Engineering Mechanical Laboratory Identification of System’s Dynamic Parameters by NAV and CRW Engineering Mechanical Laboratory, NAV & CRW, 2008

2 Identification of System’s Dynamic Parameters 1. Introduction 2. Motivation 3. Objectives 4. Apparatus Engineering Mechanical Laboratory, NAV & CRW, 2008

3 Identification of System’s Dynamic Parameters 1. Introduction Engineering Mechanical Laboratory, NAV & CRW, 2008 Vibration is the branch of engineering that deals with repetitive motion of mechanical systems. Examples: engineering structure to earthquakes unbalanced rotating machine plucked string of a musical instrument ride of an automobile or motorcycle

4 Identification of System’s Dynamic Parameters 1. Introduction Engineering Mechanical Laboratory, NAV & CRW, 2008 Only the most important features are considered in the analysis to predict the behavior of the system under specified input conditions. The analysis of a vibrating system usually involves mathematical modeling derivation of the governing equations solution of the equations interpretation of the results.

5 Identification of System’s Dynamic Parameters 2. Motivation Engineering Mechanical Laboratory, NAV & CRW, 2008 In general the vibrating system is simplified to a simple model including three basic elements. the element restoring or releasing KE => mass or a mass moment of inertia the element restoring or releasing PE => an elastic component or a spring the element dissipating energy => damper

6 Identification of System’s Dynamic Parameters 2. Motivation Engineering Mechanical Laboratory, NAV & CRW, 2008 To analyze the vibration problem, the quantities of these elements must be determined via some measurements. How important are these quantities? See movies The collapse of Tacoma bridge The Chinook resonances The MD-80 landing

7 Torsional Vibration Torsion of a beam Torsional vibration of building and bridge

8 Torsional Vibration Torsion bar Torsion bar suspension

9 Identification of System’s Dynamic Parameters 3. Objectives Engineering Mechanical Laboratory, NAV & CRW, 2008 To determine values of three basic quantities of a 3-DOF torsional system i.e. the mass moment of inertia of rotating disks, the elastic stiffness of torsional springs and the dampers through experiments by observing the time response [displacement vs time graphs].

10 Identification of System’s Dynamic Parameters Engineering Mechanical Laboratory, NAV & CRW, Apparatus The torsional apparatus may be transformed into a variety of dynamic configurations with represent important classes of real life systems. It represents physical plants including rigid bodies; flexibility in drive shafts, gearing and belts; and coupled discrete vibration.