FIVE FORCED-VIBRATION LABORATORY EXPERIMENTS USING TWO LUMPED MASS APPARATUSES WITH RESEARCH CALIBER ACCELEROMETERS AND ANALYZER

In 2004 a 3-credit engineering elective course in vibrations was created at the University of Southern Indiana. It consists of two hours of lecture and three hours of lab per week. One commercially available translational system and one rotational lumped mass system were purchased. Each turn-key system can be adjusted to study one, two, or three degrees of freedom systems in which the masses/inertial values can easily be changed. In addition, the translational system has three different types of springs and one variable air cylinder dashpot to choose from. Both systems come with an amplifier and motor which can optionally drive one of the masses in motion that is proportional to the signal on the input. However, instead of using the optical sensors to measure displacement, accelerometers were procured that are more representative of what engineers use in industry. Likewise, instead of purchasing the computer board and software that accompanies the lumped mass apparatuses (which in this case was primarily developed for controls laboratory experiments), a world-class analyzer (that also requires a PC and includes computer software for instrumentation) was purchased so that the sensors and analyzer can be used by students and faculty for research projects. This created hybrid vibration measurement apparatuses that combine the best combination of turnkey and custom systems. Another advantage with the hybrid approach is that the analyzer can also be used for acoustical measurements. A disadvantage is that the PC software that controls the analyzer is not user friendly, and requires substantial setup time by the instructor. The laboratory experiments that were developed include the study of free and forced vibration on various 1-DOF, 2-DOF, and 3-DOF vibration systems, with or without damping. Other experiments include designing a dynamic absorber visualizing modes of vibration, and determining the mechanical impedance.. In a 2010 ASEE Conference paper, four free-vibration experiments were described in detail. 1 In this paper five forced-vibration experiments are described in detail, as well as their impact on the student learning outcomes for the course. Other experiments may be developed without the turnkey apparatuses such as investigating vibrations of guitars or compressors. All experiments were developed and refined over several years. Student surveys have indicated that the laboratory experiments were effective in understanding the theory and provide an increased level of intellectual excitement for the course.