• 소음진동
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• 제11권2호
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• pp.241-248
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• 2001

The present paper describes experimental and computational work to augment the magnitude of the impulsive wave. An experiment was performed using a simple shock tube with an open end and numerical calculations were carried out to solve the unsteady, axisymmetric, inviscid, compressible governing equations. The control strategy applied was to alter the exit geometry of a straight tube to a sudden enlargement tube and a flare tube. The effects of the configurations of the tube exit on the magnitude of the impulsive wave were investigated over the range of the weak shock Mach number from 1.01 to 1.10. The results obtained were compared to those of the straight tube tests. The numerical result predicted the magnitude of the experimented impulsive waves with a good accuracy. The present passive control technique enabled the magnitude of the impulsive wave to augment by about 23 percent, compared to that of the straight tube of no control.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.550-555
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• 2003

When a shock wave arrives at an open end of tube, an impulse wave is discharged from the tube exit and complicated flow is formed near tube exit. The flow field is influenced by the cross-sectional geometry of tube exit, such as circular, square, rectangular, trapezoid and etc. In the current study, three-dimensional propagation characteristics of impulse wave discharged from the tube exit with non-circular cross section are numerically investigated using a CFD method. Total variation diminishing (TVD) scheme is used to solve the three-dimensional, unsteady, compressible Euler equations. Computations are performed for the Mach numbers of the incident shock wave $M_{s}$ below 1.5. The results obtained show that the peak pressure of the impulse wave and propagation directivity depends on the cross-sectional geometry of tube exit and the Mach number of incident shock wave.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 제5회 영호남 학술대회 논문집
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• pp.63-66
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• 2003

To diffuse Zn at solid-state, the $SiO-2$/ZnO/$SiO_2$ wafers was made by PECVD and RF Sputter. Thicknesses of bottom $SiO_2$ and cap $SiO_2$ was about 500 ${\AA}$ and about 3500 ${\AA}$. Diffusion temperatures were $760^{\circ}C$, $780^{\circ}C$, and $800^{circ}C$, and diffusion times were 1, 2, 3, 4, 5, and 6 hr. LED chips were fabricated by the diffused wafers at Fab. The peak wavelength of all chips showed about 625~650 nm and red color. Main reason for Iv change was by diffusion temperature not diffusion time. The lower temperature was the higher Iv. We thick that these properties is because of the very high diffusion temperature.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2017년도 제48회 춘계학술대회논문집
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• pp.734-738
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• 2017

본 연구에서는 가스다이내믹 공진 점화시스템 (Gas-dynamic Ignition System)의 온도상승 지배인자를 파악하고, 공진관으로의 질량유입 패턴의 영향에 대해 연구하였다. OpenFOAM 프로그램을 이용하여 세 가지 Case에 대한 전산해석을 수행하였으며, RhoCentralFoam을 적용하였다. 해석결과로, 작동유체의 가열이 공기열역학적 현상에 의한 것임을 밝히고, 공진관으로의 원활한 질량유입이 온도 상승에 중요한 지배인자임을 확인하였다.

• 한국유체기계학회 논문집
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• 제18권1호
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• pp.11-19
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• 2015

Recently, the cross flow turbines attract more attention for their good performance over a large operating regime at off design point. This study employs a very low head cross flow turbine, which has open inlet duct and has barely been studied before, to investigate the performance of the cross flow turbine with air suction from the rear part of the runner. Unlike conventional cross flow turbines, a draft tube is attached to the outlet of runner to improve the turbine performance. Water level and pressure in the draft tube are monitored to investigate the influence of air suction. Torque at local blade passage of three parts of runner is examined in detail under the conditions of different air suction. Consequently, it is found that with proper air suction in the runner chamber, the water level in the draft tube gradually drops to Stage 2 of the runner and the efficiency of the turbine can be raised by 10%. Overall, the effect of air-layer on the performance of the turbine is considerable.

