WYPIWYG Hyperelasticity

In this paper we describe a new promising procedure to model hyperelastic materials from given stress-strain data. The main advantage of the proposed method is that the user does not need to have a relevant knowledge of hyperelasticity, large strains or hyperelastic constitutive modelling. The engineer simply has to prescribe some stress strain experimental data (whether isotropic or anisotropic) in also user prescribed stress and strain measures and the model almost exactly replicates the experimental data. The procedure is based on the piece-wise splines model by Sussman and Bathe and may be easily generalized to transversely isotropic and orthotropic materials. The model is also amenable of efficient finite element implementation. In this paper we briefly describe the general procedure, addressing the advantages and limitations. We give predictions for arbitrary ?experimental data? and also give predictions for actual experiments of the behaviour of living soft tissues. The model may be also implemented in a general purpose finite element program. Since the obtained strain energy functions are analytic piece-wise functions, the constitutive tangent may be readily derived in order to be used for implicit static problems, where the equilibrium iterations must be performed and the material tangent is needed in order to preserve the quadratic rate of convergence of Newton procedures.

Effect of the Wake of the Transducer Supports on the Ultrasonic Anemometer Measurements

The wake produced by the structural supports of the ultrasonic anemometers (UAs)causes distortions in the velocity field in the vicinity of the sonic path. These distortions are measured by the UA, inducing errors in the determination of the mean velocity, turbulence intensity, spectrum, etc.; basic parameters to determine the effect of wind on structures. Additionally, these distortions can lead to indefinition in the calibration function of the sensors (Cuerva et al., 2004). Several wind tunnel tests have been dedicated to obtaining experimental data, from which have been developed fit models to describe and to correct these distortions (Kaimal, 1978 and Wyngaard, 1985). This work explores the effect of a vortex wake generated by the supports of an UA, on the measurement of wind speed done by this instrument. To do this, the Von Karman¿s vortex street potential model is combined with the mathematical model of the measuring process carried out by UAs developed by Franchini et al. (2007). The obtained results are the correction functions of the measured wind velocity, which depends on the geometry of the sonic anemometer and aerodynamic conditions. These results have been validated with the ones obtained in a wind tunnel test done on a single path UA, especially developed for research. The supports of this UA have been modified in order to reproduce the conditions of the theoretical model. Good agreements between experimental and theoretical results have been found.

Thermal behaviour of bitumen modified by sulphur addition

The most frequent use of bitumen is as binder for pavement applications. The effect of sulphur addition on the properties of the bitumen has been extensively studied several decades ago. Recently, there is a renewed interest in researching the behaviour of sulphur-bitumen combination, because off 1.The future availability of bitumen may be limited and 2. The beneficial consumption of great amounts of sulphur compounds from petroleum refining is advisable. The addition of sulphur to bitumen provokes the beginning of chemical reactions depending on the sulphur content and heating temperature. At heating temperatures T< 140 ºC liquid sulphur reacts with naphthenic-aromatic fraction forming polysulphides. At temperatures above 150 ºC dehydrogenization reactions with emission of hydrogen sulfide take place and naphthenic-aromatic molecules are transformed into asphaltenes. Therefore, the addition of sulphur to bitumen provokes changes in the chemical structure of the bitumen. The objective of this work is to analyze, the thermal behaviour of sulphur-bitumen mixtures of different composition (0-35 %wt sulphur content) prepared at 130 and 140 ºC, by means of differential scanning calorimetry (DSC). Besides, the volatile emissions of the mixtures at high temperature have been estimated from loss weight measurements as a function of stored time

Improvement of compatibility and stability on polyethylene-modified bitumen by use of an aromatic extra as compatibilizer.

