Anomaly detection on cup anemometers

The performances of two rotor-damaged commercial anemometers (Vector Instruments A100 LK) were studied. The calibration results (i.e. the transfer function) were very linear, the aerodynamic behavior being more efficient than the one shown by both anemometers equipped with undamaged rotors. No detection of the anomaly (the rotors'damage) was possible based on the calibration results. However, the Fourier analysis clearly revealed this anomaly.

Modifying the atlas of low lunar orbits using inert tethers

For long enough tethers, the coupling of the attitude and orbital dynamics may show non-negligible effects in the orbital motion of a tethered satellite about a central body. In the case of fast rotating tethers the attitude remains constant, on average, up to second order effects. Besides, for a tether rotating in a plane parallel to the equatorial plane of the central body, the attitude?orbit coupling effect is formally equal to the perturbation of the Keplerian motion produced by the oblateness of the central body and, therefore, may have a stabilizing effect in the orbital dynamics. In the case of a tethered satellite in a low lunar orbit, it is demonstrated that feasible tether lengths can help in modifying the actual map of lunar frozen orbits

The ion beam shepherd: A new concept for asteroid deflection

A novel slow push asteroid deflection strategy has been recently proposed in which an Earth threatening asteroid can be deflected by exploiting the momentum transmitted by a collimated beam of quasi-neutral plasma impinging against the asteroid surface. The beam can be generated with state-of-the art ion engines from a hovering spacecraft with no need for physical attachment or gravitational interaction with the celestial body. The spacecraft, placed at a distance of a few asteroid diameters, would need an ion thruster pointed at the asteroid surface as well as a second propulsion system to compensate for the ion engine reaction and keep the distance between the asteroid and the shepherd satellite constant throughout the deflection phase. A comparison in terms of required spacecraft mass per total imparted deflection impulse shows that the method outperforms the gravity tractor concept by more than one order of magnitude for asteroids up to about 200 m diameter. The two methods would yield comparable performance for asteroids larger than about 2 km

Detección de grietas en placas con técnicas multifrecuencia

Safety is one of the most important feature in the aviation industry, and this involves too many factors. One of these is the aircraft maintenance. Over time, the procedures have been changing, and improving themselves. Non Destructive Testing (NDT) appeared in the late 19th century as a great option, because it enabled to inspect any structure without damaging it. Nowadays, there are several kinds of NDT, but ultrasound is one of the most widely used. This Master Thesis is devoted to an innovative ultrasound technique for crack detection. A technique, whose main aim lies in getting a good location of defects from a few measures, breaking with the currently widespread methods, as phased array. It is not necessary to use trains of waves, only discrete excitations, which means a great saving of time and energy. This work is divided into two steps: the first is to develop a multiphysics simulator, which is able to solve linear elasticity 3D problems (via Finite Element Method, FEM). This simulator allows to obtain in a computationally efficient way the displacement field for different frequencies and excitations. The solution of this elastic problem is needed to be used in the second step, which consists of generating a code that implements a mathematical tool named topological derivative, allowing to locate defects in the studied domain. In this work, the domain is a plate, and the defect is a hidden spherical void. The simulator has been developed using open source software (Elmer, Gmsh, ...), achieving a highly versatile simulator, which allows to change the configuration easily: domain size and shape, number and position of transducers, etc. Just one comercial software is used, Matlab. It is used to implement the topological derivative. In this work, the performance of the method is tested in several examples comparing the results when one or more frequencies are considered for different configurations of emisors/receptors.

Fuel Cells: A Real Option for Unmanned Aerial Vehicles Propulsion

The possibility of implementing fuel cell technology in Unmanned Aerial Vehicle (UAV) propulsion systems is considered. Potential advantages of the Proton Exchange Membrane or Polymer Electrolyte Membrane (PEMFC) and Direct Methanol Fuel Cells (DMFC), their fuels (hydrogen and methanol), and their storage systems are revised from technical and environmental standpoints. Some operating commercial applications are described. Main constraints for these kinds of fuel cells are analyzed in order to elucidate the viability of future developments. Since the low power density is the main problem of fuel cells, hybridization with electric batteries, necessary in most cases, is also explored.

