• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.20 no.1
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• pp.40-46
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• 2011

This paper is to investigate the effects of the asymmetrical support stiffness on the stability of a supercritical driveshaft with asymmetrical shaft stiffness and anisotropic bearings. The equations of motion is derived for a system including a rigid disk, a massless flexible asymmetric shaft, anisotropic bearings and a support beam. The Floquet theory is applied to perform the stability analysis with the variation of the support stiffness, the shaft asymmetry, the shaft damping and the shaft speed. The results show that the asymmetric support stiffness is closely related to the stability caused by primary resonance as well as the supercritical operation. First, the stiffness variation can stabilize the system around primary resonance by weakening the parametric resonance from the shaft asymmetry. Second, it also improve the stability characteristics at a supercritical operation when the support stiffness is not so high relative to the shaft stiffness.

• Proceedings of the KSR Conference
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• 2007.11a
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• pp.1071-1076
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• 2007

In high-speed line, at some part of the track which rubber ballast-mat installed, track irregularity grew rapidly and affected riding comfort and train running stability. It is urgently requested to establish counter-measures which can be applied to track under operation. To do this, it is very important to analysis the origin of that phenomenon before. Track support stiffness is an essential factor for evaluating track condition. Sudden changes of support stiffness along track occur instability of train and bad riding comfort. Preventing sudden changes of track support stiffness is a key technique in high-speed track maintenance. Besides the sudden changes, the magnitude itself also significantly affects track and train. Low stiffness of ballast-mat makes ballast acceleration area wider. And it may accelerate track irregularity growth. So, the stiffness should be limited. To calculate track stiffness, measuring load and displacement on track is needed. In this study, the behavior of the track which rubber ballast-mat installed was measured and analyzed to understand the origin of rapid growth of it.

• Journal of the Korean Society for Railway
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• v.14 no.3
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• pp.262-270
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• 2011

Track support stiffness which affected track maintenance and riding comfort had a big effect on the track and train. Also, track support stiffness of the track design which was based on theory differs from track support stiffness of the track generated on the field. Track support stiffness was generated by several factors such as dynamic wheel loads, vertical displacement of track, and stress at rail bottom on the field test. With the results of the field test was compared with theoretical value. This paper analyzed that track support stiffness of ballast depended on condition of ballast, and support stiffness of concrete track also depended on the characteristic of track structures such as, normal elastic fastening system, rail floating system and sleeper floating system. However, on the ballast and concrete track, the designed track support stiffness was underestimated less than the measured track support stiffness. When the track condition was estimated on service line, it would not consider the track condition on the field. Therefore, this study proposed the various track type and the range of track support stiffness based on the experimental test.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.03a
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• pp.346-353
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• 2005

Track substructure(ballast, subgrade) should have sufficient strength and adequate stiffness to fully support track superstructure(rail, fastener, sleeper). Vertical support stiffness of track comes from the sufficient thickness, adequate strength and stiffness of material of substructure layers. Since the vertical support stiffness of track substructure is closely related with the track geometry, the evaluation of the stiffness is very important to understand the track states. This paper introduces the system, which are composed of Ground Penetrating Radar(GPR), Portable Ballast Sampler(PBS), and Light Falling Weight Deflectometer(LFWD), to evaluate substructure condition and summarizes the field test results performed with the reliable system.

• The Journal of the Convergence on Culture Technology
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• v.6 no.2
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• pp.461-466
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• 2020

In this study, the relationship between the track support stiffness and the track impact factor for a sleeper floating track and a turnout system with wood ties currently employed in Korean urban transit was assessed by performing field tests using actual vehicles running along the service lines. Field tests were performed on four track systems (i.e., sleeper floating track, and point, lead and crossing sections of turnout system). The theoretically designed track impact factor and track support stiffness were compared with the corresponding track impact factor and track support stiffness measured through field tests for the target tracks on the service line. The track impact factor for the service line appeared to increase with the deviation of track support stiffness according to vehicle driving direction; therefore, it was inferred that the deviation of track support stiffness between each track section directly affected the track impact factor.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.04a
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• pp.603-607
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• 2008

