first i would like to verify the case where the joints are rigid in this case i get a free undeped system M(22,22)which is the sum off all consistent mass matrix of the structure.To obtain the natural frequency i uses this code:
Z=(inv(M))*K;
[V,D]=eig(Z);
Omega=(sqrt(diag(D)));
Freq=((Omega))/(2*pi);
I get Warning: Matrix is close to singular or badly scaled. Results may be inaccurate. RCOND = 7.259337e-37
and the results are:
117,170734211211 + 0,00000000000000i
116,521653401816 + 0,00000000000000i
85,7477397600253 + 0,00000000000000i
84,6823425031470 + 0,00000000000000i
58,3180467468491 + 0,00000000000000i
56,7249257632524 + 0,00000000000000i
47,0648080171161 + 0,00000000000000i
37,0241025675458 + 0,00000000000000i
35,0297477617541 + 0,00000000000000i
29,9275737962262 + 0,00000000000000i
20,9725282351167 + 0,00000000000000i
18,8765032944196 + 0,00000000000000i
17,6881567071483 + 0,00000000000000i
11,5369555790805 + 0,00000000000000i
9,35018494595257 + 0,00000000000000i
8,67978551396229 + 0,00000000000000i
6,04021513571875 + 0,00000000000000i
3,40014895128681 + 0,00000000000000i
2,90681072742300 + 0,00000000000000i
2,17065617657641 + 0,00000000000000i
0,572290682070938 + 0,00000000000000i
0,00000000000000 + 4,07555137117127e-07i
but the frequency should be seem like this:
9.4
26.6
65.8
74 .9
100.4
173.1
220.2
232.7