The Temple of Sagrada Familia presents singularities in terms of both the original design by architect Antoni Gaudí and the duration
of the construction, which started more than 120 years ago. In fact, its design was conceived before the development of reinforced concrete. Therefore, the construction materials and processes have evolved to adapt new technologies without compromising the vision of Gaudí. This willingness to maintain the original designs has obliged the technicians to resolve details that were not defined in the project, including the issue of how to cast elements at great heights and with a high amount of reinforcement. In this context, the possibility of using self-compacting concrete (SCC) emerged. This paper describes the different experiences in the Temple of Sagrada Familia with SCC, from requirements that led to using this material to the design of the mixes and the casting of the elements in situ.
Mujal -Colilles, A.; Gironella, X.; Crespo, A. J. C.; Sanchez-Arcilla, A. Journal of waterway, port, coastal, and ocean engineering Vol. 143, num. 5, p. 1-8 DOI: 10.1061/(ASCE)WW.1943-5460.0000382 Data de publicació: 2017-09 Article en revista
Twin propellers without a rudder were studied using a physical model with a fixed clearance distance and three different rotating velocities. Experimental results were compared with results from theoretical expressions developed over the past 50 years for the efflux velocity, axial velocity, and maximum bed velocity. It was found that the efflux velocity equations overestimated the experimental results, whereas the computed axial velocities matched the experimental data reasonably well. However, when maximum bed velocity expressions were compared with experimental results, only one method was found to behave better; overestimation resulted if a quadratic superposition of single jets was used.
This work presents a general formulation and implementation in solid-shell elements of the refined zigzag theory and the trigonometric shear deformation theory in an unified way. The model thus conceived is aimed for use in the analysis, design and verification of structures made of composite materials, in which shear strains have a significant prevalence. The refined zigzag theory can deal with composite laminates economically, adding only two nodal degrees of freedom, with very good accuracy. It assumes that the in-plane displacements have a piece-wise linear shape across the thickness depending on the shear stiffness of each composite layer. The trigonometric theory assumes a cosine variation of the transverse shear strain. A modification of this theory is presented in this paper allowing its implementation with C0 approximation functions. Two existing elements are considered, an eight-node tri-linear hexahedron and a six-node triangular prism. Both elements use a modified right Cauchy-Green deformation tensor View the MathML source where five of its six components are linearly interpolated from values computed at the top and bottom surfaces of the element. The sixth component is computed at the element center and it is enhanced with an additional degree of freedom. This basic kinematic is improved with a hierarchical field of in-plane displacements expressed in convective coordinates. The objective of this approach is to have a simple and efficient finite element formulation to analyze composite laminates under large displacements and rotations but small elastic strains. The assumed natural strain technique is used to prevent transverse shear locking. An analytic through-the-thickness integration and one point integration on the shell plane is used requiring hourglass stabilization for the hexahedral element. Several examples are considered on the one hand to compare with analytical static solutions of plates, and on the other hand to observe natural frequencies, buckling loads and the non-linear large displacement behavior in double curved shells. The results obtained are in a very good agreement with the targets used.
The objective of this paper is to evaluate the influence of sulfate exposure on the pore network development of several Portland cement matrices. MIP, XRD and SEM analysis were performed at different ages in samples exposed to sulfates after 2 days of casting. Results suggest that patterns of precipitation of the expansive products are linked to the degree of refinement of the pore network. During early stages of exposure, large pores concentrate a higher proportion of the expansive product formed. At later stages, precipitation evolves towards finer pore sizes.
Chacon, R.; Oller, S. Journal of professional issues in engineering education and practice Vol. 143, num. 3, p. 1-9 DOI: 10.1061/(ASCE)EI.1943-5541.0000315 Data de publicació: 2017-07 Article en revista
In engineering, traditional approaches aimed at teaching concepts of dynamics to engineering students include the study of a dense yet sequential theoretical development of proofs and exercises. Structural dynamics are seldom taught experimentally in laboratories since these facilities should be provided with expensive equipment such as wave generators, data-acquisition systems, and heavily wired deployments with sensors. In this paper, the design of an experimental experience in the classroom based upon digital fabrication and modeling tools related to structural dynamics is presented. In particular, all experimental deployments are conceived with low-cost, open-source equipment. The hardware includes Arduino-based open-source electronics whereas the software is based upon object-oriented open-source codes for the development of physical simulations. The set of experiments and the physical simulations are reproducible and scalable in classroom-based environments.
