Overlapping waves is the whole strategy of TV soapies. The various strands never finish at the same time, but pass on the baton from one to another. The difference is that the strands in soapies are stories rather than sub-stories, and there’s no larger story or overall build-up.
In my diagram, the waves tend to get bigger and higher. Join the tips of the waves and you have a single super-wave. If I continued the diagram past the middle of the novel, I guess the peak of that super-wave would be the novel’s over-arching climax. (In Dragonflight, the super-wave would involve the relationship between Lessa and F’lar.)
As I said, I’m not sure if it’s a special type of structure or a way of thinking about structure. I suspect it could fit over the middle of almost any novel. But even as a way of thinking, it’s a great aid for someone like me.
I get past the beginning of the novel and feel daunted by the distance to the eventual climax. (Never more distant than in epic fantasy.) So much material, and all so shapeless!
Then I think in terms of overlapping waves, and the material becomes more manageable. I can deal with one wave, one phase, at a time. Phew! Events start to take their place in a definite rhythm.
Some authors write out chapter outlines, I draw overlapping waves. For me, it’s a way to find a shape and hopefully escape mid-novel sag. Whatever works!