Here is video that is somewhat similar to 2nd cake which is in buttercream. Don't know about the 1st picture. I will look and see if I can find what 1st one is or maybe someone here will know.
This is similar to the first picture only the ruffles are going up instead of down. See video below. Second cake picture looks like buttercream but I am not sure. Someone here will know!! The experts here on this site should be able to tell you.
All you do is use a rose tip...
Yep it's a petal piping tip (104 or similar will work well) for both I think. Melody of Sweet and Saucy has a great video for the method for the type of ruffle in the 2nd photo on Youtube:
Here is another tutorial for the first type of ruffle but like remnant3333 said about her video link, you'll need to adjust to have the ruffles facing down not up: http://bubbleandsweet.blogspot.com/2012/05/how-to-make-ruffled-buttercream-rainbow.html
AThose are both sweet and saucy cakes. Watch her video and practice, practice, practice.