CFX-Post Timesteps

A5729 · July 18, 2012, 06:05

Hey I'm new to CFX,

I am struggling to get different timesteps for each of my sims , every time i do so, I only see the final timestep.

I am trying to simulate waves around a floating body. If anyone can point me to a tutorial of that , it would be great (I can't follow the one in ANSYS)

monkey1 · July 18, 2012, 06:13

Hi!
I think you should specify your problem a little more...what are you exactly trying / wanting to do?

When you say you "see" only the last time time step...I suppose you are talking about CFX post? I this is so...then just click on the icon in the toolbat that looks like an old fashioned stop watch...the "time step selector" there you can then select every desired time step to have a look at... BUT in order to be able to do this you MUST have set in CFX Pre that the solver is writing transient data out for a specified number of time steps. It means if you don't have any .trn files in your calculation folder then nthere are no more time steps available for display than the last one saved in the .res file.

A5729 · July 18, 2012, 07:10

I'm modelling a boat that has a hollow cylinder as a hull. I want to be able to see the flow inside and outside the cylinder , In particular things like bow waves.

Where do i go in CFX-Pre to set that data?

I have the feeling that waves are going to get complicated to model

monkey1 · July 18, 2012, 07:19

In CFX Pre you have to go to the output control, there you will find a "Trn Results" Tab. In this tab you will have to setup that transient results will be written. You will have to define the frequency of trn output either by specifying a number of iteration loops or a defined time interval like every second.

Just be a little carefull when choosing which variables will be written. If leaving the transient results option on "standard" it will write out ALL variables, causing the trn files to be quite big. To reduce the amount of disk space required, you can select the option "selected variables" where you can specify the variables that are of interest for you.

A5729 · July 18, 2012, 07:27

I obviously doing something wrong here , Does it have to be a transient flow?

I cannot see the trn tab

monkey1 · July 18, 2012, 07:36

Of course it has to be transient flow....
How do you want to see Time steps or a time dependent behaviour in a steady state simulation?????

A5729 · July 18, 2012, 07:43

Sorry , Just started using CFD two days ago. I have a long road ahead of me , and its all uphill

Felggv · July 20, 2012, 15:34

It's normal that we get a little "blind" when using CFX.

First of all, think of the physics of your problem... Steady State is steady state everywhere, in every book and it's time independent.

I'm not criticizing you or telling you that don't know what steady state means, but you should think well of your problem before setting the boundary conditions and etc...

I'm not an expert but I think that an expert would say that to you

.

July 18, 2012, 06:05	CFX-Post Timesteps	#1
A5729 New Member Angus Bishop Join Date: Apr 2012 Posts: 17 Rep Power: 14	Hey I'm new to CFX, I am struggling to get different timesteps for each of my sims , every time i do so, I only see the final timestep. I am trying to simulate waves around a floating body. If anyone can point me to a tutorial of that , it would be great (I can't follow the one in ANSYS)

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July 18, 2012, 06:13		#2
monkey1 Senior Member Join Date: Jul 2011 Location: Berlin, Germany Posts: 173 Rep Power: 15	Hi! I think you should specify your problem a little more...what are you exactly trying / wanting to do? When you say you "see" only the last time time step...I suppose you are talking about CFX post? I this is so...then just click on the icon in the toolbat that looks like an old fashioned stop watch...the "time step selector" there you can then select every desired time step to have a look at... BUT in order to be able to do this you MUST have set in CFX Pre that the solver is writing transient data out for a specified number of time steps. It means if you don't have any .trn files in your calculation folder then nthere are no more time steps available for display than the last one saved in the .res file.

July 18, 2012, 07:10		#3
A5729 New Member Angus Bishop Join Date: Apr 2012 Posts: 17 Rep Power: 14	I'm modelling a boat that has a hollow cylinder as a hull. I want to be able to see the flow inside and outside the cylinder , In particular things like bow waves. Where do i go in CFX-Pre to set that data? I have the feeling that waves are going to get complicated to model

July 18, 2012, 07:19		#4
monkey1 Senior Member Join Date: Jul 2011 Location: Berlin, Germany Posts: 173 Rep Power: 15	In CFX Pre you have to go to the output control, there you will find a "Trn Results" Tab. In this tab you will have to setup that transient results will be written. You will have to define the frequency of trn output either by specifying a number of iteration loops or a defined time interval like every second. Just be a little carefull when choosing which variables will be written. If leaving the transient results option on "standard" it will write out ALL variables, causing the trn files to be quite big. To reduce the amount of disk space required, you can select the option "selected variables" where you can specify the variables that are of interest for you.

July 18, 2012, 07:27		#5
A5729 New Member Angus Bishop Join Date: Apr 2012 Posts: 17 Rep Power: 14	I obviously doing something wrong here , Does it have to be a transient flow? I cannot see the trn tab

July 18, 2012, 07:36		#6
monkey1 Senior Member Join Date: Jul 2011 Location: Berlin, Germany Posts: 173 Rep Power: 15	Of course it has to be transient flow.... How do you want to see Time steps or a time dependent behaviour in a steady state simulation?????

July 18, 2012, 07:43		#7
A5729 New Member Angus Bishop Join Date: Apr 2012 Posts: 17 Rep Power: 14	Sorry , Just started using CFD two days ago. I have a long road ahead of me , and its all uphill

July 20, 2012, 15:34		#8
Felggv Member Felipe Gobbi Join Date: Apr 2012 Location: Brazil Posts: 76 Rep Power: 14	It's normal that we get a little "blind" when using CFX. First of all, think of the physics of your problem... Steady State is steady state everywhere, in every book and it's time independent. I'm not criticizing you or telling you that don't know what steady state means, but you should think well of your problem before setting the boundary conditions and etc... I'm not an expert but I think that an expert would say that to you .