High Quality Content by WIKIPEDIA articles! In fluid dynamics, a cnoidal wave is a nonlinear and exact periodic wave solution of the Korteweg de Vries equation. These solutions are in terms of the Jacobi elliptic function cn, which is why they are coined cnoidal waves. They are used to describe surface gravity waves of fairly-long wavelength, as compared to the water depth. The cnoidal wave solutions were derived by Korteweg and de Vries, in their 1895 paper in which they also propose their dispersive long-wave equation, now known as the Korteweg de Vries equation. In the limit of infinite wavelength, the cnoidal wave becomes a solitary wave.