• 제목/요약/키워드: damping mechanism

검색결과 203건 처리시간 0.023초

Numerical and experimental verifications on damping identification with model updating and vibration monitoring data

  • Li, Jun;Hao, Hong;Fan, Gao;Ni, Pinghe;Wang, Xiangyu;Wu, Changzhi;Lee, Jae-Myung;Jung, Kwang-Hyo
    • Smart Structures and Systems
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    • 제20권2호
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    • pp.127-137
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    • 2017
  • Identification of damping characteristics is of significant importance for dynamic response analysis and condition assessment of structural systems. Damping is associated with the behavior of the energy dissipation mechanism. Identification of damping ratios based on the sensitivity of dynamic responses and the model updating technique is investigated with numerical and experimental investigations. The effectiveness and performance of using the sensitivity-based model updating method and vibration monitoring data for damping ratios identification are investigated. Numerical studies on a three-dimensional truss bridge model are conducted to verify the effectiveness of the proposed approach. Measurement noise effect and the initial finite element modelling errors are considered. The results demonstrate that the damping ratio identification with the proposed approach is not sensitive to the noise effect but could be affected significantly by the modelling errors. Experimental studies on a steel planar frame structure are conducted. The robustness and performance of the proposed damping identification approach are investigated with real measured vibration data. The results demonstrate that the proposed approach has a decent and reliable performance to identify the damping ratios.

유한요소를 이용한 유연성 간극기구의 동적 해석 (Dynamic Analysis of Flexible Mechanisms with Clearances Using Finite Elements)

  • 길계환;윤용산
    • 대한기계학회논문집
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    • 제14권2호
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    • pp.288-297
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    • 1990
  • The method of analyzing flexible mechanisms with clearances was studied considering flexibility of beams in the mechanism using finite elements. Both ends of a beam were modeled as free following Dubowsky's impact pair model. Instead some force constraints were imposed at imposed at the connections between adjoining links. Coulomb model has been developed using dry frictions in place of tangential damping forces in the impact pair model and the contact compliance and damping coefficient approximated in a form of root function were used. As examples, impacts of a rigid ball in a cylinder, impact beam model and four-bar mechanisms made up of three flexible links with clearance connections were simulated numerically. The results from examples showed similar but a little bit smaller magnitude of impact forces compared with published studies.

고속 주축 베어링용 예압장치의 볼 가이드 이송특성 (Feeding Characteristics of Ball Guide in High Speed Spindle's Bearing Preload Units)

  • 이찬홍
    • 한국생산제조학회지
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    • 제20권6호
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    • pp.685-691
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    • 2011
  • The Bearing preload units are used for stable rotational movements of high speed spindles. The feeding mechanism of the preload unit is important to prevent overheat of bearings and to keep constant bearing load under thermal deformation of spindle unit. In this study, ball slide guide and ball bush as feeding mechanism of preload unit are selected. The maximum static friction force, radial stiffness and damping ratio of ball slide guide with ball load, ball number and ball size are widely investigated. In conclusion, the surface of ball slide guide must be heat treated to reduce static friction force. The number and size of ball are increased to control sensitive bearing preload force.

자동차용 충격 흡수기의 동적거동 해석 (Dynamic Behaviour Analysis of Shock Absorber for Vehicle)

  • 박재우;신상윤;주동우;이시복
    • 한국정밀공학회:학술대회논문집
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    • 한국정밀공학회 1996년도 추계학술대회 논문집
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    • pp.362-370
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    • 1996
  • Even if the shock absorber is developed to Variable S/A or Active S/A, it is necessary to construct data-base or build the dynamic performance characteristic program of Oil S/A. Since both Variable S/A and Active S/A are based on the principle of Oil S/A. To obtain the design technique of Oil S/A, we model the damping mechanism and characteristics of an Oil S/A whose performance was testified. And then it is analyzed the dynamic behaviour characteristics of damping mechanism.

