• Title, Summary, Keyword: 임계속도

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비선형 임계속도 검증을 위한 실험적 연구

  • 정우진;김성연
    • Proceedings of the KSR Conference
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    • pp.574-581
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    • 1999
  • 비선형 임계속도를 주행시험대를 이용하여 측정하였으며 비선형 임계속도가 관성에 의한 과도 현상이 아님을 확인하기 위하여 주행속도를 연속 그리고 불연속적으로 감가속 하면서 선형 및 비선형 임계속도를 측정하였다. 또한 차량의 안정성을 간편하게 예측할 때 대차모델만을 사용하던 종래의 방법이 타당한지 확인하였으며 차량의 임계속도와 응답주파수를 예측하기 위하여 산업체에서 사용되던 간편 식들의 정확성을 검토한 결과 다음의 결과를 도출할 수 있었다. (중략)

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Critical Speed Analysis of a 75 Ton Class Liquid Rocket Engine Turbopump due to Load Characteristics (75톤급 액체로켓엔진 터보펌프의 하중 특성에 따른 임계속도 해석)

  • Jeon, Seong-Min;Kwak, Hyun-D.;Hong, Soon-Sam;Kim, Jin-Han
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • pp.22-29
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    • 2011
  • Critical speed of high thrust liquid rocket engine turbopump is obtained through a rotordynamic analysis and a unloaded turbopump test is peformed for validation of the numerical model. The first critical speed predicted by the numerical analysis is correlated well with the test result for the bearing unloaded rotor condition only considering mass unbalance load. Using the previous rotordynamic model, critical speed variation is estimated as a function of varied bearing stiffness due to pump and turbine radial loads with relative angle difference. From the numerical analysis, it is found that the relative angle difference of pump and turbine radial loads greatly affects the critical speed. However, additional axial load reduces the effect derived from the relative angle difference of radial loads.

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Critical Speed Analysis of a 75 Ton Class Liquid Rocket Engine Turbopump due to Load Characteristics (75톤급 액체로켓엔진 터보펌프의 하중 특성에 따른 임계속도 해석)

  • Jeon, Seong-Min;Kwak, Hyun-D.;Hong, Soon-Sam;Kim, Jin-Han
    • Journal of the Korean Society of Propulsion Engineers
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    • v.16 no.4
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    • pp.42-49
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    • 2012
  • Critical speed of high thrust liquid rocket engine turbopump is obtained through a rotordynamic analysis and a unloaded turbopump test is peformed for validation of the numerical model. The first critical speed predicted by the numerical analysis is correlated well with the test result for the bearing unloaded rotor condition only considering mass unbalance load. Using the previous rotordynamic model, critical speed variation is estimated as a function of varied bearing stiffness due to pump and turbine radial loads with relative angle difference. From the numerical analysis, it is found that the relative angle difference of pump and turbine radial loads greatly affects the critical speed. However, additional axial load reduces the effect derived from the relative angle difference of radial loads.

An Experimental Study of Critical Velocity in Sloping Tunnel Fires (경사 터널내 화재시 임계속도에 관한 실험적 연구)

  • 이성룡;김충익;유홍선;김혁순;전명배
    • Fire Science and Engineering
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    • v.18 no.1
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    • pp.49-53
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    • 2004
  • In this study, reduced-scale experiments were conducted to analyze an effect of tunnel slope on critical velocity. The 1/20 scale experiments were carried out under the Froude scaling using ethanol pool fire. Square pools ranging from 2.47 to 12.30㎾ were used experiments. Critical velocity varied with one-fourth power of the heat release rate. As the slope of the tunnel increases the critical velocity comes to be fast due to the increase of the chimney effect.

Dynamic Response for Critical Velocity Effect Depending on Supporting Stiffness of High-Speed Railway Trackbed (고속철도 노반지지조건에 따른 임계속도효과의 동적응답)

  • Lee, Il-Wha
    • Journal of the Korean Geotechnical Society
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    • v.29 no.1
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    • pp.5-12
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    • 2013
  • The critical velocity effect on railway trackbed means the amplification of vibration energy when the train running-speed and group velocity of ground surface wave are superimposed. It is called a pseudo-resonance phenomenon of time domain. In the past, it was not issued because the train speed was low and the ground group velocity was higher. But since the high-speed train is introduced, critical velocity reported causing a track irregularity. So far, theoretical analysis has been performed because of the complexity of formation process. However it requires reasonable consideration which is similar to actual track and trackbed conditions. In the present paper, finite element analysis to verify the critical velocity effect is performed considering each track structure and trackbed supporting stiffness. As a result, the deformation amplification caused by the critical velocity effect is verified to analyze each supporting stiffness and track system.

