Investigación experimental del colapso en suelos eólicos: un caso de estudio en Mayapo Colombia

The principal target of this research is to focus on the study of the volumetric behavior of the eolian soil and the influence of the geology, the soil structure, and suction on possible collapse behaviour of the eolian soils. An experimental program of laboratory tests was designed including geotechnical classification tests, Micro-structure tests, suction measurement, and oedometer tests included classical and unsaturated in order to know the characteristics and properties of the eolian soils. There are large and continuous macropores between grains and a low amount of micropores. The macropores could control the volumetric behaviour of the eolian soils. The salt concentration influences the osmotic suction and the total suction of the eolian soil, affecting its hydraulic condition. It can govern the water flow and attract more water to the soil, increasing the saturation degree, causing a decrease in total suction in the soil. The collapse potential of the eolian soils was classified as a moderated problem. The collapse potential increase with the increment of the initial void ratio. As suction decreases and soil wets, water menisci between liquid and vapour phase disappears, and the empty pores are flooded, and it causes a loss in the soil stiffness. The unsaturated oedometer tests allowed to understand the influence of suction on the volumetric behaviour of the eolian soils. A constitutive model was proposed to describe the volumetric behaviour of the eolian soil. The model is represented by a Loading Collapse (LC) curve, and to allow knowing the reversible compressive volumetric strains for any stress path of loading (L), collapse (C), or both in the elastic domain and to predict irreversible compressive volumetric strain for any stress loading or collapse paths. There is an important dependence of collapse and loading paths in the volumetric behaviour of the eolian soils. The deformations are very small at suction changes. The soils will suffer higher deformations in loading paths at low suction levels due to the soil stiffness is less.El objetivo principal de esta investigación es centrarse en el estudio del comportamiento volumétrico del suelo eólico y la influencia de la geología, la estructura del suelo y la succión en el posible colapso de los suelos eólicos. Se diseñó un programa experimental de ensayos de laboratorio que incluye ensayos de clasificación geotécnica, ensayos de visualización de la microestructura, medición de succión y ensayos edométricos convencionales realizados con el procedimiento clásico de la norma y ensayos edométricos no saturados, para conocer las características y propiedades de los suelos eólicos. La investigación experimental se realizó sobre muestras inalteradas del suelo eólico de Mayapo, Colombia. La geología se estudió mediante secciones delgadas y DRX, y la estructura del suelo de los suelos eólicos se caracterizó mediante un microscopio electrónico de barrido. La distribución de los elementos se analiza mediante EDS por difracción de energía dispersiva. La succión y succión total se mide por el método de filtro de papel y la succión osmótica por la conductividad eléctrica del agua de los poros del suelo. El comportamiento volumétrico se estudia mediante edómetro doble y edómetro a diferentes esfuerzos verticales efectivos para conocer el potencial de colapso y la carga donde el suelo sufre más colapso. Se desarrollaron pruebas de edómetro controladas por succión. Las pruebas experimentales incluyeron un aumento en la tensión neta vertical a niveles de succión constantes y variaciones en las trayectorias de tensión y succión. El principal aspecto analizado fue el comportamiento volumétrico a los niveles de succión, el límite elástico generado por el aumento de la tensión neta vertical o el aumento de los niveles de succión. El suelo eólico fue clasificado como arena limosa (SM) pobremente graduada, con muy bajo porcentaje de finos. Los principales minerales del suelo eólico de Mayapo son el cuarzo, las plagioclasas y los feldespatos. Además, hay partículas de sal en el suelo y materiales de unión de óxido de hierro y aluminio que bordean los granos. El suelo presenta gran cantidad de macroporos entre los granos y una pequeña cantidad de microporos. Los macroporos podrían controlar el comportamiento volumétrico de los suelos XXI eólicos. la presencia de estos se demuestra en la doble curva de retención de agua (WRC), donde se demuestra que el suelo presenta bajos niveles de succión y su comportamiento está controlado por macroporos del suelo. La concentración de sal influye en la succión osmótica y la succión total del suelo eólico, afectando su condición hidráulica. Puede gobernar el flujo de agua y atraer más agua al suelo, aumentando el grado de saturación, provocando una disminución de la succión total en el suelo. Este cambio en el componente de succión influye en el comportamiento de colapso de los suelos eólicos estudiados, aumentando la deformación al disminuir la succión. El potencial de colapso de los suelos eólicos se clasificó como un problema moderado. El potencial de colapso aumenta con el incremento de la proporción de vacíos inicial. La succión también juega un papel importante en el potencial de colapso. A medida que la succión disminuye y el suelo se humedece, los meniscos de agua desaparecen y los poros vacíos se inundan, lo que provoca una pérdida de rigidez del suelo. Las pruebas en el edómetro no saturado permitieron comprender la influencia de la succión en el comportamiento volumétrico de los suelos eólicos. El componente de succión en el suelo hace que este soporte una mayor tensión aplicada: cuanto mayor es la succión, mayor es la tensión que se puede sostener antes del rendimiento. La succión aumenta la rigidez de los suelos eólicos. Se utilizó el Modelo Básico de Barcelona, propuesto por Alonso et al, 1999, para describir el comportamiento volumétrico de los suelos eólicos de Mayapo, Colombia. El modelo está representado por una curva de colapso de carga (LC) y permite conocer las deformaciones volumétricas compresivas reversibles para cualquier trayectoria de carga (L), colapso (C) o ambos en el dominio elástico y para predecir deformaciones volumétricas compresivas irreversibles. para cualquier carga de tensión o rutas de colapso. Existe una dependencia importante de las rutas de colapso y carga en el comportamiento volumétrico de los suelos eólicos. Las deformaciones son muy pequeñas en los cambios de succión. Los suelos sufrirán mayores deformaciones en los caminos de carga a bajos niveles de succión debido a que la rigidez del suelo es menor. Finalmente, se propuso un procedimiento experimental para el muestreo y caracterización del comportamiento volumétrico de suelos eólicos no perturbados.MaestríaMagister en ingeniería geotecniaSuelos no saturado

