Dissertations / Theses on the topic 'Localized and distributed loading'

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2011.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 133-135).
The response of a grooved composite specimen to two contact loading situations is studied; load applied via a transversely oriented cylindrical indenter and via a localized spherical ball-ended indenter. The philosophy of the Building Block Approach is used to develop these tests in the current study in that the cylindrical indenter creates a "two-dimensional loading" (transversely distributed) case, and the spherical indenter adds complexity to the system and creates a "three-dimensional loading" (localized spherical) case. The final failure and initial permanent deformation, in the form of crushing, is investigated, along with the effect of laminate configurations and ply angles. The is done by using the two indenters, six different laminates, and two types of tests to study the grooved composite specimens, 1 inch wide by 2 inches long, of 78 to 80 plies. This work uses a specimen configuration and testing technique developed in previous work. A computed microtomography technique is used to examine select specimens to ascertain the extent of the internal damage. Specimens subjected to the "two-dimensional loading" case exhibit four Behavior Types of the load-stroke response. Several aspects of the response are used to characterize the Behavior Types, including initial linear regions, knee loads, reverse knee loads, second linear regions, and changes in slopes. The responses of the two loading cases indicate that the details of the laminate play a significant role in the load-stroke response for the "two-dimensional loading" case, whereas the details of the loading play a more significant role for the "three-dimensional loading" where only one type of load-stroke behavior is generally displayed. In the "three-dimensional loading" case, significant crushing occurs which is not seen in the "two-dimensional loading" case. This is visible due to the localized loading for the "three-dimensional loading" case, and impacts the overall load-stroke response. The 900 plies, in addition to the "mesh" created by the ply angles in the laminate, and the "ply angle mismatch" within a laminate, affect the ability of the laminate to resist indentation and the load-stroke response. Recommendations for further work are presented.
by Holly K. Jeffrey.
S.M.

Virtualized web application servers within computational clouds, such as the GoogleApp Engine, generally restrict resource usage and therefore provide limited,relationally none-complete query facilities only. This work investigates how scalable,reliable and a more powerful access to the App Engine Datastore can beaccomplished and an Optimized Distributed Datastore Exchange (ODDSE) ispresented. Being aware of the App Engine’s resource restrictions ODDSE provides areliable and failure safe query interface to transparently exchange data with thedistributed Datastore using full SQL or AmosQL. ODDSE therefore wraps Datastorerelations and utilizes the extensible database system Amos II to compensate formissing query facilities in Google’s relationally none-complete query language GQL.Under the covers ODDSE furthermore implements an adaptive and reliablemanagement of interactions with App Engine servers. For scalability and highperformance the interaction is parallelized and continuously adapted. Theperformance of ODDSE is evaluated and compared to a similar system showing itsconsiderably good results for both bulk uploading and query processing.

Tissue optical clearing aims to increase the penetration depth of near-collimated light in biological tissue to enhance optical diagnostic, therapeutic, and cosmetic procedures. Previous studies have shown the effects of chemical optical clearing on tissue optical properties. Drawbacks associated with chemical clearing include the introduction of potentially toxic exogenous chemicals into the tissue, poor site targeting, as well as slow transport of the chemicals through tissue. Thus, alternative clearing methods have been investigated. Mechanical compression is one such alternative tissue optical clearing technique. The mechanisms of action of mechanical compression may be similar to those of chemical clearing, though they have yet to be investigated systematically. This research describes the design and execution of a number of procedures useful for the quantification of the tissue optical clearing effects of localized mechanical compression. The first experimental chapter presents the effects of compression on image resolution and contrast of a target imaged through ex vivo biological tissue. It was found that mechanical optical clearing allowed recovery of smaller targets at higher contrast sensitivity when compared to chemical clearing. Also, thickness-independent tissue clearing effects were observed. In the second experimental chapter, dynamic changes in tissue optical properties, namely scattering and absorption coefficients (?s' and ?a, respectively) were monitored during a controlled compression protocol using different indentation geometries. A reduction in ?s' and ?a was evident for all indentation geometries, with greater changes occurring with smaller surface area. Results indicate that localized mechanical compression may be harnessed as a minimally-invasive tissue optical clearing technique.
Master of Science

