Wheel shape optimization approaches to reduce railway rolling noise

[EN] A wheel shape optimization of a railway wheel cross section by means of Genetic Algorithms (GAs) is presented with the aim of minimizing rolling noise radiation. Two different approaches have been implemented with this purpose, one centred on direct Sound poWer Level (SWL) minimization, calculated using TWINS methodology, and another one emphasizing computational efficiency, focused on natural frequencies maximization. Numerical simulations are carried out with a Finite Element Method (FEM) model using general axisymmetric elements. The design space is defined by a geometric parametrization of the wheel cross section with four parameters: wheel radius, a web thickness factor, fillet radius and web offset. For all wheel candidates a high-cycle fatigue analysis has been performed according to actual standards, in order to assure structural feasibility. Rolling noise reductions have been achieved, with a decrease of up to 5 dB(A) when considering the wheel component. Response surfaces have been also computed to study the dependency of the objective functions on the geometric parameters and to test the adequacy of the optimization algorithm applied.This study was financially supported by Ministerio de Ciencia, Innovacion y Universidades - Agencia Estatal de Investigacion, European Regional Development Fund (project TRA2017-84701-R), and Conselleria d'Educacio, Investigacio, Cultura i Esport (Generalitat Valenciana, project Prometeo/2016/007).García-Andrés, FX.; Gutiérrez-Gil, J.; Martínez Casas, J.; Denia, FD. (2020). Wheel shape optimization approaches to reduce railway rolling noise. Structural and Multidisciplinary Optimization. 62(5):2555-2570. https://doi.org/10.1007/s00158-020-02700-6S25552570625Beranek LL (2007) Basic acoustical quantities: levels and decibels, chapter 1 pp 1–24, John Wiley & Sons, LtdBouvet P, Vincent N, Coblentz A, Demilly F (2000) Optimization of resilient wheels for rolling noise control. J Sound Vib 231(3):765–777Bühler S (2006) Methods and results of field testing of a retrofitted freight train with composite brake blocks. J Sound Vib 293(3-5):1041–1050Cigada A, Manzoni S, Vanali M (2008) Vibro-acoustic characterization of railway wheels. Appl Acoust 69(6):530–545Clausen U, Doll C, Franklin FJ, Franklin GV, Heinrichmeyer H, Kochsiek J, Rothergatter W, Sieber N (2012) Reducing railway noise pollution. Technical Report, Policy Department Structural and Cohesion Policies, European ParliamentCoello CAC (2002) Theoretical and numerical constraint-handling techniques used with evolutionary algorithms: a survey of the state of the art. Comput Method in Appl M 191(11-12):1245–1287Cui D, Wang R, Allen P, An B, Li L, Wen Z (2019) Multi-objective optimization of electric multiple unit wheel profile from wheel flange wear viewpoint. Struct Multidiscipl Optim 59(1):279–289de Vos P (2016) Railway noise in Europe. Technical Report, International Union of RailwaysDIN (2017) Railway applications. Wheelsets and bogies. Monobloc wheels. Design assessment procedure. Part 1: forged and rolled wheels DIN-prEN-13979-1:2017. Technical standard, DIN Standards Committee RailwayEfthimeros GA, Photeinos DI, Diamantis ZG, Tsahalis DT (2002) Vibration/noise optimization of a FEM railway wheel model. Eng Computation 19(7-8):922–931Fahy F, Gardonio P (2007) Sound and structural vibration, 2nd edition. Academic Press, OxfordGarcia-Andrés X, Gutiérrez-Gil J, Martínez-Casas J, Denia FD (2019) Sound power minimization of a railway wheel by means of a modal-based geometric optimization technique. In: Proceedings of 48th International Congress and Exhibition on Noise Control EngineeringGrassie SL, Gregory RW, Harrison D, Johnson KL (1982) The dynamic response of railway track to high frequency vertical excitation. J Mechan Eng Sci 24(2):77–90Hare W, Nutini J, Tesfamariam S (2013) A survey of non-gradient optimization methods in structural engineering. Adv Eng Softw 59:19–28Holland JH (1975) Adaptation in natural and artificial systems, 1st edition. University of Michigan Press, Ann Arbor, MIJanssens MHA, Thompson DJ, de Beer FG (2014a) TWINS version 3.3 Track-Wheel Interaction Noise Software user manual. TNO reportJanssens MHA, Thompson DJ, de Beer FG, Dittrich M, Jansen