Letteratura scientifica selezionata sul tema "Geometridae Behavior"

Cobîleni Natural Forest Reserve with a surface of 33.5 ha is situated near Lopatna village, Orhei district, on the right bank of the Dniester River. The aim of the study was to assess the geometrid moths (Lepidoptera, Geometridae) fauna from this reserve. The most part of entomological materials from Cobîleni Natural Forest Reserve discussed in this paper were collected at the light trap during vegetation period of 2018. In the paper the list of fifty-five geometrids species is given, also their geographical distribution, ecological and trophic structure. The geometridae species collected from this reserve belong to five subfamilies. Most of the captured specimens belong to the Ennominae subfamily with 36 species, as it is typical for mesophilous meadows, followed by Sterrhinae with nine species, then Larentiinae with eight, and finally Orthostixinae and Geometrinae with only one species each. In the result of establishing of taxonomic affiliation of the entomological material collected during 2018, a new geometrid species for the fauna of the Republic of Moldova was identified: Cyclophora linearia.

The genus Hissarica Viidalepp (Geometridae, Geometrinae) is restored from synonymy with Xenochlorodes Warren. The moths and their male and female genitalia are illustrated and characterized in comparison with those of Hierochthonia Prout and Xenochlorodes. Taxonomic positions of “Hierochthonia” alexandraria Prout and Eucrostes petitaria Christoph are discussed and the new genus Ratsa Viidalepp & Kostjuk gen. nov. is established for them, creating the new combinations Ratsa alexandraria Prout and Ratsa petitaria Christoph.

A list of 247 species of Geometrid moths from 5 subfamilies (Archiearinae – 3 species, Ennominae – 70 species, Geometrinae – 9 species, Larentiinae – 132 species, Sterrhinae – 33 species) from the territory of Tyumen Region (including Yamalo-Nenets Autonomous Okrug and Khanty-Mansy Autunomous Okrug) is given. 86 species are reported for the first time. The historical overview of the Geometridae study in the Tyumen Region provided.

The genus Pyrochlora Warren is revised and three new species are described: P. motilonia, sp. nov. from Costa Rica and Nicaragua, P. kuklase, sp. nov. from mountainous Ecuador, and P. vogli, sp. nov. from Northern Venezuela. Wings pattern and genitalic structures of all five species are described and illustrated.

The magnetic behaviour in nanoscale structures is of great interest for the fundamental understanding of magnetisation processes and also has importance for wide ranging technological applications. This thesis examines mechanisms for the enhanced control of domain walls in these structures via focussed ion beam modifications to magnetic nanowires and through the inclusion of periodic geometrical modifications to the nanowires geometry. A detailed investigation into the effect of focussed ion beam irradiation on the structure of NiFe/Au bilayers was performed through x-ray reflectivity and fluorescence techniques. This analysis revealed the development of interfacial intermixing with low dose irradiation. This is associated with complex changes of the magnetic behaviour including a rapid decrease, followed by a recovery of the saturation magnetisation with low dose irradiation. This behaviour is attributed to changes in the local environment of the atoms at the interface; resulting in modifications to the magnetic moment on Ni and Fe. The development of an induced moment on Au and a change in the spin-orbit interaction is also suggested. Localised control of the magnetic properties in nanowires demonstrates the ability to manipulate domain walls in these structures. Here, irradiated regions provide pinning sites where the width and dose of the irradiated region give control over the pinning potential. The inclusion edge modulation to nanowires geometry provides additional control over their magnetic behaviour. The direct magnetisation reversal field of these structures is explained by an analytical model based on the torque on the spins following the modulated wire geometry. This model is scalable for different modulation parameters and combines with the effect of localised regions of orthogonal anisotropy along the wire; explaining the reversal behaviour over the entire parameter space. Domain wall mediated reversal in modulated wires was also investigated in these structures. The inclusion of modulation shows an improvement in dynamic properties by the suppression of Walker breakdown. This is due to the relationship between geometrical modulations and the periodicity of micromagnetic domain wall structural changes during the Walker breakdown process. The combination of this work shows a route to the optimisation of the dynamic properties whilst minimising the detrimental increase in the de-pinning field from the modulation.

