Problems with modeling assembly FEM in I-DEAS NX 12

[mclem]

I am currently working on modeling a gas turbine engine disc and blades assembly to simulate the effects of centrifugal loading in the disc. I had no issues modeling the parts separately (disc and blade), but I have major issues with making the FEA model for the rotor assembly to work properly. Essentialy, I am convinced that my problem lies in the definition of how the parts are in relation to each others, but can't put my finger on it.

I have build the assembly by constraining one blade in position, and then making 81 copies of it around the disc. Following this, I have locked each blade in relation to the disc, and build an assembly FEM by appending the parts FEMs. With the assembly FEM seemingly built, I use the Contact Set automatic function to identify all elements potentially in contact. Again, I-DEAS seems to respond well by identifying all the proper elements, and creating a Contact Set.

In a nutshell, everything seems to look good except the final solution!!! Blades are displaced improperly and the stress distribution through the disc does not make sense (it does if the disc is solve by itself without blades, but not with blades... the same disc FEM is used in both cases???).

Again, I think that my problem lies in how the relations between the blades and the disc are defined... I am just not sure how to go about it. I am still a rookie at this. Would anybody have a recommendation, or better yet, good knowledge of how this should be done and the kindness to share it?

 

[jelmerra]

The automatic setting could be one cause, in the past that used to be a guarantee for disaster. Things will become balloons for what ever reason.

Another item that could screw things up if you mesh the parts before you append them. One way or the other the coordinate systems of the parts get mixed up.

You also need to think about the target contact set if not set properly things will move the wrong way around.

Tetrahedron mesh and contacts are not very good try to use bricks.

When going non-linear and contact forget tetrahedrons.

jelmerra

 

[mclem]

Thanks Jelmerra... I will try your tips and keep working at it. Will post back when I get it working.

Cheers,

mclem