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Calabrese, Francesca. "Vibration Monitoring and Intelligent Diagnosis Tools for Condition-Based Maintenance." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2017.
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Ogni impianto di produzione è caratterizzato da periodi di operatività, nei quali funziona correttamente, e da periodi di fermo, dovuti alla presenza di guasti o all’esigenza di effettuare attività volte a ristabilire il suo normale comportamento. L’obiettivo principale della funzione manutenzione è minimizzare i periodi di fermo impianto, al fine di renderlo il più disponibile possibile.
Attualmente, la manutenzione basata su condizione (CBM) è una delle più politiche più efficaci adottate dalle industrie. Essa è basata sul monitoraggio di diversi parametri della macchina che ne riflettono lo stato di salute. Tra i parametri più utilizzati si trovano i segnali di vibrazione. La CBM può essere implementata attraverso quattro passi principali: raccolta dati, analisi dei segnali, diagnostica e prognostica. Tale procedura prende il nome di Prognostic Health Monitoring (PHM).
La necessità di analizzare la grande mole di dati raccolta attraverso il vibration monitoring richiede l’utilizzo di metodi sviluppati nell’ambito della teoria statistica e del data mining, che si pongono l’obiettivo di riconoscere andamenti regolari all’interno di grandi insiemi di dati, al fine di generare conoscenza funzionale al processo decisionale manutentivo. In particolare, i modelli di classificazione, come alberi decisionali, algoritmi K-NN, reti neurali e Support Vector Machine, costituiscono un potente strumento per la diagnostica. Tali modelli, sulla base del PHM, vengono applicati dopo la fase di analisi dei segnali, che consiste principalmente nell’estrazione di features sia nel dominio del tempo che nel dominio tempo-frequenza.
Il risultato principale ottenuto consiste nell’aver verificato un incremento delle performance, in termini di accuratezza, della classificazione dello stato di salute di un componente, dovuto all’introduzione dell’analisi nel dominio tempo-frequenza e allo sviluppo dei nuovi metodi “intelligenti”.
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Hassin, Osama A. A. "Condition monitoring of journal bearings for predictive maintenance management based on high frequency vibration analysis." Thesis, University of Huddersfield, 2017. http://eprints.hud.ac.uk/id/eprint/34161/.
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Journal bearings are widely used as rotor supports in many machinery systems such as engines, motors, turbines and huge pumps. The journal bearing is simply designed, highly efficient, has a long life, low cost and doesn’t fail easily. Based on preventive maintenance strategies, many monitoring techniques are developed for monitoring journal bearings such as lubricant analysis, vibration analysis, noise and acoustic emission analysis. Vibration monitoring techniques have been developed and it can be implemented online or offline without interrupting the machine operations. The vibration phenomena in a journal bearing is complicated which combined between different types of signals created by different sources. To understand this phenomenon, a vibration model is established for fault diagnosis, which includes not only conventional hydrodynamic forces but also excitations of both asperity collisions and churns. However, mis-operations and oil degradation in the journal bearings might cause unexpected and sudden failure which is risky in machines and operators. Consequently, clustering technique is used to investigate into vibration responses of journal bearings for identifying different lubrication regimes as categorised by the classic Stribeck curve. High frequency clustering allows different lubricant oils and different lubrication regimes to be identified appropriately, providing feasible ways for online monitoring of bearing conditions. Additionally, modulation signal bispectrum magnitude results represent the nonlinear vibration responses with two distinctive bifrequency patterns corresponding to instable lubrication and asperity interactions. Using entropy measures, these instable operating conditions are classified to be the low loads cases. Furthermore, average MSB magnitudes are used to differentiate the asperity interactions between asperity collisions and the asperity churns. In addition, the oil starvation of a journal bearing has been found by MSB analysis that the instable frequency can affect the measured vibration responses. Moreover, the structural resonances in the high frequency range can better reflect the separation of different oil levels under wide operating conditions. Finally, As a result of worn bearings, shaft fluctuation increases and asperity collisions decreases. Thus a worn bearing is not all the time good because of instability.
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Di, Francesco Gianluca. "Metodologie di Condition Based Maintenance applicata alle macchine idrauliche operatrici." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019. http://amslaurea.unibo.it/18242/.
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In questo elaborato di tesi si affronta uno studio della manutenzione su condizione applicata alle macchine idrauliche operatrici, utilizzate per gli impianti di distribuzione idrica e di depurazione delle acque della regione Toscana, gestite dalla società Publiacqua S.p.A.
Nel capitolo 2 viene presentata la tematica della gestione della manutenzione, descrivendo le varie tipologie di manutenzione e le strategie di scelta di queste ultime, per poi passare al concetto di Total Productive Maintenance, ovvero un sistema di gestione della manutenzione che ha come obiettivo l’integrazione tra la produzione e la manutenzione.
Nel capitolo 3 viene presentata la trasformazione digitale del mondo industriale, illustrando i principi generali dell’Industria 4.0 e il suo impatto sulla gestione della manutenzione, introducendo il concetto di Prognostic and Health Management e di manutenzione predittiva.
I capitoli 4 e 5 riguardano le metodologie di manutenzione su condizione adottate per la gestione delle pompe sommerse. Questa tipologia di pompe, ampiamente utilizzate per le acque sotterranee, sono installate a grande profondità, perciò le azioni di manutenzione ordinarie risultano difficoltose e particolarmente costose. A causa di queste problematiche, un approccio efficace risulta essere la manutenzione su condizione. Nello specifico nel capitolo 4 si descrive la metodologia basata sull’analisi dell’assorbimento di corrente, attraverso un algoritmo che analizza l’andamento del valore di assorbimento nel tempo; nel capitolo 5 viene invece illustrata una metodologia basata sull’analisi delle vibrazioni attraverso uno studio effettuato negli impianti di prova e in situ secondo le linee guida dello standard ISO 10816. I risultati delle due metodologie forniscono dei livelli di allarme sullo stato delle pompe, che permettono di poter intervenire per tempo prima di un guasto, fornendo le basi per un passaggio da una manutenzione preventiva ad una su condizione.
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Zolkiewski, G. M. "Leak detection and condition monitoring of process valves by vibration analysis as a basis for condition based maintenance." Thesis, University of Manchester, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.314626.
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Gowid, Samer S. A. A. "Improving the profitability, availability and condition monitoring of FPSO terminals." Thesis, Loughborough University, 2017. https://dspace.lboro.ac.uk/2134/25464.
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The main focus of this study is to improve the profitability, availability and condition monitoring of Liquefied Natural Gas (LNG) Floating Production Storage and Offloading platforms (FPSOs). Propane pre-cooled, mixed refrigerant (C3MR) liquefaction is the key process in the production of LNG on FPSOs. LNG liquefaction system equipment has the highest failure rates among the other FPSO equipment, and thus the highest maintenance cost. Improvements in the profitability, availability and condition monitoring were made in two ways: firstly, by making recommendations for the use of redundancy in order to improve system reliability (and hence availability); and secondly, by developing an effective condition-monitoring algorithm that can be used as part of a condition-based maintenance system. C3MR liquefaction system reliability modelling was undertaken using the time-dependent Markov approach. Four different system options were studied, with varying degrees of redundancy. The results of the reliability analysis indicated that the introduction of a standby liquefaction system could be the best option for liquefaction plants in terms of reliability, availability and profitability; this is because the annual profits of medium-sized FPSOs (3MTPA) were estimated to increase by approximately US$296 million, rising from about US$1,190 million to US$1,485.98 million, if redundancy were implemented. The cost-benefit analysis results were based on the average LNG prices (US$500/ton) in 2013 and 2014. Typically, centrifugal turbines, compressors and blowers are the main items of equipment in LNG liquefaction plants. Because centrifugal equipment tops the FPSO equipment failure list, a Condition Monitoring (CM) system for such equipment was proposed and tested to reduce maintenance and shutdown costs, and also to reduce flaring. The proposed CM system was based on a novel FFT-based segmentation, feature selection and fault identification algorithm. A 20 HP industrial air compressor system with a rotational speed of 15,650 RPM was utilised to experimentally emulate five different typical centrifugal equipment machine conditions in the laboratory; this involved training and testing the proposed algorithm with a total of 105 datasets. The fault diagnosis performance of the algorithm was compared with other methods, namely standard FFT classifiers and Neural Network. A sensitivity analysis was performed in order to determine the effect of the time length and position of the signals on the diagnostic performance of the proposed fault identification algorithm. The algorithm was also checked for its ability to identify machine degradation using datasets for which the algorithm was not trained. Moreover, a characterisation table that prioritises the different fault detection techniques and signal features for the diagnosis of centrifugal equipment faults, was introduced to determine the best fault identification technique and signal feature. The results suggested that the proposed automated feature selection and fault identification algorithm is effective and competitive as it yielded a fault identification performance of 100% in 3.5 seconds only in comparison to 57.2 seconds for NN. The sensitivity analysis showed that the algorithm is robust as its fault identification performance was affected by neither the time length nor the position of signals. The characterisation study demonstrated the effectiveness of the AE spectral feature technique over the fault identification techniques and signal features tested in the course of diagnosing centrifugal equipment faults. Moreover, the algorithm performed well in the identification of machine degradation. In summary, the results of this study indicate that the proposed two-pronged approach has the potential to yield a highly reliable LNG liquefaction system with significantly improved availability and profitability profiles.
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Tanzariello, Roberta. "Condition Monitoring of a Belt-Based Transmission System for Comau Racer3 Robots." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2017. http://amslaurea.unibo.it/14354/.
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This project has been developed in collaboration with Comau Robotics S.p.a and the main goal is the development in China of an Health Monitoring Pro-cess using vibration analysis. This project is connected to the activity of Cost Reduction carried out by the PD Cost Engineering Department in China.
The Project is divided in two part:
1. Data Acquisition
2. Data Analysis
An Automatic Acquisition of the moni.log file is carried out and is discussed in Chapter 1. As for the Data Analysis is concerned a data driven approach is considered and developed in frequency domain through the FFT transform and in time domain using the Wavelet transform.
In Chapter 2 a list of the techiques used nowadays for the Signal Analysis and the Vibration Monitoring is shown in time domain, frequency domain and time-frequency domain.
In Chapter 3 the state of art of the Condition Monitoring of all the possible ma-chinery part is carried out from the evaluation of the spectrum of the current and speed.
In Chapter 4 are evaluated disturbances that are not related to a fault but be-long to a normal behaviour of the system acting on the measured forces. Motor Torque Ripple and Output Noise Resolution are disturbance dependent on ve-locity and are mentioned in comparison to the one related to the configuration of the Robot.
In Chapter 5 a particular study case is assigned: the noise problem due to belt-based power transmission system of the axis three of a Racer 3 Robot in Endu-rance test. The chapter presents the test plan done including all the simula-tions.
