• Tribology and Lubricants
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• v.19 no.6
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• pp.342-348
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• 2003

The purpose of the paper is to investigate the noise characteristics of cylindrical roller bearings. For the sake of simplicity, it is assumed that the cylindrical roller bearing is infinitely long, and there is no outside force acting on the bearing. The effects of radial clearance of the bearing, viscosity of the lubricant and number of the roller on the noise of the bearing are also examined. Results show that the fundamental frequency of the bearing noise corresponds to the multiplication of number of the roller and whirling frequency of the roller center or the retainer. The acoustical frequency spectra of the roller bearing are pure tone spectra, containing the fundamental frequency of the bearing and its super­harmonics. The low viscosity of the lubricant, high radial clearance of the bearing, and low number of the roller decrease the bearing noise. The results and discussions of the present paper could aid in the low­noise design of the cylindrical roller bearing.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1999.06a
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• pp.156-161
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• 1999

new bearing concept, the wave journal bearing, has been developed to improve the static and dynamic performances of an air-lubricated hydrodynamic journal bearing. This concept features waves on bearing surface. In this study, we present the solution of the compressible Reynolds equation valid for arbitrary Knudsen numbers. Straight wave journal bearing is investigated numerically. The performances of straight wave bearing are compared to the plain journal bearing over relatively wide range of bearing number and eccentricity. The wave journal bearing offers better stability than the plain journal bearing under a13 bearing numbers covered in this study. The bearing load and stability characteristics are dependent on the geometric parameters such as the amplitude and the starting point of the wave relative to the applied load. Under the condition of Knudsen number)0.01, we can not ignore the effect of slip for journal bearing.

• Tribology and Lubricants
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• v.17 no.1
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• pp.28-32
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• 2001

A new bearing concept, the wave journal bearing, has been developed to improve the static and dynamic performances of an air-lubricated hydrodynamic journal bearing. This concept features waves on bearing surface. In this study, we present the solution of the compressible Reynolds equation valid for arbitrary Knudsen numbers. Straight wave journal bearing is investigated numerically. The performances of straight wave bearing are compared to the plain journal bearing over relatively wide range of bearing number and eccentricity. The wave journal bearing offers better stability than the plain journal bearing under all bearing numbers covered in this study. The bearing load and stability characteristics are dependent on the geometric parameters such as the amplitude and the starting point of the wave relative to the applied load. Under the condition of Knudsen number＞0.01, we can not ignore the effect of slip for Journal bearing.

• 한국전산유체공학회:학술대회논문집
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• 2010.05a
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• pp.258-262
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• 2010

Since MEMS based micro actuators or generating devices showed high efficiency per volume, plenty of research are ongoing. Among them, MEMS based millimeter-scale micro gas turbine is one of the most powerful item for replacing chemical batteries. However, due to MEMS manufacturing technique, it is very difficult that makes wide turbine bearing area. It causes low DN number, so sufficient bearing force is hard to achieve. Thus, the most important issue on micro gas turbine is to design the proper bearing which can keep rotor stable during operation. In order to that, micro-scale gas-lubricated bearing is generally used. In this paper, basic feasibility study of thrust bearing of 10mm diameter turbine is described. Thrust bearing is hydrostatic gas-lubricated type. Numerical simulation is performed with ANSYS CFX 11.0 which is commercial numerical tool. Relationship between bearing inlet pressure and mass flow rate and bearing force is figured while changing bearing gap and number of capillaries. The simulation results will be used for further design of micro gas turbine.

• Korean Journal of Agricultural Science
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• v.42 no.4
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• pp.293-297
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• 2015

This study was conducted to evaluate the influence of feeding leaf positions on the growth, net formation of fruits, and occurrence of leaf yellowing symptoms (LYS) in muskmelon plants. Plants having five or ten more leaves above the fruit-bearing node produced the greater biomass than those of plants having equal or five less leaves above the fruit-bearing node. The number of leaves above the fruit-bearing node also influenced on the occurrence of LYS. The number of plants with LYS decreased as the number of leaves borne on the nodes above the fruit-bearing node increased. The LYS infected ratio of BL-5 treatment were the greatest, while fruit weight of BL+5 treatment were the greatest among all the tested treatments. In addition, the net formation of BL-5 treatment showed the poorest. Results indicated that maintaining the higher number of leaves over the fruit-bearing node might be feasible the practical method for coping physiological damages from yellowing symptoms.

