When I was trying to generate a bunch of randomfields, I observed that the randomfield command was generating the same field again and again.
As it turned out, the seed for random numbers was set to default 1. The quick fix for that is as follows:
Get the current seconds as integers, feed that time as a seed to
randomfield -Nx 32 -Ny 33 -Nz 32 -a 1 -g 2 -sd $(date +"%s") u0.nc
It would be better, however, if the
randomfield.cpp would do something like this by default.