Post-tensioned segmental concrete bridges have been used in the United States since the mid 80's. Post-tensioning is very economical and efficient for bridges with very long spans. A segmental concrete bridge uses post-tensioning to connect concrete bridge segments and make a long span bridge. A problem that has occurred in some segmental concrete bridges is the corrosion of the post-tensioned strands. A tendon failure can be detrimental to service level bridge performance and reduce the flexural strength. The Varina-Enon Bridge has a history of corrosion related issues and the objective of this project was to investigate the consequences of transverse tendons rupture. In addition, to determine the behavior of tendons with grouted duct and smoot duct when a stand broke. Also, the results of this project identify if the bridge can perform adequately with no repair or if these failures would develop problems in the long term. A full scale specimen of a post-tensioned slab with two tendons was built at the laboratory. The full scale specimen was built to contain tendons similar to top flange near the delta frames in the Varina-Enon Bridge, where a transverse tendon was broken. An artificial corrosion process was conducted to corrode the tendons and investigate the effect of break on the slab. The specimen was instrumented with BDI strain gauges to monitor the behavior of the specimen, when the strand rupture occurred due to the accelerated corrosion. In addition, a finite element model was designed similar to the full scale specimen to compare the collected data with the data obtained from the analysis. / Master of Science / Bridges play a very important role in the Transportation Systems all over the world. According to American Society of Civil Engineering (ASCE), United States bridges get a C+ grade. The ASCE rating indicates that the US bridges need to be built more efficiently and be monitored more frequently. Regular inspection of bridges is very essential and will be beneficial in many ways. For instance, engineers can detect the possible flaws and problems that are in the bridge such as corrosion in structural elements. It is important to address these issues since these bridges are in service and being used by the public. Based on how serious the issues are, engineers will decide if the bridge can perform adequately with repair or it is is structurally inefficient and needs to be replaced. Moreover, rehabilitations method to keep the structure in service will save a lot of money compare to replacing the bridge. The Varian Enon Bridge, which carries Interstate 295 across the James River in Richmond, is a critical link in Richmond transportation a In the recent inspections of this bridge, Virginia Department of Transportations (VDOT) detected abnormal behavior of few structural elements. In this research, a full scale mock-up of a section of the Varina Enon Bridge was built at the lab. The purpose of this project was to conduct testing on the mock-up to investigate the cause of abnormal behavior of these few structural elements similar to the ones in Varina Enon Bridge. Furthermore, a final report was prepared for VDOT to decide if the bridge will perform adequately with no strengthening or providing forewarning of trouble that could develop with time.

No description available.

Les sandwichs composites 3D présentent de meilleures caractéristiques mécaniques que les sandwichs traditionnels, en particulier dans la direction de l'épaisseur. Les structures étudiées dans ce travail sont des sandwichs renforcés via la technologie d’aiguilletage transverse Napco®. Dans un premier temps, une analyse expérimentale complète est réalisée (fabrication des renforts, mise en oeuvre du composite, essais mécaniques de caractérisation, mesure des paramètres géométriques et matériels), permettant une meilleure connaissance et compréhension de l'architecture de ces structures et de leur comportement mécanique. Par la suite, on s'intéresse à la détermination des modules élastiques effectifs des sandwichs, par l'utilisation de différentes méthodes d'homogénéisation (périodique), analytiques et numériques, afin de pouvoir construire un modèle macroscopique équivalent de type plaque. Une attention particulière est portée au comportement hors plan, à savoir au flambement des renforts lors de la compression dans l'épaisseur et à l'importance de la prise en compte des effets du cisaillement transverse. Des modèles analytiques sont développés en 2D et un programme en langage PythonPM (sur Abaqus) permet d'automatiser la modélisation et le post-traitement des résultats lors des calculs numériques par éléments finis. Les résultats obtenus sont validés, soit par des calculs numériques de structures, soit par comparaison à des valeurs expérimentales, pour différents panneaux avec des densités de renforts variées. / 3D composite sandwichs have superior mechanical characteristics compared to usual composite sandwichs, in particular in the through-thickness direction. The structures studied in this work are 3D reinforced sandwichs using the Napco® technology which is based on transverse needling. In a first step, a complete experimental study is realized (creation of the through-thickness reinforcements, composite manufacturing by infusion process, experimental tests, measurement of geometric and material parameters) lead to better understanding of the sandwich architecture and their mechanical behaviour. In a second step, an interest is carried on the determination of the effective mechanical properties of this structures, using different homogenization techniques (periodic), analytical and numerical, in order to assess an equivalent plate model. An interest is devoted to the out-of-plane behaviour such as buckling of the reinforcements during compressive loading in the thickness direction and the importance to take into account the effects of transverse shear. Analytical models have been developed in 2D and a PythonPM program (using Abaqus software) have been created, allowing a fully parameterized modelling and mechanical analysis. The results are finally validated, using numerical computations on 3D heterogeneous structures or by experimental results, for several sandwichs considering different density of reinforcements.

