## Fluids

#### Six-Dof solver do not converge

• Alberto
Subscriber

Goodmorning,

If I've well understood, the six dof model is able to solve euler - newton system of equations for a body. I'm running a simulation with dynamic mesh and 6 dof solver, in order to simulate the falling path of a particular shaped object. I've computed the inertia tensor of the object and i've insert in the model box panel with the weigth and the center of mass coordinates.

The simulation is running and the object is falling with a rotation and a traslation, but without the expected motion (computed through the fluid forces acting on it), the fluid solver converges in few iteration but the six-dof angular solver do not. Any suggestion on why it happens ? and how can I make converge also the angular solver ?

• Rob
Ansys Employee

What initial conditions did you give the flow? Is the object falling, but too quickly? I'm assuming you turned gravity on?

• Alberto
Subscriber

Null velocity for the object and the flow is supposed to be at rest in the entire domain with no slip condition on the walls. The gravity is turned on

• Rob
Ansys Employee

Initialise the flow with a tiny velocity. If there is no flow the solver may not move anything enough for the flow to not be zero so nothing changes. If the object is still not falling correctly it could be the moment of inertia or mass that's incorrect.

• Alberto
Subscriber

Okay i will try, how about writing a udf function, can it address the problem? The point is that i have no idea on how can i write that function for a moving body, so with a time dependent variable.

Many thanks

• Rob
Ansys Employee

A UDF function may or may not help. They're another tool, but as I don't know why your model isn't behaving (and what it's actually doing) I can't make a suggestion on that.