A 2D computational parametric analysis of the sheltering effect of fences on a railway vehicle standing on a bridge and experiencing crosswinds

In a crosswind scenario, the risk of high-speed trains overturning increases when they run on viaducts since the aerodynamic loads are higher than on the ground. In order to increase safety, vehicles are sheltered by fences that are installed on the viaduct to reduce the loads experienced by the train. Windbreaks can be designed to have different heights, and with or without eaves on the top. In this paper, a parametric study with a total of 12 fence designs was carried out using a two-dimensional model of a train standing on a viaduct. To asses the relative effectiveness of sheltering devices, tests were done in a wind tunnel with a scaled model at a Reynolds number of 1 × 105, and the train’s aerodynamic coefficients were measured. Experimental results were compared with those predicted by Unsteady Reynolds-averaged Navier-Stokes (URANS) simulations of flow, showing that a computational model is able to satisfactorily predict the trend of the aerodynamic coefficients. In a second set of tests, the Reynolds number was increased to 12 × 106 (at a free flow air velocity of 30 m/s) in order to simulate strong wind conditions. The aerodynamic coefficients showed a similar trend for both Reynolds numbers; however, their numerical value changed enough to indicate that simulations at the lower Reynolds number do not provide all required information. Furthermore, the variation of coefficients in the simulations allowed an explanation of how fences modified the flow around the vehicle to be proposed. This made it clear why increasing fence height reduced all the coefficients but adding an eave had an effect mainly on the lift force coefficient. Finally, by analysing the time signals it was possible to clarify the influence of the Reynolds number on the peak-to-peak amplitude, the time period and the Strouhal number.

Trade-off aproaches for the vibroacoustic analysis of trains

Passengers’ comfort in terms of acoustic noise levels is a key design driver for train design. The problem is especially relevant for high speed trains, where the aerodynamic induced noise is dominant, but it is also important for medium speed trains where the mechanical sources of noise may have more influence. The numerical interior noise prediction inside the train is a very comp lex problem, involving many different parameters: complex geometries and materials, different noise sources, com- plex interactions among those sources, broad range of frequencies where the phenomenon is important, etc. In this paper, the main findings of this work developed at IDR/UPM (Instituto de Microgravedad “Ignacio Da Riva”, Universidad Politécnica de Madrid) are presented, concentrat ing on the different modelling methodologies used for the different frequency ranges of interest, from FEM-BEM models, hybrid FEM-SEA to pure SEA models. The advantages and disadvantages of the different approaches are summarized. Different modelling techniques have also been evaluated and compared, taking into account the various and specific geometrical configurations typical in this type of structures, and the material properties used in the models. The critical configuration of the train inside a tunnel is studied in order to evaluate the external loads due to noise sources of the train. In this work, a SEA-model composed by periodic characteristic sections of a high spee d train is analysed inside a tunnel.

Multi-objective Aerodynamic Optimization of High-speed Trains in Tunnels

A genetic algorithm (GA) is employed for the multi-objective shape optimization of the nose of a high-speed train. Aerodynamic problems observed at high speeds become still more relevant when traveling along a tunnel. The objective is to minimize both the aerodynamic drag and the amplitude of the pressure gradient of the compression wave when a train enters a tunnel. The main drawback of GA is the large number of evaluations need in the optimization process. Metamodels-based optimization is considered to overcome such problem. As a result, an explicit relationship between pressure gradient and geometrical parameters is obtained.

A parametric, experimental analysis of conical vortices on curved roofs of low-rise buildings

Different methods to reduce the high suction caused by conical vortices have been reported in the literature: vertical parapets, either solid or porous, placed at the roof edges being the most analysed configuration. Another method for alleviating the high suction peaks due to conical vortices is the use of some non-standard parapet configuration like cantilever parapets. In this paper the influence of roof curvature on the conical vortex pattern appearing on a curved roof (Fig. 1) when subject to oblique winds is experimentally analysed by testing the mean pressure distribution on the curved roofs of low-rise building models in a wind tunnel. Also, the efficiency of cantilever parapets to reduce mean suction loads on curved roofs is experimentally checked. Very high suction loads have been measured on curved roofs, the magnitude of these high suction loads being significantly decreased when cantilever parapets are used. Thus, the suitability of these parapets to reduce wind pressure loads on curved roofs is demonstrated.

