Motion-Based Design of Passive Damping Devices to Mitigate Wind-Induced Vibrations in Stay Cables

Wind action can induce large amplitude vibrations in the stay cables of bridges. To reduce the vibration level of these structural elements, different types of passive damping devices are usually installed. In this paper, a motion-based design method is proposed and implemented in order to achieve the optimum design of different passive damping devices for stay cables under wind action. According to this method, the design problem is transformed into an optimization problem. Thus, its main aim is to minimize the different terms of a multi-objective function, considering as design variables the characteristic parameters of each considered passive damping device. The multi-objective function is defined in terms of the scaled characteristic parameters, one single-function for each parameter, and an additional function that checks the compliance of the considered design criterion. Genetic algorithms are considered as a global optimization method. Three passive damping devices have been studied herein: viscous, elastomeric and friction dampers. As a benchmark structure, the Alamillo bridge (Seville, Spain), is considered in order to validate the performance of the proposed method. Finally, the parameters of the damping devices designed according to this proposal are successfully compared with the results provided by a conventional design method

Sistemas de control pasivo en cables de puentes atirantados. Diseño basado en el rendimiento

En las últimas décadas se ha producido un importante auge de los puentes atirantados, convirtiéndose en alternativas económicas frente a otras tipologías estructurales. En dichos puentes, juegan un papel fundamental los cables, que constituyen elementos flexibles y con un bajo nivel de amortiguamiento. Esto hace que sean propensos a sufrir vibraciones, por lo que se han tenido que realizar reparaciones en numerosas ocasiones, debiendo tomar en muchos casos medidas de mitigación externas. En el presente trabajo, se abordan los aspectos teóricos más importantes en el estudio de fenómenos vibratorios en cables, pasando por las posibles medidas de mitigación. En el primer apartado, se realiza una revisión sobre los mecanismos de generación de vibraciones en cables. Se presta especial atención a los fenómenos relacionados con la acción del viento, definiendo una serie de parámetros aerodinámicos que permiten caracterizar la respuesta de los cables ante dichas acciones. Posteriormente, en el segundo apartado, se aborda la problemática asociada a las vibraciones en los tirantes de estructuras, ya que estas pueden suponer un problema a largo plazo debido a daños por fatiga, rotura de elementos de los anclajes y problemas de confort. Este último aspecto ha sido considerado en ocasiones de menor importancia, sin embargo, los movimientos excesivos en los tirantes crean alarma social y falta de seguridad, por lo que se definirán unas tolerancias de usuario o requerimientos estructurales, que se materializan en unos límites de desplazamientos. Para ello se parte de los datos aportados por diversos estudios que han sido recogidos en la bibliografía. Una vez definidos los requerimientos de la estructura y sus parámetros de control asociados, se abordan las diferentes medidas de mitigación de vibraciones, prestando especial atención a los sistemas de amortiguación de tipo pasivo. Se realiza una revisión de los sistemas amortiguadores presentes en el mercado, atendiendo a las principales características de cada uno de ellos y a los métodos de diseño que se han venido utilizando a lo largo de los últimos años para dimensionar estos sistemas. En este apartado, se plantea un enfoque de diseño diferente a los tradicionales, que se englobaría en lo que se conoce como “Diseño basado en el rendimiento” y que pretende aprovechar al máximo la capacidad de los amortiguadores para cumplir las condiciones impuestas en las diferentes normativas. Para poner en práctica este procedimiento de diseño, se aplicará a un caso real de puente atirantado: el Puente del Alamillo. Se realiza un modelo de elementos finitos en el que se incorporarán las propiedades mecánicas de los cables y de los diferentes tipos de amortiguadores considerados. Posteriormente, se lleva a cabo un proceso de optimización mediante algoritmos genéticos, con el fin de obtener los parámetros de los amortiguadores que cumplan las condiciones impuestas. Con los resultados obtenidos para cada tipo de amortiguador, se realiza un estudio comparativo, evaluando la eficacia de cada uno de los sistemas. Los parámetros de los amortiguadores optimizados con el enfoque de diseño presentado en este documento se han comparado con los resultados obtenidos empleando otras metodologías. Por último, se presentan una serie de conclusiones extraídas de los diferentes análisis desarrollados.Universidad de Sevilla. Máster en Ingeniería de Caminos, Canales y Puerto

