Find Specific Faces on a 3D PDE DiscreteGeometry/ThermalModel

Question

Luke Benham 2020-6-25

0
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https://ww2.mathworks.cn/matlabcentral/answers/554743-find-specific-faces-on-a-3d-pde-discretegeometry-thermalmodel

回答： Luke Benham 2020-6-29

Hi,

I am struggling to create a universal code that is able to solve a Thermal Model of heat travelling through a cube from one face to the other with different cavity types.

I was hoping to find a way to extract the number of the faces on the outer surface of the cube on opposing sides in either the x or y direction. I wish to do this so that I can easily change the model without having to manually find the values of opposing faces. Something like this;

thermalBC(model,'Face',pos_face,'Temperature',pos_t);
thermalBC(model,'Face',zero_face,'Temperature',zero_t);

where the pos_face and zero_face variables are extracted from the model.

Cheers!

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Answer 1

Luke Benham 2020-6-29

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https://ww2.mathworks.cn/matlabcentral/answers/554743-find-specific-faces-on-a-3d-pde-discretegeometry-thermalmodel#answer_458620

在 MATLAB Online 中打开

I have something similar, and can now express the desired faces as variables such as this;

figure, h1 = pdegplot(model,'FaceLabels','on');     %Display model and create variable to find facelabels.
hp = h1.Parent;
faceLabelsArray = hp.Children;                      %Pull Facelabels from figure
LF = length(faceLabelsArray);                       %Define length so make this universally applicable
labelCells = {faceLabelsArray(1:LF-6).String};      %Pull separate cells for each face
labelNums = length(labelCells):-1:1;                %The faces are created backwards, this makes it chronilogical
positionCells = {faceLabelsArray(1:LF-6).Position}; %Find (x,y,z) coords of each face label
positionNums = cell2mat(positionCells');            %Make this into matrix
a = find(positionNums(:,1)>(cubelength/2)); pos = labelNums(a);     %Find specific faces based on a set location
b = find(positionNums(:,1)<-(cubelength/2)); zer = labelNums(b);

The reason why I have set the boundary for my desired faces to be chosen is just because I have it centred on (0,0,0).

Hope this helps anyone with a similar requirement!

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Answer 2

darova 2020-6-27

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/554743-find-specific-faces-on-a-3d-pde-discretegeometry-thermalmodel#answer_457828

在 MATLAB Online 中打开

Here is an example

[x,y] = pol2cart(pi/4:pi/2:2*pi,1); % rectangle
gd = [2;length(x);x(:);y(:)];       % geometry description
dl = decsg(gd);                     % decomposition
[p,e,t] = initmesh(dl,'hmax',0.05); % triangulation
ind = logical(t(1,:)*0)';           % indices inside a region
for i = 1:length(ind)
    vv = p(:,t(1:3,i));             % triangle vertices
    rr = hypot(vv(1,:),vv(2,:)) < 0.3;  % all vertices inside circle
    if all(rr)                      
        ind(i) = true;              % write triangle
    end
end
pdemesh(p,e,t)                      % display all mesh
ff.faces = t(1:3,ind)';
ff.vertices = p';
ff.facecolor = 'g';
patch(ff)                           % display region inside
viscircles([0 0],0.3)               % display region