• Tribology and Lubricants
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• 제20권4호
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• pp.197-203
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• 2004

As the rotational speed and the track density are increased, the vibration of disk/spindle system becomes critical issue in order to reduce the track mis-registration. In this work, we propose a simple inclined air bearing (20${\times}$20 mm) system which is located very near to the rotating poly-carbonate disk, and investigate suppressing effect for the disk vibration mode (0,0) both experimentally and numerically. We find dynamic stiffness and damping coefficients of air bearing and then apply those values to the disk vibration analysis. Numerical results show about 10 percent difference comparing to the experimental results. Also we investigate the reduction of disk vibration and power consumption with two different kinds of inclined bearing for the normal disk drive system experimentally. We find inclined air bearing can reduce about 30 percents of the transverse disk vibration.

• Geomechanics and Engineering
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• 제15권6호
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• pp.1173-1182
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• 2018

The coal wall, gob-side backfill, and gangues in goaf, constitute the support system for Gob-side entry retaining (GER) in coal mines. Reasonably allocating and utilizing their bearing capacities are key scientific and technical issues for the safety and economic benefits of the GER technology. At first, a mechanical model of GER was established and a governing equation for coordinated bearing of the coal-backfill-gangue support system was derived to reveal the coordinated bearing mechanism. Then, considering the bearing characteristics of the coal wall, gob-side backfill and gangues in goaf, their quantitative design methods were proposed, respectively. Next, taking the No. 2201 haulage roadway serving the No. 7 coal seam in Jiangjiawan Mine, China, as an example, the design calculations showed that the strains of both the coal wall and gob-side backfill were larger than their allowable strains and the rotational angle of the lateral main roof was larger than its allowable rotational angle. Finally, flexible-rigid composite supporting technology and roof cutting technology were designed and used. In situ investigations showed that the deformation and failure of surrounding rocks were well controlled and both the coal wall and gob-side backfill remained stable. Taking the coal wall, gob-side backfill and gangues in goaf as a whole system, this research takes full consideration of their bearing properties and provides a quantitative basis for design of the support system.

• 한국지반공학회논문집
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• 제20권7호
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• pp.107-117
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• 2004

느슨한 모래지반에서 보강재 층수 증가와 보강재의 강성과 형태 변화 그리고 얕은 기초 직하에 매설된 연성관의 깊이 등의 변화가 지지력-침하 곡선에 미치는 영향을 알아보기 위해 일련의 모형실험을 수행하였다. 시험결과, 무보강토 경우는 파괴형태가 국부전단으로 나타났으나 보강재 층수가 2층 이상이 되면 파괴형태는 국부전단에서 전반전단으로 바뀌고, 최적보강재 층수는 2층 이며, 지지력 개선에 있어서는 보강재의 초기강성과 형태가 최대인 장강도보다 중요한 것으로 나타났다. 무보강토에서 기초 직하에 연성관이 매설된 경우, 연성관의 매설 깊이가 기초 폭보다 얕으면 지지력과 극한지지력은 현저하게 감소하고, 보강토의 경우 연성관의 매설 깊이가 기초 폭보다 얕으면 파괴형태는 전반전단에서 국부전단으로 바뀌는 것으로 나타났다.

• Journal of Mechanical Science and Technology
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• 제15권9호
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• pp.1226-1239
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• 2001

Rotating machinery often encounters excessive vibration due to various excitation sources. Among others, the synchronous excitation due to rotating unbalance and initial deformation is acknowledged to be one of the major sources of vibration in rotor-bearing systems. In this paper, a synchronous response analysis method in the presence of the initial deformation is proposed to investigate the peculiar effect of the initial deformation on the response of general flexible rotor-bearing systems with rotational speed dependency and the anisotropy. Experiments are performed and compared with computational results to verify the proposed analysis method. Two numerical examples are also provided to illustrate the characteristics of the synchronous response of general rotor-bearing systems due to the initial deformation.

• Structural Engineering and Mechanics
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• 제55권4호
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• pp.839-856
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• 2015

A multi-contact tooth meshing model for helical gear pairs considering bearing and shaft deformations is proposed. First, to easily incorporate into the system model, the complicated Harris' bearing force-displacement relationship is simplified applying a linear least square curve fit. Then, effects of shaft and bearing flexibilities on the helical gear meshing behavior are implemented through transformation matrices which contain the helical gear orientation and spatial displacement under loads. Finally, true contact lines between conjugated teeth are approximated applying a modified meshing equation that includes the influence of tooth flank displacement on the tooth contact induced by shaft and bearing displacements. Based on the model, the bearing's force-displacement relation is examined, and the effects of shaft deformation and external load on the multi-contact tooth mesh load distribution are also analyzed. The advantage of this work is, unlike previous works to search true contact lines through time-consuming iterative strategy, to determine true contact lines between conjugated teeth directly with presentation of deformations of bearings and shafts.

