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Dawood, Tariq Ali. "Structural health monitoring of GFRP sandwich beam structures." Thesis, University of Southampton, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.438529.
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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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Lannamann, Daniel L. "Structural health monitoring : numerical damage predictor for composite structures." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2001. http://handle.dtic.mil/100.2/ADA390997.
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Nayyerloo, Mostafa. "Real-time Structural Health Monitoring of Nonlinear Hysteretic Structures." Thesis, University of Canterbury. Department of Mechanical Engineering, 2011. http://hdl.handle.net/10092/6581.
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The great social and economic impact of earthquakes has made necessary the development of novel structural health monitoring (SHM) solutions for increasing the level of structural safety and assessment. SHM is the process of comparing the current state of a structure’s condition relative to a healthy baseline state to detect the existence, location, and degree of likely damage during or after a damaging input, such as an earthquake. Many SHM algorithms have been proposed in the literature. However, a large majority of these algorithms cannot be implemented in real time. Therefore, their results would not be available during or immediately after a major event for urgent post-event response and decision making. Further, these off-line techniques are not capable of providing the input information required for structural control systems for damage mitigation. The small number of real-time SHM (RT-SHM) methods proposed in the past, resolve these issues. However, these approaches have significant computational complexity and typically do not manage nonlinear cases directly associated with relevant damage metrics. Finally, many available SHM methods require full structural response measurement, including velocities and displacements, which are typically difficult to measure. All these issues make implementation of many existing SHM algorithms very difficult if not impossible.
This thesis proposes simpler, more suitable algorithms utilising a nonlinear Bouc-Wen hysteretic baseline model for RT-SHM of a large class of nonlinear hysteretic structures. The RT-SHM algorithms are devised so that they can accommodate different levels of the availability of design data or measured structural responses, and therefore, are applicable to both existing and new structures. The second focus of the thesis is on developing a high-speed, high-resolution, seismic structural displacement measurement sensor to enable these methods and many other SHM approaches by using line-scan cameras as a low-cost and powerful means of measuring structural displacements at high sampling rates and high resolution. Overall, the results presented are thus significant steps towards developing smart, damage-free structures and providing more reliable information for post-event decision making.
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Kirikera, Goutham Raghavendra. "A Structural Neural System for Health Monitoring of Structures." University of Cincinnati / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1155149869.
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Islami, Kleidi. "System identification and structural health monitoring of bridge structures." Doctoral thesis, Università degli studi di Padova, 2013. http://hdl.handle.net/11577/3423079.
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This research study addresses two issues for the identification of structural characteristics of civil infrastructure systems. The first one is related to the problem of dynamic system identification, by means of experimental and operational modal analysis, applied to a large variety of bridge structures. Based on time and frequency domain techniques and mainly with output-only acceleration, velocity or strain data, modal parameters have been estimated for suspension bridges, masonry arch bridges, concrete arch and continuous bridges, reticular and box girder steel bridges. After giving an in-depth overview of standard and advanced stochastic methods, differences of the existing approaches in their performances are highlighted during system identification on the different kinds of civil infrastructures. The evaluation of their performance is accompanied by easy and hard determinable cases, which gave good results only after performing advanced clustering analysis. Eventually, real-time vibration-based structural health monitoring algorithms are presented during their performance in structural damage detection by statistical models.
The second issue is the noise-free estimation of high order displacements taking place on suspension bridges. Once provided a comprehensive treatment of displacement and acceleration data fusion for dynamic systems by defining the Kalman filter algorithm, the combination of these two kinds of measurements is achieved, improving the deformations observed. Thus, an exhaustive analysis of smoothed displacement data on a suspension bridge is presented. The successful tests were subsequently used to define the non-collocated sensor monitoring problem with the application on simplified modelsQuesto lavoro di ricerca mira a due obiettivi per l'identificazione delle caratteristiche strutturali dei sistemi infrastrutturali civili. Il primo è legato al problema della identificazione del sistema dinamico, mediante analisi modale sperimentale e operativa, applicata ad una grande varietà di strutture da ponte. Basandosi su tecniche nel dominio del tempo e delle frequenze e, soprattutto, su dati di output di accelerazione, velocità o strain, i parametri modali sono stati stimati per ponti sospesi, ponti ad arco in muratura, ponti a travi in calcestruzzo e ad arco, ponti reticolari e ponti in acciaio a cassone. Dopo aver dato una panoramica approfondita dei metodi stocastici standard ed avanzati, sono state evidenziate le differenze degli approcci esistenti nelle loro performance per l'identificazione del sistema sui diversi tipi di infrastrutture civili. La valutazione della loro performance viene accompagnata da casi facilmente e difficilmente determinabili, che hanno dato buoni risultati solo dopo l'esecuzione di analisi avanzate di Clustering. Inoltre, sono stati sviluppati algoritmi di identificazione dinamica automatica in tempo reale basandosi sulle vibrazioni strutturali dei ponti monitorati, a sua volta utilizzati nel rilevamento dei danni strutturali tramite modelli statistici. Il secondo problema studiato riguarda la stima di spostamenti di ordine superiore che si svolgono sui ponti sospesi, eliminando il rumore di misura e di processo. Una volta fornito un trattamento completo della fusione dei dati di spostamento e accelerazione per i sistemi dinamici tramite il filtro di Kalman, la combinazione di questi due tipi di misurazioni ha mostrato un miglioramento nelle deformazioni osservate. Pertanto, è stata presentata un'analisi esauriente di un ponte sospeso e dei sui dati dinamici e di spostamento filtrati. I test positivi sono stati successivamente utilizzati per definire il problema dei sensori non collocati alla stessa locazione ed applicazione su modelli semplificati
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Webb, Graham Thomas. "Structural health monitoring of bridges." Thesis, University of Cambridge, 2014. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708027.
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Grisso, Benjamin Luke. "Advancing Autonomous Structural Health Monitoring." Diss., Virginia Tech, 2007. http://hdl.handle.net/10919/29960.
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The focus of this dissertation is aimed at advancing autonomous structural health monitoring. All the research is based on developing the impedance method for monitoring structural health. The impedance technique utilizes piezoelectric patches to interrogate structures of interested with high frequency excitations. These patches are bonded directly to the structure, so information about the health of the structure can be seen in the electrical impedance of the piezoelectric patch. However, traditional impedance techniques require the use of a bulky and expensive impedance analyzer. Research presented here describes efforts to miniaturize the hardware necessary for damage detection. A prototype impedance-based structural health monitoring system, incorporating wireless based communications, is fabricated and validated with experimental testing. The first steps towards a completely autonomous structural health monitoring sensor are also presented. Power harvesting from ambient energy allows a prototype to be operable from a rechargeable power source.
Aerospace vehicles are equipped with thermal protection systems to isolate internal components from harsh reentry conditions. While the thermal protection systems are critical to the safety of the vehicle, finding damage in these structures presents a unique challenge. Impedance techniques will be used to detect the standard damage mechanism for one type of thermal protection system. The sensitivity of the impedance method at elevated temperatures is also investigated.
