1 / 13Vibration analysis and noise reduction of the swinging unitMagyar Bálint (BME)Magyar Bálint (BME)
A C R O B O T E R 3rd3rd OSB meeting OSB meeting Reading, Reading, 22-23 22-23 / / 1111 / 2007 / 2007
Vibration analysis and noise reduction of the swinging unit
2 / 13Vibration analysis and noise reduction of the swinging unitMagyar Bálint (BME)Magyar Bálint (BME)
A C R O B O T E R 3rd3rd OSB meeting OSB meeting Reading, Reading, 22-23 22-23 / / 1111 / 2007 / 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 / 13Vibration analysis and noise reduction of the swinging unitMagyar Bálint (BME)Magyar Bálint (BME)
A C R O B O T E R 3rd3rd OSB meeting OSB meeting Reading, Reading, 22-23 22-23 / / 1111 / 2007 / 2007
Flow source noises
• Trace noise
• Noise of the turbulent boundary layer
0
0
drag
lifting
F
FS
4 / 13Vibration analysis and noise reduction of the swinging unitMagyar Bálint (BME)Magyar Bálint (BME)
A C R O B O T E R 3rd3rd OSB meeting OSB meeting Reading, Reading, 22-23 22-23 / / 1111 / 2007 / 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 / 13Vibration analysis and noise reduction of the swinging unitMagyar Bálint (BME)Magyar Bálint (BME)
A C R O B O T E R 3rd3rd OSB meeting OSB meeting Reading, Reading, 22-23 22-23 / / 1111 / 2007 / 2007
Mechanical source noises
Finite element modal analysis
•DOF: 162168•N. of elements: 26824 •Solver: COSMOS
Mesh: Mode shape at 48.55 Hz:
6 / 13Vibration analysis and noise reduction of the swinging unitMagyar Bálint (BME)Magyar Bálint (BME)
A C R O B O T E R 3rd3rd OSB meeting OSB meeting Reading, Reading, 22-23 22-23 / / 1111 / 2007 / 2007
Mechanical source noises
Results
Number of natural frequencies in each 20 Hz range
7 / 13Vibration analysis and noise reduction of the swinging unitMagyar Bálint (BME)Magyar Bálint (BME)
A C R O B O T E R 3rd3rd OSB meeting OSB meeting Reading, Reading, 22-23 22-23 / / 1111 / 2007 / 2007
Measurement
• Four-channel-measurement 2 accelerometers microphone tachometer
8 / 13Vibration analysis and noise reduction of the swinging unitMagyar Bálint (BME)Magyar Bálint (BME)
A C R O B O T E R 3rd3rd OSB meeting OSB meeting Reading, Reading, 22-23 22-23 / / 1111 / 2007 / 2007
Measurement
Zero pitch
Max pitch direction 1
Max pitchdirection 2
9 / 13Vibration analysis and noise reduction of the swinging unitMagyar Bálint (BME)Magyar Bálint (BME)
A C R O B O T E R 3rd3rd OSB meeting OSB meeting Reading, Reading, 22-23 22-23 / / 1111 / 2007 / 2007
Waterfall diagrams
Microphone signal compared with finite element results
10 / 13Vibration analysis and noise reduction of the swinging unitMagyar Bálint (BME)Magyar Bálint (BME)
A C R O B O T E R 3rd3rd OSB meeting OSB meeting Reading, Reading, 22-23 22-23 / / 1111 / 2007 / 2007
Waterfall diagrams
Microphone signal scaled by rpm
11 / 13Vibration analysis and noise reduction of the swinging unitMagyar Bálint (BME)Magyar Bálint (BME)
A C R O B O T E R 3rd3rd OSB meeting OSB meeting Reading, Reading, 22-23 22-23 / / 1111 / 2007 / 2007
Waterfall diagrams
The 8 kHz PWM noise appearing in the signal of the 2nd accelerometer
12 / 13Vibration analysis and noise reduction of the swinging unitMagyar Bálint (BME)Magyar Bálint (BME)
A C R O B O T E R 3rd3rd OSB meeting OSB meeting Reading, Reading, 22-23 22-23 / / 1111 / 2007 / 2007
The 8 kHz PWM noise appearing in the signal of the microphone
13 / 13Vibration analysis and noise reduction of the swinging unitMagyar Bálint (BME)Magyar Bálint (BME)
A C R O B O T E R 3rd3rd OSB meeting OSB meeting Reading, Reading, 22-23 22-23 / / 1111 / 2007 / 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:dBALA 86