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.
Numerical Simulation of the shaking separation of paddy and brown rice using the discrete element method
Abstract Shaking separation of paddy and brown rice is investigated using a numerical model and by experiment at the same scale. The numerical model employs the discrete element method with two-dimensional circular particles representing rice grains. The indents on the experimental separation plate were modelled using a method of ‘virtual’ walls whereby only particles in contact with the base of the separation plate were affected by the walls which were positioned at regular intervals along the base. Exit of a particle from an indent was modelled as removal of a virtual wall once the particle-wall contact exceeded a threshold value. The model was validated against experimental results at the macroscopic scale in terms of mean particle distance from the sides and base of the separation plate, and the free surface profile. Particle movement in the experiments was tracked using a high speed video camera. There was good agreement between the results of the simulation and the experiment. The time required to achieve maximum separation of brown and paddy rice was the same in both experiment and simulation. The simulation also showed the same wave-like behaviour of the grain assembly as in the experiment.
Principles of Farm Machinery
Principles of farm machinary , Principles of farm machinary , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی