Papers by Keyword: Friction Damping

Abstract: During operation mechanical structures can experience large vibration amplitudes. One of the challenges encountered in gas-turbine blade design is avoiding high-cycle fatigue failure usually caused by large resonance stresses driven by aeroelastic excitation. A common approach to control the amplitude levels relies on increasing friction damping by incorporating underplatform dampers (UPD). An accurate prediction of the dynamics of a blade-damper system is quite challenging, due to the highly nonlinear nature of the friction interfaces and detailed validation is required to ensure that a good modelling approach is selected. To support the validation process, a newly developed experimental damper rig will be presented, based on a set of newly introduced non-dimensional parameters that ensure a similar dynamic behaviour of the test rig to a real turbine blade-damper system. An ini- tial experimental investigation highlighted the sensitivity of the measured response with regards to settling and running in of the damper, and further measurements identified a strong dependence of the nonlinear behaviour to localised damper motion. Numerical simulations of the damper rig with a simple macroslip damper model were performed during the preliminary design, and a comparison to the measured data highlighted the ability of the basic implicit model to capture the resonance frequencies of the system accuratelyю

Abstract: A new type of frictional pendulum TMD is designed. The wind-induced vibration of Henan Art Center Symbolic Tower with and without TMD is analyzed. The structural design of frictional pendulum TMD is presented in detail. The equivalent analysis model is established. The 3D analysis of the symbolic tower is established using SAP2000. The non-linear LINK unit in SAP2000 is used to simulate frictional pendulum TMD. Then, the non-linear analysis of wind control effectiveness of frictional pendulum TMD is carried out. The analysis results demonstrate that optimal frictional force can be chosen according to design wind loads and the control effectiveness can be over 30% with the chosen frictional force under 0.3 to 2 times of the designed wind loads.

Abstract: A rig was built to study the friction damping characteristics of metallic materials with non-conforming contact. The hysteresis curves which show the relationship between the tangential force and relative displacement of the contact between a spherical surface and a flat surface were measured. The effects of the vibration amplitude on the friction damping characteristics of the contact were investigated. The results show that both the amplitude of friction force and the friction coefficient increase as the vibration amplitude increases at first and then reach to a constant value. The equivalent stiffness decreases as the vibration amplitude increases, while the equivalent damping increases at first and then decreases slowly. And both of them trend to constants when the vibration amplitude is larger than 4.8μm.

Abstract: The purpose of this study is to acquire design method of machine tools with higher dynamic stiffness and consequently higher chatter stability. This study focuses on stiffness of main structures and friction damping in guide of a machine tool, because stiffness and friction damping are considered to have major influence on the dynamic stiffness. A special testing machine with variable stiffness and friction was developed to clarify effects of the stiffness of main structures and the friction in guide on the dynamic stiffness and therefore the chatter stability. The stiffness of main structures and the friction in guide were changed experimentally, and it was clarified that the optimal friction force exists at every stiffness condition, and that higher stiffness does not always lead to higher stability.

Abstract: This study explores the effect of semi-active friction damping on vibration isolation systems by means of numerical simulation. Since the Lugre friction model can describe many phenomena observed in laboratories, it is chosen to provide accurate friction force model for the analysis and simulations. The drawback of the passive friction damping system is that it decreases the resonance response at the cost of worsening the performance for high frequencies. A semi-active control method (skyhook method) is used to tune the normal force so that the energy dissipated by the friction force is maximized. Such semi-active friction damping system is simple but efficient, and it can achieve result almost as good as that of active systems. Results from numerical simulations show that compared with passive system, semi-active control method decreases the response significantly for both low and high frequencies, with harmonic and random excitations.

Abstract: Forced vibrations can lead to an irreparable damage of a blade array. Devices called “underplatform damper” that dissipate the vibration energy are employed in order to reduce blade vibration amplitude. The present paper deals with the design of the underplatform damper. A numerical code to calculate the forced response of a blade array with dampers has been previously purposely developed. A method is here proposed for the estimation of the unknown contact parameters demanded by the code. The computation results are here validated by means of comparison with experimental results on a static test rig. Three dampers with different shape are tested.