Help with modeling radial forces in ROSS (positive displacement machines)

[ndohme]

Hi everyone,

I'm currently working with ROSS (Rotordynamics Open Source Software) and trying to model radial forces that typically occur in positive displacement machines such as screw compressors. The goal is to account for these forces both in the calculation of initial static deflection and ideally in the subsequent rotordynamic analysis.

For the static analysis, I could potentially use point masses as a workaround, but I'm unsure whether this approach correctly captures deflection in the x and y directions. Additionally, I believe these point masses would need to be removed for the dynamic analysis, as they would distort the mass matrices.

Is there a way in ROSS to define stationary radial loads along the rotor axis?

I would greatly appreciate any guidance, examples, or experiences on how to approach this problem in ROSS.

Kind regards!

[ndohme]

Hello,

can anybody give me some input on this?

Kind regards!

[jguarato]

Hi, @ndohme!

Currently, ROSS doesn’t have a built-in way to apply stationary external forces along the rotor. The run_static() method only accounts for gravity loads from shafts and disks. This could be a feature to be added in future versions of ROSS.

For now, one possible workaround is to modify the source code to include external forces, or to create separate rotor objects for static and dynamic analyses. In the static case, you can add extra shaft elements or disks connected to the main shaft nodes to represent the effect of static radial loads.