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Mishra, Madhav. "Model-based Prognostics for Prediction of Remaining Useful Life." Licentiate thesis, Luleå tekniska universitet, Drift, underhåll och akustik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-17263.
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Prognostics and healthmanagement (PHM) is an engineering discipline that aims to maintain the systembehaviour and function, and assure the mission success, safety andeffectiveness. Health management using a proper condition-based maintenance (CBM)deployment is a worldwide accepted technique and has grown very popular in manyindustries over the past decades. These techniques are relevant in environmentswhere the prediction of a failure and the prevention and mitigation of itsconsequences increase the profit and safety of the facilities concerned.Prognosis is the most critical part of this process and is nowadays recognizedas a key feature in maintenance strategies, since estimation of the remaininguseful life (RUL) is essential.PHM can provide a stateassessment of the future health of systems or components, e.g. when a degradedstate has been found. Using this technology, one can estimate how long it willtake before the equipment will reach a failure threshold, in future operatingconditions and future environmental conditions. This thesis focuses especiallyon physics-based prognostic approaches, which depend on a fundamentalunderstanding of the physical system in order to develop condition monitoringtechniques and to predict the RUL.The overall research objective of thework performed for this thesis has been to improve the accuracy and precisionof RUL predictions. The research hypothesis is that fusing the output of morethan one method will improve the accuracy and precision of the RUL estimation,by developing a new approach to prognostics that combines different remaininglife estimators and physics-based and data-driven methods. There are two waysof acquiring data for data-driven models, namely measurements of real systemsand syntactic data generation from simulations. The thesis deals with two casestudies, the first of which concerns the generation of synthetic data andindirect measurement of dynamic bearing loads and was performed atBillerudKorsäs paper mill at Karlsborg in Sweden. In this study the behaviourof a roller in a paper machine was analysed using the finite element method(FEM). The FEM model is a step towards the possibility of generating syntheticdata on different failure modes, and the possibility of estimating crucialparameters like dynamic bearing forces by combining real vibration measurementswith the FEM model. The second case study deals with the development ofprognostic methods for battery discharge estimation for Mars-based rovers. Herephysical models and measurement data were used in the prognostic development insuch a way that the degradation behaviour of the battery could be modelled andsimulated in order to predict the life-length. A particle filter turned out tobe the method of choice in performing the state assessment and predicting thefuture degradation. The method was then applied to a case study of batteriesthat provide power to the rover.Godkänd; 2015; 20151116 (madmis); Nedanstående person kommer att hålla licentiatseminarium för avläggande av teknologie licentiatexamen. Namn: Madhav Mishra Ämne: Drift och underhållsteknik/Operation and Maintenance Engineering Uppsats: Model-based Prognostics for Prediction of Remaining Useful Life Examinator: Professor Uday Kumar Institutionen för samhällsbyggnad och naturresurser Avdelning Drift, underhåll och akustik Luleå tekniska universitet Diskutant: Accos. Professor Jyoti Kumar Sinha University of Manchester, Aerospace and Civil Engineering, Manchester Tid: Torsdag 17 december 2015 kl 10.00 Plats: F1031, Luleå tekniska universitet
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Huynh, Daniel Duc Cong. "Next generation probabilistic prediction model for submarine propulsion shaft life." Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/118664.
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Thesis: Nav. E., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2018.Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2018.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 81-85).
With the development of the U.S. Navy's new COLUMBIA class ballistic missile submarine, the Navy plans to implement a new, longer operational inspection interval for the propulsion shaft system, attempting to double the current 6-year inspection interval for the OHIO class of submarine it is replacing. However, an initial study conducted suggests unsatisfactory levels of failure at this interval due to corrosion fatigue, although with a high level of uncertainty. This thesis addresses that uncertainty by developing a more robust probabilistic model for submarine propulsion shaft reliability in order to more accurately predict probabilities of failure. To improve upon previous efforts, all the components and failure modes of the propulsion shaft were first identified. While the most likely scenario involves water ingress and a wetted propulsion shaft leading to corrosion, pitting, and cracking, other factors that could contribute to shaft failure include damage during installation or failure of cathodic protection systems. Using literature and data gathered during visits to Portsmouth Naval Shipyard (PNSY), these failure modes were approximated with appropriate relationships and statistical distributions and ultimately combined to form a complete probabilistic model of the propulsion shaft system, including all the expected components and the best physics available. Additionally, while this model was designed with extension to the COLUMBIA class of submarine in mind, it can be tailored and easily modified to apply to a broad range of shafting systems, including other classes of submarines, conventional surface ships, and even offshore platforms. The GoldSim program was used as the vehicle for the model, with failure probabilities for the submarine shaft predicted using Monte Carlo simulations. To calibrate the model, outputs from the probabilistic model were compared against hypothetical shaft inspection data, adjusting distributions and variables as appropriate to match target values. While the model used the OHIO class submarine as its baseline, it is expected that the new COLUMBIA class shafting system will use similar materials and have a similar configuration. These inspections have typically taken place at around the 6-year operational interval, but the calibrated model can be used to predict propulsion shaft failures at a range of inspection intervals.
by Daniel Duc Cong Huynh.
Nav. E.
S.M.
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Yu, Jianxiong. "Pavement Service Life Estimation And Condition Prediction." See Full Text at OhioLINK ETD Center (Requires Adobe Acrobat Reader for viewing), 2005. http://www.ohiolink.edu/etd/view.cgi?toledo1132896646.
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Dissertation (Ph.D.)--University of Toledo, 2005.Typescript. "A dissertation [submitted] as partial fulfillment of the requirements of the Doctor of Philosophy degree in Engineering." Bibliography: leaves 69-74.
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Nowicki, Timothy. "Statistical model prediction of fatigue life for diffusion bonded Inconel 600 /." Online version of thesis, 2008. http://hdl.handle.net/1850/7984.
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Grobaski, Thomas. "Preliminary Research for the Development of a Hot Forging Die Life Prediction Model." Ohio University / OhioLINK, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1102695461.
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Grobaski, Thomas C. "Preliminary research for the development of a hot forging die life prediction model." Ohio : Ohio University, 2004. http://www.ohiolink.edu/etd/view.cgi?ohiou1102695461.
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Karl, Justin. "Thermomechanical Fatigue Life Prediction of Notched 304 Stainless Steel." Doctoral diss., University of Central Florida, 2013. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5796.
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The behavior of materials as they are subjected to combined thermal and mechanical fatigue loads is an area of research that carries great significance in a number of engineering applications. Power generation, petrochemical, and aerospace industries operate machinery with expensive components that undergo repeated applications of force while simultaneously being exposed to variable temperature working fluids. A case of considerable importance is found in steam turbines, which subject blades to cyclic loads from rotation as well as the passing of heated gases. The complex strain and temperature histories from this type of operation, combined with the geometric profile of the blades, make accurate prediction of service life for such components challenging. Development of a deterministic life prediction model backed by physical data would allow design and operation of turbines with higher efficiency and greater regard for reliability. The majority of thermomechanical fatigue (TMF) life prediction modeling research attempts to correlate basic material property data with simplistic strain and thermal histories. With the exception of very limited cases, these types of efforts have been insufficient and imprecise in their capabilities. Early researchers did not account for the multiple damage mechanisms that operate and interact within a material during TMF loads, and did not adequately address the extent of the relationship between smooth and notched parts. More recent research that adequately recognizes the multivariate nature of TMF develops models that handle life reduction through summation of constitutive damage terms. It is feasible that a modification to the damage-based approach can sufficiently include cases that involve complex geometry. The focus of this research is to construct an experimentally-backed extension of the damage-based approach that improves handling of geometric discontinuities. Smooth and notched specimens of Type 304 stainless steel were subjected to several types of idealized fatigue conditions to assemble a clear picture of the types of damage occurring in a steam turbine and similarly-loaded mechanical systems. These results were compared with a number of idealized TMF experiments, and supplemented by numerical simulation and microscopic observation. A non-uniform damage-summation constitutive model was developed primarily based on physical observations. An additional simplistic model was developed based on phenomenological effect. Findings from this study will be applicable to life prediction efforts in other similar material and load cases.Ph.D.
Doctorate
Mechanical and Aerospace Engineering
Engineering and Computer Science
Mechanical Engineering
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Singley, Daniel Browne. "Longitudinal prediction of domain satisfaction and global life satisfaction test of a social cognitive model /." College Park, Md. : University of Maryland, 2005. http://hdl.handle.net/1903/2364.
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Thesis (Ph. D.) -- University of Maryland, College Park, 2005.Thesis research directed by: Dept. of Counseling and Personnel Services. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Sarwade, Rohit Foster Winfred A. "Life prediction analysis of a subscale rocket engine combustor using a fluid-thermal-structural model." Auburn, Ala., 2006. http://repo.lib.auburn.edu/2006%20Spring/master's/SARWADE_ROHIT_49.pdf.
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Aikio, Englund Rebecca. "A study of calculation models for fatigue life prediction : A thesis accomplished together with GKN Aerospace." Thesis, Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-67741.
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GKN Aerospace in Trollhättan don’t use the latest ANSYS version and need to upgrade their life analysis models. The aim with this thesis is to do a study of the new models and investigate the times required for the calculations. A flight mission were chosen and this mission together with different life analysis models were run in the GKN in house program Life Analysis System. The results were analyzed and depending on the results additional runs were made or the problem were sent to the life management group at GKN Aerospace. Strain levels versus time were also plotted for the runs with the new models to get a perception where any problems occurs. The results from the model 4.10.149 had no variations between equal runs for the high pressure turbine and the low pressure turbine but there was a variation between the results when equal runs was made with the high pressure compressor. The results from model 4.10.157 and 4.10.124 and 4.10.160 and 4.10.173 had variations in the fatigue life for equal runs. The variations can depend on that the calculations converges to different solutions, the reason for this can depend on the non-linear contact elements. The variation in the results between equal runs occurs when the model uses two or more cores. The time required for the calculation becomes faster with the use of more cores. The longest duration had model 4.10.173 because of the many requirements for the calculations in this model. The problem with the variation in the results is sent to ANSYS.
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Viklund, Håkan. "Formalizing life : Towards an improved understanding of the sequence-structure relationship in alpha-helical transmembrane proteins." Doctoral thesis, Stockholm University, Department of Biochemistry and Biophysics, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-7144.
