• Title/Summary/Keyword: Dynamic Coefficients

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Dynamic Friction Behavior of Interfaces Between Dense Dry Granular Soils and Construction Material(Concrete) (조밀한 건조조립토와 건설재료(콘크리트) 사이의 동마찰계수)

  • 김대상
    • Journal of the Korean Geotechnical Society
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    • v.17 no.6
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    • pp.207-213
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    • 2001
  • Shaking table tests to investigate the dynamic friction behavior of interfaces between dense dry granular soils and construction material(concrete) were performed and the results are reported. The results show the variation of dynamic interface friction coefficients between dense dry granular soils and construction material was small in the sliding velocity range employed in this study. It was also observed that dynamic interface friction coefficients decreased as mean grain sizes of granular soils increased. These coefficients were compared with the friction coefficients obtained from the peak internal friction angles of the same granular soils by plane strain compression tests.

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Dynamic Coefficients of a High-Speed Rotor Supported by a Slotted ER Squeeze Film Damper (ER 스퀴즈 필름 댐퍼로 지지된 고속 회전 로터의 동적 계수에 관한 연구)

  • 이용복;김창호;정시영;이남수;최동훈
    • Journal of KSNVE
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    • v.10 no.6
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    • pp.1029-1034
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    • 2000
  • A new electro-rheological squeeze film damper (ER-SFD) has been sealed with slotted piston rings which have electrodes at the inside of the constant gap. The slotted ER-SFD can prevent the problem of electric discharge which might be occurred in the previous configuration of an ER-SFD. The current paper presents the extraction of linearized dynamic coefficients within small orbit where these coefficients are controlled by the application of electric strength. Test rig has been modified to isolate the damper section for dynamic coefficient extraction. The results show that rotordynamic coefficients, damping and inertia terms, increase with increasing supply voltages, while stiffness coefficients decrease with increasing supply voltages. notating speed of rigid shaft does not affect these coefficients.

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Study on the Electromagnetic Excitation System for the Measurement of Dynamic Coefficients of Air Foil Bearing for High Speed Rotor (초고속 회전체용 공기 포일 베어링의 동특성 계수 측정을 위한 전자석 가진장치에 관한 연구)

  • Park, Cheol-Hoon;Choi, Sang-Kyu;Ham, Sang-Yong
    • The KSFM Journal of Fluid Machinery
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    • v.16 no.3
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    • pp.18-25
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    • 2013
  • Recently the requirement of long-term mobile energy source for mobile robot or small-sized unmanned vehicle is highly increased, and the micro turbine generator(MTG) which is known to have high energy and power density is under development. MTG is designed to have air foil bearing and high speed rotor of which operating speed is 400,000rpm. In the development stage of high speed rotor and bearing, stability analysis for the full operational speed range is essential and the dynamic coefficients such as stiffness and damping coefficients of bearing depending on the rotational speed are required for that. Although perturbation method is usually used to identify the dynamic coefficients, it's not easy to give the perturbation to the high speed rotating rotor. In this study, we present the dynamic coefficients measurement system for air foil bearing which consists of electromagnets, gap sensors, high speed motor and controller. This measurement system can exert the sine sweep force to the rotor-bearing, measure the displacement of rotor and get FRF(Frequency response function) of rotor-bearing. The least square estimation method is applied to identify the dynamic coefficients of bearing from the measured frequency response at the different rpm and the identified dynamic coefficients for the wide rotational speed range are presented.

Dynamic coefficients of A High-Speed Rotor Supported by A Slotted ER Squeeze Film Damper (ER 스퀴즈 필름 댐퍼로 지지된 고속 회전 로터의 동적 계수에 관한 연구)

  • Lee, Yong-Bok;Kim, Chang-Ho;Seok, Ki-Young;Lee, Nam-Soo;Choi, Dong-Hoon
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2000.06a
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    • pp.1286-1291
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    • 2000
  • A new electro-rheological squeeze film damper (ER SFD) has been sealed with slotted piston rings which have electrodes at the inside of the constant gap. The slotted ER SFD can prevent the problem of electric discharge which might be occurred in the previous configuration of an ER SFD. The current paper presents the extraction of linearized dynamic coefficients within small orbit where these coefficients are controlled by the application of electric strength. Test rig has been modified to isolate the damper section for dynamic coefficient extraction. The results show that rotordynamic coefficients, damping and inertia terms, increase with increasing supply voltages, while stiffness coefficients decrease with increasing supply voltages. Rotating speed of rigid Shaft does not affect these coefficients.

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Static and dynamic responses of a tied-arch railway bridge under train load

  • Gou, Hongye;Yang, Biao;Guo, Wei;Bao, Yi
    • Structural Engineering and Mechanics
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    • v.71 no.1
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    • pp.13-22
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    • 2019
  • In this paper, the static and dynamic responses of a tied-arch railway bridge under train load were studied through field tests. The deflection and stresses of the bridge were measured in different static loading scenarios. The dynamic load test of the bridge was carried out under the excitation of running train at different speeds. The dynamic properties of the bridge were investigated in terms of the free vibration characteristics, dynamic coefficients, accelerations, displacements and derailment coefficients. The results indicate that the tie of the measuring point has a significant effect on the vertical movement of the test section. The dynamic responses of arch bridge are insensitive to the number of trains. The derailment coefficients of locomotive and carriage increase with the train speed and symmetrically distributed double-line loads reduce the train derailment probability.