Bitumen modification by polyethylene addition usually improves the mechanical properties of the binder and, therefore, the behavior in service of the bituminous mix: thermal susceptibility and rutting can be diminished, whilst the resistance to low temperature cracking may increase. To achieve this improvement it is necessary a good compatibility between the base bitumen and the polyethylene. Low compatibility between bitumen and polyethylene can lead to phase separation: the polymer- asphalt incompatibility translates into a deterioration of ultimate properties. The object of this research project was to determine if these problems can be diminished by using certain compatibilizer agents, e.g. an aromatic extract from the oil refinery. Compatibility and stability of the polyethylene modified bitumen were studied using conventional test methods and dynamic shear reometer (DSR). Blends of bitumen and polyethylene were prepared with neat bitumen (PMB) or bitumen with compatibilizer as component of the binder (PMBC) and then compared. The experimental results show that “colloid instability index”(IC) is a parameter that can be used to control the compatibility between bitumen and polyethylene. From polyethylene point of view, one of the parameters that govern is the “melt flow index” (MFI). Experimental results show that PMBC formulated with low IC bitumen and hi gh MFI lineal polyethylene can be considered as stable binder.

Three decades of Space Activities at the Instituto Universitario de Microgravedad "Ignacio Da Riva" / Universidad Politécnica de Madrid (IDR/UPM) en History of Rocketry and Astronautics

Strictly speaking, space related activities at the Escuela Técnica Superior de Ingenieros Aeronáuticos (ETSIA) begun in 1973, when Prof. Ignacio Da Riva got a contract from the European Space Agency (ESA) to compile a handbook on spacecraft thermal control. By the same time, ESA issued an announcement of opportunities offering to the European scientific community the possibility of perform microgravity relevant experiments on board space platform like the European orbital laboratory Spacelab. Prof. Da Riva proposed one of the few selected experiments dealing with fluid physics under microgravity conditions, later flown on Spacelab-1 mission in 1983. These two events were the starting point where Prof. Da Riva, full professor of Aerodynamics at ETSIA, nucleated a small group of young professors and students located at the Laboratorio de Aerodinámica y Mecánica de Fluidos (LAMF) of ETSIA. Such group was leaded by Prof. Da Riva since its creation till 1991, when Prof. Da Riva died, and it was the seed of the more recently created research institute for aerospace science and technology named "Ignacio Da Riva" (IDR) in his honour. In this communication space related activities performed either at LAMF or IDR during the last three decades are briefly described.

Choked flow in water/CO2 solutions on air-independent propulsion systems

We develop a simplified model of choked flow in pipes for CO2-water solutions as an important step in the modelling of a whole hydraulic system with the intention of eliminating the carbon dioxide generated in air-independent submarine propulsion. The model is based on an approximate fitting of the homogeneous isentropic solution upstream of a valve (or any other area restriction), for given fluid conditions at the entrance. The relative maximum choking back-pressure is computed as a function of area restriction ratio. Although the procedure is generic for gas solutions, numeric values for the non-dimensional parameters in the analysis are developed only for choking in the case of carbon dioxide solutions up to the pure-water limit.

Effect of the Reference Line on Main Roughness Parameters

In the present paper the influence of the reference system with regard to the characterization of the surface finishing is analyzed. The effect of the reference system’s choice on the most representative surface finishing parameters (e.g. roughness average Ra and root mean square values Rq) is studied. The study can also be applied to their equivalent parameters in waviness and primary profiles. Based on ISO and ASME standards, three different types of regression lines (center, mean and orthogonal) are theoretically and experimentally analyzed, identifying the validity and applicability fields of each one depending on profile’s geometry.

Asymptotic Description of Flutter Amplitude Saturation by Nonlinear Friction Forces

The computation of the non-linear vibration dynamics of an aerodynamically unstable bladed-disk is a formidable numerical task, even for the simplified case of aerodynamic forces assumed to be linear. The nonlinear friction forces effectively couple dif- ferent travelling waves modes and, in order to properly elucidate the dynamics of the system, large time simulations are typically required to reach a final, saturated state. Despite of all the above complications, the output of the system (in the friction microslip regime) is basically a superposition of the linear aeroelastic un- stable travelling waves, which exhibit a slow time modulation that is much longer than the elastic oscillation period. This slow time modulation is due to both, the small aerodynamic effects and the small nonlinear friction forces, and it is crucial to deter- mine the final amplitude of the flutter vibration. In this presenta- tion we apply asymptotic techniques to obtain a new simplified model that captures the slow time dynamics of the amplitudes of the travelling waves. The resulting asymptotic model is very re- duced and extremely cheap to simulate, and it has the advantage that it gives precise information about the characteristics of the nonlinear friction models that actually play a role in the satura- tion of the vibration amplitude.

