Lecture Notes: Introduction to Finite Element Method |
Chapter 4. FE Modeling and Solution Techniques |
VII. Adaptivity (h-, p-, and hp-Methods)
•Future of FE applications
•Automatic refinement of FE meshes until converged results are obtained
•User’s responsibility reduced: only need to generate a good initial mesh
Error Indicators:
Define,
σ --- element by element stress field (discontinuous),
σ*--- averaged or smooth stress (continuous),
σE = σ - σ* --- the error stress field.
Compute strain energy,
U = ∑Ui , |
Ui = ∫1 σT E−1σdV ; |
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M |
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i =1 |
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Vi |
2 |
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M |
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1 σ*T |
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U * = ∑Ui* , |
U *i |
= ∫ |
E−1σ*dV ; |
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UE |
i =1 |
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Vi |
2 |
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= ∑UE i , |
UE i = ∫1 σTE E−1σE dV ; |
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M |
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i =1 |
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Vi 2 |
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where M is the total number of elements, Vi is the volume of the element i.
© 1997-2002 Yijun Liu, University of Cincinnati |
117 |
Lecture Notes: Introduction to Finite Element Method |
Chapter 4. FE Modeling and Solution Techniques |
One error indicator --- the relative energy error:
|
U |
E |
1/ 2 |
|
η = |
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. |
(0 ≤η ≤1) |
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U +UE |
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The indicator η is computed after each FE solution. Refinement of the FE model continues until, say
η ≤ 0.05.
=> converged FE solution.
Examples:
…
© 1997-2002 Yijun Liu, University of Cincinnati |
118 |