CFD Online Discussion Forums

CFD Online Discussion Forums (
-   CFX (
-   -   Overflow error - velocity variable HELP! (

88phil88 March 19, 2011 11:44

Overflow error - velocity variable HELP!
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?


ghorrocks March 20, 2011 22:01

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?

88phil88 March 22, 2011 10:23

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 :)

ghorrocks March 22, 2011 22:39

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.

All times are GMT -4. The time now is 17:15.