The thermal properties of fabric are an important factor in the understanding of the thermo-physiological comfort of clothing. The principal aim of this research was to develop novel numerical methods, Graphical User Interface (GUI) plug-ins and experimental setup to evaluate the effective thermal conductivity and thermal resistance of different textile structures which has significant impact on the thermal comfort of clothing. The numerical methods also include the analysis of the effect of fibre orientation, thermal anisotropy of fibre, temperature dependent thermal conductivity and fibre volume fraction on the effective thermal conductivity and thermal resistance of textile fabrics. The research covers the development of geometrical models of woven, knitted, nonwoven and the composites fabric structures, evaluation of their thermal properties by using finite element method, creation of user friendly plug-ins and the extended application tools. Micro and mesoscopic scale modelling approaches were used to investigate the effective thermal conductivity and thermal resistance of textile structures. Various techniques, including scanning electron microscopy, x-ray microtomography and experimental method have been adopted to obtain the actual 3D dimensional parameters of the fabrics for finite element analysis. Research revealed that, the thermal anisotropy of fibres, fibres material orientation and temperature dependent thermal conductivity of fibre have significant impact on the effective thermal conductivity of fabrics because experimental and simulated results were highly correlated with the consideration of above mentioned factors. In addition a unique technique has been developed in modelling fabric coated by microencapsulated phase change material for temperature stable textile and clothing system. User friendly GUI plug-ins have been developed to generate both microscopic and mesoscopic scale models for finite element analysis. The plug-ins were developed by using Abaqus/CAE as a platform. The GUI Plug-ins enable automatic model generation and property analysis of knitted fabrics and composites. Apart from finite element analysis of various fabric structures, an experimental device has been developed for testing thermal conductivity of fabrics which is capable of testing small sample size within very short period of time. The device was validated by commercial available apparatus for testing of fabric thermal conductivity.

Dissertation (Ph. D.)--University of Akron, Dept. of Polymer Engineering, 2007.
"May, 2007." Title from electronic dissertation title page (viewed 04/07/2008) Advisor, Erol Sancaktar; Committee members, Avraam I. Isayev, Sadhan C. Jana, Darrell H. Reneker, Shing-Chung Wong; Department Chair, Sadhan C. Jana; Dean of the College, George R. Newkome; Dean of the Graduate School, George R. Newkome. Includes bibliographical references.

O estudo do comportamento espectral de culturas agrícolas, por meio da radiometria de campo, contribui para a obtenção de uma maior precisão nos modelos gerados pelo sensoriamento remoto, quando utilizados na estimativa e análise de variáveis agronômicas de culturas. Tendo em vista que os sensores a bordo de satélites podem adquirir imagens sob diferentes ângulos de visada e em diferentes horários de passagem, torna-se necessário o conhecimento do efeito dessas variáveis sobre a resposta espectral das culturas. A presente pesquisa teve como objetivo avaliar a influência de três ângulos de visada (0º, 30º e 45º) e três horários de medição (10 horas, 12 horas e 14 horas), o que implica em diferentes ângulos de elevação solar, na resposta espectral da cultura de feijão, como também nas relações entre o índice de área foliar (IAF) e o Índice de Vegetação Diferença Normalizada (NDVI). O experimento foi conduzido na “Fazenda Areão”, pertencente à Escola Superior de Agricultura 'Luiz de Queiroz' (ESALQ/USP), Piracicaba, SP, de março a junho de 2005. O delineamento experimental foi o de blocos ao acaso, com parcelas subdivididas, constituído de três blocos, três tratamentos primários referentes aos horários de leitura e três tratamentos secundários relacionados ao ângulo de visada. Foram realizadas nove campanhas de medição no campo, com o espectroradiômetro SPECTRON SE-590. Dos fatores de reflectância (FR) determinados, simularam-se as bandas TM3 e TM4 e, a partir destes, foram gerados os índices de vegetação. De acordo com os resultados obtidos, concluiu-se que a variação do horário de medição não proporcionou variação significativa sobre os valores do FR nas bandas TM3 e TM4. Já a variação do ângulo zenital de visada influenciou significativamente, ao nível de 5 % de probabilidade, o FR nas bandas TM3 e TM4, para todos os dias de leitura. Quanto às relações IAF e NDVI, o modelo linear apresentou melhores ajustes, estatisticamente significativos (p≤0,05).
The study of the spectral behavior of crops, through field radiometry, contributes to a better precision in models generated by remote sensing, when they are used to estimate and analyze crops’ agronomic variables. Once sensors aboard of satellites are able to acquire images under different viewing angles and at different times of the day, it is necessary to understand the effect of such variables on the crops’ spectral response. The objective of this research was to evaluate the influence of the viewing angles (0º, 30º and 45º) and three radiometric acquisition times (10:00 a.m, 12:00 a.m and 2:00 p.m), related to different sun elevation angles, on the spectral behavior of bean crop, as well as on the relationship between Leaf Area Index (LAI) and Normalized Difference Vegetation Index (NDVI). The experiment was installed in the “Fazenda Areão”, of the ESALQ/USP, in Piracicaba, SP, from March to June, 2005. The experimental design was the randomized blocks, with split plots, with three blocks, three primary treatments (acquisition times) and three secundary treatments (viewing angles). Nine field campaigns were carried out with the SPECTRON SE-590 spectroradiometer. Bands TM3 e TM4 were simulated from the determined reflectance factors and, with these bands, vegetation indices were generated. According to the results, it was concluded that the variation on acquisition time did not lead to a significant variation on the reflectance factors in the TM3 and TM4 bands. On the other hand, the variation in the viewing angle significantly affected (p≤0,05) the reflectance factor in the TM3 and TM4 bands, for every day of measurement. Regarding the relationships between LAI and NDVI, the linear model showed the best fit (p≤0,05).

