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

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

where $c_{b}$ is the bottom friction coefficient, $u_{c}$ 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 quadratic formula 2. Soulsby (1995) Data2 Method 3. Soulsby (1995) Data13 Method 4. Fredsoe (1984) Model 5. Huynh-Thanh and Temperville (1991) Model

In this case the simplified expression for the combined wave and current mean shear stress is given by

     $\tau _{m}=\rho c_{b}{\sqrt {u_{c}^{2}+c_{w}u_{w}^{2}}}u_{c}$

For all of the other models, the general parameterization of Soulsby (1995) is used to calculate $\lambda _{wc}$.

     $\lambda _{wc}=1+bX^{p}(1-X)^{q},withX={\frac {\tau _{w}}{tau_{c}+tau_{w}}}$