• Journal of KSNVE
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• v.11 no.1
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• pp.82-88
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• 2001

In a transmission or geared rotor system a coupled phenomenon of lateral and torsional vibrations may occur due to the gear meshing effect. Particularly, in high speed or low vibration and low noise applications of geared rotor systems a coupled rotordynamic analysis is required to precisely predict their dynamic characteristics. In this paper a generalized finite element model of a gear pair element is developed, which actively couples the lateral and torsional vibrations due to the gear meshing effect. In the modeling the generalized forces due to the transmission error. geometrical eccentricities. and unbalances in the gear system are also considered. Then. using the developed gear pair element model a coupled unforced rotordynamic analysis is performed with a prototype 800 RT turbo-chiller rotor-bearing system having a hull-pinion speed increasing gear. Results show that the torsional vibration characteristics experience some changes due to the gear meshing and lateral dynamic coupling effect, but that they have no adverse effect and the lateral ones have no practical changes in an operating speed range.

• The KSFM Journal of Fluid Machinery
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• v.14 no.5
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• pp.18-23
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• 2011

A CFD analysis method is developed and applied for investigating the gas flow and the byproduct particle trajectory in Roots type vacuum pump. The internal fluid flow and thermal fields between the rotors and the housing of vacuum pump are analyzed by using the dynamic mesh, the numerical methods for unsteady 2-D Navier-Stokes equation and the standard k-$\varepsilon$ turbulence model of the Fluent code. Coupled with the flow simulation results, the particle trajectory of the byproduct flowing into the pump with gas stream is analyzed by using discrete phase modeling technique. The CFD analysis results show the pressure, the velocity and the temperature distributions in pump change abruptly due to the rotation of rotors, and back flows are produced due to the strong reverse pressure gradients at rotor/rotor and rotor/housing clearances. The predicted byproduct particle trajectory results also show the particles impinge on the clearance surfaces between the housing and the rotor of pump and then may form the deposit layer causing the failure of pump.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.11
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• pp.1129-1136
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• 2004

The structural modification to install a heavy sensor was made at the front extremities of the foreign-produced helicopter operated in the Korea Navy Mounting the sensor directly to the nose structure is unlikely to be practical because it lowers a dynamic mode of the airframe close to rotor blade passing frequencies, leading to increased helicopter vibration. Unfortunately we have no information on dynamic characteristics of the imported helicopter. So the experimental modal model derived from shake testing on the overall airframe of a working helicopter was used to solve the sensor Installation problems. The sensitivity analysis was done to evaluate what the best of modification woo)d be. Simple ID model and experimental modal data for mount system with sensor were Incorporated into overall dynamic model to assess the effects of the sensor installation on helicopter. Modal testing for the modified helicopter shows that the airframe modes are sufficiently displaced from rotor passing frequencies. The mount system has been proven fight to be sufficiently stable to meet vibration-level requirement for all required operational profiles.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.22 no.8
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• pp.784-790
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• 2012

This paper describes a stability and dynamic characteristics of bearingless helicopter main rotor in hover. Baseline rotor configuration is defined and modal analysis for the configuration is taken to verify the dynamic characteristics. The kinematic pitch-lag couplings through ways of pitch link installation are analyzed to know effects on loads, frequencies and stability. The effects of pitch link attachments in spanwise direction and chordwise direction as well as pitch link inclination on thrust, power, flpa-lag-pitch mode frequencies and inplane damping are examined. Pitch link at trailing edge location in chordwise direction has influence on aeroelastic stability of the rotor. Also, the pitch link with negative inclination angle makes inplane damping increase.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.4
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• pp.555-563
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• 2001

Support dynamics are often important in rotordynamic analyses. It may well happen in real situation of machines such as centrifugal pumps or turbines operating on flexible structure. This paper presents the applications of the impedance coupling method and the improved rotor model for including the support effects on the interaction with the rotor. The impedance coupling techniques are based on the FRFs of each substructure. Its dynamic stiffness matrix can be assembled to generate the system matrix, which satisfy the constraint conditions in the connection coordinates. And, the improved rotor uses the simplified spring-mass models as support properties. The equivalent support models are directly incorporated into the finite element rotor model. To verify the suggested analytical procedures, the results are compared to those of the pump system.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.04a
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• pp.394-399
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• 2012

