Дисертації з теми "Mechanical stre"

Lo stress meccanico è un comune stress abiotico che può considerevolmente compromettere la stabilità delle piante. Nel corso dell’evoluzione, le piante hanno evoluto diversi meccanismi atti a contrastare e/o mitigare gli effetti negativi di questo disagevole stress ambientale. Studiare l’impatto di questo stress sulle piante legnose significa fornire delle basi scientifiche sulla conoscenza della biologia della radice e sulle complesse dinamiche della formazione del legno di reazione, importante nel contesto della produttività e dell’utilizzo delle piante stesse. In questa tesi, una simulazione controllata dello stress meccanico è stata eseguita su radici Populus nigra usando un semplice sistema sperimentale. Questa tesi offre un outline sui meccanismi molecolari che regolano le risposte a lungo termine al bending, evidenziando le differenze tra i due lati della radice di pioppo (lato concavo e lato convesso) ed indaga, in particolar modo, il ruolo dei principali fitormoni coinvolti nella formazione del legno di reazione indotto dalla condizione di stress. Usando un metodo basato sulla cromatografia liquida accoppiata alla spettroscopia di massa (LC-MS/MS), è stato ottenuto il profiling ormonale dell’auxina, dell’acido abscissico e delle citochinine per differenti settori e lati del fittone e del fusto di pioppo, sottoposti a differenti intensità delle forze di tensione e compressione. I dati ottenuti sono stati comparati per verificare le similitudini e le differenze della risposta al bending della radice e del fusto di pioppo. Inoltre, al fine di approfondire il ruolo degli ormoni nell’induzione della zona cambiale della radice di pioppo sottoposta a bending, un’analisi ormonale tessuto-specifica è stata eseguita dopo la messa a punto di un metodo per l’isolamento del tessuto cambiale. Complessivamente, i dati ottenuti in questa tesi mostrano che la radice di pioppo risponde al bending producendo nella zona concava un legno di compressione, ricco di lignina, con caratteristiche simili al legno di compressione prodotto a livello del fusto nelle gimnosperme. Un alto livello di auxina ed acido abscissico sembra accompagnare questo processo di sviluppo, sin dalle fasi precoci del trattamento.
Mechanical stress is a common environmental perturbation that can considerably affect plant stability. In the course of evolution, plants evolved different mechanisms for coping with and mitigating the negative effects of this disadvantageous abiotic stress. Study the impact of this stress on the woody plant means to provide a scientific basis in the knowledge of the root biology and complex dynamics of the reaction wood formation, important in the context of plant productivity and utilization. In this thesis, a controlled simulation of mechanical stress was performed in Populus nigra roots by using a simple experimental system. After giving an outline of the molecular mechanisms that regulate the responses to long-term bending stress between the two sides of the poplar root (the convex and the concave side), this thesis lays emphasis on the roles of main plant hormones in the stress-induced reaction wood formation. Using the method based on liquid chromatography coupled to tandem mass spectrometry analysis (LC-MS/MS) auxins, abscisic acid and cytokinins profiling was obtained for different sectors and sides of the bent root and stem, subjected to different intensities of tension and compression forces. Data obtained were then compared in order to verify similarities and differences between root and stem response to bending. In order to better understand the role of hormones in the induction of cambial zone of poplar root subjected to bending, a method for isolation of cambial tissue was developed and the analysis of auxins, abscisic acid and cytokinins profile was carried out. Taking together, data of this thesis showed as poplar root responds to bending producing in the concave zone a compression wood, rich in lignin content, with features similar to the compression wood produced at stem level by gymnosperms. A high level of auxin and abscisic acid seems to accompany this development process, even in the early phases of the treatment.