Sensors are often affixed to structures as a means of identifying structural defects. However, these sensors are susceptible to damage themselves. Sensor diagnostics is a field of study directed at identifying faulty sensors. The influence of temperature on these techniques is largely unstudied. In this dissertation, a model is generated to identify damaged sensors at any temperature. A sensor diagnostics method is also adapted for use in developed hardware. The prototype used is completely digital, so standard sensor diagnostics techniques are inapplicable. A new method is developed to work with the digital hardware.Ph. D.
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Ward, Jacob Thomas Elliott. "Guided wave structural health monitoring." Thesis, University of Bristol, 2015. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.682233.
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Routine airframe Non-Destructive Testing (NDT) procedures are costly and prone to human error. Guided wave structural health monitoring (GWSHM) shows great promise to in future assist these carefully regulated aerospace NDT practices. Using automatic GWSHM to both detect and localise damage can better focus the human NDT effort and ultimately lead to safer operation of airframes. The thesis presents structural health monitoring techniques for airframes using measurements of guided waves. Work is presented on both metal plates and carbon fibre reinforced plastic panels. An active GWSHM method is considered in its capability to detect and localise damage by measurements of scattered Lamb waves from artificially placed damage. The contribution to knowledge on active GWSHM has been towards effective and practical strategies for placing a low number of transducers into arrays suitable for global coverage. Much early active GWSHM studies often adopted a uniformly sparse distribution of transducer elements, perhaps in an attempt to gain the best possible global coverage. In this thesis, active GWSHM performance has been evaluated for arrays of different geometry and has shown that a uniformly sparse distribution of transducer elements may not be the most effective strategy when using a minimal number of sensors. Simulated and artificial damage, placed with different orientations over a large area, has been used to test candidate array layouts. It finds the layout optimal for damage detection is not necessarily the layout optimal for damage localisation. The zeroth order anti-symmetric Lamb wave mode has been used at low frequency-thickness. The mode, referred to as the flexural mode when propagating with low frequency-thickness, is favoured for its short wave length and long range. At low frequency-thickness this mode is quickly outrun by its symmetric counterpart, causing coherent noise in the signals recorded. Baseline subtraction is used to suppress the coherent noise before imaging. Benign structural features, that would usually hinder damage-localisation from an image, are actually found to assist damage localisation for some array layouts when using the reference baseline signal subtraction technique. A passive GWSHM method is considered in its capability to localise impacts. Impact events on carbon fibre panels are localised using a low frequency passive array. The technique is suggested for evaluating damage from tyre-burst or propeller debris impacts to airframe surfaces. It is particularly relevant to new airframe designs that have significant usage of composite materials on their outer surface. Historically the aerospace sector has readily adopted time of arrival estimation methods similar to those found on a standard oscilloscope. As an example, acoustic emission monitoring, in recent decades has routinely used threshold-crossing as a means of time of arrival measurement. An alternative is presented requiring the whole time series to be post-processed. It extracts an alternative arrival time from propagating waves resulting from the impact, which can be used in time-difference of arrival algorithms. This method is shown to be more reliable and accurate for impact localisation than historical techniques.
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Engelbrecht, André. "Structural integrity monitoring using vibration measurements." Pretoria : [s.n.], 2006. http://upetd.up.ac.za/thesis/available/etd-07032006-122342/.
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Ciampa, Francesco. "Structural health monitoring systems for impacted isotropic and anisotropic structures." Thesis, University of Bath, 2012. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.558884.
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This thesis investigates the development of ultrasonic Structural Health Monitoring (SHM) systems, based on guided waves propagation, for the localization of low-velocity impacts and the detection of damage mechanisms in isotropic and anisotropic structures. For the identi- cation of the impact point, two main passive techniques were developed, an algorithm-based and an imaging-based method. The former approach is based on the dierences of the stress waves measured by a network of piezoelectric transducers surface bonded on plate-like structures. In particular, four piezoelectric sensors were used to measure the antisymmetrical A0 Lamb mode in isotropic materials, whilst six acoustic emission sensors were employed to record the wave packets in composite laminates. A joint time-frequency analysis based on the magnitude of the Continuous Wavelet Transform was used to determine the time of arrivals of the wave packets. Then, a combination of unconstrained optimization technique associated to a local Newton's iterative method was employed to solve a system of non linear equations, in order to assess the impact location coordinates and the wave group speeds. The main advantages of the proposed algorithms are that they do not require an a-priori estimation of the group velocity and the mechanical properties of the isotropic and anisotropic structures. Moreover, these algorithms proved to be very robust since they were able to converge from almost any guess point and required little computational time. In addition, this research provided a comparison between the theoretical and experimental results, showing that the impact source location and the wave velocity were predicted with reasonable accuracy. The passive imaging-based method was developed to detect in realtime the impact source in reverberant complex composite structures using only one passive sensor. This technique is based on the re- ciprocal time reversal approach, applied to a number of waveforms stored in a database containing the impulse responses of the structure. The proposed method allows achieving the optimal focalization of the acoustic emission source (impact event) as it overcomes the limitations of other ultrasonic impact localization techniques. Compared to a simple time reversal process, the robustness of this approach is experimentally demonstrated on a stiened composite plate. This thesis also extended active ultrasonic guided wave methods to the specic case of dissipative structures showing non-classical nonlinear behaviour. Indeed, an imaging method of the nonlinear signature due to impact damage in a reverberant complex anisotropic medium was developed. A novel technique called phase symmetry analysis, together with frequency modulated excitation signals, was used to characterize the third order nonlinearity of the structure by exploiting its invariant properties with the phase angle of the input waveforms. Then, a \virtual" reciprocal time reversal imaging process was employed to focus the elastic waves on the defect, by taking advantage of multiple linear scattering. Finally, the main characteristics of this technique were experimentally validated.
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Tarozzi, Mirco <1991>. "Damage Identification of Structures through Vibration-Based Structural Monitoring Systems." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2022. http://amsdottorato.unibo.it/10274/1/Tarozzi2022_DAMAGE%20IDENTIFICATION%20OF%20STRUCTURES%20THROUGH%20VIBRATION-BASED%20STRUCTURAL%20MONITORING%20SYSTEMS_PhDmanuscript.pdf.
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The thesis has been carried out within the “SHAPE Project - Predicting Strength Changes in Bridges from Frequency Data Safety, Hazard, and Poly-harmonic Evaluation” (ERA-NET Plus Infravation Call 2014) which dealt with the structural assessment of existing bridges and laboratory structural reproductions through the use of vibration-based monitoring systems, for detecting changes in their natural frequencies and correlating them with the occurrence of damage.
The main purpose of this PhD dissertation has been the detection of the variation of the main natural frequencies as a consequence of a previous-established damage configuration provided on a structure.
Firstly, the effect of local damage on the modal feature has been discussed mainly concerning a steel frame and a composite steel-concrete bridge. Concerning the variation of the fundamental frequency of the small bridge, the increasing severity of two local damages has been investigated. Moreover, the comparison with a 3D FE model is even presented establishing a link between the dynamic properties and the damage features.
