• Transactions of the Korean Society of Automotive Engineers
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• v.1 no.1
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• pp.101-109
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• 1993

Dynamic characteristics of an electro-magnetic clutch transmission system were investigated by using Bondgraph modeling method. Simulation results showed that when the rotor engaged with the armature, the response time of the current, the driver torque, the rotational speed and the relative sliding time between the driver and the driven side decreased, as the gap size between the rotor and the armature decreased and the number of coil turns increased. Also, when the rotor disengaged with the armature, the delay time increased with the decreased gap size and the increased number of coil turns. It was found that the experimental results of the current, the driver torque, the rotational speeds were in good accordance with the theoretical results. The results of this study can be used as basic design materials of the electro-magnetic clutch.

• Tribology and Lubricants
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• v.13 no.4
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• pp.26-32
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• 1997

The heat generation of the angular contact and the deep groove ball bearing is studied experimentally and numerically. The temperature variation of the inner and outer races and the temperature increase distribution are measured for the shaft rotational speeds, preloads, viscosities of the lubricant and lubrication methods. The measured temperature distributions are used as the input data of the numerical simulation to estimate the heat generation rate at the bearing. The temperatures of the inner and outer race increase more rapidly and approach faster to their steady values as the rotational speed increases. The optimal viscosity of the oil to minimize the heat generation is 8~10 cSt at 4$0^{\circ}C$ when the oil-air lubrication method is adopted. The heat generation of the bearing increases with the rotational speed and depends more on the lubrication method than on the preload variation.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2000.05a
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• pp.663-667
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• 2000

The spindle unit is core parts in high precision machine tools. Diverse static and dynamic charateristics of spindle unit are needed for special purpose of machine tools. Specially, high damping ability may be very useful to high precision and high speed spindle unit. But commercial bearing system has very low damping value and high stiffness. In this paper, the combined bearing system with ball-hydrostatic bearing is suggested for high damping spindle unit. The suggested bearing system has 30% damping ability more than general ball bearing's. The average rotational accuracy of spindle with combined bearing in working speed is 24% better than with ball bearing. The unbalance rotating experiment in spindle show that rotating error with combined bearing is only half value of with ball bearing.

• Proceedings of the KWS Conference
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• 2005.06a
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• pp.326-328
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• 2005

High speed rotational arc sensing is an important method to detect the torch deviation during automatic seam tracking of arc welding. In this paper, a mathematic model of high speed rotational arc sensing is analyzed. The simulation results are consistent with the experimental results. The current waveforms at the beginning of the welding are different from those at middle of the welding because of the formation of the weld bead profile. The signal patterns for seam tracking and end-point detection are proposed. A phase shift between the rotation and the current variation is also discovered in the experiments.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2733-2737
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• 2008

The present study numerically investigates three-dimensional laminar flow past a rotating circular cylinder placed in a uniform stream. For the purpose of a careful analysis of the modification of flow by the effect of the rotation on the flow, numerical simulations are performed at a various range of rotational speeds($0{\leq}{\alpha}{\leq}2.5$) at one Reynolds number of 300. As $\alpha$ increases, flow becomes stabilized and finally a steady state beyond the critical rotational speed. The 3D (three dimensional) wake mode of the stationary cylinder defined at this Reynolds number has been disorganized according to $\alpha$, which were observed by the visualization of 3D vortical structures. The variation of the Strouhal number is significant when the wake pattern is changed according to the rotational speed. As $\alpha$ increases, the lift increases, whereas the drag decreases.

• Biotechnology and Bioprocess Engineering:BBE
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• v.9 no.5
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• pp.374-378
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• 2004

