Abstract. This study examines effects of three friction models: a steady-state friction model (SS model), the LuGre model (LG model), and the revised LuGre model (RLG model) on the motion simulation accuracy of a pneumatic cylinder. An experimental set-up of an electro-pneumatic servo system is built, and characteristics of the piston position, the pressures in the two-cylinder chambers and the friction force are measured and calculated under different control inputs to the proportional flow control valves. Mathematical model of the electro-pneumatic servo system is derived, and simulations are carried out under the same conditions as the experiments. Comparisons between measured characteristics and simulated ones show that the RLG model can give the best agreement among the three friction models while the LG model can only simulate partly the stick-slip motion of the piston at low velocities. The comparison results also show that the SS model used in this study is unable to simulate the stick-slip motion as well as creates much oscillations in the friction force characteristics at low velocities.
In developing countries, the use of mathematical models in hydrological forecasting is increasing, making for optimal planning and management of water resources systems. Such application, however, faces different problems. One of these problems is that computers may not be available. Even if they are available, computer time is expensive. Hence, there is a need for simple models which can be run on pocket calculators or which are computer-time efficient, with high accuracy. This paper presents a rainfall-runoff model with a very simple structure. With simple algorithms, the model can be used with computers with small memory capacity. A method for estimating mean areal rainfall, representing the detailed distribution of rain over an area, is also put forward. The model has been applied to a small, mainly rural catchment in northern Tunisia for both single rainfall event simulation and continuous simulation for longer periods. The outcome was most encouraging. In the present paper the measured and calculated streamflows are presented and discussed.Un modèle conceptuel simple et efficace gui peut prendre en considération les variations spatiales des précipitations RESUME Dans les pays en voie de développement, l'emploi de modèles mathématiques pour la prévision hydrologique se généralise. Cette application, cependant, rencontre un bon nombre de problèmes différents. Les ordinateurs y sont rares, et s'ils sont disponibles, l'heure de calcul est coûteuse. Par conséquent, il y a besoin de modèles simples, qui peuvent être mis en oeuvre sur des calculatrices de poche ou qui exigent peu de temps de calcul, avec une grand exactitude. Un modèle pluie-écoulement qui remplit ces conditions est présenté dans cet article. Ayant des algorithmes simple, le modèle peut être utilisé sur les ordinateurs avec une faible capacité de stockage. Une méthode pour estimer la pluie moyenne spatiale, représentant la distribution détaillée de la pluie sur une surface, est aussi présentée. Le modèle a été appliqué à un petit bassin, principalement rural, dans le nord de la Tunisie pour la simulation des pluies isolés et pour des simulations continues pour des périodes longues. Les résultats ont été très encourageants. Dans cet article, 475
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