• Journal of the Korean Society for Precision Engineering
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• v.31 no.5
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• pp.381-387
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• 2014

This paper introduces a system to machine micro-sized patterns effectively on surface based on micro-milling process using tools with simultaneous rotation and oscillation, oscillation micro milling. To review the effectiveness of proposed concept, we integrated a micro-spindle supported by active magnetic bearings with a precision 3-axis air bearing stage using double-wedge mechanism, and tested this oscillation milling. Two types of oscillation milling were tested, which are linear oscillation milling with a flat end mill and elliptical oscillation milling with a ball end mill with 0.3 mm of diameter. The spindle was rotating 110 krpm and workpiece was moving constant speed of 2~8 mm/sec during the oscillation milling. As the results, multiple oval shape dimples were generated in regular spacing, and the variation of elliptical motion made different shapes of patterns. The results showed that proposed oscillation milling can be successfully used for machining repeated micro-patterns.

• Wind and Structures
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• v.19 no.4
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• pp.405-420
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• 2014

This paper examines the nonlinear behaviour of corrugated steel plate shear walls under lateral pushover load. One of the innovations in these types of walls which have used in recent years is the use of the corrugated steel shear walls rather un-stiffness plates. In the last decades many experimental studies have been done on the on the corrugated steel shear walls. A finite element analysis that includes both material and geometric nonlinearities is employed for the investigation. A comparison is made between the behaviour of steel shear walls with sinusoidal corrugated plate and trapezoidal corrugated plate. The effects of parameters such as the thickness of the corrugated plate, the corrugation depth in the corrugated plates and the corrugation length of the infill of the corrugated plates, are investigated. The results of this study have demonstrated that in the wall with constant dimensions, the trapezoidal plates have higher energy dissipation, ductility and ultimate bearing than sinusoidal waves, while decreasing the steel material consumption.

• Earthquakes and Structures
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• v.5 no.1
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• pp.23-48
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• 2013

In this study, the effect of flexibility of superstructures and nonlinear characteristics of LRB (Lead Rubber Bearing) isolator on inelastic response of base isolated structures is investigated. To demonstrate the intensity of damage in superstructures, demand response modification factor without the consideration of damping reduction factor, demand RI, is used and the N2 method is applied to compute this factor. To evaluate the influence of superstructure flexibility on inelastic response of base isolated structures, different steel intermediate moment resisting frames with different heights have been investigated. In lead rubber bearing, the rubber provides flexibility and the lead is the source of damping; variations of aforementioned characteristics are also investigated on inelastic response of superstructures. It is observed that an increase in height of superstructure leads to higher value of demand RI till 4-story frame but afterward this factor remains constant; in other words, an increase in height until 4-story frame causes more damage in the superstructure but after that superstructure's damage is equal to the 4-story frame's. The results demonstrate that the low value of second stiffness (rubber stiffness in LRBs) tends to show a significant decrease in demand RI. Increase in value of characteristic strength (yield strength of the lead in LRBs) leads to decrease in the demand RI.

• Nuclear Engineering and Technology
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• v.55 no.6
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• pp.2325-2334
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• 2023

To study the lubrication performance of tilting-pad thrust bearing (TPTBs) during start-up in nuclear pump, a hydrodynamic lubrication model of TPTBs was established based on the computational fluid dynamics (CFD) method and the fluid-structure interaction (FSI) technique. Further, a mesh motion algorithm for the transient calculation of thrust bearings was developed based on the user defined function (UDF). The result demonstrated that minimum film thickness increases first and then decreases with the rotational speed under start-up condition. The influence of pad tilt on minimum film thickness is greater than that of collar movement at low speed, and the establishment of dynamic pressure mainly depends on pad tilt and minimum film thickness increases. As the increase of rotational speed, the influence of pad tilt was abated, where the influence of the moving of the collar dominated gradually, and minimum film thickness decreases. For TPTBs, the circumferential angle of the pad is always greater than the radial angle. When the rotational speed is constant, the change rate of radial angle is greater than that of circumferential angle with the increase of loading forces. This study can provide reference for improving bearing wear resistance.

• Journal of Wind Energy
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• v.14 no.3
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• pp.34-42
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• 2023

The reduction of operation and maintenance (O&M) costs is a critical factor in determining the competitiveness of wind energy. Predictive maintenance based on the estimation of remaining useful life (RUL) is a key technology to reduce logistic costs and increase the availability of wind turbines. Although a mechanical component usually has sudden changes during operation, most RUL estimation methods use the trend of a state index over the whole operation period. Therefore, overestimation of RUL causes confusion in O&M plans and reduces the effect of predictive maintenance. In this paper, two RUL estimation methods (load based and data driven) are proposed for the bearings of a wind turbine with the results of trend classification, which differentiates constant and increasing states of the state index. The proposed estimation method is applied to a bearing degradation test, which shows a conservative estimation of RUL.

