Low-speed bearing fault diagnosis based on permutation and spectral entropy measures

Despite its influence on wind energy service life, condition-based maintenance is still challenging to perform. For offshore wind farms, which are placed in harsh and remote environments, damage detection is critically important to schedule maintenance tasks and reduce operation and maintenance costs. One critical component to be monitored on a wind turbine is the pitch bearing, which can operate at low speed and high loads. Classical methods and features for general purpose bearings cannot be applied effectively to wind turbine pitch bearings owing to their specific operating conditions (high loads and non-constant very low speed with changing direction). Thus, damage detection of wind turbine pitch bearings is currently a challenge. In this study, entropy indicators are proposed as an alternative to classical bearing analysis. For this purpose, spectral and permutation entropy are combined to analyze a raw vibration signal from a low-speed bearing in several scenarios. The results indicate that entropy values change according to different types of damage on bearings, and the sensitivity of the entropy types differs among them. The study offers some important insights into the use of entropy indicators for feature extraction and it lays the foundation for future bearing prognosis methods.Postprint (published version

Diagnosis of low-speed bearings via vibration-based entropy indicators and acoustic emissions

Tesi del Pla de doctorat industrial de la Generalitat de Catalunya. Tesi en modalitat compendi de publicacions, amb diferents seccions retallades per drets dels editorsWind energy is one ofthe main renewable energies to replace fossil fuels in the generation of electricityworldwide. To enhance and accelerate its implementation at a large scale, it is vital to reduce the costs associated with maintenance. As com ponent breakages force the turbine to stop for long repair times, the wind industry m ust switch from the old-fashioned preventive or corrective maintenance to condition-based maintenance (also called predictive maintenance). The condition­based maintenance of pitch bearings is especiallychallenging, as the operating conditions include high mechanical stress and low rotational speed. Since these operating conditions im pact negatively on the results of the standard methods and techniques applied in current condition-based monitoring systems, the condition-based maintenance of pitch bearings is still a challenge. Therefore, this thes is is focused on the research of novel methods and techniques that obtain reliable information on the state of pitch bearings for condition-based maintenance. lnitially, the acknowledgment ofthe state ofthe art is performed to recognize the methods and signals. This step endorses the decision to analyze the vibration signals and acoustic emissions throughout this thesis. Due to the particular operating conditions of pitch bearings, this research states the need to create data sets to replicate the particular operating conditions in a controlled laboratory experiment. As a res ult, a datas et based on vibrations, and a second datas et based on acoustic emissions are generated. The vibration datas et allows the validation of a novel algorithm for the low-speed bearing diagnosis, which is based on the concept of entropy by the definition of Shannon and Rényi. In com parison to the classical methods found in the literature, the diagnosis of low-speed bearings based on entropy-based indicators can extract more reliable information. Moreover, the research of the com bination of several indicators to improve the diagnosis revea Is that the entropy-based indicators can extract more information than regular indicators used in academia. The datas et of acoustic emissions from low-speed bearings helps to contribute to the development of methods for diagnosis. In this research, the analysis of the energyfrom the signals reveals a dependencyon the intensityand the presence of damage. In addition, a relation between the waveform ofthe analyzed energy and the existence of damage is em phas ized.La energía