Fatigue Life Prediction For Small Component Welds

Almost all mechanical structures that adopts weld joints as connection method is susceptible to fatigue failure when operating load is applied repeatedly. In semi-automatic honeycomb cookies dipping machine, the weld components connecting rose-shaped mould to the moulding frame becomes the most critical location in the structure since the mould tend to be detached from the frame after long operational time resulting in reduction of manufacturing quantity. The suspected causes of this problem are due to vibration fatigue and thermal fatigue. Vibration fatigue is resulting from repetitive shaking process whereas thermal fatigue resulting from repetitive thermal changes during dipping and frying process. By applying finite element method (FEM) using ANSYS Mechanical software, simulations for both scenarios have been conducted to study the fatigue behavior of weld components on moulding frame structure. At the end of this study, the results show that the thermal fatigue is the main factor to the failure that occurs on the weld components. The maximum stress that occurs on the moulding frame structure due to vibration is 12.6 MPa. The stress magnitude is too low to induce fatigue damage since it far below the fatigue endurance limit of materials applied. The results for thermal fatigue analysis show that the moulding frame with 4 weld joints is the most critical in the whole moulding frame structure. The minimum fatigue life for this model is 21 cycles of dipping and frying process. Furthermore, the graphical approach of fatigue life prediction at any stress value has been achieved by plotting the stress-life (S-N) results for all moulding frame models. An experimental study will be required to support the reliability of the results obtained from the simulation since a few parameters that naturally occur on experimental approach such as welding flaws cannot be included in simulation

