• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.21 no.2
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• pp.337-343
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• 2012

This work investigates the vibrational characteristics of the underground gas pipelines. Experiments were conducted to analyze the effects of various parameters on the vibrational characteristics from the emergency detection point of view. Influences of the various types of impact exerted on the pipe, height of free fall and measuring locations were analyzed. Especially, the difference between the vibrational signal generated by the direct impact on the pipe and the ambient noise was successfully identified. To validate the experimental observation, computer simulation was also performed with constant properties(elasticity, fluid velocity and internal pressure) which are directly conjectured from the accompanying experiment with a real pipe system.

• Journal of ILASS-Korea
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• v.24 no.2
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• pp.58-65
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• 2019

A 3D FEM (Finite Element Method) based Helmholtz solver has been commonly used to characterize fundamental acoustic behavior and investigate dynamic instability features in many combustion systems. In this approach, a geometrical simplification of the target system has been generally made in order to reduce computational time and cost because a real combustor and fuel nozzle have a very complicated flow passage. The feasibility of these simplifications is quantitatively investigated in a small aero gas turbine nozzle in term of acoustic characteristics. It is found that the simplification in a nozzle geometry during the 3D FEM analysis process has no great influence on the acoustic modeling results, while the calculation complexity can be improved for a similar modeling accuracy.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.380-384
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• 2004

A fuel spiking test was performed to measure the surge margin of the compressor in a gas turbine engine. During the test, fuel spiking signal was superimposed on the engine controller demand and the mixed signals were used to control a fuel line servo-valve. For the superimposition, a subsystem composed of a fuel controller and a function generator was used. During the fuel spiking test, the original scheduled fuel signals and the modified signals were compared to guarantee the consistency excluding the spiking signals. The spiking signals were carefully selected to maintain the engine speed constant. The fuel spiking effects were checked by three dynamic pressure sensors. Sensors were placed before the servo-valve, after the servo-valve, and after the compressor location, respectively. The modulations of the spiking signal duration and fuel flow rate were examined to make the- operating point approach the surge region. The real engine test was performed at the Altitude Engine Test Facility (AETF) in Korea Aerospace Research Institute (KARI). In the real engine test, fuel spiking signals with 25~50 ㎳ of spiking signal time and 17~46 % of base fuel flow rate condition were used. The dithering signal was 5~6 ㎃ at 490 Hz. The test results showed good agreement between the fuel spiking signals and the fuel line pressure signals. Also, the compressor discharge pressure signals showed fuel spiking effects and the changes of the operating point on the compressor characteristic map could be traced.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 2008.10a
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• pp.179-190
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• 2008

Consumers earn a number of points for every purchase and then they can exchange a specified number of points for a desired reward in a typical loyalty program. The immediate payoff of their effort given as points is not the real reward they actually care about. It is merely an instrument (or medium) which has no value in itself. In a real world, consumers frequently choose the option with a bigger medium even though the economic value of the option is not changed by the medium. We call it 'medium effect'. In this study we explored if the size of medium affects on consumers' preferences. For this we controlled the reward options with three types of medium (small, medium, big) and measured the magnitude of preference difference among the three types of reward options. In addition, we manipulated comparability of reward options with wine and gas discount coupon. We confirmed that choosing one of two wines was easier than that of the two gas coupons. 164 respondents were allocated into three experimental groups and one control group. In three experimental groups, the ratios of the focused reward option's medium to the compared reward option's medium were different. For example, the focused reward option has 10 million points whereas the compared reward option has 10 million points for 1 million won purchase amount in the first group. Then each respondent was asked to choose one of two loyalty programs (focused program vs. compared program) in two different conditions (comparability between reward options: easiness vs. difficulty). To compare the medium effects among the experiment conditions we used chi-squares tests. The empirical results show the medium effect increases and then decreases as the ratio of reward mileages/points to purchase amount increases. Additionally, they let us know that comparability of alternatives affects on the medium effects depending on the ratio of reward mileages/points to purchase amount.

