topic Re: Rotational stiffness in Robot Structural Analysis Forum

Rotational stiffness

Anonymous — Tue, 12 Dec 2017 22:14:32 GMT

Hi,

I am still struggling of validating this model (see attached image).

I dont know how to compare the rotational stiffness of the spring to the bending stiffness of the beam. The unit of the spring is kNm/rad and the beam is kNm

This model is modeled in Robot, and the spring is done as a compatible node, with elastic stiffness in place.

Any suggestion would be great.

Re: Rotational stiffness

Artur.Kosakowski — Thu, 14 Dec 2017 13:46:50 GMT

Hi @Anonymous

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.

Re: Rotational stiffness

Anonymous — Thu, 14 Dec 2017 13:56:33 GMT

Hi, thank you for your reply, can you please explain this for me, as I don’t crealy understand, and if you could send me the model please.

thank you

Re: Rotational stiffness

Artur.Kosakowski — Thu, 14 Dec 2017 16:27:18 GMT

Hi @Anonymous

For small rotations you can assume that the beam deflection (u in meters) is the same as angle of rotation at the support (alpha). Having a beam of L length (in meters) with force F [kN] at its middle:

alpha = u / 0.5*L = 0.00135 / 3 = 0.00045

You need to determine the spring value for which the force applied at the end of the cantilever rotate a cantilever of L/2 length by the alpha angle

F * 0.5L / alpha = spring value [kNm/rad] 1 * 3 / 0.00045 = 6666,667

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.