• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.6
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• pp.92-99
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• 2005

Numerical analyses of critical speed and mass unbalance response are performed for a 30 ton thrust turbopump. The stiffness and damping of ball bearings and non-contact seals are quantified under aerodynamic and hydrodynamic loads induced by a fuel pump and turbine. Critical speed margin and tip displacements of the rotating parts are evaluated using a three-dimensional finite element method. The results are used to ensure the soundness of the rotordynamic design using an one-dimensional transfer matrix method. A further study shows that sufficient resonance margin may be assured via controlling the stiffness of the rotor support by employing an additional elastic ring to the bearing support.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1997.04a
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• pp.111-121
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• 1997

The stability of a rotor-bearing system supported by swirl-controlled hybrid journal bearing with pair-type angled injection orifices is investigated for improvement of the whirl frequency ratio by allowing effective control of the tangential flow inside the bearing clearance, i.e., by achieving more freedom in controlling strength and direction of the supply tangential flow inside the bearing clearance. It is suggested that the system instability can be improved through the change of bearing dynamic characteristic parameters with the swirl control. The orifice diameter d$_0$ and recess injection angle $\alpha$ along with combinations of swirl/anti-swirl supply pressures and directions (3.0-3.0MPa, 4.0-2.0MPa, 2.0-4.0MPa) are selected for design parameters for swirl-controlled effective factors dependent on journal speeds (3000, 9000, 15000, 21000 rpm). It has been found that the orifice diameter do shows strong effects on effective maneuverability of direct-stiffness and direct damping values, while recess injection angle $\alpha$ results in substantial magnitude and direction of cross-stiffness. Specifically, recess injection parameters which are functions of angle of orifice feeding flow and recess dimensions showed very feasible effect on the stability of swirl-controlled rotor-bearing system.

• Aerospace Engineering and Technology
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• v.8 no.1
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• pp.98-107
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• 2009

Vibration analysis of a turbo compressor test rig was carried out in order to investigate the vibrational characteristics of the compressor facility in KARI before conducting the compressor performance test of 5MW-class gas turbine engine for generation. The overall compressor test facility consists largely of inlet and exit ducts, a test section and a driving part. Vibration was measured with accelerometers at the test section and the driving part, especially at a main housing, a collector, a bearing carrier, a torquemeter, a gearbox, and an electric motor. Gap sensors are also installed to measure the rotordynamic characteristics of compressor shaft.

• The KSFM Journal of Fluid Machinery
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• v.9 no.6 s.39
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• pp.45-53
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• 2006

Turbo-blower as an air supply system is one of the most important BOP (Balance of Plant) systems for FCV(Fuel Cell Vehicle). For generating and blowing compressed air, the motor of air blower consumes maximum 25% of net power, and fuel cell demands a clean air. In this study, turbo-blower supported by air foil bearings is introduced as the air supply system used by 80kW proton exchange membrane fuel systems. The turbo-blower is a turbo machine which operates at high speed, so air foil bearings suit their purpose as bearing elements. Analysis for confirming the stability and endurance is conducted. The rotordynamic stability was predicted using the numerical analysis of air foil bearings and it is verified through experimental works. In spite of various transient dynamic situation, the turbo-blower had stable performances. After the performance test, results are presented. The normal power of driving motor has about 1.6 kW with the 30,000 rpm operating range and the flow rate of air has maximum 160 SCFM. The test results show that the aerodymic performance and stability of turbo-blower are satisfied to the primary goals.

• Journal of Mechanical Science and Technology
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• v.17 no.1
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• pp.57-63
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• 2003

An eigenvalue design sensitivity formulation of a general nonsymmetric-matrix rotor-bearing system is devised. using the DDM (direct differential method). Then, investigations on the design sensitivities of critical speeds are carried out for an APU turbogenerator with a spline shaft connection. Results show that the dependence of the rate of change of the critical speed on the stiffness changes of bearing models of spline shaft connection points is negligible, and thereby their modeling uncertainty does not present any problem. And the passing critical speeds up to the 4th critical speed are not sensitive to the design stiffness coefficients of four main bearings. Further, the dependence of the rate of change of the critical speed on the shaft-element length changes shows quantitatively that the spline shaft has some limited influence on the 4th critical speed but no influence on the 1st to 3rd critical speeds. With no adverse effect from the spline shaft, the APU system achieves a critical speed separation margin of more than 40% at a rated speed of 60,000 rpm.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1995.04a
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• pp.276-281
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• 1995

마모씨일과 발란스디스크에서의 로마킨효과가 3600rpm에서 운전되는 14단 터빈펌프의 동특성에 미치는 영향을 고찰한 결과 다음과 같은 결론을 얻을 수 있었다. 1. 14단 터빈펌프 시제품 해석을 위한 유한요소 모델링 및 해석결과는 실험적 모드해석을 통하여 5% 이내의 오차로 검증되었다. 2. 마모링 및 밸런스 디스크의 로마킨효과를 고려하였을 때 시제품 펌프의 위험속도는 그렇지 않았을 때에 비하여 1차의 경우 약 50% 상승하나 고차의 경우는 그 영향이 미미하였다. 그런데 1차 위험속도가 운전속도와 밀접한 관련이 있으므로 설계시 로마킨효과는 반드시 고려되어야 한다. 3. 마모링 및 밸런스디스크의 설계변경에 의하여 시제품 펌프의 강성을 변화시킬 경우 위험속도가 크게 변화하는 것으로 나타났다. 이를 이용하면 펌프의 심각한 구조변경 없이도 씨일의 적절한 설계에 의하여 임펠러 깃등의 고조화성분을 포함한 유해한 진동을 회피하는 동특성 설계가 가능하다. 향후 계속 연구사업으로서 씨일의 동특성 해석코드 개발 및 Wet Test를 통하여 본 연구결과를 검증하고 그 결과를 다단 터빈 펌프의 동특성 설게에 적용하여 고압 다단 터빈 펌프의 독자적 개발에 활용코자 한다.

