- Yaxin Song
Joint mechanics refers to the mechanical properties of joints in multi-component systems and their impact on the structural response of the systems of which they are a part .The constitutive behavior of mechanical joints, which usually manifests as nonlinear damping, nonlinear stiffness, and a transfer of mechanical energy from low frequency to high, stems from micro-scale interfacial interaction. While the prediction of structural response of multi-component systems, which are effected significantly due to the manifestations associated with the constitutive behavior of joint, usually has a length scale of the overall structures. In the joint modeling research, we setup dynamic contact and friction models considering surface topography characteristics, as well as develop reduced-order computational methodologies to bridge the dramatically different length scales associated with the joint properties and the overall structures. Besides computational modeling, experimental studies are essential in this procedure to the understandings of the joint interfacial interaction and the effects of joint properties on dynamics of jointed structures.
- Young Lee
The main purpose of this study is by attaching relatively small mass with nonlinear stiffness and linear damper (so-called, nonlinear energy sink, or simply NES) to eliminate limit cycle oscillations (LCO), such as wing flutter problem caused by the instability through Hopf bifurcation when air flow along the wing reaches a certain relative velocity. In order to conceptually understand this phenomenon, consider van der Pol’s oscillator that has a LCO (blue line in the figures). With proper NES designs we totally eliminate/control the LCO (red line in the figures). Basically, all these studies are based on the nonlinear normal mode (NNM) analysis, and utilize energy pumping phenomenon which includes a one-way, irreversible energy transfer from linear substructures to the NES and its dissipation by a damper.
