Natural and Cartesian Coordinates of Triangular Element-Finite Element Method-Assignment Solution, Exercises of Mathematical Methods for Numerical Analysis and Optimization

This assignment solution was submitted to Amar Sharma for Finite Element Method course at Aligarh Muslim University. It includes: Derive, Relationship, Natural, Area, Cartesian, Coordinates, Triangular, Element

Typology: Exercises

2011/2012

Uploaded on 07/08/2012

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Problem 3.8: Derive the relationship between the natural ( area ) and Cartesian
coordinates of a triangular element.
Solution:
The natura
l coordinates are given as:
L1 =
L2 =
L3 =
Also
A = A1 + A2 + A3
We have
+ + = L1 + L2 + L3 = 1
Also
Ni = L1 Nj = L2 Nk = L3
Then the relation between the natural and Cartesian coordinates is given by
X = x1 L1 + x2 L2 + x3 L3
Y = y1 L1 + y2 L2 + y3 L3
These equations can be expressed as
=
This equation can be inverted to obtain
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Problem 3.8: Derive the relationship between the natural ( area ) and Cartesian coordinates of a triangular element.

Solution:

The natura l coordinates are given as:

L 1 =

L 2 =

L 3 =

Also

A = A 1 + A 2 + A 3

We have

    • = L 1 + L 2 + L 3 = 1

Also

Ni = L1 Nj = L2 Nk = L 3

Then the relation between the natural and Cartesian coordinates is given by

X = x 1 L 1 + x 2 L 2 + x 3 L 3

Y = y 1 L 1 + y 2 L 2 + y 3 L 3

These equations can be expressed as

This equation can be inverted to obtain

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Where A is given as

A =

By expanding, the relation is given as

= L 1 = (x2y3 – x3y2) + (y2 – y3)x + (x3 – x2)y

= L 2 = (x3y1 – x1y3) + (y3 – y1)x + (x1 – x3)y

= L 3 = (x1y2 – x2 y1) + (y1 – y2)x + (x2 – x3)y

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