Auswahl der wissenschaftlichen Literatur zum Thema „L-beams“

The high strength/stiffness-to-weight ratio that composite materials exhibit has led to the utilization of composites as alternative to traditional materials in weight-critical applications. However, the highly anisotropic nature of composites renders the strength prediction under complex loading challenging. To efficiently predict the failure of composite structures especially in cases where out-of-plane stresses are dominant, the modeling of damage onset and propagation plays an essential role in accurate strength predictions.Firstly, in this Thesis work the analysis of a composite L-profile, which is loaded such that significant out-of-plane stresses are generated in the curved region, is conducted. However, the inherent heterogeneity at the micro/meso scale is not modeled for the stress analysis.Secondly, in this project the target was to accurately predict the initiation of failure at the ply level, modal based Puck’s matrix failure criteria have been implemented to the failure analysis. Maximum stress failure criteria were however retained to check the possible fiber-based failure which is not directly captured with in Puck’s failure criterion.Thirdly, Cohesive Zone Material Model has also been employed to model the growth of interlaminar damage (delamination). The delamination study is based on the Inter Fibre Fracture crack initiation and doesn’t include other causes like edge effects, voids, manufacturing defects etc.Finally, the attempt to validate the analysis results with the available test results was made. Further development of the existing model and several tests are required to be carried out for material characterization and complete validation of the developed damage model for composite structure.

Esta dissertação tem por objetivo contribuir para o projeto estrutural de vigas delgadas de seção \"L\" de concreto pré-moldado, também conhecidas no Brasil como vigas suporte-peitoril. O projeto deste tipo de viga apresenta uma maior complexidade que o de vigas usuais pela seção transversal assimétrica, carregamento excêntrico e as várias possibilidades de ligações viga-pilar e viga-laje. Em função de sua ligação com a laje, o comportamento deste tipo de viga pode apresentar diferentes modelos: a) com torção de equilíbrio; b) sem torção de equilíbrio; e c) com restrição parcial da rotação da laje. É mostrado que para relações altura da viga/largura da mesa inferior maiores que 2,5, a variação da orientação dos eixos principais de inércia com relação aos eixos vertical e horizontal pode ser desprezada. Além disso, o centro de cisalhamento pode ser considerado situado na linha de centro da alma para grandes relações altura da viga/altura da aba. Também são discutidas as ações e efeitos a serem considerados no projeto de vigas de seção \"L\". Em relação ao estado limite último, é mostrado que os procedimentos de dimensionamento de momento fletor e força cortante não diferem dos outros tipos de vigas de concreto, entretanto, o momento de torção pode ser tratado como flexão de placa por um método recomendado na última revisão do ACI-318. O comportamento da ligação alma/aba é considerado como dente de concreto e os seguintes aspectos de seu dimensionamento são apresentados: cálculo do tirante, cálculo da suspensão, cálculo da armadura longitudinal e verificação da biela crítica. Além disso, é levada em conta a resistência à punção da aba para efeito de forças concentradas. Também são discutidas as considerações para a flexão do peitoril que pode ocorrer pela ação lateral do vento e do impacto de veículos. Em relação ao estado limite de serviço, são apresentadas duas situações exclusivas para vigas de seção \"L\" com peitoril alto e delgado: formação de fissuras na extremidade e deformação lateral excessiva. Por fim, um exemplo de aplicação é desenvolvido para ilustrar particularidades no dimensionamento de vigas delgadas de seção \"L\" de concreto pré-moldado.<br>This thesis aims to contribute to the structural design of precast concrete slender L-shaped beams, also known as facade beams, spandrel beams, L-shaped edge beams and others. The design of these beams shows a greater complexity than usual concrete beams due to the asymmetric cross section, eccentric loads and the various possibilities for beam-column and beam-slab connections. According to their connection with the slab, the beam behavior can be divided into different models: a) with equilibrium torsion; b) without equilibrium torsion; c) with partial restriction of the slab rotation. It is shown that for height-to-total width ratios larger than 2.5, the variation of the orientation of the principal axes with respect to the vertical and horizontal axes can be neglected. Furthermore, the shear center can be considered located at the web center line for high values of the beam height-to-ledge height ratio. It is also discussed the actions and effects to be considered in the design of L-shaped beams. Regarding the ultimate limit state, it is shown that the bending moment and shear force procedures do not differ from other types of concrete beams, however, the torsion can be treated as plate bending by a recent method recommended in the latest ACI-318 revision. The ledge is considered as dapped end beams and the following aspects of its design are presented: transverse bending; hanger requirements; longitudinal bending and shear strength, including punching shear. It is also discussed the considerations for web flexure that may occur by wind action and lateral vehicle impact. Regarding the serviceability limit state, it is presented two unique situations for precast concrete slender L-shaped beams: crack formation at end regions and excessive lateral deflection. Lastly, an example is developed to illustrate particularities of the precast concrete slender L-shaped beam design.

