\documentclass{scrartcl}


\usepackage[ngerman]{babel}
\hyphenation{ 3D-Strahlung Computer-algebra-system }

\pagestyle{empty}
\begin{document}
\showhyphens{3D\=Strahlung}
\parbox{0.3cm}{3D-Strahlung}

\parbox{2cm}{Computeralgebrasystem}
\end{document}

