# What is the name of such equation in fluid dynamics? How does it come out?

I read papers and see this equation. Honestly, I am not familiar with fluid dynamics. So I was wondering if this equation is common in fluid dynamics, or it is the special case in this paper. Could someone help me figure it out how it comes out? Thank you! First Question! $$\nabla^{2}\phi-c^{-2}\phi_{tt}=\frac{1}{2c^2}\left[\frac{d}{dt}(\nabla\phi)^{2}+\frac{\partial}{\partial t}(\nabla\phi)^{2}\right]$$

where $\phi$ is the potential function of water

• Can you give some reference of what you read ? – Tony Piccolo May 18 '14 at 8:34
• Thank you! Here is the link of the paper. scitation.aip.org/content/aip/journal/jap/27/10/10.1063/…. I was wondering if this equation is the unique equation in this model or it is actually a common equation like N-S equation in the fluid dynamics – Silentmovie May 18 '14 at 17:54