Simulation and Analysis of the Rotational Shear Cell test

This section provides instructions for running a simulation of a rotational shear cell and extracting the relevant data automatically using the provided files.

The test consists of shearing a bulk solid sample using a rotating lid while applying specific values of normal stress as shown in Figure 1. The sequence for a single test cycle is shown in Figure 2. The test cycle is repeated on the same sample under varying normal stresses and Mohr circle analysis is used to obtain the macro-mechanical parameters of the bulk solid such as the angle of internal friction, cohesion, and unconfined yield strength as shown in Figure 3.

Figure 1. Method of operation of the rotational shear cell – Brookfield PFT simulation with periodic boundaries

The response of the sample is measured in the critically consolidated state and in the quasi-static flow regime. These conditions correspond to the ones encountered during storage and discharge of silos and bins but may not be representative of highly dynamic and/or low stress systems such as mixing or conveying for example.

The simulation and analysis methodologies outlined in this section are applicable to all commercially available rotational shear cells, of which EDEM decks are provided for the Schulze RST XS and Brookfield PFT instruments.

Figure 2. Stages of the shear test cycle

Figure 3. Complete test procedure for one flow function point

Prerequisites

The simulation and analysis procedure described in this section requires EDEM version 2022 or later. The Calibration Kit examples are installed in the Altair installation folder > EDEM (version) > examples > Calibration Kits. Copy the Calibration kit and examples to a processing folder before they are configured and run.

The analysis described in this section uses EDEMpy. For more information about EDEMpy, see the EDEM Help documents.

Running the Simulations

EDEM decks are provided for the Brookfield PFT tester (152mm diameter cell) although the simulation procedure can be used to run any rotational shear cell.

Run the deck that is provided directly in EDEM until the end.

The stages of the shear test described in Figure 2 are modeled using EDEM kinematics controllers as shown in Figures 4 and 5 for the vane lid and through components respectively. The normal stress application in the physical test is achieved via a PID controlled servo, which applies a vertical correction to the vane lid position over time to maintain the normal stress. This procedure is approximated in EDEM by reducing the mass of the vane lid to limit inertial effects, capping the lid velocity and applying linear damping. Achieving an accurate and controlled normal stress application with this approach may require an adjustment of the maximum vane lid velocity as show in Figure 4. Using a maximum velocity of five average particle diameters per second typically yields good results.

Rotational shear cell tests produce measurements in the quasi-static flow regime where the macro-mechanical behavior of granular materials is strain rate independent. Therefore, the shear rate in the provided decks is accelerated in the interest of computational efficiency. If the particle properties or the applied normal stresses in the model change significantly, the strain rate may need to be adjusted to ensure the quasi-static flow regime is maintained. This can be achieved by changing the through rotational velocity as shown in Figure 5.

The simulation utilizes quarter symmetry in the interest of computational efficiency. This should not have impact the results of interest. The complete cell with no quarter symmetry can be modeled by deleting the periodic boundaries and resizing the domain.

Figure 4. Shear cell vane lid kinematics in EDEM

Figure 5. Shear cell through kinematics in EDEM

Post-processing results automatically with EDEMpy

The responses of interest in the shear cell test as well as the simulation input parameters and test operational parameters can be automatically obtained from the EDEM simulation data via the provided Shear_cell_analyst_v3.py script. The script utilizes theEDEMpy library to find all EDEM decks in the folder containing the script and subfolders in it and generates reports and figures with all relevant data. The analysis settings are defined in the Shear_cell_settings.txt file, as shown in Figure 6. Multiple simulation decks can be post- processed with the script by arranging the files into one of the two configurations shown in Figure 7. Configuration two is recommended, because it allows for individual settings files for each EDEM deck and therefore allows post-processing of different types of tests simultaneously. In configuration one a single settings file is read for post-processing all decks.

Figure 6. Settings file for the shear cell controller and analyst

Figure 7. 7 File configuration for post-processing multiple simulations using the FT4_Analyst

To run the Shear_cell_analyst_v3.py script:

Arrange the files as shown in Figure 7.
Open a blank or existing EDEM simulation file, and go to EDEM Analyst > Run > EDEMpy Script.
Go to Select File > Run Script and then select the Shear_cell_analyst _v3.py script.
Reports and graphs will be generated in the master folder. Only complete simulations with the corresponding settings files will be post-processed. Otherwise the script will produce error messages as shown in Figure 7, and then move to the next simulation in the folder tree.
Note: All simulation files must have unique folder names and simulation names. If the simulation names are identical, the results report will be overwritten.
Figure 8. Possible error messages

Script Version changes

Version 3 of the Dynamic Angle of Repose analysis script is designed to work with EDEM version 2022.0 (and later) and EDEMpy. This EDEMpy version includes a change where creatordata is indexable, and all references to creatordata have been replaced with creatordata[0].