An approximate analytic solution to a non-linear ODE for air jet velocity decay through tree crops using piecewise linear emulations and rectangle functions

The velocity of air that crosses the canopy of tree crops when using orchard sprayers is a variable that aects pesticide dispersion in the environment. Therefore, having an equation to describe air velocity decay through the canopy is of interest. It was necessary to start from a more general non-linear ordinary dierential equation (ODE) obtained from the momentum theorem. After approximating the non-linearity with some piecewise linear terms, analytic solutions were found. Subsequently, to obtain a single equation for velocity decay, a combination of these solutions was proposed by using rectangle functions formed through the hyperbolic tangent function. This single equation was assessed in comparison to the experimental value obtained on a vineyard row by measuring the air velocity at exit of canopy. The results have shown good correspondence, with a mean relative error of 6.6%; moreover, there was no significant dierence. To simplify, a combination of only two linearized solutions was also proposed. Again, there was no significant dierence between the experimental value and the predicted one, but the mean relative error between the two equations was 3.6%.