MS07.1: Nonlinear Phenomena in Mechanical and Structural Systems

This abstract marks a pivotal continuation of the research into movable bridge dynamics – a validation study. The initial lab experiments, employing a test setup to verify a novel non-linear dynamic model methodology [1] aimed at calculating dynamic torques in the driveline of movable bridge machineries, confirmed the accuracy of the models through measurements [2]. However, beyond verification, the validation process is indispensable. Hence, measuring dynamic torques in the powertrain of a full-scale movable bridge becomes a necessary next step. The chosen Crolesbrug is a bascule bridge in South-Holland, The Netherlands, which aligns with the laboratory test rig, providing an ideal real-world counterpart. In collaboration with TU Delft, Antea Group, and the Province of South-Holland, this research aims to compare dynamic forces in Crolesbrug's powertrain with lab measurements for comprehensive validation. This process involves matching refined theoretical models with real-world measures during various loading scenarios, including normal operation and emergency braking. By effectively bridging the gap between theoretical predictions and actual dynamic loads, this study significantly contributes to the accurate reassessment of the structural safety of existing movable bridge mechanisms. The validation results derived from this research play an essential role in the integration of new insights and refined computational models into bridge design standards [3]. Therefore, this study represents a significant step forward in improving the computational guidelines for designing movable bridges, ensuring optimal utilisation of the remaining lifespan of existing bridge machineries by preventing unnecessary replacements and avoiding over dimensioning in the design of new movable bridges.

Pseudo-velocity shock response spectra (PVSRS) are a standard method for predicting the response of naval shock mounts to shock loading. As mounts become more complex and performance requirements drive designs to take advantage of increasingly exotic structural and material properties, PVSRS analysis may need further development to remain in use as a design tool.

Identifying the nonlinear normal modes (NNMs) of a double, triple and quadruple pendulum, we found that all NNMs approach homoclinic orbits through the unstable upright equilibrium. The NNMs are computed by numerical continuation of conservative orbits initialized at small-amplitude linear modes around the downward stable equilibrium. Based on this insight we show a swing-up control scheme bringing the pendula from the downward equilibrium to the upright position. As NNMs collect natural trajectories, sustaining a modal oscillation does not need control. The available control force is used to walk up the NNM, gradually pumping in energy, until the homoclinic orbit is reached, and therefore the upright position is reached.

The occurrence of dynamic high-amplitude chatter vibrations in high-speed micro-drills used for delicate neural, orthopaedic, and otolaryngology surgical procedures are investigated through experimental modal analysis. Traditional modal analysis techniques are unsuitable for the small geometry of this drill, requiring alternative excitation and data acquisition methods. The effectiveness of non-contact measurement techniques such as laser doppler vibrometers, high speed cameras and microphones are explored to collect vibration data. Parallelly, alternative methods of excitation to excite the higher frequency bandwidths at which these micro-drills operate are investigated. This study aims to extract the natural frequencies, damping coefficients and mode shapes. With a better understanding of these dynamical characteristics, an equivalent dynamical model that could capture regenerative and friction effects could be devised to examine the machining stability of micro-drills on bone, comprehend the origins of instability, thereby minimizing chatter and large amplitude vibrations. This could ultimately enhance the safety of surgeries and improve patient outcomes. Subsequent experiments will delve into investigating the dynamic behaviours of the drill under cutting conditions to replicate real surgical scenarios.