Contributions to aerostructures morphing with piezoelectric actuators

Since the first models developed in the late 19th century, the applications of piezoelectric materials have been progressively growing in number. The capacity of these materials to couple electric and mechanic fields makes them perfect candidates in the study of geometrical morphing. Their application in aeronautical products has been traditionally seen from two different perspectives: their use as sensors and as actuators. Both functions present potential benefits and improvements with promising applications. While the investigations in the past years focused mainly in the analysis and integration of piezoelectric materials in structures as means of implementing what is known as structural health monitoring systems, the application of this type of materials as actuators in the geometrical control of structures also awakes interest in the scientific community. In its present state of development, the technology for morphing of structures using piezoelectric actuators is not yet advanced enough as to integrate such systems in commercial products. However, the field is in continuous development and the evolution of the materials and the integration solutions bring the technology closer to industrial application. This thesis aims at studying the feasibility of application of piezoelectric-actuated morphing aeronautical structures in current aircraft concepts. The analysis is performed at theoretical and experimental levels analyzing the static and dynamic performance of currently available actuators and motion amplification technologies. The research presented in this thesis is directed in two different applications of utilization of the actuators: as static actuators producing deformation of the aerodynamic surface and as dynamic actuators controlling a classic aerodynamic control surface. In each of the applications a different type of piezoelectric actuator architecture has been used: a piezoelectric patch has been selected for static morphing applications and a piezoelectric stack-based actuation system for the dynamic control of the conventional control surface. The static experiments performed aimed at demonstrating the suitability of piezoelectric actuators as morphing devices. This analysis was performed analyzing the deflections produced in the trailing edge of an aerodynamic profile. The analysis of the obtained experimental results showed promising results as the actuating configurations managed to perform as designed. The static experiments showed substantial deformation of the trailing edge of the wing profile making this configuration mature enough for further experimentation such as wind tunnel testing. The deflections produced were, however, not significant enough for the direct application of the solution into larger scale configurations. Scalability of the technological solutions remains one of the major challenges of the technology in the morphing applications. The dynamic results showed good performance of the actuators in an anti-flutter demonstrator application during wind tunnel testing. The experiments showed that the system remained stable well passed the flutter velocity; this allows for further experimentation in structures presenting higher flutter speeds. With the development of the next generation of advanced piezoelectric ceramics, with piezoelectric coefficients twice as large in comparison to PZT-based ceramics, the application of the deforming structure concept is very promising for application in larger demonstrators in both static and dynamic applications. The next generation of piezoelectric materials presents itself as a first step into a solution to the scalability of the technology for application into full-scale demonstrators.Des dels primers models desenvolupats durant el segle XIX, les aplicacions per a materials piezoelèctrics han anat creixent progressivament. La relació que presenten aquests materials entre el comportament mecànic i el comportament elèctric els converteix en candidats ideals en l'estudi d'estructures deformables. L'aplicació de piezoelèctrics en aeronàutica es concep tradicionalment des de dues perspectives: com a sensors o com a actuadors. Ambdues presenten potencials beneficis i aplicacions. Tot i que en els últims anys la recerca s'ha concentrat en l'estudi d'integració dels materials en sistemes que permeten controlar la salut de l'estructura (Structural Health Monitoring), l'aplicació de piezoelèctrics com a actuadors d'estructures deformables desperta l'interès de la comunitat científica. En l'estadi actual, la tecnologia necessària per deformar estructures de forma controlada utilitzant materials piezoelèctrics no està suficientment desenvolupada. No obstant, la recerca en aquest camp està en continu desenvolupament i s'apropa a solucions que permetran integrar-la en aplicacions industrials. L'objectiu de la tesi és estudiar la possibilitat d'utilitzar deformacions produïdes mitjançant actuadors piezoelèctrics en estructures aeronàutiques actuals. L'anàlisi està orientat des de punts de vista teòric i experimental i es centra en el comportament estàtic i dinàmic de solucions tecnològiques amb actuadors i tecnologies d'amplificació disponibles comercialment. La recerca que es presenta en la tesi estudia dues aplicacions diferents en l'ús d'aquest tipus d'actuadors: com a actuadors en regim estàtic, produint deformacions de la superfície aerodinàmica, i com a actuadors dinàmics, que controlin una superfície de control convencional. L'arquitectura de la solució tecnològica emprada ha estat diferent en cada aplicació: en la deformació estàtica de la superfície aerodinàmica l'actuador és de tipus "patch" mentre que en el cas dinàmic és de tipus "stack". Els experiments estàtics desenvolupats tenen com a objectiu demostrar la capacitat dels piezoelèctrics com a elements que produeixin deformacions en l'estructura (morphing). Aquest objectiu es demostra analitzant les deflexions produïdes en el caire de fuga d'un perfil aerodinàmic. Els resultats experimentals obtinguts són optimistes ja que les diferents configuracions d'actuadors es comporten tal i com prediuen els models. En règim estàtic, les deformacions produïdes en el caire de fuga son substancials. Això permet assegurar que la configuració utilitzada en els experiments és prou madura com per seguir investigant, per exemple, en túnel de vent. Malgrat això, les deformacions produïdes encara no són suficientment significatives com per integrar l'experiment en un model més gran. L'escalabilitat és un dels reptes més importants que presenta la tecnologia en aplicacions de "morphing". Els resultats dinàmics demostren una bona actuació de l'actuador integrat en un sistema anti-flameig en els experiments en túnel de vent. Els experiments demostren la capacitat del sistema de mantenir-se estable a velocitats mes enllà de l'aparició del flameig. El següent pas en aquesta línia de recerca es l'investigació en models més complexos en quant a aparició de flameig. Amb el desenvolupament d'una nova generació de materials piezoelèctrics ceràmics avançats, que promet coeficients piezoelectrics el doble d'alts en comparació amb els materials basats en PZT disponibles actualment, l'arquitectura experimentada en règim estàtic és un molt bon candidat en aplicacions a escala més gran. Aquesta propera generació de materials es presenta com un primer pas en solucionar els problemes d'escalabilitat que presenta la tecnologia actualment

