Mechanische trillingen LES 9 MODALE ANALYSE Patrick Guillaume

Mechanische trillingen LES 9 – MODALE ANALYSE Patrick Guillaume E-mail: patrick. guillaume@vub. ac. be Tel. : 02/6293566 Faculty of Engineering Department of Mechanical Engineering ACOUSTICS & VIBRATION RESEARCH GROUP Pleinlaan 2 • B-1050 Brussel • Belgium avrg@vub. ac. be • http: //avrg. vub. ac. be 1 9/14/2021 MECHANISCHE TRILLINGEN, LES 9, 2005

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 2 MECHANISCHE TRILLINGEN, LES 9, 2005 Acoustics & Vibration Research Group Vrije Universiteit Brussel

Random Noise 3 MECHANISCHE TRILLINGEN, LES 9, 2005 Acoustics & Vibration Research Group Vrije Universiteit Brussel

Uniform Window 4 MECHANISCHE TRILLINGEN, LES 9, 2005 Acoustics & Vibration Research Group Vrije Universiteit Brussel

Hanning Window 5 MECHANISCHE TRILLINGEN, LES 9, 2005 Acoustics & Vibration Research Group Vrije Universiteit Brussel

Burst Random 6 MECHANISCHE TRILLINGEN, LES 9, 2005 Acoustics & Vibration Research Group Vrije Universiteit Brussel

Burst Random with Uniform Window 7 MECHANISCHE TRILLINGEN, LES 9, 2005 Acoustics & Vibration Research Group Vrije Universiteit Brussel

Exponential Window 8 MECHANISCHE TRILLINGEN, LES 9, 2005 Acoustics & Vibration Research Group Vrije Universiteit Brussel

Periodic Random / Pseudo-Random Excitation Periodic random – No leakage errors (periodic signal) in steady-state conditions – Averaging is required Pseudo random – Constant amplitudes and random phases – No leakage errors (periodic signal) in steady-state conditions – Averaging is not required 9 MECHANISCHE TRILLINGEN, LES 9, 2005 Acoustics & Vibration Research Group Vrije Universiteit Brussel

Impact Excitation Force transducer and tip Advantages – Easy to use – No interaction with structure – Force is flat in useful frequency range – Relatively inexpensive 10 MECHANISCHE TRILLINGEN, LES 9, 2005 Acoustics & Vibration Research Group Vrije Universiteit Brussel

Impact Excitation Disadvantages – Large crest factor – Nonlinearities – Limited control of amplitude spectrum 11 MECHANISCHE TRILLINGEN, LES 9, 2005 Acoustics & Vibration Research Group Vrije Universiteit Brussel

Force Window Force window (or transient window) – Remove noise Effect of “Double Hits” 12 MECHANISCHE TRILLINGEN, LES 9, 2005 Acoustics & Vibration Research Group Vrije Universiteit Brussel

Response Window Lightly damped structure – Leakage errors Heavily damped structure – Remove noise 13 MECHANISCHE TRILLINGEN, LES 9, 2005 Acoustics & Vibration Research Group Vrije Universiteit Brussel

Overzicht 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 14 MECHANISCHE TRILLINGEN, LES 9, 2005 Acoustics & Vibration Research Group Vrije Universiteit Brussel

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 15 MECHANISCHE TRILLINGEN, LES 9, 2005 Acoustics & Vibration Research Group Vrije Universiteit Brussel

Step 2: Making the Measurements Checking the quality of the measurements – Noise – Nonlinearities? 16 MECHANISCHE TRILLINGEN, LES 9, 2005 Acoustics & Vibration Research Group Vrije Universiteit Brussel

Rigid Body Modes 17 MECHANISCHE TRILLINGEN, LES 9, 2005 Acoustics & Vibration Research Group Vrije Universiteit Brussel

Step 3: Modal Parameter Estimation SDOF – Uncoupled modes MDOF – Coupled modes 18 MECHANISCHE TRILLINGEN, LES 9, 2005 Acoustics & Vibration Research Group Vrije Universiteit Brussel

Curve-Fitters for Modal Analysis – MDOF Two step approach – Poles are global parameters – Time MDOF (LSCE) – Freq. MDOF (Poly. MAX) – Mode shape vectors are local parameters – LSFD 19 MECHANISCHE TRILLINGEN, LES 9, 2005 Acoustics & Vibration Research Group Vrije Universiteit Brussel

Stabilization Diagram 20 MECHANISCHE TRILLINGEN, LES 9, 2005 Acoustics & Vibration Research Group Vrije Universiteit Brussel

Least Squares Frequency Domain – LSFD 21 MECHANISCHE TRILLINGEN, LES 9, 2005 Acoustics & Vibration Research Group Vrije Universiteit Brussel

Residual terms – LR, UR 22 MECHANISCHE TRILLINGEN, LES 9, 2005 Acoustics & Vibration Research Group Vrije Universiteit Brussel

Step 4: Checking the Model Synthesized FRF Modal Assurance Criteria MAC 23 MECHANISCHE TRILLINGEN, LES 9, 2005 Acoustics & Vibration Research Group Vrije Universiteit Brussel

PZL Mielec Skytruck (FLi. TE Project) 24 MECHANISCHE TRILLINGEN, LES 9, 2005 Acoustics & Vibration Research Group Vrije Universiteit Brussel

Stabilization Diagrams LSCF (Poly. MAX) LSCE 25 MECHANISCHE TRILLINGEN, LES 9, 2005 Acoustics & Vibration Research Group Vrije Universiteit Brussel

Mode Shapes (3. 17 Hz, 1. 62 %) 26 MECHANISCHE TRILLINGEN, LES 9, 2005 Acoustics & Vibration Research Group Vrije Universiteit Brussel

Mode Shapes (8. 39 Hz, 1. 93 %) 27 MECHANISCHE TRILLINGEN, LES 9, 2005 Acoustics & Vibration Research Group Vrije Universiteit Brussel

Computer Simulations: What if? Modification simulation – Design optimization Response simulation – Acoustic noise calculations – Fatigue analysis – … 28 MECHANISCHE TRILLINGEN, LES 9, 2005 Acoustics & Vibration Research Group Vrije Universiteit Brussel

Dynamic Modelling Process 29 MECHANISCHE TRILLINGEN, LES 9, 2005 Acoustics & Vibration Research Group Vrije Universiteit Brussel

FE Model Updating 30 MECHANISCHE TRILLINGEN, LES 9, 2005 Acoustics & Vibration Research Group Vrije Universiteit Brussel

Structural Dynamic Modifications 31 MECHANISCHE TRILLINGEN, LES 9, 2005 Acoustics & Vibration Research Group Vrije Universiteit Brussel

Slat Track Optimisation 32 MECHANISCHE TRILLINGEN, LES 9, 2005 Acoustics & Vibration Research Group Vrije Universiteit Brussel

Forced Response Simulation 33 MECHANISCHE TRILLINGEN, LES 9, 2005 Acoustics & Vibration Research Group Vrije Universiteit Brussel