5 Replies Latest reply on Jun 19, 2012 4:45 PM by Chris Michalski

    Steady state vs. time depended analysis

    Shahar Dor Zidon

      Hi guys

      What’s up?

       

      I was wandering if anybody knows

      What is the “flow simulation” definition of steady state condition?

      If I will do an 8h time depended analysis & run a non-depended time analysis the results will be the same?

      What is the software steady state definition?

      Appreciate the help!

      Thanks

        • Re: Steady state vs. time depended analysis
          Chris Michalski

          the definition of steady state is that the simulation will reach one continuous state (temperatures, velocities, pressures, etc. will reach a steady state).

           

          For example, flow around a tube can continually oscillate downstream of the tube.  This type of simulation may never reach a steady state (depending on boundary conditions).

           

          For a time dependent simulation Flow Simulation saves each time step of information so you can look at the results as a function of time.

          For steady state it saves the final converged answer as this is the "steady state" solution.

          • Re: Steady state vs. time depended analysis
            Keith Vittitoe

            Shahar,

             

            Hello.  Steady state in flow is the same as a textbook definition.  The flow solver assumes every study is a transient analysis, so for steady state analysis (not time-dependent), it will look for convergence or run until it times out (if that is specified).

             

            Use the Time-dependent setting for transient analysis and let flow find steady state otherwise.

             

            Best Regards,

            Keith

            • Re: Steady state vs. time depended analysis
              Bill McEachern

              A little more subtelty maybe required: It is fluid dynamics we are concerned with here so in the strict sense there is no such thing as "steady state" - that would be fluid statics. It would be slightly more precise to call it quasi steady state - there will always be fluctuations in the flow in the B'layers and little eddys hera and there that are time varing. Steady state inthe context of flow sim is achieve the more or less steady conditions that results after the initial start up transients have been resolved. YOu cna get a steady state analysis where you have goals that will not be steady becuase real flow fluctuations are occuring - say eddies shedding off an obstruction ala a Karmen votex street. where you have a goal of the pressure on the surface and it fluctuates. A steady state analysis in flow sim is a transient analysis where time is not tracked explicitly and it only saves the last result.