Cylindrical shells are used for a variety of engineering applications such as undersea vehicles and aircraft. The models currently used to determine the vibration characteristics of these shells are often approximated by assuming the shell is infinitely long or has shear-diaphragm boundary conditions. These models also ignore complex loading conditions such as plane waves in favor of point forces or free vibration models. This work expands on the capabilities of these models by examining the acoustic response of a finite length cylinder with flat plate endcaps to multiple types of distributed loading conditions. Starting with the Donnell equations of motion for thin cylinders and the classical plate theory equations of motion for the endcaps, spacial domain displacement field solutions for the shell and plates take an assumed form that includes unknown wave propagation coefficients. These solutions are substituted into stress boundary conditions and continuity equations evaluated at the intersections between the shell and plates. An infinite summation is contained within the boundary conditions and continuity equations which is decoupled, truncated, and compiled in matrix form to allow for the propagation coefficients to be found via a convergent sum of vectors. System responses due to a ring loading and multiple cases of plane waves are studied and validated using a finite element analysis of the system. It is shown that the analytical model matches the finite element model well.
Master of Science

Numerical methods aid significantly the engineering efforts towards the conservation of existing masonry structures and the design of new ones. Among them, macro-mechanical finite element methods based on the smeared crack approach are commonly preferred as an affordable choice for the analysis of large masonry structures. Nevertheless, they usu-ally result in a non-realistic representation of damage as smeared over large areas of the structure, which hampers the correct interpretation of the damage pattern. Additionally, a more critical pathology of this approach is the mesh-dependency, which influences nota-bly the safety and stability predictions. To overcome these limitations, this thesis proposes a novel computational tool based on the {enrichment} of the classical smeared crack approach with a local tracking algorithm. The objective of this localized damage model is the realistic and efficient non-linear anal-ysis of masonry structures with an enhanced representation of cracking. The non-linear behaviour of masonry is simulated through the adoption of a continuum damage mechanics model with two damage indices, allowing the differentiation between the tensile and compressive mechanical responses of masonry. In this context, a novel explicit formulation for the evolution of irreversible strains is proposed and implemented. Two new expressions are derived for the regularization of the tensile and compressive softening responses according to the crack-band approach, ensuring the mesh-size objec-tivity of the damage model. The simulation of the structural behaviour of masonry structures under versatile loading and boundary conditions necessitates some developments in the context of local tracking algorithms. To this end, this thesis presents the enhancement of local tracking algorithms with novel procedures that make possible the simulation of multiple, arbitrary and inter-secting cracking under monotonic and cyclic loading. Additionally, the effect of different crack propagation criteria is investigated and the selection among more than one potential failure planes is tackled. The proposed localized damage model is validated through the simulation of a series of structural examples. These vary from small-scale tests on concrete specimens with few dominant cracks, to medium and large-scale masonry structures with multiple tensile, shear and flexural cracking. The analyses are compared with analytical, experimental and numerical results obtained with alternative methods available in the literature. Overall, the localized damage model developed in this thesis largely improves the mesh-independency of the classical smeared crack approach and reproduces crack patterns and collapse mech-anisms in an efficient and realistic way.
Los métodos numéricos son decisivos en la ingeniería para la conservación de estructuras de mampostería existentes y el diseño de estructuras nuevas. Entre ellos, los métodos macro-mecánicos de elementos finitos, basados en el concepto de fisuras distribuidas, son habitualmente los preferidos como opción asequible para el análisis de grandes estructuras de mampostería. Sin embargo, suelen resultar en a una representación poco realista del daño, distribuido en grandes áreas de la estructura, lo que impide la correcta interpretación del patrón de daño. Además, esta metodología presenta una patología más crítica, la dependencia de la malla, que influye notablemente en las predicciones de seguridad y estabilidad. Para superar estas limitaciones, esta tesis propone una nueva herramienta numérica basada en el enriquecimiento del clásico enfoque de fisuras distribuidas con un algoritmo de trazado local. El objetivo de este modelo de daño localizado es el análisis no-lineal de las estructuras de mampostería de manera realista y eficiente con una representación mejora-da de fisuras. El comportamiento no lineal de la mampostería se simula a través de la adopción de un modelo de mecánica de daño continuo con dos índices de daño, permitiendo la diferenciación entre las respuestas mecánicas de tensión y compresión de la mampostería. En este contexto, se propone e implementa una nueva formulación explícita para la evolución de deformaciones irreversibles. Se derivan dos nuevas expresiones para la regularización del ablandamiento de tracción y compresión según el ancho de banda de la fisura, garantizan-do la objetividad del modelo de daño al respecto del tamaño de la malla. La simulación del comportamiento estructural de las estructuras de mampostería en condiciones de carga y contorno generales precisa de algunos desarrollos en el contexto de los algoritmos locales de trazado. Con este objetivo, se presenta la mejora de los algoritmos locales de trazado con nuevos procedimientos que posibilitan la simulación de fisuración múltiple, arbitraria e secante bajo cargas monótonas y cíclicas. Además, se investiga el efecto de diferentes criterios de propagación de fisuras y se aborda la selección entre más de un plano de falla posible. El modelo de daño localizado propuesto se valida mediante la simulación de una serie de ejemplos estructurales. Éstos van desde pruebas a pequeña escala en probetas de hormigón, con pocas fisuras dominantes, hasta estructuras de mampostería de mediana y gran escala con fisuración múltiple de tracción, de cortante y de flexión. Los análisis se comparan con los resultados analíticos, experimentales y numéricos obtenidos con métodos alternativos disponibles en la literatura. El modelo de daño localizado mejora en gran medida la independencia de la malla del clásico método de fisuras distribuidas y reproduce patrones de daño y mecanismos de colapso de una manera eficiente y realista