Le stockage de chaleur dans des géostructures énergétiques telles que des remblais est réalisable en installant des échangeurs horizontaux au sein des différentes couches de sol compacté. Dans ce système, l'énergie thermique qui est injectée en été via un fluide caloporteur circulant dans les échangeurs de chaleur, peut être extraite en période hivernale. Dans ces conditions, lors de la mise en service, le sol compacté est soumis à des variations de température quotidiennes et saisonnières. Ces variations pourraient modifier les performances thermo-hydro-mécaniques du sol compacté. Ainsi, le but de cette étude est d'étudier les performances thermiques et mécaniques d'un sol compacté lorsqu'il est soumis à des variations de température monotones et cycliques. Le sol étudié est un limon fréquemment utilisé dans les constructions de remblais en France. Le comportement thermique et mécanique du sol est étudié à un état de compactage correspondant aux propriétés thermiques optimales. Dans cet état, le sol compacté est non saturé ce qui complexifie l'estimation de ses propriétés thermiques. Pour pallier à ces difficultés, dans cette étude, un modèle inverse est proposé pour estimer les propriétés thermiques du sol compacté. L’efficacité du modèle est testée sur un jeu de données acquises dans la gamme de 20 à 50 °C dans un modèle réduit en laboratoire. Les valeurs obtenues sont ensuite comparées à des mesures classiques en laboratoire (méthodes en régime transitoire et en régime permanent). Cette méthode pourrait permettre de suivre l’évolution des propriétés thermiques du stockage et ainsi assurer son efficacité tout au long de sa durée de vie. La question de la stabilité à long terme de ces structures soumises à des variations thermiques monotones (5, 20 et 50 °C) et cycliques (5 à 50 °C) est ensuite abordée à l'aide d'essais oedomètriques et d’essais de cisaillement direct à température contrôlée. Les résultats des essais de compressibilité ont montré que l'effet de la variation de température est plus prononcé sous une contrainte verticale supérieure à la pression de préconsolidation. Les indices de compression et de gonflement peuvent être considérés comme indépendants des variations de température. Donc le tassement global du remblai dû aux variations thermiques pourrait être considéré comme négligeable. Les résultats des essais de cisaillement direct ont montré que les variations de température (monotones ou cycliques) augmentent la cohésion ce qui est avantageux pour la capacité portante et la stabilité des pentes des remblais. Dans la phase de conception d'un remblai de stockage, ces résultats seraient utiles au dimensionnement du système si des trajectoires thermomécaniques similaires à celles de cette étude sont respectées. Dans une dernière partie, une simulation numérique prenant en compte l'interaction sol-atmosphère est réalisée afin d’évaluer la performance thermique de ce sol compacté en conditions naturelles. Différentes profondeurs d'installation de boucles d'échangeurs de chaleur sont testéss ainsi que différents scénarios de stockage. Les résultats ont montré que le sol compacté augmente de 8.5% les performances du système par rapport à l'installation d'une boucle horizontale dans le sol naturel (non compacté). Les résultats de deux scénarios différents ont montré qu’en été avec un fluide ayant une température d'entrée de 50 °C augmente significativement la performance du système. De plus, une installation plus profonde des boucles horizontales améliore également la performance du système. Il convient de noter que le remblai est en interaction avec l'atmosphère depuis ses surfaces supérieure et latérale, l'efficacité thermique de la structure pourrait être affectée en raison des pertes de chaleur. Par conséquent, il est préférable de placer les échangeurs de chaleur loin des surfaces supérieures et latérales
Nowadays, thermal energy storage in geostructures like embankments can be possible by installing the horizontal heat exchangers in different layers of compacted soil. In this system, the thermal energy is stored in summer via a fluid, circulating in the heat exchangers, to be extracted in the demand period. When the serviceability of embankment as a medium to store the thermal energy starts, the compacted soil will be subjected to the daily and seasonally temperature variations. These seasonal temperature variations could modify the thermo-hydro-mechanical performance of the compacted soil. Thus, the aim of this study is to investigate the thermal and mechanical performances of a compacted soil when it is subjected to monotonic and cyclic temperature variations. The studied soil is a sandy lean clay that is frequently used in embankment constructions in France. The thermal and mechanical behavior of the soil are investigated at a compaction state corresponding to the optimal thermal properties. However, this compacted soil is unsaturated and the estimation of its thermal properties is complex. In this study, an inverse analytical model is proposed to estimate the thermal properties of the soil using temperature monitoring in the range of 20 to 50 °C in a soil compacted in a large container. The estimated thermal parameters were compared to classical laboratory measurements (transient and steady-state methods). The comparison showed that the estimated values were close to the results obtained in transient laboratory method. Using this method, the thermal efficiency of the compacted soil can be verified in the lifetime of the storage system. To ensure the structure stability, long-term mechanical response of these systems subjected to monotonic and cyclic temperature variations should be investigated. To achieve this aim, using temperature-controlled oedometric and direct shear devices, consolidation and shear parameters of the studied soil at different monotonic (5, 20, and 50 °C) and cyclic (5 to 50 °C) temperatures were investigated. The results of temperature-controlled oedometric tests showed that the effect of the temperature variation is more pronounced under vertical pressures higher than the preconsolidation pressure. The compression and swelling indexes could be considered independent of temperature variations. Therefore, the overall settlement of the embankment due to thermal variation near the heat exchangers could be considered negligible. The results of temperature-controlled direct shear tests showed that the temperature variations (monotonic heating or cooling, or temperature cycles) increased the cohesion which is beneficial for the bearing capacity and slope stability of embankments. These results can be directly used in the design of embankments to store thermal energy exposed to similar thermo-mechanical paths. Finally, the thermal performance of the compacted soil is verified using a numerical simulation considering the soil atmosphere interaction. Different depths installation of heat exchanger loops and different heat storage scenarios were simulated. The results showed that the compacted soil increases 8.5% the systems performance compared to the horizontal loop installation in the local soil. The results of two different scenarios show that an inlet fluid temperature of 50 °C in summer increases highly the system performance (13.7% to 41.4%) while the improvement is less significant (0% to 4.8%) for the ambient inlet temperature. Moreover, a deeper installation of horizontal loops increases the system performance. From the numerical simulation results can be concealed that the embankment is in interaction with the atmosphere from its upper and lateral surfaces, the thermal efficiency of the structure could be affected due to heat losses. Therefore, it is preferable to place the heat exchangers away from the top and side surfaces

