大多數探討轉子系統時，常將基座視為剛體結構，忽略基座對整體機組造成的效應。當基座採取輕量鋼架設計時，轉子、軸承、基座的勁度比為同一個量級時，基座效應對轉子系統的影響顯得重要。大型旋轉機械，其基座形狀與結構都相當複雜，不易用有限元素模擬，本研究藉由轉子不平衡振動反應鑑別出支撐結構之動態勁度矩陣，並從支撐結構之動態勁度矩陣中求出基座接點處之頻率響應函數，再利用虛擬模態振形法，將基座接點處之頻率響應函數轉換成基座之等效
質量、阻尼、勁度矩陣，以便後續建立全系統之有限元素模型。本文利用ANSYS模擬，以Bachschmid等人設計的MODIAROT小型轉子試驗系統為範例，成效相當良好。本文方法與其他基座建模方法比較，最大優勢在於無須對轉子進行搬移動作，也不需進行模態測試。只需精確之轉子有限元素模型和轉子不平衡振動反應，即可求出基座之等效動態矩陣。適合應用於大型旋轉機械，如發電廠之汽渦輪發電機組，因轉子過於龐大不易搬移，較難單獨對基座進行模態測試。

Foundation effects are commonly ignored and rigid foundations are assumed in most rotordynamic analyses. However, steel-frame structures are adopted in modern foundation designs, and the dynamic effects of foundations may be profound,especially when the stiffness values of rotor, bearings, and foundations are of the same orders. Because of their complicated shapes and configurations, the foundations of large rotating machinery are difficult to model using finite element method. In this
study, the dynamic stiffness matrices of supporting structures are estimated from the unbalance responses of rotors, and then the frequency response functions at the junctions of foundations are derived. Subsequently, equivalent mass, damping and stiffness matrices for the foundations are conversed from the obtained frequency response functions of the foundation by Pseudo Mode Shaped Method (PMSM).MODIAROT, the rotor test rig designed by Bachschmid et al., is used to demonstrate
the effectiveness of the proposed modeling procedure by ANSYS simulation. The major advantage of the proposed procedure, compared with other foundation modeling methods, is that neither removal of the rotor nor modal testing of the foundations is necessary. Only accurate finite element models of rotors and unbalance responses are required to derive the equivalent dynamic matrices for the foundations. The proposed
procedure can be applied to large rotating machines with bulky rotors and massive structures, such as steam turbine-generators of power plants.