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Search: Posts Made By: ghorrocks
Forum: CFX February 5, 2014, 17:52
Replies: 84
Views: 24,619
Posted By ghorrocks
Actually, on second thoughts you cannot do...

Actually, on second thoughts you cannot do momentum sources with source points. Looks like only mass and energy sources an that means you are creating or destroying mass or energy. My understanding...
Forum: CFX February 4, 2014, 18:20
Replies: 84
Views: 24,619
Posted By ghorrocks
Good. Now we have a good starting point. ...

Good. Now we have a good starting point.



The thermal model will be more stable so I would start with that. But a fire will result in temperature differences big enough that a compressible...
Forum: CFX February 3, 2014, 17:12
Replies: 84
Views: 24,619
Posted By ghorrocks
That is because you have not paid attention to my...

That is because you have not paid attention to my previous post. Remove the fans and just do a simple run with your inlets and outlets. Make sure this runs properly. And if it does run then at least...
Forum: CFX February 2, 2014, 17:36
Replies: 84
Views: 24,619
Posted By ghorrocks
I cannot count the number of times people have...

I cannot count the number of times people have started by modelling the most complex model they can imagine and got nowhere and then had no results to show for all the work. Surely a better approach...
Forum: CFX November 25, 2013, 01:00
Replies: 84
Views: 24,619
Posted By ghorrocks
It depends on what you want to model the...

It depends on what you want to model the sprinklers for.

If you simply want their cooling effect then put a heat sink where they act. Simple (but very approximate).

If you want to see where the...
Forum: CFX November 21, 2013, 05:15
Replies: 84
Views: 24,619
Posted By ghorrocks
The most important thing is to define boundary...

The most important thing is to define boundary conditions which match the situation you are trying to simulate. I see from your first post you have some inlets and outlets - but what defines the flow...
Forum: CFX November 19, 2013, 05:02
Replies: 84
Views: 24,619
Posted By ghorrocks
There is an FAQ on accuracy:...

There is an FAQ on accuracy: http://www.cfd-online.com/Wiki/Ansys_FAQ#Why_are_my_results_inaccurate.3F

In this case I doubt you will find the assumption of steady state appropriate. Highly buoyant...
Forum: CFX November 17, 2013, 18:21
Replies: 84
Views: 24,619
Posted By ghorrocks
The reference pressure does not set the pressure...

The reference pressure does not set the pressure level in the simulation domain as there is still the unknown pressure offset from the reference pressure. Reference pressure is used to reduce...
Forum: CFX November 17, 2013, 17:04
Replies: 84
Views: 24,619
Posted By ghorrocks
The CFX documentation has important comments on...

The CFX documentation has important comments on boundary condition selection. If you select velocity inlet and outlet then the pressure level is not set and the simulation is badly posed. You need to...
Forum: CFX November 14, 2013, 17:37
Replies: 84
Views: 24,619
Posted By ghorrocks
I will leave the discussion on how you mesh in...

I will leave the discussion on how you mesh in Gambit to others, but the end effect is that for the mesh refinement if you had a 1m cube meshed with 10x10x10 elements you would have 0.1m edge...
Forum: CFX November 13, 2013, 19:58
Replies: 84
Views: 24,619
Posted By ghorrocks
The concept is simple (I should write a FAQ on...

The concept is simple (I should write a FAQ on this):

* Make the mesh significantly finer. Halving the element edge length is what you should aim for. This will make your mesh something like 8...
Forum: CFX November 13, 2013, 17:42
Replies: 84
Views: 24,619
Posted By ghorrocks
I can see from your image you have a very coarse...

I can see from your image you have a very coarse mesh. You are never going to get an accurate simulation with a mesh that coarse. You need to make a finer mesh. How fine? Do a mesh size sweep and...
Forum: CFX November 5, 2013, 18:14
Replies: 84
Views: 24,619
Posted By ghorrocks
I will let you do the final debugging of the CEL...

I will let you do the final debugging of the CEL - I suspect you might need to do some units stuff but you can sort that out.

The insideSource expression just determines whether you are inside a...
Forum: CFX November 4, 2013, 19:35
Replies: 84
Views: 24,619
Posted By ghorrocks
You can use if statements: ...

You can use if statements:
if(t<800[s],if(t<180[s],{function for 0-180s},{function for 180-800s}),{function for >800s})

I do not understand your second question. Your step function concept is the...
Forum: CFX October 22, 2013, 21:18
Replies: 84
Views: 24,619
Posted By ghorrocks
The momentum source is adding momentum. So look...

The momentum source is adding momentum. So look at what that addition of momentum does to the flow.

Momentum sources do not need to be constants. You can write momentum sources which force the...
Forum: CFX October 15, 2013, 20:39
Replies: 84
Views: 24,619
Posted By ghorrocks
I would not worry about the domains until you...

I would not worry about the domains until you have fixed the weird inlet. You are going to get all sorts of grief from that. If the method you are usign the generate the volume is not working then...
Forum: CFX October 14, 2013, 18:31
Replies: 84
Views: 24,619
Posted By ghorrocks
First of all, something weird has happened at...

First of all, something weird has happened at your inlet door thing. You will need to fix that up before proceeding.

How to set up solid/fluid simulations is covered in the tutorials - have a look...
Forum: CFX September 17, 2013, 08:52
Replies: 84
Views: 24,619
Posted By ghorrocks
Both the CFX Reference guide and the tutorial...

Both the CFX Reference guide and the tutorial guide are installed as part of a default CFX installation.
Forum: CFX September 17, 2013, 08:10
Replies: 84
Views: 24,619
Posted By ghorrocks
Look in the CFX reference manual for the...

Look in the CFX reference manual for the definition of CEL expressions.

step is simply a function which if the argument is negative it returns 0, if positive it returns 1 and if precisely zero it...
Forum: CFX September 16, 2013, 19:05
Replies: 84
Views: 24,619
Posted By ghorrocks
The error message means exactly what it says -...

The error message means exactly what it says - you have referenced a object called "Floor" but no appropriate object exists. You need to change the name you are referencing or fix your mesh to have...
Forum: CFX September 12, 2013, 07:47
Replies: 84
Views: 24,619
Posted By ghorrocks
Both of your questions are dealt with in the CFX...

Both of your questions are dealt with in the CFX tutorials

For additional variables there are a few tutorials which use additional variables. Have a look at them for how they are implemented.
...
Forum: CFX September 11, 2013, 19:38
Replies: 84
Views: 24,619
Posted By ghorrocks
Can you get the inert model working? That would...

Can you get the inert model working? That would seem to be the obvious first step.
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