Extracting matrices from MSC Nastran/Patran (Circulatory, mass, stiffness, gyroscopic)

[James1986K]

I am currently using Nastran rotor dynamics for my thesis and require the following matrices to be extracted:
[KC]R = Circulatory matrix due to damping in rotating frame.
[KC]S = Circulatory matrix due to damping in fixed frame.
[G] = Gyroscopic Matrix.
[K] = Stiffness matrix.
[M] = Mass matrix.
Any help you can provide will be appreciated.

 

[dmapguru]

May I ask which Nastran? MSC?

DG

 

[dmapguru]

Sorry, you put MSC Nastran in the title of your post and I didn't catch it right away.

Look in the MSC Nastran Rotordynamics User’s Guide in the chapter "Theoretical Formulation"; there you will find the equations for a fixed and a rotating reference frame along with the circulatory and gyroscopic terms for which you are looking. This will help fix the nomenclature of the different rotor specific terms.

Now you will need to use some DMAP to obtain the various matrices you need. DMAP is a macro like language that allows you to change or add to the solution steps carried out by MSC Nastran. It is Fortran like, but also has a number of quirks specific to the language.

First, create a rotor model, one defined in a fixed frame and one defined in a rotating frame of reference. If you want circulation terms generated for things like bearing stiffness (which are part of the stator), define a stator as well, otherwise a boundary condition will suffice. Run this model in a solution sequence that generates the various items you are looking for (something like SOL 107 to extract the complex eigenvalues of the rotor) and make sure there are no errors in the run.

Write DMAP alters to add some instructions, probably to subDMAP GYROMAT. This subDMAP is where most of the rotor specific matrices are generated. You can write the various matrices to one or more different files.

1. The pch file (in DMIG format) - this is ASCII, human readable and generates MSC Nastran bulk data DMIG entries which contain the matrix data
2. An op2 (OUTPUT2) file - this can be a binary or ASCII encoded and not human readable; you will need a program (python, C, Fortran,...) to read the data and make it available in human readable form.
3. An op4 (OUTPUT4) file - this can be a binary (not human readable) or ASCII (human readable) file; you will need a program (python, C, Fortran,...) to read the binary data and make it available in human readable form.
4. An HDF5 file - this is a binary file and will need pytables + python, or clever C, to read the data and make it available in human readable form. An HDF5 viewer will assist in this.

If you don't know how to write DMAP alters, you are going to need some help to do this, and it is going to be an uphill journey. Decide on the items above and come back here for help with your input file.

DG