Oscilaciones en sistemas hidráulicos

Aplicación de las técnicas de perturbaciones con métodos de escalas múltiples al estudio de los sistemas hidráulicos. En particular, se estudia el sistema de alimentación de una turbina, provisto de un regulador capaz de hacer funcionar la turbina con potencia constante. Se hace especial hincapié en la determinación de los comportamientos transitorios del sistema cuando los parámetros que lo determinan tienen valores cercanos a aquéllos en los que se produce un cambio de estabilidad en el comportamiento estacionario

Transients and limit cycles in simple surge tanks

Transients and limit cycles in simple surge tank

Fenómenos de resonancia en chimeneas de equilibrio

En lo que sigue se analiza el comportamiento oscilatorio del sistema de alimentación de una central hidroeléctrica, protegido del golpe de ariete por una chimenea de equilibrio, cuando la potencia suministrada a la red es pequeña frente a la máxima teórica y oscila con frecuencias cercanas a la de resonancia de la chimenea

Comportamiento no estacionario de las chimeneas de equilibrio en centrales hidroeléctricas

Se exponen a continuación los resultados obtenidos al aplicar técnicas de escalas múltiples, en el estudio de una central hidráulica con chimenea de equilibrio (Surge chamber). Se recogen en primer lugar los resultados bien conocidos de estabilidad lineal de las soluciones estacionarias del sistema. Se analiza a continuación el comportamiento no estacionarlo del mismo en las zonas próximas a las super ficies de cambio de estabilidad en el espacio de los parámetros. Así se describen las oscilaciones para valores de los parámetros cerca del límite de esta bilidad de Thoma, y las que aparecen cuando la potencia de funcionamiento es pequeña frente a la máxima teórica

Detecting Repetitions and Periodicities in Proteins by Tiling the Structural Space

The notion of energy landscapes provides conceptual tools for understanding the complexities of protein folding and function. Energy Landscape Theory indicates that it is much easier to find sequences that satisfy the "Principle of Minimal Frustration" when the folded structure is symmetric (Wolynes, P. G. Symmetry and the Energy Landscapes of Biomolecules. Proc. Natl. Acad. Sci. U.S.A. 1996, 93, 14249-14255). Similarly, repeats and structural mosaics may be fundamentally related to landscapes with multiple embedded funnels. Here we present analytical tools to detect and compare structural repetitions in protein molecules. By an exhaustive analysis of the distribution of structural repeats using a robust metric we define those portions of a protein molecule that best describe the overall structure as a tessellation of basic units. The patterns produced by such tessellations provide intuitive representations of the repeating regions and their association towards higher order arrangements. We find that some protein architectures can be described as nearly periodic, while in others clear separations between repetitions exist. Since the method is independent of amino acid sequence information we can identify structural units that can be encoded by a variety of distinct amino acid sequences

Experimental results on evaporation waves

We address an experimental investigation of evaporation waves. They are obtained when a liquid contained in a vertical glass tube is suddenly depressurized from a high initial pressure down to the atmospheric one. After the release of pressure, the state of the liquid, which is at ambient pressure and the initial temperature, is well known to be metastable when the corresponding stable state is vapour. For moderately large evaporation rates (moderately large initial to ambient pressure ratios), the vapour-liquid interface ultimately evolves into an evaporation wave in which a highly corrugated front propagates downwards into the liquid with a well defined mean velocity. This mean velocity turns out to be a function of the ratio between the initial and the ambient pressures. In addition, attention to some new phenomena not previously reported is brought

An Experimental Study on Pitch Compensation in Pedestrian-Protection Systems for Collision Avoidance and Mitigation

This paper describes an improved stereovision system for the anticipated detection of car-to-pedestrian accidents. An improvement of the previous versions of the pedestrian-detection system is achieved by compensation of the camera's pitch angle, since it results in higher accuracy in the location of the ground plane and more accurate depth measurements. The system has been mounted on two different prototype cars, and several real collision-avoidance and collision-mitigation experiments have been carried out in private circuits using actors and dummies, which represents one of the main contributions of this paper. Collision avoidance is carried out by means of deceleration strategies whenever the accident is avoidable. Likewise, collision mitigation is accomplished by triggering an active hood system

Local Nonlinear Stability of the Steady State in an Isothermal Catalyst

A first-order, irreversible, exothermic reaction in a bounded porous catalyst is considered, with smooth boundary, of one, two, or three dimensions. For small Prater and Nusselt numbers, ,3 and I>, and a large Sherwood number, o, two isothermal models are derived. An analysis of linear stability of the steady states of such models shows that oscillatory instabilities appear for appropriate values of the Damk6hler number if the nondimensional activation energy is larger than 7* and the Lewis number is sufficiently large, where y* = 4 if m = v/,8o-c 1 and y* = (m + 1)2/ m if m > 1. A local Hopf bifurcation analysis is carried out at neutral stability points in order to ascertain whether such bifurcation is subcritical or supercritical