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

Overflow error - velocity variable HELP!

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Display Modes
Old   March 19, 2011, 11:44
Default Overflow error - velocity variable HELP!
  #1
New Member
 
phil fenna
Join Date: Feb 2011
Posts: 14
Rep Power: 6
88phil88 is on a distinguished road
i have a water tank that runs fine for transient simulation with an inlet velocity of 2ms^-1, when i reduce the velocity down to 0.25ms^-1 i get an overflow error.

The mesh has 500,000 elements, i need the simulation time to be about 20 hours (showing the water coming in to an empty tank). my time steps vary between 1s and 4s (using adaptive time stepping).

Any help or advice how to get it to work with a lower velocity?

Thanks
88phil88 is offline   Reply With Quote

Old   March 20, 2011, 22:01
Default
  #2
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 10,960
Rep Power: 85
ghorrocks has a spectacular aura aboutghorrocks has a spectacular aura aboutghorrocks has a spectacular aura about
Steady state or transient? What Re number? What physics?

Why do you say you need the simulation time to be 20 hours? Will you buy whatever computers are required to achieve this time?
ghorrocks is offline   Reply With Quote

Old   March 22, 2011, 10:23
Default
  #3
New Member
 
phil fenna
Join Date: Feb 2011
Posts: 14
Rep Power: 6
88phil88 is on a distinguished road
Thanks for the reply, its transient flow.

my indistrial supervisor for my dissertation told be it takes about a day for the water tank to be filled, so hence the time.

I realise now after researching etc i wont be able to achieve this kind of times with a very small discharge with resources i have and time.

I'm trying to go further in my dissertation my moddeling two liquids in a watertank and visualy showing the settlement.

Before i started this extra work i did not realise that transient simulations could take days or weeks! But i have a simulation now that will hopefully give me a good visulization.

Thanks for all your help you gave me on my diferent posts that i posted, you've really helped me to get to ths stage and hopefully better marks for my dissertation
88phil88 is offline   Reply With Quote

Old   March 22, 2011, 22:39
Default
  #4
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 10,960
Rep Power: 85
ghorrocks has a spectacular aura aboutghorrocks has a spectacular aura aboutghorrocks has a spectacular aura about
I remember reading a research paper on the flow of magma in a volcano's magma chamber. The turn-over time of the molten rock in the magma chamber was 144 million years. Just because the flow takes millions of years to do anything does not mean the simulation needs to take millions of years.

Likewise simulations of MEMS structures models events with take nanoseconds. I can assure you the simulations take a lot longer than nanoseconds!

The length of time a simulation takes to complete depends on the complexity of the equations governing it, not the length of time the physical process takes.
ghorrocks is offline   Reply With Quote

Reply

Thread Tools
Display Modes

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 On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
How to limit a variable ash OpenFOAM Running, Solving & CFD 1 June 26, 2008 20:32
error in COMSOL:'ERROR:6164 Duplicate Variable' bhushas Main CFD Forum 1 May 30, 2008 04:35
Problems with additional variable Krishna Premi CFX 1 October 29, 2007 09:19
Env variable not set gruber2 OpenFOAM Installation 5 December 30, 2005 05:27
Replace periodic by inlet-outlet pair lego CFX 3 November 5, 2002 21:09


All times are GMT -4. The time now is 10:32.