• The KSFM Journal of Fluid Machinery
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• v.15 no.6
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• pp.5-10
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• 2012

The effect of pressure-side opening length on three-dimensional flow fields and aerodynamic losses downstream of a cavity squealer tip has been investigated in a turbine rotor cascade for the squealer rim height-to-chord ratio and tip gap height-tochord ratio of $h_{st}/c$ = 5.05% and h/c = 2.0% respectively. The opening length-to-camber ratio is changed to be $OL/c_c$ = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5, and 0.7 The results show that longer OL leads not only to weaker secondary flow but also to lower aerodynamic loss in the tip leakage vortex region, while it significantly widens the area with high aerodynamic loss in the passage vortex region. The aerodynamic loss coefficient mass-averaged all over the measurement plane is kept almost constant for $0.0{\leq}OL/c_c{\leq}0.3$, whereas it increases rapidly for $OL/c_c$ > 0.3 in proportion to $OL/c_c$. There is little deterioration in flow turning with increasing $OL/c_c$.

• Applied Chemistry for Engineering
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• v.10 no.3
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• pp.343-348
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• 1999

The iron silicide films were prepared by chemical vapor deposition method using rf-plasma in variations of substrate temperature. rf-power, and ratio of $SiH_4$ and Fe-precursor. While iron silicide films are generally grown by ion beam synthesis (IBS) method of multi-step process, it is confirmed that iron silicide or $\beta$-phase consolidated $Fe_aSi_bC_cH_d$ was formed by one-step process in this study. The characteristics of films is variable because the different amounts of carbon and hydrogen was involved in the films as a function of dilute ratio of Fe-precursors and silane. It was shown that the different characteristics of films in carbon and hydrogen following the ratio of Fe-precursor and silane. The optical gap energy of films fabricated according to substrate temperature was invariant because active site brought in desorption of hydrogen was limiled. When rf-power was above 240 watt, the optical gap energy turned out to have high values because of dangling bonds increased by etching.

• Journal of Biosystems Engineering
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• v.27 no.2
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• pp.89-96
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• 2002

The trend of consumption of vegetable soybeans is increasing because they are recognized as the clean vegetable. The works requiring the most intensive labor are threshing and seperation ones, and they form about 80% of total labour for vegetable soybeans production. It is necessary to develop the vegetable soybeans-thresher for the sake of cost down of vegetable soybeans production. The purpose of this study is to acquire the basic informations to design of the vegetable soybeans-thresher. We make the experimental system which control the speed of threshing cylinder and the teeth gap and investigate the detachment forces. The result are as follows ; The ratio of un-threshed soybeans-pod to stem after threshing work is decreasing as the threshing cylinder speed increases: 0.0% and 2.8% at 55m/s and 18m/s of threshing cylinder speed respectively. Also the ratio of un-threshed soybeans-pod to stem is shown as 2.0% below in the condition of 64~160mm of teeth gap and over 28m/s of threshing cylinder speed. The damaged pod ratio of detached soybeans after threshing work is decreasing as the threshing cylinder speed increases: 4.8% and 1.3% at 55m/s and 18m/s of threshing cylinder speed respectively. The minimum damaged pod ratio of detached soybeans are shown as 1.0%, 1.5% and 1.9% at 18m/s, 28m/s and 37m/s of threshing cylinder speed respectively. The average detachment forces of pods are shown as 1.5kg$_{f}$ for 3 grains, 1.2kg$_{f}$ for 2 grains and 0.8kg$_{f}$ for 1 grain respectively. The maximum detachment force of pod is shown as 2.7kg$_{f}$ for 3 grains. grains.

• International Journal of Highway Engineering
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• v.15 no.5
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• pp.217-226
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• 2013

PURPOSES : Under the capacity conditions with balanced approach flows, roundabouts give less delay than existing signalized intersections; however, flows over 450 vehicles/hour/lane with unbalanced approach flow conditions, roundabouts efficiency drops due to the short time difference between the critical gap and the follow-up headway. The purpose of this study is developing a roundabout Signal Metering operation method by considering approach lanes degree of saturation. METHODS : A four-way-approach with one-lane roundabout is selected to compare the Signal Metering performance for the case of 16 different unbalanced flow conditions. Based on these traffic conditions, the performance is evaluated for 64 different cases of Signal Metering combinations by using SIDRA software. A degree of saturation(V/C ratio) sum for two adjoined approaches is used for the performance index of choosing Metered Approach and Controlling Approach. RESULTS : When the V/C ratio sum is 0.29~0.81 and Metered Approach flow is less than Controlling Approach flow, the average delay saving per vehicle is about 7 seconds; however, after this rage the delay saving decreases gradually until the V/C ratio sum reaches around 1.0. The range of V/C ratio sum 0.93~1.09 provides average delay saving per vehicle about 3 seconds. In case of V/C ratio sum is grater than 1.0 and the flows of Metered Approach is grater than Controlling Approach, the average delay per vehicle increases 3~11 times respectively. CONCLUSIONS : As expected, the Signal Metering provides substantial improvements in delay saving for the case of V/C ratio sum is 0.3~1.0 under the traffic flow conditions of Metered Approach is less than Controlling Approach.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.32 no.6
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• pp.504-511
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• 2008

