• Tribology and Lubricants
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• v.17 no.1
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• pp.56-63
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• 2001

The dynamic behavior of rotor-bearing system used in swash plate compressor has been investigated using the combined methodologies of finite elements and transfer matrices. The finite element is formulated including the field element for a shaft section and the point element for swash plate, disk pulley and bearings. The Houbolt method is used to consider the time march for the integration of the system equations. The transient whirl response of rotating shaft supported on roller bearings is obtained, considering compression forces and unbalance forces at swash plate and driving pulley. And, the steady state displacements of the rotor are compared with a variation in unbalance mass. Results show that the loci of rotating shaft considering unbalance forces and external compression forces are more severe in flutter motion than with only unbalance forces.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• v.5B no.2
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• pp.129-136
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• 2005

This paper presents a design strategy of SPOKE type BLDC motors considering an irreversible demagnetization of a permanent magnet (PM). So the irreversible demagnetization characteristic of the motor is analyzed by rotor structure. The instantaneous currents in either starting or lock rotor condition, which are calculated from the current dynamic analysis, are applied to the analysis of the irreversible demagnetization field by FEM. In irreversible demagnetization analysis by FEM, the variation of residual flux density in PM is analyzed using the non-linearity of magnetic core on B-H plan. The analysis results are compared to several rotor structures and used for optimize the rotor structure.

• International Journal of Aeronautical and Space Sciences
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• v.10 no.2
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• pp.23-33
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• 2009

The inherent aeromechanical complexity of a rotor system necessitated the comprehensive analysis code for helicopter rotor system. In the present study, an aerodynamic analysis module has been developed as a part of rotorcraft comprehensive program. Aerodynamic analysis module is largely classified into airload calculation routine and inflow analysis routine. For airload calculation, quasi-steady analysis model is employed based on the blade element method with the correction of unsteady aerodynamic effects. In order to take unsteady effects - body motion effects and dynamic stall - into account, aerodynamic coefficients are corrected by considering Leishman-Beddoes's unsteady model. Various inflow models and vortex wake models are implemented in the aerodynamic module to consider wake induced inflow. Specifically, linear inflow, dynamic inflow, prescribed wake and free wake model are integrated into the present module. The aerodynamic characteristics of each method are compared and validated against available experimental data such as Elliot's induced inflow distribution and sectional normal force coefficients of AH-1G. In order to validate unsteady aerodynamic model, 2-D unsteady model for NACA0012 airfoil is validated against aerodynamic coefficients of McAlister's experimental data.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.2 s.233
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• pp.239-246
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• 2005

A rotor dynamic analysis is implemented to confirm the vibration stability of the high speed centrifugal chiller coupled with gear system. As the rotating speed of the centrifugal chiller under investigation is increased up to 17605rpm at the pinion rotating part, the bearing instability is getting higher and, furthermore, the rotor-bearing system might experience a few critical speed which lead to system failure due to the excessive vibration. In this study, considering the loading capacity and stability conditions, offset journal bearings are adopted for the pinion rotating system and general cylindrical bearings are used for motor part. From the modal analysis, the system is found to be stable as the critical damping ratio which shows the damping characteristics of the system are positive over all operating ranges, and in addition, the synchronous rotating frequency does not come across with any whirl natural frequency. From these results the authors confirm the vibration stability of the rotor-bearing system suggested in this study.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.10a
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• pp.547-550
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• 1997

The dynamic behavior of rotor-bearing system has been investigated using finite element method. A procedure is presented for dynamic modeling of rotor-bearing system which consist of shaft elements, rigid disk, flexible bearing and support structures. A finite element model including the effects of rotary inertia, shear deformation, gyroscopic moments is developed. Linear stiffness and damping coefficient are calculated for 3 lobe sleeve bearing. The whirl frequency, mode shape, stability and unbalance response of rotor system included effect of bearing coefficient and support structures are calculated.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1997.10a
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• pp.82-87
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• 1997

Large dynamic loads act on the rotor in rotary compressors. There are unbalance forces due to eccentric parts and gas forces induced by the pressure difference between compression and suction gases. Rotor-journal bearing system is nonlinear since the stiffness and damping coefficients of the lubricating oil film are not constant in the bearings. The system is considered as a coupled problem of flexible rotor and the journal bearings. Bearing reaction force is calculated from pressure of oil film using Reynolds equations in journal bearings. Pressure distribution in journal bearing is analyzed by finite difference method. The dynamic response of rotor and bearing characteristic are discussed when rotary compressor has a relative misalignment.

