In this dissertation, the rheological behavior of polar droplets emulsion is experimentally characterized through the use of a parallel disk rheometer equipped with a magnetic cell. The emulsions treated vary in terms of the ratio of viscosities be-tween the fluid inside the droplet and the surrounding liquid. In this context, four emulsions were generated, each with its defined viscosity ratio and different from each other, but all with the same drop volume fraction (5% v/v). Static microscopy tests were performed to determine the average diameter of the drops, as well as its polydispersity. When an external magnetic field was applied, the size distribution of the chains formed by the polar drops was also verified. Three experimental methodologies were used to characterize the rheological behavior of the emulsions. The first refers to tests under permanent shear conditions in the absence and presence of a magnetic field. With this, one can examine the behavior of the apparent viscosity and of the shear stress of the emulsions as a function of the shear rate and the intensity of the magnetic field. This allows the verification of the adherence of the rheological behavior of such fluids to generalized Newtonian fluid models. Furthermore, comparisons of viscosity behavior in the absence of an external magnetic field with Taylor's infinitely dilute emulsion model are performed. The second methodology concerns experimental tests with time dependent flows, in a step-strain impulse regime in the presence of a magnetic field. From this experimental analysis, for an emulsion with a fixed viscosity ratio, its stress relaxation functions dependent on the intensity of the applied external magnetic field were obtained. The associated relaxation times were calculated. The third methodology refers to oscillatory shear tests in the presence of an external magnetic field, in a linear viscoelastic regime. From this methodology, the viscoelastic modules were obtained for a polar emulsion with a defined viscosity ratio. Such material functions were obtained as a function of the frequency and intensity of the magnetic field in a condition of small deformations. The existence of elastic shear modulus was observed when the polar emulsion is placed in the presence of an external magnetic field, which indicates the presence of microstructure induced by dipolar interactions. It is also noted that the application of the magnetic field injects elasticity into the dynamic system of the emulsion, which is corroborated by the fact that non-zero relaxation times were obtained from experimental tests. Compatibility checks between the complex viscous modulus and apparent viscosity for equal values of frequency and shear rate are carried out and, based on this, the first normal stress difference is calculated using Laun's rule.

Bone fractures represent a growing public health problem worldwide, especially
considering the aging population. Possible solutions for fractures that do not heal naturally
are artificial implants. Metallic implants have good mechanical properties, but issues with
coupling with the host bone, as well as being bioinert materials, increase associated risks
and maintenance. Ceramic scaffolds represent a class of promising artificial grafts in terms
of bone tissue regeneration. In this context, the present work was focused on the fabrication
of hydroxyapatite (HPA) scaffolds, which is the extracellular matrix found in human bones,
using BaTiO3 and Zn0 as a way to modify the structure and properties of the scaffolds
manufactured by freeze-casting. It was observed through mechanical compression tests that
the addition of 0.25 wt.% BaTiO3 caused an increase in mechanical strength, with the best
sample exhibiting compressive strength above 7 MPa, while the porosity remained around
40%. Additionally, a reduction in compressive strength was observed with the addition of
Zn0. Furthermore, it was found through XRD and FTIR a reduction in the degradation of
HPA into OCP 𝛼-TCP promoted by the addition of BaTiO3. This effect is related to the
surface area obtained by BET of the BaTiO3 perovskite. Finally, samples containing Zn
and BT showed the formation of the hydroxyapatite phase with Zn substitution in HPA,
whose interaction with BaTiO3 and with the PVA binder was reduced due to contractions
in the OH groups of HPA, forming defects observed by the 𝜇-CT technique.

Biomass is an abundant renewable energy source, promoting sustainable environmental and socioeconomic benefits. This is obtained from biodegradable materials, such as agricultural, forestry and urban waste. Biomass residues as a renewable energy source helps reduce waste accumulation and mitigate the environmental impacts of improper disposal. In addition, producing energy from biomass can generate jobs and income in local communities, promoting socioeconomic development. The pequi (Caryocar brasiliense Camb.) is a tree species belonging to the Caryocaraceae family, native to the Brazilian Cerrado. The fruits of the pequi are widely used in regional cuisine, being a source of nutrients and characteristic flavors. In addition, the fruit has a complex and thorny skin, which protects a yellowish and oily pulp and a seed (waste). This work investigated the torrefaction process for converting pequi seed waste into energy, with torrefaction (mild pyrolysis) being a pre-treatment process (200-300 °C) that improves the chemical and physical properties of raw biomass. The present investigation aims to understand the roasting treatment of pequi waste with and without extractives using a face-centered surface response methodology exploring two scenarios. Two different plans were proposed to outline ideal roasting conditions: one focused on improving the quality of the roasted product without considering system prerequisites (Scenario 1), and the other emphasized reducing energy consumption by improving energetic properties. of the roasted product and maximizing the CO2 retention potential (Scenario 2). Meanwhile, roasting was conducted in a macro-TGA and subsequently observed (immediate, elemental and calorific analysis). The results reveal PS roasting at 274 °C and 42 min as optimal in scenario 1, resulting in biochar (CH1.30O0.33) with an energy yield of 76.18% and a higher calorific value of 24.11 MJ kg–1. In scenario 2, PS is also optimal, resulting in an ideal operating condition with 264 °C and a residence time of 31 min, providing bio coal (CH1.39O0.36) with an energy yield of 82.11%, a product roasted with a higher calorific value of 23.83 MJ kg–1 and a CO2 retention of 188.65 kg equivalent, considering the replacement of diesel oil. The increase in Higher Heating Value observed, especially in the case of PSWE, demonstrates the potential of these feedstocks as solid biofuels, with enhancement up to 21%. Thus, this shows that removing extractives is an exciting procedure since the extractive can proceed further as biodiesel. Furthermore, the results can contribute essential information for the development of the circular economy in family farming and agro-extractive communities, which can support small and medium-sized agri-food industries in Brazil with their electrical and thermal demands.

Due to rapid increase in demand for higher efficiency and capacity rotating machinery, vibration related problems also grow, demanding better solutions to vibration control. The current state of the art consists of gas lubricated bearings, but new approaches are being studied, such as the use of metamaterials on rotating machines. Various types of resonators have been studied, on those studies the problems of gyroscopic influence on frequency response was shown to be significant. Apart from that, one major problem identified was the difficulties in manufacturability of the resonators. This problem is the main focus of this work, culminating on an experimental analysis. To achieve this, the metastructure will be analysed using wave based numerical methods, the resonators will be tuned to attenuate the target frequencies and based on the tuning parameters a CAD model is designed and then manufactured. A bench test is performed to check for the band attenuation.