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Genes coding for alpha-helical transmembrane proteins constitute roughly 25% of the total number of genes in a typical organism. As these proteins are vital parts of many biological processes, an improved understanding of them is important for achieving a better understanding of the mechanisms that constitute life.
All proteins consist of an amino acid sequence that fold into a three-dimensional structure in order to perform its biological function. The work presented in this thesis is directed towards improving the understanding of the relationship between sequence and structure for alpha-helical transmembrane proteins. Specifically, five original methods for predicting the topology of alpha-helical transmembrane proteins have been developed: PRO-TMHMM, PRODIV-TMHMM, OCTOPUS, Toppred III and SCAMPI.
A general conclusion from these studies is that approaches that use multiple sequence information achive the best prediction accuracy. Further, the properties of reentrant regions have been studied, both with respect to sequence and structure. One result of this study is an improved definition of the topological grammar of transmembrane proteins, which is used in OCTOPUS and shown to further improve topology prediction. Finally, Z-coordinates, an alternative system for representation of topological information for transmembrane proteins that is based on distance to the membrane center has been introduced, and a method for predicting Z-coordinates from amino acid sequence, Z-PRED, has been developed.
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Zalewsky, Brian J. "Use of the Water Erosion Prediction Project (WEPP) Model to Predict Road Surface Erosion in Mountain Rangeland Areas." DigitalCommons@USU, 1998. https://digitalcommons.usu.edu/etd/3655.
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A significant source of sediment in many watersheds is that associated with the layout, construction, and maintenance of roadways. Much work has been done in more mesic forested environments with little or none in semiarid systems. Acc urate estimation of runoff and sediment yield from native surfaced roads located in semiarid mountainous ecosystems is important to both private and public regulatory agencies. The Watershed Erosion Prediction Project (WEPP) model represents the most current erosion prediction technology. WEPP has been applied to the problems of logging road erosion in more mesic forests but has not been tested or evaluated on roadways located in semiarid mountainous ecosystems.
Six rainfall simulation experiments were conducted to measure runoff and sediment yield off three separate plots located on Tickville Road, located on Camp W.G. Williams, a National Guard Training Center in Utah . These data were compared with runoff and erosion estimates produced by the WEPP model. WEPP cropland and rangeland erodibility equations were used to predict rill erodibility (Kr), interrill erodibility (Ki), and critical shear (TAUc). These were tested for their effectiveness in predicting road erodibilities in these environments. A sensitivity analysis was performed on those parameters that were suspected of having a substantial impact on model output and accuracy.
There was an excellent correlation between predicted and observed total runoff volumes for all simulations (R2= 0.96). The differences were greater than 10% only for plot 2 wet; otherwise, the average difference for all six simulations was 4.9%. When using Kr, K.i , and TAUc as predicted by rangeland methods, predicted sediment yields differed from those measured, on average, by 82%. Predicted sediment yields differed by only 22% compared to calculated sediment yields, when using the cropland erodibility equations to predict Kr, K.i , and TAUc. A sensitivity analysis showed that percent slope, slope length, days since last tillage, and ridge roughness all had a significant impact on WEPP predicted sediment yields. Results show the effectiveness of the WEPP model in predicting runoff and erosion off native surfaced roads in these semiarid mountainous regions.
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Huq, Fazul, and dpmeng@bigpond com. "Development of Life Prediction Models for Rolling Contact Wear in Ceramic and Steel Ball Bearings." RMIT University. Aerospace, Mechanical and Manufacturing Engineering, 2007. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20080215.145624.
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The potential for significant performance increases, using ceramic materials in un-lubricated rolling element bearing applications, has been the subject of research over the past two decades. Practical advantages over steel include increased ability to withstand high loads, severe environments and high speeds. However, widespread acceptance has been limited by the inability to predict wear life for ceramic bearing applications. In this thesis, the rolling contact wear of 52100 bearing steel and Over-aged Magnesia-Partially-Stabilised Zirconia (OA-Mg-PSZ) ceramic are examined using a newly developed rolling contact wear test rig. The new wear test rig simulates the system geometry of an un-lubricated hybrid (ceramic and steel) ball bearing. The new wear test rig is versatile in that it allows low cost samples to be utilised resulting in a larger number of samples that can be tested. Wear samples of 52100 bearing steel and OA-Mg-PSZ produced by the new wear test rig were examined for mass loss and wear depth. The wear behavior of both the steel and ceramic material showed a dependence on operating variables time and load. Load was varied between 300N to 790N. Typical mass loss after 1 hour of testing 52100 bearing steel at 790N was 0.03 grams as compared to OA-Mg-PSZ which was 0.001 grams. The rolling contact wear of the OA-Mg-PSZ was an order of magnitude lower than that of the 52100 bearing steel. The wear mechanism for 52100 bearing steel was typical of plastic deformation and shearing near and below the surface of rolling contact. Once cracks extend to reach the surface, thin flat like sheets are produced. In OA-Mg-PSZ the wear mechanism initially is that of plastic deformation on the scale of the surface asperities with asperity polishing occurring followed by lateral cracks and fatigue spallation. Results obtained using the new rolling contact wear test rig led to the establishment of a new equation for wear modeling of 52100 bearing steel and OA-Mg-PSZ ceramic materials.
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Tamssaouet, Ferhat. "Towards system-level prognostics : modeling, uncertainty propagation and system remaining useful life prediction." Thesis, Toulouse, INPT, 2020. http://www.theses.fr/2020INPT0079.
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Le pronostic est le processus de prédiction de la durée de vie résiduelle utile (RUL) des composants, sous-systèmes ou systèmes. Cependant, jusqu'à présent, le pronostic a souvent été abordé au niveau composant sans tenir compte des interactions entre les composants et l'impact de l'environnement, ce qui peut conduire à une mauvaise prédiction du temps de défaillance dans des systèmes complexes. Dans ce travail, une approche de pronostic au niveau du système est proposée. Cette approche est basée sur un nouveau cadre de modélisation : le modèle d'inopérabilité entrée-sortie (IIM), qui permet de prendre en compte les interactions entre les composants et les effets du profil de mission et peut être appliqué pour des systèmes hétérogènes. Ensuite, une nouvelle méthodologie en ligne pour l'estimation des paramètres (basée sur l'algorithme de la descente du gradient) et la prédiction du RUL au niveau système (SRUL) en utilisant les filtres particulaires (PF), a été proposée. En détail, l'état de santé des composants du système est estimé et prédit d'une manière probabiliste en utilisant les PF. En cas de divergence consécutive entre les estimations a priori et a posteriori de l'état de santé du système, la méthode d'estimation proposée est utilisée pour corriger et adapter les paramètres de l'IIM. Finalement, la méthodologie développée, a été appliquée sur un système industriel réaliste : le Tennessee Eastman Process, et a permis une prédiction du SRUL dans un temps de calcul raisonnablePrognostics is the process of predicting the remaining useful life (RUL) of components, subsystems, or systems. However, until now, the prognostics has often been approached from a component view without considering interactions between components and effects of the environment, leading to a misprediction of the complex systems failure time. In this work, a prognostics approach to system-level is proposed. This approach is based on a new modeling framework: the inoperability input-output model (IIM), which allows tackling the issue related to the interactions between components and the mission profile effects and can be applied for heterogeneous systems. Then, a new methodology for online joint system RUL (SRUL) prediction and model parameter estimation is developed based on particle filtering (PF) and gradient descent (GD). In detail, the state of health of system components is estimated and predicted in a probabilistic manner using PF. In the case of consecutive discrepancy between the prior and posterior estimates of the system health state, the proposed estimation method is used to correct and to adapt the IIM parameters. Finally, the developed methodology is verified on a realistic industrial system: The Tennessee Eastman Process. The obtained results highlighted its effectiveness in predicting the SRUL in reasonable computing time
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Mahieux, Celine Agnes. "A Systematic Stiffness-Temperature Model for Polymers and Applications to the Prediction of Composite Behavior." Diss., Virginia Tech, 1999. http://hdl.handle.net/10919/26479.
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Polymer matrix composites (PMCâ s) are now being used more and more extensively and over wider ranges of service conditions. Large changes in pressure, chemical environment or temperature influence the mechanical response of such composites. In the present effort, we focus on temperature, a parameter of primary interest in almost all engineering applications. In order to design composite structures without having to perform extensive experiments (virtual design), the necessity of establishing theoretical models that relate the macroscopic response of the structure to the microscopic properties of the constituents arises. In the first part of the present work, a new stiffness versus temperature model is established. The model is validated using data from the literature. The influence of the different polymerâ s properties (Molecular weight, crystallinity, and filler content) on the model are studied by performing experiments on different grades of four polymers PMMA, PEEK, PPS, and PB. This statistical model is proven to be applicable to very different polymers (elastomers, thermoplastics, crystalline, amorphous, cross-linked, linear, filled, unfilledâ ¦) over wide temperature ranges (from the glassy state to the flow region). The most attractive feature of the proposed model is the capability to enable a description of the polymerâ s mechanical behavior within and across the property transition regions.
In order to validate the feasibility of using the model to predict the mechanical response of polymer matrix composites, the stiffness-temperature model is used in various micromechanical models (rule of mixtures, compression models for the life prediction of unidirectional PMCâ s in end-loaded bendingâ ¦). The model is also inserted in the MRLife prediction code to predict the remaining strength and life of unidirectional PMCâ s in fatigue bending. End-loaded fatigue experiments were performed. A good correlation between theoretical and experimental results is observed. Finally, the model is used in the Classical Lamination Theory; some laminates were found to exhibit stress reversals with temperature and behaved like thermally activated mechanical switches.Ph. D.
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Zhang, Bochun. "Failure Mechanism Analysis and Life Prediction Based on Atmospheric Plasma-Sprayed and Electron Beam-Physical Vapor Deposition Thermal Barrier Coatings." Thesis, Université d'Ottawa / University of Ottawa, 2017. http://hdl.handle.net/10393/35709.
