Aeroacoustics in high speed trains

Este trabajo se centra en el estudio de problemas aeroacústicos en los trenes de alta velocidad. Se han considerado dos escenarios en los que las ondas de presión generadas son críticos para el confort de los pasajeros. Uno es el debido a las ondas de presión que genera el tren cuando entra y sale de un túnel, que a su vez producen saltos de presión de baja frecuencia en el tren (cuando se cruzan con él) y en los alrededores del túnel cuando alcanzan la salida. Se estudia este fenómeno, y se propone un sistema aeroelástico basado en el galope transversal para disminuir la energía de estas ondas, y se analiza la energía extraíble de las ondas utilizando cuerpos con diferentes secciones transversales [Sorribes-Palmer and Sanz-Andres, 2013]. La influencia de la geometría de los portales en la energía radiada hacia el exterior de túnel es analizada experimentalmente, prestando especial atención a las boquillas porosas. Las ondas de presión en el interior del túnel se han analizado mediante el método de las características. Se han realizado ensayos experimentales para estimar la energía reflejada hacia el interior del túnel al alcanzar las ondas de presión el portal de salida del túnel. Se ha estudiado la formación e interacción entre el portal del túnel y la onda de choque generada en los túneles de gran longitud y pequeña fricción. Se propone un método para describir de forma aproximada el ruido radiado al exterior. Por otro lado se ha estudiado el ruido de media y alta frecuencia de origen aerodinámico. Se ha estudiado la influencia del desprendimiento de la capa límite sobre el tren. Se propone una metodología basada en una sección de tren característica para predecir rápidamente el nivel de presión de sonido dentro y fuera del tren para todo el rango de frecuencias. Se han realizado medidas experimentales en vía de los espectros de presión sobre la superficie del tren, y de la transmisibilidad de las uniones entre estructura y revestimiento. Los resultados experimentales se han utilizado en los modelos vibroacústicos. El método de la sección del tren característica es especialmente útil a altas frecuencias cuando todo el tren se puede modelar mediante el ensamblaje de diferentes secciones características utilizando el análisis estadístico de la energía. ABSTRACT This work is focused on the study of aeroacoustic problems in high speed trains. We have considered two scenarios in which the pressure waves generated are critical for passengers comfort. The first one is due to the pressure waves generated by a train entering in a tunnel. These waves generate pressure gauges inside the train (when they find each other) and outside of the tunnel portals. This phenomenon has been studied, and an aeroelastic system based on transverse galloping to reduce the energy of these waves is proposed. The maximum extractable energy by using bodies with different cross-section shapes is analyzed. The influence of the portals geometry in the energy radiated outwards the tunnel is analyzed experimentally, with particular attention to the porous exits. The pressure waves inside the tunnel have been analyzed using the method of characteristics. Experimental tests to estimate the energy reflected into the tunnel when the pressure waves reach the tunnel portal have been performed. We have studied the generation and interaction between the tunnel portal and a shock wave generated in long tunnels with small friction. A method to describe in an approximated way the pressure radiated outside the tunnel is proposed. In the second scenario, middle and high frequency noise generated aerodynamically has been studied, including the influence of the detachment of the boundary layer around the train. A method based on a train section to quickly predict the sound pressure level inside and outside the train has been proposed. Experimental test have been performed on board to evaluate the pressure power spectra on the surface of the train, and the transmissibility of the junctions between the structure and trim. These experimental results have been used in the vibroacoustic models. The low frequency pressure waves generated with the train during the tunnel crossing has been identified in the pressure spectrum. The train characteristic section method is especially useful at high frequencies, when the whole train can be modeled by assembling different sections using the statistical energy analysis. The sound pressure level inside the train is evaluated inside and outside the tunnel.

High-speed trains and tourists: what is the link? Evidence from the French and Spanish capitals

The objective of this paper is to analyse the factors influencing tourists? choice of a destination and the role of High Speed Rail (HSR) systems in this choice. The methodology proposed consists in analysing two capitals in Europe, i.e. Paris and Madrid where HSR services are important, to investigate the factors influencing holidaymakers in choosing these cities, and the role of HSR in this choice. The main outcome of this paper is to show that several factors influence the choice of a tourist, like the presence of architectural sites, the quality of promotion of the destination itself, the presence of events, and also HSR services. However we found that the HSR system has affected the choice of Paris and Madrid in a different way. Concerning the French case study, HSR is considered a real transport mode alternative among tourists, therefore HSR is chosen to reach Paris as well as for revisiting it. On the other hand, Madrid is chosen by tourists irrespective on the presence of HSR, while HSR is chosen for reaching cities close to Madrid. Data collected from the two surveys have been used for a further quantitative analysis. Models have been specified and calibrated to identify the factors influencing holidaymakers to revisit Paris and Madrid and the role of HSR in this choice has been highlighted.

