Дисертації з теми "Simplified methods"

COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
Apresentam-se as formulações, consolidando a nomenclatura e os principais conceitos dos métodos de elementos de contorno: convencional (MCCEC), híbrido de tensões (MHTEC), híbrido de deslocamentos (MHDEC) e híbrido simplificado de tensões (MHSTEC). proposto o método híbrido simplificado de deslocamentos (MHSDEC), em contrapartida ao MHSTEC, baseando-se nas mesmas hipóteses de aproximação de tensões e deslocamentos do MHDEC e supondo que a solução fundamental em termos de tensões seja válida no contorno. Como decorrência do MHSTEC e do MHSDEC, é apresentado também o método híbrido de malha reduzida dos elementos de contorno (MHMREC), com aplicação computacionalmente vantajosa a problemas no domínio da freqüência ou envolvendo materiais não-homogêneos. A partir da investigação das equações matriciais desses métodos, são identificadas quatro novas relações matriciais, das quais uma verifica-se como válida para a obtenção dos elementos das matrizes de flexibilidade e de deslocamento que não podem ser determinados por integração ou avaliação direta. Também é proposta a correta consideração, ainda não muito bem explicada na literatura, de que forças de superfície devem ser interpoladas em função de atributos de superfície e não de atributos nodais. São apresentadas aplicações numéricas para problemas de potencial para cada método mencionado, em que é verificada a validade das novas relações matriciais.
A consolidated, unified formulation of the conventional (CCBEM), hybrid stress (HSBEM), hybrid displacement (HDBEM) and simplified hybrid stress (SHSBEM) boundary element methods is presented. As a counterpart of SHSBEM, the simplified hybrid displacement boundary element method (SHDBEM) is proposed on the basis of the same stress and displacement approximation hypotheses of the HDBEM and on the assumption that stress fundamental solutions are also valid on the boundary. A combination of the SHSBEM and the SHDBEM gives rise to a provisorily called mesh-reduced hybrid boundary element method (MRHBEM), which seems computationally advantageous when applied to frequency domain problems or non-homogeneous materials. Four new matrix relations are identified, one of which may be used to obtain the flexibility and displacement matrix coefficients that cannot be determined by integration or direct evaluation. It is also proposed the correct consideration, still not well explained in the technical literature, that traction forces should be interpolated as functions of surface and not of nodal attributes. Numerical examples of potential problems are presented for each method, in which the validity of the new matrix relations is verified.

Linear multivariate statistical methods are widely used for analysing data sets which consist of a large number of variables. These techniques, which include principal component analysis, factor analysis, canonical correlation analysis, redundancy analysis and discriminant analysis, all produce a set of new variables, commonly called 'factors', according to some criterion which differs for different techniques. Among these techniques, principal component analysis is one of the most popular techniques used for reducing the dimensions of the multivariate data set. In many applications, when Principal Component Analysis (PCA) is performed on a large number of variables, the interpretation of the results is not simple. The derived eigenvectors of the sample covariance or correlation matrix are not necessarily in a simple form, with all coefficients either 'large' or 'negligible'. To aid interpretation, it is fairly common practice to rotate the retained set of components, often using orthogonal rotation. The purpose of rotation is to simplify structure, and thus to make it easier to interpret the low-dimensional space represented by the retained set of components. Thus, quantification of simplicity is a two step process. The first set involves the extraction of the feature from the data called components, while the second stage uses a rotation method to simplify the structure. One of the two main purposes of this thesis is to combine into one step these two separate stages of dimension reduction (finding the components) and simplification (rotation). This goal is achieved by combining these two objectives in the form of a single function leading to what we call Simplified Components (SCs). Another objective is to discover which of the many possible criteria suggested in factor analysis can be adopted in the proposed procedure of SCs. Thus, a simplified one-step procedure of SCs is proposed, using four measures of simplicity, namely varimax, quartimax, orthomax and equamax indices.

This thesis presents a simple and conservative method for the analysis of inelastic cyclic thermal stress problems. It is developed for the analysis of severe cyclic thermal shocks combined with mechanical loads in thin walled tubes. The methods are intended to predict both the onset of ratchetting and the strains accumulated by small excursions into the ratchetting regime. The text begins by summarising the development of the upper bound shakedown theory-the main tool in this approach. Previous methods for simplified analysis using the upper bound method are reviewed and some ideas adopted. Building on this previous work, a new method of predicting the shakedown bound is developed. This is based on the upper bound analysis of particular ratchet mechanisms, resulting in a limiting equation for each mechanism. These equations are used to produce ratchet bounds for several thermal stress examples. These results are compared with the bounds produced by design code rules currently used for cyclic thermal stress. One observation reached in the prediction of these bounds was the lack of supporting evidence available. Therefore, a set of experiments were performed to show the bounds corresponding to two of these mechanisms. These used a new resistance heating method for applying the thermal cycles. The results are conservatively predicted by upper bound analysis. However, in some regions the effects of cyclic hardening reduces the strain accumulated, making the predictions over conservative. To investigate this effect some simple hardening rules are applied to the shakedown bounds. These are developed to give a prediction of accumulated strains within the ratchet region. Comparison is made both with the experiments and a finite element computer model. Finally, these predictions of shakedown and cyclic hardening controlled strain are combined to give a complete picture of cyclically heated tubes below the creep range.

This research effort is concerned with the methods of simplified orbit determination and orbit representation and their applications for Low Earth Orbit (LEO) satellite missions, particularly addressing the operational needs of the FedSat mission. FedSat is the first Australian-built satellite in over thirty years. The microsatellite is approximately 50cm cubed with a mass of 58 kg. The satellite was successfully placed into a low-earth near-polar orbit at an altitude of 780km by the Japanese National Space Development Agency (NASDA) H-IIA launch vehicle on 14, December 2002. Since then, it has been streaming scientific data to its ground station in Adelaide almost daily. This information is used by Australian and international researchers to study space weather, to help improve the design of space computers, communication systems and other satellite technology, and for research into navigation and satellite tracking. This research effort addresses four practical issues regarding the FedSat mission and operations. First, unlike most satellite missions, the GPS receiver onboard FedSat operates in a duty-cycle mode due to the limitations of the FedSat power supply. This causes significant difficulties for orbit tracking, Precise Orbit Determination and scientific applications. A covariance analysis was performed before the mission launch to assess the orbit performance under different operational modes. The thesis presents the analysis methods and results. Second, FedSat supports Ka-band tracking experiments that require a pointing accuracy of 0.03 degree. The QUT GPS group is obligated to provide the GPS precise orbit solution to meet this requirement. Ka-band tracking requests satellite orbital position at any instant time with respect to any of the observation stations. Because orbit determination and prediction software only provide satellite orbital data at a discrete time point, it is necessary to find a way to represent the satellite orbit as a continuous trajectory with discrete observation data, able to obtain the position of the satellite at the time of interest. For this purpose, an orbit interpolation algorithm using the Chebyshev polynomial was developed and applied to Ka-band tracking applications. The thesis will describe the software and results. Third, since the launch of FedSat, investigators have received much flight GPS data. Some research was invested in the analysis of FedSat orbit performance, GPS data quality and the quality of the onboard navigation solutions. Studies have revealed that there are many gross errors in the FedSat onboard navigation solution (ONS). Although the 1-sigma accuracy of each component is about 20 m, there are more than 11 %positioning errors that fall outside +/-50m, and 5% of the errors are outside the 100mbound. The 3D RMS values would be 35m, 87m, and 173m for the above three cases respectively. The FedSat ONS uncertainties are believed to be approximately three times greater than those from other satellite missions. Due to the high percentage of outlier solutions, it would be dangerous to use these without first applying data detection and exclusion procedures. Therefore, this thesis presents two simplified orbit determination methods that can improve the ONS. One is the "geometric method", which makes use of delta-position solutions derived from carrier phase differences between two epochs to smooth the code-based navigation solutions. The algorithms were tested using SAC-C GPS data and showing some improvement. The second method is the "dynamic method", which uses orbit dynamics information for orbit improvements. Fourth, the FedSat ground tracking team at Adelaide use the NORAD TLE orbit for daily FedSat tracking. Research was undertaken to convert an orbit trajectory into these Two Line Elements (TLE). Algorithms for the estimation of TLE solutions from the FedSat onboard GPS navigation solutions are outlined. Numerical results have shown the effects of the unmodelled forces/perturbations in the SPG4 models for the FedSat orbit determination would reach a level of ±1000m. This only includes the orbit representation errors with TLE data sets. The total FedSat orbit propagation should include both the orbit propagation and orbit representation terms. The analysis also demonstrates that the orbit presentation error can be reduced to ±200m and ±100mlevels with the EGM4x4 and EGM10x10 gravity field models respectively. This can meet the requirements for Ka-band tracking. However, a simplified tracking program based on numerical integration has to be developed to replace the SPG4 models.

This research effort is concerned with the methods of simplified orbit determination and orbit representation and their applications for Low Earth Orbit (LEO) satellite missions, particularly addressing the operational needs of the FedSat mission. FedSat is the first Australian-built satellite in over thirty years. The microsatellite is approximately 50cm cubed with a mass of 58 kg. The satellite was successfully placed into a low-earth near-polar orbit at an altitude of 780km by the Japanese National Space Development Agency (NASDA) H-IIA launch vehicle on 14, December 2002. Since then, it has been streaming scientific data to its ground station in Adelaide almost daily. This information is used by Australian and international researchers to study space weather, to help improve the design of space computers, communication systems and other satellite technology, and for research into navigation and satellite tracking. This research effort addresses four practical issues regarding the FedSat mission and operations. First, unlike most satellite missions, the GPS receiver onboard FedSat operates in a duty-cycle mode due to the limitations of the FedSat power supply. This causes significant difficulties for orbit tracking, Precise Orbit Determination and scientific applications. A covariance analysis was performed before the mission launch to assess the orbit performance under different operational modes. The thesis presents the analysis methods and results. Second, FedSat supports Ka-band tracking experiments that require a pointing accuracy of 0.03 degree. The QUT GPS group is obligated to provide the GPS precise orbit solution to meet this requirement. Ka-band tracking requests satellite orbital position at any instant time with respect to any of the observation stations. Because orbit determination and prediction software only provide satellite orbital data at a discrete time point, it is necessary to find a way to represent the satellite orbit as a continuous trajectory with discrete observation data, able to obtain the position of the satellite at the time of interest. For this purpose, an orbit interpolation algorithm using the Chebyshev polynomial was developed and applied to Ka-band tracking applications. The thesis will describe the software and results. Third, since the launch of FedSat, investigators have received much flight GPS data. Some research was invested in the analysis of FedSat orbit performance, GPS data quality and the quality of the onboard navigation solutions. Studies have revealed that there are many gross errors in the FedSat onboard navigation solution (ONS). Although the 1-sigma accuracy of each component is about 20 m, there are more than 11 %positioning errors that fall outside +/-50m, and 5% of the errors are outside the 100mbound. The 3D RMS values would be 35m, 87m, and 173m for the above three cases respectively. The FedSat ONS uncertainties are believed to be approximately three times greater than those from other satellite missions. Due to the high percentage of outlier solutions, it would be dangerous to use these without first applying data detection and exclusion procedures. Therefore, this thesis presents two simplified orbit determination methods that can improve the ONS. One is the "geometric method", which makes use of delta-position solutions derived from carrier phase differences between two epochs to smooth the code-based navigation solutions. The algorithms were tested using SAC-C GPS data and showing some improvement. The second method is the "dynamic method", which uses orbit dynamics information for orbit improvements. Fourth, the FedSat ground tracking team at Adelaide use the NORAD TLE orbit for daily FedSat tracking. Research was undertaken to convert an orbit trajectory into these Two Line Elements (TLE). Algorithms for the estimation of TLE solutions from the FedSat onboard GPS navigation solutions are outlined. Numerical results have shown the effects of the unmodelled forces/perturbations in the SPG4 models for the FedSat orbit determination would reach a level of ±1000m. This only includes the orbit representation errors with TLE data sets. The total FedSat orbit propagation should include both the orbit propagation and orbit representation terms. The analysis also demonstrates that the orbit presentation error can be reduced to ±200m and ±100mlevels with the EGM4x4 and EGM10x10 gravity field models respectively. This can meet the requirements for Ka-band tracking. However, a simplified tracking program based on numerical integration has to be developed to replace the SPG4 models.