Moiré-Fourier deflectometry for local heat transfer measurement over a backward-facing step

This paper explores the possibility of using the Moire-Fourier deflectometry for measuring the local heat transfer coefficient inside small confined flows (micro-channels) and their relevance for checking theoretical models. This optical technique, supplemented with a digital image processing method of fringes, is applied for studying the local heat transfer over a backward facing step. The experimental results are compared with numerical results obtained from a commercial code, which has been contrasted with relevant solutions from the literature and bulk fluid temperature measurements at the inlet and outlet sections. In order to show the possibilities of the experimental technique, the influence of assuming an adiabatic wall on the numerical heat-transfer model is examined and the degree of agreement is discussed. As a result, the paper shows that the proposed Moiré-Fourier technique is a simple experimental setup suitable for temperature measurements with an accuracy similar to the thermocouples but with a spatial resolution near 0.01 mm.Moiré-Fourier deflectometry for local heat transfer measurement over a backward-facing step

Recovery of Disruptions in Rapid Transit Networks

This paper studies the disruption management problem of rapid transit rail networks. Besides optimizing the timetable and the rolling stock schedules, we explicitly deal with the effects of the disruption on the passenger demand. We propose a two-step approach that combines an integrated optimization model (for the timetable and rolling stock) with a model for the passengers’ behavior. We report our computational tests on realistic problem instances of the Spanish rail operator RENFE. The proposed approach is able to find solutions with a very good balance between various managerial goals within a few minutes. Se estudia la gestión de las incidencias en redes de metro y cercanías. Se optimizan los horarios y la asignación del material rodante, teniendo en cuenta el comportamiento de los pasajeros. Se reallizan pruebas en varias líneas de la red de cercanías de Madrid, con resultados satisfactorios.

A model for setting services on auxiliary bus lines under congestion

In this paper, a mathematical programming model and a heuristically derived solution is described to assist with the efficient planning of services for a set of auxiliary bus lines (a bus-bridging system) during disruptions of metro and rapid transit lines. The model can be considered static and takes into account the average flows of passengers over a given period of time (i.e., the peak morning traffic hour) Auxiliary bus services must accommodate very high demand levels, and the model presented is able to take into account the operation of a bus-bridging system under congested conditions. A general analysis of the congestion in public transportation lines is presented, and the results are applied to the design of a bus-bridging system. A nonlinear integer mathematical programming model and a suitable approximation of this model are then formulated. This approximated model can be solved by a heuristic procedure that has been shown to be computationally viable. The output of the model is as follows: (a) the number of bus units to assign to each of the candidate lines of the bus-bridging system; (b) the routes to be followed by users passengers of each of the origin–destination pairs; (c) the operational conditions of the components of the bus-bridging system, including the passenger load of each of the line segments, the degree of saturation of the bus stops relative to their bus input flows, the bus service times at bus stops and the passenger waiting times at bus stops. The model is able to take into account bounds with regard to the maximum number of passengers waiting at bus stops and the space available at bus stops for the queueing of bus units. This paper demonstrates the applicability of the model with two realistic test cases: a railway corridor in Madrid and a metro line in Barcelona Planificación de los servicios de lineas auxiliares de autobuses durante las incidencias de las redes de metro y cercanías. El modelo estudia el problema bajo condiciones de alta demanda y condiciones de congestión. El modelo no lineal resultante es resuelto mediante heurísticas que demuestran su utilidad. Se demuestran los resultados en dos corredores de las ciudades de Barcelona y Madrid.

Optimal Impulsive Collision Avoidance

The problem of optimal impulsive collision avoidance between two colliding objects in 3-dimensional elliptical Keplerian orbits is investigated with the purpose of establishing the optimal impulse direction and orbit location that give rise to the maximum miss distance following the maneuver. Closed-form analytical expressions are provided that predicts such distance and can be employed to perform a full optimization analysis. After verifying the accuracy of the expression for any orbital eccentricity and encounter geometry the optimum maneuver direction is derived as a function of the arc length separation between the maneuver point and the predicted collision point. The provided formulas can be used for high accuracy instantaneous estimation of the outcome of a generic impulsive collision avoidance maneuver and its optimization

Multiple removal of spent rocket upper stages with an ion beam shepherd

Among the many advantages of the recently proposed ion beam shepherd (IBS) debris removal technique is the capability to deal with multiple targets in a single mission. A preliminary analysis is here conducted in order to estimate the cost in terms of spacecraft mass and total mission time to remove multiple large-size upper stages of the Zenit family. Zenit-2 upper stages are clustered at 71 degrees inclination around 850 km altitude in low Earth orbit. It is found that a removal of two targets per year is feasible with a modest size spacecraft. The most favorable combinations of targets are outlined.

