On the correctness and efficiency of independent and-parallelism in logic programs

This paper presents and proves some fundamental results for independent and-parallelism (IAP). First, the paper treats the issues of correctness and efficiency: after defining strict and non-strict goal independence, it is proved that if strictly independent goals are executed in parallel the solutions obtained are the same as those produced by standard sequential execution. It is also shown that, in the absence of failure, the parallel proof procedure doesn't genérate any additional work (with respect to standard SLDresolution) while the actual execution time is reduced. The same results hold even if non-strictly independent goals are executed in parallel, provided a trivial rewriting of such goals is performed. In addition, and most importantly, treats the issue of compile-time generation of IAP by proposing conditions, to be written at compile-time, to efficiently check strict and non-strict goal independence at run-time and proving the sufficiency of such conditions. It is also shown how simpler conditions can be constructed if some information regarding the binding context of the goals to be executed in parallel is available to the compiler trough either local or program-level analysis. These results therefore provide a formal basis for the automatic compile-time generation of IAP. As a corollary of such results, the paper also proves that negative goals are always non-strictly independent, and that goals which share a first occurrence of an existential variable are never independent.

On the effects of windbreaks on the aerodynamic loads over parabolic solar troughs

Parabolic reflectors, also known as parabolic troughs, are widely used in solar thermal power plants. This kind of power plants is usually located on desert climates, where the combined action of wind and dust can be of paramount importance. In some cases it becomes necessary to protect these devices from the joined wind and sand action, which is normally accomplished through solid windbreaks. In this paper the results of a wind tunnel test campaign, of a scale parabolic trough row having different windward windbreaks, are reported. The windbreaks herein considered consist of a solid wall with an upper porous fence. Different geometrical configurations, varying the solid wall height and the separation between the parabolic trough row and the windbreak have been considered. From the measured time series, both the mean and peak values of the aerodynamic loads were determined. As it would be expected, mean aerodynamic drag, as well as peak values, decrease as the distance between the windbreak and the parabolic increases, and after a threshold value, such drag loads increase with the distance.

Aerodinámica experimental de elementos de parques energéticos

La creciente demanda de energía eléctrica y la necesidad de implementar energías no contaminantes hace que las llamadas tecnologías verdes sean cada día más solicitadas. Entre estas tecnologías encontramos la energía solar y la energía eólica; ambas tienen una trayectoria de uso e investigación bastante amplia, sin embargo aún presentan problemas de fondo que impiden dar mayor impulso a su uso. El objetivo de la presente tesis es presentar soluciones a problemas de optimización en campos conversores de energía. Para ello se analizan y resuelven dos problemas por medio de técnicas de aerodinámica experimental: el primero sobre campos de colectores solares y el segundo sobre campos eólicos. Las técnicas de medición utilizadas en aerodinámica, y en el presente trabajo, son: medición de cargas, anemometría de hilo caliente, velocimetría por imagen de partículas y escaneo de presiones; además de un análisis estadístico de los datos. En el primer caso se ensayan experimentalmente colectores solares parabólicos en donde, por cuestiones de seguridad o por protección contra el viento, se utilizan cercas. Éstas modifican el comportamiento del flujo corriente abajo y se ha encontrado que la distancia a la cual se colocan, así como el tipo de cercas (sólida o permeable), modifican las cargas estructurales a las que los colectores están expuestos. Los resultados demuestran que existe una distancia crítica en la cual la presencia de la cerca aumenta la carga en lugar de disminuirla, por lo cual la selección adecuada del parapeto y la distancia a la cual se coloca son de suma importancia para la optimización de la estructura. En el segundo caso se ensaya experimentalmente y simula numéricamente la estela de turbinas eólicas por medio de discos porosos. En donde un disco permeable simula el rotor de una turbina. El disco es capaz de semejar la estela y los efectos que ésta puede causar corriente abajo. Los resultados muestran que seleccionando adecuadamente la porosidad, es posible simular coeficientes de empuje similares a los desarrollados por los aerogeneradores, además la estela y sus efectos son semejantes a los medidos en campo. ABSTRACT The called green energy technologies are increasingly required because of the growing demand for electricity and the need to implement nonpolluting energy. Among the green energy technologies it is found the solar and the wind energy, both have a history of use and fairly extensive research; however they still have problems which limit to give them further impetus to its use. The aim of this thesis is to present solutions to optimization problems in energy harvesting. To this end it is analysed, and solved, two problems by means of techniques in experimental aerodynamics: the first issue with regard to parabolic troughs and the second about wind farms. The measurement techniques commonly used in aerodynamics, and used in this research work, are: measurement of loads, hot wire anemometry, particle image velocimetry and scanning of pressures; where data are collected and then an statistical analysis is done. In the first case it is tested parabolic troughs where, either for security reasons or protection against the wind actions, fences are used. These fences modify the behaviour of flow downstream and it was found that the distance at which they are placed, and the type of fences (solid or permeable) modify the structural loads to which the parabolic troughs are exposed. The results show that there is a critical distance at which the presence of the fence increases the load instead of protecting the parabolic trough, hence making the proper selection of the parapet and the distance at which it stands are paramount for the optimization of the structure. In the second case it is tested, experimentally and numerically, the wake of wind turbines by means of porous disks; where the permeable disc simulates a turbine rotor. The disc is able to mimic the wake and the effects that it can cause downstream. The results show that by properly selecting the porosity, it is possible to simulate drag coefficients similar to those developed by wind turbines; moreover the porous disk wake and its effects are similar to those measured on field.

