1. Mechanische trillingen
LES 9 – MODALE ANALYSE
Patrick Guillaume
Tel.: 02/
11/27/2018
MECHANISCHE TRILLINGEN, LES 9, 2005

2. Random Excitation Random sequence with Gaussian distribution
Random amplitudes and phases
Averaging is needed
Converge to flat amplitude spectrum
Remark: Force is not flat in general due to interaction with the structure
Signal processing errors (leakage errors)
Effect of nonlinearities is reduced by averaging
MECHANISCHE TRILLINGEN, LES 9, 2005

3. Random Noise
MECHANISCHE TRILLINGEN, LES 9, 2005

4. Uniform Window
MECHANISCHE TRILLINGEN, LES 9, 2005

5. Hanning Window
MECHANISCHE TRILLINGEN, LES 9, 2005

6. Burst Random
MECHANISCHE TRILLINGEN, LES 9, 2005

7. Burst Random with Uniform Window
MECHANISCHE TRILLINGEN, LES 9, 2005

8. Exponential Window
MECHANISCHE TRILLINGEN, LES 9, 2005

9. Periodic Random / Pseudo-Random Excitation
No leakage errors (periodic signal) in steady-state conditions
Averaging is required
Pseudo random
Constant amplitudes and random phases
Averaging is not required
MECHANISCHE TRILLINGEN, LES 9, 2005

10. Impact Excitation Force transducer and tip Advantages Easy to use
No interaction with structure
Force is flat in useful frequency range
Relatively inexpensive
MECHANISCHE TRILLINGEN, LES 9, 2005

11. Impact Excitation Disadvantages Large crest factor
Nonlinearities
Limited control of amplitude spectrum
MECHANISCHE TRILLINGEN, LES 9, 2005

12. Force Window Force window (or transient window)
Remove noise
Effect of “Double Hits”
MECHANISCHE TRILLINGEN, LES 9, 2005

13. Response Window Lightly damped structure Heavily damped structure
Leakage errors
Heavily damped structure
Remove noise
MECHANISCHE TRILLINGEN, LES 9, 2005

14. Overzicht EMA EMA = Experimentele Modale Analyse
Stap 1: Experimentele opstelling
Stap 2: Opmeten van de FRF’s
Stap 3: Bepalen van de modale parameters door bvb. curve fitting
Stap 4: Validatie van de resultaten
Stap 5: Toepassingen
MECHANISCHE TRILLINGEN, LES 9, 2005

15. Step 1: Setting Up the Modal Test
Choosing DOFs
Suspension
Choice of excitation
Position/connection of force transducer
Mounting the response transducers
Transducer conditioning and calibration
Setting up the analyzer
Range setting
Frequency band
FRF estimator
MECHANISCHE TRILLINGEN, LES 9, 2005

16. Step 2: Making the Measurements
Checking the quality of the measurements
Noise
Nonlinearities?
MECHANISCHE TRILLINGEN, LES 9, 2005

17. Rigid Body Modes
MECHANISCHE TRILLINGEN, LES 9, 2005

18. Step 3: Modal Parameter Estimation
SDOF
Uncoupled modes
MDOF
Coupled modes
MECHANISCHE TRILLINGEN, LES 9, 2005

19. Curve-Fitters for Modal Analysis – MDOF
Two step approach
Poles are global parameters
Time MDOF (LSCE)
Freq. MDOF (PolyMAX)
Mode shape vectors are local parameters
LSFD
MECHANISCHE TRILLINGEN, LES 9, 2005

20. Stabilization Diagram
MECHANISCHE TRILLINGEN, LES 9, 2005

21. Least Squares Frequency Domain – LSFD
MECHANISCHE TRILLINGEN, LES 9, 2005

22. Residual terms – LR, UR
MECHANISCHE TRILLINGEN, LES 9, 2005

23. Step 4: Checking the Model
Synthesized FRF
Modal Assurance Criteria MAC
MECHANISCHE TRILLINGEN, LES 9, 2005

24. PZL Mielec Skytruck (FLiTE Project)
MECHANISCHE TRILLINGEN, LES 9, 2005

25. Stabilization Diagrams
LSCE
LSCF (PolyMAX)
MECHANISCHE TRILLINGEN, LES 9, 2005

26. Mode Shapes (3.17 Hz, 1.62 %)
MECHANISCHE TRILLINGEN, LES 9, 2005

27. Mode Shapes (8.39 Hz, 1.93 %)
MECHANISCHE TRILLINGEN, LES 9, 2005

28. Computer Simulations: What if?
Modification simulation
Design optimization
Response simulation
Acoustic noise calculations
Fatigue analysis …
MECHANISCHE TRILLINGEN, LES 9, 2005

29. Dynamic Modelling Process
MECHANISCHE TRILLINGEN, LES 9, 2005

30. FE Model Updating
MECHANISCHE TRILLINGEN, LES 9, 2005

31. Structural Dynamic Modifications
MECHANISCHE TRILLINGEN, LES 9, 2005

32. Slat Track Optimisation
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33. Forced Response Simulation
MECHANISCHE TRILLINGEN, LES 9, 2005