Solution of optimal continuous low-thrust transfer using Lie transforms

This paper addresses the problem of optimal constant continuous low-thrust transfer in the context of the restricted two-body problem (R2BP). Using the Pontryagin’s principle, the problem is formulated as a two point boundary value problem (TPBVP) for a Hamiltonian system. Lie transforms obtained through the Deprit method allow us to obtain the canonical mapping of the phase flow as a series in terms of the order of magnitude of the thrust applied. The reachable set of states starting from a given initial condition using optimal control policy is obtained analytically. In addition, a particular optimal transfer can be computed as the solution of a non-linear algebraic equation. Se investiga el uso de series y transformadas de Lie en problemas de optimización de trayectorias de satélites impulsados por motores de bajo empuje

A new set of integrals of motion to propagate the perturbed two-body problem

A formulation of the perturbed two-body problem that relies on a new set of orbital elements is presented. The proposed method represents a generalization of the special perturbation method published by Peláez et al. (Celest Mech Dyn Astron 97(2):131?150,2007) for the case of a perturbing force that is partially or totally derivable from a potential. We accomplish this result by employing a generalized Sundman time transformation in the framework of the projective decomposition, which is a known approach for transforming the two-body problem into a set of linear and regular differential equations of motion. Numerical tests, carried out with examples extensively used in the literature, show the remarkable improvement of the performance of the new method for different kinds of perturbations and eccentricities. In particular, one notable result is that the quadratic dependence of the position error on the time-like argument exhibited by Peláez?s method for near-circular motion under the J2 perturbation is transformed into linear.Moreover, themethod reveals to be competitive with two very popular elementmethods derived from theKustaanheimo-Stiefel and Sperling-Burdet regularizations.

Diagnostics of classical and dusty plasmas w ith collecting and emissive langmuir probes = Diagnosis de plasmas clásicos y granulares mediante sondas colectoras y emisoras de Langmuir

