• 한국광학회지
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• 제11권4호
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• pp.250-254
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• 2000

반도체 레이저 광원의 되먹임 효과를 이용하여 레이저 도플러 속도계를 구현하였다. 움직이는 물체의 표면에 조사된 레이저광이 산란될 때 산란광은 물체의 속도에 비례한 도플러 변이를 일으킨다. 산란광의 일부를 레이저 공진기 내부로 입사키면 공진기 안에서는 발진광과 입사된 산란광이 혼합되어 두 개 광 사이의 차주파수로 레이저 전류가 변조되는 원리를 이용한 것이다. 본 실험에서는 원형 회전체에 레이저를 조사할 때 발생하는 산란광을 사용하여 회전 속도와 도플러 편이 주파수와의 관계를 비교하였다. 또한 회전면에 대한 레이저 입사 각도에 따른 도플러 주파수의 변화를 관찰하였다. 이로부터 도플러 주파수와 회전체 각속도 사이의 비례 관계 및 측정광의 입사 각도와의 선형성을 확인하였다.

• 한국자기학회지
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• 제3권1호
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• pp.56-60
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• 1993

FeCo/Pd 초격자 다층박막의 FeCo 와 Pd sublayer 두께를 각각 $2.5\;{\AA}$ 및 $10.5\;{\AA}$으로 유지시키면서 FeCo sublayer 의 Fe 조성이 0에서 100% 까지 변화함에따른 포화자화값, 수직 자기이방성에너지, 보자력 및 Kerr 회전각의 파장 의존성을 조사 하였다. 포화자화값은 Fe 조성이 48 at.%부근에서 최 고치를 보였고, 수직 자기이방성에너 및 조자력은 Fe조성의 증가에따라 단조감소 하였다. Kerr 회전각은 Fe 조성의 증가에따라 감소하였는데 그 크기 및 변화의 폭은 단파장으로 갈수록 증가하였다.

• 한국세라믹학회지
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• 제45권2호
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• pp.119-125
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• 2008

The FAS(Fluoroalkylsilane)/Nafion inorganic-organic composite electrolyte membrane was successfully fabricated through sol-gel method. The FAS having hydrophobic functional group and silanol ligands is impregnated in $Nafion^{(R)}$ membrane to reduce methanol crossover. The prepared FAS/Nafion inorganic-organic composite electrolyte membrane consist of the hydrophobic FAS-derived silicate nano-particles and $Nafion^{(R)}$ matrix showed decrease of methanol crossover and reduction of humidity dependence without large sacrifice of proton conductivity. The microstructural analysis of the composite membranes was performed using FESEM and FTIR. And the effect of the incorporation of the hydrophobic FAS-derived silicate nano-particles into $Nafion^{(R)}$ membrane was investigated via solvent uptake, membrane expansion rate, humidity dependency of proton conductivity and contact angle measurement.

• International Journal of Fluid Machinery and Systems
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• 제8권2호
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• pp.73-84
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• 2015

Aerating hydroturbines have recently been proposed as an effective way to mitigate the problem of low dissolved oxygen in the discharge of hydroelectric power plants. The design of such a hydroturbine requires a precise understanding of the dependence of the generated bubble size distribution upon the operating conditions (viz. liquid velocity, air ventilation rate, hydrofoil configuration, etc.) and the consequent rise in dissolved oxygen in the downstream water. The purpose of the current research is to investigate the effect of location of air injection on the resulting bubble size distribution, thus leading to a quantitative analysis of aeration statistics and capabilities for two turbine blade hydrofoil designs. The two blade designs differed in their location of air injection. Extensive sets of experiments were conducted by varying the liquid velocity, aeration rate and the hydrofoil angle of attack, to characterize the resulting bubble size distribution. Using a shadow imaging technique to capture the bubble images in the wake and an in-house developed image analysis algorithm, it was found that the hydrofoil with leading edge ventilation produced smaller size bubbles as compared to the hydrofoil being ventilated at the trailing edge.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.125-130
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• 2003

This paper provides approximate J estimates for off-centred, circumferential through-wall cracks in cylinders under bending. The proposed method is based on the reference stress approach, where the dependence of elastic and plastic influence functions of J on the cylinder/crack geometry, the off-centred angle and strain hardening is minimised through the use of a proper normalising load. Based on published limited FE results for off-centred, circumferential through-wall cracks under bending, such normalising load is found, based on which the reference stress based J estimates are proposed for more general cases, such as for a different cylinder geometry. Comparison of the estimated J with extensive FE J results shows overall good agreements for different crack/cylinder geometries which provides sufficient confidence in the use of the proposed method to fracture mechanics analyses of off-centred circumferential cracks. Furthermore, the proposed method is simple to use, giving significant merits in practice.