Influence of an upstream building on the wind-induced mean suction on the flat roof of a low-rise building

The effect of an upstream building on the suction forces on the flat roof of a low-rise building placed in the wake of the former is analyzed. The analysis has been performed by wind tunnel testing of a flat roof, low-rise building model equipped with pressure taps on the roof and different block-type buildings (only configurations where the upstream building is as high or higher than the downstream one are considered in this paper). The influence of the distance between both buildings on the wind loads on the downstream building roof is analyzed, as well as the height of the upstream one and the wind angle of incidence. Experimental results reveal that the wind load increases as the relative height of the upstream building increases, the wind load being highest for intermediate distances between buildings, when a passage between them is formed.

Fourier analysis of the aerodynamic behavior of cup anemometers

The calibration results (the transfer function) of an anemometer equipped with several cup rotors were analyzed and correlated with the aerodynamic forces measured on the isolated cups in a wind tunnel. The correlation was based on a Fourier analysis of the normal-to-the-cup aerodynamic force. Three different cup shapes were studied: typical conical cups, elliptical cups and porous cups (conical-truncated shape). Results indicated a good correlation between the anemometer factor, K, and the ratio between the first two coefficients in the Fourier series decomposition of the normal-to-the-cup aerodynamic force

Influence of aerodynamic characteristics of H beams on galloping stability

This paper presents the experimental study developed on a prismatic beam with H section, sometimes used in bridges as suspenders, vertical bars or decks. The purpose of this study is to understand the physical behavior of the air around this type of section, in order to reduce the aerodynamic loads, the onset speed of galloping and even to avoid it. To achieve this, a study of the influence of all geometric parameters that define the section has been developed. Previously, the most interesting configurations have been selected using a smoke flow visualization technique in the wind-tunnel, then the corresponding static aerodynamic loads were measured, completed with dynamic tests and, finally, the parameters governing the phenomenon of galloping determined.

Static and Dynamic Experimental Analysis of the Galloping Stability of Porous H-Section Beams

The phenomenon of self-induced vibrations of prismatic beams in a cross-flow has been studied for decades, but it is still of great interest due to their important effects in many different industrial applications. This paper presents the experimental study developed on a prismatic beam with H-section.The aim of this analysis is to add some additional insight into the behaviour of the flow around this type of bodies, in order to reduce galloping and even to avoid it. The influence of some relevant geometrical parameters that define the H-section on the translational galloping behaviour of these beams has been analysed. Wind loads coefficients have been measured through static wind tunnel tests and the Den Hartog criterion applied to elucidate the influence of geometrical parameters on the galloping properties of the bodies under consideration.These results have been completed with surface pressure distribution measurements and, besides, dynamic tests have been also performed to verify the static criterion. Finally, the morphology of the flow past the tested bodies has been visualised by using smoke visualization techniques. Since the rectangular section beam is a limiting case of the H-section configuration, the results here obtained are compared with the ones published in the literature concerning rectangular configurations; the agreement is satisfactory.

How lowering speed limits in an urban highway affects traffics performance and emissions: the case of Madrid M-30 ring-road

The city of Madrid keeps not meeting the GHG and air pollutant limits set by the European legislation. A broad range of strategies have being taken into account to reduce both types of emissions; however traffic management meas ures are usually consigned to the sidelines. In 2004, Madrid City Council launched a plan to re-design its inner ring-road supported by a socioeconomic study that evaluated the environmental and operational benefits of the project. For safety reasons the planned speed limit for the tunnel section was finally reduced from 90km/h to 70km/h. Using a Macroscopic Traffic Model and the European Air Pollutant and Emissions Inventory Guidebook (EMEP/EEA), this paper examines the environmental and traffic performance consequences of this decision. Results support the thesis that reduced speed limits leads to GHG and air pollution reductions in the area affected by the measure without substantially altering traffic performance. The implementation of the new speed limit policy brings about a 15% and 16% reduction in both CO2 and NOx emissions respectively. Emissions’ reduction during off-peak hours is larger than during peak hours.