In Chapter 6 all the results are shown demostrating how the vibration analysis carried out from an external sensor can be confirmed looking at the spectral content of the speed and the current.
In the last Chapter the final conclusions and a possible development of this thesis are presented considering both a a Model of Signal and a Model Based approach.
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Milakovic, Stefan. "Utvärdering och användning av maskindata för tillståndsbaserat underhåll i en industriell kontext." Thesis, Blekinge Tekniska Högskola, Institutionen för industriell ekonomi, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:bth-12829.
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Industriellt underhåll har upplevt en utveckling från det ursprungliga akuta avhjälpande underhållet till dagens möjligheter till underhåll baserat på data, så kallat tillståndsbaserat underhåll (CBM). För CBM genomförs endast underhåll vid behov och detta bestäms av aktuell data från den studerade utrustningen. Onödigt underhåll minimeras och antalet plötsliga haverier minskar. Utvecklingen mot Internet of Things (IoT) ger upphov till en stor mängd data som potentiellt kan användas vid CBM-underhåll. En utmaning uppstår dock i att identifiera sådan data och hur denna data kan användas. Denna studie har syftat till att undersöka hur sådan data kan identifieras och hur den kan tänkas användas vid CBM-underhåll. Studien har utförts tillsammans med Quant i Karlskrona där Quant genomför alla underhållsrelaterade aktiviteter åt ABB High Voltage Cables, ett industriföretag som tillverkar högspänningskablar. Arbetet har utgått från tre frågeställningar som har syftat till att: Identifiera datavariabler som kan tänkas ha relevans för CBM-underhåll. Tolka de identifierade datavariablerna för att bedöma hur de kan användas i CBM. Bedöma lämpligheten av en potentiell CBM-implementation baserat på identifierad data jämfört med existerande underhållsmetod. Arbetet har avgränsats genom att fokusera på ett enskilt företag och en enskild fabrik. Utöver detta har en avgränsning gjorts där fokus lagts på några få enskilda maskiner och komponenter. Sekretess har även behövt beaktas vid hantering av känslig information. Studien har huvudsakligen utförts kvalitativt, genom att på djupet fokusera på ett fåtal maskiner och komponenter. Arbetet har genomförts i nära samarbete med några av Quants anställda. Processdata har samlats in direkt från maskinerna och analyserats genom att identifiera och studera avvikelser i data. Intervjuer av olika slag, kompletterade med dokument, har varit en viktig metod för att inhämta information från anställda på Quant, både kring hur data kan tolkas men även kring hur olika processer fungerar. Analytic hierarchy process (AHP) genomfördes i fokusgrupp med anställda för att bedöma lämplig underhållsstrategi. Ett potentiellt tillvägagångssätt har identifierats som tillåter användning av processdata för CBM hos en särskild komponenttyp på företaget. Metoden behöver implementeras och testas men potential finns att minska underhållskostnaderna. Intressanta avvikelser i processdata har identifierats hos en annan komponent som bör studeras vidare för att förstå om processdata och avvikelserna kan användas i en CBM-kontext eller inte. Förbättringsområden hos företaget har identifierats i tillämpningen av vibrationsmätning, vilket är en metod med god potential att användas för CBM-underhåll och därmed minska underhållskostnaderna. Oljeanalys tillämpas redan men en intressant fundering är hur företagets oljefiltrering påverkar möjligheterna att implementera ett prediktivt underhåll i framtiden. Detta är ett område som framtida studier behöver titta på och bedöma hur det ska tacklas. AHP har även bekräftats vara en användbar metod för att bedöma lämpligaste underhållspolicyn.Industrial maintenance has experienced an evolution from the initial corrective maintenance to the possibility of using data based maintenance techniques, so called condition-based maintenance (CBM). Maintenance is only performed when needed under CBM and this is decided based on the data retrieved from the studied equipment. Unnecessary maintenance is minimized and the number of sudden breakdowns decreases. The trend towards Internet of Things (IoT) gives rise to a large amount of data that can potentially be used in CBM maintenance. 'A challenge arises in identifying and using such data. This study has aimed to investigate how such data can be identified and how it might be used in CBM maintenance. This study has been carried out together with Quant in Karlskrona, Sweden, where Quant performs all maintenance related activities for ABB High Voltage Cables, an industrial manufacturing company. The study has been based on three questions that have aimed to: Identify data variables that might be relevant for CBM maintenance. Interpret the identified data variables to assess how they can be used in CBM. Assess the suitability of a potential CBM implementation based on the identified data compared to the existing maintenance method. The study has been delimited by focusing on a single company and a single factory. In addition, a delimitation has been made to focus on a few individual machines and components. A nondisclosure agreement also had to be considered when dealing with sensitive information. This study has mainly been conducted qualitatively, by focusing in-depth on a few machines and components. The work has been done in close collaboration with Quant’s employees. Process data has been collected from the machines and analyzed by identifying and studying data anomalies. Interviews, complemented with documents, has been an important method in obtaining information from Quant employees, both regarding how data can be interpreted but also on how the various processes work. Analytic hierarchy process (AHP) was conducted in a focus group with employees to determine the most appropriate maintenance strategy. One potential approach has been identified that allows the use of process data for CBM on a particular type of component at the company. The method needs to be implemented and tested but the potential exists to reduce maintenance costs. Interesting anomalies in the process data have been identified in another component which should be studied further to understand if the process data and the anomalies can be used in a CBM context or not. Areas for improvement at the company have been identified in the application of vibration measurements, which is a method with good potential to be used in CBM maintenance, thereby reducing maintenance costs. Oil analysis is already used but an interesting question is how the company’s oil filtration affects its ability to implement a predictive maintenance scheme in the future. This is an area that future studies need to look at and assess how it should be tackled. AHP has also been confirmed to be a useful method to determine the most appropriate maintenance policy.
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Honc, Lukáš. "Řádová analýza signálů." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2016. http://www.nusl.cz/ntk/nusl-240940.
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This master's thesis deals with order analysis. The first part of the thesis describes common methods for order analysis and methods for processing tacho and vibration signal. The second part contains a brief description of some open source tools for order analysis focusing on Sound and Vibration Measurement Suite (SVMS) package for LabVIEW by National Instruments company. The main purpose of the thesis has been designing and realization of own library for order analysis as a plugin for development tool LabVIEW. In the library, there are implemented methods for order analysis including basic functions for processing vibration and tacho signal. Their brief description with manual for its usage is in the third part of the thesis. In the last chapter, implemented functions are compared with those, which are implemented in SVMS by National Instruments, using both simulated and real data.
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Smit, Wynand Gerhardus. "Fan blade damage detection using on-line vibration monitoring." Diss., Pretoria : [s.n.], 2002. http://upetd.up.ac.za/thesis/available/etd-11302005-091637/.
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Canal, Luiz Antonio. "Proposta de um método para priorização de investimento em monitoramento instrumentado contínuo de equipamentos dinâmicos aplicado em planta petroquímica." Universidade do Vale do Rio dos Sinos, 2017. http://www.repositorio.jesuita.org.br/handle/UNISINOS/6770.
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A busca pela maior segurança industrial em plantas petroquímicas tem sido a pauta principal deste tipo de negócio, já que a possibilidade de acidentes é potencializada pela própria natureza da operação, que envolve inventários inflamáveis, combustíveis ou tóxicos. Muitos dos iniciadores destes eventos advêm de mau funcionamento de seus equipamentos dinâmicos, como motores, bombas e compressores, com causas ligadas a manutenção, operação ou projeto. Neste contexto, é proposto neste trabalho um método para a implantação de melhorias e projetos direcionados para o monitoramento contínuo de equipamentos dinâmicos. O objetivo é de aumentar a segurança industrial e a disponibilidade dos equipamentos, já que o contínuo monitoramento dos equipamentos permite uma melhor supervisão dos mesmos, além de fortalecer a manutenção preventiva baseada em condição. Será apresentada a solução focando no monitoramento de temperatura e vibração em mancais, que normalmente são foco da maior parte das falhas em equipamentos dinâmicos. Inicia-se pela escolha do método para priorização da implantação, baseado em análise multicritério e análise de risco, passando pela proposição e definição dos critérios, culminando com a exemplificação do trabalho em uma planta petroquímica real. Como resultado tem-se uma matriz de risco para apoio na priorização de investimento em monitoramento contínuo, agregando ainda simulações de análise de sensibilidade para a tomada de decisão.
The search for greater industrial safety has been the main guideline in petrochemical business, since the most of accidents are potentiated by the own nature of the operation, which involves flammable, combustible or toxic inventories. Many of the initiators of these events arise from the malfunction of their dynamic equipment, such as motors, pumps and compressors, with causes related to maintenance, operation or design. In this context, it is proposed a method for the implementation of improvements and projects directed to the continuous monitoring of dynamic equipment. The main objective is to increase the industrial safety and the availability, since the continuous monitoring allows a better supervision of the dynamic equipment, besides strengthening the application of condition based maintenance policy. The solution will be presented focusing on the monitoring of equipment temperature and vibration, which indicate of most failures or a situation of non-appropriated operation. This work starts with determining the method to prioritize the implementation, based on multicriteria and risk analysis, explain the criteria and their definition, culminating with the exemplification of the work in a real petrochemical plant. As a result, a risk matrix is presented for support in the prioritization of investment in continuous monitoring, also adding sensitivity analysis simulations for decision making.
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Guan, Hong. "Vibration-based structural health monitoring of highway bridges." Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC IP addresses, 2006. http://wwwlib.umi.com/cr/ucsd/fullcit?p3211821.
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CAMERINI, MURILO GIRON. "FLEXIBLE RISERS MONITORING TECHNIQUE BASED ON VIBRATION MEASUREMENTS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2012. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=20697@1.
