Dear @Massimo.Sirigu,
I’m not aware of an issue with the convolution solution of HydroDyn, assuming that the radiation damping data from WAMIT is of good quality. I do know, however, that the state-space solution in HydroDyn is only as good as the state-space fit to the WAMIT data. So, when the state-space and convolution-based solutions from HydroDyn disagree, I would generally cast “blame” on inaccuracies in the state-space fit.
I’m not too familiar with the hydrodynamic capabilities of WecSim and am not familiar with how much it is has been verified against OpenFAST/HydroDyn.
Best regards,