Enforcement of user-defined modal properties

A new project is set-up in tuto_test_SCIM_17 by copy/paste tuto_test_SCIM_01.
The idea is to short circuit some or all the modal calculations of MANATEE by enforcing some user defined values. This feature is (for now) not available in the GUI.

By default, the damping of all structural modes used by MANATEE is given by the input

Input.Simu.ksi_damp = 2/100;
Input.Simu.type_damping = 0;

If you have run an experimental test and you want to use more accurate values within MANATEE, it is possible by specifying the modal parameters of some specific mode shapes. To do that the modal parameter enforcement must be set:

Input.Simu.is_force_natfreq = 1;

In the first simulation project tuto_test_SCIM_01 a resonance occurs due to the ovalization mode of the stack at 1150 rpm due to a natural frequency close to 650 Hz. Let’s change the ovalization mode natural frequency to 500 Hz and the associated damping to 1%. Additionally the breathing mode (order 0) of the stack is changed to 2.78% without changing the calculated associated natural frequency. Finally, the circumferential mode order 5 natural frequency is changed to 4000 Hz, but the associated damping is kept unchanged.

Input.Simu.ExpModes=[[2 0];[0 0];[5 0]];
Input.Simu.ExpDamp=[1/100 2.78/100 NaN];
Input.Simu.ExpFreq=[500 NaN 4000];

Result interpretation

The order tracking of the sound power level at variable speed is done using plot_VS_ASWL_order_analysis

The two following graphs contains the tuto_test_SCIM_01 and tuto_test_SCIM_17 order tracking analysis

tuto_SCIM_01 order analysis
tuto_SCIM_01 order analysis
tuto_SCIM_17 order analysis
tuto_SCIM_17 order analysis

One can notice that the order 2 excitation resonance with the ovalization mode of the lamination occurs at lower speed due to reduced natural frequency, and that the width of the peak is thinner due to lower enforced damping value. The noise level is roughly unchanged because the flux level is constant in this speed range.

This feature of MANATEE allows you to check the influence of a structural redesign, or enforce your own modal parameters which can be based on FEA simulations or experimental modal analysis.

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