Calibração de parâmetros de contato de frutos de café pelo método dos elementos discretos

Abstract

The characterization of Coffea arabica L. fruits is essential for representing coffee harvesting, transport, and processing operations through the Discrete Element Method (DEM). This study aimed to experimentally characterize and calibrate a DEM model for coffee fruits of the Mundo Novo cultivar, considering green, semi-ripe, and ripe maturation stages, as well as a representative mixture for the angle of repose test. Physical, morphometric, and contact properties were determined, including static friction, dynamic friction, restitution, rolling resistance, and angle of repose, for fruit–fruit and fruit–surface interactions with wood and metal. The numerical modeling was conducted in Rocky DEM, with fruits represented by equivalent spheres, and calibration was based on the experimental angle of repose of the mixture on a metal surface. The procedure included a Plackett–Burman design (PB), local refinement of rolling resistance, an exploratory Box–Behnken design (BB), and validation using five independent granular beds. The final calibrated parameters were: fruit–fruit static friction = 1.300; fruit–fruit dynamic friction = 0.280; fruit–fruit restitution = 0.433; rolling resistance = 0.145; fruit–metal static friction = 0.444; fruit–metal dynamic friction = 0.423; and fruit–metal restitution = 0.559. The final parameter set showed a mean absolute error (MAE) of 2.645° and a root mean square error (RMSE) of 3.047° during validation. The initial arrangement of particles in the granular bed was found to be a source of variation in the macroscopic response. Rolling resistance showed the largest estimated effect among the contact parameters evaluated during the screening stage.