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En este trabajo se propone el diseño de un controlador IMC-PID con filtro de orden fraccionario (IMC-FPID) para el control efectivo de la distribución del agua en un tramo de un canal principal de riego. A partir de datos en tiempo real y aplicando el procedimiento de identificación de sistemas se obtiene un modelo matemático dinámico de este proceso representado mediante una función de transferencia de primer orden con retardo de tiempo. En base al modelo obtenido se diseñó un controlador IMC-PID con filtro de orden fraccionario que se comporta de forma efectiva. Los resultados de simulación comparan el desempeño del controlador propuesto con un controlador IMC-PID convencional. En esta comparación se utilizó el índice de desempeño de la integral del error absoluto (IAE). Los resultados obtenidos muestran que el controlador propuesto proporciona valores más bajos de este índice y en consecuencia supera al controlador IMC-PID convencional en términos de desempeño y precisión

En este trabajo se desarrolla una revisión del estado del arte de las estrategias de control utilizadas para la distribución de agua en los sistemas de riego, orientadas a aumentar la operatividad de estos sistemas, así como a disminuir las pérdidas de agua por concepto de operación. Se muestran los avances históricos de esta clase de sistemas de control. Finalmente, se ofrecen algunos de los desafíos de la comunidad científica internacional para continuar mejorando las prestaciones y el desempeño de los controladores utilizados en los sistemas de riego.

In this paper a fractional order model for an irrigation main canal is proposed. It is based on the experiments developed in a laboratory prototype of a hydraulic canal and the application of a direct system identification methodology. The hydraulic processes that take place in this canal are equivalent to those that occur in real main irrigation canals and the results obtained here can therefore be easily extended to real canals. The accuracy of the proposed fractional order model is compared by deriving two other integer-order models of the canal of a complexity similar to that proposed here. The parameters of these three mathematical models have been identified by minimizing the Integral Square Error (ISE) performance index existing between the models and the real-time experimental data obtained from the canal prototype. A comparison of the performances of these three models shows that the fractional-order model has the lowest error and therefore the higher accuracy. Experiments showed that our model outperformed the accuracy of the integer-order models by about 25%, which is a significant improvement as regards to capturing the canal dynamics.

Se propone una modificación de la estructura del predictor de Smith mediante un modelo interno que posibilita aumentar su rechazo al efecto de las per-turbaciones externas no medibles en comparación con la estructura clásica del predictor de Smith. Los resultados obtenidos se aplican en el diseño de un sistema de control del proceso de variación de la temperatura del jugo en los calentadores de una fábrica de azúcar. Los resultados de la simulación del sistema diseñado mostraron su efectividad y robustez en cuanto al rechazo de perturbaciones externas no medibles. Palabras claves: Predictor de Smith, predictor de Smith modificado, rechazo a perturbaciones externas no medibles, robustez de los sistemas de control.

The transient response to a current pulse applied to steel reinforcement bars in concrete has been analyzed by means of a new computational algorithm based on discretised approximation of the fractional difference operator. An optimization strategy has been designed to obtain a set of optimal values for the characteristic corrosion parameters from the information contained in the potential-time transient (specially, in the decaying part of the trace). The method compares the experimental response with the simulated response in the time domain obtained from an electrical circuit model which includes the effects of a constant-phase element and diffusion coupled with charge transfer. The practical possibilities of this method for extracting corrosion parameters (in particular, the charge-transfer resistance) have been demonstrated with steel reinforcements embedded in concrete in the presence and absence of chloride additions. © 2004 The Electrochemical Society. All rights reserved.

The application of the Stern-Geary equation in the determination of steel corrosion rates in reinforced concrete often implies the acceptance of certain assumptions. When a steady state is not reached in D.C. measurements it is accepted that the determinations made after a certain polarization time provide a very approximate value for polarization resistance. In A.C. measurements it is not unusual to resort to hazardous extrapolations of the impedance data. This paper examines the potential errors introduced by such practices. | The application of the Stern-Geary equation in the determination of steel corrosion rates in reinforced concrete often implies the acceptance of certain assumptions. When a steady state is not reached in D.C. measurements it is accepted that the determinations made after a certain polarization time provide a very approximate value for polarization resistance. In A.C. measurements it is not unusual to resort to hazardous extrapolations of the impedance data. This paper examines the potential errors introduced by such practices.

This paper experimentally confirms the participation of diffusion in the response of reinforced concrete specimens to the different electrical signals applied. Therefore, in the modelling of the steel-concrete system, it seems necessary to incorporate elements representing the diffusion together with the effects of the corrosion reaction and the non-ideal capacitative behaviour at the interface. A knowledge of the interaction between all these phenomena is indispensable for interpreting the response of the system to the application of DC and AC signals, and for the correct estimation of the corrosion rate of reinforcements. An examination is made of which equivalent circuit might be most suitable for modelling the system. | This paper experimentally confirms the participation of diffusion in the response of reinforced concrete specimens to the different electrical signals applied. Therefore, in the modelling of the steel-concrete system, it seems necessary to incorporate elements representing the diffusion together with the effects of the corrosion reaction and the non-ideal capacitative behaviour at the interface. A knowledge of the interaction between all these phenomena is indispensable for interpreting the response of the system to the application of DC and AC signals, and for the correct estimation of the corrosion rate of reinforcements. An examination is made of which equivalent circuit might be most suitable for modelling the system.

A new equivalent circuit model of the behaviour of the steel/concrete system is proposed. The theoretical basis for calculating the elements of this model from transient potentiostatic decay curves is given. Finally, a simplified method for determining the instantaneous corrosion rate from the transient response is proposed.

Direct estimation of the true polarization resistance (RT) of embedded metallic bars in concrete is not feasible in a large concrete structure, since the electric signal tends to vanish with increasing distance from the smaller counter electrode located on its surface. Measurements give apparent values of polarization resistance and erroneous corrosion rates when this parameter is introduced into the Stern-Geary equation. The possibility of estimating the true RT value in large-sized reinforced concrete slabs by means of a simple model of easy mathematical treatment is discussed. Despite the approximations made, the model proves sufficiently correct for such a purpose.

The numerous cases of failure of concrete structures due to the corrosion of steel reinforcements increase the need to find an appropriate non-destructive technique to be used on-site for measuring the degradation rate of the rebars. Although corrosion potential mapping has been used, this technique has been shown to give only qualitative indications of the corrosion risk. In this paper, a preliminary attempt to apply the Polarization Resistance (Rp) method in large structures is presented. This method has proved to be a fast and quantitative technique in laboratory experiments. Assuming the model of 'transmission line', the distribution of the polarizing potential applied from a small counter electrode and the current flow are mathematically calculated. Three possibilities are given in order to calculate the true Polarization Resistance, Rp: (a) the apparent polarization resistance method; (b) the attenuation of potential method, and (c) the two counters method. Finally, the results of applying these equations to beams, fabricated in order to check the validity of the theory, are given. The agreement found confirms the promise of the model chosen.