• Journal of the Korean Society of Propulsion Engineers
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• v.8 no.4
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• pp.43-54
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• 2004

A visualization study was carried out to investigate the effects of phase difference qualitatively by examining wake pattern on the phase difference of a dragonfly type wing model. The model was built with scaled-up, flapping wings composed of a paired wing with fore- and hind-wings in tandem that mimick the wing form of a dragonfly. The present study was conducted by using the smoke-wire technique and an electronic device below the tandem wings was mounted to find the exact wing position angles. Uncertainties in wing position angle are about $\pm$$1.0^{\cire}$ and instantaneous wing positional angle varies from $-16.5^{\cire}$ to $+22.8^{\cire}$. The tests were made at phase differences between the fore-wing and hind-wing at $0^{\cire}$, $90^{\cire}$, $180^{\cire}$ and $270^{\cire}$. The results show that Karman vortex structures were produced at phase differences of $90^{\cire}$, $180^{\cire}$ and $270^{\cire}$, but Karman vortex structures were not observed at the phase difference of $0^{\cire}$.

• Journal of the Korean housing association
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• v.12 no.2
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• pp.191-198
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• 2001

The aim of this research was to examine the thermal performance of the flat roof in proportion to various directional changes, the results of which were drawn from the miniature model experiment. In this process, various thermal environmental factors were measured and compared with one another to research their aspects of changes. The brief results of this research are as follows: 1) The indoor temperature and load per hour in proportion to directional changes shows the same degree of changes. As for the results of the clear-sky and cloudy-sky experiments, both of them generally appear advantageous in the order of S, $S-30^{\cire}C$-E, $S-30^{\cire}C$-W, $S-60^{\cire}C$-W, E, $S-60^{\cire}C$-E, despite slight differences in the indoor temperature and load per hour in proportion to directional changes. 2) As for the total load of degree day per direction of the clear-sky and cloudy-sky experiments, both of them shows their advantageous results in the order of S, $S-30^{\cire}C$-E, $S-30^{\cire}C$-W, $S-60^{\cire}C$-W, E, $S-60^{\cire}C$-E, despite minor differences in their loads. 3) As for the peak load of degree hour, while the clear-sky experiment shows its advantage in the order of $S-30^{\cire}C$-E, S, $-30^{\cire}C$-W, $S-60^{\cire}C$-W, E, $S-60^{\cire}C$-E, the cloudy-sky experiment does so in the order of S, $S-30^{\cire}C$-E, $S-30^{\cire}C$-W, E, $S-60^{\cire}C$-W, $S-60^{\cire}C$-E.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.05a
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• pp.745-750
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• 2001

This study is about application to real construction site of estimating a early strength with use of microwave. Based on the exist studies, it is tried to confirm the correlation between curing temperature and estimating early strength method with microwave. The result of this study are as follows. 1) Coefficient figure of common use concrete's accelerating strength and 28 days strength after curing at $10^{\cire}C$, $20^{\cire}C$, $30^{\cire}C$ is 0.84, 0.80, 0.80 2) Coefficient figure of concrete's-has a low fine aggregate ratio- accelerating strength and 28 days strength after curing at $10^{\cire}C$, $20^{\cire}C$, $30^{\cire}C$ is 0.86, 0.82, 0.81

• Proceedings of the Korea Concrete Institute Conference
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• 1997.04a
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• pp.301-307
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• 1997

This paper is evaluated for properties of aggregate and antiwashout admixture not only to minimize segregation and water contamination of underwater concrete but also to meet concrete quality required. Two antiwashout admixtures used in this study were available domestically and slump flow, pH, setting time, and filing property of fresh concrete and the compressive strength, flexural strength under water and in the air under 2 different curing conditions ($10^{\cire}C$ and $20^{\cire}C$ ) were measured. Compressive strength ratio of specimens cured in and water temperature $10^{\cire}C$ /$20^{\cire}C$ added HPEC and HPMC was 64% and 89%, respectively. Relative compressive strength of 2 kinds observed higher concrete added HPEC, 3% at $10^{\cire}C$ curing temperature, 34% at $20^{\cire}C$ . The flexural strength of specimens made under water was 1/4~1/6 of compressive strength similar to the existing data in the literature.

