• 한국가시화정보학회지
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• 제18권2호
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• pp.35-38
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• 2020

Airfryer is used to heat a food up by convecting hot air upward around the food. In this study, we investigated the effect of the bottom-shape of the food container in airfryer on the upward convection velocity of hot air to find an optimal bottom-shape by computational fluid dynamics. Numerical experiments were performed by solving the incompressible Navier-Stokes equations with turbulence model. We found that the maximum upward velocity with concave flow-passage on the bottom was bigger than that with the flat bottom and that the maximum upward convection velocity was achieved when the number of concave flow-passage with fan-shape is around six. The pressure drop by the internal flow was found to increase as the number of the concave flow-passage on the bottom increased probably due to increase of the surface area of the bottom. Therefore, it can be said that the optimal number of the concave flow-passage is around six for the flow rate considered in this study.

• Journal of Advanced Marine Engineering and Technology
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• 제27권5호
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• pp.617-623
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• 2003

In the present study, the characteristics of upward bubble flow were experimentally investigated in a liquid bath. The velocity of upward bubble flow was calculated for two different experimental conditions：1) bubble flow without kinetic energy 2) bubble flow with kinetic energy. Bubble flow without kinetic energy starts to undergo the effect of buoyancy l0cm away from the nozzle. Whereas. kinetic energy is dominant before 30 cm away from the nozzle in bubble flow but after this point kinetic energy and inertial force are applied on bubble flow at the same time In addition, as the flow rate increases the maximum velocity point moves to the nozzle. The velocity Profiles near free surface is extremely irregular due to surface flow. Gas volume fraction is high near the nozzle due to gas concentration. but decreases with the increasement of axial position. Gas volume fraction does not vary after the axial position, z=60 in spite of the increasement of flow.

• 한국융합학회논문지
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• 제11권6호
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• pp.393-400
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• 2020

본 연구는 테니스 1st 플랫서브 동작에서 어깨 통증 유무에 따른 견갑골의 움직임 차이를 확인하기 위해 테니스 선수 15명(남8, 여7)을 대상으로 3차원 영상분석시스템을 활용하여 견갑골의 앞쪽/뒤쪽 기울임, 아래쪽/위쪽 회전 및 안쪽/바깥쪽 회전에 대한 각속도와 모멘트를 산출하여 이를 집단 간 비교 분석을 하였다. 그 결과, 앞쪽/뒤쪽 기울임에 대한 최대 각속도는 실험군인 어깨통증집단(SPG)보다 대조군 집단(CG)이 빠른 경향을 보였으며, 팔로우 스로우 구간을 제외하고 모든 국면에서 안쪽/바깥쪽 회전 최대 각속도가 SPG가 CG보다 빠른 것으로 나타났다. 후기 코킹 구간에서의 앞쪽/뒤쪽 기울임 최대 모멘트가 SPG보다 CG가 더 크게 나타났고 통계적으로 유의한 차이를 보였다. 코킹 구간의 위쪽/아래쪽 회전 최대 모멘트 또한 SPG가 CG보다 작게 나타나면서 통계적으로 유의한 차이를 보였다. 안쪽/바깥쪽 회전 모멘트는 모든 국면에서 CG가 SPG보다 큰 것으로 나타났다.

• 한국자동차공학회논문집
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• 제10권6호
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• pp.19-26
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• 2002

The objective of this study is to examine a DI(Direct Injection) gasoline spray development process under different ambient pressures using PIV(Particle Image Velocimetry). fuel spray experiments were performed within a constant volume chamber. The spray structure, velocity maps, velocity and vorticity contours were obtained to investigate its spray characteristics. It was found that higher ambient pressure has a significant effect on radial growth of the spray. The position which has a maximum velocity moved from the spray edge to the spray center as ambient pressure was increased. Higher ambient pressure moved a maximum vorticity position upward of the spray.

• 한국운동역학회지
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• 제17권2호
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• pp.157-166
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• 2007

This study was to compare the major kinematic factors between the success and failure group on performing the back somersault motion in floor exercise. Three gymnasts(height : $167.3{\pm}2.88cm$, age : $22.0{\pm}1.0years$, body weight : $64.4{\pm}2.3kg$) were participated in this study. The kinematic data was recorded at 60Hz with four digital video camera. Two successful motions and failure motions for each subject were selected for three dimensional analysis. 1. Success Trail It was appear that success trail was larger than failure group in projection velocity, but success trail was smaller than failure trail in projection angle. Also it was appear that success trail was longer than failure group in the time required. Hand segment velocity and maximum velocity in success trail were larger than those in failure trail, and this result was increasing the projection velocity and finally increasing the vertical height of center of mass. At the take-off(event 2), flection amount of hip and knee joint angle was contributed to the optimal condition for the take-off and at the peak point, hip and knee joint angle was maximum flexed for reducing the moment of inertia. Also in this point, upper extremities of success trail extended more than those of failure trail. in this base, success trail in upward phase(p3) 2. Failure Trail It was appear that failure trail was smaller than success trail in projection velocity, but failure trail was larger than success trail in projection angle. Also it was appear that failure trail was more short than success trail in the time required. Hand segment velocity and maximum velocity in failure trail were smaller than those in success trail, and this result was reducing the projection velocity and finally reducing the vertical high of center of mass. At the take-off(event 2), flection amount of hip and knee joint angle wasn't contributed to the optimal condition for the take-off and at the peak point, hip and knee joint angle wasn't maximum flexed for reducing the moment of inertia. Also in this point, upper extremities of failure trail didn't extended more than those of success trail.

