CFX - the introduction of a wall into an air duct.

Opaque · June 24, 2021, 08:16

For example,

if ( probe(Velocity)@MyPointofInterest < Tiny, ... , ... )

I think you should use some tiny value, and not 0 exactly. We are dealing with convergence and plenty of round-off here, are you certain it can reach 0 exactly? If you are, go for it; otherwise, the expression is just consuming cpu cycles.

Keep in mind, that Velocity is always positive since it is the magnitude of the vector in that expression. When dealing with components or other scalars, you may want to use abs( )

if ( abs (probe (MyVar)@MyPointofInterest)) < Tiny, .. )

or more generically

if (abs (probe(MyVar)@MyPointofInterest) - MyTargetValue) < Tiny, ..., ..)

Hope the above helps,

visitor · June 24, 2021, 13:42

I'm looking there, I couldn't find anything, was hoping to put his in an 'if' condition.

Also, I'm looking for away where I can apply a load on a boundary condition. But not to go into the obvious Static Structural ANSYS tool.

Thanks.

ghorrocks · June 24, 2021, 18:35

What version of CFX are you using?

I do not understand your boundary condition comment. What "load"? Load of what?

visitor · June 25, 2021, 04:06

Thanks Opaque, but what command stops solver? What shall I enter in the true return condition?

if ( probe(Velocity)@MyPointofInterest < Tiny, ... , ... )
----
Thanks Ghorrocks, its a boundary condition I have created on the air-duct, about 100 mm diameter. This will have a 10 kg load on it (100 N). ANSYS 2021 academic, CFX.

ghorrocks · June 25, 2021, 05:01

I told you in post #20 how to stop a simulation with a condition. If you don't understand a comment ask for it to be explained, do not ignore it.

CFX-Pre, Solver Control/Basic Settings/Interrupt Control. You can then set how the interrupts work (whether they AND or OR), and any user defined conditions (like yours would be). Look in the CFX-Pre manual section 22.1.1.6 for details.

You cannot put 100N load on a fluid without further information. The load needs to act on a surface, or be a thrust load, or some other action - and in all these cases you also need to define an area, object or surface for it to act on. So how do you intend to apply your load?

visitor · June 25, 2021, 17:12

I did look at this interrupt control, but did not understand how to utilize an if condition.

Regarding the load condition in CFX, the load acts on the air duct surface, sheet metal. It is a boundary condition I have created in space claim, an area 200 mm dia with a load acting on it.

ghorrocks · June 25, 2021, 21:14

The documentation explains it - a CEL expression which evaluates to 0.5 or higher is taken as true. So you can generate a user defined stopping condition from that. Bear in mind the details of how to evaluate expressions in a numerical framework as described by Opaque.

If the load acts on the duct wall then the duct wall is fundamental to how the load is reacted. This sounds like rigid bodies or FSI, depending on details.

visitor · June 26, 2021, 13:59

Yes I have seen Opaque's reply, thanks to both of you. I will try this once I am back on computing.
if ( probe(Velocity)@MyPointofInterest < 0.5, 1 , 0 ) , where the point of interest is defined in domain.

For the load it is just an area of selected elements on the air duct's wall. Just nee to apply 100 N on this these selected (within the mesher) elements.

June 24, 2021, 08:16		#21
Opaque Senior Member Join Date: Jun 2009 Posts: 1,816 Rep Power: 32	For example, if ( probe(Velocity)@MyPointofInterest < Tiny, ... , ... ) I think you should use some tiny value, and not 0 exactly. We are dealing with convergence and plenty of round-off here, are you certain it can reach 0 exactly? If you are, go for it; otherwise, the expression is just consuming cpu cycles. Keep in mind, that Velocity is always positive since it is the magnitude of the vector in that expression. When dealing with components or other scalars, you may want to use abs( ) if ( abs (probe (MyVar)@MyPointofInterest)) < Tiny, .. ) or more generically if (abs (probe(MyVar)@MyPointofInterest) - MyTargetValue) < Tiny, ..., ..) Hope the above helps, __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

June 24, 2021, 18:35		#23
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,732 Rep Power: 143	What version of CFX are you using? I do not understand your boundary condition comment. What "load"? Load of what? __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

June 25, 2021, 05:01		#25
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,732 Rep Power: 143	I told you in post #20 how to stop a simulation with a condition. If you don't understand a comment ask for it to be explained, do not ignore it. CFX-Pre, Solver Control/Basic Settings/Interrupt Control. You can then set how the interrupts work (whether they AND or OR), and any user defined conditions (like yours would be). Look in the CFX-Pre manual section 22.1.1.6 for details. You cannot put 100N load on a fluid without further information. The load needs to act on a surface, or be a thrust load, or some other action - and in all these cases you also need to define an area, object or surface for it to act on. So how do you intend to apply your load? __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

June 25, 2021, 21:14		#27
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,732 Rep Power: 143	The documentation explains it - a CEL expression which evaluates to 0.5 or higher is taken as true. So you can generate a user defined stopping condition from that. Bear in mind the details of how to evaluate expressions in a numerical framework as described by Opaque. If the load acts on the duct wall then the duct wall is fundamental to how the load is reacted. This sounds like rigid bodies or FSI, depending on details. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

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June 24, 2021, 13:42		#22
visitor Senior Member AH Join Date: Apr 2014 Posts: 282 Rep Power: 13	I'm looking there, I couldn't find anything, was hoping to put his in an 'if' condition. Also, I'm looking for away where I can apply a load on a boundary condition. But not to go into the obvious Static Structural ANSYS tool. Thanks.

June 25, 2021, 04:06		#24
visitor Senior Member AH Join Date: Apr 2014 Posts: 282 Rep Power: 13	Thanks Opaque, but what command stops solver? What shall I enter in the true return condition? if ( probe(Velocity)@MyPointofInterest < Tiny, ... , ... ) ---- Thanks Ghorrocks, its a boundary condition I have created on the air-duct, about 100 mm diameter. This will have a 10 kg load on it (100 N). ANSYS 2021 academic, CFX.

June 25, 2021, 17:12		#26
visitor Senior Member AH Join Date: Apr 2014 Posts: 282 Rep Power: 13	I did look at this interrupt control, but did not understand how to utilize an if condition. Regarding the load condition in CFX, the load acts on the air duct surface, sheet metal. It is a boundary condition I have created in space claim, an area 200 mm dia with a load acting on it.

June 26, 2021, 13:59		#28
visitor Senior Member AH Join Date: Apr 2014 Posts: 282 Rep Power: 13	Yes I have seen Opaque's reply, thanks to both of you. I will try this once I am back on computing. if ( probe(Velocity)@MyPointofInterest < 0.5, 1 , 0 ) , where the point of interest is defined in domain. For the load it is just an area of selected elements on the air duct's wall. Just nee to apply 100 N on this these selected (within the mesher) elements.