Then, moving towards a diffused damage pattern, four concrete beams and a small concrete deck were loaded achieving the yielding of the steel reinforcement. The stiffness deterioration in terms of frequency shifts has been reconsidered by collecting a large set of dynamic experiments on simply supported R.C. beams discussed in the literature. The comparison of the load-frequency curves suggested a significant agreement among all the experiments. Thus, in the framework of damage mechanics, the “breathing cracks” phenomenon has been discussed leading to an analytical formula able to explain the frequency decay observed experimentally.
Lastly, some dynamic investigations of two existing bridges and the corresponding FE Models are presented in Chapter 4. Moreover, concerning the bridge in Bologna, two prototypes of a network of accelerometers were installed and the data of a few months of monitoring have been discussed.
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Stalker, R. "Engineer-computer interaction for structural monitoring." Thesis, Lancaster University, 2000. http://eprints.lancs.ac.uk/11792/.
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Brigman, Nicholas (Nicholas Allen). "Structural health monitoring in commercial aviation." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/73846.
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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. 87-90).
The number of aging commercial aircraft in service is steadily increasing as airlines continue to extend the life of their aircraft. Aging aircraft are more susceptible to fatigue and corrosion and require more frequent and intensive inspections and maintenance, which is a financial drain on operators. One way to improve the economics and safety of commercial aircraft is through implementation of a structural health monitoring (SHM) system. An ideal SHM would be able to give be capable of indicating damage type, location, severity, and estimate the remaining life of the structure while the structure is in use. This paper is an overview of how SHM can be applied in commercial aviation including discussion of requirements, implementation, challenges, and introducing several possible SHM systems. The SHM systems introduced in this paper are: vibration based monitoring, fiber optic sensors, and high frequency wave propagation techniques including acoustic emission, ultrasonic, Lamb waves, piezoelectric and MEMS actuator/sensors. The limitations and challenges inhibiting introduction of SHM to industry and recommendations for the future are also discussed.
by Nicholas Brigman.
M.Eng.
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Mani, Girindra N. "Structural Health Monitoring of Rotordynamic Systems." University of Akron / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=akron1144522032.
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Ashwin, Belle. "WIRELESS INTELLIGENT STRUCTURAL HEALTH MONITORING SYSTEM." VCU Scholars Compass, 2008. http://scholarscompass.vcu.edu/etd/1626.
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Metal structures are susceptible to various types of damages, including corrosion, stress damage, pillowing deformation, cracks etc. These kinds of damages in the metal structures occur mainly due to operational conditions and exposure to the environment. Our research involves a portable integrated wireless sensor system with video camera and ultrasound capabilities which is being developed to investigate corrosion damage on real structures in real time. This system uses images of the metal surfaces, which are captured from an integrated wireless sensor and then quantified and analyzed using computational intelligence. The quantification of the obtained images is done with specialized component analysis software which enhances and performs wavelet transforms on the received images. Through this quantized analysis of the images we can detect and isolate regions of degradation on the metal surface. We believe that the final developed system will allow us to detect damage in metallic structures in its early stages, thereby ensuring proper safety and maintenance of its structural health. This system will further be targeted towards medical applications with capabilities of remote health monitoring. The initial target areas being bone structure and cancer detection and analysis. Applying such a wireless data capture system in these areas will reveal a broad spectrum of the usage of such an application system.
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Bogomolov, Denis <1992>. "Structural health monitoring of storage tanks." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2022. http://amsdottorato.unibo.it/10215/1/Bogomolov%20-%20PhD%20thesis.pdf.
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In this thesis, Ph.D candidate presents a compact sensor node (SN) designed for long-term and real-time acoustic emission (AE) monitoring of above ground storage tanks (ASTs). Each SN exploits up to three inexpensive low-frequency sensors based on piezoelectric diaphragms for effective leakage detection, and it is capable by means of built-in Digital Signal Processing functionalities to process the acquired time waveforms extracting the AE features usually required by testing protocols. Alternatively, capability to plug three high frequency AE sensors to a SN for corrosion simulated phenomena detection is envisaged and demonstrated.
Another innovative aspect that the Ph.D candidate presents in this work is an alternative mathematical model of corrosion location on the bottom of the AST. This approach implies considering the three-dimensional localization model versus the two-dimensional commonly used according to the literature. This approach is aimed at significant optimization in the number of sensors in relation to the standard approach for solving localization problems as well as to allow filtering the false AE events related to the condensate droplets from AST ceiling. The technological implementation of this concept required the solution of a number of technical problems, such as the precise time of arrival (ToA) signal estimation, vertical localization of the AE source and multilaration solution that were discussed in detail in this work.
To validate the developed prototype, several experimental campaigns were organized that included the simulation of target phenomena both in laboratory conditions and on a real water storage tank. The presented test results demonstrate the successful application of the developed AE system both for simulated leaks and for corrosion processes on the tank bottom. Mathematical and technological algorithms for localization and characterization of AE signals implemented during the development of the prototype are also confirmed by the test results.
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Hudson, Carmen Campos 1972. "Overview of monitoring systems used during construction and permanent structural monitoring." Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/84792.
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Thesis (M.Eng.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2002.Includes bibliographical references (leaves 94-95).
by Carmen Campos Hudson.
M.Eng.
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Singh, Gurjashan. "Health Monitoring of Round Objects using Multiple Structural Health Monitoring Techniques." FIU Digital Commons, 2010. http://digitalcommons.fiu.edu/etd/330.
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Structural Health Monitoring (SHM) techniques are widely used in a number of Non – destructive Evaluation (NDE) applications. There is a need to develop effective techniques for SHM, so that the safety and integrity of the structures can be improved. Two most widely used SHM methods for plates and rods use either the spectrum of the impedances or monitor the propagation of lamb waves. Piezoelectric wafer – active sensors (PWAS) were used for excitation and sensing. In this study, surface response to excitation (SuRE) and Lamb wave propagation was monitored to estimate the integrity of the round objects including the pipes, tubes and cutting tools. SuRE obtained the frequency response by applying sweep sine wave to surface. The envelope of the received signal was used to detect the arrival of lamb waves to the sensor. Both approaches detect the structural defects of the pipes and tubes and the wear of the cutting tool.
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Liang, Ming-Te. "Condition monitoring of piled foundations." Thesis, University of Aberdeen, 1986. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU005228.
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In this thesis a brief history of dynamic pile analysis methods and the associated background theory are presented. In addition an unpublished rigorous mathematic proof of the Case method and new general theoretical model for dynamic pile analysis, developed as the Aberdeen method, are given. The dynamic and static response of model concrete piles in dry sand to impact and static loads have also been investigated experimentally and the results are reported in this thesis. Pile response has been found to be crucially dependent on the damping in the system. The method of modal analysis has been found to be the best approach to determine the damping factor of both the onshore and the offshore piles and is discussed in detail. A theoretical relationship between the initial and the reflected stress waves and the dynamic point resistance is used to calculate the force-penetration relationship and nonlinear parameters for the special case of pile points on dry sand. The shock relation, equations of motion and compatibility of the dynamic measurement at pile top are given by the Aberdeen method. This method gives a mathematical description of the behaviour of impact response which has not been achieved in either the Case or the TNO method. At present, the Case and TNO methods are used to investigate the integrity of piled foundations by means of the impact concept. This thesis introduces a third method, the J-integral method in the study of piled foundation. In addition, the thesis also gives a theoretical explanation to the TNO method which have not been provided elsewhere.
