Optimal TMD-based control strategy for human-induced vibrations

Congreso celebrado en la Escuela de Arquitectura de la Universidad de Sevilla desde el 24 hasta el 26 de junio de 2015.Civil engineering structures such as office floors and singular footbridges may present vibration modes locally spatially distributed with closely spaced natural frequencies. A set of tuned mass dampers (TMDs) may control several vibration modes at the same time and make the control system more robust. However, under these circumstances, Den Hartog’s theory may not be applicable. In this paper, an optimum algorithm to design a set of TMDs is proposed to cancel effectively human-induced vibrations for floor structures. A comparative study is carried out in terms of the same performance indicator to find the optimum system, considering different configurations by Den Hartog’s classical approach and this optimal algorithm. This proposed algorithm will contribute to motivate future researches on passive vibration control (PVC) for floor vibrations with closely spaced natural frequencies

Acceleration feedback control of human-induced floor vibrations

Active vibration control (AVC) via a proof-mass actuator is considered to be a suitable technique for the mitigation of vibrations caused by human motions in floor structures. It has been observed that actuator dynamics strongly influence structure dynamics despite considering collocated actuator/sensor control. The well-known property of the interlacing of poles and zeros of a collocated control system is no longer accomplished. Therefore, velocity-based feedback control, which has been previously used by other researchers, might not be a good solution. This work presents a design process for a control scheme based on acceleration feedback control with a phase-lag compensator, which will generally be different from an integrator circuit. This first-order compensator is applied to the output (acceleration) in such a way that the relative stability and potential damping to be introduced are significantly increased accounting for the interaction between floor and actuator dynamics. Additionally, a high-pass filter designed to avoid stroke saturation is applied to the control signal. The AVC system designed according to this procedure has been assessed in simulation and successfully implemented in an in-service open-plan office floor. The actual vibration reductions achieved have been approximately 60% for walking tests and over 90% for a whole-day vibration monitoring. (C) 2009 Elsevier Ltd. All rights reserved

Dynamic characterization, modelling and model updating of a lively footbridge

Congreso celebrado en la Escuela de Arquitectura de la Universidad de Sevilla desde el 24 hasta el 26 de junio de 2015.This paper presents finite element analyses, experimental measurements and finite element model updating of a lively footbridge consisting on an arched main span 40m long and several shorter access spans. Firstly, a finite element model of the bridge is created in a commercial CAE software and static and modal response are numerically estimated. Then, experimental measurements using static loading test and ambient vibration tests are performed. Initial finite element model is adjusted to match with the static response by fitting some selected parameters. Modal parameters (natural frequencies, mode shapes and modal damping) are extracted and after that the current finite element model is updated. Among the selected parameters, semi-rigid connections in some joints, concrete Young’s modulus and mass density of the concrete deck (to account on pavement mass) are selected to minimize the differences between numerical and experimental structural response. Sensitivity of the modal response to these parameters is also shown. At the end of the study, good agreement between analytical and experimental results is achieved, revealing the suitability of the entire process

Serviceability conditions of pedestrian structures using a simplified moving mass model

Congreso celebrado en la Escuela de Arquitectura de la Universidad de Sevilla desde el 24 hasta el 26 de junio de 2015.A simple mechanical model for pedestrian loading, consisting on a mass with a single degree of freedom that moves at constant speed along the footbridge, is presented. The footbrigde is modelled using a reduced number of beam 2D finite elements, simply supported at its ends. The dynamic interaction is ensured through direct requirement of contact conditions between the mass and the corresponding interpolated point in the beam. When the beam is massive enought, the results are similar to those obtained with models of mobile forces. However, if the beam is lightweight, the effect of the mass of the pedestrian can be significant, resulting in a more realistic modelling. The coupled model allows to study the interaction between the pedestrian and the structure and the results can be used to estimate by simulation the serviceability conditions of this type of slender structures under pedestrian loading

A common framework for the robust design of tuned mass damper techniques to mitigate pedestrian-induced vibrations in lively footbridges

The dynamic response of modern slender footbridges is usually sensitive to both the pedestrian actions and the uncertainties associated with their inherent structural behavior. Thus, tuned mass dampers have been widely integrated in the design of these structures to guarantee the fulfillment of the vibration serviceability limit state during their overall life cycle. Three different techniques of tuned mass dampers (active, semi-active and passive) are usually considered for this purpose. Although there are algorithms for the robust design of each particular technique, however, this specificity makes difficult the implementation of all these techniques in practical en gineering applications. Herein, the motion-based design method under uncertainty conditions is proposed and further implemented to create a common framework for the robust design of all these techniques when they are employed to mitigate pedestrian-induced vibrations in slender footbridges. According to this method, the design problem may be transformed into the combination of two sequential sub-problems: (i) a reliability multi objective optimization sub-problem; and (ii) a decision-making sub-problem. Subsequently, the performance of this proposal has been validated through a numerical case study in which the dynamic response of a steel footbridge has been controlled by three different tuned mass damper techniques designed according to the proposed common framework.Ministerio de Economía y Competitividad ( España) RTI2018-094945-B-C21Ministerio de Ciencia, Innovación y Universidades (España) RTI2018-099639-B-I0

