• Tribology and Lubricants
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• v.33 no.5
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• pp.220-227
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• 2017

In this work, carbon nanotube and nano-size alumina particle are exploited as additive for lubrication experiment. We used pin-on-disk type tribometer to investigate the tribological characteristics of lubricants with respect to additives and rotational speed. We conducted more than 15 trials of tribotests for two hours for each specimen to obtain stable and accurate frictional force and to create measurable wear track on the substrate. We conducted tests at the boundary/mixed lubrication regime to evaluate the influence of additives on the tribological characteristics. We found that the friction coefficient decreased as the rotational speed increased and as additives were added. In particular, the reduction of friction by adding additives was more significant at low rotational speed than at high rotational speed. We speculate that the additives helped to separate and protect the two contacting surfaces at low speed, while the influence of additives was not significant at high speed since sufficiently thick lubricant film was formed. The wear of the substrate was also reduced by adding additives to the lubricant. However, in contrast to friction, the amount of wear at high rotational speed was less when alumina particles were added to the lubricant than the amount of wear at low speed. We speculate that the increased wear at low rotational speed is as a result of the intermittent abrasive wear caused by alumina particles with uneven shape, while the reduced wear at high speed is as a result of sufficient film thickness which prevented the abrasive wear.

• Restorative Dentistry and Endodontics
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• v.35 no.4
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• pp.246-256
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• 2010

The purpose of this study was to evaluate a rotational stability of endodontic electronic motors by comparing the changes of rotational speed, depending on the number of usages and with/without static load. Twelve new endodontic electronic motors were used in this study. Non contact type digital tachometer was used for measuring the rotational speed of handpiece. True RMS Multimeter was used for measuring the voltages and the electric currents. All measurements were recorded every 10 seconds during 10 minutes and repeated 9 times. Five repetition was done per each electronic motor. To statistical analysis, student t-test, repeated measures and Scheffe's post-hoc tests were performed. In the same motor group, there was no significant difference in all measurements. In all groups, there was no significant difference in the amount of rotational speed changes depending on the number of usages and with/without static load. In the limitation of this study, the results showed that all kinds of endodontic electronic motors in this study had an established rotational stability. Therefore they could be safely used in root canal treatment with a reliable maintenance of rotational speed, regardless of the number of usages and with/without load.

• Fisheries and Aquatic Sciences
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• v.2 no.1
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• pp.52-57
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• 1999

Air-drived rotating biological contactor (RBC) system, which is effective method in filtering performance, was tested for the nitrification capacity in a recirculating system. At ammonia concentrations between 0.029 and 0.528 mg/l, the effect of ammonia loading rate on ammonia removal rate at three different hydraulic loading rates could be defined by the following first­order regression models: Hydraulic loading rate of $14.8 m^3/m^3/day:\;y=39.2\times+3.4 (r^2=0.9137)$, Hydraulic loading rate of $26.5 m^3/m^3/day: y=53.3\times+4.0 (r^2=0.8686)$, Hydraulic loading rate of $37.3 m^3/m^3/day: y=58.4\times+4.2 (r^2=0.7755)$, where, $\times$ is ammonia loading rate (mg/l), y is ammonia removal rate $(g/m^3/day)$, The equations showed the optimal ammonia removal rate at the hydraulic loading rate of $26.5m^3/m^3/day$. Below the ammonia concentration of 2.72 mg/l, first-order regression models between ammonia loading rate and ammonia removal rate at three different rates of speed are defined as follows: Rotational speed of $0.75 rpm: y=28.5\times+4.7 (r^2=0.9143)$, Rotational speed of $1.0 rpm: y=33.6\times+8.4 (r^2=0.9534)$, Rotational speed of $2.0 rpm: y=28.9\times+3.6 (r^2=0.9488)$, where, x is ammonia loading rate (mg/l), y is ammonia removal rate $(g/m^3day)$. The equations show the ammonia removal rate at the rotational speed of 1.0 rpm is significantly higher than that at the rotational speed of either 0.75 rpm or 2.0 rpm (P<0.05).

• Journal of Biosystems Engineering
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• v.41 no.1
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• pp.12-20
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• 2016

Purpose: Pepper prices have risen continuously because of a decrease in cultivation area; therefore, mechanical harvesting systems for peppers should be developed to reduce cost, time, and labor during harvest. In this study, a screw type picking head for a self-propelled pepper harvester was developed, and the optimal working conditions were evaluated considering helix types, winding directions of helix, and rotational speeds of the helix. Methods: The screw type was selected for the picking head after analyzing previous studies, and the device consisted of helices and a feed chain mechanism for conveying pepper branches. A double helix and a triple helix were manufactured, and rotational speeds of 200, 300, and 400 rpm were tested. The device was controlled by a variable speed (VS) motor and an inverter. Both the forward and reverse directions were tested for the winding and rotating directions of the helix. An experiment crop (cultivar: Longgreenmat) was cultivated in a plastic greenhouse. The test results were analyzed using the SAS program with ANOVA to examine the relationship between each factor and the performance of the picking head. Results: The results of the double and triple helix tests in the reverse direction showed gross harvest efficiency levels of 60-95%, mechanical damage rates of 8-20%, and net marketable portion rates of 50-80%. The dividing ratio was highest at a rotational speed of 400 rpm. Gross harvest efficiency was influenced by the types of helix and rotational speed. Net marketable portion was influenced by rotational speed but not influenced by the type of helix. Mechanical damage was not influenced by the type of helix or rotational speed. Conclusions: Best gross harvest efficiency was obtained at a rotational speed of 400 rpm; however, operating the device at that speed resulted in vibration, which should be reduced.