L'inquiétude croissante concernant le futur des ressources énergétique a fait de l'optimisation énergétique une priorité dans tous les secteurs. De nombreux sujets de recherche se sont focalisés sur celui du bâtiment étant le principal consommateur d'énergie, en particulier à cause de ses besoins en chauffage. Beaucoup de propositions pour réduire la consommations ont été faites. Ceux-ci vont de l'amélioration de l'isolation au changement du système de gestion du thermostat en passant par la formation des occupants à une meilleure gestion de leur bâtiment. Cette thèse propose une nouvelle méthode de contrôle qui permet de minimiser la consommation énergétique et dépenses budgétaires. La méthode génère un planning énergétique sur une période de temps pré-définie, ceci en prenant compte du confort thermique des occupants. Elle est basée sur l'application de la méthode de Monte Carlo, un générateur aléatoire appliqué au système de chauffage. L'objectif est de déterminer le planning de chauffage optimal, qui respecte les trois contraintes suivantes: - Le confort thermique des résidents; - La minimisation de l'énergie consommée / du budget; - Le déplacement de la charge. De plus, pour tester cette méthode, l'identification du comportement thermique du bâtiment a été requise. De ce fait, un modèle thermique du bâtiment a été développé. Ce modèle a été volontairement simplifié afin de l'intégrer plus simplement dans le processus de contrôle. De plus, une nouvelle approche d'identification thermique du bâtiment aussi bien qu'une nouvelle méthode de contrôle en temps réel ont été présentées
With the highly developing concerns about the future of energy resources, the optimization of energy consumption becomes a must in all sectors. A lot of research was dedicated to buildings regarding that they constitute the highest energy consuming sector mainly because of their heating needs. Many proposals of new strategies to minimize building consumption were done. These proposals vary between recommending better insulation, advising change in occupants' behavior and changing the heating control management. This thesis proposes a new control method that helps minimizing the heating consumption and expenses. This method generates an energy plan over a defined prediction horizon respecting the occupants’ thermal comfort. It is based on the application of Monte Carlo method, i.e., a random generator for the heating system scenarios. The aim is to determine the optimal heating plan for the prediction horizon that fulfills the constraints regarding the following three factors: • The thermal comfort of occupants; • The minimization of the energy consumption/expenses; • Load shifting. However, to test this method, an identification of the building thermal behavior was needed. Thus, a building thermal model to simulate the building behavior was developed. This model was meant to be simplified in order to better integrate it in the control process. Furthermore, a new parameter estimation approach as well as a real time temperature control method are presented to ensure the implementation of the optimal predicted plan

For many situations it is obvious that an understanding of how different types of cracks arise and methods to estimate the risk of early age cracking is needed. This thesis deals with parts of this phenomenon namely thermal through cracking caused by restraint from an adjoining structure. Different existing material models used in a thermal stress analysis are compared with a tested behaviour. The main work focus on evaluating simplified manual methods for thermal crack estimation that are based on direct formulations by means of the results from a more advanced differential type method. One of the studied methods is selected and formulated for practical use. Possilble measures against thermal cracking are described together with recommendations on how they may be implemented in the method. Comparisons with observations from full-scale castings give an indication about the accurary of the simplified method.
Godkänd; 2000; 20070318 (ysko)

In recent impact and penetration mechanical tests, steel projectiles (AISI4340) were impacted into targets like concrete with striking velocities (1200 m/s to 1500 m/s). Results indicated a material removal from the nose of the projectile, phase changes of the projectile materials, a reduction in the length of the projectile, and a blunting of the nose shape. These observations cannot be explained by current theories and numerical integration code that are used to study impact and penetration mechanics. Thus, the objectives of the thesis research are to (a) formulate and characterize the mechanisms responsible for the material erosion of the impacting projectile and the mass loss from the nose region; and (b) to determine the physical properties of alloy steels that are important to penetration mechanics from ab initio methods. The results can be used to design new projectile materials that can provide the desired penetration characteristics. These objectives are accomplished by investigating two related problems. The first problem is to formulate simplified models that can explain the penetration mechanics. The new models include the varying cross-section nose, changes of yield stress behind the shock wave and high strain rate phase transitions. Nose erosion effects, and time-dependent penetration path can be determined by integrating ODEs. A cavity expansion theory model is used to obtain the target resistance that is responsible slowing and deforming the penetrating projectile. The second problem concerns the determination of the constitutive relations from ab initio methods. The equation of state (EOS) and magnetic moments for alloy steels are investigated by using a special quasirandom structure technique and ab initio methods. Specifically, EOS for an interstitial disordered alloy Fe1-x-yNixCy is developed. First, the EOS of iron and phase transition of iron are studied and validated. Second, Nickel is considered to investigate the substitutional disordered alloy Fe1-x-yNixCy. Third, Carbon is placed at an interstitial position in the substitutional disordered alloy. These investigations will form foundation for future work involving new projectile with steel nose and shank made of multifunctional structural energetic materials.

Thesis (Ph. D.)--University of North Carolina at Chapel Hill, 2008.
Title from electronic title page (viewed Feb. 17, 2009). "...in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Computer Science." Discipline: Computer Science; Department/School: Computer Science.

Le calcul non-linéaire par éléments finis est aujourd’hui l’approche la plus précise pour l’étude des échouements de navires. Néanmoins, les temps de calculs importants rendent cette méthode inadaptée lorsque de nombreux scenarios doivent être étudies. Dans le cadre du projet de recherche Européen FLARE (FLooding Accident REsponse), ces travaux de thèse visent à développer un solveur basé sur des formulations simplifiées permettant d’estimer rapidement l’endommagement subi par un navire à passagers lors d’un échouement. Le fond marin est représenté par un paraboloïde elliptique, permettant de générer des rochers à la fois tranchants ou larges, en faisant varier deux coefficients. Le navire quant à lui est divise en macro-éléments appelés Super-Eléments (S.E), qui représentent les principaux composants d’un fond de navire. Pour chaque S.E, des simulations par E.F. sont réalisées avec le code Ls-Dyna. A l’issue de ces simulations, des expressions analytiques de la force résistante sont construites, puis validées individuellement par comparaison aux résultats numériques. Dans la seconde partie de la thèse, les expressions simplifiées sont implémentées dans un solveur nomme FLAGS qui est couple au solveur existant « fluide » MCOL afin de prendre en compte les effets hydrodynamiques. L’outil FLAGS/MCOL est confronté avec succès aux calculs par éléments finis Ls-Dyna/MCOL pour différents échouements de navire a échelle 1. Pour finir, l’outil est utilisé pour simuler des milliers de scenarios dans le but de quantifier l’influence de divers renforcements structurels sur la taille de brèche
Although non-linear finite element method is the most accurate approach for ship grounding damage analyses, its high computing cost makes it unsuitable when numerous scenarios have to be simulated. As part of the European research project FLARE (Flooding Accident REsponse), this PhD thesis aims to develop a solver based on simplified formulae to rapidly assess cruise ship grounding damage. The seabed is represented by an elliptic paraboloid allowing to generate both sharp and shallow rocks varying two parameters. The ship is divided into large elements, called Super- Elements (S.E), representing the main bottom components. For each S.E, Ls-Dyna simulations are carried out. Based on these simulations, closed-form expressions are derived for the resistant force according to the Upper-Bound theorem of plasticity. Finally, the analytical expressions are validated by comparison with numerical results. In the second part of the thesis, the developments are implemented in a structural solver named FLAGS, which is coupled with the external dynamics solver MCOL to account for the action of the surrounding water. FLAGS/MCOL solver is validated by confrontation to Ls-Dyna/MCOL F.E. solutions for various full scale grounding accidents. Finally, the simplified tool is used to simulate thousands of grounding events with the aim of quantifying the influence of different reinforcements on the ship damage extent

Mathematics is perceived as a difficult subject to many students internationally and Sweden ranks among EU/OECD countries that perform poorly, cited in the TIMSS 2007 assessments. The aim of this essay is to investigate the causes of the poor performance in Mathematics in many of Swedish Secondary schools and it will contribute to the solutions of this problem. The framework of this essay takes into consideration issues on; school curriculum, instruction of knowledge by teachers, construction of knowledge by students, their interactions and experiences in the situation of learning. Teaching methods have been seen as the starting point upon which students can be invited to carry out communications, reasoning and arguments in mathematics. This can be useful in developing capabilities of solving mathematical problems as recommended in Secondary School regulations book. The interviewed teachers’ experiences and approaches in selecting teaching methods have been interpreted to correspond with students’ involvement in learning mathematics. The essay has found out that there is a positive effect on understanding mathematics if teachers can select teaching methods that suits a specific object of learning. This however, has left one disturbing question for further researchers to answer; to whether it is enough for highly motivated and hard working students to study mathematics based on memorized wisdom (ideas) as it does not promote mathematical awareness.

The superior advantage of a nodal method for reactor cores with hexagonal fuel assemblies discretized as cells consisting of equilateral triangles is its mesh refinement capability. In this thesis, a diffusion and a simplified P3 (or SP3) neutron transport nodal method are developed based on trigonal geometry. Both models are implemented in the reactor dynamics code DYN3D. As yet, no other well-established nodal core analysis code comprises an SP3 transport theory model based on trigonal meshes. The development of two methods based on different neutron transport approximations but using identical underlying spatial trigonal discretization allows a profound comparative analysis of both methods with regard to their mathematical derivations, nodal expansion approaches, solution procedures, and their physical performance. The developed nodal approaches can be regarded as a hybrid NEM/AFEN form. They are based on the transverse-integration procedure, which renders them computationally efficient, and they use a combination of polynomial and exponential functions to represent the neutron flux moments of the SP3 and diffusion equations, which guarantees high accuracy. The SP3 equations are derived in within-group form thus being of diffusion type. On this basis, the conventional diffusion solver structure can be retained also for the solution of the SP3 transport problem. The verification analysis provides proof of the methodological reliability of both trigonal DYN3D models. By means of diverse hexagonal academic benchmark and realistic detailed-geometry full-transport-theory problems, the superiority of the SP3 transport over the diffusion model is demonstrated in cases with pronounced anisotropy effects, which is, e.g., highly relevant to the modeling of fuel assemblies comprising absorber material.

PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO
COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
FUNDAÇÃO DE APOIO À PESQUISA DO ESTADO DO RIO DE JANEIRO
Esta tese apresenta as formulações dos métodos de elementos de contorno convencional e híbrido simplificado para problemas axissimétricos de elasticidade, empregando-se as soluções fundamentais do espaço completo e do semi-espaço. Para problemas de elasticidade axissimétricos no semi-espaço pelos métodos de elementos de contorno, o uso das soluções fundamentais para espaço completo exige a discretização e o truncamento da superfície livre. No entanto, essa discretização é dispensada se as soluções fundamentais empregadas satisfizerem a condição de forças de superfície nulas. Este trabalho apresenta a implementação dessas soluções fundamentais axissimétricas para o espaço completo e o semi-espaço elástico, em termos de integrais do tipo Lipschitz-Hankel. São apresentadas todas as expressões necessárias para o cálculo de resultados em pontos internos e a correta integração numérica das integrais de contorno. Partindo da formulação do espaço completo, mostra-se que é necessária pouca modificação para a implementação da formulação proposta. Esse trabalho também desenvolve a formulação axissimétrica para o método híbrido simplificado dos elementos de contorno, tanto para o espaço completo como para o semi-espaço. Na sua versão original, o uso de propriedades espectrais para a total formulação do problema não era possível para certas configurações topológicas. No entanto, a aplicação de um princípio de contragradiência híbrida às equações do método levou à obtenção de uma nova relação matricial que tornou possível sua total formulação para qualquer topologia, independentemente de propriedades espectrais. A necessidade de se integrar apenas uma matriz e a facilidade de obtenção de resultados em pontos internos tornam o método híbrido simplificado dos elementos de contorno ainda mais vantajoso para problemas axissimétricos. Alguns exemplos numéricos validam as formulações apresentadas. Essa tese é composta por oito capítulos e dois apêndices, como descritos a seguir. O Capítulo 2 trata das soluções fundamentais axissimétricas para o espaço completo e o semi-espaço elástico. As equações governantes para um meio elástico axissimétrico são apresentadas em coordenadas cilíndricas. As soluções fundamentais correspondentes são deduzidas, em termos de integrais do tipo Lipschitz-Hankel, a partir da solução de Muki das equações de equilíbrio de Navier. O Capítulo 3 apresenta o método dos elementos de contorno para problemas axissimétricos no espaço completo e no semi-espaço. A partir das soluções fundamentais apresentadas no Capítulo 2, as equações integrais no contorno são deduzidas, bem como as equações matriciais governantes. Além disso, discute-se a obtenção de uma matriz de rigidez e o cálculo das inversas generalizadas presentes na formulação. As expressões para o cálculo de deslocamentos e tensões no domínio e ao longo do contorno são fornecidas de maneira explícita. O Capítulo 4 apresenta o método híbrido simplificado dos elementos de contorno para problemas axissimétricos no espaço completo e no semi-espaço. Uma nova versão do método é proposta, em que as equações governantes do problema são obtidas a partir de trabalhos virtuais de deslocamentos, uma equação de compatibilidade de deslocamentos e um teorema híbrido de contragradiência. O esquema para o cálculo dos coeficientes indeterminados de U está descrito detalhadamente para o espaço completo, incluindo as soluções analíticas necessárias. A obtenção de uma matriz de rigidez, bem como de deslocamentos e tensões em pontos internos, também é discutida. Bases ortonormais, projetores e inversas generalizadas presentes na formulação são apresentados ao longo do capítulo. O Capítulo 5 apresenta os esquemas numéricos para o cálculo das integrais presentes nos métodos de elementos de contorno convencional e híbrido simplificado aplicados a problemas axissimétricos no espaço completo e no semi-espaço.
This thesis presents the formulation of the conventional and simplified-hybrid boundary element methods for axisymmetric problems, employng fullspace as well as halfspace fundamental solutions. As it is mostly found in the literature on axisymmetric problems in the elastic halfspace, the boundary element formulations make use of fullspace fundamental solutions and insert a mesh discretization of the free surface, with truncation at a reasonable distance from the axis of axisymmetry. This discretization can be circunvented if one employs the fundamental solutions that satisfy in advance the traction free boundary condition on the free surface. This work presents the implementation of these axisymmetric fundamental solutions for both the fullspace and the halfspace, given in terms of integrals of Lipschitz-Hankel type. Explicit equations for post-processing results at internal points are provided, as well as the adequate numerical schemes to evaluate the boundary integrals that arise in the formulation. It is shown that the boundary element method for the halfspace can be easily implemented from existing computation codes for fullspace problems, requiring only a few modifications. This work also addresses the simplified-hybrid boundary element method for the axisymmetric fullspace and halfspace problems. In its original version, the use of spectral properties to completely formulate the method was possible for only strictly non-convex topological configurations. The key contribution of the present developments consisted in the correct application of a hybrid contragradient theorem to derive a simple means of using analytical solutions of the elastic problem in order to substitute for the spectral properties that have been originally proposed. In the simplified-hybrid boundary element method, only one matrix requires integration and the results at internal points can be evaluated directly, which makes the method extremely advantageous for axisymmetric problems. Some numerical examples validate the proposed formulations.

Thesis (S.M. in Transportation)--Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 2013.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 169-172).
This thesis reviews a select group of transit environmental mitigation proposals through the application of ridership estimation methodologies. In recent years, rider demands and environmental concerns have led many transit agencies to explore options for increasing service even within constrained budgets. Anticipated state and metropolitan area climate change mitigation strategies are likely to result in the need for further transportation system changes in many cities. In response to environmental concerns raised during the construction of the Central Artery/Tunnel, Massachusetts committed to extending the Green Line light rail from its Cambridge terminal at Lechmere into Somerville and Medford. The Massachusetts State Implementation Plan requires that the Green Line be extended in two branches by the end of 2014. Massachusetts has delayed construction on the extension, and it must therefore undertake mitigation for the delay. Facing both financial constraints and pressure to increase service, transit agencies such as the MBTA need new ways to improve transportation systems with limited financial input and means by which to evaluate the impact of proposals. Several mitigation proposals focusing on transit services in the Lechmere Station area are presented in this thesis. Increasing service on the Green Line to Lechmere is found to be a good first step towards improving service in Somerville. Proposals for increasing bus feeder service to and from Lechmere and the surrounding areas include both increasing service on existing routes and introducing new routes. Partnerships with existing private providers could also help decrease the costs to the MBTA of introducing a new route. In order to analyze the mitigation proposals, several methodologies are explored including area wide transportation planning models, direct demand (regression) models and comparison equations. A rail elasticity of demand with respect to service is calculated based on a prior MBTA system experience, while elasticities from literature are used for buses. In addition, a direct demand model is estimated for the MBTA bus network, and the results are compared to elasticity analysis. Regional planning models are found to be important for predicting system-wide responses but often are too detailed and expensive to use to evaluate every proposal. Instead, direct demand models can help with initial rankings of proposals, and service elasticities can help further examine expected ridership changes due to service improvements.
by Jamie C. Rosen.
S.M.in Transportation

Thesis (MEng)--Stellenbosch University, 2013.
ENGLISH ABSTRACT: The management of physical assets has become a popular eld of study over recent years and is being acknowledged in multiple disciplines world wide. In this project, research on Physical Asset Management (PAM), maintenance and decision making are presented. PAM is a complex subject and requires the participation of multiple disciplines in order to successfully manage physical assets. Moreover, the management of maintenance makes a big contribution in achieving successful PAM. Decision making is a core element to manage maintenance e ciently, both on strategic and operational level. Various methods and techniques can be used to aid the decision making process such as, using past experience, xed decision making techniques and techniques involving numerical calculations, to mention only a few. However, using numerical calculations to make decisions are not very popular. This is due to various reasons, for example the inherent complexity of the mathematics and the time required to execute such calculations are disliked. People tend to avoid complex numerical calculations and rather rely on past experience and discussion of circulating opinions to make decisions. This is not ideal and can lead to inconsistent and inaccurate decisions. In this project, the importance of numerical decision making is researched, especially in maintenance related decisions. The focus is placed on the simpli cation of numerical decision making techniques with the aim to make it easy and quick to use to support operational PAM decisions. Di erent decisions regarding PAM, especially decisions with regards to managing maintenance in order to achieve PAM, are discussed by means of a literature study. This is done to clarify the applicability of using numerical decision making techniques to support this type of decisions. A few di erent available numerical techniques are highlighted that can be used to support the decision making process. The decisions together with numerical decision making techniques are evaluated in order to combine the most appropriate techniques in a simpli ed manner. The purpose of this is that it can be used by anyone with the necessary knowledge of a speci c system or operation. As a result a simpli ed numerical decision making toolbox is developed that can support maintenance related decision. This toolbox is applied to a real life situation by means of a case study, made possible by Anglo American Platinum Limited (Amplats). An evaluation and validation of the toolbox is done through the case study to conclude wether it has value in practice or not.
AFRIKAANSE OPSOMMING: Die bestuur van siese bates het die afgelope paar jaar 'n gewilde studieveld geword en word erken in verskeie dissiplines reg oor die w^ereld. In hierdie projek word navorsing gedoen oor Fisiese Bate Bestuur (FBB), instandhouding en besluitneming. FBB is 'n komplekse onderwerp en vereis die deelname van verskeie dissiplines om sukses te behaal. Die bestuur van instandhouding maak 'n groot bydrae tot suksesvolle FBB. 'n Kern element van doeltre ende instandhouding is besluitneming, beide op strategiese en operasionele vlak. Verskillende metodes en tegnieke kan gebruik word om die besluitnemingsproses te ondersteun soos byvoorbeeld om gebruik te maak van ondervinding en vorige gebeurtenisse, vaste besluitnemingstegnieke, tegnieke wat numeriese berekeninge gebruik en nog meer. Die gebruik van numeriese metodes om besluite te neem is nie baie gewild nie. Dit is as gevolg van verskeie redes soos byvoorbeeld die inherente kompleksiteit en ingewikkeldheid van die wiskunde en ook die tyd wat benodig word om sulke berekeninge uit te voer. Mense is geneig om ingewikkelde numeriese berekeninge te vermy en eerder staat te maak op vorige ervaring en die bespreking van menings om besluite te neem. Dit is nie ideaal nie en kan lei tot onkonsekwente besluite, of selfs verkeerde besluite. In hierdie projek is die belangrikheid van numeriese besluitneming nagevors, veral in die onderhoudsverwante besluite. Die fokus word geplaas op die vereenvoudiging van die numeriese besluitnemings tegnieke. Die doel is om dit op so 'n manier te vereenvoudig dat dit maklik en vinnig is om te gebruik vir operasionele FBB besluite. Verskillende besluite oor FBB, veral besluite met betrekking tot instandhouding om suksesvolle FBB te bereik, word bespreek deur middel van 'n literatuurstudie. Die literatuurstudie ondersoek die toepaslikheid van die gebruik van numeriese besluitnemingstegnieke vir hierdie soort besluite. 'n Paar verskillende beskikbare numeriese tegnieke wat gebruik kan word om die besluitnemingsproses te ondersteun word uitgelig. Die besluite, saam met numeriese besluitnemingtegnieke, word ge evalueer om die mees gepaste tegnieke te kombineer in 'n vereenvoudigde manier. Uiteindelik moet dit deur enige iemand met die nodige kennis van 'n spesi eke stelsel of proses gebruik kan word. As resultaat is 'n vereenvoudigde numeriese besluitnemingstegniekkombinasie ontwikkel wat besluite verwant aan instandhouding kan ondersteun. Hierdie tegniek-kombinasie word toegepas in 'n werklike situasie deur middel van 'n gevallestudie, wat moontlik gemaak is deur Anglo American Platinum Limited. 'n Evaluering en validering van die tegniek-kombinasie word gedoen in die gevallestudie om te bepaal of dit wel waarde het in die praktyk of nie.

