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GEBT: failed to analyze an isotropic cantilever beam with tip bending moment

1. Hello,

I am using GEBT to analyze an isotropic cantilever beam subject to a tip bending moment, a well-known problem in the geometrically nonlinear analysis of beams.

The analysis conditions of the beam are given as follows.

- Cross-section: width (b) = 0.1in., height (h) = 0.01in.

- Beam length (L) = 10in.

- Young's modulus (E) = 1x10^7psi

- Poisson's ratio (nu) = 0.3

- Reference frame : Global frame (a1: axial direction, a2: lag direction, a3: flap direction)

- Tip bending moment: n x 2 x pi x EI_2 / L (The moment is acting about a2 axis, n is the loadfactor, EI_2 = b*h^3/12)

- Shear flexiblities are suppressed to be zeros for the analysis under Euler-Bernoulli level.

- GEBT (Rodriguez rotation parameters ver.) used for the analysis

As already known, the beam should form a circle when n = 1. However, GEBT fails to find the converged solution under that loadfactor.

For your information, I have posted my input file for this problem as follows.

0 100 10 # analysis_flag, niter, nstep

2 1 2 1 0 0 0 0 0 # nkp, nmemb, ncond_pt, nmate, nframe, ncond_mb, ndistrfun, ntimefun, ncurv

1  0 0 0
2 10 0 0

1 1 2 1 1 0 10 0 # memb_no, kp1, kp2, mate1, mate2, frame_no, nelem, curv_no

1
1 2 3 4 5 6
0 0 0 0 0 0
0 0 0 0 0 0
0 0 0 0 0 0

2
7 8 9 10 11 12
0 0 0 0 5.23598776E-02 0
0 0 0 0 0 0
0 0 0 0 0 0

1
1.00000000E-04    0.00000000E+00    0.00000000E+00    0.00000000E+00    0.00000000E+00    0.00000000E+00
0.00000000E+00    0.00000000E+00    0.00000000E+00    0.00000000E+00    0.00000000E+00    0.00000000E+00
0.00000000E+00    0.00000000E+00    0.00000000E+00    0.00000000E+00    0.00000000E+00    0.00000000E+00
0.00000000E+00    0.00000000E+00    0.00000000E+00    7.80000000E+00    0.00000000E+00    0.00000000E+00
0.00000000E+00    0.00000000E+00    0.00000000E+00    0.00000000E+00    1.20000000E+01    0.00000000E+00
0.00000000E+00    0.00000000E+00    0.00000000E+00    0.00000000E+00    0.00000000E+00    1.20000000E-01

The input file for the problem is attached.

I think I am missing something when making the input.

It would be grateful if someone leaves me a reply.

Thank you.

Best regards,

Jaeseong

P.S: Thanks for the approval of my membership!