• Title, Summary, Keyword: Critical speed

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Evaluation of Critical Speed for Active Steering Bogie Prototype (능동형 시제 조향대차의 임계속도 평가)

  • Hur, Hyun Moo;Park, Joon-Hyuk
    • Journal of the Korean Society for Precision Engineering
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    • v.34 no.3
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    • pp.205-210
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    • 2017
  • Critical speed analysis was conducted for a active steering bogie prototype, developed to improve the curving performance of railway vehicles. The critical speed for the design concept was about 169.2k m/h. To validate the analysis result, we performed a critical speed test for the prototype bogie using a roller-rig tester. The test results showed that the critical speed for the prototype bogie was about 165 km/h. From the analysis and test results, The critical speed for the prototype bogie was determined to be 165 km/h. Considering the maximum operating speed of the test vehicle is 100 km/h, the prototype bogie is considered stable.

DDM Rotordynamic Design Sensitivity Analysis of an APU Turbogenerator Having a Spline Shaft Connection

  • Lee, An-Sung;Ha, Jin-Woong
    • Journal of Mechanical Science and Technology
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    • v.17 no.1
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    • pp.57-63
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    • 2003
  • An eigenvalue design sensitivity formulation of a general nonsymmetric-matrix rotor-bearing system is devised. using the DDM (direct differential method). Then, investigations on the design sensitivities of critical speeds are carried out for an APU turbogenerator with a spline shaft connection. Results show that the dependence of the rate of change of the critical speed on the stiffness changes of bearing models of spline shaft connection points is negligible, and thereby their modeling uncertainty does not present any problem. And the passing critical speeds up to the 4th critical speed are not sensitive to the design stiffness coefficients of four main bearings. Further, the dependence of the rate of change of the critical speed on the shaft-element length changes shows quantitatively that the spline shaft has some limited influence on the 4th critical speed but no influence on the 1st to 3rd critical speeds. With no adverse effect from the spline shaft, the APU system achieves a critical speed separation margin of more than 40% at a rated speed of 60,000 rpm.

A study on the Critical speed of Korean Tilting Train (한국형 틸팅열차의 임계속도에 관한 연구)

  • Kim, Nam-Po;Kim, Jung-Seok;Park, Tae-Won
    • Proceedings of the KSR Conference
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    • pp.162-168
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    • 2007
  • The critical speed above which the vehicle become unstable should be fundamentally verified in the development of new train. In case of high speed tilting train, which require both higher critical speed and higher curving speed, the critical speed should be more carefully treated because the both requirements are conflicting each other in the conventional train design. This research has been performed to estimate the linear and non-linear critical speed of 200km/h Korean Tilting Train which has been developing. The newly developed self-steering mechanism was attached to the tilting train to secure critical speed under the lower yaw stiffness which was inevitable to secure higher curving performance. The simulation to predict critical speed was done by commercial vehicle dynamic S/W. Full scale roller rig test was carried out for the validation of numerical results and effectiveness of self-steering mechanism.

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Study on the Prediction of the Nonlinear Critical Speed of a Train (철도차량의 비선형 임계속도 예측연구)

  • 정우진;오일근;허만선;김성원;서정희;조광수
    • Proceedings of the KSR Conference
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    • pp.313-320
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    • 1998
  • The critical speed of a train running on the straight railway track is investigated by in-house program. The program is developed to find out nonlinear critical speed and it bases on the bifurcation theory. As a result, it is found that nonlinear critical speed exists on the lower speed band than linear critical speed and this fact imply a possibility of induction of a big accident.

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A study on the Critical speed of Korean Tilting Train Hanbit200 (한국형 틸팅열차 한빛200의 임계속도에 관한 연구)

  • Kim, Nam-Po;Kim, Jung-Seok;Park, Tae-Won
    • Journal of the Korean Society for Railway
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    • v.10 no.3
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    • pp.257-263
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    • 2007
  • The critical speed above which the vehicle become unstable is one of the items that should be verified in the development of a new train. In the case of a high speed tilting train, which requires both higher critical speed and higher curving speed, the critical speed should be more carefully treated because the both requirements are in conflict with each other in the conventional train design. The main purpose of the present work is to estimate the linear and non-linear critical speeds of 200km/h Korean Tilting Train 'Hanbit200' under development. The newly developed self-steering mechanism was attached to the tilting train to ensure that the critical speed falls under the lower yaw stiffness which is needed to secure higher curving performance. The simulation for predicting the critical speed was done by a commercially available vehicle dynamics software. A full scale roller rig test was carried out to validate the numerical results and to verify the effectiveness of the self-steering mechanism.