Enseñanza en la universidad: Percepciones de profesores y alumnos

El contenido de este articulo versa sobre los resultados obtenidos en una investigación realizada con estudiantes y profesores de la Universidad de Sevilla. El propósito que perseguía dicha investigación era el de aportar algunos datos sobre el complejo proceso de enseñanza-aprendizaje que tiene lugar en la universidad y posibilitar con ello la organización de estrategias institucionales de apoyo a los estudiantes en ese proceso. Se presentan, por una parte, el diseño de la investigación y los resultados obtenidos de varias muestras de profesores y de estudiantes de todos los centros de la Universidad de Sevilla, mediante técnicas de corte cualitativo y cuantitativo. Dichos resultados hacen referencia a la percepción que docentes y estudiantes tienen sobre las exigencias del trabajo en la universidad, las características del proceso de enseñanza-aprendizaje que se oferta en los centros, sobre las causas del éxito y fracaso académico y sobre las posibles medidas a poner en práctica para potenciar el éxito y disminuir el fracaso. Finalmente se presentan las principales conclusiones del estudio en forma de propuestas de actuaciones docentes e institucionales tendentes a optimizar la docencia y el aprendizaje en la universidad.This article is about the resulta obtained in a research done with students and professors at the University of Sevilla. The research's purpose was te) add some data on the complex teaching-leaming process which takes place in the university, and to make possible the organization of institutional strategies to support students in this process. On one hand, we present the research's design and the resulta obtained from several samples of professors and students from all educational establishments of Sevillas University, through qualitative and quantitative techniques. The resulta show professors and students - perceptions on the demanda of the work done at the university, the characteristics of the teaching-leaming process offered in the educational institutions, the causes of academic success and failure and measures to take in order to promote success and decre-ase failure. Finally, we present the main conclusions of the study in the shape of proposals of teaching and institutional performances, aimed at optimizing teaching and leaming in the university

The sound of a Martian dust devil

Dust devils (convective vortices loaded with dust) are common at the surface of Mars, particularly at Jezero crater, the landing site of the Perseverance rover. They are indicators of atmospheric turbulence and are an important lifting mechanism for the Martian dust cycle. Improving our understanding of dust lifting and atmospheric transport is key for accurate simulation of the dust cycle and for the prediction of dust storms, in addition to being important for future space exploration as grain impacts are implicated in the degradation of hardware on the surface of Mars. Here we describe the sound of a Martian dust devil as recorded by the SuperCam instrument on the Perseverance rover. The dust devil encounter was also simultaneously imaged by the Perseverance rover's Navigation Camera and observed by several sensors in the Mars Environmental Dynamics Analyzer instrument. Combining these unique multi-sensorial data with modelling, we show that the dust devil was around 25m large, at least 118m tall, and passed directly over the rover travelling at approximately 5ms-1. Acoustic signals of grain impacts recorded during the vortex encounter provide quantitative information about the number density of particles in the vortex. The sound of a Martian dust devil was inaccessible until SuperCam microphone recordings. This chance dust devil encounter demonstrates the potential of acoustic data for resolving the rapid wind structure of the Martian atmosphere and for directly quantifying wind-blown grain fluxes on Mars.We are most grateful for the support of the Mars 2020 project team, including hardware and operation teams. This project was supported in the US by the NASA Mars Exploration Program, and in France by CNES. It is based on observations with SuperCam embarked on Perseverance (Mars2020). The research carried out at the Jet Propulsion Laboratory, California Institute of Technology, is under a contract with the National Aeronautics and Space Administration (80NM0018D0004). The JPL co-author (M.T.) acknowledges funding from NASA’s Space Technology Mission Directorate and the Science Mission Directorate. A. V-R is supported by the Spanish State Research Agency (AEI) Project No. MDM-2017-0737 Unidad de Excelencia “María de Maeztu”- Centro de Astrobiología (INTA-CSIC), and by the Comunidad de Madrid Project S2018/NMT-4291 (TEC2SPACE-CM). R.H. and A.S-L. were supported by Grant PID2019-109467GB-I00 funded by MCIN/AEI/10.13039/501100011033/ and by Grupos Gobierno Vasco IT1742-22. A.M. was supported by Grant PRE2020-092562 funded by MCIN/AEI/10.13039/501100011033 and by “ESF Investing in your future”. R.L. acknowledges InSight PSP Grant 80NSSC18K1626 as well as the Mars 2020 project. B.C. is supported by the Director’s Postdoctoral Fellowship from the Los Alamos National Laboratory, grant 20210960PRD3. JA.RM., M.M, J.T and J.G-E were supported by MCIN/AEI’s Grant RTI2018-098728-B-C31

The Mars Environmental Dynamics Analyzer, MEDA. A Suite of Environmental Sensors for the Mars 2020 Mission

