• Journal of the Korean Society for Precision Engineering
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• v.24 no.8 s.197
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• pp.89-96
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• 2007

In this paper, a new air bearing stage with magnetic preload and a linear motor has been developed for the small precision machine systems. The new air bearing stage is unique in the sense that permanent magnets attached bottom of the iron core of table are used not only for preloading air bearings in vertical direction but also for generating thrust force by current of the coil at base. The characteristics of air bearings using porous pads were analyzed with numerical method, and the magnetic circuit model was derived for linear motor for calculating required preload force and thrust force. A prototype of single axis miniature stage with size of $120(W){\times}120(L){\times}50(H)\;mm^3$ was designed and fabricated and examined its performances, vertical stiffness, load capacity, thrust force and positioning resolution.

• Geomechanics and Engineering
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• v.36 no.6
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• pp.545-561
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• 2024

Piled raft foundation has become widely used in the recent years because it can increase bearing capacity of foundation with control settlement. The design for a piled raft in terms vertical load and lateral load need to understands contribution load behavior to raft and pile in piled raft foundation system. The load-bearing behavior of the piled raft, especially concerning lateral loads, is highly complex and challenge to analyze. The complex mechanism of piled rafts can be clarified by using three dimensional (3-D) Finite Element Method (FEM). Therefore, this paper focuses on free-standing head pile group, on-ground piled raft, and embedded raft for the piled raft foundation systems. The lateral resistant of piled raft foundation was investigated in terms of relationship between vertical load, lateral load and displacement, as well as the lateral load sharing of the raft. The results show that both vertical load and raft position significantly impact the lateral load capacity of the piled raft, especially when the vertical load increases and the raft embeds into the soil. On the same condition of vertical settlement and lateral displacement, piled raft experiences a substantial demonstrates a higher capacity for lateral load sharing compared to the on-ground raft. Ultimately, regarding design considerations, the piled raft can reliably support lateral loads while exhibiting behavior within the elastic range, in which it is safe to use.

• The KSFM Journal of Fluid Machinery
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• v.18 no.5
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• pp.42-48
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• 2015

To improve the core technology of the micro gas turbine, the performance test facility was developed. This paper is focusing on the explanation of the characteristics of micro gas turbine and its assist devices. Major part of micro gas turbine were radial type of compressor, annular type of combustor, radial type of turbine, thrust foil bearing, radial foil bearing and generator. The assist devices were consist of exhaust duct, inverter, data acquisition system, load bank and test cell. Before building up the test facility, the component test was previously conducted to confirm the component performance. After the test facility was prepared, the motoring test was conducted to investigate the rotor dynamic characteristics of the micro gas turbine. Also, the part load performance test was performed. With a developed micro gas turbine test facility, the improved core technology about the micro gas turbine can be suggested to the related industries.

• Structural Engineering and Mechanics
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• v.27 no.6
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• pp.697-711
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• 2007

Though extensive research has been carried out for the ultimate strength of steel reinforced concrete (SRC) members under static and cyclic load, there was only limited information on the applied analysis models. Modeling of the inelastic response of SRC members can be accomplished by using a microcosmic model. However, generally used microcosmic model, which usually contains a group of parameters, is too complicated to apply in the nonlinear structural computation for large whole buildings. The intent of this paper is to develop an effective modeling approach for the reliable prediction of the inelastic response of SRC columns. Firstly, five SRC columns were tested under cyclic static load and constant axial force. Based on the experimental results, normalized trilinear skeleton curves were then put forward. Theoretical equation of normalizing point (ultimate strength point) was built up according to the load-bearing mechanism of RC columns and verified by the 5 specimens in this test and 14 SRC columns from parallel tests. Since no obvious strength deterioration and pinch effect were observed from the load-displacement curve, hysteresis rule considering only stiffness degradation was proposed through regression analysis. Compared with the experimental results, the applied analysis model is so reasonable to capture the overall cyclic response of SRC columns that it can be easily used in both static and dynamic analysis of the whole SRC structural systems.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2000.11a
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• pp.247-250
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• 2000

This paper presents the dynamic analysis and experiment for a shaft system supported by angular contact ball bearings. Among others, the dynamic characteristics of bearings are significantly affected by axial preload and radial load applied. This paper rigorously analyzes the dynamic characteristics of a shaft system with angular contact ball bearings subject of axial preload so as to result in eigenvalues as well as bearing stiffness characteristics. Experiments are also performed to identify natural frequencies and stiffness characteristics of bearings implemented. Comparison is made on the theoretical and experimental results.

