| Matlab command | plot_ODS |
|---|---|
| Module | SM.pp |
| Description | PLOT_ODS plots the Operational Deflection Shape of the structure at the input frequency |
| Parameters | Frequency (Hz) |
| Restrictions |
Result
This MANATEE software post processing allows to visualize the outer structure (stator or rotor) operational deflection shape at a given frequency. This animation is equivalent to the experimental ODS (Operational Deflection Shape) analysis obtained by placing a series of accelerometers around the stator or rotor circumference. For an induction machine with 3 pole pairs, one obtains at twice the fundamental frequency with
plot_ODS(2*Output.Electrical.freq0)the following animation:
- Operational deflection shape of the stator with 64 accelerometers
- plot_ODS
One can see that the deflection has 6 minima/maxima which corresponds to a wavenumber r=2p=6, in agreement with theory (magnetic force is proportional to the square of the flux density). This post processing is useful to compare simulation with measurements, and observe the effect of the Shannon theorem. For instance, when reducing the number of virtual accelerometers of the simulation from 64 to Input.Simu.Nacc_xy=8, the new deflection shape has a wavenumber 2:
- Operational deflection shape of the stator with 8 accelerometers
To correctly "see" a wavenumber 6 vibration one should use at least 12 accelerometers. 8 accelerometers result in undersampling of the vibration wave, which is then observed as a r=2 vibration wave.
In case of eccentricities, one can also see some unbalance in the vibration waves:
- Operational deflection shape with eccentricities
Note that the operational deflection shape is not necessarily an image of the structure modal shape. In case of forced excitation, the deflection shape is an image of the electromagnetic excitations and is generally rotating whereas at resonance (match between force frequency and wavenumber with mode natural frequency and shape), the deflection is an image of the modal shape where the vibration nodes should have a fixed position.