eólica es una de las principales energías renovables consideradas para reemplazar los combustibles fósiles en la generación de electricidad a nivel mundial. Para mejorar y acelerar su implementación a gran escala, es vital reducir los costes asociados con el mantenimiento. Como las roturas de los componentes obligan a la turbina a detenerse durante largos períodos de reparación, la industria eólica necesita cambiar del anticuado mantenimiento preventiv o correctivo al mantenimiento basado en la condición (también llamado mantenimiento predictivo). El mantenimiento basado en la condición de los rodamientos pitch es especialmente desafiante, porque las condiciones de operación incluyen un alto estrés mecánico y bajas velocidades de rotación. Debido a que estas condiciones de operación impactan negativamente en los resultados de los métodos y técnicas estándar aplicados en los sistemas actuales de monitoreo basados en el estado, el mantenimiento basado en el estado de los rodamientos pitch sigue siendo un desafío. Por tanto, esta tesis se centra en la investigación de métodos y técnicas novedosas que obtengan información fiable sobre el estado de los rodamientos pitch para el mantenimiento basado en la condición. Inicialmente, se realiza el reconocimiento del estado del arte para reconocer los métodos y señales utilizados. Este paso avala la decisión de analizar las señales de vibración y las emisiones acústicas a lo largo de esta tesis. Debido a las condiciones de funcionamiento particulares de los rodamientos pitch, esta investigación reconoce la necesidad de crear un conjunto de datos para replicar las condiciones de funcionamiento particulares del rodamiento pitch en una experiencia de laboratorio controlado. Como resultado, se genera un conjunto de datos basado en vibraciones y un segundo conjunto de datos basado en emisiones acústicas. El conjunto de datos de vibraciones permite la validación de un algoritmo novedoso para el diagnóstico de rodamientos de baja velocidad, el cual se basa en el concepto de la entropía según la definición de Shannon y Rényi. En comparación con los métodos clásicos que se encuentran en la literatura, el diagnóstico de rodamientos de baja velocidad basado en indicadores basados en la entropía puede extraer información más confiable. Además, la investigación de la combinación de varios indicadores para mejorar el diagnóstico revela que los indicadores basados en la entropía pueden extraer más información que los indicadores habituales utilizados en la academia. El conjunto de datos de las emisiones acústicas de los rodamientos de baja velocidad ayuda a contribuir al desarrollo de métodos de diagnóstico. En esta investigación, el análisis de la energía de las señales revela una dependencia de la intensidad y la presencia de daño. Además, se enfatiza una relación entre la forma de onda de la energía analizada y la existencia de daño.L'energia eòlica és una de les principals energies renovables considerades per reemplaçar els combustibles fòssils en la generació d'electricitat a nivell mundial. Per millorar i accelerar la seva implementació a gran escala, és vital reduir els costos associats amb el manteniment. Com els trencaments dels components obliguen a la turbina a aturar-se durant llargs períodes de reparació, la industria eòlica necessita canviar de l'antiquat manteniment preventiu o correctiu al manteniment basat en la condició (també anomenat manteniment predictiu). El manteniment basat en la condició dels rodaments de pas és especialment desafiant, perquè les condicions d’operació inclouen un alt estrès mecànic i baixes velocitats de rotació. A causa de que aquestes condicions d’operació impacten negativament en els resultats dels mètodes i tècniques estàndard aplicats en els sistemes actuals de monitorització basats en l'estat, el manteniment basat en l'estat dels rodaments de pas segueix sent un desafiament. Per tant, aquesta tesi se centra en la investigació de mètodes i tècniques noves que obtinguin informació fiable sobre l'estat dels rodaments de pas per al manteniment basat en la condició. Inicialment, es realitza el reconeixement de l'estat de l'art per reconèixer els mètodes i senyals utilitzats. Aquest pas avala la decisió d'analitzar els senyals de vibració i les emissions acústiques al llarg d'aquesta tesi. A causa de les condicions de funcionament particulars dels rodaments de pas, aquesta investigació reconeix la necessitat de crear un conjunt de dades per replicar les condicions de funcionament particulars del rodament de pas en un experiment de laboratori controlat. Com a resultat, es genera un conjunt de dades basat en vibracions i un segon conjunt de dades basat en emissions acústiques. El conjunt de dades de vibracions permet la validació d'un algoritme nou per al diagnòstic de rodaments de baixa velocitat, el qual es basa en el concepte de l'entropia segons la definició de Shannon i Renyi. En comparació amb els mètodes clàssics que es troben a la literatura, el diagnòstic de rodaments de baixa velocitat basat en indicadors basats en l'entropia pot extreure informació més fiable. A més, la investigació de la combinació de diversos indicadors per millorar el diagnòstic revela que els indicadors basats en l'entropia poden extreure més informació que els indicadors habituals utilitzats en la literatura. El conjunt de dades de les emissions acústiques dels rodaments de baixa velocitat ajuda a contribuir al desenvolupament de mètodes de diagnòstic. En aquesta investigació, l’anàlisi de l'energia de les senyals revela una dependència de la intensitat i la presència de dany. A més, s'emfatitza una relació entre la forma d'ona de l'energia analitzada i l’existència de dany.Energia eolikoa mundu mailan elektrizitatea sortu eta erregai fosilak ordezkatzeko energia berriztagarri nagusietako bat da. Eskala handiko ezarpena hobetu eta bizkortzeko, ezinbestekoa da mantentze-lanekin lotutako kostuak murriztea. Osagaien hausturek turbina konponketa-aldi luzeetan gelditzera behartzen dutenez, industria eolikoak mantentze-lan prebentibo edo zuzentzaile zaharkitutik egoeran oinarritutako mantentzelanetara aldatu behar du (mantentze-lan prediktiboa ere esaten zaio). Pitch errodamenduen egoeran oinarritutako mantentzea bereziki desa atzailea da, tentsio mekaniko handiak jasaten baitituzte eta errotazio-abiadura txikietan egoten baitira abian. Operaziobaldintza horiek eragin negatiboa dutenez egoeran oinarritutako egungo monitorizazio sistemetan erabiltzen diren metodo eta teknika estandarren emaitzetan, pitch errodamenduen egoeran oinarritutako mantentze-lanak erronka bat izaten jarraitzen du. Tesi hau egoeran oinarritutako mantenurako pitch errodamenduen egoerari buruzko informazio dagarria lortzen duten metodo eta teknika berritzaileen ikerketan oinarritzen da. Hasieran, teknologiaren egungo egoera aztertzen da, erabilitako metodoak eta seinaleak ezagutzeko. Urrats honek tesi honetan zehar bibrazio-seinaleak eta emisio akustikoak aztertzeko erabakia bermatzen du. Pitch errodamenduen funtzionamendu baldintza bereziak direla eta, ikerketa honek adierazten du beharrezkoa dela datu multzo bat sortzea pitch errodamenduaren funtzionamendu baldintza partikularrak erreplikatzeko laborategi kontrolatuko testuinguru batean. Ondorioz, bibrazioetan oinarritutako datu-multzo bat eta emisio akustikoetan oinarritutako bigarren datu-multzo bat sortzen dira. Bibrazioen datu-multzoak abiadura txikiko errodamenduen diagnostikorako algoritmo berritzaile bat baliozkotzea ahalbidetzen du, zeina entropiaren kontzeptuan oinarritzen baita Shannon eta R enyiren de nizioaren arabera. Literaturan dauden metodo klasikoekin alderatuta, entropian oinarritutako adierazleek abiadura txikiko errodamenduen diagnostikorako informazio dagarriagoa atera dezakete. Gainera, diagnostikoa hobetzeko hainbat adierazleren konbinazioaren ikerketak agerian uzten du entropian oinarritutako adierazleek akademian erabiltzen diren ohiko adierazleek baino informazio gehiago atera dezaketela. Abiadura txikiko errodamenduen emisio akustikoen datu multzoak diagnostiko metodoak garatzen laguntzen du. Ikerketa lan honetan, seinaleen energiaren azterketak intentsitatearekiko eta kaltearen presentziarekiko dependentzia adierazten du. Gainera, aztertutako energiaren uhin-formaren eta kaltearen arteko erlazioa nabarmentzen da.Postprint (published version

Technology needs of advanced Earth observation spacecraft

Remote sensing missions were synthesized which could contribute significantly to the understanding of global environmental parameters. Instruments capable of sensing important land and sea parameters are combined with a large antenna designed to passively quantify surface emitted radiation at several wavelengths. A conceptual design for this large deployable antenna was developed. All subsystems required to make the antenna an autonomous spacecraft were conceptually designed. The entire package, including necessary orbit transfer propulsion, is folded to package within the Space Transportation System (STS) cargo bay. After separation, the antenna, its integral feed mast, radiometer receivers, power system, and other instruments are automatically deployed and transferred to the operational orbit. The design resulted in an antenna with a major antenna dimension of 120 meters, weighing 7650 kilograms, and operating at an altitude of 700 kilometers

Large deployable antenna program. Phase 1: Technology assessment and mission architecture

The program was initiated to investigate the availability of critical large deployable antenna technologies which would enable microwave remote sensing missions from geostationary orbits as required for Mission to Planet Earth. Program goals for the large antenna were: 40-meter diameter, offset-fed paraboloid, and surface precision of 0.1 mm rms. Phase 1 goals were: to review the state-of-the-art for large, precise, wide-scanning radiometers up to 60 GHz; to assess critical technologies necessary for selected concepts; to develop mission architecture for these concepts; and to evaluate generic technologies to support the large deployable reflectors necessary for these missions. Selected results of the study show that deployable reflectors using furlable segments are limited by surface precision goals to 12 meters in diameter, current launch vehicles can place in geostationary only a 20-meter class antenna, and conceptual designs using stiff reflectors are possible with areal densities of 2.4 deg/sq m

Development of a solar furnace heliostat.

Master of Science in Mechanical Engineering. University of KwaZulu-Natal, Durban 2016.The Solar Energy Research Amplified Flux Facility (SERAFF) is the flagship project of University of KwaZulu-Natal’s Group for Solar Energy Thermodynamics (GSET). SERAFF will assume an on-axis optical configuration, common in solar furnaces around the world, comprising a flat, non-imaging heliostat reflector and a paraboloidal primary concentrator. At design-point conditions, a thermal power output of approximately 5 kW is expected with a peak flux in the region of 3 MW/m2. The facility will provide the University of KwaZulu-Natal with a platform to undertake wide-ranging research in disciplines including concentrating solar power, materials testing and processing, and solar thermochemistry, amongst others. The primary goal of this research was to design and fabricate a flat heliostat which will enable SERAFF to meet the specified thermal requirements. The first phase of this study was to characterise the available solar resource for Durban, South Africa, where SERAFF will be installed. A statistical algorithm was developed that processes historical ground-based solar measurements to generate a continuous function that estimates clear-sky direct normal irradiance (DNI) as a function of solar time and day number over a typical year. The three-dimensional surface that results from this function is termed a temporal DNI topograph (TDT) and can be used to define solar flux input for the modelling of concentrator systems. The heliostat dimensions are dependent on the size of the concentrator aperture it is tasked with illuminating. As such, sizing the concentrator was key. A geometrically based approximation of the maximum theoretical power output of a parabolic primary concentrator was developed. This model was used to calculate the diameter of the parabolic concentrator needed to achieve SERAFF’s specified power output. The model was validated against real solar furnaces around the world and it was found that the model approximated the power output for these solar furnaces within 12% of their published power output values. Following an optical analysis and illumination study, and after taking into consideration the practical and financial constraints placed on the project, it was decided that 3 m x 3 m was the most suitable size for SERAFF’s heliostat. A finite element analysis was used in the design process to assess the survivability (under load from a worst-case wind speed of 100 km/hr) and the rigidity (under load from an operational wind speed of 20 km/hr) for the different heliostat design concepts considered. After analyses of the FEA results it was decided that a classical T-shape design with an aluminium mirror backing frame would be employed. Fabrication of the structural components was undertaken at the department of Mechanical Engineering’s workshop and assembled at a temporary site in close proximity. Consideration was given to the effect the fabrication process would have on the tracking and optical accuracy of the heliostat. The total cost of fabrication was R91,655, exceeding the budget of R85,000 by R6,655. This was due to high import taxes paid on the slewing drive actuator and polished aluminium mirror facets. The actual cost of materials and components was R70,353 excluding the import taxes

Advances in Bearing Lubrication and Thermal Sciences

This reprint focuses on the hot issue of bearing lubrication and thermal analysis, and brings together many cutting-edge studies, such as bearing multi-body dynamics, bearing tribology, new lubrication and heat dissipation structures, bearing self-lubricating materials, thermal analysis of bearing assembly process, bearing service state prediction, etc. The purpose of this reprint is to explore recent developments in bearing thermal mechanisms and lubrication technology, as well as the impact of bearing operating parameters on their lubrication performance and thermal behavior