• 한국전산유체공학회지
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• 제15권3호
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• pp.81-86
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• 2010

In this paper, a three-dimensional numerical study on flow pattern in winter along connecting passageway of a composite building was conducted using a commercial CFD package. The incompressible Navier-Stokes equation coupled was solved by using SIMPLE algorithm in order to find steady solutions. It was shown that a upward flow is generated inside the building in winter due to buoyancy effect and that the air inside connecting passageway flows from the shorter building to the taller one regardless of the slope of the passageway. Further, it was found that the magnitude of air velocity inside connecting passageway increases as the uphill slope to the taller building increases and decreases as the downhill slope to the taller one increases, although the variation in the magnitude of fluid velocity is not substantial. Lastly, it was shown that the maximum air velocity inside connecting passageway is less than the allowable limit for all the cases considered in this study.

• 한국기계가공학회지
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• 제19권11호
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• pp.16-22
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• 2020

This study was aimed at analyzing the velocity and pressure changes in the airflow corresponding to different configurations of a diffuser for three types of cars. According to the flow results of the three automotive models, in model 3, the vortex was formed slightly upward on the outlet plane, whereas in models 1 and 2, the vortex was generated lower than that in model 3. The values of the pressure distribution in model 3 were larger than those for models 1 and 2 on the planes located at the same distance from the end of the rear part. The maximum turbulent kinetic energies in models 1 and 2 occurred at a location lower than that in model 3. The shape corresponding to the airflow that enhanced the driving performance was determined through the flow analysis.

• 대한설비공학회지:설비저널
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• 제14권2호
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• pp.87-97
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• 1985

Experimental measurements of the heat flux to a upward impinging water jet on high heated test surface were obtained in the transition and film boiling regimes. Test variables were nozzle outlet velocity, subcooled water temperature and height of supplementary water. Boiling curve of this investigation is similar to a pool boiling curve, but it has one or two cap-shaped peaks in the transition regime. In the film boiling regime, the heat transfer rates are increased along with the increment of nozzle outlet velocity and subcooled temperature. There is optimum height of supplementary water for the augmentation of heat transfer Generalized correlations of boiling heat transfer are presented for maximum heat flux, minimum heat flux and $q_c$ at each supplementary height.

• Journal of Biosystems Engineering
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• 제32권3호
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• pp.145-152
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• 2007

Uniformity of spray deposit is one of the important factors in spray performance affecting efficacy of pest management. Distributions of spray deposit on artificial targets were measured and analyzed to enhance the efficiency of spray application. The research was studied to understand the deposition characteristics of spray droplets and to determine the optimum conditions of chemical application. The deposit and its pattern by the lower fan speed was more uniform and higher than that by the higher fan speed. The upward blasting distance was limited within 3 m, but the limit to the ground level was expanded the distance more than 3.5 m because of the accumulated droplets. When the fan speed was higher at the distance of 2.5 m, deposit reached to maximum. When the distance increased, deposit was getting lower. At the both fan speeds, the deposit was concentrated below $30^{\circ}$ because of the gravitation and the resistance of wind. This research can be useful in designing an orchard sprayer and its operation for various tree canopies. To achieve a uniform distribution of deposit using the air-blast type orchard sprayer, the application rate from the middle boom should be increased as the air velocity to the upward increased. The spray rate to the side boom should be limited in a minimal level.

• 대한기계학회논문집B
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• 제20권5호
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• pp.1649-1660
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• 1996

The flow around a circular cylinder was controlled by an acoustic excitation issued from a thin slit along the cylinder axis. The static pressure distributions around the cylinder wall and flow characteristics in the near wake have been measured. Experiments were performed under three cases of Reynolds number, 7.8 * 10$\^$4/, 2.3 * 10$\^$5/ and 3.8 * 10$\^$5/. The effects of excitation frequency, sound pressure level and the location of the slit were examined. Data indicate that the excitation frequency and the slit location are the key parameters for controlling the separated flow. At Re$\_$d/, = 7.8 * 10$\^$4/, the drag is reduced and the lift is generated to upward direction, however, at Re$\_$d/, =2.3 * 10$\^$5/ and 3.8 * 10$\_$5/, the drag is increased and lift is generated to downward direction inversely. It is thought that the lift switching phenomenon is due to the different separation point of upper surface and lower surface on circular cylinder with respect to the flow regime which depends on the Reynolds number. Vortex shedding frequencies are different at upper side and lower side. Time-averaged velocity field shows that mean velocity vector and the points of maximum intensities are inclined to downward direction at Re$\_$d/ = 7.8 * 10$\^$4/, but are inclined to upward direction at Re$\_$d/ = 2.3 * 10$\^$5/.