Inferring Geodesic Cerebrovascular Graphs: Image Processing, Topological Alignment and Biomarkers Extraction

A vectorial representation of the vascular network that embodies quantitative features - location, direction, scale, and bifurcations - has many potential neuro-vascular applications. Patient-specific models support computer-assisted surgical procedures in neurovascular interventions, while analyses on multiple subjects are essential for group-level studies on which clinical prediction and therapeutic inference ultimately depend. This first motivated the development of a variety of methods to segment the cerebrovascular system. Nonetheless, a number of limitations, ranging from data-driven inhomogeneities, the anatomical intra- and inter-subject variability, the lack of exhaustive ground-truth, the need for operator-dependent processing pipelines, and the highly non-linear vascular domain, still make the automatic inference of the cerebrovascular topology an open problem. In this thesis, brain vessels’ topology is inferred by focusing on their connectedness. With a novel framework, the brain vasculature is recovered from 3D angiographies by solving a connectivity-optimised anisotropic level-set over a voxel-wise tensor field representing the orientation of the underlying vasculature. Assuming vessels joining by minimal paths, a connectivity paradigm is formulated to automatically determine the vascular topology as an over-connected geodesic graph. Ultimately, deep-brain vascular structures are extracted with geodesic minimum spanning trees. The inferred topologies are then aligned with similar ones for labelling and propagating information over a non-linear vectorial domain, where the branching pattern of a set of vessels transcends a subject-specific quantized grid. Using a multi-source embedding of a vascular graph, the pairwise registration of topologies is performed with the state-of-the-art graph matching techniques employed in computer vision. Functional biomarkers are determined over the neurovascular graphs with two complementary approaches. Efficient approximations of blood flow and pressure drop account for autoregulation and compensation mechanisms in the whole network in presence of perturbations, using lumped-parameters analog-equivalents from clinical angiographies. Also, a localised NURBS-based parametrisation of bifurcations is introduced to model fluid-solid interactions by means of hemodynamic simulations using an isogeometric analysis framework, where both geometry and solution profile at the interface share the same homogeneous domain. Experimental results on synthetic and clinical angiographies validated the proposed formulations. Perspectives and future works are discussed for the group-wise alignment of cerebrovascular topologies over a population, towards defining cerebrovascular atlases, and for further topological optimisation strategies and risk prediction models for therapeutic inference. Most of the algorithms presented in this work are available as part of the open-source package VTrails

Local Fluidization of Concentrated Emulsion in Microfluidic Channels Textured at the Droplet Scale

