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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
421

Behaviour of axially restrained steel beams with web openings at elevated temperatures

Najafi, Mohsen January 2014 (has links)
Steel beams with web openings are frequently used in construction to achieve attractive, flexible and optimised design solutions. These beams are used to provide passages for building services, to reduce the overall construction height and to achieve long spans. However, the presence of the openings may lead to a substantial reduction in the load carrying capacity of the beam at both ambient and elevated temperatures and introduce additional failure modes including shear-moment interaction at the location of the openings causing the Vierendeel mechanism. Steel beams in practical construction are axially restrained and the presence of this axial restraint can drastically change the behaviour of the beams in comparison to those without axial restraint. One particular issue is premature buckling of the compressive tee-sections around the openings. The aim of this research is to investigate the effects of openings on axially restrained steel beams at elevated temperatures so as to develop an analytical method for design consideration. The analytical derivation will be based on the results of extensive numerical simulations. The research starts with the behaviour of steel beams with web openings under combined axial compression, bending moment and shear force at ambient temperature. The results show that buckling of the compressive tee-sections at the openings can reduce the plastic moment capacity of the openings; and an analytical method has been proposed to incorporate the influences of axial compression and tee-section buckling into the existing shear-moment design equations. The elevated temperature simulations show that axially restrained steel beams with web openings may enter catenary action at much lower temperatures than the commonly accepted critical failure temperatures calculated assuming no axial restraint and no tee-section buckling. Therefore, at the commonly accepted critical failure temperatures, many perforated steel beams exert tensile forces on the adjacent connections. It is important that the connections have the strength and deformation (rotation) capacity to enable catenary action to develop. The parametric study examines, in detail, how changing the different design parameters may affect the elevated temperature behaviour of perforated beams. The examined parameters including load ratio, level of axial restraint, cross-section temperature distribution profile, opening shape, opening size and opening position. Based on the results of the numerical parametric study, an analytical method has been derived to obtain the complete axial force-temperature relationship for axially restrained perforated steel beams. The key points of the analytical method include initial stiffness, point of initial failure under combined axial compression, bending moment and shear force, transition temperature at which the axial force on the beam changes from compression to tension and the magnitude of the tensile force resulting from the beams going into catenary action. Using the analytical method, it is possible to assess the maximum tensile force in the beam and the corresponding temperature so that the safety of the connections can be checked.
422

Contribución al estudio del comportamiento de pilares de hormigón armado reparados mediante morteros predosificados sometidos a comprensión centrada