Simplified methods of seismic verification, using equivalent single degree of freedom systems for the response prediction, have been the subject of great emphasis on research in the field of earthquake engineering particularly since the mid-1990s. This interest is justified still today by the great uncertainty characterizing the prediction of the seismic response: the variability of the parameters influencing the structural capacity and the seismic input definition, makes the use of sophisticated models not always effective and warranted. Furthermore, the extensive use of Non Linear Time-History (NLTH) analyses requires a calibration of the hysteretic model parameters and ground motions that seems still to date hardly applicable to day to day engineering practice. At the same time in last decade the design for earthquake resistance has undergone a critical review, triggered by the concept of Performance-Based Design. Performance objectives represent the attainment of certain damage levels for a given seismic intensity, and it has been widely recognized that the damage measure for a structure is directly related to deformations: displacements are the fundamental index of structural damage in seismic events and the achievement of the target displacement in relation to the different limit states should be the main objective of the verification procedure. Displacement-Based methods for seismic verification of structures hold together the two aspects evidenced so far, being simplified procedures which rely on a substitute SDOF structure and use as reference control parameter the target limit displacement for the system under exam. At present Displacement-Based Design (DBD) methods for new structures have reached a degree of formalization almost complete, with the recent publication of a Model Code for their adoption into seismic codes (Calvi and Sullivan, 2009). However, several aspects related to the method calibration are still matter of research, being the representativeness of the substitute linear structure a critical issue, in particular the formulation of equivalent viscous damping and the definition of the target displacement profile for a given structural system. With regard to the appraisal of existing structures, the development of Displacement-Based Assessment (DBA) approach represents the state of the art of research in this field, since so far the calibration of the methods dealt essentially with new structures only. The specific problems of the development of DBA methodologies include the prediction of the possible collapse mechanisms due to brittle rupture of members (which may be substantially different from those of the new ductile structures, designed following capacity design criteria), and the inclusion of local damage effects caused by nodes not adequately confined. In this context the research activity focuses on the evaluation, calibration and development of simplified Displacement-Based approaches for seismic verification of bridge structures, with particular reference to their use in a probabilistic framework, represented by vulnerability analyses and risk calculation on a large scale. In the first part the thesis addresses the methodological aspects of the DBD procedures focusing on the error sources of the simplified methods. In particular the current design methods for new structures with flexural ductile behaviour are evaluated, with reference to the formulations of the equivalent viscous damping and target displacement profile to be adopted in the analysis. A first study investigates the accuracy of the current Direct Displacement-Based Design (DDBD) procedure applied to simple SDOF systems (with specific reference to multi-span simply supported rc bridge piers), the main error sources being the approximation of the substitute linear structure characterized by the equivalent viscous damping, and the scaling of the displacement elastic spectrum through the modification damping factor. Using different formulations proposed in literature for equivalent viscous damping and spectrum reduction factor, a parametric study is carried out on an ample set of SDOF systems (previously designed with the DDBD method and subsequently verified with NLTH analyses), and an average error chart is obtained, allowing the prediction of the expected error for the design cases of multi-span simply supported bridge piers. A second work investigates the representativeness of the equivalent SDOF structure related to the estimation of the design displacement profile within a displacement-based framework. In the case of transverse response prediction for continuous rc girder bridges, the accuracy of the current iterative Direct Displacement-Based method (called DBD-IT in this work) is evaluated, and compared to an alternative direct design method (named DBD-DEM) herein proposed. The alternative methods combine in a non-iterative procedure the DBD framework with a Response Spectrum Analysis carried out with effective stiffness. In the second part the methodological aspects are addressed with regard to the specific issues of the existing bridge structures, not seismically designed (and not satisfying capacity design principles), and thus characterized by failure modes, limit states, hysteretic behaviour, and local ductility of the nodes that are different from those characterizing new seismically designed structures. In particular the calibration effort regards the assessment of pier capacity, piers generally representing the most vulnerable elements in existing bridges. A simplified numerical model is defined for the aggregation of phenomenological non linear shear behaviour and fiber representation of flexural behaviour for piers, calibrated by using experimental results on rc columns with flexure and shear failure extracted from on line databases (PEER database). A parametrical study is then developed for single bent and multiple bent piers (cantilever, walls frame), considering all main geometrical and material properties that can influence the pier capacity, aiming at the determination of the effective properties for existing rc bridge piers, to be used in a Displacement-Based framework. The effective ranges of the selected parameters were determined by a preliminary statistical analysis on the bridges of the reference database (the Veneto Region road network bridge stock, named VR stock). With regard to the appraisal of existing structures, the specific advantage in the use of simplified analytical procedures becomes apparent when a probabilistic seismic risk estimation is carried out on a large-scale. In this study, in the final part, the DBA method previously calibrated, is applied to assess the seismic vulnerability of the bridge stock under exam on a regional scale. A limited number of bridges are chosen as reference examples for each homogeneous subclass of multi-span bridges, comparing simplified DBA procedures with NLTH analyses for the development of analytical fragility curves, and an extensive vulnerability analysis for the class of multi-span rc bridges of the VR stock is then developed, using the previously calibrated DB fragility curves. Finally regional seismic risk maps are drafted including all the multi-span rc bridges of the VR stock, for three different scenarios of damage: the seismic risk is obtained by the convolution of hazard functions, defined on the base of the PGA exceedance probabilities provided by the current Italian seismic code, and the analytical fragility curves calculated with the Displacement-Based approaches. An immediate extension of the research on existing rc bridges, may be represented by the development of fragility curves for the whole classes of multi-span structures: these fragility functions could be obtained considering the variability in the range of geometrical and mechanical characteristics obtained from the statistical analysis of the VR database for that specific classes, and the envelope curves obtained could than be applied for the vulnerability evaluation of typical bridges of the Italian or European stocks. A long-term development of the work may regard the extension of the simplified Displacement-Based procedures to the evaluation of different classes of structures, particularly of single span rc bridges and masonry arch bridges, which represent the other major category of existing bridges, to complete as much as possible the scenario of seismic risk for the infrastructure network under examination. In this context it will be possible to calibrate the seismic input for risk analysis through the use of hazard curves, obtained from micro-zonation studies in the areas of interest.
I metodi semplificati di verifica sismica, che utilizzano sistemi equivalenti ad un grado di libertà per la predizione della risposta, hanno avuto larga diffusione nello scorso decennio, non solo per il progetto di nuove opere ma soprattutto in relazione alla valutazione del comportamento strutturale dell’esistente. Parallelamente, con l’affermazione di approcci alla progettazione basati su criteri di performance, si è consolidato il concetto che il parametro più adeguato di misura della risposta sismica è rappresentato dallo spostamento, e il raggiungimento dello spostamento target in relazione ai diversi stati limite rappresenta il vero obiettivo della procedura di verifica. Le metodologie semplificate di progetto e valutazione basate sugli spostamenti (Displacement-Based), tengono insieme questi due aspetti, basandosi nella formulazione corrente su un sistema equivalente lineare ad un grado di libertà rappresentativo del sistema non lineare reale, e utilizzando come parametro di controllo della procedura lo spostamento limite accettabile per quel dato sistema strutturale. Per quanto riguarda gli aspetti del progetto di nuove strutture, tali metodologie hanno ormai raggiunto un grado di formalizzazione pressoché completo, con la pubblicazione in tempi molto recenti della proposta finale di un Model Code (Settembre 2012) per il loro recepimento nei codici normativi. Restano tuttavia oggetto di ricerca e sperimentazione gli aspetti legati alla calibrazione del metodo, in relazione alla rappresentatività del sistema equivalente lineare ad un grado di libertà, legata alle caratteristiche di smorzamento viscoso equivalente e al profilo di spostamento target da assumere per le diverse tipologie di strutture. Per quanto riguarda il tema della valutazione delle strutture esistenti, lo sviluppo di approcci agli spostamenti rappresenta lo stato dell’arte della ricerca in quest’ambito, avendo la taratura del metodo riguardato sinora sostanzialmente le sole nuove strutture. Le problematiche specifiche dei metodi di valutazione riguardano la necessità di estendere la previsione dei possibili meccanismi globali di rottura per crisi di tipo fragile degli elementi, che possono essere del tutto dissimili da quelli delle nuove strutture duttili progettate secondo i criteri del capacity design, e l’inclusione degli effetti locali dovuti a fenomeni di danneggiamento per crisi dei nodi non adeguatamente confinati. E’ di attualità inoltre l’applicazione dei metodi di valutazione basati sugli spostamenti nelle analisi di rischio sismico a larga scala, in molti studi sinora basate sulle metodologie di analisi statica non lineare, che presentano molti aspetti comuni ai metodi displacement-based. In questo contesto si inserisce il lavoro di ricerca sulle strutture da ponte, che si focalizza nella prima parte sull’aspetto dell’affidabilità dei metodi di progetto per le nuove opere (Displacement-Based Design) e nella seconda sulle procedure di valutazione dell’esistente (Dispalcement-Based Assessment) con metodi deterministici e stime in ambito probabilistico della vulnerabilità sismica. Per quanto riguarda il tema del design, un primo studio affronta la valutazione dell’errore del metodo semplificato DDBD per strutture ad un grado di libertà, individuando come principale fonti di approssimazione del metodo la formulazione dello smorzamento viscoso per il sistema 1gdl lineare equivalente, e la taratura del fattore di riduzione dello spettro elastico in spostamento. Sulla base di un’estesa analisi parametrica su un campione di sistemi SDOF, progettati con il metodo DDBD e verificati con analisi dinamiche non lineari in time history, si è pervenuti alla determinazione di un abaco semplificato e alla stima dell’errore per sistemi reali, rappresentati da pile da ponte in c.a. per impalcati in semplice appoggio. Un secondo lavoro sulle procedure di progetto riguarda la risposta sismica in direzione trasversale dei ponti continui a travata, e la valutazione dell’ attuale procedura iterativa, in relazione alla regolarità strutturale. La predizione della risposta trasversale con un approccio Displacement-Based presenta alcuni aspetti critici legati alla rappresentatività del sistema equivalente 1gdl rispetto al sistema mgdl di partenza, e in particolate alla difficoltà di una corretta stima del profilo di spostamento di progetto per ponti irregolari. La procedura corrente viene comparata con una procedura proposta (non iterativa) che utilizza in modo diretto l’output del metodo DBD in termini di stima delle rigidezze della struttura per effettuare un’analisi spettrale con rigidezze effettive, e che consente di combinare l’effetto dei modi superiori nella risposta. Per quanto attiene al metodo di valutazione dell’esistente, l’interesse specifico dell’utilizzo di procedure semplificate affidabili ed efficienti dal punto di vista computazionale rispetto a metodi più complessi quali analisi dinamiche non lineari nel dominio del tempo, risulta del tutto evidente con analisi probabilistiche per stime di rischio a larga scala. Il quest’ambito il lavoro si è incentrato sulla valutazione di vulnerabilità sismica di opere da ponte con i metodi agli spostamenti, utilizzando come caso studio di riferimento il sistema della rete stradale della regione Veneto, che consta di circa 2700km di strade provinciali e regionali in cui si inseriscono 495 opere da ponte considerate strategiche, collocate prevalentemente in zona sismica 2 e 3. Un’ approfondita analisi statistica preliminare è stato svolta nell’ambito del lavoro di tesi per la determinazione delle caratteristiche dello stock di ponti oggetto dell’indagine: il database disponibile raccoglie i dati dei ponti oggetto di verifiche sismiche svolte nel periodo 2007-2010 dall’Università di Padova per gli enti gestori della rete, e della campagna di indagini strutturali svolta a supporto. A partire da alcuni dati di anagrafica generale e utilizzando le informazioni disponibili su ciascun manufatto, è stato possibile individuare con specifico riferimento ai ponti a travata in c.a., che rappresentano il 70% circa dei manufatti dello stock, le caratteristiche geometriche, meccaniche e di armatura per classi omogenee di strutture, ottenendo un inventario di dati con un livello di dettaglio molto più approfondito dei comuni database utilizzati per le analisi di rischio a larga scala. Questo lavoro preparatorio ha rappresentato la base di dati necessari per svolgere una serie di analisi parametriche per la caratterizzazione delle curve di capacità dei ponti esistenti in c.a., che rappresentano il primo step di calcolo per la valutazione sismica con procedure semplificate agli spostamenti. Dallo studio parametrico è stato inoltre possibile calibrare con maggior precisione gli stati limite da assumere con riferimento a predefiniti livelli di danno, e ottenere una miglior taratura delle formulazioni dello smorzamento equivalente per le pile in c.a. esistenti. La seconda parte del lavoro sulle strutture esistenti riguarda lo studio di vulnerabilità per i ponti a travata in c.a. costituenti lo stock e la successiva analisi di rischio: i metodi semplificati DBA sono stati utilizzati per la creazione di curve di fragilità per i ponti a travata in c.a per 3 prefissati livelli di danno, e l’analisi di rischio è stata ottenuta come convoluzione con le curve di pericolosità sismica fornite dalla normativa italiana vigente, ottenendo delle mappe di scenario di danno atteso a larga scala. Tali mappe costituiscono il primo esempio della mappatura estesa del rischio simico applicata alla rete infrastrutturale della Regione Veneto, con la particolarità di essere state ottenute sulla base di curve di fragilità analitiche con metodi semplificati di valutazione agli spostamenti, calibrate sulle caratteristiche specifiche di queste tipologie di ponti esistenti, che sono del tutto rappresentative dei ponti stradali realizzati in Italia dal secondo dopoguerra ad oggi. Altri studi analoghi svolti negli ultimi anni per la valutazione del rischio infrastrutturale a larga scala si sono basati su procedure consolidate quali il metodo HAZUS (RISK-UE), che non sono tarati sulle caratteristiche specifiche dei ponti italiani non essendo generalmente disponibili database per studi a larga scala con informazioni di dettaglio tali da consentire una calibrazione delle curve di fragilità come in questo studio. Un’ estensione dello studio sull’esistente è rappresentato dalla costruzione di curve di fragilità per intere classi omogenee di strutture per ponti esistenti in c.a.: tali curve sono state ottenute a partire dalle curve di fragilità analitiche calcolate per una serie di opere master scelte come rappresentative delle classi omogenee di ponti del database, utilizzando la variabilità sui range delle caratteristiche geometriche e meccaniche ottenute dall’analisi statistica del database di riferimento precedentemente descritta. Sviluppi futuri del lavoro riguardano infine l’estensione delle procedure proposte di valutazione a classi diverse di strutture rispetto ai ponti in c.a., in particolare ai ponti ad arco in muratura che rappresentano l’altra categoria rilevante di opere dello stock, per arrivare ad una definizione il più possibile completa del rischio sismico sulle opere della rete in esame e ad una taratura di curve di fragilità specifiche per queste classi di opere. Sarà inoltre possibile calibrare in modo più puntuale la definizione dell’input sismico attraverso l’utilizzo di curve di hazard ottenute da mappe di pericolosità sismica locale mediante studi di micro zonazione per le aree di interesse.

