\begin{center}
\subfigure[horizontal drift force]{\includegraphics
[width=110mm,height=90mm]{fig8-1}}\\
\subfigure[vertical drift force]{\includegraphics
[width=110mm,height=90mm]{fig8-2}}\\
\figcaption{Horizontal (a) and vertical (b) drift force as a
function of the body
submergence $ H/R $ for $ kR=0.4,kA=0.12,h/R=12 $.}
\label{fig:fig8}
\end{center}