Modelos de explotación a corto plazo de centrales hidroeléctricas : Aplicación a la generación hidroeléctrica con velocidad variable

En esta tesis, se estudia con detalle el problema de planificación de la operación o la explotación a corto plazo de una central hidroeléctrica tomadora de precios que vende su energía en un mercado eléctrico liberalizado y organizado sobre la base de un sistema de ofertas de compra y venta de energía, poniendo un énfasis especial en el caso de las centrales con una capacidad de regulación semanal, diaria o menor, en las que es muy importante tener en cuenta, en el corto plazo, el efecto de la variación del salto, o del volumen. Analizando los modelos de explotación a corto plazo descritos en la bibliografía, se detectan en éstos ciertas limitaciones que pueden resumirse en los siguientes puntos: a) Es frecuente ignorar en los estudios a corto plazo la influencia de la variación del volumen del embalse a lo largo del periodo de explotación. b) Se recurre generalmente a dividir el problema en dos partes o problemas distintos: la asignación óptima de grupos y el despacho económico o de carga de los grupos asignados. En esta tesis, se desarrollan tres modelos de explotación a corto plazo originales, que se basan respectivamente en programación lineal entera mixta, programación no lineal y programación dinámica. Los tres modelos resuelven simultáneamente la asignación y el despacho económico de los grupos de la central y los dos últimos tienen en cuenta el efecto de la variación del salto durante el proceso de optimización, superando así las principales limitaciones de la mayoría de los modelos existentes. Los tres modelos se apoyan en la metodología que se propone en la tesis para obtener la característica de generación de la central, quedando implícitos en la solución de los tres modelos el estado óptimo (arranque/parada) y la potencia que producen todos los grupos de la central. Los tres modelos se apoyan además en una serie de procedimientos iterativos, de modelado y de discretización, algunos de los cuales son originales, y otros se basan parcialmente en procedimientos conocidos. Para comprobar la validez de los modelos, se estudia con éstos la explotación a corto plazo de una central de referencia formada por dos grupos generadores, bajo distintas condiciones de operación Además del desarrollo de nuevos modelos de explotación a corto plazo, se encuentran entre los objetivos de esta tesis la aplicación de los modelos desarrollados a una central de generación hidroeléctrica con velocidad variable y su utilización como herramienta de apoyo en estudios de rentabilidad de centrales hidroeléctricas. De acuerdo con los objetivos previstos, se describe en la tesis la metodología a seguir para aplicar los modelos desarrollados a una central de velocidad variable y se estudia la explotación a corto plazo de la central de referencia con dos grupos de velocidad variable bajo distintas condiciones de operación, demostrándose que, al permitir que los grupos de la central giren siempre a su velocidad óptima, aumentan considerablemente: a) El rango de caudales turbinables para cada nivel o volumen de embalse. b) La carrera de embalse aprovechable para producir energía. c) La potencia que produce la central en las mismas condiciones de caudal y salto. d) Los ingresos que recibe la central por vender su energía en el mercado. Cabe destacar que la aplicación de estos modelos a una central de velocidad variable constituye una de las principales aportaciones de esta tesis, ya que no se ha encontrado en la bibliografía ningún modelo de explotación a corto plazo aplicado a una central de este tipo. Por último, se presenta en esta tesis una metodología para estimar, a partir de unas previsiones de aportaciones y de precios horarios, los ingresos anuales que produce una central hidroeléctrica, utilizando los modelos desarrollados. Aplicando esta metodología se obtienen unos resultados más precisos que los que se obtienen en la mayoría de los estudios de rentabilidad consultados, ya que se tienen en cuenta los siguientes aspectos: a) La variación del rendimiento global de la planta en función de las condiciones de operación y del número de grupos que están en funcionamiento. b) La variación horaria de los precios de venta de la energía. c) La capacidad de gestión de la central para maximizar sus ingresos, distribuyendo el agua de la mejor forma posible entre todas las etapas del periodo de estudio, y para maximizar la energía generada en cada etapa, repartiendo de forma óptima el agua asignada entre todos los grupos disponibles. Cabe señalar que toda la tesis se desarrolla bajo un enfoque determinista en lo que se refiere al tratamiento de las aportaciones, los precios y la disponibilidad de los grupos. In this thesis, the short-term scheduling of a price-taker hydropower plant that sells its energy in pool-based electricity market is studied in detail, with special emphasis in the case of plants associated to a reservoir the regulating capability of which is weekly, daily or even smaller, where it is specially important to consider, in the short-term, the influence of the head, or volume, variation. When analyzing the short-term scheduling models found in the technical literature, it is noticeable that there are some limitations that can be summarized as follows: a) In short-term studies, it is usual to neglect the influence of the head, or volume, variation throughout the time horizon. b) The short-term scheduling problem is generally decomposed into two different problems: the unit commitment and the economic dispatch of the committed units. In this thesis, three novel short-term scheduling models, based respectively on mixed integer linear programming, nonlinear programming and dynamic programming are developed. The three models solve simultaneously the commitment and load dispatch of all the plant generating units, and the last two models consider also the influence of the head, or volume, variation during the optimization process, thus overcoming the main limitations found in the existing models. The three models are based on the methodology proposed in this thesis to obtain the plant generation characteristic, which implicitly includes the optimal status (on/off) and the power produced by all the plant generating units. Furthermore, these models use some iterative, modelling and discretization procedures, some of which are original, whereas others are partially based on known procedures. In order to check the validity of these models, they are applied to solve the short-term scheduling of a hydropower plant with two generating units, under different operating conditions. Besides the development of new short-term scheduling models, two more objectives are pursued in this work: the application of the developed models to an adjustable speed hydropower plant and the use of these models as a supporting tool to estimate the economic feasibility of a hydropower plant project. According to the proposed objectives, the application of the developed models to an adjustable speed hydropower plant is discussed in this thesis. The results of the short-term scheduling of a hydropower plant with two adjustable speed generating units are presented. It is demonstrated that, by allowing all the plant generating units to run at their optimal speed, an increase in the following magnitudes results: a) The range of operating flows for each reservoir level or volume. b) The range of operating volumes to produce energy. c) The power produced by the plant under the same operating conditions. d) The income that the plant receives from selling energy in the electricity market. It is worthy to mention that the application of the developed models to an adjustable speed hydropower plant is one of the main contributions of this thesis, provided that, so far, no short-term scheduling model applied to such type of hydropower plants has been found in the technical literature. Finally, it is presented a methodology based on the developed models to estimate the annual income of a hydropower plant, given a series of forecasted water inflows and energy prices. Compared with usual procedures, the approach proposed in this thesis leads to more accurate results, since the following aspects are considered in detail: a) The variation of the plant efficiency with the operating conditions and the number of generating units in operation. b) The hourly variation of the energy prices. c) The management capability of the plant to optimally distribute the water among the available generating units and throughout the time, thus maximizing the energy generated stage and the income that the plant receives from selling energy. It is important to note that the entire thesis is developed in a deterministic framework in that respect to the water inflows, the energy prices and the units’ availability