• Design & Manufacturing
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• v.14 no.4
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• pp.46-51
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• 2020

The purpose of this study was to analyze the change in tensile strength characteristics of the weld when the welding speed and rotational speed of the tool, which are representative variables of the friction stir welding process. The equipment used in the experiment was Machining Center No. 5. The material used in the experiment is an AA6061-T6 alloy, and a rolled plate with a thickness of 2mm was used. Two experimental variables were selected, the welding speed of the tool and the rotational speed of the tool. The experimental conditions were selected in the range in which a healthy weld could be obtained through a preliminary experiment. The welding speed of the tool was increased to 100mm/min, 200mm/min, and 300mm/min, and the rotational speed of the tool was increased to 1000rpm, 2000rpm, and 3000rpm. As a result of the experiment, the tensile strength increased as the rotational speed of the tool changed at each tool welding speed. In addition, as the welding speed of the tool increased, the tensile strength of the weld was increased. The condition with the highest tensile strength of the weld was found to be a tool feed speed of 300 mm/min and a tool rotation speed of 3000rpm.

• Journal of Institute of Control, Robotics and Systems
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• v.8 no.7
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• pp.539-546
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• 2002

This paper presents a new direct seek control scheme that provides fast data access capability and robust performance for high-speed rotational optical disk drives (ODD). When a disk is rotating at a high speed to obtain fast data transfer in ODD, the magnitude and frequency of velocity disturbance caused by eccentric rotation of the disk increase in proportion to the rotational speed of the disk. Such disturbances make it almost impossible for the conventional seek control scheme to achieve stable and satisfactory seek performance. We analyze the problems that may arise when the conventional seek control scheme is applied to the high-speed rotational ODD and propose a new direct seek control scheme that will solve such problems. In the proposed scheme, a seek control system is designed such that its performance is guaranteed for a set of plants with parameter perturbations. The performance of the proposed seek control scheme is shown by experiments using a high-speed rotational ODD.

• Transactions of the Korean Society of Mechanical Engineers
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• v.8 no.1
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• pp.86-94
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• 1984

In order to improve the rotational performances of NC lathe spindle system in high speed range, a new type(Floating-type driven by V-belt)spindle system was optimally designed and experimented. Through the results of the experiments, the rotational performances of the new type spindle system was discussed and compared with the three equivalent conventional lathe spindle systems. The spindle rotational accuracy( radial error motion of spindle axis), the accelation and the temperature rise of the front spindle bearings for the non-cutting operation were considered as the spindle rotational performances. The radial error motion of the spindle axis was measured by applying the modified L.R.L. method. Compared with the equivalent conventional spindle systems, the following results were obtained. (1) The new type spindle system reduces the radial error motion of the spindle axis in high speed range(1800rpm-2000rpm). (2) The new type spindle system reduces the acceleration and the temperature rise of the spindle bearings considerably with increasing the spindle speed. It is also confirmed that, by this new type spindle system, the max. allowable speed can be increased with satisfying the spindle rotational performances.

• Journal of KSNVE
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• v.5 no.4
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• pp.483-492
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• 1995

For evaluation of rotational accuracy performance of high speed machine tool spindle system, the characteristics of main spindle and tool motion behavior are presented by means of three point accuracy testing method. The results of experiments and analyses are as follows: (1) The high speed spindle rotational accuracy can be evaluated by the combination of the spindle and tool motion behavior. (2) The spindle motion behavior increases up to more that 4 times the tool motion behavior. (3) For the influence of oil viscosity on spindle and tool taper application, 32 cSt of oil viscosity showed the most satisfactory result for rotational accuracy. (4) In order to improve the rotational accuracy of high speed machine tool spindle system, it is needed to reduce the combination error. This can be achieved by improving the working accuracy and supplying the proper lubrication with contact area at the spindle and tool.

• Proceedings of the KIEE Conference
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• 1999.11c
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• pp.621-624
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• 1999

In this paper, we propose the non-contact method to measure rotational speed vector using spatial filtering method. The rotational speed $\omega$ is known by the frequency of output sinusoidal signal direct proportional to that and the rotational direction is given by the phase delay from the weighting function design of spatial filter.

• 유체기계공업학회:학술대회논문집
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• 2002.12a
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• pp.227-233
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• 2002

It is common for highly loaded supersonic stage to have very high relative inlet Mach number. To get this level of inlet Mach number, rotor blade outer diameter or rotational speed should be increased. In the case of commercial turbo-fan engine, it is preferred to make the rotor blade outer diameter large than increasing the rotational speed. But, for multi-stage fan of military engines, overall diameter is often restricted and they are apt to increase the rotational speed. With high rotational speed, relative inlet Mach number is likely to be well supersonic over the entire rotor blade span and the characteristic of the stage is affected with meridional shape of the stage, especially at near hub or tip. In this paper, the aerodynamic performance of two different hub surface shape is compared and it's merit and demerits were discussed.