Investigación experimental del flujo aerodinámico sobre helipuertos embarcados

La investigación del flujo aerodinámico sobre helipuertos embarcados se encuentra estrechamente relacionada con la operación segura de las aeronaves, pues las condiciones del flujo que tiene lugar en ese entorno pueden exceder los límites para los que están certificadas dichas aeronaves. El ambiente aerodinámico en las inmediaciones de un barco es altamente complejo y se encuentra influenciado por gran número de factores (chimeneas, antenas, mástiles, etc.) relacionados con la configuración específica del propio barco. El flujo objeto de investigación corresponde a la estela que se desarrolla sobre la cubierta de vuelo de una fragata, el cual está fuertemente influenciado por la superestructura de la misma, y que cualitativamente es similar al flujo que tiene lugar entre edificios altos o helipuertos situados en áreas urbanas, pues comprende estructuras tipo caja, con bordes afilados, que generan flujos tridimensionales altamente turbulentos. En esta Tesis se aborda el estudio del problema desde el punto de vista experimental, mediante simulación en túnel aerodinámico y medida de las variables del campo fluido sobre maquetas de fragatas a escala reducida. Las herramientas empleadas para tal cometido, han sido técnicas experimentales, tales como la visualización del flujo, la velocimetría láser por imágenes de partículas, la anemometría láser Doppler y los scanners electrónicos de presión, que han permitido investigar el flujo problema con objeto de obtener información, y adquirir así, un conocimiento más profundo de dicho flujo. La explotación de este conocimiento, ha dado lugar al diseño de una nueva solución, basada en la modificación de geometría básica de la fragata, por medio del cambio de la curvatura del techo del hangar, permitiendo suavizar el escalón descendente que se produce aguas abajo del mismo. Las geometrías modificadas han sido ensayada en túnel mediante la misma metodología empleada para la fragata original, de modo que, ha podido establecerse un análisis comparativo, para valorar la efectividad de la solución propuesta, el cual ha mostrado resultados satisfactorios, retirando el flujo adverso de la zona de operación de helicópteros y desplazándolo hacia el hangar, donde resulta menos peligroso, de modo que se reduce la carga del piloto y los riesgos de accidente durante las operaciones a bordo de embarcaciones. ABSTRACT The investigation of aerodynamic flow above the ship’s heliports is directly related to the aircraft safe operation, because the environment flow conditions may exceed the aircraft certification limits. Aerodynamic ship’s environment is highly complex and it is influenced by a large number of factors (stacks, antennae, masts, …) related to each specific ship configuration. The flow under investigation occurs into the wake produced above the flight deck of a frigate, that is strongly influenced by the superstructure. This flow is similar to one produced around tall buildings or heliports located in urban areas, thus in both of them, the air is flowing around sharp-edges box-like structures, producing three-dimensional and highly turbulent flows. This Thesis studies the problem from an experimental point of view, by means of wind tunnel simulations and measurements of the flow field around reduced scale frigates models. Tools used in this work are the experimental techniques, as flow visualization, particle image velocimetry, laser Doppler anemometry and pressure electronic scanners. These techniques provide information about the flow in order to obtain a more complete insight of this kind of flows. The exploitation of this insight is used for the design of a new flow control concept, based on the modification of the basic frigate geometry. This new design consists in the hangar roof curvature modification that produces a smoothing of the descendent step located downstream the hangar. Modified geometries are tested in wind tunnel by means of the same methodology as the original frigate, thus a comparative analysis is established in order to perform an assessment of effectiveness. This analysis has shown good results in displacing the adverse flow from the helicopter operation path to the nearest hangar region, reducing the pilot load and the accident risks during on board operations.