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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROUm dos principais mecanismos de falha em risers flexíveis é o rompimento de arames da armadura de tração. A experiência tem mostrado que esta classe de dano tende a surgir primariamente na parte emersa do riser, próximo à sua terminação. A ruptura dos arames ocorre de forma progressiva, podendo ser causada por diferentes processos, tais como corrosão pelo ingresso de fluido no espaço anular entre capa e armadura, desgaste excessivo associado com o contato e atrito entre arames adjacentes ou entre as diferentes camadas metálicas da armadura, ou mesmo a presença de níveis elevados de tensões produzidas pelos carregamentos mecânicos aos quais o riser é submetido durante a operação. O deterioramento progressivo pode dar origem a defeitos localizados que agem como concentradores de tensão e levam o arame à ruptura através de um processo de fadiga. O duto flexível é capaz de manter-se em operação mesmo com alguns dos arames de suas armaduras rompidos, porém uma sequencia de rupturas pode levar à ocorrência de vazamentos ou mesmo a falhas catastróficas. O monitoramento contínuo em tempo real é uma das principais alternativas para evitar que o dano progressivo nas armaduras do riser resulte em acidentes com severas consequências econômicas e ambientais. As técnicas de monitoramento da integridade de risers flexíveis podem ser classificadas como diretas, onde é possível identificar diretamente a existência de um dano/falha, ou indiretas, em que o sistema de sensoriamento registra indicações secundárias, possivelmente consequência da falha. Esta dissertação relata o desenvolvimento de um sistema de monitoramento baseado em vibrações. Trata-se de uma técnica indireta baseada em eventos, onde no momento da ruptura do arame um sinal de vibração, distinto tanto na frequência quanto na amplitude, é detectado por acelerômetros instalados na capa polimérica externa do riser. No trabalho, são apresentados resultados de quatro ensaios em escala real que demonstraram a viabilidade do sistema para um primeiro teste de campo. Estratégias de instrumentação dos dutos e as variações dos sinais detectados são apresentadas e discutidas. Os resultados mostraram que a resposta vibratória do sinal de ruptura apresenta características específicas, garantindo uma boa confiabilidade na detecção. Porém, em se tratando de uma técnica indireta, verifica-se que quando dois sistemas de monitoramento de naturezas complementares são empregados em conjunto, as probabilidades de detecção dos eventos de rupturas aumentam significativamente.
The main failure in flexible risers is the disruption of the wires from the tensile armor layer. Experience has shown that this class of damage occurs primarily near to the top riser connector. The breaking of the wires occurs gradually and may be caused by different processes as corrosion by inflow of fluid in the annular space, excessive wear associated with the contact and friction between adjacent wires or between different riser layers. The progressive deterioration can lead to localized defects that act as stress concentrators and may break the wire from the tensile armor layer through a fatigue process. The flexible pipe is able to remain in operation even with some broken wires, but a sequence of ruptures can conduce to a catastrophic failure. Real time continuous monitoring is one of the main alternatives to prevent progressive wire damage results in an accident with severe economic and environmental consequences. This thesis describes the development of a monitoring system based on vibrations. This is an indirect technique based on events, where in the moment of the wire break, one vibration signal is registered. This signal can be distinguished both in frequency and amplitude and detected by accelerometers installed on the polymeric outer layer of the riser. We present results of four tests in real scale that demonstrated the viability of the system for an initial field test. Instrumentation strategies in riser and the variations of the signals detected are presented and discussed. The results showed that the vibrational signal has specific characteristics ensuring good detection reliability.
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Yang, Chen. "Vibration-based structural health monitoring of composite laminates." Thesis, University of Manchester, 2017. https://www.research.manchester.ac.uk/portal/en/theses/vibrationbased-structural-health-monitoring-of-composite-laminates(b762020d-f2c6-49ed-84ba-dfc2e3ece187).html.
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Over the past three decades, carbon-fibre reinforced plastics (CFRP) and glass fibre-reinforced plastics (GFRP) have been increasingly used in modern engineering designs to make composite laminated structures. This increase is due to their attractive mechanical performances and their stable physical and chemical properties. However, these composites are subjected to distinctive failure modes which are different from those of metallic alloys. These failure modes include delamination, matrix cracking and fibre breakage. Therefore, structural health monitoring (SHM) of composite laminated structures during the operational phase has become increasingly important. This thesis presents the development of vibration-based SHM approaches. A non-contact fibre optic sensor is developed for modal testing and structural health monitoring of composite laminate structures. Signal processing methods are used on the acquired modal data to produce a new damage index. The main investigations and contributions of the thesis are summarised as follows,1) A delamination detection method using additional mass loading and modal frequencies is numerically and experimentally studied. The study shows that the interaction between local inertia and delaminations affects the vibration characteristics of composite laminated beams for delaminations located at different depths. 2) A two-step delamination producing technique through mechanical pull-up is proposed and experimentally validated for composite laminated plates. The proposed technique overcomes the inadequate performance of PTFE inserts approach and shows the ability to produce both near surface and far surface delaminations at inaccessible regions from the boundaries. 3) A delamination detection approach using wavelet coefficients of the multiple-mode modal frequency curve for beam-like structures is developed. The method does not require the knowledge of the intact state nor the use of artificial noise filtering procedures.4) The proposed intact-free wavelet coefficients of modal frequency surface are further applied to two-dimensional composite laminate plate-like structures. In conjunction with the wavelet-based edge detection method in imaging processing, the proposed method shows the satisfactory performance in delamination identification and localisation for laminate plates.5) A cost-effective non-contact fibre optic displacement sensor is developed based on the theoretical model. The parameters of the sensor are calibrated following standard procedures. The sensor shows satisfactory performance in structural modal testing. 6) The application of the developed fibre optic sensor in structural health monitoring for composite laminate structures is demonstrated by experiments and its performance is compared with that of commercial sensors.
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Ullah, Israr. "Vibration-based structural health monitoring of composite structures." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/vibrationbased-structural-health-monitoring-of-composite-structures(f21abb03-5b46-4640-9447-0552d5e0c7d6).html.
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Composite materials are in use in several applications, for example, aircraft structural components, because of their light weight and high strength. However the delamination which is one of the serious defects often develops and propagates due to vibration during the service of the structure. The presence of this defect warrants the design life of the structure and the safety. Hence the presence of such defect has to be detected in time to plan the remedial action well in advance. There are a number of methods in the literature for damage detection. They are either 'baseline free/reference free method' or using the data from the healthy structure for damage detection. However very limited vibration-based methods are available in the literature for delamination detection in composite structures. Many of these methods are just simulated studies without experimental validation. Grossly 2 kinds of the approaches have been suggested in the literature, one related to low frequency methods and other high frequency methods. In low frequency approaches, the change in the modal parameters, curvatures, etc. is compared with the healthy structure as the reference, however in the high frequency approaches, excitation of structures at higher modes of the order of few kHz or more needed with distributed sensors to map the deflection for identification of delamination. Use of high frequency methods imposes the limitations on the use of the conventional electromagnetic shaker and vibration sensors, whereas the low frequency methods may not be feasible for practical purpose because it often requires data from the healthy state which may not be available for old structures. Hence the objective of this research is to develop a novel reference-free method which can just use the vibration responses at a few lower modes using a conventional shaker and vibration sensors (accelerometers/laser vibrometers). It is believed that the delaminated layers will interact nonlinearly when excited externally. Hence this mechanism has been utilised in the numerical simulations and the experiments on the healthy and delaminated composite plates. Two methods have been developed here - first method can quickly identify the presence of the delamination when excited at just few lower modes and other method identify the location once the presence of the delamination is confirmed. In the first approach an averaged normalised RMS has been suggested and experimentally validated for this purpose. Latter the vibration data have then been analysed further to identify the location of delamination and its size. Initially, the measured acceleration responses from the composite plates have been differentiated twice to amplify the nonlinear interaction clearly in case of delaminated plate and then kurtosis was calculated at each measured location to identify the delamination location. The method has further been simplified by just using the harmonics in the measured responses to identify the location. The thesis presents the process of the development of the novel methods, details of analysis, observations and results.
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Esu, Ozak O. "Vibration-based condition monitoring of wind turbine blades." Thesis, Loughborough University, 2016. https://dspace.lboro.ac.uk/2134/21679.
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Significant advances in wind turbine technology have increased the need for maintenance through condition monitoring. Indeed condition monitoring techniques exist and are deployed on wind turbines across Europe and America but are limited in scope. The sensors and monitoring devices used can be very expensive to deploy, further increasing costs within the wind industry. The work outlined in this thesis primarily investigates potential low-cost alternatives in the laboratory environment using vibration-based and modal testing techniques that could be used to monitor the condition of wind turbine blades. The main contributions of this thesis are: (1) the review of vibration-based condition monitoring for changing natural frequency identification; (2) the application of low-cost piezoelectric sounders with proof mass for sensing and measuring vibrations which provide information on structural health; (3) the application of low-cost miniature Micro-Electro-Mechanical Systems (MEMS) accelerometers for detecting and measuring defects in micro wind turbine blades in laboratory experiments; (4) development of an in-service calibration technique for arbitrarily positioned MEMS accelerometers on a medium-sized wind turbine blade. This allowed for easier aligning of coordinate systems and setting the accelerometer calibration values using samples taken over a period of time; (5) laboratory validation of low-cost modal analysis techniques on a medium-sized wind turbine blade; (6) mimicked ice-loading and laboratory measurement of vibration characteristics using MEMS accelerometers on a real wind turbine blade and (7) conceptualisation and systems design of a novel embedded monitoring system that can be installed at manufacture, is self-powered, has signal processing capability and can operate remotely. By applying the conclusions of this work, which demonstrates that low-cost consumer electronics specifically MEMS accelerometers can measure the vibration characteristics of wind turbine blades, the implementation and deployment of these devices can contribute towards reducing the rising costs of condition monitoring within the wind industry.
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Ashwear, Nasseradeen. "Vibration-based Assessment of Tensegrity Structures." Doctoral thesis, KTH, Strukturmekanik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-185789.
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Vibration structural health monitoring (VHM) uses the vibration properties to evaluate many civil structures during the design steps, building steps and service life.The whole function, expressed by stiffness and frequencies of tensegrity structures are primarily related to the level of pre-stress. The present work investigates the possibilities to use this relation in designing, constructing and evaluating the tensegrity structures.One of the aims of the thesis was to improve the current models for resonance frequency simulation of tensegrities. This has been achieved by introducing the bending behaviour of all components, and by a one-way coupling between the axial force and the stiffness.The environmental temperature effects on vibration properties of tensegrity structures have been also investigated. Changes in dynamic characteristics due to temperature variations were compared with the changes due to decreasing pre-tension in one of the cables. In general, it is shown that the change in structural frequencies coming from temperature changes could of several magnitude as those from damage.Coinciding natural frequencies and low stiffness are known issues of tensegrity structures. The former can be an obstacle in VHM, while the later normally limits their uses in real engineering applications. It has been shown that the optimum self-stress vector of tensegrity structures can be chosen such that their lowest natural frequency is high, and separated from others.The environmental temperature effects on vibration properties of tensegrity structures were revisited to find a solution such that the natural frequencies of the tensegrity structures are not strongly affected by the changes in the environmental temperature. An asymmetric self-stress vector can be chosen so that the criterion is fulfilled as well as possible. The level of pre-stress can also be regulated to achieve the solution. The last part of this thesis, services as a summary of the work.QC 20160429
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Novo, Fabio da Mota Ferreira. "Condition monitoring based systematic modeling of equipment maintenance." Thesis, University of Macau, 2008. http://umaclib3.umac.mo/record=b1942840.
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Pinero, Juan Carlos. "A Framework for Monitoring Performance-Based Road Maintenance." Diss., Virginia Tech, 2003. http://hdl.handle.net/10919/30010.
