double gravity double pressure and a rotating object problem

[nagypetern95]

Hello,

I am a student at BME. I downloaded CFD and set up a simple validation problem.

I went through the help file but I cant understand why gravitational and pressure are returned double. Using free surface in the water to get the pressure with gravity. (is there any other way?)

Gravity:

Pressure:

I have an other problem as well. I set a simple rotating domain problem and the water flows into the domain slowly and then doing something weird with the velocity. My problem basically a rotating volume where the centrifugal force should create some flow. I attach and other screen as well. Its also set up with free surface and rotating material using 1 radian/sec. 

Thank you for your help.

[Jon.Wilde]

Regarding the double gravity - within the Free Surfaces window, did you apply a 0,0,1 (for example) gravity and then an additional accellerational load?

Regaring the rotating model - can I suggest you start with the guide here?

Thanks,

Jon

[nagypetern95]

extra load No i didnt.

well, I will check the tutorial again

btw the gravity vector is  0,0,-1 isnt it? pointing downwards. and then -9.81 at the gravity type in in the free surface dialog.

[Jon.Wilde]

Hi,

That would give you double gravity, just use the 0,0,-1 🙂

The accelleration boxes are used if the model is under additional accelleration (a truck braking for example).

[nagypetern95]

Oh tanks, I tried many combination.

[Jon.Wilde]

No problem - does this answer your original question?

[Jon.Wilde]

No problem, is this solved now?

[nagypetern95]

Thank you, the gravity come right, but I got an other question if you dont mind.

Is it possible to simluate the force required to move and accel an object agains the water pressure and the drag in autodesk cfd?

The pressure seems not moving the object in free motion, but maybe my setup wrong.

The model is that a cylinder moving out from  the block and I want to know how much force it requires to do this by cfd calculating it for me.

My first approach is that I set it to free motion and free surface that water does extert force on it, and I increase the applieed force (roughly hand calculated first) and see if it is moving.  It didnt work.

So i wonder if its possible because help file says free motion is always flow driven, And this case would be the other way around free motion causes flow.

[nagypetern95]

Hmm, it seem the pressure is coming out right, using free surface and linear motion. But the problem itself still have to be solved.

[Jon.Wilde]

Hi,

I am not sure I understand the question. The flow is driving the motion and this is in turn driving flow?