Arashiro, L.; Montero, N.; Ferrer, I.; Acién, F.; Gómez, C.; Marianna Garfi' Science of the total environment Vol. 622-623, p. 1118-1130 DOI: 10.1016/j.scitotenv.2017.12.051 Data de publicació: 2018-05 Article en revista
The aim of this study was to assess the potential environmental impacts associated with high rate algal ponds (HRAP) systems for wastewater treatment and resource recovery in small communities. To this aim, a Life Cycle Assessment (LCA) was carried out evaluating two alternatives: i) a HRAP system for wastewater treatment where microalgal biomass is valorized for energy recovery (biogas production); ii) a HRAP system for wastewater treatment where microalgal biomass is reused for nutrients recovery (biofertilizer production). Additionally, both alternatives were compared to a typical small-sized activated sludge system. An economic assessment was also performed. The results showed that HRAP system coupled with biogas production appeared to be more environmentally friendly than HRAP system coupled with biofertilizer production in the climate change, ozone layer depletion, photochemical oxidant formation, and fossil depletion impact categories. Different climatic conditions have strongly influenced the results obtained in the eutrophication and metal depletion impact categories. In fact, the HRAP system located where warm temperatures and high solar radiation are predominant (HRAP system coupled with biofertilizer production) showed lower impact in those categories. Additionally, the characteristics (e.g. nutrients and heavy metals concentration) of microalgal biomass recovered from wastewater appeared to be crucial when assessing the potential environmental impacts in the terrestrial acidification, particulate matter formation and toxicity impact categories. In terms of costs, HRAP systems seemed to be more economically feasible when combined with biofertilizer production instead of biogas. On the whole, implementing HRAPs instead of activated sludge systems might increase sustainability and cost-effectiveness of wastewater treatment in small communities, especially if implemented in warm climate regions and coupled with biofertilizer production.
Roca, D.; Lloberas-Valls, O.; Cante, J.C.; Oliver, J. Computer methods in applied mechanics and engineering Vol. 330, p. 415-446 DOI: 10.1016/j.cma.2017.10.025 Data de publicació: 2018-03 Article en revista
A framework, based on an extended Hill–Mandel principle accounting for inertial effects (Multiscale Virtual Work principle), is developed for application to acoustic problems in the context of metamaterials modelling. The classical restrictions in the mean values of the micro-displacement fluctuations and their gradients are then accounted for in a saddle-point formulation of that variational principle in terms of Lagrange functionals. A physical interpretation of the involved Lagrange multipliers can then be readily obtained.
The framework is specifically tailored for modelling the phenomena involved in Locally Resonant Acoustic Metamaterials (LRAM). In this view, several additional hypotheses based on scale separation are used to split the fully coupled micro-macro set of equations into a quasi-static and an inertial system. These are then solved by considering a projection of the microscale equations into their natural modes, which allows for a low-cost computational treatment of the multiscale problem. On this basis, the issue of numerically capturing the local resonance phenomena in a FE
context is addressed. Objectivity of the obtained results in terms of the macroscopic Finite Element (FE) discretization is checked as well as accuracy of the homogenization procedure by comparing with direct numerical simulations (DNS). The appearance of local resonance band-gaps is then modelled for a homogeneous 2D problem and its extension to multi-layered macroscopic material is presented as an initial attempt towards acoustic metamaterial design for tailored band-gap attenuation.
Attenuation due to liquid water is one of the largest uncertainties in radar observations. The effects of attenuation are generally inversely proportional to the wavelength, i.e. observations from X-band radars are more affected by attenuation than those from C- or S-band systems. On the other hand, X-band radars can measure precipitation fields in higher temporal and spatial resolution and are more mobile and easier to install due to smaller antennas. A first algorithm for attenuation correction in single-polarized systems was proposed by Hitschfeld and Bordan (1954) (HB), but it gets unstable in case of small errors (e.g. in the radar calibration) and strong attenuation. Therefore, methods have been developed that restrict attenuation correction to keep the algorithm stable, using e.g. surface echoes (for space-borne radars) and mountain returns (for ground radars) as a final value (FV), or adjustment of the radar constant (C) or the coefficient a. In the absence of mountain returns, measurements from C- or S-band radars can be used to constrain the correction. All these methods are based on the statistical relation between reflectivity and specific attenuation. Another way to correct for attenuation in X-band radar observations is to use additional information from less attenuated radar systems, e.g. the ratio between X-band and C- or S-band radar measurements. Lengfeld et al. (2016) proposed such a method based isotonic regression of the ratio between X- and C-band radar observations along the radar beam. This study presents a comparison of the original HB algorithm and three algorithms based on the statistical relation between reflectivity and specific attenuation as well as two methods implementing additional information of C-band radar measurements. Their performance in two precipitation events (one mainly convective and the other one stratiform) shows that a restriction of the HB is necessary to avoid instabilities. A comparison with vertically pointing micro rain radars (MRR) reveals good performance of two of the methods based in the statistical k-Z-relation: FV and a. The C algorithm seems to be more sensitive to differences in calibration of the two systems and requires additional information from C- or S-band radars. Furthermore, a study of five months of radar observations examines the long-term performance of each algorithm. From this study conclusions can be drawn that using additional information from less attenuated radar systems lead to best results. The two algorithms that use this additional information eliminate the bias caused by attenuation and preserve the agreement with MRR observations.
The interaction of dislocation pile-ups with several tilt grain boundaries (GB) is studied in copper by using a hybrid continuum-atomistic approach. The effects of temperature, pile-up intensity and GB structure on absorption and transmission of slip as a function of local stress state are explored. By considering several high-angle GBs with different misorientation angles, we demonstrate that GB atomic structure primarily defines its ability to accommodate incoming pile-up dislocations, thus limiting the direct transmission of pile-ups through the interface.
Cavaco, E.; Neves, L.; Casas, J. Structure and infrastructure engineering: maintenance, management, life-cycle design and performance Vol. 14, num. 2, p. 1-55 DOI: 10.1080/15732479.2017.1333128 Data de publicació: 2018-02 Article en revista
Management of existing structures has traditionally been based on condition assessment, based on visual inspections, disregarding the susceptibility of different structural types to aging and deterioration. Robustness, as a measure of the effects of unpredictable damage to structural safety can be a complementary information to the results of inspection. Although robustness has mostly been used to evaluate the consequences of extreme events, a similar framework can be used to investigate the result of aging, allowing a better understanding of the potential effects of deterioration and allowing a better allocation of available maintenance funding. In this work, a probabilistic structural robustness indicator is used to quantify the susceptibility of structures to corrosion. The methodology is exemplified through a case study comprising an existing reinforced concrete bridge deck, heavily damaged due to reinforcement corrosion, and finally demolished due to safety concerns. Robustness measures the bridge deck safety tolerance to reinforcement corrosion. The principal effects of corrosion, including loss of area and bond between concrete and steel are modelled using a non-linear finite-element model, coupled with a Response Surface Method to compute the bridge reliability as a function of the corrosion level, and finally used to assess robustness. Results show that the redundancy of the bridge allows significant redistribution of loads between elements with different corrosion levels. As a result, the bridge presents significant robustness and tolerance to reinforcement corrosion.
