Movimentação discreta das torres de um pivô central e sua aplicação de água

Abstract

The movement of the center pivot is referred as one factor that can affect its water application uniformity, reason for carrying out this research. Therefore, three GNSS satellite signal receivers were installed on three mobile towers of a center pivot to acquire georeferenced positions of each tower during equipment operation, every 3 seconds interval. With the collected data, mathematical models were fitted, to turn possible to calculate tower position versus time along its route. These models were used to develop a computer program to simulate the towers movement and determine the effect of the misalignment angle between spans on water depth distribution and uniformity coefficient. Collectors were positioned under each span, in three sampling forms: radial, circular and at regular mesh, with objective to compare irrigation uniformities obtained due to these different water depths sampling patterns. The fitted mathematical models proved to be efficient to determine tower position per unit of time. It was verified that the towers’ stoppage and movement times affected the distribution of applied depths and irrigation uniformity; greater variability of water depths and irrigation uniformity coefficients were observed as the misalignment angle between towers increased. As for water sampling, the arrangement of radial collectors was statistically different from the circular and mesh. It was possible to verify that the radial arrangement presents greater water depth variability, as it detects problems that occur between sets of emitters; in addition, the width of the sampling area along the towers direction movement is short; circular pattern can detects problems caused by terrain irregularities in the system’s movement direction, but the width of sampling area at the direction of radius is also short, a fact that causes the overlapping of water depths to occur only at direction of movement; the mesh arrangement, on the other hand, showed less variability because the collectors are more concentrated, which allows greater water depth overlapping, both along the direction of radius as well as at the movement direction. In addition, this sampling pattern made it possible to detect problems caused by the wind regardless its direction.