• 한국수산과학회지
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• 제48권2호
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• pp.207-220
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• 2015

This study identified the species-specific, frequency-dependent characteristics of broadband acoustic scattering that facilitate classifying fish species using the pulse compression (PC) technique. Controlled acoustic scattering laboratory experiments were conducted with nine commercially important fish species using linear chirp signals (95-220 kHz) over an orientation angle range of ${\pm}45^{\circ}$ in the dorsal plane at approximately $1^{\circ}$ increments. The results suggest that the angular-dependent characteristics of the broadband echoes and the frequency-dependent variability in target strength (TS) were useful for inferring the fish species of interest. The scattering patterns in the compressed pulse output were extremely complex due to morphological differences among fish species, but the x-ray images strongly suggested that spatial separation correlated well with scattering for the head, skeleton, bone, otoliths, and swim bladder within each specimen.

• Advances in aircraft and spacecraft science
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• 제2권4호
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• pp.427-443
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• 2015

The present paper is the follow-on of a former work in which the influence of the gas-surface interaction models was evaluated on the aerodynamic coefficients of an aero-space-plane and on a section of its wing. The models by Maxwell and by Cercignani-Lampis-Lord were compared by means of Direct Simulation Monte Carlo (DSMC) codes. In that paper the diffusive, fully accommodated, semi-specular and specular accommodation coefficients were considered. The results pointed out that the influence of the interaction models, considering the above mentioned accommodation coefficients, is pretty strong while the Cercignani-Lampis-Lord and the Maxwell models are practically equivalent. In the present paper, the comparison of the same models is carried out considering the dependence of the accommodation coefficients on the angle of incidence (or partial accommodation coefficients). More specifically, the normal and the tangential momentum partial accommodation coefficients, obtained experimentally by Knetchel and Pitts, have been implemented. Computer tests on a NACA-0012 airfoil have been carried out by the DSMC code DS2V-64 bits. The airfoil, of 2 m chord, has been tested both in clean and flapped configurations. The simulated conditions were those at an altitude of 100 km where the airfoil is in transitional regime. The results confirmed that the two interaction models are practically equivalent and verified that the use of the Knetchel and Pitts coefficients involves results very close to those computed considering a diffusive, fully accommodated interaction both in clean and flapped configurations.

• Steel and Composite Structures
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• 제25권4호
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• pp.403-413
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• 2017

The fabric braided braking hose that delivers the driver's braking force to brake cylinder undergoes the large deformation cyclic motion according to the steering and bump/rebound motions of vehicle. The cyclic large deformation of braking hose may give rise to two critical problems: the interference with other adjacent vehicle parts and the micro cracking stemming from the fatigue damage accumulation. Hence, both the hose deformation and the fatigue damage become the critical issue in the design of braking hose. In this context, this paper introduces a multi-objective optimization method for minimizing the both quantities. The total length of hose and the helix angles of fabric braided composite layers are chosen for the design variables, and the maximum hose deformation and the critical fatigue life cycle are defined by the individual single objective functions. The trade-off between two single objective functions is made by introducing the weighting factors. The proposed optimization method is validated and the improvement of initial hose design is examined through the benchmark simulation. Furthermore, the dependence of optimum solutions on the weighting factors is also investigated.

• Progress in Superconductivity
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• 제11권2호
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• pp.96-99
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• 2010

We measured electrical shot noise in a metal-insulator-metal tunnel junction, which was made by using electron-beam lithography and double-angle evaporation technique. Since the dependence of the shot noise on bias voltage and temperature is theoretically well known, we can determine the temperature of the junction by measuring the noise as the voltage across the junction is changed. A cryogenic low noise amplifier was used to amplify the noise signal in the frequency range of 600-800 MHz, which enabled fast measurement of noise signal and thus temperature. With further study, this method could be useful for primary thermometry in cryogenic temperatures.

• 대한기계학회논문집A
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• 제20권9호
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• pp.2792-2799
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• 1996

It was shown in the previous study that the numerically derived elastic work factor for CLS specimen was independent of fiber direction for a unidirectional case. Also, it was proposed the elastic work factor could be used to determine energy release rate from a single test record. In the present study, elastic work factor was derived from a simple beam theory to investigate its dependence on material property and geometric condition. Also, the elastic work factor of CLS specimen was applied experimentally to determine critical energy release rate in order to prove its validity determining critical energy release rate from a single specimen. For this purpose, critical energy release rate determined using the elastic work factor was compared with that determined by the compliance method. The results showed that while elastic work factor is affected by $t_2/t_1$ and $L_2/L_1$ it is independent of fiber angle for a unidirectional case. It was also found that critical energy release rates determined by both methods are comparable each other, thus elastic work factor approach can be used to determine energy release rate from a single test specimen.