Construction of a Vibrating Structure for Demonstration of Vibration Measurement and FFT Analysis

Aaron Alexander, Kenneth Belanus
2014 ASEE Annual Conference & Exposition Proceedings   unpublished
Many Mechanical Engineering Technology (MET) programs include a Basic Instrumentation class structured to give students hands-on experiences with measurement and analysis systems. As part of a module on vibrations and the Fast Fourier Transform (FFT), a lab was developed to create a three-tiered vibrating structure. This test apparatus consists of relatively inexpensive components with threaded rods for the columns, plywood for the tiers, and an adjustable orbital sander for the vibration
more » ... the vibration source. The vibration source is mounted to the top tier, and its rotational speed is adjusted by a controller made for common power tools. Different vibrational modes for the structure can be observed by varying the speed of the vibration source. In one mode the entire structure sways back-and-forth with the top tier showing the largest displacement. In a second mode the center tier is vibrating while the upper and lower tiers remain nearly motionless. One or more accelerometers may be attached to the tier having the largest displacement for a specific mode. The accelerometer output is measured using either an oscilloscope or a computer data acquisition system (DAS). A second test may be performed using a weight on the center tier to demonstrate a change in natural frequency with the added mass to the system. It is also possible to adjust the natural frequency by adjusting the position of the center tier relative to the upper and lower tiers. Including the oscilloscope in the required measurements gives the student exposure to a second measurement system as well as allowing them to double-check the results of their analysis of the data from the DAS. Analysis of the data is performed outside of the lab using MathCAD or Excel and builds off a previous tutorial lab on frequency analysis methods based on Fast Fourier Transform (FFT) methods. The students are required to use the FFT results to identify the resonant frequencies as part of their lab report. Introduction:
doi:10.18260/1-2--20208 fatcat:jymfdx5d7rhdxfp2epfun3v7zu