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A novel nonlinear gas-spring TMD for the seismic vibration control of a MDOF structure

  • Rong, Kunjie;Lu, Zheng
    • Structural Engineering and Mechanics
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    • 제83권1호
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    • pp.31-43
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    • 2022
  • A nonlinear gas-spring tuned mass damper is proposed to mitigate the seismic responses of the multi-degree-of-freedom (MDOF) structure, in which the nine-story benchmark model is selected as the controlled object. The nonlinear mechanical properties of the gas-spring are investigated through theoretical analysis and experiments, and the damper's control parameters are designed. The control performance and damping mechanism of the proposed damper attached to the MDOF structure are systematically studied, and its reliability is also explored by parameter sensitivity analysis. The results illustrate that the nonlinear gas-spring TMD can transfer the primary structure's vibration energy from the lower to the higher modes, and consume energy through its own relative movement. The proposed damper has excellent "Reconciling Control Performance", which not only has a comparable control effect as the linear TMD, but also has certain advantages in working stroke. Furthermore, the control parameters of the gas-spring TMD can be determined according to the external excitation amplitude and the gas-spring's initial volume.

Effects of viscoelastic memory on the buffeting response of tall buildings

  • Palmeri, A.;Ricciardelli, F.;Muscolino, G.;De Luca, A.
    • Wind and Structures
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    • 제7권2호
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    • pp.89-106
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    • 2004
  • The response of tall buildings to gust buffeting is usually evaluated assuming that the structural damping is of a viscous nature. In addition, when dampers are incorporated in the design to mitigate the response, their effect is allowed for increasing the building modal damping ratios by a quantity corresponding to the additional energy dissipation arising from the presence of the devices. Even though straightforward, this procedure has some degree of inaccuracy due to the existence of a memory effect, associated with the damping mechanism, which is neglected by a viscous model. In this paper a more realistic viscoelastic model is used to evaluate the response to gust buffeting of tall buildings provided with energy dissipation devices. Both cases of viscous and hysteretic inherent damping are considered, while for the dampers a generic viscoelastic behaviour is assumed. The Laguerre Polynomial Approximation is used to write the equations of motion and find the frequency response functions. The procedure is applied to a 25-story building to quantify the memory effects, and the inaccuracy arising when the latter is neglected.

일체형원자로 제어봉구동장치의 낙하 및 완충특성 (Drop and Damping Characteristics of the CEDM for the Integral Reactor)

  • 최명환;김지호;허형;유제용
    • 한국소음진동공학회논문집
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    • 제20권7호
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    • pp.658-664
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    • 2010
  • A control element drive mechanism(CEDM) is a reactor regulating system, which inserts, withdraws or maintains a control rod containing a neutron absorbing material within a reactor core to control the reactivity of the core. The ball-screw type CEDM for the integral reactor has a spring-damper system to reduce the impact force due to the scram of the CEDM. This paper describes the experimental results to obtain the drop and damping characteristics of the CEDM. The drop tests are performed by using a drop test rig and a facility. A drop time and a displacement after an impact are measured using a LVDT. The influences of the rod weight, the drop height and the flow area of hydraulic damper on the drop and damping behavior are also estimated on the basis of test results. The drop time of the control element is within 4.5s to meet the design requirement, and the maximum displacement is measured as 15.6 mm. It is also found that the damping system using a spring-hydraulic damper plays a good damper role in the CEDM.