• Journal of Mechanical Science and Technology
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• v.20 no.10
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• pp.1590-1606
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• 2006

Slider bearings are widely applied in mechanical systems, where the design needs cover increased load capacity, lowered friction and power consumption and creative designs. This work is governed to perform a parametric characterization, by generating a novel structure on the upper slider surface, which can formally be expressed in micro-machined wavy-form, where the individual and combined influences of various structural design parameters and boundary conditions, on the performance records, are also evaluated. Computations put forward that the contribution of the wave amplitude on power loss values is highly dependent on the level of inlet pressure; higher amplitudes are determined to increase power loss in the lowest inlet pressure case of 1.01, whereas the contrary outcome is determined in the higher inlet pressure cases of 3.01 & 5.01. Designing the slider bearing system, based on optimal load capacity, produced the optimum wave number ranges as 10-45, 7-11 and 5-8 for the pad inclinations of $5^{\circ},\;4^{\circ}$ and $3^{\circ}$ respectively.

• Steel and Composite Structures
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• v.46 no.4
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• pp.497-512
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• 2023

Using light weight concrete as infill material in conventional cold-formed steel (CFS) shear wall systems can considerably increase their load bearing capacity, ductility, integrity and fire resistance. The compressive strength of the filler concrete is a key factor affecting the structural behaviour of the composite wall systems, and therefore, achieving maximum compressive strength in lightweight concrete while maintaining its lightweight properties is of significant importance. In this study a new type of optimum polystyrene lightweight concrete (OPLC) with high compressive strength is developed for infill material in composite CFS shear wall systems. To study the seismic behaviour of the OPLC-filled CFS shear wall systems, two full scale wall specimens are tested under cyclic loading condition. The effects of OPLC on load-bearing capacity, failure mode, ductility, energy dissipation capacity, and stiffness degradation of the walls are investigated. It is shown that the use of OPLC as infill in CFS shear walls can considerably improve their seismic performance by: (i) preventing the premature buckling of the stud members, and (ii) changing the dominant failure mode from brittle to ductile thanks to the bond-slip behaviour between OPLC and CFS studs. It is also shown that the design equations proposed by EC8 and ACI 318-14 standards overestimate the shear force capacity of OPLC-filled CFS shear wall systems by up to 80%. This shows it is necessary to propose methods with higher efficiency to predict the capacity of these systems for practical applications.

• Journal of Institute of Control, Robotics and Systems
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• v.6 no.4
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• pp.261-267
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• 2000

In this study, a heavy-load servo-control driving system, which are composed of controller, electro-hydraulic servomechanism, hydraulic motor, reduction gearbox, turret slew bearing and turret structure, are investigated to simplify the servo-control system. To estimate the effect of each component, nonlinear modeling and simulation are carried out. In the first stage, to prove the validity of the performance estimation program, simulation results are compared with experimental results. In the second stage, the effect of each component of the control system is evaluated and then a simplified control system is suggested.

• Journal of the Korean Vacuum Society
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• v.19 no.4
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• pp.256-264
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• 2010

In this paper, a digital controller of magnetic bearing system for a high vacuum turbomolecular pump (TMP) is designed and examined. For stabilizing and providing damping in magnetic bearing, the digital PID controller is applied for each 5 control axes, and the inter-axis cross feedback controller is also applied to suppress low frequency vibration caused by gyroscopic moment of the rotor at high speed of rotation. The fabricated rotor-shaft has its first flexible natural frequency lower than maximum speed, about 614Hz, so the two lead filters are applied to increase damping of flexible mode. Notch filters with rotating frequency were selected to reduce vibration of the pump housing caused by unbalance load. The implemented controllers are verified by examination of frequency response and rotating test up to 40,000 rpm, which is higher than critical speed of backward flexible mode.

• Tribology and Lubricants
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• v.34 no.3
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• pp.75-83
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• 2018

Microturbomachinery (< 250 kW) using gas foil bearings can function without oil lubricants, simplify rotor-bearing systems, and demonstrate excellent rotordynamic stability at high speeds. State-of-the-art technologies generally use bump foil bearings or leaf foil bearings due to the specific advantages of each of the two types. Although these two types of bearings have been studied extensively, there are very few studies on leaf-bump foil bearings, which are a combination of the two aforementioned bearings. In this work, we illustrate a simple mathematical model of the leaf-bump foil bearing with leaf foils supported on bumps, and predict its static and dynamic performances. The analysis uses the simple elastic model for bumps that was previously developed and verified using experimental data, adds a leaf foil model, and solves the Reynolds equation for isothermal, isoviscous, and ideal gas fluid flow. The model predicts that the drag torques of the leaf-bump foil bearings are not affected significantly by static load and bearing clearance. Due to the preload effect of the leaf foils, rotor spinning, even under null static load, generates significant hydrodynamic pressure with its peak near the trailing edge of each leaf foil. A parametric study reveals that, while the journal eccentricity and minimum film thickness decrease, the drag torque, direct stiffness, and direct damping increase with increasing bump stiffness. The journal attitude angle and cross-coupled stiffness remain nearly constant with increasing bump stiffness. Interestingly, they are significantly smaller compared to the corresponding values obtained for bump foil bearings, thus, implying favorable rotor stability performance.