Computing Black Hole entropy in Loop Quantum Gravity from a Conformal Field Theory perspective

Motivated by the analogy proposed by Witten between Chern-Simons and Conformal Field Theories, we explore an alternative way of computing the entropy of a black hole starting from the isolated horizon framework in Loop Quantum Gravity. The consistency of the result opens a window for the interplay between Conformal Field Theory and the description of black holes in Loop Quantum Gravity.Comment: 9 page

Un viajero en tierras salvajes: La resignificación de la raza y la otredad en el filme Get out de Jordan Peele

From the transdisciplinary position of Visual Studies and Decolonial Studies, an intratextual analysis of the ideological discourse of the film Get Out (2017) by Jordan Peele is presented. Through a reading focused on the intentio operis of the work, which uses the narrative analysis models of Zavala (2014), Žižek (2009) and Yepez (Yepez, 2020), it is proposed that Peele's work appropriates the generic conventions of western horror cinema, to emit an allegory where an inversion of the representation of otherness is made (Quijano, 2014; Smith, 2017). Throughout this text, it is argued that —within the film— whiteness (Echeverría, 2010; Frankenberg, 1993; Morrison, 1992) and the values ​​of American liberal society are the sources of terror and threat for the African-American protagonist. Such resignification of otherness is opposed to the canonical structure of homogeneous cinematography, where the plot presents the main characters entering the threatening world of racialized populations. Such a structure is represented by the film Cannibal Holocaust  (Deodato, 1980) and literary antecedents such as Conrad's Heart of Darkness (2013). In this sense, it is possible to affirm that historically horror cinema has produced cultural representations where racialized people are shown as dangerous and abject bodies (Montes, 2017). Peele's aesthetic proposal, which marks a distance from hegemonic discourses, can only be explained from the historical conjuncture and the racial tensions that currently occur in the United States and that have a historical trajectory in social movements around racialization processes in that country.A partir de la postura transdisciplinar de los Estudios Visuales y los Estudios Decoloniales, se presenta un análisis intratextual del discurso ideológico del filme Get Out (2017) de Jordan Peele. Por medio de una lectura enfocada en el intentio operis de la obra, la cual recurre a los modelos de análisis narrativo de Zavala (2014), Žižek (2009) y Yepez (2020), se propone que la obra de Peele se apropia de las convenciones genéricas del cine de terror occidental, para emitir una alegoresis donde se realiza una inversión de la representación de la otredad (Quijano, 2014; Smith, 2017). A lo largo de este texto, se argumenta que —dentro del filme— la blanquitud (Echeverría, 2010; Frankenberg, 1993; Morrison, 1992) y los valores de la sociedad liberal americana son las fuentes del terror y amenaza para el protagonista afroamericano. Tal resignificación de la otredad se contrapone a la estructura canónica de la cinematografía homogénica, donde la trama presenta a los personajes principales internándose al mundo amenazante de las poblaciones racializadas. Tal estructura tiene como representante a la película Holocausto Caníbal (Deodato, 1980) y antecedentes literarios como Corazón de las tinieblas de Conrad (2013). En ese sentido, es posible afirmar que históricamente el cine de terror ha producido representaciones culturales donde las personas racializadas se muestran como cuerpos peligrosos y abyectos (Montes, 2017). La propuesta estética de Peele, que marca una distancia con los discursos hegemónicos, sólo es posible explicarse desde la coyuntura histórica y las tensiones raciales que actualmente ocurren en Estados Unidos y que tienen una trayectoria histórica en los movimientos sociales en torno a los procesos de racialización en dicho país

Study of overall and local electrochemical responses of oxide films grown on CoCr alloy under biological environments

The interaction of the physiological medium and living tissues with the implant surfaces in biological environments is regulated by biopotentials that induce changes in the chemical composition, structure and thickness of the oxide film. In this work, oxide films grown on CoCr alloys at 0.5 V vs Ag/AgCl and 0.7 V vs Ag/AgCl have been characterized through overall and localized electrochemical techniques in a phosphate buffer solution and 0.3% hyaluronic acid. Nanopores of 10–50 nm diameter are homogeneously distributed along the surface in the oxide film formed at 0.7 V vs Ag/AgCl. The distribution of the Constant Phase Element studied by local electrochemical impedance spectroscopy showed a three-dimensional (3D) model on the oxide films grown at 0.5 V vs Ag/AgCl and 0.7 V vs Ag/AgCl. This behaviour is especially noticeable in oxide films grown at 0.7 V vs Ag/AgCl, probably due to surface inhomogeneities, and resistive properties generated by the potentiostatic growth of the oxide film.This work was supported by the Spanish National government [MINECO-MAT2011-29152-C02-01].Peer reviewe