Basic issue with plotting derivative

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Michael Renaud

Michael Renaud

February 21, 2013 10:40am UTC

Basic issue with plotting derivative

Hi everybody,

I am using the 2d structural mechanics for static simulations of a cantilever undergoing a point force. I want to plot the derivative of the deflection u by respect to the position x along a boundary. But plotting d(u,x) gives me a zeroed value function.
By digging in the forum, I thought first that this may be due to the order of the shape function, but it should not be an issue in my case as I just want to know a first order derivative. It looks like a basic issue but I do not find the solution.


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Henrik Sönnerlind

Henrik Sönnerlind
COMSOL Employee

February 21, 2013 1:23pm UTC in response to Michael Renaud

Re: Basic issue with plotting derivative


There are two issues here:

1. Since the Solid Mechanics interface is defined on the 'Material frame', the displacements are functions of the material coordinates (X,Y,Z) rather than the spatial coordinates (x,y,z).

2. Still, it will not be possible to evaluate d(u,X) on a boundary or an edge, since such derivatives are only available in the domain. So in a Volume plot, you would be able to display that quantity.

The solution to your problem is however simple: There are built-in variables uX, vX etc. which you can use in your graphs.


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