Las sondas eléctricas se emplean habitualmente en la diagnosis de plasmas. La presente tesis aborda la operación de las sondas colectoras y emisoras de Langmuir en plasmas fríos de baja densidad. El estudio se ha centrado en la determinación del potencial de plasma, Vsp, mediante el potencial flotante de una sonda emisora. Esta técnica consiste en la medida del potencial de la sonda correspondiente a la condición de corriente neta igual a cero, el cual se denomina potencial flotante, VF. Este potencial se desplaza hacia el potencial del plasma según aumenta la emisión termoiónica de la sonda, hasta que se satura cerca de Vsp. Los experimentos llevados a cabo en la pluma de plasma de un motor iónico y en un plasma de descarga de glow muestran que la corriente de electrones termoiónicos es mayor que la corriente de electrones recogidos para una sonda polarizada por debajo del potencial del plasma, resultado inconsistente con la teoría tradicionalmente aceptada. Para investigar estos resultados se ha introducido el parámetro R, definido como el cociente entre la corriente de electrones emitidos y recogidos por la sonda. Este parámetro, que está relacionado con la diferencia de potencial VF - Vsp, también es útil para la descripción de los modos de operación de la sonda emisora (débil, fuerte y más allá del fuerte). Los resultados experimentales evidencian que, al contrario de lo que indica la teoría, R es mayor que la unidad. Esta discrepancia se puede solucionar introduciendo una población efectiva de electrones. Con dicha población, el nuevo modelo para la corriente total de la sonda reproduce los datos experimentales. El origen de este grupo electrónico es todavía una cuestión abierta, pero podría estar originada por una nueva estructura de potencial cerca de la sonda cuando ésta trabaja en el régimen de emisión fuerte. Para explicar dicha estructura de potencial, se propone un modelo unidimensional compuesto por un mínimo de potencial cerca de la superficie de la sonda. El análisis numérico indica que este pozo de potencial aparece para muy altas temperaturas de la sonda, reduciendo la cantidad de electrones emitidos que alcanzan el plasma y evitando así cualquier posible perturbación de éste. Los aspectos experimentales involucrados en el método del potencial flotante también se han estudiado, incluyendo cuestiones como las diferentes técnicas de obtención del VF, el cociente señal-ruido, el acoplamiento de la señal de los equipos utilizados para la obtención de las curvas I-V o la evidencia experimental de los diferentes modos de operación de la sonda. Estas evidencias empíricas se encuentran en todos los aspectos de operación de la sonda: la recolección de electrones, el potencial flotante, la precisión en las curvas I-V y la emisión electrónica. Ésta última también se estudia en la tesis, debido a que un fenómeno de super emisión tiene lugar en el régimen de emisión fuerte. En este modo de operación, las medidas experimentales indican que las corrientes termoiónicas de electrones son mayores que aquéllas predichas por la ecuación de Richardson-Dushman clásica. Por último, la diagnosis de plasmas usando sondas eléctrica bajo presencia de granos de polvo (plasmas granulares) en plasmas fríos de baja densidad también se ha estudiado, mediante la aplicación numérica de la técnica del potencial flotante de la sonda emisora en un plasma no convencional. Los resultados apuntan a que el potencial flotante de una sonda emisora se vería afectado por altas densidades de polvo o grandes partículas. ABSTRACT Electric probes are widely employed for plasma diagnostics. This dissertation concerns the operation of collecting and emissive Langmuir probes in low density cold plasmas. The study is focused on the determination of the plasma potential, Vsp, by means of the floating potential of emissive probes. This technique consists of the measurement of the probe potential, corresponding to the zero net probe current, which is the so-called floating potential, VF . This potential displaces towards the plasma potential as the thermionic electron emission increases, until it saturates near Vsp. Experiments carried out in the plasma plume of an ion thruster and in a glow discharge plasma show the thermionic electron current of the emissive Langmuir probe is higher than the collected electron current, for a probe with a bias potential below Vsp, which is inconsistent with the traditional accepted theory. To investigate these results, a parameter R is introduced as the ratio between the emitted and the collected electron current. This parameter, which is related to the difference VF - Vsp, is also useful for the description of the operation modes of the emissive Langmuir probe (weak, strong and beyond strong). The experimental results give an inconsistency of R > 1, which is solved by a modification of the theory for emissive probes, with the introduction of an effective electron population. With this new electron group, the new model for the total probe current agrees with the experimental data. The origin of this electron group remains an open question, but it might be originated by a new potential structure near the emissive probe when it operates in the strong emission regime. A simple one-dimension model composed by a minimum of potential near the probe surface is discussed for strongly emitting emissive probes. The results indicate that this complex potential structure appears for very high probe temperatures and the potential well might reduce the emitted electrons population reaching the plasma bulk. The experimental issues involved in the floating potential method are also studied, as the different obtaining techniques of VF, the signal-to-noise ratio, the signal coupling of the I-V curve measurement system or the experimental evidence of the probe operation modes. These empirical proofs concern all the probe operation aspects: the electron collection, the floating potential, the I-V curve accuracy as well as the electron emission. This last issue is also investigated in this dissertation, because a super emission takes place in the strong emission regime. In this operation mode, the experimental results indicate that the thermionic electron currents might be higher than those predicted by the classical Richardson-Dushman equation. Finally, plasma diagnosis using electric probes in the presence of dust grains (dusty plasmas) in low density cold plasmas is also addressed. The application of the floating potential technique of the emissive probe in a non-conventional complex plasma is numerically investigated, whose results point out the floating potential of the emissive probe might be shifted for high dust density or large dust particles.

Bare-tape scaling laws for de-orbit missions in a space debris environment

El entorno espacial actual hay un gran numero de micro-meteoritos y basura espacial generada por el hombre, lo cual plantea un riesgo para la seguridad de las operaciones en el espacio. La situación se agrava continuamente a causa de las colisiones de basura espacial en órbita, y los nuevos lanzamientos de satélites. Una parte significativa de esta basura son satélites muertos, y fragmentos de satélites resultantes de explosiones y colisiones de objetos en órbita. La mitigación de este problema se ha convertido en un tema de preocupación prioritario para todas las instituciones que participan en operaciones espaciales. Entre las soluciones existentes, las amarras electrodinámicas (EDT) proporcionan un eficiente dispositivo para el rápido de-orbitado de los satélites en órbita terrestre baja (LEO), al final de su vida útil. El campo de investigación de las amarras electrodinámicas (EDT) ha sido muy fructífero desde los años 70. Gracias a estudios teóricos, y a misiones para la demostración del funcionamiento de las amarras en órbita, esta tecnología se ha desarrollado muy rápidamente en las últimas décadas. Durante este período de investigación, se han identificado y superado múltiples problemas técnicos de diversa índole. Gran parte del funcionamiento básico del sistema EDT depende de su capacidad de supervivencia ante los micro-meteoritos y la basura espacial. Una amarra puede ser cortada completamente por una partícula cuando ésta tiene un diámetro mínimo. En caso de corte debido al impacto de partículas, una amarra en sí misma, podría ser un riesgo para otros satélites en funcionamiento. Por desgracia, tras varias demostraciones en órbita, no se ha podido concluir que este problema sea importante para el funcionamiento del sistema. En esta tesis, se presenta un análisis teórico de la capacidad de supervivencia de las amarras en el espacio. Este estudio demuestra las ventajas de las amarras de sección rectangular (cinta), en cuanto a la probabilidad de supervivencia durante la misión, frente a las amarras convencionales (cables de sección circular). Debido a su particular geometría (longitud mucho mayor que la sección transversal), una amarra puede tener un riesgo relativamente alto de ser cortado por un único impacto con una partícula de pequeñas dimensiones. Un cálculo analítico de la tasa de impactos fatales para una amarra cilindrica y de tipo cinta de igual longitud y masa, considerando el flujo de partículas de basura espacial del modelo ORDEM2000 de la NASA, muestra mayor probabilidad de supervivencia para las cintas. Dicho análisis ha sido comparado con un cálculo numérico empleando los modelos de flujo el ORDEM2000 y el MASTER2005 de ESA. Además se muestra que, para igual tiempo en órbita, una cinta tiene una probabilidad de supervivencia un orden y medio de magnitud mayor que una amarra cilindrica con igual masa y longitud. Por otra parte, de-orbitar una cinta desde una cierta altitud, es mucho más rápido, debido a su mayor perímetro que le permite capturar más corriente. Este es un factor adicional que incrementa la probabilidad de supervivencia de la cinta, al estar menos tiempo expuesta a los posibles impactos de basura espacial. Por este motivo, se puede afirmar finalmente y en sentido práctico, que la capacidad de supervivencia de la cinta es bastante alta, en comparación con la de la amarra cilindrica. El segundo objetivo de este trabajo, consiste en la elaboración de un modelo analítico, mejorando la aproximación del flujo de ORDEM2000 y MASTER2009, que permite calcular con precisión, la tasa de impacto fatal al año para una cinta en un rango de altitudes e inclinaciones, en lugar de unas condiciones particulares. Se obtiene el numero de corte por un cierto tiempo en función de la geometría de la cinta y propiedades de la órbita. Para las mismas condiciones, el modelo analítico, se compara con los resultados obtenidos del análisis numérico. Este modelo escalable ha sido esencial para la optimización del diseño de la amarra para las misiones de de-orbitado de los satélites, variando la masa del satélite y la altitud inicial de la órbita. El modelo de supervivencia se ha utilizado para construir una función objetivo con el fin de optimizar el diseño de amarras. La función objectivo es el producto del cociente entre la masa de la amarra y la del satélite y el numero de corte por un cierto tiempo. Combinando el modelo de supervivencia con una ecuación dinámica de la amarra donde aparece la fuerza de Lorentz, se elimina el tiempo y se escribe la función objetivo como función de la geometría de la cinta y las propietades de la órbita. Este modelo de optimización, condujo al desarrollo de un software, que esta en proceso de registro por parte de la UPM. La etapa final de este estudio, consiste en la estimación del número de impactos fatales, en una cinta, utilizando por primera vez una ecuación de límite balístico experimental. Esta ecuación ha sido desarollada para cintas, y permite representar los efectos tanto de la velocidad de impacto como el ángulo de impacto. Los resultados obtenidos demuestran que la cinta es altamente resistente a los impactos de basura espacial, y para una cinta con una sección transversal definida, el número de impactos críticos debidos a partículas no rastreables es significativamente menor. ABSTRACT The current space environment, consisting of man-made debris and tiny meteoroids, poses a risk to safe operations in space, and the situation is continuously deteriorating due to in-orbit debris collisions and to new satellite launches. Among these debris a significant portion is due to dead satellites and fragments of satellites resulted from explosions and in-orbit collisions. Mitigation of space debris has become an issue of first concern for all the institutions involved in space operations. Bare electrodynamic tethers (EDT) can provide an efficient mechanism for rapid de-orbiting of defunct satellites from low Earth orbit (LEO) at end of life. The research on EDT has been a fruitful field since the 70’s. Thanks to both theoretical studies and in orbit demonstration missions, this technology has been developed very fast in the following decades. During this period, several technical issues were identified and overcome. The core functionality of EDT system greatly depends on their survivability to the micrometeoroids and orbital debris, and a tether can become itself a kind of debris for other operating satellites in case of cutoff due to particle impact; however, this very issue is still inconclusive and conflicting after having a number of space demonstrations. A tether can be completely cut by debris having some minimal diameter. This thesis presents a theoretical analysis of the survivability of tethers in space. The study demonstrates the advantages of tape tethers over conventional round wires particularly on the survivability during the mission. Because of its particular geometry (length very much larger than cross-sectional dimensions), a tether may have a relatively high risk of being severed by the single impact of small debris. As a first approach to the problem, survival probability has been compared for a round and a tape tether of equal mass and length. The rates of fatal impact of orbital debris on round and tape tether, evaluated with an analytical approximation to debris flux modeled by NASA’s ORDEM2000, shows much higher survival probability for tapes. A comparative numerical analysis using debris flux model ORDEM2000 and ESA’s MASTER2005 shows good agreement with the analytical result. It also shows that, for a given time in orbit, a tape has a probability of survival of about one and a half orders of magnitude higher than a round tether of equal mass and length. Because de-orbiting from a given altitude is much faster for the tape due to its larger perimeter, its probability of survival in a practical sense is quite high. As the next step, an analytical model derived in this work allows to calculate accurately the fatal impact rate per year for a tape tether. The model uses power laws for debris-size ranges, in both ORDEM2000 and MASTER2009 debris flux models, to calculate tape tether survivability at different LEO altitudes. The analytical model, which depends on tape dimensions (width, thickness) and orbital parameters (inclinations, altitudes) is then compared with fully numerical results for different orbit inclinations, altitudes and tape width for both ORDEM2000 and MASTER2009 flux data. This scalable model not only estimates the fatal impact count but has proved essential in optimizing tether design for satellite de-orbit missions varying satellite mass and initial orbital altitude and inclination. Within the frame of this dissertation, a simple analysis has been finally presented, showing the scalable property of tape tether, thanks to the survivability model developed, that allows analyze and compare de-orbit performance for a large range of satellite mass and orbit properties. The work explicitly shows the product of tether-to-satellite mass-ratio and fatal impact count as a function of tether geometry and orbital parameters. Combining the tether dynamic equation involving Lorentz drag with space debris impact survivability model, eliminates time from the expression. Hence the product, is independent of tether de-orbit history and just depends on mission constraints and tether length, width and thickness. This optimization model finally led to the development of a friendly software tool named BETsMA, currently in process of registration by UPM. For the final step, an estimation of fatal impact rate on a tape tether has been done, using for the first time an experimental ballistic limit equation that was derived for tapes and accounts for the effects of both the impact velocity and impact angle. It is shown that tape tethers are highly resistant to space debris impacts and considering a tape tether with a defined cross section, the number of critical events due to impact with non-trackable debris is always significantly low.

Diseño y ensayos en tierra de paneles solares para un satélite de órbita baja = Design and testing procedures of a Low Earth (LEO)satellite solar panels

El Proyecto Fin De Carrera presentado a continuación contiene una descripción del prediseño del microsatélite de observación terrestre Gaia, particularizando ésta especialmente en el sistema de potencia del mismo. En el presente capítulo se describen los objetivos de la misión expuesta y los requerimientos del satélite objeto de este proyecto.