The hydrodynamic effects only exist between the diffraction structures in the hydrodynamic interaction group. In your model, the second structure is a line body which is modelled by Morison tube elements in Aqwa, and cannot be in a hydrodynamic interaction group with other diffraction structures in Hydrodynamic Diffraction analysis. Please set the Structure Group 1 to have the first surface body, and set the Structure Group 2 to have the second line body.
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