H (2014b) TWINS version 3.3 Track-Wheel Interaction Noise Software theoretical manual. TNO reportJones CJC, Hardy AEJ, Jones RRK, Wang A (1996) Bogie shrouds and low track-side barriers for the control of railway vehicle rolling noise. J Sound Vib 193(1):427–431Jones CJC, Thompson DJ (2003) Extended validation of a theoretical model for railway rolling noise using novel wheel and track designs. J Sound Vib 267(3):509–522Kalker JJ (1967) On the rolling contact of two elastic bodies in the presence of dry friction. PhD thesis, Technical University of DelftKnothe K, Gross-Thebing A (1986) Derivation of frequency dependent creep coefficients based on an elastic half-space model. Vehicle Syst Dyn 15(3):133–153Lang S (1985) Complex analysis, 2nd edition. Springer New York, New YorkLee S, Lee DH, Lee J (2019) Integrated shape-morphing and metamodel-based optimization of railway wheel web considering thermo-mechanical loads. Struct Multidiscipl Optim 60(1):315–330Marler RT, Arora JS (2004) Survey of multi-objective optimization methods for engineering. Struct Multidiscipl Optim 26(6):369–395Merideno I, Nieto J, Gil-Negrete N, Giménez Ortiz JG, Landaberea A, Iartza J (2014) Theoretical prediction of the damping of a railway wheel with sandwich-type dampers. J Sound Vib 333(20):4897–4911Nielsen JCO (1994) Dynamic interaction between wheel and track - A parametric search towards an optimal design of rail structures. Vehicle Syst Dyn 23(1):115–132Nielsen JCO (2000) Acoustic optimization of railway sleepers. J Sound Vib 231(3):753–764Nielsen JCO, Fredö CR (2006) Multi-disciplinary optimization of railway wheels. J Sound Vib 293(3-5):510–521Petyt M (2010) Vibration of solids, 2nd edition. Cambridge University Press, CambridgeRemington PJ (1976) Wheel/rail noise part IV: rolling noise. J Sound Vib 46(3):419–436Remington PJ (1987) Wheel/rail rolling noise, II: validation of the theory. J Acoust Soc Am 81 (6):1824–1832Rios LM, Sahinidis NV (2013) Derivative-free optimization: a review of algorithms and comparison of software implementations. J Global Optim 56(3):1247–1293Thompson DJ (1988) Predictions of acoustic radiation from vibrating wheels and rails. J Sound Vib 120(2):275–280Thompson DJ (1991) Wheel-rail noise: theoretical modelling of the generation of vibrations. PhD thesis, University of SouthamptonThompson DJ (1993a) Wheel-rail noise generation, part I: introduction and interaction model. J Sound Vib 161(3):387–400Thompson DJ (1993b) Wheel-rail noise generation, part II: wheel vibration. J Sound Vib 161 (3):401–419Thompson DJ (1993c) Wheel-rail noise generation, part IV: contact zone and results. J Sound Vib 161(3):447–466Thompson DJ (2010) Railway noise and vibration. Mechanisms, modelling and means of control, 1st edition. Elsevier, AmsterdamThompson DJ, Fodiman P, Mahé H (1996a) Experimental validation of the TWINS prediction program for rolling noise, part 2: results. J Sound Vib 193(1):137–147Thompson DJ, Hemsworth B, Vincent N (1996b) Experimental validation of the TWINS prediction program for rolling noise, part 1: description of the model and method. J Sound Vib 193(1):123–135Thompson DJ, Jones CJC (2002) Sound radiation from a vibrating railway wheel. J Sound Vib 253(2):401–419Thompson DJ, Squicciarini G, Zhang J, Lopez-Arteaga I, Zea E, Dittrich M, Jansen E, Arcas K, Cierco E, Magrans F, Malkoun A, Iturritxa E, Guiral A, Stangl M, Schleinzer G, Martin-Lopez B, Chaufour C, Wändell J (2018) Assessment of measurement-based methods for separating wheel and track contributions to railway rolling noise. Appl Acoust 140:48–62Timoshenko SP, Gere JM (1963) Theory of elastic stability. Dover, Mineola, New York, 2nd editionUNE (2011) Railway applications. Wheelsets and bogies. Monobloc wheels. Technical approval procedure. Part 1: forged and rolled wheels UNE-EN-13979-1:2006. Technical standard, Asociación Española de Normalización (UNE)Vincent N, Bouvet P, Thompson DJ, Gautier PE (1996) Theoretical optimization of track components to reduce rolling noise. J Sound Vib 193(1):161–171Wang Z, Jiao Y, Chen Z (2019) Parameter study of friction damping ring for railway wheels based on modal analysis. Appl Acoust 153:140–146WHO (2011) Burden of disease from environmental noise. Technical Report, European Centre for Environment and Healt

