Vehicle-induced force on pedestrians

The main object of this study is to contribute to the study of the train-induced force on pedestrians with a theoretical model based on unsteady potential flow. The same method can be applied to other bodies and other kind of moving vehicles. The outcome of this theoretical model is that the force coefficient (referred to the vehicle speed and the pedestrian cross-section diameter) acting on the pedestrian are proportional to a single parameter which involves the pedestrian cross-section diameter, the vehicle cross-section area and the distance between the pedestrian and the vehicle. The results of the present model concerning the change in modulus and orientation experienced by the pedestrian, as the vehicles pass by, has a similar appearance to that considered in the European standards. The results obtained are mainly qualitative because of the simplifying assumptions needed to obtain a simple formulation leading to analytical results, except in the case of a vehicle with streamlined front shapes, where quantitative results can be expected.

Vehicle-induced loads on traffic sign panels

The determination of the loads on traffic sign panels in the current standards does not, in general, take into account the vehicle-induced loads, as explained by Quinn, Baker and Wright (QBW in what follows) (J. Wind Eng. Ind. Aerodyn. 89 (2001) 831). On the other hand, a report from Cali and Covert (CC) (J. Wind Eng. Ind. Aerodyn. 84 (2000) 87) indicates that in highway sign support structures, vehicle-induced loads have led to premature failures in some cases. The aim of this paper is to present a mathematical model for the vehicle-induced load on a flat sign panel, simple enough to give analytical results, but able to explain the main characteristics of the phenomenon. The results of the theoretical model help to explain the behaviour observed in the experiments performed in previous studies.

Train-induced pressure on pedestrians

A simple analytical model for the train-induced flow and its effects on pedestrians is presented in this paper. The expressions developed for the induced air velocity and pressure on the pedestrian surface, as well as their dependence with time, are obtained from unsteady potential theory. The relevant parameters and their effects are analysed, in particular the sensitivity of the pressure coefficient and its rate of change on the train and pedestrian transverse size, the distance to the tracks and the pressure measurement location on the pedestrian surface. In spite of the extreme simplicity of the model and the expressions obtained, good correlation is observed with previously existing experiments. With this work, an absence of published studies concerning analytical approaches to the problem of vehicle-induced pressure on pedestrians is intended to be covered, allowing for simplified testing procedures.

Computational and Experimental Modelling of Mooring Lines Dynamics for Offshore Floating Wind Turbines