A Combined Numerical and Experimental Approach for Rolling Bearing Modelling and Prognostics

Rolling-element bearings are widely employed components which cover a major role in the NVH behaviour of the mechanical systems in which they are inserted. Therefore, it is crucial to thoroughly understand their fundamental properties and accurately quantify their most relevant parameters. Moreover, their inevitable failure due to contact fatigue leads to the necessity of correctly describing their dynamic behaviour. In fact, they permit to develop diagnostic and prognostic schemes, which are heavily requested in the nowadays industrial scenario due to their increasingly important role in the development of efficient maintenance strategies. As a result, throughout the years several techniques have been developed by researchers to address different challenges related to the modelling of these components. Within this context, this thesis aims at improving the available methods and at proposing novel approaches to tackle the modelling of rolling-element bearings both in case of static and dynamic simulations. In particular, the dissertation is divided in three major topics related to this field, i.e. the estimation of bearing radial stiffness trough the finite-element method, the lumped-parameter modelling of defective bearings and the development of physics-based prognostic models. The first part of the thesis deals with the finite-element simulations of rolling-element bearings. In particular, the investigation aims at providing an efficient procedure for the generation of load-dependent meshes. The method is developed with the primary objective of determining the radial stiffness of the examined components. In this regard, the main contribution to the subject is the definition of mesh element dimensions on the basis of analytical formulae and in the proposed methodology for the estimation of bearing stiffness. Then, the second part describes a multi-objective optimization technique for the estimation of unknown parameters in lumped parameter models of defective bearings. In fact, it was observed that several parameters which are commonly inserted in these models are hardly measurable or rather denoted by a high degree of uncertainty. On this basis, an optimization procedure aimed at minimizing the difference between experimental and numerical results is proposed. The novelty of the technique lies in the approach developed to tackle the problem and its peculiar implementation in the context of bearing lumped-parameter models. Lastly, the final part of the dissertation is devoted to the development of physics-based prognostic models. Specifically, two models are detailed, both based on a novel degradation-related parameter, i.e. the Equivalent Damaged Volume (EDV). An algorithm capable of extracting this quantity from experimental data is detailed. Then, EDV values are used as input parameters for two prognostic models. The first one aims at predicting the bearing vibration under different operative conditions with respect to a given reference deterioration history. On the other hand, the objective of the second model is to predict the time until a certain threshold on the equivalent damaged volume is crossed, regardless of the applied load and the shaft rotation speed. Therefore, the original aspect of this latter part is the development of prognostic models based on a novel indicator specifically introduced in this work. Results obtained from all proposed models are validated through analytical methods retrieved from the literature and by comparison with data acquired on a dedicated test bench. To this end, a test rig which was set-up at the Engineering Department of the University of Ferrara was employed to perform two type of tests, i.e. stationary tests on bearings with artificial defects and run-to-failure tests on initially healthy bearings. The characteristics of acceleration signals acquired during both tests are extensively discussed.I cuscinetti a rotolamento sono componenti meccanici che influenzano in maniera considerevole il comportamento dinamico dei sistemi all’interno dei quali sono montati. Pertanto, è di fondamentale importanza possedere strumenti atti alla stima dei loro parametri più rilevanti e avere a disposizione modelli dedicati allo studio delle loro caratteristiche dinamiche. Questo aspetto è di estrema importanza soprattutto nell’ottica dello sviluppo di schemi di diagnostica e prognostica, i quali sono sempre più richiesti all’interno dello scenario industriale odierno. In questo contesto, questa tesi si propone di migliorare le tecniche numeriche già esistenti e di fornire nuovi approcci