• Journal of Energy Engineering
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• v.29 no.1
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• pp.34-43
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• 2020

A study has been done for self-starting torque of vertical axis wind turbine blade. It is especially concentrated to evaluate the torque coefficient before starting rotation. Two different aerofoils(AMI903 and AMI904) are proposed to benchmark the possible best blade(supercritical airfoil) for self-starting performance. Torque coefficients in the tangential direction of rotation are given with respect to the angle of attack in terms of drag coefficient and lift coefficient. Torque coefficient shows that the effect of Reynolds number is minimal. The thicker blade(AMI904) between two different proposed airfoils has bigger torque coefficient, which is attributed to lower lift coefficient and higher drag coefficient.

• Aerospace Engineering and Technology
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• v.5 no.2
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• pp.149-158
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• 2006

A review has been made on what kind of method can be applied to predict the dynamic derivatives of the separated PLF(Payload Fairing) halves of a launch vehicle in consideration of technology and budget. An optimal approach is selected considering the geometric characteristics of the PLF halves, the aerodynamic conditions and the required accuracy. The time history of aerodynamic force/moment coefficients are obtained for the forced harmonic motions by solving the unsteady Euler equations derived with respect to the inertial reference frame. and the dynamic derivatives are deduced by integration of the aerodynamic coefficients for one period. In this research, the dynamic derivatives are presented for 0.6$\leq$ M $\leq$2.0, $-180^{\circ}$ $\leq$$\alpha$ $\leq$$180^{\circ}$ and $-90 ^{\circ}$$\leq$$\beta$$\leq$$90 ^{\circ}$.

• Journal of the Korean Society of Propulsion Engineers
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• v.17 no.2
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• pp.24-30
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• 2013

To guarantee the exact control of missile warhead, it is inevitable to ensure the stabilities in the view points of structural and fluid/thermo dynamics of the rocket motor. Specially, despite of shortness in operating time of the rocket motor which is initial turning type of missile, it occurs frequently some problems of ablation at the neighborhood of the nozzle throat, with the result that the system itself gets to failure. In these connections, in the present study, the effect of the operating time of a rocket motor on the coefficient of convective heat transfer at the nozzle wall is investigated by numerical analysis. As a result, it is turned out that the heat transfer coefficient is largest at the just ahead of nozzle throat and decreases with the increase of operating time of the rocket motor. Furthermore, we found that the radius of curvature of throat becomes smaller, the maximum coefficient of convective heat transfer becomes larger.

• Proceedings of the Membrane Society of Korea Conference
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• 1994.04a
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• pp.57-57
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• 1994

졸-겔 침지코팅 (dipcoating) 또는 가압 졸-겔 코팅 (pressurized coating) 법으로 제조한 $\gamma-Al_2O_3, SiO_2, TiO_2$ 및 aluminosilicate 복합막에 대하여 $CO_2$, He, $N_2$, 및 $O_2$ 기체 투과율과 $CO_2$ 분리계수를 측정하였다. 이들 막을 통한 모든 기체의 이동은 Knudsen 유동이 지배적이었으며 $CO_2/N_2$의 분리계수는 0.9 ~ 1.1 정도로 Knudsen 분리계수 ($CO_2/N_2$의 경우 0.8)보다 약간 높은 값을 보여주었다. $CO_2$ 분리계수를 향상시키기 위하여 silane coupling 및 산화물 도핑법에 의한 복합막의 표면개질을 시도하였으며 분리막의 재질 및 표면개질 조건에 따른 $CO_2/N_2$ 분리계수 변화를 측정 비교하였다. Silane coupling에 의한 표면개질이 $CO_2$의 표면 친화성 (affinity)에 의한 표면확산속도를 증가시키기 때문에 $CO_2$ 분리에 있어서 산화물 도핑에 의한 표면개질보다 더욱 효과적이었다.

