• Proceedings of the Korean Society of Precision Engineering Conference
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• 2000.05a
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• pp.922-925
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• 2000

Generally, the machining accuracy in ball end milling directly depends on the rotational accuracy affected by the spindle speeds. The effects of spindle speeds for rotational accuracy in the high speed regions are more dominant than those in the low speed regions. This paper will investigate effects that the Increased speed affects on the rotational error according to the increase of a rotational speed and machining characteristics of the high speed ball-end milling in various rotational speeds and on various materials by using the high speed air-bearing spindle.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.2
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• pp.241-248
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• 2013

In this study, bearings were developed for a high-power propulsion motor operating in inclined operation conditions through a simulation and similitude-experimental methods using commercial rotating machinery dynamics analysis software. The developed journal bearing is electrically insulated and has low thermal conductivity because each part is connected with 2-4 -mm-thick epoxy plates. To realize an appropriate oil thickness, an oil lift system is adopted, and a half separated structure is applied to ensure the feasibility of maintaining very heavy components. This study discusses some of the key design aspects of sleeve bearing design for high-torque and low-speed propulsion motor applications. Furthermore, the conditions of variable slope tests are examined to prevent oil leakage from the bearing lip seal on the test rig.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.03a
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• pp.1065-1072
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• 2010

Case studies published in Korea versus the low ground fault is applied on the bridge based on theory or experience in the design of pile bearing capacity by the value of the expression is designed to conduct field tests Disclosure Load bearing capacity value, the result of applying a reasonable construction cost savings of approximately 10 eokyeowon Has, in the design of site investigation was insufficient to require additional efforts. Apply the appropriate value from the extra support in the design of accurate ground survey and air speed to cut the budget and social technology can ensure the reliability was unknown.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1992.10a
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• pp.249-254
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• 1992

Hydrostatic Bearings have been applied to ultra high precision machine tools and precision instruments, because of their low friction characteristic, high load carrying capacity and high moving accuracy at all range of speed. In regard to realizing the Hydrostatic Bearing, various restrictors such as capillary, orifice, diaphram valve, spool valve, and etc can be used. However, their stiffness and flexibility are not sufficient in practical use for ultra precision machine tool elements. In this study dynamic equations were derived and the dynamic characteristics were simulated for both orifice and flow control servo valve. Simulation was carried out on the condition that static and sinusoidal dynamic loads were applied to the table of CNC jig Boring machine. The simulation results indicate the improvement of the performance of the Bearing system when flow control servo valve has been used as restrictor of Hydrostatic Bearing.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.1
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• pp.585-591
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• 2017

Turbocharging is widely used in diesel and gasoline engines as an effective way to reduce fuel consumption. But turbochargers have turbo-lag due to mechanical friction losses. Bearing friction losses are a major cause of mechanical friction losses and are particularly intensified in the lower speed range of the engine. Current turbochargers mostly use oil bearings (two journal bearings and one thrust bearing). In this study, we focus on the bearing friction in the lower speed range. Experimental equipment was made using a drive motor, load cell, magnetic coupling, and oil control system. We measured the friction losses of the turbocharger while considering the influence of the rotation speed, oil temperature, and pressure. The friction power losses increased exponentially when the turbocharger speed increased.

• Tribology and Lubricants
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• v.25 no.6
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• pp.409-413
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• 2009

This paper presents the hardness and friction characteristics of pb-free pin-bush bearing metal, which is manufactured by a centrifugal casting technology. A bronze metal with a high hardness and low friction properties is usually used for Diesel engine pin-bush bearing and high pressure cylinder. Pb-free metal for pin-bush bearings shows a little high hardness of 120 Hv compared with that of a conventional Pb bearing metal of 100~110 Hv. In general, the friction coefficient of pin-bush bearings is affected by a rotating speed and a load for various rubbing contact modes. But a contact load is more influential parameter when the contact rubbing mode transits from a mixed lubrication to a dry friction contact. The experimental result shows that the friction coefficient is more unstable at the dry contact mode compared with that of other two rubbing modes such as oil film contact and mixed friction conditions.