This paper describes a stability and dynamic characteristics of bearingless helicopter main rotor in hover. Baseline rotor configuration is defined and modal analysis for the configuration is taken to verify the dynamic characteristics. The kinematic pitch-lag couplings through ways of pitch link installation are analyzed to know effects on loads, frequencies and stability. The effects of pitch link attachments in spanwise direction and chordwise direction as well as pitch link inclination on thrust, power, flpa-lag-pitch mode frequencies and inplane damping are examined. Pitch link at trailing edge location in chordwise direction has influence on aeroelastic stability of the rotor. Also, the pitch link with negative inclination angle makes inplane damping increase.

• Journal of the Korean Society of Safety
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• v.12 no.1
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• pp.9-18
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• 1997

This paper is a study on the dynamic characteristics of truncated cone type squeeze film damper(SFD) bearing and rotor system. This model can alter the radial oil film gap which Is Important to the performance of rotor-bearing system and manufactured easily to change the shape concept of traditional circular type SFD bearing. In theoretical analysis, the oil film pressure distribution, the oil film force, the film damping coefficient and the eccentricity ratio, etc. were induced with regard to the film inertia effect. The film damping coefficients and optimum design parameters are calculated. When unbalance parameter U is greater than 0.2, the nonlinear vibration such as "Jump" phenomena appears in the vicinity of rotor critical speed. At this time, the increases of bearing parameter U, journal distance S, Reynolds number Re can control this unstable vibration. The experimental results show that SFD hearing and rotor system which are designed according to the design parameters in the stable region are operated stably in rotational speed 9,600rpm without nonsynchronous behavior.

• Transactions of the Korean Society of Mechanical Engineers
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• v.10 no.5
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• pp.698-705
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• 1986

The dynamic behaviour of bearing-rotor system with flexible and damped supports is systematically investigated. To find out the obvious trend of the influence of the external damping on the resonance peak of a rolling bearing-rotor system and on the stability linit of a cylindrical journal bearing-rotor system, some important characteristic design parameters are derived. Those are the dimensionless stiffness and damping ratio of the external damping refered to the rotor stiffness. For an optimal design of the external damping a relation between the stiffness and damping coefficients can be obtained from the dynamic analysis of the whole system.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.18 no.1
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• pp.35-46
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• 2008

Harmonic vibration characteristics for the general rotor model having a breathing crack are analyzed. Analyses are performed at the half critical speed ranges. The vibration characteristics are explained by using the additional slope and bending moment at the crack position and the influence coefficient showing the structural dynamic characteristics of the rotor. With the low crack depth the magnitude of the additional slope is kept constant even at the speed range at which the orbit magnitude is very sensitive to the rotational speed change. At this speed range the vibration is affected by the influence coefficient only. As the dynamic bending moment exceeds the static bending moment with the increase of crack depth. the additional slope affects the vibration amplitude of cracked rotor and the crack propagation rate increases.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.55 no.6
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• pp.325-336
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• 2006

This paper deals with the dynamic analysis of variable speed wind power systems with doubly-fed induction generators (DFIG). First, the mathematical modeling of wind farm which consists of turbine rotor, DFIG, rotor side and grid side converter and control systems is presented. In particular, the equation for dynamic modeling of the DFIG and the AC/DC/AC converter is expressed as dq reference frame. And then, on the basis of mathematical modeling for each component of wind farm, dynamic simulation algorithms for speed and pitch angle control of wind turbine and generated active and reactive power control of the DFIG and the AC/DC/AC converter are established. Finally, Using the MATLAB/SIMULINK, this paper presents dynamic simulation model for 6MW wind power generation systems with the DFIG considering distribution systems and performs the dynamic analysis of wind power systems in steady state. Moreover, this paper also presents the dynamic performance for the case when the voltage sag in grid source and phase fault in bus are occurred.