Seismic response of a structure is influenced by the inertial interaction between structure and deformable medium, on which the structure rests, due to flexibility and energy dissipation capability of the surrounding soil. The inertial interaction analyses can be performed by utilizing simplified soil-structure interaction (SSI) analyses methods. In literature, it is noted that varying soil conditions and foundation types can be modeled by using these SSI approaches with springdashpot couples having certain stiffness and damping. In this study, the seismic response of superstructure obtained by using simplified SSI methods is compared with those of the fixed base systems. For this purpose, single and multi degree of freedom structural systems are modeled with both spring&ndash
dashpot couple and fixed base models. Each system is analyzed for varying structural and soil stiffness conditions under the excitation of three different seismic records. Next, the total base shear acting on the structural system and internal forces of load bearing members are investigated to observe the inertial interaction and foundation uplift effects on the superstructure. It is also aimed to examine the compatibility of the simplified SSI approaches utilized in the analyses. It is concluded that the structural and soil stiffness parameters are the most influential parameters that affect seismic structural response. Structures becomemore sensitive to varying soil properties as the structural stiffness increases. On the other hand, decreasing soil stiffness also increases the sensitivity of the structure to the seismic excitation. Calculated values of total base shear and internal member forces revealed that the inertial interaction might be detrimental for the superstructure. Contrary to general belief, the fixed base approach does not always yield to the results, which are on the safe side. Considering the analysis results, it is concluded that SSI analysis is very useful for more precise and economical design for the seismic behavior.

United Nations has lately stated ambitious health targets for 2030 in the Sustainable Development Goal agenda, following the already achieved progress between 1990 and 2015 when the number of children dying before the age of five was reduced by more than half. However, the mortality reduction in the first month of life after birth has not kept the same pace. Furthermore, a large number of stillbirths have previously not been accounted for. The aim of this thesis was to evaluate the impact of clinical training in neonatal resuscitation, and to identify strategies for an effective implementation at a maternal health facility in Nepal. Focus group discussions were used to explore the perceptions of teamwork among staff working closest to the infant at the facility. A prospective cohort study with nested referents was applied to determine effect on birth outcomes after an intervention with Helping Babies Breathe, a simplified protocol for neonatal resuscitation. Sustainability of the acquired skills after training was addressed by employing a quality improvement cycle. Video recordings of health workers performance were collected to analyse adherence to protocol. Midwives described the need for universal protocols in neonatal resuscitation and management involvement in clinical audit and feedback. There was a reduction of intrapartum stillbirth (aOR 0.46, 95% CI 0.32–0.66) and neonatal mortality within 24 hours of life (aOR 0.51, 95% CI 0.31–0.83) after the intervention. Ventilation of infants increased (OR 2.56, 95% CI 1.67–3.93) and potentially harmful suctioning was reduced (OR 0.13, 95% CI 0.09–0.17). Neonatal death from intrapartum-related complications was reduced and preterm infants survived additional days in the neonatal period after the intervention. Low birth weight was not found to be a predictor of deferred resuscitation in the studied context. This study confirmed the robustness of Helping Babies Breathe as an educational tool for training in neonatal resuscitation. Accompanied with a quality improvement cycle it reduced intrapartum stillbirth and mortality on the day of delivery in a low-income facility setting. Improved postnatal care is needed to maintain the gains in survival through the neonatal period. Increased management involvement in audit and quality of care could improve clinical performance among health workers.

Abstract Cognitive Radio (CR) improves the efficiency of spectrum utilization by allowing non- licensed users to utilize bands when not occupied by licensed users. In this thesis, we address several challenges currently limiting the wide use of cognitive radios. These challenges include identification of unoccupied bands, energy consumption and other technical challenges. Improved accuracy edge detection techniques are developed for CR to mitigate both noise and estimation error variance effects. Next, a reduced complexity Simplified DFT (SDFT) is proposed for use in CR. Then, a sub-Nyquist rate A to D converter is introduced to reduce energy consumption. Finally, a novel multi-resolution PSD estimation based on expectation-maximization algorithm is introduced that can obtain a more accurate PSD within a specified sensing time.

