I get infinite response when I replace bushings by analytical bearings, in the runup function of Rotor Software package of Cambridge University.

Hi to everyone. I’m using the Rotor Software package of Cambridge University to solve a rotor runup analysis. I’m trying to replace the simple bushings by analytical rolling element bearings to get more detailed results. I’m using the 2 degree of freedom model of the bearings that is described in the attached .pdf file. In the shared link I also have 5 Matlab files, 1 script file and 4 functions. In the script, the model of the rotor, the analysis of the runup and a plot are defined. In the function rotormtx.m the matrices of the rotor are defined with the help of the function shftelem.m. In the function runup_RK4_modified_bearings.m the response of the rotor is defined with the help of Runge-Kutta 4th order numerical method and the function deriv_modified_bearings.m, in which the forces of the analytical rolling element bearings are also calculated.

The problem that I face is that when I replace one bushing by an analytical bearing, the response becomes infinite. Does anyone know why does this happen? Thanks to everyone in advanced.

https://drive.google.com/drive/folders/1DqDuMMKzW7wHnwAWYxyNv8eJM3sW7E96?usp=drive_link