Update multiple-perpendicular-flaps/README.md

Co-authored-by: Benjamin Uekermann <[email protected]>

Author: MakisH

multiple-perpendicular-flaps/README.md

@@ -111,6 +111,6 @@ After the simulation has finished, you can visualize your results using e.g. Par
 
 ## References
 
-[1] H. Bungartz, F. Linder, M. Mehl, B. Uekerman. A plug-and-play coupling approach for parallel multi-field simulations. 2014.
+[1] H. Bungartz, F. Linder, M. Mehl, B. Uekermann. A plug-and-play coupling approach for parallel multi-field simulations. _Comput Mech_ **55**, 1119-1129 (2015). https://doi.org/10.1007/s00466-014-1113-2
 
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