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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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Singh-Levett, Ishan. "Real-time integral based structural health monitoring." Thesis, University of Canterbury. Mechanical Engineering, 2006. http://hdl.handle.net/10092/1171.
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Structural Health Monitoring (SHM) is a means of identifying damage from the structural response to environmental loads. Real-time SHM offers rapid assessment of structural safety by owners and civil defense authorities enabling more optimal response to major events. This research presents an real-time, convex, integral-based SHM methods for seismic events that use only acceleration measurements and infrequently measured displacements, and a non-linear baseline model including hysteretic dynamics and permanent deformation. The method thus identifies time-varying pre-yield and post-yield stiffness, elastic and plastic components of displacement and final residual displacement. For a linear baseline model it identifies only timevarying stiffness. Thus, the algorithm identifies all key measures of structural damage affecting the immediate safety or use of the structure, and the long-term cost of repair and retrofit. The algorithm is tested with simulated and measured El Centro earthquake response data from a four storey non-linear steel frame structure and simulated data from a two storey non-linear hybrid rocking structure. The steel frame and rocking structures exhibit contrasting dynamic response and are thus used to highlight the impact of baseline model selection in SHM. In simulation, the algorithm identifies stiffness to within 3.5% with 90% confidence, and permanent displacement to within 7.5% with 90% confidence. Using measured data for the frame structure, the algorithm identifies final residual deformation to within 1.5% and identifies realistic stiffness values in comparison to values predicted from pushover analysis. For the rocking structure, the algorithm accurately identifies the different regimes of motion and linear stiffness comparable to estimates from previous research. Overall, the method is seen to be accurate, effective and realtime capable, with the non-linear baseline model more accurately identifying damage in both of the disparate structures examined.
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Boettcher, Dennis N. "A Resistance Based Structural Health Monitoring System for Composite Structure Applications." DigitalCommons@CalPoly, 2012. https://digitalcommons.calpoly.edu/theses/843.
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This research effort explored the possibility of using interwoven conductive and nonconductive fibers in a composite laminate for structural health monitoring (SHM). Traditional SHM systems utilize fiber optics, piezoelectrics, or detect defects by nondestructive test methods by use of sonar graphs or x-rays. However, these approaches are often expensive, time consuming and complicated.
The primary objective of this research was to apply a resistance based method of structural health monitoring to a composite structure to determine structural integrity and presence of defects.
The conductive properties of fiber such as carbon, copper, or constantan - a copper-nickel alloy - can be utilized as sensors within the structure. This allows the structure to provide feedback via electrical signals to a user which are essential for evaluating the health of the structure. In this research, the conductive fiber was made from constantan wire which was embedded within a composite laminate; whereas prepreg fiberglass, a nonconductive material, serves as the main structural element of the laminate. A composite laminate was constructed from four layers of TenCate 7781 “E” fiberglass and BT250E-1 resin prepreg. Integrating the constantan within the composite laminate provides a sensory element which supplies measurements of structural behavior. Thus, with fiberglass, epoxy, and a constantan conductive element, a three-part composite laminate is developed.
Test specimens used in this research were fabricated using a composite air press with the recommended manufacturer cure cycle. A TenCate BT250E-1 Resin System and 7781 "E" impregnated glass-fiber/epoxy weave was used. A constantan wire of 0.01” gauge diameter was integrated into the composite structure. The composite laminate specimen with the integrated SHM system was tested under tensile and flexural loads employing test standards specified by ASTM D3039 and D7264, respectively. These test methods were modified to determine the behavior of the laminate in the elastic range only. A tension and flexural delamination test case was also developed to investigate the sensitivity of the SHM system to inherent defects. Moreover, material characteristic tests were completed to validate manufacturer provided material characteristics. The specimens were tested while varying the constantan configurations, such as the sensor length and orientation. A variety of techniques to integrate the sensor were also investigated. Two different measurement methods were used to determine strain. Strain measurements were made with Instron Bluehill 2 software and correlated to strain obtained by the structural health monitoring system with the use of a data acquisition code written to interact with a micro-ohm-meter.
The experimental results showed good agreement between measurements made by the two different methods of measurement. Observations discovered that varying the length of the sensor element improved sensitivity, but resulted in different prediction models when compared to cases with less sensor length. The predictions are based on the gauge factor, which was determined for the each test case. This value provides the essential relationship between resistance and strain. Experiments proved that the measured gauge factor depended greatly on the sensor length and orientation. The correlation was of sufficient accuracy to predict strain values in a composite laminate without the use of any added tools or equipment besides the ohm-meter.
Analytical solutions to the loading cases were developed to validate results obtained during experiments. The solutions were in good agreement with the experimental results.
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Fekrmandi, Hadi. "Development of New Structural Health Monitoring Techniques." FIU Digital Commons, 2015. http://digitalcommons.fiu.edu/cgi/viewcontent.cgi?article=2923&context=etd.
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During the past two decades, many researchers have developed methods for the detection of structural defects at the early stages to operate the aerospace vehicles safely and to reduce the operating costs. The Surface Response to Excitation (SuRE) method is one of these approaches developed at FIU to reduce the cost and size of the equipment. The SuRE method excites the surface at a series of frequencies and monitors the propagation characteristics of the generated waves. The amplitude of the waves reaching to any point on the surface varies with frequency; however, it remains consistent as long as the integrity and strain distribution on the part is consistent. These spectral characteristics change when cracks develop or the strain distribution changes. The SHM methods may be used for many applications, from the detection of loose screws to the monitoring of manufacturing operations.
A scanning laser vibrometer was used in this study to investigate the characteristics of the spectral changes at different points on the parts. The study started with detecting a load on a plate and estimating its location. The modifications on the part with manufacturing operations were detected and the Part-Based Manufacturing Process Performance Monitoring (PbPPM) method was developed. Hardware was prepared to demonstrate the feasibility of the proposed methods in real time.
Using low-cost piezoelectric elements and the non-contact scanning laser vibrometer successfully, the data was collected for the SuRE and PbPPM methods. Locational force, loose bolts and material loss could be easily detected by comparing the spectral characteristics of the arriving waves. On-line methods used fast computational methods for estimating the spectrum and detecting the changing operational conditions from sum of the squares of the variations. Neural networks classified the spectrums when the desktop – DSP combination was used. The results demonstrated the feasibility of the SuRE and PbPPM methods.
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Bartoli, Ivan. "Structural health monitoring by ultrasonic guided waves." Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2007. http://wwwlib.umi.com/cr/ucsd/fullcit?p3283893.
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Thesis (Ph. D.)--University of California, San Diego, 2007.Title from first page of PDF file (viewed December 3, 2007). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 311-325).
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Azhari, Faezeh. "Cement-based sensors for structural health monitoring." Thesis, University of British Columbia, 2008. http://hdl.handle.net/2429/7324.
