Good Vibrations Engineering Ltd.

Home CO2 Compressor Mechanical concept paper

Finite element First is a based on an old design approach: detailed design drawings were preceeded with layout drawings. The layout drawings were done by a designer, and then passed onto a finite element analyst for what was a quick & dirty FE model. The FE model form was generally reflective of the structure itself - usually either plate or beam elements.

Areologist offers an opportunity to display FE First design approach. It's a shell + frame structure, and thus most suited to plate & beam elements. The tanks were modelled using femap generation for one tank. The six tanks were just replications of that first tank, with individual coordinate system. The equivalent accuracy model in solids would be MUCH larger. But model size isn't really an issue, its the time it takes to generate a model from CAD drawings. While program managers are under the impression its just 'push a button' to generate the FE model from the detailed drawings, I've never seen that work. So each design change takes a significant FE effort. Nastran code for the tank is listed ( Tank FE model), and a FEMAP version of whole model model is shown. The entire Nastran dat file was a bit large to include, just for demo.

Initial DesignFor simple structures, back of the envelop sketch will do
FE Model Plannning
  1. select element and grid numbers to components or areas for easy retrieval
  2. set up types and locations for individual coordinate systems - this can make moving something around later more easily. And for axi-symmetric structures such as this, a cyclindrical coordinate system makes things a lot easier
  3. record numbering selections
Integration of Generation & Meshing
  1. for some structures, with no strange shapes or interfaces - such as our tanks, meshing is quite useful - but maintain control of your number and coordinate systems
  2. element and grid replication still works in basic Nastran, and it can reduce hand input by quite a lot. But more importantly, changing something like a cylinder radius becomes quite trivial, for updated design iterations.

Areologist FE model