Problems at periodic boundaries

[asimonder]

Both RDF and height function curvature models seem to have issues with periodic boundaries.

I have been testing the library for the propagation of 2D gravity-capillary waves. The wavelength of the waves is 5 cm and their steepness is ak=0.28. A periodic domain containing two waves is used.

1. Height function model leads to a kink when a wave passes through a periodic boundary. To show this, I extended the domain to four wavelengths:
   

2. RDF-based curvature model yields some instabilities in the velocity field when the wave passes the periodic boundary:
   

I am attaching the case files for these tests.

cases.zip