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Este trabalho teve o propósito de determinar o comportamento dos gases na seção de radiação de um combustor de ar que pertence a uma planta industrial. O corpo metálico do equipamento rompeu em seu primeiro ano de operação, devido a um problema conceitual em sua geometria. A fluidodinâmica computacional (CFD), por meio do método dos volumes finitos, foi utilizada para desenvolver um modelo tridimensional que pudesse reproduzir o perfil de temperatura e o comportamento do fluxo do ar de combustão no equipamento. Na simulação, através do uso do software ANSYS CFX, foram utilizados: (i) o modelo de turbulência Reynolds Stress Model (RSM); (ii) as malhas hexaédrica, tetraédrica e prismática; (iii) o modelo de radiação P-1; e (iv) o modelo de combustão Eddy Dissipation Concept (EDC). Como resultado, foram apresentadas quatro possíveis mudanças na geometria do combustor de ar que, caso adotadas, eliminariam os riscos de novas falhas e garantiriam a continuidade operacional da unidade de processo.
This paper has the objective to describe the behavior of the flow and temperature of the flue gas in the radiation section of the vessel used to preheat air in a combustor. The equipment failed in its first operational year, due to a conceptual problem in its geometry. The CFD code based on finite volume method was applied to simulate the physical model of combustor using the ANSYS CFX software, reproducing the main features of the preheater. The simulation had considered: (i) Reynolds Stress Model (RSM) as turbulence model, (ii) The meshes applied were the hexahedral, tetrahedral and prismatic, (iii) P-1 was used as the radiation model and (iv) Eddy Dissipation Concept (EDC) as combustion model. Through the simulation was possible to propose four different kind of combustor geometry modification, that the application of anyone of them would eliminate the risk of new failures, ensuring the unit production availability.

