Learning Forum

[mmd]

Hi, I'm trying to simulate a movement of a ball attached to a string in water free stream by 6ِDOF solver. According to equilibrium equations (has been attached) we know final position of the ball. I got correct answers in The X،Y plane My question is why I got a lot of movements in the Z direction
I will be grateful for any help

[Rob]

Assuming z is into the page, have you got shedding on the ball? 

[mmd]

thanks for your reply 
I don't understand your mean by ''shedding''. I would be grateful if you explain more.

[m.shafiee1374]

"vortex shedding" means generation of vortices around bluff bodies due to flow sepration which are then shed/washed downstream because of the fluid flow. At certain flow regimes (particularly low Re) these vortices will generate fluctuating pressure (then forces) around the body which can cause it to oscillate.
Considering your Re number is relatively low and a sphere is not a streamlined shape, this is probably what's happening here; as was pointed out by Robert.