A simple algorithm for the estimation of road traffic space mean speeds from data available to most management centres

[Abstract:] The control of the evolution of road traffic streams is highly related to productivity, safety, sustainability and, even, comfort. Although, nowadays, the findings from research efforts and the development of new technologies enable accurate traffic forecasts in almost any conditions, these calculations are usually limited by the data and the equipment available. Most traffic management centres depend on the data provided, at best, by double-loop detectors. These loops supply time means over different aggregation periods, which are indiscriminately used as the bases for subsequent estimations. Since space mean speeds are those needed in most applications (note the fundamental relationship between flow and density in traffic flow theory), most current practice begins with an error. This paper introduces a simple algorithm that the allows estimation of space mean speeds from the data provided by the loops without the need for any additional financial outlay, as long as the traffic in each time interval of aggregation is stationary and its speed distribution is log-normal. Specifically, it is focused on the calculation of the variance of the speeds with regard to the time mean, thus making possible to use the relationship between time mean speeds and space mean speeds defined by Rakha (2005). The results obtained with real data show that the algorithm behaves well if the calculation conditions help fulfil the initial hypotheses. The primary difficulties arise with transient traffic and, in this case, other specific methodologies should be used. Data fusion seems promising in this regard. Nevertheless, it cannot be denied that the improvement provided by the algorithm turns out to be highly beneficial both when used alone in the case of stationarity or as a part of a fusion

