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about Unit Converter

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  • #4984
    iJokerify
    Participant

    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

    #4985
    iJokerify
    Participant

    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 2 years, 2 months ago by iJokerify.
    #4987
    mgaedtke
    Keymaster

    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

    #4989
    iJokerify
    Participant

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

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