La lamina nucleare (NL) è un reticolo di proteine fibrillari che riveste la superficie interna della membrana nucleare. Essa è principalmente composta da filamenti intermedi di tipo V , chiamati lamìne, e proteine ausiliari ad esse associate (lamin-associated proteins, LAPs). Nei mammiferi le lamìne sono codificate da tre geni : LMNA, che codifica per la lamìna A e lamìna C (lamìne di tipo A), LMNB1 e LMNB2 che codificano rispettivamente per la lamìna B1 e B2 (lamìne di tipo B). Lamìne e LAPs si associano a formare una matrice tridimensionale densa e dinamica che stabilisce numerose interazioni, sia stabili che transitorie, con diverse classi di molecole biologiche: DNA, fattori di trascrizione, proteine strutturali. Tutte queste interazioni sono essenziali per fornire stabilità strutturale e preservare l’integrità nucleare, per collegare fisicamente e funzionalmente la lamina nucleare al citoscheletro e per organizzare la cromatina. In questo modo, oltre a svolgere un ruolo strutturale fondamentale, la lamina nucleare risulta ricoprire ruoli chiave anche nei processi di meccanotrasduzione del segnale e nella regolazione dell’espressione genica ed epigenetica. Mutazioni a carico dei geni che codificano per le lamìne nucleari sono associate ad un'ampia ed etogenea classe di patologie note come laminopatie. Tra queste, una delle più controverse ed interessanti è la Hutchison-Gillford Progeria Syndrome (HGPS), una malattia genetica rara dovuta a una mutazione puntiforme nel gene LMNA. Tale mutazione risulta nella produzione di una versione tronca della lamìna A, mancante di 50 amminoacidi, conosciuta come Progerina. HGPS è principalmente caratterizzata da alterazioni morfologiche del nucleo e invecchiamento precoce. I soggetti affetti da Progeria, infatti, fin dai primi anni di vita sviluppano condizioni patologiche tipiche dell’età senile quali cataratta, diabete e l'osteoporosi pur preservando le normali funzioni congnitive. Questi pazienti muoiono tipicamente per complicanze cardiovascolari intorno ai 14 anni di età, in media. Considerando la sindrome di Hutchinson-Guilford come un esempio estremo di ciò che alterazioni della lamina nucleare comportano, durante il mio dottorato di ricerca ho investigato diversi aspetti riguardanti la biologia della lamina nucleare con particolare interesse all'impatto che perturbazioni strutturali della lamina nucleare possono avere sulle normali funzioni cellulari, la meccanica cellulare, la regolazione dell'espressione genica e l’ interconnessione esistente tra integrità della lamina nucleare, processo di invecchiamento e stress ossidativo. Per ottenere una visione d’insieme del contributo della lamina nucleare sia in condizioni fisiologiche che patologiche, sono state adottate strategie di ricerca basate su approcci interdisciplinari e integrativi in grado di tenere conto degli aspetti strutturali, meccanici e molecolari. Per fa questo, in prima instanza sono state effetuate delle analisi bionformatiche: tutti i dati di trascrittomica relativi a pazienti HGPS, presenti in database pubblici e in letteratura, sono stati raccolti e analizzati rispetto a dati equivalenti ottenuti da controlli sani. Tale analisi ha permesso di delineare profilo di espressione genica tipico di pazienti HGPS e di individuare i pathways deregolati in presenza della patologia. È stato inoltre studiato l’impatto che alterazioni della lamina nucleare hanno sulle connessioni fisiche e funzionali che questa stabilisce sia con elementi nucleari ed extra-nucleari, in un modello cellulare in cui è possibile indurre sperimentalmente, in modo controllato, l’espressione della forma mutata di Lamìn A responsabile dell’ HGPS. Tale modello cellulare ricapitola fedelmente il peculiare fenotipo cellulare dei pazienti risultando essere una valida alternativa all’utilizzo di linee primarie derivanti dai pazienti. Infine, l'interdipendenza tra stress ossidativo, invecchiamento e lamìne nucleari è stata investigata in un nuovo modello cellulare di stress ossidativo sviluppato nel nostro laboratorio, efficiente nel ricapitolare il processo di invecchiamento, in vitro.
ABSTRACT The nuclear lamina (NL) is a fibrillary protein network lining the inner surface of the nuclear envelope. It is mainly composed by type V intermediate filaments called lamins and lamin-associated proteins. Three lamin genes are present in Mammals: LMNA, which encodes lamin A and lamin C (Atype lamins), as well as, LMNB1 and LMNB2 that encode lamin B1 and B2 (B-type lamins) respectively. Lamins and LAPs associate to form a dense and dynamic three-dimensional matrix that establishes a huge number of stable and transient interactions with different classes of molecules: DNA, transcription factors, nuclear pore complexes and structural proteins of the cytoskeleton. All of these interactions are essential to provide nuclear structural stability and integrity, to physically and functionally link nuclear lamina to the cytoskeleton and to organizes chromatin. Thus NL, in addition to play a fundamental structural role, it is also a key player in cellular mechanotransduction processes and gene expression and epigenetic regulation. Mutations in genes encoding for lamins are associated with a wide a range of diseases, named laminopathies. Among these, the most interesting one is Hutchison-Gilford Progeria Syndrome (HGPS), a rare fatal genetic disorder due to do a point mutation in LMNA. This mutation results in the production of a truncated version of lamina A, lacking 50 amino acids, known as Progerin. HGPS is mainly characterized by morphological changes in the nucleus and premature aging. HGPS patients indeed, from their first years of life, develop pathological conditions typical of the elderly such as cataracts, diabetes and osteoporosis while preserving the normal cognitive functions. These patients typically die from cardiovascular complications around 14 years of age, on average. Considering Hutchinson-Guilford Progeria Syndrome as an extreme example of what nuclear lamina aberration entails, during my PhD I investigated many aspects of nuclear lamina biology with particular regard to the impact of nuclear lamina structural perturbations on cell functions, mechanics, gene expression regulation and the interconnection existing between nuclear lamina integrity, ageing process and oxidative stress. Indeed, to gain a comprehensive picture of nuclear lamina biology in health and disease, it has been adopted interdisciplinary and integrative research strategies able to take into account structural, mechanical and molecular aspects. Bioinformatics study has been performed: public available transcriptomic data of HGPS patients have been analysed with respect of those of healthy matched controls. This analysis allowed to delineate the typical global gene expression profile of HGPS patients and to identify all the deregulated pathways in the presence of the pathology. Moreover, impacts of lamina alterations on its physical and functional connections with extra-nuclear and nuclear elements have been studied in an inducible expression cellular model of the mutated form of Lamin A responsible for HGPS. This cellular model faithfully recapitulates the peculiar cellular phenotype of the HGPS patients resulting to be a valid alternative to primary cell lines deriving from the patients.Finally, the interdependence between oxidative stress, ageing and lamins has been investigated in a novel oxidative stress cellular model developed in our laboratory, that is also efficient in recapitulating typical ageing profile.