Full textAbstract:
The purpose of structural health monitoring is to continuously and accurately assess the performance of structures using a sensory system.
Recently introduced, cement-based sensors are piezoresistive and therefore can be used to sense stress/strain, simply by monitoring their electrical resistivity. These sensors, also known as smart (self-monitoring) structural materials can be used as a part or total component of structures and provide both structural capability and response to applied stress and damage.
In this study cement-based sensors are developed using two types of carbon fibres, as well as both single-walled and multi-walled carbon nano-tubes. A wide range of experiments were conducted to pinpoint the most efficient fibre content, frequency, electrode type and resistivity measurement technique. The influence of different parameters such as curing, temperature, moisture and chloride were also investigated.
The resistivity of the specimens increased with curing time, but became almost constant after a certain amount of time. The resistivity values decreased with increasing temperature and increased with the decrease in temperature at a rate of about 22-35 ohm-cm/°C. It was further found that moisture and chloride have a considerable influence on the electrical resistivity of these sensors.
Next, the response of the developed cement-based sensors to compressive, tensile and flexural loading was explored. The resistivity values from the sensors were compared with load and displacement values as well as strain data acquired from conventional strain gauges.
The results indicate that electrical resistivity of the sensors increases reversibly upon tension and decreases reversibly under compression provided that substantial cracking does not occur and the sensor remains in the elastic range. Once a dense field of micro-cracking followed by macro-cracking occurs, these sensors respond distinctly, possibly even prior to the appearance of visible cracks, providing an early prediction of any upcoming failure.
The resistivity measurements under both compressive and tensile stress demonstrated an excellent correlation with strain. The developed sensors offer gauge factors well above those of electrical strain gauges.
It is concluded, therefore, that cement-based sensors can be the future alternative for conventional sensors in the structural health monitoring of concrete structures.
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Badcock, Rodney Alan. "Optical fibre sensors for structural stain monitoring." Thesis, Brunel University, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.389265.
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Leeuw, Bart de. "Analysis and assessment of structural integrity monitoring." Thesis, University College London (University of London), 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.412583.
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Kreibich, Christian Peter. "Structural traffic analysis for network security monitoring." Thesis, University of Cambridge, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.613090.
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Zeileis, Achim, Friedrich Leisch, Christian Kleiber, and Kurt Hornik. "Monitoring structural change in dynamic econometric models." SFB Adaptive Information Systems and Modelling in Economics and Management Science, WU Vienna University of Economics and Business, 2002. http://epub.wu.ac.at/1296/1/document.pdf.
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The classical approach to testing for structural change employs retrospective tests using a historical data set of a given length. Here we consider a wide array of fluctuation-type tests in a monitoring situation - given a history period for which a regression relationship is known to be stable, we test whether incoming data are consistent with the previously established relationship. Procedures based on estimates of the regression coefficients are extended in three directions: we introduce (a) procedures based on OLS residuals, (b) rescaled statistics and (c) alternative asymptotic boundaries. Compared to the existing tests our extensions offer better power against certain alternatives, improved size in finite samples for dynamic models and ease of computation respectively. We apply our methods to two data sets, German M1 money demand and U.S. labor productivity.Series: Report Series SFB "Adaptive Information Systems and Modelling in Economics and Management Science"
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Movva, Gopichand. "Optimal Sensor Placement for Structural Health Monitoring." Thesis, University of North Texas, 2014. https://digital.library.unt.edu/ark:/67531/metadc700010/.
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In large-scale civil structures, a limited number of sensors are placed to monitor the health of civil structures to reduce maintenance, communication and energy costs. In this thesis, the problem of optimal sensor location placement to infer the health of civil structures is explored. First, a comparative study of approaches from the fields of control engineering and civil engineering is conducted . The widely used civil engineering approaches such as effective independence (EI) and modal assurance criterion (MAC) have limitations because of the negligence of modes and damping parameters. On the other hand, control engineering approaches consider the entire system dynamics using impulse response-type sensor measurement data. Such inference can be formulated as an estimation problem, with the dynamics formulated as a second-order differential equation. The comparative study suggests that damping dynamics play significant impact to the selection of best sensor location---the civil engineering approaches that neglect the damping dynamics lead to very different sensor locations from those of the control engineering approaches. In the second part of the thesis, an initial attempt to directly connect the topological graph of the structure (that defines the damping and stiffness matrices) and the second-order dynamics is conducted.
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Storozhev, Dmitry Leonidovich. "Smart Rotating Machines for Structural Health Monitoring." Cleveland State University / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=csu1262724991.
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Kolli, Phaneendra K. "Wireless Sensor Network for Structural Health Monitoring." Youngstown State University / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=ysu1274304285.
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Valiante, Rossella. "Innovative techniques for Structural Health Monitoring: a." Doctoral thesis, Universita degli studi di Salerno, 2011. http://hdl.handle.net/10556/213.
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2009 - 2010The here considered SHM procedure concerns innovative techniques for a structural monitoring of aeronautical components, all of them based upon the use of a Scanning Laser Doppler Vibrometer. The vibrometer is used to detect the dynamic response of the component under test, in wave propagation regime. The signal so recorded consists of space and time maps of vibration velocity offplane. The purpose of the study lies in the analysis of such maps, using filtering techniques that separate reflected waves from the incident ones, so that they can enable to identify defects. The innovative application of a novel technique (introduced by Ruzzene) for the first time to stringerized composite specimens, allowed the generation of baseline information directly from the measured dataset. The effectiveness of these methods has been demonstrated through their application to detection of a delamination in a composite stiffened plate and detection of defect/wrinkling in a T-shaped skin to stringer component. The most significant technological innovations achieved through these theses are: • The option key to excite the surface of a complex structure (in this case, the skins of a composite stingerized panel) and to derive the velocity profile on surfaces orthogonal to the excited one (in our case the web of the stringer) has been checked. This is crucial, as it would allow to install the piezo elements on the stringers, to excite them and to read velocities of points over the entire surface of the skin, without disassembly. Up to now, only cases of standard solicitation have been analyzed in literature, or cases where the velocities were acquired on the same surfaces excited. Today, therefore, there is no published study on the analysis conducted in such a manner. • The damage index was also applied to stiffened and greatly complex geometries. Up to now, in literature only analysis applied to simple flat panels can be found. • The FEM simulation was carried out on stiffened panels. In literature there are only simulations carried out on simple structural elements like flat panels without any stiffener. [edited by author]
IX n.s.
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Raziq, Noor. "GPS structural deformation monitoring : the mid-height problem /." Connect to thesis, 2008. http://repository.unimelb.edu.au/10187/3340.