El cálculo de cargas de aerogeneradores flotantes requiere herramientas de simulación en el dominio del tiempo que consideren todos los fenómenos que afectan al sistema, como la aerodinámica, la dinámica estructural, la hidrodinámica, las estrategias de control y la dinámica de las líneas de fondeo. Todos estos efectos están acoplados entre sí y se influyen mutuamente. Las herramientas integradas se utilizan para calcular las cargas extremas y de fatiga que son empleadas para dimensionar estructuralmente los diferentes componentes del aerogenerador. Por esta razón, un cálculo preciso de las cargas influye de manera importante en la optimización de los componentes y en el coste final del aerogenerador flotante. En particular, el sistema de fondeo tiene gran impacto en la dinámica global del sistema. Muchos códigos integrados para la simulación de aerogeneradores flotantes utilizan modelos simplificados que no consideran los efectos dinámicos de las líneas de fondeo. Una simulación precisa de las líneas de fondeo dentro de los modelos integrados puede resultar fundamental para obtener resultados fiables de la dinámica del sistema y de los niveles de cargas en los diferentes componentes. Sin embargo, el impacto que incluir la dinámica de los fondeos tiene en la simulación integrada y en las cargas todavía no ha sido cuantificada rigurosamente. El objetivo principal de esta investigación es el desarrollo de un modelo dinámico para la simulación de líneas de fondeo con precisión, validarlo con medidas en un tanque de ensayos e integrarlo en un código de simulación para aerogeneradores flotantes. Finalmente, esta herramienta, experimentalmente validada, es utilizada para cuantificar el impacto que un modelos dinámicos de líneas de fondeo tienen en la computación de las cargas de fatiga y extremas de aerogeneradores flotantes en comparación con un modelo cuasi-estático. Esta es una información muy útil para los futuros diseñadores a la hora de decidir qué modelo de líneas de fondeo es el adecuado, dependiendo del tipo de plataforma y de los resultados esperados. El código dinámico de líneas de fondeo desarrollado en esta investigación se basa en el método de los Elementos Finitos, utilizando en concreto un modelo ”Lumped Mass” para aumentar su eficiencia de computación. Los experimentos realizados para la validación del código se realizaron en el tanque del École Céntrale de Nantes (ECN), en Francia, y consistieron en sumergir una cadena con uno de sus extremos anclados en el fondo del tanque y excitar el extremo suspendido con movimientos armónicos de diferentes periodos. El código demostró su capacidad para predecir la tensión y los movimientos en diferentes posiciones a lo largo de la longitud de la línea con gran precisión. Los resultados indicaron la importancia de capturar la dinámica de las líneas de fondeo para la predicción de la tensión especialmente en movimientos de alta frecuencia. Finalmente, el código se utilizó en una exhaustiva evaluación del efecto que la dinámica de las líneas de fondeo tiene sobre las cargas extremas y de fatiga de diferentes conceptos de aerogeneradores flotantes. Las cargas se calcularon para tres tipologías de aerogenerador flotante (semisumergible, ”spar-buoy” y ”tension leg platform”) y se compararon con las cargas obtenidas utilizando un modelo cuasi-estático de líneas de fondeo. Se lanzaron y postprocesaron más de 20.000 casos de carga definidos por la norma IEC 61400-3 siguiendo todos los requerimientos que una entidad certificadora requeriría a un diseñador industrial de aerogeneradores flotantes. Los resultados mostraron que el impacto de la dinámica de las líneas de fondeo, tanto en las cargas de fatiga como en las extremas, se incrementa conforme se consideran elementos situados más cerca de la plataforma: las cargas en la pala y en el eje sólo son ligeramente modificadas por la dinámica de las líneas, las cargas en la base de la torre pueden cambiar significativamente dependiendo del tipo de plataforma y, finalmente, la tensión en las líneas de fondeo depende fuertemente de la dinámica de las líneas, tanto en fatiga como en extremas, en todos los conceptos de plataforma que se han evaluado. ABSTRACT The load calculation of floating offshore wind turbine requires time-domain simulation tools taking into account all the phenomena that affect the system such as aerodynamics, structural dynamics, hydrodynamics, control actions and the mooring lines dynamics. These effects present couplings and are mutually influenced. The results provided by integrated simulation tools are used to compute the fatigue and ultimate loads needed for the structural design of the different components of the wind turbine. For this reason, their accuracy has an important influence on the optimization of the components and the final cost of the floating wind turbine. In particular, the mooring system greatly affects the global dynamics of the floater. Many integrated codes for the simulation of floating wind turbines use simplified approaches that do not consider the mooring line dynamics. An accurate simulation of the mooring system within the integrated codes can be fundamental to obtain reliable results of the system dynamics and the loads. The impact of taking into account the mooring line dynamics in the integrated simulation still has not been thoroughly quantified. The main objective of this research consists on the development of an accurate dynamic model for the simulation of mooring lines, validate it against wave tank tests and then integrate it in a simulation code for floating wind turbines. This experimentally validated tool is finally used to quantify the impact that dynamic mooring models have on the computation of fatigue and ultimate loads of floating wind turbines in comparison with quasi-static tools. This information will be very useful for future designers to decide which mooring model is adequate depending on the platform type and the expected results. The dynamic mooring lines code developed in this research is based in the Finite Element Method and is oriented to the achievement of a computationally efficient code, selecting a Lumped Mass approach. The experimental tests performed for the validation of the code were carried out at the `Ecole Centrale de Nantes (ECN) wave tank in France, consisting of a chain submerged into a water basin, anchored at the bottom of the basin, where the suspension point of the chain was excited with harmonic motions of different periods. The code showed its ability to predict the tension and the motions at several positions along the length of the line with high accuracy. The results demonstrated the importance of capturing the evolution of the mooring dynamics for the prediction of the line tension, especially for the high frequency motions. Finally, the code was used for an extensive assessment of the effect of mooring dynamics on the computation of fatigue and ultimate loads for different floating wind turbines. The loads were computed for three platforms topologies (semisubmersible, spar-buoy and tension leg platform) and compared with the loads provided using a quasi-static mooring model. More than 20,000 load cases were launched and postprocessed following the IEC 61400-3 guideline and fulfilling the conditions that a certification entity would require to an offshore wind turbine designer. The results showed that the impact of mooring dynamics in both fatigue and ultimate loads increases as elements located closer to the platform are evaluated; the blade and the shaft loads are only slightly modified by the mooring dynamics in all the platform designs, the tower base loads can be significantly affected depending on the platform concept and the mooring lines tension strongly depends on the lines dynamics both in fatigue and extreme loads in all the platform concepts evaluated.