Analysis of Thematic Classified Aerial Images Trough Multispectral and LIDAR Data

The application of thematic maps obtained through the classification of remote images needs the obtained products with an optimal accuracy. The registered images from the airplanes display a very satisfactory spatial resolution, but the classical methods of thematic classification not always give better results than when the registered data from satellite are used. In order to improve these results of classification, in this work, the LIDAR sensor data from first return (Light Detection And Ranging) registered simultaneously with the spectral sensor data from airborne are jointly used. The final results of the thematic classification of the scene object of study have been obtained, quantified and discussed with and without LIDAR data, after applying different methods: Maximum Likehood Classification, Support Vector Machine with four different functions kernel and Isodata clustering algorithm (ML, SVM-L, SVM-P, SVM-RBF, SVM-S, Isodata). The best results are obtained for SVM with Sigmoide kernel. These allow the correlation with others different physical parameters with great interest like Manning hydraulic coefficient, for their incorporation in a GIS and their application in hydraulic modeling.

A technical note on application of internally finned tubes in solar parabolic trough absorber pipes

The heterogeneous incoming heat flux in solar parabolic trough absorber tubes generates huge temperature difference in each pipe section. Helical internal fins can reduce this effect, homogenising the temperature profile and reducing thermal stress with the drawback of increasing pressure drop. Another effect is the decreasing of the outer surface temperature and thermal losses, improving the thermal efficiency of the collector. The application of internal finned tubes for the design of parabolic trough collectors is analysed with computational fluid dynamics tools. Our numerical approach has been qualified with the computational estimation of reported experimental data regarding phenomena involved in finned tube applications and solar irradiation of parabolic trough collector. The application of finned tubes to the design of parabolic trough collectors must take into account issues as the pressure losses, thermal losses and thermo-mechanical stress, and thermal fatigue. Our analysis shows an improvement potential in parabolic trough solar plants efficiency by the application of internal finned tubes.

Analysis of internal helically finned tubes for parabolic trough design by CFD tools

This paper has analysed the effect of the utilization of internal finned tubes for the design of parabolic trough collectors with computational fluid dynamics tools. Our numerical approach has been qualified with the computational estimation of reported experimental data regarding phenomena involved in finned tube applications and solar irradiation of parabolic trough collector. The application of finned tubes to the design of parabolic trough collectors must take into account features as the pressure losses, thermal losses and thermo-mechanical stress and thermal fatigue. Our analysis shows an improvement potential in parabolic trough solar plants efficiency by the application of internal finned tubes.

An application of the finite element method to curve fitting

An application of the Finite Element Method (FEM) to the solution of a geometric problem is shown. The problem is related to curve fitting i.e. pass a curve trough a set of given points even if they are irregularly spaced. Situations where cur ves with cusps can be encountered in the practice and therefore smooth interpolatting curves may be unsuitable. In this paper the possibilities of the FEM to deal with this type of problems are shown. A particular example of application to road planning is discussed. In this case the funcional to be minimized should express the unpleasent effects of the road traveller. Some comparative numerical examples are also given.

Fresnel-based modular solar fields for performance/cost optimization in solar thermal power plants: A comparison with parabolic trough collectors.

Linear Fresnel collectors are identified as a technology that should play a main role in order to reduce cost of Concentrating Solar Power. An optical and thermal analysis of the different blocks of the solar power plant is carried out, where Fresnel arrays are compared with the most extended linear technology: parabolic trough collectors. It is demonstrated that the optical performance of Fresnel array is very close to that of PTC, with similar values of maximum flux intensities. In addition, if the heat carrier fluid flows in series by the tubes of the receiver, relatively high thermal efficiencies are achieved. Thus, an annual solar to electricity efficiency of 19% is expected, which is similar to the state of the art in PTCs; this is done with a reduction of costs, thanks to lighter structures, that drives to an estimation of LCOE of around 6.5 c€/kWh.