• Journal of KSNVE
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• v.8 no.3
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• pp.450-456
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• 1998

A rotordynamic analysis is performed with a centrifuge rotor-bearing system for the raing speed of 100,000 rpm. The system is composed of a centrifuge rotor(or simply the rotor), flexible shaft, motor rotor and shaft, and two support rolling element bearings of the motor shaft. Design goals are to achieve wide separation margins of critical speeds and favorable unbalance responses of the rotor at the associated critical speeds. The latter requirements are especially important as the system crosses multiple numbers of critical speeds and as the system may not have enough separaton margins around the rating speed. As the system adopts an extra-flexible shaft, it is shown that the rotor has satisfactory small unbalance responses over higher criticals while having an unsatisfactory large one at the first critical. To supress this a bumper ring or guide bearing needs to be installed at a suitable location of the flexible shaft. It is also shown that even with the flexible shaft the dynamics of the motor must be incoporated into the full system model to accurately identify the fourth critical speed, which is close to the rating speed, and higher ones. The analysis is based on the finite element method.

• Tribology and Lubricants
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• v.30 no.2
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• pp.77-85
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• 2014

This study set out to predict the load capacity and rotordynamic coefficients of tilting-pad journal bearings, taking the pivot stiffness into account. The analysis uses rocker-back (cylindrical) and ball in socket (spherical) pivot models, both of which are based on Hertzian contact stress theory. The models ascertain the non-linear elastic deformation of the pivots according to the applied load, pivot geometry, and material properties. At present, the Reynolds equation for an isothermal, isoviscous, and incompressible fluid is used to calculate the film pressure by using the finite-element method, after which the Newton-Raphson method is used to simultaneously find the journal center location, pad angles, and pivot deflections. The bearing analysis, excluding the pivot models, is validated using predictions those are readily available in the literature. As the rotor speed increases, the predicted journal eccentricity and damping coefficients decrease, but the stiffness coefficients increase, as expected. Most importantly, the implementation of the pivot models increases the journal eccentricity but significantly decreases the stiffness and damping coefficients of the tilting-pad journal bearings.

• Tribology and Lubricants
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• v.21 no.3
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• pp.114-121
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• 2005

As fuel cell system is environmental friendly generator, its performance depends on its air supply system. Because, fuel cell stack generates electrical energy by electron and the electron is generated by reacting between air and hydrogen. So, more and more compressed air is supplied, more and more the energy can be obtained. In this study, turbo-expander supported by air foil bearing is introduced as the air supply system used by fuel cell systems. The turbo-expander is a turbo machine which operates at high speed, so air foil bearings suit its purpose for the bearing elements. Analysis for confirming the stability and endurance is conducted. Based on FDM and Newton-Raphson method, characteristics of air foil bearing, dynamic coefficients, pressure field and load capacity, are obtained. Using the characteristics of air foil bearing, the rotordynamic analysis is performed by finite element method. The analysis (stability analysis and critical speed map) shows that turbo-expander is stability at running speed. After the analysis, the test process and results are presented. The goals of test are running up to 90,000 RPM, flow rate of 150 $m^3/h$ and pressure ratio of 1.15. The test results show that the aerodynamic performance and stability of turbo-expander are satisfied to the primary goals.

• Tribology and Lubricants
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• v.13 no.3
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• pp.63-72
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• 1997

The stability of a rotor-bearing system supported by swirl-controlled hybrid journal bearing with pair-type angled injection orifices is investigated for improvement of the whirl frequency ratio by allowing effective control of the tangential flow inside the bearing clearance, i.e., by achieving more freedom in controlling strength and direction of the supply tangential flow inside the bearing clearance. It is suggested that the system instability can be improved through the change of bearing dynamic characteristic parameters with the swirl control. The orifice diameter $d_0$ and recess injection angle $\alpha$ along with combinations of swirl/anti-swirl supply pressures and directions (3.0~3.0 MPa, 4.0~2.0 MPa, 2.0~4.0 MPa) are selected for design parameters for swirl-controlled effective factors dependent on journal speeds (3000, 9000, 15000, 21000 rpm). It has been found that the orifice diameter $d_0$ shows strong effects on effective maneuverability of direct-stiffness and direct damping values, while recess injection angle $\alpha$ results in substantial effects on the magnitude and direction of cross-stiffness. Specifically, recess injection parameters which are functions of angle of orifice feeding flow and recess dimensions showed very feasible effect on the stability control of swirl-controlled rotor-bearing system.