Abstracto
- A tuning method for Two-Degree-of-Freedom (2-DoF) proportional integral (PI) controllers for First-Order-Plus-Dead-Time (FOPDT) models is presented. It allows the designer to deal with the closed-loop control system performance-robustness tradeoff specifying the required minimum robustness level selecting its maximum sensitivity in the 1.2 to 2.0 range. In addition, the performance is measured by forcing the closed-loop transfer functions to perform as close as possible to a target non-oscillatory dynamics. Controller tuning equations are provided for FOPDT models with normalized dead-times from 0.1 to 2.0. Examples show the effectiveness of the proposed tuning method.
- The vertical rainfall distribution in Costa Rica along a topographic profile which crosses the country from the Pacific to the Caribbean coast is studied. The mountain profile, whose highest peak is at about 3000 m, is oriented parallel to the prevailing large-scale northeasterly trade winds. Analysis of the yearly rainfall amounts and of Revista Geofísica 44 the seasonal and diurnal variations using records at fourteen rain-gauge stations located on or very close to the topographic profile shows that there is a considerable variation with altitude and that the maxima on both the windward (Caribbean) and leeward (Pacific) sides of the main mountain range occur at intermediate altitudes rather than on the mountain tops. Average yearly maxima of 7735 mm on the windward side and 6692 mm on the leeward side at about 2000 m and 800 m respectively are observed. An interesting feature of the rainfall distribution on the windward side is the occurrence of a minimum at about 1000 m. Rainfall patterns occurring on both sides of the mountain profile are also described. Physical causes for the observed vertical rainfall distributions are suggested; these depend on the interaction of thermally driven mesoscale circulations and the large-scale flow.