Streamline simulators have received increased attention because of their ability to effectively handle multimillion cell detailed geologic models and large simulation models. The efficiency of streamline simulation has relied primarily on their ability to take large timesteps with fewer pressure solutions within an IMPES formulation. However, unlike conventional finite-difference simulators, no clear guidelines are currently available for the choice of timestep for pressure and velocity updates. That is why we need largely an uncontrolled approximation, either managed by engineering judgment or by potentially time-consuming timestep size sensitivity studies early in a project. This will clearly lead us to the lack of understanding of numerical stability and error estimates during the solution. This research presents a novel approach for timestep selection during streamline simulation that is based on three elements. First, we reformulate the equations to be solved by a streamline simulator to include all of the three-dimensional flux terms - both aligned with and transverse to the flow directions. These transverse flux terms are totally neglected within the existing streamline simulation formulations. Second, we propose a simple grid-based corrector algorithm to update the saturation to account for the transverse flux. Third, we provide a discrete CFL (Courant-Friedrich-Levy) formulation for the corrector step that leads to a mechanism to ensure numerical stability via the choice of a stable timestep for pressure updates. This discrete CFL formulation now provides us with the same tools for timestep control as are available within conventional reservoir simulators. We demonstrate the validity and utility of our approach using a series of numerical experiments in homogeneous and heterogeneous ¼ five-spot patterns at various mobility ratios. For these numerical experiments, we pay particular attention to favorable mobility ratio displacements, as they are known to be challenging to streamline simulation. Our results clearly demonstrate the impact of the transverse flux correction on the accuracy of the solution and on the appropriate choice of timestep, across a range of mobility ratios. The proposed approach eliminates much of the subjectivity associated with streamline simulation, and provides a basis for automatic control of pressure timestep within full field streamline applications.

Streamline simulators have received increased attention because of their ability to effectively handle multimillion cell detailed geologic models and large simulation models. The efficiency of streamline simulation has relied primarily on their ability to take large timesteps with fewer pressure solutions within an IMPES formulation. However, unlike conventional finite-difference simulators, no clear guidelines are currently available for the choice of timestep for pressure and velocity updates. That is why we need largely an uncontrolled approximation, either managed by engineering judgment or by potentially time-consuming timestep size sensitivity studies early in a project. This will clearly lead us to the lack of understanding of numerical stability and error estimates during the solution. This research presents a novel approach for timestep selection during streamline simulation that is based on three elements. First, we reformulate the equations to be solved by a streamline simulator to include all of the three-dimensional flux terms - both aligned with and transverse to the flow directions. These transverse flux terms are totally neglected within the existing streamline simulation formulations. Second, we propose a simple grid-based corrector algorithm to update the saturation to account for the transverse flux. Third, we provide a discrete CFL (Courant-Friedrich-Levy) formulation for the corrector step that leads to a mechanism to ensure numerical stability via the choice of a stable timestep for pressure updates. This discrete CFL formulation now provides us with the same tools for timestep control as are available within conventional reservoir simulators. We demonstrate the validity and utility of our approach using a series of numerical experiments in homogeneous and heterogeneous ¼ five-spot patterns at various mobility ratios. For these numerical experiments, we pay particular attention to favorable mobility ratio displacements, as they are known to be challenging to streamline simulation. Our results clearly demonstrate the impact of the transverse flux correction on the accuracy of the solution and on the appropriate choice of timestep, across a range of mobility ratios. The proposed approach eliminates much of the subjectivity associated with streamline simulation, and provides a basis for automatic control of pressure timestep within full field streamline applications.

