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The primary focus in this research is on proposing a methodology for modeling of discrete crack propagation in geomaterials such as soil, rock, and concrete. Structures made of such materials may undergo damage due to several reasons. Here, mechanical loading and chemo-mechanical interactions that result in degradation of strength parameters are considered as the sources of damage initiation. Both tensile and compressive cracks are investigated. For analysis of crack propagation, two different methodologies are employed; the Constitutive Law with Embedded Discontinuity (CLED) and the Extended Finite Element Method (XFEM). The CLED approach is enhanced here to describe the discrete nature of crack propagation. This is done by coupling the CLED with explicit modeling of crack path using the Level-Set method. The XFEM is used as a verification tool to check the results from CLED analysis. An algorithm is proposed for crack initiation and propagation that results in stable and a mesh-independent solution. The CLED approach is further improved by developing the return-mapping and closest-point projection algorithms. Extensive numerical investigations are conducted that include mode I cracking in a three point bending test, mode I cracking in notched cantilever beam, mixed cracking mode in a plate subjected to shear and tension, and a mixed mode cracking in a notched beam under four point loading. For frictional interfaces, the shear band formation in a sample subjected to bi-axial compression and the shear band formation in a geo-slope are studied. The thesis also addresses the topic of the response of unsaturated cohesive soils undergoing an infiltration process. The problem is approached within the framework of Chemo-Plasticity. It is assumed that the complex chemo-mechanical interactions are the controlling factors for degradation of strength parameters during this process. A return mapping integration scheme is developed and the approach is employed to investigate the stability of a geoslope subjected to a heavy rainfall. Analysis of shear band formation is further investigated in the context of sedimentary rocks. The microstructure tensor approach is used to describe the inherent anisotropy in this class of materials. The orientation of the shear band is defined by invoking the Critical Plane approach and the closest-point projection algorithm is developed for numerical integration of the governing constitutive relations. The model is used along with CLED for analysis of the mechanical response of Tournemire argillite. It is shown that the friction between loading platens and sample can play an important role in the process of shear band formation and the associated assessment of the ultimate load. A mesh-sensitivity analysis employing the CLED framework is also conducted here. The research clearly demonstrates that the discrete representation of crack path propagation is essential for an accurate analysis of failure in various engineering structures. It is shown that if the classical smeared Constitutive Law with Embedded Discontinuity is enhanced to simulate the discrete nature of the damage process, it can yield very accurate results that are virtually identical to those obtained from discrete approaches such as XFEM. / Thesis / Candidate in Philosophy

This paper examines the causal effect of niche parties’ council representation on policy outcomes in Spain between 2003 and 2022. Focusing on the far-left IU and far-right VOX as niche parties, it utilizes local-level data on municipal elections. To account for possible endogeneity, I apply a regression discontinuity design using the 5% electoral admission threshold, generating quasi-experimental variation in the probability that a niche party is represented in the council. I show that if IU obtains council representation, municipal budgets shift from a surplus to a deficit. Moreover, I find large effects on revenue and spending if PSOE is forming the coalition, even if it is not the strongest party in the election. These findings suggest that IU plays a crucial role as a coalition partner, exerting a considerable influence on local policies. Conversely, there seem to be no effects of IU’s representation for single-party majority governments. This indicates that in contrast to research looking at parties’ policy positions, bargaining about resources rather than electoral competition for voters drives the results. Additionally, I provide evidence for spillover effects to the regional level, resulting in a higher level of party favoritism between regional and local governments due to IU’s council representation. Regarding VOX’s entry into the council, I find a substantial reduction in fee revenues.

