The CALIPER research program focused on three major challenges in granular materials-related calibration and simulations: deformable grains, irregular grains and cohesive grains. In each of these subject areas we moved beyond the “spherical cow” paradigm that has understandably dominated the granular field for a long time. In each of these subjects, our envisioned approach consisted of developing experimental imaging and mechanical testing methods suitable for resolving the physical mechanisms at play, while extracting calibration information from such methods to develop numerical methods for the granular mechanisms/systems involved.

Of key importance is to provide a deep fundamental understanding of the dominant physical mechanisms that contribute to the mechanics of deformable, irregular or cohesive grain packings. The developed calibration methods and appropriate computational schemes were therefore applied on both industrially relevant materials and on appropriately simplified granular model systems. The outcomes are then a generic academic understanding of granular materials, but also application specific knowledge that can support the development of e.g. digital twins for “industrial plant simulators”.
Research Articles
The Caliper peer reviewed scientific output so far can be found in the list below, or via a search on the project number:
- Beyond classical CFD-DEM Forgotten Challenges and New Tools (S. Radl)
- A combined SPH-DEM approach for extremely deformed granular packings: validation and compression tests
- Transparent experiments: releasing data from mechanical tests… and a WCCM-ECCOMAS presentation
- Particle flow rate in silos with rotational shear
- Flow in an hourglass: particle stiffness and friction matter
- Intermittent flow and transient congestion of soft spheres passing narrow orifices
- Silo discharge of mixtures of soft and rigid grains
- Evolution of fabric anisotropy of granular soils: x-ray tomography measurements and theoretical modelling
- Continuously heated granular gas of elongated particles
- Contact evolution in granular materials with inherently anisotropic fabric
- X-ray tomographies of a water-sensitive granular material (couscous) exposed to high relative humidity: an experimental study
- Discharge of elongated grains from silo with rotating bottom
- Modeling Combined Fabric Evolution in an Anisometric Granular Material Driven by Particle-Scale X-Ray Measurements
- Discrete element modeling of strongly deformed particles in dense shear flows
- Self-diffusion of spherocylindrical particles flowing under non-uniform shear rate
- Creep control in soft particle packings
- The effect of obstacles near a silo outlet on the discharge of soft spheres
- The effect of high relative humidity on a network of water-sensitive particles (couscous) as revealed by in situ X-ray tomography
- The role of the particle aspect ratio in the discharge of a narrow silo
- Secondary flow in ensembles of nonconvex granular particles under shear
- Gardner-like crossover from variable to persistent force contacts in granular crystals
- Shape matters: Competing mechanisms of particle shape segregation
- Fabric evolution and strain localisation in inherently anisotropic specimens of anisometric particles (lentils) under triaxial compression
- A combined SPH-DEM approach for extremely deformed granular packings: validation and compression tests
- Heterogeneous swelling of couscous particles exposed to a high relative humidity air, as revealed by TD-NMR and X-ray tomography
- Implementation and validation of a bonded particle model to predict rheological properties of viscoelastic materials
- Force on a sphere suspended in flowing granulate
- Flow of asymmetric elongated particles
- Elongated particles discharged with a conveyor belt in a two-dimensional silo
- Lessons learned from matching 3D DEM and experiments at macro, meso and fabric scales for triaxial compression tests on lentils
- Discharge of elongated grains in silos under rotational shear
- Discharge of soft and hard grains and their mixtures from 2D silos
- Rate dependence in adhesive particle–particle contacts affect ceramic suspension bulk flow behavior
- A viscoelastic bonded particle model to predict rheology and mechanical properties of hydrogel spheres
- BPM model with Generalized maxwell relation into LIGGGHTS
- Effect of Particle Shape on the Flow of an Hourglass
- Comparative Study of Adhesive Elastoplastic Model Between LIGGGHTS Software and EDEM Software
- Dynamical Behaviour of Non-spherical Grains in Granular Rapid Flows
- How to Gamble with DEM Contact Models and their Validation
- Effect of Microscopic Properties on Flow Behavior of Industrial Cohesive Powder
- Discharge of rice-shaped particles from a monolayer flat-bottom silo
- A viscoelastic bonded particle model to predict rheology and mechanical properties of hydrogel spheres
Research Presentations
Caliper contributed to the organization of several conferences, notably the 2023 Lorentz Center conference “Getting Into Shape” and the 2024 Gordon Research Conference on Granular matter
Caliper students presented at several conferences:
- American Physical Society March Meeting 2021
- Annual European Rheology Conference 2021
- ICTAM 2021
- DPG 2021
- Powders & Grains 2021
- Particles 2021
- Physics@Veldhoven 2022
- American Physical Society March Meeting 2022
- Annual European Rheology Conference 2022
- ESMC 2022
- SoftComp 2022
- ICTMS 2022
- Gordon Research Seminar/Conference 2022
- CHOPS 2022
- IUTAM 2022
- WCPT 2022
- Transport in Narrow Channels Workshop, Cargese 2022
- DPG 2022
- APS 2023
- DFG 2023
- Physics@Veldhoven 2023
- Salamina Grain Works 2023, 2024
- ALERT 2023
- International Symposium on “Numerical Analysis of Geomaterials” (2023)
- Particles 2023
- AERC Leeds 2024
Open Science: data & methods
Caliper also aimed to leave behind reproducible methods and science, for others to use and build upon. Evidently releasing all methods and data is a huge endeavor, but below we show a list of open science evidence the program produced.
- Transparent experiments: releasing data from mechanical tests on three dimensional hydrogel sphere packings
- CaliParticles: A Benchmark Standard for Experiments in Granular Materials
- Fabric evolution and strain localisation in inherently anisotropic specimens of anisometric particles under triaxial compresion
- Neutron / X-Ray tomography data 1 + 2
- Github Repo for Bonded Particle Model including calibrations and postprocessing routines

