When the point under consideration is not near to the source of vibration, the strains developed in the rock mass due to the passage of waves are usually of small magnitude, and within the elastic range. However, the rock mass may be subjected to a wide range of strain levels depending on the source of vibration and the wave frequency, even within the elastic limit. The present study is based on the two general conditions existing at field, long wave length propagation of waves and intermediate wavelength propagation of waves. When the wavelength of propagating wave is much longer than the joint spacing, it is referred to as long wavelength condition and is associated with propagation of low frequency waves across closely spaced joints. When wavelength of propagating wave is nearly equal to joint spacing, it is known as intermediate wavelength condition and is associated with propagation of high frequency waves. Long wave length propagation of waves has been studied by conducting laboratory experiments using Resonant Column Apparatus on developed plaster gypsum samples. The influence of joint types, joint spacing and joint orientation on wave propagation has been analyzed at three confining stresses under various strain levels. The wave velocities and damping ratios at various strain levels have been obtained and presented. Shear wave velocities are more dependent on confining stress than compression wave velocities across frictional joints whereas, compression wave velocities are more dependent on confining stress than shear wave velocities across filled joints. Wave velocities are at minimum and wave damping is at maximum across horizontal joints whereas wave velocities are at maximum and wave damping is at minimum across vertical joints. Shear wave velocity and shear wave damping are more dependent on joint orientations than compression wave velocity and compression wave damping. As Resonant Column Apparatus has some limitations in testing stiff samples, a validated numerical model has been developed using Discrete Element Method (DEM) that can provide resonant frequencies under torsional and flexural vibrations. It has been found from numerical simulations, that reduction of normal and shear stiffness of joint with increasing strain levels leads to wave velocity reduction in jointed rock mass. Intermediate wave length propagation of waves has been studied by conducting tests using Bender/ extender elements and the numerical simulations developed using 3DEC (Three Dimensional Distinct Element Code).Parametric study on energy transmission, wave velocities and wave amplitudes of shear and compression waves, has been carried out using the validated numerical model. The propagation of waves across multiple parallel joints was simulated and the phenomenon of multiple reflections of waves between joints could be observed. The transformations of obliquely incident waves on the joint have been successfully modeled by separating the transmitted transformed P and S waves. The frequency dependent behavior of jointed rocks has been studied by developing a numerical model and by applying a wide range of wave frequencies. It has been found that low frequency shear waves may involve slips of rock blocks depending on the strength of rock joint, leading to less transmission of energy; while low frequency compression waves are well transmitted across the joints. High frequency shear and compression waves experience multiple reflections and absorptions at joints.

