38 lines
No EOL
983 B
Matlab
38 lines
No EOL
983 B
Matlab
function [K, F] = ApplyRobinBC_mult(model, K, F, alpha, u_out)
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mesh = model.Mesh;
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nodes = mesh.Nodes;
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elements = mesh.Elements;
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%Boundary edges
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edgesAll = [elements([1 2],:), elements([2 3],:), elements([3 1],:)];
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edgesSorted = sort(edgesAll,1);
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[edgesUnique,~,ic] = unique(edgesSorted','rows');
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counts = accumarray(ic,1);
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boundaryEdges = edgesUnique(counts==1,:); % Nx2 array
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for k = 1:size(boundaryEdges,1) %Loop over Robin boundary edges
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i = boundaryEdges(k,1);
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j = boundaryEdges(k,2);
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ri = nodes(1,i);
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rj = nodes(1,j);
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%find the edges on the axis -> homogeneous Neumann BC, no Robin contribution
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if ri == 0 && rj == 0
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continue;
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end
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xi = nodes(:,i);
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xj = nodes(:,j);
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L = norm(xi - xj); % edge length
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% Robin boundary element matrices
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Ke = alpha * L / 6 * [2 1; 1 2];
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Fe = alpha * u_out * L / 2 * [1; 1];
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% Assemble
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K([i j],[i j]) = K([i j],[i j]) + Ke;
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F([i j]) = F([i j]) + Fe;
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end
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end |