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In the late 1980s and early 1990s few transportation agencies around the world considered performance-based specifications as an alternative to improve the efficiency of the services provided to the public. These initiatives are better known as Performance-Based Road Maintenance (PBRM). PBRM calls for performance-based work, in which a desired outcome is specified rather than a material or method. This type of specification promises to be an excellent tool to improve government efficiency in maintaining transportation networks; however, without proper monitoring, it could likely yield adverse outcomes. Since PBRM is relatively new, the availability of reliable and comprehensive sets of guidelines to evaluate the effectiveness and efficiency of this type of specifications in the roadway maintenance arena is limited. Transportation agencies currently rely on criteria and procedures they have had developed from their traditional methods used to evaluate performance. Unfortunately, some of these procedures cannot appropriately assess the benefits, if any, accrued by the government as a result of implementing performance-based specifications for the maintenance of the roadway system. This research presents the development of a framework for monitoring PBRM more comprehensively and accurately. The framework considers the assessment of five main areas -- Level of Service Effectiveness, Cost-Efficiency, Timeliness of Response, Safety Procedures, and Quality of Services -- in order to guarantee the comprehensiveness and reliability of the evaluation process. The major contribution of this framework is to provide transportation agencies with guidelines for evaluating the effectiveness and efficiency of PBRM as an alternative delivery method to maintain and preserve the roadway system.Ph. D.
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Riley, Caryn M. "Current-based sensorless vibration monitoring of small ac machines." Diss., Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/13741.
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Charles, Peter. "Torsional vibration-based monitoring of medium-speed diesel engines." Thesis, University of Manchester, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.706131.
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Goi, Yoshinao. "Bayesian Damage Detection for Vibration Based Bridge Health Monitoring." Kyoto University, 2018. http://hdl.handle.net/2433/232013.
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Bisht, Saurabh Singh. "Vibration Measurement Based Damage Identification for Structural Health Monitoring." Diss., Virginia Tech, 2010. http://hdl.handle.net/10919/77301.
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The focus of this research is on the development of vibration response-based damage detection in civil engineering structures. Modal parameter-based and model identification-based approaches have been considered. In the modal parameter-based approach, the flexibility and curvature flexibility matrices of the structure are used to identify the damage. It is shown that changes in these matrices can be related to changes in stiffness values of individual structural members. Using this relationship, a method is proposed to solve for the change in stiffness values. The application of this approach is demonstrated on the benchmark problem developed by the joint International Association of Structural Control and American Society of Civil Engineers Structural Health Monitoring task group. The proposed approach is found to be effective in identifying various damage scenarios of this benchmark problem. The effect of missing modes on the damage identification scheme is also studied.
The second method for damage identification aims at identifying sudden changes in stiffness for real time applications. It is shown that the high-frequency content of the response acceleration can be used to identify the instant at which a structure suffers a sudden reduction in its stiffness value. Using the Gibb's phenomenon, it is shown why a high-pass filter can be used for identifying such damages. The application of high-pass filters is then shown in identifying sudden stiffness changes in a linear multi-degree-of-freedom system and a bilinear single degree of freedom system. The impact of measurement noise on the identification approach is also studied. The noise characteristics under which damage identification can or cannot be made are clearly identified. The issue of quantification of the stiffness reduction by this approach is also examined. It is noted that even if the time at which the reduction in stiffness happens can be identified, the quantification of damage requires the knowledge of system displacement values. In principle, such displacements can be calculated by numerical integration of the acceleration response, but the numerical integrations are known to suffer from the low frequency drift error problems. To avoid the errors introduced due to numerical integration of the acceleration response, an approach utilizing the unscented Kalman filter is developed to track the sudden changes in stiffness values. This approach is referred to as the adaptive unscented Kalman filter (AUKF) approach. The successful application of the proposed AUKF approach is shown on two multi-degree of freedom systems that experience sudden loss of stiffness values while subjected to earthquake induced base excitation.Ph. D.
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Rehman, Anees ur. "Vibration-based condition monitoring of a turbomachinery bladed system." Thesis, University of Sheffield, 2012. http://etheses.whiterose.ac.uk/2557/.
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He, Xianfei. "Vibration-based damage identification and health monitoring of civil structures." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2008. http://wwwlib.umi.com/cr/ucsd/fullcit?p3289036.
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Thesis (Ph. D.)--University of California, San Diego, 2008.Title from first page of PDF file (viewed February 5, 2008). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references.
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Ibrahim, Ghalib Rzayyig. "Design and implementation of gearboxes vibration based condition monitoring system." Thesis, Manchester Metropolitan University, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.543248.
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The use of gearboxes for power transfer is widespread throughout industry. However, machines today are operating at higher speeds than ever before and gear wear and fatigue failures are serious and legitimate concerns. Incipient fault detection in gears has thus become the subject of intensive investigation and at this stage of development there are many competing condition monitoring methods based on vibration signal analysis. Vibration signals obtained from a gearbox were complex multi-component signals, generated by tooth meshing, gear shaft rotation, gearbox resonance vibration signatures and a substantial amount of noise. This thesis summarizes the research steps taken after a review of (i) current maintenance strategies, (ii) gearbox condition monitoring techniques, (iii) gear vibration fundamentals and (iv) common gearbox failure modes. A mathematical model of the gearbox was used to predict the effects of load and tooth breakage effects on induced vibrations. A test rig was built around an 11 kW two stage helical gearbox, designed and fabricated for experimental data collection. Simulation and experimental work was carried out for a healthy pair of gears under different loads for different drive speeds and a pair suffering from degrees of tooth breakage. Conventional methods using the time-domain of the vibration signal (RMS, kurtosis, skewness and the zero figure of merit) were used for detecting and diagnose the seeded faults. The total energy method was applied to the gear meshing frequency and its sidebands, as obtained from the FFT, to detect the presence of the faults, and the results compared with those obtained by the conventional techniques. The proposed method appears much more effective at detecting and diagnosing tooth breakage than statistical features extracted from the time-domain. Joint time-frequency domain techniques were then used to determine their effectiveness for diagnosing the seeded faults in the gearbox system when the gearbox operates under output loads and at different speeds. A comparison was made between empirical mode decomposition and smoothed pseudo Wigner-Ville distribution methods based on vibration signature. From the results obtained it appears that the empirical mode decompose technique offers a more effective and faster way to detect faults. To improve signal-to-noise ratio, a novel scheme based on adaptive noise cancellation technique with a least squares algorithms was used on the gearbox experimental vibration signals. It is concluded that this method offers the most effective way of all those tested to detect faults.
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Abboud, Dany. "Vibration-based condition monitoring of rotating machines in nonstationary regime." Thesis, Lyon, INSA, 2015. http://www.theses.fr/2015ISAL0106/document.
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Dans les dernières décennies, la surveillance vibratoire des machines tournantes a acquis un intérêt particulier fournissant une aide efficace pour la maintenance dans l'industrie. Aujourd'hui, de nombreuses techniques efficaces sont bien établies, ancrées sur des outils puissants offerts notamment par la théorie des processus cyclostationnaires. Cependant, toutes ces techniques reposent sur l'hypothèse d’un régime de fonctionnement (c.à.d. vitesse et/ou charge) constant ou éventuellement fluctuant d’une façon stationnaire. Malheureusement, la plupart des machines surveillées dans l'industrie opèrent sous des régimes non stationnaires afin de remplir les tâches pour lesquelles elles ont été conçues. Dans ce cas, ces techniques ne parviennent pas à analyser les signaux vibratoires produits. Ce problème a occupé la communauté scientifique dans la dernière décennie et des techniques sophistiquées de traitement du signal ont été conçues pour faire face à la variabilité du régime. Mais ces tentatives restent limitées, dispersées et généralement peu soutenues par un cadre théorique. Le principal objectif de cette thèse est de combler partiellement cette lacune sur la base d'une formalisation théorique du sujet et d’un développement systématique de nouveaux outils de traitement du signal. Dans ce travail, la non-stationnarité du régime est limitée à celle de la vitesse— c.à.d. vitesse variable et charge constante— supposée connue a priori. Afin d'atteindre cet objectif, la méthodologie adoptée consiste à étendre le cadre cyclostationnaire avec ses outils dédiés. Nous avons élaboré cette stratégie en distinguant deux types de signatures. Le premier type comprend des signaux déterministes connus comme cyclostationnaires au premier ordre. La solution proposée consiste à généraliser la classe cyclostationnaire au premier ordre à la classe cyclo-non-stationnaire au premier ordre qui comprend des signaux déterministes en vitesse variable. Le second type comprend des signaux aléatoires périodiquement corrélés connus comme cyclostationnaires au deuxième ordre. Trois visions différentes mais complémentaires ont été proposées pour traiter les variations induites par la non-stationnarité de la vitesse de fonctionnement. La première adopte une approche cyclostationnaire angle\temps, la seconde une solution basée sur l'enveloppe et la troisième une approche cyclo-non-stationnaire (au second ordre). De nombreux outils ont été conçus dont les performances ont été testées avec succès sur des signaux vibratoires réels et simulésIn the last decades, vibration-based condition monitoring of rotating machine has gained special interest providing an efficient aid for maintenance in the industry. Nowadays, many efficient techniques are well-established, rooted on powerful tools offered in particular by the theory of cyclostationary processes. However, all these techniques rely on the assump-tion of constant— or possibly fluctuating but stationary— operating regime (i.e. speed and/or load). Unfortunately, most monitored machines used in the industry operate under nonstationary regimes in order to fulfill the task for which they have been designed. In this case, these techniques fail in analyzing the produced vibration signals. This issue, therefore, has occupied the scientific committee in the last decade and some sophisticated signal processing techniques have been conceived to deal with regime variability. But these works remain limited, dispersed and generally not supported by theoretical frameworks. The principal goal of this thesis is to partially fill in this gap on the basis of a theoretical formalization of the subject and a systematic development of new dedicated signal processing tools. In this work, the nonstationarity of the regime is confined to that of the speed— i.e. variable speed and constant load, assumed to be known a priori. In order to reach this goal, the adopted methodology consists in extending the cyclostationary framework together with its dedicated tools. We have elaborated this strategy by distinguishing two types of signatures. The first type includes deterministic waveforms known as first-order cyclostationary. The proposed solution consists in generalizing the first-order cyclostationary class to the more general first-order cyclo-non-stationary class which enfolds speed-varying deterministic signals. The second type includes random periodically-correlated waveforms known as second-order cyclostationary. Three different but complementary visions have been proposed to deal with the changes induced by the nonstationarity of the operating speed. The first one adopts an angle\time cyclostationary approach, the second one adopts an envelope-based solution and the third one adopts a (second-order) cyclo-non-stationary approach. Many tools have been conceived whose performances have been successfully tested on simulated and real vibration signals
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Gavrilovic, Nenad. "VIBRATION-BASED HEALTH MONITORING OF ROTATING SYSTEMS WITH GYROSCOPIC EFFECT." DigitalCommons@CalPoly, 2015. https://digitalcommons.calpoly.edu/theses/1358.