Topology and shape optimization of dissipative and hybrid mufflers

[EN] This article presents a Topology Optimization (TO) method developed for maximizing the acoustic attenuation of a perforated dissipative muffler in the targeted frequency range by optimally distributing the absorbent material within the chamber. The Finite Element Method (FEM) is applied to the wave equation formulated in terms of acoustic pressure (chamber) and velocity potential (central duct, due to the existence of thermal gradients and mean flow) in order to evaluate the acoustic performance of the noise control device in terms of Transmission Loss (TL). Sound propagation through the chamber fibrous material is modelled considering complex equivalent acoustic properties, which vary spatially not only as a function of temperature, but also as a function of the lling density, since non-homogeneous density distributions are considered. The acoustic coupling at the perforated duct is performed by introducing a coordinate-dependent equivalent impedance. The objective function to maximize is expressed as the mean TL in the targeted frequency range. The sensitivities of this function with respect to the filling density of each element in the chamber are evaluated following the standard adjoint method. The Method of Moving Asymptotes (MMA) is used to update the design variables at each iteration of the TO process, keeping the weight of absorbent material equal or lower than a given value, while maximizing attenuation. Additionally, several particular designs inferred from the topology optimization results are analyzed. For example, the sizing optimization of a number of rings is carried out simultaneously with the aforementioned TO process (density layout). A reactive chamber is added in order to evaluate the TL of a hybrid muffler and its shape optimization is also carried out simultaneously with the aforementioned TO. Results show an increase in the muffler's mean TL at target frequencies, for all cases under study, while the amount of absorbent material used is maintained or even reduced.Ferrándiz-Catalá, B.; Denia, FD.; Martínez Casas, J.; Nadal, E.; Ródenas, JJ. (2020). Topology and shape optimization of dissipative and hybrid mufflers. Structural and Multidisciplinary Optimization. 62(1):269-284. https://doi.org/10.1007/s00158-020-02490-xS269284621Allard JF, Atalla N (2009) Propagation of Sound in Porous Media: Modelling Sound Absorbing Materials. Wiley, ChichesterAntebas AG, Denia FD, Pedrosa AM, Fuenmayor FJ (2013) A finite element approach for the acoustic modelling of perforated dissipative mufflers with non-homogeneous properties. Math Comput Model 57:1970–1978Atkinson KE (1989) An Introduction to Numerical Analysis. John Wiley & Sons, 2nd EditionAzevedo FM, Moura MS, Vicente WM, Picelli R, Pavanello R (2017) Topology optimization of reactive acoustic mufflers using a bi-directional evolutionary optimization method. Struct Multidiscip Optim 58:2239–2252Barbieri R, Barbieri N (2006) Finite element acoustic simulation based shape optimization of a muffler. Appl Acoust 67:346–357Chang YC, Chiu MC (2008) Shape optimization of one-chamber perforated plug/non-plug mufflers by simulated annealing method. Int J Numer Methods Eng 74:1592–1620Chiu M (2011) Optimization design of hybrid mufflers on broadband frequencies using the genetic algorithm. Arch Acoust 36:795–822Christie DRA (1976) Measurement of the acoustic properties of a sound-absorbing material at high temperatures. J Sound Vib 46:347–355De Lima KF, Lenzi A, Barbieri R (2011) The study of reactive silencers by shape and parametric optimization techniques. Appl Acoust 72:142–150Delany ME, Bazley EN (1970) Acoustical properties of fibrous absorbent materials. Appl Acoust 3:105–116Denia FD, Sánchez-Orgaz EM, Baeza L, Kirby R (2016) Point collocation scheme in mufflers with temperature gradient and mean flow. J Comput Appl Math 291:127–141Denia FD, Sánchez-Orgaz EM, Martínez-Casas J, Kirby R (2015) Finite element based acoustic analysis of dissipative mufflers with high temperature and thermal-induced heterogeneity. Finite Elem Anal Des 