• International Journal of Fluid Machinery and Systems
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• v.8 no.1
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• pp.46-54
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• 2015

Thrust-ring-pump is a kind of extreme-low specific speed centrifugal pump with special structure as numerous restrictions from thrust bearing and operation conditions of hydro-generator units. Because the oil circulatory and cooling system with thrust-ring-pump has a lot of advantages in maintenance and compactness in structure, it has widely been used in large and medium-sized hydro-generator units. Since the diameter and the speed of the thrust ring is limited by the generator set, the matching relationship between the flow passage inside the thrust ring (equivalent to impeller) and oil bath (equivalent to volute) has great influence on hydrodynamic performance of thrust-ring-pump. On another hand, the head and flow rate are varying with the operation conditions of hydro-generator units and the oil circulatory and cooling system. As so far, the empirical calculation method is employed during the actual engineering design, in order to guarantee the operating performance of the oil circulatory and cooling system with thrust-ring-pump at different conditions, a collaborative hydrodynamic design and optimization is purposed in this paper. Firstly, the head and flow rate at different conditions are decided by 1D flow numerical simulation of the oil circulatory and cooling system. Secondly, the flow passages of thrust-ring-pump are empirically designed under the restrictions of diameter and the speed of the thrust ring according to the head and flow rate from the simulation. Thirdly, the flow passage geometry matching optimization between thrust ring and oil bath is implemented by means of 3D flow simulation and performance prediction. Then, the pumps and the oil circulatory and cooling system are collaborative hydrodynamic optimized with predicted head-flow rate curve and the efficiency-flow rate curve of thrust-ring-pump. The presented methodology has been adopted by DFEM in design process of thrust-ring-pump and it shown can effectively improve the performance of whole system.

• Journal of Advanced Marine Engineering and Technology
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• v.16 no.5
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• pp.50-59
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• 1992

A critical speed analysis of a pump shaft has been investigated. Among various methods in the shaft critical speed calculation, a transfer matrix method has been examined in this research. After a brief review on the transfer matrix method, a modeling procedure for a continuous structure has been discussed. Then, a critical speed of a multistage pump shaft has been estimated up to several low modes. Throughout an analysis, parametric effects on the bearing stiffness, a degree of the modeling order, and attachmant of the impeller have been investigated. As an application example, a critical speed analysis of a verical pump which has been implemented in domestic electric power plants for cooling water circulation has been conducted in order to provide a safe operation as far as a pump vibration is concerned.

• Tribology and Lubricants
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• v.27 no.5
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• pp.256-263
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• 2011

Bearings of marine engines are operated under severe conditions because of dynamic load and low sliding speed. This paper deals with lubrication analysis of a crank pin bearing for a marine diesel engine. Journal center locus and oil film thickness are compared of crank pin bearing. In the past researches, journal bearings have been studied only about the surface of bearing. In addition to this conventional research, this paper analyzes the effect of roundness error of a journal and a bearing on the minimum film thickness. Numerical analysis has been studied by using Reynolds equation and also Half-Sommerfeld condition is applied as boundary condition. Futhermore, this study investigates the effect of roundness error change on the minimum film thickness. The results demonstrate that the bigger amplitude of roundness error yields, the lower minimum oil film thickness is. In comparison to previous research considered a journal and a bearing individually, the results considering a journal and a bearing together show that amplitude of roundness error of journal has very little effect on the minimum oil film thickness.

• The KSFM Journal of Fluid Machinery
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• v.12 no.6
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• pp.41-46
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• 2009

This paper deals with the operating-speed (high-speed) balancing of a refinery gasoline HDS (hydrodesulfurization) process recycle-gas 8-stages compressor rotor. A low-speed balancing condition of the rotor was measured as maintaining the G2.5 level. But an inspection run of operating-speed balancing condition, using tilting-pad journal bearings of actual use, showed that while it could be continuously-operated safely at a rated speed of 10,500 rpm, the rotor would not be able to run over 11,000 rpm as the vibration increased very sharply, approaching 11,000 rpm. In order to cure that a series of operating-speed balancing, which first calculated balance correction-weights by applying the influence coefficient measured and calculated at 10,500 rpm and then implemented correction works, was carried-out. The final operating-speed balancing results showed that the vibrations at the bearing pedestals represented very good levels of 0.2 mm/s by decreasing to as much as the 1/10 of the original vibrations and particularly, even at a targeted maximum continuous operating speed, MCS, of 11,500 rpm the vibrations represented about 1 mm/s, which is the operating-speed balancing vibration specification of API. Therefore, the expansion of MCS was successfully accomplished through the operating-speed balancing.