Instructor: Dr .- Ing . Mostafa Ranjbar

1. Selected Topics in Engineering Acoustics (MCE 540 Graduate Course – Mechanical Engineering Department) • Instructor: • Dr.-Ing. Mostafa Ranjbar • Ph.D. (Dr-Ing.), Multidisciplinary Engineering Design Optimization of Structures, TechnischeUniversität Dresden, Germany, 2011 • M.Sc., Vibration Monitoring and Fault Diagnosis of Structures, TarbiatModares University, Tehran, Iran, 2000 • B.Sc., Mechanical Engineering, Shiraz university, Iran, 1998

2. Text Materials No textbook is required. These are the optional reference books: • Steffen Marburg, Bodo Nolte, Computational Acoustics of Noise Propagation in Fluids – Finite and Boundary Element Methods, Springer-Verlag, Berlin Heidelberg, 2008. • Pierce, A.D.; Acoustics: An Introduction to its Physical Principles and Applications, published by the Acoustical Society of America, 1993.

3. Topics to be covered: • 1-D Wave Example: Strings • Sound in fluids • Acoustic Impedance • Source energy, intensity and power • Sources, reciprocity, Green’s functions, etc. • Sound absorption and absorbing materials • Sound in waveguides, mufflers, and silencers • Sound in enclosures

4. Grading: • Midterm Exam (30%) • Final Exam (50%) • HW (20%)

5. What is Vibration?

6. What is Vibration? • Scientific Definition Any motion that repeats itself after an interval of time

7. What is Vibration? • Scientific Definition Any motion that repeats itself after an interval of time • Engineering Definition Deals with the relationship between forces and oscillatory motion of mechanical systems

8. Why is Vibration Important? The Tacoma Narrows Bridge Disaster November 7, 1940

9. Why is Vibration Important? Amplitude of oscillation reached 3 meters!

10. What was the cause?

11. Vortex Shedding …Caused Wind-Induced Vibration (?)

12. Why is Vibration Important?

13. Why is Vibration Important?

14. Why is Vibration Important?

15. Wing Flutter Failures

16. Basic Concepts Every object has: • Frequencies at which it “likes” to vibrate • Characteristic geometries of vibration

17. Basic Concepts Every object has: • Frequencies at which it “likes” to vibrateç • Characteristic geometries of vibration

18. Modeling Vibration The Ingredients: • Inertia(stores kinetic energy) • Elasticity(stores potential energy) 1 Realistic Addition: • Energy Dissipation

19. Modeling Vibration The Ingredients: • Inertia(stores kinetic energy) • Elasticity(stores potential energy) 1 2 Realistic Addition: • Energy Dissipation

20. Modeling Vibration The Ingredients: • Inertia(stores kinetic energy) • Elasticity(stores potential energy) 1 2 Realistic Addition: • Energy Dissipation 3

21. Modeling Vibration The Ingredients: • Inertia(stores kinetic energy) • Elasticity(stores potential energy) 1 2 3 Realistic Addition: • Energy Dissipation

22. Modeling Vibration The Ingredients: • Mass, m • Stiffness, k m k c Realistic Addition: • Damping, c

23. How is this model useful? m k c

24. Basic Concepts • Resonance

25. Basic Concepts • Resonance • A vibration of large amplitude • Occurs when an object is forced near its natural frequency

26. Resonance • A vibration of large amplitude • Occurs when an object is forced near its natural frequency Object

27. Resonance • A vibration of large amplitude • Occurs when an object is forced near its natural frequency Object Model

28. Vibration Absorbers • Used to eliminate vibration of an object Object (that vibrates too much)

29. Vibration Absorbers • Used to eliminate vibration of an object Vibration Absorber (‘absorbs’ vibration) Object (that vibrates too much)

30. Vibration Absorbers • Used to eliminate vibration of an object Vibration Absorber Choose these to eliminate motion of object. Object (that vibrates too much)

31. Vibration Absorbers

32. Mode Shapes “Characteristic Geometry” of Vibration • Mode Shapes • Resonance • Natural Frequencies