Aeroacoustic noise prediction in high speed trains due to attached and detached flow

This paper aims to set out the influence of the flow field around high speed trains in open field. To achieve this parametric analysis of the sound pressure inside the train was performed. Three vibroacoustic models of a characteristic train section are used to predict the noise inside the train in open field by using finite element method FEM, boundary element method (BEM) and statistical energy analysis (SEA) depending on the frequency range of analysis. The turbulent boundary layer excitation is implemented as the only airborne noise source, in order to focus on the study of the attached and detached flow in the surface of the train. The power spectral densities of the pressure fluctuation in the train surface proposed by [Cockburn and Roberson 1974, Rennison et al. 2009] are applied on the exterior surface of the structural subsystems in the vibroacoustic models. An increase in the sound pressure level up to10 dB can be appreciated due to the detachment of the flow around the train. These results highlight the importance to determine the detached regions prediction, making critical the airborne noise due to turbulent boundary layer.

Vibroacoustic Problems in High Speed Trains

Passengers comfort in terms of acoustic noise levels is a key train design parameter, especially relevant in high speed trains, where the aerodynamic noise is dominant. The aim of the work, described in this paper, is to make progress in the understanding of the flow field around high speed trains in an open field, which is a subject of interest for many researchers with direct industrial applications, but also the critical configuration of the train inside a tunnel is studied in order to evaluate the external loads arising from noise sources of the train. The airborne noise coming from the wheels (wheelrail interaction), which is the dominant source at a certain range of frequencies, is also investigated from the numerical and experimental points of view. The numerical prediction of the noise in the interior of the train is a very complex problem, involving many different parameters: complex geometries and materials, different noise sources, complex interactions among those sources, broad range of frequencies where the phenomenon is important, etc. During recent years a research plan is being developed at IDR/UPM (Instituto de Microgravedad Ignacio Da Riva, Universidad Politécnica de Madrid) involving both numerical simulations, wind tunnel and full-scale tests to address this problem. Comparison of numerical simulations with experimental data is a key factor in this process.

Numerical Simulation of the Aerodynamic Behavior of High Velocity Trains under Synthetic Crosswinds of Different Shear and Turbulence Characteristics

A numerical simulation of the aerodynamic behavior of high-speed trains under synthetic crosswinds at a 90º yaw angle is presented. The train geometry is the aerodynamic train model (ATM). Flow description based on numerical simulations is obtained using large eddy simulation (LES) and the commercial code ANSYSFluent V14.5. A crosswind whose averaged velocity and turbulence characteristics change with distance to the ground is imposed. Turbulent fluctuations that vary temporally and spatially are simulated with TurbSim code. The crosswind boundary condition is calculated for the distance the train runs during a simulation period. The inlet streamwise velocity boundary condition is generated using Taylor?s frozen turbulence hypothesis. The model gives a time history of the force and moments acting on the train; this includes averaged values, standard deviations and extreme values. Of particular interest are the spectra of the forces and moments, and the admittance spectra. For comparison, results obtained with LES and a uniform wind velocity fluctuating in time, and results obtained with Reynolds averaged Navier Stokes equations (RANS), and the averaged wind conditions, are also presented.

Temporal self-imaging effect for periodically modulated trains of pulses

In this paper, the mathematical description of the temporal selfimaging effect is studied, focusing on the situation in which the train of pulses to be dispersed has been previously periodically modulated in phase and amplitude. It is demonstrated that, for each input pulse and for some specific values of the chromatic dispersion, a subtrain of optical pulses is generated whose envelope is determined by the Discrete Fourier Transform of the modulating coefficients. The mathematical results are confirmed by simulations of various examples and some limits on the realization of the theory are commented.