Fotodiodos basados en (Zn,Mg)O para la detección de luz ultravioleta

La presente tesis fue ideada con el objetivo principal de fabricar y caracterizar fotodiodos Schottky en capas de ZnMgO y en estructuras de pozo cuántico ZnMgO/ZnO para la detección de luz UV. La elección de este material semiconductor vino motivada por la posibilidad que ofrece de detectar y procesar señales simultáneamente, en un amplio margen de longitudes de onda, al igual que su más directo competidor el GaN. En esta memoria se da en primer lugar una visión general de las propiedades estructurales y ópticas del ZnO, prestando especial atención a su ternario ZnMgO y a las estructuras de pozo cuántico ZnMgO/ZnO. Además, se han desarrollado los conocimientos teóricos necesarios para una mejor compresión y discusión de los resultados alcanzados. En lo que respecta a los resultados de esta memoria, en esencia, estos se dividen en dos bloques. Fotodiodos desarrollados sobre capas delgadas de ZnMgO no-polar, y sobre estructuras de pozo cuántico de ZnMgO/ZnO no-polares y semipolares Fotodiodos de capas delgadas de ZnMgO. Es bien conocido que la adición de Mg a la estructura cristalina del ZnO desplaza el borde de absorción hacia energías mayores en el UV. Se ha aprovechado esto para fabricar fotodiodos Schottky sobre capas de ZnMgO crecidas por MOCVD y MBE, los cuales detecten en un ventana de energías comprendida entre 3.3 a 4.6 eV. Sobre las capas de ZnMgO, con diferentes contenidos de Mg(5.6-18.0 %), crecidas por MOCVD se han fabricado fotodiodos Schottky. Se han estudiado en detalle las curvas corrientevoltaje (I-V). Seguidamente, se ha realizado un análisis de la respuesta espectral bajo polarización inversa. Tanto los valores de responsividad obtenidos como el contraste UV/VIS están claramente aumentados por la presencia de ganancia. Paralelamente, se han realizado medidas de espectroscopia de niveles profundos (DLOS), identificándose la presencia de dos niveles profundos de carácter aceptor. El papel desempeñado por estos en la ganancia ha sido analizado meticulosamente. Se ha demostrado que cuando estos son fotoionizados son responsables directos del gran aumento de la corriente túnel que se produce a través de la barrera Schottky, dando lugar a la presencia de la ganancia observada, que además resulta ser función del flujo de fotones incidente. Para extender el rango detección hasta 4.6 eV se fabricaron fotodiodos sobre capas de ZnMgO de altísima calidad cristalina crecidas por MBE. Sobre estos se ha realizado un riguroso análisis de las curvas I-V y de las curvas capacidad-voltaje (CV), para posteriormente identificar los niveles profundos presentes en el material, mediante la técnica de DLOS. Así mismo se ha medido la respuesta espectral de los fotodetectores, la cual muestra un corte abrupto y un altísimo contraste UV/VIS. Además, se ha demostrado como estos son perfectos candidatos para la detección de luz en la región ciega al Sol. Por otra parte, se han fabricado fotodiodos MSM sobre estas mismas capas. Se han estudiado las principales figuras de mérito de estos, observándose unas corrientes bajas de oscuridad, un contraste UV/VIS de 103, y la presencia de fotocorriente persistente. Fotodiodos Schottky de pozos cuánticos de ZnO/ZnMgO. En el segundo bloque de esta memoria, con el objeto final de clarificar el impacto que tiene el tratamiento del H2O2 sobre las características optoelectrónicas de los dispositivos, se ha realizado un estudio detallado, en el que se han analizado por separado fotodiodos tratados y no tratados con H2O2, fabricados sobre pozos cuánticos de ZnMgO/ZnO. Se ha estudiado la respuesta espectral en ambos casos, observándose la presencia de ganancia en los dos. A través de un análisis meticuloso de las características electrónicas y optoeletrónicas de los fotodiodos, se han identificado dos mecanismos de ganancia internos diferentes en función de que la muestra sea tratada o no-tratada. Se han estudiado fotodetectores sensibles a la polarización de la luz (PSPDs) usando estructuras de pozo cuántico no-polares y semipolares sobre sustratos de zafiro y sustratos de ZnO. En lo que respecta a los PSPDs sobre zafiro, en los cuales el pozo presenta una tensión acumulada en el plano, se ha visto que el borde de absorción se desplaza _E _21 meV con respecto a luz linealmente polarizada perpendicular y paralela al eje-c, midiéndose un contraste (RE || c /RE c)max _ 6. Con