On sonic anemometer measurement theory

In this paper a model for the measuring process of sonic anemometers (ultrasound pulse based) is presented. The differential equations that describe the travel of ultrasound pulses are solved in the general case of non-steady, non-uniform atmospheric flow field. The concepts of instantaneous line-average and travelling pulse-referenced average are established and employed to explain and calculate the differences between the measured turbulent speed (travelling pulse-referenced average) and the line-averaged one. The limit k1l=1 established by Kaimal in 1968, as the maximum value which permits the neglect of the influence of the sonic measuring process on the measurement of turbulent components is reviewed here. Three particular measurement cases are analysed: A non-steady, uniform flow speed field, a steady, non-uniform flow speed field and finally an atmospheric flow speed field. In the first case, for a harmonic time-dependent flow field, Mach number, M (flow speed to sound speed ratio) and time delay between pulses have revealed themselves to be important parameters in the behaviour of sonic anemometers, within the range of operation. The second case demonstrates how the spatial non-uniformity of the flow speed field leads to an influence of the finite transit time of the pulses (M≠0) even in the absence of non-steady behaviour of the wind speed. In the last case, a model of the influence of the sonic anemometer processes on the measurement of wind speed spectral characteristics is presented. The new solution is compared to the line-averaging models existing in the literature. Mach number and time delay significantly distort the measurement in the normal operational range. Classical line averaging solutions are recovered when Mach number and time delay between pulses go to zero in the new proposed model. The results obtained from the mathematical model have been applied to the calculation of errors in different configurations of practical interest, such as an anemometer located on a meteorological mast and the transfer function of a sensor in an atmospheric wind. The expressions obtained can be also applied to determine the quality requirements of the flow in a wind tunnel used for ultrasonic anemometer calibrations.

An engineering modification of the blade element momentum combination applicable in vertical descent flight :fundamentals and validation

An engineering modification of blade element/momentum theory is applied to describe the vertical autorotation of helicopter rotors. A full non‐linear aerodynamic model is considered for the airfoils, taking into account the dependence of lift and drag coefficients on both the angle of attack and the Reynolds number. The proposed model, which has been validated in previous work, has allowed the identification of different autorotation modes, which depend on the descent velocity and the twist of the rotor blades. These modes present different radial distributions of driven and driving blade regions, as well as different radial upwash/downwash patterns. The number of blade sections with zero tangential force, the existence of a downwash region in the rotor disk, the stability of the autorotation state, and the overall rotor autorotation efficiency, are all analyzed in terms of the flight velocity and the characteristics of the rotor. It is shown that, in vertical autorotation, larger blade twist leads to smaller values of descent velocity for a given thrust generated by the rotor in the autorotational state.

La ciudad y el viento : la morfología urbana y su relación con el uso estancial del espacio público abierto en territorios con vientos fuertes y climas fríos : el caso de la ciudad de Punta Arenas, región de Magallanes, Chile