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This thesis focuses on the simulation of the gyroscopic effect using the software MSC Adams. A simple shaft-disk system was created and parameter of the sys-tem were changed in order to study the influence of the gyroscopic effect. It was shown that an increasing bearing stiffness reduces the precession motion. Fur-thermore, it was shown that the gyroscopic effect vanishes if the disk of system is placed symmetrically on the shaft, which reduces the system to a Jeffcott-Ro-tor. The second objective of this study was to analyze different defects in a simple fixed axis gear set. In particular, a cracked shaft, a cracked pinion and a chipped pinion as well as a healthy gear system were created and tested in Adams. The contact force between the two gears was monitored and the 2D and 3D frequency spectrum, as well as the Wavelet Transform, were plotted in order to compare the individual defects. It was shown that the Wavelet Transform is a powerful tool, capable of identifying a cracked gear with a non-constant speed. The last part of this study included fault detection with statistical methods as well as with the Sideband Energy Ratio (SER). The time domain signal of the individual faults were used to compare the mean, the standard deviation and the root mean square. Furthermore, the noise profile in the frequency spectrum was tracked with statistical methods using the mean and the standard deviation. It was demonstrated that it is possible to identify a cracked gear, as well as a chipped gear, with statistical methods. However, a cracked shaft could not be identified. The results also show that SER was only capable to identify major defects in a gear system such as a chipped tooth.
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Jhinaoui, Ahmed. "Subspace-based identification and vibration monitoring algorithms for rotating systems." Thesis, Rennes 1, 2014. http://www.theses.fr/2014REN1S161.
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Les méthodes d'identification dites sous-espace sont largement utilisées pour la caractérisation des modes propres et la surveillance des structures mécaniques. Elles ont fait leurs preuves pour les systèmes dont la dynamique est invariante dans le temps. Elles ne sont, toutefois, pas adaptées à des systèmes à rotors comme les hélicoptères et les éoliennes qui, de part leurs parties tournantes, sont périodiques dans le temps. Le but de cette thèse est d'étendre le champ d'application de ces méthodes à cette classe particulière de systèmes. Tout d'abord, un algorithme qui permet d'identifier certaine structure modale, dite de Floquet, est proposée. Ensuite, une étude de sensibilité est réalisée dans le but de quantifier les incertitudes, liées aux bruits ou à d'autres facteurs, sur les paramètres modaux identifiés. Enfin et partant de l'algorithme d'identification, une méthode de détection d'instabilité est développée. Cette méthode est basée sur la définition d'un résidu, fonction des paramètres modaux, et la surveillance d'un changement éventuel de ce résidu qui correspond à une déviation vers un régime instable. Ces méthodes ont été appliquées à des modèles numériques et à des données expérimentalesSubspace identification methods are widely used for caracterizing modal param-eters and for vibration monitoring of mechanical structures. They were shown powerful for the so-called linear time-invariant systems. However, they are not adapted to rotating sys-tems such as helicopters and wind turbines, which are inherently time-periodic systems. The goal of this thesis is to extend the applicability of these methods to this particular class of systems. First, a new identification algorithm is suggested. This algorithm permits to iden-tify the so-called Floquet modal structure. Then, a sensitivity study is conducted in order to quantify uncertainties, related to noises and other sources, about the identified modal param-eters. Finally and based on the suggested identification algorithm, a method for instability detection is developed. The main feature of this method is to define some residual, which is function of modal parameters, then to detect an eventual change over it which means a possible deviation toward an unstable regime. The suggested methods were applied to both numerical and experimental data
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Chen, Zhidong. "Machine condition monitoring based on the analysis of transient vibration signals." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape4/PQDD_0016/NQ58400.pdf.
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Smith, Chandler B. "Sparsity Constrained Inverse Problems - Application to Vibration-based Structural Health Monitoring." ScholarWorks @ UVM, 2019. https://scholarworks.uvm.edu/graddis/1143.
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Vibration-based structural health monitoring (SHM) seeks to detect, quantify, locate, and prognosticate damage by processing vibration signals measured while the structure is operational. The basic premise of vibration-based SHM is that damage will affect the stiffness, mass or energy dissipation properties of the structure and in turn alter its measured dynamic characteristics. In order to make SHM a practical technology it is necessary to perform damage assessment using only a minimum number of permanently installed sensors. Deducing damage at unmeasured regions of the structural domain requires solving an inverse problem that is underdetermined and(or) ill-conditioned. In addition, the effects of local damage on global vibration response may be overshadowed by the effects of modelling error, environmental changes, sensor noise, and unmeasured excitation. These theoretical and practical challenges render the damage identification inverse problem ill-posed, and in some cases unsolvable with conventional inverse methods.
This dissertation proposes and tests a novel interpretation of the damage identification inverse problem. Since damage is inherently local and strictly reduces stiffness and(or) mass, the underdetermined inverse problem can be made uniquely solvable by either imposing sparsity or non-negativity on the solution space. The goal of this research is to leverage this concept in order to prove that damage identification can be performed in practical applications using significantly less measurements than conventional inverse methods require. This dissertation investigates two sparsity inducing methods, L1-norm optimization and the non-negative least squares, in their application to identifying damage from eigenvalues, a minimal sensor-based feature that results in an underdetermined inverse problem. This work presents necessary conditions for solution uniqueness and a method to quantify the bounds on the non-unique solution space. The proposed methods are investigated using a wide range of numerical simulations and validated using a four-story lab-scale frame and a full-scale 17 m long aluminum truss. The findings of this study suggest that leveraging the attributes of both L1-norm optimization and non-negative constrained least squares can provide significant improvement over their standalone applications and over other existing methods of damage detection.
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Fang, Brian. "CAE Methods on Vibration-based Health Monitoring of Power Transmission Systems." DigitalCommons@CalPoly, 2013. https://digitalcommons.calpoly.edu/theses/1143.
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This thesis focuses on different methods to analyze power transmission systems with computer software to aid in detection of faulty or damaged systems. It is split into three sections. The first section involves utilizing finite element software to analyze gear stiffness and stresses. A quasi-static and dynamic analysis are done on two sets of fixed axis spur gears and a planetary gear system using ABAQUS to analyze the stress, strain and gear mesh stiffness variation. In the second section, the vibrational patterns produced by a simple bevel gear system are investigated by an experiment and by dynamic modeling in ADAMS. Using a Fast Fourier Transform (FFT) on the dynamic contact forces, a comprehensive frequency-domain analysis will reveal unique vibration spectra at distinct frequencies around the gear mesh frequencies, their super- and sub- harmonics, and their side-band modulations. ADAMS simulation results are then compared with the experimental results. Constraints, bearing resistant torques, and other key parameters are applied as closely as possible to real operating conditions. The third section looks closely at the dynamic contact forces of a practical two-stage planetary gear. Using the same FFT approach in the second section, a frequency-domain analysis will reveal distinct frequencies around both the first-stage and the second-stage gear mesh frequencies, and their harmonics. In addition, joint time-frequency analysis (JTFA) will be applied to damaged and undamaged planetary gear systems with transient start-up conditions to observe how the frequency contents of the contact force evolve over time.
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Afshari, Mana. "Vibration- and Impedance-based Structural Health Monitoring Applications and Thermal Effects." Diss., Virginia Tech, 2012. http://hdl.handle.net/10919/27954.
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Structural Health Monitoring (SHM) is the implementation of damage detection and characterization algorithms using in vitro sensing and actuation for rapidly determining faults in structural systems before the damage leads to catastrophic failure. SHM systems provide near real time information on the state of the integrity of civil, mechanical and aerospace structures. A roadblock in implementing SHM systems in practice is the possibility of false positives introduced by environmental changes. In particular, temperature changes can cause many SHM algorithms to indicate damage when no damage exists. While several experimentally based efforts have been attempted to alleviate temperature effects on SHM algorithms, fundamental research on the effects of temperature on SHM has not been investigated.
The work presented in this dissertation composes of two main parts: the first part focuses on the experimental studies of different mechanical structures of aluminum beams, lug samples and railroad switch bolts. The experimental study of the aluminum lug samples and beams is done to propose and examine methods and models for in situ interrogation and detection of damage (in the form of a fatigue crack) in these specimen and to quantify the smallest detectable crack size in aluminum structures. This is done by applying the electrical impedance-based SHM method and using piezoceramic sensors and actuators. Moreover, in order to better extract the damage features from the measured electrical impedance, the ARX non-linear feature extraction is employed. This non-linear feature extraction, compared to the linear one, results in detection of damages in the micro-level size and improves the early detection of fatigue cracks in structures. Experimental results also show that the temperature variation is an important factor in the structural health monitoring applications and its effect on the impedance-based monitoring of the initiation and growth of fatigue cracks in the lug samples is experimentally investigated. The electrical impedance-based SHM technique is also applied in monitoring the loosening of bolted joints in a full-scale railroad switch and the sensitivity of this technique to different levels of loosening of the bolts is investigated.
The second part of the work presented here focuses on the analytical study and better understanding of the effect of temperature on the vibration-based SHM. This is done by analytical modeling of the vibratory response of an Euler-Bernoulli beam with two different support conditions of simply supported and clamped-clamped and with a single, non-breathing fatigue crack at different locations along the length of the beam. The effect of temperature variations on the vibratory response of the beam structure is modeled by considering the two effects of temperature-dependent material properties and thermal stress formations inside the structure. The inclusion of thermal effects from both of these points of view (i.e. material properties variations and generation of thermal stresses) as independent factors is investigated and justified by studying the formulations of Helmholtz free energy and stresses inside a body. The effect of temperature variations on the vibratory response of the cracked beam are then studied by integrating these two temperature-related effects into the analytical modeling. The effect of a growing fatigue crack as well as temperature variations and thermal loadings is then numerically studied on the deflection of the beam and the output voltage of a surface-bonded piezoceramic sensor.Ph. D.
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García, Cava David. "Data-based vibration structural health monitoring methodology for composite laminated structures." Thesis, University of Strathclyde, 2016. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=26903.
