• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.05a
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• pp.271-276
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• 2006

This paper shows the rotordynamic characteristics of a turbo-generator for a BOP of a fuel cell system. The rotor-bearing system consists of magnetic shaft and compressor-turbine shaft, and the two shafts are connected by spline coupling and supported by oil free air foil bearing. Preliminary design according to several parameter is considered in detail. Static and dynamic characteristics of the AFB are estimated by the soft elasto-hydrodynamic analysis technique and the perturbation method. The results of the natural frequencies, mode shape, and unbalance response analysis are presented.

• The KSFM Journal of Fluid Machinery
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• v.12 no.5
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• pp.47-53
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• 2009

A rotordynamic and detailed stability analysis in accordance with API 617 standard were performed with a turbo-compressor, which is one of key rotating machinery in refinery, petroleum, and power plants. The system is composed of rotor shaft, impeller, sleeve hub, balance drum, and coupling hub. The rotor system is supported by tilting pad bearings, which has 5 pads and pad on loading condition. The rotordynamic analysis specified by API 617 includes the critical speed map, mode shape analysis, Campbell diagram, unbalance response analysis, and stability analysis. In particular, the specifications of stability analysis consist of a Level 1 analysis that approximates the destabilizing effects of the labyrinth seals and aerodynamic excitations, and Level 2 analysis that includes a detailed labyrinth seal aerodynamic analysis. The results of a rotordynamic analysis and stability analysis can evaluate the operating compressor health and can be utilized as a guide of its maintenance, repair and trouble solution.

• The KSFM Journal of Fluid Machinery
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• v.14 no.5
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• pp.69-74
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• 2011

This paper deals with the detail rotordynamic analysis for the vertical rotor system as development of vertical sea water lift pump for FPSO deep well. In a vertical rotor system, since linearized stiffness and damping coefficients of fluid film bearing are no longer be valid, hence the transient response analysis considering a fluid film force for every journal position in the bearing needs to be required. In this study, the transient response analysis of the proposed vertical pump rotor system was carried out in dry-run and wet-run conditions, respectively. The results show that orbital vibration responses of the rotor system remain stable at rated speed and thereby operating reliability of the vertical rotor system is confirmed. To overcome complexity of calculation pr ocedure and time consuming calculation of transient analysis, the calculating technique of steady-state response analysis is also proposed. The results of steady-state response obtained by applying the proposed technique to the rotor system are good agreement with the reference results, that is, transient responses.

• The KSFM Journal of Fluid Machinery
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• v.13 no.5
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• pp.35-42
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• 2010

This paper deals with the development of analytical model of a turbocharger and its detail rotordynamic analysis. Two analytical models, which are verified by experimental modal testing, are proposed and the analytical model including rotor shaft extended to compressor and turbine wheel end side is chosen. A rotordynamic analysis includes the critical map, Campbell diagram, stability, and unbalance response, especially nonlinear transient response considering nonlinear fluid film force at bearings. Although the linearized analysis accurately predicts the critical speeds, stability limit, and stability threshold speed, the predicted vibration results are not valid for speeds above the stability threshold speed since the rotor vibrates with a subsynchronous component much larger than the one synchronous with rotor speed. Hence, for operating speed above the stability threshold, a nonlinear transient analysis considering nonlinear fluid film force must be performed in order to accurately predict vibration responses of rotor and guarantee results of analysis.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.17 no.2 s.119
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• pp.105-113
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• 2007

In this study, three-dimensional rotordynamic analyses have been conducted using equivalent beam, hybrid and full three-dimensional models. The present computational method is based on the general finite element method with rotating gyroscopic effects of the rotor system. General purpose commercial finite element code, SAMCEF which includes practical rotordynamics module with various types of rotor analysis tools and bearing elements is applied. For the purpose of numerical verification, comparison study for a benchmark rotor model with support bearings is performed first. Detailed finite element models based on three different modeling concepts are constructed and then computational analyses are conducted for the realistic and complex three-dimensional rotor system. The results for rotor stability and mass unbalance response are presented and compared with the experimental vibration test data conducted herein.

• Tribology and Lubricants
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• v.28 no.5
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• pp.197-202
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• 2012

In this study, with the purpose of fundamentally improving the unbalance response vibration of a large PRT motor-generator rotor by design, a performance improvement design analysis is carried-out by retrofitting tilting pad bearings, replacing the plain partial journal bearings that were originally applied for operation at a rated speed of 1,800 rpm. In this process, a goal of the design analysis is to obtain a design solution for maximizing the direct stiffness of the bearings while satisfying the key basic lubrication performance requirements such as the minimum lift-off speed and maximum oil-film temperature. The results show that with a careful design application of tilting pad journal bearings for operation at such a relatively low speed of 1,800 rpm, direct stiffness increment of the bearings by about two times can be effectively achieved. Prevention of pad unloading is also considered in the analysis. Moreover, the designs of elliptical and offset half journal bearings are also analyzed and reviewed.

• The KSFM Journal of Fluid Machinery
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• v.6 no.1 s.18
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• pp.51-56
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• 2003

The feasibility study on the oil-free turbocharger supported by air foil bearings is investigated. Using the perturbation method, dynamic characteristics of air foil bearings are calculated based on the static equilibrium position of a turbocharger rotor is predicted. With collaboration of calculated stiffness and damping of foil bearing, rotordynamic analysis is performed using the finite element method. The effects of bump compliance and bearing clearance on rotordynamic characteristics of the oil-free turbocharger such as the critical speeds, eccentricity ratio, vibration amplitude and stability are investigated.

• The KSFM Journal of Fluid Machinery
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• v.12 no.3
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• pp.26-30
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• 2009

This paper predicts the critical speeds of a 5MW industrial gas turbine by using commercial rotordynamic tool, DYNAMICS 4.3. The gas turbine is operated at 12,975 rpm on squeeze film dampers. The stiffness of the squeeze film dampers are estimated. The critical speeds of the gas turbine rotor are calculated to have a sufficient separation margin (2%) from the 1st bending mode and pass over 2 rigid body modes below 4,000 cpm. This paper discussed the coupling effects on the dynamic response of the gas turbine.

• Tribology and Lubricants
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• v.24 no.3
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• pp.147-153
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• 2008

The effect of oil supply pressure on the performance of vapor cavitated short squeeze film dampers is examined. Vapor cavitation is characterized by film rupture occurring as a result of evaporating oils. The pressure of vapor cavity in the film is almost zero in absolute pressure and nearly constant. Pan's model about the shape of vapor cavity is utilized for studying the effect of vapor cavitation on the damping capability of a short squeeze film damper. As the level of oil supply pressure is increasing, vapor cavitation is suppressed so that the direct damping coefficient increases and the cross coupled damping coefficient decreases. Futhermore, the analysis of the unbalance responses of a rigid rotor supported on cavitated squeeze film dampers shows that a significant reduction in rotor amplitude and force transmissibility is possible by controlling the oil supply pressure into short squeeze film dampers.

• 한국초전도학회:학술대회논문집
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• v.13
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• pp.18-18
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• 2003