I’m trying to make a model that has SQP cubes of varying sizes using a particle size distribution. If I set up a PSD, I have the option to specify the probability of particle diameters. In the case of an SQP, would this diameter be the bounding diameter?
If, for example, I set the X, Y, and Z semiaxes to be 0.002820986 (with m=n=6), I get a bounding diameter of 0.008137. Yet if I setup a PSD with completely different diameters (max is 0.00644 and min is 0.00276), the 0.008137 bounding diameter shouldn’t be used; it should use the PSD diameters (if the answer to my first question is yes). However, when running the simulation, it seems the mesh requires the cell size to be larger than 0.008137 even though the particles should be using the PSD diameters rather than this 0.008137.
Why would the 0.008137 diameter be used as the reference for mesh sizing when I’m using a PSD with other diameters that should require the mesh size to be larger than 0.00644 instead?
I’m afraid the interaction between PSD and SQP is not well-documented. We probably have to examine the code to see what’s really going on - it’s a bit complex.
For superquadric particles, the bounding diameter is not the primary definition - the shape is completely defined in terms of the three semiaxes (A,B,C) and two shape exponents (M,N). The bounding sphere is computed from these values. MFiX allows you to input the bounding sphere diameter, but really it is best not to specify this but to allow MFiX to compute it from A,B,C,M,N. (The ability to change the bounding diameter is an advanced option, to allow for users to modify the collision-checking behavior. I’m not sure there’s really a good case for specifying it, though).
I believe that, if you use a PSD, thenz the diameter in the PSD is compared to the bounding diameter d_p0 (either specified or computed), and then A,B,C are scaled by this ratio. Again, we need to either examine the code, or look at the generated particles, to see if this is correct.
When you use a PSD with SQP model, the PSD diameter is the bounding diameter. The data check uses the max of all defined diameters (whether they are actually used or not) when comparing particle size and cell size. We should improve that in the next release, so it only the max diameter of used particles is considered. However, I would suggest to always define the baseline particle size such that its diameter does not exceed the max diameter of the PSD. That way you can switch back and forth between the baseline and PSD particles or use both the baseline and PSD in several ICs or BCs.
