Respuesta estática y sísmica de gasoductos

El objetivo de esta tesis es el estudio de la respuesta estructural de los gasoductos sometidas a solicitaciones estáticas y dinámicas, enfocando prioritariamente en la respuesta sísmica. Los gasoductos, como las tuberías en general, se utilizan principalmente para la transportación de fluidos, como agua, gas o petróleo, de ahí la importancia de que el diseño y la estructura se realicen adecuadamente. La tubería debe ser capaz de soportar tanto los efectos de cargas estáticas como las debidas al peso propio o de la presión de la tierra, así como los diferentes tipos de cargas dinámicas ocurridas durante un evento sísmico, como los debidos a las ondas o el desplazamiento de fallas. En la primera parte de la tesis se describen aspectos generales de la tubería y su uso, y se da una breve historia de uso en la industria y las redes de abastecimiento urbano. Aparte de otros aspectos, se discuten las ventajas y desventajas de los diferentes materiales de las tuberías. En la segunda parte de la tesis se desarrollan las ecuaciones de equilibrio de una sección transversal de la tubería bajo cargas estáticas, tales como la presión interna, peso propio, presión de la tierra y las cargas externas. Un número de diferentes combinaciones de carga es analizado por medio de programas codificados como Matlab, los cuales se han desarrollado específicamente para este propósito. Los resultados se comparan con los obtenidos en Ansys utilizando un código de elementos finitos. En la tercera parte se presenta la respuesta dinámica de las tuberías, que abarca los efectos de las ondas y los desplazamientos de fallas. Se presentan las características relevantes del suelo como las velocidades de ondas, así como los métodos para estimar el desplazamiento máximo de las fallas. Un estudio paramétrico se emplea para ilustrar la influencia de estos parámetros en la respuesta estructural de la tubería. Con este fin se han utilizado dos métodos, el Pseudoestático y el Simplificado. En la última parte de la tesis son desarrollados los modelos de elementos finitos que permiten simular adecuadamente el comportamiento no lineal del suelo y la tubería. Los resultados se comparan con los obtenidos por un método simplificado utilizado con frecuencia que fue propuesto por Kennedy en 1977. Estudios paramétricos se presentan con el fin de examinar la validez de las hipótesis del método de Kennedy. La tesis concluye con recomendaciones que indican en qué casos los resultados obtenidos por el método de Kennedy son conservadores y cuando es preferible utilizar modelos de elementos finitos para estimar la respuesta de las tuberías durante los terremotos. ABSTRACT The subject of this thesis is the study of the structural response of pipelines subjected to static and dynamic loads with special attention to seismic design loads. Pipelines, as pipes in general, are used primarily for the transportation of fluids like water, gas or oil, hence the importance of an adequate design and structural behaviour. The pipe must be able to withstand both the effects of static loads like those due to self-weight or earth pressure as well as the different types of dynamic loads during a seismic event like those due to wave passing or fault displacements. In the first part of the thesis general aspects of pipelines and their use are described and a brief history of their usage in industry and for urban supply networks is given. Apart from other aspects, the advantages and disadvantages of different pipe materials are discussed. In the second part of the thesis the equilibrium equations of a transverse section of the pipe under static loads such as internal pressure, self-weight, earth pressure and external loads are developed. A number of different load combinations is analysed by means of programs coded in Matlab that have been specifically developed for this purpose. The results are compared to those obtained with the commercial Finite Element code Ansys. In the third part the dynamic response of pipelines during earthquakes is presented, covering the effects of passing waves and fault displacements. Relevant soil characteristics like wave propagation velocities as well as methods to estimate the maximum fault displacements are presented. A parametric study is employed to illustrate the influences of these parameters on the structural response of the pipe. To this end two methods have been used, the Pseudostatic and the Simplified method. In the last part of the thesis Finite Element models are developed which allow to adequately simulate the nonlinear behaviour of the soil and the pipe. The results are compared to those obtained by a frequently used simplified method which was proposed by Kennedy in 1977. Parametric studies are presented in order to examine the validity of the hypotheses Kennedys’ method is based on. The thesis concludes with recommendations indicating in which cases the results obtained by Kennedy’s method are conservative and when it is preferable to use Finite Element models to estimate the response of pipelines during earthquakes.