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GPS has been used to monitor engineering structures for a number of reasons. One important reason for monitoring high rise buildings (and other engineering structures) is their safety assessment in events of extreme loading, such as earthquakes and storms. Decisions must be made as soon as possible, whether to allow re-occupation of such buildings, or to assess them for further damage. The time required to reach such decisions is cost-critical, both for the building owner or manager and for the agency doing the assessment. Peak inter-storey drift ratio and detection of permanent damage are some of the damage assessment parameters recommended by assessment agencies. Traditionally, accelerometers have been used to monitor these parameters. Accelerometers measure accelerations which are double-integrated to get displacements. These double integrated displacements are then used for computing the inter-storey drift ratios and locating permanent damage. Displacements obtained by double-integration and inter-storey drift ratios by subtraction of these displacements, are often erroneous and unreliable and direct measurement of displacement is preferred. Direct measurement of displacement is required at a number of points along the height of the building. For example, for computing inter-storey drift ratios, measurements of displacement at both the floor level and roof level are required. Such points on buildings and other engineering structures of vertical profile are termed as mid-height points in this thesis. While GPS has been used for deformation monitoring of engineering structures and to assist in damage assessment during and after extreme loading events, its use has been limited to roof top installations.This research is an attempt to measure displacements at mid-height locations of engineering structures of vertical profile using GPS. (For complete abstract open document).
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Tibaduiza, Burgos Diego Alexander. "Design and validation of a structural health monitoring system for aeronautical structures." Doctoral thesis, Universitat Politècnica de Catalunya, 2013. http://hdl.handle.net/10803/116811.
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Structural Health Monitoring (SHM) is an area where the main objective is the verification of the state or the health of the structures in order to ensure proper performance and maintenance cost savings using a sensor network attached to the structure, continuous monitoring and algorithms. Different benefits are derived from the implementation of SHM, some of them are: knowledge about the behavior of the structure under different loads and different environmental changes, knowledge of the current state in order to verify the integrity of the structure and determine whether a structure can work properly or whether it needs to be maintained or replaced and, therefore, to reduce maintenance costs. The paradigm of damage identification (comparison between the data collected from the structure without damages and the current
structure in orderto determine if there are any changes) can be tackled as a pattern recognition problem. Some statistical techniques as Principal Component Analysis (PCA) or Independent Component Analysis (ICA) are very useful for this purpose because they allow obtaining the most relevant information from a large amount of variables.
This thesis uses an active piezoelectric system to develop statistical data driven approaches for the detection, localization and classification of damages in structures. This active piezoelectric system is permanently attached to the surface of the structure under test in order to apply vibrational excitations and sensing the dynamical responses propagated through the structure at different points. As pattern recognition technique, PCA is used to perform the main task of the proposed methodology: to build a base-line model of the structure without damage and subsequentlyto compare the data from the current structure (under test) with this model. Moreover, different damage indices are calculated to detect abnormalities in the structure under test. Besides, the localization of the damage can be determined by means of the contribution of each sensor to each index. This contribution is calculated by several different methods and their comparison is performed. To classify different damages, the damage detection methodology is extended using a Self-Organizing Map (SOM), which is properly trained and validated to build a pattern baseline model using projections of the data onto the PCAmodel and damage detection indices. This baseline is further used as a reference for blind diagnosis tests of structures. Additionally, PCA is replaced by ICAas pattern recognition technique. A comparison between the two methodologies is performed highlighting advantages and disadvantages. In order to study the performance of the damage classification methodology under different scenarios, the methodology is tested using data from a structure under several different temperatures.
The methodologies developed in this work are tested and validated using different structures, in particular an aircraft turbine blade, an aircraft wing skeleton, an aircraft fuselage,some aluminium plates and some composite matarials plates.La monitorización de daños en estructuras (SHM por sus siglas en inglés) es un área que tiene como principal objetivo la verificación del estado o la salud de la estructura con el fin de asegurar el correcto funcionamiento de esta y ahorrar costos de mantenimiento. Para esto se hace uso de sensores que son adheridos a la estructura, monitorización continua y algoritmos. Diferentes beneficios se obtienen de la aplicación de SHM, algunos de ellos son: el conocimiento sobre el desempeño de la estructura cuando esta es sometida a diversas cargas y cambios ambientales, el conocimiento del estado actual de la estructura con el fin de determinar la integridad de la estructura y definir si esta puede trabajar adecuadamente o si por el contrario debe ser reparada o reemplazada con el correspondiente beneficio del ahorro de gastos de mantenimiento. El paradigma de la identificación de daños (comparación entre los datos obtenidos de la estructura sin daños y la estructura en un estado posterior para determinar cambios) puede ser abordado como un problema de reconocimiento de patrones. Algunas técnicas estadísticas tales como Análisis de Componentes Principales (PCA por sus siglas en inglés) o Análisis de Componentes Independientes (ICA por sus siglas en ingles) son muy útiles para este propósito puesto que permiten obtener la información más relevante de una gran cantidad de variables. Esta tesis hace uso de un sistema piezoeléctrico activo para el desarrollo de algoritmos estadísticos de manejo de datos para la detección, localización y clasificación de daños en estructuras. Este sistema piezoeléctrico activo está permanentemente adherido a la superficie de la estructura bajo prueba con el objeto de aplicar señales vibracionales de excitación y recoger las respuestas dinámicas propagadas a través de la estructura en diferentes puntos. Como técnica de reconocimiento de patrones se usa Análisis de Componentes Principales para realizar la tarea principal de la metodología propuesta: construir un modelo PCA base de la estructura sin daño y posteriormente compararlo con los datos de la estructura bajo prueba. Adicionalmente, algunos índices de daños son calculados para detectar anormalidades en la estructura bajo prueba. Para la localización de daños se usan las contribuciones de cada sensor a cada índice, las cuales son calculadas mediante varios métodos de contribución y comparadas para mostrar sus ventajas y desventajas. Para la clasificación de daños, se amplia la metodología de detección añadiendo el uso de Mapas auto-organizados, los cuales son adecuadamente entrenados y validados para construir un modelo patrón base usando proyecciones de los datos sobre el modelo PCA base e índices de detección de daños. Este patrón es usado como referencia para realizar un diagnóstico ciego de la estructura. Adicionalmente, dentro de la metodología propuesta, se utiliza ICA en lugar de PCA como técnica de reconocimiento de patrones. Se incluye también una comparación entre la aplicación de las dos técnicas para mostrar las ventajas y desventajas. Para estudiar el desempeño de la metodología de clasificación de daños bajo diferentes escenarios, esta se prueba usando datos obtenidos de una estructura sometida a diferentes temperaturas. Las metodologías desarrolladas en este trabajo fueron probadas y validadas usando diferentes estructuras, en particular un álabe de turbina, un esqueleto de ala y un fuselaje de avión, así como algunas placas de aluminio y de material compuesto
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Liu, Wei Lin. "Integrated and flexible ultrasonic transducers for structural health monitoring on aircraft structures." Thesis, McGill University, 2010. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=97155.
