• 한국생산제조학회지
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• 제20권1호
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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.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2007년도 추계학술대회 논문집
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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.

• 한국철도학회논문집
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• 제14권3호
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• pp.262-270
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• 2011

궤도지지강성은 차량이 주행함에 있어 궤도와 차량에 매우 큰 영향을 미치며, 이는 궤도 파괴이론에 근거한 궤도유지관리와 승객의 승차감에 영향을 준다. 또한 궤도설계 시 고려되는 궤도지지강성은 이론에 근거한 계산치이며 이는 공용중인 궤도에서의 실제 궤도지지강성과는 상이하다. 따라서 본 연구에서는 현장측정을 통해 동적 윤중과 레일수직변위, 레일저부응력을 측정하여 궤도지지강성을 산출하였고 이를 이론 궤도지지강성과 비교 분석하였다. 현장측정결과 자갈도상궤도에서의 궤도지지강성은 자갈의 상태에 직접적인 영향을 받으며 콘크리트궤도의 경우 궤도구조별(일반적인 침목매입식, 레일플로팅, 침목플로팅) 궤도구조특성에 직접적인 영향을 받는 것으로 나타났다. 그러나 자갈 및 콘크리트궤도 모두 설계 시 적용되는 궤도지지강성이 측정된 궤도지지강성에 비해 과소평가되는 것으로 분석되었다. 이는 공용중인 궤도의 상태평가 시 현장의 궤도상태를 반영하지 못한 예측 및 평가가 될 소지가 있을 것으로 판단된다. 이에 본 연구에서는 궤도구조형식 및 궤도상태별 궤도지지 강성의 범위를 실험적으로 제시하였다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2005년도 춘계 학술발표회 논문집
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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.

• 문화기술의 융합
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• 제6권2호
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• pp.461-466
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• 2020

본 연구는 도시철도 콘크리트궤도에 적용된 침목플로팅궤도와 목침목 분기기 궤도의 궤도지지강성과 궤도충격계수의 상관관계분석을 위해 운행선 현장측정을 수행하여 분기기 궤도의 위치별 궤도지지강성과 궤도충격계수를 측정하였다. 본선의 일반 궤도구조인 침목플로팅궤도의 궤도지지강성은 침목방진패드의 스프링강성에 지배적인 영향을 받는 것으로 분석되었다. 일반궤도와 분기기 위치별 궤도지지강성의 차이는 궤도충격계수에 직접적인 영향을 미치는 것으로 분석되었다. 연구결과, 침목플로팅 궤도구조와 분기기 궤도구조의 궤도지지강성과 궤도충격계수는 위치별로 큰 차이를 나타내는 것으로 나타났다. 따라서 본선 일반구간과 분기기 궤도의 궤도지지강성의 편차를 최소화 하여 궤도충격을 저감시키는 방안이 필요한 것으로 분석되었다.

• PNF and Movement
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• 제22권2호
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• pp.181-189
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• 2024

Purpose: This study aimed to identify the effect of sling-applied plank exercise on the frequency, stiffness, and decrement of the rectus abdominis and longissimus muscles of the trunk according to the stability of the base of support. Methods: Thirty-three young adults volunteered to participate and were randomly assigned to one of three groups (SS, stable support; LES, lower extremity support; and ULES, upper and lower extremity support) according to the stability of the base of support. The muscular properties of the rectus abdominis and longissimus muscles during sling-assisted plank exercise according to the stability of the base of support. were measured by using Myoton PRO (Myoton AS, Tallinn, Estonia). Statistical analysis was performed MANOVA to determine the effect of sling-assisted plank exercise on the muscular properties of the rectus abdominis and longissimus muscles according to the stability of the base of support. Post hoc analysis was conducted using Bonferroni. The level of statistical significance was set at α = 0.05. Results: When comparing the muscular properties, the muscle frequency and stiffness of the left rectus abdominis of ULES were significantly decreased compared to that of SS (p < 0.05). In the measurement time, the muscle frequency and the muscle stiffness of the right rectus abdominis increased significantly after the intervention (p < 0.05). Conclusion: It was concluded that the more unstable the base of support (ULES), the higher the exercise strength, and the muscle frequency and stiffness decreased on the rectus abdominis at rest.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2008년도 춘계학술대회논문집
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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.

• 한국철도학회논문집
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• 제17권4호
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• pp.281-288
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• 2014

본 연구는 고가정거장 구간에 부설된 고무방진매트 플로팅궤도시스템의 방진성능 및 적용효과를 실험적으로 입증하고자 고무방진매트가 적용되지 않은 개소와 비교 측정을 수행하였다. 또한 고무방진매트 플로팅 궤도시스템의 측정 궤도지지강성 및 궤도충격계수를 산출하고 이론 및 설계치와 비교하여 현재 시공된 고무방진매트 플로팅궤도시스템에 대한 궤도상태의 건전성 및 궤도 충격의 수준을 평가하였다.

• Structural Engineering and Mechanics
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• 제57권1호
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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.

• 한국소음진동공학회논문집
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• 제23권10호
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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.