101:46–57Denia FD, Selamet A, Fuenmayor FJ, Kirby R (2007) Acoustic attenuation performance of perforated dissipative mufflers with empty inlet/outlet extensions. J Sound Vib 302:1000–1017Denia FD, Selamet A, Martínez MJ, Torregrosa AJ (2006) Hybrid mufflers with short lateral chambers: analytical, numerical and experimental studies. In: 13th International Congress on Sound and Vibration (ICSV 13) ViennaFok VA (1963) in Russian. Alternatively, see S.N. Rschevkin, A course of lectures on the theory of sound, Pergamon, LondonIngard KU (1953) On the design of acoustic resonators. J Acoust Soc Am 25:1037–1061Jensen JS (2012) Topology optimization. In: Romeo F, Ruzzene M (eds) Wave Propagation in Linear and Nonlinear Periodic Media. CISM Courses and Lectures, vol 540. Springer, ViennaKirby R, Cummings A (1999) Prediction of the bulk acoustic properties of fibrous materials at low frequencies. Appl Acoust 56:101–125Kirby R, Denia FD (2007) Analytic mode matching for a circular dissipative muffler containing mean flow and a perforated pipe. J Acoust Soc Am 122:3471–3482Kirby R, Williams PT, Hill J (2013) The effect of temperature on the acoustic performance of splitter silencers. In: 42nd International Congress and Exposition on Noise Control Engineering – INTERNOISE, 7, pp 5826–5833Lee JS, Göransson P, Kim YY (2015) Topology optimization for three-phase materials distribution in a dissipative expansion chamber by unified multiphase modeling approach. Comput Methods Appl Mech Eng 287:191–211Lee JW (2015) Optimal topology of reactive muffler achieving target transmission loss values: Design and experiment. Appl Acoust 88:104–113Lee JW, Kim YY (2009) Topology optimization of muffler internal partitions for improving acoustical attenuation performance. Int J Numer Methods Eng 80:455–477Lee SH, Ih JG (2003) Empirical model of the acoustic impedance of a circular orifice in grazing mean flow. J Acoust Soc Am 114:98–113Munjal ML (2014) Acoustics of Ducts and Mufflers, John Wiley & Sons, 2nd EdnPeat KS, Rathi KL (1995) A finite element analysis of the convected acoustic wave motion in dissipative mufflers. J Sound Vib 184:529–545Pierce AD (1990) Wave equation for sound in fluids with unsteady inhomogeneous flow. J Acoust Soc Am 87:2292–2299Rao SS (2011) The Finite Element Method in Engineering, Butterworth-Heinemann. 5th EditionSánchez-Orgaz EM (2016) Advanced numerical techniques for the acoustic modelling of materials and noise control devices in the exhaust system of internal combustion engines, Ph. D, Thesis, Universitat Politècnica de ValènciaSelamet A, Lee IJ, Huff NT (2003) Acoustic attenuation of hybrid mufflers. J Sound Vib 262:509–527Selamet A, Xu MB, Lee IJ, Huff NT (2005) Dissipative expansion chambers with two concentric layers of fibrous material. International Journal of Vehicle Noise and Vibration 1:341– 357Selamet A, Xu MB, Lee IJ, Huff NT (2006) Effect of voids on the acoustics of perforated dissipative mufflers. International Journal of Vehicle Noise and Vibration 2:357–372Sigmund O (2007) Morphology-based black and white filters for topology optimization. Struct Multidiscip Optim 33:401–424Sigmund O, Maute K (2013) Topology optimization approaches. Struct Multidiscip Optim 48:1031–1055Stolpe M, Svanberg K (2001) An alternative interpolation scheme for minimum compliance optimization. Struct Multidiscip Optim 22:116–124Svanberg K (1987) The method of moving asymptotes - a new method for structural optimization. Int J Numer Methods Eng 24:359– 373Williams PT, Kirby R, Malecki C, Hill J (2014) Measurement of the bulk acoustic properties of fibrous materials at high temperatures. Appl Acoust 77:29–36Yedeg EL, Wadbro E, Berggren M (2016) Interior layout topology optimization of a reactive muffler. Struct Multidiscip Optim 53:645–656Yoon GH (2013) Acoustic topology optimization of fibrous material with Delany–Bazley empirical material formulation. J Sound Vib 332:1172–1187Zienkiewicz OC, Taylor RL, Zhu JZ (2005) The Finite Element Method: its Basis and Fundamentals. Elsevier Butterworth-Heinemann, BurlingtonZoutendijk G (1960) Methods of Feasible Directions. Elsevier, Amsterda