Fatigue is associated with the deterioration caused by applying repeated loads, and is affected by temperature or aging. Generally, time sweep tests are used to simulate fatigue, in order to obtain the fatigue laws. However, this requires too much time, often preventing its use. A method to estimate the fatigue laws from a strain sweep test is presented. The test was performed on a semi-dense mixture with different types of binder (unconditioned or aged) tested at different temperatures. This test is able to estimate fatigue laws more quickly, allowing the effect of different factors on the mixtures' fatigue life to be studied.
Cuesta, A.; Rejmak, P.; Ayuela, A.; De La Torre, A.; Santacruz, I.; Fernandez-Carrasco, L.; Popescu, C.; Garcia Aranda, Miguel Angel Cement and concrete research Vol. 97, p. 1 DOI: 10.1016/j.cemconres.2017.03.011 Data de publicació: 2017-07 Article en revista
Five calcium hydroxyaluminate phases have been investigated by synchrotron powder diffraction at high-pressure: two hydrogarnets, kuzelite, stratlingite and ettringite. The obtained bulk modulus, K0, for kuzelite, stratlingite and ettringite were 23(1), 27(1) and 30(3) GPa, respectively. Kuzelite and stratlingite underwent transformations above 1 GPa likely releasing interlayer water. Kuzelite becoming markedly amorphous and stratlingite remained crystalline, K0 = 58(6) GPa in the 1.5–5.5 GPa pressure range. The structural behavior for hydrogarnet samples is prone to the use of pressure transmitting media. K0 for Ca3Al2(OH)12 was 81(2) and 76(2) GPa for silicone oil and alcohol mixture, respectively. A similar study for Ca3Al1.7Fe0.3(OH)12 yielded 73(1) and 58(1) GPa for silicone oil and alcohol mixture, respectively. Atomistic calculations using periodic Density Functional Theory showed that the softening in iron-doped katoite, when compared to stoichiometric katoite, can be assigned primarily to greater compressibility of Casingle bondO dodecahedra, which overcompensates strengthening of hydrogen bonding between Al/Fe hydroxide groups.
At a global level, access to safe drinking water and sanitation has been monitored by the Joint Monitoring Programme (JMP) of WHO and UNICEF. The methods employed are based on analysis of data from household surveys and linear regression modelling of these results over time. However, there is evidence of non-linearity in the JMP data. In addition, the compositional nature of these data is not taken into consideration. This article seeks to address these two previous shortcomings in order to produce more accurate estimates.
We employed an isometric log-ratio transformation designed for compositional data. We applied linear and non-linear time regressions to both the original and the transformed data. Specifically, different modelling alternatives for non-linear trajectories were analysed, all of which are based on a generalized additive model (GAM).
Results and discussion
Non-linear methods, such as GAM, may be used for modelling non-linear trajectories in the JMP data. This projection method is particularly suited for data-rich countries. Moreover, the ilr transformation of compositional data is conceptually sound and fairly simple to implement. It helps improve the performance of both linear and non-linear regression models, specifically in the occurrence of extreme data points, i.e. when coverage rates are near either 0% or 100%.
This work is devoted to the design of interior penalty discontinuous Galerkin (dG) schemes that preserve maximum principles at the discrete level for the steady transport and convection–diffusion problems and the respective transient problems with implicit time integration. Monotonic schemes that combine explicit time stepping with dG space discretization are very common, but the design of such schemes for implicit time stepping is rare, and it had only been attained so far for 1D problems. The proposed scheme is based on a piecewise linear dG discretization supplemented with an artificial diffusion that linearly depends on a shock detector that identifies the troublesome areas. In order to define the new shock detector, we have introduced the concept of discrete local extrema. The diffusion operator is a graph-Laplacian, instead of the more common finite element discretization of the Laplacian operator, which is essential to keep monotonicity on general meshes and in multi-dimension. The resulting nonlinear stabilization is non-smooth and nonlinear solvers can fail to converge. As a result, we propose a smoothed (twice differentiable) version of the nonlinear stabilization, which allows us to use Newton with line search nonlinear solvers and dramatically improve nonlinear convergence. A theoretical numerical analysis of the proposed schemes shows that they satisfy the desired monotonicity properties. Further, the resulting operator is Lipschitz continuous and there exists at least one solution of the discrete problem, even in the non-smooth version. We provide a set of numerical results to support our findings.