• Proceeding of EDISON Challenge
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• 2014.03a
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• pp.585-590
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• 2014

Chowdbury. H.는 인체를 다수의 원형 실린더로 단순화하여 스키점프와 사이클 운동복의 항력계수를 각각 측정하였다. 이처럼 원형 실린더에 스피드 스케이팅 운동복을 씌운 모습과 골프공에서 사용하는 딤플의 2차원 형상이 서로 유사한 모양임을 착안하여, 2차원 원형 실린더 표면의 딤플이 유동 현상에 어떤 효과를 일으키는지 살펴보았다. 본 연구에서는 초기 형상을 토대로 3가지 딤플 형상 변수에 대한 매개변수 설정을 통해 항력계수를 비교하였다. 또한 3가지 딤플 형상 중 가장 낮은 항력계수를 갖는 딤플 형상에 대해서 요철 높이에 따른 항력계수를 비교하였다. 이를 통하여 딤플 형상이 각진 모양보다 둥근 모양일수록 항력계수가 작은 것을 확인하였으며, 요철 높이를 제외한 모든 조건이 동일할 때 최적의 요철 높이가 존재할 수 있음을 확인하였다.

• Aerospace Engineering and Technology
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• v.10 no.1
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• pp.70-78
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• 2011

The Equations of inherent flow coefficient are different from compressible to incompressible flow. The paper has been conducted to measure the inherent flow coefficient of solenoid valve under various flows. Experimental results for compressible and incompressible flow were confirmed to inherent flow coefficient correctly. The value of inherent flow coefficient for the 0.5" solenoid valve is about 2. Dynamic characteristics of a solenoid valve, which plays an important role in real model, have been analysed by AMESim simulator modeling.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.24 no.2
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• pp.227-234
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• 2006

Ministry of construction & transportation is operating for the soil and rock information system and is considered to accurate application of soil conversion factor that is essentially necessary for accurate calculation of earth volume. Since the balance of cutting earth in public work, the plan of spoil bank or borrow pit are directly related to construction costs, accurate calculation of earth volume and efficient scheme of haul are important. As such, this study has provided methods that can acquire information that is more rapid, applicable to job sites, and trustworthy by comparing resultant values of photogrammetry, laser scanning, or inside job site experimentations, and calculated soil conversion factor by applying photogrammetry and laser scanning methods for hard rock that has difficulty in calculating soil conversion factor. The study can provide alternatives that can resolve the problems of unbalanced earth volume that may arise in applying to plans the earth conversion factor that relies on planning books and experience without considering the characteristics of job site earth, and can establish its relevancy by calculating soil conversion factor for hard rock that has relative difficulties in doing inside or job site testing.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.8 no.3
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• pp.256-267
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• 1996

In estuarine 3-dimensional numerical modeling. it is very important to calculate vertical eddy viscosity accurately. Various turbulence models employing eddy viscosity concept were applied to the steady flow in an open-channel and the tidal flow in long tidal channel and compared. The evaluations include the verification tests against experimental data sets for steady and tidal flows. The simulation results have shown that the compared models are in good agreements with experimental data of steady flow while only $textsc{k}$-$\varepsilon$ model, $textsc{k}$-ι model, and 1-equation model with well-defined mixing length profile give good agreements with experimental data of tidal flow.

• Journal of Energy Engineering
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• v.29 no.3
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• pp.25-33
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• 2020

In this study, flow and structural computational analysis were performed to investigate the structural safety of the lightweight butterfly valve disc designed by topology optimization. After flow analysis, as the opening angle increased, the flow coefficient increased non-linearly and showed a gentle slop. When the opening angle was 12 degree, the cavitation could be predicted. After FE analysis, all FE von-Misses stresses of the lightweight disc were smaller than the yield strength of the material, and all FE maximum deformations were also smaller than the conservative deformation of the previous study. Ultimately, it was confirmed that the structural safety of the lightweight valve disc based on computational analysis is effective.

• Journal of KSNVE
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• v.5 no.3
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• pp.303-311
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• 1995

Tests on flow-induced vibration of inclined cylinders in uniform flow were performed in the cavitation tunnel at the Korea Instituteof Machinery and Metals. The test program was intended to investigate flow-induced vibration characteristic of the cylinders with three different inclined angles of 10$^\circ$, 20$^\circ$ and 30$^\circ$ and to estimate the fluid force coefficients acting on the cylinders. Important observations are as follows: 1) Numal drag is dominant compared with viscous drag for the inclined angle over 20.deg. and it has the value from 1.7 to 2.0 as was observed by other researchers. 2) Lift force coefficient has large value at the lock-in range determined by 4$\Theta/f_nD$<8. Measured maximum lift force coefficients at the inclined angle of 30.$^\circ$ and 20$^\circ$ were 0.9 and 0.4 respectively.