Bibliographies thématiques / CIRCULAR TUNNELS

Littérature scientifique sur le sujet « CIRCULAR TUNNELS »

Auteur : Grafiati
Publié le 11 septembre 2023

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Articles de revues sur le sujet "CIRCULAR TUNNELS"

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Pham, Van Vi, Ngoc Anh Do et Daniel Dias. « Sub-Rectangular Tunnel Behavior under Seismic Loading ». Applied Sciences 11, no 21 (23 octobre 2021) : 9909. http://dx.doi.org/10.3390/app11219909.

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Circular and rectangular tunnel shapes are usually chosen when excavating at shallow depths in urban areas. However, special-shaped tunnels such as sub-rectangular tunnels have recently been used to overcome some drawbacks of circular and rectangular tunnels in terms of low space utilization efficiency and stress concentration, respectively. In the literature, experimental studies as well as analytical and numerical models have been developed for the seismic analysis and vulnerability assessment of circular and rectangular tunnels since the early 1990s. However, knowledge gaps regarding the behavior of sub-rectangular tunnels under seismic loading remain and still need to be bridged. The present paper focuses on introducing a numerical analysis of sub-rectangular tunnels under seismic loading. The numerical model of sub-rectangular tunnels is developed based on the numerical analyses of circular tunnels validated by comparing well-known, analytical solutions. This paper aims to highlight the differences between the behavior of sub-rectangular tunnels compared with circular tunnels when subjected to seismic loadings. Special attention is paid to the soil–lining interface conditions. The influence of parameters, such as soil deformations, maximum horizontal acceleration, and lining thickness, on sub-rectangular tunnel behavior under seismic loading is also investigated. The results indicate a significant behavior difference between sub-rectangular and circular tunnels. The absolute extreme incremental bending moments for a circular tunnel (no-slip condition) are smaller than that for the corresponding full-slip condition. The absolute extreme incremental bending moments of sub-rectangular tunnels (no-slip condition) are, however, greater than the corresponding full-slip conditions.
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Yan, Li, et Jun Sheng Yang. « Displacements around Two Closely Adjacent Circular Openings ». Applied Mechanics and Materials 170-173 (mai 2012) : 1397–401. http://dx.doi.org/10.4028/www.scientific.net/amm.170-173.1397.

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Deformations of the tunnels may results in settlements of the ground surface. Based on the characters of deformation of twin closely adjacent tunnels excavated, a basic deformation mechanism of two parallel tunnels constructed close together was present, which is not uniform but oval-shaped ground deformation pattern and represent the ground loss occurred during construction of the tunnels. An improved convergence model of the tunnel boundary for twin closely adjacent tunnels and the related expressions are proposed. Using a computer package FLAC2D, the certain given deformations as the boundary condition were applied to the boundaries of two tunnels, and the surface settlements caused by the excavation of two tunnels were obtained. It is found that the results match well with the measured field results.
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Pham, Vi Van, Anh Ngoc Do, Hung Trong Vo, Daniel Dias ., Thanh Chi Nguyen et Do Xuan Hoi. « Effect of soil Young’s modulus on Sub-rectangular tunnels behavior under quasi-static loadings ». Journal of Mining and Earth Sciences 63, no 3a (31 juillet 2022) : 10–21. http://dx.doi.org/10.46326/jmes.2022.63(3a).02.

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Tunnels are an important component of the transportation and utility system of cities. They are being constructed at an increasing rate to facilitate the need for space expansion in densely populated urban areas and mega-cities. The circular and rectangular tunnels cannot completely meet the requirements of underground space exploitation regarding the cross-section. Sub-rectangular tunnels are recently used to overcome some drawbacks of circular and rectangular tunnels in terms of low utilization space ratio and stress concentration, respectively. However, the behavior of the sub-rectangular tunnels under seismic loading is still limited. This need to be regarded and improved. This paper focuses on conducting a numerical analysis to study the behavior of the sub-rectangular tunnels under seismic loadings. Here seismic loadings in this study are represented by quasi-static loadings. Based on the numerical model of the circular tunnel that was validated by comparison with analytical solutions, the numerical model of the sub-rectangular tunnel is created. This paper is devoted to highlight the differences between the behavior of the sub-rectangular tunnels compared with the circular ones subjected to quasi-static loadings. The soil-lining interaction, i.e., full slip and no-slip conditions are particularly considered. The influence of soil’s Young’s modulus on the sub-rectangular tunnel behavior under quasi-static loading is also investigated. The results indicated that soil’s Young’s modulus significantly affects static, incremental, and total internal forces in the tunnel lining under quasi-static loadings. Special attention is a significant difference in total internal forces in the sub-rectangular tunnel lining in comparison with the circular tunnel ones and the stability of the lining tunnel for both the full slip and no-slip conditions when subjected to quasi-static loadings.
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Duan, Yawei, Mi Zhao, Jingqi Huang, Huifang Li et Xiuli Du. « Analytical Solution for Circular Tunnel under Obliquely Incident P Waves considering Different Contact Conditions ». Shock and Vibration 2021 (22 décembre 2021) : 1–23. http://dx.doi.org/10.1155/2021/1946184.