Mechanistic-empirical pavement design guide : características y elementos distintivos

[Abstract] This paper is aimed at describing the most distinctive features of the pavement design method known as Mechanistic-Empirical Pavement Design Guide and to compare it with other renowned methodologies, while emphasizing its advantages and disadvantages. The MEPDG can accurately predict damage evolution, thus helping to choose the most appropriate design for new pavements or to schedule the conservation of the already existing ones. After analyzing different pavement design and management methods, the MEPDG stands out as the most comprehensive one as it takes into account and properly combines the greatest number of factors that affect the pavement. Therefore, some countries outside the USA have already imported and calibrated this method, what, at the same time, allows the scientific community to carry out comparative studies and improve its small deficiencies.[Resumen] El objetivo de este artículo es describir los rasgos más característicos del método de diseño de firmes conocido como Mechanistic-Empirical Pavement Design Guide, así como compararlo con otras metodologías de renombre, destacando sus ventajas y desventajas. El MEPDG puede predecir con precisión la evolución de los deterioros, ayudando por tanto a elegir el diseño más adecuado para el caso de firmes de nueva construcción, o a programar la conservación de los ya existentes. Tras analizar diferentes métodos de diseño y gestión de firmes, el MEPDG destaca como el más completo al ser el que tiene en cuenta un mayor número de factores que afectan al firme. Por ello algunos países fuera de EEUU ya han importado y calibrado este método, lo que al mismo tiempo permite a la comunidad científica llevar a cabo estudios comparativos y mejorar sus pequeñas deficiencias

Autonomous driving: a bird's eye view

[Abstract:] The introduction of autonomous vehicles (AV) will represent a milestone in the evolution of transportation and personal mobility. AVs are expected to significantly reduce accidents and congestion, while being economically and environmentally beneficial. However, many challenges must be overcome before reaching this ideal scenario. This study, which results from on-site visits to top research centres and a comprehensive literature review, provides an overall state-of-the-practice on the subject and identifies critical issues to succeed. For example, although most of the required technology is already available, ensuring the robustness of AVs under all boundary conditions is still a challenge. Additionally, the implementation of AVs must contribute to the environmental sustainability by promoting the usage of alternative energies and sustainable mobility patterns. Electric vehicles and sharing systems are suitable options, although both require some refinement to incentivise a broader range of customers. Other aspects could be more difficult to resolve and might even postpone the generalisation of automated driving. For instance, there is a need for cooperation and management strategies geared towards traffic efficiency. Also, for transportation and land-use planning to avoid negative territorial and economic impacts. Above all, safe and ethical behaviour rules must be agreed upon before AVs hit the road.Ministerio de Economía y Competitividad; TRA2016-79019-R/COO

Technology: a necessary but not sufficient condition for future personal mobility