Submitted by Jesiel Ferreira Gomes (jesielgomes@ufcg.edu.br) on 2018-04-17T23:15:52Z No. of bitstreams: 1 FELIPE DE OLIVEIRA APOLINÁRIO – DISSERTAÇÃO (PPGEPM) 2016.pdf: 5151929 bytes, checksum: f4706d54cb97c9b01a64299ddb28cd7d (MD5) / Made available in DSpace on 2018-04-17T23:15:52Z (GMT). No. of bitstreams: 1 FELIPE DE OLIVEIRA APOLINÁRIO – DISSERTAÇÃO (PPGEPM) 2016.pdf: 5151929 bytes, checksum: f4706d54cb97c9b01a64299ddb28cd7d (MD5) Previous issue date: 2016-09-06 / Capes / O presente trabalho teve como objetivo analisar a influência da saturação fluida nas propriedades elásticas de rochas carbonáticas, bem como a eficácia dos modelos de substituição de fluidos e de simulação computacional. Foram estudadas 9 amostras de rochas carbonáticas, sendo dois calcários laminados e sete tufas. As medições de velocidade foram realizadas em amostras secas, saturadas com água ou com óleo, sob diferentes pressões efetivas. A simulação de propagação de ondas foi feita no COMSOL Multiphysics 5.1, utilizando o Avizo Fire 8.1 para a criação das amostras digitais. Análise por difração de raios X (DRX) foi realizada para determinar a composição das amostras de rocha. Os resultados obtidos nos ensaios laboratoriais e nas simulações computacionais foram comparados com as estimativas dos modelos de substituição de fluidosGassmann, Biot e Brown & Korringa. Foi observado que a saturação das amostras com agua ou óleo geraram aumentos nas velocidades de propagação de onda P, porém sem apresentar um comportamento padrão. Para o caso das ondas S, a saturação por óleo predominantemente gerou aumentos nas velocidades, com exceção para os casos em que as amostras possuíam porosidade secundária do tipo vugular, devido à pouca influência que o óleo oferece para o módulo de cisalhamento nestes casos. A saturação por água resultou em diminuições das velocidades de propagação de onda S devido ao aumento da densidade total. Também foi constatado que o modelo de Gassmann foi o mais efetivo na estimativa de velocidades de onda P e S, enquanto que o de Biot mostrou-se eficaz apenas para a estimativa de velocidades de ondas S, sendo ineficiente para a estimativa de velocidades de ondas P, com erros de até 20%. A simulação computacional gerou resultados superdimensionados, porém que evidenciam que um aperfeiçoamento da metodologia, tal como o aumento do número de pontos de leitura pode gerar resultados mais próximos dos obtidos laboratorialmente e de maior confiabilidade. / This research aimed to analyze the influence of the saturating fluid in carbonate rocks, as well as verify the effectiveness of the fluid substitution models and computational simulations of wave propagation. To do so, nine carbonate rock samples were analyzed, which two of them were laminated limestones and seven were carbonate tufas. The measurement of velocities were made in dry, water saturated and oil saturated samples, under different effective pressures. The wave propagation simulations were made in COMSOL Multiphysics 5.1 using Avizo Fire 8.1 to generate the digital rock samples. The results obtained in lab procedures and in computer simulations were compared with the estimated velocities of the fluid substitution models of Gassmann, Biot and Brown & Korringa. It was observed that the saturation of the samples with water or oil resulted in an increasing of P-wave velocities, however without a pattern. The saturation with oil resulted in most cases in an increasing of S-wave velocities, the exceptions occurred in samples which had vugular porosity, due to the small influence of the oil in the shear modulus in this cases. T he saturation with water resulted in a decreasing of S-wave velocities due to the increment of the bulk density. It was found that the Gassmann’s model was more effective than the other two models in estimating P-wave and S-wave velocities. Biot’s model generated unsatisfying results to P-wave velocities, with errors up to 20%. However, this model had a good accuracy in estimating S-wave velocities. The computer simulations produced mainly overestimated results, though it was shown that an optimization of methodology, such as and addition in the number of the measure points, could improve the quality of the data, providing more representative results.

Dans le cadre du projet européen Clean Sky, Snecma construit un démonstrateur de Contra Rotating Open Rotor (CROR). La conception du système de régulation du moteur nécessite d'avoir connaissance du comportement aérodynamique de chacune des hélices du doublet. Les objectifs de cette thèse sont dans un premier temps de comprendre les interactions entre les différents éléments constitutifs d'un CROR ayant un effet sur les performances des hélices, d'isoler leurs contributions respectives et dans un deuxième temps de développer un modèle prédictif des performances individuelles des hélices d'un CROR intégrable dans un environnement de calcul de cycles thermodynamiques. Pour cela, le comportement des hélices en doublet est rapproché de celui d'hélices isolées dont les effets macroscopiques sont bien connus. Des calculs Euler et NS3D ont servi de base pour proposer un couplage entre les hélices isolées permettant de retrouver le champ de vitesses induits entre les hélices d'un calcul doublet. Pour respecter les exigences de rapidité d'exécution et de robustesse numérique imposées par l’environnement de calcul de cycles thermodynamiques, les performances individuelles des hélices du doublet sont calculées à partir de champs hélice isolée. Une approche monodimensionnelle permet de calculer les vitesses induites propres des hélices à partir de la traction et de la puissance absorbée et une méthode pour estimer les vitesses induites mutuelles à partir des vitesses induites propres est donnée. Le calcul des performances individuelles des hélices d'un doublet contrarotatif est itératif. Cette méthode estime les performances avec une erreur relative inférieure à 5%. Elle est utilisée dans le développement du système de régulation du démonstrateur CROR SAGE2. / Within the scope of the European research project Clean Sky, Snecma builds a ground demonstrator of the concept engine Contra Rotating Open Rotor (CROR). Engine control system design requires knowing how each propeller will behave aerodynamically under the interaction of each other. The aim of this work is to design a predictive model of contra rotating propeller individual performance fitting in a thermodynamic cycle calculation environment. A coupling is proposed in order to represent the dual propellers thanks to isolated propeller behavior. It has been shown that by matching the isolated propellers thrust and torque to the doublet values, the good values of mutual induced velocities can be found. Hence contra rotating propellers individual performance can be reached with a good variation in parameters. In addition to that, in order to meet withthermodynamic cycle calculation environment requirements of rapidity and numerical robustness, performance is calculated from pre-generated propeller maps. One-dimensional approach is used to calculate mutual induced velocities from propellers thrust and torque. Contra rotating propellers individual performance calculation is an iterative process. The method developed gives the performance within a 5% relative error margin and is currently used for the design of the ground demonstrator control system.

