726 research outputs found
Experimental strain modal analysis for beam-like structure using distributed fiber optics
No full textExperimental strain modal analysis for beam-like structure by using distributed fiber optics and its damage detection
No full textModal analysis is commonly considered as an effective tool to obtain the intrinsic characteristics of structures including natural frequencies, modal damping ratios, and mode shapes, which are significant indicators for monitoring the health status of engineering structures. The complex mode indicator function (CMIF) can be regarded as an effective numerical tool to perform modal analysis. In this paper, experimental strain modal analysis based on the CMIF has been introduced. Moreover, a distributed fiber-optic sensor, as a dense measuring device, has been applied to acquire strain data along a beam surface. Thanks to the dense spatial resolution of the distributed fiber optics, more detailed mode shapes could be obtained. In order to test the effectiveness of the method, a mass lump - considered as a linear damage component - has been attached to the surface of the beam, and damage detection based on strain mode shape has been carried out. The results manifest that strain modal parameters can be estimated effectively by utilizing the CMIF based on the corresponding simulations and experiments. Furthermore, damage detection based on strain mode shapes benefits from the accuracy of strain mode shape recognition and the excellent performance of the distributed fiber optics
Damage Detection Based on Strain Transmissibility for Beam Structure by Using Distributed Fiber Optics
No full textTransmissibility function analysis for the detection and localization of damage with nonlinear features in MDOF structural systems
Full text linkTransmissibility function analysis refers to the evaluation of the ratio between the spectra of two different outputs of a system and has been widely used for the detection and localization of damage in linear structural systems. In this article, a new transmissibility function analysis methodology is proposed to detect and localize damage with nonlinear features in multidegree-of-freedom (MDOF) structural systems. The methodology assumes the MDOF systems are subject to a general input with only the frequency range known a priori so is applicable to address damage detection and location issues for a wide range of engineering structures and systems. This methodology is derived based on the concept of nonlinear output frequency response functions (NOFRFs) and the concept of transmissibility of nonlinear systems introduced based on the NOFRFs. The transmissibility function analysis over output frequencies contributed by system nonlinearities is exploited to detect and localize damage with nonlinear features in MDOF structural systems. Both numerical simulations and experimental studies on a cracked beam structure in the laboratory have been conducted. The results verify the effectiveness and demonstrate the potential applications of the proposed methodology in the detection and localization of damage in practical engineering structures
Calibrating static measurement data from distributed fiber optics by the integration of limited FBG sensors based on the extended kernel regression method
No full textThanks to the rapid development of fiber optic sensors, the arrival of distributed sensors makes continuous and dense measurement possible for real structures. The distributed fiber optic sensors could provide a very high number of sensors along one single fiber, which is of great significance for structural health monitoring, especially for the detection of the damage position. However, the accuracy of data measured from fiber optic distributed sensors, such as strain and displacement etc., are sometimes not as accurate as those obtained from traditional fiber optic sensors such as fiber Bragg gratings (FBGs) and strain gauges. In this paper, to enhance the accuracy of static strain data measured from distributed fiber optic sensors, an extended kernel regression (EKR) method is applied to combine the distributed sensor measurement with those from four FBG sensors. These provide quite accurate static strain data; the strain values at locations where the FBGs are absent can therefore be predicted by the EKR method, which uses the data from distributed fiber optics as a biased model. The static experimental activities have been carried out in a laboratory, using a cantilever beam structure under different static loads
A Preliminary Case Study on the Dynamic Testing of a Masonry Arch Rail Bridge Using a Distributed Fiber Optic Sensing System
Full text linkMasonry arch bridges are an integral part of the European transportation infrastructure. Regular inspections are essential for preserving the historical significance of these bridges and ensuring their safe operation. Despite recent advancements in assessment techniques, monitoring masonry arch bridges remains a difficult and essential field of research. This article describes field tests conducted in Gavirate, Italy, to preliminary understand the dynamic response of a masonry arch rail bridge to train-induced moving loads, as a proof of concept study. The objective of this field investigation is to quantify the dynamic strain induced by train moving loads and to reveal the dynamic behaviors of the masonry arch bridge using a novel distributed fiber optical sensing-based technique. The results may provide a useful guideline for monitoring masonry arch bridges using distributed fiber optical sensing.<br/
Dynamic testing for design and construction validation of the new bridges on the Ticino river, Italy