The morphological properties of rock fractures may have a significant influence on their hydromechanical behaviour. Fracture surface roughness could change the fluid flow regime from laminar to turbulent, while it causes the flow properties to deviate from cubic law for smooth channels due to a change in fracture equivalent hydraulic aperture. Different empirical (including the well known Joint Roughness Coefficient, JRC) and statistical methods have been proposed for surface roughness characterisation in an attempt to link them to the hydromechanical behaviour of fractures.This thesis aims to investigate the potential for assessment of fluid behaviour by studying its surface geometrical properties. D[subscript]R[subscript]1 and D[subscript]R[subscript]2, the 2D and 3D roughness parameters developed recently using Riemannian geometry, were used to correlate fracture geometry to its flow behaviour. Also, the 2D Riemannian isotropy parameter (I[subscript]R[subscript]2) was used to correlate surface roughness anisotropy with directionality in fluid flow behaviour along different directions.Numerical simulations in both 2D and 3D were performed assuming the laminar flow regime using FLUENT software. This assumption is, to a large extent, acceptable for situations where the height to length ratios of a fracture is very small. 2D analysis of synthetic profiles with different geometries demonstrated how a change in profile roughness can affect flow response, for example, the pressure drop. JRC flow channels developed in this work as combinations of pairs of JRC profiles were simulated numerically. The analysis results indicated that channels with a similar JRC average for the upper and lower walls but a different JRC profile number responded differently when they were subjected to fluid flow. Therefore, assuming special fluid properties, correlations developed using the pressure drop of a fracture can be estimated by its analogy to JRC flow channels.3D simulations of a corrugated plane were performed assuming different asperity height distributions, for fluid travelling along different directions with respect to surface geometry and at different shear displacements. No asperity contact and failure is assumed in the analysis performed in this work. D[subscript]R[subscript]2 analysis results of the corrugated plane indicated how fluid flow could be related to surface geometry. For instance, it was observed that the pressure drop was maximised along the direction of maximum roughness and reduced to its minimum along a perpendicular direction which shows anisotropy in fluid flow behaviour. Significant changes in pressure drop due to shear offset indicated the importance of fracture wall displacements with respect to each other. A detailed analysis of one synthetically generated surface, and also five surfaces with identical statistical parameters except their correlation distances being different, further confirmed the above concepts. This was followed by analysing a real rock like fracture which was studied elsewhere for fracture shear tests in the lab. Simulation of this surface was performed with particular interest in identifying the locations where the velocity magnitude reduced to nearly zero after the fracture was subjected to a shear offset corresponding to maximum shear stress. These areas were found to be very similar to the locations of asperity degradations as observed through lab experiments. The roughness analysis of the surface was in agreement with the correlation found between the mechanical and hydraulic behaviour of the surface.The results of this research demonstrate how detailed analysis of surface geometry could provide valuable information with respect to surface flow behaviour. Detailed discussions and interpretations of the results will be presented and various conclusions will be made.

Cette thèse introduit le concept de comportement géométrique d'un assemblage mécanique. Cette notion permet de rendre compte du caractère assemblable ou mobile d'un mécanisme sous la forme d'un système de relations algébriques entre les paramètres géométriques permettant de le décrire. Dans un premier temps, cette thèse montre l'intérêt de ce concept pour traiter des problèmes faisant intervenir plusieurs effets physiques et plusieurs scénarios d'utilisation. Ce chapitre est appliqué à l'étude de l'assemblabilité d'un treillis pyramidal de conception à 4 barres décrit par un modèle géométrique non cartésien issu de la littérature. Dans un second temps, après avoir constaté le manque de modèles adaptés permettant de représenter des mécanismes mobiles, ce travail en propose un non cartésien. Il détaille aussi une méthode de mise en équation afin de traduire la mobilité d'un mécanisme. Une application de ce modèle et de la méthode est également faite. Elle permet de résoudre localement le problème de la mobilité d'un mécanisme de Bennett. Enfin, la dernière partie de ce travail expose une solution pour associer et comparer deux objets décrits par des représentations non cartésiennes. Cette technique est utile pour comparer deux états physiques du même objet utilisé dans différents scénarios pour assurer le suivi d'une exigence géométrique. Elle peut également être utilisée pour associer des objets réels et des objets idéalisés pour traiter des problèmes de tolérancement