Wireless sensor networks (WSNs) have recently achieved a great deal of attention due to its numerous attractive applications in many different fields. Sensors and WSNs possesses a number of special characteristics that make them very promising in many applications, but also put on them lots of constraints that make issues in sensor network particularly difficult. These issues may include topology control, routing, coverage, security, and data management. In this thesis, we focus our attention on the coverage problem. Firstly, we define the Sensor Energy-efficient Scheduling for k-coverage (SESK) problem. We then solve it by proposing a novel, completely localized and distributed scheduling approach, naming Distributed Energy-efficient Scheduling for k-coverage (DESK) such that the energy consumption among all the sensors is balanced, and the network lifetime is maximized while still satisfying the k-coverage requirement. Finally, in related work section we conduct an extensive survey of the existing work in literature that focuses on with the coverage problem.

This project was an innovative approach in developing smart coordination of available energy resources to improve the integration level of PV in distribution network. Voltage and loading issues are considered as the main concerns for future electricity grid which need to be avoided using such resources. A distributed control structure was proposed for the resources in distribution network to avoid noted power quality issues.

Wireless sensor networks (WSNs) have recently attracted a great deal of attention due to their numerous attractive applications in many different fields. Sensors and WSNs possess a number of special characteristics that make them very promising in a wide range of applications, but they also put on them lots of constraints that make issues in sensor network particularly challenging. These issues may include topology control, routing, coverage, security, data management and many others. Among them, coverage problem is one of the most fundamental ones for which a WSN has to watch over the environment such as a forest (area coverage) or set of subjects such as collection of precious renaissance paintings (target of point coverage) in order for the network to be able to collect environment parameters, and maybe further monitor the environment. In this dissertation, we highly focus on the area coverage problem. With no assumption of sensors’ locations (i.e., the sensor network is randomly deployed), we only consider distributed and parallel scheduling methods with the ultimate objective of maximizing network lifetime. Additionally, the proposed solutions (including algorithms, a scheme, and a framework) have to be energy-efficient. Generally, we investigate numerous generalizations and variants of the basic coverage problem. Those problems of interest include k-coverage, composite event detection, partial coverage, and coverage for adjustable sensing range network. Various proposed algorithms. In addition, a scheme and a framework are also suggested to solve those problems. The scheme, which is designed for emergency alarming applications, specifies the guidelines for data and communication patterns that significantly reduce the energy consumption and guarantee very low notification delay. For partial coverage problem, we propose a universal framework (consisting of four strategies) which can take almost any complete-coverage algorithm as an input to generate an algorithm for partial coverage. Among the four strategies, two pairs of strategies are trade-off in terms of network lifetime and coverage uniformity. Extensive simulations are conducted to validate the efficiency of each of our proposed solutions.

