Evaluation of 3D rotordynamics capabilities within NX nastran
Abstract: In today's industry, companies within the jet engine industry are trying to
make their product development more effective. One way is to use product
models to enable upfront evaluation through simulation.
To model the dynamic behaviour of rotors, mainly beam and shell elements
are used in the common rotor-dynamics software. As the geometry becomes
more complex, 3D rotor-dynamics can be used to solve vibration problems as
well as the interactions with bearings and the non-rotating structure. This
3D-modelling could also give a more realistic post-processing than the
current software in the market and the dynamics of the whole engine could
be assessed.
To try to solve these rotor-dynamics problems, NX7 was used, a commercial
CAD/CAM/CAE software developed by Siemens PLM software. The solver used is
NX Nastran Rotor-Dynamics. The main interest in this choice (with the 3D
capabilities) is that both the CAD and CAE will be performed on the same
platform and adjustments can be done faster if some problems in meshing or
modelling occur.
The aim of this Master's thesis is thus to develop a whole engine with the
Computer Aided Design capabilities of NX7 and investigate the possibilities
of doing rotor-dynamics analyses with NX Nastran Rotor Dynamics. First of
all, simpler models were studied to validate the analyses and more
complicated elements were added piece by piece until all the problems are
solved to build the whole engine and analyse it.
The results presented in this Master's thesis reveals several aspects of
rotordynamics analysis. First of all, a section is dedicated to the mode
shapes of the rotor for several common models. Then plots of Campbell
diagram are shown and compared with theoretical results. Finally, a mass
unbalance analysis is performed for all types of rotor and the displacement
and rotation response are plotted for some particular nodes. These
displacement curves are also compared with the Campbell diagrams to check
if the simulation are run properly.
The main problem in this Master's thesis is that the program is today too
undeveloped for efficient 3D modelling of rotors. Indeed, it was found that
rotating and stationary parts could not be coupled in the Campbell diagram.
Also a lot of commands and execution needs to be done manually and the
possibilities of post-processing have to be developed to facilitate an
effective evaluation of the results.
CLICK HERE TO DOWNLOAD THE WHOLE ESSAY. (in PDF format)