Ortega Palanco, Ana Irene 15 April 2016 (has links)
[EN] The importance of the maintenance and rehabilitation of existing structures has grown significantly in recent years. This accompanied by a very important decrease in the investments in the new construction, again after a period of growth in the number of constructed buildings. These facts have motivated that, currently, there is a large park of buildings need to be repaired and strengthened. The columns are the elements which failure may cause a complete collapse of the structure. In the case of reinforced concrete columns, it is possible to intervene well by means of a strengthening or a repair, whose goal will be to increase or to maintain its resistance, respectively. In fact, the repair of damages of different scope and magnitude on the outside of a column by means of repair mortars is an operation very usual in rehabilitation works. There are even European standards that prescribe the characteristics of the mortars to be used. Despite this, there are no references to study the effectiveness of a repair in reinforced concrete columns, which gives rise to a large uncertainty in the level of security that is reached in the repaired element. This lack of experimental results, together with the importance of this type of the action is that has motivated this investigation, which has studied the effectiveness of repair, using pre-bagged concrete repair mortars, of columns subjected to axially loaded. It has been determined the influence of the different geometric, mechanical and construction variables that they affect to the repair in the compressive strength of the column repaired. In order to do so, an experimental study has been realized in laboratory, in which the three most frequent cases of repair have been tested: complete repair of 4 sides, complete repair of one side and patch repair, with the variables raised in this investigation, kind of mortar (Class R3 and R4) and use or not of bonding primer. The final aim of this investigation will be to determine the efficacy of the repair according to the conditions in which it has been realized and to obtain a series of basic rules of design and execution of the repair. The results are analyzed and compared with the columns pattern, undamaged section without repair. The results of the investigation carried out indicates that repairs carried out with mortar Class R3 presented excellent results, while mortar Class R4, for the tested columns, only restores partially load-carrying capacity. In the case of the repair to 4 sides, if used a mortar Class R4 the load-carrying capacity on the column repaired only reached 64% of the original. In the case of the repair to 4 sides with mortar Class R3, the use of bonding primer does not have significant influence on the recovery of the load-carrying capacity. Not this way if there uses a mortar Class R4, where the use of a bonding primer improves significantly the result. Patch repair restores practically the load-carrying capacity of the structural element for both mortars (R3 and R4). In this case the use of bonding primer only has significant influence in the repair using mortar Class R4, showing an improvement of 9% more than if bonding primer is not used. In the complete repair of one side whit mortar Class R3 restores 97% of the load-carrying capacity loss while with mortar Class R4 only reaches to 66%, and without influence of the use or not of bonding primer. These results highlight the importance of the choice of the system, method and materials of the repair. These must be compatible with the materials and the state of the original structure. / [ES] En los últimos años ha crecido de manera significativa la importancia del mantenimiento y rehabilitación de estructuras existentes. Esto viene acompañado de un descenso muy importante en las inversiones en la construcción de obra nueva, después de un periodo de crecimiento en el número de edificios construidos. Estos hechos han motivado que, actualmente, exista un gran parque de edificaciones con necesidad de ser reparado o reforzado. Dentro de un edificio, los pilares son los elementos cuyo fallo puede provocar un colapso completo de la estructura. En el caso de los pilares de hormigón armado, se puede intervenir bien mediante un refuerzo o una reparación, cuyo fin será incrementar o mantener su resistencia, respectivamente. De hecho, la reparación de daños de diverso alcance y magnitud en la parte externa de un pilar mediante morteros de reparación es una operación muy habitual en obras de rehabilitación. Incluso existen normas europeas que prescriben las características de los morteros a utilizar. Pese a ello, no se dispone de referencias que estudien la efectividad de una reparación en pilares de hormigón armado, lo que da lugar a una gran incertidumbre en el grado de seguridad que se alcanza en el elemento reparado. Esta falta de resultados experimentales, junto con la importancia de este tipo de actuaciones es la que ha motivado esta investigación, en la que se ha estudiado la efectividad de la reparación, mediante morteros predosificados, de pilares sometidos a compresión centrada. Se ha determinado la influencia de las distintas variables geométricas, mecánicas y constructivas que afectan a la reparación en la resistencia a compresión del pilar reparado. Para ello se ha realizado un estudio experimental en laboratorio, en el que se han ensayado los tres casos de reparación más frecuentes en la práctica: reparación integral a cuatro caras, reparación integral a una cara y reparación por parcheo, con las variables planteadas en esta investigación, clase de mortero (Clases R3 y R4) y utilización o no de puente de unión. El objetivo final de esta investigación