Overhead conductors are the mechanical components used in transmission lines to transport electricity over long distances. In-service conductors are susceptible to several types of oscillatory motions, including wind-induced vibrations. One of the most common types of wind-induced cyclic motion is the aeolian vibration, which is caused by the vortex shedding that occurs when wind flows by the conductor. It has been widely known that the aeolian vibrations can be critical to the safe operation of transmission lines, as they can lead to fretting fatigue. Fretting occurs at the contact surfaces of the conductor’s wires and is usually critical near or within clamp devices. Cracks usually initiate and propagate from the fretting marks and can eventually lead to wire rupture. The fatigue behavior of conductors is a complex problem, involving several contact regions, localized plasticity, wear, and friction. These complexities have led utilities to traditionally rely on fatigue test data obtained from resonant test benches for the safe design and operation of transmission lines. However, the recent advances in finite element (FE) 3D modeling of conductor-clamp systems have motivated researchers to pursue FE-based approaches for the fatigue damage analysis of the conductor. These approaches are based on a combination of a global-scale analysis of the conductor-clamp system with a local-scale analysis of the wires under fretting fatigue. Compared to the traditional approach based on stress-life curves, these global-local approaches require simpler and less expensive laboratory infrastructure, and can be used to optimize the design of the conductor-clamp system. Since the last decade, significant progress has been made regarding the fatigue damage analyses of conductors and their wires, aimed at the development of the aforementioned global-local approaches for fatigue life prediction. However, additional research is still required to better evaluate the applicability of these approaches to different conductor geometries, wire materials, and loading conditions. In this regard, this thesis aims to investigate methodologies for life prediction of overhead conductors and their wires by means of experimental and numerical analyses. This thesis is organized as a collection of three research papers by the author and collaborators, which have already been published or are under the process of submission/review. In the first paper, fretting fatigue tests under constant amplitude loading (CAL) were performed using 1120 aluminum alloy (AA) wires of an AAAC (All Aluminum Alloy Conductor) 823 MCM conductor. A tension test and axial fatigue tests on smooth and V-notched wire specimens were also carried out. The fatigue test data were used to compare the AA1120 with the AA1350 and AA6201, two alloys typically used to manufacture the wires of conductors. Under tension, the AA1120 displayed an intermediate ultimate tensile strength between the ones from the AA1350 and the AA6201. For the same stress amplitudes, the AA1120 wires used in the axial fatigue tests had longer lives than the AA1350 wires but considerably shorter lives than the AA6201 wires. However, under fretting fatigue, both AA1120 and AA6201 wires had similar fatigue strength. The test data were also used to evaluate a life prediction criterion for wires under fretting fatigue based on the Theory of Critical Distances (TCD). Most of the predicted lives were within a factor of 3 of the measured lives. The accuracy of the predictions was similar to that observed in previous studies, in which the same methodology was applied to data from fretting fatigue tests on AA1350 and AA6201 wires. These results show that the methodology can be a reliable tool for the fatigue damage analysis of wires made of different materials subjected to fretting fatigue and CAL. In the second paper, fretting fatigue tests under variable amplitude loading (VAL) were carried out on AA6201-T81 wires of an AAAC 900 MCM conductor. The amplitude variation was represented by a three-block loading history. The loading conditions were defined using vibration measurements from an operating transmission line located in the center-west region of Brazil. Two methodologies for life prediction of wires were extended to VAL conditions and were evaluated using the fretting fatigue test data. One of the methodologies is the same TCD-based criterion considered in the first paper, while the other is based on a master fatigue curve. Both methodologies provided life predictions within factors of 4 of the measured lives. The accuracy achieved in this study supports the use of the proposed methodologies for predicting the lives of wires under VAL conditions. The third paper is concerned with the life prediction of an ACSR (Aluminum Conductor Steel Reinforced) Ibis 397.5 MCM conductor under high-low and low-high loading sequences. To this end, a life prediction methodology based on finite element 3D modeling of conductor–clamp systems was extended to include VAL conditions. Firstly, the methodology was applied to CAL fatigue test data to assess whether it can accurately describe the fatigue failure of the ACSR Ibis conductor. Subsequently, the methodology was evaluated using the data from fatigue tests conducted under a two-block loading history. Most life predictions were within factors of 3 of the measured lives. For the VAL tests, the methodology accurately took into account the effect of loading sequence on fatigue failure, providing longer life estimates for the tests under high-low sequence than for those under low-high sequence. Additionally, the methodology was capable of predicting the positions of the wire breaks for the VAL tests in accordance with the experimental observations. These results suggest that the methodology can be extended to VAL conditions and be used to accurately predict the lives, the loading sequence effects, and the fatigue critical regions of conductors.

  Technological advancement has been driving the need for sensors in various applications, which raises environmental concerns related to the use of non-biodegradable and potentially toxic materials. In response, the scientific community has been dedicated to the development of flexible and conductive devices, using materials from renewable sources. In this scenario, biopolymers, especially hemicellulose extracted from plant fibers, stand out due to their natural abundance and renewability, good thermal stability, biodegradability, and biocompatibility. However, as hemicellulose is not a natural conductor, the addition of conductive fillers becomes essential. This research focuses on the use of hemicellulose as a base for flexible sensors, aiming to develop hemicellulose conductive films with metallic nanoparticles and pure hemicellulose substrates with printed circuits, to evaluate their effectiveness as sensors. Hemicellulose was extracted from jute fibers using 10% w/v KOH, followed by the production of pure hemicellulose polymer films and films with silver nanoparticles (AgNPs) at different concentrations, employing the water casting technique. The films were analyzed using a variety of techniques, including Thermogravimetry (TGA), Differential Scanning Calorimetry (DSC), Fourier Transform Infrared Spectroscopy (FTIR), Ultraviolet-Visible (UV-Vis) Spectroscopy, Scanning Electron Microscopy (SEM), Dynamic Mechanical Analysis (DMA), and tensile mechanical tests. Roughness was assessed through optical microscopies and Gwyddion 2.55 software, while surface tension was determined by contact angle measurements. Electrical properties were tested with a bench multimeter, and tests for pressure, temperature, and humidity variation were conducted. The results showed that the hemicellulose films possess good thermal stability, low porosity, low roughness, and hydrophilic properties. The inclusion of silver nanoparticles not only improved the electrical conductivity but also the thermal stability of the material. The performance of the nanocomposites as sensors for pressure, temperature, and humidity varies according to the concentration of incorporated nanoparticles. For the pressure sensor, under high pressures, the nanocomposite containing 5% silver nanoparticles (AgNP) showed the best results, also proving to be effective in temperature detection. In situations of lower pressures, the nanocomposite with a concentration of 0.50% AgNP had the most satisfactory response. As for humidity measurement, the nanocomposites with 1% and 5% AgNP showed superior performances. Moreover, hemicellulose proved to be an effective substrate for the printing of conductive inks, especially for pressure and temperature sensors. These findings confirm the potential of hemicellulose as a promising material for the development of multifunctional flexible sensors, contributing both to scientific and technological advancement and to global efforts in search of more sustainable and eco-friendly solutions.

The process of identifying parameters using various optimization methodologies has been shown
to be an important tool in the determination of parameters of constitutive models characteristic of
materials. The degree of complexity of the constitutive relation of the material is a determining
factor in the choice of the optimization method, since the objective function can present many
local minima or maximums. The present study sought to identify and explore the problems and
difficulties that may arise during the process of identifying parameters. We developed
computational routines that involved an evolutionary algorithm, the Genetic Algorithm (GA) and
a gradient-based algorithm, the Split Levenberg-Marquardt Algorithm (LMD) and proposed a
hybrid model that would unite the search robustness of GA and the speed and accuracy of the
LMD Algorithm. The developed routines were tested and several analyses were performed, both
of the Genetic Algorithm (GA) and of the Split Levenberg-Marquardt Algorithm (LMD) that
received as input the values from the GA. Overall, the performance of both was good, arriving at
the solutions within a desired precision in a few iterations. The critical point verified was the
Finite Element method, represented here by the HYPLAS system. An academic system useful in
the development of the hybrid method, but which added to each iteration of GA and the LMD
Algorithm several seconds of processing. As for the traction test, widely used to obtain
information about a given material and also as a specification control test, some important
characteristics were evaluated and a routine was created to automate it. In conjunction with the
results obtained via the tensile test for the 4340 standardized and annealed steels and the alloy
1524 U2 it was verified the application of the idealized routines in the PYTHON language for the
GA, the LMD and the hybrid method in the determination of crunching parameters according to
the model of Kleinermann and Ponthot (2003) for these materials. Finally, a case study was
carried out in which it was sought to verify the applicability of the porous materials model of
Gurson (1977) in the characterization of the mechanical properties of specimens produced via
additive manufacturing (AM). The hardening curve of the material until fracture and the level of
initial and critical porosity at different points and directions of metal deposition were measured.
It was concluded that the model based on Gurson (1977) can describe the mechanical behavior of
materials supplied by additive manufacturing and can be used as an alternative to predict the
fraction of volumetric void, a defect present in these types of materials. It was also observed that
in the different directions of deposition, the porosity of the material ranged from 5% to 18%,
which influenced the resistance characteristics, such as flow stress, modulus of elasticity and level
of plastic deformation accumulated in the fracture.

