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 a discrete element approach with bendable strawparticles.
Grain losses are the principal quality indicator of the threshing and separation process in combine harvesters. The acceptable grain loss over all sub-processes is typically not higher than 1% and the losses due to an incomplete separation of the threshed grain kernels from the straw layer (separation losses) usually have the biggest share. The efficiency in separating the grain kernels from the straw in a combine harvester depends on the crop properties and the settings and configuration of the separation system. Traditionally, the configuration and settings of a separation system are optimized through trial and error. A separation model allowing to simulate the impact of the crop properties, the system configuration and the settings would allow to optimize these system parameters in silico prior to building a prototype system. Discrete element modeling (DEM) is a natural choice to model the behavior of granular materials, like grain kernels, as it allows to model the behavior of each kernel through its interactions with the other kernels and the system elements. However, simulating the straw particles with discrete elements is more challenging as straw has a large aspect ratio resulting in a clear orientation. Moreover, straw is bendable, a property which is known to have an important impact on the separation process. To our knowledge this property of straw has always been neglected in DEM simulations of the separation process. To overcome this limitation, a discrete element approach including bendable straw has been implemented in the DEMeter++ software. In this study, a separation experiment described in literature involving a shaking box filled with straw and kernels has been repeated in silico to validate the DEM simulations.by comparing the simulated separation profiles to the measured ones.
Simulation of Flow Behaviour of Bulk Solids in Bins. Part 1: Model Development and Validation
Abstract A numerical model is developed, utilizing the discrete element method, to simulate the mechanical behaviour of a simulated bulk solid material consisting of uniform, inelastic, frictional and deformable discs. Two algorithms for contact search are incorporated in the simulation program to increase the computation efficiency. The design and the utilization of the simulation program are discussed. To validate the numerical model, a two-dimensional model bin was built to observe the gravity flow of hollow cylindrical particles. Two series of tests were conducted involving the variables: particle surface roughness, outlet location, outlet width and number of particles. The motion of the particles was recorded during discharge with a high speed video camera. The numerical predictions were compared with the experimental data. The numerically generated particle trajectories and velocities agree well with the observed flow behaviour.