Modeling and Analysis of SEIG-STATCOM Systems Based on the Magnitude-Phase Dynamic Method

  • Wang, Haifeng;Wu, Xinzhen;You, Rui;Li, Jia
    • Journal of Power Electronics
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    • v.18 no.3
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    • pp.944-953
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    • 2018
  • This paper proposes an analysis method based on the magnitude-phase dynamic theory for isolated power systems with static synchronous compensators (STATCOMs). The stability margin of an isolated power system is greatly reduced when a load is connected, due to the disadvantageous features of the self-excited induction generators (SEIGs). To analyze the control process for system stability and to grasp the dynamic characteristics in different timescales, the relationships between the active/reactive components and the phase/magnitude of the STATCOM output voltage are derived in the natural reference frame based on the magnitude/phase dynamic theory. Then STATCOM equivalent mechanical models in both the voltage time scale and the current time scale are built. The proportional coefficients and the integral coefficients of the control process are converted into damping coefficients, inertia coefficients and stiffness coefficients so that analyzing its controls, dynamic response characteristics as well as impacts on the system operations are easier. The effectiveness of the proposed analysis method is verified by simulation and experimental results.

Determination of the Dynamic Coefficients of the Coupled Journal and Thrust Bearings by the Perturbation Method (수학적 섭동법을 이용한 저널과 스러스트가 연성된 유체 동압 베어링의 동특성 계수 해석)

  • Lee, Sang-Hoon;Jang, Gun-Hee
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.16 no.7 s.112
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    • pp.746-753
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    • 2006
  • This paper proposes a method to calculate the stiffness and the damping coefficients of the coupled journal and thrust bearings. The Reynolds equations and their perturbation equations are transformed to the finite element equations by considering the continuity of pressure and flow at the interface between bearings. The Reynolds boundary condition is used in the numerical analysis to simulate the cavitation phenomena. The dynamic coefficients of the proposed method are compared with those of the numerical differentiation of the loads with respect to finite displacements and velocities of bearing center. It shows that the proposed method is more accurate and efficient than the differentiation method.

Added Mass, Viscous Damping and Fluid-stiffness Coefficients on the Rotating Inner Cylinder in Concentric Annulus (동심환내의 회전체 진동에 의한 부가질량, 유체감쇠계수 및 유체탄성계수에 관한 연구)

  • 심우건;박진호;김기선
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2001.05a
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    • pp.695-701
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    • 2001
  • While a rotating inner cylinder executes a periodic translational motion in concentric annulus, the vibration of the rotating inner cylinder is induced by fluid-dynamic forces acting on the cylinder. In the previous study related to journal bearing, the unsteady viscous flow in the annulus and the fluid-dynamic forces were evaluated based on a numerical approach. Considering the dynamic-characteristics of unsteady viscous flow, an approximate analytical method has been developed for estimating added mass, viscous damping and fluid-stiffness coefficients. For the study of flow-induced vibrations and related instabilities, it is of interest to separate the coefficients from the fluid-dynamic forces. The added-mass and viscous damping coefficients for very narrow annular configurations, as journal bearing. can be approximated by considering the gap ratio to the radius of inner cylinder, while the fluid-stiffness coefficient is related to the Reynolds number, the oscillatory Reynolds number and the gap ratio.

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An Experimental Study on the Structural Dynanmic Coefficients of Self-Acting Compliant Foil Journal Bearings (범프 포일 베어링들의 동적 계수에 관한 실험적 연구)

  • Kim, Tae-Ho;Kim, Chang-Ho;Lee, Nam-Soo;Choi, Dong-Hoon;Lee, Yong-Bok
    • Tribology and Lubricants
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    • v.18 no.1
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    • pp.42-48
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    • 2002
  • Experiments were conducted to determine the structural dynamic characteristics of bump foil bearing. The housing of the bearing on the journal was driven by two shakers which were used to simulate dynamic forces acting on the bump foil strips. Three different bump foils(Cu-coated bump, silicon bump, viscoelastic bump) are tested and the dynamic coefficients of three bump foils compared, based on the experimental measurements for a wide range of operating conditions. From the test results, the high damping coefficients of viscoelastic bump are achieved and the possibility of the super-bending-critical operation is suggested.

Determination of the Dynamic Coefficients of the Coupled Journal and Thrust Bearings by the Perturbation Method (수학적 섭동법을 이용한 저널과 스러스트가 연성된 유체 동압 베어링의 동특성 계수 해석)

  • Lee, Sang-Hoon;Jang, Gun-Hee
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2006.05a
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    • pp.666-671
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    • 2006
  • This paper proposes a method to calculate the stiffness and the damping coefficients of the coupled journal and thrust bearings. The Reynolds equations and their perturbation equations are transformed to the finite element equations by considering the continuity of pressure and flow at the interface between bearings. The Reynolds boundary condition is used in the numerical analysis to simulate the cavitation phenomena. The dynamic coefficients of the proposed method are compared with those of the numerical differentiation of the loads with respect to finite displacements and velocities of bearing center. It shows that the proposed method is more accurate and efficient than the differentiation method.

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