Ceramic materials have increasingly attracted the interest of researchers in studies for their use in osseointegrated dental implants. The development of composite materials based on alumina and zirconia have demonstrated biocompatibility. They are aesthetically attractive due to the similarity with the color of natural teeth and have excellent mechanical properties, being an alternative to the use of titanium implants. The objective of this work was to evaluate the fatigue strength of the ceramic composite of zirconia stabilized with yttria and ceria reinforced with alumina platelets (Ce, Y) − TZP/AlଶOଷ and to characterize the physical and mechanical properties of sintered specimens. In the present work, the commercial powder of (Ce, Y) − TZP/AlଶOଷ (uprYZe-Intense G, ZirPro) was used. Bar-shaped specimens were compacted by uniaxial pressing in a rigid die, with a pressure of 100 MPa for 60 seconds, followed by sintering at 1500°C. Subsequent phases included determination of density, quantification of crystalline phases present by X-ray diffraction, determination of modulus of elasticity, microhardness, fracture toughness, four-point bending strength and fatigue strength limit. Observations on fracture mechanisms were performed with the aid of optical and scanning electron microscopy. The sintered samples of (Ce, Y) − TZP/AlଶOଷ without binder and polished showed results of 98.56% relative density. More complex microstructures with equiaxed submicrometric grains, homogeneously distributed and an elongated planar shape of the alumina platelets were observed by SEM. The modulus of elasticity found for the composite was 247.51 GPa and the Vickers hardness was 13.68 GPa. The composite samples showed high values of fracture toughness, around 7.07 MPa. mభమ. This high value occurs due to the transformation from tetragonal to monoclinic phase, creating compression zones around the crack and thus hindering its propagation, this compression acts due to the increase in volume by the t-m transformation. Flexural strength values were 460.36 MPa, Weibull modulus (m = 16.82), revealing low scattering of the flexural strength data. The fatigue strength found for the specimens was 286.64 MPa. In the composite evaluated in this work, the occurrence of the tetragonal - monoclinic transformation that occurs in the Ce -TZP grains present in the triple points and in the grain boundaries during the cyclic loading produces the “crack tip shielding”, that is, a restricted elastic zone ( shielding) that surrounds the crack tip. This phenomenon leads to a reduction in the stress intensity factor at the crack tip and delays its growth, generating an increase in the fatigue strength of the composite.

In horizontal-axis wind turbines, two elements that influence energy conversion are the height of the rotor in relation to the ground and the roughness of the terrain. The present work presents an experimental study on the influence of these two factors on the power curve of small-scale models of horizontal axis free turbines. The experiments were carried out in the wind tunnel of the Laboratory of Energy and Environment at UnB. Three different heights and two surface roughness conditions are evaluated. The hot wire anemometry technique is used to determine the mean longitudinal velocity and turbulence intensity in specific regions of interest in the flow. To simulate a rough terrain, chains were installed over the originally smooth surface of the wind tunnel test section. Experiments were carried out on the smooth surface and on the rough surface. We have noticed that, for the smooth surface, two competing mechanisms which alter power generation by the rotor take place: the partial confinement of the flow, observed as the rotor approaches the surface, with a tendency to increase the power coefficient; and the velocity deficit in the boundary layer over the tunnel surface, which tends to reduce the power coefficient. It was identified that when the height of the turbine is close to the minimum possible height in relation to the surface, the partial confinement of the flow increases the average velocity through the rotor, resulting in an expressive power coefficient elevation, compared to the case in which the turbine is in the far field from the ground. On the other hand, at intermediary heights, the flow velocity deficit in the boundary layer overcame the flow confinement and leads to a reduction of the power coefficient. The study considering a rough ground surface indicated that roughness can significantly change the dynamics observed in a situation where the surface is smooth. When there is roughness, the power elevation observed for the case with lower height does not occur at the same levels. All results are discussed in conjunction with fields of flow average velocity and turbulence intensity upstream and downstream rotor. The present study leads to the conclusion that using very high towers to isolate the rotor from the ground’s influence is not necessarily beneficial when only energy generation is considered.

Due to the need to increase the efficiency of operational processes, machines are being subjected to severe work operations. This leads to premature wear of their mechanical components, which results in a decrease in their useful life and an increase in maintenance costs. To extend the useful life of machine components under these severe operating conditions, materials are used for surface protection such as: electrodes, polymers, composites, tubular wire, among others. This work presents the numerical evaluation of the sphere-on-plane compression test. Two steel base materials (SAE 1045 and SAE 1020) and four coatings are studied. The objective is to evaluate the behavior of surface coatings when subjected to compressive loads, in order to protect the base material, as well as their Equivalent von Mises Stress, indentation and equivalent plastic deformation obtained in the critical contact node. Sphere – plane configuration compression tests are performed on samples using the hard electrode coating, in order to obtain information on the mechanical properties of this coating. For Nylon, PC-ABS and Polyurethane, information obtained from the literature on their mechanical behavior is used. All this information is used for the calibration of a finite element model. The simulation consists of five configurations, one of which is just the base material and four with surface coatings. All models are subjected to four loading conditions: 500N, 1000N, 1500N and 2000N. Given the results, it is concluded that the use of coatings can lead to a significant increase in the useful life of the equipment in which they are applied. However, for the choice of coating, it is necessary to evaluate the workloads that the coating can undergo. It is recommended to use electrodes for high loads and polymers for applications with compressive loads of small magnitude and high number of cycles.

In conductor cables, one of the main external agents that can lead to fatigue, and consequently the decrease in its lifetime, is wind excitation. The rupture of conductor cables causes enormous damage from the economic and social points of view. The objective of this work is to investigate the dynamic behavior of cable samples using the Finite Element Method. Modal and harmonic analyzes were carried out in order to find the resonance frequencies and understand the dynamics of the structure in the frequency range of 30 Hz. The solutions found via the Finite Element Method through the software ANSYS Mechanical APDL, were compared with existing studies in the literature to validate the results. The results from the modal and harmonic analyzes were very consistent with the existing results in the literature. Then, the modal and harmonic analyzes were performed for the frequency range from 0 to 65 Hz. Then, in the first transient analysis, impulsive loads were applied for a time of 50 s on the 13,385 m cable sample, in order to evaluate the transient response of the structure. It was observed that the closer to the supports (node 128) the greater the frequency spectrum when compared to the middle of the cable (node 513). Another observed fact is that the system responds to low amplitude frequencies. It was noted that the lowest frequencies induced the greatest displacements in the cable, which could lead to fatigue failure. Finally, the cable was sinusoidally excited at frequencies of 5.2205 Hz and 36.5 Hz, and it was noticed that the system vibrates harmonically at these frequencies.