Campus of Excellence: The Power of Diversity in Engineering Education

This paper presents the results of a strategy to modernise the Spanish University system through the establishment of an International Campus of Excellence (CEI). The current, ambitious but realistic, project is a joint initiative of a number of institutions located in the Moncloa Campus, amongst them the Complutense and the Technical Universities, as well as CIEMAT, CSIC and INIA. The aim of the project is to transform the Moncloa Campus into an international point of reference with regard to research, education and innovation. This paper describes the project and presents the qualitative and quantitative results.

Low-Dimensional Modelling for optimal streaks in the blasius boundary layer

This paper is concerned with the low dimensional structure of optimal streaks in the Blasius boundary layer. Optimal streaks are well known to exhibit an approximate self-similarity, namely the streamwise velocity re-scaled with their maximum remains almost independent of both the spanwise wavenumber and the streamwise coordinate. However, the reason of this self-similar behavior is still unexplained as well as unexploited. After revisiting the structure of the streaks near the leading edge singularity, two additional approximately self-similar relations involving the velocity components and their wall normal derivatives are identified. Based on these properties, we derive a low dimensional model with two degrees of freedom. The comparison with the results obtained from the linearized boundary layer equations shows that this model is consistent and provide good approximations.

El impacto ambiental del transporte aéreo y las medidas para mitigarlo

La preocupación medioambiental guía en la actualidad muchas de las estrategias globales y nacionales de aplicación al sector del transporte. En transporte aéreo, el impacto ambiental es importante, pero los beneficios socioeconómicos también lo son. El crecimiento del transporte aéreo es el mayor de los desafíos del sector. Por el momento, está limitado por el mantenimiento de la seguridad y por la disponibilidad de infraestructuras, pero el impacto ambiental puede convertirse en el principal factor limitador. El transporte aéreo presenta actualmente el mayor crecimiento de todos los modos de transporte. La aviación comercial se enfrenta al reto de tomar un papel activo en la búsqueda e impulso de soluciones para alcanzar la sostenibilidad del sector, por lo tanto es necesario realizar un diagnóstico de situación a través de unos indicadores y modelos adecuados que midan el impacto ambiental del transporte aéreo. Los tipos de impacto ambiental del transporte aéreo se pueden clasificar como de efecto local (ruido, contaminación de aire local, uso de espacio), o de efecto global (consumo de materiales no renovables, aportación al cambio climático). La gestión del impacto ambiental comprende, además de medidas de reducción técnicas, diversas posibilidades económicas, que utilizan mecanismos de mercado (acuerdos voluntarios entre administración, operadores y consumidores, o cualquier combinación de ellos, impuestos y tasas, comercio de emisiones). En este trabajo se pasa revista a las diferentes medidas de gestión del impacto ambiental que se están implantando, tanto de carácter técnico como de contenido económico. Algunas de estas medidas están ya en vigor, otras en estudio. El análisis se centra fundamentalmente en el seno de la Unión Europea, que ha adoptado un papel de liderazgo mundial en la adopción de regulaciones ambientales, y el objetivo final es sacar conclusiones sobre la repercusión de estas medidas en general, y sobre el transporte aéreo en particular.

Gestión docente de la creatividad en la Escuela Técnica Superior de Ingenieros Industriales (ETSII) de Madrid: análisis de los procesos de generación, transmisión y absorción de conocimiento

El análisis de la metodología docente empleada en la ETSII se ha llevado a cabo con encuestas realizadas a profesores y alumnos del Centro. Las conclusiones de las encuestas apuntan a que hay un amplio campo de mejoras encaminadas a mejorar la transmisión de habilidades creativas a los futuros ingenieros. La aplicación de las TICs, potenciación del trabajo en equipo, mayor control de la calidad de la enseñanza impartida, desarrollo de grupos de investigación de las metodologías docentes, reducción del número de alumnos por clase y contratación de profesores con experiencia profesional, son aspectos a potenciar.

