\large
\[
D_{manifold}  = \left( {\frac{{8Q_{manifold} ^2 }}
{{gh_l \pi ^2 }}\frac{{1 + \left( {f\frac{{L_{manifold} }}
{{D_{manifold} }} + \sum K } \right)\left( {\frac{1}
{3} + \frac{1}
{{2n}} + \frac{1}
{{6n^2 }}} \right)}}
{{1 - Q_{ratio} ^2 }}} \right)^{\frac{1}
{4}} 
\]