Learning Forum

[Hamed Majidiyan]

Hello everybody,

I am trying to replicate a test of a solid sphere exposed to waves in a model basin experiment in Ansys Aqwa, though the answer that is obtained does not make sense. To be more specific, it is a sphere with a mass of 4.305 kg attached to a spring which has a load cell installed with stiffness of 20568.75. The depth is 0.8 m and the sphere dia is 0.8, but the sphere stays at 0.2 m draft. In the experiment, the mooring passed through a pulley at the bottom instead of an anchor and it was secured with a pre-tension of 12.2 kg. I used the above-mentioned size for geometry, then I did the decay test by measuring the cable tension which was a quite reasonable period, but with a higher cable tension value compared to the experiment. In terms of the regular wave test, sphere responses in the Z direction are lower than in the experiment, while for Gaussian waves, the amplitude of the response is way higher. I would appreciate any help since I am stuck at this point, and have nobody around to give me a clue.

Cheers

[Shuangxing Du]

From your test setting, the submerged volume of the sphere is (3.1415926/3)d^2(3*R-d), where d is the draft and R is the radius. It gives 0.041867 m^3. To be balanced in still water, the pre-tension may be 0.041867*1000-4.305=37.583kg. But your pre-tension is 12.2 kg.  Please check.

[abuzarabazari]