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Using experimentally measured temperature-process-dependent model parameters, the failure analysis and life prediction were conducted for Atmospheric Plasma Sprayed Thermal Barrier Coatings (APS-TBCs) and electron beam physical vapor deposition thermal barrier coatings (EB-PVD TBCs) with Pt-modified -NiAl bond coats deposited on Ni-base single crystal superalloys. For APS-TBC system, a residual stress model for the top coat of APS-TBC was proposed and then applied to life prediction. The capability of the life model was demonstrated using temperature-dependent model parameters. Using existing life data, a comparison of fitting approaches of life model parameters was performed. The role of the residual stresses distributed at each individual coating layer was explored and their interplay on the coating’s delamination was analyzed. For EB-PVD TBCs, based on failure mechanism analysis, two newly analytical stress models from the valley position of top coat and ridge of bond coat were proposed describing stress levels generated as consequence of the coefficient of thermal expansion (CTE) mismatch between each layers. The thermal stress within TGO was evaluated based on composite material theory, where effective parameters were calculated. The lifetime prediction of EB-PVD TBCs was conducted given that the failure analysis and life model were applied to two failure modes A and B identified experimentally for thermal cyclic process. The global wavelength related to interface rumpling and its radius curvature were identified as essential parameters in life evaluation, and the life results for failure mode A were verified by existing burner rig test data. For failure mode B, the crack growth rate along the topcoat/TGO interface was calculated using the experimentally measured average interfacial fracture toughness.
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Jordan, Ann B. "The shuttle effect : the development of a model for the prediction of variability in cognitive test performance across the adult life span." Thesis, Rhodes University, 1998. http://hdl.handle.net/10962/d1008556.
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The aim of this thesis was to investigate inter-individual variability on cognitive task performance in normal older adults. In a review of the cognitive aging literature, the implications of a differential perspective were drawn out in order to establish a theoretical and methodological basis for an investigation into variability. A number of regularly occurring patterns, identified on the basis of available reports in the literature, were used to develop a model of variability (the shuttle model). The empirically-based model was located broadly within a neuropsychological framework, and derived explanatory power from the tenets of brain reserve capacity (BRC) theory. It served to describe the bulge in interindividual variability due to aging (the shuttle bulge), and the shifting occurrence of the bulge in relation to the age axis due to cohort and task-related influences (the shuttle shift). A two phase research study was conducted in order to test hypotheses derived from the model. Phase 1 comprised between-groups analyses of normative data covering a broad range of neuropsychological tests in the domains of attention, memory, language, visual and hand motor skills, in order to examine the progression of variability effects across the adult age range. Phase 2 constituted between and within-groups analyses of normative data from a more limited number of neuropsychological tests. It included the examination of raw score distributions and the characteristics of outliers, and was undertaken to explore more closely the nature of the variability phenomena detected in the first phase of the analysis. Taken together, the results of both phases of the investigation revealed statistically significant variability effects in support of the shuttle model. There was a consistent pattern of increased variability in association with older age regardless of functional modality; frequently, in association with later old age, there was also a subsequent decrease in variability (the shuttle bulge). The age of onset of the initial increase in variability occurred earlier or later (the shuttle shift) as a function of four factors: education, gender, task challenge and age-sensitivity of task. The finding of an earlier onset of variability effects for low education, male gender, high task challenge and high age-sensitivity of task was interpreted in terms of BRC threshold theory. The clinical and social implications of the outcome were discussed with special emphasis on the need for a differential perspective on aging, as a complement to the prevailing normative tradition. It was concluded that the shuttle model has considerable heuristic value. It presents an integrative framework for understanding existing variability data and provides clear indications for future research.
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Inforzato, Diego José. "Estudo do comportamento dos aços ferramenta Thyrotherm 2999 EFS supra e H13 sob fadiga de baixo ciclo a altas temperaturas." Universidade de São Paulo, 2005. http://www.teses.usp.br/teses/disponiveis/88/88131/tde-04012011-141307/.
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Realizou-se neste trabalho uma investigação comparativa do comportamento dos aços ferramenta H13 e THYROTHERM 2999 EFS SUPRA, destinados à fabricação de matrizes para conformação a quente, quando submetidos à fadiga de baixo ciclo a altas temperaturas (FBCAT). A partir de suas curvas de revenimento, foram definidas três durezas de trabalho para cada material (durezas de 42, 52 e 58 HRC), correspondendo a três temperaturas de revenimento distintas e três condições de estudo, buscando-se a condição ótima apresentada por estes materiais para este tipo de aplicação, visando-se então analisar a influência da dureza inicial do material na vida do componente. Foi determinada também a temperatura de ensaio de fadiga isotérmica, em 400°C, correspondente à temperatura de utilização da matriz, ou seja, uma temperatura crítica típica que a matriz atinge durante a solicitação em trabalho. A seguir foram realizados para cada material os ensaios de tração a temperatura ambiente, e na seqüência, os ensaios de tração na temperatura de trabalho definida, que permitiram a determinação dos primeiros parâmetros monotônicos dos materiais, dentre eles uma previsão para os níveis de deformação a serem utilizados nos ensaios de fadiga (0.5,0.6,0.7,0.8,0.9,1.0 e 1.1%), e demais parâmetros como E, k, n, σe, σ’f, ε’f, b, c, que permitiram a elaboração de curvas ε−N, com um modelo estimativo já existente. Finalmente, foram então realizados os ensaios de fadiga isotérmica de baixo ciclo, à temperatura de 400°C, e os resultados foram utilizados para a elaboração das curvas ε−N, resultando então na proposta de um modelo de previsão de resistência à fadiga específico para os materiais pesquisados.It was made in this work an investigative comparison of the behavior of the tool steels H13 and THYROTHERM 2999 EFS SUPRA, designed for die steels for hot forming, when exposed to high temperature low cycle fatigue (HTLCF). From their tempering curves three material working hardness were defined for each material (hardness of 42, 52 and 58 HRC), corresponding to three different tempering temperatures, and so three study cases for each material, searching for the best condition for this kind of application, and to assess the influence of the initial hardness on the part material life. The isothermal low cycle fatigue test temperature was either defined at 400°C, corresponding to the used temperature at the die steel, i.e., a critical typical temperature that the forging dies reach on hot working. After that, tensile tests were performed for both materials, at room temperature, and at the working temperature formerly defined, and these tests allowed the definition of the first monotonic parameters for these materials, among them predictions for strain levels (0.5, 0.6, 0.7, 0.8, 0.9, 1.0 and 1.1%), to be used on fatigue tests, and further parameters like E, k, n, σe, σ’f, ε’f, b, c, that allowed the elaboration of ε−N curves, based on a still existing prediction model. Finally, isothermal low cycle fatigue tests were performed, at 400°C, and the results were used for ε−N curves elaboration, resulting on a prediction model of the fatigue strength specified for the assessed materials.
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Stewart, Calvin. "A Hybrid Constitutive Model For Creep, Fatigue, And Creep-Fatigue Damage." Doctoral diss., University of Central Florida, 2013. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/6023.
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In the combustion zone of industrial- and aero- gas turbines, thermomechanical fatigue (TMF) is the dominant damage mechanism. Thermomechanical fatigue is a coupling of independent creep, fatigue, and oxidation damage mechanisms that interact and accelerate microstructural degradation. A mixture of intergranular cracking due to creep, transgranular cracking due to fatigue, and surface embrittlement due to oxidation is often observed in gas turbine components removed from service. The current maintenance scheme for gas turbines is to remove components from service when any criteria (elongation, stress-rupture, crack length, etc.) exceed the designed maximum allowable. Experimental, theoretical, and numerical analyses are performed to determine the state of the component as it relates to each criterion (a time consuming process). While calculating these metrics individually has been successful in the past, a better approach would be to develop a unified mechanical modeling that incorporates the constitutive response, microstructural degradation, and rupture of the subject material via a damage variable used to predict the cumulative “damage state” within a component. This would allow for a priori predictions of microstructural degradation, crack propagation/arrest, and component-level lifing. In this study, a unified mechanical model for creep-fatigue (deformation, cracking, and rupture) is proposed. It is hypothesized that damage quantification techniques can be used to develop accurate creep, fatigue, and plastic/ductile cumulative- nonlinear- damage laws within the continuum damage mechanics principle. These damage laws when coupled with appropriate constitutive equations and a degrading stiffness tensor can be used to predict the mechanical state of a component. A series of monotonic, creep, fatigue, and tensile-hold creep-fatigue tests are obtained from literature for 304 stainless steel at 600°C (1112°F) in an air. Cumulative- nonlinear- creep, fatigue, and a coupled creep-fatigue damage laws are developed. The individual damage variables are incorporated as an internal state variable within a novel unified viscoplasticity constitutive model (zero yield surface) and degrading stiffness tensor. These equations are implemented as a custom material model within a custom FORTRAN one-dimensional finite element code. The radial return mapping technique is used with the updated stress vector solved by Newton-Raphson iteration. A consistent tangent stiffness matrix is derived based on the inelastic strain increment. All available experimental data is compared to finite element results to determine the ability of the unified mechanical model to predict deformation, damage evolution, crack growth, and rupture under a creep-fatigue environment.Ph.D.
Doctorate
Mechanical and Aerospace Engineering
Engineering and Computer Science
Mechanical Engineering
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Deshpande, Rutooj D. "UNDERSTANDING AND IMPROVING LITHIUM ION BATTERIES THROUGH MATHEMATICAL MODELING AND EXPERIMENTS." UKnowledge, 2011. http://uknowledge.uky.edu/cme_etds/4.
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There is an intense, worldwide effort to develop durable lithium ion batteries with high energy and power densities for a wide range of applications, including electric and hybrid electric vehicles. For improvement of battery technology understanding the capacity fading mechanism in batteries is of utmost importance. Novel electrode material and improved electrode designs are needed for high energy- high power batteries with less capacity fading. Furthermore, for applications such as automotive applications, precise cycle-life prediction of batteries is necessary.
One of the critical challenges in advancing lithium ion battery technologies is fracture and decrepitation of the electrodes as a result of lithium diffusion during charging and discharging operations. When lithium is inserted in either the positive or negative electrode, there is a volume change associated with insertion or de-insertion. Diffusion-induced stresses (DISs) can therefore cause the nucleation and growth of cracks, leading to mechanical degradation of the batteries. With different mathematical models we studied the behavior of diffusion induces stresses and effects of electrode shape, size, concentration dependent material properties, pre-existing cracks, phase transformations, operating conditions etc. on the diffusion induced stresses. Thus we develop tools to guide the design of the electrode material with better mechanical stability for durable batteries.