Fracturas de extremidad proximal de cubito en el niño

Las fracturas y epifisiolisis proximales de cubito, son lesiones raras y cuando se producen suelen estar mínimamente ó no desplazadas, pudiendo ser tratadas de forma conservadoras. En los casos en que existe desplazamiento significativo, requieren reducción abierta y osteosíntesis. Independientemente del tipo de tratamiento utilizado, el resultado final suele ser satisfactorio. Realizamos un estudio retrospectivo de 13 casos de fractura-epifisiolisis de extremo proximal de cubito, ocurridas durante el periodo 1992-2001. Nuestro objetivo es analizar los resultados obtenidos en el tratamiento de las lesiones y realizar una revisión bibliográfica, teniendo en cuenta los distintos métodos de clasificación, valoración de resultados y las valoraciones descritas para la iniciación de tratamiento quirúrgico de estas lesiones.The epiphysiolisis and proximal lunar fractures in children rare injuries and usually the aren't displaced. In these cases they can be managed nonoperatively. If there's a marked displacement, open reduction and internal fixation is mandatory. The final outcome uses to be successful despite the management; 13 patients with epiphysiolisis or fracture of the proximal ulna between 1992-2001 ere revised. Our aim is to evaluate our outcomes and reviewed the literatur

Development of a calibration satellite for a CMB telescope flying in formation about L2 libration point

Trabajo presentado a la 8th European Conference for aeronautics and aerospace sciences (EUCASS), celebrada en Madrid (España) del 1 al 4 de julio de 2019.The new generation of cosmic microwave background (CMB) telescopes have reached unprecedented levels of sensitivity. These telescopes measure several cosmological parameters with different levels of accuracy. In particular, considerable effort has been made to measure the B-mode polarization, which is related to the inflationary process of the universe. The power spectrum of this signal is about four orders of magnitude fainter than the CMB temperature power spectrum. Due to the signal weakness, the instruments must be subjected to calibration processes before and after launching. Additionally, data from the same sky area is gathered repeatedly to mitigate during data analysis the systematic errors induced by instruments. Celestial sources are often used as an external reference for calibration after launch, but these sources are not perfectly characterized. In this paper we study the concept of using a calibration satellite (CalSat) flying in formation with a CMB telescope in an orbit located at the second Lagrange point (L2). The CalSat is conceived as a micro satellite (10-100 kg) and serves as a perfectly known source of a reference signal to reduce the polarization angle measurement uncertainty. According to the scanning law followed by the telescope, the influence of the relative position between the spacecrafts in the calibration process is studied. The relative motion of the spacecrafts is considered with a simplified dynamic model. Based on the mission requirements, the different subsystems are sized and a preliminary design to evaluate the feasibility is obtained. The design has been carried out under the principle of reducing at minimum the impact on the telescope architecture. It would require to be launched along with the telescope to reach L2 at the same time and being able to communicate with the telescope. This new calibration element could have a huge impact on the performance of this kind of missions, providing a significant improvement in the measurements accuracy without requiring new and costly technological developments.The authors would like to thank Spanish Ministry for Economy and Competitiveness (currently Ministry of Science,innovation and Universities) for the financial support provided under the projects with references ESP2017-92135-EXP all co-financed with EU FEDER funds