The aim of this thesis is to develop a test facility in order to validate the safe separation of a store model from the aircraft model with the analysis of the acquired data. Different alternatives are considered in the conceptual design and a facility is selected which contains the rail constructed 5 meters above the ground. 300 meter test range is used to accelerate the aircraft model, attached to the carriage with solid rocket engines. The concept is to accelerate the carriage within the first 100 meters, to perform the separation of the model at the desired velocity when the rocket engine is burned out, and in the last 100 meters, to decelerate the carriage in order to recover the models. After the parts of the carriage are designed with respect to the requirements of the separation and completing the similitude study of scaled models with the ratio of 1/8, separation tests are performed. These tests are constrained with 0.9 Mach due to the store and test aircraft limitations. Doppler radar is issued to measure the velocity and photogrammetry method is used to validate and analyze the separation and to obtain the vertical trajectory of the store model. Measured trajectory of the store model is compared with the trajectory of the full scale store.

Fatigue performance is one of the important mechanical properties which is hindering some of the additive manufacturing build structures. The main objective of this study is to investigate the fatigue life dependence of the 21-6-9 austenitic stainless-steel build using the laser powder bed fusion (LPBF) technique. The study is mainly focused on the fracture surface based on defects and the micro constituents, how they are related to the fatigue performance of the samples. 21 samples were build using optimized process parameters in which 9 of the samples were built-in vertical direction and the remaining 12 were built in the horizontal direction. Low cycle fatigue (LCF) testing was carried out with the samples with 2 conditions i.e., room temperature 24⁰C and 750 ⁰C. Before the specimens were subjected to testing the samples were stress relived at 600⁰C for 2 hours. Fractography was carried out on the fracture surface to pinpoint the initiation sites (concluded by analyzing the striations) and the cause of failure. Microstructural characterization was carried out in both the vertical and the horizontal direction of the build. The fatigue crack growth initiated from the surface where defects were present, when the cyclic loads were applied the stress concentration at these regions caused the crack initiation to take place. In some cases, the defect size was smaller at the initiation site, and that correlated to increased fatigue life. To optimize the fatigue life of LPBF built 21-6-9 is important to minimize the grain size. However, the absence of defects is crucial as well, as those typically are the weakest link. Therefore, minimizing those during the manufacturing is essential.

Thesis (M.B.A.)--Massachusetts Institute of Technology, Sloan School of Management; and, (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering; in conjunction with the Leaders for Manufacturing Program at MIT, 2008.
Includes bibliographical references (p. 57).
One of the biggest opportunities for this consumer goods company today is reducing retail stockouts at its Direct Store Delivery (DSD) customers via pre-selling, which represents approximately 70% of the company's total sales volume. But reducing retail stock-outs is becoming constantly more challenging with an ever-burgeoning number of SKUs due to new product introductions and packaging innovations. The main tool this consumer goods company uses to combat retail stock-outs is the pre-sell handheld, which the company provides to all field sales reps. The handheld runs proprietary software developed by this consumer goods company that creates suggested orders based on a number of factors including: * Baseline forecast (specific to store-item combination) * Seasonality effects (i.e., higher demand for products during particular seasons) * Promotional effects (i.e., lift created from sale prices) * Presence of in-store displays (i.e., more space for product than just shelf space) * Weekday effects (i.e., selling more on weekends when most people shop) * Holiday effects (i.e., higher demand for products at holidays) * Inventory levels on the shelves and in the back room * In-transit orders (i.e., orders that may already be on their way to the customer) The more accurate that the suggested orders are, the fewer retail stock-outs will occur. This project seeks to increase the accuracy of the consumer demand forecast, and ultimately the suggested orders, by improving the baseline forecast and accounting for the effect of cannibalization on demand.
by Susan D. Bankston.
S.M.
M.B.A.

External stores mounted on aircraft generate loads which need to be estimated before first takeoff. These loads can be measured in a wind tunnel but since the possible store configurations are basically endless, testing them all is neither economically feasible nor time efficient. Thus, scaling based on geometrical similarity is used. This can, however, be a crude method. Stores with similar geometrical properties can still behave in different ways due to aerodynamic interference caused by adjacent surfaces.

To improve the scaling performance, this work focuses on investigating two CFD codes, ADAPDT and Edge. The CFD simulations are used to derive the difference in aerodynamic coefficients, or the Δ-effect, between a reference store and the new untested store. The Δ-effect is then applied to an existing wind tunnel measurement of the reference store, yielding an estimation of the aerodynamic properties for the new store.

