User Forum of Software BASEMENT

nicolagroff

User

Registered: 2017-08-07

Posts: 13

Volume fraction

Hi!

I'm using the new BASEMENT v4.1.
I'm trying to define the volume fraction for a specific mixture.

I have the following grain size analysis for the mixture:

d10=24mm
d30=43mm
d50=61mm
d70=88mm
d90=178mm

In BASEMENT I assigned the volume fraction relative to the percentage of grains retained, as follows:
"GRAIN_CLASS": {
              "diameters": [
                0.016,
                0.024,
                0.043,
                0.061,
                0.088,
                0.178
              ]
            },
            "MIXTURE": [
              {
                "name": "mixture_inflow",
                "volume_fraction": [
                  10,
                  20,
                  20,
                  20,
                  20,
                  10
                ]
              }
            ],

I have also calculated the "volume fraction" of each class i using the following formula:

%Vi=Vi/Vtot

where Vi is the volume of the sphere of diameter i multiplied by the number of grains
"GRAIN_CLASS": {
              "diameters": [
                0.045,
                0.064,
                0.09,
                0.128,
                0.18,
                0.256,
                0.362,
                0.512
              ]
            },
            "MIXTURE": [
              {
                "name": "mixture_inflow",
                "volume_fraction": [
                  0.5,
                  1.3,
                  3.4,
                  5.9,
                  10.7,
                  23.6,
                  46.4,
                  8.2
                ]
              }

In both cases, the diameters d16, d50, d84 and d90 in the output at the beginning of the simulation are different from those of the grain size analysis.

I probably did not quite understand what is meant by volumetric fraction.

Thanks

Nicola

Matteo Facchini

Developer

From: Trento

Registered: 2014-09-05

Posts: 286

Re: Volume fraction

Hi Nicola,

you could have a look at my phd thesis where at par. 5.2 I explain how one should discretize a grain size distribution.
The content is adapted from Gary Parker's e-book.
Basically, if you are to -let's say- discretize your GSD with 3 classes, i.e., d16, d50 and d84, you have to think that the d16 represents a class from 0% to 32% in volume, the d50 from 32% to 68% and the d84 from 68% to 100%. So your volume_fractions would be 32, 36, 32.

You have a python tool among the BASEtools that performs this steps for you.

Furthermore, I might be mistaken, but your GSD is different from the one declared in basement's "GRAIN_CLASS", am I wrong? You declare a diameter more (16 mm) than the ones described in your GSD.

I hope this helps!
Matteo

Last edited by Matteo Facchini (2025-03-10 15:25:57)

nicolagroff

User

Registered: 2017-08-07

Posts: 13

Re: Volume fraction

Hi Matteo,

Thank you for your support!
Your thesis and example were very helpful.
I was wrong to discretize the grain size distribution.
Now the diameters in the outputs are the same as the grain size curve.

Thank you!

Nicola