Nel corso di questa tesi si svilupperà il metodo del Beam-forming acustico, uno dei più semplici algoritmi di elaborazione segnale che permette di isolare spazialmente un suono proveniente da una precisa direzione decisa da noi, creando quindi un microfono super-direzionale orientabile a partire da un array microfonico di caratteristiche note. Inoltre si implementerà in modo pratico l'algoritmo per descrivere il livello sonoro emesso da ogni punto di una sorgente sonora estesa in modo da mappare l'intensità di quest'ultima in un'immagine 2D da sovrapporre all'immagine stessa dell'oggetto. Volendo schematizzare in breve questa tesi, essa è composta da una prima parte teorica contenente gli argomenti che ci servono per descrivere lo spazio acustico e le onde acustiche, una seconda parte riguardante i microfoni e i suoi vari parametri, una terza parte riguardante la teoria sull'elaborazione segnale nel dominio del tempo e delle frequenze e in particolare cenni sulla trasformata di Fourier. Nella parte successiva verranno descritti i due principali metodi di Beam-forming acustico trattando sia gli apparati di misura sia i due algoritmi, facendo sempre riferimento alle parti di teoria necessarie alla spiegazione del metodo. Infine nell'ultima parte della tesi verrà discusso in primo luogo la creazione del microfono virtuale, in particolare parleremo della sua sensibilità in funzione della direzione avvalendoci di uno schema che in letteratura viene denominato Beam-pattern, in secondo luogo parleremo di come creare la mappa 2D dove effettivamente possiamo vedere l'intensità sonora dell'onda proveniente da ogni punto dell'oggetto preso in considerazione.

The main goal of this research was to determine the feasibility of using electron beam irradiation as an alternative disinfestation technology while preserving the overall quality of mangoes, and to verify its suitability for the preservation shelf life of blueberries. Physicochemical and sensory characteristics of the fruits were evaluated. Mangoes were irradiated at 1.0, 1.5 and 3.1 kGy using a 10MeV (10 kW) linear accelerator (LINAC) with double beam fixture. Samples were stored at 12ºC and 62.7% RH for 21 days. Blueberries packed in plastic clamshell containers were irradiated at 1.1, 1.6 and 3.2 kGy doses using the same linear accelerator with a single beam. The shelf life of the berries stored at 5ºC and 70.4% RH was evaluated for 14 days. The firmness of mangoes irradiated at 1.5 and 3.1 kGy significantly (p > 0.05) decreased during storage. There was a reduction of total sugars (8.1% and 14.1%) in samples irradiated at 1.0 kGy and 1.5 kGy, respectively. All irradiated mangoes had significantly lower (50- 70 %) ascorbic acid content throughout storage. The phenolic compounds increased in samples irradiated at 1.5 kGy (27.4%) and 3.1 kGy) (18.3%). Sensory evaluation of the fruits irradiated with 3.1 kGy showed significantly less acceptability for overall quality, color, texture and aroma. Irradiation of blueberries at 1.1 kGy had no significant (p > 0.05) effect on the fruits' physicochemical characteristics with the exception of ascorbic acid which decreased by 17% after 14 days. A significant decrease in texture (firmness) of irradiated berries was observed during storage time. Total sugars decreased in all irradiated fruits while total phenolics and tannins increased (10 -20%). Sensory attributes of samples irradiated with 1.1 kGy and 1.6 kGy were found acceptable by the panelists. The high dose-treated fruits were considered unacceptable. The results from this research suggest that a 1.5 kGy is the best treatment to maintain the quality attributes of mangoes and increase the shelf life by three days. The electron beam irradiation of packed blueberries at doses of 1.1 and 1.6 kGy ensures and enhances the quality and the shelf life of blueberries up to 14 days.

Il presente lavoro prende le mosse da un problema di dinamica dei fasci relativo a un metodo di separazione di un fascio di particelle recentemente messo in funzione nell’sincrotrone PS al CERN. In questo sistema, variando adiabaticamente i parametri di un campo magnetico, nello spazio delle fasi si creano diverse isole di stabilità (risonanze) in cui le particelle vengono catturate. Dopo una parte introduttiva in cui si ricava, a partire dalle equazioni di Maxwell, l’hamiltoniana di una particella sottoposta ai campi magnetici che si usano negli acceleratori, e una presentazione generale della teoria dell’invarianza adiabatica, si procede analizzando la dinamica di tali sistemi. Inizialmente si prende in considerazione l’hamiltoniana mediata sulle variabili veloci, considerando perturbazioni (kick) dei termini dipolare e quadrupolare. In ognuno dei due casi, si arriva a determinare la probabilità che una particella sia catturata nella risonanza. Successivamente, attraverso un approccio perturbativo, utilizzando le variabili di azione ed angolo, si calcola la forza della risonanza 4:1 per un kick quadrupolare.