This work presents a study on thermo-sensitive ferrofluid flow inside a two-dimensional cavity with insulated vertical walls and constant-temperature horizontal walls. The aim is to understand the influence of an external magnetic field and the impact of a rectangular obstacle inside the cavity on the flow field and heat transfer. The flow is assumed incompressible and laminar, and the ferrofluid is superparamagnetic, with susceptibility varying as a function of the temperature. The external magnetic field is generated by the electric current passing through a conducting wire, near the cavity. The set of governing equations comprises mass conservation, linear momentum, and energy equations. The problem is solved numerically using a finite differences method in a regular mesh. The pressure–velocity coupling and time evolution are carried out by a second-order projection method. When the wire is placed in the middle of the right insulated wall, the results show an increase in the average Nusselt with the magnetic field intensity. In addition, one observes that the wire position dramatically influences the flow topology, with significant variations in the average Nusselt number. A study on the effects of the presence of an obstacle inside a cavity was conducted. Two cases were considered: one where the obstacle is thermally insulated and another where the temperature is kept constant. The results reveal that the presence of the obstacle changes the way the magnetic field modifies the flow, such that the position that maximizes the Nusselt number varies considerably between the situations with and without the obstacle. It was observed that the presence of this object, depending on the thermal boundary conditions, can induce the formation of flow structures similar to Bénard cells. Motivated by this observation, a preliminary study on the effect of the magnetic field on a natural convection flow in the Bénard cell regime was conducted. It was shown that the presence of the magnetic field can alter the number of these cells and increase the average Nusselt number of the flow by more than 50%.

The most common approaches for computational aeroacoustics are the direct noise computation through the solution of the governing equations and the use of linear equations to describe sound propagation. An interesting alternative to these methods is a reduced-order model (ROM) approach. The Dynamic Modes Decomposition (DMD) and the Proper Orthogonal Decomposition (POD) are data driven analysis tools that have been used recently as the basis of ROMs. With that in mind, this dissertation aims to use the POD and DMD methods to study the transonic flow past a 2D circular cylinder with Mach numbers 0.5 and 0.75 and modelled with the Euler equations. The flow past the cylinder was chosen as the subject of this work because it is a relatively simple flow, especially for $M_{\infty}=0.5$ but presents rich dynamics. The acceleration of the flow as it passes around the cylinder causes the formation of shock waves, and the resulting adverse pressure gradient causes the separation of the flow. As vortices are emitted and form a von Karman street at the wake, the shock waves also detach and propagate through the domain as sound waves. The Strouhal numbers for both cases were around 0.2, the well-known value for the flow around a cylinder. The POD and DMD are methods that decompose a data set, in this case composed of pressure field snapshots, into coherent structures, or modes. The POD modes are spatially orthogonal structures, while the DMD modes have specific frequencies and rates of growth. The analysis of the modes' structures revealed that the cylinder emits noise in a manner similar to an acoustic dipole, with contributions from other multipoles. Furthermore, the modes for $M_{\infty}=0.75$ revealed that the vortex wake is also a noise source in this case. The DMD decomposition also provided frequencies associated with the modes that matched the peaks in the pressure spectra. The POD and DMD modes were also used to reconstruct the flow fields. The reconstruction with the POD agreed almost exactly with the original data. The results with the DMD, on the other hand, had significant discrepancies. For $M_{\infty}=0.5$ the error for the pressure fluctuations root mean square value was around 15\% to 25\% for most of the domain and had a maximum value of over 200\%. The results showed that the DMD is an analysis tool capable of revealing important information about the system but the POD is a better method to reconstruct the data set.

Cloud dynamics is relevant for several areas, such as meteorology, agriculture, and airport operation, among others. In particular, for short-term solar forecasting, important for the management of solar power plants and distribution networks with high participation of solar energy, a more accurate characterization of cloud motion can improve generation forecasting as their presence is the major responsible for the variability of irradiance on intra-day time scales. Thus, in this paper, a methodology is proposed that uses triangulation of images from two fisheye-lens cameras to measure the position of objects in space, aiming at its use in short term solar forecast platforms based on sky images. A two-camera system, together with a wireless router, was installed on the roof of the Energy and Environment Laboratory of the University of Brasilia. The methodology developed is based on a stereo vision model, used to process the images and determine the location of visible objects in the images. The proposed model for image processing does not require the removal of image distortion for pinhole images, normally used in fisheye cameras, nor the rectification of the original images, being these the main contributions compared to other existing models. For the validation of the model, a drone was used as an object with known position. For this, the drone, in stationary night flight, was positioned at various points and altitudes desired and, with its lower light on, images of the sky were captured with the cameras. The coordinates of the drone in the images obtained by the model were then verified and compared with those reported by the drone. The results showed an average percentage error around 10% (relative to the value reported by the drone) at altitudes ranging from 90 to 490 meters. These values are acceptable for the desired application, with measurement uncertainties comparable to cloud height obtained by ceilometers, with the advantage of enabling a wide field of view, and with lower computational costs than traditional models.

This work presents an investigation of the effects of external uniform magnetic fields on the
rheology and magnetization of dilute ferrofluid emulsions subjected to planar extensional
flows. To this end, we performed three-dimensional numerical simulations of a single
superparamagnetic ferrofluid droplet suspended in a nonmagnetizable viscous fluid. This
system corresponds to the emulsion’s microstructural unit. The full incompressible
Navier-Stokes equations for a biphase system with the addition of the magnetic term are
solved using a projection method. The interface problem is addressed with the Level-Set
method. We find that the droplet’s configuration and magnetization depend on the external
field intensity and direction. Macroscopically, the droplet contribution to the bulk stress state
is anisotropic. The two extensional viscosities associated with the normal stresses of the
emulsion either remain constant or increase with the field intensity; the only exception occurs
when the field direction is perpendicular to the extension plane, in which the second
extensional viscosity decreases. When the external field is not aligned with the flow main
directions, the droplet tilts in the flow and the droplet magnetization points no longer in the
external field direction. At the emulsion level, this results in internal torques that lead to a
nonsymmetric stress tensor. In order to account for the unexpected shear components and
fully characterize the extensional rheology, we introduce new extensional material functions
such as shear and rotational viscosity coefficients. We also analyze the conditions for droplet
breakup. We find that the external field either induces or prevents the breakup depending on
the field direction. The subcritical deformations in the plane formed by the extension and
field directions vary linearly with the critical extension rate, regardless of the field direction.
Overall, this study provides new insights into applications for field-controlled smart materials
and precise manipulation of ferrofluid droplets.

The main objective of this study is to technically and environmentally assess the utilization of waste from Distrito Federal, Brasil, for energy generation, employing Life Cycle Assessment as the tool, with 1 Mg of treated waste as the functional unit. Two primary waste types are being evaluated: Urban Solid Waste, under public responsibility, and Agrosilvopastoral Waste, under producer responsibility. The USW is evaluated under two different scenarios: the implementation of incineration with energy recovery and the current disposal method, landfilling, including the transportation stage. The AW is evaluated under three distinct scenarios: on-site decomposition and harvesting waste, centralized and decentralized collection with anaerobic digestion, and also accounting for transportation. Through this analysis, the aim is to provide material for public decision-makers in situations requiring technical decisions regarding optimal investment areas from an environmental perspective. For the analysis, a Life Cycle Inventory was developed and assessed using the GaBi software. Given the study's limitations, landfilling is recommended for USW disposal, primarily due to the characteristics of the Brazilian energy matrix. Additionally, centralized anaerobic digestion of AW is recommended. For public decision-makers, this study is suggested to be utilized as a supplementary tool when analyzing various potential scenarios, not only for waste management but also for any project aiming at mitigating environmental impacts.

