MET 415 Lecture Notes

Chapter 10

Text: Building Better Products with FEA,
by V. Adams & A. Askenazi, (Read Chapter 10)


CONVERGENCE

Assumption:  The mesh is sufficient to capture the behavior of interest.

Evaluating, after solution, to decide if mesh refinement is needed = convergence

Accuracy is controlled by the mesh.

Page 316: "... an "ideal" model is one that enables you to solve your problem in the time allotted."

Page 317: "... convergence is directly related to the load and constraints applied to a specific run."

... "uncertainty is preferable to the term "error" ....... NOT !

"Error estimates in FEA refer to the relative difference between results across an element edge or at a node."

Page 319:  Simple error estimate equations. ANSYS uses strain energy.

Figure 10.6:  NOTICE, displacement converges before stress

Figure 10.8 and 10.9:  are "converged" when <10% change in stress occurs

P-elements go through automatic convergence during a solution

H-elements are usually manually converged (ANSYS: adaptive meshing)

Page 323, referring to P-elements: "... if they indeed converge" ???

Element Quality:  effects accuracy (and therefore, effects convergence)

Refers to page 246:  aspect ratio, taper, corner angles, warp

Summary:  "... only through correlation to test data and reconciliation of ALL detected discrepancies, that confidence in analysis results can be achieved."