Graduate students at The University of Massachusetts Lowell have been performing an ongoing series of student class projects on vibration. Research Assistant Sergio Obando explains that the students conducted MIMO (Multiple Input Multiple Output) and OMA (Operational Modal Analysis) testing on various academic structures. In particular, they tested a 1.5-ft (0.4572-m) aluminum frame and a multiple component system consisting of three aluminum plates mounted to a 50-ft (15.24-m) rectangular steel tube frame. The goal of the project was to simulate a support system and conduct exploratory testing to see what factors influence measurements. "We ran a comparison using one Modal Shop Mini Shaker, two shakers, four shakers, and varying the location of the shakers. We also were trying to explore measurements with different sized stingers, and stingers not attached properly to shakers. The results of these exploratory experiments set guidelines for what is the best way to conduct experiments," says Obando.
Another interesting experiment was actually on display at IMAC (International Modal Analysis Conference), and a paper was submitted about it at the conference as well. Three 2- to 3-ft long wind turbine blades were fitted with 32 PCB 352A24 teardrop accelerometers. Each one was attached to a Modal Shop 2007E Mini Shaker, with LMS Test Lab as the data acquisition software. The project goal was to calculate stress and strain on turbine blades created by exciting the blades at a given frequency. The graduate students would then take measurements with a laser vibrometer, which tracks the displacement in space on the blades.