Vanadium-Doped In and Sn Sulphides: Photocatalysts able to use the whole visible light spectrum

Using photocatalysis for energy applications depends, more than for environmental purposes or selective chemical synthesis, on converting as much of the solar spectrum as possible; the best photocatalyst, titania, is far from this. Many efforts are pursued to use better that spectrum in photocatalysis, by doping titania or using other materials (mainly oxides, nitrides and sulphides) to obtain a lower bandgap, even if this means decreasing the chemical potential of the electron-hole pairs. Here we introduce an alternative scheme, using an idea recently proposed for photovoltaics: the intermediate band (IB) materials. It consists in introducing in the gap of a semiconductor an intermediate level which, acting like a stepstone, allows an electron jumping from the valence band to the conduction band in two steps, each one absorbing one sub-bandgap photon. For this the IB must be partially filled, to allow both sub-bandgap transitions to proceed at comparable rates; must be made of delocalized states to minimize nonradiative recombination; and should not communicate electronically with the outer world. For photovoltaic use the optimum efficiency so achievable, over 1.5 times that given by a normal semiconductor, is obtained with an overall bandgap around 2.0 eV (which would be near-optimal also for water phtosplitting). Note that this scheme differs from the doping principle usually considered in photocatalysis, which just tries to decrease the bandgap; its aim is to keep the full bandgap chemical potential but using also lower energy photons. In the past we have proposed several IB materials based on extensively doping known semiconductors with light transition metals, checking first of all with quantum calculations that the desired IB structure results. Subsequently we have synthesized in powder form two of them: the thiospinel In2S3 and the layered compound SnS2 (having bandgaps of 2.0 and 2.2 eV respectively) where the octahedral cation is substituted at a â?10% level with vanadium, and we have verified that this substitution introduces in the absorption spectrum the sub-bandgap features predicted by the calculations. With these materials we have verified, using a simple reaction (formic acid oxidation), that the photocatalytic spectral response is indeed extended to longer wavelengths, being able to use even 700 nm photons, without largely degrading the response for above-bandgap photons (i.e. strong recombination is not induced) [3b, 4]. These materials are thus promising for efficient photoevolution of hydrogen from water; work on this is being pursued, the results of which will be presented.

Cuerpos de forma óptima en vuelo hipersónico

Se estudia la obtencion de la forma del fuselaje optimo de un vehiculo hipersonico, tipo planeador,de gran radio de accion, para el que es fundamental conseguir un valor alto de ( L / D ) inAx.Se utiliza la teoria de NEWTON-BUSEMANN para el cálculo de las caracteristicas aerodinámicas. Para la solucion del problema variacional, se consideran fijos ciertos parámetros (por ejemplo, el radio de curvatura en el morro) que afectan directamente al calor recibido por el cuerpo y a las caracteristicas en vuelo subsónico. Como ejemplo, se considera la solucion de un caso particular.

Theory of a probe in a strong magnetic field

An asymptotic analysis of the Langmuir-probe problem in a quiescent, fully ionized plasma in a strong magnetic field is performed, for electron cyclotron radius and Debye length much smaller than probe radius, and this not larger than either ion cyclotron radius or mean free path. It is found that the electric potential, which is not confined to a sheath, controls the diffusion far from the probe; inside the magnetic tube bounded by the probe cross section the potential overshoots to a large value before decaying to its value in the body of the plasma. The electron current is independent of the shape of the body along the field and increases with ion temperature; due to the overshoot in the potential, (1) the current at negative voltages does not vary exponentially, (2) its magnitude is strongly reduced by the field, and (3) the usual sharp knee at space potential, disappears. In the regions of the C-V diagram studied the ion current is negligible or unaffected by the field. Some numerical results are presented.The theory, which fails beyond certain positive voltage, fields useful results for weak fields, too.