Candela, L.; Jiménez, J.; Valdes-Abellan, J.; Jacques, D.; Kohfahl, C.; Tamoh, K. Journal of hydrology Vol. 549, p. 114-124 DOI: 10.1016/j.jhydrol.2017.03.061 Data de publicació: 2017-06 Article en revista
The use of non-conventional water (e.g., treated wastewater, desalinated water) for different purposes is increasing in many water scarce regions of the world. Its use for irrigation may have potential drawbacks, because of mineral dissolution/precipitation processes, such as changes in soil physical and hydraulic properties (e.g., porosity, permeability), modifying infiltration and aquifer recharge processes or blocking root growth. Prediction of soil and groundwater impacts is essential for achieving sustainable agricultural practices. A numerical model to solve unsaturated water flow and non-isothermal multicomponent reactive transport has been modified implementing the spatio-temporal evolution of soil physical and hydraulic properties. A long-term process simulation (30 years) of agricultural irrigation with desalinated water, based on a calibrated/validated 1D numerical model in a semi-arid region, is presented. Different scenarios conditioning reactive transport (i.e., rainwater irrigation, lack of gypsum in the soil profile, and lower partial pressure of CO2 (pCO2)) have also been considered. Results show that although boundary conditions and mineral soil composition highly influence the reactive processes, dissolution/precipitation of carbonate species is triggered mainly by pCO2, closely related to plant roots. Calcite dissolution occurs in the root zone, precipitation takes place under it and at the soil surface, which will lead a root growth blockage and a direct soil evaporation decrease, respectively. For the studied soil, a gypsum dissolution up to 40 cm depth is expected at long-term, with a general increase of porosity and hydraulic conductivity.
Estimating the statistical parameters (mean, variance, and integral scale) that define the spatial structure of the transmissivity or hydraulic conductivity fields is a fundamental step for the accurate prediction of subsurface flow and contaminant transport. In practice, the determination of the spatial structure is a challenge because of spatial heterogeneity and data scarcity. In this paper, we describe a novel approach that uses time drawdown data from multiple pumping tests to determine the transmissivity statistical spatial structure. The method builds on the pumping test interpretation procedure of Copty et al. (2011) (Continuous Derivation method, CD), which uses the time-drawdown data and its time derivative to estimate apparent transmissivity values as a function of radial distance from the pumping well. A Bayesian approach is then used to infer the statistical parameters of the transmissivity field by combining prior information about the parameters and the likelihood function expressed in terms of radially-dependent apparent transmissivities determined from pumping tests. A major advantage of the proposed Bayesian approach is that the likelihood function is readily determined from randomly generated multiple realizations of the transmissivity field, without the need to solve the groundwater flow equation. Applying the method to synthetically-generated pumping test data, we demonstrate that, through a relatively simple procedure, information on the spatial structure of the transmissivity may be inferred from pumping tests data. It is also shown that the prior parameter distribution has a significant influence on the estimation procedure, given the non-uniqueness of the estimation procedure. Results also indicate that the reliability of the estimated transmissivity statistical parameters increases with the number of available pumping tests.
During the process of structural system identification, errors are unavoidable. This paper analyzes the effects of measurement and simulation errors in structural system identification based on observability techniques. To illustrate the symbolic approach of this method a simply supported beam is analyzed step-by-step. This analysis provides, for the very first time in the literature, the parametric equations of the estimated parameters. The effects of several factors, such as errors in a particular measurement or in the whole measurement set, load location, measurement location or sign of the errors, on the accuracy of the identification results are also investigated. It is found that error in a particular measurement increases the errors of individual estimations, and this effect can be significantly mitigated by introducing random errors in the whole measurement set. The propagation of simulation errors when using observability techniques is illustrated by two structures with different measurement sets and loading cases. A fluctuation of the observed parameters around the real values is proved to be a characteristic of this method. Also, it is suggested that a sufficient combination of different load cases should be utilized to avoid the inaccurate estimation at the location of low curvature zones.
