Maybe a error of the equation in the Users Guide for DualSPHysics code.
In page 28, equation 53 of Users Guide for DualSPHysics code (about the coupling with DEM), the minus sign before the damping coefficient (γ) should be a plus sign? Because there was a minus sign before the damping coefficient (γ) in equation 55. That may be a mistake.
Comments
please notice that the damping term in the normal and frictional directions have the derivative of the relative position, ie the relative velocity. This makes the equation consistent with the signal as it is written, I believe. cheers