• 제목/요약/키워드: damping coefficient

검색결과 580건 처리시간 0.032초

열린 끝단과 중앙 홈을 갖는 스퀴즈 필름 댐퍼의 감쇠 특성에 대한 실험적 규명 (Experimental Identification of the Damping Characteristics of a Squeeze Film Damper with Open Ends and Central Groove)

  • 김남규;김태호;강경대
    • Tribology and Lubricants
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    • 제40권1호
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    • pp.28-37
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    • 2024
  • This paper presents the development of a squeeze film damper (SFD) test rig and experimental identification of the effects of clearance, damper length, journal eccentricity ratio, excitation amplitude, oil supply pressure, and oil flow rate on the damping coefficients of a test SFD with open ends and a central groove. Test data are compared with predictions from a simple model developed for short SFDs with open ends and a central groove. The test results show a significant decrease in the damping coefficient with increasing clearance and a dramatic increase with damper length, which are in good agreement with the simple model predictions. According to the simple model, the damping coefficient is inversely proportional to the cube of the clearance and directly proportional to the cube of the length. An increase in the journal eccentricity ratio results in a dramatic increase in the damping coefficient by as much as 15 times that of the concentric case, particularly at low excitation frequencies. By contrast, the measured damping coefficient remains almost constant with changes in the excitation amplitude and supply pressure, which are not major factors in the damper design. In general, the test data agree well with the simple model predictions, excluding cases that show increases in the SFD length and journal eccentricity, which indicate significant dependency on the excitation frequency.

투과성 격벽을 이용한 수평 운동하는 사각형 탱크내의 슬로싱 감쇠 (Sloshing Damping in a Swaying Rectangular Tank Using a Porous Bulkhead)

  • 조일형
    • 한국해양공학회지
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    • 제32권4호
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    • pp.228-236
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    • 2018
  • The performance of a porous swash bulkhead for the reduction of the resonant liquid motion in a swaying rectangular tank was investigated based on the assumption of linear potential theory. The Galerkin method (Porter and Evans, 1995) was used to solve the potential flow model by adding a viscous frictional damping term to the free-surface condition. By comparing the experimental results and the analytical solutions, we verified that the frictional damping coefficient was 0.4. Darcy's law was used to consider the energy dissipation at a porous bulkhead. The tool that was developed with a built-in frictional damping coefficient of 0.4 was confirmed by small-scale experiments. Using this tool, the free-surface elevation, hydrodynamic force (added mass, damping coefficient) on a wall, and the horizontal load on a bulkhead were assessed for various combinations of porosity and submergence depth. It was found that the vertical porous bulkhead can suppress sloshing motions significantly when properly designed and by selecting the appropriate porosity(${\approx}0.1$) and submergence depth.

Influence of structure coupling effect on damping coefficient of offshore wind turbine blades

  • Zhang, Jianping;Gong, Zhen;Li, Haolin;Wang, Mingqiang;Zhang, Zhiwei;Shi, Fengfeng
    • Wind and Structures
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    • 제29권6호
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    • pp.431-440
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    • 2019
  • The aim of this study was to explore the influence of structure coupling effect on structural damping of blade based on the blade vibration characteristic. For this purpose, the scaled blade model of NREL 5 MW offshore wind turbine was processed and employed in the wind tunnel test to validate the reliability of theoretical and numerical models. The attenuation curves of maximum displacement and the varying curves of equivalent damping coefficient of the blade under the rated condition were respectively compared and analyzed by constructing single blade model and whole machine model. The attenuation law of blade dynamic response was obtained and the structure coupling effect was proved to exert a significant influence on the equivalent damping coefficient. The results indicate that the attenuation trend of the maximum displacement response curve of the single blade varies more obviously with the increase of elastic modulus as compared to that under the structure coupling effect. In contrast to the single blade model, the varying curve of equivalent damping coefficient with the period is relatively steep for the whole machine model. The findings are of great significance to guide the structure design and material selection for wind turbine blades.

공기윤활 포일 베어링의 특성해석 (An Analysis of Characteristics of Air-Lubricated Foil Journal Bearings)

  • 김종수;이준형;최상규
    • Tribology and Lubricants
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    • 제17권2호
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    • pp.97-108
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    • 2001
  • This paper describes the development of performance analysis technique for a leaf-type gas lubricated fail bearing. Stiffness coefficient and frictional damping due to the slip between all contacts of leaves are evaluated for various leaf structures. The fluid film thickness and pressure distribution are computed but it is not considered the elastic deformation by film pressure. The analysis results include the effects that the curvature radius and the length of leaf and the friction coefficient have on the static and dynamic characteristics of the foil bearings.

틸팅 패드 추력베어링의 동특성 해석 (An Analysis of Dynamic Characteristics of Tilling Pad Thrust Bearings)

  • 김종수
    • Tribology and Lubricants
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    • 제13권3호
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    • pp.33-41
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    • 1997
  • In this paper the linearized stiffness and damping coefficients of tilting pad thrust bearing are calculated by the perturbation method. The coefficients are obtained for a wide range of pivot positions. The effects of exciting frequency and pad mass on stiffness and damping coefficients are investigated. Critical frequencies due to the tilting motions of the pad are presented and are shown to be strongly influenced by the pivot position and the pad mass.