86 pags., 49 figs., 24 tabs.NASA’s Mars 2020 (M2020) rover mission includes a suite of sensors to monitor current environmental conditions near the surface of Mars and to constrain bulk aerosol properties from changes in atmospheric radiation at the surface. The Mars Environmental Dynamics Analyzer (MEDA) consists of a set of meteorological sensors including wind sensor, a barometer, a relative humidity sensor, a set of 5 thermocouples to measure atmospheric temperature at ∼1.5 m and ∼0.5 m above the surface, a set of thermopiles to characterize the thermal IR brightness temperatures of the surface and the lower atmosphere. MEDA adds a radiation and dust sensor to monitor the optical atmospheric properties that can be used to infer bulk aerosol physical properties such as particle size distribution, non-sphericity, and concentration. The MEDA package and its scientific purpose are described in this document as well as how it responded to the calibration tests and how it helps prepare for the human exploration of Mars. A comparison is also presented to previous environmental monitoring payloads landed on Mars on the Viking, Pathfinder, Phoenix, MSL, and InSight spacecraft.This work has been funded by the Spanish Ministry of Economy and Competitiveness, through the projects No. ESP2014-54256-C4-1-R (also -2-R, -3-R and -4-R) and AYA2015-65041-P; Ministry of Science, Innovation and Universities, projects No. ESP2016-79612-C3-1-R (also -2-R and -3-R), ESP2016-80320-C2-1-R, RTI2018-098728-B-C31 (also -C32 and -C33) and RTI2018-099825-B-C31; Instituto Nacional de Técnica Aeroespacial; Ministry of Science and Innovation’s Centre for the Development of Industrial Technology; Grupos Gobierno Vasco IT1366-19; and European Research Council Consolidator Grant no 818602. The US co-authors performed their work under sponsorship from NASA’s Mars 2020 project, from the Game Changing Development program within the Space Technology Mission Directorate and from the Human Exploration and Operations Directorate

Radiation and Dust Sensor for Mars Environmental Dynamic Analyzer Onboard M2020 Rover

32 pags., 26 figs., 3 tabs. -- This article belongs to the Section Remote SensorsThe Radiation and Dust Sensor is one of six sensors of the Mars Environmental Dynamics Analyzer onboard the Perseverance rover from the Mars 2020 NASA mission. Its primary goal is to characterize the airbone dust in the Mars atmosphere, inferring its concentration, shape and optical properties. Thanks to its geometry, the sensor will be capable of studying dust-lifting processes with a high temporal resolution and high spatial coverage. Thanks to its multiwavelength design, it will characterize the solar spectrum from Mars' surface. The present work describes the sensor design from the scientific and technical requirements, the qualification processes to demonstrate its endurance on Mars' surface, the calibration activities to demonstrate its performance, and its validation campaign in a representative Mars analog. As a result of this process, we obtained a very compact sensor, fully digital, with a mass below 1 kg and exceptional power consumption and data budget features.This work has been funded with the help of the Spanish National Research, Development and Innovation Program, through the grants RTI2018-099825-B-C31, ESP2016-80320-C2-1-R and ESP2014-54256-C4-3-R. DT acknowledges the financial support from the Comunidad de Madrid for an “Atracción de Talento Investigador” grant (2018-T2/TIC10500). ASL is supported by Grant PID2019-109467GB-I00 funded by MCIN/AEI/10.13039/501100011033/ and by Grupos Gobierno Vasco IT1366-19. The US co-authors performed their work under sponsorship from NASA’s Mars 2020 project, from the Game Changing Development program within the Space Technology Mission Directorate, and from the Human Exploration and Operations Directorate.Peer reviewe

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements

The Mars Environmental Dynamics Analyzer, MEDA. A Suite of Environmental Sensors for the Mars 2020 Mission

86 pags, 49 figs, 24 tabsNASA's Mars 2020 (M2020) rover mission includes a suite of sensors to monitor current environmental conditions near the surface of Mars and to constrain bulk aerosol properties from changes in atmospheric radiation at the surface. The Mars Environmental Dynamics Analyzer (MEDA) consists of a set of meteorological sensors including wind sensor, a barometer, a relative humidity sensor, a set of 5 thermocouples to measure atmospheric temperature at ∼1.5 m and ∼0.5 m above the surface, a set of thermopiles to characterize the thermal IR brightness temperatures of the surface and the lower atmosphere. MEDA adds a radiation and dust sensor to monitor the optical atmospheric properties that can be used to infer bulk aerosol physical properties such as particle size distribution, non-sphericity, and concentration. The MEDA package and its scientific purpose are described in this document as well as how it responded to the calibration tests and how it helps prepare for the human exploration of Mars. A comparison is also presented to previous environmental monitoring payloads landed on Mars on the Viking, Pathfinder, Phoenix, MSL, and InSight spacecraft.This work has been funded by the Spanish Ministry of Economy and Competitiveness, through the projects No. ESP2014-54256-C4-1-R (also -2-R, -3-R and -4-R) and AYA2015-65041-P; Ministry of Science, Innovation and Universities, projects No. ESP2016-79612-C3-1-R (also -2-R and -3-R), ESP2016-80320-C2-1-R, RTI2018-098728-B-C31 (also -C32 and -C33) and RTI2018-099825-B-C31; Instituto Nacional de Tecnica Aeroespacial; Ministry of Science and Innovation's Centre for the Development of Industrial Technology; Grupos Gobierno Vasco IT1366-19; and European Research Council Consolidator Grant no 818602.Peer reviewe