Dear all,
I have the parameters of my Herschel-bulkley model for fresh concrete.
tau=tau0+k*gamma^n
and I want to model a valve.
In OF the tau0 and the k parameters in the transportPropertyDict should be diveded by the density while the exponent n should not be divided, correct?
Than another parameter nu0 (a viscosity) is requested. What is it's phisical meaning?
I have seen that if I put a value, let say 1e-3, in each time step the nu field is 1e-3 and not calculated according to the Herschl-Bulkley model.
Some suggestions?
Franco
Hi !
Yes, the coefficients k and tau0 are indeed divided by the density, while the parameter n is not.
To your second question, nu0 corresponds to the viscosity under very low strain-rate. To obtain a solid-like behavior under low strain-rate, this value should be set as large as possible.
Best,
Dear Frederic,
I'm trying to simulate fresh concrete with OF using the Herschel-Bulkley model.
I have following parameters from literature:
tau0 [Pa] a [Pa*s^b] B [-]
1804 111 1,23
so in OF (the density is 1400Kg/m^3) I will have
tau0 [Pa]/[Kg/m^3] k [Pa*s^b]/[Kg/m^3] n [-]
1,288 0,079 1,23
Now according to your suggestion I should set nu0 to a very high value.
Now if I set nu0 to 0.008, the calculated nu file in each folder appears as
/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: 2.3.0 |
| \\ / A nd | Web: www.OpenFOAM.org |
| \\/ M anipulation | |
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format binary;
class volScalarField;
location "67";
object nu;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
dimensions [0 2 -1 0 0 0 0];
internalField uniform 0.008;
boundaryField
{
patches_name
{
type calculated;
value uniform 0.008;
}
etc.
}
If I set nu0 to 100 (high value), I get forces of a wrong order of magnitude
smoothSolver: Solving for Ux, Initial residual = 0.665612, Final residual = 2.48012e-05, No Iterations 25
smoothSolver: Solving for Uy, Initial residual = 0.559982, Final residual = 1.92865e-05, No Iterations 25
smoothSolver: Solving for Uz, Initial residual = 0.649273, Final residual = 2.05462e-05, No Iterations 25
GAMG: Solving for p, Initial residual = 0.461244, Final residual = 0.0335985, No Iterations 4
GAMG: Solving for p, Initial residual = 0.0031342, Final residual = 0.000248612, No Iterations 1
GAMG: Solving for p, Initial residual = 0.000523932, Final residual = 3.57448e-05, No Iterations 2
GAMG: Solving for p, Initial residual = 0.000134293, Final residual = 8.17402e-06, No Iterations 2
GAMG: Solving for p, Initial residual = 2.77999e-05, Final residual = 2.03199e-06, No Iterations 2
GAMG: Solving for p, Initial residual = 7.14375e-06, Final residual = 5.00659e-07, No Iterations 2
time step continuity errors : sum local = 2.7234, global = 0.172896, cumulative = 0.240496
smoothSolver: Solving for epsilon, Initial residual = 0.171581, Final residual = 1.73496e-14, No Iterations 25
bounding epsilon, min: -1.11366e+06 max: 2.27262e+08 average: 1.60725e+06
smoothSolver: Solving for k, Initial residual = 0.948208, Final residual = 2.28427e-11, No Iterations 25
ExecutionTime = 53.45 s ClockTime = 54 s
forces valveForces output:
sum of forces:
pressure : (-90485.8 -1.47324e+09 1.52142e+09)
viscous : (-411.764 216421 -521637)
porous : (0 0 0)
sum of moments:
pressure : (1.18322e+08 -1.52143e+07 -1.47032e+07)
viscous : (-34016.4 5146.98 2233.21)
porous : (0 0 0)
and the calculated nu file apperas like
/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: 2.3.0 |
| \\ / A nd | Web: www.OpenFOAM.org |
| \\/ M anipulation | |
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format binary;
class volScalarField;
location "1";
object nu;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
dimensions [0 2 -1 0 0 0 0];
internalField nonuniform List
1606466
([{i¾$ñ?SMö?ì"î(ð?¯DÅlá? pÛASá?ÿ
I think this is because the numbers are to high... but where I'm wrong?
Thanks
Franco
Cite
Ashok Moravaneni
TUD Dresden University of Technology
Hello Franco Concli,
I have the same question related to Herschel Bulkley coefficients in openFOAM. My material properties are plastic viscosity=50Pa.s; Yields stress=50Pa;density 2300kg/m3. Now my doubt is for nu0,tau0,k,n values. I have divided Yield stress with density and assigned it to tauo.
Now could you please help me in inputting correct nuo,n,k values. K is consistancy factor, Is it (plastic viscosity/density) ?
Thanks and Regards,
Ashok.M
Cite
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