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The railway vehicles are an increasing mean of transportation due to, its reduced impact on environment and high level of comfort provided. These reasons have contributed to settle a positive perception of railway traffic into the European society. In this upward context, the railway industrial sector tackles some important challenges; maintaining low operational costs and controlling the nuisance by-products of trains operation, the most important being railway noise. Track dynamic plays a main role for both issues, since a significant part of the operational costs are associated with the track maintenance tasks and, the noise generated by the track can be dominant in many operational situations. This explains why prediction tools are highly valued by railway companies. The work presented in this licentiate thesis proposes methodologies for accurate and efficient modelling of railway track dynamics. Two core axes have led the development of this task, on one hand, the rail modelling and, on the other hand, the characterisation of the finite length nature of track supports. Firstly, concerning the rail modelling technique, it has evolved under two major premises. On one hand, regarding the frequency domain, it should describe high frequency behaviour of the rail. In order to accomplish with this first premise, a model based on Timoshenko beam theory is used, which can accurately account for the vertical rail behaviour up to 2500 Hz. On the other hand, with respect to the time domain, the response should be smooth and free of discontinuities. This last condition is fulfilled by implementation of the Timoshenko local deformation. Secondly, a model of support that considers its finite length nature is sought. For this purpose, a Timoshenko element over elastic foundation is formulated. Thus, the common model of support, which is based on a concentrated connection, is substituted by a distributed model of support. In this way, several enhancements are achieved; the temporal contact force response is smoothed and a more realistic shape is obtained, the amplitude of the displacement due to the parametric excitation is reduced and the magnitude associated to the ‘pin-pin’ frequency is not overestimated. / <p>QC 20170522</p>

The objective of this dissertation is to present a modeling and simulation methodology for MEMS devices and identify and understand the associated nonlinearities due to large deflections, electric actuation, impacts, and friction. In the first part of the dissertation, we introduce a reduced-order model of flexible microplates under electric excitation. The model utilizes the von Karman plate equations to account for geometric nonlinearities due to large plate deflections. The Galerkin approach is employed to reduce the partial-differential equations of motion and associated boundary conditions into a finite dimensional system of nonlinearly coupled ordinary-differential equations. We use the reduced-order model to analyze the mechanical behavior of a simply supported microplate and a fully clamped microplate. Effect of various design parameters on both the static and dynamic characteristics of microplates is studied. The second part of the dissertation presents comprehensive modeling and simulation tools for impact microactuators. Nonsmooth dynamics due to impacts and friction are studied, combining various approaches, including direct numerical integration, root-finding technique for periodic motions, continuation of grazing periodic orbits, and local analysis of the near grazing dynamics. The transition between nonimpacting and impacting long term motions, referred to as grazing bifurcations, indicates the transition between on and off states of an impact microactuator. Three different on-off switching mechanisms are identified for the Mita microactuator. These mechanisms also generalize to arbitrary impacting systems with a similar nonlinearity. A local map based on the concept of discontinuity mapping provides an effcient and accurate tool for the grazing bifurcation analysis. Nonlinear impacting dynamics of the microactuator are studied in detail to identify various bifurcations and parameter ranges corresponding to chaotic motions. We find that the frequency-response curves of the impacting dynamics are significantly different from those of the nonimpacting dynamics. / Ph. D.

