Initial value to accelerate a simulation

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 February 18, 2013, 10:15 Initial value to accelerate a simulation #1 New Member   Join Date: Jun 2011 Posts: 19 Rep Power: 8 Hello, I'm working with a project where we're trying to figure out how much an "appropriate" initial value would save computational effort during a simulation. We will run simulations under different conditions. However, I find it hard to find any literature about the topic. Does anybody have an idea where I could read about the effect the initial value has on the convergence of a simulation? Thank you!

February 18, 2013, 11:32
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andy
Join Date: May 2009
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Quote:
 Originally Posted by The_Architect I'm working with a project where we're trying to figure out how much an "appropriate" initial value would save computational effort during a simulation. We will run simulations under different conditions. However, I find it hard to find any literature about the topic. Does anybody have an idea where I could read about the effect the initial value has on the convergence of a simulation?
Are these steady-state or time accurate simulations?

The broad answer is not much so long as you avoid a big bang. I don't think it is much of an academic topic but more practical knowledge one tends to pick up after doing a few CFD simulations. If your flow is prone to big bangs (e.g. aggressively diffusing flows) then turning on the inlet steadily over a few steps rather than instantly can help quite a lot, as can starting from a previous solution or, for transient flows, imposing a tight tolerance for mass conservation on the first iteration to get the flow moving everywhere although this can sometimes backfire if the generated flow is grossly unrealistic and takes a long time to blow out the exit.

 February 22, 2013, 06:56 #3 New Member   Join Date: Jun 2011 Posts: 19 Rep Power: 8 Thanks for your reply Andy. To me more precise, I'm looking into ship hull simulations. "Big bangs" do happen at the early stages of simulations, the free surface and the wake both create problems. My idea would be to use a previous flow field of a hull as the initial value (MapFields in OpenFoam) for the simulation of a new ship hull. However, as this is an academic work, I am still looking for any kind of references about the topic.

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