adds missing default value

Author: ValentinKaisermayer

src/Mechanical/Rotational/utils.jl

@@ -122,7 +122,7 @@ Partial model for a component with one rotational 1-dim. shaft flange and a supp
 function PartialElementaryOneFlangeAndSupport2(;name, use_support=false)
     @named flange = Flange()
     sys = [flange]
-    @variables phi_support(t)
+    @variables phi_support(t)=0.0
     if use_support
         @named support = Support() 
         eqs = [