Hello to all
First of all, thank you very much for your fantastic work 
I have a question: When modelling with large platform yaw offset using PtfmYMod=1, I have got this error:
“With PtfmYMod=1, we need the lowest and highest wave headings to be exactly -180 deg and 180 deg, respectively, in “.\HydroData/ANALYSIS.3” (inclusive).”.
However, apparently having both180 and -180 degrees is redundant.
Does this limit also apply to QTF calculations, meaning that the heading pairs 180/180, 180/-180, -180/180, -180/-180 and combinations with the other headings are mandatory?
Best regards
Iñaki
Hi @Inaki.Zabala,
Yes, you are correct that having both -180 and +180 wave heading is strictly speaking redundant. However, we decided to enforce this requirement because it greatly simplifies the wave-heading interpolation and, more importantly, the corresponding sanity check performed by HydroDyn. On balance, we believe this is a small price to pay for more reliable results.
Note that we currently don’t support full sum- or difference-frequency QTFs with PtfmYMod = 1. This is because with second-order wave loads, the current HydroDyn implementation requires fully populated tables that includes all pairs of possible wave headings (including different headings for the two first-order wave components). In most cases, it is not feasible to generate full QTF tables that satisfy this requirement. We do support mean drift loads and Newman’s approximation for slow drift loads, but again, HydroDyn requires all pairs of possible wave headings from -180 deg to +180 deg including combinations of different wave headings for the two first-order components.
In the future, we will consider implementing a special case for second-order wave loads with long-crested waves, so that HydroDyn only requires second-order coefficients for two aligned wave components from -180 deg to + 180 deg, but there is no concrete plan for this at the moment.
Best,
Lu
Thank you @Lu.Wang,
I understand what you are saying. I will take steps to facilitate interaction between other solvers and OpenFAST, following your advice.
Best regards
Iñaki