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siw March 17, 2008 11:38

CFX with trajectory model

I'm putting together a trajectory model so that CFX runs and the vehicle moves using the forces from the CFX flowfield. I've got the mesh motion and trajectory equations sorted out. But I need help on putting the equations into CFX.

I can use the Expressions for them but as I've been improving the trajectory features it looks like I need to use a Loop statement to separate the initial velocities and position of the vehicle from the carried over values from the previous time step.

Has anyone been able to put a 3 degree of freedom, or higher, into CFX? I know these can take awhile to solve but I'm not fussed about that. And the movement should not be too much that the mesh becomes too bad.


CycLone March 17, 2008 13:20

Re: CFX with trajectory model
The variables available to CEL expressions are always lagged (i.e. from the previous timestep). If you keep this in mind while writing your expressions, you should be able to acheive what you want.

Alternatively, if you contact technical support they can provide you with a User Fortran routine for a 6 DOF solver that is already written. This 6 DOF solver will be included in the core code at version 12.


siw March 18, 2008 04:39

Re: CFX with trajectory model

I contacted tech support when I first started this task but they never said that one was available.

Have you used it? What's is actually called, just so I can ask them directly for it?

CycLone March 18, 2008 14:51

Re: CFX with trajectory model

siw March 19, 2008 06:28

Re: CFX with trajectory model

I did not know that ANSYS provided any pre-written Junction Box Routines, first I've ever known about it. That would save me time and effort by using it.

Have you tried it? I guess I would need to use the Expressions for setting up initial data: mass properties, rates and accelerations etc.

I was confused in the CFX (v11.0) Help by having both CEL and Junction Box under User Fortran. Are they two ways of doing the same thing?

CycLone March 19, 2008 16:27

Re: CFX with trajectory model
CEL and Junction Box routines are different. A user CEL function allows you to create your own function to be used in CEL expressions. This can be useful if there is a specific function you need which doesn't exist in CEL and allows you to easily pass parameters to your function and use it in other expressions. A Junction Box routine is for doing external IO, solver control, etc.

I haven't used the 6DOF solver myself but know of others who have. CFX is adding it to the core solver for version 12, but you can ask for it through support. It's not commonly known, so the support rep may have to ask around to find it. I think it came out of the UK office, but you can probably find it through the Waterloo, Canada office as well.


Kushagra April 12, 2008 01:41

Re: CFX with trajectory model
What you guys are talking about? Are you talking something related to Lagrangian Tracking model in CFX-11? And what does this 6DOF do? Please brief me about it if you do not mind. Thanks very much, Kushagra

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