In this paper we analyse the ejection-collision (EC) orbits of the planar restricted three body problem. Being µ¿¿¿(0, 0.5] the mass parameter, and taking the big (small) primary with mass (µ), an EC orbit will be an orbit that ejects from the big primary, does an excursion and collides with it. As it is well known, for any value of the mass parameter µ¿¿¿(0, 0.5] and sufficiently restricted Hill regions (that is, for big enough values of the Jacobi constant C), there are exactly four EC orbits. We check their existence and extend numerically these four orbits for µ¿¿¿(0, 0.5] and for smaller values of the Jacobi constant. We introduce the concept of n-ejection-collision orbits (n-EC orbits) and we explore them numerically for µ¿¿¿(0, 0.5] and values of the Jacobi constant such that the Hill bounded possible region of motion contains the big primary and does not contain the small one. We study the cases 1¿=¿n¿=¿10 and we analyse the continuation of families of such n-EC orbits, varying the energy, as well as the bifurcations that appear.
For complex geometries, the definition of the subsystems is not a straightforward task. We present here a subsystem identification method based on the direct transfer matrix, which represents the first-order paths. The key ingredient is a cluster analysis of the rows of the powers of the transfer matrix. These powers represent high-order paths in the system and are more affected than low-order paths by damping.
Once subsystems are identified, the proposed approach also provides a quantification of the degree of coupling between subsystems. This information is relevant to decide whether a subsystem may be analysed in a computer model or measured in the laboratory independently of the rest or subsystems or not. The two features (subsystem identification and quantification of the degree of coupling) are illustrated by means of numerical examples: plates coupled by means of springs and rooms connected by means of a cavity.
This volume addresses challenges and solutions in transport and mobility of people and goods with respect to environment, safety, security and socio–economics issues, exploring advanced computational research work and the latest innovations in transport. This book brings together lectures presented at the ECCOMAS Thematic CM3 Conference on Transport held in Jyväskylä, Finland, 25-27 May 2015. It is divided into three parts, I: Reviews and Perspective, II: Computational Methods and Models and III: Translational Research. Each of these parts consists of contributions that present solutions to many transport challenges in this complex, rapidly changing subject. The work contains the latest achievements of European research and technological developments needed for the next decade through computational results of scientific and technical experts who have made essential contributions in transport efficiency in Europe. The material presented here is the state of the art in Transport Modeling, Simulation and Optimization in the fields of Aeronautics, Automotive, Logistics, Maritime and Rails. Furthermore, this volume also answers the question how to apply Computational Research in Transport in order to provide innovative solutions to Green Transportation challenges of identified in the ambitious Horizon 2020 program. This book is intended for students, researchers, engineers and practitioners that are computationally involved in the deployment of Intelligent Transport Systems (ITS) in the areas of optimal use of road, traffic and travel data, traffic and freight management ITS services, road safety and security, sea traffic management, etc.
We present a conceptual and numerical approach to model processes in the Earth's interior that involve multiple phases that simultaneously interact thermally, mechanically and chemically. The approach is truly multiphase in the sense that each dynamic phase is explicitly modelled with an individual set of mass, momentum, energy and chemical mass balance equations coupled via interfacial interaction terms. It is also truly multi-component in the sense that the compositions of the system and its constituent thermodynamic phases are expressed by a full set of fundamental chemical components (e.g. SiO$_2$, Al$_2$O$_3$, MgO, etc) rather than proxies. In contrast to previous approaches these chemical components evolve, react with, and partition into, different phases with different physical properties according to an internally-consistent thermodynamic model. This enables a thermodynamically-consistent coupling of the governing set of balance equations. Interfacial processes such as surface tensions and/or surface energy contributions to the dynamics and energetics of the system are also taken into account. The model presented here describes the evolution of systems governed by Multi-Phase Multi-Component Reactive Transport (MPMCRT) based on Ensemble Averaging and Classical Irreversible Thermodynamics principles. This novel approach provides a flexible platform to study the dynamics and non-linear feedbacks occurring within various natural systems at different scales. This notably includes major-and trace-element transport, diffusion-controlled trace-element re-equilibration or rheological changes associated with melt generation and migration in the Earth's mantle.
Rambo, D.; Blanco, A.; de Figueiredo, A.D.; dos Santos , E.; Toledo Filho, R.; Martins Gomes , O. Construction & building materials Vol. 158, p. 443-453 DOI: 10.1016/j.conbuildmat.2017.10.046 Data de publicació: 2018-01 Article en revista
This paper presents an experimental investigation on the applicability of the Barcelona (BCN) test to evaluate the mechanical properties of a macro-synthetic fiber reinforced concrete (MSFRC) submitted to high temperature environments (up to 600 °C). BCN tests demonstrated that the MSFRC gradually loses tensile strength an energy consumption density with increasing temperature. Temperatures of 400 °C and 570 °C shown to be critical to the MSFRC mechanical performance. The residual mechanical behavior of the macro-synthetic fibers was not affected by the temperature up to 100 °C. For higher temperatures, the reinforcement showed that may lose part of its crystallinity compromising the MSFRC post-cracking performance. The constitutive model used to determine the stress-strain curves of the MSFRC was capable to reproduce the composite behavior after the event of a fire.
Urqueta, H.; Jódar, J.; Herrera Lameli, Ch.; Wilke, H.; Medina, A.; Urrutia, J.; Custodio, E.; Rodríguez, J. Science of the total environment Vol. 612, p. 1234-1248 DOI: 10.1016/j.scitotenv.2017.08.305 Data de publicació: 2018-01 Article en revista
Land surface temperature (LST) seems to be related to the temperature of shallow aquifers and the unsaturated zone thickness (¿ Zuz). That relationship is valid when the study area fulfils certain characteristics: a) there should be no downward moisture fluxes in an unsaturated zone, b) the soil composition in terms of both, the different horizon materials and their corresponding thermal and hydraulic properties, must be as homogeneous and isotropic as possible, c) flat and regular topography, and d) steady state groundwater temperature with a spatially homogeneous temperature distribution. A night time Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) image and temperature field measurements are used to test the validity of the relationship between LST and ¿ Zuz at the Pampa del Tamarugal, which is located in the Atacama Desert (Chile) and meets the above required conditions. The results indicate that there is a relation between the land surface temperature and the unsaturated zone thickness in the study area. Moreover, the field measurements of soil temperature indicate that shallow aquifers dampen both the daily and the seasonal amplitude of the temperature oscillation generated by the local climate conditions. Despite empirically observing the relationship between the LST and ¿ Zuz in the study zone, such a relationship cannot be applied to directly estimate ¿ Zuz using temperatures from nighttime thermal satellite images. To this end, it is necessary to consider the soil thermal properties, the soil surface roughness and the unseen water and moisture fluxes (e.g., capillarity and evaporation) that typically occur in the subsurface.