The results show that ADAPDT, using a coarse geometry representation, has large difficulties predicting the new store properties, even for a very simple store configuration on the aircraft. Therefore it is not suited to use as a scaling tool in its present condition. Edge on the other hand uses a more precise geometry representation and proves to deliver good estimations of the new store load behavior. Results are well balanced and mainly conservative. Some further work is needed to verify the performance but Edge is the recommended tool for scaling.

 

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With the objective to promote sustainable development, the fibres found in nature in abundance, which are biodegradable, of low cost in comparison to synthetic fibres are being used in the manufacture of composites. The mechanical behavior of the curau? and pineapple leaf fibre (PALF) composites in different proportions, 25% x 75% (P1), 50% x 50% (P2) e 75% x 25% (P3) were respectively studied, being initially treated with a 2% aqueous solution of sodium hydroxide. Mechanical analyses indicated that with respect to studies of traction, for the combination of P1 and P3, better results of 22.17 MPa and 16.98 MPa, were obtained respectively, which are higher than that of the combination P2. The results of the same pattern were obtained for analysis of bending resistance where P1 is 1.21% and P3 represents 0.96%. In the case of resistance to bending, best results were obtained for the combination P1 at 49.07 MPa. However, when Young's modulus values were calculated, the values were different to the pattern of the results of other tests, where the combination P2 with the value of 4.06 GPa is greater than the other combinations. This shows that the PALF had a greater influence in relation to curau? fibre. The analysis of the results generally shows that in combinations of two vegetable fibers of cellulosic origin, the fiber which shows higher percentage (75%) is the best option than to the composition of 50%/50%. In the meantime, according to the results obtained in this study, in the case where the application should withstand bending loads, the better composition would be 50%/50%
Com o objetivo de promover o desenvolvimento sustent?vel, as fibras encontradas em abund?ncia na natureza, que s?o biodegrad?veis e de baixo custo quando comparado com as fibras sint?ticas, vem sendo utilizadas na aplica??o de produ??o de comp?sitos. Neste trabalho foi analisado o comportamento mec?nico ? partir do ensaio de tra??o e flex?o, em um comp?sito h?brido tendo como matriz uma resina sint?tica ortoft?lica refor?ada com fibras de curau? e fibras da folha de abacaxizeiro (PALF), nas propor??es de 25% x 75% (P1), 50% x 50% (P2) e 75% x 25% (P3), respectivamente, com as fibras de curau? e as fibras da folha do abacaxizeiro sendo tratadas quimicamente por uma solu??o aquosa de hidr?xido de s?dio (NaOH) com 8% de concentra??o. As an?lises mec?nicas indicaram que com rela??o aos estudos de tra??o, para a combina??o P1 e P3, foram obtidas melhores resultados de 22,17 MPa e 16,98 MPa, respectivamente, que ? maior que da outra combina??o de P2. Os resultados do mesmo padr?o foram obtidos para an?lise de flex?o onde P1 ? 1,21% e P3 de 0,96% que s?o maiores do que o resultado obtido da combina??o P2. No caso de resist?ncia ? flex?o, melhores resultados foram obtidos para a combina??o P1 de 49,07 MPa. Mas, quando foi calculado o m?dulo de Young, os valores foram diferentes do padr?o dos resultados dos outros testes realizados, com a combina??o P2 com o valor de 4,06 GPa que ? maior que das outras combina??es. Isto mostra que as fibras PALF tiveram uma influ?ncia maior com rela??o ? fibra de curau?. A an?lise dos resultados em geral demonstra que nas combina??es de duas fibras vegetais celul?sicas, uma ou a outra fibra com porcentagem maior (75%) ? a melhor op??o do que na composi??o de 50%/50%, entretanto no caso onde a aplica??o ser? para suportar cargas de flex?o, a melhor composi??o seria 50%/50%

This thesis consists of two different research problems. In the first one, the aim is to model and simulate a solar-powered, single-effect, absorption refrigeration system using a flat-plate solar collector and LiBr-H2O mixture as the working fluid. The cooling capacity and the coefficient of performance of the system are analyzed by varying all independent parameters, namely: evaporator pressure, condenser pressure, mass flow rate, LiBr concentration, and inlet generator temperature. The cooling performance of the system is compared with conventional vapor-compression systems for different refrigerants (R-134a, R-32, and R-22). The cooling performance is also assessed for a typical year in Tampa, Florida. Higher COP values are obtained for a lower LiBr concentration in the solution. The effects of evaporator and condenser pressures on the cooling capacity and cooling performance are found to be negligible. The LiBr-H2O solution shows higher cooling performance compared to other mixtures under the same absorption cooling cycle conditions. For typical year in Tampa, Florida, the model shows a constant coefficient of performance of 0.94. In the second problem, a numerical model is developed for a typical food retail store refrigeration/HVAC system to study the effects of indoor space conditions on supermarket energy consumption. Refrigerated display cases are normally rated at a store environment of 24ºC (75ºF) and a relative humidity of 55%. If the store can be maintained at lower relative humidity, significant quantities of refrigeration energy, defrost energy and anti-sweat heater energy can be saved. The numerical simulation is performed for a typical day in a standard store for each month of the year using the climate data for Tampa, Florida. This results in a 24 hour variation in the store relative humidity. Using these calculated hourly values of relative humidity for a typical 24 hour day, the store relative humidity distribution is calculated for a full year. The annual average supermarket relative humidity is found to be 51.1%. It is shown that for a 5% reduction in store relative humidity that the display case refrigeration load is reduced by 9.25%, and that results in total store energy load reduction of 4.84%. The results show good agreement with available experimental data.