Le travail présenté dans ce mémoire contribue au domaine de l’entreprise étendue et le développement des systèmes d’informations distribués. et le développement des systèmes d’informations distribués. C’est bien évidemment un sujet d’étude important pour la communauté Logistique (chaîne logistique), mais aussi pour la communauté Génie logiciel. C’est dans cette perspective que se situent les objectifs de proposer une modélisation de la chaîne logistique globale dans un environnement de transport intermodal de porte à porte en vue de résoudre les problèmes : (i) d’interfaces entre les différents acteurs intervenants le long de la chaîne et (ii) de rupture des charges engendrés par les opérations de transfert de marchandises d’un mode de transport à l’autre. Ainsi, l’amélioration de performance de la chaine logistique dépend fortement du niveau de coopération et de coordination, et surtout du partage et de la validité des informations et des connaissances, entre ces différents acteurs de la chaîne (organisateur du transport, transitaire, fournisseur, etc.). L’applicatif se situe dans le corridor de la vallée de Seine. Le travail s’inscrit dans le projet APLOG (Amélioration et Performance de la LOgistique Globale) financé par la région Haute Normandie
The work presented in this thesis contributes to the field of the extended enterprise and the development of distributed information systems. This is obviously an important subject of study for the logistics community (supply chain), but also for the software engineering community. It is in this context that the objectives are to provide a model of global supply chain in an intermodal environment door to door service to solve the problems: (i) interfaces between the different actors involved along the chain and (ii) trans-loading operations generated by the goods transfer operations from one mode of transport to another. Thus, improved performance of the supply chain depends heavily on the level of cooperation and coordination, and especially sharing and validity of information and knowledge between the different actors in the chain (transport organizer, forwarding, Supplier, etc.). The application is located in the corridor of the Seine valley. The work is part of the project APLOG (Performance Improvement and global logistics) financed by the Haute Normandie region

Single Carrier Frequency Division Multiple Access (SC-FDMA) is a multiple access transmission scheme that has been adopted in the 4th generation 3GPP Long Term Evolution (LTE) of cellular systems. In fact, its relatively low peak-to-average power ratio (PAPR) makes it ideal for the uplink transmission where the transmit power efficiency is of paramount importance. Multiple access among users is made possible by assigning different users to different sets of non-overlapping subcarriers. With the current LTE specifications, if an SC-FDMA system is operating at its full capacity and a new user requests channel access, the system redistributes the subcarriers in such a way that it can accommodate all of the users. Having less subcarriers for transmission, every user has to increase its modulation order (for example from QPSK to 16QAM) in order to keep the same transmission rate. However, increasing the modulation order is not always possible in practice and may introduce considerable complexity to the system. The technique presented in this thesis report describes a new way of adding more users to an SC-FDMA system by assigning the same sets of subcarriers to different users. The main advantage of this technique is that it allows the system to accommodate more users than conventional SC-FDMA and this corresponds to increasing the spectral efficiency without requiring a higher modulation order or using more bandwidth. During this work, special attentions wee paid to the cases where two and three source signals are being transmitted on the same set of subcarriers, which leads respectively to doubling and tripling the spectral efficiency. Simulation results show that by using the proposed technique, it is possible to add more users to any SC-FDMA system without increasing the bandwidth or the modulation order while keeping the same performance in terms of bit error rate (BER) as the conventional SC-FDMA. This is realized by slightly increasing the energy per bit to noise power spectral density ratio (Eb/N0) at the transmitters.