The asthenosphere, a weak layer beneath the rigid lithosphere, plays a fundamental role in the operation of plate tectonics and mantle convection. While this layer is often characterized by low seismic velocity and high seismic attenuation, the global structure of the asthenosphere remains poorly understood. In this dissertation, twelve years of SS precursors reflected off the top and bottom of the asthenosphere, namely, the LAB and the 220-km discontinuity, are processed to investigate the boundaries of the asthenosphere at a global scale. Finite-frequency sensitivities are used in tomography to account for wave diffraction effects that cannot be modeled in global ray-theoretical tomography. Strong SS precursors reflected off the LAB and the 220-km discontinuity are observed across the global oceans and continents. In oceanic regions, the LAB is characterized by a large velocity drop of about 12.5%, which can be explained by 1.5%-2% partial melt in the oceanic asthenosphere. The depth of the Lithosphere Asthenosphere Boundary is about 120 km, and its average depth is independent of seafloor age. This observation supports the existence of a constant-thickness plate in the global oceans. The base of the asthenosphere is imaged at a depth of about 250 km in both oceanic and continental areas, with a velocity jump of about ∼ 7% across the interface. This finding suggests that the asthenosphere in oceanic and continental regions share the same defining mechanism. The depth perturbations of the oceanic 220-km discontinuity roughly follow the seafloor age contours. The 220-km topography is smoother beneath slower-spreading seafloors while it becomes rougher beneath faster-spreading seafloors. In addition, the roughness of the 220-km discontinuity increases rapidly with spreading rate at slow spreading seafloors, whereas the increase in roughness is much slower at fast spreading seafloors. This observation indicates that the thermal and compositional structures of seafloors formed at spreading centers may have a long-lasting impact on asthenospheric convections. In continental regions, a broad correlation is observed between the 220-km discontinuity depth structure and surface tectonics. For example, the 220-km discontinuity depth is shallower along the southern border of the Eurasian plate as well as the Pacific subduction zones. However, there is no apparent correlation between 3-D seismic wavespeed in the upper mantle and the depths of the 220-km discontinuity, indicating that secular cooling has minimum impact on the base of the asthenosphere. / Doctor of Philosophy / In classic plate tectonic theory, the outermost shell of the Earth consists of a small number of rigid plates (lithosphere) moving horizontally on the mechanically weak asthenosphere. In the classic half space cooling (HSC) model, the lithosphere is formed by gradual cooling of the hot mantle. Therefore, the thickness of the plate depends on the age of the seafloor. The problem with the HSC model is that bathymetry and heat flow measurements at old seafloors do not follow its predicted age dependence. A modified theory, called plate cooling model, can better explain those geophysical observations by assuming additional heat at the base of an oceanic plate with a constant thickness of about 125 km. However, such a constant-thickness plate has not been observed in seismology. In this thesis, the asthenosphere boundaries are imaged using a global dataset of seismic waves reflected off the Earth's internal boundaries. Strong reflections from the top of the asthenosphere are observed across all major oceans. The amplitudes of the SS precursors can be explained by 1.5%-2% of partial melt in the asthenosphere. The average boundary depths are independent of seafloor age, and this observation supports the existence of a constant-thickness plate in the global oceans with a complex origin. The 220-km discontinuity, also called the Lehmann Discontinuity, was incorporated in the Preliminary Reference Earth Model in the 1980's to represent the base of the asthenosphere. However, the presence and nature of this boundary have remained controversial, particularly in the oceanic regions. In contrast to many studies which suggest the 220-km discontinuity does not exist in the global oceans, SS precursors reflected from this interface are observed across the oceanic regions in this thesis. Furthermore, there is a positive correlation between the topography of the 220-km discontinuity and seafloor spreading rate. Specifically, the 220-km discontinuity is smoother beneath slower-spreading seafloors and much rougher beneath faster-spreading seafloors. In addition, the roughness increases faster at slowerspreading seafloors while much more gradual at faster-spreading seafloors. This indicates a close connection between seafloor spreading and mantle convections in the asthenosphere, and seafloors have permanent memories of their birth places. Different melting processes at slow and fast spreading centers produce seafloors with different physical and chemical properties, modulating convections in the asthenosphere and ultimately shaping the topography of the 220-km discontinuity. Reflections from the 220-km discontinuity are also observed across the global continental regions. In addition, the 220-km discontinuity beneath the continents is comparable to that under oceanic regions in terms of their average depth (∼ 250 km) and velocity contrast across the discontinuity (∼ 7%). In continental regions, there is a general connection between the 220-km depth structure and plate tectonics. For example, the boundary is shallower along the southern border of the Eurasian plate from the Mediterranean region to East Asia where mountain belts were formed as a result of collision between the Eurasian plate and the Nubian, Arabian and Indian plates. Depth perturbations of the 220-km discontinuity are also observed along the Pacific subduction zones including the Cascadia Subduction Zone, Peru-Chile Trench and Japan-Kuril Kamchatka Trench. In addition, depth anomalies are mapped in the interior of continents, for example, along the foothills of high topography in the interior of the Eurasian plate, which may be controlled by far-field convection associated with the convergent processes at the plate boundaries.

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