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Fatigue crack initiating from fastener holes in aluminum plates is a typical damagefrequently found on modern aircraft structures. Requirements for life extension of agingaircraft fleets and reduced maintenance costs have been accelerating the developments ofstructural health monitoring (SHM) technologies. This thesis considers the active sensingapproach of SHM that involves the integrated ultrasonic transducer (IUT) and the flexibleultrasonic transducer (FUT). The main component of IUT and FUT was piezoelectriclead-zirconate-titanate composite films which were fabricated using the sol-gel spraytechnique. The crack growth monitoring capability of the IUT and FUT was successfullydemonstrated on aluminum plates with fatigue cracks. The artificial damages on analuminum test article representing aircraft structural complexity were also detected by theFUT array bonded on both planar and curved surfaces. Finally, the design and fabricationof miniature angle beam wedges having low spurious noise are presented. The fatiguecrack on an aluminum thin plate was detected using the FUT bonded onto such anglebeam wedges.Les fissures dues à la fatigue du métal initiées aux trous de fixation dans lesplaques d'aluminium sont des problèmes communs dans les avions modernes. De plus,l'utilisation d'avions de plus en plus âgés et le besoin de réduire leurs coûts d'entretien àaccélérer le développement de la technologie de la surveillance de la santé structurelle(SSS) de ces derniers. Ce mémoire considère l'approche active de la SSS en incorporantla capacité des capteurs intégrés ultrasonores (CIU) et des capteurs flexibles ultrasonores(CFU). L'ingrédient principal des CIU et CFU est des films à base de plomb-zirconatetitanatequi sont fabriqués à partir de la technique sol-gel. La capacité des CIU et CFU àsurveiller la croissance des fissures sur des plaques d'aluminium fissurées par fatigue futdémontrée avec succès. Les défauts artificiels mis dans des échantillons de plaquesd'aluminium représentant la complexité structurelle furent également détectés par unematrice de CFU collée sur des surfaces plane et courbe. Finalement, la conception et lafabrication de coins d'angles miniatures ayant comme caractéristiques de faibles bruitsparasites sont présentées. Les fissures par fatigue sur de minces plaques d'aluminiumfurent détectées en utilisant les CFU collés sur de tels coins.
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Kefal, Adnan. "Structural health monitoring of marine structures by using inverse finite element method." Thesis, University of Strathclyde, 2017. http://digitool.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=27863.
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Structural health monitoring (SHM) is a process aimed at providing accurate and real-time information concerning structural condition and performance. SHM is a very important discipline in the areas of civil, aerospace, and marine engineering because the utilization of SHM allows us to increase both human and environmental safety in conjunction with reduction in direct economic losses. A key component of the SHM process is real-time reconstruction of a structure’s three-dimensional displacement and stress fields using a network of in situ strain sensors and measured strains, which is commonly referred to as “shape and stress sensing”. The inverse finite element method (iFEM) is a revolutionary shape- and stress-sensing methodology shown to be fast, accurate, and robust for usage as a part of SHM systems. In the present thesis, the general framework of iFEM, i.e., least-squares variational principle, is adopted to develop unconventional and more effective shape- and stress-sensing techniques, with focus on general engineering structures and marine structures in particular. Firstly, the original iFEM formulation for plate and shell structures, developed on the basis of first-order shear deformation theory, is summarized. Then, this formulation is utilized to develop a new four-node quadrilateral inverse-shell element, iQS4, which further extends the practical utility of iFEM for shape sensing of large-scale structures including marine structures. Various numerical examples are presented and it is demonstrated that the iQS4 formulation is robust with respect to the membrane- and shear-locking phenomena. Moreover, the iFEM/iQS4 methodology is applied to various types of marine structures including a stiffened plate, a chemical tanker, and a container ship. To simulate experimentally measured strains and to establish reference displacements, a coupled hydrodynamic and high-fidelity finite element analyses are performed. Utilizing the simulated strain-sensor strains, iFEM analysis of each marine structure is performed. As a result, the optimum locations of the on-board strain sensors are determined for each marine structure. Furthermore, a novel isogeometric Kirchhoff–Love inverse-shell element (iKLS) for more accurate shape-sensing analysis of curved/complex shell structures is presented. The new formulation employs the iFEM as a general framework and the non-uniform rational B-splines (NURBS) as the discretization technology for both structural geometry and displacement domain. Therefore, this new formulation couples the concept of isogeometric analysis with iFEM methodology and creates an innovative “isogeometric iFEM formulation”. The superior shape-sensing capability of the isogeometric iFEM formulation (i.e., iKLS) is demonstrated for curved shell structures when using low-fidelity discretizations with few strain sensors. Finally, an improved iFEM formulation for dealing with shape and stress sensing of multilayered composite and sandwich plate/shell structures is described. The present iFEM formulation is based upon the minimization of a weighted-least-squares functional that uses the complete set of strain measures of refined zigzag theory (RZT). A new three-node inverse-shell element, i3-RZT, is developed based on the enhanced iFEM formulation. Various validation and demonstration problems are solved to examine the precision of the iFEM/i3-RZT methodology. The numerical results demonstrate the superior accuracy and robustness of the i3-RZT element for performing accurate shape and stress sensing of complex composite structures. In conclusion, all proposed iFEM frameworks are computationally efficient, accurate, and powerful, hence they can be helpful for shape sensing and SHM of general engineering structures, especially of marine structures.
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Sunny, Mohammed Rabius. "Towards Structural Health Monitoring of Gossamer Structures Using Conductive Polymer Nanocomposite Sensors." Diss., Virginia Tech, 2010. http://hdl.handle.net/10919/28797.
Full textAbstract:
The aim of this research is to calibrate conductive polymer nanocomposite materials for
large strain sensing and develop a structural health monitoring algorithm for gossamer
structures by using nanocomposites as strain sensors. Any health monitoring system works
on the principle of sensing the response (strain, acceleration etc.) of the structure to an
external excitation and analyzing the response to find out the location and the extent of
the damage in the structure. A sensor network, a mathematical model of the structure, and
a damage detection algorithm are necessary components of a structural health monitoring
system. In normal operating conditions, a gossamer structure can experience normal strain
as high as 50%. But presently available sensors can measure strain up to 10% only, as
traditional strain sensor materials do not show low elastic modulus and high electrical
conductivity simultaneously. Conductive polymer nanocomposite which can be stretched
like rubber (up to 200%) and has high electrical conductivity (sheet resistance 100 Ohm/sq.)
can be a possible large strain sensor material. But these materials show hysteresis and
relaxation in the variation of electrical properties with mechanical strain. It makes the
calibration of these materials difficult. We have carried out experiments on conductive
polymer nanocomposite sensors to study the variation of electrical resistance with time
dependent strain. Two mathematical models, based on the modified fractional calculus and
the Preisach approaches, have been developed to model the variation of electrical resistance
with strain in a conductive polymer. After that, a compensator based on a modified Preisach
model has been developed. The compensator removes the effect of hysteresis and relaxation
from the output (electrical resistance) obtained from the conductive polymer nanocomposite
sensor. This helps in calibrating the material for its use in large strain sensing. Efficiency of
both the mathematical models and the compensator has been shown by comparison of their
results with the experimental data. A prestressed square membrane has been considered
as an example structure for structural health monitoring. Finite element analysis using
ABAQUS has been carried out to determine the response of the membrane to an uniform
transverse dynamic pressure for different damage conditions. A neuro-fuzzy system has been
designed to solve the inverse problem of detecting damages in the structure from the strain
history sensed at different points of the structure by a sensor that may have a significant
hysteresis. Damage feature index vector determined by wavelet analysis of the strain history at different points of the structure are taken by the neuro-fuzzy system as input. The neuro-fuzzy system detects the location and extent of the damage from the damage feature index
vector by using some fuzzy rules. Rules associated with the fuzzy system are determined
by a neural network training algorithm using a training dataset, containing a set of known
input and output (damage feature index vectors, location and extent of damage for different
damage conditions). This model is validated by using the sets of input-output other than
those which were used to train the neural network.Ph. D.
