CMS-Flow:Bottom Friction

Bottom Friction

Flow without Waves

In the situation without waves, the bottom shear stress is calculated based on the quadratic formula

     $\tau _{m}=\tau _{c}=\rho c_{b}|U|U$

where $c_{b}$ is the bottom friction coefficient, $U$ is the depth-averaged current velocity.

Flow with Waves

In the case with waves, the bottom friction is calculated with the generalized formula

     $\tau _{m}=\lambda _{wc}\tau _{c}$

where $lambda_{wc}$ is the nonlinear wave enhancement factor which varies depending on the model selected. There are five models available in CMS.

1. Simplified Quadradric Formula

in this case the enhancement factor is equal to

     $\lambda _{wc}={\frac {\sqrt {u_{c}^{2}+c_{w}u_{w}^{2}}}{u_{c}}}$