This paper is to investigate the effects of support conditions on the whirling stability of a supercritical composite driveshaft. Two system parameters are rigorously considered: one is the bending stiffness of the support beam/bearings and the other is the rotating internal damping of the shaft. An analytic model is developed based on finite element methods and an eigenvalue analysis is employed to estimate the shaft stability under supercritical operating conditions. Results show that the internal damping causes the whirling instability at a supercritical speed, as demonstrated in other previous studies. However, the bending stiffness of the support beam is found to affect greatly the stability behaviors of a supercritical shaft and several combinations of the shaft/beam stiffness can be identified to guarantee the stable operation even in a supercritical region.

• Journal of the Korean Society for Railway
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• v.17 no.4
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• pp.281-288
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• 2014

The objective of this study was to estimate the vibration reduction capacities of a floating track system using a resilient rubber mat, and to compare the results with the track support stiffness and track impact factor of a conventional slab track system by performing field tests using actual vehicles running along a service line. The theoretically designed track support stiffness and track impact factor were compared with the measured track support stiffness and track impact factor for each tested track. The calculated and measured track support stiffness of the floating track system were found to be similar, and the floating track system satisfied the design specifications of the track impact factor. The overall vibration level and track support stiffness of the floating track system were thereupon found to be significantly lower than those of the conventional slab track system. The experimental results thus showed that the vibration reduction effect of the floating track system is greater than that of the conventional slab track.

• Structural Engineering and Mechanics
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• v.57 no.1
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• pp.141-159
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• 2016

Bearing joint dynamic parameter identification is crucial in modeling the high speed spindles for machining centers used to predict the stability and natural frequencies of high speed spindles. In this paper, a hybrid method is proposed to identify the dynamic stiffness of bearing joint for the high speed spindles. The hybrid method refers to the analytical approach and experimental method. The support stiffness of spindle shaft can be obtained by adopting receptance coupling substructure analysis method, which consists of series connected bearing and joint stiffness. The bearing stiffness is calculated based on the Hertz contact theory. According to the proposed series stiffness equation, the stiffness of bearing joint can be separated from the composite stiffness. Then, one can obtain the bearing joint stiffness fitting formulas and its variation law under different preload. An experimental set-up with variable preload spindle is developed and the experiment is provided for the validation of presented bearing joint stiffness identification method. The results show that the bearing joint significantly cuts down the support stiffness of the spindles, which can seriously affects the dynamic characteristic of the high speed spindles.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.23 no.10
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• pp.869-877
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• 2013

Tension force of hanger ropes has been recognized and utilized as an important parameter for health monitoring of suspension bridges. Conventional vibration method based on string theory has been utilized to estimate tension forces of relatively long hanger ropes without any problem, however it is convinced that the vibration method is not applicable for shorter hanger ropes in which the influence of flexural stiffness is not ignorable. Therefore, as an alternative of vibration method, a number of feasibility studies of system identification(SI) technique considering flexural stiffness of the hanger ropes are recently performed. In this study, the influence of support condition of the finite element model utilized for the SI method is investigated with numerical examples. The numerical examples are prepared with the specification of the Kwang-Ahn bridge hanger ropes, and it is revealed that the estimation result of the tension force can be varied from -21.6 % to +35.3 % of the exact value according to the consideration of the support condition of FE model. Therefore, it is concluded that the rotational stiffness of the support spring should be included to the list of the identification parameters of the FE model to improve the result of tension estimation.

• Proceedings of the KSR Conference
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• 2001.05a
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• pp.281-288
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• 2001

In order to evaluate the effect of impact load at support stiffness transition area, the field estimations are performed at the transition zone between earthwork and bridge on test operation of KTX. Due to differential settlement caused by the variations of track support stiffness, large impact forces are investigated. However, the measured values such as wheel load, rail stress, displacement and acceleration in the transition area shows that the stiffness changes in the transition area are not abrupt, and the stiffness in the infra track structure varies continuously. In this experimental study, the parameters influencing safety of transition area are not governed by partial or local stiffness because cumulative passing loads are not sufficient on test operation of KTX.