We study the motion of giant stars in the Solar neighbourhood and what they tell us about the dynamics of the Galaxy: we thus contribute to the huge project of understanding the structure and evolution of the Galaxy as a whole. <p><p>We present a kinematic analysis of 5952 K and 739 M giant stars which includes for the first time radial velocity data from an important survey performed with the CORAVEL spectrovelocimeter at the Observatoire de Haute Provence. Parallaxes from the Hipparcos catalogue and proper motions from the Tycho-2 catalogue are also used.<p><p>A maximum-likelihood method, based on a bayesian approach, is applied to the data, in order to make full use of all the available stars, and to derive the kinematic properties of the subgroups forming a rich small-scale structure in velocity space. Isochrones in the Hertzsprung-Russell diagram reveal a very wide range of ages for stars belonging to these subgroups, which are thus most probably related to the dynamical perturbation by transient spiral waves rather than to cluster remnants. A possible explanation for the presence of young group/clusters in the same area of velocity space is that they have been put there by the spiral wave associated with their formation, while the kinematics of the older stars of our sample has also been disturbed by the same wave. The emerging picture is thus one of "dynamical streams" pervading the Solar neighbourhood and travelling in the Galaxy with a similar spatial velocity. The term "dynamical stream" is more appropriate than the traditional term "supercluster" since it involves stars of different ages, not born at the same place nor at the same time. We then discuss, in the light of our results, the validity of older evaluations of the Solar motion in the Galaxy. <p><p>We finally argue that dynamical modeling is essential for a better understanding of the physics hiding behind the observed kinematics. An accurate axisymmetric model of the Galaxy is a necessary starting point in order to understand the true effects of non-axisymmetric perturbations such as spiral waves. To establish such a model, we develop new galactic potentials that fit some fundamental parameters of the Milky Way. We also develop new component distribution functions that depend on three analytic integrals of the motion and that can represent realistic stellar disks. / Doctorat en sciences, Spécialisation physique / info:eu-repo/semantics/nonPublished

Le géoradar, ou Ground Penetrating Radar (GPR) en anglais, est une méthode non destructive couramment utilisée pour l'auscultation des ouvrages en béton. L'intérêt de cette méthode réside sur sa capacité à ausculter rapidement des très grandes surfaces, elle est de plus en plus employée en Génie Civil. Habituellement, cette méthode est utilisée en Génie Civil pour la localisation les aciers de renforcements, ou bien pour l'estimation de l'épaisseur d'enrobage du béton. Toutefois, la méthode GPR peut aussi être utilisée pour l'auscultation du béton. En effet, le béton est un matériau diélectrique poreux qui peut modifier la propagation des ondes électromagnétiques (EM). Les résultats les plus récents présentent la capacité du GPR à évaluer la teneur en eau. Cependant, le GPR pourrait très bien aussi être utilisé pour la détection des ions chlorure présents dans la solution interstitielle du béton, car comme les chlorures modifient la conductivité du béton ils sont susceptibles d'atténuer les ondes électromagnétiques. Néanmoins, seulement quelques études ont été menées dans ce domaine. Par conséquent, dans cette étude, nous proposons d'utiliser les ondes EM du géoradar pour estimer conjointement la teneur en eau et la teneur en chlorure du béton pour différents corps d'épreuves. Pour cela, plusieurs séries de corps d'épreuves sont utilisées avec des modes de contaminations par les chlorures différents. Une procédure de mesure de la vitesse à partir de l'analyse des signaux réfléchis est proposée. On démontre que la vitesse des ondes EM est essentiellement affectée par la teneur en eau alors que l'atténuation est sensible à la fois à la teneur en eau et à la teneur en chlorures. Ensuite, dans un second temps, nous testons différents modèles de permittivité pour prédire les mesures de constante diélectrique et du facteur de pertes évalués à partir des mesures par GPR ou de résistivité électrique. / Ground Penetrating Radar (GPR) is an usual nondestructive testing method for the assessment of concrete structures. The benefit of this method lies within its ability to assess quickly a large scale of concrete surface. Generally, GPR is used for the localization of reinforcements or for the thickness measurements. However, GPR can be also used for the diagnosis of concrete because concrete is a porous dielectric material which can modify the propagation of the electromagnetic (EM) waves. Most common results present the ability of GPR to assess moisture. But, GPR could be also used to detect the presence of chlorides into the interstitial concrete solution as chlorides can modify the concrete conductivity and altered the electromagnetic signal waves. However, only few studies have been carry-out on that field. Therefore, in this study, we propose to use GPR electromagnetic waves to evaluate both the water content and the chloride content inside the interstitial concrete solution of several tests concrete samples. So, several groups of concrete samples with the same formulation will be conditioned for different chloride contamination modes. Thereafter, a velocity measurement process will be proposed from the reflected signal wave analysis. In that process, we will show that the velocity is only affected by the water content while the attenuation strongly affected by both the water content and the chloride content. Furthermore, we will test several permittivity models to predict the dielectric permittivity and the loss factor estimated from the concrete samples measurements with the GPR device and the electrical resistivity device.