• Proceedings of the Korea Concrete Institute Conference
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• 1997.10a
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• pp.755-760
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• 1997

The comprehensive performance of the water-proofing materials which are sealer, liquid and preformed membranes were investigated as basic experimental data for guide line of field workers. The water-proofing performance, shear strength and bond strength were tested under the ambient temperature of $20^{\cire}C$ and after 60 cycles of freezing and thawing ($-17.8^{\cire}C$~$4^{\cire}C$, 6cycle/day). The performance includes workability, permeability, cost and the influence of water-proofing materials to environment.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2000.11a
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• pp.15-15
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• 2000

두 개의 사각형 유입구가 $90^{\cire}$의 각도를 이루고 있는 액체 램제트 엔진의 연소실 형상을 최적화하기 위해서 수조를 이용한 연소실 유동 계측 실험을 수행하였다. 공기 유입구의 연소실 유입 각도는 $30^{\cire}$, $45^{\cire}$ 및 $60^{\cire}$인 세 가지 형상의 연소실 모형을 제작하였으며, 각각의 유입 각도에 대하여 연소실 재순환 영역의 크기를 5가지로 변화시킬 수 있도록 모형을 제작하였다. 그리고 연소실의 배면은 돔의 형태로 하여 재순환이 잘 이루어지도록 모형을 제작하였으며, 유입구에서 연소실로 들어가는 유동의 안정화를 위해 안내깃을 세 개 설치하여 실험하였다.(중략)

• Journal of the Korean Society of Propulsion Engineers
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• v.5 no.1
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• pp.26-33
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• 2001

Thrust vector control system is control device which is mounted exit of the nozzle to generate pitch, yaw and roll directional force by deflecting flow direction of the supersonic jet from the nozzle. By obtaining control force, jetvane which is exposed in jet flow is working thermal and aerodynamic load. Axial thrust loss and side thrust is affected by shock patterns and interactions between jetvanes according to jetvane geometry and turning angle. In this study, we designed 6 types of jetvane to evaluate pitch, yaw and roll characteristics of ietvane in supersonic flow, and perform the cold flow test in range of turning angles of jetvanes between $0^{\cire}$ and $25^{\cire}$ by $5^{\cire}$ respectively. Also, calculation is going side by side to analyse flow interaction. Results show that there is no interactions between jetvanes upto turning angle 20$^{\circ}$, chord and lead length ratio is very important parameter to aerodynamic performance and maximum thrust loss is appeard to 17% of axial thrust in roll directional control.

• Journal of the Institute of Convergence Signal Processing
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• v.3 no.4
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• pp.67-73
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• 2002

There have been increased concerns on mobile stratospheric communication system(SCS) for the purpose of advanced service of personal and high speed communication systems. In fact, this SCS is considered and studied for IMT-2000 service by ITU. Although, it is important to make accurate channel model for prediction of the SCS performance, there is no measured channel data in this system. Thus, in this paper, we estimate the performance of SCS bye use of channel model provided by Corazza(2) and modified by You(3). And also, the effects of channel codings on system performance are analyzed by deriving bit error performance based on realistic Rician log-normal fading channel models. The performance results are divided into three kinds of areas with three kinds of elevation angles 20$^\cire$, 45$^\cire$, and 80$^\cire$. And also the effects of forward error correction channel codings on system performance with Hamming(7,4), HCH( IS,7) and convolutional code of constraint length 3 and code rate R=1/2.

• Journal of the Korean Society of Propulsion Engineers
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• v.8 no.1
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• pp.8-15
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• 2004

Supersonic jets impinging on $60^{\cire}$ wedge were investigated to obtain fundamental design data for jet deflector It was of interest to study flow phenomena such as shock interaction and separation induced by shear layer. Experiments using supersonic cold flow system were conducted for Schlieren flow visualization and measurement of surface pressure. Numerical results were compared with the experimental results. The major parameters are underexpansion ratio, distance from nozzle to apex and design Mach number. Flow conditions were obtained for the wedge shock to attach on or detach from the wedge. The dominant feature of flow-field is shock pattern induced by the Interaction between the wedge shock and the barrel shock.

• Journal of the Korean Society of Propulsion Engineers
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• v.3 no.1
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• pp.48-54
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• 1999

A method was disclosed for making phase stabilized ammonium nitrate(PSAN), where the process involves precipitation of ammonium nitrate(AN) with potassium dinitramide(KDN) from the aqueous solutions of their salts using a salting out technique. The organic solvent used as a precipitant was acetonitrile. The DSC results showed that the precipitates are PSAN, and AN is stable over the temperature range from $0^{\cire}C$ to $80^{\cire}C$ if the KDN concentration in the precipitated solids is greater than about 6 wt.%. The particles prepared are expected to be useful as an oxidizer for the solid rocket propellants and explosives.