모형 로켓 연소실에서 배플형 분사기의 간극에 의한 음향 감쇠 효과에 관한 수치적 연구 (A Numerical Study on Acoustic Damping Induced by Gap between Baffled Injectors in a Model Rocket Combustor)

  • 손채훈;이중연
    • 한국추진공학회지
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    • 제11권3호
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    • pp.35-42
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    • 2007
  • 로켓 엔진의 음향 불안정을 제어하기 위해 모형 연소실에 배플형 분사기가 장착된 경우의 음향 감쇠 특성을 수치해석적으로 조사하였다. 기존에 보고된 배플형 분사기의 효용성을 확인하였고 분사기간 간극이 존재할 때 음향 감쇠 효과가 증대되는 메커니즘을 규명하였다. 여러 가지 크기의 간극에 따라 음향학적 감쇠능력을 조사하였고, 본 연소실에서는 0.1 mm 정도의 간극에서 최적의 감쇠능력을 가짐을 알 수 있었다. 음향 감쇠 효과가 증대되는 메커니즘을 규명하기 위해, 분사기 사이의 간극에 따른 에너지 소산율과 와도를 계산하였고, 소산율 변화 추이와 감쇠인자 변화 추이가 유사함을 알았다. 이를 통해, 간극에 의한 에너지 소산의 종대로 음향 감쇠 효과가 증가함을 알았다.

Performance evaluation of inerter-based damping devices for structural vibration control of stay cables

  • Huang, Zhiwen;Hua, Xugang;Chen, Zhengqing;Niu, Huawei
    • Smart Structures and Systems
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    • 제23권6호
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    • pp.615-626
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    • 2019
  • Inerter-based damping devices (IBBDs), which consist of inerter, spring and viscous damper, have been extensively investigated in vehicle suspension systems and demonstrated to be more effective than the traditional control devices with spring and viscous damper only. In the present study, the control performance on cable vibration reduction was studied for four different inerter-based damping devices, namely the parallel-connected viscous mass damper (PVMD), series-connected viscous mass damper (SVMD), tuned inerter dampers (TID) and tuned viscous mass damper (TVMD). Firstly the mechanism of the ball screw inerter is introduced. Then the state-space formulation of the cable-TID system is derived as an example for the cable-IBBDs system. Based on the complex modal analysis, single-mode cable vibration control analysis is conducted for PVMD, SVMD, TID and TVMD, and their optimal parameters and the maximum attainable damping ratios of the cable/damper system are obtained for several specified damper locations and modes in combination by the Nelder-Mead simplex algorithm. Lastly, optimal design of PVMD is developed for multi-mode vibration control of cable, and the results of damping ratio analysis are validated through the forced vibration analysis in a case study by numerical simulation. The results show that all the four inerter-based damping devices significantly outperform the viscous damper for single-mode vibration control. In the case of multi-mode vibration control, PVMD can provide more damping to the first four modes of cable than the viscous damper does, and their maximum control forces under resonant frequency of harmonic forced vibration are nearly the same. The results of this study clearly demonstrate the effectiveness and advantages of PVMD in cable vibration control.

Mechanism analysis on fluidelastic instability of tube bundles in considering of cross-flow effects

  • Lai, Jiang;Sun, Lei;Gao, Lixia;Li, Pengzhou
    • Nuclear Engineering and Technology
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    • 제51권1호
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    • pp.310-316
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    • 2019
  • Fluidelastic instability is a key issue in steam generator tube bundles subjected in cross-flow. With a low flow velocity, a large amplitude vibration of the tube observed by many researchers. However, the mechanism of this vibration is seldom analyzed. In this paper, the mechanism of cross-flow effects on fluidelastic instability of tube bundles was investigated. Analysis reveals that when the system reaches the critical state, there would be two forms, with two critical velocities, and thus two expressions for the critical velocities were obtained. Fluidelastic instability experiment and numerical analysis were conducted to obtain the critical velocity. And, if system damping is small, with increases of the flow velocity, the stability behavior of tube array changes. At a certain flow velocity, the stability of tube array reaches the first critical state, a dynamic bifurcation occurs. The tube array returns to a stable state with continues to increase the flow velocity. At another certain flow velocity, the stability of tube array reaches the second critical state, another dynamic bifurcation occurs. However, if system damping is big, there is only one critical state with increases the flow velocity. Compared the results of experiments to numerical analysis, it shows a good agreement.