The recent improvement of additive manufacturing has allowed designers to achieve a level of complexity and customizability that is difficult or impossible to accomplish using traditional manufacturing processes. As a result, much research has been conducted on developing new methods to utilize the larger design space brought by additive manufacturing. One such research area is in the design of mesoscale lattice structures. Mesoscale lattice structures are a type of cellular structure with support element sizes on the order of magnitude of centimeters. These types of structures are engineered for high performance and have applications in industries where both low weight and high strength are desired. However, due to the small size of their struts, these structures can easily have hundreds to thousands of individual struts. As a result, design poses a unique challenge. Current methods approach design of mesoscale lattice structures as a topological optimization problem, treating each strut diameter in the structure as a design variable. For structures with a fewer number struts, these optimization methods can converge, but will generally be very time-consuming. For structures with a large number of struts, the optimization problem becomes too large for current algorithms to solve. In previous research, a new, highly efficient design method for mesoscale lattice structures was presented that eliminates the need for global size or topological optimization. This method, termed the Size, Matching and Scaling method, used a unique combination of a solid-body finite element analysis and a library of pre-defined lattice configurations, termed the "unit-cell library," to generate lattice topologies. The results from this method were highly promising: design time was significantly reduced when compared to optimization methods. Furthermore, lattices designed using the SMS method had performance results that were either comparable or better than their optimized counterparts. However, the method developed was highly conceptual, lacking a true systematic methodology for generating topologies and suffering from some gaps in implementation. In this research, we present a modified Size Matching and Scaling (SMS) design method. Firstly, we introduce and outline the modified methodology. This methodology particularly includes an optimization step for determining strut diameters that replaces the manual search used in the original method. Secondly, we expand and explore the unit-cell library in an attempt to improve the performance of lattices generated using the SMS method. In particular, we optimize several unit-cell configurations and compare their performance in the context of the SMS method. Finally, we test the updated SMS methodology and unit-cell library using various design examples. Results from the various example problems indicate that optimization is not only a viable systematic method for determining diameter values, but is actually preferred to the manual, iterative process used in the original method. Furthermore, various optimization algorithms and approaches yield different results. Between the two optimization algorithms utilized in this method: constrained optimization and least-squares minimization, constrained minimization converges faster, but least-squares minimization yields slightly improved performance results. In addition to these algorithms, a one-variable approach using an untested, simplifying assumption, dubbed the "28% approach," was tested. Results indicate that this assumption was incorrect and cannot be utilized. Finally, results from the expanded unit-cell library indicate that the best unit-cell configuration is still the same original unit-cell configuration utilized in the first SMS method. The addition of more unit-cell does not improve the performance of structures generated using the SMS method. In fact, both performance and design time worsen when additional configurations are utilized.

Gli artefatti da ricostruzione sono problemi comuni nella tomografia computerizzata con raggi X. Essi possono degradare la qualità di una immagine al punto da renderla inutilizzabile. Scopo dell’elaborato è l’analisi di diversi tipi di artefatti, a partire dai fenomeni che li causano, fino ad arrivare ai metodi impiegati per eliminarli o quantomeno ridurli. A tal fine si è proceduto ad una approfondita ricerca bibliografica e allo studio dei testi scientifici fondamentali riguardo all’argomento. Particolare attenzione è stata rivolta al fenomeno fisico del Beam Hardening, che è tra le maggiori cause di artefatti grafici, e di cui si sono viste diverse metodologie di correzione. Sono stati poi trattati gli artefatti dovuti all’apparato di misura e gli artefatti dovuti al paziente. Per quanto riguarda le tecniche di correzione, oltre ai procedimenti di più vecchia concezione e ormai consolidati, si è dato largo spazio alle metodologie innovative, di recente applicazione e ancora oggetto di studio e ricerca, come la Dual-Energy CT e la ricostruzione iterativa. Si è visto come la ricostruzione iterativa garantisca risultati di gran lunga superiori in merito alla qualità dell’immagine ricostruita, rispetto alla canonica Filtered Back-Projection, in particolare per quanto riguarda la Low-dose CT, di grande interesse in campo medico.