strength and brittleness values using acoustic emission (AE) technology and the energy evolution and AE characteristics were evaluated. Based on dissipated energy density and AE counts, the damage variable of specimen was characterized and two damage evolution processes were analyzed and compared. The obtained results showed that the change of AE counts was closely related to radial deformation. Higher cyclic loading values result in more significant radial strain of limestone specimen and larger accumulative AE counts of cyclic loading segment, which indicated Felicity effect. Regarding dissipated energy density, the damage of limestone specimen was defined without considering the influence of radial deformation, which made the damage value of cyclic loading segment higher at lower amplitude loads. The damage of cyclic loading segment was increased with the magnitude of load. When dissipated energy density was applied to define damage, the damage value at unloading segment was smaller than that of AE counts. Under higher cyclic loading values, rocks show obvious damage during both loading and unloading processes. Therefore, during deep rock excavation, the damages caused by the deformation recovery of unloading rocks could not be ignored when considering the damage caused by abutment pressure.

• 대한기계학회논문집
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• 제17권5호
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• pp.1054-1065
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• 1993

본 연구에서는 정상상태의 단일 주파수에서의 임의의 음압분포로 조화가진되 는 3차원 정방형 밀폐계 음장의 경우에 대한 능동제어를 시도함으로써 사무실과 같은 실내 공간에 대한 능동적 소음저감의 응용 가능성을 검토하고자 하였다. 또한 변환기 의 위치선정을 위하여 상태공간 모드 모델의 모드 근사화에 따른 계수행렬의 요소를 평가함으로써 가제어성과 가광측성을 만족하는 최적한 변환기 (부가음원, 마이크로폰) 의 위치를 선정하였다. 밀폐계 내부의 음압을 저감시키는 목적함수로는 전체 시간평 균 음향 포텐셜에너지를 사용하였으며 폐공간의 음압변동을 이론적으로 규명함으로써 부가적인 음원의 복소세기를 적절히 선정하여 이 음향 포텐셜 에너지의 양을 최소화 시킬 수 있음을 보였다.

• 비파괴검사학회지
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• 제24권1호
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• pp.45-51
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• 2004

발전소 보일러튜브는 장시간 동안 고온고압하의 기혹한 조건으로 운전됨에 따라 크리프, 열피로와 같은 각종 열화에 의해 누설손상이 발생하고 있다. 이러한 누설손상을 실시간 감시하고 진단하기 위하여 음향방출기술을 이용한 현장적용 연구를 수행하였다. 또한 고장예측 진단기술, 튜브의 수명관리 및 설비 감시에 활용할 수 있도록 음향방출 진단시스템을 개발하여 현장에 설치하고, 보일러 운전상태에 따른 신호측정 및 평가, 누설위치 판별 등에 대해 고찰하였다. 누설감지는 저주파 및 고주파대역의 누설로 구분하여 음향방출신호를 각각 측정 및 평가하였다. 현장적용 연구결과로부터 실시간으로 보일러튜브 상태감시와 누설위치 추적이 가능하였으며, 향후 본 기술을 이용하면 발전설비 안전운전과 발전소 정지에 따른 경제적 손실 예방에 크게 기여할 것으로 기대된다.

• 한국소음진동공학회논문집
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• 제21권12호
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• pp.1098-1103
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• 2011

The structural integrity of APR1400 reactor vessel internals has been being assessed referring the US Nuclear Regulatory Commission regulatory guide 1.20, comprehensive vibration assessment program. The program is composed of a vibration and stress analysis, a vibration and stress measurement, and an inspection. This paper covers the vibration and stress analysis on the reactor vessel internals by the pulsation of reactor coolant pump. 3-dimensional models to calculate the hydraulic loads and structural responses were built and the pressure distributions and the structural responses were predicted using ANSYS. This paper presents that APR1400 reactor vessel internals have enough structural integrity against the pulsation of reactor coolant pump as the peak stress of the reactor vessel internals is much lower than the acceptance limit.