No description available.

Structural shape optimisation is a field that has been studied since early on in the development of finite element methods. The sub-fields of shape and topology optimisation are continuously growing in industry and aim to leverage the benefits of technologies such as 3D printing and additive manufacturing. These fields are also being used to optimise designs to improve quality and reduce cost. Gradient-based optimisation is well understood as an efficient method of obtaining solutions. In order to implement gradient-based optimisation methods in the context of structural shape optimisation, sensitivities describing the change of the domain stiffness are required. To obtain the stiffness sensitivities, mesh deformation sensitivities are required. In this study, a mesh generating method is developed that provides mesh deformation sensitivities. For shape optimisation it is advantageous to employ an optimisation algorithm that allows for the manipulation of CAD geometry. This means that the CAD geometry is finalised upon completion of the optimisation process. This, however, necessitates the calculation of accurate sensitivities associated with non-linear geometries, such as NURBS (those present in CAD), by the mesher. The meshing method developed in this study is analogous to a linear truss system. The system is solved for static equilibrium through a geometrically non-linear finite element analysis using Newton’s method. Sensitivities are made available by Newton’s method for use in generating mesh sensitivities for the system. It is important for the mesher to be able to accurately describe the geometrical domain which approximates the geometry being modelled. To do so, nodes on the boundary may not depart from the boundary. Instead of prescribing all boundary nodes, this mesher frees the boundary nodes to move University of Pretoria ii Department of Mechanical and Aeronautical Engineering along, but not away from the boundary. This is achieved using multipoint constraints since they allow for an analytical relationship between boundary node movement and the boundary. Two multipoint constraint (MPC) methods are investigated for boundary discretisation, namely, the Lagrangian and master-slave elimination methods (MSEM). The MSEM presents several difficulties in obtaining convergence on non-linear boundaries in general when compared to the Lagrangian method. The MSEM has reduced computational requirements for a single Newton step, especially when direct solvers are used. However, when indirect solvers are implemented the time difference between the two MPC methods reduces significantly. For a “medium” curvature geometry the Lagrangian implementation has only a 6% time penalty. The Lagrangian method is selected as the preferred MPC method for implementation in the mesher to avoid the convergence problems associated with the MSEM. This is justified on the basis of reliability outweighing the 6% time penalty for what is intended to be a tool in the shape optimisation process. Analytical sensitivities are obtained for the truss system in order to account for the MPC boundaries. The analytical mesh sensitivities are proven to be accurate through comparison with numerical sensitivities. The method is demonstrated to be able to accurately described the mesh deformation throughout the domain for both uniform and non-uniform meshes in the presence of non-linear boundaries. / Dissertation (MEng)--University of Pretoria, 2020. / Mechanical and Aeronautical Engineering / MEng (Mech) / Unrestricted

