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Assembling Global Stiffness Matrix

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Sharanya
Sharanya el 12 de Dic. de 2022
Respondida: Arif Hoq el 13 de Dic. de 2022
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)

Respuestas (2)

Torsten
Torsten el 12 de Dic. de 2022
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 comentarios
Sharanya
Sharanya el 12 de Dic. de 2022
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 el 13 de Dic. de 2022
Editada: Torsten el 13 de Dic. de 2022
You will have to explore how the global stiffness matrix is computed from the C's.

Iniciar sesión para comentar.


Arif Hoq
Arif Hoq el 13 de Dic. de 2022
% 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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