Calculation of Critical Speed of Railway Vehicle by Multibody Dynamics Analysis (다물체 동역학 해석방법을 이용한 철도차량의 임계속도 계산)

  • Kang, Juseok
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.37 no.11
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    • pp.1371-1377
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    • 2013
  • In this analysis, a method is presented to calculate the critical speed of a railway vehicle by using a multibody dynamic model. The contact conditions and contact forces between the wheel and the rail are formularized for the wheelset model. This is combined with the bogie model to obtain a multibody dynamic model of a railway vehicle with constraint conditions. First-order linear dynamic equations with independent coordinates are derived from the constraint equations and dynamic equations of railway vehicles using the QR decomposition method. Critical speeds are calculated for the wheelset and bogie dynamic models through an eigenvalue analysis. The influences of the design parameters on the critical speed are presented.

Effectiveness of critical velocity method for evacuation environment in a railroad tunnel at fire situation (철도터널 내 화재 시 대피환경 확보를 위한 임계속도 산정식의 유효성 평가)

  • Lee, Seung-Chul;Lee, Jae-Heon;Lee, Seung-Ho
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.6 no.1
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    • pp.51-59
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    • 2004
  • The effectiveness of one dimensional critical velocity method for evacuation environment at 10MW fire size in a railroad tunnel have been investigated in this paper by three dimensional CFD method. It was performed to evaluate the evacuation environment in terms of temperature distribution, visible distance distribution and CO concentration at some tunnel inlet velocity, 1m/s, 2m/s (near critical velocity), and 3m/s. At all inlet velocity, passenger should give away downward the flow direction because the inlet velocity can not afford to sufficient evacuation environment for passengers. In case of 3m/s inlet velocity, however, the evacuation environment for passengers is better than the other cases. To provide more safe evacuation environment on fire situation, tunnel inlet velocity should be larger than critical velocity.

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Numerical Simulation of Self-Compensating Dynamic Balancer in a Rotating Mechanism (수치해석을 통한 자기보상 동적균형기의 작동성 검토)

  • 이종길
    • Journal of the Korean Society for Precision Engineering
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    • v.12 no.1
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    • pp.142-151
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    • 1995
  • 회전체의 자동밸런싱을 위하여 고안된 자기보상 동적균형기는 홈이파인 원판에 강구와 저점성유체를 지닌 구조체이다. 유도된 운동방정식으로 부터 자기보상 동적균형기의 작동조건을 조사하기 우하여 수치해석을 통한 동 특성을 검토하였다. 수치해석의 결과에 근거하여 임계속도보다 높은 범위에서는 자기보상 동적균형기는 정상작동을 보여주었다. 임계속도에서는 회전계의 균형이 강구와 점성유체와의 감쇠계수에 의존하였으나 임계속도보다 낮은 범위에서는 어떠한 조건에 대해서도 작동하지 않음을 알 수 있었다. 자동차 및 항공기에도 응용가은한 자기보상 동적균형기의 작동조건들을 본 논문에서 예시하였다.

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Detecting Location and Depth of Cracks in Rotor using Critical Speed (임계속도를 이용한 로터의 결함 위치와 크기 판별)

  • Kim, Heung-Su;Jo, Maeng-Hyo
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.34 no.5
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    • pp.39-45
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    • 2006
  • Structural health monitoring has been conducted by non-destructive evaluation method when a turbine rotor system of an aircraft engine has cracks. Local stiffness of a turbine rotor system is degraded and critical speed is changed due to the presence of cracks in rotor. Critical speed which is affected by location and depth of crack, is obtained using compliance matrix of cracked rotor. The database of the obtained critical speed is used to evaluate structural health monitoring of a rotor system of a gas turbine engine.

A Study on the Critical Speed of 1/5 Scaled Bogie Model (1/5 스케일 축소대차 모델 임계속도에 관한 연구)

  • Hur, Hyun-Moo;Park, Joon-Hyuk;Kim, Min-Soo;You, Won-Hee;Park, Tae-Won
    • Journal of the Korean Society for Railway
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    • v.10 no.6
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    • pp.800-805
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    • 2007
  • The critical speed of railway bogie is very important in terms of the verification of the vehicle design procedure and safety. The dynamic performance of bogie is tested on the railway roller rig in a laboratory in place of field testing on track. But, the testing on the full scale roller rig caused many problems relating to test costs, test time and has the difficulty in test condition setup. To overcome these problems, scaled models were used in the filed of railway vehicle design and test. In this paper, we have studied the critical speed of scaled bogie model. We have made the 1/5 scaled bogie, the scaled roller rig and analyzed the critical speed of the scaled bogie through the numerical simulation and running test of the scaled bogie. We have confirmed that the analysis results of the critical speed correspond with the test results.