Is it possible to calculate the reaction forces in a PDEModel if i use enforced displacement as load?

Hello,

I am analysing cantilever-Beams using pdemodels. (I don't use structuralmodel) As BC i have to DC. First one is for the fixation of the beam and the second one applies enfroced displacement. I would like to calculate the reaction force, which would cause to this displacement. Is it possible to do this with pde Toolbox. Do you have any ideas?

Thank You

Answer 1

[Ravi Kumar]

You can evaluate reaction at the boundary using evaluateReaction function.

[Baturay Yalvac]

Hey,

I am familier with that function. But i am not working with structuralmodel but general pdemodel.

model = createpde(3);

I tried to use the assembly the matrices with:

FEM = assembleFEMatrices(model,'nullspace')

It gives me the corresponding load vector Fc.But i am not sure if it is the matrix i need. What do you think.

PS: the problem is a simple beam deformation problem with a fixed region and with a enforced displaced region.

[Ravi Kumar]

Sorry, I did not notice, you do say in your original post that you don't use structuralmodel.

In that case, you need to use evaluateCGradient to get stress on the boundary that you want the reactions. Once you know stress you can compute the force using the are on which the stress acts. This is a bit of post-processing code you need to write on your own to go from stress to force.

By the way what is lacking in structuralmodel that forces you to use equation based approach?

[Baturay Yalvac]

Hello,

In my project i am loading and fixing the 3D beams not with faces but with solids. Two cubes are in collision with the beam. One Cube-Beam collision gives the faces to fix the geometry and the other Cube-Beam collision gives the faces for enforced displacement or load conditions. I only could do that with using the coefficient like h u r g etc. Thats way i use the general model. I have alread calculated the Stresstensor like this:

....there is bit more code 

if ~isempty(p)
    [cgradx,cgrady,cgradz] = evaluateCGradient(result,p(:,1),p(:,2),p(:,3),[1 2 3]);
else
    [cgradx,cgrady,cgradz] = evaluateCGradient(result);
end

sxx = cgradx(:,1);
sxy = cgradx(:,2);
syy = cgrady(:,2);
syz = cgrady(:,3);
szx = cgradz(:,1);
szz = cgradz(:,3);

stresstensor(:,1) = sxx;
stresstensor(:,2) = syy;
stresstensor(:,3) = szz;
stresstensor(:,4) = sxy;
stresstensor(:,5) = szx;
stresstensor(:,6) = syz;

And then i write a small function to do the nodal sum of the stresses

function [F] =  reactionForce_BY(nodeIDs,stresstensor,width,thickness) ;
id_max = size(nodeIDs,2) ;
F = zeros(3,1) ;
Area = width*thickness ;

for ii =  1:id_max
   nnumber =  nodeIDs(1,ii) ;
   F(1,1) = stresstensor(nnumber,1)+F(1,1);
   F(2,1) = stresstensor(nnumber,2)+F(2,1);
   F(3,1) =stresstensor(nnumber,3)+F(3,1);
end 
F = F*(Area);

I want to learn the reaction force, that i need to realize the enforced displacement. So should i take the nodes only in the forcely displaced volume or the nodes in the whole beam? Or something else ?

[Baturay Yalvac]

Hello,

can you please answer me? I could not make any progress.

Thanks