• 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.

• Tribology and Lubricants
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• v.37 no.6
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• pp.261-272
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• 2021

This study investigates the structural characteristics of oil-free, gas beam foil journal bearings (GBFJBs) for use in high speed motors. Mathematical modeling was carried out, and reaction force modeling for static load was performed to predict the structural characteristics of the GBFJB. Mathematical modeling and reaction force modeling for static load are performed to predict the structural characteristics of GBFJBs. The reaction force of the test bearing against static loads was measured during experiments and compared with the predicted results. The measured experimental data reveal the nonlinear stiffness characteristics of the GBFJB against varying displacement and agree well with the predictions. Dynamic load tests using an exciter allow to identify the vibration characteristics of the GBFJB. Test results show that the vibration displacement, dynamic force, and acceleration measured on the test bearing are most dominant at the applied dynamic load (synchronization) frequency. Futhermore, the test results show that the hysteresis area recorded during the dynamic tests increases with the excitation amplitude and frequency, and that the beam stick phenomena occurr at high excitation frequencies. The single degree of freedom (DOF) vibration model aids to identify the stiffness and damping coefficient of the GBFJB, which decrease as the excitation frequency increases.

• Journal of the Korean Society for Precision Engineering
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• v.16 no.2 s.95
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• pp.23-30
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• 1999

This paper investigates the radial performance of self-acting spiral-grooved air bearing, used to support small high-speed rotating bodies. Repeatable runout, nonrepeatable runout, stiffness and supporting load are selected as the performance. The clearance between rotor and stator, the stator groove depth, and the rotating speed are chosen as three main parameters affecting the performances. Force application and displacement measurement are done in a noncontact manner, in order not to disturb operation: electromagnetic force is applied to the rotor and gap sensors are used to measure the displacement of the rotor. Experimental results show that repeatable runout decreases as speed, groove depth and clearance decrease. Nonrepeatable runout decreases as clearance decreases, and it has a minimum value at $5.5{\mu}m$ of grove depth and a maximum value at speed of 18.000rpm. Stiffness increases as speed increases and clearance decreases, and has a maximum value around $5.5{\mu}m$ of groove depth. The relationship between force and displacement is linear for small displacement, but becomes nonlinear for large displacement. Supporting load is linearly proportional to the stiffness, and it is a maximum value around $4.75{\mu}m$ of clearance.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1996.10a
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• pp.202-206
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• 1996

An experimental study of the characteristics of the repulsiveytype magnetic bearing using high Tc superconductor is presented. In field cooling superconductor has the position-stability due to a flux pinning effect and the strong damping due to hysterisis, while in zero field cooling it has the only strong repulsive force due to Meissner effect. Lift force in superconducting levitation has a hysterisis characteristics, and it is the dissipation of energy, the mechanism of damping. As the relative linear velocity between a magnet and a superconductor increases, the area of the hysterisis loop becomes smaller. It means the decrease of damping. In field cooling, the static stiffness is very nonlinear in smaller than initial gap, but almost linear in larger than initial gap.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.7 s.238
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• pp.955-963
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• 2005

This research investigates dynamic characteristics of a linear motion (LM) guide through a experimental result and theoretical analysis. The stiffness in the LM guide is determined by the preloading due to the minus clearance between the ball bearing and the contact surface and it can be derived by Hertzian contact theory and the nonlinear motion of equation. The vibration analysis is performed using Lagrange equations and its result agrees with the experiment result. Using the sensitivity analysis on design parameters such as the contact angles of ball bearings and the eccentricity of mass center, the variation of the natural frequencies can be predicted.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1997.04a
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• pp.260-265
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• 1997

Large dynamic loads act on the rotor in rotary compressors. There are unbalance forces due to eccentric rotation parts and gas forces induced by the difference in pressure between compression and suction gases6 Rotor-journal bearing system is nonlinear since the stiffness and damping coefficients of the lubricating oil film are not constant in the bearings. In this paper, the program for predicting the behaviors of rotor-journal bearing system of rotary compressor is developed. Finite element modeling is used to analyze the flexible rotor. The numerical results are compared with experimental results. The location of balancer weight are suggested for reducing rotor whiring displacement.

• Earthquakes and Structures
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• v.5 no.6
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• pp.625-655
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• 2013

This paper investigated the seismic behaviour of an innovated non-ductile precast concrete wall structural system; namely HC Precast System (HCPS). The system comprises load-bearing precast wall panels merely connected only to column at both ends. Such study is needed because there is limited research information available in design codes for such structure particularly in regions having low to moderate seismicity threats. Experimentally calibrated numerical model of the wall system was used to carry out nonlinear pushover analyses with various types of lateral loading patterns. Effects of laterally applied single point load (SPL), uniformly distributed load (UDL), modal distributed load (MDL) and triangular distributed load (TDL) onto global behaviour of HCPS were identified. Discussion was focused on structural performance such as ductility, deformability, and effective stiffness of the wall system. Thus, a new method for engineers to estimate the nonlinear deformation of HCPS through linear analysis was proposed.

• Structural Engineering and Mechanics
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• v.12 no.6
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• pp.615-632
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• 2001

Ductility of open piled wharves under reversed cyclic loads has been investigated. Experimental testing of five wharf models having a scale of about 1:4 was conducted under the application of horizontal reversed cyclic loading. The experiments were designed to focus on the horizontal ultimate load, ductility and failure mode of the considered wharf models. Nonlinear numerical analyses using the finite element method were also performed on numerical models representing the experimentally tested wharves. The results of the experimental tests showed that open piled wharves possessed favourable ductile behaviour and that their load bearing capacity did not depreciate until a ductility factor of 3 to 4 was reached. The numerical analysis showed that the relative rotation that took place at the joints between the steel piles and the R.C. beam was responsible for a considerable portion of the total horizontal deformation of the wharves. Therefore, it was concluded that introducing the joint stiffness in calculating the deformations of open piled wharves was important to achieve reasonable accuracy.

• Structural Engineering and Mechanics
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• v.74 no.1
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• pp.1-18
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• 2020

For the large deformation of shear walls under vertical and horizontal loads, there are difficulties in obtaining accurate simulation results using the response analysis method, even with fine mesh elements. Furthermore, concrete material nonlinearity, stiffness degradation, concrete cracking and crushing, and steel bar damage may occur during the large deformation of reinforced concrete (RC) shear walls. Matrix operations that are involved in nonlinear analysis using the traditional finite-element method (FEM) may also result in flaws, and may thus lead to serious errors. To solve these problems, a planar four-node element was developed based on vector mechanics. Owing to particle-based formulation along the path element, the method does not require repeated constructions of a global stiffness matrix for the nonlinear behavior of the structure. The nonlinear concrete constitutive model and bilinear steel material model are integrated with the developed element, to ensure that large deformation and damage behavior can be addressed. For verification, simulation analyses were performed to obtain experimental results on an RC shear wall subjected to a monotonically increasing lateral load with a constant vertical load. To appropriately evaluate the parameters, investigations were conducted on the loading speed, meshing dimension, and the damping factor, because vector mechanics is based on the equation of motion. The static problem was then verified to obtain a stable solution by employing a balanced equation of motion. Using the parameters obtained, the simulated pushover response, including the bearing capacity, deformation ability, curvature development, and energy dissipation, were found to be in accordance with the experimental observation. This study demonstrated the potential of the developed planar element for simulating the entire process of large deformation and damage behavior in RC shear walls.

• 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.