• Structural Engineering and Mechanics
• /
• 제66권6호
• /
• pp.783-792
• /
• 2018

This paper presents a detailed theoretical study of the sleeved compression members based on a mechanical model. In the mechanical model, the core protrusion above sleeve and the contact force between the core and sleeve are specially taken into account. Via the theoretical analyses, load-displacement relationships of the sleeved compression members are obtained and verified by the experimental results. On the basis of the core moment distribution changing with the increase of the applied axial load, failure mechanism of the sleeved compression members is assumed and proved to be consistent with the experimental results in terms of the failure modes and the ultimate bearing capacities. A parametric study is conducted to quantify how essential factors including the core protrusion length above sleeve, stiffness ratio of the core to sleeve, core slenderness ratio and gap between the core and sleeve affect the mechanical behaviors of the sleeved compression members, and it is concluded that the constrained effect of the sleeve is overestimated neglecting the core protrusion; the improvement of ultimate bearing capacity for the sleeved compression member is considered to be decreasing with the decrease of the core slenderness ratio and for the sleeved compression member with core of small slenderness ratio, small gap and small stiffness ratio are preferred to obtain larger ultimate bearing capacity and stiffness.

• 한국산학기술학회논문지
• /
• 제7권4호
• /
• pp.697-703
• /
• 2006

본 논문에서는 국내. 외에서 처음으로 시도되는 현장타설 팽이기초공법의 거동특성을 검토하기 위하여 기초형식을 현장타설 팽이기초(In-Situ TBF), 공장제작 콘크리트 팽이기초(PC-TBF) 전면기초, 무처리 원지반으로 나누어 모형토조실험을 수행하였다. 모형실험결과 현장타설 팽이기초와 공장제작 콘크리트 팽이기초의 거동특성은 거의 유사하게 나타났으며, 이들 팽이기초는 원지반 및 전면기초에 비하여 지지력 증대효과가 있는 것으로 나타났다. 또한, 기초 형식에 따른 지중연직응력 분포를 검토한 결과 팽이기초 설치시 지중연직응력의 영향범위가 감소하는 것을 확인할 수 있었다. 한편, 지반이 조밀할수록 팽이기초의 응력분산효과가 감소하는 것을 알 수 있었으며, 향후 다양한 지반조건에서 모형실험과 수치해석을 통해 보다 많은 검토가 수행되어야 할 것으로 판단된다.

• 제어로봇시스템학회:학술대회논문집
• /
• 제어로봇시스템학회 2005년도 ICCAS
• /
• pp.123-128
• /
• 2005

A novel tri-mode ultraprecision positioning system for machine tools and measuring machine is proposed. The basic coarse mode uses a Twist-roller Friction Drive (abbr. TFD), and controls several tens of millimeters of the machine-table travel with nanometer order of positioning resolution. The fine mode also utilizes the TFD with a fine adjusting mechanism. The resolution of the fine mode is in the range of sub-nanometer. For realizing picometer positioning, the ultra-fine mode is executed by using an active aerostatic guideway. On the bearing surface of this active guideway, several Active Inherent Restrictors (abbr. AIRs) are embedded for controlling the table position. An AIR unit consists of a piezoelectric actuator having a through hole, one end of the hole on the bearing surface acts as an inherent restrictor. Owing to the aerostatic mechanism of the AIR, the deformation of the piezoelectric actuator in the AIR unit causes much reduced table displacement. Such motion reduction is effective for ultraprecision positioning. Current positioning resolution of the ultra-fine mode is 50pm, however the final goal of the positioning resolution is expected to be in the order of picometer.

• 한국지반공학회:학술대회논문집
• /
• 한국지반공학회 2005년도 춘계 학술발표회 논문집
• /
• pp.597-602
• /
• 2005

The present precast top-base method create many problems of requiring it plant facilities, transportation and installation, due to the heavy weight of and it takes too long time to set it up on site. In order to improve and solve these problems, in-situ Top-Base method is developed. It include processes that install Top-Base mold made of poly-ethylene into ground, then pouring concrete into the mold, and fill the rest gaps with broken stones. Considerable advantages can be obtained by applying in-situ Top-Base method in aspects of the stability, economical and construction efficiency. In this research, model tests for in-situ Top-Base system are carried out in other to the investigate the load delivering mechanism and the effect of bearing capacity.

