Simulação e avaliação do comportamento dinâmico de frutos do cafeeiro na derriça

• Autor(a) principal: Santos, Fábio Lúcio
• Data de Publicação: 2008
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/623
• topic: Simulação; Elementos finitos; Café; Colheita; Vibrações mecânicas; Simulation; Finite elements; Coffee; Harvesting; Mechancial vibrations; CNPQ::CIENCIAS AGRARIAS::ENGENHARIA AGRICOLA::MAQUINAS E IMPLEMENTOS AGRICOLAS

Harvesting procedure can be considered one of the most important operations in coffee production systems due the high cost and impact on quality of the product. To reduce production costs, the producers have looked for ways to mechanize this operation. Coffee harvesting machines, generally, uses mechanical vibrations and impact to detach the fruits from the plants. Therefore, the dynamic behavior study of the coffee fruit-stem systems is fundamental to design adequate harvesting machines for this specific task. The objective of this work was to study the dynamic behavior of the coffee fruit-stem systems. It was used a three- dimensional finite element numerical model base on linear elasticity theory. All computational programs were developed in FORTRAN 90 programming language. The first part of this work was based on developing and implementation of the finite element model. Geometric, physical and inertial characteristics were experimental determined for Catuaí Vermelho e Mundo Novo varieties considering different ripeness stages. A computational program was developed to determine the coffee fruit-stem natural frequencies and mode shapes for both varieties and ripeness stages in this work. Another computer program was developed to calculate the stresses generated in coffee fruit-stem system during the vibration process. Equivalent von Mises stresses were determine to study the dynamic behavior of the system during harvesting procedure. Both proposed models were validated according specific methodologies developed for each case. In the second part of this work, experimental tests were carried out using an electromagnetic shaker, to determine the effect of several factors in coffee harvesting efficiency. The evaluated factors were: frequency (13.33 to 26.67 Hz), amplitude (7.5 to 15.0 mm), direction of vibration (transversal and longitudinal), ripeness stage (green, half-ripe, ripe, over ripen), number of fruits per stem (one and two fruits) and branches length (5, 10 and 15 cm). Two experiments were performed for Catuaí Vermelho and Mundo Novo varieties: the main goal of the first experiment was to evaluate the localized effect (one and two fruits per stem) of the factors related to harvesting efficiency during the vibration process; the goal of the second experiment was to evaluate the frequency and amplitude effect in harvesting efficiency in branches with ripe fruits. From the modal analysis using finite element technique for Catuaí Vermelho variety, the first three natural frequencies were 23.21, 57.66 and 295.69 Hz for green fruits; 21.81, 53.58 e 275.81 Hz for half-ripe fruits and 19.86, 50.37 e 254.18 Hz for ripe fruits. Natural frequencies determined for Mundo Novo variety were 23.17, 59.87 and 300.59 Hz for green fruits; 23.62, 55.63 and 292.79 Hz for half-ripe fruits and 20.56, 49.57 and 257.44 Hz for ripe fruits. From the stress analysis performed using the finite element technique, the stresses in the region of union between the fruit and stem determined were 23.75 and 13.36 MPa for Catuaí Vermelho and 34.67 e 19.50 MPa for Mundo Novo variety for green and ripe fruits, respectively, these results were obtained using a frequency of vibration of 26.67 Hz and amplitude of 15.0 mm. From the experimental work, it was obtained that the frequency of 26.67 Hz presented the highest harvesting efficiency for both studied varieties and for all ripeness stages. Frequencies in the range of the 23.33 to 26.67 Hz and amplitudes in the ranges of 12.5 to 15.0 mm presented highest harvesting efficiency for ripe fruits in both studied varieties.