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Composite materials are steadily replacing traditional materials in a wide range of industry sectors thanks to their remarkable properties. Damage in composite materials exhibits complex failure modes which are difficult to identify by conventional techniques. Composite materials demonstrate complex nonlinear vibration behaviour where conventional vibration-based structural health monitoring (VSHM) methods might not give adequate information for damage identification. This thesis investigates the capabilities of singular spectrum analysis (SSA) as a technique for developing a completely data-based VSHM methodology. The methodology decomposes the vibration responses in a certain number of principal components having in consideration all rotational patterns at any frequency including the nonlinear oscillations. This thesis develops two approaches to use SSA in the time and frequency domain. The methodology has been validated using a numerical system and an experiment with delaminated beams. The results demonstrate the methodology capability for assessing damages at different locations and with different sizes. The progression of damage can also be tracked. Delamination was successfully assessed in composite laminated plates with different delamination locations, in-plane and through different layers. Damage in wind turbine blades was assessed by the damage assessment methodology with a statistical hypothesis inspection phase based on probability distribution functions. Different damage locations and sizes were assessed as well as damage progression. This thesis explores the use of smart materials which enable self-sensing and self-diagnosing of its structural integrity coupled with the data-based VSHM. The results demonstrate the substantial potential of this approach. Overall, the data-based VSHM methodology presented in this thesis is proven to give adequate information about the presence, location and extent of delamination and other defects in different composite laminated structures.
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El-Haram, Mohamed Abdulla. "Integrated approach to condition-based reliability assessment and maintenance planning." Thesis, University of Exeter, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.318185.
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Ou, Qing. "Vibration-based Energy Harvesting for Wireless Sensors used in Machine Condition Monitoring." Thesis, University of Canterbury. Mechanical Engineering, 2012. http://hdl.handle.net/10092/7234.
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In a wide range of industries, machine condition monitoring is one of the most cost effective ways to minimise maintenance efforts and machine downtime. To implement such a system, wireless solutions have increasingly become an attractive proposition due to the ease of installation and minimal infrastructure alternation. However, currently most wireless sensors in the world are powered by a finite battery source. The dependence of batteries not only requires frequent maintenance, but also has adverse environmental consequences associated with battery disposal. These reasons render massive deployment of wireless sensors in the industry problematic. With the advances in semiconductors, power consumption of wireless sensors has been continuously decreasing. It is an inevitable trend for self-powered wireless sensors to emerge and become the norm for machine and environmental monitoring. In this research, vibration is chosen to be the energy source to enable self-powered wireless sensors due to its ubiquitousness in machinery and industrial environments. As a result of relying on resonance, the biggest challenge for vibration-based energy harvesters is their narrow bandwidth. Even a small deviation of the vibration frequency can dramatically reduce the power output. The primary goal of this research is to address this problem. In particular, Piezoelectric generators are identified to be the most suitable technology. In this work, extensive theoretical and experimental studies are conducted in single mass and multi-modal harvesters, and in resonance tuning harvesters by modulus and impedance matching as well as by mechanical actuation. Mathematical modelling plays a significant role in energy harvester designs. A dynamic model that generalises the single degree of freedom models and the continuum models is derived and validated by experiments. The model serves as the building block for the whole research, and it is further refined for the investigation of modulus and impedance matching. In the study of multi-modal harvesters, a continuum model for double-mass piezoelectric cantilever beams is derived and experimentally validated. To study the feasibility of resonance tuning by mechanical means, prototypes were built and performance evaluated. This document details the theoretical basis, concepts and experimental results that extend the current knowledge in the field of energy harvesting. This research work, being highly industrially focused, is believed to be a very significant step forward to a commercial energy harvester that works for a wide range of vibration frequencies.
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Abouhnik, Abdelnasser Abouzid. "An investigation into vibration based techniques for wind turbine blades condition monitoring." Thesis, Manchester Metropolitan University, 2012. http://e-space.mmu.ac.uk/313141/.
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The rapid expansion of wind power has been accompanied by reported reliability problems and the aim is to provide a means of increasing wind turbine reliability, prevent break downs, increase availability and reduce maintenance costs and power outages. This research work reports the development of condition monitoring (CM) for early fault detection in wind turbine blades based on vibration measurements. The research started with a background and a survey of methods used for monitoring wind turbines. Then, finite element modelling (FEM) of three bladed horizontal axis wind turbine (HAWT) was developed to understand the nature and mechanism of the induced vibration. A HAWT test rig was constructed and equipped with computerised vibration measuring system for model verification. Statistical and spectral processing parameters then were used to analyse vibration signals that collected in healthy and faulty cases. Results obtained using time and frequency based techniques are not suitable for extracting blades condition related information. Consequently, empirical mode decomposition method (EMD), principal component analysis method (PCA) and continuous wavelet transform (CWT) are applied for extraction blade condition related features from the measured vibration. The result showed that although these methods generally proved their success in other fields, they have failed to detect small faults or changes in blade structure. Therefore, new techniques were developed using the above mentioned methods combined with feature intensity level (FIL) and crest factor. Namely, those are EDFIL, RMPCA and wavelet based FIL. The new techniques are found to be reliable, robust and sensitive to the severity of faults. Those analysis techniques are suitable to be the detection tool for an integrated wind turbine condition monitoring system. Directions for future work are also given at the end of the thesis.
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Oruganti, Krishna, and krishnaov@yahoo com. "Evaluation of Damage in Structures using Vibration-based Analyses." RMIT University. Aerospace, Mechanical and Manufacturing Engineering, 2009. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20091002.143408.
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Composite materials are supplanting conventional metals in aerospace, automotive, civil and marine industries in recent times. This is mainly due to their high strength and light weight characteristics. But with all the advantages they have, they are prone to delamination or matrix cracking. These types of damage are often invisible and if undetected, could lead to appalling failures of structures. Although there are systems to detect such damage, the criticality assessment and prognosis of the damage is often more difficult to achieve. The research study conducted here primarily deals with the structural health monitoring of composite materials by analysing vibration signatures acquired from a laser vibrometer. The primary aim of the project is to develop a vibration based structural health monitoring (SHM) method for detecting flaws such as delamination within the composite beams. Secondly, the project emphasises on the method's ability to recognise the locatio n and severity of the damage within the structure. The system proposed relies on the examination of the displacement mode shapes acquired from the composite beams using the laser vibrometer and later processing them to curvature mode shapes for damage identification and characterization. Other identification techniques such as a C-scan has been applied to validate the location and size of the defects with the structures tested. The output from these plots enabled the successful identification of both the location and extent of damage within the structure with an accuracy of 96.5%. In addition to this, this project also introduces a method to experimentally compute the critical stress intensity factor, KIC for the composite beam. Based on this, a technique for extending the defect has been proposed and validated using concepts of fatigue and fracture mechanics. A composite specimen with a 40 mm wide delamination embedded within was loaded under fatigue conditions and extension of the defect by 4mm on either s ide of the specimen's loading axis was achieved satisfactorily. The experimental procedure to extend the defect using fatigue was validated using the SLV system. Displacement and Curvature mode shapes were acquired post-fatigue crack extension. Upon analysing and comparing the displacement and curvature mode shapes before and after crack extension, the extended delamination was identified satisfactorily.
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Oscar, Sergio Luna Vera. "Vibration-Based Performance Assessment of Prestressed Concrete Bridges." Kyoto University, 2018. http://hdl.handle.net/2433/235075.
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Khan, A. F. "Condition monitoring of rolling element bearings : a comparative study of vibration-based techniques." Thesis, University of Nottingham, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.292225.
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Brethee, Khaldoon F. "Condition monitoring of helical gear transmissions based on vibration modelling and signal processing." Thesis, University of Huddersfield, 2018. http://eprints.hud.ac.uk/id/eprint/34519/.
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Condition monitoring (CM) of gear transmission has attracted extensive research in recent years. In particular, the detection and diagnosis of its faults in their early stages to minimise cost by maximising time available for planned maintenance and giving greater opportunity for avoiding a system breakdown. However, the diagnostic results obtained from monitored signals are often unsatisfactory because mainstream technologies using vibration response do not sufficiently account for the effect of friction and lubrication. To develop a more advanced and accurate diagnosis, this research has focused on investigating the nonlinearities of vibration generation and transmission with the viscoelastic properties of lubrication, to provide an in-depth understanding of vibration generating mechanisms and hence develop more effective signal processing methods for early detection and accurate diagnosis of gear incipient faults. A comprehensive dynamic model has been developed to study the dynamic responses of a multistage helical gear transmission system. It includes not only time-varying stiffness but also tooth friction forces based on an elastohydrodynamic lubrication (EHL) model. In addition, the progression of a light wear process is modelled by reducing stiffness function profile, in which the 2nd and 3rd harmonics of the meshing frequency (and their sidebands) show significant alteration that support fault diagnostic at early stages. Numerical and experimental results show that the friction and progressive wear induced vibration excitations will change slightly the amplitudes of the spectral peaks at both the mesh frequency and its sideband components at different orders, which provides theoretical supports for extracting reliable diagnostic signatures. As such changes in vibrations are extremely small and submerged in noise, it is clear that effective techniques for enhancing the signal-to-noise ratio, such as time synchronous averaging (TSA) and modulation signal bispectrum (MSB) are required to reveal such changes. MSB is preferred as it allows small amplitude sidebands to be accurately characterised in a nonlinear way without information loss and does not impose any addition demands regarding angular displacement measurement as does TSA. With the successful diagnosis of slight wear in helical gears, the research progressed to validate the capability of MSB based methods to diagnose four common gear faults relating to gear tribological conditions; lubrication shortfall, changes in lubrication viscosity, water in oil, and increased bearing clearances. The results show that MSB signatures allows accurate differentiation between these small changes, confirming the model and signal processing proposed in this thesis.
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Elbarghathi, Fathalla. "Condition monitoring of helical gearboxes based on the advanced analysis of vibration signals." Thesis, University of Huddersfield, 2016. http://eprints.hud.ac.uk/id/eprint/30647/.
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Condition monitoring of rotating machinery and machine systems has attracted extensive researches, particularly the detection and diagnosis of machine faults in their early stages to minimise maintenance cost and avoid catastrophic breakdowns and human injuries. As an efficient mechanical system, helical gearbox has been widely used in rotating machinery such as wind turbines, helicopters, compressors and internal combustion engines and hence its vibration condition monitoring is attracting substantial research attention worldwide. However, the vibration signals from a gearbox are usually contaminated by background noise and influenced by operating conditions. It is usually difficult to obtain symptoms of faults at the early stage of a fault. This study focus on developing effective approaches to the detection of early stage faults in an industrial helical gearbox. In particular, continuous wavelet transformation (CWT) has been investigated in order to select an optimal wavelet to effectively represent the vibration signals for both noise reduction and fault signature extraction. To achieve this aim, time synchronous average (TSA) is used as a tool for preliminary noise reduction and mathematical models of a gearbox transmission system is developed for characterising fault signatures. The performance of three different wavelet families was compared and henceforth a criterion and method for the selection of the most discerning has been established. It has been found that the wavelet that gives the highest RMS value for the baseline vibration signal will show the greatest difference between baseline and gearbox vibration with a fault presence. Comparison of the three wavelets families shows that the Daubechies order 1 can give best performance for feature extraction and fault detection and fault quantification. However, there are limitations that undermine CWT application to fault detection, in particular the difficulty in selecting a suitable wavelet function. A major contribution of this research programme is to demonstrate a possible route on how to overcome this deficiency. An adaptive Morlet wavelet transform method has been proposed based on information entropy optimization for analysing the vibration signal and detecting and quantifying the faults seeded into the helical gearbox. This research has also developed a nonlinear dynamic model of the two-stage helical gearbox involving time–varying mesh stiffness and transmission error. Based on experimental data collected with different operating loads and the simulating results vibration signatures for gear faults are fully understood and hence confirms the CWT based scheme for signal enhancement. These results also indicate that the dynamic model can be used in studying gear faults and would be useful in developing gear fault monitoring techniques.