Since ancient times, master builders have used arches to cover large spans in masonry structures. As a consequence, nowadays the safety assessment of these structural elements plays a fundamental role in the conservation of built cultural heritage. Due to their frequent occurrence, support displacements are one of the primary sources of damage for masonry arches. Among the potential causes of support displacements, slow-moving landslides have received very little attention from the scientific community. The present thesis is motivated by the observation of extensive and severe damage in the arches of historic masonry churches exposed to slow-moving landslides. These phenomena produce a combination of vertical and horizontal supports displacements, whose effect on the arch structural behaviour has never been thoroughly investigated in the literature, especially in the framework of large displacements. In view of the above, this thesis aims at providing a full understanding of the mechanics of masonry arches subjected to large support displacements, with special attention to inclined displacements. The methodology used to accomplish this goal included both experimental tests and numerical analyses on a segmental scaled dry-joint masonry arch subjected to different combinations of horizontal and vertical support displacements. The numerical simulations were carried out in the framework of large displacements using two different numerical approaches based on finite element (FE) and rigid block (RB) modelling. A micro-modelling strategy was adopted, where the arch was modelled as an assemblage of voussoirs, very stiff and infinitely resistant in compression in the FE model and rigid in the RB model, interacting at no-tension friction interfaces. Preliminary numerical simulations, aimed at designing the experimental set-up and gaining a first insight in the arch response, were carried out considering the arch as a rigid-no tension structure. To this aim, a very large value of interface normal stiffness was adopted in the FE model. A large experimental campaign was performed on a 1:10 small-scale model built as a dry-joint assemblage of voussoirs made of a bicomponent composite material. The results of the tests allowed, for the first time in the literature, to accurately assess the effect of the direction of the imposed support displacements on the arch response in the framework of large displacements. The comparison between numerical and experimental results showed that the numerical models were not able to accurately predict the experimental response. To investigate this discrepancy, a sensitivity analysis on the effect of the interface normal stiffness on the FE predictions was performed. The results demonstrated that the difference between numerical and experimental results could be attributed due to the imperfections, and resulting deformability, of the joints of the physical model. A strategy to include imperfections in the numerical modelling, consisting in calibrating the interface normal stiffness based on the experimental results, was thus proposed and validated by performing further FE simulations, whose results were in very good agreement with the experimental evidence. Finally, to investigate the effect of geometrical imperfections on the arch response, a further experimental test was performed on a physical model made of bicomponent composite voussoirs exhibiting more imperfections. The test was simulated using a FE calibrated model to further validate the strategy proposed to model imperfections. The comparison between the experimental results for the two tested physical models showed that imperfections play a fundamental role in the response of small-scale arches to large support displacements. Furthermore, reducing the interface normal stiffness with respect to the large value adopted to model rigid interfaces proved to be an effective strategy to simulate the amount of imperfections of the experimental models.
Desde la antigüedad, los maestros constructores han utilizado el arco como elemento estructural para salvar grandes luces en estructuras de mampostería. En consecuencia, para la conservación del patrimonio arquitectónico es hoy en día de fundamental importancia la correcta verificación estructural de este tipo de elementos. Se ha observado frecuentemente que el desplazamiento de los apoyos es una de las principales causas de daño en arcos de mampostería. De entre las distintas causas que pueden provocar dicho desplazamiento, el deslizamiento de tierras ha recibido poca atención por parte de la comunidad científica. La presente tesis encuentra su motivación en el daño extenso y severo observado en los arcos de las iglesias de mampostería ubicadas en zonas expuestas a deslizamiento de tierras. Este fenómeno produce una combinación de desplazamientos verticales y horizontales, cuyo efecto en el comportamiento estructural de los arcos no ha sido investigado en profundidad, especialmente en lo relativo a grandes desplazamientos. Esta tesis aspira a contribuir al conocimiento del comportamiento mecánico de los arcos de mampostería sometidos a grandes desplazamientos de apoyos, con especial atención a los desplazamientos inclinados. La metodología utilitzada para dicho fin incluye ensayos experimentales y análisis numéricos en un modelo a escala de un arco de mampostería a junta seca. El modelo fue ensayado bajo diferentes combinaciones de desplazamientos horizontales y verticales en uno de sus apoyos. La simulación numérica fue desarrollada en el marco de grandes desplazamientos usando dos métodos numéricos diferentes: un modelo de elementos finitos (FE) y un modelo de bloques rígidos (RB). Los modelos fueron concebidos como un conjunto de dovelas rígidas con infinita resistencia a compresión en el modelo FE y como dovelas infinitamente rígidas en el modelo RB. En ambos modelos la interfaz entre dovelas fue modelada sin resistencia a tracción. Con el objetivo de diseñar la configuración experimental y adquirir una comprensión inicial de la respuesta del arco, se llevaron a cabo simulaciones numéricas preliminares en las cuales se consideró al arco estudiado como una estructura rígida. Para ello en el modelo FE del arco, la rigidez normal de la interfaz fue inicialmente caracterizada