respecto a los PSPDs crecidos sobre ZnO, los cuales tienen el pozo relajado, se ha obtenido un 4E _30-40, y 21 meV para las heteroestructuras no-polar y semipolar, respectivamente. Además el máximo contraste de responsividad fue de (RE || c /RE c)max _ 6 . Esta sensibilidad a la polarización de la luz ha sido explicada en términos de las transiciones excitónicas entre la banda de conducción y las tres bandas de valencia. ABSTRACT The main goal of the present thesis is the fabrication and characterization of Schottky photodiodes based on ZnMgO layers and ZnMgO / ZnO quantum wells (QWs) for the UV detection. The decision of choosing this semiconductor was mainly motivated by the possibility it offers of detecting and processing signals simultaneously in a wide range of wavelengths like its main competitor GaN. A general overview about the structural and optical properties of ZnO, ZnMgO layers and ZnMgO/ZnO QWs is given in the first part of this thesis. Besides, it is shown the necessary theoretical knowledge for a better understanding of the discussion presented here. The results of this thesis may be divided in two parts. On the one hand, the first part is based on studying non-polar ZnMgO photodiodes. On the other hand, the second part is focused on the characterization of non-polar and semipolar ZnMgO / ZnO QWs Schottky photodiodes. ZnMgO photodiodes. It is well known that the addition of Mg in the crystal structure of ZnO results in a strong blue-shift of the ZnO band-gap. Taking into account this fact Schottky photodiodes were fabricated on ZnMgO layers grown by MOCVD and MBE. Concerning ZnMgO layers grown by MOCVD, a series of Schottky photodiodes were fabricated, by varying the Mg content from 5.6% to 18 %. Firstly, it has been studied in detail the current-voltage curves. Subsequently, spectral response was analyzed at reverse bias voltage. Both the rejection ratio and the responsivity are shown to be largely enhanced by the presence of an internal gain mechanism. Simultaneously, measurements of deep level optical spectroscopy were carried out, identifying the presence of two acceptor-like deep levels. The role played for these in the gain observed was studied in detail. It has been demonstrated that when these are photoionized cause a large increase in the tunnel current through the Schottky barrier, yielding internal gains that are a function of the incident photon flux. In order to extend the detection range up to 4.6 eV, photodiodes ZnMgO grown by MBE were fabricated. An exhaustive analysis of the both I-V and CV characteristics was performed. Once again, deep levels were identified by using the technique DLOS. Furthermore, the spectral response was measured, observing sharp absorption edges and high UV/VIS rejections ratio. The results obtained have confirmed these photodiodes are excellent candidates for the light detection in the solar-blind region. In addition, MSM photodiodes have also been fabricated on the same layers. The main figures of merit have been studied, showing low dark currents, a large UV/VIS rejection ratio and persistent photocurrent. ZnMgO/ZnO QWs photodiodes. The second part was focused on ZnMgO/ ZnO QWs. In order to clarify the impact of the H2O2 treatment on the performance of the Schottky diodes, a comparative study using treated and untreated ZnMgO/ZnO photodiodes has been carried out. The spectral response in both cases has shown the presence of gain, under reverse bias. Finally, by means of the analysis of electronic and optoelectronic characteristics, two different internal gain mechanisms have been indentified in treated and non-treated material. Light polarization-sensitive UV photodetectors (PSPDs) using non-polar and semipolar ZnMgO/ZnO multiple quantum wells grown both on sapphire and ZnO substrates have been demonstrated. For the PSPDs grown on sapphire with anisotropic biaxial in-plain strain, the responsivity absorption edge shifts by _E _21 meV between light polarized perpendicular and parallel to the c-axis, and the maximum responsivity contrast is (RE || c /RE c)max _ 6 . For the PSPDs grown on ZnO, with strain-free quantum wells, 4E _30-40, and 21 meV for non-polar and semipolar heterostructures, and maximum (R /R||)max _10. for non-polar heterostructure was achieved. These light polarization sensitivities have been explained in terms of the excitonic transitions between the conduction and the three valence bands.