• 대한건축학회논문집:구조계
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• 제34권5호
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• pp.43-50
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• 2018

The temperature of underground water generally remains constant regardless of the season. therefore, it is possible to get plenty of energy if we use characteristics of underground water for both cooling and heating. This study evaluates efficiency of real size coaxial and U-tube type complex geothermal system which is combined with underground water well. This study also evaluates relative efficiency/adaptability through comparison with existing geothermal systems(vertical closed loop system, open loop system(SCW)). The heat exchange capacity of complex geothermal system according to temperature difference between circulating water and underground water shows very high significance by increasing proportionally. The temperature change of underground water according to injection energy, shows very high linear growth aspect as injection thermal volume heightens. As a result of evaluation of heat exchange volume between complex geothermal system and comparative geothermal system, coaxial type has 26.1 times greater efficiency than comparative vertical closed type and 2.8 times greater efficiency than SCW type. U-tube type has 26.5 tims greater efficiency than comparative vertical closed type and 2.8 times greater than SCW type as well. This means complex geothermal system has extremely outstanding performance.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집E
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• pp.317-322
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• 2001

This study depicts an experimental work of the impulsive wave discharged from the open end of several kinds of right-angle bend pipes, which are attached to the open end of a simple shock tube. The weak normal shock wave with its magnitude of Mach number from 1.03 to 1.20 is employed to obtain the impulsive wave propagating outside the open end of the bend pipes. The experimental data of the magnitude of the impulsive wave and its propagation directivity are analyzed to characterize the impulsive waves discharged from the right-angle bend pipes and compared with those from a straight pipe. The results obtained show that a right-angle miter bend considerably reduces the magnitude of the impulsive wave and its directivity toward to the pipe axis, compared with the straight pipe. It is believed that the right angle miter bend pipe can playa role of passive control against the impulsive wave.

• Journal of Chest Surgery
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• 제26권7호
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• pp.532-537
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• 1993

To assess the therapy of spontaneous pneumothorax in the aged patients, the treatment methods and results in 60 patients 50 years of age or older were retrospectively reviewed. Most of the patients were male [56 of 60 patients] and the major underlying lung diseases associated with spontaneous pneumothorax were tuberculosis [32 patients] and chronic obstructive lung disease [20 patients]. The recurrence rate of thoracostomy tube drainage with or without chemical pleurodesis using tetracycline was 39.6% [21 of 53 patients], but there was no recurrence in the patients treated with open thoracotomy, pleural abrasion, and chemical pleurodesis using talcum powder[Asbestosis free]. In the patients treated with open thoracotomy, the bullous or bleb lesions were placed in the various sites of both lungs. We concluded that even though thoracostomy tube drainage is the first choice of therapy for spontaneous pneumothorax in the aged patients, the recurrence rate is high, especially in the patients with persistent air leakage for more than 2 days, and the open thoracotomy with pleural abrasion and chemical pleurodesis using talcum powder can prevent the recurrence in the selected patients.

• 전기학회논문지
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• 제58권3호
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• pp.566-572
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• 2009

This paper has studied breakage possibility of glass insulators by resonance and accelerated deterioration through the comparison of the natural vibration and on site vibration. The natural frequencies of the strut tube glass insulator was measured within a range of less than 1kHz. In the on site vibration, the largest frequency that was imposed on strut tube glass insulators was 80Hz with 1.13g of vertical vibration in the viaduct section, the largest vertical vibration (0.38g) was detected at 103Hz in the open route section. When site vibration and natural vibration of strut tube glass insulators were compared in terms of characteristics, the resonance frequency was not the same. In both the viaduct and open route sections, it seems that the impact by vertical vibration in strut tube glass insulators is large. It's very unlikely that glass insulators were damaged by fatigue accumulation of vibration since the possibility of damage by resonance was very low in consideration of the characteristics of natural vibration and site vibration of glass insulators. In addition, no damage was detected in the accelerated deterioration test.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2008년도 Techno-Fair 및 합동춘계학술대회 논문집 전기물성,응용부문
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• pp.189-190
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• 2008

This study was investigated a possibility of fault of glass insulator due to vibration on high-speed railway. The proper vibration of 1-glass insulator have many frequency band and high amplitude showed in high frequency than low frequency. The proper vibration of strut tube insulator was lowest 170Hz, highest 1.5kHz. The field signal amplitude of viaduct and open route were biggest moment pantograph of high-speed rail. The surface vibration(V3) amplitude of strut tube insulator was biggest. From the FFT analysis of viaduct and open route, the strut tube insulator effect by vertical vibration was big, the frequency was 82.5Hz and 105Hz, respectively. However, in comparison with the proper vibration of strut tube insulator, the resonance was not observed. Although the amplitude of insulator is high, the possibility of fault is low because the glass insulator deterioration by the accumulation of vibration do not happen.