Modelado de la propagación acústica submarina para comunicaciones PtP

El objetivo principal del proyecto es el desarrollo de un simulador de comunicaciones submarinas, que permite la caracterización del canal a través de datos reales que son usados para establecer la comunicación entre dos puntos, empleando diferentes técnicas de modulación. Dicho simulador, ofrece un interfaz gráfico sencillo de usar y ha sido desarrollado en MatLab, basado en Bellhop [14] y Simulink. Dicho simulador desarrollado se ha usado para realizar simulaciones en diferentes escenarios, con datos reales del océano extraídos de la base de datos WOD [2]. Se ha divido el proyecto en seis partes: INTRODUCCIÓN, MARCO TEÓRICO, IMPLEMENTACIÓN, CONCLUSIONES, MANUAL y PROPUESTA DE PRÁCTICA. Se describen a continuación: En la primera parte, se realiza una introducción al proyecto, indicando las motivaciones que llevaron a desarrollarlo, una breve introducción, los objetivos fijados y un análisis de la evolución histórica de las comunicaciones submarinas, hasta llegar al estado del arte existente. En la segunda parte se describen los fundamentos teóricos necesarios para el desarrollo del proyecto, por una parte lo relativo a las ondas acústicas y su propagación, y por otra lo relativo a las técnicas de modulación digital empleadas. En la tercera parte se describe la implementación del simulador, explicando las funcionalidades existentes y un resumen de cómo fue desarrollado y su arquitectura lo que facilita su uso para proyectos futuros. La cuarta parte analiza las simulaciones realizadas en diversos escenarios, empleando datos reales y datos artificiales para la temperatura y salinidad del agua. En la quinta parte se proporciona un manual de usuario del simulador desarrollado, para que pueda ser usado correctamente. Se describe también el procesado de extracción de datos de WOD para que sean compatibles. Por último, en propuesta didáctica se propone un guión de práctica para desarrollar en la asignatura P.A.S. ABSTRACT. The main goal of this project is the development of an underwater communication simulator, that allows the determination of the underwater channel through real data, using different modulation techniques. The simulator, offers a graphic interface, easy to use and developed in MatLab, based on Bellhop [14] and Simulink. The simulator was given the name of UWACOMSIM and it was used to simulate different scenarios, using data from the WOD [2]. The project is divided into six parts: INTRODUCTION, THEORETICAL FRAMEWORK, IMPLEMENTATION, CONCLUSIONS, MANUAL and DIDACTAL PROPOSAL. These parts are described bellow: In the first part an introduction is given, remarking the motivations that lead to develop the project. Also objectives are explained, a historical analysis of the underwater communications is given, and finish with the state of the art. Secondly, theoretical part is described. First, everything related with acoustics and wave propagation throgh water, secondly, digital modulation techniques are explained. In the third part, the simulation implementation is explained. Main functionalities are highlighted and a brief overview of the architecture is given. This part can be useful for related works. Simulations and conclusions about the results, are done in the fourth part. In this section, different significant scenarios are chosen, and many simulations are launched in order to analyse the data. In the fifth parth, a user manual is provided in order to show the user how to use the simulator and how to download data from WOD if needed. In the final part of the project, a laboratory session is proposed for the subject P.A.S.

An Efficient Hybrid GO-PWS Algorithm to Analyze Conformal Serrated-Edge Reflectors for Millimeter-Wave Compact Range

A method to analyze parabolic reflectors with arbitrary piecewise rim is presented in this communication. This kind of reflectors, when operating as collimators in compact range facilities, needs to be large in terms of wavelength. Their analysis is very inefficient, when it is carried out with fullwave/MoM techniques, and it is not very appropriate for designing with PO techniques. Also, fast GO formulations do not offer enough accuracy to reach performance results. The proposed algorithm is based on a GO-PWS hybrid scheme, using analytical as well as non-analytical formulations. On one side, an analytical treatment of the polygonal rim reflectors is carried out. On the other side, non-analytical calculi are based on efficient operations, such as M2 order 2-dimensional FFT. A combination of these two techniques in the algorithm ensures real ad-hoc design capabilities, reached through analysis speedup. The purpose of the algorithm is to obtain an optimal conformal serrated-edge reflector design through the analysis of the field quality within the quiet zone that it is able to generate in its forward half space.

Influence of Crystal Quality on the Excitation and Propagation of Surface and Bulk Acoustic Waves in Polycrystalline AlN Films

We investigate the excitation and propagation of acoustic waves in polycrystalline aluminum nitride films along the directions parallel and normal to the c-axis. Longitudinal and transverse propagations are assessed through the frequency response of surface acoustic wave and bulk acoustic wave devices fabricated on films of different crystal qualities. The crystalline properties significantly affect the electromechanical coupling factors and acoustic properties of the piezoelectric layers. The presence of misoriented grains produces an overall decrease of the piezoelectric activity, degrading more severely the excitation and propagation of waves traveling transversally to the c-axis. It is suggested that the presence of such crystalline defects in c-axis-oriented films reduces the mechanical coherence between grains and hinders the transverse deformation of the film when the electric field is applied parallel to the surface.

A canonical UTD solution for electromagnetic scattering by an electrically large impedance circular cylinder illuminated by an obliquely incident plane wave

A uniform geometrical theory of diffraction (UTD) solution is developed for the canonical problem of the electromagnetic (EM) scattering by an electrically large circular cylinder with a uniform impedance boundary condition (IBC), when it is illuminated by an obliquely incident high frequency plane wave. A solution to this canonical problem is first constructed in terms of an exact formulation involving a radially propagating eigenfunction expansion. The latter is converted into a circumferentially propagating eigenfunction expansion suited for large cylinders, via the Watson transform, which is expressed as an integral that is subsequently evaluated asymptotically, for high frequencies, in a uniform manner. The resulting solution is then expressed in the desired UTD ray form. This solution is uniform in the sense that it has the important property that it remains continuous across the transition region on either side of the surface shadow boundary. Outside the shadow boundary transition region it recovers the purely ray optical incident and reflected ray fields on the deep lit side of the shadow boundary and to the modal surface diffracted ray fields on the deep shadow side. The scattered field is seen to have a cross-polarized component due to the coupling between the TEz and TMz waves (where z is the cylinder axis) resulting from the IBC. Such cross-polarization vanishes for normal incidence on the cylinder, and also in the deep lit region for oblique incidence where it properly reduces to the geometrical optics (GO) or ray optical solution. This UTD solution is shown to be very accurate by a numerical comparison with an exact reference solution.

Hard transition to chaotic dynamics in Alfven wave fronts

The derivative nonlinear Schrodinger DNLS equation, describing propagation of circularly polarized Alfven waves of finite amplitude in a cold plasma, is truncated to explore the coherent, weakly nonlinear, cubic coupling of three waves near resonance, one wave being linearly unstable and the other waves damped. In a reduced three-wave model equal dampings of daughter waves, three-dimensional flow for two wave amplitudes and one relative phase, no matter how small the growth rate of the unstable wave there exists a parametric domain with the flow exhibiting chaotic relaxation oscillations that are absent for zero growth rate. This hard transition in phase-space behavior occurs for left-hand LH polarized waves, paralleling the known fact that only LH time-harmonic solutions of the DNLS equation are modulationally unstable, with damping less than about unstable wave frequency 2/4 x ion cyclotron frequency. The structural stability of the transition was explored by going into a fully 3-wave model different dampings of daughter waves,four-dimensional flow; both models differ in significant phase-space features but keep common features essential for the transition.

Reduced three-wave model to study the hard transition to chaotic dynamics in Alfven wave-fronts

The derivative nonlinear Schrödinger (DNLS) equation, describing propagation of circularly polarized Alfven waves of finite amplitude in a cold plasma, is truncated to explore the coherent, weakly nonlinear, cubic coupling of three waves near resonance, one wave being linearly unstable and the other waves damped. In a reduced three-wave model (equal damping of daughter waves, three-dimensional flow for two wave amplitudes and one relative phase), no matter how small the growth rate of the unstable wave there exists a parametric domain with the flow exhibiting chaotic dynamics that is absent for zero growth-rate. This hard transition in phase-space behavior occurs for left-hand (LH) polarized waves, paralelling the known fact that only LH time-harmonic solutions of the DNLS equation are modulationally unstable.

Fully 3-wave model to study the hard transition to chaotic dynamics in alfven wave-fronts

The derivative nonlinear Schrödinger (DNLS) equation, describing propagation of circularly polarized Alfven waves of finite amplitude in a cold plasma, is truncated to explore the coherent, weakly nonlinear coupling of three waves near resonance, one wave being linearly unstable and the other waves damped. No matter how small the growth rate of the unstable wave, the four-dimensional flow for the three wave amplitudes and a relative phase, with both resistive damping and linear Landau damping, exhibits chaotic relaxation oscillations that are absent for zero growth-rate. This hard transition in phase-space behavior occurs for left-hand (LH) polarized waves, paralleling the known fact that only LH time-harmonic solutions of the DNLS equation are modulationally unstable. The parameter domain developing chaos is much broader than the corresponding domain in a reduced 3-wave model that assumes equal dampings of the daughter waves

Deployment of an all-in-one millimetre-wave anechoic chamber

This paper describes the new anechoic chamber available at The University of Kent, UK. This facility includes a spherical near/far field, planar near field, cylindrical near field and a compact range. The facility allows measurement from 600 MHz up to 110 MHz. The spherical, planar and cylindrical ranges covers up to 40 GHz and the compact range is available from 50 GHz up to 110 MHz. Immediate plans are to use the new facility to measure body-centric antennas and sensing nodes together with near field sampling of finite sized Frequency Selective Surfaces.

New device for continuous-wave THz emission: large area emitter

We discuss two different approaches to overcome the power limitations of CW THz generation imposed to conventional photomixers. The increase in power achievable by using arrays of AEs is studied. Then ?large area emitters? are proposed as an alternate approach to overcome the power limitations. In this antenna-free new scheme of photomixing, the THz radiation originates directly from the acceleration of photo-induced charge carriers generated within a large semiconductor area. The quasi-continuous distribution of emitting elements corresponds to a high-density array and results in particularly favorable radiation profiles.