Comparative study of the effect of several trains on the ballast rotation

The ballast pick-up (or ballast train-induced-wind erosion (BTE)) phenomenon is a limiting factor for the maximum allowed operational train speed. The determination of the conditions for the initiation of the motion of the ballast stones due to the wind gust created by high-speed trains is critical to predict the start of ballast pick-up because, once the motion is initiated, a saltation-like chain reaction can take place. The aim of this paper is to present a model to evaluate the effect of a random aerodynamic impulse on stone motion initiation, and an experimental study performed to check the capability of the proposed model to classify trains by their effect on the ballast due to the flow generated by the trains. A measurement study has been performed at kp 69 + 500 on the Madrid – Barcelona High Speed Line. The obtained results show the feasibility of the proposed method, and contribute to a technique for BTE characterization, which can be relevant for the development of train interoperability standards

Gust wind tunnel study on ballast pick-up by high-speed trains

This paper describes the experimental setup, procedure, and results obtained, concerning the dynamics of a body lying on a floor, attached to a hinge, and exposed to an unsteady flow, which is a model of the initiation of rotational motion of ballast stones due to the wind generated by the passing of a high-speed train. The idea is to obtain experimental data to support the theoretical model developed in Sanz-Andres and Navarro-Medina (J Wind Eng Ind Aerodyn 98, 772–783, (2010), aimed at analyzing the initial phase of the ballast train-induced-wind erosion (BATIWE) phenomenon. The experimental setup is based on an open circuit, closed test section, low-speed wind tunnel, with a new sinusoidal gust generator mechanism concept, designed and built at the IDR/UPM. The tunnel’s main characteristic is the ability to generate a flow with a uniform velocity profile and sinusoidal time fluctuation of the speed. Experimental results and theoretical model predictions are in good agreement.

Train scheduling and rolling stock assignment in high speed trains

The Train Timetabling Problem (TTP) has been widely studied for freight and passenger rail systems. A lesser effort has been devoted to the study of high-speed rail systems. A modeling issue that has to be addressed is to model departure time choice of passengers on railway services. Passengers who use these systems attempt to travel at predetermined hours due to their daily life necessities (e.g., commuter trips). We incorporate all these features into TTP focusing on high-speed railway systems. We propose a Rail Scheduling and Rolling Stock (RSch-RS) model for timetable planning of high-speed railway systems. This model is composed of two essential elements: i) an infrastructure model for representing the railway network: it includes capacity constraints of the rail network and the Rolling-Stock constraints; and ii) a demand model that defines how the passengers choose the departure time. The resulting model is a mixed-integer programming model which objective function attempts to maximize the profit for the rail operator

Modelado de sistemas de inteligencia ambiental para el entrenamiento de las cualidades físicas