With the growing interest in wind energy in urban environments, vertical axis turbines are gaining prominence due to their low cost of installation and maintenance and their ability to operate in regions with constantly changing winds. However, these devices still face challenges in terms of their power coefficient, which is relatively low compared to horizontal axis turbines. One of the current lines of research to increase the performance of these turbines is the study of the pitch angle of their blades. The state of the art indicates an improvement in the power coefficient of up to about 10% by changing the pitch angle. This increase is attributed to the delay in the release of the dynamic stall vortex of the blades. However, in vertical axis turbines, each blade creates an individual wake. During turbine operation, the wake of one blade interacts with another blade. This
interaction affects its torque production, a phenomenon that has not been explored in the literature for vertical axis turbines. This research focuses on the changes that varying the pitch angle causes in he wake-blade interactions of H-Darrieus turbines. It also analyzes how varying the pitch angle alters the phenomenon of dynamic stall in the blades. To study these phenomena, URANS-type numerical analyses have been performed using the 𝜅−𝜔 SST turbulence model. In addition, the study includes theoretical approaches based on aerodynamic force data obtained using the panel method. The analyses have been carried out using configurations that include both three blades and a single blade. These multiple configurations make it possible to evaluate the differences between blade passage with and without wake interaction. The analysis of the wake interaction leads to the conclusion that changing the pitch angle causes an increase in the incidence of the boundary layer separation phenomenon and displaces the vortex that detaches from the blades,
changing the way it impacts the downstream blade. Applying these findings to a study of the pitch angle of the turbine, this research shows that changing the pitch angle to -5° causes an increase in the power coefficient of the turbine of 22%, 12% more than reported in the literature.

Chaos exhibits a wealth of periodic patterns exploited by chaos control through small perturbations, stabilizing one of its countless trajectories. This work aims to explore a generalization of the ETDF method to stabilize UPOs. This generalization involves considering the complete matrix gain K, instead of the conventional scalar gain approach. A nonlinear pendulum was chosen as the system for applying the method. Three UPOs, with periodicities 1, 2 and 3, were selected to evaluate the control strategy. The controller gains were evaluated by determining stability through the largest Lyapunov exponent. The matrix term K12 consistently increased system instability across all evaluated cases, leading to its exclusion for control purposes. Cases involving two parameters with K11 and K22, as well as K21 and K22, and the three-parameter case comprising K11, K21 and K22 were considered. All combinations considered revealed a broader region of stability for the system when compared to the scalar-base approach, but generally with similar magnitudes for the Lyapunov exponent. The actuation of the controller and the corresponding energy consumption were compared for each stabilization scenario. The possibility of migration between the selected UPOs was also evaluated. The results showed good flexibility when using the matrix K, prioritizing the system's needs, whether with smaller actuations or energy consumption. In the control implementations without K21, it was possible to transition between all orbits according to the control rule, whereas in those that considered this parameter, the stabilization of the period-1 UPO was not achieved.

A large portion of the fatigue life of materials consists in the growth of small cracks. Despite the progress in the understanding of small fatigue crack growth over the last 50 years, it remains a fundamental and active research topic. In this context, the aims of the present work were twofold: (i) to experimentally characterize the small crack growth of 1045 carbon steel with a small surface defect when subjected to cyclic loading and (ii) to assess the accuracy of small crack growth models in predicting fatigue life. Cylindrical specimens with an artificial cylindrical hole (diameter and depth of 400 µm) were subjected to cyclic axial loading under load ratios of -1 and 0.1. The tests were conducted in the high-cycle fatigue regime, with lives ranging from 10^4 to 10^7 cycles. Crack growth in the vicinity of the hole was monitored by periodically interrupting the tests and measuring the crack length using a confocal laser microscope. The incremental polynomial method was then used to obtain the crack growth rate vs. crack length. A modified form of the Fatemi model for small crack growth rate was developed by substituting the Smith–Watson–Topper parameter for a Walker-type parameter. The constants of the model were determined by fitting the small crack growth data obtained under uniaxial loading. To verify the accuracy of fatigue life predictions under multiaxial loading, axial/torsional test data previously produced by the Fatigue, Fracture, and Materials research group of the University of Brasília were used. The data included in-phase and out-of-phase loading conditions and the presence of mean stress. It was demonstrated that the use of the Walker-type parameter yielded improved life estimates, especially for the tests involving mean stress. Most of the fatigue life estimates were within a factor of 3 with respect to the measured lives. 

This study presents a methodology for the conceptual development of the first Brazilian naval version of a supersonic solid-fuel-based ramjet missile. This tactical weapon plays a crucial role in safeguarding sensitive installations and maritime communication lines within the exclusive economic zone. The research draws upon the European Cooperation for Space Standardization practices, commonly employed in space activities, as a reference for the conceptual design of the missile. To achieve the study’s objectives, novel numerical tools for assessing external and internal ballistics performance are introduced, enabling comprehensive system analysis and optimization. These computational programs utilize motion equations and internal ballistics calculations to estimate various stages of the missile’s trajectory, including ascent, cruise, and coasting. They also facilitate the design of a solid-fueled ramjet engine. Subsequently, the proposed methodology is implemented to develop two baseline conceptual versions of the supersonic missile. The first version incorporates a booster that has been tested in Brazil as its first stage, followed by a ramjet engine as the second stage. The second conceptual missile is entirely defined by a specific methodology, featuring a diameter of 600 mm and a length of 8,300 mm. This missile is designed to fly at Mach 3, at an altitude of 14,000 m, and is capable of carrying a warhead weighing 200 kg, with a range exceeding 300 km. The methodology outlined in this study offers a preliminary design for a high-performance, long-range anti-ship missile tailored for the Brazilian Navy.

In recent years, the increase in population and, consequently, the demand for energy has led to a search for sustainable solutions. One of these solutions involves the utilization of urban forest waste (UFW), which are often improperly discarded, causing environmental problems. Faced with the challenge of ensuring sustainable energy and protecting the environment, it is essential to study alternatives that minimize environmental impacts and improve the management of these residues in the economy. Recent studies show that torrefaction is a promising and important technique for the thermochemical pretreatment of lignocellulosic biomass. The torrefied product acquires properties like coal and characteristics optimized for sustainable energy and heat generation, improving biomass properties such as energy density, hydrophobicity, decomposition resistance, and storage performance. In this study, a biomass torrefaction model was developed to provide essential information for waste-to-energy solutions, specifically for future exergetic analysis. Experimental data from a mixture of UFW from the Brasília forest ecosystem were used as input data for simulations. The model, implemented in Aspen Plus® software, was validated at various torrefaction temperatures (225-275°C), showing good agreement with reported experimental data and estimating various parameters for the qualification of the torrefied material (Absolute Deviation < 9%). Torrefaction was successfully modeled using an RYield reactor, employing a two-step kinetic reaction model for biomass decomposition. Subsequently, using the Response Surface Methodology (RSM), the model's potential was explored by varying residence time, initial moisture content of raw biomass, and treatment temperature, obtaining statistically significant mathematical models (p-value < 0.05) with R² > 0.99. The model demonstrated the ability to i) provide a detailed distribution of products and by-products during the biomass torrefaction process and ii) predict important fuel properties, such as proximate and elemental analyses. Additionally, the model allows the estimation of energy consumption and irreversibility properties.