• Journal of Aerospace System Engineering
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• v.12 no.2
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• pp.30-36
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• 2018

In this study, a small-scaled test system for a tip jet rotor was developed to contribute to the research on unmanned compound rotorcraft. The performance and dynamic characteristics of the tip jet rotor were investigated using the test system. The diameter of the tip jet rotor was set to 2m in consideration of the size of the test site and the pneumatic supply capacity of the. The rotating speed of the rotor was controlled by the pressure of the compressed air. The thrust and forces during the rotor rotation were measured using a load measuring device. A hydraulic actuator was installed for the dynamic test and full-bridge strain gages were attached to the root of each blade to measure the flap, lag, and torsion-wise responses generated when the rotor is excited by the actuator. The performance and dynamic characteristic tests were conducted at various rotor speeds and blade pitches. In order to check the validity of the test results, the results were also compared with the CAMRAD II analysis.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2004.10a
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• pp.108-111
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• 2004

Structural dynamic characteristics and aeroelastic stability of a small-scale bearingless rotor system have been investigated. A flexbeam is one of the most important component of bearingless hub system. It must have sufficient torsional flexibility as well as baseline stiffness in order to produce feathering motion. In the present paper, a cross-shaped composite flexbeam has been proposed for a guarantee of torsional flexibility and flapwise and lagwise bending stiffness. One dimensional elastic beam model was used for the construction of a structural model. Equivalent isotropic sectional stiffness was used in the blade model, and the flexbeam was regarded as anisotropic; which has ten independent stiffness quantities. CAMRAD II has been used for the analysis of structural dynamic characteristics of the bearingless rotor system. Rotational natural frequencies and aeroelastic stability at hovering have been investigated. Analysis result shows that the cross-shaped flexbeam has the rotational natural frequency tuning capacity.

• Journal of KSNVE
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• v.8 no.1
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• pp.81-86
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• 1998

A 500Wh class high-speed Flywheel Energy Storage System (FESS) driven by a built-in BLDC motor/generator has been designed, which runs from 30000 to 60000rpm nominally. Due to the motor/generator inside, the flywheel rotor made of composites supported by PM/EM hybrid bearing system has a shape of bell or pendulum and thus requires accurate rotordynamic analysis and prediction of its dynamic behavior to secure the operating reliability. Rotordynamic analyses of the flywheel rotor-bearing system revealed that the bell shaped rotor has two conical rigid-body modes in the system operating range and the first conical mode, of which nodal point lies in the radial EM bearing position, can adversely affect the dynamic response of the rotor at the corresponding critical speed. To eliminate the possibility of wild behavior of the rotor, two guide bearings are adopted at the upper end of the rotor and motor/generator. It was also revealed that the EM bearing stiffness if 0.5~1.0E+6 N/m and damping of 2000 Ns/m are favirable for smooth operation of the system around the 2nd critical speed.

• Journal of the Korean Society for Precision Engineering
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• v.12 no.9
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• pp.137-147
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• 1995

The unbalance response analysis is one of the essential area in the forced vibration analysis of rotor-bearing systems. Local bearing parameters in rotor-bearing systems are the major sources which give rise to a difficulty in unbalance response computation due to the complicated dynamic properties such as rotational speed dependency and anisotropy. In the present paper, an efficient method for unbalance responses is proposed so as to easily take into account bearing parameters in computation. An exact matrix condensation procedure is proposed which enables the present method to compute unbalance responses by dealing with condensed, small matrices. The proposed method causes no errors even though the computation procedure is based on the small matrices condensed from the full matrices. The present method is illustrated through a numerical example and compared with the conventional method.