This study evaluated the influence of the strength mismatch of HAZ for a plastic ${\eta}$-factor, which is the principle parameter determining the plastic portion of J-integral to assess the fracture toughness of the weldment. The specimen of tensile and hardness test was manufactured from the piping applying narrow-gap welding, and the mechanical properties of weldment, HAZ and a base metal were obtained. To perform the finite element analysis according to the ratio of strength mismatch, the material properties was chosen with the change of strength using the determination method of Ramberg-Osgood constant. Also, the influence of the strength mismatch of HAZ was determined using finite element analysis by those properties.

• 전기의세계
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• v.25 no.1
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• pp.87-94
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• 1976

The characteristic of flashover electric discharge has been brought to light in this paper for the situation in which the space and creeping gaps are laid out in series. The result of this study has disclosed the facts that the over all flashover characteristics have three kind of features such as unilateral increase after increase, and increase after decrease in compliance with varied layout method and relative magnitude of gap length, and accordingly there exist a ratio among the magnitudes of gap length and a proper layort method through which the over all flashover voltage reaches the highest. Also involved with this study is the theoretic analysis of flashover characteristics even in the case of creeping electric discharge from hand tip of the gauge, where the over all value of flashover voltage can be estimated from the peculiar value of flashover voltage and flicker voltage for the space and creeping gap within the extent of 5% error.

• Applied Science and Convergence Technology
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• v.24 no.1
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• pp.9-15
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• 2015

The practical pumping speed of a dry pump is considerably lower than the intrinsic speed because of back-streaming through finite gaps of the rotor assembly. The maximum compression ratio and the ultimate pressure of the pump are also directly influenced by the back-streaming rate. Therefore, information on the gap conductance, which determines the back-streaming characteristics of the rotor assembly, is the most important key for estimating the pumping performance of a dry pump. In this paper, the feasibility of calculating analytically the pumping performance of a multi-stage Roots pump, one of the most popular types of dry pumps, by quantifying the gap conductance in a rational way, is discussed.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.3
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• pp.333-339
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• 2004

For an electrical insulation design of HTS cable, it is important to understand the dielectric characteristics of insulation materials in L$N_2$ and the insulation type. Generally, the electrical insulation of HTS Cable is classified into two types of the composite insulation and solid insulation type. In this research, we selected the insulation paper/L$N_2$ composite insulation type for the electric insulation of a HTS cable, and studied electric insulation characteristics of synthetic Laminated Polypropylene Paper(LPP) in liquid nitrogen(L$N_2$) for the application to high temperature superconducting(HTS) cable. Furthermore, we compared the breakdown characteristics of the butt gap and bended mini-model cable. It is necessary to understand the winding parameter of insulation paper/LN2 composite insulation.

• Tribology and Lubricants
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• v.15 no.4
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• pp.304-313
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• 1999

High-speed rotors set a lot of high vibration and stability problems especially when the speed of rotation is going through the first or the second critical speed. The aim of this paper is to investigate the possibility of an active control of a rigid rotor with squeeze film damper which has a good configuration of easily controlled end seal clearances and/or adjustment of a feed pressure. A theoretical method is presented and some numerical results are compared with test measurements. Both results show that the vibration or bit sizes are decreased when the end seal gap decreases with constant supply pressure, and when the supply oil pressure increases with constant seal gap. The experimental results show also a pleasing similarity on both orbit sizes and their decrement ratio compared with theoretical analysis. The possibility of an active control with the squeeze film damper was verified by adjusting the seal gap and the supply pressure.

• Journal of radiological science and technology
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• v.40 no.1
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• pp.71-78
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• 2017

Scattered radiation is inherent phenomenon of x-ray, which occurs to the subject (or patient). Therefore it cannot be avoidable but also interacts as serious noise factor because the only meaningful information on x-ray radiography is primary x-ray photons. The purpose of this study was to quantify scattered radiation for various shooting parameters and to verify the effect of anti-scatter grid. We employed beam stopper method to characterize scatter to primary ratio. To evaluate effect on the projection images calculated contrast to noise ratio of given shooting parameters. From the experiments, we identified the scattered radiation increases in thicker patient and smaller air gap. Moreover, scattered radiation degraded contrast to noise ratio of the projection images. We find out that the anti-scatter grid rejected scattered radiation effectively, however there were not fewer than 100% of scatter to primary ratio in some shooting parameters. The results demonstrate that the scattered radiation was serious problem of medical x-ray system, we confirmed that the scattered radiation was not considerable factor of dig ital radiog raphy.