Hi Mike,
I tried to add some stiffness for the surge and sway motions to prevent the vessel from drifting away in the time domain simulation. I used the option Connection Stiffness. However, after I run the diffraction solver I found that this stiffness was not used. I got the following warning. 
What does this mean? How do I correct this? I checked the thread which discussed about this but, I understand that was about Hydrodynamic Response and not Diffraction. I did not find NASF option in the .DAT file in case of Diffraction. Also, what is the difference between adding Additional Hydrostatic Stiffness in geometry and the Connection Stiffness?
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