Acoustic modelling of large aftertreatment devices with multimodal incident sound fields

[EN] The influence of multimodal incident sound fields on the acoustic behaviour of large aftertreatment devices (ATD) is analysed in detail. The mode matching method is applied to the compatibility conditions of the three-dimensional (3D) acoustic fields at the device geometric discontinuities, leading to the computation of the complex wave amplitudes in all the subdomains involved and the corresponding transmission loss (TL). To have a realistic model, 3D propagation must be considered in the inlet/outlet ducts and chambers, while 1D wave propagation has to be assumed along the small capillaries of the catalytic converter/particulate filter monoliths of the ATD; therefore, these monoliths can be replaced by plane wave four pole transfer matrices from an acoustical point of view [1]. On the other hand, for large ATD inlet ducts such as those found in heavy-duty and off-road engines, the usual models with plane incident wave excitation are not accurate since the onset of higher order incident modes in the inlet duct is expected for the frequency range of interest. Therefore, a TL variation is likely to occur depending on these modes, similar to the results found in large dissipative silencers [2]. Results are presented for three different multimodal incident sound field hypotheses [3]: equal modal amplitude (EMA), equal modal power (EMP) and equal modal energy density (EMED). A relevant influence on the sound attenuation is found for the test problems considered in the current investigation. References [1] Denia, F. D., Martínez-Casas, J., Carballeira, J., Nadal, E., Fuenmayor, F. J., Computational performance of analytical methods for the acoustic modelling of automotive exhaust devices incorporating monoliths. Journal of Computational and Applied Mathematics, 330: 995--1006, 2018. [2] Kirby, R., Lawrie, J. B., A point collocation approach to modelling large dissipative silencers. Journal of Sound and Vibration, 286: 313--339, 2005. [3] Mechel, F. P., Formulas of Acoustics. Berlin, Springer, 2008.The authors gratefully acknowledge Grants PID2020-112886RA-I00 and PID2020-118013RB-C21 funded by MCIN/AEI/10.13039/501100011033 and Project PROMETEO/2021/046 from Generalitat Valenciana.Denia, FD.; Sánchez-Orgaz, EM.; Martínez Casas, J.; Carballeira, J.; Baeza González, LM. (2021). Acoustic modelling of large aftertreatment devices with multimodal incident sound fields. Universitat Politècnica de València. 208-215. http://hdl.handle.net/10251/19055620821

Modelo mejorado de interacción vehículo ferroviario-vía negociando una curva en el dominio de la alta frecuencia

[ES] La interacción dinámica entre un vehículo ferroviario y la vía se presenta como un problema complejo dado el acoplamiento vibracional entre ambos subsistemas a través de las fuerzas que aparecen en el área de contacto. Aunque el transporte ferroviario se considera generalmente respetuoso con el medio ambiente, el ruido proveniente de la interacción rueda-carril es un inconveniente relevante que ha recibido especial atención en las últimas décadas. Los chirridos en curva, ruido de fuerte carácter tonal en el dominio de las altas frecuencias, aparecen generalmente cuando el tren negocia una curva cerrada. Con el objetivo de alcanzar una mejor comprensión del fenómeno, se han implementado modelos de Elementos Finitos (EF) de la rueda para incluir su flexibilidad y extender así el rango de frecuencias; recientes trabajos han introducido también los efectos inerciales debidos a la rotación del eje. Por otra parte, se ha desarrollado un modelo flexible de vía cíclica mediante un tipo de elementos finitos conocido como Moving Elements (ME), que permite refinar la malla únicamente alrededor del área de contacto. En el presente artículo, se han llevado a cabo distintas simulaciones en el dominio del tiempo para circulación en vía curva considerando dos radios de curva y cuatro coeficientes de fricción distintos, evaluándose las fuerzas de contacto tangenciales en busca de inestabilidades que puedan estar asociadas a este fenómeno de chirridos en curva. A su vez, se ha estudiado la influencia de los efectos giroscópicos asociados a la rotación del eje.Los autores desean agradecer el apoyo recibido del Ministerio de Economía y Competitividad y del Fondo Europeo de Desarrollo Regional mediante el proyecto TRA2013-45596-C2-1-R, así como a la Generalitat Valenciana mediante los proyectos Prometeo/2016/007 y GV/2016/011 de la Conselleria d¿Educació, Investigació, Cultura i Esport.Giner Navarro, J.; Martínez Casas, J.; Denia, FD.; Carballeira, J. (2017). Modelo mejorado de interacción vehículo ferroviario-vía negociando una curva en el dominio de la alta frecuencia. International Center for Numerical Methods in Engineering (CIMNE). 1-15. http://hdl.handle.net/10251/179958S11

