• Earthquakes and Structures
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• v.7 no.6
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• pp.1171-1186
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• 2014

Damping is one of the parameters that control the performance of structures when they are subjected to seismic, wind, blast or other transient shock and vibration disturbances. By adding supplemental viscous dampers, the energy input from a transient deformation is absorbed, not only by the structure itself, but also by the supplemental dampers. The aim of this study is to evaluate the values of both damping and ductility reduction factors for steel moment resisting frames with supplemental linear viscous dampers. Two-dimensional finite element models have been established for a range of low to mid rise buildings with different parameters: number of floors; number of bays; and number of dampers with different supplemental damping ratios (from 5% to 30%). A parametric study has been performed using time history analyses and a well-documented research method (N2-method). In addition, an equation has been proposed for each reduction factor based on regression analysis for the obtained results. The results of the Time history analyses are compared with those of a modified N2-method. Moreover, a comparison with values specified in the European code EC8 and the Egyptian code ECP-201 has been performed.

• Journal of Korean Association for Spatial Structures
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• v.21 no.4
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• pp.31-38
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• 2021

The precast-buckling restrained braces(PC-BRB) reinforced with engineering plastics that can compensate for the disadvantages in the manufacturing process of the existing buckling restrained brace. In this study, to examine the applicability of PC-BRB to actual structures, example structures similar to school facilities were selected and the reinforcement effect was analyzed analytically according to the damping design procedure of PC-BRB. Load-displacement curve through the incremental loading test appeared similar to the bilinear curve. Applying test result, Analytical model of PC-BRB model was constructed and applied to the example structure. As a result of the analysis, the PC-BRB showed stable hysteresis behavior without lowering the strength, and the inter story drift ratio and the shear force were reduced due to the damping effect. In addition, the reduction ratio of the shear force was similar to the reduction ratio assumed when designing the damping device.

• Journal of the Korea institute for structural maintenance and inspection
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• v.13 no.2 s.54
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• pp.165-171
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• 2009

This research developed two semi-active MR dampers whose gaps in the orifice area were different from each other, and evaluated their damping performance by loading tests. The Damping performance of MR dampers characteristically depends on various factors like their material and mechanical ones, but most importantly on the size of gap in the orifice area. For this research, we designed the orifice gaps of two dampers as each 1.0mm and 2.0mm, both with the 80mm outer diameter of the orifice. We also designed two loading test sets with different input currents, and acquired different control ability from them. The acquired test results were analyzed and evaluated with their maximum and minimum damping force and also their dynamic range from the force-displacement hysteresis loops and the force-input current relationship curve. This research clearly proved how the damping performance of control devices depends on the gap effect, and also presented a possibility that the two dampers developed in this research could be used for the smart control of construction structures by effectively adapting the input current and the number of coil turns.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.369-374
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• 2007

This paper presents yaw vibration control performances of railway vehicle featuring controllable magnetorheological damper. A cylindrical type of MR damper is devised and its damping force is evaluated by considering fluid resistance and MR effect. Design parameters are determined to achieve desired damping force level. The MR damper model is then incorporated with the governing equations of motion of the railway vehicle which includes vehicle body, bogie and wheel-set. Subsequently, computer simulation of vibration control via proportional-integral-derivative (PID) controller is performed using Matlab. Various control performances are demonstrated under external excitation by creep force between wheel and rail.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.18 no.5
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• pp.524-532
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• 2008

This paper presents yaw vibration control performances of railway vehicle featuring controllable magnetorheological damper. A cylindrical type of MR damper is devised and its damping force is evaluated by considering fluid resistance and MR effect. Design parameters are determined to achieve desired damping force level. The MR damper model is then incorporated with the governing equations of motion of the railway vehicle which includes vehicle body, bogie and wheel-set. Subsequently, computer simulation of vibration control via proportional-integral-derivative(PID) controller is performed using Matlab. Various control performances are demonstrated under external excitation by creep force between wheel and rail.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.20 no.6
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• pp.685-691
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• 2011

