The natbib
package support the following command, in case you need to write: "shown in ref. 3".
shown in ref.\citenum{VanCappellen1994}\nocite{VanCappellen1994}.
Note that \citenum
insert a space before, so it is better to leave no space between ref.
and the command. \nocite
is needed to register a particular citation in the bibtex compliation.