Número especial: Sustainable Road Transportation Planning[Abstract:] Technological advances revolutionize industrial processes, science, communications, and our way of life. However, developed societies have reached a stage in which the fascination with technological innovations often results in their indiscriminate consumption. In this paper, road traffic is used as a line of argument to demonstrate that the random introduction of technology does not imply benefits to society. Particularly, it is analyzed why some of the potential benefits of technological progress are lost in fields such as traffic monitoring, data handling, and traffic management, or in sustainable mobility initiatives, such as the introduction of electric vehicles or the implementation vehicle sharing projects. The risks faced in the future advent of autonomous vehicles are also discussed, and ideas for improvement suggested. A critical reflection on other transportation modes that are expected to be realized in the near future is included as well. The performed analysis evidences that the potential improvement in personal mobility will not become a reality if it exclusively relies on the latest technological devices, in line with consumers’ fantasies or economic interests. This is a statement that could be generalized to many other fields. The implementation/consumption of a particular technology should not be an objective in itself, but a tool to bring benefits to society.Ministerio de Economía y Competitividad; TRA2016-79019-R/COO

Preliminary investigation on the use of waste cork dust as filler in hot-mix asphalt

Este póster foi presentado no congreso "Cork in Science and Applications 2019. New Trends in Cork Innovation: From the Wine Industry to the New Applications" que foi organizado polo Institut Catalá del Suro e que tivo lugar en Palafrugell (Girona) o 22 e 23 de maio de 2019.[Abstract:] The cork contains significant amounts of a biopolymer called suberin (45%). Polymers have been frequently used in the manufacture of hot-mix asphalt (HMA) to improve their properties. At the Universidade da Coruña (UDC), a preliminary investigation was carried out in which the feasibility of using waste cork dust from the manufacture of plugs, as filler in the manufacture of HMA was analyzed. Firstly, the aggregate-binder adhesion was analyzed by means of two types of tests: the boiling water test and the rolling bottle method. The performance of the cork filler was compared with the performance of conventional natural filler. In both tests it was obtained that with the cork filler, the aggregate-binder adhesion was better than with the natural filler. Secondly, a HMA type AC 22 bin S was manufactured, with a bitumen content of 3.8%. Indirect tensile test after immersion in water were conducted, in order to compare the moisture damage resistance of mixtures made with filler cork and natural filler. It was concluded that the filler cork helped to slightly improve the water resistance of the mixture. Although further investigation is needed, it can be stated that the filler cork could replace the conventional natural filler in the production of HMA

Adhesion Analysis of Waste Cork Dust as Filler for Bituminous Mixtures

No libro: Wastes: Solutions, Treatments and Opportunities III: Selected Papers from the 5th International Conference Wastes 2019, September 4-6, Lisbon, Portugal (pp.1-6). CRC Press, 2020. ISBN 978-0-367-25777-4[Abstract] Suberin is a biopolymer that can be found in high amounts in natural cork. As is well known, polymers can be used as bitumen modifiers to improve the properties of bituminous mixtures. This paper describes laboratory adhesion analysis that was conducted to analyse the use of waste cork dust as a filler in hot-mix asphalt (HMA). The performance of the waste cork dust as a filler was compared with that of a typically used natural filler and with Portland cement. These three fillers were characterized by their grain size distributions, morphological studies, and X-ray fluorescence spectroscopy experiments. The adhesion between the aggregates and the binder was analysed using two adhesion tests: a “boiling water test” and using the “roll-ing bottle method”. Both tests led to the same result: the waste cork dust was a better filler than the natural filler.https://doi.org/10.1201/978042928979

Las políticas del agua en España: bases para un desarrollo turístico equilibrado, en el contexto de la desglobalización

