This command defines shear traction on a surface. It can be used to model drag forces and prescribed friction loads. The local direction of the traction $\hat{\mathbf t}$ is in that of the reference velocity ${\mathbf v}_{ref}$ vector minus the local velocity vector ${\mathbf v}({\mathbf x})$, projected onto the surface.

$\displaystyle{ \hat{\mathbf t} = \frac{({\mathbf I}-\hat{\mathbf n} \otimes \hat{\mathbf n})({\mathbf v}_{ref}-{\mathbf v})} {\Vert ({\mathbf I}-\hat{\mathbf n} \otimes \hat{\mathbf n})({\mathbf v}_{ref}-{\mathbf v}) \Vert}}$

Here $\hat{\mathbf n} = \hat{\mathbf n}({\mathbf x})$ is the local surface normal direction.

Shear loading

The following commands apply shear traction on the part with ID 1. The traction is a linear function of the relative tangential velocity vtang. Note that vtang is a built in variable that can be accessed in FUNCTION. The reference velocity is ramping up from 0 to 100 in x-direction.