per la modellazione dei cuscinetti a rotolamento sia nel caso di problemi statici che dinamici. Nello specifico, il lavoro tratta in maniera dettagliata tre diversi argomenti relativi a questo tema, ossia la stima della rigidezza radiale tramite il metodo agli elementi finiti, la modellazione a parametri concentrati di cuscinetti con difetti e lo sviluppo di modelli di prognostica physics-based. La prima parte della tesi concerne la simulazione di cuscinetti a rotolamento tramite il metodo ad elementi finiti. In particolare, lo studio si propone di fornire una procedura per la generazione di griglie le cui dimensioni dipendano dal carico applicato. Il metodo è sviluppato con l’obbiettivo di stimare in maniera computazionalmente efficace la rigidezza radiale del componente in esame. Pertanto, il contributo principale sul tema dato da questa prima parte riguarda il metodo analitico che permette di definire a priori le dimensioni degli elementi che costituiscono la mesh e la metodologia utilizzata per la stima della rigidezza. La seconda parte descrive una procedura di ottimizzazione multi obbiettivo per la stima dei parametri incogniti all’interno dei modelli a parametri concentrati di cuscinetti con difetti. Questa esigenza nasce dall’osservazione che numerosi parametri tipicamente inseriti in questa tipologia di modelli sono difficilmente misurabili oppure caratterizzati da un alto grado di incertezza. Perciò, nella seconda parte viene introdotta una tecnica innovativa che consente di stimare i parametri di modello che minimizzano la differenza fra risultati numerici e sperimentali in diverse condizioni di funzionamento. Infine, l’ultima parte è dedicata allo sviluppo di modelli di prognostica physics-based. A tal riguardo, vengono dettagliati due modelli basati su un nuovo indicatore di degrado del cuscinetto, denominato Equivalent Damaged Volume (EDV). Questo indicatore viene calcolato durante il funzionamento del cuscinetto tramite un algoritmo dedicato. I valori così ottenuti sono poi utilizzati come dati di input per i due modelli prognostici. Il primo mira a predire la vibrazione del cuscinetto in condizioni operative diverse rispetto ad una storia di degrado di riferimento. Diversamente, il secondo modello permette di prevedere il tempo rimanente prima del superamento di una soglia critica di volume equivalente danneggiato, indipendentemente da carico applicato e velocità di rotazione. Dunque, l’aspetto originale di quest’ultima parte ricade nello sviluppo di tecniche prognostiche basate su un nuovo indicatore introdotto ad-hoc in questo lavoro. I risultati ottenuti da tutti i modelli proposti sono validati grazie a metodi analitici di letteratura e a dati acquisiti in laboratorio per mezzo di un banco prova installato presso il Dipartimento di Ingegneria dell’Università di Ferrara. Il banco prova è stato utilizzato per realizzare due tipologie di prove, ossia test stazionari su cuscinetti che presentano difetti artificiali e prove di tipo run-to-failure su cuscinetti inizialmente sani. Le caratteristiche dei segnali di accelerazione acquisiti in entrambe le prove sono discussi in maniera esaustiva

NASA Tech Briefs, August 1991

Topics: New Product Ideas; NASA TU Services; Electronic Components and Circuits; Electronic Systems; Physical Sciences; Materials; Computer Programs; Mechanics; Machinery; Fabrication Technology; Mathematics and Information Sciences; Life Sciences

Large space structures and systems in the space station era: A bibliography with indexes (supplement 04)

Bibliographies and abstracts are listed for 1211 reports, articles, and other documents introduced into the NASA scientific and technical information system between 1 Jul. and 30 Dec. 1991. Its purpose is to provide helpful information to the researcher, manager, and designer in technology development and mission design according to system, interactive analysis and design, structural concepts and control systems, electronics, advanced materials, assembly concepts, propulsion, and solar power satellite systems

Technology for large space systems: A bibliography with indexes (supplement 19)

This bibliography lists 526 reports, articles, and other documents introduced into the NASA scientific and technical information system between January 1, 1988 and June 30, 1988. Its purpose is to provide helpful information to the researcher, manager, and designer in technology development and mission design according to system, interactive analysis and design, structural and thermal analysis and design, structural concepts and control systems, electronics, advanced materials, assembly concepts, propulsion, and solar power satellite systems