Economic activities related to tourism need, at different scales, a policy related to water, in our case in Spain. The main objective of the present investigation is to show the guidelines that mark, or should indicate, the path for the use of a scarce resource such as water, so that the tourist activities can be developed in a balanced way, marking and favoring the growth of the different tourist destinations, contributing to the achievement of more equanimous living conditions. Thus, when analyzing the Water policy in detail, it is determined as in Spain, since the appearance in the current democratic era, of the Water Law of 1985, until approximately the presentation of the Royal Decree that approves the regulation of Hydrological Planning, it has been denoting a progressive development in terms of the issues that have had to face the different water policies. Along these lines, the legal guidelines related to water resources have been adapting to the demands of the circumstances, mainly to the community trends embodied in the renowned Directive 2000/60/EC, which essentially required that rational water availability be guaranteed, so that the various social activities were revitalized.  Las actividades económicas relacionadas con el turismo necesitan, a diferentes escalas, de una política relacionada con el agua, en nuestro caso en España. El objetivo principal de la presente investigación es mostrar las directrices que marcan, o debieran señalar, el camino para la utilización de un recurso escaso como es el agua, para que las actividades turísticas puedan desarrollarse de forma equilibrada, marcando y favoreciendo el crecimiento de los diferentes destinos turísticos, coadyuvando al logro de unas condiciones de vida más ecuánimes. De esta forma, al analizar la política de Aguas con detenimiento, se determina como en España, desde la aparición en la época democrática actual, de la Ley de Aguas de 1985, hasta aproximadamente la presentación del Real Decreto que aprueba el reglamento de la Planificación Hidrológica, se ha ido denotando un progresivo desarrollo en cuanto a los asuntos que han tenido que ir afrontando las diferentes políticas hídricas. En esta línea, las directrices legales relativas al recurso hídrico, han ido amoldándose a las exigencias de las circunstancias, principalmente a las tendencias comunitarias encarnadas en la renombrada Directiva 2000/60/CE, que exigía esencialmente, que se garantizase una disponibilidad de aguas racional, de tal forma que se revitalizase las diversas actividades sociales

Neural Networks for optimal operation of a run-of-river adjustable speed hydro power plant with axial-flow propeller turbine

This paper analyzes the regulating capabilities of both turbine speed and guide vanes position in an axial-flow propeller turbine. Two neural networks are implemented in order to simulate the turbine behavior and the turbine efficiency. A maximum-efficiency-tracking algorithm is developed to set the guide vanes position. An experimental power plant built in the Hydraulics Laboratory is described. In order to validate the proposed operation control, the dynamics of this run-of- river pilot plant has been simulated. Substantial increases in the turbine efficiency have been found

Compensación de los errores de alineación provocados por las deflexiones de los ejes en transmisiones de engranajes cónicos espirales diseñadas con distintos tipos de huella de contacto

[SPA] En el presente trabajo se analiza una metodología para compensar los errores de alineación debidos a las deflexiones de los ejes en transmisiones de engranajes cónicos espirales cuando se transmite una carga nominal o de diseño, considerando cuatro tipos de patrones de contacto: lineal, localizado en la dirección longitudinal, localizado en la dirección del perfil, y localizado en una dirección ajustada diagonal. Para ello se determinan en primer lugar los parámetros de máquina correspondientes al proceso Cyclo-Palloid que permiten diseñar dichos patrones de contacto. A continuación se aplica un proceso iterativo en cada uno de los cuatro diseños. Este proceso iterativo requiere analizar, en cada etapa del proceso, la transmisión con ejes mediante el método de los elementos finitos, para obtener los errores de alineación debidos a la deflexión de los ejes. Los resultados muestran la eficacia de la metodología propuesta para compensar, desde el diseño de las geometrías de las superficies de contacto, las deflexiones de los ejes en los cuatro tipos de patrones de contacto, así como la mayor tolerancia de los diseños con contacto localizado en la dirección del perfil y en la dirección diagonal ajustada a variaciones de la carga de diseño. Se presentan varios ejemplos numéricos. [ENG] In this paper, a methodology to compensate alignment errors due to shaft deflections for a given design load in spiral bevel gear drives is presented, considering four types of contact pattern, linear and localized in longitudinal, profile and adjusted diagonal directions. Firstly, the machine-tool settings corresponding to a Cyclo-Palloid process are determined to design the mentioned four contact patterns. Secondly, an iterative process for each contact design is required where a finite element analysis provides the alignment errors due to shaft deflections. The results show the efficency of the proposed methodology to compensate alignment errors from the design of the gear tooth surfaces in the four types of contact pattern, and the larger tolerance in the profile and adjusted diagonal directions designs to variations of the design load. Several numerical examples are presented