• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.383-386
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• 2005

An integrated analytical model which should have essential dynamics on the longitudinal railway vehicle is developed. The model consists of translational movement, rotational movement, brake actuator, adhesion force between rail and wheel, and brake friction force between wheel and pad. Thus, during the deceleration for stopping, a feedback controller controlling the brake cylinder pressure is designed to improve ride quality and to release friction problems. Through the developed model, the feasibility of controlling the cylinder pressure is verified for the better performances during braking.

• International Journal of Precision Engineering and Manufacturing
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• v.1 no.1
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• pp.42-48
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• 2000

Friction in bearing exerts an important effect upon power dissipation and heat generation of spindle system. This paper presents frictional moments derived from rotational axis coordinate system of spindle and frictional characteristics to spindle speed A frictional moment of spindle bearings is derived by work-energy method. Differential sliding moments in outer raceway has a major effect upon frictional resistance; spin sliding moments in inner raceway has a secondary effect. As spindle speed increases, also the frictional moments increase. In high-speed region, ceramic ball bearing 몬 smaller frictional moment than steel ball bearing.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.20 no.6
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• pp.685-691
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• 2011

The Bearing preload units are used for stable rotational movements of high speed spindles. The feeding mechanism of the preload unit is important to prevent overheat of bearings and to keep constant bearing load under thermal deformation of spindle unit. In this study, ball slide guide and ball bush as feeding mechanism of preload unit are selected. The maximum static friction force, radial stiffness and damping ratio of ball slide guide with ball load, ball number and ball size are widely investigated. In conclusion, the surface of ball slide guide must be heat treated to reduce static friction force. The number and size of ball are increased to control sensitive bearing preload force.

• International Journal of Concrete Structures and Materials
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• v.11 no.2
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• pp.285-300
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• 2017

This study investigates the seismic performance of a staggered wall structure designed with conventional strength based design, and compares it with the performance of the structure designed by capacity design procedure which ensures strong column-weak beam concept. Then the seismic reinforcement schemes such as addition of interior columns or insertion of rotational friction dampers at the ends of connecting beams are validated by comparing their seismic performances with those of the standard model structure. Fragility analysis shows that the probability to reach the dynamic instability is highest in the strength designed structure and is lowest in the structure with friction dampers. It is also observed that, at least for the specific model structures considered in this study, R factor of 5.0 can be used in the seismic design of staggered wall structures with proposed retrofit schemes, while R factor of 3.0 may be reasonable for standard staggered wall structures.

• International Journal of High-Rise Buildings
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• v.8 no.3
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• pp.221-227
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• 2019

In this paper passive seismic retrofit devices for building structures developed by the author in recent years are introduced. The proposed damping devices were developed by slightly modifying the configuration of conventional devices and enhancing their effectiveness. First a seismic retrofit system consisting of a pin-jointed steel frame and rotational friction dampers installed at each corner of the steel frame was developed. Then two types of steel slit dampers were developed; box-type slit damper and multi-slit damper. In addition, hybrid dampers were developed by combining a slit damper and a friction damper connected in parallel. Finally a self-centering system was developed by using preloaded tendons and viscous dampers connected in series. For each retrofit system developed, an appropriate analytical model was developed, and the seismic performance was verified by loading test and earthquake analysis of case study structures. The experimental and analysis results show that the proposed systems can be used efficiently to enhance the seismic performance of building structures.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.10b
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• pp.289-290
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• 2002

Stainless steel ball bearings are used in the control element drive mechanism and driving mechanisms such as step motor and gear boxes for the integral nuclear reactor, SMART. The bearings operate in pressurized pure water (primary coolant) at high temperature and should be lubricated with only this water because it is impossible to supply greases or any additional lubricant since the whole nuclear rector system should be perfectly sealed and the coolant cannot contain ingredients for bearing lubrication. Temperature of water changes from room temperature to about 120 degree Celsius and pressure rises up to 15MPa in the nuclear reactor. It can be anticipated that the frictional characteristics of the ball bearings changes according to the operating conditions, however little data are available in the literature. It is found that friction coefficient of 440C stainless steel itself does not change sharply according to temperature variation from the former research, and the friction coefficient is about 0.45 at low speed range. In this research frictional characteristics of the assembled ball bearings are investigated. A special tribometer is used to simulate the axial loading and the bearing operating conditions, temperature and pressure in the driving mechanism in the nuclear reactor. Highly purified water is used as lubricant ‘ and the water is heated up to 120 degree Celsius and pressurized to 15MPa. Friction force is monitored by the torque transducer.