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Use of natural fibres as a reinforcement material in the manufacture of composites show a series of advantages: availability, biodegradability, low weight and regeneration in relation to synthetic fibres, thus justifying its utilization. In the present research work, composites were developed with chicken feathers (KF), using unsaturated polyester resin as matrix, for diversified applications, mainly in the furniture/timber industry.At present, in Brazil the chicken feathers are used as part of the animal feed, even though this material possesses low aggregated value. The chicken feathers are hollow, light and resistant. After washing with water at room temperature, a part of the chicken feathers were treated with 2% NaOH. Composites were manufactured using treated and untreated chicken feathers with unsaturated orthothalic polyester resin and 1% peroxide as catalyser, obtained in the commerce. Samples with size 150x25x3 mm for mechanical tests were cut by laser in the composite plate. Mechanical analyses were carried out in the Laborat?rio de Metais e Ensaios Mec?nicos UFRN. All the analyses were in accordance with ASTM standards. SEM analyses were also carried out on the samples.In the analyses of the results obtained, it was observed that the composites made with untreated chicken feathers showed better results (Traction 11.406 MPa and 9.107 MPa Bending 34.947 and 20.918 MPa for samples with and without treatment respectively) compared to the composite with treated feathers. Very low values of the water absorption results, evidenced the impermeability characteristic of the feathers. From the SEM images, the structure, fracture and the fibre/matrix adsorption can be evidenced. In the flammability test, it was observed that despite the feathers having sulfur as a constituent, natural inhibitor of flame, no burning support of the composites, because the manufacturing process of the composite
O uso de fibras naturais como refor?o em comp?sitos apresenta uma s?rie de vantagens: abund?ncia, biodegradabilidade, baixo peso e regenerabilidade em rela??o ?s fibras sint?ticas, justificando sua utiliza??o. Na presente pesquisa foram desenvolvidos comp?sitos com penas de frango (KF), utilizando resina de poli?ster n?o-saturado como matriz. Atualmente, no Brasil, as penas de frango s?o utilizadas como parte de ra??o animal, por?m este produto possui um baixo valor agregado. As penas s?o um material oco, leve e resistente. Ap?s a lavagem com ?gua em temperatura ambiente uma parte das penas foi tratada com 2% de NaOH. Foram fabricados dois comp?sitos, um com as penas tratadas e outro sem tratamento, usando o processo de molde fechado por compress?o, utilizando a resina de poli?ster ortoft?lica e 1% de per?xido MEK (per?xido de metil etil cetona) como iniciador, adquiridos no com?rcio local. As amostras com 150x25x3 mm de tamanho para os ensaios mec?nicos foram cortadas a laser na placa do comp?sito. Os ensaios de tra??o e flex?o em tr?s pontos foram realizados no Laborat?rio de Metais e Ensaios Mec?nicos - UFRN. Todas as an?lises estavam de acordo com as normas da ASTM. As amostras resultantes dos ensaios mec?nicas foram avaliadas no MEV. Com base nas observa??es dos resultados nos ensaios mec?nicos, (Tra??o 11,2 Mpa e 8,3 Mpa; Flex?o 34,9 Mpa e 22,9 MPa para as amostras sem e com tratamento respectivamente) observou-se que os comp?sitos refor?ados com as penas sem tratamento apresentaram um melhor comportamento quando foram expostos a carregamentos tanto de tra??o quanto de flex?o. O ensaio de absor??o evidenciou nos valores de absor??o de ?gua, uma das caracter?sticas da prote?na existente nas penas, a queratina, a sua capaciade de impermiabiliza??o a ?gua. Nas imagens do MEV foi poss?vel verificar a estrutura da pena, as regi?es de ruptura do comp?sito e a ades?o fibra/matriz. No ensaio de inflamabilidade, observou-se que apesar das penas terem como constituinte o enxofre, inibidor natural de chama, n?o houve a susten??o da queima nos comp?sitos, devido o processo de fabrica??o do comp?sito