• 대한기계학회논문집 C: 기술과 교육
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• 제3권2호
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• pp.125-130
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• 2015

Using flexible multibody system dynamic method, the rigid-flexible coupling multibody dynamic analysis model of the drum brake system was developed, and the kinematic and dynamic simulation of the system was processed as its object of study. Simulations show that the friction will increase with the dynamic friction coefficient, but high dynamic friction coefficient will cause the abnormal vibration and worsen the stability of the brake system, even the stability of the whole automobile. The modeling of flexible multi-body can effectively analyze and solve complex three-dimensional dynamic subjects of brake system and evaluate brake capability. Further research and study on this basis will result in a convenient and effective solution that can be much helpful to study, design and development of the brake system.

• 대한조선학회논문집
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• 제52권1호
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• pp.61-69
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• 2015

In the beginning of the 1990's, numerous shaft bearing damages, especially in aft stern tube bearing, were reported. The main reasons of bearing damages were estimated that hull deflections have been increased by more flexible hulls and propeller dynamic loads have not been considered in shaft alignment. After that time, studies to take into account hull deflections in shaft alignment have been actively carried out, but for the latter leave much to be desired. In this study, the effects of the propeller forces on the propeller shaft bearing have been investigated by estimating thrust eccentricity as reasonable as possible although some assumptions to simulate turning of ship were introduced. Three dimensional nominal wake to estimate thrust eccentricity have been calculated by using CFD analysis and model test in the towing tank. This study presents the procedure to estimate the propeller eccentric forces and their influence on the stern tube bearing for a container carrier. As a result, it has been found that the lateral propeller forces in turning condition should be considered in shaft alignment to prevent shaft bearing damages.

• Geomechanics and Engineering
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• 제18권4호
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• pp.439-448
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• 2019

The bearing capacity of roadside support is the key problem in gob-side entry retaining technology. To study the cooperative bearing characteristics of the roof-roadside support-floor along the gob-side entry retaining, a mechanical model of the composite structure of the roof-roadside support-floor was first established. A method for determining the structural parameters of gob-side entry retaining was then proposed. Based on this model, adaptability analysis of roadside support was carried out. The results showed that the reasonable width of the gob-side entry roadway was inversely proportional to the mining height, and directly proportional to the bearing strength of the roof and floor. And the reasonable width of the "flexible-hard" roadside support was directly proportional to its own strength, and inversely proportional to the width of the gob-side entry retaining. When determining the position and size of the roadside support along the gob-side entry retaining, the surrounding rock environment should be fully considered. Measured results from case study also show the rationality of the model and calculation method.

• 대한물리의학회지
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• 제9권4호
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• pp.355-361
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• 2014

PURPOSE: The purpose of this study was to determine the immediate effect of low-dye taping on balance performance in subjects with flexible flatfoot. METHODS: Fifteen asymptomatic volunteers who had flexible flatfoot (age, $21.7{\pm}1.81$years; height, $164.80{\pm}7.57cm$; weight, $56.47{\pm}10.48kg$) were participated for this study. Navicular drop test was used to evaluate pronation of foot in three different conditions; non-weight bearing position without low-dye taping, weight bearing position without low-dye taping, weight bearing position with low-dye taping. And balance performance (anterio/ posterior, medial/lateral, and overall) was evaluated using the Biodex Balance System in three different conditions; one-leg standing without low-dye taping, one-leg standing with low-dye taping, and one-leg standing with low-dye taping in one week later. Repeated-measures analysis of variance (ANOVA) was used to assess navicular height and balance performance across the three testing conditions. RESULTS: Significant and clinically meaningful improvement in navicular height was found after application of the low-dye taping. However, there was no statistically significant change in balance performance. CONCLUSION: The results of this study provide evidence to suggest that low-dye taping does not affect balance performance.

• 대한기계학회논문집
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• 제10권5호
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• pp.698-705
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• 1986

본 연구에서는 윤활이론에 따라 명확히 계산되고 그 신빙성이 실험적으로 검 증된 "동압유막 댐퍼"의 감쇠계수를 이용하여 외부댐핑을 갖는 회전축-구름베어링계와 회전축-저어널베어링계의 진동특성을 해석하고저 한다. 또한 해석결과를 토대로 회 전축계의 진동특성에 미치는 특성수 및 설계변수를 명확히 도출하여 동특성을 고려한 회전축계의 최적설계에 기여하고저 한다. 기여하고저 한다.