INTRODUCTION: The aim of this study was to determine if there is a correlation between divergency, age, and the transverse width of the maxilla and mandible at the first molar level, as well as the angulation of the 1st molar teeth. MATERIALS AND METHODS: CBCT images of 94 patients between the ages of 12-62 were selected randomly and concurrently for this retrospective study. Patients were grouped into hypo-, normo- and hyperdivergent groups with Frankfort horizontal to the mandibular plane angle (FMA) <20.5, ≥22-≤28, >29.5 degrees respectively. RESULTS: The hypodivergent group’s maxilla was on average 1.6 mm wider than that of the hyperdivergent group (p ≤ 0.05). The inclination of the right first maxillary molar showed a R2 value of 0.165 for age alone (p-value = 0.000023), while the inclination of the left first maxillary molar had a R2 value of 0.136 (p-value = 0.003) for both divergency and age. The correlations between hyperdivergent, normodivergent, and hypodivergent groups and the inclinations of the upper molars were R2= 0.13, 0.19, and -0.13 respectively. CONCLUSIONS: Our study agreed with the literature in that hyperdivergent patients have palatal widths that are narrower than in hypodivergent patients. We saw a positive correlation between age and molar angulations for all ages and divergences except in the left maxillary first molar of the hypodivergent patients where we saw a negative correlation.

Craniofacial deficiencies in 3-dimensions and their relationships to airway volume have been studied in the past. Much research has investigated maxillary transverse, sagittal or vertical dimensions with correlations to airway volume. Similarly, mandibular characteristics such as its anteroposterior or vertical dimensions have been analyzed. To the author’s current knowledge, there have been limited studies which investigated the relationship between transverse dimensions of the mandible and airway volume. The objectives of our study were to investigate: 1) If there is a significant association between mandibular transverse dimensions and airway volume, mandibular anteroposterior or vertical measurements in the pediatric population. 2) If mandibular anteroposterior and vertical measurements correlated to airway volume. 3) If an OSA symptomatic group had any significant differences in mandibular morphologies, pediatric sleep questionnaire (PSQ), Apnea-hypoxia index (AHI), or Respiratory Disturbance index (RDI), compared to an asymptomatic control group in the pediatric population. This was a cohort, retrospective, correlational study comprised of 22 males, and 14 females (Mean age of 6.8 ± 2.8, range: 2 to 13 years old). Digital CBCT images were acquired from a single private pediatric practice. Utilizing Mimics v.21 analytical software, airway was measured and segmented into right nasal cavity (RNC), left nasal cavity (LNC), nasopharynx (NP), oropharynx (OP) and hypopharynx (HP). Mandibular traits in sagittal, vertical and transverse dimensions were analyzed to see if correlations exist with airway volume, PSQ, AHI, or RDI scores. Differences were also evaluated between symptomatic and asymptomatic groups. Results revealed that asymptomatic patients had significantly greater width between the right and left gonions (Trans-Go) as compared to symptomatic patients. Within each group, Trans-Go was shown to have significant positive correlations to total airway volume, corpus length and ramus height (p < 0.05). There are significant correlations between mandibular transverse dimension and total airway volume, sagittal, and vertical dimensions of the mandible. There may also be transverse differences between symptomatic and asymptomatic patients for sleep disorders in the pediatric population.

Dans cette thèse, les instabilités de combustion sont étudiées sur deux types de configuration. Tout d’abord, un cas académique stabilisé par un dièdre (Volvo) est étudié. Les simulations sont validées par comparaison avec les données expérimentales. En faisant varier le point de fonctionnement, des modes transverses et longitudinaux sont observés, en bon accord avec les données expérimentales en termes de fréquence des fluctuations de pression et de la dynamique de l’écoulement. Dans un second temps, une configuration proche des cas industriels a été étudiée dans le cadre du projet européen KIAI (Lotar). Les données expérimentales ont été obtenues lors d’une campagne d’essais à l’ONERA. Plusieurs simulations aux grandes échelles sont conduites sur cette configuration. Les instabilités transverses de combustion sont analysées et les mécanismes essentiels qui les pilotent sont identifiés. Sur la base de ces observations, la forme du modèle à Fonction de Transfert de Flamme est modifiée et associée à un solveur de Helmholtz pour prédire la stabilité des modes transverses. Les résultats obtenus par le solveur acoustique sont en bon accord avec la carte de stabilité obtenue par la simulation aux grandes échelles. / In this work longitudinal and transverse combustion instabilities are studied in two types of configurations. While longitudinal modes have been observed in many previous studies at low frequencies, the present work also focusses on high-frequency transverse modes. First, a premixed flame stabilized on a V-fame holder is investigated where experimental results obtained by Volvo are used to validate the simulations. For different operating conditions, longitudinal and transverse modes are observed in Large Eddy Simulations (LES) and show good agreement with the experimental data in terms of pressure frequency and flow dynamics. In a second step, a semi-industrial case is examined within the European project KIAI. Experiments are conducted by ONERA and LES of this two-phase flow configuration (called Lotar) are carried out. Transverse combustion instabilities are analyzed and key elements which drive instabilities are identied. These observations are used to reformulate the classic Flame Transfer Function (FTF) in order to predict the stability of transverse modes by use of an Helmholtz solver. The results reproduce fairly well the stability map generated by LES.

