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Derive the shape function for a linear quadrilateral element and show its variation over the element.
1 Answer
written 6.9 years ago by | • modified 6.9 years ago |
Shape function for Quadratic Element
The element has 3 nodes.
Pilot function will be ϕ=Aˉx[ˉx−he2][ˉx−he] ....(1)
∴ϕ1=A[ˉx−he2][ˉx−he]
At node 1, ϕ1=1 & ˉx=0, above equation becomes
1=A[−he2](−he)
∴A=2h2e
∴ϕ1=2h2e(ˉx−he2)(ˉx−he)
Rearranging the term
ϕ1=(1−2ˉxhe)(1−ˉxhe)
Equation (1) becomes ϕ2=Aˉx(ˉx−he)
At node 2, ˉx=he2 ϕ2=1
∴1=A.he2(he2−he)
=A(he2)(−he2)
A=−4h2e
∴ϕ2=−4h2eˉx(ˉx−he)
Rearranging the term we get
ϕ2=4ˉxhe(1−ˉxhe)
Equation (1) becomes ϕ3=Aˉx(ˉx−he2)
At node 3, ϕ3=1 ˉx=he
∴1=A.he(he−he2)
=A(he)(he2)
∴A=2h2e
ϕ3=2h2e.ˉx(ˉx−he)
Rearranging the term we get
ϕ3=−ˉxhe(1−2ˉxhe)