Along with mechanical degradation, chemical degradation of batteries also plays an important role in deciding battery cycle life. The instability of commonly employed electrolytes results in solid electrolyte interphase (SEI) formation. Although SEI formation contributes to irreversible capacity loss, the SEI layer is necessary, as it passivates the electrode-electrolyte interface from further solvent decomposition. SEI layer and diffusion induced stresses are inter-dependent and affect each-other. We study coupled chemical-mechanical degradation of electrode materials to understand the capacity fading of the battery with cycling. With the understanding of chemical and mechanical degradation, we develop a simple phenomenological model to predict battery life.
On the experimental part we come up with a novel concept of using liquid metal alloy as a self-healing battery electrode. We develop a method to prepare thin film liquid gallium electrode on a conductive substrate. This enabled us to perform a series of electrochemical and characterization experiments which certify that liquid electrode undergo liquid-solid-liquid transition and thus self-heals the cracks formed during de-insertion. Thus the mechanical degradation can be avoided. We also perform ab-initio calculations to understand the equilibrium potential of various lithium-gallium phases.
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Ernault, Estève. "Thermo-oxydation de résines époxy/amine." Thesis, Paris, ENSAM, 2016. http://www.theses.fr/2016ENAM0060/document.
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Les résines époxy/amine obtenues grâce au mélange d’un prépolymère époxy et d’un durcisseur amine, sont utilisées dans divers domaines d’applications : peinture, potting de composés électroniques... L’objectif de cette thèse est la prédiction de la durée de vie de trois résines : DGEBA ou DGEBU/cycloalipahtique diamine, DGEBA/aliphatique diamine, soumises à un vieillissement thermo-oxydant. Pour cela, une étude multi échelle de l’oxydation est réalisée à différentes conditions de température (de 110°C à 200°C) et de pression d’oxygène (0,2 bars et 50 bars). A l’échelle moléculaire, la spectroscopie IRTF a montré la formation d’amides et de carbonyles. A l’échelle macromoléculaire, les coupures de chaînes semblent prédominantes lorsque le durcisseur est une diamine cycloaliphatique. En revanche, lorsque le système contient des séquences méthylènes portées par des segments flexibles, elles peuvent induire un mécanisme de réticulation qui peut prédominer. Ces résultats gouvernent l’évolution des propriétés fonctionnelles : la fragilisation mécanique et la dégradation des propriétés diélectriques de DGEBA/cycloaliphatique diamine se produit pour des temps d’exposition inférieurs à ceux observés pour DGEBA/aliphatique diamine. L’extrapolation des durées de vie est réalisée grâce à une modélisation cinétique basée sur un schéma mécanistique de l’oxydation des trois résines. La résolution de ce schéma cinétique permet la modélisation de l’ensemble des résultats expérimentaux (concentration en produits d’oxydation, coupures de chaînes et réticulation) pour une oxydation homogène ou bien sur des échantillons épais présentant un gradient d’oxydation. Les contraintes mécaniques engendrées lors de l’oxydation d’un échantillon épais (3 mm) de DGEBA/cycloaliphatique diamine ont été simulées afin de prédire la fissuration spontanéeEpoxy/amine resins are thermoset materials made of epoxy prepolymer and amine hardener. Those materials are used in several industrial applications, such as paint or to encapsulate electronics. The main goal of this work is to predict lifetime of three resins: DGEBA or DGEBU/cycloaliphatic diamine, DGEBA/aliphatic diamine, in thermo-oxidative environment. In order to achieve this, a multi scale study of the oxidation is done, at several temperatures (from 110°C to 200°C) and oxygen partial pressures (0,2 bars et 50 bars). At molecular scale, the formation of amides and carbonyls has been noticed. At macromolecular scale, chain scission has been observed in epoxy/cycloaliphatic diamine but in DGEBA/aliphatic diamine cross linking seems to be predominant. Those properties are directly related to functional properties: mechanical and dielectric break down appear later in DGEBA/aliphatic diamine than in epoxy/cycloaliphatic diamine. The extrapolation of life is possible thank to kinetic modelling, based on chemical mechanistic scheme. The resolution of this kinetic scheme allowed us to model all experimental data (concentration of oxidation products, chain scission and cross linking), either in homogenous oxidation and in thick samples (3 mm). Stresses induced by oxidation in a thick sample of DGEBA/cycloaliphatic diamine have been simulated thanks to Matlab ® and finite elements by Abaqus ®
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Cross, Richard J. (Richard John). "Inference and Updating of Probabilistic Structural Life Prediction Models." Diss., Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/19828.
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Aerospace design requirements mandate acceptable levels of structural failure risk. Probabilistic fatigue models enable estimation of the likelihood of fatigue failure. A key step in the development of these models is the accurate inference of the probability distributions for dominant parameters. Since data sets for these inferences are of limited size, the fatigue model parameter distributions are themselves uncertain.
A hierarchical Bayesian approach is adopted to account for the uncertainties in both the parameters and their distribution. Variables specifying the distribution of the fatigue model parameters are cast as hyperparameters whose uncertainty is modeled with a hyperprior distribution. Bayes' rule is used to determine the posterior hyperparameter distribution, given available data, thus specifying the probabilistic model. The Bayesian formulation provides an additional advantage by allowing the posterior distribution to be updated as new data becomes available through inspections. By updating the probabilistic model, uncertainty in the hyperparameters can be reduced, and the appropriate level of conservatism can be achieved.
In this work, techniques for Bayesian inference and updating of probabilistic fatigue models for metallic components are developed. Both safe-life and damage-tolerant methods are considered. Uncertainty in damage rates, crack growth behavior, damage, and initial flaws are quantified. Efficient computational techniques are developed to perform the inference and updating analyses. The developed capabilities are demonstrated through a series of case studies.
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Barnholdt, Jacob, and Josefin Grafford. "Predicting Large Claims within Non-Life Insurance." Thesis, KTH, Matematisk statistik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-228983.
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This bachelor thesis within the field of mathematical statistics aims to study the possibility of predicting specifically large claims from non-life insurance policies with commercial policyholders. This is done through regression analysis, where we seek to develop and evaluate a generalized linear model, GLM. The project is carried out in collaboration with the insurance company If P&C Insurance and most of the research is conducted at their headquarters in Stockholm. The explanatory variables of interest are characteristics associated with the policyholders. Due to the scarcity of large claims in the data set, the prediction is done in two steps. Firstly, logistic regression is used to model the probability of a large claim occurring. Secondly, the magnitude of the large claims is modelled using a generalized linear model with a gamma distribution. Two full models with all characteristics included are constructed and then reduced with computer intensive algorithms. This results in two reduced models, one with two characteristics excluded and one with one characteristic excluded.Det här kandidatexamensarbetet inom matematisk statistik avser att studera möjligheten att predicera särskilt stora skador från sakförsäkringspolicys med företag som försäkringstagare. Detta görs med regressionsanalys, där vi ämnar att utveckla och bedöma en generaliserad linjär modell, GLM. Projektet utförs i samarbete med försäkringsbolaget If Skadeförsäkring och merparten av undersökningen sker på deras huvudkontor i Stockholm. Förklaringsvariablerna som är av intresse att undersöka är egenskaper associerade med försäkringstagarna. På grund av sällsynthet av storskador i datamängden görs prediktionen i två steg. Först används logistisk regression för att modellera sannolikheten för en storskada att inträffa. Sedan modelleras storskadornas omfattning genom en generaliserad linjär modell med en gammafördelning. Två grundmodeller med alla förklaringsvariabler konstrueras för att sedan reduceras med datorintensiva algoritmer. Det resulterar i två reducerade modeller, med två respektive en kundegenskap utesluten.
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Košťál, Josef. "Posouzení tepelně-mechanické únavy výfukového potrubí." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2020. http://www.nusl.cz/ntk/nusl-418196.
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Tato diplomová práce se zabývá posouzením tepelně-mechanické únavy výfukového potrubí. Nejprve byla provedena rešeršní studie, ve které je rozebrán fenomén tepelně-mechanické únavy. Byly prezentovány hlavní mechanismy poškození a přístupy k jejich modelování. Diskutována byla i specifická chování materiálu vystavenému tepelně-mechanickému zatěžování. Byl vypracován přehled vhodných modelů materiálu a modelů únavové životnosti společně s algoritmem predikce tepelně-mechanické únavy komponenty. Poté byl tento teoretický základ aplikován na praktický případ výfukového potrubí podléhajícího tepelně-mechanickému zatěžování. Dva tepelně závislé elasto-plastické modely materiálu byly nakalibrovány a validovány na základě experimentálních dat. Byl vytvořen diskretizovaný konečnoprvkový model sestavy výfukového potrubí. Model tepelných okrajových podmínek byl předepsán na základě výpočtů ustáleného sdruženého přestupu tepla. Slabě sdružená tepelně-deformační úloha byla vyřešena metodou konečných prvků pro oba modely materiálů. Bylo použito paradigma nesvázaného modelu únavy, které je vhodné pro nízkocyklovou únavu. Životnost byla tedy vyhodnocena jako součást post-procesoru. Použity byly dva modely únavové životnosti – energeticky založený model a deformačně založený model. Získané hodnoty životnosti byly porovnány vzhledem k použitým modelům materiálu a modelům únavové životnosti. Nakonec jsou diskutovány závěry této práce, oblasti dalšího výzkumu a navrženy možnosti na zlepšení použitých přístupů.
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Jones, Julie Elizabeth. "A series of mathematical models of the life-cycle of the nematode Ostertagia ostertagia." Thesis, University of Exeter, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.328834.
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Miller, Matthew P. "Life prediction models for high temperature fatigue based on microcrack propagation." Thesis, Georgia Institute of Technology, 1990. http://hdl.handle.net/1853/16059.
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Gebremariam, Merhawi Tewolde. "Predicting the life cycle of technologies from patent data." Thesis, Linköpings universitet, Statistik och maskininlärning, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-154866.
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Analysis of patent documents is one way to learn about trends in the evolutionof technologies. In this thesis, we propose a mixture of life cycle Poisson modelfor predicting the life cycle of technologies from patent count data. The aim is topredict the life cycle of technologies and determine the stage of the technology inthe development S-curve. The model is constructed from historical data on patentpublications of technologies and also from experts’ belief of life cycle of technologies. The methods used to estimate the model are based on Bayesian methods, inparticular we use a combination of Gibbs sampling and slice sampling to simulatefrom the posterior distribution of the model parameters. We apply the model on adataset of 123 technologies from the electricity sector. As a preliminary exploratorystep clustering analysis is also applied on the dataset. Finally we evaluate the modelhow it performs to predict the trend of life cycle of technologies based on differentbase years. Results reveal that the model is capable of predicting the life cycleof technologies based on its different stages. However, the predictions of expectedbehavior become more accurate when more data is used to construct the prediction.
