Four free-vibration laboratory experiments using two lumped mass apparatuses with research caliber accelerometers and analyzer

Abstract

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. Both systems come with an amplifier and motor which can optionally drive one of the masses in motion that is proportional to the voltage signal on the input. However, instead of using the optical sensors, accelerometers were procured that are more representative of what engineers use in industry and research, as well as provide instrumentation knowledge and skills. 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 includes computer software for control) was purchased so that the sensors and analyzer can be used by students and faculty for research projects. This analyzer can also be used for acoustic measurements. A disadvantage is that the 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 vibration, forced vibration, 1 DOF, 2DOF, and 3 DOF systems, dynamic absorber, modes of vibration, and the effects of damping. In this paper, only the free vibration experiments, four in all, will be described in detail, as well as their impact on the student learning outcomes for the course. These experiments were developed and refined over several years. Each laboratory workstation can accommodate two students at a time. 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. A subsequent paper is planned to describe the forced vibration experiments. © American Society for Engineering Education, 2010.