El presente trabajo ahonda en el conocimiento del viento urbano. La investigación pasa revista a la historia de la relación del viento y la ciudad y revisa tres pares de disciplinas implicadas en comprender mejor dicha relación: la arquitectura y el urbanismo, la meteorología y la climatología y, por último, la ingeniería aeroespacial y la aerodinámica civil. Se estudian el comportamiento y la fluidez del viento al desplazarse por cuerpos romos no fuselados (los edificios y la trama urbana), así como sus efectos dentro de la ciudad. Asimismo, se examinan las metodologías existentes para comprenderlo, medirlo y analizarlo, desde los estudios de proporción y modelamiento en túneles de viento hasta las simulaciones virtuales y las dinámicas de fluidos CFD. Posteriormente se reconoce un caso de estudio que permite analizar el viento como un factor aislado, pero desde los parámetros morfológicos de una ciudad en la que se generan patrones aerodinámicos muy característicos: Punta Arenas, la ciudad más austral del mundo, donde los vientos corren casi siempre desde la misma dirección, el “oeste”, a más de 33,3 m/s, lo que equivale a 120 Km/h. La hipótesis de la investigación es que la morfología del casco histórico de Punta Arenas genera patrones aerodinámicos que condicionan el bienestar en los espacios públicos. El objetivo general de la investigación es estudiar los efectos aerodinámicos presentes en la morfología urbana para mejorar la permanencia en los espacios públicos, proponiendo estrategias para el desarrollo morfológico y volumétrico de los cuerpos edificados. En el desarrollo del caso de estudio se reconocen, al interior del cañón urbano, las temperaturas, los índices de asoleamiento y sus conos de sombra, la dirección del viento y la visualización del vórtice al interior del cañón urbano, para determinar cómo estos factores impactan en el espacio público. Las conclusiones indican que los patrones aerodinámicos presentes en la morfología urbana conducen el viento hacia los espacios públicos que se encuentran o desprotegidos del viento o con excesiva turbulencias, por tanto, los patrones aerodinámicos inciden en el uso estancial de los espacios públicos, generando problemas mecánicos al peatón e incidiendo en la sensación térmica en dichos espacios. Ello permite confirmar que es posible modificar y mejorar el uso de los espacios públicos si somos capaces de modelar la morfología urbana con el fin de reorientar los patrones aerodinámicos que afectan significativamente a dichos espacios. ABSTRACT This work deepens into the knowledge of urban wind. The study reviews the history of the relationship between the wind and the city and reviews three pairs of disciplines involved in understanding better these relationship: Architecture and Urbanism, Meteorology and Climatology and, finally, Aerospace and Civil Aerodynamics. The behavior and flow of wind through blunt bodies not fairings (the buildings and the urban fabric) and its effects within the city are studied. Also, existing methodologies to understand, measure and analyze the wind are examined, from the studios of proportion and modeling in wind tunnels to virtual simulations and fluid dynamics CFD. Subsequently, a case study to analyze the wind as an isolated factor is recognized, but from the morphological parameters of a city where very characteristic aerodynamic patterns are generated: Punta Arenas, the southernmost city in the world, where the winds run almost always from the same direction, the "West", at more than 33.3 m/s, which is equivalent to 120 km/h. The research hypothesis is that the morphology of the historic center of Punta Arenas generates aerodynamic patterns that determine the well-being in public spaces. The overall objective of the research is to study the aerodynamic effects present in the urban morphology to improve retention in public spaces, proposing strategies for morphological and volumetric development of the built bodies. In developing the case study are recognized, within the urban canyon, temperatures, rates of sunlight and shadow cones, wind direction and visualization of the vortex into the urban canyon, to determine how these factors impact in public space. The findings indicate that the aerodynamic patterns in urban morphology lead wind to public spaces that are unprotected or find themselves in a condition of excessive wind or turbulence; therefore, aerodynamic patterns affect the use of public spaces, generating mechanical problems for pedestrians and affecting the thermal sensation in such spaces. This confirms that it is possible to modify and improve the use of public spaces if we are able to model the urban morphology in order to reorient the aerodynamic patterns that significantly affect those spaces.

An engineering modification of the blade element momentum equation for vertical descent : an autoration case study

An engineering modification of blade element/momentum theory is applied to describe the vertical autorotation of helicopter rotors. A full non-linear aerodynamic model is considered for the airfoils, taking into account the dependence of lift and drag coefficients on both the angle of attack and the Reynolds number. The proposed model, which has been validated in previous work, has allowed the identification of different autorotation modes, which depend on the descent velocity and the twist of the rotor blades. These modes present different radial distributions of driven and driving blade regions, as well as different radial upwash/downwash patterns. The number of blade sections with zero tangential force, the existence of a downwash region in the rotor disk, the stability of the autorotation state, and the overall rotor autorotation efficiency, are all analyzed in terms of the flight velocity and the characteristics of the rotor. It is shown that, in vertical autorotation, larger blade twist leads to smaller values of descent velocity for a given thrust generated by the rotor in the autorotational state.

Arquitectura y construcción, paisaje y territorio : los refugios de la Cuenca Alta del río Tajo