• Steel and Composite Structures
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• v.52 no.4
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• pp.475-485
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• 2024

The mechanical behavior of the steel tube encased high-strength concrete (STHC) composite walls under constant axial load and cyclically increasing lateral load was studied. Conclusions are drawn based on experimental observations, grey evolutionary algorithm and finite element (FE) simulations. The use of steel tube wall panels improved the load capacity and ductility of the specimens. STHC composite walls withstand more load cycles and show more stable hysteresis performance than conventional high strength concrete (HSC) walls. After the maximum load, the bearing capacity of the STHC composite wall was gradually reduced, and the wall did not collapse under the influence of the steel pipe. For analysis of the bending capacity of STHC composite walls based on artificial intelligence tools, an analysis model is proposed that takes into account the limiting effect of steel pipes. The results of this model agree well with the test results, indicating that the model can be used to predict the bearing capacity of STHC composite walls. Based on a reasonable material constitutive model and the limiting effect of steel pipes, a finite element model of the STHC composite wall was created. The finite elements agree well with the experimental results in terms of hysteresis curve, load-deformation curve and peak load.

• Journal of the Korean Geotechnical Society
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• v.20 no.5
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• pp.127-134
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• 2004

Rammed Aggregate Pier (RAP) has extensive applicability as for a foundation of structures. In this study, bearing capacity of the reinforced ground by RAP and the failure behavior of RAP are investigated through experiments. RAPs with diameters of 45, 60, 70 mm were installed in sand, of which relative densities are 60, 70, 90%. Then, two columns of pressure gauges, near the RAPs and one diameter off from the center of piers, are installed 5, 10, 15, 20, 25, 30 cm from the surface of the ground. The test results show that maximum lateral earth pressure is observed near 5∼10 cm (1.0∼2.0D) from the surface, which indicates the occurrence of bulging failure type. In addition, deformation of RAP in radial direction increases with lower relative density of the ground. Furthermore, lateral stress distribution decreases with depth.

• Journal of Korean Society of Steel Construction
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• v.26 no.6
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• pp.559-570
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• 2014

In this study, compression and shear characteristics of laminated rubber bearings and lead rubber bearings with various parameters are investigated by using material and geometric nonlinear three-dimensional finite element analysis. Rubber coupon tests are performed to make a model of the laminated rubber bearings. In addition, the material constants of the rubber are calculated by the curve fitting process of stress-strain relationship. The finite element analysis and experimental tests of the laminate rubber bearings are used to verify the validity of the rubber material constants. It is seen that the compression behavior of the laminated rubber bearings and lead rubber bearings mainly varies depending on the first shape factors and their shear behavior significantly varies depending on the second shape factors. In addition, the horizontal stiffness and energy dissipation capacity of lead rubber bearing are increased when the diameter of a lead bar is increased.

• Tribology and Lubricants
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• v.30 no.3
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• pp.131-138
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• 2014

This study investigates the effects of the slopes of the rotational axis and bearing preloads on the natural frequencies and onset speeds of the instability of a rotor supported on gas foil bearings (GFBs). The predictive model for the rotating system consists of a rigid rotor supported on two gas foil journal bearings (GFJBs) and a pair of gas foil thrust bearings (GFTBs). Each GFJB supports approximately half the rotor weight. As the slope of the rotational axis increases from $0^{\circ}$(horizontal rotor operation) to $90^{\circ}$(vertical rotor operation), the applied load on the GFJB owing to the rotor weight decreases. The predictions show that the natural frequency and onset speed of instability decrease significantly with an increase in the slope of the rotational axis. In a parametric study, the nominal radial clearance and preload for the GFJB were changed. In general, a decrease in the nominal radial clearance lead to an increase in the natural frequency and onset speed of instability. For constant assembly clearance, the decrease in the preload changed the natural frequency and onset speed of instability with insignificant improvements in the rotordynamic stability. The present predictions can be used as design guidelines for GFBs for oil-free high-speed rotating machinery with improved rotordynamic performance.

• Journal of the Earthquake Engineering Society of Korea
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• v.6 no.4
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• pp.39-49
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• 2002

In this paper, the characteristics of RB(rubber bearing) were studied by various prototype tests on RB with low hardness rubber. The characteristics of RB were tested on displacements, repeated cycles, frequencies, vertical pressures, temperature, vertical stiffness and the capability of shear deformation. The prototype test showed that the displacement and vertical pressures were the most governing factors influencing on characteristics of RB. The effective stiffness and equivalent damping of RB showed small increment in high frequency range. After the repeated cyclic test with 50's cycles, the effective stiffness and equivalent damping of RB were almost constant compared with those of the 1st cycles due to low hysteretic damping. The shear modulus of RB was reduced after large deformation, and this value of RB was partly recovered after 40 days. Finally, the shear failure test of RB was conducted, the prototype was failed over 490% of shear strain, and real size RB was failed over 430% of shear strain.