Mike Pettit
Ansys Employee

Hi Greg,

You can either model these fins using Morison Discs, as described above; or, you can create Line Bodies in SpaceClaim, assign them with rectangular cross-sections, and they will be modelled as Morison line elements in Aqwa. This will give you a more realistic appearance in the Aqwa Workbench window, though the actual results may be similar (depending on how you define the discs/line bodies).

To create the line bodies in SpaceClaim:

  • start by sketching some lines either side of the spar, along the axis of each fin
  • in the Prepare tab, click Profiles, and from the New Profile Library select 'Rectangle' or 'Rectangular Tube'
  • in the Structure tree a Beam Profiles icon will appear. Expand this and right-click > Edit Beam Profile on the beam profile you just created
  • in the Groups panel, set the cross-section dimensions by clicking on Ruler Dimension for each dimension:

  • switch back to your platform geometry by clicking on the bottom tab in the graphical window
  • click to select the lines that you sketched previously
  • in the Prepare tab, click on 'Rectangle' (or 'Rectangular Tube' etc) to assign the current beam profile to the selected lines
  • in the same part of the Prepare tab, click the 'Display' dropdown menu and select 'Solid Beams' to show the beam profile on the model.

Note that the Morison loads in Aqwa will only be calculated along the axis of each line body; you could create several adjacent line bodies on each side of the spar if you want to account for e.g. the variation in fluid velocity across the fin.

Note also that the line bodies introduce their own mass to the model. If you do not want this, you can either:

  • set the beam cross-section to be thin in SpaceClaim, and/or
  • set the beam density to be small in Aqwa Workbench, by expanding Line Body Data in the Outline tree, selecting the appropriate beam section (e.g. 'Solid Rectangular 1'), and setting the Material Density value. You can also define the hydrodynamic properties (added mass/drag coefficients) here.

I hope this helps!