I should add: the Hydrodynamic Diffraction analysis does not include the Joint objects that you have defined - these are only used in Hydrodynamic Response calculations. If you want to model the effect of the joints in the Hydrodynamic Diffraction calculation, you should create Connection Stiffness objects (under Connections) to represent the linear stiffnesses between each structure, which you can set as large values for the translational terms.
Mike
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