An incompressible fluid is flowing through a contraction section of length $L$ and has a $1-D$ ($x$- direction steady state velocity distribution, $u=u_{0}\left ( 1+\frac{2x}{L} \right )$. If $u_{0}=2\:m/s$ and $L=3m$, the convective acceleration (in $m/s^{2}$) of the fluid at $L$ is _________