Elastic Buckling Simplified Methods for Structural Members with Edge-Stiffened Holes: Presently, the current design methods available to engineers to predict the strength of cold-formed steel members with edge-stiffened holes remains largely unaddressed in the North American Specification for the Design of Cold-Formed Steel Structural Members (NAS). Research was conducted to explore and develop a further understanding of the effects of stiffened edge holes on the elastic buckling parameters for local, distortional, and global buckling. Elastic buckling parameter studies have been conducted on a suite of cold-formed members including recently developed DeltaSTUDs manufactured by Steelform Building Products, Inc. and a series of common Steel Stud Manufacturers Association (SSMA) members. Furthermore, a suite of simplified methods for determining elastic buckling parameters used to predict capacity with the Direct Strength Method (DSM) for members with edge stiffened holes were developed and validated. The elastic buckling studies are used to validate the simplified methods presented in this thesis. All simplified methods are further validated with thin shell finite element eigen-buckling parameter studies where the edge-stiffened holes are explicitly modeled. Purlin Distortional Buckling Strength Under Gravity Loading: Laterally braced cold-formed steel beams generally fail due to local and/or distortional buckling in combination with yielding. For many members, distortional buckling is the dominant buckling mode and is addressed in the current North American Specification for the Design of Cold-formed Steel Structural Members. The current main code equation, AISI C3.1.4-10 for calculating the available distortional buckling stress was derived experimentally based on a series of four-point bending tests at John Hopkins University. Where this provides a good basis for determining capacity, in most loading conditions purlins are subjected to a downward uniform loading that provides additional resistance to distortional buckling in the top flange beyond the resistance of the steel roofing panel. This research describes an experimental study to explore and quantify the difference in distortional buckling flexural capacity of metal building Z-purlins treated as isolated components and Z-purlins loaded with a constant pressure applied to metal roof panels. A series of three different types of tests have been developed to quantify the system effect provided by the metal roof panels as well as downward pressure on distortional buckling. Results are also extended to validate the Direct Strength Method when predicting flexural capacity of purlins in a roof system.
Master of Science

The advantages of cold-formed thin-walled steel studs are many and their applications in building constructions continue to grow. They are used as load-bearing members. An example is lightweight wall panel assemblies which consist of channel steel studs with gypsum plasterboard layers attached to the two flanges, often with interior insulation. At present, expensive fire tests or advanced numerical modelling methods are necessary in order to discover the fire resistance of such wall assemblies. For common practice this is not effective and a simplified method, suitable for use in daily design, is necessary. The aim of this research is to develop such simplified methods. The first main objective of this study is to develop a simple approach to calculate the temperature distributions in the steel section, in particular the temperatures on both the exposed and unexposed sides when the panel is exposed to fire exposure from one side. These two temperatures are the most influential factors in the fire resistance of this type of wall assembly. The proposed method calculates the average temperatures in the flanges of the steel section and assumes that the temperature in the web is linear. The proposed method is based on a simple heat balance analysis for a few nodes representing the key components of the wall panel. The thermal resistance of these nodes are obtained by the weighted average of thermal resistances in an effective width of the panel within which heat transfer in the panel width direction is assumed to occur. The proposed method has been extensively validated by comparison with numerical parametric studies. In order to calculate the ultimate capacity of steel studs, the traditional method is by using effective width. However, this method is now being questioned as it considers elements of section in isolation and does not consider interaction between the elements. In addition, this method is not appropriate to be extended to steel studs under fire conditions. The cross-section under fire conditions has non-uniform temperature distribution which results in the non-uniform distribution of mechanical properties. Using an effective width method to deal with this problem will require many assumptions whose accuracy is uncertain. Recently, the direct strength method (DSM) has been developed and its accuracy for ambient applications has been comprehensively validated. This method calculates cross-sectional plastic resistance and elastic critical loads for local, distortional and global buckling modes with the aid of simple computer programs. The elastic and plastic resistances are then combined to give the ultimate resistance of the structure using interaction equations. This method is suited to steel studs with non-uniform temperature distribution in the cross-section. The second main objective of this study is to extend the direct strength method for application to thin-walled steel studs having non-uniform elevated temperature distributions in the cross-section. It has been found that the DSM concept is applicable, but the interaction equations should be modified to allow for the effects of elevated temperature (non-uniform temperature distribution and changes in stress-strain relationships). Also the effects of thermal bowing should be included when calculating the plastic resistance and the elastic buckling loads of the cross-section. This research has proposed new interaction equations and has developed design tools. By comparing the results of the proposed method with validated Finite Element simulations over a very large range of parametric studies, the proposed method has been demonstrated to be valid. The validation studies include both standard and parametric fire exposures and are generally applicable.

In the last three decades, seismic performance assessment of buried structures has evolved through the following stages : i) buried structures are not prone to seismically-induced damages, thus no need for detailed investigations, ii) eliminating soil-structure-earthquake interaction and use of seismically-induced free field ground deformations directly as the basis for seismic demand, thus producing conservative results, and finally iii) soil-structure and earthquake interaction models incorporating both kinematic and inertial interactions. As part of soil-structure and earthquake interacting models, simplified frame analysis established the state of practice and is widely used. Within the confines of this thesis, the results of simplified frame analysis based response of buried structures are compared with those of 2-D finite element dynamic analyses. For the purpose, 1-D dynamic and 2-D pseudo-dynamic analyses of free field and buried structural systems are performed for a number of generic soil, structure and earthquake combinations. The analyses results revealed that, in general, available closed form solutions are in pretty good agreement with the results of finite element analyses. However, due to the fact that dynamic analyses can model both kinematic and inertial effects
it should be preffered for the design of critical structures.

O trabalho trata da formulação e análise da resposta numérica de um modelo de danificação e plastificação localizadas em zonas previamente definidas ao longo de elementos estruturais de barra, estendendo-se os conceitos dos modelos clássicos de plasticidade concentrada. Inicialmente é feita uma breve revisão bibliográfica sobre modelos de dano e plasticidade, destacando-se alguns que contém propostas voltadas para a simplificação de suas formulações ou então da etapa de implementação numérica adotando-se, neste caso, a técnica de discretização em estratos dos elementos de barra. Em seguida, já no âmbito dos modelos ditos simplificados e estendendo-se a formulação de um modelo para estruturas de barras proposto na bibliografia, deduz-se a matriz de rigidez para o caso de barra em regime elástico com dano. Na dedução, considera-se que os processos de danificação, associados à flexão e restritos às extremidades do elemento de viga, são dependentes entre si e afetam diretamente os coeficientes de transmissão de esforços ao longo do elemento. Nesta etapa, através de dois exemplos numéricos, avalia-se a resposta do modelo quando implementado em um programa de elementos finitos. Apresenta-se, na seqüência, um estudo sobre a viabilidade da aplicação do modelo estudado às estruturas em concreto armado, incluindo-se casos em que a distribuição da armadura longitudinal é assimétrica. Como resultado desse estudo, sugere-se uma modificação da função critério de danificação, originalmente empregada, para melhor representar o processo de dissipação de energia relacionada à danificação. A partir dos confrontos entre respostas experimentais de vigas e pórtico em concreto armado e resultados numéricos, conclui-se pelo bom desempenho do modelo modificado. Finalmente, reúnem-se sugestões para a continuidade dos estudos.
This work is related to formulation and numerical analysis of a damage and plasticity model which considers such effects localised on zones previously defined along the structural beam elements, extending the concepts of the classics lumped plasticity models. First of all, a brief bibliography revision on damage and plasticity based models is given, enlightening the ones which propose some kind of simplification at the level of the formulation or only at the stage of the numerical implementation, for instance using a layered technique in a beam element discretization. Afterwards, on the field of the so called simplified models, a stiffness matrix of an elastic damage beam element is deduced, extending the formulation of a framed structures model proposed in the bibliography. The main characteristic of the new element is that the damage processes is localized on hinges at the extremities of the beam element, being the associated damage variables dependent on each other and reducing progressively the transmission efforts factor along the element. Two basic numerical examples show the performance of the model when implemented in a finite element code. Next, a study on the feasibility of the model to analyse reinforced concrete structures is presented. In order to enlarge the application field, cases where longitudinal reinforcement is asymmetrically distributed in the cross section are also considered. As a result of the study, a change in the damage criteria function originally used is suggested, aiming to improve the valuation of the dissipated energy related to the damage process. The response of the modified resulting model is valuated by a confront between experimental and numerical results of beams and frame reinforced concrete structures. The results show a very good performance of the modified model. Finally, some topics for further research on the theme explored in this work are suggested.

Buildings are responsible for approximately half of the energy used in the UK and are therefore responsible for significant quantities of CO2 emissions. Thermal assessment methods enable the building designer to reduce the likely energy consumption of those buildings. Dynamic thermal simulation programs can be used for thermal assessment but are generally considered difficult and time consuming to use. The advantages of such methods are high levels of accuracy and the range of information that can be obtained. Simplified methods are intended to be quicker and easier to use than dynamic thermal simulation. However, they are often of low accuracy and limited in the number of building and operational parameters that can be altered. This thesis describes a simplified thermal assessment method that combines some of the flexibility and accuracy of dynamic thermal simulation, while being quick and easy to use. Steady state and transient heat flow algorithms are combined with a new calibration process that determines the effect on space heating energy use of the thermal mass of different types of construction element. All major building and occupancy parameters can be altered and the use of hourly calculations enables the user to explore the effect on thermal performance of various strategies such as the use of night shutters, or increased ventilation rates during the day. A discussion of the further development of the method focuses on results that suggest that the calibration of different constructions will not be an open ended process. There is a high correlation between the effective heat capacity and the actual heat capacity of the constructions tested to date, although further work will be required in this area. The effective heat capacity is currently determined as part of the calibration process. The accuracy of annual heating energy prediction is good and accuracy of overheating prediction reasonable.

Permettant de protéger les populations des inondations, de canaliser l'eau à des fins d'irrigation ou de production d'électricité, les digues en terre sont des ouvrages stratégiques dont la rupture peut avoir des conséquences dramatiques. La stabilité de ces ouvrages doit ainsi pouvoir être assurée, notamment en cas de séisme. Cependant, étant donné le très grand linéaire qu'ils représentent, la mise en œuvre de vastes campagnes de reconnaissances et de modèles numériques complexes n'est pas toujours envisageable dans les zones de sismicité modérée. L'utilisation d'outils simplifiés, faisant appel à des données facilement mesurables, se révèle indispensable pour fournir une indication sur la stabilité de tronçons de digue soumis à un chargement sismique. Les méthodes simplifiées existantes permettant d'estimer la réponse dynamique des remblais sont inadaptées au contexte des digues. En effet, alors que les digues sont pour la plupart construites dans des vallées sédimentaires, la majorité de ces méthodes, développées pour l’étude des barrages, supposent que l’ouvrage est fondé directement au rocher. Seules deux approches permettent de prendre en compte l’interaction entre l’ouvrage et son sol d’assise (effets de site) : la méthode de Sarma(1979) et celle de Papadimitriou(2014). Cependant, la première est basée sur des hypothèses très fortes (elle considère notamment un rocher rigide et un amortissement uniforme, qui plus est très fort) et la seconde se limite à des ouvrages ayant une hauteur supérieure à 20 si{m}. L'approche développée au cours de cette thèse repose sur des hypothèses plus réalistes, en considérant notamment des géométries adaptées à celles des digues, en prenant en compte les effets de site et en adaptant la dissipation d'énergie au niveau de sollicitation. Une étude paramétrique numérique (calcul de la réponse visco-élastique par éléments spectraux en deux dimensions) est utilisée pour couvrir un ensemble de configurations géométriques et mécaniques de digues. Pour prendre en compte la non-linéarité, les valeurs d'amortissement et de dégradation du module de cisaillement sont adaptées en chaque point des modèles à partir des résultats fournis par une série de calculs en linéaire équivalent 1D. Les réseaux de neurones artificiels, dont l'apprentissage est basé sur les résultats des simulations numériques, sont utilisés pour le développement d'une nouvelle méthode simplifiée. Des abaques sont réalisés, à partir des réseaux de neurones établis, pour offrir une alternative visuelle à leur utilisation "mathématiques". Les outils simplifiés auxquels aboutit cette thèse font appel à des paramètres facilement mesurables sur le terrain. Des méthodes géophysiques sont mises en œuvre au niveau de quatre sites de digues afin d'identifier le meilleur compromis de mesures permettant d'estimer les paramètres nécessaires à l'évaluation de la réponse dynamique de l'ouvrage
Embankments are strategic facilities that, among other things, protect population from flooding and canalize rivers for energy production or for irrigation concerns. Since their rupture can lead to terrible consequences, they must remain stable, especially in case of earthquake. However, given the very large length of embankments, it is rarely possible to conduct complete investigations and complex numerical models in regions of moderate seismicity. Therefore, simplified tools to estimate the dynamic response of embankments using accessible embankments’ features are necessary to estimate their capacity to resist seismic loadings. Existing simplified methods, generally developed to assess the dynamic response of embankment-dams, turn out to be inappropriate to study the particular case of embankments along rivers – or other types of embankment, with small height and large length. The majority of these simplified methods do not take into account site effects: they assume the presence of rock directly at the base of the embankment, whereas most of large length embankments are located in alluvial valleys. Two methods only - Sarma(1979) and Papadimitriou(2014) - take into account the interaction between the embankment and its soil foundation. However, the first one relies on strong assumptions (among others, that the bedrock is considered rigid and that the viscous damping is supposed to be both spatially uniform and very large) and the second one is limited to tall embankments (higher than 20 si{m}).The method developed in this thesis relies on assumptions that are more realistic: it considers geometries adapted to large length embankments, it accounts for the presence of a soil foundation and includes an energy dissipation process consistent with expected levels of strain. A numerical parametric study is performed based on the computation with the spectral element method of the viscoelastic response of a large set of embankments spanning a wide range of geometrical and mechanical properties. In order to take into account nonlinearity, damping and shear modulus reduction are adapted in each point of the numerical models according to the results of a set of 1D linear equivalent computations. A new simplified method is derived from the obtained numerical results using artificial neural networks. Abacuses are produced from the neural networks so that engineers can have at their disposal a visual tool. This thesis leads to a simplified method that uses some accessible features of embankments as input parameters. The ability of classical geophysical methods to provide those input parameters is further estimated on four sites corresponding to different realistic configurations

