Discrete element modeling of machine-manure interactions

The discrete element method (DEM) was applied to the study of the machine-product interactions occurring in manure handling and land application equipment. Two types of conveying systems (scraper and 4-auger system) were modeled along with a hopper and a flow-control gate and the results of the simulations were compared to experimental data. A numerical simulation of the scraper conveyor including clustered particles to simulate the clumps contained in the manure used during field experiments was carried out. The simulated results correlated the measured data for a conveyor velocity of 38mm/s and the bottom of the gate 560mm above the bottom of the hopper. The ratios of simulated to measured characteristic flow rate and unloading time were 0.9 and 1.2, respectively. The effect of the gate on the energy requirements was replicated by the simulations but to a lesser extent than the experimental results. The 4-auger conveying system was modeled and simulations were carried out with virtual manure including clusters. The predicted characteristic flow rate, unloading time and peak power values were in agreement with the experimental results for both the high velocity-low gate (840mm/s and 560mm) and low velocity-high gate (471mm/s and 1282mm) configurations. The ratios of simulated to measured characteristic flow rate, unloading time and peak power were 1.4, 0.9 and 1.0, respectively, for the high velocity-low gate configuration. The same ratios were 0.8, 1.1 and 1.9 for the low velocity-open gate setting. The 4-auger system model was able to predict the effect of the gate on the energy requirements but not on the discharge rate. It is expected that improvements in the manure model would enhance the accuracy of the interactions models. The detailed simulation of a transverse distribution system for banded manure application gave results that were in agreement with experimental results obtained with a prototype land applicator. The simulated and experimental transversal coefficients of variation were 4 and 6%, respectively.