1. By Chanat Ratanasumawong (CRW) Identification of System’s Dynamic Parameters 2142-391 Engineering Mechanical Laboratory, CRW, 2014 2142-391 Engineering Mechanical Laboratory 1

2. Contents  1. Introduction  2. Motivation  3. Objectives  4. Apparatus 2 Tacoma bridge collapses 2142-391 Engineering Mechanical Laboratory, CRW, 2014

3. 1. Introduction 3 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  vibrations of an automobile or a motorcycle 2142-391 Engineering Mechanical Laboratory, CRW, 2014

4. Analysis of a vibration system (1) 4 The real system Physical modeling Only the most important features are considered Mathematical modeling Newton’s Laws 2142-391 Engineering Mechanical Laboratory, CRW, 2014

5. Analysis of a vibration system (2) 5 Derivation of the governing equation Solution of the equation(s) Interpretation of the results 2142-391 Engineering Mechanical Laboratory, CRW, 2014

6. 6 2. Motivation In general the vibrating system is simplified to a simple model including three basic elements.  Element restoring or releasing KE Mass (Mass moment of inertia)  Element restoring or releasing PE Elastic component (spring)  Element dissipating energy Damper To analyze the vibration problem or to control vibration characteristics of a system, the quantities of these elements must be determined via some measurements. 2142-391 Engineering Mechanical Laboratory, CRW, 2014

7. 7 3. Objectives Part 1: Free vibration To determine values of three basic quantities of a simplified beam system through experiments by observing the time response [displacement vs. time]. To study the vibration behavior of the system when the conditions/ parameters vary. To find the vibration response due to harmonic excitation. Part 2: Force vibration 2142-391 Engineering Mechanical Laboratory, CRW, 2014

8. 8 4. Apparatus  The apparatus consists of a beam, a spring, an adjustable damper.  The apparatus may be transformed into a variety of dynamic configurations.  Required excitation can be applied by a unbalance motor.  Displacement of the beam is measured by a displacement sensor.  Signals are collected by a PC. 2142-391 Engineering Mechanical Laboratory, CRW, 2014