Approaches for mathematical modelling of grain separation
This paper presents a review of former approaches for mathematical modelling of grain separation in combine harvesters and proposes a new approach on the base of extended exponential functions. The model equations for the remaining unseparated grain versus the separation length as well as for the cumulative sum of already separated grain based on empirical as well as on statistical approaches are put together in two tables; one containing single exponential functions, the other approaches with two exponential functions, to better describe the delayed separation start at the front of the separation unit. In addition to that the extended convection diffusion model and an analytical approach are described. Experimental data can be reproduced quite well by these equations, fitting the data by proper determination of the different threshing and separation coefficients. But the influences of crop properties, design and adjustment of the separation units on these coefficients have to be worked out in the future.
Simulation of grain-straw separation by Discrete Element Modeling with bendable straw particles
The combine harvester owes its name to the integration of the whole chain of grain harvesting steps in one machine. Running these interdependent processes simultaneously requires insight in the influence of crop factors and adjustments on the individual processes and the consequences for downstream processes. This paper introduces changes to the Discrete Element Method (DEM) in order to be suitable for the simulation of grain-straw separation, which is one of the most critical processes in the combine harvester. Segmented bendable straw particles have been constructed in the DEMeter++ simulation environment and their physical properties have been calibrated with realistic straw properties. The use of these particles for modeling separation has been validated by reconstructing an existing separation experiment by Beck (1992) in DEMeter++ and comparing the simulation result with the experiment. Once validated, the practical use of the simulation framework to assess the sensitivity of separation to crop properties is illustrated.
Separation Characteristics of Conventional and Non-Conventional Grain Combines
ABSTRACT THREE threshing and separating principles are dis-cussed. Results from the field measurement of grain loss are presented for combines with (a) a transverse cylinder and straw walkers, (b) a transverse cylinder and longitudinal drum, (c) two longitudinal rotors.