CALCULATION OF FERTILIZER DISTRIBUTION PATTERNS FROM A SPINNING DISC SPREADER BY MEANS OF A SIMULATION-MODEL

Manipulation of the spreader pattern produced by spinning disc fertili zer spreaders, for site-specific applications, requires a continuous c hange of several spreader parameters, such as orifice position and ang ular speed of the disc, to keep the working width and the shape of the spreader pattern constant for varying fertilizer rates. To design an efficient control system, a model of the system is developed which tak es account of spreader and particle parameters. The model is used for calculations of spreader patterns and forms the basis for further deve lopment of a spreader control system. An initial validation comparing measured and simulated spreader patterns, demonstrates that the mathem atical model approximates reality quite well. By means of the model, s preader patterns for single- and twin-disc spreaders are calculated an d the influence is examined of several spreader characteristics on the distribution pattern. Simulations for variations of angular velocity of the disc as well as the effects of a changing position of the orifi ce, referred to the driving direction, show a large effect on the spre ading width and the shape of the distribution pattern. The shape of th e orifice also has a large influence on the shape and the width of the distribution pattern. The simulation results further show that spread ing site-specifically, simply by changing the mass flow, leads to a fl uctuating spreader pattern, which results in large deviations from the intended application rates. (C) 1996 Silsoe Research Institute.