Mean water level drift with Jonswap irregular waves

Jvaz

I have the same problem as another user (post from August 2017 from user HoaXNguyen) which identified a positive drift in the mean water level. This was corrected by switching off the deltaSPH but I have other simulations with regular waves where the deltaSPH produces very good results compared to theory. I am running the base case of 09_WavesPiston for irregular waves and the only changes are a longer flume, coefh=1.5 and deltaSPH=0.1.
So is it the case that for irregular waves it works better without deltaSPH?

iarba27

are you using Active Wave Absorption System (AWAS)?

Jvaz

No AWAS, just a piston generating irregular waves on a flat seabed leading to a smooth beach slope. Attached is the time series of wave heights at a distance of 6m to 7.1m from the piston (wavelength ~ 4.2m) just running the base case, this time I haven't changed the coefh so the only change to the base .xml file is the deltaSPH from 0 to 0.1.

iarba27

You should take care with the use of deltaSPH. In some cases that negative effect can occur.