Glass has sophisticated front properties and are used as facades in high buildings. During cold periods, these glass facades could cause thermal discomfort, due to cold downdraught. Cold downdraught can be countered by placing heaters under glass surfaces. Nowadays technology offers highly insulating windows, which is why there is an interest to investigate the indoor climate with only underfloor heating. The research in this area is limited, and few empirical methods are available. Theoretical analysis has begun but it still brand new. The aim of this investigation was to present the thermal indoor climate influenced by various parameters, such as outdoor temperature, U-value and the glass height. The results were also meant to be used as reference tools in future projects. A reference building was modeled in simulation software called CFD Star-CCM+. The assignment was initiated by Incoord, a leading consulting company in energy, indoor climate and installation planning. The results showed that the air velocity increases with decreasing outdoor temperature and decreases with increasing thermal insulation (lower U-value). At the edges of the glass the air velocity becomes twice as large compared to the velocity of the air in the middle of the atrium. The air velocity (maximum and average) at 0.1 m above the floor is always higher than at 2.0 m. The lowest air velocities start from about 0.25 m/s at 0 ℃ and reaches to 0.60 m/s at -20 ℃. That means these air velocities are too high for what is accepted as a good indoor climate, where the maximum allowable air velocity is 0.15 m/s. The outdoor temperatures and the glass facade’s U-value also have an effect on the surface temperature of the glass facade. This decreases the surface temperature with decreased outdoor temperature, and the surface temperature increases at lower U-value. The height of the glass facades proved to affect both the air velocity in the occupied zone and in the glass surface temperature. The air velocity increases with the glass’ height. The increase is higher at 0.1 m than at 2.0 m above the floor. The result shows also that the average air velocity is lower than 0,15 m/s at window height lower than 5 m. But, at the same height the maximum air velocity is higher than 0.3 m/s. The surface temperature of the glass facades increases with the glass’ height. This is because the indoor heat transfer coefficient increases with height. The outdoor heat transfer coefficient is a function of the wind speed and was assumed to be constant. The underfloor heating, which is represented in the simulations with a floor surface temperature of 27 ℃, is not enough to maintain a good indoor climate in any of simulations. The results of this thesis showed a strong relation between indoor climate, outdoor temperature, U-value and the glass height. This study also showed that the floor heating is not enough to counteract the cold draft during extreme cold periods, in high glass buildings. The presented results can be used as a reference tool for the assessment of air velocities and surface temperatures, in similar high buildings.

The thesis deals with processing of epoch-wise GNSS measurements from local geodynamic network Sněžník. Its aim is to evaluate the geodynamics in the area of Králický Sněžník Massif and to assess the capabilities of epoch-wise GNSS measurements to detect the geodynamic movements. Within the thesis the comprehensive processing of all the GNSS measurements observed between years 1997 and 2011 is realized using the reprocessed products of first IGS reprocessing Repro1. Bernese GPS software version 5.0 is used for all the processing.

The real estate industry is one of the largest industries in the world and using data-driven decision-making has been shown to increase companies’ profitability. A technique to apply data-driven decision-making is machine learning. Within the real estate industry, predicting property selling prices and sale velocities (the duration a property remains on the market) are crucial factors of interest. Knowing the selling price and the sale velocity can motivate businesses to alter their plans in an effort to increase their profitability. The research conducted in this thesis employs a comparative approach to evaluate the performance of various machine learning methods in predicting both the selling price and the sale velocity of properties. The machine learning methods this study investigated are random forest, decision tree, K-nearest neighbor, support vector regression, and multilayer perceptron. After pre-processing, the data set used comprises 560,000 distinct data points from the Swedish housing market. The data set has a wide geographic scope, covering almost the entire country of Sweden. The data set was subjected to both normalization and standardization techniques in order to determine how they affected the machine learning methods. The results demonstrate that random forest oEutperforms the other machine learning methods in predicting property selling prices. However, the assessed machine learning methods encountered difficulties in predicting the sale velocity. The best-performing machine learning method for sale velocity is random forest. Notably, SVR demonstrates a lower MAE for sale velocity, but performs worse in the R² metric. / Fastighetsbranschen är en av de största industrierna i världen och att använda datadrivet beslutsfattande har visat sig öka företags lönsamhet. En teknik för att tillämpa datadrivet beslutsfattande är maskininlärning. Inom fastighetsbranschen är förutsägelser av fastigheters försäljningspriser och försäljningshastigheter viktiga faktorer av intresse. Kunskap om försäljningspriset och försäljningshastigheten kan motivera företag att ändra sina planer i syfte att öka lönsamheten. I den forskning som bedrivs i denna avhandling används en jämförande metod för att utvärdera olika maskininlärningsmetoders prestanda när det gäller att förutsäga både försäljningspriset och försäljningshastigheten för fastigheter. De metoder för maskininlärning som undersökts i denna studie är random forest, decision tree, K-nearest neighbor, support vector regression och multilayer perceptron. Efter förbehandling består den använda datamängden av 560 000 distinkta datapunkter från den svenska bostadsmarknaden. Datamängden har en stor geografisk räckvidd och täcker nästan hela Sverige. Datamängden utsattes för både normaliserings- och standardiseringstekniker för att avgöra hur de påverkade maskininlärningsmetoderna. Resultaten visar att random forest överträffar de andra maskininlärningsmetoderna när det gäller att förutsäga försäljningspriser på fastigheter. De utvärderade maskininlärningsmetoderna stötte dock på svårigheter när det gällde att förutsäga försäljningshastigheten. Den bäst presterande maskininlärningsmetoden för försäljningshastighet är random forest. I synnerhet visar SVR en lägre MAE för försäljningshastighet, men presterar sämre i R² måttet.