Manipulate[
Animate[
Plot3D[Cos[t-nx x-ny y]/.{nx->Cos[α],ny->Sin[α]},{x,-15.,15.},{y,-15.,15.},PlotRange->{-2.,2.},PlotPoints->35],
{t,0.,4.π},ControlPlacement->Top],
{{α,0,Dynamic["n = ("<>ToString[Round[Cos[α],0.01]]<>", "<>ToString[Round[Sin[α],0.01]]<>")"]},0.,2.π},ControlPlacement->Top]

imtable=Table[Plot3D[Cos[t-nx x-ny y]/.({nx->Cos[α],ny->Sin[α]}/.{α->π/4}),{x,-15.,15.},{y,-15.,15.},PlotRange->{-2.,2.},PlotPoints->50,ImageSize->900],{t,0,2π,((2π)/25)}];

Export["2Dvlna.gif",imtable,"GIF","DisplayDurations"->0.04,"AnimationRepetitions"->∞]