我希望它比 comsol 更容易:)
\documentclass[tikz]{standalone}
\begin{document}
\begin{tikzpicture}
\fill[red] (0,0) circle (3mm);
\draw (0,0) circle (2cm);
\foreach \x in {1,...,20}{\draw[ultra thick,-latex] ({\x*360/20}:2cm) -- ++({\x*360/20}:1cm);}
\end{tikzpicture}
\end{document}