This paper studies the cross-sectional behaviour of austenitic, ferritic and duplex stainless steel hollow sections subjected to several loading conditions and presents a full slenderness range DSM approach for the prediction of cross-sectional strengths. Pure compression, pure bending moment and combined uniaxial bending and compression loading resistances are predicted using the same strength curve, which is based on experimental data gathered from the literature and ultimate strengths generated through parametric studies. The proposed approach is applicable to slender and stocky cross-sections leading to an accurate full slenderness range DSM design approach since the resistance reduction due to local buckling and the effect of strain hardening are taken into account, as is the effect of partial yielding of the cross-section in bending. A new method based on the actual stress distribution of the cross-section is also presented for combined loading conditions, where the cross-sectional behaviour is directly tackled through the same strength curve, providing more accurate results than the methods considering the uncoupled problem. Finally, a statistical analysis is presented to demonstrate the reliability of the proposed DSM approach.
Sole, M.; Carrère, H.; Marianna Garfi'; Ferrer, I. Algal research: biomass, biofuels and bioproducts Vol. 24, part A, p. 199-206 DOI: 10.1016/j.algal.2017.03.025 Data de publicació: 2017-06 Article en revista
The aim of this study was to evaluate for the first time the effect of a thermo-alkaline pretreatment with lime (CaO) on microalgae anaerobic digestion. The pretreatment was carried out by adding different CaO doses (4 and 10%) at different temperatures (room temperature (25 °C), 55 and 72 °C). The exposure time was 4 days for pretreatments at 25 °C, and 24 h for pretreatments at 55 and 72 °C. Following, a biochemical methane potential test was conducted with pretreated and untreated microalgae. According to the results, the pretreatment enhanced proteins solubilisation by 32.4% and carbohydrates solubilisation by 31.4% with the highest lime dose and temperature (10% CaO and 72 °C). Furthermore, anaerobic digestion kinetics were improved in all cases (from 0.08 to 0.14 day- 1 for untreated and pretreated microalgae, respectively). The maximum biochemical methane potential increase (25%) was achieved with 10% CaO at 72 °C, in accordance with the highest biomass solubilisation. Thus, lime pretreatment appears as a potential strategy to improve microalgae anaerobic digestion.
In contrast to terrestrial environment, the harsh lunar environment conditions include lower gravity acceleration, ultra-high vacuum and high (low) temperature in the daytime (night-time). This paper focuses on the effects of those mentioned features on soil cutting tests, a simplified excavation test, to reduce the risk of lunar excavation missions. Soil behavior and blade performance were analyzed under different environmental conditions. The results show that: (1) the cutting resistance and the energy consumption increase linearly with the gravity. The bending moment has a bigger increasing rate in low gravity fields due to a decreasing moment arm; (2) the cutting resistance, energy consumption and bending moment increase significantly because of the raised soil strength on the lunar environment, especially in low gravity fields. Under the lunar environment, the proportions of cutting resistance, bending moment and energy consumption due to the effect of the van der Waals forces are significant. Thus, they should be taken into consideration when planning excavations on the Moon. Therefore, considering that the maximum frictional force between the excavator and the lunar surface is proportional to the gravity acceleration, the same excavator that works efficiently on the Earth may not be able to work properly on the Moon.
The Campo de Cartagena (Eastern Spain) is one of Europe’s driest areas with a mean precipitation of around 300 mm. One of the main challengesin the region is to secure a reliable water supply in both quantity and quality terms, to provide a water supply and agricultural irrigation, while water desalination has become an extensively applied solution, and one of the most sustainable solutions to the water scarcity problem. As water availability is lacking and groundwater quality is poor, the agricultural sector in Campo de Cartagena has developed small private brackish groundwater desalination plants (15-20 m3/h) through already existing agricultural wells. Costs and benefits (C-B) for citrus cultivation (1 ha) in three such plants have been assessed. The results indicate that for the studied cases, current agricultural management is feasible and costs outweigh benefits, with a positive NPV and a cost/benefit ratio higher than 1. The internal rate of return is also positive and higher than 11%. The results evidence practical and theoretical implications as to how to increase water resources in areas where water is scarce by closing the loop, ensuring farmers’ profitability and encouraging private sector investments.