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Majumdar, Prasun Kanti. "Strength and Life Prediction of FRP Composite Bridge Deck." Diss., Virginia Tech, 2008. http://hdl.handle.net/10919/27285.
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Fiber reinforced polymer (FRP) composites are considered very promising for infrastructure applications such as repair, rehabilitation and replacement of deteriorated bridge decks. However, there is lack of proper understanding of the structural behavior of FRP decks. For example, due to the localization of load under a truck tire, the conventionally used uniform patch loading is not suitable for performance evaluation of FRP composite deck systems with cellular geometry and relatively low modulus (compared to concrete decks). In this current study, a simulated tire patch loading profile has been proposed for testing and analysis of FRP deck. The tire patch produced significantly different failure mode (local transverse failure under the tire patch) compared to the punching-shear mode obtained using the conventional rectangular steel plate. The local response of a cellular FRP composite deck has been analyzed using finite element simulation and results are compared with full scale laboratory experiment of bridge deck and structure. Parametric studies show that design criteria based on global deck displacement is inadequate for cellular FRP deck and local deformation behavior must be considered.
The adhesive bonding method is implemented for joining of bridge deck panels and response of structural joint analyzed experimentally. Strength, failure mode and fatigue life prediction methodologies for a cellular FRP bridge deck are presented in this dissertation.Ph. D.
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Tillman, Måns. "On-Line Market Microstructure Prediction Using Hidden Markov Models." Thesis, KTH, Matematisk statistik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-208312.
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Over the last decades, financial markets have undergone dramatic changes. With the advent of the arbitrage pricing theory, along with new technology, markets have become more efficient. In particular, the new high-frequency markets, with algorithmic trading operating on micro-second level, make it possible to translate ”information” into price almost instantaneously. Such phenomena are studied in the field of market microstructure theory, which aims to explain and predict them. In this thesis, we model the dynamics of high frequency markets using non-linear hidden Markov models (HMMs). Such models feature an intuitive separation between observations and dynamics, and are therefore highly convenient tools in financial settings, where they allow a precise application of domain knowledge. HMMs can be formulated based on only a few parameters, yet their inherently dynamic nature can be used to capture well-known intra-day seasonality effects that many other models fail to explain. Due to recent breakthroughs in Monte Carlo methods, HMMs can now be efficiently estimated in real-time. In this thesis, we develop a holistic framework for performing both real-time inference and learning of HMMs, by combining several particle-based methods. Within this framework, we also provide methods for making accurate predictions from the model, as well as methods for assessing the model itself. In this framework, a sequential Monte Carlo bootstrap filter is adopted to make on-line inference and predictions. Coupled with a backward smoothing filter, this provides a forward filtering/backward smoothing scheme. This is then used in the sequential Monte Carlo expectation-maximization algorithm for finding the optimal hyper-parameters for the model. To design an HMM specifically for capturing information translation, we adopt the observable volume imbalance into a dynamic setting. Volume imbalance has previously been used in market microstructure theory to study, for example, price impact. Through careful selection of key model assumptions, we define a slightly modified observable as a process that we call scaled volume imbalance. The outcomes of this process retain the key features of volume imbalance (that is, its relationship to price impact and information), and allows an efficient evaluation of the framework, while providing a promising platform for future studies. This is demonstrated through a test on actual financial trading data, where we obtain high-performance predictions. Our results demonstrate that the proposed framework can successfully be applied to the field of market microstructure.Under de senaste decennierna har det gjorts stora framsteg inom finansiell teori för kapitalmarknader. Formuleringen av arbitrageteori medförde möjligheten att konsekvent kunna prissätta finansiella instrument. Men i en tid då högfrekvenshandel numera är standard, har omsättningen av information i pris börjat ske i allt snabbare takt. För att studera dessa fenomen; prispåverkan och informationsomsättning, har mikrostrukturteorin vuxit fram. I den här uppsatsen studerar vi mikrostruktur med hjälp av en dynamisk modell. Historiskt sett har mikrostrukturteorin fokuserat på statiska modeller men med hjälp av icke-linjära dolda Markovmodeller (HMM:er) utökar vi detta till den dynamiska domänen. HMM:er kommer med en naturlig uppdelning mellan observation och dynamik, och är utformade på ett sådant sätt att vi kan dra nytta av domänspecifik kunskap. Genom att formulera lämpliga nyckelantaganden baserade på traditionell mikrostrukturteori specificerar vi en modell—med endast ett fåtal parametrar—som klarar av att beskriva de välkända säsongsbeteenden som statiska modeller inte klarar av. Tack vare nya genombrott inom Monte Carlo-metoder finns det nu kraftfulla verktyg att tillgå för att utföra optimal filtrering med HMM:er i realtid. Vi applicerar ett så kallat bootstrap filter för att sekventiellt filtrera fram tillståndet för modellen och prediktera framtida tillstånd. Tillsammans med tekniken backward smoothing estimerar vi den posteriora simultana fördelningen för varje handelsdag. Denna används sedan för statistisk inlärning av våra hyperparametrar via en sekventiell Monte Carlo Expectation Maximization-algoritm. För att formulera en modell som beskriver omsättningen av information, väljer vi att utgå ifrån volume imbalance, som ofta används för att studera prispåverkan. Vi definierar den relaterade observerbara storheten scaled volume imbalance som syftar till att bibehålla kopplingen till prispåverkan men även går att modellera med en dynamisk process som passar in i ramverket för HMM:er. Vi visar även hur man inom detta ramverk kan utvärdera HMM:er i allmänhet, samt genomför denna analys för vår modell i synnerhet. Modellen testas mot finansiell handelsdata för både terminskontrakt och aktier och visar i bägge fall god predikteringsförmåga.
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Villaume, Erik. "Predicting customer level risk patterns in non-life insurance." Thesis, KTH, Matematisk statistik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-103590.
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Several models for predicting future customer profitability early into customer life-cycles in the property and casualty business are constructed and studied. The objective is to model risk at a customer level with input data available early into a private consumer’s lifespan. Two retained models, one using Generalized Linear Model another using a multilayer perceptron, a special form of Artificial Neural Network are evaluated using actual data. Numerical results show that differentiation on estimated future risk is most effective for customers with highest claim frequencies.
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Promchote, Parichart. "Linkage of Climate Diagnostics in Predictions for Crop Production: Cold Impacts in Taiwan and Thailand." DigitalCommons@USU, 2019. https://digitalcommons.usu.edu/etd/7512.
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This research presents three case studies of low temperature anomalies that occurred during the winter–spring seasons and their influence on extreme events and crop production. We investigate causes and effects of each climate event and developed prediction methods for crops based on the climate diagnostic information. The first study diagnosed the driven environmental-factors, including climate pattern, climate change, soils moisture, and sea level height, associated with the 2011 great flood in Thailand and resulting total crop loss. The second study investigated climate circulation and indices that contributed to wet-and-cold (WC) events leading to significant crop damage in Taiwan. We developed empirical–dynamical models based on prominent climate indices to confidently predict WC events as much as 6 months before they occur. The final study extends from the second study and predict chronic damage to rice crops from climate change by using a crop simulation model. The long-term prediction of rice growth and yield effectively illustrated both decreases and increases in yield depending on climate scenarios. The three studies are different in location and circumstances but the methodologies can be applied across Thailand, Taiwan, and other areas with similar agroclimatology.
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Thor, Nandan G. "Using Computer Vision to Build a Predictive Model of Fruit Shelf-life." DigitalCommons@CalPoly, 2017. https://digitalcommons.calpoly.edu/theses/1721.
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Computer vision is becoming a ubiquitous technology in many industries on account of its speed, accuracy, and long-term cost efficacy. The ability of a computer vision system to quickly and efficiently make quality decisions has made computer vision a popular technology on inspection lines. However, few companies in the agriculture industry use computer vision because of the non-uniformity of sellable produce. The small number of agriculture companies that do utilize computer vision use it to extract features for size sorting or for a binary grading system: if the piece of fruit has a certain color, certain shape, and certain size, then it passes and is sold. If any of the above criteria are not met, then the fruit is discarded. This is a highly wasteful and relatively subjective process.
This thesis proposes a process to undergo to use computer vision techniques to extract features of fruit and build a model to predict shelf-life based on the extracted features. Fundamentally, the existing agricultural processes that do use computer vision base their distribution decisions on current produce characteristics. The process proposed in this thesis uses current characteristics to predict future characteristics, which leads to more informed distribution decisions. By modeling future characteristics, the process proposed will allow fruit characterized as “unfit to sell” by existing standards to still be utilized (i.e. if the fruit is too ripe to ship across the country, it can still be sold locally) which decreases food waste and increases profit. The process described also removes the subjectivity present in current fruit grading systems. Further, better informed distribution decisions will save money in storage costs and excess inventory.
The proposed process consists of discrete steps to follow. The first step is to choose a fruit of interest to model. Then, the first of two experiments is performed. Sugar content of a large sample of fruit are destructively measured (using a refractometer) to correlate sugar content to a color range. This step is necessary to determine the end-point of data collection because stages of ripeness are fundamentally subjective. The literature is consulted to determine “ripe” sugar content of the fruit and the first experiment is undertaken to correlate a color range that corresponds to the “ripe” sugar content. This feature range serves as the end-point of the second experiment. The second experiment is large-scale data collection of the fruit of interest, with features being recorded every day, until the fruit reaches end-of-life as determined by the first experiment. Then, computer vision is used to perform feature extraction and features are recorded over each sample fruit’s lifetime. The recorded data is then analyzed with regression and other techniques to build a model of the fruit’s shelf-life. The model is finally validated. This thesis uses bananas as a proof of concept of the proposed process.
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Farreras, Alcover Isaac. "Data-based models for assessment and life prediction of monitored civil infrastructure assets." Thesis, University of Surrey, 2014. http://epubs.surrey.ac.uk/807811/.