No description available.

In most cases of seismic processing and interpretation, elastic isotropy is assumed. However, velocity anisotropy is found to exist in most subsurface media. Hence, there exists a fundamental inconsistency between theory on the one hand, and practice on the other. If not recognised, this can invalidate interpretation of seismic data. In this thesis, inversion methods for elastic parameters are developed to quantify the degree of velocity anisotropy of multi-layered transversely isotropic media. This primarily involves examining the velocity fields of layered media using anisotropic elastic wave propagation theory, and developing inversion programs to recover elastic parameters from those velocity fields. The resolved elastic parameter information is used in carrying out further studies on the effects of seismic anisotropy on normal moveout (NMO). Mathematical analyses, numerical simulations, and physical modelling experiments are used in this research for verification purposes before application to field survey data. Numerical studies show the transmission velocity field through layered media appears to be equivalent to that through a single-layered medium, within the practical offset limits in field surveys. The elastic parameters, which describe the property of such equivalent single-layered media, can be used as apparent elastic parameters to describe the collective mechanical property of the layered media. During this research, Snell's law was used in ray tracing to determine ray paths through the interface between any two component layers. By analyzing the signals recorded by any receiver in a walkaway VSP survey, the apparent transmission velocity field for the layered media above this receiver depth was inverted. / Software was developed to recover the apparent elastic parameters for the layered media above this receiver depth using the transmission velocity field as input. Based on a two-layered model, another method was developed to recover the interval elastic parameters for an individual layer of interest, using the signals recorded by receivers on the upper and lower surfaces of this layer. The recovered elastic parameters may be considerably different from the real values if a transversely isotropic medium with a tilted symmetry axis (TTI) is treated as a transversely isotropic medium with a vertical symmetry axis (VTI). A large angle of tilt of the symmetry axis significantly influences the recorded velocity field through the medium. An inversion program was written to recover the value of the tilt angle of a TTI medium, and the elastic parameters of the medium. Programs were also developed to combine information from P, SV, and SH-waves in an inversion procedure. This capability in inversion programs enables us to use the additional information provided by a multi-component VSP survey to obtain accurate estimates of the elastic parameters of geological formations. Software testing and development was carried out on numerically generated input data. Up to 10 milliseconds of random noise in travel time was added to the input to confirm the stability of the inversion software. Further testing was carried out on physical model data where the parameters of the model were known from direct measurements. Finally the inversion software was applied to actual field data and found to give plausible results. / In software testing in the physical modelling laboratory, other practical problems were encountered. System errors caused by the disproportionately large size of the transducers used affected the accuracy of the inversion results obtained. Transducer performance was studied, and it was found that reducing the size of transducers or making offset corrections would decrease the errors caused by the disproportionately large transducer dimensions. In using the elastic parameters recovered, it was found that the elastic parameter δ significantly influences the seismic records from a horizontal reflector. The normal moveout velocity was found to show variations from the zero-offset normal moveout velocity depending on the value and sign of elastic parameter δ. New approximate expressions for anisotropic normal moveout, phase and ray velocity functions at short offsets were developed. The value of anisotropic parameter δ was found to be the major factor controlling these relations. If the recovered parameter δ has a large negative value, analytical and numerical studies demonstrated that the new expression for moveout velocity developed herein should be used instead of Thomsen's normal moveout equation.