• 한국음향학회지
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• 제8권1호
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• pp.75-80
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• 1989

단일모드 광섬유를 이용하여 호모다인 검출방식으로 동작하는 Mach-Zehner 광섬유 간섭계를 구성하여 공기중 음압반응을 조사하였다. 광섬유 간섭계 센서가 직각조건에서 동작하도록 하기 위해 기준 광섬유에 원통형 압전신장기를 사용하는 신호안정화 장치를 제작하였다. 이는 온도변화나 주위환경의 영향에 관계없이 광섬유 간섭계 센서의 감도를 최대의 크기로 일정하게 유지시켜 준다.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2000년도 제20회 KOSCO SYMPOSIUM 논문집
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• pp.142-151
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• 2000

Dump combustor is a combustor having a dump plane to make coherent structures. A non-premixed flame dump combustor of simple geometry was constructed. We conducted basic experiments such as frequency response on the combustor to confirm the characteristics of the phenomena as a typical dump combustion and unsteady combustion. Furthermore we visualized the flame front behavior by CH chemiluminescence and high speed motion analysis. In spite of the lack of another data such as velocity, species concentration and temperature, the results showed not only the periodic motion of flame front but the ignition process of vortex ring flame. Also we could check out Rayleigh criterion by combining the visualization data with the pressure data.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2005년도 제31회 KOSCO SYMPOSIUM 논문집
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• pp.294-301
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• 2005

The instabilities in rocket engines and gas turbine combustors due to the interaction between the fluid flow (acoustics) and the heat transfer (thermal energy) are called thermoacoustic or combustion instabilities. Almost all analysis assumes constant hot section temperature for Modern mathematical analysis of acoustic oscillations in Rijke type devices. However, it is impossible to predict whether a system is stable or not because the flame or heater response model can have a dramatic effect on predicted growth rates. In this study, A standard ${\kappa}-{\varepsilon}$ turbulent model and hybrid combustion model(eddy breakup model and chemical reaction) were used. After steady solution was gotten, unsteady calculation is simulated by perturbating on pressure boundary. As a result, we obtained the relationship of equivalence ratio and frequency by numerical simulation, and they are comparable to the experimental result. In addition, in spite of these results, there are limitations of using turbulent and combustion model in simulation method of thermoacoutic instability

• 대한의용생체공학회:의공학회지
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• 제2권1호
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• pp.15-20
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• 1981

In this study, the scattering of ultrasound by blood is theoretically studied. At first, the Chernow equation which represents acoustic propagation inside the region of inhomogenieties is modified to be fitted for blood. Then, scattering amplitude and scattering Cross-section at the far-field region are obtained from this equation. In this case, hemotocrit is assumed to be less than 26 per cent, and the red blood cell is modeled as independent scatterer. This study also develops a practical approximation for the backscattering of periodic sinewave bursts by a volume of randomly distributed scatterers, i.e., whole red blood cells. This expression for the received backscattering ultrasound pressure after the n-th burst of narrowband transducer is obtained from an ideal continuous wave transducer's response.

• 한국소음진동공학회논문집
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• 제17권8호
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• pp.757-765
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• 2007

Enhanced PSPICE circuit model for vented-box loudspeaker system with lumped parameters was proposed to more accurately simulate real vented-box loudspeaker system. Frequency dependent parameters were used to model voice coil inductor. Acoustic pressure response curves and electrical impedance curves were simulated and investigated by PSPICE circuit model according to circuit parameters' variations. Finally, it was used to identify faults detection in woofers manufactured by unskilled persons.

• 정보저장시스템학회논문집
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• 제8권1호
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• pp.16-21
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• 2012

SAW device is widely used as filters, sensors, actuators in various technologies. And capacitive sensor is tremendously used to measure pressure, gap, etc. The application of SAW device as signal conditioner of capacitive sensor reduces noise level and enables high precision measurement. The response increase of SAW based capacitive sensor is produced just before the two capacitive electrode contacts by the existence of parasitic resistance of capacitive electrode. In this paper, we analyze the effects of parasitic resistance and propose the calibrating method using lumped component and execute the high precision gap measurement using calibrated system. And xx nm resolution and yy ${\mu}m$ stroke was attained.