ABSTRACT
Pre-stressed structures can be found in many technical applications, such as rotor and bladed disk assemblies. Press fits in particular are commonly used in high-speed rotating machinery. However, this design leads to questions about contact modelling, contact behavior and contact friction/damping, which have to be addressed during the design process.
In a first step, press fits are evaluated in a contact analysis based on a finite element approach by using solid elements. This method allows a realistic description of the contact in comparison with simplified beam models. Due to temperature and centrifugal loads, the contact gaps are generally not completely closed for increasing speeds of the rotor. These effects must be taken into account in a subsequent dynamic analysis. For this purpose, the active contacts are replaced by multipoint constraints. The following static analysis with linearized contacts serves to provide the internal stress state for the calculation of the geometric stiffness matrix. The solution of the generalized eigenvalue problem considers both the geometric and the convective stiffness matrix.
The last step is to solve the complex eigenvalue problem using a state-space representation of the reduced second-order system under consideration of the gyroscopic matrix for the speed range of interest. To lower the computing time in industrial applications, the system matrices are usually transformed into modal space using the real eigenmodes. A special procedure performs mode-tracking of the changing eigenfrequencies with increasing rotational speed.
This contribution is based on recently published works and presents further improvements. An implementation is demonstrated based on the FEA package PERMAS. Computations and examples are all carried out by using this commercially available software to emphasize the relevance of the findings for industrial applications.