será determinar la eficacia de la reparación en función de las condiciones en las que se ha realizado y obtener una serie de reglas básicas de diseño y ejecución para la reparación. Los resultados son analizados y comparados con los pilares patrón, sección intacta sin reparación. De los resultados de la investigación realizada se desprende que, las reparaciones realizadas con mortero Clase R3 presentan unos excelentes resultados, mientras que el mortero Clase R4, para los pilares ensayados, únicamente restituye de forma parcial la capacidad portante. Para el caso de la reparación a 4 caras, si se emplea un mortero Clase R4 la capacidad portante del pilar reparado tan sólo alcanza un 64% de la original. Para el caso de reparación de las 4 caras con mortero Clase R3, el empleo de un puente de unión no tiene una influencia significativa en la recuperación de la capacidad portante. No así si se emplea un mortero Clase R4, donde el empleo de un puente de unión mejora significativamente el resultado. La Reparación por Parcheo prácticamente restaura la capacidad portante del elemento estructural para ambos morteros (R3 y R4). En este caso la utilización del puente de unión solo tiene influencia significativa en la reparación mediante mortero Clase R4, presentando una mejoría de un 9% más que si no se utiliza el puente de unión. En la Reparación Integral a 1 Cara con mortero Clase R3 se restituye un 97% de la capacidad portante perdida mientras que con mortero Clase R4 tan solo se llega a un 66%, y sin influencia de la utilización o no del puente de unión. Estos resultados resaltan la importancia de la elección del sistema, método y materiales de la reparación. Estos deben ser compatibles con los materiales y el estado de la estructura original. / [CAT] En els últims anys ha crescut de manera significativa la importància del manteniment i rehabilitació d'estructures existents. Açò ve acompanyat d'un descens molt important en les inversions en la construcció d'obra nova, després d'un període de creixement en el nombre d'edificis construïts. Estos fets han motivat que, actualment, existisca un gran parc d'edificacions amb necessitat de ser reparat o reforçat. Dins d'un edifici, els pilars són els elements la fallada dels quals pot provocar un col·lapse complet de l'estructura. En el cas dels pilars de formigó armat, es pot intervindre bé per mitjà d'un reforç o una reparació, el fi de la qual serà incrementar o mantindre la seua resistència, respectivament. De fet, la reparació de danys de divers abast i magnitud en la part externa d'un pilar per mitjà de morters de reparació és una operació molt habitual en obres de rehabilitació. Inclús hi ha normes europees que prescriuen les característiques dels morters a utilitzar. A pesar d'això, no es disposa de referències que estudien l'efectivitat d'una reparació en pilars de formigó armat, la qual cosa dóna lloc a una gran incertesa en el grau de seguretat que s'aconseguix en l'element reparat. Esta falta de resultats experimentals, junt amb la importància d'este tipus d'actuacions és la que ha motivat aquesta investigació, en la que s'ha estudiat l'efectivitat de la reparació, per mitjà de morters predosificats, de pilars sotmesos a compressió centrada. S'ha determinat la influència de les distintes variables geomètriques, mecàniques i constructives que afecten la reparació en la resistència a compressió del pilar reparat. Per a això s'ha realitzat un estudi experimental en laboratori, en el que s'han assajat els tres casos de reparació més freqüents en la pràctica: reparació integral a quatre cares, reparació integral a una cara i reparació per parcheo, amb les variables plantejades en esta investigació, classe de morter (Classes R3 i R4) i utilització o no de pont d'unió. L'objectiu final d'esta investigació serà determinar l'eficàcia de la reparació en funció de les condicions en què s'ha realitzat i obtindre una sèrie de regles bàsiques de disseny i execució per a la reparació. Els resultats són analitzats i comparats amb els pilars patró, secció intacta sense reparació. Dels resultats de la investigació realitzada es desprén que, les reparacions realitzades amb morter Classe R3 presenten uns excel·lents resultats, mentres que el morter Classe R4, per als pilars assajats, únicament restituïx de forma parcial la capacitat portant. Per al cas de la reparació a 4 cares, si s'empra un morter Classe R4 la capacitat portant del pilar reparat tan sols aconseguix un 64% de l'original. Per al cas de reparació de les 4 cares amb morter Classe R3, l'ocupació d'un pont d'unió no té una influència significativa en la recuperació de la capacitat portant. No així si s'empra un morter Classe R4, on l'ocupació d'un pont d'unió millora significativament el resultat. La Reparació per Parcheo pràcticament restaura la capacitat portant de l'element estructural per a ambdós morters (R3 i R4). En este cas la utilització del pont d'unió només té influència significativa en la reparació per mitjà de morter Classe R4, presentant una millora d'un 9% més que si no s'utilitza el pont d'unió. En la Reparació Integral a 1 Cara amb morter Classe R3 es restituïx un 97% de la capacitat portant perduda mentres que amb morter Classe R4 tan sols s'arriba a un 66%, i sense influència de la utilització o no del pont d'unió. Estos resultats ressalten la importància de l'elecció del sistema, mètode i materials de la reparació. Aquestos han de ser compatibles amb els materials i l'estat de l'estructura original. / Ortega Palanco, AI. (2016). Contribución al estudio del comportamiento de pilares de hormigón armado reparados mediante morteros predosificados sometidos a comprensión centrada [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/62583 / TESIS
423

