5 Replies Latest reply on Feb 6, 2014 5:28 PM by Steve Calkins

Time-dependent calculation: any shortcuts?

Steve Calkins Feb 3, 2014 2:07 PM

Hi,

My application involves cooling an object from an initial temperature (500C) in an array of air nozzles over 90 seconds. Running the simulation on the entire assembly is taking ridiculous amounts of time (I set it to run over the weekend, and Monday morning the solver had made it through under one second of physical time, and said it had over 800 hours of computation time left).

The individual nozzles solve quickly, when simulated as a steady-state flow problem. Is there a way to solve for the flow conditions, then assign the temperature to the part, and solve for the transient case?

I've been looking into the transferred boundary condition technique, but I'm either doing something wrong, or it's not a valid way to approach this.

Thanks,

Steve

Re: Time-dependent calculation: any shortcuts?

Jared Conway Feb 5, 2014 11:44 PM (in response to Steve Calkins)

How long does a steady state of all the nozzles take?

You should be able to setup the steady state and use it as the starting point even if you override the temp conditions of a component at the start. What is your work flow? Suggest you start with a simple model that you can post to get help.
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- Re: Time-dependent calculation: any shortcuts?
  
  Steve Calkins Feb 6, 2014 11:22 AM (in response to Jared Conway)
  
  Hi Jared,
  
  Thanks for the response.
  
  I've been plugging away at this for a few days now, and I came up with pretty much the solution you suggest. I ran just the steady state simulation, which ran pretty quickly by itself, then set up another configuration for the transient simulation, using the SS results as the initial conditions. The transient simulation starts out using very small time steps, but they get progressively larger, and the total run time is only about 5 to 10 minutes.
  
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  - Re: Time-dependent calculation: any shortcuts?
    
    Jared Conway Feb 6, 2014 11:24 AM (in response to Steve Calkins)
    
    you can also experiment with constant time steps
    
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Re: Time-dependent calculation: any shortcuts?

Chris Michalski Feb 6, 2014 11:46 AM (in response to Steve Calkins)

Another way to speed things up would be to use flow freezing so that once it solves the fluid motion you can suspend that portion of the calculation and only have it calculate the heat transfer aspects.
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- Re: Time-dependent calculation: any shortcuts?
  
  Steve Calkins Feb 6, 2014 5:28 PM (in response to Chris Michalski)
  
  I used flow freezing, as well. I set it to freeze at time = 0, rather than after a set time or number of intervals.
  
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