Learning Forum

[mdti]

Hi,
I am designing a floating platform for which hydrostatic stability analysis is completed and now I have the vessel geometry, displacement and centre of gravity data. Now, I am planning to do a frequency domain hydrodynamic diffraction and motion analysis in Ansys Aqwa. The body also has Morison elements in it. I have following queries:

1. What could be the correct way to get the Morison elements in Ansys Aqwa? 
2. How can I add a heaving plate at one end of a vertical cylinder (modelled as a Morison element) with "Disc" that has a larger diameter than the vertical cylinder?

Regards,

Touhid

[Yu Bi]

Hi, each Line Body should be assigned a cross section and an orientation in DesignModeler/SpaceClaim Direct Modeler. In the Aqwa editor, when importing the geometry, each valid cross sections is automatically paired with a Beam Section object. Beam Sections are created under the Line Body Data object in the Outline tree. Apart from storing the geometric properties of the cross section, a Beam Section object also allows mass and hydrodynamic properties to be defined. In short, to have slender bodies (e.g. tubes) in Aqwa, you need first have their geometry in the SpaceClaim/DesignModeler as beams, and then Aqwa will automatically recognize them as Morsion elements. Details can be found in Aqwa User's Manual Section 5.5.2.

The disc doesn't need to be defined in the SpaceClaim. It can be added by right-clicking on a Part in the tree view in the Aqwa editor. Details about it can be found in Aqwa User's Manual Section 5.5.6. 

[mdti]

Thank you for your answer, Yu Bi.

Other related questions regarding Morison element are: 

1. Do these Morison elements need to be meshed like diffracting elements?
2. Do the tube diameter and thickness for Morison elements contribute to the mass of the rigid body?
3. When defining a disc at one ends of a Morison element, how to know which end is A and which end is B? Is it possible to view the disc in ansys aqwa? 
4. How to define a disc at one end of Morison element which has larger diameter than the element?

Thanks,

Touhid

[Yu Bi]

The mesh for Morison elements (except disc as no mesh for disc) will be done following the same procedure of meshing for diffracting elements. The mass of the tubes will be automatically calculated based on the geometry dimension and material density defined. Discs are defined directly and independently in the Aqwa editor, so you can view them in the Aqwa editor. Please see the slide below for more info. If you have access to the Ansys learning hub, you can find Aqwa training material, in which workshop 8 shows a good example for your case. 

[mdti]

Many thanks, Yu Bi.