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In the present work, three composites with distinct reinforcements (polyester, modal e polyester + modal), all if a unsaturated orthophthalic polyester resin as matrix were used, in order to conduct a comparative study by mechanical tests and water absorption. The fibre mats were prepared in a mat preparatory by immersion developed in the Textile Engineering Laboratory. The composites were manufactured using a closed mould process by compression using an unsaturated orthophthalic polyester resin as matrix and 1% MEK (methyl ethyl ketone peroxide) as an initiator. In each composite twelve samples with the dimensions of 150x25x3 mm were cut randomly for the mechanical analysis (tension x extension, three points bending and water absorption and Scanning Electron Micsroscopy). The mechanical tests were carried out in the Laborat?rio de Metais e Ensaios Mec?nicos UFRN . All the analyses were carried out according to the ASTM norms. The resultant samples from the mechanical analysis were subjected for the Scanning Electron Microscopy analysis. Based on the results obtained, it was observed that the reinforced composite with two fibres (modal + polyester) presented better results in comparison to the other two composites both in the tension/extension as well on the three point bending tests. In the water absorption test, it was possible to observe an equilibrium in the water absorption by the modal and polyester composite, due to the union of the two fibres. In the SEM images, the regions of rupture in the composites as well as the adsorption between the fiber and the matrix could be observed
No presente trabalho foram fabricados tr?s comp?sitos com refor?os distintos (poli?ster, modal e poli?ster + modal), todos com uma matriz de resina de poli?ster ortofit?lico n?o saturado, com o objetivo de realizar um estudo comparativo atrav?s de ensaios mec?nicos e absor??o d ?gua. As mantas de fibras foram preparadas num preparador de manta por imers?o desenvolvido no Laborat?rio de Engenharia T?xtil da UFRN. Os comp?sitos foram fabricados usando o processo de molde fechado por compress?o, utilizando a resina de poli?ster ortoft?lica e 1% de per?xido MEK (per?xido de metil etil cetona) como iniciador. Em cada comp?sito foram cortadas doze amostras aleatoriamente, com as dimens?es 150x25x3 mm, para avalia??o atrav?s de ensaios mec?nicos (resist?ncia ? tra??o e ? flex?o, absor??o d agua e microscopia eletr?nica de varredura). Os ensaios de tra??o e flex?o em tr?s pontos foram realizados no Laborat?rio de Metais e Ensaios Mec?nicos - UFRN. Todas as an?lises estavam de acordo com as normas da ASTM. As amostras resultantes dos ensaios mec?nicas foram avaliadas no MEV. Com base nos resultados dos ensaios mec?nicos, observou-se que o comp?sito refor?ado com as duas fibras em conjunto (poli?ster+modal) apresentou um melhor comportamento quando foram expostos a carregamentos tanto de tra??o quanto de flex?o. No ensaio de absor??o d agua foi poss?vel observar um equilibribio na absor??o de umidade do comp?sito com modal e poli?ster, devido a uni?o das duas fibras. Nas imagens do MEV foi poss?vel ver as regi?es de ruptura do comp?sito e a ades?o entre a fibra e a matriz

La compréhension du comportement de structures jusqu'à leur ruine est nécessaire pour concevoir au mieux ces structures. Selon le matériau et les sollicitations considérées, les mécanismes physiques à l'origine de la rupture changent. Nous nous intéresserons à des matériaux homogènes pour lesquels la ruine passe par le développement de fissures autour desquelles les non-linéarités de comportement n'ont pas un rôle dominant. Ces conditions sont réunies pour les matériaux fragiles pour lesquels la source principale de dissipation est la génération non réversible d'une surface libre, et pour certaines fissures de fatigue. Sur un cycle de chargement, il existe de nombreuses applications pour lesquelles les non-linéarités restent confinées. La théorie de la mécanique linéaire élastique de la rupture est alors un modèle pertinent pour approcher le comportement de la structure. Sous ces hypothèses, le front de la fissure introduit une singularité. L'étude asymptotique de cette singularité dans des situations plane et anti-plane permet de définir les séries de Williams. La singularité est alors d'ordre un demi et elle est quantifiée par les facteurs d'intensité des contraintes (FIC) pour chacun des trois modes de sollicitations. En 3D, la fissure peut avoir une géométrie complexe, et aucune expression générale de la singularité n'existe. Dans cette thèse, les séries de Williams en déplacements sont utilisées et régularisées le long du front au sens des éléments finis. À partir de cette définition 3D des séries asymptotiques en pointe de fissure, une méthode d'extraction directe des FIC (DEK-FEM) est étendue au cas 3D. Le domaine est décomposé en deux domaines, raccordés en moyenne sur l'interface. Au voisinage du front, les champs mécaniques sont approchés par une troncature des champs asymptotiques. La singularité est donc traitée avec des champs adaptés, et les degrés de liberté associés sont directement les coefficients asymptotiques. Parmi ces coefficients asymptotiques, on retrouve les FIC et les T-stresses. Pour des raisons d'efficacité numérique et pour pouvoir relier l'échelle de la structure à l'échelle de la fissure, cette méthode est intégrée dans un contexte multigrilles localisées X-FEM. Ainsi nous montrons que cette approche permet une bonne évaluation des évolutions des FIC et du T-stress. Cette méthode est développée en parallèle d'une stratégie de post-traitement expérimental (mesure de champs de déplacements par corrélation d'images) basée sur les mêmes séries asymptotiques. Les images tridimensionnels d'un essai de fatigue in situ sont obtenues par micro-tomographie à rayons X et reconstruction. La corrélation et la régularisation basées sur les séries asymptotiques permettent d'obtenir la géométrie de la fissure et les FIC pour pouvoir identifier des lois de propagation de fissures 3D en fatigue. L'efficacité de cette méthode en parallèle d'une simulation DEK-FEM est illustrée en 2D
It is necessary to understand the behavior of structures up to their failure to enhance their design. The mechanisms and phenomena undergoing failure vary according to the considered material and boundary conditions. We consider homogeneous materials for which cracks propagate in a context where behavior nonlinearities are not dominants. These conditions are matched for brittle and quasi-brittle materials and for some fatigue cracks. For the former, the main source of dissipation is the crack propagation which can be seen as the generation of a new free-surface. For the later, there is many applications where, in one loading cycle, the nonlinearities remains confined around the crack tip. The linear elastic fracture mechanics theory is then a pertinent model to approximate the structure behavior. Under such hypotheses, a singularity appears in the crack tip vicinity. The Williams' series expansion is computed from the asymptotic study of plane and anti-plane states. The stress is singular at the crack tip and the order of this singularity is one out of two. The singularity amplitude is quantified by the stress intensity factors (SIF), one for each of the three loading modes. In 3D, the crack shape is potentially complex (front curvature and non-planar crack), and no general asymptotic series expansion exists. In this PhD thesis, the 2D Williams' series in displacements are used and regularized with a finite element evolution along the front. From this 3D definition of the asymptotic fields in the crack tip vicinity, a numerical method for direct estimation of the SIF (DEK-FEM) is extended to 3D. This method is based on domain decomposition, the two domains are bounded in a weak sense on their interface. In the crack tip vicinity, the mechanical fields are approximated by a truncation of the asymptotic series expansion. Therefore, appropriate fields are used to deal with the singularity, and the associated degrees of freedom are directly the asymptotic coefficients. Among these coefficients are the SIF and the T-stresses. To bridge the scales between the structure and the crack front singularity and to increase the numerical efficiency, this method is embedded in a localized X-FEM multigrids approach. The proposed method is shown to provide an accurate evaluation of the SIF and T-stresses evolution. This approach has been developed in combination of an experimental post-processing method (full field displacement measurement through image correlation) based on the same asymptotic series expansion. The 3D images can be obtained for in situ fatigue experiments by X-ray microtomography and reconstruction. The crack geometry and the SIF are then provided by image correlation and regularization based on Williams series expansion. These data can be used for identifying a 3D fatigue crack growth law. The efficiency of the method is illustrated in 2D