The main objective of this study was to select and grow wastewater-borne cyanobacteria in a closed photobioreactor (PBR) inoculated with a mixed consortium of microalgae. The 30 L PBR was fed with a mixture of urban secondary effluent and digestate, and operated in semi-continuous mode. Based on the nutrients variation of the influent, three different periods were distinguished during one year of operation. Results showed that total inorganic nitrogen (TIN), inorganic phosphorus concentration (PO43 -), phosphorus volumetric load (LV-P) and carbon limited/non-limited conditions leaded to different species composition, nutrients removal and biomass production in the culture. High TIN/PO43 - concentrations in the influent (36 mg N L- 1/3 mg P L- 1), carbon limitation and an average LV-P of 0.35 mg P L- 1d- 1 were negatively related to cyanobacteria dominance and nutrients removal. On the contrary, cyanobacteria predominance over green algae and the highest microbial biomass production (averaging 0.084 g Volatile Suspended Solids (VSS) L- 1d- 1) were reached under TIN/PO43 - concentrations of 21 mg N L- 1/2 mg P L- 1, no carbon limitation and an average LV-P of 0.23 mg P-PO43 - L- 1d- 1. However, although cyanobacteria predominance was also favored with a LV-P 0.15 mg L- 1d- 1, biomass production was negatively affected due to a P limitation in the culture, resulting in a biomass production of 0.0.39 g VSS L- 1d- 1. This study shows that the dominance of cyanobacteria in a microalgal cyanobacterial community in an agitated PBR using wastewater as nutrient source can be obtained and maintained for 234 days. These data can also be applied in future biotechnology applications to optimize and enhance the production of added value products by cyanobacteria in wastewater treatment systems.
La presente invención se refiere, en estructuras flotantes de soporte de turbinas eólicas, a la materialización mediante una lámina de hormigón pretensado de la zona de transición entre la torre, de menor diámetro, y el flotador de hormigón de mayor diámetro, tanto si la torre es metálica como de hormigón. Dicha lámina de revolución presenta una geometría óptima para la correcta transmisión de esfuerzos entre ambas partes, torre y flotador, con un espesor reducido y sin necesidad de elementos de rigidización y refuerzo exteriores a sus superficies que aumentarían el peso y el coste de la estructura.
La explotación de recursos energéticos y mineros marinos a menudo requiere el despliegue de instalaciones fijas o semi apoyadas ancladas al fondo marino. El diseño geotécnico de estas estructuras requiere información específica acerca de la naturaleza y propiedades de los suelos y rocas allí presentes. Como en el caso de proyectos en tierra, para evaluar con precisión la rigidez y resistencia ¿in situ¿ se necesitan muestras de suelo que presenten la menor cantidad de alteraciones posible. La recuperación de muestras en proyectos en tierra puede ser en sí una tarea bastante difícil que se vuelve aún más problemática al trasladarse a ambientes marinos.La exploración geotécnica submarina está experimentando un cambio de paradigma debido a la aplicación de técnicas de disciplinas como robótica y automatización a (hasta ahora) procedimientos de perforación tradicionales. La MD500 es una máquina submarina de perforación geotécnica y de sondeo in situ, desarrollada con el objetivo de recuperar muestras físicas de suelos marinos de alta calidad a profundidades de perforación de hasta 150 m con caladas de hasta 500 m. Las aplicaciones del sistema varían en áreas de actividad marina, tales como: infraestructura portuaria, proyectos en costas y alta mar, energías renovables en mar, petróleo y gas, minería, etc.La máquina consiste en un grupo de dispositivos operados de forma remota que deben sincronizarse: torre de perforación, patas de estabilización y tres manipuladores, concretamente dos robots cartesianos y un brazo antropomórfico. La automatización y operación remota de estos dispositivos implica que todas las tareas usualmente llevadas a cabo por un sondistas de un equipo de perforación deben ser realizadas por maquinaria y robots, estos últimos deben ser lo bastante versátiles para enfrentarse a una gran variedad de problemas imprevisibles. Esta tesis presenta el análisis del sistema, el diseño de bucles avanzados de control, evaluación de desempeño y la arquitectura de la red de control descentralizado usados de la MD500.