Den axiella ålderns innebörd : En studie av Karl Jaspers idé om människans kulturella ursprung och existentiella liv i moderniteten / The meaning of axial age : Thesis of Karl Jasper's idea on the cultural origins of man and the existential life in modernity

Astborg, Robert January 2020 (has links)
This thesis examines Karl Jaspers' theory of the origin of man in a historical period 2500 years ago.Jaspers believes that it was then that man's current mental and spiritual consciousness was formed and developed. Jaspers was convinced that man should use the abilities of his origin as a counterforce in the struggle in modern reality, a development which in many respects was based on myths, dogmas and irrationality, and which characterized man's living conditions. After suffering the trauma of World War II until 1945, Jaspers decided to identify the good qualities that he believed all people should have in common, thereby creating new existential conditions. Jaspers started from the archaic and classical times in history and then found a period where man had obviously been endowed with specific soul gifts and cognitive qualities. He called the period "the axial age" in the book published in 1949, Vom Ursprung und Ziel der Geschichte, which was then translated into English in 1953 with the title The Origin and Goal of History. The English edition is the primary source in this study. In his book, Jaspers uses a philosophical-historical perspective on the origins and events that he associates with human development during the axial age, in order to draw attention to the normative image we have of our selves and others as human beings in the world. Jaspers pedagogically describes the life man lives in modernity in the same way as when Plato explains the world of ideas. As it is demonstrated in the thesis, Jasper's idea is based on a speculative reflection on the origin and properties of man and regards it as a "tabula rasa" with new existential conditions intended for man in the modern world, facing a charge and a prelude to the future. Furthermore, the thesis explores comments on and critique of this theory expressed by other scholars.
424

BRAIN-INSPIRED MACHINE LEARNING CLASSIFICATION MODELS

Amerineni, Rajesh 01 May 2020 (has links)
This dissertation focuses on the development of three classes of brain-inspired machine learning classification models. The models attempt to emulate (a) multi-sensory integration, (b) context-integration, and (c) visual information processing in the brain.The multi-sensory integration models are aimed at enhancing object classification through the integration of semantically congruent unimodal stimuli. Two multimodal classification models are introduced: the feature integrating (FI) model and the decision integrating (DI) model. The FI model, inspired by multisensory integration in the subcortical superior colliculus, combines unimodal features which are subsequently classified by a multimodal classifier. The DI model, inspired by integration in primary cortical areas, classifies unimodal stimuli independently using unimodal classifiers and classifies the combined decisions using a multimodal classifier. The multimodal classifier models are be implemented using multilayer perceptrons and multivariate statistical classifiers. Experiments involving the classification of noisy and attenuated auditory and visual representations of ten digits are designed to demonstrate the properties of the multimodal classifiers and to compare the performances of multimodal and unimodal classifiers. The experimental results show that the multimodal classification systems exhibit an important aspect of the “inverse effectiveness principle” by yielding significantly higher classification accuracies when compared with those of the unimodal classifiers. Furthermore, the flexibility offered by the generalized models enables the simulations and evaluations of various combinations of multimodal stimuli and classifiers under varying uncertainty conditions. The context-integrating model emulates the brain’s ability to use contextual information to uniquely resolve the interpretation of ambiguous stimuli. A deep learning neural network classification model that emulates this ability by integrating weighted bidirectional context into the classification process is introduced. The model, referred to as the CINET, is implemented using a convolution neural network (CNN), which is shown to be ideal for combining target and context stimuli and for extracting coupled target-context features. The CINET parameters can be manipulated to simulate congruent and incongruent context environments and to manipulate target-context stimuli relationships. The formulation of the CINET is quite general; consequently, it is not restricted to stimuli in any particular sensory modality nor to the dimensionality of the stimuli. A broad range of experiments are designed to demonstrate the effectiveness of the CINET in resolving ambiguous visual stimuli and in improving the classification of non-ambiguous visual stimuli in various contextual environments. The fact that the performance improves through the inclusion of context can be exploited to design robust brain-inspired machine learning algorithms. It is interesting to note that the CINET is a classification model that is inspired by a combination of brain’s ability to integrate contextual information and the CNN, which is inspired by the hierarchical processing of visual information in the visual cortex. A convolution neural network (CNN) model, inspired by the hierarchical processing of visual information in the brain, is introduced to fuse information from an ensemble of multi-axial sensors in order to classify strikes such as boxing punches and taekwondo kicks in combat sports. Although CNNs are not an obvious choice for non-array data nor for signals with non-linear variations, it will be shown that CNN models can effectively classify multi-axial multi-sensor signals. Experiments involving the classification of three-axis accelerometer and three-axes gyroscope signals measuring boxing punches and taekwondo kicks showed that the performance of the fusion classifiers were significantly superior to the uni-axial classifiers. Interestingly, the classification accuracies of the CNN fusion classifiers were significantly higher than those of the DTW fusion classifiers. Through training with representative signals and the local feature extraction property, the CNNs tend to be invariant to the latency shifts and non-linear variations. Moreover, by increasing the number of network layers and the training set, the CNN classifiers offer the potential for even better performance as well as the ability to handle a larger number of classes. Finally, due to the generalized formulations, the classifier models can be easily adapted to classify multi-dimensional signals of multiple sensors in various other applications.
425