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In a context of deteriorating civil infrastructure and limited funds available to ensure their functionality and safety, there is a need for accurate assessment methods leading to a better allocation of the available resources and a timely detection of abnormal behaviours. Nowadays, technological advances have enabled the acquisition of reliable monitoring data concerning environmental conditions, loadings and structural responses from civil infrastructure assets. With massive amounts of data generated by monitoring systems, the challenge lies on how to extract relevant information that can be used for an enhanced management of civil infrastructure. Motivated by this, the research presented herein is devoted to the development of data-based models and associated methodologies for monitoring data interpretation, assessment and probabilistic life prediction in the specific area of fatigue reliability of welded joints in orthotropic steel decks. Moreover, it contributes to the definition of temporal and spatial requirements for monitoring campaigns and to the assessment of their cost-effectiveness within the present work's application framework. The proposed data-based models, associated methodologies and analysis are illustrated using the monitoring data from the Great Belt Bridge (Denmark). Polynomial regression models are firstly developed to characterize the correlation patterns between environmental conditions (pavement temperatures), operational loads (heavy traffic counts) and a strain-based performance indicator proportional to S-N fatigue damage at monitored welded joints. Monitoring outcomes are also used to develop time series models for simulating the main actions contributing to the fatigue process under consideration, namely pavement temperatures and heavy traffic counts. A methodology for probabilistic fatigue life prediction is then developed by integrating the different data-based models within an S-N fatigue reliability framework. It is based on Monte Carlo Simulation to account for the uncertainty in random variables (e.g. material properties, fatigue model) and random processes (e.g. traffic, temperature) and estimate the remaining fatigue life of selected welded details. The developed method enables to quantify the effect of different scenarios in terms of changes in pavement temperatures and heavy traffic counts. Moreover, an algorithm based on statistical control charts defined by the prediction bands of the regression models is proposed for the interpretation of new monitoring data and the identification of abnormal behaviours, as part of an envisaged "real-time" assessment. Temporal and spatial requirements for monitoring campaigns are determined on the basis of the quantification of the epistemic uncertainty reduction provided by increasing monitoring datasets within the context given by the developed methodology for probabilistic life prediction. Finally, the benefit of monitoring techniques is assessed at different points in time through a posterior decision analysis. The work presented in this thesis provides a theoretical framework that could be adopted in assessing other structural components under different deterioration mechanisms, hence contributing to a wider and more effective use of monitoring-based techniques for enhanced infrastructure asset management.
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Sahlin, Jakob. "Line Loss Prediction Model Design at Svenska kraftnät : Line Loss Prediction Based on Regression Analysis on Line Loss Rates and Optimisation Modelling on Nordic Exchange Flows." Thesis, KTH, Skolan för elektro- och systemteknik (EES), 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-193675.
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Forecast and estimation on transmission line losses is a vital task in the daily operation and planning of the Swedish power system. The aim with this thesis is to design a new line loss prediction model at Svenska kraftnät (Svk), which provides a hourly forecast of the transmission line losses the next day for the Swedish bidding areas (SE1-SE4). The final goal is to reduce the additional cost related to inaccurate predictions. The developed model is based on regression analysis on historical line losses and estimated exchange flows between the adjacent bidding areas computed by linear programming. Simulation results for 2015 show that it is, with rather simple estimates and assumptions, possible to increase the prediction accuracy with up to 27% compared with the existing method and to reduce the related costs in a similar way. The study also shows that future modelling has potential to increase the precision even further and recommends a Neural Network approach as the next step.Prognoser och estimering av stamnätsförluster är en central del i den dagliga driften av det svenska kraftsystemet. Den här uppsatsen har därför syftat till att utveckla en simuleringsmodell som ger en timvisprognos över morgondagens förluster i varje elområde (SE1-SE4). Detta verktyg är senare tänkt att precisera den dagliga upphandlingen av förluster och därmed minska kostnaden kopplad till osäkra prognoser. Den utvecklade modellen bygger på en regressionsanalys av tidigare uppmätta förluster och uppskattade transmissionsflöden mellan de närliggande elområdena beräknad med linjär programmering. Simulerignar för 2015 visar att, det med föhrhållandesvis enkla antaganden och uppskattningar av indata, går att precisera förlusterna med uppemot 27% jämfört med dagens prognos och därmed minska kostnaderna i liknande omfattning. Studien visar också att förbättringspotentialen är stor och rekommende-rar fortsatta studier utifrån en Neurala Nätverk modell.
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Case, Scott Wayne. "Mechanics of Fiber-Controlled Behavior in Polymeric Composite Materials." Diss., Virginia Tech, 1996. http://hdl.handle.net/10919/30568.
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Modern durability and damage tolerance predictions for composite material systems rely on accurate estimates of the local stress and material states for each of the constituents, as well as the manner in which the constituents interact. In this work, an number of approaches to estimating the stress states and interactions are developed. First, an elasticity solution is presented for the problem of a penny-shaped crack in an N-phase composite material system opened by a prescribed normal pressure. The stress state around such a crack is then used to estimate the stress concentrations due to adjacent fiber fractures in a composite materials. The resulting stress concentrations are then used to estimate the tensile strength of the composite. The predicted results are compared with experimental values.
In addition, a cumulative damage model for fatigue is presented. Modifications to the model are made to include the effects of variable amplitude loading. These modifications are based upon the use of remaining strength as a damage metric and the definition of an equivalent generalized time. The model is initially validated using results from the literature. Also, experimental data from APC-2 laminates and IM7/K3B laminates are used in the model. The use of such data for notched laminates requires the use of an effective hole size, which is calculated based upon strain distribution measurements. Measured remaining strengths after fatigue loading are compared with the predicted values for specimens fatigued at room temperature and 350°F (177°C).Ph. D.
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Lamine, Slim 1965. "A predictive model of shelf life enhancement for meat packed under modified atmospheres." Thesis, The University of Arizona, 1991. http://hdl.handle.net/10150/277920.
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A dynamic model of fresh beef packaged under modified atmospheres has been developed. This model links the change in meat color with the permeation of gases (O₂, CO₂, N₂) through the packaging film. Its viability is demonstrated with experimental data using muscle semimembranosus with which it was shown that color change of the meat surface and the change of headspace gas concentration were well described by the model. Moreover, the model parameters were obtained independently of the model itself through the literature. A major result of the model showed that surface color is independent of oxygen concentration above 5%. Moreover, under aseptic conditions and ambient atmosphere concentrations, shelf-life of muscle semimembranosus was shown to be 11 days with this value possibly being a minimum.
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Singh, Naveen Chandra Lall Pradeep. "Thermo-mechanical reliability models for life prediction of area array electronics in extreme environments." Auburn, Ala., 2006. http://repo.lib.auburn.edu/2006%20Spring/master's/SINGH_NAVEEN_54.pdf.
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AZEVEDO, THAIS TUYANE DE. "MACHINE LEARNING METHODS APPLIED TO PREDICTIVE MODELS OF CHURN FOR LIFE INSURANCE." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2018. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=35235@1.
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O objetivo deste estudo foi explorar o problema de churn em seguros de vida, no sentido de prever se o cliente irá cancelar o produto nos próximos 6 meses. Atualmente, métodos de machine learning vêm se popularizando para este tipo de análise, tornando-se uma alternativa ao tradicional método de modelagem da probabilidade de cancelamento através da regressão logística. Em geral, um dos desafios encontrados neste tipo de modelagem é que a proporção de clientes que cancelam o serviço é relativamente pequena. Para isso, este estudo recorreu a técnicas de balanceamento para tratar a base naturalmente desbalanceada – técnicas de undersampling, oversampling e diferentes combinações destas duas foram utilizadas e comparadas entre si. As bases foram utilizadas para treinar modelos de Bagging, Random Forest e Boosting, e seus resultados foram comparados entre si e também aos resultados obtidos através do modelo de Regressão Logística. Observamos que a técnica SMOTE-modificado para balanceamento da base, aplicada ao modelo de Bagging, foi a combinação que apresentou melhores resultados dentre as combinações exploradas.The purpose of this study is to explore the churn problem in life insurance, in the sense of predicting if the client will cancel the product in the next 6 months. Currently, machine learning methods are becoming popular in this type of analysis, turning it into an alternative to the traditional method of modeling the probability of cancellation through logistics regression. In general, one of the challenges found in this type of modelling is that the proportion of clients who cancelled the service is relatively small. For this, the study resorted to balancing techniques to treat the naturally unbalanced base – under-sampling and over-sampling techniques and different combinations of these two were used and compared among each other. The bases were used to train models of Bagging, Random Forest and Boosting, and its results were compared among each other and to the results obtained through the Logistics Regression model. We observed that the modified SMOTE technique to balance the base, applied to the Bagging model, was the combination that presented the best results among the explored combinations.
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Kaewpradap, Ussama. "Validation of Top of the Line Corrosion Prediction Model Using Laboratory and Field Measurements." Ohio University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1353072616.
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Sánchez, Delgado Albert Miquel. "Electric-Device Characterization for Interference Prediction and Mitigation by an Optimal Filtering Design." Doctoral thesis, Universitat Ramon Llull, 2010. http://hdl.handle.net/10803/9144.
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Les interferències de mode comú i diferencial que es propaguen en un cable de la xarxa elèctrica monofàsica s'acostumen a suprimir utilitzant els filtres de xarxa. Aquesta classe de filtres estan formats per xocs de mode comú, condensadors X i condensadors Y per a mitigar tant el mode comú com el mode diferencial. Tot i això, les metodologies actuals de disseny de filtres de xarxa presenten alguns inconvenients: els filtres es dissenyen per treballar en un entorn ideal amb impedàncies de 50 Ω i les atenuacions del mode comú i del mode diferencial s'analitzen de manera independent, sense considerar la conversió modal que es produeixen en les asimetries presents a la xarxa elèctrica, al dispositiu elèctric o al mateix filtre de xarxa. Aquests fets impliquen que les prediccions del comportament del filtre siguin inexactes i, conseqüentment, el filtre més adequat en una situació particular s'acaba majoritàriament escollint mitjançant la prova i error en llargues i costoses sessions de mesura. Per tal de millorar aquesta situació, aquest treball presenta:- Nous sistemes de mesura i caracterització per modelar completament el comportament dels filtres de xarxa, xarxa elèctrica i dispositius elèctrics. Amb aquesta finalitat, s'introdueix una nova metodologia de caracterització: la caracterització modal, que confina el mode comú i el mode diferencial en ports diferents, proporcionant així informació sobre la propagació de la interferència modal. Aquesta informació pot ser d'utilitat a l'hora de seleccionar el filtre de xarxa adient.