La resolución de problemas de localización de deformaciones y fallos cuasi-frágiles en materiales friccional-cohesivos sigue siendo un tema abierto a discusión. Debido a su complejidad y a las implicaciones en numerosos problemas de ingeniería, se ha dedicado un considerable esfuerzo al desarrollo de teorías y técnicas capaces de manejar el comportamiento inelástico de los sólidos.La introducción de los métodos numéricos en los años '70 proporcionó técnicas rápidas de cálculo que permitían obtener una solución, aunque aproximada, del problema a tratar. El Método de Elementos Finitos (FEM) es capaz de describir de manera eficiente un gran número de geometrías, problemas de ingeniería y condiciones de contorno, por lo que hace de la formulación irreducible la opción mayoritariamente escogida en el análisis de cuerpos sólidos. Asimismo, considerando la regularización del salto por el desplazamiento producido por una grieta a través de una banda de elementos, es posible calcular la aparición y evolución de una fractura.Sin embargo, los elementos finitos estándar se comportan de manera inadecuada en cálculos de localización de deformaciones en materiales con ablandamiento. La formulación irreducible está altamente influenciada por la malla empleada, y frecuentemente la dirección de fractura resultante es incorrecta. Este fenómeno aparece de manera significativa en plasticidad, siendo ortotrópica. De igual manera, con modelos isocóricos, el bloqueo de las deformaciones provoca oscilaciones de presión espurias, que hacen inutilizable la solución numérica obtenida. Es posible demostrar que ambos problemas no están relacionados por la definición continua del problema, sino con su formulación discreta.En este trabajo se presenta una nueva formulación mixta e-u de elementos finitos en desplazamientos y deformaciones para la localización de deformaciones y fallo en plasticidad. Solucionando independientemente deformaciones y desplazamientos, la formulación se caracteriza por la mejora de las capacidades cinemáticas, que da como resultado una mejora crucial en la precisión del cálculo de tensiones y deformaciones. Además, se demuestra que los problemas numéricos de la formulación irreducible se ven mitigados con el uso de la técnica de los elementos finitos mixtos.En los ejemplos, se considera el fallo con carga de Modo I (apertura) a través de un criterio de fallo de Rankine para describir el comportamiento mecánico de materiales, como el hormigón, que fallan por carga de tracción. Luego, se estudia el fallo con carga en Modo II (cizallamiento), empleando los criterios de fallo de J2 von Mises y de Drucker-Prager para la plasticidad incompresible y compresible. Por fin, se discute el fallo en Modo III (rasgado) y en Modo Mixto. Se implementan los criterios de Rankine y Drucker-Prager, tanto en plasticidad como en daño continuo para estudiar el estado de tensión en casos de flexión desviada y de torsión.Entonces, surgen tres conclusiones principales: (i) el método de elementos finitos mixto e-u es capaz de superar los desafíos planteados por la localización de la deformación en sólidos, con soluciones confiables y precisas; (ii) el modelo de fisura distribuida describe la creación y propagación de superficies de fractura por carga en Modo I, Modo II, Modo III y Modo Mixto; (iii) la mejora de la descripción cinemática, con continuidad de desplazamientos y deformaciones, se considera un factor clave para mejorar la solución numérica.El e-u FEM comparte muchos detalles de implementación de leyes constitutivas, conjunto inicial de datos y discretización geométrica con el método estándar. Sin embargo, la formulación mixta propuesta es superior en la predicción de las cargas máximas, patrones de localización de deformación y mecanismos de fallo. Además, demuestra su generalidad y sus posibilidades para un uso favorable en la práctica de la ingeniería.