The effects of various environmental factors such as pH (5, 6, 7, 8 and 9), temperature (30, 37 and $40^{\circ}C$) and rotational speed (150, 200 and 250 rpm) on the growth and the hepatitis B core antigen (HBcAg) production of Escherichia coli W3110IQ were examined in the present Study. The highest growth rate is achieved at pH 7, $37^{\circ}C$ and at a rotational Speed of 250 rpm which is 0.927 $h^{-1}$. The effect of pH on cell growth is more substantial compared to other parameters; it recorded a $123\%$ different between the highest growth rate (0.927 $h^{-1}$) at pH 7 and lowest growth at pH 5. The highest protein yield is achieved at pH 9, rotational speed of 250 rpm and $40^{\circ}C$. The yield of protein at pH 7 is $154\%$ higher compared to the lowest yield achieved at pH 5. There is about $28\%$ different of the protein yield for the E. coli cultivated at 250 rpm compared to that at 150 rpm which has the lowest HBcAg yield. The yield of protein at $40^{\circ}C$ is $38\%$ higher compared to the lowest yield achieved at $30^{\circ}C$.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.4
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• pp.239-248
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• 2017

It is important to understand the dispersion and deposition characteristics of particles in the flow around a circular cylinder. The rotation of a cylinder is considered as a means to modify the particle deposition in this study. We numerically investigate the effects of the rotational speed of a cylinder and the particle Stokes number on particle dispersion and deposition as well as flow characteristics. Results show that the deposition efficiency of small particles (with the Stokes number smaller than 4) decreases significantly as the rotational speed increases. However, when the Stokes number is larger than 4, the deposition efficiency increases slightly with the rotational speed of the cylinder. Meanwhile, for a given rotational speed, the increase in the Stokes number leads to an increase in deposition efficiency and deposited area.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.3
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• pp.1252-1257
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• 2013

This study was used homomixer as one of the manufacturing method to establish optimal manufacturing condition with magnesium chloride emulsion as coagulant. The more rotational speed of homomixer was fast, the more particle size of magnesium chloride emulsion was minute. The particle size was distributed between 1 and $5{\mu}m$. The more minute particle size of emulsion had an effect on increasing viscosity of emulsion and delay of oil phase separation during storage period, so the quality of magnesium chloride emulsion had correlation with dispersed phase particle size. After all the experiments, when manufacturing magnesium chloride emulsion, it used more than 10,000 rpm of rotational speed of homomixer, it showed the best result as coagulant according to the state of texture and the water separation ratio of soybean curd.

• 제어로봇시스템학회:학술대회논문집
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• 1998.10a
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• pp.413-418
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• 1998

We often use induction motor in the hard environment including vibration and high ambient temperature, or in maintenance free operation, because induction motor has durable and simple structure. However, when we use it as servo actuator or accurate speed control motor, we have to equip sensor such as encoder and tachogenerator with the motor control system. And generally those sensor's abilities against bad environment are less than the induction motor itself, So if we can remove these sensors from the system, it'll have more environmental resistance, and the cost will also be reduced. Actually this removal has been achieved in limited field. However, that needs complex calculations and a certain elapse time for data processing. In our study, we intended to estimate the rotational speed from the motor current instead of speed sensor, easily and rapidly in comparison to former methods.

• Restorative Dentistry and Endodontics
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• v.31 no.3
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• pp.179-185
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• 2006

This study was conducted to evaluate canal configuration after shaping by $ProTaper^{TM}$ with various rotational speed in J-shaped simulated resin canals. Forty simulated root canals were divided into 4 groups, and instrumented using by $ProTaper^{TM}$ at the rotational speed of 250, 300, 350 and 400 rpm. Pre-instrumented and post-instrumented images were taken by a scanner and those were superimposed. Outer canal width, inner canal width, total canal width, and amount of transportation from original axis were measured at 1, 2, 3, 4, 5, 6, 7 and 8 mm from apex. Instrumentation time, instrument deformation and fracture were recorded. Data were analyzed by means of one-way ANOVA followed by Scheffe's test. The results were as follows 1. Regardless of rotational speed, at the $1{\sim}2mm$ from the apex, axis of canal was transported to outer side of a curvature, and at 3~6 mm from the apex, to inner side of a curvature. Amounts of transportation from original axis were not sienifcantly different among experimental groups except at 5 and 6 mm from the apex. 2. Instrumentation time of 350 and 400 rpm was significantly less than that of 250 and 300 rpm (p<0.01). In conclusion the rotational speed of $ProTaper^{TM}$ files in the range of $250{\sim}400rpm$ does not affect the change of canal configuration, and high rotational speed reduces the instrumentation time. However appearance of separation and distortion of Ni-Ti rotary files can occur in high rotational speed.