Boano, F.; Rizzo, A.; Samsó, R.; Garcia, J.; Revelli, R.; Ridolfi, L. Science of the total environment Vol. 612, p. 1480-1487 DOI: 10.1016/j.scitotenv.2017.08.265 Data de publicació: 2018-01 Article en revista
The average organic and hydraulic loads that Constructed Wetlands (CWs) receive are key parameters for their adequate long-term functioning. However, over their lifespan they will inevitably be subject to either episodic or sustained overloadings. Despite that the consequences of sustained overloading are well known (e.g., clogging), the threshold of overloads that these systems can tolerate is difficult to determine. Moreover, the mechanisms that might sustain the buffering capacity (i.e., the reduction of peaks in nutrient load) during overloads are not well understood. The aim of this work is to evaluate the effect of sudden but sustained organic and hydraulic overloads on the general functioning of CWs. To that end, the mathematical model BIO_PORE was used to simulate five different scenarios, based on the features and operation conditions of a pilot CW system: a control simulation representing the average loads; 2 simulations representing +10% and +30% sustained organic overloads; one simulation representing a sustained +30% hydraulic overload; and one simulation with sustained organic and hydraulic overloads of +15% each. Different model outputs (e.g., total bacterial biomass and its spatial distribution, effluent concentrations) were compared among different simulations to evaluate the effects of such operation changes. Results reveal that overloads determine a temporary decrease in removal efficiency before microbial biomass adapts to the new conditions and COD removal efficiency is recovered. Increasing organic overloads cause stronger temporary decreases in COD removal efficiency compared to increasing hydraulic loads. The pace at which clogging develops increases by 10% for each 10% increase on the organic load.
The role of edge dislocations as sinks for small radiation induced defects in bcc-Fe is investigated by means of atomistic computer simulation. In this work we investigate by Molecular Statics (T = 0K) the interaction between an immobile dislocation line and defect clusters of small sizes invisible experimentally. The study highlights in particular the anisotropy of the interaction and distinguishes between absorbed and trapped defects. When the considered defect intersects the dislocation glide plane and the distance from the dislocation line to the defect is on the range between 2 nm and 4 nm, either total or partial absorption of the cluster takes place leading to the formation of jogs. Residual defects produced during partial absorption pin the dislocation. By the calculation of stress-strain curves we have assessed the strength of those residues as obstacles for the motion of the dislocation, which is reflected on the unpinning stresses and the binding energies obtained. When the defect is outside this range, but on planes close to the dislocation glide plane, instead of absorption we have observed a capture process. Finally, with a view to introducing explicitly in kinetic Monte Carlo models a sink with the shape of a dislocation line, we have summarized our findings on a table presenting the most relevant parameters, which define the interaction of the dislocation with the defects considered.
A diffusion-reaction model for the carbonation process of oilwell cement exposed to carbonated brine under CO2 geological storage conditions is presented. The formulation consists of two main diffusion/reaction field equations for the concentrations of aqueous calcium and carbon species in the pore solution of the hardened cement paste, complemented by two diffusion-only field equations for chloride and alkalis concentrations, and by a number of chemical kinetics and chemical equilibrium equations. The volume fraction distribution of the solid constituents of the hardened cement paste and the reaction products evolve with the progress of the reaction, determining the diffusivity properties of the material. The model is used to simulate experimental tests performed by Duguid and Scherer (2010), leading to promising results indicating that the fundamental aspects of the phenomenon are captured.
Sierra, J.P.; Garcia, M.; Gracia, V.; Sanchez-Arcilla, A. Proceedings of the Institution of Civil Engineers. Maritime engineering Vol. 170, num. 2, p. 55-66 DOI: 10.1680/jmaen.2016.23 Data de publicació: 2017-12-22 Article en revista
Harbour operability may be hampered by climate change. Green solutions can be used to provide extra flexibility with respect to present grey infrastructure to adapt to, and mitigate, such functional disruptions with affordable costs. This paper assesses the performance of a green solution (a seagrass meadow) by assessing its effectiveness through numerical modelling. The analysis is carried out at two harbours that, under the present climate, are prone to wave agitation and overtopping problems. The efficiencies of different seagrass layouts are tested at both sites, by comparing the relevant hydrodynamic parameters. It is concluded that, for moderate sea level rise (SLR) rates, illustrated by the central trend of a medium scenario from the Intergovernmental Panel on Climate Change, the use of seagrass meadows would be effective enough to attenuate the impact of SLR on breakwater overtopping. In addition, the use of such measures could attenuate the increases in port agitation due to changes in wave direction caused by climate change. Nevertheless, the complexity of the interactions between hydrodynamics and seagrass would require periodic monitoring and re-evaluation to maintain acceptable risk levels, especially in case of extreme scenarios.
Life cycle assessment (LCA) is recognised as a powerful technique to determine the environmental impact component of sustainability assessments of structures in civil engineering projects at the time of design. This paper explains the principal parts and stages in an LCA methodology and demonstrates the approach using the examples of two conventional retaining wall types (gravity and cantilever type) and two mechanically stabilised earth (MSE) wall solutions using steel and polymeric soil reinforcement. The analyses include structures built to four different heights. The LCA methodology was able to quantitatively distinguish between the component environmental impacts of different wall solutions and thus provide a practical numerical score-based tool for designers to choose between candidate solutions. The MSE wall solutions resulted in lower environmental impacts than gravity and cantilever wall solutions as measured by global warming potential, cumulative energy demand, six major midpoint environmental indicator categories, three endpoint damage categories and in terms of overall endpoint scores. The target audiences for this paper are geotechnical and structural engineers engaged in the design of earth retaining
wall structures but are less familiar with recent developments in LCA and how LCA can be linked to the design of these systems.
Corada, M.; Candela, L.; Torres-Fuentes, N.; Pintado-Herrera, M.; Paniw, M.; González-Mazo, E. Science of the total environment Vol. 605-606, p. 770-783 DOI: 10.1016/j.scitotenv.2017.06.049 Data de publicació: 2017-12 Article en revista
This study is focused on the Guadalete River basin (SW, Spain), where extreme weather conditions have become common, with and alternation between periods of drought and extreme rainfall events. Combined sewer overflows (CSOs) occur when heavy rainfall events exceed the capacity of the wastewater treatment plants (WWTP), as well as pollution episodes in parts of the basin due to uncontrolled sewage spills and the use of reclaimed water and sludge from the local WWTP. The sampling was carried out along two seasons and three campaigns during dry (March 2007) and extreme rainfall (April and December 2010) in the Guadalete River, alluvial aquifer and Jerez de la Frontera aquifer. Results showed minimum concentrations for synthetic surfactants in groundwater (< 37.4 µg·L- 1) during the first campaign (dry weather conditions), whereas groundwater contaminants increased in December 2010 as the heavy rainfall caused the river to overflow. In surface water, surfactant concentrations showed similar trends to groundwater observations. In addition to surfactants, pharmaceuticals and personal care products (PPCPs) were analyzed in the third campaign, 22 of which were detected in surface waters. Two fragrances (OTNE and galaxolide) and one analgesic/anti-inflammatory (ibuprofen) were the most abundant PPCPs (up to 6540, 2748 and 1747 ng·L- 1, respectively). Regarding groundwater, most PPCPs were detected in Jerez de la Frontera aquifer, where a synthetic fragrance (OTNE) was predominant (up to 1285 ng·L- 1).