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Lagnebäck, Robert. "Evaluation of wayside condition monitoring technologies for condition-based maintenance of railway vehicles /." Luleå : Luleå University of Technology, 2007. http://epubl.ltu.se/1402-1757/2007/18/.
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Lagnebäck, Robert. "Evaluation of wayside condition monitoring technologies for condition-based maintenance of railway vehicles." Licentiate thesis, Luleå tekniska universitet, Drift, underhåll och akustik, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-18158.
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Luossavaara-Kiirunavaara AB (LKAB) is an iron ore mining company in Sweden that strives to be one of the leading suppliers of iron ore products. In the chain from mining to end customers, transportation efficiency plays a mayor role in the outcome of the company's total financial result. The transportation of the ore from the LKAB mines in Kiruna and Malmberget is made by trains to the harbors in Narvik and Luleå. The railway transportations are made by LKAB subsidiaries Malmtrafik i Kiruna AB (MTAB) on the Swedish side and Malmtrafikk AS (MTAS) on the Norwegian side. The efficiency of the railway transportation is therefore a key function in the LKAB mining operations. In a benchmarking, comparing the total operating efficiency, with other heavy haul railways around the world it became evident that the efficiency of the railway transportations at LKAB had potential for improvement. One of the factors with potential for improved efficiency was the maintenance strategy. There is an indication that a change from a time-based maintenance strategy to a condition-based maintenance strategy would increase the efficiency of the train operations. The purpose of this thesis is to study and analyze wayside condition monitoring equipment for railway vehicles, in order to support the implementation of a condition-based maintenance strategy. To fulfill the stated purpose, five case studies, supported by a literature study, have been performed. The five case studies have been conducted to increase the knowledge of the abilities of available wayside condition monitoring equipment as a support for condition-based maintenance of railway vehicles. The literature study focused on railway operations around the world with a particular focus on the development, deployment and use of wayside condition monitoring equipment. The literature study indicates that there is an increasing implementation and use of equipment for wayside condition monitoring of railway vehicles. Through the studies it has become evident that the direct interaction in the wheel and rail interface also creates a huge potential for savings on the infrastructure due to an implementation of wayside condition monitoring equipment for railway vehicles. The case studies highlight the need for different systems that complement each other by measuring different parameters. It is also important that the systems are integrated with existing systems and practices in order to exploit the potential benefits of the new technology. Furthermore, it is important to have a joint approach between both infrastructure owners and train operators in the deployment and use of wayside condition monitoring equipment, since the technology can support a condition-based maintenance strategy on both sides that could have a great impact on the efficiency of railway operations.Luossavaara-Kiirunavaara AB (LKAB) är ett Svenskt gruvbolag som bryter järnmalm. Man har som målsättning att bli en av de ledande leverantörerna i världen av järnmalmsprodukter. I kedjan från brytning till slutkund, spelar transporteffektivitet en avgörande roll i företagets totala ekonomiska resultat. Transporterna av malm från LKAB:s gruvor i Kiruna och Malmberget utförs med järnvägstransporter till utskeppningshamnar i Narvik och Luleå. Järnvägstransporterna utförs av LKAB:s dotterbolag Malmtrafik i Kiruna AB (MTAB) på den Svenska sidan och av Malmtrafikk AS (MTAS) på den Norska sidan. Järnvägs transporternas effektivitet är därför en nyckelfunktion i LKAB:s gruvbrytningsverksamhet. I en benchmarkingstudie utförd på den totala effektiviteten av verksamheten hos gruvverksamheter med tunga järnvägstransporter runt om i världen blev det uppdagat att det finns en potential att förbättra effektiviteten hos LKAB:s järnvägstransporter. En av faktorerna som har potential att förbättra effektiviteten är underhållsstrategin. Det finns tydliga indikationer på att en förändring från ett förutbestämt underhåll till ett tillståndsbaserat underhåll skulle kunna öka järnvägstransporternas effektivitet. Syftet med denna licentiat avhandling är att utvärdera tekniska system som kan placeras vid spåret och användas som tillstånds övervakande utrustning för järnvägsfordon för att stödja en implementering av en tillståndsbaserad underhållsstrategi.För att uppnå det utsatta syftet har fem fallstudier, samt en litteratur studie genomförts. De fem fallstudierna har utförts för att öka kunskapen om egenskaperna hos tillgänglig tillståndsövervakande utrustning för placering vid spåret som stöd för tillståndsbaserat underhåll av järnvägsfordon. Litteraturstudien har fokuserats på järnvägsverksamheter i runt om i världen med speciellt fokus på utveckling, utplacering och användande av spårbunden tillståndsövervakningsutrustning .Litteraturstudien indikerar att det pågår en ökande implementering och användning av tillståndsövervakande utrustning för järnvägsfordon. Genom studierna har det framkommit att den direkta interaktionen mellan hjul och räl också skapar en stor potential för besparingar på infrastrukturen med hjälp av en implementering av spårbunden tillståndsövervakande utrustning för järnvägsfordonen.Case studierna belyser nödvändigheten av att ha olika system som kan komplettera varandra genom att mäta olika parametrar. Det är också viktigt att systemen är integrerade med existerande system och metoder för att uppnå de potentiella fördelarna med den nya teknologin. Det är dessutom viktigt att ha ett gemensamt tillvägagångssätt mellan både infrastrukturägare och tågoperatörer i implementeringen och användandet av spårbunden tillståndsövervakande utrustning, eftersom teknologin kan stödja en tillståndsbaserad underhålls strategi för båda sidor, vilket kan ha stor positiv inverkan på järnvägsdriftens effektivitet.
Godkänd; 2007; 20070315 (ysko)
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Serra, López Roger. "Numerical and experimental investigation of spectral domain vibration based indicators for structural health monitoring." Doctoral thesis, Universitat Politècnica de Catalunya, 2018. http://hdl.handle.net/10803/586170.
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Structural health monitoring has been defined as the acquisition, validation and analysis of technical data to facilitate life- cycle management decisions. It is the result of a convergent path from many previous existing disciplines the two most influential being condition monitoring for rotary machinery and non-destructive testing. Vibration based testing presents the greatest stage of maturity of all non-destructive techniques applied to structural health monitoring. Although modal domain use is convention, spectral domain data is by nature more complete in information and requires less manipulation. The use of spectral-domain measurements brings the need to develop new damage detection indicators, as much of the literature existing is focused on modal derived damage indicators.
In this work, an integrated methodology for the evaluation of some spectral domain vibration based indicators for structural health monitoring is proposed. These indicators, namely the CFDAC and SCIs, are based on the correlation between covariance matrices of frequency response functions obtained from experimental modal analysis.
An extensive numerical campaign is performed on a simple structure (consisting on a 1-edge clamped square aluminium plate) over multiple structural alteration scenarios to assess the sensibility and stability of the proposed indexes in front of common acquisition parameters. The ability of the proposed indicators to assess structural alteration progression is also evaluated. This numerical analysis is used as well to observe the relationship between proposed indicators and the residual stiffness of the simple structure evaluated in terms of relative shift from the pristine condition. Finally, the numerical methodology proposed is applied to a different and more complex typology of structure, a 3d latticed and downscaled power transmission tower to investigate the validity of the methodology for other structural configurations.
Some of the cases studied in the numeric campaign are later reproduced in experimental scenarios using two specimens of aluminium plates and a downscaled prototype of a power transmission tower. Stability analysis on the indicators are reproduced and confirmed. For the aluminium plates, the relationship between indicators and residual stiffness is also obtained, showing close agreement with numerical data. Sensibility of the indicators to detect different damage typologies is found to be very similar to the one obtained in the initial numerical analysis. Results for the downscaled prototype model tower shown more dispersion than the results observed in the numerical investigation due to the influence of the boundary conditions in the model.
The research finally applies the structural damage alteration indexes studied to the detection of degradation in a real scale structure in an operational environment. An installation consisting of 3 full-scale medium-voltage power transmission towers is constructed. An experimental modal analysis campaign is performed on the central tower of the installation by introducing a series of intentionally made structural alterations on the structure. Spectral indicators developed are applied to the detection of those structural modifications with noticeable success. Cases involving changes in the structural components of the tower are successfully detected. Changes in the interface between power lines and their supports of the tower are hardly noticeable using this methodology.
