Remove some mesh elements from a structural pde model

Hi everyone,

I have a simple pde model with an autogenerated mesh with "generateMesh".

After generating the mesh I would like to remove some Mesh elements to get new geometry. It would be useful to do this with a logical (0 or 1) that turns individual mesh elements on or off.

Could any of you help me?

Thank you

%%
model = createpde('structural','modal-solid');
importGeometry(model,'Plate10x10x1.stl');
generateMesh(model,'Hmin',3);
figure 
pdeplot3D(model); % Then I have to remove some mesh elements from the model

Answer 1

[Garmit Pant]

Hello

It is my understanding that you are trying to generate a mesh from PDE model and subsequently trying to modify the mesh by removing some Mesh elements to get new geometry.

The code that you have provided is utilising the ‘generateMesh’ function of the Partial Differential Equation Toolbox. The function returns an object of the FEMesh class. The properties of the object are read-only, thus modifying the Elements of the mesh object wouldn’t be possible.

model = createpde('structural','modal-solid');
importGeometry(model,'Plate10x10x1.stl');
generateMesh(model,'Hmin',3)

ans = 
  FEMesh with properties:

             Nodes: [3×195 double]
          Elements: [10×78 double]
    MaxElementSize: 3
    MinElementSize: 3
     MeshGradation: 1.5000
    GeometricOrder: 'quadratic'

figure 
pdeplot3D(model);

You can still access the Elements and Nodes of the FEMesh and modify them. You can then use the ‘pdeplot3D’ function to plot the modified Elements and Nodes separately. The following code snippet takes the elements from the above-created mesh and then removes the elements where the x-coordinate of the centroid is less than 5.

% Initialize a logical mask with all elements initially set to 'true' (keep).
numElements = size(model.Mesh.Elements, 2);
elementMask = true(1, numElements);

% Set 'false' for elements you want to remove based on some condition.
% For example, remove elements where the x-coordinate of the centroid is less than 5.
elementCentroids = mean(model.Mesh.Nodes(:, model.Mesh.Elements), 1);
xCoordinates = elementCentroids(1, :);
elementsToRemove = xCoordinates < 5;
elementMask(elementsToRemove) = false;
% Store the elements of the mesh after applying the mask in the variable. Also store the nodes in a separate variable.
e= model.Mesh.Elements(:,elementMask);
n = model.Mesh.Nodes;
pdeplot3D(n,e)

You can refer to the following documentation pages to further understand the functionalities of the above-mentioned functions:

https://in.mathworks.com/help/pde/ug/pde.pdemodel.generatemesh.html

https://in.mathworks.com/help/pde/ug/pdeplot3d.html