In this work, we study the combined effects of surfactant elasticity (𝐸), coverage factor (𝑋),

Péclet number (𝑃𝑒) and the magnetic field on the flow at droplet’s scale, in addition to its

impacts on the emulsion’s rheology and the mean magnetization of the system. Our analysis

consider a single two-dimensional surfactant-covered droplet of a superparamagnetic

ferrofluid suspended in an immiscible, non-magnetizable liquid confined in a channel

between parallel plates. The system is simultaneously subjected to a simple shear flow

and an external uniform magnetic field. An alternative methodology is proposed here,

combining the level set method, to capture the interface, and the closest point method

to solve the surfactant transport equation. We separate the dilute phase contribution to

emulsion viscosity in the capillary viscosity (𝜂𝑐), associated to the normal stress jump, the

Marangoni viscosity (𝜂𝑚), related to the stress tangent to the interface, and the magnetic

viscosity (𝜂𝑚𝑎𝑔), linked to the magnetic field intensity. In addition, when the droplet is

subjected to an external field, we also separate the symmetric and antisymmetric parts of

the stress tensor ⟨𝜎⟩, dividing the emulsion viscosity into two distinct contributions: shear

(𝜂𝑠) and rotational (𝜂𝑟) viscosities, respectively. Our results show that, in the absence of

magnetic field, 𝐸 and 𝑋 affect the droplet shape more intensely than the 𝑃𝑒. On the other

hand, 𝑃𝑒 directly affects the emulsion’s bulk viscosity. For 𝑃𝑒 ≫ 1, the capillary viscosity

decreases with 𝑋, while the Marangoni viscosity grows with 𝑋. Such compensation

mechanism allows the increase of the bulk viscosity with 𝑋. We also present results for the

first normal stresses difference. In the presence of a magnetic field, the emulsion rheological

behavior is strongly altered, mainly in purely advective regimes (𝑃𝑒 ≫ 1), where the

surfactant is swept, no longer to the droplet tips, but to posterior or anterior regions to

these locations, depending on the direction of the field. This behavior, added to the droplet

alignment in relation to the flow, results in large variations of the system rheology, mainly

regarding the Marangoni viscosity, since the droplet locations of larger ∇𝑠𝜎 are in regions

of high and low local shear rate when the magnetic field is perpendicular and parallel to

the main flow direction, respectively. We found that, although Marangoni stresses have no

effect on the rotational viscosity, [𝜂𝑟] ̸= [𝜂𝑚𝑎𝑔] and [𝜂𝑠] ̸= [𝜂𝑐]+[𝜂𝑚]. The difference between

them increases with the strength of the magnetic field and 𝑋. In turn, the surfactant

distribution along the droplet surface has a larger effect on shear viscosity, increasing it as

𝑃𝑒 and 𝑋 increases. Regarding the system mean magnetization, our results showed that

|M*| is a stronger function of the length projected in the direction of the external field,

where the variations along of 𝑋 range are due the droplet shape. Finally, we shows that

the magnetic torque magnitude increases with 𝑋 when the magnetic field is perpendicular

and when the magnetic field is parallel, 𝑋 has small effect on the magnetic torque.

As Redes Neurais Artificiais (RNA) podem ser entendidas como um sistema computacional complexo formado por uma série de elementos de processamento interconectados inspirados nas Redes Neurais Biológicas, que têm como finalidade o processamento de informações com o objetivo de gerar uma resposta. Este estudo visa combinar as capacidades de RNA’s e Elementos Finitos, desenvolvida por meio de algoritmos de aprendizado supervisionado para prever o comportamento mecânico e as propriedades materiais através de modelos constitutivos para metais e polímeros. A avaliação dos polímeros restringe-se a polímeros termoplásticos e adota-se um modelo elasto-viscoplástico baseado no modelo constitutivo de Mulliken-Boyce. A implementação do modelo é realizada via sub-rotinas VUMAT (integração explícita) no software comercial ABAQUS® para o estudo de compressão uniaxial em grandes deformações. As previsões desejadas para o estudo dos polímeros avaliados são: (1) Previsão dos parâmetros materiais do modelo constitutivo modificado de Mulliken-Boyce implementado, a partir da curva tensão-deformação experimental e (2) previsão da curva tensão-deformação a partir das propriedades do material. O estudo dos metais é baseado em testes de indentação em grandes deformações. A equação de Ludwik é adotada para a descrição do comportamento mecânico e é implementada via integração implícita no mesmo software comercial. As predições almejadas para os metais são: (1) predição da curva tensão-deformação a partir da curva deslocamento-força obtida através do teste de indentação e (2) predição da curva deslocamento-força, indentação residual e pressão de contato a partir das principais propriedades mecânicas de metais. Todas as previsões são realizadas através da implementação de redes neurais via treinamento supervisionado. O desempenho das previsões feitas para todos os casos avaliados mostra boa acurácia com uma redução significativa no tempo de processamento em comparação com implementações via Elemento Finito.

Wind and hydrokinetic energy sources have great potential to meet global energy needs while helping to mitigate environmental problems. Among technologies for converting renewable energy, horizontal axis turbines are the most advanced. However, there are still gaps in knowledge when it comes to the influence of turbulence kinetic energy on energy conversion by horizontal axis turbines. This thesis aims to advance scientific knowledge regarding the mechanisms of conversion of kinetic energy of turbulence into mechanical energy, in horizontal axis rotors subjected to flows with high levels of turbulence intensity. Experimental studies were carried out in a wind tunnel and numerical simulations using Computational Fluid Dynamics (CFD). In the experiments, a cylinder was used upstream of the turbine to maintain average speed and change speed fluctuations in the rotor plane. The power of the wind tunnel fan was adjusted so that the average speed of the rotor plane with the cylinder was the same as in the experiments without the cylinder. The vortices generated by the cylinder concentrated kinetic energy from the turbulence at a specific frequency. In the numerical modeling, the Large Eddy Simulation (LES) technique was used and the same configurations of the experiments were computationally replicated. The average flow and the spectral of points upstream and downstream of the turbine with and without the cylinder were analyzed. In addition, a spectral analysis of the torque was performed and the entire power curve was determined with and without the upstream cylinder. An analysis of the kinetic energy transport of turbulence in the turbine control volume was also carried out. The results showed that the turbine converts kinetic energy from turbulence when it is transported by turbulent structures with a frequency equal to the turbine rotation frequency. When the frequencies are the same, there is a peak in the power curve (Cp), indicating the existence of a mechanism for converting turbulence kinetic energy into shaft power. The numerical analysis identified that this occurs due to pressure diffusion in the control volume during the interaction of the rotor with the large-scale structures that have the same turbine rotation frequency.

In projects involving mechanical structures and components, the presence of notches, grooves, holes, cavities, inclusions, and scratches is common. In the presence of cyclic loads, these features can influence their fatigue strength and life. The objective of this thesis is to propose a methodology for estimating 'SN' curves for components with micro-defects and using them to calibrate critical-plane models for multiaxial fatigue life estimation. The approach of this work is formulated based on a calibration strategy for the Fatemi-Socie, Smith-Watson-Topper, and Susmel and Lazzarin models. The proposed methodology utilizes Murakami criteria, a Bandara et al. strategy, material static properties, and notch sensitivity factors to compute the micro-defect effect. The obtained results were compared and validated against experimental data and further corroborated with literature data for various steel and aluminum alloy materials, demonstrating its promising nature. Among the notable outcomes, the MWCM model stood out, with 92% of estimates falling within a 2-band range and 100% within a 3-standard deviation band. To extend and apply the proposed methodology more broadly, it is recommended to perform life prediction comparisons for different materials, loadings, and defect geometries

The use of reinforced concrete in the construction industry is widespread around the world and this makes some aspects need to be characterized in several technical aspects; it is a material that does not have good behavior in case of dynamic loads, due to its great rigidity and little, if any, deformation. Using a ductile material as reinforcement allows the structural system to have greater freedom to resist vibration and also reduce such abrupt rupture, giving greater security to the building. Therefore, the proposal to use the Nickel-Titanium (NiTi) alloy as reinforcement in concrete tends to favor the recovery of deformations of a structural element and avoid abrupt collapse. This experimental research is limited to the verification of the mechanical behavior of a beam in bending and is mainly based on the international standard ASTM C78. The specimens were manufactured with conventional steel reinforcement and Nickel-Titanium reinforcement; and, tested, carefully following the requirements suggested by the technical standard in force. The results showed that, for the conventional steel, bending strength of 7.37 ± 0.67 MPa and displacement of 10.47 ± 0.47 mm were obtained, making it possible to verify that the conventional steel reinforcement supported greater stress compared to Nickel-Titanium, however, lower displacement; for the Nickel-Titanium reinforcement, the beam presented a mechanical bending strength of 5.42 ± 0.44 MPa and a displacement of 67.30 ± 1.46 mm, demonstrating that the system resisted 26.48% less in bending, however, the displacement was about 642.79% greater in relation to steel reinforcement and also showed partial recovery of the initial position of the beam even after complete failure of concrete.