• The korean journal of orthodontics
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• v.49 no.1
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• pp.21-31
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• 2019

Objective: This study was performed to explore the effect of different bracket, archwire, and ligature combinations on resistance to sliding (RS) and rotational control in first-order angulation. Methods: Three types of brackets (multi-level low friction [MLF], self-ligating, and conventional brackets) coupled with four nickel-titanium archwires (0.012, 0.014, 0.016, and 0.018-inch diameter) and two stainless steel ligatures (0.20 and 0.25 mm) were tested in different first-order angulations ($0^{\circ}$, $2^{\circ}$, $4^{\circ}$, $6^{\circ}$, $8^{\circ}$, $10^{\circ}$, $15^{\circ}$, $20^{\circ}$) by using an Instron universal mechanical machine in the dry state at room temperature. RS value was evaluated and compared by one-way ANOVA. Results: Under the same angulation, the RS values showed the following order: conventional brackets > MLF brackets > self-ligating brackets. The RS was the highest for conventional brackets and showed a tendency to increase. The RS for MLF brackets coupled with thinner archwires and ligatures showed a similar tendency as the RS for the self-ligating bracket. In contrast, the RS for MLF brackets coupled with thicker archwires and ligatures increased like that for conventional brackets. MLF brackets showed the greatest range of critical contact angles in first-order angulation. Conclusions: The RS in first-order angulation is influenced by bracket design, archwire, and ligature dimension. In comparison with self-ligating and conventional brackets, MLF brackets could express low friction and rotational control with their greater range of critical contact angles.

• Tribology and Lubricants
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• v.30 no.3
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• pp.177-182
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• 2014

To stop a high speed train running at the speed of 300 km/h, the disc brake for the train should be able to dissipate enormous kinetic energy of the train into frictional heat energy. Sintered pin-type metals are mostly used for friction materials of high speed brake pads. A pad comprises several friction pins, and the topology, length, flexibility, composition, etc. have a great influence on the tribological properties of the disc brake. In this study, the topology of the friction pins in a pad was our main concern. We presented the optimization of the topology of a railcar brake pad with nine-pin-type friction materials by thermo-mechanical contact analysis. We modeled the brake pad with/without a back plate. To simulate a continuous braking, the pad or friction materials were rotated at constant velocity on the friction surface of the disc. We varied the positions of the nine friction materials to compare the temperature distributions on the disc surface. In a non-optimized brake pad, the distance between two neighboring friction materials in the radial direction from the rotational center of the disc was not equal. In an optimized pad, the distance between two neighboring friction materials in the radial direction was equal. The temperature distribution on the disc surface fluctuated more for the former than the latter. Optimizing the pad reduced the maximum temperature of the brake disc by more than 10%.

• Tunnel and Underground Space
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• v.12 no.4
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• pp.277-283
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• 2002

This experimental study concerns the characteristics of a helical flow in a concentric annulus with a diameter ratio of 0.52, whose outer cylinder is stationary and inner one is rotating. The pressure losses and skin friction coefficients have been measured for the fully developed flow of Non-Newtonian fluid, aqueous solution of sodium carbomethyl cellulose (CMC) and bentonite with inner cylinder rotational speed of 0~400 prm. Also, the visualization of helical flows has been performed to observe the unstable waves. The results of present study reveal the relation of the Reynolds number Re and Rossby number Ro with respect to the skin friction coefficients. In somehow, they show the existence of flow instability mechanism. The pressure losses increase as the rotational speed increases, but the gradient of pressure losses decreases as the Reynolds number increases in the regime of transition and turbulence. And the increase of flow disturbance by Taylor vortex in a concentric annulus with rotating inner cylinder results in the decrease of the critical Reynolds number with the increase of skin friction coefficient.

• Journal of Biosystems Engineering
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• v.8 no.1
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• pp.17-29
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• 1983

The milling process is considered as causing one of the greatest grain losses among all the processes in rice post-production. Major source of grain losses in the rice milling is considered as the whitening process. This study was attempted to develop an abrasive-type whitener, the whitening chamber of which being supplied by jet-air evenly and continuously. To investigate the milling performance by the new whitener, three kind of emery-stone grit(#36, #41, and #46), and three levels of rotational speed of emery stone roller (950, 1070, and 1200 rpm) were tested. The jet-air abrasive-type whitener was also compared with the conventional abrasive-type having no jet-air blower in terms of their milling performance. In addition, the effect of different combinations of sequential uses of the abrasive- and friction-type whiteners on the milling performance was also experimentally evaluated. The results of this study are summarized as follows; 1. In general, the whitening system combined with the abrasive type whitener with jet-air supply, which was newly designed, and the existing jet-air friction type whiteners produces more milled- and head-rice by about 0.3% points and 2.8% points, respectively than the system combined with the existing abrasive type without the jet-air supply under the same operational conditions. The former also consumed less electricity by 0.024 KwH per 100kg of milled rice production and gave more milling capacity by about 35 kg/hr. As compared with the conventional whitening system consisting of jet-air friction type whiteners only, the former yielded more milled- and head-rice by 1.5% points and 4.4% points, respectively. 2. The abrasive roller having 46 grit emery was better than the roller having 36 grit in aspects of milling performance and machine efficiency, in general. 3. With regard to the effect of combination method of abrasive type and friction type whiteners, one pass in abrasive type plus three passes in friction type gave better milling performance and energy efficiency than the two passes in abrasive type plus two passes in friction type regardless of the designs of the emery stone rollers. 4. The increase in rotational speed of the emery stone roller from 950 rpm to 1200 rpm presented negative effects on milled and head-rice yields and machine efficiency, but slightly positive effect on milling capacity.