111,865 research outputs found
An innovative only-output method to identify a structural system
No full textStructural Health Monitoring (SHM) is nowadays common in many branches of engineering since it allows to have a continuous or periodic report of the structural conditions and therefore to promptly intervene if there are incipient damages. The first step to perform a SHM is the identification of the dynamic parameters, i.e. natural frequencies, damping ratios and modal shapes, and it is a crucial step since a modification of the structural parameters can be a direct consequence of structural damages. Among the structural identification methods, Operational Modal Analysis (OMA) methods have received increasing attention from the researchers since they do not require the knowledge of the structural excitation that is due to ambient vibrations and that is usually modeled as a white noise. This aspect makes this kind of methods cheaper and simpler than the classical Experimental Modal Analysis (EMA) methods.
In this paper an innovative OMA method is proposed. It is a semi - automated method that allows to identify natural frequencies, damping ratios and modal shapes of a structural system and that can be used also from users that have not knowledge in stochastic dynamics and signal analysis. First of all, the modal shapes are estimated through the use of signal filtering techniques applied on the stochastic properties of the output process and then natural frequencies and damping ratios can be estimated from the mono - component analytical signals obtained by performing a decomposition of the analytical signals matrix. The proposed method has been used to perform the dynamic identification of a real historic building situated in Palermo, i.e. Chiaramonte palace, and the results obtained have been compared with those obtained by using other OMA methods
Minimal requirements for the vibration-based identification of the axial force, the bending stiffness and the flexural boundary conditions in cables
No full textThis paper aims at presenting the guidelines to follow in order to set up an identification procedure which is able to determine the axial force, the flexural rigidity and the rotational end stiffnesses of slender and tensioned structural elements, based on measurements of their natural frequencies and mode shapes. First of all, when such an element is slightly affected by bending stiffness effects, perturbation methods can be applied to get a composite approximation for its natural frequencies and an asymptotic expression for its mode shapes. These simple analytical formulas allow to understand the role played by each model parameter in the modal response and show that the axial force, the flexural rigidity and the rotational end stiffnesses can be correctly identified under some conditions, which are established and provided in this document. Among others, it is necessary that the identification procedure relies on the first few natural frequencies and mode shapes, which are measured near each extremity of the element, as well as some natural frequencies associated with higher modes
On the Seismic Response of Anchoring Elements for Submerged Floating Tunnels
No full textSubmerged Floating Tunnels (SFTs) are interesting modular structures that lend themselves well to the crossing of water bodies. In a widespread design configuration the SFTs retain positive buoyancy and are kept at a fixed depth under the water surface by anchoring devices connected to the seabed. Different technological solutions have been proposed for the anchoring devices. They all share the properties of being slender, axially stiff and very flexible in transverse direction. The positive buoyancy of the SFT is typically tailored such to avoid detensioning (slackening) of the anchoring elements under design loading conditions, e.g. wave and earthquake loading. Whenever the tunnel is located in seismic prone areas, the seismic loading can be the dominant one. The present paper focuses on the local dynamic response of anchoring elements of a proposal for the Messina Strait crossing. The seismic input is modeled according to a suitable power spectral density of the ground acceleration and a reduced-order model of anchoring element is set up according to the classic theory of small-sag cables. The seismic working conditions are assessed with respect to slackening requirements
A stochastic and continuous model of aeolian vibrations of conductors equipped with stockbridge dampers
No full textSuspended conductors and guard wires of overhead electrical transmission lines (OHL) are prone to aeolian vibrations, resulting from the alternate shedding of vortices in the wake of the cable. These vibrations can occur under light to moderate wind and, whenever not properly controlled, can induce wear damage and fatigue failures of the cables. Nonlinear passive control devices such as Stockbridge dampers, hence, are often installed along the line spans to reduce the vibration severity. The technical approach to the assessment of aeolian vibrations is based on the Energy Balance Method (EBM) and relies on the simplifying assumption of mono-modal oscillations. Typical aeolian vibration records, however, clearly show that several modes can be simultaneously excited due to wind variations in time and along the span. Aiming at overcoming the mono-modal vibration assumption of the EBM, in the present paper wind forces are modeled as a narrow band stochastic process, centered around the Strouhal frequency of the conductor and with arbitrary cross-correlation in space. A new approach, based on the well-known smooth endochronic Bouc-Wen model, is developed to describe the hysteretic dynamic response of Stockbridge dampers. An iterative solution strategy based on a stochastically equivalent linear damper model is then developed to investigate aeolian vibrations of a suspended cable with a Stockbridge damper attached along its length
Bayesian forces identification in cable networks with small bending stiffness
No full textpeer reviewedThe regular monitoring of cable forces is essential for ensuring the safety of cable structures both during construction and throughout their lifetime. This paper aims at developing a vibration-based identification procedure of the axial forces, bending stiffness, and, secondarily, the crossing point position of cable networks. A model constituted by two crossing stays having small bending stiffness and negligible sag effects is considered. The in-plane direct dynamic problem is solved both numerically and through a perturbation approach. The obtained results are compared to the outcomes of a finite element model for verification purposes. The theoretical studies are also supported by experimental tests performed on a real cable-stayed bridge (Haccourt bridge), which provide insights into the dynamics of the system showing that models of cables with small bending stiffness are more appropriate than taut string models. The inverse analysis based on non-linear Bayesian regression is developed and the closed-form asymptotic formulations are used to prove that the bending stiffness, the cable forces, and the crossing point position can be separately identified from a set of observed frequencies. The implemented procedure is then applied to the tested bridge as a proof of concept, showing that the proposed in-plane identification strategy provides satisfactory results
author-bios-SRD-19-0063.R1 – Supplemental material for The Network Structure of Police Misconduct
No full textSupplemental material, author-bios-SRD-19-0063.R1 for The Network Structure of Police Misconduct by George Wood, Daria Roithmayr and Andrew V. Papachristos in Socius</p
Participez à l'acquisition du bréviaire de Charles V
No full textLa BnF souhaite acquérir un exceptionnel manuscrit enluminé réalisé vers 1370 pour le roi de France Charles V (1338-1380), le Bréviaire à l’usage de la Sainte-Chapelle. Cette acquisition permettrait au manuscrit de rejoindre les collections nationales, dont l’histoire commence avec Charles V dit «le Sage», célèbre pour son amour des livres et du savoir. La librairie qu’il installa au Louvre vers 1368 constitue le cœur historique de la BnF. Le Bréviaire à l’usage de la Sainte-Chapelle provient..
Bayesian Identification of the Axial Forces, the Bending Stiffnesses, and the Connecting Point in Crossed Cables
No full textIn this paper, an asymptotic expression is derived for the natural frequencies of two interconnected cables with small but non-negligible bending stiffness. This simple analytical formulation serves as a starting point for solving the inverse problem. First, it ensures that it is possible to univocally identify five parameters: the axial force and the bending stiffness in each of the two cables, as well as the position of the crossing point. A Bayesian framework based on the Metropolis-Hasting sampling algorithm is then used to calculate the most probable values and posterior distributions of these five parameters. The methodology is finally verified on a lab experimental setup, and applied to vibration data collected on an actual bridge
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
No full text“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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