3. Modeling A#
3.1. Characteristics of modeling#
The rotor is modelled by linear volume elements (“3D” modeling, MECA_HEXA8).
CALC_MODES calculates the modes specific to standstill (ie. without gyroscopic damping) and in rotation, ie. with gyroscopic damping (option MECA_GYRO), but taking into account or not taking into account the softening effect by centrifugal stiffness (option RIGI_ROTA).
3.2. Characteristics of the mesh#
Number of stitches HEXA8 |
896 |
Table 3.2-1
3.3. Results: comparison between Code_Aster and ANSYS calculations#
The table gives the numerical values tested in this test case. These are the natural frequencies of the cylinder in a free-free configuration at standstill and at 3000 rpm.
Identification |
Reference type |
Reference value |
Tolerance |
Mode 1 |
“EXTERNE” |
2627.2 |
|
Mode 2 |
“EXTERNE” |
2627.6 |
|
Mode 3 |
“EXTERNE” |
3017.1 |
|
Mode 4 |
“EXTERNE” |
3017.3 |
|
Mode 5 |
“EXTERNE” |
6276.1 |
|
Mode 6 |
“EXTERNE” |
6276.1 |
|
Mode 7 |
“EXTERNE” |
6327 |
|
Mode 8 |
“EXTERNE” |
6487.5 |
|
Mode 9 |
“EXTERNE” |
6487.6 |
|
Fashion 10 |
“EXTERNE” |
6937.8 |
|
Fashion 11 |
“EXTERNE” |
6938.8 |
|
Mode 12 |
“EXTERNE” |
7090.9 |
|
Mode 13 |
“EXTERNE” |
7091 |
|
Mode 14 |
“EXTERNE” |
7410.5 |
|
Table 3.3-1 : Summary of results tested at standstill
The gap at standstill between the two models seems significant (up to 6%). The explanation lies in the fact that code ANSYS underintegrates linear solid elements. Since Code_Aster does not allow the sub-integration of elements HEXA8, we used exact integration. It is therefore not possible to verify whether the difference decreases with these elements. On the other hand, Code_Aster allows sub-integration for elements HEXA20 (cf. models B and C).
Identification |
Reference type |
Reference value |
Tolerance |
Mode 1 |
“EXTERNE” |
53.42 |
|
Mode 2 |
“EXTERNE” |
100 |
|
Mode 3 |
“EXTERNE” |
2588.8 |
|
Mode 4 |
“EXTERNE” |
266.6 |
|
Mode 5 |
“EXTERNE” |
2982.4 |
|
Mode 6 |
“EXTERNE” |
3052.4 |
|
Mode 7 |
“EXTERNE” |
6256.1 |
|
Mode 8 |
“EXTERNE” |
6296.5 |
|
Mode 9 |
“EXTERNE” |
6326.2 |
|
Mode 10 |
“EXTERNE” |
6455.1 |
|
Mode 11 |
“EXTERNE” |
6520.1 |
|
Table 3.3-2 : Summary of results tested in rotation without centrifugal sweetening
Identification |
Reference type |
Reference value |
Tolerance |
Mode 1 |
“EXTERNE” |
26.63 |
|
Mode 2 |
“EXTERNE” |
26.63 |
|
Mode 3 |
“EXTERNE” |
50 |
|
Mode 4 |
“EXTERNE” |
50 |
|
Mode 5 |
“EXTERNE” |
2588.4 |
|
Mode 6 |
“EXTERNE” |
266.1 |
|
Mode 7 |
“EXTERNE” |
2982.1 |
|
Mode 8 |
“EXTERNE” |
3052 |
|
Mode 9 |
“EXTERNE” |
6255.8 |
|
Mode 10 |
“EXTERNE” |
6296.2 |
|
Mode 11 |
“EXTERNE” |
6326 |
|
Mode 12 |
“EXTERNE” |
6455 |
|
Mode 13 |
“EXTERNE” |
6519.9 |
|
Table 3.3-3 : Summary of results tested in rotation with centrifugal sweetening