# BOUNDARY CONDITION THAT CHANGES WITH TIME

 User Name Remember Me Password
 Register Blogs Members List Search Today's Posts Mark Forums Read

 LinkBack Thread Tools Display Modes
 August 29, 2003, 08:42 BOUNDARY CONDITION THAT CHANGES WITH TIME #1 George Guest   Posts: n/a Hi I really appreciate if someone could help me out. How can I set BC's that aren't constant in time, like an inlet that work for 15 seconds in a 3 minutes transient simulation. How can I do that using fluid sub-domains as energy sources that also vary on time. Thanks.

 August 29, 2003, 10:12 Re: BOUNDARY CONDITION THAT CHANGES WITH TIME #2 cfd guy Guest   Posts: n/a It's the same approach for the both problems. Create an expression in CEL and combine it with the step function. Suppose that you have a B.C. that follows the equation: Vel = A * t Where A is a constant and t is time according to CFX-5 VARIABLES file (located on ~CFXROOT/etc). If you set this you'll get a linear variation until the solver ends. But if you want to get it just for the first 15 seconds, use the STEP function. Example: step(any negative dimensionless number) returns 0. step(0 dimensionless) returns 0.5 step(any positive dimensionless number) returns 1. In your case(assuming 15 seconds): Vel = step( (15 [s] - t)/ 1[s] ) * A * t Note that is divided by 1[s] to keep the argument dimensionless. Supposing that your time step is 1s, in the 15th iteration you'll get 0.5*A*t, 16th A*t, 17th A*t, and so on. If you want to get rid of 0.5*A*t, just do this: Vel = step( (15.0001 [s] - t)/ 1[s] ) * A * t This way you'll never get 0.0 and you'll really get a stepwise behavior on the activation of your function. Hope this helps, cfd guy

 Thread Tools Display Modes Linear Mode

 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 OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post Lord Kelvin OpenFOAM Running, Solving & CFD 8 March 28, 2016 11:08 Niklas Wikstrom (Wikstrom) OpenFOAM Running, Solving & CFD 122 June 15, 2014 06:20 flakid OpenFOAM Running, Solving & CFD 2 April 13, 2011 07:32 nuengao FLUENT 0 December 13, 2010 03:42 xujjun CFX 9 June 9, 2009 07:59

All times are GMT -4. The time now is 03:44.

 Contact Us - CFD Online - Top