con un valor muy elevado. La campaña experimental fue llevada a cabo en modelos a escala 1:10. Los resultados de los ensayos experimentales permitieron, por primera vez en la literatura, un análisis preciso del efecto que tiene la dirección del desplazamiento impuesto en el comportamiento del arco en marco de grandes desplazamientos. La comparaci ón entre los resultados numéricos y experimentales mostró que los modelos numéricos no eran capaces de capturar de manera precisa la respuesta experimental. Para investigar esta discrepancia, se realizó un estudio de sensibilidad relativo al efecto de la rigidez normal de la interfaz sobre las predicciones del modelo FE. Los resultados demostraron que la diferencia entre los resultados numéricos y experimentales se debía a las imperfecciones de las juntas del modelo físico. Como consecuencia, se propuso la inclusión de imperfecciones en el modelo numérico. Para ello se calibró la rigidez normal de la interfaz según los resultados experimentales y el modelo se validó con nuevas simulaciones. Finalmente, con el fin de investigar el efecto de las imperfecciones en la respuesta del arco, se llevó a cabo otro ensayo con el mismo modelo experimental, pero añadiéndole imperfecciones. El ensayo fue simulado con un modelo calibrado FE. Los resultados obtenidos mostraron que las imperfecciones juegan un rol fundamental en la respuesta de arcos a pequeña escala con grandes desplazamientos en los apoyos. Además, la reducción de la rigidez normal de la interfaz con respecto al valor muy elevado inicialmente adoptado demostr ó ser una estrategia efectiva para simular las imperfecciones de los modelos experimentales.
Fin dall’antichità, i maestri costruttori hanno utilizzato gli archi per coprire grandi luci nelle strutture in muratura. Di conseguenza, ad oggi la valutazione della sicurezza di questi elementi strutturali gioca un ruolo fondamentale nella conservazione del patrimonio architettonico. A causa del loro frequente verificarsi, gli spostamenti degli appoggi sono una delle principali fonti di danno per gli archi in muratura. Tra le potenziali cause di questi spostamenti, le frane a cinematica lenta hanno ricevuto pochissima attenzione da parte della comunità scientifica. La presente tesi è motivata dall'osservazione di danni ingenti negli archi di chiese storiche in muratura interessate da frane a cinematica lenta. Questi fenomeni producono una combinazione di spostamenti verticali e orizzontali agli appoggi, il cui effetto sul comportamento strutturale dell'arco non è mai stato studiato a fondo in letteratura, soprattutto nell’ambito di grandi spostamenti. Alla luce di queste osservazioni, questa tesi si propone di fornire una piena comprensione della meccanica degli archi in muratura soggetti a grandi spostamenti degli appoggi, con particolare attenzione agli spostamenti inclinati. La metodologia utilizzata per raggiungere questo obiettivo ha incluso sia prove sperimentali che analisi numeriche su un arco ribassato in muratura di giunti a secco in piccola scala, in cui sono state applicate diverse combinazioni di spostamenti orizzontali e verticali in corrispondenza di un appoggio. Le simulazioni numeriche sono state eseguite nell’ambito dei gradi spostamenti utilizzando due diversi approcci numerici basati su una modellazione ad elementi finiti (FE) ed una modellazione a blocchi rigidi (RB). È stata adottata una strategia di micro-modellazione, in cui l'arco è stato modellato come un assemblaggio di blocchi, molto rigidi e infinitamente resistenti a compressione nel modello FE e infinitamente rigidi nel modello RB. In entrambi i modelli i blocchi erano collegati da interfacce senza resistenza a trazione. Simulazioni numeriche preliminari, finalizzate a progettare il set-up sperimentale e ad acquisire una prima conoscenza della risposta dell'arco, sono state eseguite considerando l'arco come una struttura rigida non resistente a trazione. A tal fine, nel modello FE è stato adottato un valore molto elevato di rigidezza normale delle interfacce. Un’ampia campagna sperimentale è stata eseguita su un modello in scala 1:10 costruito come un assemblaggio a secco di blocchi realizzati con un materiale composito bicomponente. I risultati delle prove sperimentali hanno permesso, per la prima volta in letteratura, di valutare con precisione l'effetto della direzione degli spostamenti imposti sulla risposta dell'arco nell’ambito dei grandi spostamenti. Il confronto tra i risultati numerici e sperimentali ha mostrato che i modelli numerici non erano in grado di cogliere in maniera accurata la risposta sperimentale, specialmente in termini di spostamento ultimo al collasso. Al fine di indagare le ragioni di questa discrepanza, è stata quindi eseguita un'analisi di sensitività relativa all’effetto della rigidezza normale delle interfacce sulle previsioni del modello FE. I risultati hanno dimostrato che la differenza tra risultati numerici e sperimentali poteva essere attribuita alle imperfezioni, e conseguente deformabilità, delle interfacce del modello fisico. Una strategia per includere le imperfezioni nella modellazione numerica, consistente nel calibrare la rigidezza normale delle interfacce sulla base dei risultati sperimentali, è stata quindi proposta e validata attraverso ulteriori simulazioni FE, i cui risultati si sono rivelati in ottimo accordo con le evidenze sperimentali. Infine, per indagare l'effetto delle imperfezioni geometriche sulla risposta dell'arco, è stata eseguita un’ulteriore prova sperimentale su un modello fisico costituito da blocchi dello stesso materiale composito bicomponente che presentavano però più imperfezioni. Al fine di validare ulteriormente la strategia proposta per modellare le imperfezioni, la prova sperimentale è stata simulata utilizzando un modello FE calibrato. Il confronto tra i risultati sperimentali per i due modelli fisici ha mostrato che le imperfezioni giocano un ruolo fondamentale nella risposta di archi in piccola scala a grandi spostamenti degli appoggi. Inoltre, ridurre la normale rigidezza dell'interfaccia rispetto al valore molto alto adottato per modellare interfacce rigide si è rivelata una strategia efficace per simulare la quantità di imperfezioni dei modelli sperimentali
Enginyeria de la construcció