The Bearing preload units are used for stable rotational movements of high speed spindles. The feeding mechanism of the preload unit is important to prevent overheat of bearings and to keep constant bearing load under thermal deformation of spindle unit. In this study, ball slide guide and ball bush as feeding mechanism of preload unit are selected. The maximum static friction force, radial stiffness and damping ratio of ball slide guide with ball load, ball number and ball size are widely investigated. In conclusion, the surface of ball slide guide must be heat treated to reduce static friction force. The number and size of ball are increased to control sensitive bearing preload force.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1996.10a
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• pp.295-300
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• 1996

In this study, the dynamic instabilities of a nonlinear elastic system subjected to follower force are investigated. The two-degree-of-freedom double pendulum model with nonlinear geometry, cubic spring, and linear viscous damping is used for the study. The constant and periodic follower forces are considered. The chaotic nature of the system is identified using the standard methods, such as time histories, phase portraits, and Poincare maps, etc.. The responses are chaotic and unpredictable due to the sensitivity to initial conditions. The sensitivities to parameters, such as geometric initial imperfections, magnitude of follower force, and viscous damping, etc. is analysed. The strange attractors in Poincare map have the self-similar fractal geometry. Dynamic buckling loads are computed for various parameters, where the loads are changed drastically for the small change of parameters.

• Journal of Advanced Marine Engineering and Technology
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• v.6 no.2
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• pp.69-91
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• 1982

The major factors which affect the crankshaft axial vibration are such items as the axial stiffness and mass of crankshaft, the thrust block stiffness, the propeller's entrained water and the exciting and damping forces of engine, propeller and shafting. Among above mentioned items, the axial stiffness and mass of crankshaft, thrust block stiffness and propeller's entrained water were treated in detail in part I, and so in this paper, the rest of above items will be studied. The exciting forces of crankshaft axial vibration are generated mainly from the gas explosion pressure of cylinder, the thrust fluctuation of propeller, and sometimes the torsional vibration of crankshaft induces the crankshaft axial vibration. As for the propeller thrust fluctuation, its harmonic components can be fairly exactly calculated from the experimental results of propeller in the towing tank, but as the calculation process is rather tedious and laborious, the empirical values are ordinarily used. On the other hand, the table of harmonic components of gas pressure has been already published by major slow speed diesel engine makers, but the axial thrust conversion factor of radial force is not unknown yet, and as its estimated value is unreliable, the axial vibration force of gas pressure is uncertain. As the calculation of damping force is very complicated and it includes some uncertain factors, the thoretically estimated amplitudes of axial vibration are much more incorrect in comparison with those of torsional vibrations. Authors have paid special attentions to deriving the theoretical calculation formula of axial conversion factor of radial force and damping force of crankshaft axial vibration and developed a computer program to calculate resonance amplitudes and additional stresses of crankshaft axial vibrations. Also, to check the reliability of the developed computer program, the axial vibrations of three ships' propulsion shaftings were analyzed and their results were compared with those of measured values and makers' results.

• Journal of the Korean Institute of Gas
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• v.12 no.4
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• pp.46-51
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• 2008

The damping of a shock absorption device composed of nonlinear disk spring stacks and rubber rings was investigated. Friction forces of rubber rings and hysteresis of disk springs were obtained experimentally. The hysteresis curves of several types of disk spring stacks were approximated, from which the energy dissipated was estimated. Based upon the friction force and the energy dissipated, 4 damping models were presented and shock responses of the damping models were investigated. The hysteresis of disk spring is more meaningful than the friction of the rubber ring for the damping. For practical use, equivalent viscous damping model for total energy dissipated per cycle was suggested.

• Journal of Korean Association for Spatial Structures
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• v.22 no.4
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• pp.31-38
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• 2022

In this study, an incremental loading test of the HRS(Hybrid Rubber Slit) damper was additionally performed to define the physical characteristics according to the incremental test results, and an analytical study was performed according to the damping design procedure by selecting an example structure. As a result of performing seismic performance evaluation before reinforcement by selecting a RC structure similar to an actual school structure as an example structure, the story drift ratio was satisfied, but some column members collapsed due to bending deformation. In order to secure the seismic performance, the damping design procedure of the HRS damper was presented and performed. As a result of calculating the amount of damping device according to the expected damping ratio and applying it to the example structure, the hysteresis behavior was stable without decrease in strength, and the story drift ratio and the shear force were reduced according to the damping effect. Finally the column members that had collapsed before reinforcement satisfied the LS Level.