In contrast to a two (2) degrees-of-freedom flexible support, a foundation can possess NDOFF degrees-of-freedom and NDOFF >= 2. If not specified, foundation is considered to be rigid. The foundation matrices are usually created by using Guyan reduction from general Finite Element Analysis programs, such as NASTRAN or ANSYS, and only the coordinates which are pertinent to the rotor motion are retained. The foundation is connected to the rotor assembly by bearings. The foundation box needs to be checked in the bearing connected to the foundation. The (X,Y,Rx,Ry) are the coordinate entries in the foundation matrices. When foundation is included, one should always review the text output from Lateral Vibration Model Summary, which includes the modal analysis for the foundation alone. This can be used to verify the foundation data. For static deflection and critical speed analysis, foundation is neglected and assumed to be rigid.
****************************** Foundation Data *****************************
C:\DyRoBeS\Example\LargeTurbine\Foundation.fdn
Foundation DOF = 15
************************ Foundation Modal Analysis ***********************
Mode Damping Factor Damping Coef. Damped Freq.(R/S) Hz
1 .15534E-01 -96.522 6212.8 988.81
2 .69470E-02 -96.522 13894. 2211.2
3 .80217E-02 -128.70 16043. 2553.3
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15 .21968E-01 -965.22 43926. 6991.1
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Example: The foundation has 15 degrees-of-freedom and has two connections to the rotor system. The first connection is from a support station 17 to the Foundation DOF 4 and 5. The second connection is from a rotor station 8 to the Foundation DOF 10 and 11 for the X and Y translational displacements, and 13 and 14 for the Rx and Ry rotational displacements.
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