11. (10 points) The emblem of XiXi's army is the regular octagon pattern shown in the figure. Given that the side length of the regular octagon is 18, what is the area of the shaded part?
【Analysis】According to the problem, transform the figure to equal area, convert the area of the shaded part into the area of other triangles, and finally convert it to $S_{\text {square }}=4 S_{\triangle A B O}=2 S_{\triangle \mathrm{ABF}}=2 \mathrm{~S}_{\triangle \mathrm{ABD}}=\mathrm{AD}^{2}=18^{2}=324$.

【Solution】Solution: According to the analysis, as shown in the figure,
$S_{\text {shaded }}=2 S_{\triangle A B O+2 S_{\triangle C O D}}$, obviously $S_{\triangle C O E}=S_{\triangle C O D}=S_{\triangle B O A}$, so:
$S_{\text {clearly }}=4 S_{\triangle A B O}=2 S_{\triangle \mathrm{ABF}}=2 S_{\triangle \mathrm{ABD}}=\mathrm{AD}^{2}=18^{2}=324$
Therefore, the answer is: 324.