Nowadays, the forging industry has a great importance in the fabrication of metallic parts. Therefore, new theoretical models, or modifications to others already existing, continuously appear to improve the process. New investigations culminated, recently, in equations designed to obtain the necessary pressure to forge a part. The purpose is to have a fast, not expensive and efficient alternative to the numerical methods in such calculation. With the double intention of divulgating this new theory created in the University of Málaga (Spain) and confirming its validity, it is interesting to carry out a comparison with the finite element method. In this comparison, geometrical factors relative to the workpiece (part subjected to forging) and the friction coefficient come into play. The goal is then to find validity ranges in the equations for the variables previously mentioned, with the aim to delimit those forging situations in which they could be applied. The implementation of these variables into the commercial FE-code Abaqus is simple, although two aspects arise: the meshing and the correct modeling of the contact between the workpiece and the upper die. The limitation of the Abaqus Student Version (used throughout the analyses) in the allowed number of nodes, prevented performing sufficiently dense meshes. Many alternatives are investigated that, unfortunately, do not show any satisfactory result for the simulation of the process. Performing forging simulations is quite complex and requires a great knowledge in the field and an extraordinary knowledge of how different elements work in large plastic strain. However, this project leaves a collecting data method and a procedure to determine the initial geometry of the workpiece to ensure plastification and to reach a determined shape factor after the forging. The most important is that the way to further analyses has been cleared by confirming the suitability for certain parameters in the simulation (element type, non-linear geometry, contact model, etc.). The recommendation for future simulation efforts is to use ALE (Arbitrary Lagrangian-Eulerian) adaptive meshing.

The presentation was a web conference from Spain.

Compliant layered bearings could improve the useful life of replacement load-bearing joints. By incorporating an elastic bearing material, fluid film separation of the articulating surfaces can be maintained and so low friction and negligible wear should occur. Compliant bearings are still under development and so require extensive testing before they can be implanted. To give a realistic evaluation of their performance, the test conditions must be representative of the in vivo situation. To date this has meant using joint simulators. A simplified test method has been developed to measure the friction of compliant layered bearings. It uses a reciprocating materials-screening apparatus adapted to include a dynamic load, very low friction bearings, and a curved counterface. It has been validated by comparison with simulator tests and predictions made from Hertzian contact and elastohydrodynamic theories. An alternative to the Sommerfeld parameter\has been defined to allow comparison of the different test methods. Tests have shown that of the parameters which affect friction, the predicted Hertzian contact area was the most important. Similar predicted areas gave rise to similar coefficients of friction in both mixed and fluid film lubrication regimes. The simplified method showed improved repeatability and lower systematic errors than the simulator. The method has been used to examine the effect of design factors on the friction generated in compliant layered bearings, comparing the results obtained with those of the simulator. Increased load, decreased counterface roughness, increased entraining velocity and the use of a compliant layer over UHMWPE all reduced the coefficient of friction. Bearing conformity had a mixed effect on friction. Point contacts and line contacts showed similar trends. The mechanical properties of the compliant materials have also been considered including hardness, hysteresis in compression, and creep.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2004.
Includes bibliographical references (p. 105-108).
This thesis studies the influence of the roll-up of a wake on the benefits in induced drag and rolling moment experienced by a close formation of two elliptically loaded wings. The roll-up of the leading wake is computed in the Trefftz plane using a linear vorticity panel method. A smoothing parameter as well as a truncation of the vortex sheet in the highly rolled-up areas are introduced in order to stabilize the computations. The trailing wing is simply modeled as a lifting line, and its induced drag is computed thanks to a near-field analysis. The results are compared to computations using simple horseshoe-vortex methods, either with or without a viscous core. Maximum induced drag benefits comprised between 60% and 70% are observed for a lateral overlap of both wings of about 5% to 10% of the span. The maximum rolling moment is in average attained for 1.5% of the span less overlap. It is found that a horseshoe vortex with a viscous core of radius over semi-span ratio (2r[c])/b = 0.12 modeled according to Burnham can account well for the effects of the roll-up of the wake on the benefits in induced drag that can be gained from formation flight. Actually, the difference between both results is mainly confined in a small region around the maximum and the relative error is generally low. Taking the vertical drift of the whole wake into account is not found to be beneficial to the agreement between the results around the maximum. In the case of the rolling moment, the predictions given by simple horseshoe vortex models do not agree very well with the predictions given by the rolled-up sheet model, the relative error between both predictions being very high in many areas.
by Amandine Denis.
S.M.

The aims and motivations that were driven this PhD thesis arise from the common interest on the mitigation of the seismic risk, wide field of continuous relevance and of interest for different disciplines. The scientific community, specially in engineering field, reserves attentions on the mitigation of the seismic risk. The human and economic losses, caused by fragilities of the urban centres, manifested in the aftermath of a seismic event, confirm the need of research effort. The PhD thesis presents a multi criteria method for seismic assessment of unreinforced masonry buildings, URMs. The majority of the built environment consists of URMs. The study of their seismic behaviour is exasperated by the ageing of materials, the lack of anti-seismic criteria, construction process, architectural alterations or restorations, and the poor mechanical properties of used materials. Nevertheless, URMs are unique constructions for their historical and architectural value, that need to be protected against earthquakes. The knowledge of structural fragilities of urban centres is a prerequisite to face the mitigation of the seismic risk. Simplified assessment methods arise to overcome the effort and time consuming of analysis at a large scale of the built environment, by means the introduction of several simplifications. The proposed multi criteria vulnerability method provides a quick assessment based on few structural parameters, known from field observations and geometric survey, to overcome excessive computational demand, thanks to two different levels of evaluation. The first level of the vulnerability assessment method bases on the evaluation of few structural parameters to perform a first screening of the seismic fragilities. The second level predicts the seismic capacity of masonry walls more accurately respect to the empirical one, to establish strengthening measures or strategies more accurately. Therefore, the multi criteria method could support the activities of authorities and stakeholders in the mitigation of the seismic risk of the built environment. The thesis consists of eight chapters. The first chapter introduces an overview on the seismic risk, as field of the research activity. The second chapter concerns the state of the art of structural vulnerability, the structural vulnerability. An in-depth classification of seismic vulnerability assessment methods is reported. The third chapter regards the test-site of the research activity. The fourth chapter reports the dynamic campaign on a URM, chosen as representative of the structural class. The aim of this activity was to investigate the influence of a suite of structural parameters influencing the building behaviour. The fifth chapter introduces the first level of the predictive multi-criteria method. The empirical method aims to estimate the seismic vulnerability through the evaluation of a few structural parameters, ensuring a quick application. The derivation and validation of the formulations' method are reported. The last part of the chapter compares the method with others available from the literature, to highlight its reliability and advantages. The sixth chapter illustrates possible applications of the empirical predictive method. The seventh chapter discusses the second level of the proposed method. It aims to grasp the seismic vulnerability of buildings, with a higher accuracy than the first level. The eighth chapter completes the PhD thesis, with a broader point of view, to explain the results and future developments.

L'idee principale dans cette methode simplifiee est que les contraintes varient peu dans une structure massive. Le but de cette methode est un calcul rapide de l'effet interieur a grande longueur de variation. Dans cette approche, une approximation est construite a partir de la structure mathematique des solutions pour un domaine etoile. Ensuite, une formulation variationnelle pour des domaines simples est introduite. Elle est consistante avec l'approximation et differe des formulations classiques. Finalement, des structures plus complexes sont etudiees par deux techniques de sous-structuration

The research focuses on developing a methodology for modeling a pneumatic bias-ply tire with the finite element method for vehicle dynamics simulation. The tire as a load-carrying member in a vehicle system deserves emphasized formulation especially for the contact patch because its representation of mechanics in the contact patch directly impacts the handling and ride performance of a vehicle. On the other hand, the load transfer from the contact patch to the wheel hub is necessary for determining the inputs to a chassis. A finite element (FE) tire model has strong capability to handle these two issues. However, the high cost of computing resources restrains its application mainly in the tire design domain. This research aims to investigate how to balance the complexity of a simplified FE tire model without diminishing its capability towards representing the load transmission for vehicle dynamics simulation. The traditional FE tire model developed by tire suppliers usually consists of an extremely large number of elements, which makes it impossible to be included in a full-vehicle dynamics simulation. The material properties required by tire companies' FE tire models are protected. The car companies have an increasing need for a physical-based tire model to understand more about the interaction between the tire and chassis. A gap between the two sides occurs because the model used for tire design cannot directly help car companies for their purpose. All of these reasons motivate the current research to provide a solution to narrow this gap. Other modern tire models for vehicle dynamics, e.g. FTire or TAME, require a series of full-tire tests to calibrate their model parameters, which is expensive and time-consuming. One great merit of the proposed simplified FE tire model is that determining model inputs only requires small-scale specimen tests instead of full-tire tests. Because much of the usability of a model hinges on whether its input parameters are easily determined, this feature makes the current model low cost and easily accessible in the absence of proprietary information from the tire supplier. A Hoosier LC0 racing tire was selected as a proof of modeling concept. All modeling work was carried out using the general purpose commercial software Abaqus. The developed model was validated through static load-deflection test data together with Digital Image Correlation (DIC) data. The finite element models were further evaluated by predicting the traction/braking and cornering tire forces against Tire Test Consortium (TTC) data from the Calspan flat-track test facility. The emphasis was put on modeling techniques for the transient response due to the lack of available test data. The in-plane and out-of-plane performance of the Hoosier tire on the full-tire test data is used for model validation, not for "calibrating" the model. The agreement between model prediction and physical tests demonstrate the effectiveness of the proposed methodology.
PHD

