Discrete element representation of manure products

To simulate the machine-product interactions taking place in land application equipment, models of manure products must first be developed and validated. Several parameters must be defined to appropriately represent organic fertilizers in the discrete element method (DEM) framework. The work reported herein was aimed at determining the properties of the virtual product that would allow mimicking the behaviour of manure in the DEM software PFC3D. A procedure was developed to generate an assembly of particles within the domain under investigation according to a user-defined particle size distribution, as would be measured by screening. The results generated by this procedure in terms of granulometry of the assembly of particles were very close to the user specifications with errors on the number of particles and on their size averaging 0.53% and 0.33%, respectively. A procedure was also developed to create clusters of particles randomly oriented and located within the modeled domain. The cluster-generation code was tested for clusters made of up to six particles, but could be expanded to include more particles. A calibration procedure based on a virtual direct shear test was developed to define the properties of the resulting virtual manure. A sensitivity analysis was performed to study the influence of parameters defining the linear and Hertz-Mindlin contact constitutive models. The simulations were based on experimental results obtained for pig manure at a total solids (TS) concentration of 48%. The results showed that numerous parameters have an influence on the behaviour of the virtual product in the direct shear test. Implementing the measured particle size distribution for pig manure at 48% TS, a friction coefficient of 0.8 and a Young's modulus value of 0.3 MPa allowed reaching an angle of internal friction of 27.4° and an apparent cohesion value of 25.1 kPa that favourably compared to the 24.5° and 16.5 kPa values measured experimentally.