• 천문학회보
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• 제41권2호
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• pp.67.1-67.1
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• 2016

We examined the relations between CME speed and properties of magnetic helicity in the source region such as helicity injection rate and total unsigned magnetic flux, which reflect the magnetic energy in the active region. For this, we selected 22 CMEs occurred during the increasing phase of solar cycle 24, which shows extremely low activities and classified them into two groups according to evolution pattern of helicity injection rate. We then compared the relations with those from previous study based on the events in solar cycle 23. As the results, we found several properties as follows: (1) Both of CME speed and helicity parameters have very small values since we only considered increasing phase; (2) among 22 CMEs, only 6 events (27%) are classified as group B, which show sign reversal of helicity injection and they follow behind of appearance of group A events. This fact is well coincide with the trend of solar cycle 23 that only group A events was observed in the first 3 years of the period; (3) as the solar activity is increasing, the CME speed and helicity parameters are also increasing. Based on the observations of solar cycle 23, the helicity parameters was still increasing in spite of decreasing solar activity after maximum period.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2005년도 제31회 KOSCO SYMPOSIUM 논문집
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• pp.221-228
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• 2005

The tribrachial flame in laminar coflow jet has been investigated experimentally with unsteady propagating condition. In this experiment, we found that the tribrachial point has an angle of flame surface because the location of tribrachial point is not on the base point of flame but on the inclined surface of flame. This angle of Flame surface at tribrachial point are increasing when the flame is approaching to the nozzle exit. With considering this angle of flame surface, the radial velocity gradient can affect flame propagation speed by increasing flow-stretch effect. The propagation speed of tribrachial flame was calculated with including above stretch effect. The speed decreases with increasing velocity gradient due to the increment of stretch effect.

• 한국철도학회논문집
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• 제13권1호
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• pp.51-57
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• 2010

본 연구에서는 진공튜브 내 초고속열차의 공기저항을 전산유체역학을 이용하여 계산하였으며, 튜브-열차 시스템의 주요 시스템 파라메타인 열차 속도, 공기밀도, 터널 직경을 변화시켜가면서 공기저항의 변화를 살펴보았다. 튜브 내에서의 열차 공기저항은 속도의 제곱보다 더 급격히 증가하며, 튜브 직경이 증가함에 따라 감소하는 경향을 보였으며, 공기밀도가 감소함에 따라 개활지와 마찬가지로 거의 선형적으로 감소하는 특성을 보여주었으며, 특정 파라메타 공간에 대하여 파라메타에 따른 공기저항 변화의 불규칙성이 다소 나타났다.

• 한국산업융합학회 논문집
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• 제2권1호
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• pp.27-33
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• 1999

Effects of spinning speed and draw ratio on structure and mechanical properties of PP filament. A The crystalline structure and mechanical properties of uniaxially deformed polypropylene filament has been examined by XRD, birefringence, UTM and density method. Uniaxially deformed PP filament was prepared of various spinning speeds (300, 600, 900m/min.) and draw ratio(x2, x3, x4). From the results of these studies, it found the following facts. Firstly, it was found that the crystallinity and crystallite size (110plane) of the samples were increased with increasing of spinning speed and draw ratio, especially, it was rapidly increased between as spun yarn and 2 times draw ratio. Secondly, birefringence value was increased with increasing of spinning speed and draw ratio. The mechanical properties of initial modulus, tensile strength were increased with increasing of spinning speed and draw ratio also, but the degree of elongation decreased as spinning speed and draw ratio.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2001년도 제33회 춘계학술대회 개최
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• pp.201-211
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• 2001

The influence of aerated oil on high-speed journal bearing is examined by classical thermohydrodynamic lubrication theory coupled with analytical models for viscosity and density of aerated oil in fluid-film bearing. Convection to the walls, mixing with supply oil and re-circulating oil, and some degree of journal misalignment are considered. The considered Parameters for the study of bubbly lubrication are oil aeration level, air bubble size, shaft misalignment and shaft speed. The results show that deliberate oil aeration can more clearly bring on the increasing load capacity under high-speed operation of plain journal hearing than previous normal speed operation. And the load capacity may be increased more by oil aeration under the conditions of shaft misalignment and the increasing speed.

