Assembling Global Stiffness Matrix

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Sharanya
Sharanya 2022-12-12
回答： Arif Hoq 2022-12-13
I am trying to make a global stiffness matrix using a for loop from several smaller (4X4) matrices. I was able to get a loop to run for 2X2 matrices, but when I increase the number of rows and colums in my smaller matrices it no longer works. I want the loop to run when the kn matrices is rand(4). This is what I have currently:
k1=rand(2);
k2=rand(2);
k3=rand(2);
C = {k1,k2,k3};
N = numel(C);
M = zeros(1+N,1+N);
for k = 1:N
M(k:k+1,k:k+1) = M(k:k+1,k:k+1)+C{k};
end
disp(M)

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回答（2 个）

Torsten
Torsten 2022-12-12
Ran in:
This is analogous to your 2x2 code.
I don't know if it's the right way to code M.
k1=rand(4);
k2=rand(4);
k3=rand(4);
C = {k1,k2,k3};
N = numel(C);
M = zeros(3+N,3+N);
for k = 1:N
M(k:k+3,k:k+3) = M(k:k+3,k:k+3)+C{k};
end
disp(M)
0.6812 0.4903 0.5574 0.1710 0 0 0.9156 1.2886 0.9432 0.6481 0.5245 0 0.2805 1.4433 0.6168 1.3751 0.6339 0.7170 0.1670 1.5541 0.9690 1.3091 0.4106 0.6047 0 0.4948 0.9290 0.3031 0.9958 0.0024 0 0 0.1797 0.8201 0.7794 0.7742
  2 个评论
Sharanya
Sharanya 2022-12-12
This is ouputting a 23X23 matrix, but I only want a 20x20 matrix. Each stiff(n) is a 4x4 matrix
k1=stiff(1);
k2=stiff(2);
k3=stiff(3);
k4=stiff(4);
k5=stiff(5);
k6=stiff(6);
k7=stiff(7);
k8=stiff(8);
k9=stiff(9);
k10=stiff(10);
k11=stiff(11);
k12=stiff(12);
k13=stiff(13);
k14=stiff(14);
k15=stiff(15);
k16=stiff(16);
k17=stiff(17);
k18=stiff(18);
k19=stiff(19);
k20=stiff(20);
C = {k1,k2,k3,k4,k5,k6,k7,k8,k9,k10,k11,k12,k13,k14,k15,k16,k17,k18,k19,k20};
N=numel(C)
M = zeros(3+N,3+N);
for k = 1:N
M(k:k+3,k:k+3) = M(k:k+3,k:k+3)+C{k};
end
disp(M)
Torsten
Torsten 2022-12-13
编辑：Torsten 2022-12-13
You will have to explore how the global stiffness matrix is computed from the C's.

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Arif Hoq
Arif Hoq 2022-12-13
Ran in:
% creating stiff matrix
for i=1:20
stiff{i}=randi(100,4,4);
end
k1=stiff(1);
k2=stiff(2);
k3=stiff(3);
k4=stiff(4);
k5=stiff(5);
k6=stiff(6);
k7=stiff(7);
k8=stiff(8);
k9=stiff(9);
k10=stiff(10);
k11=stiff(11);
k12=stiff(12);
k13=stiff(13);
k14=stiff(14);
k15=stiff(15);
k16=stiff(16);
k17=stiff(17);
k18=stiff(18);
k19=stiff(19);
k20=stiff(20);
C = [k1,k2,k3,k4,k5,k6,k7,k8,k9,k10,k11,k12,k13,k14,k15,k16,k17,k18,k19,k20];
N=numel(C);
M = zeros(N,N);
for k = 1:N-3
M(k:k+3,k:k+3) = M(k:k+3,k:k+3)+C{k};
end
disp(M)
4 5 37 70 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 70 112 133 126 50 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 63 116 157 136 24 98 0 0 0 0 0 0 0 0 0 0 0 0 0 0 6 107 167 135 245 149 49 0 0 0 0 0 0 0 0 0 0 0 0 0 0 35 161 122 166 181 91 42 0 0 0 0 0 0 0 0 0 0 0 0 0 0 46 98 103 176 149 110 43 0 0 0 0 0 0 0 0 0 0 0 0 0 0 66 125 129 144 115 124 3 0 0 0 0 0 0 0 0 0 0 0 0 0 0 87 77 157 83 165 153 63 0 0 0 0 0 0 0 0 0 0 0 0 0 0 39 126 107 213 201 53 25 0 0 0 0 0 0 0 0 0 0 0 0 0 0 24 92 190 87 155 74 68 0 0 0 0 0 0 0 0 0 0 0 0 0 0 68 102 85 244 165 110 54 0 0 0 0 0 0 0 0 0 0 0 0 0 0 45 90 155 241 204 87 7 0 0 0 0 0 0 0 0 0 0 0 0 0 0 42 116 177 219 134 90 58 0 0 0 0 0 0 0 0 0 0 0 0 0 0 40 34 238 245 96 147 49 0 0 0 0 0 0 0 0 0 0 0 0 0 0 43 71 221 165 133 101 73 0 0 0 0 0 0 0 0 0 0 0 0 0 0 19 145 115 142 158 61 11 0 0 0 0 0 0 0 0 0 0 0 0 0 0 29 71 153 274 146 53 21 0 0 0 0 0 0 0 0 0 0 0 0 0 0 88 141 119 116 173 67 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 78 80 110 90 37 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 93 39 5 96

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