Compute the angular orientation for the bending moment

Hi all,

In the discrete element method, the normal contact between two spheres i and j has the same direction than the n-axis (in the local reference (n,s,t)).Thus, it is possible to compute the angular orientation of the particle "i" following the s-axis and t-axis (tethai_s and thetai_t) in the global reference (x,y,z).

To compute tethai_s and thetai_t in the global reference (x,y,z), I do:

thetai_1 = omega[i][0] * dt;

thetai_2 = omega[i][1] * dt;

thetai_3 = omega[i][2] * dt;

thetanr = thetai_1*delx + thetai_2*dely + thetai_3*delz;

thetan_1 = delx* thetanr * rsqinv;

thetan_2 = dely* thetanr * rsqinv;

thetan_3 = delz* thetanr * rsqinv;

thetat_1 = thetai_1 - thetan_1;

thetat_2 = thetai_2 - thetan_2;
thetat_3 = thetai_3 - thetan_3;

Can you confirm me that: thetat_1, thetat_2, thetat_3 are tethai_s and thetai_t in the global reference. Maybe, my reflexion is wrong.

I use these values to compute the bending moment (Mi=k*(thetaj-thetai)). Unfortunately, when I add the bending moment my simulation does not work anymore.

Regards
JF