AbstractNumerical simulations for blood flows related to cardiovascular diseases are presented. Differences in vessel morphologies produce different flow characteristics, stress distributions, and ultimately different outcomes. Some examples illustrating the effects of curvature and torsion on blood flows are presented both for simplified and patient-specific simulations. The goal of this study is to understand relationships between geometrical characteristics of blood vessels and blood flow behaviors.

Abstract A finite element analysis model was developed to predict flexural behavior of thick composites with uniform, graded and localized fiber waviness. In the analyses, material and geometrical nonlinearties due to fiber waviness were incorporated into the model utilizing energy density and an incremental method. In the model, two kinds of geometrical nonlinearity were considered, one due to reorientation of fibers and the other due to difference of curvatures from one finite element to another during deformation. The finite element analyses utilize the iterative mapping method to incorporate these geometrical nonlinear factors. The model was used to predict not only the flexural behavior of a flat thick composite plate but also of a thick composite plate with initial curvature. Flat composite specimens with various degrees of fiber waviness were fabricated and four-point flexural tests were conducted. The predicted nonlinear behavior by the current model was compared with results from the thin slice model [7] and experiments. Good agreement was observed among them.

This paper presents a new built-up beam-column joint with a spacer employed between channel sections under monotonic loading to study its static behavior. A validated finite element model was used to simulate the cold-formed steel (CFS) joint's moment-rotation behavior and failure mode by utilizing ABAQUS. It accounts for both material and geometrical nonlinearity. The model was further adopted to investigate the influence of bolt arrangement, spacing of intermediate connecting plates, diaphragms and various beam-column stiffness ratios on the joint behavior. The results indicate that the bolt arrangement and spacing of intermediate connecting plates have little influence on the joint performance. The internal vertical diaphragm can be adopted for the built-up beam-column joint, and diaphragm thickness should not be less than spacer thickness. The critical beam-to-column stiffness ratio is determined to be 0.38.