- Hiroshi Yabuno (Faculty of Engineering, Information and Systems, University of Tsukuba): Self-excited oscillations in some mechanical systems. Analysis, Control and Application.
Self-excited oscillations have been known to occur in a variety of engineering systems and have a long history of study. In the 1980’s, the dynamics received much attention with the advancement of the nonlinear approach to dynamical systems. Much of that work focused on the analyses of their occurrence and response.
In this presentation, we propose the stabilization control methods for some self-excited mechanical systems theoretically and experimentally. The self-excited oscillation in a fluid-conveying pipe, which is produced due to the nonself-adjointness depending on the boundary, is stabilized through a boundary bifurcation control. We deal with also the self-excited oscillation in a railway vehicle wheelset. To enhance the running performance on both straight and curved rails, we propose the use of a gyroscopic damper; the gyroscopic damper can suppress not only static destabilization but also dynamics destabilization. Furthermore, we introduce high-performance sensors as the positive applications of self-excited oscillation. Then, the self-excited oscillation for a resonator realizes the high-accurate measurement of biological samples in liquid environment because the self-excitation of resonator compensates the viscous damping effect. We demonstrate an ultrasensitive mass detection using self-excited coupled microcantilevers.
- Oleg Gendelman (Faculty of Mechanical Engineering, Technion – Israel Institute of Technology): Transient phenomena in vibro-impact and other strongly nonlinear systems.
Essentially nonlinear behavior is common in traditional mechanical systems due to clearances, cracks, impacts, friction, material nonlinearities and plasticity. In many of the listed instances, such behavior is unwanted and may be even destructive. In the same time, in in last two decades it was realized that intentional use of strongly nonlinear elements in mechanical systems could bring about significant enhancements and advantages in their performance. In this respect, one can mention targeted energy transfer in essentially nonlinear systems with applications for energy absorption and harvesting, wave propagation in granular crystals, granular media and other systems with acoustic vacuum, acoustic metamaterials with essentially nonlinear elements.
All mentioned applications, traditional and modern, involve some form of energy transfers, transient processes and/or wave propagation. Essential nonlinearity poses major challenge for analytic exploration and understanding of these processes. Traditional methods stemming from quasilinear approximation have limited applicability for such problems, and often produce the results with uncontrolled inaccuracy. In certain important cases, for instance, when the impacts are involved, these traditional methods turn irrelevant for exploration of the transient responses.
The talk will cover a set of archetypal problems, in which the strong nonlinearity appears as the undesirable complication, or is introduced intentionally to improve the performance. Peculiar features of dynamic responses, and approaches to analytic treatment and qualitative understanding of these phenomena will be discussed. Among other issues, the analytic framework for treatment of transient responses and energy exchanges in regular vibro-impact systems and vibro-impact systems with compliance will be outlined and discussed.
- Shigehiko Kaneko (Department of Mechanical Engineering, The University of Tokyo): Dynamic Model for Free Standing Fuel Racks under Seismic Excitation Considering Planar and Non-slide Rocking Motion.
A free-standing rack (FS rack) is a type of a spent nuclear fuel rack, which is just placed on a floor of a pool. For this characteristic, seismic loads can be reduced by fluid force and friction force, but a collision between a rack and another rack or a wall must be avoided. Therefore, it is necessary for designing an FS rack to figure out how it moves under seismic excitation. In this research, a dynamic model of an FS rack is developed considering seismic inertial force, friction force and fluid force. This model consists of two sub-models: a translation model, which simulates planar translational and rotational motion; and a rocking model, which simulates non-slide rocking motion.
First, simulations with sinusoidal inertial force were conducted, changing values of a friction coefficient. Next, to validate this dynamic model, a miniature experiment was conducted. Finally, the model is applied to a real-size FS rack and actually observed seismic acceleration. It is found that translational movement of a rack varies depending on the value of friction coefficient in the simulation with sinusoidal and actual acceleration.
Also, simulation results are similar to the experimental results in the aspects of translational and rocking motion provided friction coefficient is selected properly. Through this research, the knowledge is acquired that friction force plays a significant role in a motion of FS rack so that estimating and controlling a friction coefficient is important in designing an FS rack.
- Jörg Wallascheck (Institute of Dynamics and Vibration Research, Leibniz University Hannover): Contact mechanics and friction processes in ultrasonic wire bonding - Basic theories and experimental investigations.
Ultrasonic wire bonding is widely applied in microelectronic packaging. It is a friction welding process consisting of four phases: 1) Pre-deformation and activation of the ultrasonic vibration, 2) Friction between tool, wire and substrate 3) Ultrasonic softening and 4) Interdiffusion. The process is characterized by operating frequencies between 40 kHz and 200 kHz, amplitudes in the order of a few micrometers and contact normal forces between a few cN and a few N, depending on the wire material and size (typically between 20 micrometer and 500 micrometer in diameter). In the present paper we report experimental results on the relative motion between wire, substrate and bonding tool, which are of fundamental importance for modeling of the ultrasonic wire bonding process. We also discuss local temperatures at the wire/substrate interface and the process of oxide removal in the contact zone. This „self-cleaning“ process is the core of a theoretical model for calculating the bond strength as a function of process parameters. Other elements of the theoretical modeling include the softening-effect of the wire material as well as the microwelds formation and breakage rates. Experimental results, obtained by advanced high speed video techniques are used to validate the theoretical modeling.