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An analytical solution for the seismic-induced thrust and moment of the circular tunnel in half-space under obliquely incident P waves is developed in this study, which is the superposition of the solution for deep tunnels under incident and reflected P waves and the reflected SV waves. To consider tangential contact stiffness at the ground-tunnel interface, a spring-type stiffness coefficient is introduced into the force-displacement relationship. Moreover, the tunnel lining is treated as the thick-wall cylinder, providing more precise forecasts than beam or shell models used in previous analytical solution, especially for tunnels with thick lining. The reliability of the proposed analytical solution is assessed by comparing with the dynamic numerical results. Based on the proposed analytical solution, parametrical studies are conducted to investigate the effect of some critical factors on the tunnel’s seismic response, including the incident angles, the tangential contact stiffness at the ground-tunnel interface, and the relative stiffness between the ground and the tunnel. The results demonstrate that the proposed analytical solution performs well and can be adopted to predict the internal forces of circular tunnels under obliquely incident P waves in seismic design.
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Xu, Hua, Tianbin Li, Jingsong Xu et Yingjun Wang. « Dynamic Response of Underground Circular Lining Tunnels Subjected to Incident P Waves ». Mathematical Problems in Engineering 2014 (2014) : 1–11. http://dx.doi.org/10.1155/2014/297424.

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Dynamic stress concentration in tunnels and underground structures during earthquakes often leads to serious structural damage. A series solution of wave equation for dynamic response of underground circular lining tunnels subjected to incident plane P waves is presented by Fourier-Bessel series expansion method in this paper. The deformation and stress fields of the whole medium of surrounding rock and tunnel were obtained by solving the equations of seismic wave propagation in an elastic half space. Based on the assumption of a large circular arc, a series of solutions for dynamic stress were deduced by using a wave function expansion approach for a circular lining tunnel in an elastic half space rock medium subjected to incident plane P waves. Then, the dynamic response of the circular lining tunnel was obtained by solving a series of algebraic equations after imposing its boundary conditions for displacement and stress of the circular lining tunnel. The effects of different factors on circular lining rock tunnels, including incident frequency, incident angle, buried depth, rock conditions, and lining stiffness, were derived and several application examples are presented. The results may provide a good reference for studies on the dynamic response and aseismic design of tunnels and underground structures.
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Jearsiripongkul, Thira, Suraparb Keawsawasvong, Chanachai Thongchom et Chayut Ngamkhanong. « Prediction of the Stability of Various Tunnel Shapes Based on Hoek–Brown Failure Criterion Using Artificial Neural Network (ANN) ». Sustainability 14, no 8 (11 avril 2022) : 4533. http://dx.doi.org/10.3390/su14084533.

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In this paper, artificial neural network (ANN) models are presented in order to enable a prompt assessment of the stability factor of tunnels in rock masses based on the Hoek–Brown (HB) failure criterion. Importantly, the safety assessment is one of the serious concerns for constructing tunnels and requires a reliable and accurate stability analysis. However, it is challenging for engineers to construct finite element limit analysis (FELA) algorithms with the HB failure criterion for tunnel stability solutions in rock masses. For the first time, a machine-learning-aided prediction of tunnel stability based on the HB failure criterion is proposed in this paper. Three different shapes of tunnels, i.e., heading tunnel, dual square tunnels, and dual circular tunnels, are considered. The inputs include four dimensionless parameters for the heading tunnel including the cover-depth ratio, the normalized uniaxial compressive strength, the geological strength index (GSI), and the mi parameter. Moreover, dual square and circular tunnels include one more additional parameter namely the distance ratio. The results present the best ANN models for each tunnel shape, providing very reliable solutions for predicting the tunnel stability based on the HB failure criterion.
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Cilingir, Ulas, et S. P. Gopal Madabhushi. « Effect of depth on seismic response of circular tunnels ». Canadian Geotechnical Journal 48, no 1 (janvier 2011) : 117–27. http://dx.doi.org/10.1139/t10-047.

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Tunnels in seismically active areas are vulnerable to adverse effects of earthquake loading. Recent seismic events have shown that there is a need to validate current design methods to better understand the deformation mechanisms associated with the dynamic behaviour of tunnels. The research described in this paper consists of physical and numerical modelling of circular tunnels with dynamic centrifuge experiments and complementary finite element simulations. The aim is to develop an understanding of the effects of tunnel depth on the seismic behaviour of tunnels. Tunnels with different depth-to-diameter ratios were tested in dry, loose silica sand. Accelerations around the tunnel and earth pressures on the lining were measured. A high-speed digital camera was used to record soil and lining deformations. Particle image velocimetry analyses were carried out on the recorded images to measure the deformations. Complementary dynamic finite element simulations were also conducted with a code capable of managing contact simulations at the soil–lining interface. Measurement of centrifuge experiments and finite element analyses show that the tunnel shifts from a static equilibrium to a dynamic equilibrium state as soon as the earthquake starts. The nature of the dynamic equilibrium, however, is difficult to predict using conventional analysis methods.
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Dang, Van Kien, Ngoc Anh Do, Tai Tien Nguyen, Anh Duy Huynh Nguyen et Van Vi Pham. « An overview of research on metro tunnel lining in the sub-rectangular shape ». Journal of Mining and Earth Sciences 62, no 4 (31 août 2021) : 68–78. http://dx.doi.org/10.46326/jmes.2021.62(4).08.