碩士
國立臺灣科技大學
營建工程技術學系
81
In architectural structure analysis,the simplified frame model is usually adopted for analyzed.And the determination of the equivalent distributed vertical load is almost based on the yielding line theory of slab,that is,to use partition zone of yielding line as the equivalent distributed vertical load on beam. The research of this thesis is to disuss the accuracy of the general loading mode as the above mentioned. At first, by the structural analysis software SAP-90, using the frame model that included shell element to analysis indiated loading condition.When the calculations for all the usually used aspect ratio is done,take the analyzed shear and torsion on the frame regressing to shear and torsional fitting curve. When the polynomial shear curve is differentiated , we can get the equivalent distributed vertical load , as the same , when differentiated the polymial torsion curve , we can get the distributed torsion on beam.As the distributed load for all the aspect ratio is get ,from appropriate numerial method, we can determine all the load on the simplified frame model. When the loading is determinated from the above mentioned method , to verify the analysis accuray from this method is another another important task of this thesis. It is the final destination of this thesis,that, if we can get more accurately analysis than the traditional load method.

Supporting emerging mobile applications in densely populated environments requires connecting mobile users and their devices with the surrounding digital landscape. Specifically, the volume of digitally-available data in such computing spaces presents an imminent need for expressive mechanisms that enable humans and applications to share and search for relevant information within their digitally accessible physical surroundings. Device-to-device communications will play a critical role in facilitating transparent access to proximate digital resources. A wide variety of approaches exist that support device-to-device dissemination and query-driven data access. Very few, however, capitalize on the contextual history of the shared data itself to distribute additional data or to guide queries. This dissertation presents Gander, an application substrate and mobile middleware designed to ease the burden associated with creating applications that require support for sharing and searching of hyper-localized data in situ. Gander employs a novel trajectory-driven model of spatiotemporal provenance that enriches shared data with its contextual history -- annotations that capture data's geospatial and causal history across a lifetime of device-to-device propagation. We demonstrate the value of spatiotemporal data provenance as both a tool for improving ad hoc routing performance and for driving complex application behavior. This dissertation discusses the design and implementation of Gander's middleware model, which abstracts away tedious implementation details by enabling developers to write high-level rules that govern when, where, and how data is distributed and to execute expressive queries across proximate digital resources. We evaluate Gander within several simulated large-scale environments and one real-world deployment on the UT Austin campus. The goal of this research is to provide formal constructs realized within a software framework that ease the software engineering challenges encountered during the design and deployment of several applications in emerging mobile environments.
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The self-assembly of polystyrene-stabilized cadmium sulfide nanoparticles (PS-CdS) with amphiphilic stabilizing chains of polystyrene-block-poly(acrylic acid) (PS-b-PAA) into colloidal quantum dot compound micelles (QDCMs) is studied on two-phase gas-liquid segmented microfluidic reactors. The resulting particle sizes are found to arise from the interplay of shear-induced coalescence and particle breakup, depending on a combination of chemical and flow conditions. Variation of water content, gas-to-liquid ratio, and total flow rate, enable control of QDCM sizes in the range of 140 – 40 nm. The flow-variable shear effect on similar microfluidic reactors is then applied to direct the solution self-assembly of a PS-b-PAA block copolymer into various micelle morphologies. The difference between off-chip and on-chip morphologies under identical chemical conditions is explained by a mechanism of shear-induced coalescence enabled by strong and localized on-chip shear fields, followed by intraparticle chain rearrangements to minimize local free energies. Time-dependent studies of these nanostructures reveal that on-chip kinetic structures will relax to global equilibrium given sufficient time off-chip. Further investigations into the effect of chemical variables on on-chip shear-induced morphologies reveal a combination of thermodynamic and kinetic effects, opening avenues for morphology control via combined chemical (bottom-up) and shear (top-down) forces. An equilibrium phase diagram of off-chip micelle morphologies is constructed and used in conjunction with kinetic considerations to rationalize on-chip mechanisms and morphologies, including cylinders and vesicles, under different chemical conditions. Finally, we extend our strategy of two-phase microfluidic self-assembly of PS-b-PAA to the loading of fluorescent hydrophobic probes (pyrene and naphthalene) with different affinities for the PS core. The on-chip loading approach provides a fast alternate to the slow off-chip method, with implications for the potential development for point-of-care devices for drug loading. On-chip loading results indicate that loading efficiencies are dependent on water content and, to a lesser extent, on flow rate; the results also suggest that the on-chip morphologies of the PS-b-PAA micelles are an important factor in the loading efficiencies.
Graduate