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INNOVATIVE EXPERIMENTAL PRACTICES IN VIBRATION MECHANICS

Abstract

This paper presents the laboratory stands and the methodology that are used to provide the laboratory experiments as a supplement to the courses of dynamics and vibration. It is shown in what way the knowledge from the lectures can be used for analyzing the dynamics of mechanical systems or in what way the relations describing vibration can be used to determine some parameters of the system.

Keywords: dynamics, vibration, laboratory experiment, identification of parameters, verification of results

1. Introduction

The class-room teaching of mechanics courses, especially of dynamics and vibrations, involves theoretical models and mathematical computations. It is difficult for students to imagine in what way the systems work, what mechanical properties they have, and predict their behavior if a force or moment is applied. It is difficult to evaluate the behavior of the systems if they are governed by non-linear equations. The nonlinearity of the system can be the result of large displacement, friction force, impacts between the elements of the system, and external forces. One option is to make a computer simulation and define the most important parameters as a function of time or the system’s parameters. Usually our theoretical models do not consider all the factors that exist in a real world. If we investigate the vibration of the system with excitation it is usually taken as a harmonic one. But the excitation can be very complicated and there can be more sources of excitation; e.g., there are vibrations of the base on which the system is supported or the motor has eccentricity. It gives more degrees of freedom and more complicated mathematical models. In this paper we are going to present in what way to provide experiments so the theoretical knowledge can be confronted with the results that students obtain in laboratory and what conclusion and observation should be drawn out. For the computer simulation Matlab software is used. Some of the problems we verify in laboratory and for this purpose we built special laboratory stands. They have given us good results and therefore we are going to present what is positive and what should be improved. For some of problems with vibration we develop a new theory that allows explaining much more easily the behavior of the system. The vibration forces (component of inertial force) exist, and they can change the behavior of the system, move the system to a position of equilibrium or change stability of the equilibrium. Using the vibration forces we are able to explain why some systems can balance themselves automatically and why the elements move in vibratory transport. We can also explain an apparent change of dry friction into viscous damping and why the upper position of the pendulum is stable if its pivot vibrates. This theory gives very good results for parametric vibration of the pendulum, automatic balancing, and vibratory transport, and they will be presented in the paper. If we introduce vibration forces then we can demonstrate to the students why the unstable upper position of the pendulum is now stable and why the elements move under the action of vibration 2, 4.

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Sudhakar, K. V., & Majewski, T., & Maus, L. (2006, June), Innovative Experimental Practices In Vibration Mechanics Paper presented at 2006 Annual Conference & Exposition, Chicago, Illinois. 10.18260/1-2--428