• Journal of the Korean Society for Precision Engineering
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• v.16 no.1 s.94
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• pp.68-74
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• 1999

One of the recent changes in machining technology is rapid application of micro- and high precision grinding processes. A fine groove generation is necessary for the fabrication of optic, electronic and semiconductor parts, and achieved by chemical or mechanical processes. Slot grinding is very efficient for the generation of micro ordered groove with hard and brittle materials. As slot grinding is continuous, the ground depth become gradually shallow because of wheel wear. The form accuracy become worse from the increase of ground slot width by the loading phenomena at wheel side, results on chipping damage of the workpiece. The experiments achieve to the enhancement of the form accuracy and chipping free of the brittle materials using V shaped cast iron bonded diamond wheels. In this study we focused on the investigation of the effect of the high pressure air jet on the grinding characteristics. As a results, we found that the high pressure air jet is very effective on the reductions of the wheel wear, enhancement of the form accuracy.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.13 no.5
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• pp.445-450
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• 2002

We analyzed and measured a CPW(coplanar waveguide)-to-microstrip right-angled transition. Asymmetric CPW-to-microstrip transitions show significant resonances by the slot mode generation at the discontinuities. The air-bridge just shifting the resonance frequency can not fundamentally suppress the occurrence of the slot mode. So, we proposed the structure using offset microstrip section to eliminate the resonance. The proposed structure may be useful for the application of multi-layed structure.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.26 no.12
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• pp.594-599
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• 2014

There have been many cases that the air curtain installed in the apartment can not well remove the gases such as carbon dioxide and particles such as smokes, oils and vapors generated during the cooking to disperse the pollutants into the room. This study uses the numerical analysis to show how the pollutant-removing performance of the range hood is changed when the air curtain is installed on the range hood of kitchen. As a result of the study, it turned out that, when the air amount supplied by air curtain through the slot was about 60% of exhaust amount, the capturing efficiency of range hood for pollutants increased by 70~80% more than the case without the air curtain. Even when the exhaust amount was small, the capturing efficiency was improved a lot with the use of air curtain. In case that the air flow velocity of slot was greater than 2 m/s, the capturing efficiency turned out to decrease.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.23 no.11
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• pp.754-761
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• 2011

The present study numerically investigates two-dimensional flow and heat transfer in the multiple confined impinging slot jet. Numerical simulations are performed for the different Reynolds numbers(Re=100 and 200) in the range of nozzles from 1 to 9 and height ratios(H/D) from 2 to 5, where H/D is the ratio of the channel height to the slot width. The vector plots of velocity profile, stagnation and averaged Nusselt number distributions are presented in this paper. The dependency of thermal fields on the Reynolds number, nozzle number and height ratio can be clarified by observing the Nusselt number as heat transfer characteristic at the stagnation point and impingement surface. The Nusselt number at the stagnation point of the central slot shows unsteadiness at H/D=3 and Re=200. The value of Nusselt number at the stagnation point of the central slot decreases with higher Reynolds number and number of nozzle although overall area averaged Nusselt number increases. Hence careful selection of geometrical parameters and number of nozzle are necessary for optimization of the heat transfer performance of multiple slot impinging jet.

• Fire Science and Engineering
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• v.33 no.1
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• pp.30-38
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• 2019

Mixing characteristics and backdraft dynamics were investigated using large eddy simulation for compartments initially filled with methane fuel. Four different opening geometries, i.e. conventional door opening case (Door) and the cases where horizontal door was implemented on the upper ($Slot_U$), middle ($Slot_M$) and lower part ($Slot_L$) of side wall, were considered in the simulations. For cases without ignition, the amounts of inflow oxygen and outflow fuel from the compartment opening were, from largest to smallest, Door > $Slot_U$ ~ $Slot_M$ > $Slot_L$. However, the fuel and oxygen were the best mixed for the $Slot_U$ case while the fuel and oxygen were not well mixed and in relatively separated two layers for the $Slot_L$ case. The global equivalence ratio defined by the amounts of fuel and oxygen in the compartment was not correlated reasonably with the peak pressure of backdraft. The peak pressure during backdraft was the highest for the $Slot_U$ case, a well mixed condition of fuel and air, and backdraft was not found for the $Slot_L$ where the pressure rise was not so high due to the mixing status. The peak pressures for the Door and $Slot_M$ cases were in between Door and $Slot_L$ cases. The peak pressure during backdraft was well correlated with the total amount of heat release until the instance of backdraft occurrence.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.5
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• pp.832-842
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• 2006

Wireless Personal Area Networks(WAPANs) are designed for short-range ad hoc connectivity among portable devices. They have gained much attention in the industry recently. One of them, High-rate WPAN, is designed to support multimedia traffic that requires high data rates. But, High-rate WPAN standards don't specify the time slot assignment scheduling method of CAT(Channel Time Allocation). So, there has been many studies regarding time slot assignment scheduling of CAT. However, present studies involve demerits about not applying various types of errors in air interlace or having a starvation of a specific DEV(data device). In this paper, we propose algorithms about supplying the intermediate channel assignment in order to avoid these demerits. This method will help other methods that use time slot assignment scheduling of CTA.

• Journal of Magnetics
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• v.21 no.1
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• pp.78-82
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• 2016

Cogging torque will affect the performance of a permanent magnet Brushless DC Motor (BLDCM), thus the reduction of cogging torque is key for BLDCM optimization. In this paper, the phase shifting of cogging torque for a fractional-slot concentrated winding BLDCM is analyzed using the Maxwell tensor method. Moreover, a 9-slot 10-pole concentrated winding BLDCM driven by ideal square waveform is studied with the finite element method (FEM). An effective method to reduce the cogging torque is obtained by adjusting the slot opening. In addition, the influences of different slot openings on back electromotive force (back-EMF), air gap flux density and flux linkage are investigated and experimentally validated using the prototype BLDCM.

• Proceedings of the Korea Contents Association Conference
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• 2005.11a
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• pp.354-358
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• 2005

High-rate WPAN doesn't define the time slot assignment scheduling method of CAT So, there has been many studies regarding time slot assignment scheduling of CAT. However, present studies involve demerits about not applying various types of errors in air interface or having a starvation of a specific DEV. In this paper, we propose algorithms about supplying the intermediate channel assignment in order to avoid these demerits.

• Journal of Electrical Engineering and Technology
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• v.13 no.2
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• pp.812-821
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• 2018

An electromagnetic excitation force is caused by the air-gap flux density, which greatly influences the noise and vibration of the motor. In many real projects, skewed slot technology is widely used to reduce the harmonic components of the air-gap flux density to reduce the noise and vibration of the motor. However, a skewed slot has several side effects such as a transverse current and axial drifting. Thus, a double skewed slot rotor is selected with the aim of eliminating these side effects. This paper presents the exact structure of the double skewed slot rotor and the mechanism whereby the electromagnetic excitation force can be reduced. A multi-slice method is adopted to model the special structure. Finite element simulation is used to verify the theory.

• Proceedings of the KIEE Conference
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• 2015.07a
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• pp.802-803
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• 2015

본 논문에서는 영구자석 동기전동기의 극수와 Slot수 조합에 따른 특성을 분석하고 비교해 보았다. 동기전동기의 극수를 8극으로 고정하고 Slot의 수를 9,12,30,42 Slot으로 설정하고, 이에 따라 Flux Line, Air Gap Flux, 토크특성, 역기전력을 각각 분석하였다. 또 사용용도에 따라 적합한 극수 Slot수 조합을 제시하였다.