Modelo integral de interacción vehículo-vía que contempla la dinámica de baja y alta frecuencia para circulación en vía recta, transición y curva

[ES] Actualmente hay un elevado interés en analizar ciertos fenómenos ferroviarios que surgen de la interacción dinámica vehículo-vía cuando se negocia una curva, como son el ruido de rodadura, los chirridos y la corrugación de los carriles en curva. En la literatura se detallan, por un lado, modelos de baja frecuencia (hasta 20 Hz) que formulan la dinámica de todo el vehículo completo, y por otro lado, modelos de interacción de alta frecuencia que describen la dinámica de las masas no suspendidas. Sin embargo, para estudiar con precisión los fenómenos citados anteriormente, no sólo debe incluirse la dinámica de alta frecuencia asociada a la flexibilidad de las masas no suspendidas, sino que también deben adoptarse las hipótesis más avanzadas de los modelos de baja frecuencia, fundamentalmente en lo que respecta a la geometría del contacto y a la dinámica del vehículo completo. El presente trabajo pretende ser una contribución para resolver los problemas anteriormente indicados a través del modelado de la interacción dinámica vehículo-vía en curva. Para ello, el modelo contempla tanto la dinámica de alta frecuencia asociada a la flexibilidad de los ejes montados y la vía como la componente de baja frecuencia referente a las masas suspendidas, considerando que el vehículo circula por vía recta, transición y curva. Se llevan a cabo simulaciones con el modelo de interacción vehículo-vía propuesto para diferentes condiciones de circulación en curva y diferentes casos propuestos en el Benchmark de Manchester. Finalmente, los resultados se presentan, discuten y comparan con programas comerciales basados en dinámica de sistemas multicuerpo.Los autores desean agradecer el apoyo recibido del Ministerio de Economía y Competitividad y del Fondo Europeo de Desarrollo Regional mediante el proyecto TRA2013-45596-C2-1-R, así como a la Generalitat Valenciana mediante los proyectos Prometeo/2016/007 y GV/2016/011 de la Conselleria d¿Educació, Investigació, Cultura i Esport.Martínez Casas, J.; Carballeira, J.; Denia, FD.; Baeza González, LM. (2017). Modelo integral de interacción vehículo-vía que contempla la dinámica de baja y alta frecuencia para circulación en vía recta, transición y curva. International Center for Numerical Methods in Engineering (CIMNE). 1-10. http://hdl.handle.net/10251/180307S11

Development of a patient rated scale for mental health global state for use during humanitarian interventions

Funding: Médecins Sans FrontièresWe present the results of a cross-cultural validation of the Mental Health Global State (MHGS) scale for adults and adolescents (<14 years old). We performed two independent studies using mixed methods among 103 patients in Hebron, Occupied Palestinian Territories and 106 in Cauca, Colombia. The MHGS was analyzed psychometrically, sensitivity and specificity, ability to detect clinically meaningful change, compared to the Clinical Global Impression-Severity scale (CGI-S). Principal component analysis was used to reduce the number of questions after data collection. The scale demonstrated good internal consistency, with a Cronbach alpha score of 0.80 in both settings. Test retest reliability was high, ICC 0.70 (95% CI [0.41-0.85]) in Hebron and 0.87 (95% CI [0.76-0.93]) in Cauca; inter-rater reliability was 0.70 (95% CI [0.42-0.85]) in Hebron and 0.76 (95% CI [0.57-0.88]) in Cauca. Psychometric properties were also good, and the tool demonstrated a sensitivity of 85% in Hebron and 100% in Cauca, with corresponding specificity of 80% and 79%, when compared to CGI-S. The MHGS showed promising results to assess global mental health thereby providing an additional easy to use tool in humanitarian interventions. Additional work should focus on validation in at least one more context, to adhere to best practices in transcultural validation