반파장 공명기를 장착한 모형연소실의 흡음특성에 대한 실험적 연구 (An Experimental Study on Acoustic Absorption in a Model Chamber with a Half-Wave Resonator)

  • 손채훈;박주현
    • 한국추진공학회지
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    • 제12권3호
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    • pp.34-40
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    • 2008
  • 로켓엔진 연소기의 음향 안정성 향상을 위해, 반파장 공명기의 음향학적 설계인자를 실험적으로 연구하였다. 표준 음향시험 절차에 따라 음향파 응답 신호가 측정되었다. 감쇠인자와 흡음계수가 정량적으로 평가되었고, 이로부터 공명기의 음향감쇠 성능을 파악하였다. 공명기의 직경과 개수, 배치, 연소실의 직경이 설계 인자로 채택되었다. 공명기 직경이 증가함에 따라 음향감쇠 성능이 증가하였다. 연소실 단면에 대한 공명기의 면적비가 최적 값을 초과할 때 과감쇠가 발생하였고, 이로 인해 음향 감쇠 성능이 저하됨을 확인하였다. 공명기 직경이 증가할수록 작은 면적비에서 최적 흡음성능이 달성되었다.

항공기의 도어 댐퍼용 교축 오리피스의 설계 (Design of Throttle Orifices for an Aircraft Door Damper)

  • 권용철;김종혁;홍예선;김상범
    • 드라이브 ㆍ 컨트롤
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    • 제9권3호
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    • pp.23-28
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    • 2012
  • In this study the flow rate-to-pressure difference characteristics of short-tube type damping orifices for an aircraft door damper were investigated by CFD analyses and experiments. As the design parameters of the damping orifice its diameter, inlet and outlet angle, tube length and the viscosity of the working fluid were taken into consideration. The results showed that the discharge coefficient of the orifices are dependant on the inlet and outlet angle and the oil viscosity, while their length plays an little significant role. Although the short-tube type damping orifice was employed to induce a turbulent flow, their discharge coefficient decreases rapidly as the oil viscosity gets higher than 50mm2/s. Therefore, in order to determine the orifice size, satisfying the working temperature range of the door damper, the oil viscosity as well as the friction force on the damper piston should be kept within proper values. For the verification of the CFD analysis results the actual performance of a door damper was measured and compared with them.

전통악기 음향판의 양면도장이 음향성에 미치는 영향 (Effects of Double Surfaces Finishing on Acoustical Properties of Soundboard for Traditional Musical Instruments)

  • 정희석;유태경;권주용
    • Journal of the Korean Wood Science and Technology
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    • 제26권4호
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    • pp.26-33
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    • 1998
  • Acoustical properties of chestnut and paulownia woods have been determined in four film thicknesses of oriental lacquering and cashew varnishing on double surfaces of soundboard to elucidate effects of finishing. Accelerometer was attached to the specimen at one third position from one end, and specimen was hit by the impact hammer at one third position from opposite end. Data were processed by vibration analyzer. The ratio of axial-to-transverse sound velocity of untreated specimens of chestnut and paulownia were 3.25 and 5.34, respectively. Natural frequency, specific Young's modulus, acoustical coefficient, sound velocity, damping of sound radiation(DSR) and acoustical converting efficiency(ACE) decreased by oriental lacquering and cashew varnishing for both species. Damping of internal friction of chestnut decreased by oriental lacquering and cashew varnishing, but that of paulownia increased. Natural frequency. specific Young's modulus, acoustical coefficient, sound velocity, and DSR decreased with increased film thickness of both finishing materials. However, damping of internal friction and ACE showed irregular tendency with increased film thickness. Acoustical properties of cashew varnished chestnut specimen were better than those of oriental lacquered specimen. Acoustical properties of oriental lacquered paulownia specimen were better than those of cashew varnished specimen.

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반능동형 충격흡수기의 연속가변 감쇠특성에 대한 CFD 해석 (CFD Analysis on the Continuous and Variable Damping Characteristics of a Semi-Active Shock Absorber)

  • 윤준원
    • 한국자동차공학회논문집
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    • 제12권2호
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    • pp.101-108
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    • 2004
  • Recently, a semi-active shock absorber has been taking interest because of its low cost and simple structure than the active one. CFD analysis has been conducted to investigate the continuous and variable damping characteristics of the semi-active shock absorber. Also, the flow resistance characteristics of a spool valve has been examined to identify individual parameters(namely, exponent and discharge coefficient) of pressure-flow rate relation needed for the accurate valve modeling. The flow field in the damping valve was simulated using the commercial code, CFX-5.3. The numerical results showed reasonable agreement with the experimental outputs. The pressure distribution with the variation of spool opening length and volume flow rate were discussed in detail. And the continuous and variable damping performance was found clearly. The individual parameters of spool valve were obtained as a function of orifice area. The exponent and discharge coefficient were fitted in with the first and the third polynomial respectively.

OWC형 파력발전 공기챔버의 공기감쇠력 실험연구 (An Experimental Study of Pneumatic Damping at the Air Chamber for OWC type Wave Energy Device)

  • 최학선;류재문;홍석원;김진하
    • 한국해양공학회:학술대회논문집
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    • 한국해양공학회 2004년도 학술대회지
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    • pp.138-144
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    • 2004
  • Pneumatic damping through a orifice type duct for OWC type wave energy device is studied experimentally. Forced oscillation tests are made to measure chamber pressure and velocity of air flaw through orifice. Pneumatic damping coefficient are deducted from the experimental research, and discussion are made far the influence of frequency, heave amplitude, and orifice size. Finally two formula are proposed for the estimation of non-dimensional pneumatic damping coefficient by regression analysis. The proposed formula proves to be a reliable method far practical application.

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