Qualifying the FE Model
The nonlinear option for the Adams flexible body is based on a SOL400-legal MSC Nastran bulk data file (BDF) describing at a minimum the nodes, elements and materials which make up the component. Subject to some limitations, the BDF used to create an MNF can be used as the source file for the nonlinear flexible body. See "
Appendix I: Using a BDF from which an MNF was Generated" for more details. Nonlinear finite element analysis, by itself, is complex; coupling it with multi-body dynamics can be even more complex. So, taking steps to ensure the nonlinear finite element model is suitable for such coupled analysis is strongly advisable. The following guidelines should be adopted by the user to minimize the modelling errors:
1. The user is encouraged to simulate the multi-body system with simpler linear flexible bodies (MNF) instead of nonlinear flexible bodies with similar loading. The response of this system can help identify modelling mistakes (locking, over-constraint model and incorrect topology and so on.) and can serve as a baseline for the nonlinear flexible body results.
2. Before importing the nonlinear flexible body into an Adams model the user, if possible, should run a standalone SOL 400 MSC Nastran nonlinear static/dynamic analysis. The user can approximate the loading and the boundary conditions applied to the nonlinear FE model with what he expects the part to be subjected to in the multi-body system. If this is not practical, it would be valuable to at least make sure the deck is syntactically correct according to SOL400 standard by checking that FE model can pass the IFPL (pre-processing) stage of a SOL400 run. If it cannot, then one should not expect to be successful using this BDF as the basis for a nonlinear flexible body in Adams.
3. The user should identify all the boundary nodes (nodes on which Markers are placed in Adams models).
4. Each boundary node should have 6 degrees of freedom. Therefore, makers cannot be placed on nodes that are connected to only solid elements. Examples of valid boundary nodes on which makers can be placed are:
a. RBE2 independent nodes
b. Beam or shell element nodes
5. In a majority of cases RBE2 independent nodes would be used as boundary nodes of nonlinear flexible bodies, just like they are for linear flexible bodies. It is therefore important for the user to only connect the makers to RBE2 independent nodes (and not on the dependent nodes). Connecting to RBE2 dependent nodes will result in the failure of the simulation.
6. RBE2 elements should be carefully defined in the FE model. Nodes should not be shared across RBE2 elements which will cause inconsistent constraints and failure of simulation. In addition, convergence may be aided by removing the "456" dependent degree of freedom.