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Circular tunnels are the most popular shapes used in urban underground transportation systems when mechanized tunneling is used for tunnel excavation. However, circular tunnels have a small space utilization ratio. With the material development, non - circular tunnels such as sub - rectangular, U - shaped lining, etc. are now common, and their cross - section helps to improve the underground space utilization. However, there have been not many studies on the structure and the calculation method of the metro tunnels with the above cross - sections. The paper uses the analytical synthesis method to find out the advantages and disadvantages, the application conditions of the sub - rectangular shape, as well as the development direction for the complete calculation methods for this cross - section in Vietnamese conditions.
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Leong, Jik Chang, C. L. Chang, Y. C. Chen et L. W. Chen. « Smoke Propagation in an Inclined Semi-Circular Long Tunnel ». Advanced Materials Research 446-449 (janvier 2012) : 2143–48. http://dx.doi.org/10.4028/www.scientific.net/amr.446-449.2143.

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This work used FDS to simulate tunnel fires occur in a semi-circular longitudinally ventilated tunnel. By varying the parameters such as the tunnel gradient, the fire size, and the ventilation velocity, their influence on the backlayering effect and downstream propagation rate can be recognized. Under weak ventilation, the backlayering effect either advances or vanishes depending on the slope of the tunnel. Under stronger ventilation, the backlayering effect would break up. The temperature distributions may become less and less dependent on the tunnel gradient when the ventilation velocity is increased. Although the hot gases and smoke in uphill tunnels propagate faster than those in downhill tunnels, their difference reduces with ventilation velocity.
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Gonzalez, F. J., P. K. Kaiser et M. S. Diederichs. « Energy Release Resulting from Sudden Excavation Shape Changes during Two-sided Strainbursts ». IOP Conference Series : Earth and Environmental Science 1124, no 1 (1 janvier 2023) : 012082. http://dx.doi.org/10.1088/1755-1315/1124/1/012082.

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Abstract When tunnels in underground hard rock mines experience strainbursts, the effective shape of the tunnel suddenly changes as part of the rock fails, notches form and the broken rock bulks inside the strainburst volume. For circular tunnels, this dynamic rupture and bulking process causes a shape change with associated displacements and velocities in the surrounding elastic rockmass and at the excavation walls. This process can be approximated for circular tunnel bursting in elastic rock by a shape change from circular to elliptical and Maugi’s solution [1] can be adapted to estimate related displacements and average ground velocities. If these velocities are imposed on a volume of rock or shotcrete with a given mass, the mass can be ejected, and the corresponding kinetic energy can be estimated. When combined with the sudden bulking of the fractured rock, displacements and velocities are magnified between the elliptical shape and the pre-burst (circular) shape of the tunnel. This study focuses on the effect of the combined excavation response with elastic and bulking deformations to assess frequently observed excavation damage processes involving ‘shotcrete rain’ and heave of floor slabs caused by these shape changes. An analytical solution is presented for circular tunnels to estimate the elastic and bulking displacements, the resulting velocities, and energy demands.
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Thèses sur le sujet "CIRCULAR TUNNELS"

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Boncu, Altan. « Structural Fire Safety Of Standart Circular Railroad Tunnels Under Different Soil Conditions ». Master's thesis, METU, 2004. http://etd.lib.metu.edu.tr/upload/12609537/index.pdf.

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In many tunnel designs, reinforced concrete tunnel lining design is selected based on construction requirements rather than design loads. A constant cross-section is typically used along a tunnel even if the design loads change from one location to another, especially for tunnels constructed by tunnel boring machines (TBM). Factor of safety against failure is not constant along the length of tunnel and is typically high at shallow depth regions. Factor of safety during a rare event is usually much less than the ones set for service load states. Rare events such as earthquake, train derailment, explosion and long duration fires do not happen daily and generally a minor reparable damage is targeted at the structure during those types of events. The focus of this study is to analytically investigate structural fire safety of reinforced concrete circular tunnel linings in terms of reduction in service load safety and to develop recommendations for preliminary assessment of structural fire endurance of circular tunnel linings. Analytical methods accounting for thermal non-linearity, material degradation, tunnel lining-ground interaction and fire time stages are available to assess the structural fire safety of the concrete tunnel linings. Analytical results are determined to be in good agreement with tunnel key segment hydrocarbon fire test.
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Brito, Jaime Francisco. « Computer aided design of circular tunnels using analysis and knowledge-based rules ». Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/12103.

