Some Problems with Element Connectivity Matrix 2

[frztrb]

Hi All

trying to write the Element Connectivity matrix in MATLAB , reading about it somewhere , I have a bit of doubts that how it is done here , it say that it is done in a counter clockwise way , I don't see that , how ?

and also for example , for the node 1 it is mentioned that it is connected to node 2 which is a successive node . but for node 2 it is not mentioned . but this is not the same for node 4 , that is mentioned for the second time that node 2 is connected to node 4 and node 4 is connected to node 2

why is that ?

the structure

http://i61.tinypic.com/20rl4ax.jpg

the matrix

http://i60.tinypic.com/k1dfra.jpg

 

[csk62]

Node numbering convention is important. You need to make sure that it guarantees a positive determinant for the Jacobian matrix. Connectivity matrices should be straight forward given a "master element" with a given local convention.

Its been a while for me, but at first glance at your matrix I am unsure about the third row entries.

 

[bkal]

I am not sure about MATLAB implementation, but generally connectivity tells you which nodes create each element. In your case it should be (assuming that you have triangular elements):

element 1, nodes: 1, 2, 3
element 2, nodes: 2, 4, 3
element 3, nodes: 3, 4, 5
element 4, nodes: 5, 4, 6

 

[frztrb]

thanks a lot , yes but I from one side doubt if the source I was studying was assuming triangular elements , I think only truss elements

so it would be different not ? still I don't get the rule , for triangular is understandable though , for truss , for me , not.

here is the source of it :

http://www.math.purdue.edu/~zcai/math615/matlab_fem.pdf

I need to understand the way they have done the elem conn matrice .

then I don't get the equation 10 to 14

thank you very much

 

[bkal]

The caption for figure 1 states it is for triangular elements, and in my opinion there is a typo in the third row of the matrix which should read 4 5 3 (circled numbers in the figure are element numbers, which correspond to the matrix row numbers). For truss elements, the equivalent matrix would need only two columns, i.e. start node - end node.