Assistance with one-way wave equation

Frank

Thanks guys - there's some great advice on these forums )

I finally managed to get the equation solved (you guys were right - the problem was to do with the boundary conditions) and got some really good results. I did have a problem, however, when I moved on to solving the same problem on a stretched grid.

I'm not too sure why but when I use a stretched cartesian grid all my results become nonsense - it's like some big instability is setting in. Could someone please advise?

Thanks for all your help so far! F