• Journal of the Korean Society for Precision Engineering
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• v.17 no.3
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• pp.129-135
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• 2000

Air-dynamic bearings are increasingly used in supporting small high-speed rotating bodies. This study investigates the effects of design parameters on the axial stiffness of spiral-grooved air bearings of various curvatures. Design parameters are fundamental clearance, groove depth, and bearing number. The pressure distribution at the clearance between the stator and rotor of the bearing is obtained by solving the Reynolds equation, and the supporting load and the axial linear stiffness are calculated from the pressure distribution. It is found that a larger curvature increases the axial linear stiffness more and that there exist an optimal groove depth for the linear stiffness of the air bearing. It is also found that the linear stiffness has a linear relationship with the bearing number.

• Tribology and Lubricants
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• v.13 no.2
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• pp.16-26
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• 1997

In this paper, the characteristics of lubrication and wear phenomena of journal bearing with respect to film parameter and Sommerfeld number variation are investigated experimentally and the design criterion for the hydrodynamic journal bearing is presented to avoid wear and seizure. Experimental work is performed with various rotating speed and load, and lubricant is used synthetic oil and mineral oil. By the results of the experiment, it is found that friction coefficient is decreased as Sommerfeld number is decreased, and that wear phenomenon is observed when Sommerfeld number is below $9$\times$10^{-4}$ and there are much alike in wear properties between synthetic and mineral oil.

• Journal of Community Nutrition
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• v.7 no.2
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• pp.93-99
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• 2005

This study investigated associations between exercise habit and bone mineral density (BMD) and bone mineral content (BMC) in postmenopausal women. The BMD and BMC of the spinal skeleton was measured by dual energy x-ray absorptiometry. Exercise and energy expenditure of physical activity were estimated by questionnaire. For exercise activities, subjects were asked to identify all exercises they have participated in. The subjects were further asked to estimate the number of years of participation, the number of weeks per year, the number of times per week, and the number of hours per time. Subjects were then categorized into exercise (more than 3 times/wk, more than 30min per session exercise (n = 47) and nonexercise group (n = 72). Results indicated that there were no significant differences in BMD and BMC when comparisons were made between subjects in exercise habit, a general exercise group and a nonexercise control group. However, when exercise subjects were divided into weight-bearing and nonweight-bearing groups, significant differences were found. These results suggest that weight-bearing exercise positively influences bone mineral density and bone mineral content in postmenopausal women. Sedentary women should be encouraged to adopt a weight-bearing exercise to maintain the health of their skeletons. Exercise interventions are practical and feasible for healthy women and should be encouraged at the earliest possible age. Our findings lend support to recommendations for physical activity and weight-bearing exercise as a means of osteoporosis prevention.

• 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.

• KSTLE International Journal
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• v.2 no.1
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• pp.46-54
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• 2001

The herringbone groove journal bearing (HGJB) has chevron type grooves on stationary or rotating member of the bearing so that they pump the lubricant inward the grooves when journal rotates. As a result, the pressure is generated around the journal so that the radial stiffness and dynamic stability are improved comparing to the plain journal bearing (PJB) when the bearing operates near the concentric condition. The narrow groove theory, conventionally adopted to simulate the concentric operation of HGJB, is limited to the infinite number of grooves. A numerical study of air-lubricated HGJB is presented for the finite number of grooves. The compressible isothermal Reynolds equation is solved by using Finite Element Method together with the Newton-Raphson iterative procedure and perturbation method. The solutions render the static and dynamic performances of HGJB. Comparison of present results with a PJB validates previously published finite difference solution. The HGJB's geometric parameters influence its static and dynamic characteristics. The optimum geometric parameters are presented for the air-lubricated HGJB in particular conditions.