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Base vector coordinate system

Posted 02.05.2013, 15:05 GMT-4 Structural Mechanics Version 4.3a 3 Replies

John R Puentes
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I am modeling the anisotropic behavior of a plate that have fibers oriented in different directions. For this purpose, I am using the structural mechanics feature. I am orienting my fibers using a based vector system. Does this system work for angles other than 0,-45,45 and 90? I have not been able to rotate my coordinate system at other angles ( I would like to try 10,15, 25 and so on)

Any advise
3 Replies Last Post 14.08.2013, 17:30 GMT-4
Henrik Sönnerlind COMSOL Employee

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Posted: 1 decade ago 02.05.2013, 17:03 GMT-4
Hi,

There is no restriction in the base vector system. Actually it is more general than most users want or need, since it can define non-orthogonal axes and axes which do not have unit length. But to make proper use of that, you have to be familiar with tensor calculus in non-orthogonal systems.

The simplest way of defining a pure rotation in the e.g. the xy plane is to fill in the cells with

cos(angle) sin(angle) 0
-sin(angle) cos(angle) 0
0 0 1

where angle can be a parameter for easy modification. In 2D only the upper left 2x2 matrix is needed.

For efficiency, select the "Assume orthonormal" checkbox.

In your case it may however be even easier to use a "Rotated system" Instead of the Base vector system.

Regards,
Henrik




Hi, There is no restriction in the base vector system. Actually it is more general than most users want or need, since it can define non-orthogonal axes and axes which do not have unit length. But to make proper use of that, you have to be familiar with tensor calculus in non-orthogonal systems. The simplest way of defining a pure rotation in the e.g. the xy plane is to fill in the cells with cos(angle) sin(angle) 0 -sin(angle) cos(angle) 0 0 0 1 where angle can be a parameter for easy modification. In 2D only the upper left 2x2 matrix is needed. For efficiency, select the "Assume orthonormal" checkbox. In your case it may however be even easier to use a "Rotated system" Instead of the Base vector system. Regards, Henrik
John R Puentes
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Posted: 1 decade ago 15.05.2013, 17:04 GMT-4
Thanks alot, that was exactly what I needed!!
Thanks alot, that was exactly what I needed!!
Alireza Bayat
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Posted: 1 decade ago 14.08.2013, 17:30 GMT-4
Hi All

I have a little problem with coordinate transformation using the Base vector coordinate system.

When I'm changing the coordinates e.g. from x,y,z to ------>>>> x1,y1,z1 as below:

x1=n1*(fxx*x+fxy*y+fxz*z)+n2*(fyx*x+fyy*y+fyz*z)+n3*(fzx*x+fzy*y+fzz*z)
x2=a1*(fxx*x+fxy*y+fxz*z)+a2*(fyx*x+fyy*y+fyz*z)+a3*(fzx*x+fzy*y+fzz*z)
x3=b1*(fxx*x+fxy*y+fxz*z)+b2*(fyx*x+fyy*y+fyz*z)+b3*(fzx*x+fzy*y+fzz*z)

Nothing changes in the equation view under Base Vector System!

I was just wondering why the expressions in the equation view for sys2.T11=sys2.T22=sys3.T33=1 & sys2.T12=sys2.T13=....=0

???


Hi All I have a little problem with coordinate transformation using the Base vector coordinate system. When I'm changing the coordinates e.g. from x,y,z to ------>>>> x1,y1,z1 as below: x1=n1*(fxx*x+fxy*y+fxz*z)+n2*(fyx*x+fyy*y+fyz*z)+n3*(fzx*x+fzy*y+fzz*z) x2=a1*(fxx*x+fxy*y+fxz*z)+a2*(fyx*x+fyy*y+fyz*z)+a3*(fzx*x+fzy*y+fzz*z) x3=b1*(fxx*x+fxy*y+fxz*z)+b2*(fyx*x+fyy*y+fyz*z)+b3*(fzx*x+fzy*y+fzz*z) Nothing changes in the equation view under Base Vector System! I was just wondering why the expressions in the equation view for sys2.T11=sys2.T22=sys3.T33=1 & sys2.T12=sys2.T13=....=0 ???

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