Active Re-identification Attacks on Periodically Released Dynamic Social Graphs

Active re-identification attacks pose a serious threat to privacy-preserving social graph publication. Active attackers create fake accounts to build structural patterns in social graphs which can be used to re-identify legitimate users on published anonymised graphs, even without additional background knowledge. So far, this type of attacks has only been studied in the scenario where the inherently dynamic social graph is published once. In this paper, we present the first active re-identification attack in the more realistic scenario where a dynamic social graph is periodically published. The new attack leverages tempo-structural patterns for strengthening the adversary. Through a comprehensive set of experiments on real-life and synthetic dynamic social graphs, we show that our new attack substantially outperforms the most effective static active attack in the literature by increasing the success probability of re-identification by more than two times and efficiency by almost 10 times. Moreover, unlike the static attack, our new attack is able to remain at the same level of effectiveness and efficiency as the publication process advances. We conduct a study on the factors that may thwart our new attack, which can help design graph anonymising methods with a better balance between privacy and utility

Modelado numérico eficiente del comportamiento acústico de silenciadores de escape con material absorbente granular

[ES] En este trabajo se presenta una técnica numérica precisa y de bajo coste computacional para el análisis del comportamiento acústico de silenciadores de escape con sección transversal arbitraria y material absorbente granular en su interior. Se plantea la utilización de dicho material como una posible alternativa a las tradicionales fibras utilizadas en silenciadores de tipo disipativo. Entre las ventajas de los materiales granulares en la aplicación concreta planteada aquí, cabe destacar la ausencia de su emisión al medio ambiente como consecuencia del arrastre provocado por los gases de escape y la posibilidad de conseguir configuraciones geométricas adaptables a la fuente de ruido mediante un proceso de llenado/vaciado in situ relativamente sencillo. La caracterización acústica del material granular se lleva a cabo mediante la utilización de propiedades como su impedancia y número de onda [1], a partir de las cuales pueden obtenerse la densidad y velocidad del sonido equivalentes, complejas y dependientes de la frecuencia. Con el objetivo de reducir el coste computacional de una formulación completa 3D de EF, se presenta una técnica computacionalmente eficiente basada en un problema de autovalores 2D y el método de ajuste modal, en su versión numérica para contemplar la posibilidad de secciones transversales de geometría arbitraria y propiedades no homogéneas [2, 3]. Para ello, en primer lugar, se resuelve el problema de autovalores y autovectores de la sección transversal mediante un planteamiento 2D de EF. Posteriormente, se acoplan los campos de presión y velocidad acústica en las discontinuidades geométricas mediante ajuste modal. Hallada la solución completa de la ecuación de ondas en el interior del silenciador, se cuantifican sus prestaciones acústicas con distintos niveles de llenado de material absorbente granular. REFERENCIAS [1] P. Cobo and F. Simón, A comparison of impedance models for the inverse estimation of the non-acoustical parameters of granular absorbers , Applied Acoustics, 104, 119-126 (2016). [2] R. Kirby, A comparison between analytic and numerical methods for modelling automotive and dissipative silencers with mean flow , Journal of Sound and Vibration, 325, 565-582 (2009). [3] F. D. Denia, E. M. Sánchez-Orgaz, L. Baeza and R. Kirby, Point collocation scheme in silencers with temperature gradient and mean flow , Journal of Computational and Applied Mathematics, 291, 127-141 (2016).Proyecto realizado con la Ayuda Fundación BBVA a Investigadores y Creadores Culturales 2016. La Fundación BBVA no se responsabiliza de las opiniones, comentarios y contenidos incluidos en el proyecto y/o los resultados derivados del mismo, los cuales son total y absoluta responsabilidad de los autoresSánchez Orgaz, EM.; Denia, FD.; Martínez Casas, J.; Baeza González, LM. (2017). Modelado numérico eficiente del comportamiento acústico de silenciadores de escape con material absorbente granular. International Center for Numerical Methods in Engineering (CIMNE). 12-22. http://hdl.handle.net/10251/179954S122