La Tesis estudia un tipo de refugio ganadero de la Cuenca Alta del río Tajo, conocidos como chozones. Singular arquitectura ligada a la ganadería extensiva ovina que servía de abrigo al ganado durante la noche invernal y umbráculo en estío. Construcciones de muros bajos de mampuesto colocados a hueso de planta circular o rectangular, levantadas alrededor de una estructura leñosa o un árbol en posición de vida que soportan una cubierta de ramas de la poda de la sabina. Son cientos diseminados por toda la región, si bien concentrados en la Sesma del sabinar, una de las cuatro divisiones históricas del Señorío de Molina. La decadencia de la ganadería en la comarca, sumada a otras causas de sociales y económicas, ha llevado a que estén cada vez en peor estado de conservación; con todo lo que ello supone de pérdida de una memoria histórica inseparable del paisaje del que son parte. Mi primera aproximación a estos refugios fue una oferta que aceptó el equipo de dirección del Parque Natural del Alto Tajo para catalogar los que se encontraban en su área de protección, un paisaje de Alto Valor Natural donde la ganadería ha sido el sustento tradicional. Tras terminar el inventario se produjo el gran incendio en Riba de Saélices (2005). Además de calcinar a 11 retenes voluntarios, quemó parte de las chozones inventariados. Tomé entonces consciencia de la fragilidad de este patrimonio popular y del valor que cobraba el trabajo realizado, pues en muchos casos era el único testimonio que había de los chozones desaparecidos. De ahí nació esta investigación. Al comienzo el enfoque analítico fue eminentemente disciplinar, como recoge la primera parte del título de la tesis: arquitectura y construcción. Pronto comprendí que este enfoque no era suficiente para entender las preguntas dejadas abierta por el análisis espacial, tales como su origen, razón de ser, función social, etc. Profundizando en estos temas la investigación fue haciéndose más amplia y transversal, hasta llegar a lo indicado en la segunda parte del título: paisaje y territorio. En síntesis, la tesis pasó del análisis de un objeto en sí a su entendimiento como parte de una sociedad y un paisaje del que es indisoluble. Para lograr estos objetivos transversales, los refugios ganaderos se estudiaron considerando desde sus aspectos geográficos e históricos a los propios de la arquitectura y del sistema ganadero que acoge. A cada enfoque se dedica un capítulo de la Tesis, lo que nos obligó a utilizar distintas metodologías de análisis: de un amplio trabajo de campo para catalogar y levantar los casi un centenar de chozones inventariados a la búsqueda de información documental en archivos históricos. Por el carácter del estudio fue también fundamental la revisión del material etnográfico de la zona, así como las entrevistas con vecinos y los pocos pastores que quedaban en los municipios estudiados. Los resultados de la Tesis muestran que los refugios ganaderos son construcciones con una serie de valores de distinto tipo. Entre ellos destacaría: (a) ambientales, porque son arquitecturas integradas en el medio ambiente, con empleo de materiales del territorio y adaptación a sus condiciones físicas; (b) históricos, porque son testimonio de un patrimonio arquitectónico que al menos desde la Edad Media se mantiene sin apenas modificaciones; (c) etnográficos, porque son un elemento arquitectónico con usos estrechamente ligados a la cultura tradicional, ganadera y rural de la cuenca del Alto Tajo. Tan clara es la relación entre estos tres aspectos que no es exagerado afirmar que desde el comienzo hasta su final, pasando por las distintas actividades cotidianas, la vida de los habitantes de la comarca giraba en torno al patrimonio vernáculo estudiado. Por ello, entendemos que todos estos elementos son lo suficientemente relevantes como para intentar evitar su destrucción, fomentar una reutilización que contribuya a un desarrollo sostenible de este singular paisaje etnológico. ABSTRACT My first approach to these refugees was commissioned by the management of the Alto Tajo Natural Park to catalog those who were in their protection area, a landscape of high natural value where livestock has been the traditional livelihood. After completing the inventory came the great fire in Riba de Saelices (2005). Besides calcine 11 firefighters, burned many of these popular architectures. I took then awareness of the fragility of this vernacular heritage and the value of the work charged, since in many cases it was the only witness who had disappeared from the shelters. At that time, this research was born. At the begging our study was eminently from the point of view of our discipline, as it picks up the first part of the title of the Thesis: architecture and construction. Soon I realized that this approach was not sufficient to understand the questions left open by the spatial analysis, such as its origin, purpose, social function, etc. By studying topics, my research become to be more comprehensive and transversal, up to coming to the indicated in the second part of the title: landscape and territory. In synthesis, the Thesis went on from the analysis of an object in itself to its understanding like part of a society and a landscape of which it is indissoluble. To achieve these cross-cutting objectives, livestock shelters were studied considering from its geographic and historic aspects to this relating to his architecture own the livestock system to which they belong. To each approach we devoted a chapter of the Thesis, which forced us to use different methodologies of analysis: an extensive field work in cataloguing and lift the nearly a hundred chozones inventoried to the search of documentary information in historical archives. By the nature of the study, the review of the ethnographic material in the area was also essential, as well as interviews with neighbors and the few remaining shepherds in the municipalities studied. The results of our Thesis show that livestock shelters are constructions with a series of values of different types. Among them I would highlight three: (a) environmental, because they are architectures integrated in the territory, with the use of materials of the location and adapted to their physical conditions; (b) historical, because they are testimony of an architectural heritage that at least since the Middle Ages remains with little modifications; (c) ethnographic, because they are architectural elements closely linked to livestock, rural and traditional culture of the Alto Tajo basin. So clear is the relationship between these three aspects, that is not an exaggeration to say that from the beginning until the end, passing through the various daily activities, the life of the inhabitants of the region was in completed connection with the studied vernacular heritage. For it, we understand that all these elements are relevant enough to try to prevent their destruction and promote a recycling that contributes to a sustainable development of this unique ethnological landscape.