No full textDeveloping a class of dual atom materials for multifunctional catalytic reactions
Full text linkDual atom catalysts, bridging single atom and metal/alloy nanoparticle catalysts, offer more opportunities to enhance the kinetics and multifunctional performance of oxygen reduction/evolution and hydrogen evolution reactions. However, the rational design of efficient multifunctional dual atom catalysts remains a blind area and is challenging. In this study, we achieved controllable regulation from Co nanoparticles to CoN4 single atoms to Co2N5 dual atoms using an atomization and sintering strategy via an N-stripping and thermal-migrating process. More importantly, this strategy could be extended to the fabrication of 22 distinct dual atom catalysts. In particular, the Co2N5 dual atom with tailored spin states could achieve ideally balanced adsorption/desorption of intermediates, thus realizing superior multifunctional activity. In addition, it endows Zn-air batteries with long-term stability for 800 h, allows water splitting to continuously operate for 1000 h, and can enable solar-powered water splitting systems with uninterrupted large-scale hydrogen production throughout day and night. This universal and scalable strategy provides opportunities for the controlled design of efficient multifunctional dual atom catalysts in energy conversion technologies
Digitizing Real-World Scenes from Images
No full text3D computer models are starting to play a more and more important role in our society. Realworldsituations are often too complex to explain in a 2D map and also the interest in virtualreality, serious gaming and other technologies that can be based on 3D computer models, isgrowing.Synthesis Project 2018Geomatic
A new damage detection technique
No full textMolte infrastrutture e strutture meccaniche sono inevitabili a subire danni con l'invecchiamento, che ha richiamato molta attenzione durante la ricerca degli ultimi decenni in termini di localizzazione del danno e di quantificazione delle strutture ingegneristiche per la valutazione della salute. L'identificazione dei danni basata su dati a vibrazione è stata sviluppata rapidamente, in quanto la modifica della struttura fisica provoca naturalmente un cambiamento della proprietà del sistema, come la frequenza naturale, lo smorzamento modale e la forma. Esiste una varietà di metodologie basate su vibrazioni per rilevare i danni: mediante la variazione della frequenza naturale, la modifica della forma del modo, la variazione della funzione di risposta in frequenza e la modifica della funzionalità di trasmissibilità e così via. Tra queste metodologie, la misurazione della variazione della funzione di trasmissibilità è preferibile in quanto non solo ha una migliore sensibilità al danno ma anche nessuna informazione preliminare del carico del sistema è necessaria.
Funzionalità di trasmissibilità come uno dei metodi più diffusi ampiamente applicati per identificare i danni. Inoltre, è tradizionalmente definito come rapporto di spettro di risposta tra due gradi di libertà. Negli ultimi decenni sono stati proposti altri indicatori di danno basati sulla funzione di trasmissibilità e i loro risultati di identificazione dei danni hanno dimostrato l'eccellente prestazione di questo approccio in termini di sensibilità rispetto alla funzione classica di risposta in frequenza (FRF). L'autore sottolinea anche l'importanza dei poli e degli zeri per localizzare i danni nel sistema dinamico. Più di recente, è stato dimostrato che il valore della funzione di trasmissibilità converge al rapporto forma forma quando la larghezza di banda di frequenza è limitata ai poli del sistema.
La comodità e l'efficacia dell'utilizzo della trasmissibilità in pratica è la base per farlo selezionarlo come oggetto di ricerca principale in questo lavoro.
In questo studio è stata proposta una nuova concezione, vale a dire la funzionalità di trasmissibilità del ceppo, per il fatto che il ceppo è più sensibile in relazione ai danni rispetto allo spostamento, che potrebbe essere dimostrato attraverso l'analisi di sensibilità relativa. Inoltre, l'accuratezza della localizzazione del danno si basa anche sul numero di sensori. Soprattutto quando viene eseguita una prova dinamica su grandi strutture come ponti, tunnel e edifici, è estremamente difficile raggiungere l'obiettivo di copertura completa sugli oggetti. Inoltre, solitamente un numero elevato di sensori è necessario e quindi l'idea è praticabile principalmente per ragioni economiche. Fortunatamente, le tecniche di fibre ottiche distribuite hanno mantenuto sviluppi piuttosto maturi e sono stati applicati in vari domini che possono misurare continuamente la tensione e la temperatura lungo il layout della struttura. Durante la convalida della fattibilità della nuova concezione e approccio proposti, sono stati condotti una serie di studi di simulazione e gli esperimenti relativi a fibre ottiche distribuite.
Tuttavia, molti ricercatori si concentrano principalmente sul caso di danno lineare in cui i danni possono essere considerati come la riduzione lineare della massa e della rigidità, apparentemente, la loro metodologia non è in grado di rilevare il cambiamento causato dal danno non lineare. Gli scenari di danni nelle strutture ingegneristici si manifestano come comportamenti non lineari in molti casi, che potrebbero essere considerati come potenziali pericoli per la sicurezza. Alcuni tipi di danni nei sistemi MDOF creano una notevole modifica non lineare, anziché una linea, come respirazione (rigidità bilineare), strutture post-bloccate (non lineare Duffing) e articolazioni a catena (Il sistema con discontinuità). Lo studio sulla identificazione dei danni non lineari è di grande importanza.
