1. 1 / 13 Vibration analysis and noise reduction of the swinging unit Magyar Bálint (BME) A C R O B O T E R 3rd OSB meeting Reading, 22-23 / 11 / 2007 Vibration analysis and noise reduction of the swinging unit

2. 2 / 13 Vibration analysis and noise reduction of the swinging unit Magyar Bálint (BME) A C R O B O T E R 3rd OSB meeting Reading, 22-23 / 11 / 2007 Noise components of ducted fans Flow source  Trace noise  Noise of the turbulent boundary layer  Noise of the separated flow region Mechanical source  Noise of the drive train  Noise of the excited cover  Noise of the PWM control

3. 3 / 13 Vibration analysis and noise reduction of the swinging unit Magyar Bálint (BME) A C R O B O T E R 3rd OSB meeting Reading, 22-23 / 11 / 2007 Flow source noises Trace noise Noise of the turbulent boundary layer

4. 4 / 13 Vibration analysis and noise reduction of the swinging unit Magyar Bálint (BME) A C R O B O T E R 3rd OSB meeting Reading, 22-23 / 11 / 2007 Flow source noises Noise of the separated boundary layer Proper and improper constructions for the entrance region (1) Separation bubble (1)Laminar sublayer (2)Turbulent boundary layer

5. 5 / 13 Vibration analysis and noise reduction of the swinging unit Magyar Bálint (BME) A C R O B O T E R 3rd OSB meeting Reading, 22-23 / 11 / 2007 Mechanical source noises Finite element modal analysis DOF: 162168 N. of elements: 26824 Solver: COSMOS Mesh:Mode shape at 48.55 Hz:

6. 6 / 13 Vibration analysis and noise reduction of the swinging unit Magyar Bálint (BME) A C R O B O T E R 3rd OSB meeting Reading, 22-23 / 11 / 2007 Mechanical source noises Results Number of natural frequencies in each 20 Hz range

7. 7 / 13 Vibration analysis and noise reduction of the swinging unit Magyar Bálint (BME) A C R O B O T E R 3rd OSB meeting Reading, 22-23 / 11 / 2007 Measurement Four-channel-measurement  2 accelerometers  microphone  tachometer

8. 8 / 13 Vibration analysis and noise reduction of the swinging unit Magyar Bálint (BME) A C R O B O T E R 3rd OSB meeting Reading, 22-23 / 11 / 2007 Measurement Zero pitch Max pitch direction 1 Max pitch direction 2

9. 9 / 13 Vibration analysis and noise reduction of the swinging unit Magyar Bálint (BME) A C R O B O T E R 3rd OSB meeting Reading, 22-23 / 11 / 2007 Waterfall diagrams Microphone signal compared with finite element results

10. 10 / 13 Vibration analysis and noise reduction of the swinging unit Magyar Bálint (BME) A C R O B O T E R 3rd OSB meeting Reading, 22-23 / 11 / 2007 Waterfall diagrams Microphone signal scaled by rpm

11. 11 / 13 Vibration analysis and noise reduction of the swinging unit Magyar Bálint (BME) A C R O B O T E R 3rd OSB meeting Reading, 22-23 / 11 / 2007 Waterfall diagrams The 8 kHz PWM noise appearing in the signal of the 2nd accelerometer

12. 12 / 13 Vibration analysis and noise reduction of the swinging unit Magyar Bálint (BME) A C R O B O T E R 3rd OSB meeting Reading, 22-23 / 11 / 2007 The 8 kHz PWM noise appearing in the signal of the microphone

13. 13 / 13 Vibration analysis and noise reduction of the swinging unit Magyar Bálint (BME) A C R O B O T E R 3rd OSB meeting Reading, 22-23 / 11 / 2007 Conclusions Reduction or elimination of noise components Flow source components  Trace noise - Not significant  Noise of the turbulent boundary layer - By choosing better airfoil  Noise of the separated flow region - Proper contstruction of the entrance region Mechanical source components  Noise of the excited cover - By increasing stiffness, rarefying natural frequencies  Noise of the PWM control - By raising controller frequency above human hearing limit Estimated total possible noise reduction: