Un modelo viscoplástico para la caracterización tenso-deformacional de materiales asfálticos

La presente tesina pretende adordar el problema del diseño y el análisis estructural de los pavimentos flexibles. Se propone modelar el comportamiento del material asfalto mediante un modelo viscoplástico. El objetivo de este trabajo es en primer lugar validar el modelo propuesto, para a acontinuación calibrarlo en base a ensayos experimentales de laboratorio. Conociendo los valores de los parametros fundamentales del modelo ajustados a los resultados experimentales, ya podemos caracterizar el material. Se estudiará el grado de aproximación conseguido con el nueco modelo viscoplástico, la flexibilidad del mismo, y la influencia de las variables constitutivas en la respuesta de con el objetivo de evaluar las posibilidadesde la formulación de cra al desarrollo de un método de dieseño y análisis estructural de firmes que mejore los actuales métodos que no dejan de ser aproximaciones empíricas de la realidad

A viscoplastic model with strain rate constitutive parameters for asphalt mixtures' response simulation

The mechanical behavior of the asphalt pavements is a complex phenomenon conditioned by the heterogeneity of the asphalt composite material. Experimental tests in the laboratory show a clear strain rate dependency in the material’s response. A new viscoplastic model has been developed to simulate de asphalt mixture’s response under dynamic loads, assuming the strain rate dependency of the material’s response observed in the experimental tests. It has been noted that the strain rate affects significantly the Young modulus and the viscosity. Taking into account this influence, a new formulation has been developed, implemented in a finite element code. The new viscoplastic model has been validated and calibrated according to laboratory test to obtain mathematical expressions for the constitutive equations. The new viscoplastic model allows us to simulate the asphalt mixture’s response, under dynamic loads and temperature variations, with a significant degree of precision, using few constitutive parameters obtained from simple experimental tests.Postprint (published version

EFFECTS OF LOUVERS SHADING DEVICES ON VISUAL COMFORT AND ENERGY DEMAND OF AN OFFICE BUILDING. A CASE OF STUDY

This paper evaluates the building energy demand and visual comfort of a real case with a glazed façade office building placed in Málaga (Mediterranean city in the south of Spain). South oriented facades receive such a high solar gain that cooling demand cannot be handled by the current HVAC system. As an environmental friendly solution, a shading control strategy based on vertical and horizontal louvers is proposed. The study consists of a comparison between the actual and the refurbished building with shading devices. Daylighting simulation is done with Daysim (Daysim, 2016). A group of offices with south, east and north oriented facades is chosen for the study. Horizontal louvers in the south façade and vertical louvers in the east facade are modelled and simulated. The simulation changes the angle of the louver: 0º (perpendicular to the glazing), -30º, 30º, -60º, 60º. Visual comfort parameters analyzed are: illuminance, daylight autonomy (DA) and useful daylight index (UDI). With respect to the thermal comfort, not only louvers orientation try to provide solar protection for glazed areas in cooling period but also maximize solar gains in heating period. However, an excessive daylight could affect discomfort glare. Shading control strategy must provide the equilibrium between both aspects. Thermal demand is calculated with Trnsys (TRNSYS, 2016).Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Caracterización térmica y evaluación de diversas estrategias de control de condensación de vigas frías activas

La aparición de condensación en la batería de intercambio de calor es uno de los principales problemas a evitar en una viga fría activa (VFA). En climas húmedos, por las infiltraciones de aire exterior, y en espacios de elevada ocupación, las vigas frías pueden presentar el problema de la condensación. Mediante simulaciones térmicas anuales realizadas con Trnsys, el presente artículo demuestra que el sistema de prevención de condensación comúnmente utilizado puede dar lugar a un elevado número de horas de disconfort térmico durante las horas de mayor ocupación del local. En este sentido, se hace indispensable añadir a los modelos térmicos actuales de VFA controles adicionales para evaluar el riesgo de condensación, y llevar a cabo las medidas correctoras necesarias. Así, el objetivo del presente artículo es el de proponer un modelo térmico de VFA que incluya diversas estrategias de prevención de condensación alternativas, que se compararán desde el punto de vista de consumo eléctrico y confort térmicoUniversidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Structural analysis and design of a large inflatable hangar for aircrafts

This is an Accepted Manuscript of an article published by Taylor & Francis Group in Structural Engineering International on 2022, available online at: http://www.tandfonline.com/10.1080/10168664.2022.2064403.Buildair S.A. has designed, manufactured and built an inflatable hangar (called hangar H75) for the aeronautical industry at Jeddah Airport, Kingdom of Saudi Arabia. H75 is the largest air-cell inflated structure ever built in the world, finally erected in July 2019. The structural analysis and design of the main body of the hangar has involved complex structural concepts due to the specificity of the structural elements employed, like membranes and straps that lead to a highly nonlinear mechanical problem, or the treatment of wind over the structure without a defined standard for inflatable structures. In this article, the structural concept and specificities of the structure are presented, as well as the design procedure for H75 based on numerical analysis, to fulfil the design requirements in terms of stress and deformation of the main body.This work was supported by the Ministry of Science, Innovation and Universities [MCIN/AEI/10.13039/501100011033: Grant Number CEX2018-000797-S].Peer ReviewedPostprint (author's final draft

Numerical analysis of the manufacturing processes of a mock-up of the ITER NHF First Wall Panel

The objective of ITER is to build a new Tokamak, with the goal of demonstrating the scientific and technical feasibility of fusion power. The First Wall Panels are the inner component of the reactor, built with different materials that must support high heat flux levels inside the vacuum vessel. The manufacturing processes of the First Wall are a complex procedure including bending, hipping and cutting procedures which, in general, lead to residual stresses and distortions of the fabricated component. In this work, the analysis of the thermo-mechanical response of a simplified prototype of the ITER NHF First Wall Panel is presented from the numerical point of view. The experimental procedure within each phase of the whole manufacturing process is described. Residual stresses and distortions have been measured and analyzed. The numerical simulation of the manufacturing process includes the description of the main hypothesis, the applied loads and the boundary conditions assumed at every stage of the process. Special attention is paid to the simulation of machining and cutting by means of an ad-hoc element deactivation strategy. The numerical results are compared with the experimental evidence to show the prediction capability and the limitations of the proposed numerical model.Peer ReviewedPostprint (author's final draft

Estudio experimental y numérico del comportamiento de un modelo de difusor de aire por desplazamiento acoplado a un suelo frío

En la última década se han realizado muchos trabajos sobre sistemas de refrigeración para grandes superficies usando ventilación por desplazamiento con suelos radiantes (por ejemplo en aeropuertos y estaciones). De especial interés tiene el conocimiento de los campos de velocidad y de temperatura. De forma simplificada, en este estudio se presentan los resultados de un difusor a escala que utiliza ventilación por desplazamiento con suelo radiante frío. Tres son los parámetros que se modifican: el caudal (Q), la diferencia entre la temperatura ambiente y el aire de impulsión (dT1) y la diferencia entre la temperatura del suelo y el aire de impulsión (dT2). Las visualizaciones y mediciones del campo de velocidad del flujo se han realizado para un régimen laminar en estado estacionario. Además, las simulaciones numéricas del campo de temperatura representado en la figura muestran buena concordancia con los datos experimentales. Las zonas de mayor interés en este estudio son: la salida del difusor, la zona cercana al suelo y la zona lejos del difusor sobre el suelo, donde las condiciones de contorno se discuten con detalle. La distancia radial (r) para la que cada difusor afecta a su alrededor en los términos de gradiente de temperatura y de velocidad es un parámetro importante para el diseño de la distribución espacial de estos difusores. Los principales resultados de este trabajo se basan en la relación r = f (Q, dT1, dT2).AIRZON

