[ghoroobeaakhar]

Hi

I need to put a constant velocity on my rigid body in one direction.
but I don't know where and how I have to do it?

thanks

[ghorrocks]

Is it an immersed solid or a moving mesh rigid body?

Does the degrees of freedom controls do what you want?

If you have a rigid body in constant motion then it is not really rigid body motion and really just a moving mesh model. So you could just model it with moving mesh (or a pre-defined source term)

[ghoroobeaakhar]

Thanks.
I put one degree of freedom for it so It moves only in one direction.

I first simulate the body under gravity force and I got results but now I want to simulate the same body with a constant velocity (3 m/s) in the same direction.

I defined a rigid body and a wall condition for the surfaces of my rigid body.

In rigid body options I have an initial velocity and in wall condition's option I have specified displacement ans specified location. I tried to set specified displacement as 3[m]*t but it doesn't work.

how can I say to my rigid body that moves all the time in 3 m/s?

[ghorrocks]

Try defining an initial velocity of 3m/s and give it a massive mass. Then the fluid forces acting on it will not affect it.

[ghoroobeaakhar]

Thanks ghorrocks
I have another question. I defined wall condition for the surfaces of my rigid body and I need to calculate the velocity of the wall. I want to check that the wall is moving at 3 m/s .
In fact how can I know the velocity of the wall at every moment and acceleration of that?
Thanks

[ghorrocks]

Have a look at the reference manual. It lists all the variables available on rigid bodies.

[hhhhhsssss]

Originally Posted by ghoroobeaakhar

Thanks ghorrocks
I have another question. I defined wall condition for the surfaces of my rigid body and I need to calculate the velocity of the wall. I want to check that the wall is moving at 3 m/s .
In fact how can I know the velocity of the wall at every moment and acceleration of that?
Thanks

by output setting in cfx-pre or timestep selector in post or chart(transient xy....)

[acasas]

Originally Posted by ghorrocks

Try defining an initial velocity of 3m/s and give it a massive mass. Then the fluid forces acting on it will not affect it.

Is it initial velocity set in Dynamic Mesh Zones/ Motion Attributes/Center of Gravity Velocity ?

I´m working under Fluent

[ghorrocks]

This is the CFX forum. Try the fluent forum.

[ld1305]

I'm looking to do something similar - I have two bodies submerged in a field at a given velocity, and then need to be able to move one relative to the other along a prescribed path. I'm pretty sure I'd be able to do this kind of thing in Fluent, but can't see how to in CFX (and I don't have access to Fluent) as I only seem able to apply forces.

I'm hesitant to try the initial velocity and high mass approach as I need to change direction at some point. The only way I can think of doing that would be to have two simulations where the end of one is the start of the next.

I'd thought about trying to implement a constantly changing force profile, dependent on the velocity, but I'm not quite sure how to go about writing the function (and don't know if it's possible). This could also come into issues when I have to change direction, as this would be triggered by reaching a specified location, which I might not hit dead on depending on time-step etc.

Any advice is much appreciated

[ghorrocks]

This sounds like a moving mesh thing, not a rigid body thing. You can prescribe the mesh to move any way you like in moving mesh.