En un ejercicio no extenuante la frecuencia cardíaca (FC) guarda una relación lineal con el consumo máximo de oxígeno (V O2max) y se suele usar como uno de los parámetros de referencia para cuantificar la capacidad del sistema cardiovascular. Normalmente la frecuencia cardíaca puede remplazar el porcentaje de V O2max en las prescripciones básicas de ejercicio para la mejora de la resistencia aeróbica. Para obtener los mejores resultados en la mejora de la resistencia aeróbica, el entrenamiento de los individuos se debe hacer a una frecuencia cardíaca suficientemente alta, para que el trabajo sea de predominio dinámico con la fosforilación oxidativa como fuente energética primaria, pero no tan elevada que pueda suponer un riesgo de infarto de miocardio para el sujeto que se está entrenando. Los programas de entrenamiento de base mínima y de base óptima, con ejercicios de estiramientos para prevenir lesiones, son algunos de los programas más adecuados para el entrenamiento de la resistencia aeróbica porque maximizan los beneficios y minimizan los riesgos para el sistema cardiovascular durante las sesiones de entrenamiento. En esta tesis, se ha definido un modelo funcional para sistemas de inteligencia ambiental capaz de monitorizar, evaluar y entrenar las cualidades físicas que ha sido validado cuando la cualidad física es la resistencia aeróbica. El modelo se ha implementado en una aplicación Android utilizando la camiseta inteligente “GOW running” de la empresa Weartech. El sistema se ha comparado en el Laboratorio de Fisiología del Esfuerzo (LFE) de la Universidad Politécnica de Madrid (UPM) durante la realización de pruebas de esfuerzo. Además se ha evaluado un sistema de guiado con voz para los entrenamientos de base mínima y de base óptima. También el desarrollo del software ha sido validado. Con el uso de cuestionarios sobre las experiencias de los usuarios utilizando la aplicación se ha evaluado el atractivo de la misma. Por otro lado se ha definido una nueva metodología y nuevos tipos de cuestionarios diseñados para evaluar la utilidad que los usuarios asignan al uso de un sistema de guiado por voz. Los resultados obtenidos confirman la validez del modelo. Se ha obtenido una alta concordancia entre las medidas de FC hecha por la aplicación Android y el LFE. También ha resultado que los métodos de estimación del VO2max de los dos sistemas pueden ser intercambiables. Todos los usuarios que utilizaron el sistema de guiado por voz para entrenamientos de 10 base mínima y de base óptimas de la resistencia aeróbica consiguieron llevar a cabo las sesiones de entrenamientos con un 95% de éxito considerando unos márgenes de error de un 10% de la frecuencia cardíaca máxima teórica. La aplicación fue atractiva para los usuarios y hubo también una aceptación del sistema de guiado por voz. Se ha obtenido una evaluación psicológica positiva de la satisfacción de los usuarios que interactuaron con el sistema. En conclusión, se ha demostrado que es posible desarrollar sistemas de Inteligencia Ambiental en dispositivos móviles para la mejora de la salud. El modelo definido en la tesis es el primero modelo funcional teórico de referencia para el desarrollo de este tipo de aplicaciones. Posteriores estudios se realizarán con el objetivo de extender dicho modelo para las demás cualidades físicas que suponen modelos fisiológicos más complejos como por ejemplo la flexibilidad. Abstract In a non-strenuous exercise, the heart rate (HR) shows a linear relationship with the maximum volume of oxygen consumption (V O2max) and serves as an indicator of performance of the cardiovascular system. The heart rate replaces the %V O2max in exercise program prescription to improve aerobic endurance. In order to achieve an optimal effect during endurance training, the athlete needs to work out at a heart rate high enough to trigger the aerobic metabolism, while avoiding the high heart rates that bring along significant risks of myocardial infarction. The minimal and optimal base training programs, followed by stretching exercises to prevent injuries, are adequate programs to maximize benefits and minimize health risks for the cardiovascular system during single session training. In this thesis, we have defined an ambient intelligence system functional model that monitors, evaluates and trains physical qualities, and it has been validated for aerobic endurance. It is based on the Android System and the “GOW Running” smart shirt. The system has been evaluated during functional assessment stress testing of aerobic endurance in the Stress Physiology Laboratory (SPL) of the Technical University of Madrid (UPM). Furthermore, a voice system, designed to guide the user through minimal and optimal base training programs, has been evaluated. Also the software development has been evaluated. By means of user experience questionnaires, we have rated the attractiveness of the android application. Moreover, we have defined a methodology and a new kind of questionnaires in order to assess the user experience with the audio exercise guide system. The results obtained confirm the model. We have a high similarity between HR measurements made of our system and the one used by SPL. We have also a high correlation between the VO2max estimations of our system and the SPL system. All users, that tried the voice guidance system for minimal and optimal base training programs, were able to perform the 95% of the training session with an error lower than the 10% of theoretical maximum heart rate. The application appeared attractive to the users, and it has also been proven that the voice guidance system was useful. As result we obtained a positive evaluation of the users' satisfaction while they interacted with the system. In conclusion, it has been demonstrated that is possible to develop mobile Ambient Intelligence applications for the improvement of healthy lifestyle. AmIRTEM model is the first theoretical reference functional model for the design of this kind of applications. Further studies will be realized in order to extend the AmIRTEM model to other physical qualities whose physiological models are more complex than the aerobic endurance.

Analysis of jitter influence in fast frequency measurements

This paper presents a theoretical analysis of possible jitter impact in application of numeric criterion for fastmeasurement of frequency by coincidence principle. The primary goal is the generation of a signal containing a known amount of each jitter components. This signal was used for testing signals with regular pulse trains. Initially, jitter components are analyzed and modeled individually. Next, sequences for combining different kinds of jitter are modeled, simulated and evaluated. Jitter model simulation in Matlab is utilized to show the independence of frequencymeasurement results on the total jitter present in the reference and desired pulse trains independently. A good agreement between previously introduced theory of fastmeasurement of frequency and simulation in jitter presence is verified; these results allows to engineers use the numeric criterion for fastmeasurement of frequency in spite to interactions among jitter components in various applications for frequency domain sensors.

