• Tribology and Lubricants
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• v.40 no.1
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• pp.1-7
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• 2024

Ball bearings are a major component of mechanical parts for transmitting rotation. Compared to tapered roller bearings, ball bearings offer less rolling resistance, which leads to reduced heat generation during operation. Because of these characteristics, ball bearings are widely used in electric vehicles and machine tools. The design of ball bearing cages has recently emerged as a major issue in ball bearing design. Cage design requires pre-verification of performance using theoretical or experimental formula or computational fluid dynamics (CFD). However, CFD analysis is time-consuming, making it difficult to apply in case studies for design decisions and is mainly used in performance prediction following design confirmation. To use CFD in the early stages of design, main-taining analytical accuracy while reducing the time required for analysis are necessary. Accordingly, this study proposes a laminar steady-state segment CFD technique to solve the problem of long CFD analytical times and to enable the use of CFD analysis in the early stages of design. To verify the reliability of the CFD analysis, a bearing drag torque test is performed, and the results are compared with the analytical results. The proposed laminar steady-state segment CFD technique is expected to be useful for case studies in bearing design, including cage design.

• Korean Journal of Applied Biomechanics
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• v.17 no.4
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• pp.83-88
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• 2007

The purpose of this study was to investigate the ball velocity changes depending on the different linear momentum of putter head. For this study, two different moving conditions(25cm free fall and 35cm free fall) of putter head were set. And two different types of ground conditions were used which are artificial grass green($180cm{\times}600cm{\times}1cm$) and glass green($40cm{\times}130cm{\times}1cm$). Movements of putter head and ball were recorded with 2 HD video cameras(60 Hz, 1/500s shutter speed). Small size control object($18.5cm{\times}18.5cm{\times}78.5cm$) was used in this study. Ball and putter head velocities were calculated by the First Central Difference Method(Hamill & Knutzen, 1995). Linear momentum of ball and putter head were calculated with mass and its velocities. Before impact, the velocity of the putter head of 35cm free fall was about 30% greater than that of the putter head of 25cm free fall. Linear momentum of putter head of 35cm free fall was about 0.355-0.364kg m/s and 25cm free fall was 0.251 kg m/s. After impact, putter head lost its linear momentum about 14-19% and adjusting time of putter head after impact would be 0.1 second. After 0.1 second, putter moved the route same as before impact. Maximum ball velocities were appeared 0.08s-0.10s after impact no matter what the ground conditions are. Ball velocities struck by 35cm free fall were 30 % faster than 25cm free fall. Linear momentum of ball struck by putter head was greater than that of expected amount because the moving ball has translational energy and rotational energy. Future study must treat three things. One is ball must struck by the different putters with different materials. Another is two-piece ball and three-piece ball should be used for the same condition studies. The other is height of center of rotation of club should be changed. In this study, the height of center of rotation of club head is 71cm from the ground. But recently many golfers used the long putter. Therefore next study should apply the different height of center of rotation of club head.

• Asian Journal of Turfgrass Science
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• v.20 no.2
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• pp.203-211
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• 2006

This study was initiated to investigate the difference of playing ability among soccer fields established with natural turfgrass, artificial turf and bare ground. The soccer fields with natural turfgrasses were established with cool-season grass(Kentucky bluegrass 80%+Perennial ryegrass 20%) and zoysiagrass. The artificial turf field was constructed with Konigreen $DV5000^{TM}$. Bare ground was sandy soil. Data such as ball rolling distance and vertical ball rebound were collected at the Sports Science Town of Konkuk University from 2005 to 2006. A ball in the study was Hummel Air Vision #1, certified by KFA(Korea Football Association) in ball pressure of 1.01b. Ball rolling distance was the longest on bare ground(13.6m), followed by artificial grass(11.4m), cool-season grass(7.8m) and zoysiagrass(4.7m). It decreased with lower frequency in use, stronger rigidity and higher density of turfgrass. Vertical ball rebound was the highest on bare ground(1.0m), followed by artificial grass(0.9m), cool-season grass(0.6m) and zoysiagrass(0.4m). It was lower under conditions of low use frequency, strong rigidity, and high density. Both ball rolling distance and vertical ball rebound were not greatly affected by cool-season grass maintained with high intensity of culture by years after establishment. However, zoysiagrass field under low intensity of culture showed longer in ball rolling distance and higher in vertical ball rebound with time after establishment.

