• 한국유체기계학회 논문집
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• 제5권3호
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• pp.7-14
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• 2002

A new foil bearing, ViscoElastic Foil Bearing(VEFB) is suggested with the need for a high damping foil bearing. Sufficient damping capacity is a key technical hurdle to super-bending-critical operation as well as widespread use of foil bearings into turbomachinery. The super-bending-critical operation of the conventional bump foil bearing and the VEFB is examined, as well as the structural dynamic characteristics. The structural dynamic test results show that the equivalent viscous damping of the VEFB is much larger than that of the bump bearing, and that the structural dynamic stiffness of the VEFB is comparable or larger than that of the bump bearing. The results of super-bending-critical operation of the VEFB indicate that the enhanced structural damping of the viscoelastic foil dramatically reduces the vibration near the bending critical speed. With the help of increased damping resulting from the viscoelasticity, the suppression of the asynchronous orbit is possible beyond the bending critical speed.

• Tribology and Lubricants
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• 제18권1호
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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.

• Tribology and Lubricants
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• 제33권1호
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• pp.9-14
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• 2017

This paper presents a rotordynamic analysis and the operation of a power turbine applied to a 250 kW super-critical $CO_2$ cycle. The power turbine consists of a turbine wheel and a shaft supported by two fluid film bearings. We use a tilting pad bearing for the power turbine owing to the high speed operation, and employ copper backing pads to improve the thermal management of the bearing. We conduct a rotordynamic analysis based on the design parameters of the power turbine. The dynamic coefficients of the tilting pad bearings were calculated based on the iso-thermal lubrication theory and turbine wheel was modeled as equivalent inertia. The predicted Cambell diagram showed that there are two critical speeds, namely the conical and bending critical speeds under the rated speed. However, the unbalance response prediction showed that vibration levels are controlled within 10 mm for all speed ranges owing to the high damping ratio of the modes. Additionally, the predicted logarithmic decrement indicates that there is no unstable mode. The power turbine uses compressed air at a temperature of $250^{\circ}C$ in its operation, and we monitor the shaft vibration and temperature of the lubricant during the test. In the steady state, we record a temperature rise of $40^{\circ}C$ between the inlet and outlet lubricant and the measured shaft vibration shows good agreement with the prediction.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2001년도 제34회 추계학술대회 개최
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• pp.282-289
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• 2001

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.