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Three families of \(C^1\)-\(P_{2m+1}\) Bell finite elements on triangular meshes

  • Xuejun Xu,
  • Shangyou Zhang

摘要

The \(C^1\) C 1 - \(P_5\) P 5 Bell finite element removes the three degrees of freedom of the edge normal derivatives of the \(C^1\) C 1 - \(P_5\) P 5 Argyris finite element. We call a \(C^1\) C 1 - \(P_k\) P k finite element a Bell finite element if it has no edge-degree of freedom and it contains the \(P_{k-1}\) P k - 1 space locally. We construct three families of odd-degree \(C^1\) C 1 - \(P_{2m+1}\) P 2 m + 1 Bell finite elements on triangular meshes. Comparing to the \(C^1\) C 1 - \(P_{2m}\) P 2 m Argyris finite element, the \(C^1\) C 1 - \(P_{2m+1}\) P 2 m + 1 Bell finite elements produce same-order solutions with much less unknowns. For example, the second \(C^1\) C 1 - \(P_7\) P 7 Bell element (from the second family) and the \(C^1\) C 1 - \(P_6\) P 6 Argyris element have numbers of local degrees of freedom of 31 and 28 respectively, but oppositely their numbers of global degrees of freedom are 12V and 19V asymptotically, respectively, where V is the number of vertices in a triangular mesh. A numerical example says the new element has about 3/4 number of unknowns, but is about 5 times more accurate. Numerical computations with all three families of elements are performed.