Mendez, C.; Podestá, J.; Lloberas-Valls, O.; Toro, S.; Huespe, A.; Oliver, J. International journal for numerical methods in engineering Vol. 112, num. 10, p. 1353-1380 DOI: 10.1002/nme.5560 Data de publicació: 2017-12 Article en revista
A topology optimization technique based on the topological derivative and the level set function is utilized to design/synthesize the micro-structure of a pentamode material for an acoustic cloaking device. The technique provides a micro-structure consisting of a honeycomb lattice composed of needle-like and joint members. The resulting metamaterial shows a highly anisotropic elastic response with effective properties displaying a ratio between bulk and shear moduli of almost 3 orders of magnitude. Furthermore, in accordance with previous works in the literature, it can be asserted that this kind of micro-structure can be realistically fabricated. The adoption of a topology optimization technique as a tool for the inverse design of metamaterials with applications to acoustic cloaking problems is one contribution of this paper. However, the most important achievement refers to the analysis and discussion revealing the key role of the external shape of the prescribed domain where the optimization problem is posed. The efficiency of the designed micro-structure is measured by comparing the scattering wave fields generated by acoustic plane waves impinging on bare and cloaked bodies.
The most singular characteristic of pervious concrete is its interconnected porosity that allows water to flow through at high rates. The objective of this paper is to develop and validate an advanced DEM-CFD model to assess the permeability of pervious concrete numerically, taking into account the influence of the composition and of the compaction process. An extensive experimental program with 1 aggregate grading size, 4 paste contents and 3 degrees of compaction was conducted to validate the numerical approach. Results show that the DEM-CFD model is capable of predicting the permeability depending on the variables considered here. Moreover, flow parameters derived from the numerical simulations help understand the experimental results. The study confirms that, instead of relying on trial and error experiments, it is possible to use advanced numerical models to accelerate the definition of mixes and the production process, reducing the time, efforts and costs required.
The search for environmentally neutral alternative fuels had revived the interest for microalgae-bacteria wastewater treatment systems. The potential achieving of bioproducts from microalgae biomass has also greatly contributed. The reactions that occur in these systems are complex, and the degree of scientific knowledge is still scarce compared to that of conventional bacteria wastewater treatments. Mathematical models offer a great opportunity to study the simultaneous effect of the multiple factors affecting microalgae and bacteria, thus allowing for the prediction of final biomass production, and contributing to the system design optimization in terms of operation and control. During the last decades, numerous models describing microalgae growth have been proposed. However, a lower number of integral models considering microalgae as well as bacteria is available. In this paper, the evolution of microalgae models from simple steady-state models (usually dependent on one factor) to more complex dynamic models (with two or more factors) has been revised. A summary of integrated microalgae-bacteria models has been reviewed, outlining their main features and presenting their processes and value parameters. Eventually, a critical discussion on integrated models has been put forward.
An integral mechanistic model describing the complex interactions in mixed algal-bacterial systems was developed. The model includes crucial physical, chemical and biokinetic processes of microalgae as well as bacteria in wastewater. Carbon-limited microalgae and autotrophic bacteria growth, light attenuation, photorespiration, temperature and pH dependency are some of the new features included. The model named BIO_ALGAE was built using the general formulation and structure of activated sludge models (ASM), and it was implemented in COMSOL Multiphysics™ platform. Calibration and validation were conducted with experimental data from two identical pilot HRAPs receiving real wastewater. The model was able to simulate the dynamics of different components in the ponds, and to predict the relative proportion of microalgae (58–68% in average of total suspended solids (TSS) and bacteria (30–20% in average of TSS). Microalgae growth resulted strongly influenced by the light factor fL(I), decreasing microalgae concentrations from 40 to 60%. Furthermore, reducing the influent organic matter concentration of 50% and 70%, model predictions indicated that microalgae production increased from (8.7 g TSS m- 2d- 1 to 13.5 g TSS m- 2d- 1) due to the new distribution of particulate components. The proposed model could be an efficient tool for industry to predict the production of microalgae, as well as to design and optimize HRAPs.
Nadal, A.; Alamús, R.; Pipia, L.; Ruiz , A.; Corbera, J.; Cuerva, E.; Rieradevall, J.; Josa, A. Science of the total environment Vol. 601-602, p. 1-15 DOI: 10.1016/j.scitotenv.2017.03.214 Data de publicació: 2017-12-01 Article en revista
The integration of rooftop greenhouses (RTGs) in urban buildings is a practice that is becoming increasingly important in the world for their contribution to food security and sustainable development. However, the supply of tools and procedures to facilitate their implementation at the city scale is limited and laborious. This work aims to develop a specific and automated methodology for identifying the feasibility of implementation of rooftop greenhouses in non-residential urban areas, using airborne sensors. The use of Light Detection and Ranging (LIDAR) and Long Wave Infrared (LWIR) data and the Leica ALS50-II and TASI-600 sensors allow for the identification of some building roof parameters (area, slope, materials, and solar radiation) to determine the potential for constructing a RTG. This development represents an improvement in time and accuracy with respect to previous methodology, where all the relevant information must be acquired manually.
The methodology has been applied and validated in a case study corresponding to a non-residential urban area in the industrial municipality of Rubí, Barcelona (Spain). Based on this practical application, an area of 36,312 m2 out of a total area of 1,243,540 m2 of roofs with ideal characteristics for the construction of RTGs was identified. This area can produce approximately 600 tons of tomatoes per year, which represents the average yearly consumption for about 50% of Rubí total population.
The use of this methodology also facilitates the decision making process in urban agriculture, allowing a quick identification of optimal surfaces for the future implementation of urban agriculture in housing. It also opens new avenues for the use of airborne technology in environmental topics in cities.
The Discrete Element Method (DEM) has been used for modelling continua, like concrete or rocks. However, it requires a big calibration effort, even to capture just the linear elastic behavior of a continuum modelled via the classical force-displacement relationships at the contact interfaces between particles. In this work we propose a new way for computing the contact forces between discrete particles. The newly proposed forces take into account the surroundings of the contact, not just the contact itself. This brings in the missing terms that provide an accurate approximation to an elastic continuum, and avoids calibration of the DEM parameters for the purely linear elastic range.
