CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > ANSYS > CFX

Transient analysis time step

Register Blogs Community New Posts Updated Threads Search

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   February 25, 2013, 04:12
Default Transient analysis time step
  #1
Senior Member
 
Govindaraju
Join Date: Apr 2010
Posts: 209
Rep Power: 17
kmgraju is on a distinguished road
Dear all
I would like to clarify the time steps.
I have a sinusoidal function and the frequency is 1 Hz. I did the transient simulation for one cycle
one of my friends told me and insist me to do the multiple cycle simulations.Is it necessary to do the simulations for multiple cycles?. If I do the multiple cycles the solution time is too large. Is there any way to short cut.

Thank you

Regards
kmgraju is offline   Reply With Quote

Old   February 25, 2013, 05:15
Default
  #2
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,872
Rep Power: 144
ghorrocks is just really niceghorrocks is just really niceghorrocks is just really niceghorrocks is just really nice
If you want the startup transient then you do not need to do multiple cycles. If you want the repeating cycle it depends how long it settles to a repeating pattern. It could be 1 cycle, it could be hundreds - it depends on how stable the system is and how long it takes to settle.

But you will need to run it long enough to show that you have run long enough - so the change in the last few cycles is small enough that you can call it converged.
ghorrocks is offline   Reply With Quote

Old   February 25, 2013, 06:55
Default
  #3
Senior Member
 
Lance
Join Date: Mar 2009
Posts: 669
Rep Power: 22
Lance is on a distinguished road
Glenn is (as always) correct, you will need to perform a sensitivity analysis on the number of cycles in order to avoid initial effects - otherwise the initial conditions will affect your solution.
Lance is offline   Reply With Quote

Old   March 2, 2013, 21:01
Default
  #4
Senior Member
 
Govindaraju
Join Date: Apr 2010
Posts: 209
Rep Power: 17
kmgraju is on a distinguished road
Quote:
Originally Posted by Lance View Post
Glenn is (as always) correct, you will need to perform a sensitivity analysis on the number of cycles in order to avoid initial effects - otherwise the initial conditions will affect your solution.
Dear all

I have a set of data from 0 s to 2 s. I used one dimensional interpolation and activated extended minimum and maximum.

My question is

How to run this simulation for repeated cycles.( at least for 4 cycles) ?

Thank you

Regards

Govind
kmgraju is offline   Reply With Quote

Old   March 3, 2013, 06:19
Default
  #5
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,872
Rep Power: 144
ghorrocks is just really niceghorrocks is just really niceghorrocks is just really niceghorrocks is just really nice
The simple nasty approach is just to repeat the 1D function 4 times.

The better approach is to use the mod function, so the time input to the interpolation is t-mod(t,2) which should return a function which increase to 2, then goes to zero and increases to 2 again when t is 4, and repeats that forever.
ghorrocks is offline   Reply With Quote

Old   March 3, 2013, 14:14
Default
  #6
Senior Member
 
Govindaraju
Join Date: Apr 2010
Posts: 209
Rep Power: 17
kmgraju is on a distinguished road
Quote:
Originally Posted by ghorrocks View Post
The simple nasty approach is just to repeat the 1D function 4 times.

The better approach is to use the mod function, so the time input to the interpolation is t-mod(t,2) which should return a function which increase to 2, then goes to zero and increases to 2 again when t is 4, and repeats that forever.
Dear Mr Glenn

Thank you . It works

Govind
kmgraju is offline   Reply With Quote

Reply


Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Extrusion with OpenFoam problem No. Iterations 0 Lord Kelvin OpenFOAM Running, Solving & CFD 8 March 28, 2016 12:08
InterFoam negative alpha karasa03 OpenFOAM 7 December 12, 2013 04:41
SLTS+rhoPisoFoam: what is rDeltaT??? nileshjrane OpenFOAM Running, Solving & CFD 4 February 25, 2013 05:13
Choosing the apt time step size for a transient run saisanthoshm88 CFX 1 March 31, 2012 17:11
Time step for wind turbine analysis amoolraina FLUENT 4 March 25, 2011 03:58


All times are GMT -4. The time now is 17:24.