Turbo machines such as fans, compressors and turbines are among the most important sources of aeroacoustic noise. Typically, the aeroacoustic interaction between the rotor and stator blades of aeronautical turbofan generates tonal noises that propagate along the nacelle duct and has great contribution in the total aeronautical noise generated by modern aircraft. The acoustic modes generated from this interaction depend on the number of blades of the rotor and the stator, known as the Tyler and Sofrin relationship. In this sense, acoustic liners used in the nacelle walls are commonly used for noise control, using the Helmholtz resonator mechanism for acoustic attenuation. In this work, an analytical investigation is proposed for the acoustic modes resulting from the rotor-stator iteration of lined ducts with mean flow. Despite of the existence of analytical expression, these are not in closed form expression and require numerical schemes for root-finding in transcendental equations while also tracking their corresponding modes over a certain frequency band. Subsequently, these results are used to construct the wave dispersion curve of the acoustic modes, i.e., their wavenumber as a function of the frequency. From these curves, the attenuation performance of the liners can be investigated based on the frequency of the cut-on mode and on the behaviour of the imaginary part of the wavenumber. First, a numerical validation of the implemented methodology, using the Muller’s method, is proposed using results from the literature. Then, three different models for liners are investigated, the Tam and Auriault model, and the single degree of freedom and the two degrees of freedom Helmholtz resonator models. The evolution of the radial mode shapes along the frequency is also shown and discussed. In addition, the physical interpretation of the obtained dispersion curves for the different liners’ models is discussed. It is shown that they present significant qualitative and quantitative differences in terms of attenuation performance and main attenuation mechanism. The proposed approach has the potential of being used as a low cost computational design methodology for acoustic attenuation in lined ducts.

In Brazil, the management of solid urban waste (MSW) is a problem that has spread for years. In Brasília city, lignocellulosic residues (tree pruning), present particular difficulties that result in landfill overload and are closely related to environmental problems. As a technological proposal for energy use and environmental remediation, the objective of this work is to characterize the biofuel constituted by lignocellulosic residues of Brasília. For this, a mixture of the six species with the greatest representativeness in the forest ecosystem of the city was established. The proportionally representative mixture was subjected to torrefaction treatment in a thermogravimetric analyzer (TGA) at temperatures of 225, 250 and 275 °C for 60 minutes under inert conditions. In natura samples and torrefied product were chemically analyzed (proximate and elemental analysis and calorific value). A numerical model for was established to determine the kinetics of thermochemical degradation enabling the prediction of blend mass loss at different torrefaction severities. Torrefaction severity was assessed using the Torrefaction Severity Index (TSI) and the Torrefaction Severity Factor (TSF) and models for predicting the properties of torrefied products were statistically evaluated. The gasification of the torrefied product was compared to the raw material, providing information on the use of this biochar for the production of syngas. Finally, the raw product characterization data allowed to establish an optimal mixture through a multicriteria analysis aiming its application as biofuel. Torrefaction treatment showed a significant improvement in the properties of the samples (burning power, homogeneity and hydrophobicity), enhancing it ideal for downstream applications (direct firing and gasification). The indices used to measure the severity of roasting showed effectiveness in terms of accuracy in predicting the chemical properties of the treated products. The results obtained provided quantitative information on the thermal xi and kinetic improvement of biofuel degradation, allowing an analysis of its viability and energy potential.

In this work, a numerical methodology for evaluating the hydrokinetic potential in natural channels is presented. The methodology is validated using a meandering benchmark channel found in the literature. The benchmark channel is modeled and simulated employing CFD tools. The results from the literature are compared to results generated by three different turbulence models: the standard k-epsilon model, an anisotropic k-epsilon model and a RSM. The RSM is proven to be the most consistent and proficient at generating results similar to the literature. This development proves the proposed methodology capable of reproducing the flow in the benchmark channel. Therefore, this methodology is employed for simulating the flow in a natural channel, along with the turbulence model proven to be the most consistent and proficient in replicating the flow in the benchmark channel. As a geometric model for this phase of the research, the bathymetric data of the channel downstream of the Sefac hydroelectric facility is utilized. In order to assess the hydrokinetic potential available within this channel, areas with velocities of ≈1 m/s and a depth of ≈ 1.5 m are desired. A total of five areas are found complying to these requirements. Out of these five areas, three are found to contain the highest velocity and depth values. These areas were also studied for their turbulence levels, to prolong the lifespan of the turbines, by analyzing the occurrence of secondary currents and turbulence intensity profiles. The turbulence levels, although negligible by their value, are found to be the highest near the channel bed, where no turbines would be installed, while the secondary currents are low to none. In contemplation of evaluating the hydrokinetic potential produced yearly by these three areas, additional flow rate scenarios were simulated, representing the most frequent occurring flow rates of the year 2018. Subsequently, the velocities in the three previously selected areas were studied to the end of finding specific potential locations for installing hydrokinetic turbines. Ultimately, the three sections allow for installing a total of 24 turbines, capable of generating ≈ 70 MWh in the year of 2018.

In this work, the rheological effects of applying an external magnetic field to a suspension composed of NaCl crystals dispersed on an aqueous supersaturated solution of the same salt are studied using experimental protocols of the Laboratory of Microhydrodynamics and Rheology of the University of Brasília. The device used in the experiments is a parallel disk rheometer equipped with a magnetic cell. Static tests at constant temperature are performed in the absence of flow. Crystals grow in the solution because salt molecules meet up and interlock, arranging themselves in a lattice structure. These tests indicate, by microscopy observation, that the mean length of the crystals’ microstructure after recrystallization is greater the more intense the magnetic field applied to the samples is. By rheometric experiments (flow regime), we evaluated the behavior of the suspension viscosity in a weak flow regime at a controlled temperature for six increasingly higher magnetic field intensities. These tests show that the suspension viscosity decreases in a nonlinear fashion as the magnetic field intensity increases. This behavior is understood as a result of a weakening of the bonds in the crystal structures, which makes them more susceptible to breakups under the action of a shearing flow. The suspensions present a shear-thinning for every applied magnetic field, which is well described by a power-law model. Experiments in the regime of small amplitude oscillatory shear are also carried out. The viscoelastic modules are determined and we find that the storage modulus does not vanish at low frequencies, indicating the existence of a shear elastic modulus at equilibrium. Experiments using a step-strain in the presence of a magnetic field were also conducted. The stress relaxation function as a function of the magnetic field was obtained and a spectrum of relaxation times determined, showing complex memories of the examined suspensions with three relaxation times. The stress is found to relax to a residual stress, which decreases as the intensity of the applied magnetic field is increased. The results of this work can all be related to changes in the growth rate distribution and size distribution of the salt crystals with the intensity of an applied magnetic field. The present study could be important in the applications involving treatments of kidney stone formation by monitoring an external magnetic field.

