Thanks @mico for your help!
it is not sofistik problem anymore but rather structural mechanics one
yes of course, but I was hoping that they could help me derive the definition of the spring stiffness and thus help me understand the mechanics.
I tried your code and its a good benchmark example indeed. However, did you get it to run and if so, did you achieve the same results?
The variable #phi was not defined, so I defined it as you suggested
phi=12L/h^3 - 12 L/H^3
That lead to large rotations and the analysis didn’t converge however. I then had a look at the units, and when multiplying 1/#phi with #B/2 (as in your code) that resulted in [m³]. Multiplying this with the E-modulus however, brings us to [kNm] which is the correct unit, and also gives the correct results (see below).
Where 12L/H³ comes from I know, but why we take the difference, I don’t understand. Intuitively I would’ve taken 12L/h³, could you try to explain this? And also, why do we multiply with #B/2 and not #B?
Again, thanks for your help and patience!