Un'altra parte di questo studio si concentra sull'identificazione del danno non lineare basata sulla concezione della funzione di risposta in frequenza di uscita non lineare (NOFRF). Il punto forte di questo lavoro è l'estensione dell'approccio NOFRF alla condizione di input generale e la corrispondente simulazione su un sistema MDOF dimostra chiaramente la sua disponibilità. In particolare, questo lavoro scopre e dimostra anche la relazione tra la funzione di trasmissibilità basata sul NOFRF e la funzionalità di trasmissione basata sull'uscita in condizioni di input generali, che offre una strategia più conveniente e affidabile per individuare e localizzare componenti danneggiati, a causa di diversi scenari danneggiati, Inclusa l'esistenza di componenti singoli danneggiati e componenti multipli danneggiati. Inoltre, vengono presi in considerazione anche diversi scenari di caricamento, tra cui il caricamento a singolo punto, il carico a più punti e il carico uniforme distribuito.Many infrastructures and mechanical structures are inevitable to suffer damage along with aging, which has drawn a lot of attention during the research of last decades in terms of the damage localization and quantification of engineering structures for health evaluation. Damage identification based on vibration-based data has been developed rapidly, since the change of physical structure naturally causes a change of system property such as natural frequency, modal damping and mode shape. There exists a variety of vibration-based methodologies for damage detection: by means of the change of natural frequency, the change of mode shape, the change of frequency response function and the change of transmissibility function, and so on. Among these methodologies, measuring the change of transmissibility function is preferable since it not only has a better sensitivity to the damage but also none prior information of the system loading is required.
Transmissibility function as one of the most popular methods widely applied for identifying damage. Moreover, it is traditionally defined as response spectrum ratio between two degrees of freedom. During the recent decades, more damage indicators based on transmissibility function have been proposed and their results of damage identification have proved the excellent performance of this approach in terms of the sensitivity than the classical frequency response function (FRF). The author also points out the significance of poles and zeros to localize damage in the dynamic system. More recently, it has been proved that the value of transmissibility function converges to the mode shape ratio when frequency bandwidth is restricted to the system’s poles.
The convenience and effectiveness of using transmissibility in practice is the basis of making it selected as the main research object in this work.
A new conception, namely strain transmissibility function, has been proposed in this study due to the fact that strain is more sensitive regarding to damage in comparison with displacement, which could be proved through the related sensitivity analysis. In addition, the accuracy of damage localisation also relies on the number of sensors. Especially when dynamic test is performed on large structures such as bridges, tunnels and buildings, it is extremely difficult to reach the target of full coverage on the objects. Also, usually a large number of sensors are need and then the idea is impracticable mainly for economic reasons. Fortunately, distributed fiber optics techniques have kept developing rather maturely and they have been applied into various domains which can measure continuously strain and temperature along the structure layout. During the validation of the feasibility of the proposed new conception and approach, a series of simulation studies and the related experiments based on distributed fiber optics have been carried out.
However, many researchers mainly concentrate on linear damage case where damage can be considered as the linear reduction of mass and stiffness, apparently, their methodology is unable to detect the change caused by the nonlinear damage. Damage scenarios in engineering structures are manifested as nonlinear behaviours in many cases, which could be deemed as the potential security hazard. Certain types of damage in MDOF systems create a significant nonlinear change instead of a linear one, such as breathing crack (Bilinear stiffness), post-buckled structures (Duffing nonlinearity) and rattling joints (The system with discontinuity), etc. Therefore, the study on nonlinear damage identification is of great importance.
Another part of this study focuses on nonlinear damage identification based on the conception of nonlinear output frequency response function (NOFRF). The highlight of this work is the extension of the NOFRF approach to the general input condition and corresponding simulation on a MDOF system clearly demonstrates its availability. In particular, this work also discovers and proves the relationship between NOFRF-based transmissibility function and Output-based transmissibility function under general input condition, which offers a more convenient and reliable strategy for detecting and localizing damaged components, on account of various damaged scenarios, including existence of single damaged component and multiple damaged components. In addition, various loading scenarios are taken into consideration as well, including single-point loading, multiple-point loading and distributed uniformed loading.DIPARTIMENTO DI MECCANICAMeasurements and experimental techniques29PENNACCHI, PAOLO EMILIO LINO MARIACOLOSIMO, BIANCA MARI
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