Reply To: Problems with step size

[Julen]

 

 

Hello,

the Simulation that gave the error message in the original post had exactly the evolution parameters that the expert system suggests in the listing file.

I’ve run two simulations with different parameters since, in both of those I aditionally turned on viscous heating (because I forgot in the previous one), the the evolution parameters are not the only thing I changed:

 

 

1. Evol parameters at  f(s) = 1/s    //    S-ini = 0.3     //    Delta_S-ini = 0.2    //    Delta_S-max = 0.25

 

I still get an error message, with the following suggestions:

*****************************
     *  Expert tool diagnostics  *
     *****************************

     The problem F.E.M. Task      has not converged.

     The evolution scheme can not reach the final value of the evolution 
     parameter 1.  Evolution stops for a value of the evolution parameter 
     equals to 0.9984 because the step size has been reduced below the 
     minimum (as assigned in Polydata).

     *****************************
     *  Expert tool suggestions  *
     *****************************

     The grid Brinkman number (Br), which is defined as follows: 
         Viscous heating/ Thermal diffusion (ONLY IF TEMPERATURE IS NOT 
           CONSTANT) ,
     is equal to 7.97e+08 (greather than 20.0).  
     It could be too large and induce convergence difficulties.  Please 
     check the setup of the simulation and more specifically :
       – the flow rate or the entry velocity,
       – the viscosity,
       – the thermal conductivity,
       – the coordinates,
       – the coherence of system units.

     There is a non-linearity in the problem Navier-Stokes 3D introduced 
     by the viscous heating.
     The expert system suggests to use an evolution for the scaling factor 
     related to the viscous heating.  The evolution scheme must be the 
     following :
        –   f(s) = s
        –   S-ini = order of 0.001 such as the viscous heating could be 
          neglected 
        –   S-final = 1.0 
        –   Initial increment = S-in

     There is a non-linearity in the problem Navier-Stokes 3D introduced 
     by the viscous heating.
     The expert system suggests to use an evolution for the thermal 
     conductivity.  The evolution scheme must be the following :
        –   f(s) = 1/s
        –   S-ini = order of 0.001 such as the diffusivity is dominant.
        –   S-final = 1.0 
        –   Initial increment = S-ini

     If you can not define the evolution with those typical values of the 
     evolution parameters, maybe your problem is not well defined.  Please 
     check the setup of your simulations.

 

2. Evol parameters of the second simulation f(s) = 1/s    //    S-ini = 0.755     //    Delta_S-ini = 0.09437    //    Delta_S-max = 0.25

*****************************
     *  Expert tool diagnostics  *
     *****************************

     The problem F.E.M. Task      has not converged.

     The evolution scheme can not reach the final value of the evolution 
     parameter 1.  Evolution stops for a value of the evolution parameter 
     equals to 0.9993 because the step size has been reduced below the 
     minimum (as assigned in Polydata).

     *****************************
     *  Expert tool suggestions  *
     *****************************

     The grid Brinkman number (Br), which is defined as follows: 
         Viscous heating/ Thermal diffusion (ONLY IF TEMPERATURE IS NOT 
           CONSTANT) ,
     is equal to 9.47e+08 (greather than 20.0).  
     It could be too large and induce convergence difficulties.  Please 
     check the setup of the simulation and more specifically :
       – the flow rate or the entry velocity,
       – the viscosity,
       – the thermal conductivity,
       – the coordinates,
       – the coherence of system units.

     There is a non-linearity in the problem Navier-Stokes 3D introduced 
     by the viscous heating.
     The expert system suggests to use an evolution for the scaling factor 
     related to the viscous heating.  The evolution scheme must be the 
     following :
        –   f(s) = s
        –   S-ini = order of 0.001 such as the viscous heating could be 
          neglected 
        –   S-final = 1.0 
        –   Initial increment = S-ini

     There is a non-linearity in the problem Navier-Stokes 3D introduced 
     by the viscous heating.
     The expert system suggests to use an evolution for the thermal 
     conductivity.  The evolution scheme must be the following :
        –   f(s) = 1/s
        –   S-ini = order of 0.001 such as the diffusivity is dominant.
        –   S-final = 1.0 
        –   Initial increment = S-ini

     There is a non-linearity in problem Navier-Stokes 3D introduced by 
     the power law index (n) of the viscosity law.  The value of the power 
     law index is 0.755.
     The expert system suggests to use a Picard iterative scheme with a 
     number of iterations about 30 or 40.

     There is a non-linearity in problem Navier-Stokes 3D introduced by 
     the power law index (n) of the viscosity law.  The value of the power 
     law index is 0.755.
     The expert system suggests to use an evolution for this parameter 
     coupling with Newton-Raphson iterative scheme.  The evolution scheme 
     must be the following : 
        –   f(s) = 1/s
        –   S-ini = n = 0.755
        –   S-final = 1.0 
        –   Initial increment = 0.9437 = n/0.8.

     If you can not define the evolution with those typical values of the 
     evolution parameters, maybe your problem is not well defined.  Please 
     check the setup of your simulations.

 

What I don’t understand is the expert system suggesting multiple different evolution parameters, ranging from the f(s) being different and even the values for the different s being different, as it is one FEM Task. Doesn’t this mean that I can only ever have the same parameters?

What should I do next? I don’t know where I can change the Brinkman number, I don’t even know if I can change the visous heating bit…

 

I hope the answer isn’t too much all over the place. Thank you in adavance for your help!