The rheology of soft-flowing systems, such as concentrated emulsions, foams, gels, slurries, colloidal glasses and related complex fluids, has a larger and larger impact in modern science and engineering. Much of the fascination of these systems stems from the fact that they do not fall within any of three basic states of matter, gas-liquid-solid, but live rather on a moving border between them. To understand the flow mechanism, it is necessary to have a look at the micro-scale dynamics of its constituents (i.e, droplets for emulsions, bubbles for foams, blobs for gels, etc.). In fact, in these fluids, the flow occurs via successive elastic deformations and plastic rearrangements, which create fragile regions enhancing the “fluidization” of the material. Despite the fluidization of Soft Glassy Materials (SGMs) is strongly affected by the surface roughness, the role played by the density, the orientation and the periodicity of rough elements has not been quantitatively addressed so far. In fact, predict and control the flow of SGMs is particularly important for an ample variety of technological applications from food to pharmaceutical industries. In this work, we study the flow of concentrated emulsions in microfluidic channels, one wall of which is patterned with micron-size grooves with different patterns. Using equally spaced grooves, we find a scaling law describing the roughness-induced fluidization as a function of the density of the grooves, thus fluidization can be predicted and quantitatively regulated. Furthermore, we quantitatively report the existence of two physically different scenarios. When the gap is large, compared to the droplets in the emulsion, the droplets hit the solid obstacles and easily escape scrambling with their neighbors. Conversely, as the gap spacing is reduced, droplets get trapped inside, creating a “soft roughness” layer, i.e., a complementary series of deformable posts. Introducing an asymmetrical micro-roughness (herringbone pattern), the flow presents, in turn an asymmetric behavior. The emulsion flows faster in the same direction of the herringbone groove respect when it flows in the opposite direction. Our experimental observations are suitably complemented and confirmed by lattice Boltzmann simulations. These numerical simulations are key to highlight the change in the spatial distribution of the plastic rearrangements caused by surface roughness and to elucidate the micro-mechanics of the roughness induced fluidization

Registration of histology and magnetic resonance imaging of the brain

Combining histology and non-invasive imaging has been attracting the attention of the medical imaging community for a long time, due to its potential to correlate macroscopic information with the underlying microscopic properties of tissues. Histology is an invasive procedure that disrupts the spatial arrangement of the tissue components but enables visualisation and characterisation at a cellular level. In contrast, macroscopic imaging allows non-invasive acquisition of volumetric information but does not provide any microscopic details. Through the establishment of spatial correspondences obtained via image registration, it is possible to compare micro- and macroscopic information and to recover the original histological arrangement in three dimensions. In this thesis, I present: (i) a survey of the literature relative to methods for histology reconstruction with and without the help of 3D medical imaging; (ii) a graph-theoretic method for histology volume reconstruction from sets of 2D sections, without external information; (iii) a method for multimodal 2D linear registration between histology and MRI based on partial matching of shape-informative boundaries

STUDY OF SEQUENTIAL EFFECTS OF BLAST WAVES IN CONFINED AND ADJACENT STRUCTURES

The study of the effect of explosive blast in confined spaces, particularly the conditions under which blast is transmitted to adjacent compartments and the effects produced, is of relevance for the vulnerability assessment of buildings, aircraft and ships, being of paramount importance in the context of national security and defence due to the permanent and diverse threats of present times. In particular it is aimed, through numerical modelling of the phenomena, to study the response of adjacent compartments, one of them subjected to an internal explosion, to identify the effect of compartment volume and material properties in the conditions that will cause rupture and loss of structural integrity and the effect in neighbouring structures of the sequential wave blast. Together with the study of the modes of collapse and rupture of materials used in naval shipbuilding, in this case the AA5083-H111 aluminium alloy, the present work will be the basis for the setting-up of a tool for the design of naval ships and vessels, providing the means to analyse and predict their vulnerability to several types of military ordnance

Stratospheric constituent measurements using UV solar occultation technique

The photochemistry of the stratospheric ozone layer was studied as the result of predictions that trace amounts of pollutants can significantly affect the layer. One of the key species in the determination of the effects of these pollutants is the OH radical. A balloon flight was made to determine whether data on atmospheric OH could be obtained from lower resolution solar spectra obtained from high altitude during sunset