Aerodynamic Study of Airfoils with Leading Edge Imperfections at Low Reynolds Number

A study has been made on the influence of the leading edge imperfections in airfoils used in different devices relating their aerodynamic performances. Wind tunnel tests have been made at different Reynolds numbers and angle of attacks in order to show this effect. Later, a quantitative study of the aerodynamic properties has been made based on the different leading edge imperfections and their size.

Probabilistic approach for longitudinal ventilation system design in fire situations

The main objective of ventilation systems in tunnels is to reach the highest possible safety level both in service and fire situation; being the fire one, the most relevant when designing the system. When designing a longitudinal ventilation system, the methodology to evaluate the capacity of the system is similar both in service and fire situation, with the exception of the chimney effect and the phenomena of thermal transfer which is responsible or the changes in the density of the air. When facing the dimensioning task for longitudinal ventilated tunnels, although similar methodologies are used in different countries, specific hypothesis (aerodynamic, thermal properties, traffic) even if discussed in the literature or current practice, are not usually detailed in the regulations or recommendations. The aim of this paper is to propose a probabilistic approach to the problem which would allow the designer, and the tunnel owner, to understand the uncertainty and sensibility adopted in the results and, eventually, identify possible ways of optimizing the ventilation solution to be adopted.

Ventilation and FFFS fire tests for “Calle 30” road tunnels

Between 2003 and 2007 an urban network or road tunnels with a total constructed tubes length of 45 km was built in the city of Madrid. This amazing engineering work, known as "Calle 30 Project" counted with different kinds of tunnel typologies and ventilation systems. Due to the length of the tunnels and the impact of the work itself, the tunnels were endowed with a great variety of installations to provide the maximum levels of safety both for users and the infrastructure includieng, in some parts of the tunnel, fixed fire fighting system based on water mist. Whithin this framework a large-scale programme of fire tests was planned to study different aspects related to fire safety in the tunnels including the phenomena of the interaction between ventilation and extinguishing system. In addition, these large scale fire tests allowed fire brigades of the city of Madrid an opportunity to define operational procedures for specific fire fighting in tunnels and evaluate the possibilities of fixed fire fighting systems. The tests were carried out in the Center of Experimentation "San pedro of Anes" which includes a 600 m tunnel with a removable false ceiling for reproducing different ceiling heights and ventilation conditions (transverse and longitudinal ones). Interesting conclusions on the interaction of ventilation and water mist systems were obtained but also on other aspects including performance of water mist system in terms of reduction of gas temperatures or visibility conditions. This paper presents a description of the test's programme carried out and some previous results obtained.

Large Scale Fire Tests for the “Calle 30 Project"

Between 2003 and 2007 an urban network of road tunnels with a total constructed tubes length of 45 km was built in the city of Madrid. This amazing engineering work, known as “Calle30 Project” counted with different kinds of tunnel typologies and ventilation systems. Due to the length of the tunnels and the impact of the work itself, the tunnels were endowed with a great variety of installations to provide the maximum levels of safety both for users and the infrastructure including,in some parts of the tunnel, fixed fire fighting system based on water mist. Within this framework a large-scale campaign of fire tests were planned to study different aspects related to fire safety in the tunnels including the phenomena of the interaction between ventilation and extinction system. In addition, this large scale fire tests allowed fire brigades of the city of Madrid an opportunity to define operational procedures for specific fire fighting in tunnels and evaluate the possibilities of fixed fire fighting systems. The tests were carried out in the Center of Experimentation "San Pedro of Anes" which counts with a 600 m tunnel with a removable false ceiling for reproducing different ceiling heights and ventilation conditions (transverse and longitudinal ones). Interesting conclusions on the interaction of ventilation and water mist systems were obtained but also on other aspects including performance of water mist system in terms of reduction of gas temperatures or visibility conditions. This paper presents a description of the test’s campaign carried out and some previous results obtained.