A91. Interpolation of spectra

Spectra are interpolated by Swan during the generation of boundary conditions, and in the output of spectra. The interpolation procedure is not a linear interpolation bin-by-bin, but such that the shape of the spectra is preserved as well as possible.
This tested by interpolating two Jonswap spectra with different parameters.

2 cases are considered:

A91a
a stationary with two spectra given by means of parameters at two ends of one side of the computational grid
A91b
two spectra are given by means of TPAR files at two ends of a time interval on one side of the computational grid
It is noted that the wave height does not vary linearly; the energy varies linearly, so the wave height varies as the square root of distance or time. The wave period and direction also do not vary linearly; this is mainly because Swan computes a weighted average, so the larger energy has the largest influence on the outcome.

© 2012: Nico Booij