Critical Speed Analysis of Geogrid-Reinforced Rail Roadbed (지오그리드로 보강된 철도노반의 한계속도에 관한 연구)

  • 신은철;이규진;오영인
    • Proceedings of the KSR Conference
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    • pp.534-539
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    • 2001
  • This paper presents the critical speed analysis of geogrid-reinforced rail roadbeds on soft soil. A rail roadbed on soft ground must be designed to avoid intolerable stress in the underlying soil and to give sufficient support for the rail system. At high speeds, the deformation of rail systems will gain dynamic amplification, and reach excessive values as a certain speed, here termed critical speed is approached. The elastic Winkler foundation model was used to predict the critical speed of geogrid-reinforced rail roadbeds on soft soil and the model properties were determined by the in-situ cyclic plate load test. Based on the parametric study of elastic beam on Winkler foundation model, the critical speed increase with the increase of the flexural risidity of subgrade EI and the stiffness coefficient of Winkler foundation k. From the in-situ cyclic load tests and analysis of elastic beam on Winkler foundation model, the critical speed increase with increase in number of reinforced layer and non-dimensional value for depth of first geogrid layers and the thickness of reinforced rail roadbed u/d.

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A Study on Spindle Shape Design using Design of Experiments (실험계획법을 이용한 주축 형상 설계에 관한 연구)

  • Shin, Jae-Ho;Lee, Choon-Man
    • Journal of the Korean Society for Precision Engineering
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    • v.26 no.4
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    • pp.120-127
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    • 2009
  • Spindle units of machine tool are very important part in the manufacturing area. Recently high speed machining has become the main issue of metal cutting. To develop high speed machine tools, a lot of studies have been carried out for high speed spindle. Due to increase of the rotational speed of the spindle, there has been renewal of interest in vibration of spindle. This paper concerns the improvement of spindle design using design of experiments. To improve the design of critical speed and weight of spindle, the experiments using central composite method have been carried out. The targets are critical speed and weight of spindle. For optimization of critical speed and weight and optimization of only critical speed by operation of all area search through response optimizer, the result of analysis has improved design of each factor. Finite element analyses are performed by using the commercial codes ARMD, CATIA V5 and ANSYS workbench. From the results, it has been shown that the proposed method is effective for modification of spindle design to improve critical speed and weight.

A Study on the Factors Influencing the Abnormal Vibration of the Lateral Direction in Railway Vehicles Caused by Hysteresis of Critical Speed (임계속도 이력현상에 의한 철도차량 횡방향 이상 진동에 영향을 미치는 인자들에 관한 연구)

  • 정우진;심재경;조동현
    • Journal of KSNVE
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    • v.11 no.2
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    • pp.265-275
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    • 2001
  • This research has been performed to reveal the hysteresis phenomena of the hunting motion in a railway passenger cars. It is found that there are some factors and its operation region to make the nonlinear critical speed reacts to them more sensitively than the linear critical speed. The simulation results show that a self steering bogie system can be a substitute proposal to improve curving Performance together with the reduction of hysteresis of critical speed. Full scale roller rig test is carried out for the validation of the numerical results. Finally, it is certified that wear of wheel profile and stiffness discontinuities of wheelset suspension caused by deterioration have to be considered in the analysis to predict the hysteresis of critical speed precisely.

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Critical Speeds Evaluation of Turbo Pump Unit with a Elasticring Inserted Ball Bearing (탄성 링을 갖는 볼 베어링 지지의 터보 펌프 임계 속도에 관한 연구)

  • Lee, Yong-Bok;Kim, Chang-Ho;Kwak, Hyun-Duck;Ha, Tae-Woong;Yoo, Woo-Chul
    • The KSFM Journal of Fluid Machinery
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    • v.4 no.2
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    • pp.22-28
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    • 2001
  • This study was performed to evaluate the dynamic behavior of turbo pump unit. The acceptable separate margin of $1^{st}$ critical speed was obtained by the use of elastic-ring inserted ball bearing, while the poor separate margin of $1^{\st}$ critical speed was appeared in the case without the elastic-ring. In addition, the results show that the stiffness and damping of plain seals give more separate margin of $2^{nd}$ critical speed. However the wear or the failure of seals could reduce the $2^{nd}$ critical speed near the operating speed.

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CRITICAL SPEED ANALYSIS OF JUDDERING DUE TO CHANGE IN SURFACE TEMPERATURE OF DISK BRAKE

  • Kim, M.G.;Cho, C.
    • International Journal of Automotive Technology
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    • v.7 no.6
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    • pp.697-702
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    • 2006
  • The change in the critical speed due to surface temperature of automotive disk brakes may be analyzed both theoretically as well as experimentally. Juddering of disk brakes is closely related to its critical speed. In analyzing the critical speed, if $\sigma$ is positive, Disk develops TEI(Thermo-Elastic Instability) resulting in juddering in disk brakes. And $\sigma$ is affected not only by the critical speed but also by the initial temperature of disk surface. As the initial temperature of the disk surface rises, the critical speed decreases and juddering is developed more easily. Also, when hot spots are developed by TEI, they show large temperature difference in small local range.