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Noori, Behshad. « Application of dynamic vibration absorbers on double-deck circular railway tunnels to mitigate railway-induced ground-borne vibration ». Doctoral thesis, Universitat Politècnica de Catalunya, 2019. http://hdl.handle.net/10803/667305.

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This dissertation is concerned with investigating the efficiency of dynamic vibration absorbers (DVAs) as measures to mitigate ground-borne vibrations induced by railway traffic in double-deck tunnels. The main topics of the dissertation are the coupling of a set of longitudinal distributions of DVAs to the interior floor of a double-deck tunnel dynamic model, the computation of the response of this coupled system due to train traffic and obtaining the optimum design parameters of the DVAs to minimize this response. To address the first concern, a methodology for coupling a set of longitudinal distributions of DVAs to any railway subsystem in the context of a theoretical dynamic model of railway infrastructure is developed. The optimum design parameters of the DVAs are obtained using an optimization process based on a genetic algorithm. The effectiveness of the DVAs is assessed by two response parameters, which are used as objective functions to be minimized in the optimization process: the energy flow radiated upwards by the tunnel and the maximum transient vibration value (MTVV) in the building near the tunnel. The model used to compute the former is a two-and-a-half dimensional (2.5D) semi-analytical model of a train-track-tunnel-soil system that considers a full-space soil model, and the one used to compute the latter is a hybrid experimental-numerical model of a train-track-tunnel-soil-building system. In the hybrid model, a numerical model of the track-tunnel system based on 2.5D coupled finite element-boundary element formulation along with a dynamic rigid multi-body model of the vehicle is used to compute the response in the tunnel wall, and then, the response in the building is computed using experimentally obtained transfer functions between the tunnel wall and the building. The triaxial response in the building is used to compute the MTVV. An alternative option to evaluate the MTVV in a building is to use a fully theoretical model of the train-track-tunnel-soil-building system. In the context of this modeling strategy, a computationally efficient method to calculate the 2.5D Green's functions of a layered soil is also presented. The results show that the DVAs would be an effective mitigation measure for railway-induced vibrations in double-deck tunnels as reductions up to 6.6 dB in total radiated energy flow and up to 3.3 dB in the vibration inside a nearby building are achieved in the simulations presented in this work.
En esta tesis se estudia la eficiencia de los absorbedores de vibraciones dinámicos (DVAs) como medidas de mitigación de las vibraciones inducidas por infraestructuras ferroviarias aplicados a túneles ferroviarios de dos niveles. Los principales desarrollos de la tesis son el acoplamiento de un conjunto de distribuciones longitudinales de DVAs a la losa intermedia de un modelo dinámico de túnel de dos niveles, el cálculo de la respuesta de este sistema acoplado debido al paso del tren y la obtención de los parámetros óptimos de los DVAs para minimizar esta respuesta. Para abordar la primer punto, se ha desarrollado una metodología con el fin de acoplar un conjunto de distribuciones longitudinales de DVAs a cualquier subsistema ferroviario en el contexto de modelos teóricos de la dinámica de infraestructura ferroviarias. Los parámetros óptimos de los DVAs han sido obtenidos mediante un proceso de optimización basado en un algoritmo genético. La eficiencia de los DVAs se evalúa mediante dos quantificadores de la respuesta dinámica del sistema, los cuales se utilizan como funciones objetivo a minimizar en el proceso de optimización: el flujo de energía total radiado hacia arriba desde el túnel y el valor máximo de vibración transitoria (MTVV) en el forjada de un edificio cercano al túnel. El modelo utilizado para calcular el primero es un modelo semi-analítico del sistema vehículo-vía-túnel-terreno que considera un modelo de terreno de espacio completo, y el que se utiliza para calcular el segundo es un modelo híbrido experimental-numérico del sistema vehículo-vía-túnel-terreno-edificio. En el modelo híbrido, se utiliza un modelo numérico del sistema vía-túnel basado en la formulación acoplada de elementos finitos-elementos de contorno acoplados, formulada en el dominio del número de onda y la frecuencia, junto con un modelo dinámico multicuerpo del vehículo con el objetivo de calcular la respuesta en la pared del túnel. Luego, la respuesta en el edificio se calcula utilizando funciones de transferencia obtenidas experimentalmente entre la pared del túnel y el edificio. Para calcular el MTVV, se utiliza la respuesta triaxial en el edificio. Una opción alternativa para evaluar el MTVV en un edificio es utilizar un modelo totalmente teórico del sistema vehículo-vía-túnel-terreno-edificio. En el contexto de esta estrategia de modelado, también se presenta un método computacionalmente eficiente para calcular las funciones de Green de un terreno en capas en el dominio 2.5D. Los resultados muestran que los DVAs pueden ser una medida de mitigación efectiva para las vibraciones inducidas por infraestructuras ferroviarias en el marco de un túnel ferroviario de dos niveles, ya que en las simulaciones presentadas en esta tesis se alcanzan reducciones de hasta 6.6 dB en el flujo de energía total radiado y hasta 3.3 dB en la vibración dentro de un edificio cercano.
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Christopoulos, George P. « Oscillating-flow wind tunnel studies for a circulation control circular cylinder ». Thesis, Monterey, California. Naval Postgraduate School, 1991. http://hdl.handle.net/10945/28435.

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Miranda, Sergio. « Active Control of Separated Flow over a Circular-Arc Airfoil ». Thesis, Virginia Tech, 2000. http://hdl.handle.net/10919/34411.

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An experimental study of active control of fully separated flow over a symmetrical circular-arc airfoil at high angles of attack was performed. The experiments were carried out in a low-speed, open circuit wind tunnel. Angles of attack from 10 to 40 degrees were tested. Low-power input, unsteady excitation was applied to the leading or trailing edge shear layers. The actuation was provided by the periodic oscillation of a 4-percent-chord flap placed on the suction side of the airfoil and facing the sharp edge. Vortex-shedding frequencies were measured and harmonic combinations selected as the applied actuator frequencies. Pressure measurements over the airfoil show that the control increased the normal force coefficient by up to 70%. This supports the idea of vortex capture in the time-averaged sense, enhancing the lift on the airfoil by managing the shear layer roll up. The results indicate the viability of the control of large-scale flow fields by exploiting the natural amplification of disturbances triggered by small-scale actuators. The application of flow control on sharp-edged aircraft wings could lead to improved maneuverability, innovative flight control and weight reduction. These can be achieved by inexpensive, low-power, rugged actuators.
Master of Science
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Clot, Razquin Arnau. « A dynamical model of a double-deck circular tunnel embedded in a full-space ». Doctoral thesis, Universitat Politècnica de Catalunya, 2014. http://hdl.handle.net/10803/145255.

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This thesis presents a three-dimensional dynamic model of a double-deck circular tunnel embedded in a full-space. The model uses the receptance method to obtain the response of the complete structure from the response of its parts. The considered subsystems are the interior floor and the tunnel-soil coupled system. The classical thin plate theory is considered to represent the behaviour of the first and the Pipe in Pipe model is chosen to describe the second. Because the complete model is assumed to be geometrically invariant in the train circulation direction, the coupling of both systems is performed in the wavenumber-frequency domain. After the model formulation, some important issues about its numerical computation are detailed and the obtained results are discussed. The response of a double-deck tunnel to a dynamic and to a quasistatic excitation is compared to the response obtained for a simple tunnel. The first comparison is done performing a power flow study of both tunnel structures when a harmonic line load is applied on them. The main differences between their radiation magnitudes and patterns are identified and discussed. The second comparison is done calculating the total amount of energy crossing a certain surface when a static load moving at a constant speed is considered. Results for a wide range of load speeds and radial distances are presented. A complete track-tunnel-soil model is finally obtained coupling a superstructure model to the interior floor model previously presented.
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Zagadou, Franck. « Numerical analysis of acoustic scattering by a thin circular disk, with application to train-tunnel interaction noise ». Thesis, Boston University, 2002. https://hdl.handle.net/2144/42324.

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The sound generated by high speed trains can be exacerbated by the presence of trackside structures. Tunnels are the principal structures that have a strong influence on the noise produced by trains. A train entering a tunnel causes air to flow in and out of the tunnel portal, forming a monopole source of low frequency sound ["infrasound"] whose wavelength is large compared to the tunnel diameter. For the compact case, when the tunnel diameter is small, incompressible flow theory can be used to compute the Green's function that determines the monopole sound. However, when the infrasound is "shielded" from the far field by a large "flange" at the tunnel portal, the problem of calculating the sound produced in the far field is more complex. In this case, the monopole contribution can be calculated in a first approximation in terms of a modified Compact Green's function, whose properties are determined by the value at the center of a. disk (modelling the flange) of a diffracted potential produced by a thin circular disk. In this thesis this potential is calculated numerically. The scattering of sound by a thin circular disk is investigated using the Finite Difference Method applied to the three dimensional Helmholtz equation subject to appropriate boundary conditions on the disk. The solution is also used to examine the unsteady force acting on the disk.
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Besse, Michaël. « Etude d'un demi-métal : Sr2FeMoO6, caractérisation du matériau massif et croissance de couches minces ». Paris 11, 2002. http://www.theses.fr/2002PA112190.

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La magnétorésistance des jonctions tunnel magnétiques(TMR) est d'autant plus grande que la polarisation en spin des électrodes est importante. L'utilisation de demi-métaux ferromagnétiques devrait théoriquement permettre d'obtenir des TMR infinies. La double pérovskite Sr2FeMoO6 (SFMO) est un demi-métal ferromagnétique présentant une température de Curie de 415K bien supérieure à la température ambiante. L'étude que nous avons menée sur ce matériau comporte deux volets. Dans un premier temps, nous avons mesuré par dichroi͏̈sme magnétique les moments portés par le fer et le molybdène et mis en évidence leur configuration antiparallèle ainsi que la valence mixte du fer dans ce composé. Ces résultats sont en accord avec les calculs de structure de bande existants. En parallèle, nous avons élaboré des couches minces de ce matériau par ablation laser. Par une caractérisation structurale et magnétique approfondie, nous avons mis en évidence l'existence de phases parasites riches en fer qui apparaissent dans les premiers stades de la croissance à haute température. Afin d'éviter leur apparition, nous avons mis au point un procédé de croissance en trois étapes. Les couches ainsi obtenues présentent une faible rugosité et une aimantation de surface identique à celle du SFMO massif. Des jonctions tunnel SFMO/SrTiO3/Co ont également été élaborées. Elles présentent des courbes courant tension non linéaires caractéristiques de l'effet tunnel. Les premiers résultats sur les jonctions sont donc encourageants et les études sur celles-ci se poursuivent
For magnetoresistance of magnetic tunnel junctions (TMR), the bigger is the spin polarization of the electrodes, the more important is the magnetoresistance. Use of ferromagnetic half metals should give infinite TMR. Double perovskite Sr2FeMO6 (SFMO) is a ferromagnetic half metal having a Curie temperature of 415K far higher than room temperature. The study we made on this material is in, two parts. First, we measured by magnetic dichroism the iron and molybdenum spin moments and we made obvious their antiparallel configuration and the mixed valence of iron in this compound. These results agree the existing structure band calculations. In the same time, we elaborated thin films of this material by pulsed laser deposition. By an advanced structural and magnetic characterization, we brought to the fore the existence of iron rich parasitic phases which were developing in the early stage of the high temperature growth. In order to avoid their apparition, we developed a three steps method. Films obtained in this way are presenting a low roughness and a surface magnetization close to the bulk material. Tunnel junctions SFMO/SrTiO3/Co have also been elaborated. These junctions present non-linear current-voltage curves which are characteristics of tunnel effect. First results on junctions are promising and studies on it are going on
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Fisher, David T. « Wind tunnel performance comparative test results of a circular cylinder and 50% ellipse tailboom for circulation control antitorque applications ». Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1994. http://handle.dtic.mil/100.2/ADA283335.

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Mesrobian, Chris Eden. « Concept Study of a High-Speed, Vertical Take-Off and Landing Aircraft ». Thesis, Virginia Tech, 2009. http://hdl.handle.net/10919/35574.

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The purpose of the study was to evaluate the merits of the DiscRotor concept that combine the features of a retractable rotor system for vertical take-off and landing (VTOL) with an integral, circular wing for high-speed flight. Tests were conducted to generate basic aerodynamic characteristics of the DiscRotor in hover and in fixed-wing flight.

To assess the DiscRotor during hover, small scale tests were conducted on a 3ft diameter rotor without the presence of a fuselage. A â hover rigâ was constructed capable of rotating the model rotor at speeds up to 3,500 RPM to reach tip speeds of 500fps. Thrust and torque generated by the rotating model were measured via a two-component load cell, and time averaged values were obtained for various speeds and pitch angles. It has been shown that the DiscRotor will perform well in hover. Ground Effects in hover were examined by simulating the ground with a movable, solid wall. The thrust was found to increase by 50% compared to the ground-independent case. Pressure distributions were measured on the ground and disc surfaces. Velocity measurements examined the flow field downstream of the rotor by traversing a seven hole velocity probe. A wake behind the rotor was shown to contract due to a low pressure region that develops downstream of the disc.

Wind tunnel experimentation was also performed to examine the fixed wing flight of the DiscRotor. These experiments were performed in the VA Tech 6â X6â Stability Tunnel. A model of the fuselage and a circular wing was fabricated based upon an initial sizing study completed by our partners at Boeing. Forces were directly measured via a six degree of freedom load cell, or balance, for free stream velocities up to 200fps. Reynolds numbers of 2 and 0.5 million have been investigated for multiple angles of attack. Low lift-to-drag ratios were found placing high power requirements for the DiscRotor during fixed-wing flight. By traversing a seven-hole velocity probe, velocities in a 2-D grid perpendicular to the flow were measured on the model. The strengths of shed vortices from the model were calculated. A method to improve fixed-wing performance was considered where two blades were extended from the disc. An increase of 0.17 in the CL was measured due to the interaction between the disc and blades.

This research utilized a wide range of experiments, with the aim of generating basic aerodynamic characteristics of the DiscRotor. A substantial amount of quantitative data was collected that could not be included in this document. Results aided in the initial designs of this aircraft for the purpose of evaluating the merit of the DiscRotor concept.
Master of Science

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Livres sur le sujet "CIRCULAR TUNNELS"

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Christopoulos, George P. Oscillating-flow wind tunnel studies for a circulation control circular cylinder. Monterey, Calif : Naval Postgraduate School, 1991.

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M, Ware George, MacConochie Ian O et Langley Research Center, dir. Subsonic aerodynamic characteristics of a circular body earth-to-orbit vehicle. Hampton, Va : National Aeronautics and Space Administration, Langley Research Center, 1996.

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Fox, T. A. On the use of end plates with circular cylinders in wind tunnel studies. St.Lucia : University of Queensland, Dept. of Civil Engineering, 1990.

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Burley, James R. Static investigation of circular-to-rectangular transition ducts for high-aspect-ratio nonaxisymmetric nozzles. [Washington, D.C.] : National Aeronautics and Space Administration, Scientific and Technical Information Branch, 1986.

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Chapitres de livres sur le sujet "CIRCULAR TUNNELS"

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Madalina, Ciotlaus, Marusceac Vladimir et Alexandra D. Danciu. « Impact of Soil Type Transition on Circular Tunnels Behavior ». Dans The 16th International Conference Interdisciplinarity in Engineering, 57–67. Cham : Springer International Publishing, 2022. http://dx.doi.org/10.1007/978-3-031-22375-4_5.

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Sinha, Shipra, Swapnil Mishra, K. S. Rao et T. Chakraborty. « Analysis of Twin Circular Tunnels Subjected to Impact Loads ». Dans Lecture Notes in Civil Engineering, 683–94. Singapore : Springer Singapore, 2021. http://dx.doi.org/10.1007/978-981-33-6466-0_63.

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de Silva, F., S. Fabozzi, N. Nikitas, E. Bilotta et R. Fuentes. « Site Specific Seismic Performance of Circular Tunnels in Dry Sand ». Dans Lecture Notes in Civil Engineering, 537–44. Cham : Springer International Publishing, 2019. http://dx.doi.org/10.1007/978-3-030-21359-6_57.

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Wang, Hua Ning, Guang Shang Zeng et Ming Jing Jiang. « Analytical Prediction of Stresses Around Non-circular Tunnels Excavated at Shallow Depth ». Dans Proceedings of GeoShanghai 2018 International Conference : Rock Mechanics and Rock Engineering, 39–47. Singapore : Springer Singapore, 2018. http://dx.doi.org/10.1007/978-981-13-0113-1_5.

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Huo, Hongbin, Lizhen Zhou, Yaqing Wang et Tao Zhang. « A Method for Predicting Seismic Stress and Deformation of Circular Tunnels Based on BP Artificial Neural Network ». Dans Challenges and Innovations in Geomechanics, 369–76. Cham : Springer International Publishing, 2021. http://dx.doi.org/10.1007/978-3-030-64518-2_44.

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Thouvenin, G., et A. Giraud. « Thermoporoelastic Analysis of a Deep Circular Tunnel ». Dans Application of Numerical Methods to Geotechnical Problems, 583–92. Vienna : Springer Vienna, 1998. http://dx.doi.org/10.1007/978-3-7091-2512-0_56.

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Kretzschmar, Linn. « Leveraging the Economic Potential of FCC’s Technologies and Processes ». Dans The Economics of Big Science, 85–91. Cham : Springer International Publishing, 2020. http://dx.doi.org/10.1007/978-3-030-52391-6_12.

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Abstract An international consortium of more than 150 organizations worldwide is studying the feasibility of various future particle colliders to expand our understanding of the inner workings of the Universe. At the core of the Future Circular Collider (FCC) study is the design of a 100 km long circular particle collider infrastructure that could extend CERN’s current accelerator complex with an integral research program that spans 70 years. The first step would be an intensity-frontier electron-positron collider allowing to study with precision the Higgs couplings with many of the Standard Model particles and search with high-precision for new physics while the ultimate goal is to build a proton collider with a c.m.s collision energy seven times larger than the Large Hadron Collider. Hosted in the same tunnel and profiting from the new infrastructure, FCC-hh would allow to explore a new energy regime where new physics may be at play.
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Al-Mirza, Hayder A., et Mahdi O. Karkush. « Numerical Modeling of Circular Tunnel Alignment Under Seismic Loading ». Dans Geotechnical Engineering and Sustainable Construction, 15–27. Singapore : Springer Singapore, 2022. http://dx.doi.org/10.1007/978-981-16-6277-5_2.

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Zafeiropoulos, A., et P. Nomikos. « Numerical simulation of circular tunnel intersections in anisotropic rock mass ». Dans Expanding Underground - Knowledge and Passion to Make a Positive Impact on the World, 2363–70. London : CRC Press, 2023. http://dx.doi.org/10.1201/9781003348030-284.

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Yu, Jian-qiang, Qi Li, Yong-lu Wang et Shuai Tao. « Numerical Simulation of Rockburst Characteristics of Tunnel Surrounding Rock Under Dilatancy Effect ». Dans Advances in Frontier Research on Engineering Structures, 163–73. Singapore : Springer Nature Singapore, 2023. http://dx.doi.org/10.1007/978-981-19-8657-4_15.

