• 동력기계공학회지
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• 제20권5호
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• pp.60-65
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• 2016

Dynamic performance of transmission has a substantial effect on dynamic performance and fuel efficiency of a vehicles. Dynamic performance of transmission and mass moments of inertia of transmission gears are related directly each other. Then a smaller amount of kinetic energy from vehicles that repeat acceleration and deceleration requires lighter rotating part in transmission. It is going to increases fuel efficiency as a result. In this study, equivalent inertia moments of inertia at different speeds were calculated by simplifying the transmission system. To find out lightening effect at low speed level gear on fuel efficiency, the powerflow of transmission was analyzed. And the lightning effect of the rotating parts in transmission is compared with the mass reduction of sprung parts in vehicle.

• 한국환경과학회지
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• 제25권4호
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• pp.517-524
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• 2016

In order to treat groundwater containing high levels of nitrate, nitrate reduction by nano sized zero-valent iron (nZVI) was studied using batch experiments. Compared to nitrate removal efficiencies at different mass ratios of $nitrate/Fe^0$, the removal efficiency at the mass ratio of 0.02% was the highest(54.59%). To enhance nitrate removal efficiency, surface modification of nZVI was performed using metallic catalysis such as Pd, Ni and Cu. Nitrate removal efficiency by Cu-nZVI (at $catalyst/Fe^0$ mass ratio of 0.1%) was 66.34%. It showed that the removal efficiency of Cu-nZVI was greater than that of the other catalysts. The observed rate constant ($k_{obs}$) of nitrate reduction by Cu-nZVI was estimated to $0.7501min^{-1}$ at the Cu/Fe mass ratio of 0.1%. On the other hand, TEM images showed that the average particle sizes of synthetic nZVI and Cu-nZVI were 40~60 and 80~100 nm, respectively. The results imply that catalyst effects may be more important than particle size effects in the enhancement of nitrate reduction by nZVI.

• 대한기계학회논문집
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• 제18권6호
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• pp.1598-1603
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• 1994

A preliminary design procedure for a multi-stage axial compressor is developed, which is based on the stage-stacking method. It determines the flow coefficient which gives rise to the design conditions required such as pressure ratio, mass flow rate and rotational speed for a given specific mass flow rate at inlet to a compressor. With this flow coefficient, blade radii, every stage and compressor performance characterics such as stage pressure ratio, adiabatic efficiency etc. are calculated by stacking each stage performance characteristics. It is shown that there is an optimum number of stage which results in the maximum of compressor overall efficiency for a given specific mass flow rate at inlet to a compressor. A test design was tried for three different geometric design constraints, and comparison with a previous study shows that present procedure could be used reliably in determining the number of compressor stage in preliminary design stage.

• 경영과학
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• 제16권2호
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• pp.1-11
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• 1999

A well-designed location strategy is an integral and important part of corporate strategy for retail firms. The last five years witnessed major changes in retailing industry. A growing city population, rising income levels. and the emergence of suburb areas presented ratailers with new challenges. Mass discount merchandisers and supermarkets expanded rapidly, spreading from Seoul into smaller cities. The rapid increase of mass discount stores raised new concerns and gave rise to the need from a systematic approach to location analysis. In this paper, we present the mathematical background and characteristics of DEA(Data Envelopment Analysis) model, and give a short case study where we apply the DEA model to compute the relative efficiency of 11 Korean mass discount merchandisers. Interpretation of the result is also provided.

• 한국지구과학회지
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• 제34권5호
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• pp.407-414
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• 2013

This study presents the global star formation efficiency (SFE) of 272 local star-forming galaxies based on the HI gas mass, stellar mass, star formation rate (SFR), and morphology. The SFE increases as the stellar mass increases while the specific SFR decreases. The SFE is enhanced for galaxies with large H$\acute{a}$ equivalent widths, which is primarily due to the large SFR, not due to the large available amount of gas. The SFE is also enhanced by a factor of ~2 for merging systems compared to the normal spirals, showing that the merger-induced high pressure and density environment are crucial for the active star formation. Based on the SFR scaling relation, I present a SFR calibration formula using the HI gas mass.

