Particle Scale Up Summary Blogs
Altair EmployeeComputational time has always been one of the most important aspects of DEM Modelling. Initially, it could be assumed that having an accurate and realistic material model through material calibration is the main target. If you want to learn about material calibration, read this post:
However, even though calibration is always the right approach, it serves no purpose if the model cannot be calculated in a reasonable time, which is a subjective concept. Moreover, it does not matter who you ask nor the application they are modelling, faster simulation times are always desired.
There are many factors affecting computational time: from modelling aspects such as the chosen particle size to hardware attributes like the GPU used for calculation. For the latter, the user has often little to non flexibility on which card to select or its setup. On the contrary, user input is key to define particle size and it can come down to experience or feasibility to define a 1 to 1 relationship between DEM particles and real particles, which is very often impossible. However, 1 to 1 size scale is closer every day:
In this blog post I would like to summarize, list and share all the scale up processes and techniques recorded within the EDEM community so that our users can learn how to define their particle size in order to have their simulations running as efficiently as possible.
A common scenario in DEM modelling is to have a material with a size distribution where most of the range can be simulated at the real scale, mining rock/minerals like materials, for example. These naturally occuring materials usually have a certain amount of fines (typically small compared to the full size distribution) as a result of having been processed. Translating those fines into a DEM model at real scale can often push the computational requirement at no real benefit. This scenario can be avoided by discarding the lower end of the real size distribution. How much to discard? It would depend on the hardware available and time to be afforded waiting. This is called “Curtailing a size distribution”. Three things must be taken into account when curtailing:
1- Be mindful of gaps in the equipment where particle material can go through
2- Calibrate the material model once the size has been curtailed so that fines are taken into account in the calibrated response via frictions or other parameters
3- Note that analysis on the curtailed sizes will not be available
A good exmaple of a system with a curtailed size distribution can be seen here:
Following the brake dust example above, If coupling to CFD is required and particle sizes are larger in simulation than in reality, make sure scaling parameters are applied to correctly calculate buoyancy and drag forces as shown in this post:
Following on with small particles, it is fair to say that in most cases real sizes cannot be used in DEM modelling when the quantity of material to be simulated is significant. For those cases Meso-scopic modelling is recommended. The objective of this methodology is to capture the complex behaviours of bulk materials made out of micron sized particles (powders and soils) by representing them with compurtationally efficient sizes and advanced physics:
MESO-SCOPIC APPROACH FOR POWDERS AND SOILS:
The Meso-scopic approach has been widely validated in literature. In the following link you will find an Additive manufacturing case in industry where EDEM was used together with Meso-scopic modelling:
In general, if you are working with bulk powders and need to go down the meso-scopic route, EDEM’s unique powders database is the best starting point: