I have been looking at using Filter > Distort > Shear to create wave effect. I can click on the vertical and horizontal lines to create nodes and drag them left, right up or down with the mouse. It works OK except that it does seem rather sensitive.
I then tried using the up, down, left and right keys to move nodes and I found that this works fine on the horizontal shear (right-hand graph), but not the vertical shear (left-hand graph). In the vertical shear, the up key moves the line to the left, and the down key moves it to the right. The left key moved the node up along the line, and the right key moves it down along the line. In the horizontal shear graph, the keys move the nodes in the expected direction (strictly horizontally or vertically).
John