• 국제초고층학회논문집
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• 제10권2호
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• pp.99-107
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• 2021

This research investigates the potential of Adaptive TMDs for tall building damping. The Adaptive TMD under consideration is based on real-time controlled hydraulic dampers generating purely dissipative control forces. The control approach is designed to enhance the Adaptive TMD efficiency for moderate wind loads with return periods below 50 years. The resulting enhanced TMD efficiency is used to reduce the pendulum mass by 15% compared to the passive TMD while still guaranteeing the acceleration limits of the one and ten year return period winds. Furthermore, the adaptive control approach is designed to disproportionally increase the controlled damping force at wind loads with return periods of 50 years and more in order to reduce the maximum relative motion of the Adaptive TMD with only 85% pendulum mass. Compared to the passive TMD with 100% pendulum mass the maximum relative motion is reduced by 20%. Both the pendulum mass reduction and the maximum relative motion reduction significantly reduce the foot print of the Adaptive TMD which is highly desirable from the economic point of view.

• 한국환경과학회지
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• 제11권6호
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• pp.605-610
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• 2002

The absorption of benzene in nonpolar solution was studied in a laboratory-scale of bubble column varying of gas flow rates and gas-to-liquid ratios. A bubble column had a 0.8∼l$\times$10$\^$-3/ m$^3$ total volume (height 1500 mm, diameter 50 mm). Solution analysis was performed by GC-FID and GC-MSD. The objectives of this research were to select the best absorption fluid and to evaluate the mass transfer characteristics under specific conditions of each absorption. The results of this research were follow as: First, the heat transfer fluid is more efficient than the other nonpolar solution in removing VOC. Second, The benzene removal efficiency improved according to an increasing rate of gas flow. Also, volumetric mass transfer rate of column can be enhanced by increasing gas flow rate. Finally, the relation of gas flow rates, liquid amount, and volumetric mass transfer coefficient was obtained as follows. K$\_$y/a: 0.5906(V$\_$g//L)$\^$0.7611/ The following correlation of mass transfer coefficient and efficiency was proposed. v= 0.06078 K$\_$y/a$\^$0.2444/.

• 한국분무공학회지
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• 제27권3호
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• pp.161-166
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• 2022

To measure the change in friction loss due to the control of fuel mass and oil temperature in a gasoline engine, the floating liner method was used to measure the friction generated by the piston of a single-cylinder engine. First, to check the effect of combustion pressure on friction, the friction loss was measured by adjusting the fuel mass. It was confirmed that the friction loss increased as the fuel mass increased under the same lubrication conditions. In addition, it was confirmed that the mechanical efficiency decreased as the fuel mass increased. Next, to check the effect of lubrication conditions on friction, the friction loss was measured by controlling the oil temperature. It was confirmed that friction loss increased as the oil temperature decreased at the same fuel mass. As the oil temperature decreases, the viscosity increases, resulting in decreased mechanical efficiency and increased friction loss.

• 대한기계학회논문집B
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• 제38권1호
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• pp.95-101
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• 2014

본 연구는 고속 회전형(~10,000 rpm) 기어펌프의 질량유량과 효율을 예측하기 위해서 2 차원 immersed solid method(ISM)를 이용한 수치해석을 수행하였다. 기어펌프와 하우징의 순환유동을 고려하기 위하여 유체 유동을 난류 유동으로 가정하였고, 기어 펌프의 입 출구의 일정 압력 조건하에 기어펌프의 회전 속도를 부가하였다. 기어펌프의 다양한 회전 속도 및 기어 끝 단과 하우징 사의의 서로 다른 간극에 대한 질량유량 및 효율을 검토하였다. 해석 결과로서, 회전 속도가 증가할수록 평균 질량유량 및 효율은 증가하였고, 기어펌프와 하우징의 간격이 증가할수록 평균 질량유량 및 효율은 감소하였다. 간격이 없는 조건하의 6,000 rpm, 8,000 rpm, 10,000 rpm 회전속도에의 효율은 각각 85.11 %, 90.94 %, 93.62 % 를 얻었고, 간격이 0 m, 0.00001 m, 0.00003 m 에 대해서 효율은 각각 93.62 %, 93.29 %, 92.74 % 를 얻었다.

• 대한기계학회논문집B
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• 제24권10호
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• pp.1359-1367
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• 2000

In-situ particle monitors(ISPMs) are widely used for monitoring contaminant particles in vacuum-based semiconductor manufacturing equipment. In the present research, the performance of a Particle Measuring Systems(PMS) Vaculaz-2 ISPM at low pressures has been studied. We generated the uniform sized methylene blue particle beams using three identical aerodynamic lenses in the center of the vacuum line, and measured the detection efficiency of the ISPM. The effects of particle size, particle concentration, mass flow rate, system pressure, and arrangement of aerodynamic lenses on the detection efficiency of the ISPM were examined. Results show that the detection efficiency of the ISPM greatly depends on the mass flow rate, and the particle Stokes number. We also found that the optimum Stokes number ranges from 0.4 to 1.9 for the experimental conditions.