A new method of adaptive impulse control is developed to precisely and quickly control the position of machine components subject to friction. Friction dominates the forces affecting fine positioning dynamics. Friction can depend on payload, velocity, step size, path, initial position, temperature, and other variables. Control problems such as steady-state error and limit cycles often arise when applying conventional control techniques to the position control problem. Studies in the last few decades have shown that impulsive control can produce repeatable displacements as small as ten nanometers without limit cycles or steady-state error in machines subject to dry sliding friction. These displacements are achieved through the application of short duration, high intensity pulses. The relationship between pulse duration and displacement is seldom a simple function. The most dependable practical methods for control are self-tuning; they learn from online experience by adapting an internal control parameter until precise position control is achieved. To date, the best known adaptive pulse control methods adapt a single control parameter. While effective, the single parameter methods suffer from sub-optimal settling times and poor parameter convergence. To improve performance while maintaining the capacity for ultimate precision, a new control method referred to as Adaptive Impulse Control (AIC) has been developed. To better fit the nonlinear relationship between pulses and displacements, AIC adaptively tunes a set of parameters. Each parameter affects a different range of displacements. Online updates depend on the residual control error following each pulse, an estimate of pulse sensitivity, and a learning gain. After an update is calculated, it is distributed among the parameters that were used to calculate the most recent pulse. As the stored relationship converges to the actual relationship of the machine, pulses become more accurate and fewer pulses are needed to reach each desired destination. When fewer pulses are needed, settling time improves and efficiency increases. AIC is experimentally compared to conventional PID control and other adaptive pulse control methods on a rotary system with a position measurement resolution of 16000 encoder counts per revolution of the load wheel. The friction in the test system is nonlinear and irregular with a position dependent break-away torque that varies by a factor of more than 1.8 to 1. AIC is shown to improve settling times by as much as a factor of two when compared to other adaptive pulse control methods while maintaining precise control tolerances.

abstract: Hydraulic fracturing is an effective technique used in well stimulation to increase petroleum well production. A combination of multi-stage hydraulic fracturing and horizontal drilling has led to the recent boom in shale gas production which has changed the energy landscape of North America. During the fracking process, highly pressurized mixture of water and proppants (sand and chemicals) is injected into to a crack, which fractures the surrounding rock structure and proppants help in keeping the fracture open. Over a longer period, however, these fractures tend to close due to the difference between the compressive stress exerted by the reservoir on the fracture and the fluid pressure inside the fracture. During production, fluid pressure inside the fracture is reduced further which can accelerate the closure of a fracture. In this thesis, we study the stress distribution around a hydraulic fracture caused by fluid production. It is shown that fluid flow can induce a very high hoop stress near the fracture tip. As the pressure gradient increases stress concentration increases. If a fracture is very thin, the flow induced stress along the fracture decreases, but the stress concentration at the fracture tip increases and become unbounded for an infinitely thin fracture. The result from the present study can be used for studying the fracture closure problem, and ultimately this in turn can lead to the development of better proppants so that prolific well production can be sustained for a long period of time.
Dissertation/Thesis
Masters Thesis Mechanical Engineering 2014

The objective of the study was to analyze the relationship of psychrotrophic lipolytic bacteria in bulk samples of cow?s raw milk and their metabolic activity based on the content of free fatty acids and identifying the factors that may influence their levels. The contents of free fatty acids (FFA) and counts of total bacteria, psychrotrophic lipolytic bacteria (PLiBC) and somatic cells were determined in 150 samples of cow?s bulk raw milk on 20 farms with three different milking technologies in South Bohemia during 2008?10. FFA were determined using an extraction-titration method. Within the compared technologies, the highest mean values of FFA (38,8 mmol?kg-1; P<0,001) and PLiBC (696 CFU?ml?1) were observed on farms with pipeline milking in stalls. The lowest mean FFA level (15,4 mmol?kg-1) was determined on farms with an automatic milking system. Medium values were determined on farms with parlour milking. From the aspect of the inhibition of an increase in psychrotrophic bacteria, and mainly in psychrotrophic lipolytic bacteria in conditions of cold storage of raw milk the temperature of 4°C seems optimum as it markedly inhibits the growth of mesophilic and psychrotrophic bacteria and at the same time the increase in the values of free fatty acids is slower at this temperature compared to the temperatures of 6,5 and 10°C.