Results of this investigation show that spectral domain damage indicators present some advantages over modal domain and temporal domain based indicators such as convenient condensing procedures without loss of information through the Fourier transform, added post-process simplicity and enhanced sensitivity to degradation that state of the art indexes.Es coneix com monitorització de la salut estructural a l'adquisició, validació i anàlisis de dades tècniques que faciliten la presa de decisions al llarg del cicle de vida d'un sistema. Aquesta tecnologia és resultat de la convergència tecnològica d'altres disciplines, com la monitorització operacional per màquines rotatòries i les tècniques d'assaig no destructiu. Els mètodes d'assaig basats en vibracions presenten el major grau de maduresa d'entre totes elles. Malgrat que la pràctica industrial sovint usa informació condensada en el domini modal, les dades en domini espectral son per naturalesa més completes i requereixen de menys post-procés. La utilització del domini espectral requereix desenvolupar nous indicadors d'alteració ja que la major part de la literatura existent se centra en indicadors basats en el domini modal. Es proposa una metodologia integrada per a la avaluació d'alguns indicadors d'alteració estructural en domini modal basats en vibració i aplicats a la monitorització de la salut estructural. Aquests indicadors, referits com a CFDAC i SCIs, estan basats en la correlació entre les matrius de covariància generades a partir de les funcions de resposta en freqüència obtingudes mitjançant anàlisi modal experimental. Es realitza una extensa campanya numèrica en una estructura senzilla (una placa d'alumini quadrada i encastada) a través d'una multitud d'estats estructuralment alterats per avaluar la sensibilitat i l'estabilitat dels indicadors enfront els paràmetres d?adquisició més comuns. En segon lloc, també s?avalua la capacitat dels indicadors per avaluar l'alteració estructural introduïda en cada cas. L'anàlisi numèrica s'utilitza a continuació per observar una possible relació entre els indicadors proposats i la rigidesa residual avaluada com a variació relativa respecte el seu valor intacte. Finalment, la metodologia numèric proposada s'aplica a una tipologia estructural diferent i més complexa, una estructura reticulada 3d que reprodueix una torre de transmissió d'energia elèctrica a escala per investigar la validesa de la metodologia en altres configuracions estructurals. Alguns dels casos estudiats a la campanya numèrica es reprodueixen experimentalment en un parell d?espècimens de placa d'alumini i en un prototip a escala de torre de transmissió elèctrica. Els anàlisis d'estabilitat numèrics sobre els indicadors es reprodueixen experimentalment, tot confirmant els resultats obtinguts. Per les plaques d'alumini, s'estudia la relació entre els indicadors i la rigidesa residual mostrant una correlació molt propera amb els resultats numèrics. La sensibilitat dels indicadors en la detecció de diferents tipologies de dany també s'observa molt similar als casos numèrics. Pere altra banda, els resultats experimentals sobre el prototip de torre a escala presenten més dispersió respecte a la corresponent campanya numèrica degut a la variabilitat en les condicions de contorn. Els indicadors proposats s'apliquen finalment en la detecció d'alteracions estructurals en una torre a escala real en condicions operacionals. Es construeix una línia que consisteix en tres torres de mitja tensió i s'executen anàlisis modals experimentals en la torre central de la mencionada instal·lació tot introduint una sèrie d'alteracions estructurals intencionals. Els indicadors espectrals presentats s'apliquen a la detecció de dites alteracions amb un èxit apreciable. Els casos que incorporen canvis en els membres de l'estructura son detectats amb èxit, mentre que la detecció en els casos que incorporen modificacions sobre les interfícies cable-estructura son més difusament detectables. Els resultats de la investigació mostren que els indicadors estructurals espectrals estudiats presenten algunes avantatges sobre els indicadors basats en domini com ara un procés de condensació més senzill sense pèrdua d'informació vibratòria (...)
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Ojeda, Alejandro P. "MATLAB implementation of an operational modal analysis technique for vibration-based structural health monitoring." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/74412.
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Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2012.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 72-73).
Vibration-based structural health monitoring (SHM) has become an attractive solution for the global monitoring and evaluation of damage in structures. Numerous damage detection schemes used in vibration-based SHM require knowledge of the modal properties of the structure under evaluation in its current state. The technique of operational modal analysis allows for these modal properties to be obtained by using the structure's dynamic response to ambient excitation. Using MATLAB, a type of operational modal analysis technique called time domain decomposition (TDD) based on [15] was implemented. The MATLAB TDD implementation was applied to the dynamic responses from two finite element models of simply-supported beams and their modal frequencies and shapes were extracted. The first three modal frequencies were obtained with less than 6 percent error from the actual values and the fundamental mode shape values obtained contained negligible deviations from the actual mode shape values. However, the higher order mode shapes obtained were more inaccurate, suggesting limitations to the current MATLAB TDD implementation. Lastly, changes to the moment of inertia of the simply-supported beam models were used to simulate damage in the finite element models and cause their fundamental mode frequency to change. The MATLAB TDD implementation was able to distinguish changes in the fundamental frequency of both finite element models with a resolution of approximately 1.7 radians per second (7.2 percent).
by Alejandro P. Ojeda.
M.Eng.
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Veta, Jacob E. "Analysis and Development of a Lower Extremity Osteological Monitoring Tool Based on Vibration Data." Miami University / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=miami1595879294258019.
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Obiora, Obinna Chukwuemeka. "Wireless condition monitoring to reduce maintenance resources in the Escravos–Gas–To–Liquids plant, Nigeria / Obiora, O.C." Thesis, North-West University, 2011. http://hdl.handle.net/10394/7040.
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The purpose of this research is to reduce maintenance resources and improve Escravos–Gas–to–Liquids plant availability (EGTL) in Escravos, Nigeria using wireless condition monitoring. Secondary to the above is to justify the use of this technology over other conventional condition monitoring methods in petrochemical plants with specific reference to cost, reliability and security of the system.
Wireless and continuous condition monitoring provides the means to evaluate current conditions of equipment and detect abnormalities. It allows for corrective measures to be taken to prevent upcoming failures. Continuous monitoring and event recording provides information on the energized equipment's response to normal and emergency conditions.
Wireless/remote monitoring helps to coordinate equipment specifications and ratings, determine the real limits of the monitored equipment and optimize facility operations. Bentley N, (2005).
Using wireless techniques eliminate any need for special cables and wires with lower installation costs if compared to other types of condition monitoring systems.
In addition to this, wireless condition monitoring works well under difficult conditions in strategically important locations. The Escravos gas–to–liquid plant in Nigeria, located in a remote and offshore area where accommodation and space for offices is a factor for monitoring plant conditions in every office, is a typical example. Wireless technology for condition monitoring of energized equipment is applicable to both standalone and remote systems.
In the research work of Meyer and Brambley (2002), they characterized the current problem with regards to cost effectiveness and availability of wireless condition monitoring. Maintenance of rotating equipment provides probability estimates of the total impact of the problem, cost implication of plant equipment maintenance and describes a generic system in which these developing technologies are used to provide real–time wireless/remote condition monitoring for rotating main air compressor (MAC) units and their components as a case study.
Costs with today’s technology are provided and future costs are estimated, showing that benefits will greatly exceed costs in many cases, particularly if low–cost wireless monitoring is used.
With management trends such as “re–engineering” and “downsizing” of the available workforce, wireless condition–monitoring of critical machines has been given more importance as a way to ensure quality production with fewer personnel. Wireless condition–monitoring using inexpensive wireless communication technology frees up existing plant maintenance personnel work on machines that are signaling problems and focusing the maintenance efforts away from attempting to work on a large population of machines to only those machines requiring immediate attention.
Lloyd and Buddy (200) suggested that Point–to–point wireless data transmission systems, an excellent example of recent technological advances in communication systems, are now practical and cost–effective for industrial use. While both complex infrastructures and complex protocols are required for cellular communications, non– cellular communication systems, such as the point–to–point wireless data transmission system example, require no elaborate infrastructure.
Limited research was done on the immediate benefits of implementing wireless condition monitoring systems in plants. All papers on the subject have been drawn up by manufacturers of such equipment. This research will thus also deliver a "third–party" perspective on the effectiveness of such devices, justifying their impact on data gathering security, cost and reliability.Thesis (M.Ing. (Development and Management Engineering))--North-West University, Potchefstroom Campus, 2012.
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RAMOS, JOSÉ DIVAL PASTOR. "DESENVOLVIMENTO DE UM SISTEMA MULTICANAL PARA ANÁLISE DE PULSAÇÃO DE PRESSÃO EM COMPRESSORES ALTERNATIVOS VISANDO A MANUTENÇÃO PREDITIVA." Escola Politécnica / Instituto de Matemática, 2006. http://repositorio.ufba.br/ri/handle/ri/21587.
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A necessidade de novas metodologias para análise e monitoramento de compressores alternativos motivou o desenvolvimento de um sistema digital multicanal com capacidade de medir diferentes grandezas simultaneamente. Como base para este trabalho escolheu-se medir pressão dinâmica, vibração e deslocamento do pistão. O desenvolvimento deste trabalho dentro de um curso de Mecatrônica produziu um sistema simples e eficiente cujos resultados experimentais, apresentados sob a forma de gráficos e dados de desempenho, confirmaram os defeitos introduzidos artificialmente. Isto permitiu validar o Sistema de Diagnóstico de Compressores Alternativos (SDCA) e demonstrou o quanto este recurso é poderoso para o diagnóstico de defeitos, tanto nos componentes da parte de compressão (fluid end) quanto nos de acionamento (power end). Estas informações, transformadas em recomendações de reparo, serão a base para uma atuação preditiva dos setores de Planejamento de Manutenção.
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Goncalves, Rafael dos Santos. "Applications of Vibration-Based Occupant Inference in Frailty Diagnosis through Passive, In-Situ Gait Monitoring." Thesis, Virginia Tech, 2021. http://hdl.handle.net/10919/104868.
Full textAbstract:
This work demonstrates an application of Vibration-Based Occupant Inference (VBOI) in frailty analysis. The rise of both Internet-of-Things (IoT) and VBOI provide new techniques to perform gait analysis via footstep-induced vibration which can be analyzed for early detection of human frailty. Thus, this work provides an application of VBOI to passively track gait parameters (e.g., gait speed) using floor-mounted accelerometers as opposed to using a manual chronometer as it is commonly performed by healthcare professionals.
The first part of this thesis describes the techniques used for footstep detection by measuring the power of the footstep-generated vibration waves. The extraction of temporal gait parameters from consecutive footsteps can then be used to estimate temporal features such as cadence and stride time variation.
VBOI provides many algorithms to accurately detect when a human-induced vibration event happened, however, spatial information is also needed for many gait parameters used in frailty diagnosis. Detecting where an event happened is a complicated problem because footsteps waves travel and decay in different ways according to the medium (floor system), the number of people walking, and even the walking speed. Therefore, the second part of this work will utilize an energy-based approach of footstep localization in which it is assumed that footstep waves decay exponentially as they travel across the medium. The results from this approach are then used to calculate spatial and tempo-spatial parameters.
The main goal of this study is to understand the applicability of VBOI algorithms in gait analysis for frailty detection in a healthcare setting.Master of Science
Human frailty is responsible for one of the highest healthcare costs and the death of many people every year. Although anyone suffering from frailty has a higher chance of death, it is particularly dangerous for the elderly population and for those suffering from other comorbidities. Diagnosing frailty is hard because it usually happens slowly over time. However, it has been shown that changes in some walking parameters (such as gait speed) can be an early indication of frailty. Many technologies have been created in order to track gait parameters, many of which either require expensive equipment (e.g., force plates) or the use of wearable devices, which can introduce privacy concerns. It has been proposed in the literature that Vibration-Based Occupant Inference (VBOI) techniques could be used in healthcare applications. Such algorithms measure footstep-induced vibration waves in order to detect and track footsteps. This system can provide several advantages in frailty analysis because of its affordability, ease of use, and little impact on patients' privacy. Therefore, the aim of this study is to understand the applicability of VBOI algorithms in gait analysis for frailty detection to be used in a healthcare setting. This thesis will proceed as follows: 1- The demonstration of an energy-based footstep detection and localization algorithm in VBOI. 2 - The application of such algorithms for gait parameters extraction with simulated frail walkers. 3 - Finally, an analysis of the proposed VBOI techniques for deployment in a real hospital setting.
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Haji, Agha Mohammad Zarbaf Seyed Ehsan. "Vibration-based Cable Tension Estimation in Cable-Stayed Bridges." University of Cincinnati / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1535636861655531.
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