• Journal of Auto-vehicle Safety Association
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• v.12 no.1
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• pp.33-38
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• 2020

Since a diesel vehicle scandal related to the 'A' automobile company was issued in the United States in 2015, many countries have been interested in emission defeat devices. Being embedded in some diesel passenger cars sold in Korea, a defeat device for exhaust gas may have influence on both fuel economy and NOx emissions. In order to examine such effects, we carried out laboratory indoor tests as well as real road driving tests using four models of 'A' automobile company which may employ defeat devices. Those tests were performed observing the test modes of FTP-75, HWFET, and NEDC. Although fuel economy and NOx emissions according to indoor tests comply with the suggested tolerance, the findings in the real road driving tests do not satisfy the tolerance. Along with the results provided in this study, further evaluation may be necessary to investigate the noticeable difference between the indoor and real road tests.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.1
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• pp.9-19
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• 2002

Accuracy of AUSM-type schemes is closely related to a speed of in a cell-interface. Effect to accuracy by a speed of sound invastigated in the region of subsonic, transonic, and supersonic flows repectively. The advantage of the speed of sound in AUSMPW+ are summerized as the improvement of accuracy in capturing an oblique shock and the removal of an expansion shock to satisfy the entropy condition. They are proven by mathmatics and numerical result. Moreover AUSMPW+ is extended to a real gas flow and the speed of sound for equilibrium and nonequilibrium gas which could give exact soultions in an oblique shock is proposed.

• Journal of Animal Environmental Science
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• v.5 no.1
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• pp.37-44
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• 1999

This study was carried out to improve utilization of substitute fly-ash in bedding material of animal waste treatments. The amount used of fly-ash used in a pigpen or beef stall was 50% lower than that of existing bedding material of animal waste treatments. From the results, substitution effect of fly-ash put over the floor of the stable became much better. Effects of processed fly ash as a spread straw decreased ammonia(NH3) and Hydrogensulfide (H2S) gas at beef stall, but there was no benefit of replacement terms. Effect of processed fly ash as a spread straw increased 4∼5 times replacement terms more than control NH3 and H2S gas was decreased. A lot of maggots and porasites were grown at sawdust pig farm, but fly ash inhibited to grow maggots and paraeters. In conclusion, as substituting fly-ash for 5% sawdust(DM basis) in making animal waste into a compost with fly ash, we can reduce the sawdust purchasing costs and produce the high quality of a compost, especially a pollutant as NH3 and H2S gas, etc. from the process of biodegradation, and as substituting fly-ash(1,540 won per ton ; can be extended the replacement period of spreading straw approximatively 4∼5 times) for sawdusts(111,000 won per ton) will increase a real income in livestock house.

• Journal of the Architectural Institute of Korea Structure & Construction
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• v.34 no.10
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• pp.37-44
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• 2018

In this study, the effects of considering hourly metabolic rate variations for predicted mean vote (PMV) control on the heating and cooling energy and greenhouse gas emission were investigated. The case adopting PMV control taking the hourly metabolic rate into account was comparatively analyzed against the conventional dry-bulb air temperature control, using a detailed simulation technique. Under the assumption that all the apartments in Korea adopt the PMV control incorporating real-time metabolic rate measurements, nationwide reductions of primary energy and greenhouse gas emission were analyzed. As a result, PMV control considering hourly metabolic rate variations is expected to reduce national primary energy by 6.2% compared to conventional dry-bulb air temperature control, corresponding to reduction of 10,342 GWh. In addition, it turned out that 6.6% of tCO2 emission can be reduced by adopting PMV control, corresponding to nationwide reduction of greenhouse gas emission by approximately 1,720,000 tCO2.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.12
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• pp.3360-3371
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• 1995

Hydrodynamic characteristics of a stratified flow at a Y-junction were examined analytically. Gas is supplied through the main horizontal channel and liquid is introduced into the gas stream from the Y-shaped bottom branch. Analysis was performed with irrational flow and inviscid fluid assumptions. The Stokes' inverse transformation technique was adopted to convert the real x-y plane into the x-.psi. plane. The potential flow equation was solved numerically in the transformed (x-.psi.) plane and the interface profile, pressure distribution and the streamlines were obtained. The effects of the inlet conditions, injection angle and the gravity on the flow characteristics were also examined. To check the validity of the present method, the previous resultant the two-dimensional obtuse wedge flow was compared. The inverse transformation technique turned out to be also very useful to predict the hydrodynamic characteristics of a stratified flow with the pressure variation at a Y-shaped mixing junction.

• Journal of the Korean Society of Safety
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• v.23 no.3
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• pp.30-35
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• 2008

The recent fire incident in an elementary school of Chonan city causes the media focus on the fire safety of residential container buildings. In this study, real fire tests were conducted in this kind of buildings. Combustion products including $O_2$, $CO_2$, CO, $NO_x,$, $SO_x$, HCI, HCN were measured, in order to investigate the hazard-reduction effects of employing gas mask protected with filter during the fire emergency of residential container buildings. According to the test results, whether or not employing the filter showed a sheer difference in the toxicity of the fire-induced gases, and then the importance of wearing a gas mask was evidently demonstrated.