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Basic issue with plotting derivative

Michael Renaud
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.

Thanks

1 Reply Last Post Feb 21, 2013, 8:23 AM EST
Henrik Sönnerlind COMSOL Employee
Posted: 5 years ago Feb 21, 2013, 8:23 AM EST
Hi,

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.

Regards,
Henrik
Hi, 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. Regards, Henrik

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