Folks-
Please be gentle on the newbie...
I have been asked to provide a customer with "interface loads" for a water tank in an aircraft application. We generally know the shape of the tank and the attachment points and methods are all well defined. Being statically indeterminant, I have been using MSC-NASTRAN to perform a rigid body analysis. (This is the approach our customer has specified as well.)
My approach has been to define nodes at each of the attachment points and the CG. I created a rigid (RBE2) with the attachment points as dependant nodes and the CG as the independant node. All okay so far...
There are several tie-rods with spherical bearings that support the tank assembly. These I modelled with bars (CONROD) and gave them artificially high stiffnesses.
Where I run into a problem is with two attachment points where the bearings are pressed into the tank struture. I figured that I would just apply the correct boundary conditions at these two nodes and be off to the races.
What I have run into is that NASTRAN will not allow you to apply single point constraints (SPC) directly to an RBE2. [I suppose this is because an RBE2 is a multi-point constraint (MPC).] To get around this, I created an additional node along the line connecting the CG with the problematic node (1% from attachment point) and created a short (~.25") beam (CBEAM) with artificially high stiffness between the RBE2 and the attachment point.
TWO SIMPLE QUESTIONS:
1) How is anyone else dealing with this type of problem?
2) Is the solution that I chose going to provide accurate answers?
Your comments are appreciated.
Mark Hampson Sr. Product Engineer GOODRICH Corp.