• 한국지진공학회논문집
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• 제7권3호
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• pp.23-30
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• 2003

면진격리 고무베어링의 설계법을 수정하여 구조물의 성능점 예측을 위한 간편한 해석방법을 제안하였다. 이러한 적용이 가능한 것은 구조물이 지진력의 작용으로 인하여 손상을 입게 되면 구조물의 항복 후 강성은 연화되고, 이로 말미암아 구조물의 동적 특성이 장주기화 하기 때문이다. 제안된 해석법이 기존의 방법에 비하여 우월한 것은 능력스펙트럼법이 요구하는대로 보유능력곡선과 요구량스펙트럼을 가속도-변위 좌표계로 치환하지 않고서도 비교적 정확한 성능점을 예측할 수 있다는 것이다. 제안된 방법의 타당성은 문헌에서 보이는 정확한 값과의 비교에 의하여 입증하였다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 춘계학술대회논문집
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• pp.1135-1141
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• 2006

Air foil bearing supports the rotating journal using hydrodynamic force generated at thin air film. The bearing performance, stiffness, damping coefficient and load capacity, depends on the rotating speed and the performance of the elastic foundation, bump foil. The main focus of this study is to decide the dynamic performance of corrugated bump foil, structural stiffness and Coulomb damping caused by friction between bump foil and top foil/bump foil and housing. Structural stiffness is determined by the bump shape (bump height, pitch and bump thickness), dry-friction, and interacting force filed up to fixed end. So, the change of the characteristics was considered as the parameters change. The air foil bearing specification for analysis follows the general size; diameter 38.1 mm and length 38.1mm (L/D=1.0). The results show that the stiffness at the fixed end is more than the stiffness at the free end, Coulomb damping is more at the fixed end due to the small displacement, and two dynamic characteristics are dependent on each other.

• 한국추진공학회지
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• 제18권2호
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• pp.35-41
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• 2014

베어링 하우징의 구조 유연성을 고려하여 7톤급 액체 로켓 엔진용 터보펌프의 회전체동역학 해석이 수행되었다. 볼 베어링과 펌프 비접촉 실의 강성 및 감쇠 특성이 회전체동역학 모델에 반영되었으며, 베어링 하우징의 동특성이 집중 질량 및 강성으로 모델링 되어 해석에 반영되었다. 동기 회전체 질량 불평형 응답 해석과 회전 속도에 따른 복소 고유치 해석으로부터 회전체의 임계속도와 불안정 운전 시작 속도를 예측하였다. 회전체동역학적 특성에 베어링 하우징이 미치는 영향이 베어링 부하 조건 및 무부하 조건에서 각각 검토되었다. 수치 해석 결과 베어링 하우징의 구조 유연성은 회전체의 임계속도와 불안정 운전 속도를 의미있게 감소시킬 수 있는 것으로 확인되었다.

• 한국소음진동공학회논문집
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• 제22권8호
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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.

• 대한기계학회논문집
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• 제19권2호
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• pp.313-321
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• 1995

The effects of the temperature rise and the turbulence are very important factors to predict the accurate performance of a large tilting pad journal bearing. In this study, the dynamic characteristics of a large tilting pad journal bearing are analyzed, taking into account the three dimensional variation of lubricant viscosity and turbulence. The effects of the temperature rise and the turbulence on the stiffness and damping coefficients are investigated in comparison with the results from the laminar or isothermal theory. The stiffness and damping coefficients increase due to the turbulence but decrease due to the temperature rise. The results show that the effects of both the temperature rise and turbulence must be considered simultaneously in order to predict the dynamic characteristics of a large tilting pad journal bearing more accurately.

• 소음진동
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• 제9권3호
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• pp.525-534
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• 1999

The present paper proposes a generalized modal analysis procedure for non-uniform, distributed-parameter rotor-bearing systems. An exact element matrix is derived for a Timoshenko shaft model which contains rotary inertia, shear deformation, gyroscopic effect and internal damping. Complex coordinates system is adopted for the convenience in formulation. A generalized orthogonality condition is provided to make the modal decomposition possible. The generalized modal analysis by using a modal decomposition delivers exact and closed form solutions both for frequency and time responses. Two numerical examples are presented for illustrating the proposed method. The numerical study proves that the proposed method is very efficient and useful for the analysis of distributed-parameter rotor-bearing systems.

• 한국정밀공학회지
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• 제19권7호
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• pp.20-27
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• 2002

An analysis model for an elliptical fluid film bearing is described. The principles of hydrodynamic lubrication are outlined together with an expanded version of the governing pressure field equation as related to elliptical journal bearing. Finite element method approximations are given for the pressure field equation and a temperature model, both related to the fluid film thickness. The thermal effects in the lubricant viscosity, lubricant film thickness, variation of the journal rotating speed and influence of turbulence are investigated in this paper A finite element model and an iterative computational process are described, whereby full simultaneously converged field solutions for fluid film thickness, temperature, viscosity, pressure, stiffness and damping coefficient are obtained.

• 한국정밀공학회지
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• 제19권10호
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• pp.37-44
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• 2002

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 consists of shaft elements, rigid disk, flexible bearing and support structure. A finite element model including the effects of rotary inertia, shear deformation, gyroscopic moments is developed. Linear stiffness and damping coefficients are calculated for 2 lobe sleeve bearing. The whirl frequency, mode shape, stability and unbalance response of rotor system including effects of bearing coefficient and support structures are calculated.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2005년도 연구개발 발표회 논문집
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• pp.803-809
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• 2005

This paper presents the theoretical model to investigate the effect of Coulomb damping in the sub-structure of a foil bearing. Foil deflection is restricted by friction of bumps. Equivalent viscous damping of the bump foils is derived from the Coulomb friction. Dynamic equation of the bumps is constituted by stiffness and damping terms. This point give the difference from Heshmat's frictionless and simple compliance bump model. The fluid is modeled with the compressible Reynolds equation. A perturbation approach is used to determine the static and dynamic performance of the bearing from the coupled fluid-structural model. The analysis result shows that the static and dynamic performance is enhanced by bump friction. This analysis technique would be extended to development of a high performance bearing.

• 한국유체기계학회 논문집
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• 제9권1호
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• pp.47-55
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• 2006

This paper presents the theoretical model to investigate the effect of Coulomb damping in the sub-structure of a foil bearing. Foil deflection is restricted by friction of bumps. Equivalent viscous damping of the bump foils is derived from the Coulomb friction. Dynamic equation of the bumps is constituted by stiffness and damping terms. This point give the difference from Heshmat's frictionless and simple compliance bump model. The fluid is modeled with the compressible Reynolds equation. A perturbation approach is used to determine the static and dynamic performance of the bearing from the coupled fluid-structural model. The analysis result shows that the static and dynamic performance is enhanced by bump friction. This analysis technique would be extended to development of a high performance bearing.