Determine the hydraulic radius (m) for a circular pipe for the flow situation shown in the following figure, if d is the depth of fluid flow, D is the diameter of the pipe, and R is the radius of the pipe.
1
\(m = \frac{R}{{2\theta }}\left\{ {\theta - \frac{{{\mathop{\rm Sin}\nolimits} 2\theta }}{2}} \right\}\)
2
\(m = \frac{R}{{2\theta }}\left\{ {\theta + \frac{{{\mathop{\rm Sin}\nolimits} \theta }}{2}} \right\}\)
3
\(m = \frac{R}{{2\theta }}\left\{ {\theta - \frac{{{\mathop{\rm Sin}\nolimits} \theta }}{2}} \right\}\)
4
\(m = \frac{R}{{2\theta }}\left\{ {\theta + \frac{{{\mathop{\rm Sin}\nolimits} 2\theta }}{2}} \right\}\)