• 대한기계학회논문집A
• /
• 제37권12호
• /
• pp.1535-1540
• /
• 2013

본 논문에서는 볼 베어링의 접촉 메커니즘이 고려된 유한요소 모델링 방법을 제안 하였으며 내륜형과 외륜형 회전체의 해석과 실험을 통하여 검증하였다. 그 결과 제안된 방법은 내륜 회전형일 경우 차이가 적지만 외륜 회전형일 경우 회전부와 지지부의 연성으로 인하여 기존 방법보다 더 정확히 예측함을 확인하였고 향후 외륜 회전형 기기의 동특성을 정확히 예측하는데 활용될 수 있다.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2002년도 추계학술대회논문집
• /
• pp.1022-1027
• /
• 2002

This paper describes the fluttering characteristics of the upper pad in a tilting pad journal bearing(6-pad, LOP type) using a steam turbine. In order to investigate the phenomena of the upper pad fluttering experimentally, the absolute vibration of the upper pads the relative vibration between bearing and shaft and the circumferential distribution of the film thickness are measured under the different values of supply oil flow rate, shaft speed and bearing load. It can be known that the fluttering mechanism of the upper pads has a tendency of the self-excited vibration from the study of fluttering frequencies and amplitudes with the change of shaft speed. furthermore, it is observed that the incipient upper pad fluttering velocity is increased by the increase of oil supply flow rate and fluttering amplitude of the upper pads is increased by the decrease of the oil flow rate and by the increase of the bearing load.

• 한국생산제조학회지
• /
• 제21권5호
• /
• pp.741-746
• /
• 2012

The increase of energetic efficiency in plane bearing is getting more important in the transfer mechanism of semi-conductor and display panel manufacturing processes. To accomplish this objective, the technique of surface texturing on bearing surface has recently emerged as one of the most effective candidates. In this study, the effects of various pattern parameters on two bearing performance indices(load carrying capacity and effective friction coefficient) are investigated through a semi-analytic method, i.e., the 2-dimensional Reynolds equation incorporated into the finite difference scheme. Here, cavitation effect is also taken into account by employing an appropriate numerical scheme. In this study, the patterns in the textured surface are composed of a series of semi-spheres or semi-ellipsoids in shape. The effects of their size and number density on the performance indices are examined through the performance of various numerical experiments. Also, the effects of the anisotropy of the semi-ellipsoidal pattern on the bearing's lubrication characteristics are investigated and discussed.

• Tribology and Lubricants
• /
• 제25권1호
• /
• pp.43-48
• /
• 2009

It is reported by many researchers that the textured bearing surfaces, where many tiny micro-pockets or enclosed recesses were incorporated, can enhance the load support and reduce friction force. Recently, the basic lubrication mechanism of micro-pocketed parallel surfaces are explained in terms of "inlet suction" using continuity equation and simply cavitation condition. However, it is required that more actual cavitation condition in the pocket region should be applied to estimate exact bearing performance. In this paper, a commercial computational fluid dynamics (CFD) code, FLUENT is used to investigate the exact lubrication characteristics of infinitely long slider bearing with micro-pockets. The results show that the pressure distributions are highly affected by pocket depths, its positions and numbers. The numerical method adopted in this paper and results can be use in optimal design of textured sliding bearings.

• 한국소음진동공학회논문집
• /
• 제13권6호
• /
• pp.467-473
• /
• 2003

This paper describes the fluttering characteristics of the upper pad in a tilting pad journal bearing(6-pad, LOP type) using a steam turbine. In order to investigate the phenomena of the upper pad fluttering experimentally, the absolute vibration of the upper pads, the relative vibration between bearing and shaft and the circumferential distribution of the film thickness are measured under the different values of supply oil flow rate, shaft speed and bearing load. It can be known that the fluttering mechanism of the upper pads has a tendency of the self-excited vibration from the study of fluttering frequencies and amplitudes with the change of shaft speed. Furthermore, it is observed that the incipient upper pad fluttering velocity is increased by the increase of oil supply flow rate and the fluttering amplitude of the upper pads is increased by the decrease of the ell flow rate and by the increase of the bearing load.

• Geomechanics and Engineering
• /
• 제19권2호
• /
• pp.127-139
• /
• 2019

Available methods to determine the ultimate bearing capacity of shallow foundations may not be accurate enough owing to the complicated failure mechanism and diversity of the underlying soils. Accordingly, applying new methods of artificial intelligence can improve the prediction of the ultimate bearing capacity. The M5' model tree and the genetic programming are two robust artificial intelligence methods used for prediction purposes. The model tree is able to categorize the data and present linear models while genetic programming can give nonlinear models. In this study, a combination of these methods, called the M5'-GP approach, is employed to predict the ultimate bearing capacity of the shallow foundations, so that the advantages of both methods are exploited, simultaneously. Factors governing the bearing capacity of the shallow foundations, including width of the foundation (B), embedment depth of the foundation (D), length of the foundation (L), effective unit weight of the soil (${\gamma}$) and internal friction angle of the soil (${\varphi}$) are considered for modeling. To develop the new model, experimental data of large and small-scale tests were collected from the literature. Evaluation of the new model by statistical indices reveals its better performance in contrast to both traditional and recent approaches. Moreover, sensitivity analysis of the proposed model indicates the significance of various predictors. Additionally, it is inferred that the new model compares favorably with different models presented by various researchers based on a comprehensive ranking system.