# Can Fluent start a simulation from a negative time

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 November 23, 2008, 15:06 Can Fluent start a simulation from a negative time #1 Ted Chu Guest   Posts: n/a Hi all, I am trying to do a simple 2D wave tank simulation. A solitary wave will be generated and propagate from left to right. I am using the DEFINE_CG_MOTION udf on the left wall (as a wavemaker). The velocity profile in the udf is a hyperbolic secant function varying with time. In order to have the left wall to follow the profile, the simulation needs to start from a negative time. I was just wondering if Fluent can start a simulation from a negative time? Thanks..

 November 23, 2008, 16:12 Re: Can Fluent start a simulation from a negative #2 Rogerio Fernandes Brito Guest   Posts: n/a I donīt think so! http://rapidshare.de/files/40979319/0_wave.rar.html

 November 23, 2008, 16:43 Re: Can Fluent start a simulation from a negative #3 Ted Chu Guest   Posts: n/a Thank you Rogerio. I already have this tutorial. It uses sine function which starts at time 0 to generate waves. Do you know how to use sech function which starts at a negative time in Fulent?? Or, is there another way to get around??

 November 23, 2008, 17:18 Re: Can Fluent start a simulation from a negative #4 Rogerio Fernandes Brito Guest   Posts: n/a I will talk with others researchers about it, īcause iīm new in Fluent. Best regards, Rogerio.

 November 23, 2008, 19:58 Re: Can Fluent start a simulation from a negative #5 Ted Chu Guest   Posts: n/a Thanks Rogerio.. At the mean time, can anyone else help??

 November 24, 2008, 16:49 Re: Can Fluent start a simulation from a negative #6 CDE Guest   Posts: n/a You can set Fluent's flow time using the text command: (rpsetvar 'flow-time 0.0) Replace 0.0 with the the flow-time you require. I have never tried using this with a negative time so I don't know if it will do what you require.

 November 25, 2008, 16:48 Re: Can Fluent start a simulation from a negative #7 Ted Chu Guest   Posts: n/a Thanks.. I am trying it now, but I got this message saying INVALID COMMAND [rpsetvar]. Don't know why....

 November 25, 2008, 22:30 Re: Can Fluent start a simulation from a negative #8 CDE Guest   Posts: n/a did you include the brackets when inputting the command? copy the command below exactly (rpsetvar 'flow-time 0.0)

 November 26, 2008, 07:00 Re: Can Fluent start a simulation from a negative #9 Ted Chu Guest   Posts: n/a No, I did not include the brackets. I copied the command line into the console window, then got that message. I just tried it again, but no luck still getting the invalid command rpsetvar. I am using Fluent 6.3.26 on Windows. Thanks...

 November 26, 2008, 16:00 Re: Can Fluent start a simulation from a negative #10 CDE Guest   Posts: n/a you need to include the brackets....it won't work without them. Its a scheme command

 November 26, 2008, 21:06 Re: Can Fluent start a simulation from a negative #11 Ted Chu Guest   Posts: n/a Thanks a lot CDE!!! It worked. Yes, now I can start the simulation from a negative time.