I eventually got around to create a UML class diagram to OWL converter. The very first version of it is available at https://github.com/henrietteharmse/uml2semantics. I hope to add an example based on DCAT version 2 and support for enumerations shortly.

Please let me know whether this may be something that you find useful by commenting on this post, or starring the repository. Please feel free to open an issue if you have suggestions.