• 한국세라믹학회지
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• 제51권4호
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• pp.344-349
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• 2014

$RuO_2$-based high frequency thick-film resistor paste was printed at the speed of 10, 100, 300 mm/sec on the AlN substrate, and then sintered at between 750 and $900^{\circ}C$. The sintered thick films were characterized in terms of printing and sintering conditions. With increasing printing speed, the thickness and roughness of sintered film increased. The resistance of the thick film resistor was reduced by increasing the printing speed from 10 to 100 mm/sec, but did not significantly change at 300 mm/sec speed. With increasing sintering temperature, the surface roughness and thickness of sintered resistor film decreased. The reduction rate was large in case of fast printed resistor. The resistance of the resistor increased up to $800^{\circ}C$ with sintering temperature, but again decreased at the higher sintering temperature.

• Journal of Welding and Joining
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• 제35권3호
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• pp.44-51
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• 2017

In the present study, AA 5083-O plates are joined by friction stir welding technique. A universal milling machine was used to perform the welding process of the work-pieces which were fixed on the proper position by a vice. The joints were friction stir welded by two tools with different pin profiles; cylindrical threaded pin and tapered smooth one at different rotational speed values; 400 rpm and 630 rpm, and different welding speed values; 100 mm/min and 160 mm/min. During FSW of each joint, the temperature was measured by infra-red thermal image camera. The welded joints were inspected by visually as well as by the macro- and microstructure evolutions. Furthermore, the joints were tested for measuring the hardness and the tensile strength to study the effect of changing the FSW parameters on the mechanical properties. The results show that increasing the rotational speed results in increasing the peak temperature, while increasing the welding speed results in decreasing the peak temperature for the same tool pin profile. Defect free welds were obtained at lower rotational speed by the threaded tool profile. Moreover, the threaded tool pin profile gives superior mechanical properties at lower rotational speed.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2010년도 춘계학술대회 논문집
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• pp.1081-1099
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• 2010

The TVM 430 system manufactured by Ansaldo STS in France is currently used in ground signalling system for Kyungbu HSR. It transmits the speed information to the on-board signalling system in the form of continuous signal via the track, and the rolling stock in Kyungbu HSR runs with 300km/h max. operating speed by using the corresponding information. Looking from the recent international trends in HSR, reducing the travelling time and increasing of the line capacity is promoting via the improvement of train speed. In case of TGV Est, they are realizing the normal operation with 320km/h max. operating speed by using TVM SEI signalling system, which is similar to TVM 430. Furthermore, in case Honam HSL, which is under construction, is looking over faster speed than the limited one of Kyungbu HSR(i.e. over 300km/h). In this paper, it is assumed that the existing TVM 430 ground signalling system is used and train speed is improved, therefore the number of block section to be increased depending on the increase of train speed and the standard speed to be used in this case is drawn via the simulation of the train model and described the method accordingly.

• 전기학회논문지
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• 제59권10호
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• pp.1803-1808
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• 2010

Electric railway system consists of rolling stock, track, signal and catenary system. ATP system in railway signaling system is the important one grasping the position and velocity of a train. The wayside device of ATP system is installed between rails. Recently, the research about increasing train speed has been developed in total departments of the railroad systems. The study on the information transmission between on-board device and wayside device is required for increasing the train speed in the ATP system. When the train speed is increased as to same transmission distance, the problem on information transmission occurs because the transmission time is decreased. In case that the transmission distance is extended, the transmission time is decreased with respect to the train speed. Therefore, we have to define the standard magnetic field intensity as to the train speed in order to transmit correctly telegram. In this paper, the transmission distance for the telegram is suggested on the basis of the train speed. Also, the standard magnetic field intensity from the wayside device to on-board device is proposed by using transmission distance regarding the train speed in the ERTMS/ETCS system by using Matlab program. Also, BER according to the train speed is presented by calculating electric field intensity from the magnetic field intensity.

• Wind and Structures
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• 제32권5호
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• pp.487-499
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• 2021

The wind-blown sand effect on the high-speed train is investigated. Unsteady RANS equation and the SST k-ω turbulent model coupled with the discrete phase model (DPM) are utilized to simulate the two-phase of air-sand. Sand impact force is calculated based on the Hertzian impact theory. The different cases, including various wind velocity, train speed, sand particle diameter, were simulated. The train's flow field characteristics and the sand impact force were analyzed. The results show that the sand environment makes the pressure increase under different wind velocity and train speed situations. Sand impact force increases with the increasing train speed and sand particle diameter under the same particle mass flow rate. The train aerodynamic force connected with sand impact force when the train running in the wind-sand environment were compared with the aerodynamic force when the train running in the pure wind environment. The results show that the head car longitudinal force increase with wind speed increasing. When the crosswind speed is larger than 35m/s, the effect of the wind- sand environment on the train increases obviously. The longitudinal force of head car increases 23% and lateral force of tail increases 12% comparing to the pure wind environment. The sand concentration in air is the most important factor which influences the sand impact force on the train.