A Viscoplastic constitutive model with strain rate variables for asphalt mixtures’ numerical simulation

The study and development of recycling techniques for pavements is an increasing activity in engineering nowadays. This research line demands a more realistic characterization of the material properties with the aim of simulate the asphalt mixture’s response placed into a multilayered system over granular bases, under dynamic loads, considering also temperature variation or strenght reduction for cyclic loads. In order to improve the current formulations, a new viscoplastic model has been developed assuming the strain rate dependency of the material’s response observed in the experimental tests. The strain rate variable affects in a significant way the Young modulus and the viscosity parameter of the model. According to these hypothesis constitutive equations have been formulated. The mechanical variables involved have been calibrated according to experimental results, developing new expressions for the strain rate dependent parameters. The new viscoplastic model permit us to characterize the material’s response with a few mechanical values, easily obtained from standard laboratory tests. The results obtained show a good approximation to experimental laboratory curves for different rates of loading and temperatures. The model has been applied to simulate the response of a real flexible pavement structure conformed by two asphalt layers over two granular bases, that’s materials with different constitutive behaviors. Experimental tests in the recycled track have been made obtaining the horizontal strain evolution under dynamic load. Different loading rates and temperatures, as well as cracked and continuum pavement responses have been considered in the study. Strains were measured in the interface between the two asphalt layers and simulated using the here proposed model offering a fairly good approximation of the real response observed in the track, although the degree of variation even in the experimental curves is quite high. The results of this study represent a proper base for further developments in structural analysis of pavement layers, considering more complex phenomena, determinant in the long term material’s response, to develop a numerical tool for pavements’ design and lifetime prediction.Peer Reviewe

Numerical simulation of an inflated structure for an aircraft hangar

BuildAir S.A. has projected and built the H75 hangar in Jeddah (Saudi Arabia) for aircraft storage and maintenance tasks. The hangar is mainly conceived as a set of inflatable tubes where the stiffness is provided by the internal pressure and the stability of the structure is assured by a textile straps network. The structural analysis and design of this structure involves complex structural concepts due to the specificity of the structural elements employed which makes the problem highly non-linear. In this paper, the numerical simulation of the hangar and its structural units is presented as well as some structural and numerical conclusions and/or recommendations coming out from the work developed in the H75 structural analysis. The lack of standards for wind loads over this type of structures lead to oversized pressure distribution over the hangar. To improve the knowledge about the wind loads a coupled fluid-structure interaction is being developed a Panel Method approach for the fluid. Preliminary and promising results for an inflatable hangar are also presented.Postprint (published version

Investigation of EBT3 radiochromic film’s response to humidity

Purpose: The aim of this work is to investigate the effects of immersing EBT3 radiochromic film in water and to evaluate its contribution to the total uncertainty in dose determination. Materials and methods: We used 3 cm 9 3 cm EBT3 radiochromic films irradiated in the range of 0–70 Gy to study the impact of water immersion on the change in net optical density. These films were placed in a water container for a period of 24 h. The net optical density was measured before (0 h) and after of the immersion in water (1, 3, 6, 12, 18, and 24 h). The absorbance spectrum of the EBT3 radiochromic film was measured at 0 h and 24 h after immersion in water. The uncertainty in dose determination due to the effects of keeping the EBT3 radiochromic film submerged in water at 0, 1, and 24 h were recorded in the red, green, and blue channels. Results: We observed an increase in the net optical density as an effect on the film due to its immersion in water. The penetration of the water at the edges of the radiochromic film was observed to be a function of time during which the film remained in the water. On the other hand, the penetration of water at the edges of the film was found to be independent of irradiation dose. Conclusions: EBT3 radiochromic film is found more resistant to water penetration through the edges than its predecessors. However, there is evidence that suggest that liquid water damage the Nylon cover layer of the film by changing its optical properties. Therefore, it is recommended to build a new calibration curve for radiochromic films for a specific situation involving dose measurements in liquid water.UAEMex INN