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Philipps, Joseph Caleb. "Sensor characterization for long-term remote monitoring of bridge piers." Diss., Columbia, Mo. : University of Missouri-Columbia, 2007. http://hdl.handle.net/10355/4907.
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Thesis (M.S.)--University of Missouri-Columbia, 2007.The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on April 2, 2008) Includes bibliographical references.
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Erazo, Kalil. "Bayesian Filtering In Nonlinear Structural Systems With Application To Structural Health Monitoring." ScholarWorks @ UVM, 2015. http://scholarworks.uvm.edu/graddis/513.
Full textAbstract:
During strong earthquakes structural systems exhibit nonlinear behavior due to low-cycle fatigue, cracking, yielding and/or fracture of constituent elements. After a seismic event it is essential to assess the state of damage of structures and determine if they can safely resist aftershocks or future strong motions. The current practice in post-earthquake damage assessment relies mainly on visual inspections and local testing. These approaches are limited to the ability of inspectors to reach all potentially damaged locations, and are typically intended to detect damage near the outer surfaces of the structure leaving the possibility of hidden undetected damage. Some structures in seismic prone-regions are instrumented with an array of sensors that measure their acceleration at different locations. We operate under the premise that acceleration response measurements contain information about the state of damage of structures, and it is of interest to extract this information and use it in post-earthquake damage assessment and decision making strategies.
The objective of this dissertation is to show that Bayesian filters can be successfully employed to estimate the nonlinear dynamic response of instrumented structural systems. The estimated response is subsequently used for structural damage diagnosis. Bayesian filters combine dynamic response measurements at limited spatial locations with a nonlinear dynamic model to estimate the response of stochastic dynamical systems at the model degrees-of-freedom. The application of five filters is investigated: the extended, unscented and ensemble Kalman filters, the particle filter and the model-based observer.
The main contributions of this dissertation are summarized as follows: i) Development of a filtering-based mechanistic damage assessment framework; ii) Experimental validation of Bayesian filters in small and large-scale structures; iii) Uncertainty quantification and propagation of response and damage estimates computed using Bayesian filters.
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Pawar, Prashant M. "Structural Health Monitoring Of Composite Helicopter Rotor Blades." Thesis, Indian Institute of Science, 2006. http://hdl.handle.net/2005/273.
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Helicopter rotor system operates in a highly dynamic and unsteady aerodynamic environment leading to severe vibratory loads on the rotor system. Repeated exposure to these severe loading conditions can induce damage in the composite rotor blade which may lead to a catastrophic failure. Therefore, an interest in the structural health monitoring (SHM) of the composite rotor blades has grown markedly in recent years. Two important issues are addressed in this thesis; (1) structural modeling and aeroelastic analysis of the damaged rotor blade and (2) development of a model based rotor health monitoring system. The effect of matrix cracking, the first failure mode in composites, is studied in detail for a circular section beam, box-beam and two-cell airfoil section beam. Later, the effects of further progressive damages such as debonding/delamination and fiber breakage are considered for a two-cell airfoil section beam representing a stiff-inplane helicopter rotor blade. It is found that the stiffness decreases rapidly in the initial phase of matrix cracking but becomes almost constant later as matrix crack saturation is reached. Due to matrix cracking, the bending and torsion stiffness losses at the point of matrix crack saturation are about 6-12 percent and about 25-30 percent, respectively. Due to debonding/delamination, the bending and torsion stiffness losses are about 6-8 percent and about 40-45 percent after matrix crack saturation, respectively. The stiffness loss due to fiber breakage is very rapid and leads to the final failure of the blade. An aeroelastic analysis is performed for the damaged composite rotor in forward flight and the numerically simulated results are used to develop an online health monitoring system. For fault detection, the variations in rotating frequencies, tip bending and torsion response, blade root loads and strains along the blade due to damage are investigated. It is found that peak-to-peak values of blade response and loads provide a good global damage indicator and result in considerable data reduction. Also, the shear strain is a useful indicator to predict local damage. The structural health monitoring system is developed using the physics based models to detect and locate damage from simulated noisy rotor system data. A genetic fuzzy system (GFS) developed for solving the inverse problem of detecting damage from noise contaminated measurements by hybridizing the best features of fuzzy logic and genetic algorithms. Using the changes in structural measurements between the damaged and undamaged blade, a fuzzy system is generated and the rule-base and membership functions optimized by genetic algorithm. The GFS is demonstrated using frequency and mode shape based measurements for various beam type structures such as uniform cantilever beam, tapered beam and non-rotating helicopter blade. The GFS is further demonstrated for predicting the internal state of the composite structures using an example of a composite hollow circular beam with matrix cracking damage mode. Finally, the GFS is applied for online SHM of a rotor in forward flight. It is found that the GFS shows excellent robustness with noisy data, missing measurements and degrades gradually in the presence of faulty sensors/measurements. Furthermore, the GFS can be developed in an automated manner resulting in an optimal solution to the inverse problem of SHM. Finally, the stiffness degradation of the composite rotor blade is correlated to the life consumption of the rotor blade and issues related to damage prognosis are addressed.
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Kuok, Sin Chi. "Ambient effects on structural health monitoring of buildings." Thesis, University of Macau, 2009. http://umaclib3.umac.mo/record=b2099636.
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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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Hejll, Arvid. "Civil structural health monitoring : strategies, methods and applications /." Luleå : Division of Structural Engineering, Department of Civil and Mining Engineering, Luleå University of Technology, 2007. http://epubl.ltu.se/1402-1544/2007/10/.
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Konstantinidis, Georgios. "Structural health monitoring of plates using lamb waves." Thesis, University of Bristol, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.495779.
Full textAbstract:
It is desirable for any structural health monitoring (SHM) system to achieve maximum sensitivity with minimum sensor density. This may be accomplished using guided waves. The structural health monitoring system described herein is based on the excitation and reception of guided waves using piezoelectric elements as sensors. One of the main challenges faced is that in all but the most simple structures the wave interactions become too complex for the time domain signals to be interpreted directly.
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Lienhart, Werner [Verfasser]. "Analysis of Inhomogeneous Structural Monitoring Data / Werner Lienhart." Aachen : Shaker, 2007. http://d-nb.info/1170527647/34.
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Reed, Stephen C. "Indirect aircraft structural monitoring using artificial neural networks." Thesis, University of Sheffield, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.434603.
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Stephen, Graham Alexander. "Visual determination of dynamic displacements for structural monitoring." Thesis, University of Bristol, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.303675.
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Amraoui, Mohamed Yacine. "Non-invasive damage detection and structural health monitoring." Thesis, University of Bristol, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.271865.
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