about Unit Converter

[iJokerify]

Hi all,

I ran into the problem of correctly setting the values ​​in the converter.
My geometry is a cube with impenetrable thin lintels inside it throughout its volume, like a porous medium. When i need a great resolution. The size of model is 3x3x3m, but i use stlReader where thrid parameter is equals 0.001. The cross-sectional area of lintels is average equals 0.2m (in model, when 0.0002m in simulation).

Then i set converter like this:

  UnitConverter<T, DESCRIPTOR> const converter(
    (T)   0.0001,     // physDeltaX: spacing between two lattice cells in __m__
    (T)   0.000002, // physDeltaT: time step in __s__
    (T)   0.0035,       // charPhysLength: reference length of simulation geometry
    (T)   0.5,          // charPhysVelocity: maximal/highest expected velocity during simulation in __m / s__
    (T)   0.003/1055.,   // physViscosity: physical kinematic viscosity in __m^2 / s__
    (T)   1055           // physDensity: physical density in __kg / m^3__
  );

But during simulation i catch an error:

[LatticeStatistics] step=1200; t=0.3; uMax=0.73463; avEnergy=nan; avRho=nan
"./tmp/imageData/data/heatMapEuklidNormphysVelocity.p", line 21: warning: matrix contains missing or undefined values

What parameters should I set for the simulation to complete successfully? And what is right way to set the converter’s parameters?

Grateful,
Sergey

[iJokerify]

I set this values at random, using the dependency seen in the examples like:
dt has to be less, when dx.

The velocity in real test has to be 0.05 to 0.5 m/s.
The maximum simulation time is 2 seconds.

Thanks for your help!

• This reply was modified 5 years, 5 months ago by iJokerify.

[mgaedtke]

Hi iJoker,

I can only recommend to have a look in the text book of Krüger et al. https://www.springer.com/de/book/9783319446479. Chapter 7 is about dimensionalization of the Lattice Boltzmann Equation and on how to choose stable discretization parameters.

Best,
Max

[iJokerify]

70 euro is little bit less than I can afford…)
BTW, thank you!

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