This thesis presents an Isogeometric Boundary Elements formulation (IGABEM) for solving bidimensional elastostatics and contact problems. It is applied to the calculation of the stresses and displacements fields. The difference between isogeometric and isoparametric formulations is that while the latter uses polynomial functions, the former uses nonuniform rational B-splines (NURBS), T-splines or similar. Aiming to facilitate the implementation of the isogeometric formulation to existing BEM codes, the Bézier decomposition is used. In this way, NURBS are decomposed in simpler basis functions, which resembles lagrangian polynomials. For the contact problems, a node-to-node formulation is adopted, which is a traditional technique in the literature for defining the contact modes. When it comes to treating the singularities, Telles transformation and Singularity Subtraction Technique (SST) are used for weak and strong singularities, respectively. Collocation, in turn, is made according to Greville’s abscissae, for they are a better fit to isogeometric. IGABEM has more acurate results when compared to standard BEM because the former is able to exactly describe complex geometries, which are only approximated by polynomial functions. The results corroborate this hypothesis, since IGABEM is consistently more accurate than standard BEM considering the same number of degrees of freedom. The obtained results are compared to those available in the literature, showing good agreement. IGABEM requires more processor time for running the same problem, as it was expected due to NURBS being more costly than Lagrangian polynomials. BEM is also compared to NTS-FEM, STS-FEM, and DMT-FEM for fatigue life estimation. Firstly, the stress history during a complete loading cycle is computed by each framework. Then, a critical plane approach is used to obtain the shear stress amplitude and the maximum normal stress. Lastly, the Fatemi-Socie criterion of failure is used for estimating fatigue life.

This thesis has exploratory objectives of an experimental nature, whose main objective is to present an analysis on how the influence of temperature affects the fatigue life of the Orchid conduit. In this sense, to reach the general objective it was necessary to implement an engineering solution based on a PID control that provides real temperature conditions, whose high voltage cables are subjected daily during their useful life. Thus, the development of controlled infrared heating equipment for the connection between the conductor cable and the suspension clamp (regions susceptible to fatigue failure) will be presented. In this sense, a device responsible for heating and temperature control in the connection region was implemented and tested. The series of tests was carried out to evaluate the operation, the experimental device demonstrated excellent performance and satisfactory operation, and the operational criteria were fulfilled, to carry out the fatigue test on the cables under high temperature conditions. Continuing the investigation, two test steps were performed under fatigue conditions, nine tests at 75°𝐶 (maximum conductor temperature for ampacity calculation) for step one (E1), whose results were compared with literature data at room temperature. And seven trials for step two (E2), with four trials at 21°𝐶 and three trials at 75°𝐶. The analysis of E1 allowed to verify a reduction of the order of 30% in the useful life in the samples tested at 75°𝐶, considering as failure criterion the rupture of 10% of the total number of aluminum wires. Assuming the first breakage of the aluminum wire as a failure criterion, the average reduction in the useful life of the conductor was only 10%, the E2 analyzes corroborated this result and presented an average reduction between the tested amplitudes of 9% reduction. This comparison allows us to affirm that the survey of the comparative experimental curves for the cable/clamp assembly constitutes an interesting and strategic tool for the design of transmission lines, as well as establishing parameters capable of leading to projects of retraining, preventive and corrective maintenance of existing transmission lines. Considering these results, it was observed that there is room to improve design approaches at high temperatures, which could be a valuable tool to define new design boundaries.

This work has been developed within the scope of a joint PhD agreement between the University of Paris-Saclay (UPS) and the University of Brasilia (UnB). The scientific context of the thesis has been chosen to try to provide data and solutions for problems in the aeronautical sector, as Safran Aircraft Engines has been an important industrial partner for this and other thesis in both universities. In this setting, one of the motivations to study the effect of a variable contact normal loading in the fretting fatigue problem comes, not only from the fact that there are few reliable experimental data and analyses in these conditions, but also that, in practical applications, such as the one existing between the blade root and the disk interface of an aircraft turbine, such contact load is also time-varying. Within this context, to be more precise, the present thesis has three main goals. The first one is to design and construct a new fretting fatigue apparatus capable of performing different types of tests, where the loads and their respective actuators involved in the experiments can be independently controlled. The test rig will be designed so that fretting fatigue experiments can also be carried out at high temperatures. The second goal is to evaluate the effect of cyclic normal load in fretting fatigue strength for the titanium alloy Ti-6Al-4V at room temperature and for the Inconel 718 alloy at room and elevated temperature. These materials were specially chosen due to the great interest of the aeronautical industry. The third and final aim is to assess fretting life by means of a finite element model which considers wear effects and a multiaxial fatigue parameter. A new four actuators fretting fatigue apparatus was entirely designed to tackle the problem of imposing cyclic contact normal load. The cyclic normal load is now applied by two MTS servo-hydraulic actuators, which were installed perpendicularly to the fretting specimen. Further, the tangential and fatigue loads are applied by independent servo-hydraulic actuators. Due to these upgrades, the new fretting fatigue rig of the University of Brasilia can independently control all the loads involved in the fretting tests (bulk, normal and tangential loads). All these loads can not only vary with time in-phase or out-of-phase, but their waveforms can also be applied synchronously or asynchronously. Moreover, two ceramic igniters were placed next to the contact parts to conduct tests at elevated temperatures. The heating system is capable to reaches to reach temperatures up to 750°C and maintaining it stable within a range of ±$ 10°C. In order to evaluate the influence of the cyclic normal load on the fretting fatigue strength, tests under the partial-slip condition with a constant and cyclic contact normal load were conducted at room temperature for the Ti-6Al-4V alloy and at room and 540°C for the Inconel 718 alloy. The experimental results indicate that cyclic normal load has a beneficial effect on fretting life for the specific conditions of tests here conducted. This behaviour was observed for the Ti-6Al-4V and Inconel 718 alloys at both tested temperatures. Besides that, an experimental campaign to assess the influence of time-varying normal load on the friction coefficient was also carried out. Based on this experimental evaluation, the presence of cyclic normal loads does not seem to influence the coefficient of friction under partial slip conditions. However, comparing the friction coefficient results of the Inconel 718 alloy at room and elevated temperature, a significant reduction was observed for both contact normal loading situations with the increase of the temperature. In addition, a finite element model (considering and neglecting wear effects) was used in conjunction with the Smith-Watson-Topper critical plane parameter and a non-local stress averaging approach to estimate fretting life. Concerning the life estimate approaches considered in this study, for the constant and cyclic normal load cases, both implemented methodologies, whether accounting or neglecting wear, provided satisfactory results, with the one disregarding wear being slightly more accurate.

This work presents two fast isogeometric formulations of the Boundary Element Method (BEM) applied to heat conduction problems, one accelerated by Fast Multipole Method (FMM) and other by Hierarchical Matrices. The Fast Multipole Method uses complex variables and expansion of fundamental solutions into Laurant series, while the Hierarchical Matrices are created by low rank CUR approximations from the k−Means clustering technique for geometric sampling. Both use Non-Uniform Rational B-Splines (NURBS) as shape functions. To reduce computational cost and facilitate implementation, NURBS are decomposed into Bézier curves, making the isogeometric formulation very similar to the conventional BEM. A description of the hierarchical structure of the data and the implemented algorithms are presented. Validation is performed by comparing the results of the proposed formulations with those of the conventional BEM formulation. The computational cost of both formulations is analyzed showing the advantages of the proposed formulations for large scale problems.