O Método Híbrido dos Elementos de Contorno foi introduzido em 1987. Desde então, o método foi aplicado com sucesso a diferentes tipos de problemas de elasticidade e potencial, inclusive problemas dependentes do tempo. Esta Tese apresenta uma tentativa para consolidar a formulação simplificada do Método Híbrido dos Elementos de Contorno para a análise geral da resposta dinâmica de sistemas elásticos. Baseado em um método de superposição modal, um conjunto acoplado de equações diferenciais de movimento de alta ordem é transformado em um conjunto desacoplado de equações diferenciais de segunda ordem que podem ser integradas normalmente por meio de procedimentos conhecidos. Este método também é uma extensão de uma formulação introduzida por J. S. Przemieniecki, para a análise de vibração livre de barras e elementos de viga baseada em uma série de freqüências. O método trata estruturas restringidas, com condições iniciais não homogêneas dadas como valores nodais e também através de campos prescritos no domínio, assim como forças genéricas de massa (além de forças inerciais). Esta tese também tem por objetivo estabelecer a consolidação conceitual da aplicação da versão simplificada do Método Híbrido dos Elementos de Contorno a materiais com gradação funcional. São obtidas várias classes de soluções fundamentais para problemas de potencial dependentes e independentes do tempo, para a análise no domínio da freqüência combinada com uma técnica avançada (mencionada acima) de superposição modal baseada em séries de freqüências. Com isso, consegue- se a utilização de integrais somente no contorno mesmo para materiais heterogêneos. Apresenta-se um grande número de resultados numéricos de problemas bidimensionais, para validação dos desenvolvimentos teóricos realizados.
The hybrid boundary element method was introduced in 1987. Since then, the method has been successfully applied to different problems of elasticity and potential, including time-dependent problems. This thesis presents an attempt to consolidate a formulation for the general analysis of the dynamic response of elastic systems. Based on a mode- superposition technique, a set of coupled, higher-order differential equations of motion is transformed into a set of uncoupled second order differential equations, which may be integrated by means of standard procedures. The first motivation for these theoretical developments is the hybrid boundary element method, a generalization of T. H. H. Pian`s previous achievements for finite elements, which, requiring only boundary integrals, yields a stiffness matrix for arbitrary domain shapes and any number of degrees of freedom. The method is also an extension of a formulation introduced by J. S. Przemieniecki, for the free vibration analysis of bar and beam elements based on a power series of frequencies. It handles constrained and unconstrained structures, non-homogeneous initial conditions given as nodal values as well as prescribed domain fields and general domain forces (other than inertial forces). This thesis also focuses on establishing the conceptual framework for applying the simplified version of the hybrid boundary element method to functionally graded materials. Several classes of fundamental solutions for steady-state and time-dependent problems of potential are derived for a frequency-domain analysis combined with an advanced mode superposition technique based on a power series of frequencies. Thus, the boundary-only feature of the method is preserved even with such spatially varying material property.Several numerical examples are given in terms of an efficient patch test for irregular bounded, unbounded and multiply connected regions submitted to high gradients.

Les écrans de filet pare-blocs sont des ouvrages de protection souples utilisés pour protéger les habitants ainsi que leurs biens du danger des éboulements rocheux dans les régions à risques. Ces structures placées sur la trajectoire des masses en mouvement sont formées d’un filet métallique maintenu au terrain naturel par des poteaux rigides. Lorsqu’elles sont impactées par un bloc, elles subissent des grandes déformations qui nécessitent de modéliser leur comportement en tenant compte de non-linéarités à la fois géométriques et matérielles. Leurs composants sont ainsi représentés dans ce travail par des éléments discrets et le problème mécanique est résolu quant à lui avec un outil de calcul numérique adapté aux grandes transformations. Cet algorithme est ensuite utilisé pour évaluer l’influence de différentes stratégies de modélisation de la nappe de filet, toutes tirées de la littérature scientifique, sur le comportement global d’un écran de protection pare-blocs. Les conclusions de cette étude ainsi que des observations expérimentales ouvrent la voie vers de nouvelles stratégies de modélisation discrète, pour lesquelles le filet est représenté par un nombre restreint de degrés de liberté. La famille de modèles simplifiés développée dans ce travail permet de simuler le comportement d’un ouvrage avec des faibles coûts en temps de calcul, offrant ainsi l’opportunité de mettre en œuvre des études paramétriques complexes et des méthodes de dimensionnements probabilistes
Rockfall barriers are flexible structures that mitigate the risk of rockfall and thus protect people living in risk areas, as well as their property. These structures, placed on the trajectories of the moving blocks, are made of a steel net held on the natural ground by rigid posts. When they are impacted, they undergo large deformations that require modelling their behaviour by taking into account both geometric and material non-linearities. Their components are therefore represented in this work with discrete elements and the mechanical problem is thus solved with a calculation tool adapted to the large déformations problem. This algorithm is also used to assess the influence of different net modelling strategies, from the scientific literature, on the overall behaviour of a rokfall barrier. The conclusions of this study as well as experimental observations pave the way to new discrete modelling strategies, for which the net is represented by a limited number of degrees of freedom. The family of simplified models developed in this work makes it possible to simulate the behaviour of a structure with a low computation time costs, thus offering the opportunity of implementing complex parametric studies or probabilistic dimensioning methods

Gas turbine vanes find themselves in very hostile environments – extremely high temperature combustion gases, much exceeding material melting temperatures, flowing over them at enormous pressures. It is necessitated due to the increased efficiency and power output at these conditions. However, this also means that, in spite of the technological advancements made, these parts need frequent repairing compared to parts placed in milder environments. Primarily due to economic reasons, gas turbine parts are repaired by companies other than the original equipment manufacturer (OEM). While multitude of condition monitoring techniques have been developed and are used in the industry for regular maintenance checks, there is no easy way to characterize the impact on thermal performance of the repairing processes involved. This thesis reports the development of a technique to address this issue. It also chronicles the test rig design, experiments conducted, development and significance of the thermal performance metric. Heated air (250 ̊C – 300 ̊C) is flown through the internal cooling passages of 8 samples each of OEM and repaired parts at two different pressure ratios (vane inlet over ambient pressure), 1.1 and 1.3. First, steady state mass flow rates through each airfoil (one part is a cluster of 4 airfoils) is experimentally determined and compared among the OEM and repaired sample sets. Second, a transient experiment is run and the surface temperatures of the airfoils are measured using multiple infrared cameras viewing both the pressure and suction side of the airfoils. A parameter involving localized vane surface temperature, airfoil inlet temperature and ambient temperature is formulated to characterize the vane thermal performance. Using statistical analysis, it is found that there is no significant difference between the OEM and repaired samples tested. The development of the discussed technique, it is expected, will help companies in the gas turbine vane repairing business to qualify their parts in a robust and efficient manner without the need to invest a lot of money in buying precision equipment, or, control chambers. Finally, a couple of further studies are recommended to further improve the qualifying procedure and thereby increase the efficiency of the technique.
Master of Science

Cette thèse traite du développementde méthodes analytiques pour l’analyse de laréponse aux collisions de navires d’éoliennesoffshores tubulaires telles que les monopieux etles flotteurs de type Spar, en considérant lesdéformations non seulement plastiques maisaussi élastiques, ceci afin de traiter des impactsà faible et à haute énergies.Le travail de recherche s’articule en deuxparties. La première concerne la réponse àl’impact d’éoliennes classiques tubulaires endéformation élastoplastique quasi-statique. Unalgorithme « pas à pas » est développé sur labase de formulations théoriques puisimplémenté dans un solveur permettant deprédire le processus de déformation complet del'éolienne.Dans la seconde partie, la réponse dynamiqueélastique d’un monopieu impacté par un navireest étudiée. Une méthode basée sur desmatrices de transfert est développée pourquantifier la réponse de l'éolienne à une chargeimpulsionnelle donnée et en particulierl'accélération vue par la nacelle.Ce travail de thèse s’inscrit dans le cadre duprojet de recherche ColFOWT, qui vise àdévelopper un outil complet et rapide d'analysede collisions navire-éolienne offshore. L'outilpermettra à terme de modéliser le processusde transfert d'énergie multi-mécanismes qui alieu lors d'une collision de navire, y compris lesmodes de déformation locaux et globaux ainsique l’effet des chargements hydrodynamiqueset des lignes d’ancrage
This thesis focuses on thedevelopment of simplified methodologies toassess the ship collision response of offshorewind turbines (OWT) supported by standalonetubular members such as monopiles and sparfloaters, with the inclusion of elasticcontributions, and the capability to address bothlow and high-energy impactsThe research is divided into two parts. The firstpart concerns the quasi-static elasto-plasticimpact response of typical OWTs. A timesteppingalgorithm was developed based ontheoretical formulations and implemented in astructural solver that is capable of predicting theOWT’s complete deformation process.The second part examines the dynamic elasticresponse of a monopile to a ship impact. Asimplified two-step framework based ontransfer matrices was developed to assess theresponse of the OWT to a given collision load,in particular the RNA acceleration.This thesis was conducted in the framework ofthe ColFOWT project, which aims to develop acomprehensive and rapid assessment tool forship-OWT collisions. The tool will be capable ofmodelling the multi-mechanism energy transferprocess that takes place during a collisionevent, including local and global deformationmechanisms, hydrodynamic effects, andmooring response

Une methode d'analyse du delaminage des structures stratifiees carbone-epoxy, de type t300-914, basee sur la mecanique de l'endommagement est presentee. Un programme elements finis a ete realise pour predire et localiser l'initiation et la propagation du delaminage en un meme modele a cout numerique reduit. Les hypotheses principales de la methode sont: les phenomenes d'endommagement dans les zones bord des structures sont reduits a ceux des liaisons entre les couches; le bord de la structure est faiblement courbe. Le stratifie est modelise par un empilement de couches homogenes et d'interfaces elastiques endommageables. L'interface est une entite surfacique assurant le transfert des deplacements et contraintes entre deux couches adjacentes. Le probleme a resoudre est un probleme d'evolution non lineaire. Un algorithme de type riks est utilise pour detecter d'eventuels points critiques et continuer le calcul au-dela avec une bonne convergence. Pour les grands nombres de couches, le traitement numerique d'un probleme elastique permet de se ramener a un calcul parallele et separe sur chacune des couches. Des simulations numeriques de delaminage d'eprouvettes ont ete menees et comparees avec des resultats experimentaux