- Una nova metodologia per a predir amb exactitud el nivell de les emissions conduïdes que un dispositiu elèctric introdueix a la xarxa elèctrica a través del filtre de xarxa. Aquesta metodologia està basada en les metodologies de caracterització presentades anteriorment. Caracteritzacions acurades permetran obtenir prediccions similars a les emissions conduïdes reals, evitant així llargues sessions de mesura.
- Noves metodologies de disseny de filtres de xarxa per aconseguir implementacions òptimes i de baix cost. En una primera proposta, els components dels filtres de xarxa (condensadors i xocs) es caracteritzen modalment per trobar la combinació que obté el filtratge desitjat amb el mínim nombre de components. Aquesta metodologia és millorada posteriorment utilitzant filtres de xarxa asimètrics, obtenint així un filtratge òptim del mode comú i del mode diferencial.
Tots els sistemes de mesura, així com les metodologies de caracterització, predicció i disseny, han estat provats amb èxit sobre equips reals.
Las interferencias de modo común y diferencial que se propagan en un cable de la red eléctrica monofásica se acostumbran a suprimir utilizando los filtros de red. Esta clase de filtros están formatos por choques de modo común, condensadores X y condensadores Y para mitigar tanto el modo común como el modo diferencial. Aún así, las metodologías actuales de diseño de filtros de red presentan algunos inconvenientes: los filtros se diseñan para trabajar en un entorno ideal con impedancias de 50 Ω y las atenuaciones del modo común y del modo diferencial se analizan de manera independiente, sin considerar la conversión modal que se producen en las asimetrías presentes en la red eléctrica, en el dispositivo eléctrico o en el mismo filtro de red. Estos hechos implican que las predicciones del comportamiento del filtro sean inexactas y, consecuentemente, el filtro más adecuado en una situación particular se acaba escogiendo mayoritariamente mediante la prueba y error en largas y costosas sesiones de medida. Para mejorar esta situación, este trabajo presenta:
- Nuevos sistemas de medida y caracterización para modelar completamente el comportamiento de los filtros de red, red eléctrica y dispositivos eléctricos. Con este objetivo, se introduce una nueva metodología de caracterización: la caracterización modal, que confina el modo común y el modo diferencial en puertos diferentes, proporcionando así información sobre la propagación de la interferencia modal. Esta información puede ser de utilidad a la hora de seleccionar el filtro de red adecuado.
- Una nueva metodología para predecir con exactitud el nivel de las emisiones conducidas que un dispositivo eléctrico introduce en la red eléctrica a través del filtro de red. Esta metodología está basada en las metodologías de caracterización presentadas anteriormente. Caracterizaciones precisas permitirán obtener predicciones similares a las emisiones conducidas reales, evitando así largas sesiones de medida.
- Nuevas metodologías de diseño de filtros de red para conseguir implementaciones óptimas y de bajo coste. En una primera propuesta, los componentes de los filtros de red (condensadores y choques) se caracterizan modalmente para encontrar la combinación que obtiene el filtraje deseado con el mínimo número de componentes. Esta metodología es mejorada posteriormente utilizando filtros de red asimétricos, obteniendo así un filtraje óptimo del modo común y del modo diferencial.
Todos los sistemas de medida, así como las metodologías de caracterización, predicción y diseño, han sido probados con éxito sobre equipos reales.
The common mode and differential mode interference propagated through the single-phase power-line cable is usually suppressed with power-line filters. This kind of filters is composed by common-mode chokes, X capacitors and Y capacitors to mitigate both the common mode and the differential mode. However, the present-day power-line filter design methodologies present some disadvantages: they are designed to be placed in an ideal 50-Ω system and the common mode and differential mode attenuations are analyzed independently, without considering the mode conversion that can be produced by asymmetries in the power-line filter, in the power-line network or in the electric device. These facts lead to inaccurate predictions of the power-line filter behavior and, consequently, the suitable filter is usually selected by trial and error in long and expensive measurement sessions. In order to improve this situation, this work presents:
- New measurement systems and characterization methodologies to completely model the behavior of power-line filters, power-line networks and electric devices. To this end, a new characterization methodology is presented: the modal characterization, which confines the common mode and the differential mode into a different port and provides the information about the propagation of the modal interference, information that can be useful to select the suitable filter for its mitigation.
- A new methodology to accurately predict the level of conducted emissions that an electric device supplies to the power-line network through its power-line filter, based on the measurement systems and characterization methodologies presented before. Accurate characterizations will allow predictions similar to the actual conducted emissions, avoiding long measurement sessions.
- New design methodologies of power-line filters to achieve optimal and low cost implementations. In a first proposal, the components of the power-line filters are modally characterized to find, by computation, the combination that gets the desired filtering response with the minimum number of components. This methodology is further improved by using asymmetric power-line filters, obtaining an optimal mitigation of the common and differential mode.
All measurement systems, as well as characterization, prediction and designing methodologies, have been successfully tested on actual devices.
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SOUTO, MAIOR Caio Bezerra. "Remainig useful life prediction via empirical mode decomposition, wavelets and support vector machine." Universidade Federal de Pernambuco, 2017. https://repositorio.ufpe.br/handle/123456789/24930.
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The useful life time of equipment is an important variable related to reliability and maintenance. The knowledge about the useful remaining life of operation system by means of a prognostic and health monitoring could lead to competitive advantage to the corporations. There are numbers of models trying to predict the reliability’s variable behavior, such as the remaining useful life, from different types of signal (e.g. vibration signal), however several could not be realistic due to the imposed simplifications. An alternative to those models are the learning methods, used when exist many observations about the variable. A well-known method is Support Vector Machine (SVM), with the advantage that is not necessary previous knowledge about neither the function’s behavior nor the relation between input and output. In order to achieve the best SVM’s parameters, a Particle Swarm Optimization (PSO) algorithm is coupled to enhance the solution. Empirical Mode Decomposition (EMD) and Wavelets rise as two preprocessing methods seeking to improve the input data analysis. In this paper, EMD and wavelets are used coupled with PSO+SVM to predict the rolling bearing Remaining Useful Life (RUL) from a vibration signal and compare with the prediction without any preprocessing technique. As conclusion, EMD models presented accurate predictions and outperformed the other models tested.
O tempo de vida útil de um equipamento é uma importante variável relacionada à confiabilidade e à manutenção, e o conhecimento sobre o tempo útil remanescente de um sistema em operação, por meio de um monitoramento do prognóstico de saúde, pode gerar vantagens competitivas para as corporações. Existem diversos modelos utilizados na tentativa de prever o comportamento de variáveis de confiabilidade, tal como a vida útil remanescente, a partir de diferentes tipos de sinais (e.g. sinal de vibração), porém alguns podem não ser realistas, devido às simplificações impostas. Uma alternativa a esses modelos são os métodos de aprendizado, utilizados quando se dispõe de diversas observações da variável. Um conhecido método de aprendizado supervisionado é o Support Vector Machine (SVM), que gera um mapeamento de funções de entrada-saída a partir de um conjunto de treinamento. Para encontrar os melhores parâmetros do SVM, o algoritmo de Particle Swarm Optimization (PSO) é acoplado para melhorar a solução. Empirical Mode Decomposition (EMD) e Wavelets são usados como métodos pré-processamento que buscam melhorar a qualidade dos dados de entrada para PSO+SVM. Neste trabalho, EMD e Wavelets foram usadas juntamente com PSO+SVM para estimar o tempo de vida útil remanescente de rolamentos a partir de sinais de vibração. Os resultados obtidos com e sem as técnicas de pré-processamento foram comparados. Ao final, é mostrado que modelos baseados em EMD apresentaram boa acurácia e superaram o desempenho dos outros modelos testados.
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Seifert, Thomas. "Computational methods for fatigue life prediction of high temperature components in combustion engines and exhaust systems /." Aachen : Shaker, 2008. http://d-nb.info/987900854/04.
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Fairbrother, Dana. "Differential prediction of life satisfaction in individualistic and collectivistic cultures towards integration of personality and cultural models /." Pullman, Wash. : Washington State University, 2010. http://www.dissertations.wsu.edu/Thesis/Spring2010/d_fairbrother_042210.pdf.
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Thesis (M.A. in counseling psychology)--Washington State University, May 2010.Title from PDF title page (viewed on July 29, 2010). "Department of Educational Leadership and Counseling Psychology." Includes bibliographical references (p. 40-45).
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Chang, Wei-Te. "The analysis of random effects regression model for predicting the shelf-life of gun propellant." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1995. http://handle.dtic.mil/100.2/ADA295246.
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Ma, Zepeng. "Fatigue models for life prediction of structures under multiaxial loading with variation in time and space." Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLX117/document.
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L'objet de ce travail est de proposer une approche multi-échelle de la fatigue fondée sur l'énergie, et susceptible d'estimer les durées de vie associées à des chargements multidimensionnels variables. Le fondement de la démarche consiste à supposer que l'énergie dissipée à petite échelle régit le comportement à la fatigue. À chaque point matériel, est associée une distribution stochastique de points faibles qui sont susceptibles de plastifier et de contribuer à la dissipation d'énergie sans affecter des contraintes macroscopiques globales. Ceci revient à adopter le paradigme de Dang Van en fatigue polycyclique. La structure est supposée élastique (ou adaptée) à l'échelle macroscopique. De plus, on adopte à l'échelle mésoscopique un comportement élastoplastique avec une dépendance de la fonction de charge plastique non seulement de la partie déviatorique des contraintes, mais aussi de la partie hydrostatique. On considère également un écrouissage cinématique linéaire sous l'hypothèse d'une plasticité associée. Au lieu d'utiliser le nombre de cycles comme variable incrémentale, le concept d'évolution temporelle du chargement est adopté pour un suivi précis de l'historique du chargement réel. L'effet de la contrainte moyenne est pris en compte dans la fonction de charge mésoscopique ; une loi de cumul non linéaire de dommage est également considérée dans le modèle. La durée de vie à la fatigue est ensuite déterminée à l'aide d'une loi de phénoménologique fondée sur la dissipation d'énergie mésoscopique issue du cycle d'accommodation plastique. La première partie du travail a porté sur une proposition d'un modèle de fatigie à gradient de mise en oeuvre plus simple que les précédents modèlesThe aim of this work is to propose a multi-scale approach to energy-based fatigue, which can estimate lifetimes associated with variable multidimensional loading. The foundation of the approach is to assume that the energy dissipated on a small scale governs the fatigue behavior. Each material point is associated to a stochastic distribution of weak points that are likely to plasticize and contribute to the dissipation of energy without affecting global macroscopic stresses. This amounts to adopting Dang Van's paradigm of high cycle fatigue. The structure is supposed to be elastic (or adapted) on a macroscopic scale. In addition, we adopt on the mesoscopic scale an elastoplastic behavior with a dependence of the plastic load function not only of the deviatoric part of the stresses, but also of the hydrostatic part. Linear kinematic hardening is also considered under the assumption of an associated plasticity. Instead of using the number of cycles as an incremental variable, the concept of temporal evolution of the load is adopted for a precise follow-up of the history of the actual loading. The effect of mean stress is taken into account in the mesoscopic yield function; a law of nonlinear accumulation of damage is also considered in the model. Fatigue life is then determined using a phenomenological law based on mesoscopic energy dissipation from the plastic accommodative cycle. The first part of the work focused on a proposal for a fatigue model with a simpler implementation gradient than the previous models
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Leelahavarong, Pattara. "Development of an alcohol intervention model for predicting healthcare costs, life years, quality-adjusted life years and using for economic evaluation." Thesis, University of Glasgow, 2018. http://theses.gla.ac.uk/30672/.