Adverse aerodynamics effects of a high speed train under the influence of cross winds, analysis and optimization of wind fence

The research work that here is summarized, it is classed on the area of dynamics and measures of railway safety, specifically in the study of the influence of the cross wind on the high-speed trains as well as the study of new mitigation measures like wind breaking structures or wind fences, with optimized shapes. The work has been developed in the Research Center in Rail Technology (CITEF), and supported by the Universidad Politécnica de Madrid, Spain.

Safety assessment of underground vehicles passing over highly resilient straight tracks in the presence of a broken rail

In this paper, vehicle-track interaction for a new slab track design, conceived to reduce noise and vibration levels has been analyzed, assessing the derailment risk for trains running on curved track when encountering a broken rail. Two different types of rail fastening systems with different elasticities have been analysed and compared. Numerical methods were used in order to simulate the dynamic behaviour of the train-track interaction. Multibody system (MBS) modelling techniques were combined with techniques based on the finite element method (FEM). MBS modelling was used for modelling the vehicle and FEM for simulating the elastic track. The simulation model was validated by comparing simulated results to experimental data obtained in field testing. During the simulations various safety indices, characteristic of derailment risk, were analysed. The simulations realised at the maximum running velocity of 110 km/h showed a similar behaviour for several track types. When reducing the running speed, the safety indices worsened for both cases. Although the worst behaviour was observed for the track with a greater elasticity, in none of the simulations did a derailment occur when running over the broken rail.

Migration to an a on-line laboatory in mechanical engineering. The case of a cam-follower design practice.

The European Higher Education Area (EHEA) has leaded to a change in the way the subjects are taught. One of the more important aspects of the EHEA is to support the autonomous study of the students. Taking into account this new approach, the virtual laboratory of the subject Mechanisms of the Aeronautical studies at the Technical University of Madrid is being migrated to an on-line scheme. This virtual laboratory consist on two practices: the design of cam-follower mechanisms and the design of trains of gears. Both practices are software applications that, in the current situation, need to be installed on each computer and the students carry out the practice at the computer classroom of the school under the supervision of a teacher. During this year the design of cam-follower mechanisms practice has been moved to a web application using Java and the Google Development Toolkit. In this practice the students has to design and study the running of a cam to perform a specific displacement diagram with a selected follower taking into account that the mechanism must be able to work properly at high speed regime. The practice has maintained its objectives in the new platform but to take advantage of the new methodology and try to avoid the inconveniences that the previous version had shown. Once the new practice has been ready, a pilot study has been carried out to compare both approaches: on-line and in-lab. This paper shows the adaptation of the cam and follower practice to an on-line methodology. Both practices are described and the changes that has been done to the initial one are shown. They are compared and the weak and strong points of each one are analyzed. Finally we explain the pilot study carried out, the students impression and the results obtained.

Migration to an a on.line laboratory in mechanical engineering. The case of a cam follower design practice.

The European Higher Education Area (EHEA) has leaded to a change in the way the subjects are taught. One of the more important aspects of the EHEA is to support the autonomous study of the students. Taking into account this new approach, the virtual laboratory of the subject Mechanisms of the Aeronautical studies at the Technical University of Madrid is being migrated to an on-line scheme. This virtual laboratory consist on two practices: the design of cam-follower mechanisms and the design of trains of gears. Both practices are software applications that, in the current situation, need to be installed on each computer and the students carry out the practice at the computer classroom of the school under the supervision of a teacher. During this year the design of cam-follower mechanisms practice has been moved to a web application using Java and the Google Development Toolkit. In this practice the students has to design and study the running of a cam to perform a specific displacement diagram with a selected follower taking into account that the mechanism must be able to work properly at high speed regime. The practice has maintained its objectives in the new platform but to take advantage of the new methodology and try to avoid the inconveniences that the previous version had shown. Once the new practice has been ready, a pilot study has been carried out to compare both approaches: on-line and in-lab. This paper shows the adaptation of the cam and follower practice to an on-line methodology. Both practices are described and the changes that has been done to the initial one are shown. They are compared and the weak and strong points of each one are analyzed. Finally we explain the pilot study carried out, the students impression and the results obtained.