A Comparison of Crushing Parameters of Graphite Composite Thin-Walled Cylinders Cured in Low and High Pressures

Matson, Trenton John 01 September 2019 (has links)
Out-of-Autoclave (OoA) processes for manufacturing aerospace-grade parts needs to be better understood to further the development and success of industries that are manufacturing reusable launch vehicles, military and commercial aircraft, and spacecraft. Overcoming the performance limitations associated with OoA, also known as low-pressure prepreg curing, methods (void count, energy absorption, etc.) will help decrease the costs associated with aerospace composite manufacturing and the negative environmental effects correlated with high-pressure composite curing methods. Experimental, theoretical, and numerical approaches are used to explore both low and high-pressure curing cycles and how the two different processes affect final cured parts. Quasi-static uniaxial compression tests on 33mm diameter tubular specimens concluded that the high-pressure curing methods (up to 90 psi) increased the likelihood of a final part with increased stiffness compared to the lower atmospheric-pressure methods (14.7 psi) on an order of 22%. After further extension and deformation past the linear elastic region, tests concluded that although the autoclaved specimens may have been higher-quality parts, the low-pressure-cured specimens performed more efficiently with respect to energy absorption. Considering the specific energy absorption (SEA) and crush force efficiency (CFE) are both on average around 6% higher for the low-pressure specimens, it is concluded that they can perform similarly to the high-pressure specimens and possibly even more efficiently depending on the loading conditions and desired purpose of the structure.
426

Malý axiální motor pro čerpadlo / Small axial magnetic flux motor for pump

Lacina, David January 2017 (has links)
This thesis aims to design a motor with axial magnetic flux, which could be used as a direct propeller of heart replacement pump. It is divided into several parts, first of which deals with describing possible axial motors construction design. Next follows up the description of possible motor designs, from which the non-ferrous one was chosen. After that, an analytic calculation of motor’s properties is conducted. Calculated parameters are thereafter verified by software tools using finite element method. Finally, the whole motor was manufactured and had its parameters tested and verified.
427

Návrh dvoustupňového čerpadla s protiběžnými koly na zadané parametry / The design of two-stage pump with counter rotating runners for given parameters

Vrbka, Tomáš January 2018 (has links)
This diploma thesis deals with hydraulic design and optimization of the blades of the axial pump. Main objective of the thesis is to design two stage pump with counter-rotating rotors meeting conditions of design point. In addition to the design solution the thesis includes theoretical part which deals with dividing and function description of hydrodynamic pumps.
428

Optimalizace tvaru mazací mezery hydrodynamického ložiska s využitím umělých neuronových sítí / Lubricant gap shape optimization of the hydrodynamic thrust bearing using artificial neural networks

Kukla, Lukáš January 2020 (has links)
The thesis deals with the description of the main parts of the turbocharger and explains the concept of optimization. Furthermore, the work deals with the description of the flow of real fluids and lubrication of the hydrodynamic bearing. The work deals with the creation of a computational model, metamodel and subsequent search for a global extreme. In particular, the neural network metamodel technique is used in metamodel formation.
429

Návrh aeroderivátu pro využití v kompresních stanicích / Design of aeroderivative for use in compression stations

Dominik, Dávid January 2020 (has links)
This thesis is concerned with the calculation of the power turbine. This turbine should be used in the automatic drive of the compressor used for compression of natural gas in compressor stations. Flight engine aeroderivate from the Rolls-Roye company, type RB211-22B, was used as gas generator. The main aim of the thesis is to summarize of the base atributes of the combustion turbines and aeroderivates. They are used for automatic engine, application a thermodynamic calculation of the power turbine, for reaction stage and basic strength calculations.
430

Analýza vyztužené opěrné stěny založené na jemnozrnných zeminách / Analysis of mechanicaly stabilized earth wall on fine-grained subsoil

Střižík, Jakub January 2013 (has links)
In the reinforced backings, the pulling capacity is transmitted by built-in reinforcements for which design it is necessary to determinate accurately this capacity. In the diploma thesis, there is the effect of subsoil stiffness and selected constitutional relation on the capacity transmitted by individual reinforcements by the method of parametric study monitored.

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