CMS-Flow:Ripple Dimensions

The bed forms calculated by CMS are the wave- and current-related ripples. The ripple height (used to calculate the mixing layer thickness) is estimated as the maximum of the current- and wave-related ripple heights

$H_r=max(H_{r,c},H_{r,w})$

(1)

The current-related ripple height and length are calculated as (Soulsby 1997)

$H_{r,c}=L_{r,c}/7$

(2)

$L_{r,c}=1000d_{50}$

(3)

The wave-related ripple height and length are calculated using the expressions proposed by van Rijn (1984b, 1989):

$H_{r,w}=\{\begin{array}{rl}& 0.22A_{w}for{\psi }_w<10\\ & 2.8x10^{-13}(250-{\psi }_w{)}^5{A}_{w}for10\le {\psi }_w<250\\ & 0for250\le {\psi }_w\end{array}$

(4)

$L_{r,w}=\{\begin{array}{rl}& 1.25A_{w}for{\psi }_w<10\\ & 1.4x10^{-6}(250-{\psi }_w{)}^{2.5}for10\le {\psi }_w<250\\ & 0for250\le {\psi }_w\end{array}$

(5)

where:

A_w = semi-orbital excurision = $\frac{u_{w}T}{2\pi }[m/s]$

${\psi }_w$ = wave mobility parameter = $\frac{u_w^2}{(s-1)g{d}_{50}}[-]$

d₅₀ = median grain size [m]

s = sediment specific gravity [-]

g = gravitational constant (9.81 m/s²)

u_w = bottom orbital velocity [m/s] (for random waves u_w = $\sqrt{2}{u}_{rms})$

T = wave period [s] (for random waves T = T_p).

The current- and wave-related ripple height and length are used in calculating the bed form roughness for use in the Lund-CIRP transport formula.

References

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