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Objectives To develop an alcohol intervention model that predicts life years (LYs), quality adjusted life years (QALYs), and healthcare costs classified by the Alcohol Use Disorder Identification Test (AUDIT) screening tool and other various risk factors related to alcohol consumption. Furthermore, the developed model was transferred to the Thai setting. Methods Eight Scottish Health Surveys from 1995-2012 were linked to Scottish morbidity records and death records for the period 1981 to the end of 2013. Parametric survival analysis was used to estimate the hazard risks of first alcohol-related and non-alcohol related hospitalisations and deaths. For men and women, multivariate data analyses were applied separately for each gender in modelling the utility score, risks of subsequent hospitalisation and annual healthcare costs within the follow-up period. Risk profiles were used for the covariates of the models as follows: age, socio-economic status, health condition, alcohol drinking (i.e. AUDIT and binge drinking), smoking, body mass index, and physical activity. According to the under-reporting bias of alcohol consumption among the survey population, this study adjusted the reported alcohol consumption using alcohol sales data. Multiple imputation approach was applied to deal with missing data. A health-state transition model with annual cycle length was developed to predict LYs, QALYs, lifetime costs, and cost-effectiveness. Probabilistic sensitivity analysis was also performed to deal with parameter uncertainty. Moreover, a methodological transferability protocol of the Thai study was detailed. Results The sample size of the cohort was 46,230. The developed model showed the association between drinking and alcohol-related and non-alcohol related hospitalisations and deaths which were calculated as LYs and QALYs. Other risk factors were also taken into account that would likely affect the outcomes of interest. The modelling showed that an increasing AUDIT score and the number of cigarettes per day were associated with an increased risk of first alcohol-attributable hospitalisation. Predicted outcomes for a male aged 30 year with high-risk drinking levels (AUDIT >7) were worse than males with low risk drinking (AUDIT ≤7), with approximately 5 LY gained and 7 QALY gained. The same results for females were obtained for high-risk drinking (AUDIT >4) compared to low-risk drinking (AUDIT ≤4), with approximately 10 LY gained and 12 QALY gained. Furthermore, an economic evaluation was performed to compare the no-intervention situation with a hypothetical health promotion intervention - which aimed to stop drinking (measured by the AUDIT) and smoking (measured by the number of cigarettes per day) behaviours. To compare the costs and benefits of the hypothetical intervention and no intervention over the lifetime period, a within-trial analysis combined with the developed model was able to capture both short- and longer-term consequences (i.e. LYs, QALYs, and healthcare costs) of the intervention. Finally, the model was able to compare cost-effectiveness ratio between risk behaviours without the new intervention and the modified risk behaviours when the new intervention is implemented. Conclusions The study highlights the potential and importance of developing health economic models utilising data from routine national health surveys linked to national hospitalisation and death records. The developed framework can be used for further economic evaluation of alcohol interventions and other health behaviour change interventions. The framework can further be transferred to other country settings.
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Meng-Heng, Lee, and 李孟航. "SAC305 Solder Ball Life Prediction Model." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/47aa5c.
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碩士中華大學
機械工程學系碩士在職專班
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The continuous development of IC has the electronic components thin, compact and versatile which makes our lives more convenient. As one of the most important components in the electronics, solder ball can not only enable telecommunications but also strengthen its mechanical structure, therefore, the reliability of solder ball becomes a discussion topic of the researchers. This paper mainly discusses SAC305 lead-free solder ball in the fatigue life prediction of WLCSP package, and uses existing experimental data and finite element simulation results to deduce the fatigue life prediction equation for SAC305 Anand mode in the destruction indicator of accumulated plastic work density. In order to meet the demand of researchers lack of the finite element model analysis techniques for structural analysis to complete the common WLCSP package with the solder ball distribution of peripheral array or global array, the program code of ANSYS finite element model was created. Users can enter the desired analyzed geometry, while material parameters and thermal cyclic loading with a set of user-defined values can be amended by the designer at discretion. Both WLCSP packages were Module A with the solder ball distribution of peripheral array and a chip length of 6mm as well as Module B with the solder ball distribution of global array and a chip length of 8mm, respectively, and successfully carry out validation of the program code of ANSYS finite element model. Existing experimental data include the four different chip package thicknesses (400, 550, 715, 815 m) of thermal shock Module A and the chip package thickness (400 m) of thermal recycling Module B. Based on limited data and known from Schubert's solder ball failure mode analysis, the accumulated creep strain energy density range (W) and the accumulated von Mises creep strain range () for thermal cycle and third cycle of thermal shock of both WLCSP packages are respectively linear by taking logarithm; W and for different loads are parallel, showing good correlation. But Schubert's fatigue life prediction equation has errors of a certain degree, resulting from the difference in SAC305 solder ball characteristics. In the thermal shock loads, the experiment life and analysis results are treated with the least square linear regression method to get two fatigue life prediction modes for two different fatigue failure indices having a difference between life expectancy and experimental error of 8% or less. Thus deduce the life prediction mode for two different fatigue failure indices for thermal cycle loading, which can be used to predict the simulation experiment life. Finally by use of the above-mentioned simulation experiment life and the actual experiment life, in the Anand mode, the accumulated creep strain energy density range (W) is obtained, and also, the least square linear regression method is used to get the solder ball life prediction equation for thermal cycle and thermal shock, showing that there is a small error with the life expectancy. The author applied the above-mentioned solder ball life prediction equation to another WLCSP which is divided into a conventional standard design and new Ankor type design. The large difference between them is whether the copper post of solder ball is contact with green paints. After two packages were treated with thermal shock and thermal cycle analysis, the author found that there is also a small error between the actual experiment fatigue life and the simulation experiment fatigue life.
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Hsieh, Wen-Chou, and 謝文洲. "Lifetime prediction model for supercapacitors using accelerated life testing." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/cdkz33.
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碩士國立清華大學
工業工程與工程管理學系碩士在職專班
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As the next generation of energy storage component, supercapacitors has the characteristic of high capacitance with quick charge/discharge under high current. Although major manufacturers around the globe claim supercapacitor can operate for 10 years, none of them has provided complete empirical data as hard supporting evidence. In order to build a suitable life prediction model for supercapacitor, this research uses two major factors from designing phase; rated load voltage and ambient temperature; as the condition of environmental stress plan to perform accelerated life test in hoping to get product deterioration and eventual failure in set time. 30% of capacitance decay is set as the basis of test termination. Activation energy Ea and coefficient m is then calculated and used to complete the construction of stress model. In the end, through failure analysis, we not only get to understand how voltage and temperature affects the life of supercapacitor, but also can estimate its average life expectancy under normal and specific condition.
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Zhang, Jianmin. "Development of LCF life prediction model for wrinkled steel pipes." Phd thesis, 2010. http://hdl.handle.net/10048/894.
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Thesis (Ph. D.)--University of Alberta, 2010.Title from pdf file main screen (viewed on June 11, 2010). A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Structural Engineering, Department of Civil & Environmental Engineering, University of Alberta. Includes bibliographical references.
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LEE, HSIANG-HAO, and 李祥豪. "Finite Element Model to Solder Ball Life Prediction of PBGA." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/mn6843.
Full textAbstract:
碩士中華大學
機械工程學系碩士在職專班
101
Abstract The trend of electronic products today is moving toward further miniaturization, high functionality and improved performance. To accomplish this, packaging needs to be able to integrate higher I/O counts, smaller pitches, and greater heat densities, while being pushed into smaller and smaller footprints. Solder joint reliability is of great concern to semiconductor and electronic product manufacturers. This study focuses on the finite element strategy to the reliability of PBGA in solder joint life prediction. Firstly, the general purpose ANSYS finite element code was created. This code was satisfied with full array PBGA package and the designer could simply modify the geometric dimension, loading condition and nonlinear solder joint behavior. Two types of model assumption were considered with (model A) and without (model B) copper pad on both sides of solder joint. There are two different finite element approaches in each model including 1/4 model A; 1/4 model A+submodel; 1/8 model B; 1/8 model B+submodel. Eutetic solder connections considering the hyperbolic sine creep model and thermal cycling test in ranging of -40 °C to 125 °C, are performed to demonstrate the overall results of this research. According to the simulation results, the predicted life of model B was converged in all four models. Model A did not provide a good life convergence due to the neglected copper pad. The predicted life of model A + submodel can modified the convergence but still 30 % higher than those of model B. It is believed that the global model should be covered the major component which represented the mechanical behavior of the package. As for the sobmodel combined with 1/4 model and 1/8 model, the cut boundary in the symmetric plane of 1/8 model has not to be imposed as traditional manner due to the solder joint presented in the symmetric plane. Instead of the cut boundary condition from the global analysis, the symmetric boundary applied to the submodel greatly enhances the predicted life. Other thermal-mechanical behaviors of package were analyzed, such as von Mises stress and von Mises plastic strain, and plastic work density. It is found that the maximum values occur in the farthest ball due to DNP effect. In addition, the time domain responses of various thermal mechanical behaviors provided a further understanding on the thermal-mechanical behavior of the packages. Keywords : Finite Element Method, Plastic Ball Grid Array, Solder Joint Fatigue Life, Global model, Submodel, Solder Joint Reliability