• Journal of Korea Entertainment Industry Association
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• v.14 no.6
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• pp.301-309
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• 2020

The purpose of this study was to determine whether swiss ball exercise combined with taping would improve low back pain, disability and quality of life in women with pregnancy-related Low Back Pain (PR-LBP). Sixteen patients with PR-LBP were recruited and were randomly divided into two groups: taping and swiss ball exercise group (n=8) and taping and stretching group (n=8). The taping and swiss ball exercise group was treated with swiss ball exercise with kinesio taping, while the taping and stretching group received only taping. The taping and swiss ball exercise group performed swiss ball exercise for 30 minutes a day, 5 times a week for 4weeks, while the taping and stretching group conducted stretching exercise for the same amount of time. VAS was used to assess pain level of low back. Disability was measured using a Roland Morris Disability Questionnaire(RMDQ). Quality of life were measured by SF-36. The pain intensity of low back in the taping and swiss ball exercise group improved significantly greater than the taping and stretching group (p<0.05). Significant improvement in the disability was observed in the taping and swiss ball exercise group compared to the taping and stretching group (p<0.05). The SF 36 in the taping and swiss ball exercise group improved significantly greater than the taping and stretching group (p<0.05). Our findings indicate that swiss ball exercise combined with taping is beneficial and effective to improve low back health and quality of life in women with PR-LBP.

• Tribology and Lubricants
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• v.20 no.4
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• pp.177-182
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• 2004

In a turbopump cryogenic ball bearings are used to carry static and hydraulic loads, and these ball bearings must stand up to high load and speed in cryogenic circumstance. Verification of bearing performance is crucial to successful development of a turbopump. In this paper, focusing on the turbopump under developing by KARI, the performances of 203 and 207 bearings are verified through the series of tests simulating the real operating condition of turbopump.

• Proceedings of the Korea Multimedia Society Conference
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• 2012.05a
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• pp.143-146
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• 2012

Ball-Plate를 기반으로 하는 균형제어 로봇은 크게 공의 상태를 파악하는 부분과 균형을 유지하는 제어부분 2가지로 구성되어진다. 본 논문은 공의 상태를 파악하기 위해서 단일 카메라를 이용하여 CAMShift 알고리즘으로 볼을 추적한다. 그리고 칼만 필터를 사용하여 발생하는 오차를 줄이는 방법을 제안하고 그 실험 결과에 대해서 설명한다.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.04a
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• pp.1025-1028
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• 2001

In this report, a new method compounding the electrolytic machining with ball end milling process to increase the machining efficiency was introduced. From the experimental result, it was confirmed that effect of cutting force reduction and finer surface roughness can be obtained in a certain condition of ball end milling and electrolytic machining conditions.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2000.11a
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• pp.959-962
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• 2000

A new method compounding the electrolytic machining with ball end milling process to improve machined surface toughness was examined. From this study, it was confirmed that much smaller cutting force and finer surface roughness can be obtained in a certain condition of ball end milling and electrolytic machining conditions.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1994.10a
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• pp.254-259
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• 1994

Recently, the precision ball screw becomes the essence of the high-precision industries and is playing a key role in the positioning devices. The standard and definition of pitch error in a precision ball screw is specified by KS, JIS or ISO. However, the method of measuring the pitch error is not concrete. In this study. laser measurement system(LMS) with a laser position transducer and a machine-tools is developed. In order to verify the stability of the LMS, several experiments with the standard ball screw is performed.

• YAKHAK HOEJI
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• v.43 no.1
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• pp.23-27
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• 1999

We previously reported that the extract of unripe cotton ball of Gossypium indicum shows cytotoxic activity and induces an apoptosis in vitro. In present study, its antitumor activity was investigated in vivo. Butanol soluble extract of unripe cotton ball reduced the weight of solid tumor in sarcoma 180 transplanted mouse model. It showed stronger activity than that of Krestin.