The assessment of historical structures requires appropriate knowledge of the behaviour of the investigated materials. Concerning masonry, its mechanical characterisation is a challenging task, since its composite nature requires the careful evaluation of the behaviour of its material components. In particular, the experimental assessment of the strength of existing mortar in historical structures still encounters several difficulties. This study investigates a novel Minor Destructive Testing (MDT) technique virtually equivalent to the vane test used for soils. The instrumentation, called herein Torque Penetrometric Test (TPT), is composed of a steel nail with four protruding teeth and a torque wrench. The test consists in inserting the toothed nail into a mortar joint and then applying a torque by means of a dynamometric key, until reaching the failure of the material. This work presents a novel interpretation theory based on basic concepts of fracture mechanics and applied to the micro-mechanical analysis of the stress state induced by the instrument on the investigated mortar. The proposed interpretative theory is validated through the execution of experimental tests in the laboratory and in a historical masonry building. The test proves to be effective for a quick in-situ MDT evaluation of the strength of existing mortars.
Licensee MDPI, Basel, Switzerland. This article presents a methodology to process information from a Terrestrial Laser Scanner (TLS) from three dimensions (3D) to two dimensions (2D), and to two dimensions with a color value (2.5D), as a tool to document and analyze heritage buildings. Principally focused on the loss of material in stone, this study aims at creating an evaluation method for loss control, taking into account the state of conservation of a building in terms of restoration, from studying the pathologies, to their identification and delimitation. A case study on the Cathedral of the Seu Vella de Lleida was completed, examining the details of the stone surfaces. This cathedral was affected by military use, periods of abandonment, and periodic restorations.
Hydrogeological models of mountain regions present the opportunity to understand the role of geological factors on groundwater resources. The effects of sedimentary facies and fracture distribution on groundwater flow and resource exploitation are studied in the ancient fan delta of Sant Llorenç de Munt (central Catalonia, Spain) by integrating geological field observations (using sequence stratigraphy methods) and hydrogeological data (pumping tests, hydrochemistry and environmental isotopes). A comprehensive analysis of data portrays the massif as a single unit, constituted by different compartments determined by specific layers and sets of fractures. Two distinct flow systems—local and regional—are identified based on pumping test analysis as well as hydrochemical and isotopic data. Drawdown curves derived from pumping tests indicate that the behavior of the saturated layers, whose main porosity is given by the fracture network, corresponds to a confined aquifer. Pumping tests also reflect a double porosity within the system and the occurrence of impervious boundaries that support a compartmentalized model for the whole aquifer system. Hydrochemical data and associated spatial evolution show the result of water–rock interaction along the flow lines. Concentration of magnesium, derived from dolomite dissolution, is a tracer of the flow-path along distinct stratigraphic units. Water stable isotopes indicate that evaporation (near a 5% loss) occurs in a thick unsaturated zone within the massif before infiltration reaches the water table. The hydrogeological analysis of this outcropping system provides a methodology for the conceptualization of groundwater flow in similar buried systems where logging and hydrogeological information are scarce.
The final publication is available at Springer via http://dx.doi.org/10.1007/s10040-017-1618-9
Passos, F.; Gutierrez, R.; Uggetti, E.; Marianna Garfi'; Garcia, J.; Ferrer, I. Algal research: biomass, biofuels and bioproducts Vol. 28, p. 235-243 DOI: 10.1016/j.algal.2017.11.006 Data de publicació: 2017-12 Article en revista
The aim of this study was to assess the energy balance of a hypothetical microalgae-based wastewater treatment plant (10,000 PE) located in the Mediterranean Region, where harvested microalgal biomass and primary sludge would be co-digested to produce biogas and bioenergy. The assessment was based on experimental results obtained over one year in pilot high rate algal ponds followed by anaerobic digesters for biogas production from harvested microalgal biomass and primary sludge. The energy balance compared four scenarios: 1) anaerobic co-digestion of microalgal biomass and primary sludge, and cogeneration from biogas in a combined with heat and power (CHP) unit; 2) co-digestion with thermal pretreatment of microalgal biomass, and cogeneration from biogas in a CHP unit; 3) co-digestion and heat generation from biogas in a boiler; and 4) co-digestion with thermal pretreatment of microalgal biomass, and heat generation from biogas in a boiler. According to the results, when biogas was used to cogenerate electricity and heat (scenarios 1 and 2), the electricity balance was always positive, and the best results were obtained with pretreated microalgal biomass (scenario 2). Similarly, the heat balance was always positive when biomass was thermally pretreated (scenario 2). On the other hand, when biogas was only used to produce heat (scenarios 3 and 4), heat requirements were covered during the whole year. The sensibility analysis of the scenarios with pretreatment (2 and 4) confirmed that the microalgae-based WWTP would be energy neutral or even net energy producer.
Chiumenti, M.; Neiva, E.; Salsi, E.; Cervera, M.; Badia, S.; Moya, J.; Chen, Z.; Lee, C.; Davies, C. Additive Manufacturing Vol. 18, p. 171-185 DOI: 10.1016/j.addma.2017.09.002 Data de publicació: 2017-12 Article en revista
In this work a finite-element framework for the numerical simulation of the heat transfer analysis of additive manufacturing processes by powder-bed technologies, such as Selective Laser Melting, is presented. These kind of technologies allow for a layer-by-layer metal deposition process to cost-effectively create, directly from a CAD model, complex functional parts such as turbine blades, fuel injectors, heat exchangers, medical implants, among others. The numerical model proposed accounts for different heat dissipation mechanisms through the surrounding environment and is supplemented by a finite-element activation strategy, based on the born-dead elements technique, to follow the growth of the geometry driven by the metal deposition process, in such a way that the same scanning pattern sent to the numerical control system of the AM machine is used. An experimental campaign has been carried out at the Monash Centre for Additive Manufacturing using an EOSINT-M280 machine where it was possible to fabricate different benchmark geometries, as well as to record the temperature measurements at different thermocouple locations. The experiment consisted in the simultaneous printing of two walls with a total deposition volume of 107 cm3 in 992 layers and about 33,500 s build time. A large number of numerical simulations have been carried out to calibrate the thermal FE framework in terms of the thermophysical properties of both solid and powder materials and suitable boundary conditions. Furthermore, the large size of the experiment motivated the investigation of two different model reduction strategies: exclusion of the powder-bed from the computational domain and simplified scanning strategies. All these methods are analysed in terms of accuracy, computational effort and suitable applications.
Botella, R.; Perez, F.; Riahi, E.; López-Montero, T.; Miro, R.; Martinez, A. Construction & building materials Vol. 156, p. 809-818 DOI: 10.1016/j.conbuildmat.2017.09.036 Data de publicació: 2017-12 Article en revista
This paper's objective is to evaluate the reversible phenomena that take place when asphalt materials are subjected to cyclic loads, i.e., self-heating and thixotropy. A strain sweep test was adapted to capture the stiffness variation of binders with the change in strain amplitude. The evolution of the internal temperature of the binder during the test was measured. Results show that the temperature can increase very significantly during cyclic testing and can account for a great part of all stiffness reduction captured during the test at different strain amplitudes. These results led to the conclusion that internal heating should be very important in asphalt mixtures as well. For that reason two types of time sweep tests were performed on the same mixture, with the introduction of rest periods in one of them long enough to let the inside temperature of the material lower after cycling. The results showed that the specimen that was allowed to cool down did not experience any loss of stiffness, while the specimen submitted to the conventional time sweep test failed in a few cycles. These results show the importance of the sequencing of loading and discourage the application of the Miner's law to estimate pavement life.
Ortiz, J. A.; de la Fuente, A.; Mena Sebastia, F.; Segura, I.; Aguado, A. Construction & building materials Vol. 156, p. 230-241 DOI: 10.1016/j.conbuildmat.2017.08.188 Data de publicació: 2017-12 Article en revista
This research focuses on designing and characterizing steel-fibre-reinforced self-compacting concrete using recycled aggregates (SFR-SCC-RA). Six different concrete dosages have been designed, and two extensive mechanical and physical characterization programs have been conducted. The first program was developed in a concrete production plant to verify the compatibility of the new material with the existing production systems. The second program was developed in a laboratory under controlled temperature and humidity conditions. Although compressive strengths greater than 25 N/mm2 have been reached (which allows the material to be classified as structural), the design in this initial phase is oriented to applications with limited mechanical requirements (e.g., foundations, earth retaining walls and pavements, in which design forces are moderate).
Actualmente es frecuente en diversos ámbitos profesionales y educativos el debate sobre las
condiciones físicas de los centros escolares y sobre todo de los patios. La necesaria revisión y actualización de aspectos estrictamente pedagógicos y de las condiciones espaciales en su configuración formal y funcional, convergen en procesos de reflexión para el cambio y la innovación. Las diagnosis desde diversos enfoques coinciden en identificar, sugerir, reclamar y proponer acciones y proyectos para la mejora de los espacios escolares, dada su vital importancia en la educación y socialización tanto en la escuela como en la ciudad. Proponemos una reflexión para promover el patio escolar como proyecto de arquitectura y de espacio colectivo urbano: por un lado destacando la vigencia y actualidad de las metodologías de enseñanza basadas en la estrecha relación entre espacios interiores y exteriores, en sus planteamientos pedagógicos. Y por otro, haciendo un repaso a la coyuntura actual que se está dando en Barcelona, y en Cataluña en general, donde se están llevando a cabo iniciativas de intervención y mejora en los patios y entornos escolares, asociadas a un cambio de modelo educativo y de ciudad en curso. Del proceso mostramos tres casos de intervención en tres centros, proyectos que se caracterizan por ser estratégicos, participativos, de baja inversión y de alto impacto en la mejora de la habitabilidad del patio escolar y la ciudad.
Los métodos numéricos son decisivos en la ingeniería para la conservación de estructuras de mampostería existentes y el diseño de estructuras nuevas. Entre ellos, los métodos ma-cro-mecánicos de elementos finitos, basados en el concepto de fisuras distribuidas, son habitualmente los preferidos como opción asequible para el análisis de grandes estructuras de mampostería. Sin embargo, suelen resultar en a una representación poco realista del daño, distribuido en grandes áreas de la estructura, lo que impide la correcta interpretación del patrón de daño. Además, esta metodología presenta una patología más crítica, la de-pendencia de la malla, que influye notablemente en las predicciones de seguridad y estabi-lidad.Para superar estas limitaciones, esta tesis propone una nueva herramienta numérica basada en el enriquecimiento del clásico enfoque de fisuras distribuidas con un algoritmo de tra-zado local. El objetivo de este modelo de daño localizado es el análisis no-lineal de las estructuras de mampostería de manera realista y eficiente con una representación mejora-da de fisuras.El comportamiento no lineal de la mampostería se simula a través de la adopción de un modelo de mecánica de daño continuo con dos índices de daño, permitiendo la diferen-ciación entre las respuestas mecánicas de tensión y compresión de la mampostería. En este contexto, se propone e implementa una nueva formulación explícita para la evolución de deformaciones irreversibles. Se derivan dos nuevas expresiones para la regularización del ablandamiento de tracción y compresión según el ancho de banda de la fisura, garantizan-do la objetividad del modelo de daño al respecto del tamaño de la malla.La simulación del comportamiento estructural de las estructuras de mampostería en condi-ciones de carga y contorno generales precisa de algunos desarrollos en el contexto de los algoritmos locales de trazado. Con este objetivo, se presenta la mejora de los algoritmos locales de trazado con nuevos procedimientos que posibilitan la simulación de fisuración múltiple, arbitraria e secante bajo cargas monótonas y cíclicas. Además, se investiga el efecto de diferentes criterios de propagación de fisuras y se aborda la selección entre más de un plano de falla posible.El modelo de daño localizado propuesto se valida mediante la simulación de una serie de ejemplos estructurales. Éstos van desde pruebas a pequeña escala en probetas de hormi-gón, con pocas fisuras dominantes, hasta estructuras de mampostería de mediana y gran escala con fisuración múltiple de tracción, de cortante y de flexión. Los análisis se compa-ran con los resultados analíticos, experimentales y numéricos obtenidos con métodos al-ternativos disponibles en la literatura. El modelo de daño localizado mejora en gran medi-da la independencia de la malla del clásico método de fisuras distribuidas y reproduce patrones de daño y mecanismos de colapso de una manera eficiente y realista.Palabras clave: Mampostería, Materiales cuasi-frágiles, Método de elementos finitos, Lo-calización de deformaciones, Algoritmo de trazado, Mecánica de daño continuo, Defor-maciones irreversibles, Fisuración de tracción/cortante/flexión, Fisuras secantes, Depen-dencia de la malla, carga cíclica de cortante
El Laboratorio de Caminos de la Universidad Politécnica de Cataluña (Barcelona, España) ha desarrollado un nuevo ensayo a tracción directa, ensayo Fénix, que permite determinar la rigidez, energía de fractura y ductilidad de las mezclas bituminosas de forma rápida y sencilla. El ensayo ha sido aplicado a la caracterización de diferentes tipos de mezclas, en un amplio rango de temperaturas, lo que ha permitido establecer unos criterios de diseño.
En el trabajo que aquí se presenta, se recogen los resultados de la aplicación del ensayo Fénix a una serie de mezclas recicladas con diferentes contenidos de material bituminoso fresado del pavimento (RAP), 20, 40 y 60%; y con la utilización de un agente rejuvenecedor en el caso del mayor contenido de RAP. Todos estos resultados han sido comparados con los de una mezcla convencional, sin RAP, de similar granulometría, usada como referencia.
El Laboratorio de Caminos de la Universidad Politécnica de Cataluña (Barcelona, España) ha desarrollado un nuevo ensayo a tracción directa, ensayo Fénix, que permite determinar la rigidez, energía de fractura y ductilidad de las mezclas bituminosas de forma rápida y sencilla. El ensayo ha sido aplicado a la caracterización de diferentes tipos de mezclas, en un amplio rango de temperaturas, lo que ha permitido establecer unos criterios de diseño. En el presente trabajo se analiza la aplicación del ensayo Fénix en mezclas recicladas en frío, mezclas recicladas templadas con emulsión y mezclas recicladas en caliente con betunes de alta penetración, todas ellas compactadas con equipo giratorio. Las ventajas medioambientales de las mezclas templadas residen en el ahorro energético al bajar la temperatura de calentamiento de sus componentes y en la reducción de emisiones de gases efecto invernadero. En este estudio se ha considerado una tasa de reciclado del 100%, con lo cual se economiza también en el consumo de recursos naturales. El objeto de este estudio ha sido valorar la posibilidad técnica de fabricar mezclas templadas recicladas, persiguiendo las mismas prestaciones mecánicas que tiene una mezcla en caliente y maximizando el contenido de material fresado a reciclar.
Durante su vida útil los materiales que componen los firmes están expuestos a las cargas del tráfico, que tienen un marcado carácter cíclico. Las mezclas bituminosas se caracterizan por presentar un comportamiento muy complejo cuando se someten a este tipo de cargas debido a la coexistencia de fenómenos que pueden cambiar las propiedades de estos materiales de manera reversible e irreversible. El hecho de que se produzcan cambios reversibles e irreversibles en las propiedades de las mezclas, otorga especial importancia a la secuencia en que las cargas actúen sobre el firme, o dicho de otra manera, a los periodos de reposos que se intercalen entre las cargas cíclicas. El objetivo de este trabajo es evaluar los fenómenos reversibles que tienen lugar cuando se aplican cargas cíclicas en los materiales bituminosos y como esta reversibilidad se ve afectada con la introducción de periodos de reposos en ensayos cíclicos. Se ha adaptado el ensayo de barrido de deformaciones conocido como EBADE para diferenciar fenómenos reversibles de irreversibles y se ha monitorizado la evolución de la temperatura interna del material durante este ensayo. Se ha demostrado que debido al cambio de la temperatura, los periodos de reposo afectan directamente a la vida a fatiga del material.
Los pavimentos asfálticos durante su vida de servicio se ven expuestos a los esfuerzos provocados por el tráfico, además de a las condiciones climáticas, lo cual provoca una reducción de su vida útil. Por este motivo, resulta interesante el uso de nanomateriales que mejoren el comportamiento de las mezclas asfálticas. El objetivo de este trabajo es estudiar la influencia del uso de un ligante modificado con nanoarcilla, tipo bentonita hidrofílica, en la resistencia a tracción indirecta de una mezcla asfáltica tipo AC14, así como su efecto frente al envejecimiento y al daño por humedad de la mezcla. Para ello, se ha utilizado un ligante 35/50 modificado mediante la dispersión mecánica de un 4% de nanoarcilla sobre el peso de ligante total.
Para estudiar el efecto del envejecimiento, tanto la mezcla de referencia (sin modificar el ligante) como la modificada con nanoarcilla han sido envejecidas en laboratorio mediante dos procedimientos: calentamiento prolongado en horno, Long-Term Oven Ageing (LTOA), y UV, Técnico Accelerated Ageing (TEAGE). Los resultados obtenidos muestran que la mezcla fabricada con el ligante modificado presenta una mayor resistencia a tracción indirecta respecto a la mezcla de referencia, y un mejor comportamiento frente al envejecimiento, así como a la acción del agua.
El Laboratorio de Caminos de la Universidad Politécnica de Cataluña (Barcelona, España) ha desarrollado un ensayo a tracción directa, ensayo Fénix, que permite determinar la rigidez, energía de fractura y ductilidad de las mezclas bituminosas de forma rápida y sencilla. El ensayo ha sido aplicado a la caracterización de diferentes tipos de mezclas, en un amplio rango de temperaturas, lo que ha permitido establecer unos criterios de diseño.
En el trabajo que aquí se presenta, se recogen los resultados de la aplicación del ensayo Fénix para evaluar el efecto del tipo de ligante en la resistencia a la fisuración de una mezcla asfáltica, a distintas temperaturas. Para evitar la inferencia de los finos y del fíller, se ha considerado una mezcla patrón de referencia, sin finos ni fíller, fabricada con unos áridos tipo, variando exclusivamente el tipo de ligante. Se han utilizado dos ligantes de penetración diferentes (B15/25 y B70/100) y se ha determinado la variación de la energía de fractura y de la ductilidad con la temperatura, tanto sobre la mezcla original (sin envejecer) como sobre la mezcla envejecida. Esto ha permitido obtener la curva de comportamiento de los ligantes y ver como varía con el envejecimiento.
Separable approximations efficiently deal with high-dimensional data. In particular the Proper Generalized Decomposition (PGD) provides separable functions as solutions of boundary value problems. The general PGD framework contains a large family of methodologies, all of them providing solutions in for of separable objects, that is a sum of terms, being each term a product of J D functions (or arrays). Some of the PGD methodologies have been conceived to tackle nonlinear problems. We present a general methodology to perform basic operations (sum, product, division. exponentiation .... ) for this type of objects. The idea is based on the principie of the PGD compression, that is a separable least squares approximation of any multidimensional function. The PGD compression is extensively used in practice to compact the separable solution in less terms without loss of accuracy. Here, this concept is applied to both algebraic tensor structures and functions in multidimensional Cartesian domains. Moreover, a straightforward extension of this concept is devised to operate with multidimensional objects stored in the separable format. That allows creating a toolbox of PGD arithmetic operators. Thus, the toolbox is used to perform elemental operations with PGD type objects. This is of particular interest to solve nonlinear problems with PGD techniques by simply replicating the iterative algebraic solvers that are used in the standard Finite Element framework.
Design optimization, among other applications of industrial interest, requi re fast and multi ple queries of some parametric model. The Proper Generalized Decomposition (PGD) provides a separable so\ution, a computational vademecum, explicitly dependent on the parameters. This explicit parametric solution is efficiently computed with a greedy algorithm combined with an alternated directions scheme and can be stored in a compact form. This strategy has been successfully employed in many problems in com putational mechanics. The application to problems with saddle paint structure raises some difficulties requiring further attention in particular when the parameters descrihe the geometry of the computational domain. This presentation proposes a novel PGD formulation for the parameterized Stokes problem. Various possibilities of the separated forms of the PGD solutions are discussed and analyzed, selecting the more viable opti on. The efficacy of the proposed methodology is demonstrated in numerical exam ples for both Stokes and Brinkman models. Moreover, geometrically parameterized problems are further studied and discussed. These ftow problems require in many occasions to use high order methods in order to efticiently capture all the complexity of the ftow. Thus, the specificities or Lhe geometrically parameterized PGD strategy a discussed and high fidelity techniques are proposed to improve accurncy and performance in the offline phase.
Datasets collected by high-throughput sequencing (HTS) of 16S rRNA gene amplimers, metagenomes or metatranscriptomes are commonplace and being used to study human disease states, ecological differences between sites, and the built environment. There is increasing awareness that microbiome datasets generated by HTS are compositional because they have an arbitrary total imposed by the instrument. However, many investigators are either unaware of this or assume specific properties of the compositional data. The purpose of this review is to alert investigators to the dangers inherent in ignoring the compositional nature of the data, and point out that HTS datasets derived from microbiome studies can and should be treated as compositions at all stages of analysis. We briefly introduce compositional data, illustrate the pathologies that occur when compositional data are analyzed inappropriately, and finally give guidance and point to resources and examples for the analysis of microbiome datasets using compositional data analysis.
Forcada, N.; Serrat, C.; Rodríguez-Puente, S.; Bortolini, R. Journal of management in engineering Vol. 33, num. 6, p. 1-8 DOI: 10.1061/(ASCE)ME.1943-5479.0000552 Data de publicació: 2017-11 Article en revista
It is vital to select the right project bidders, as this affects the success of a project. Although there are numerous methods for assessing bidders, communication is rarely taken into account. This paper discusses the results of a survey on communication key performance indicators (KPIs) and the success of construction projects. Data were collected from 390 construction partners in Spain. The results indicate that the most significant communication KPI is the quality of information: basically, its accuracy and timeliness. In addition, experienced respondents placed less importance on communication flow structures and communication management than did inexperienced respondents. Experienced respondents distrusted new trends and/or management theories and mainly relied on experience. The findings also reveal that the communication flow structure, the communication and information management plan, and the channels of communication are relevant aspects for the success of a project. The results of this research can be used to assess bidders' communication abilities and systems.
A modelling procedure to address the tunnel–anhydritic rock interaction is described in this paper. The model incorporates the basic physico-chemical phenomena involved in rock swelling, often observed during excavation and subsequent operation of tunnels. It includes (a) a provision for rock damage during tunnel excavation, (b) the precipitation of gypsum crystals in discontinuities and (c) a stress-dependent relationship between swelling strains and mass of gypsum precipitation. The model includes hydro-mechanical coupling and the transport of sulfate salts dissolved in the massif water. Rock damage is described by the development of a network of fractures that increases permeability and allows gypsum crystal growth. Field information, laboratory data and monitoring records available for Lilla tunnel, located in the province of Tarragona, Spain and excavated in Tertiary anhydritic claystone, were selected as a convenient benchmark case to test model capabilities. Predictions and measurements (swelling records of the unlined tunnel floor and swelling pressures against a structural invert) were found to agree reasonably well.
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In this paper we propose a Finite Element model for analyzing closed membranes (“bags”) interacting with internal and external (surrounding) fluids. The approach is based on embedding a Lagrangian monolithic model describing the membrane containing an internal fluid into an Eulerian external fluid model. The combination of kinematic frameworks allows us to accurately track the location of the membrane and naturally represent flow variables discontinuities across it. In order to obtain stable coupling for membrane materials with low density, a slight fluid compressibility is assumed. The coupling between the membrane and the internal fluid is automatically accounted for by a monolithic set-up. The filled membrane and the external fluid are coupled in a Dirichlet–Neumann fashion. The model is validated in several numerical examples and its potential application to a civil engineering problem of coast protection via water-filled bag reefs is shown.
This paper discusses the finite element modeling of cracking in quasi-brittle materials. The problem is addressed via a mixed strain/displacement finite element formulation and an isotropic damage constitutive model. The proposed mixed formulation is fully general and is applied in 2D and 3D. Also, it is independent of the specific finite element discretization considered; it can be equally used with triangles/tetrahedra, quadrilaterals/hexahedra and prisms. The feasibility and accuracy of the method is assessed through extensive comparison with experimental evidence. The correlation with the experimental tests shows the capacity of the mixed formulation to reproduce the experimental crack path and the force–displacement curves with remarkable accuracy. Both 2D and 3D examples produce results consistent with the documented data. Aspects related to the discrete solution, such as convergence regarding mesh resolution and mesh bias, as well as other related to the physical model, like structural size effect and the influence of Poisson’s ratio, are also investigated. The enhanced accuracy of the computed strain field leads to accurate results in terms of crack paths, failure mechanisms and force displacement curves. Spurious mesh dependency suffered by both continuous and discontinuous irreducible formulations is avoided by the mixed FE, without the need of auxiliary tracking techniques or other computational schemes that alter the continuum mechanical problem.
The final publication is available at Springer via http://dx.doi.org/10.1007/s00466-017-1438-8
In this paper, the flexural response of extruded wrought aluminium girders is presented. This structural element is intended for usage in marine structures such as light docks, marinas and yacht ports. Ease of use, durability, reduced weight, manoeuvrability and the potential development of bespoke sections are appealing properties in such structures that are fulfilled satisfactorily by this type of aluminium elements. Both experimental and numerical analyses are presented. Experimentally, modules of the girders are tested with loading about both minor and major axes. Numerically, the tests are satisfactorily reproduced for the sake of validation and a subsequent exploitation of the model is addressed for further study of the structural response of the girders. A discussion of the results is presented with some design recommendations of these particular structural elements.
Dialami , N.; Chiumenti, M.; Cervera, M.; Segatori, A.; Osikowicz, W. International journal of mechanical sciences Vol. 133, p. 555-567 DOI: 10.1016/j.ijmecsci.2017.09.022 Data de publicació: 2017-11 Article en revista
Friction is one of the main heat generation mechanisms in Friction Stir Welding (FSW). This phenomenon occurs between the pin and the workpiece as the rotating tool moves along the weld line. An accurate friction model is essential for obtaining realistic results in a FSW simulation in particular temperature, forces and torque. In this work, a modified Norton's friction law is developed. The suggested enhanced friction model aims at providing not only the realistic temperature field but also the forces and torque. This model does not exclusively relate the frictional shear stress to the sliding velocity; conversely it takes into account the effect of non-uniform pressure distribution under the shoulder, as this latter has an important role in the process of heat generation. Longitudinal, transversal and vertical forces and torque are numerically calculated. The effect of the enhanced friction model is reflected in these forces. In particular, it leads to a more realistic estimation of the transversal and longitudinal forces in comparison with the results obtained using former models. The friction model is successfully validated by the experimental measurements provided by the industrial partner (Sapa). The experimental analysis is performed for the material characterization, the calibration of the friction model and, more generally, the assessment of the overall numerical strategy proposed for the FSW simulation.
Design optimization and uncertainty quantification, among other applications of industrial interest, require fast or multiple queries of some parametric model. The Proper Generalized Decomposition (PGD) provides a separable solution, a computational vademecum explicitly dependent on the parameters, efficiently computed with a greedy algorithm combined with an alternated directions scheme and compactly stored. This strategy has been successfully employed in many problems in computational mechanics. The application to problems with saddle point structure raises some difficulties requiring further attention. This article proposes a PGD formulation of the Stokes problem. Various possibilities of the separated forms of the PGD solutions are discussed and analyzed, selecting the more viable option. The efficacy of the proposed methodology is demonstrated in numerical examples for both Stokes and Brinkman models.