Grid display issue

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Grid display issue

tkdiff
I am new to FEATool, so please forgive my lack of understanding.  I was evaluating the latest version (1.12) using Matlab 2019b, and was manually going through the steps for the example problem Fluid Structure Interaction - Elastic Beam.  When I followed the tutorial exactly, everything worked properly.  However, at the end of the tutorial, it indicated that "one could use a finer grid along the cylinder and beam boundaries, as well as higher order elements".  
First, it is not obvious to me how to use higher order elements using the internal mesher and solver.  When I tried to mesh with gmsh, it yielded an error.
Second, when I went back and tried to refine the grid, either by using the refine button or manually changing the element size in settings, it seemed to execute but there was no grid display.
Are these software issues or my lack of understanding how to use the software.  
Thanks for any help
Tom
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Re: Grid display issue

Leon Robers
This post was updated on .
Hi

In FEATool, the element order or the shape function order respectively is indicated with 'sflag1' for first order discretization and 'sflag2' for second order. To change between those two, there are two ways:

In the FEA-Tool Gui, go to the equation tab. There you have a field with "FEM-Discretization". As you change it from "first order conforming" to "second order conforming", you will see the change in the right field from "sflag1" to "sflag2" which is done automatically.

In Matlab, it is nearly as straight forward. In the tutorial you specify some strings directly at the beginning, which will later be used for the property assignment of the shape function and some other things:

cOptDef = { 'sf_u',     'sflag1';
             'sf_p',     'sflag1';...

sf_u stands for the shape function of the velocity, sf_p for the pressure. I recommend not to change the order of the pressure shape function, but the velocity sf is easily changed just by replacing "1" with "2".

Note that the shape function property is not yet implemented. This is done by the following line of code:

fea.phys.fsi.sfun = { opt.sf_u, opt.sf_u, opt.sf_p, opt.sf_u, opt.sf_u };
which would be equal to directly typing
fea.phys.fsi.sfun = { 'sflag1', 'sflag1', 'sflag1', 'sflag1', 'sflag1', 'sflag1' };

You specify the shape function order for each variable (here velocity and pressure), whereas the velocity is split into two or three variables depending on your problem dimension (2D or 3D). For 2D-CFD problems, you specify 3 shape function (x-velocity, y-velocity, pressure). Maybe check a cfd only tutorial for a better understanding. Since this is a fluid structure interaction, you have 2 more shape functions to specify. They most likely stand for the deflection in x and y direction. So the above mentioned line of code in other words is

fea.phys.fsi.sfun = { sf_ux, sf_uy, sf_p, sf_dx, sf_dy }; where each shape function string can either be "sflag1" or "sflag2"

Concerning your second question

The meshing, in this case, is really buggy. I experience the same issues as you, for the new and old version of FEA-Tool. Normally, refining and changing grid size works fine (maybe this is again an issue due to the two domains, structural and fluid) Here, only the admin can help you...

I hope I could help you.
Best,
Leon

Edit: it is 'sflag1' not just sflag1 in the line of code above

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Re: Grid display issue

tkdiff
Leon,
Thanks for the help with the shape function order.  I was successful with that help.

I'm still seeing the issues with the grid display not uniformly appearing after refinement with this sample problem.  Hoping Johan chimes in on this one.

I'm also wondering if it is possible to specify a log or semilog plot in the FEAtool app?

Tom
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Re: Grid display issue

Precise Simulation
Administrator
In reply to this post by Leon Robers
Thank you for helping out with answering questions Leon.

Regarding the mesh display issue, it was due to fsi models having an additional mesh stored (to display the deformation) which did not match up after changing the original mesh. This will be fixed in an update.

Leon Robers wrote
In FEATool, the element order or the shape function order respectively is indicated with 'sflag1' for first order discretization and 'sflag2' for second order. To change between those two, there are two ways:

...

I hope I could help you.
Best,
Leon