Session: 15-01-01: ASME International Undergraduate Research and Design Exposition

Paper Number: 100540

100540 - An Experiment on the Influence of Noise in a Circular Array Exhibiting High Amplitude Localization 

Unchecked and misunderstood vibrations can result in catastrophic failure. First analysis tools fail to predict the possibility of high amplitude vibrations. These stable high-energy localized modes are seen in nonlinear systems. High-energy localized modes have been observed in turbomachinery as well as micro-electromechanical systems. An active area of research is the influence of noise on response localizations in mechanical oscillator arrays. Experimental studies of the effects of noise have been conducted on systems with multiple stable vibrational states of cantilever beams. By building a circular oscillator modeled after turbo machinery a study into the influence of noise on localizations was conducted. The experiment was able to find evidence of the influence of noise on response localizations of rotating macro-scale cantilever structures.

In previous experiments, nonlinear characteristics were achieved using beams connected to large a shaker. A permanent magnet and electromagnet are attracted to each other on the free end of cantilever beams, creating the nonlinear force. Large electromagnets use current to adjust the system’s natural frequency. To design a circular array a more compact system requiring less power needed to be designed to reduce torsion loads while oscillating. The components of the circular array need to be symmetric, with strong coupling between beams, and similar natural frequencies in all the beams. The experiment is automated to collect data from hundreds of trials with high consistency to find the probability distribution.

 The system is designed to operate in the (10-40) x  [rad/s] range due to the servo motor provided. The hub that connects the motor of the shaft to eight cantilever beams was made using a 3D printer. For similar natural frequencies, a thin stainless-steel sheet is used for the beam material. Two permanent magnets are used for each beam, the inner magnet connected to the beam and the outer mounted to a linear actuator fixed to a circular plate. To reduce the mass moment of inertia and the stresses on the system light components and ferrous fasteners were used, allowing for fine-tuning of the beams’ natural frequency. Processing and data collection were performed by LabVIEW and Arduino. Data analysis was done with MATLAB.
The decision to use eight cantilever beams was arbitrary and resulted in too strong of coupling for any stable localized modes. To reduce the effects of coupling forces only 4 beams are tuned, and the remaining 4 beams oscillate without a magnetic force acting on the free end. The strong coupling is reduced to allow for localized modes to be observed. On rare occasions, the magnetic force will stall the linear actuator and prevent the change in frequency resulting in multiple beams remaining in high energy states. If the actuator is stalled it may not be discovered until the data has been analyzed. While the severity is moderate for actuator failure the frequency of detectability is low. Once the system was built control of the experiment can be done remotely with a wide range of programs available.

In conclusion, vibrations have the capability of resulting in catastrophic failure. Noise may be capable of controlling high-energy localized vibrations seen in nonlinear systems like turbomachinery. An experiment was developed and found evidence of the influence of noise on response localizations.
Future iterations to consider for the experiment include trying to enlarge the hub diameter and thickness and tailer a material property distribution using finite element analysis to reduce the effects of coupling.

Presenting Author: Jonathan DeBoer University of Maryland collegepark

Presenting Author Biography: Jonathan DeBoer is an undergraduate student at the University of Maryland College Park. Jonathan is being supported to pursue research in the Dynamics and Control Laboratory and Vibrations Laboratory of the Department of Mechanical Engineering.

Authors:

Jonathan DeBoer University of Maryland collegepark