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AbstractRockburst is one of the most intense reactions in various instability phenomena of underground cavern surrounding rock, which seriously threatens the safety of underground engineering construction personnel and equipment. Based on Mohr–Coulomb strain softening model, the non-associated flow rule is adopted for plastic flow after material yield. By implanting Gu Ming-cheng and Tao Zhen-yu rockburst criterion in the software, the effects of different dilatancy angles on rockburst grade and circumferential stress distribution of surrounding rock of circular tunnel are simulated. The calculation results show that the larger the dilatancy angle is, the more difficult the rock burst pit is to form. The elements of serious rockburst are mainly concentrated in the wall of the tunnel, and the shear bands formed in the high value area of shear strain increment are short. When the dilatancy angle is small, the circumferential stress reaches the maximum at the interface of elastic-plastic zone. With the increase of dilatancy angle, the number of elements entering the plastic state and occurring medium and severe rockburst increases first and then decreases, while the number of elements occurring slight rockburst decreases monotonously. Different dilatancy angles have significant effects on the number of elements occurring rockburst at all levels.
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Actes de conférences sur le sujet "CIRCULAR TUNNELS"

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Dudley, D. G. « Propagation in circular tunnels : ring source excitation ». Dans IEEE Antennas and Propagation Society Symposium, 2004. IEEE, 2004. http://dx.doi.org/10.1109/aps.2004.1332006.

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Yang, Xuexia, et Yimin Lu. « Propagation Characteristics of Millimeter Wave in Circular Tunnels ». Dans 2006 7th International Symposium on Antennas, Propagation & EM Theory. IEEE, 2006. http://dx.doi.org/10.1109/isape.2006.353508.

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Mollon, Guilhem, Daniel Dias et Abdul-Hamid Soubra. « Probabilistic Analysis of the Face Stability of Circular Tunnels ». Dans International Foundation Congress and Equipment Expo 2009. Reston, VA : American Society of Civil Engineers, 2009. http://dx.doi.org/10.1061/41022(336)45.

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Deling Wang et Richard J. Bathurst. « Research on shock mitigation on circular tunnels using expanded polystyrene ». Dans 2011 International Conference on Electric Technology and Civil Engineering (ICETCE). IEEE, 2011. http://dx.doi.org/10.1109/icetce.2011.5775176.

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Bilotta, E., R. M. S. Maiorano, A. Viglione et S. Aversa. « THREE-DIMENSIONAL NUMERICAL MODELLING OF CIRCULAR TUNNELS UNDER SEISMIC ACTIONS ». Dans 5th International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering Methods in Structural Dynamics and Earthquake Engineering. Athens : Institute of Structural Analysis and Antiseismic Research School of Civil Engineering National Technical University of Athens (NTUA) Greece, 2015. http://dx.doi.org/10.7712/120115.3581.1654.

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Mahmoud, S. F. « Guided mode propagation in tunnels with non-circular cross section ». Dans 2008 IEEE Antennas and Propagation Society International Symposium and USNC/URSI National Radio Science Meeting. IEEE, 2008. http://dx.doi.org/10.1109/aps.2008.4619721.

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Dias, Daniel, Jean-Pierre Janin, Abdul-Hamid Soubra et Richard Kastner. « Three-Dimensional Face Stability Analysis of Circular Tunnels by Numerical Simulations ». Dans GeoCongress 2008. Reston, VA : American Society of Civil Engineers, 2008. http://dx.doi.org/10.1061/40972(311)111.

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Soubra, Abdul-Hamid, Daniel Dias, Fabrice Emeriault et Richard Kastner. « Three-Dimensional Face Stability Analysis of Circular Tunnels by a Kinematical Approach ». Dans GeoCongress 2008. Reston, VA : American Society of Civil Engineers, 2008. http://dx.doi.org/10.1061/40972(311)112.

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ZHANG, JINFENG, et MING ZHAO. « A Method to Monitor the Circular Deformation of Metro Shield Tunnels in Soft Soils ». Dans Structural Health Monitoring 2017. Lancaster, PA : DEStech Publications, Inc., 2017. http://dx.doi.org/10.12783/shm2017/13991.

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Wei, Hui, Guoxin Zheng et Minghua Jia. « The Measurements and Simulations of Millimeter Wave Propagation at 38ghz in Circular Subway Tunnels ». Dans 2008 China-Japan Joint Microwave Conference (CJMW 2008). IEEE, 2008. http://dx.doi.org/10.1109/cjmw.2008.4772373.

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Rapports d'organisations sur le sujet "CIRCULAR TUNNELS"

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Kandalaft-Ladkany, N. Design management and stress analysis of a circular rock tunnel for storage of spent nuclear fuel. Office of Scientific and Technical Information (OSTI), juin 1992. http://dx.doi.org/10.2172/10146824.

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Kandalaft-Ladkany, N. Design management and stress analysis of a circular rock tunnel for storage of spent nuclear fuel. Office of Scientific and Technical Information (OSTI), janvier 1992. http://dx.doi.org/10.2172/5353754.

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LAZEMI, H. A., M. FATEHI MARJI et M. ZAREI MAHMOUDABADI. Effect of Axial in Situ Stress on the Elasto-Plastic Analysis of Circular Tunnel in a Generalized Hoek-Brown Rock. Cogeo@oeaw-giscience, septembre 2011. http://dx.doi.org/10.5242/iamg.2011.0263.

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