Las reacciones y los procesos que ocurren en sistemas mixtos de microalgas y bacterias son difíciles de entender ya que la mayoría de ellos tienen lugar simultáneamente y dependen de muchos parámetros tales como temperatura, radiación solar, disponibilidad de nutrientes (e.g. carbono y nitrógeno) así como ciertas condiciones inhibitorias (e.g. exceso de oxígeno en el medio de cultivo). En comparación con las tecnologías convencionales de tratamiento de aguas residuales, actualmente hay poco conocimiento de las reacciones físicas, químicas y bioquímicas y de los procesos que se producen en los sistemas de tratamiento de microalgas y bacterias.El objetivo principal de la presente tesis doctoral fue desarrollar un nuevo modelo mecanístico integrado, denominado BIO_ALGAE, que incluye procesos físicos y bioquinéticos cruciales para simular el crecimiento de microalgas en diferentes tipos de cultivos, principalmente en aguas residuales. El modelo se utilizó para comprender de una mejor forma las interacciones que se llevan a cabo entre microalgas y bacterias en lagunas de alta carga (LAC) y fotobiorreactores.El modelo BIO_ALGAE se construyó mediante el acoplamiento del River Water Quality Model 1 (RWQM1) y del modelo ASM3 modificado, y se implementó en la plataforma de simulación COMSOL MultiphysicsTM. El carbono inorgánico, utilizado como sustrato limitante para el crecimiento de microalgas, es una de las principales características innovadoras de BIO_ALGAE. Además, la temperatura, la fotorespiración, la dinámica del pH, la radiación solar, la atenuación de la luz y la transferencia de gases a la atmósfera se consideraron los principales factores limitantes del crecimiento de las microalgas.Para reducir la complejidad del modelo en las etapas iniciales de su desarrollo, se decidió empezar por estudiar los procesos físicos, químicos y bioquinéticos sólo de las microalgas, dejando de lado los procesos bacterianos. Una vez calibrados los parámetros más sensibles del modelo, se añadieron los procesos bacterianos, lo que dio lugar al modelo integral BIO_ALGAE. Este modelo fue calibrado y validado con datos experimentales de alta calidad procedentes de LAC operadas a corto y largo plazo. El modelo BIO_ALGAE ha demostrado ser una herramienta eficaz para entender las interacciones de microalgas y bacterias en el tratamiento de aguas residuales y simular la dinámica de diferentes componentes en las LAC. El modelo se utilizó para investigar el efecto de las condiciones ambientales y la disponibilidad de nutrientes en el crecimiento de microalgas. También se estudió el efecto del tiempo de retención hidráulica sobre la proporción relativa de microalgas-bacterias y la producción de biomasa.Gracias al modelo fue posible optimizar el rendimiento tanto de las lagunas de alta carga como del fotobiorreactor.
Serafin, K.; Magnain, B.; Florentin, E.; Pares, N.; Diez, P. International journal for numerical methods in engineering Vol. 110, num. 5, p. 440-466 DOI: 10.1002/nme.5363 Data de publicació: 2017-05-04 Article en revista
This work focuses on providing accurate low-cost approximations of stochastic ¿nite elements simulations in the framework of linear elasticity. In a previous work, an adaptive strategy was introduced as an improved Monte-Carlo method for multi-dimensional large stochastic problems. We provide here a complete analysis of the method including a new enhanced goal-oriented error estimator and estimates of CPU (computational processing unit) cost gain. Technical insights of these two topics are presented in details, and numerical examples show the interest of these new developments.
Perez, F.; Botella, R.; López-Montero, T.; Miro, R.; Martinez, A. International journal of fatigue num. 98, p. 111-120 DOI: 10.1016/j.ijfatigue.2017.01.026 Data de publicació: 2017-05 Article en revista
This paper compares the results obtained in two types of cyclic tension-compression tests, a time sweep test, constant strain amplitude, and a strain sweep test, increasing strain amplitude every 5000 cycles, called EBADE (standing for the Spanish words for strain sweep test). This comparison has shown that the rapid loss of stiffness during the initial part of cyclic testing is recoverable in bituminous materials. It has been found that reversible phenomena dominate in asphalt binders, while in mixtures are as important as damage. A damage equation has been proposed to describe the evolution of the material distress during the phase II in time sweep tests. In addition, a new methodology to estimate the fatigue law of bituminous mixtures is proposed.
The testing of mode III and mixed mode failure is every so often encountered in the dedicated literature of mechanical characterization of brittle and quasi-brittle materials. In this work, the application of the mixed strain displacement e-ue-u finite element formulation to three examples involving skew notched beams is presented. The use of this FE technology is effective in problems involving localization of strains in softening materials.
The objectives of the paper are: (i) to test the mixed formulation in mode III and mixed mode failure and (ii) to present an enhancement in terms of computational time given by the kinematic compatibility between irreducible displacement-based and the mixed strain-displacement elements.
Three tests of skew-notched beams are presented: firstly, a three point bending test of a PolyMethyl MethaAcrylate beam; secondly, a torsion test of a plain concrete prismatic beam with square base; finally, a torsion test of a cylindrical beam made of plain concrete as well. To describe the mechanical behavior of the material in the inelastic range, Rankine and Drucker-Prager failure criteria are used in both plasticity and isotropic continuum damage formats.
The proposed mixed formulation is capable of yielding results close to the experimental ones in terms of fracture surface, peak load and global loss of carrying capability. In addition, the symmetric secant formulation and the compatibility condition between the standard irreducible method and the strain-displacement one is exploited, resulting in a significant speedup of the computational procedure.
The Discrete Element Method (DEM) was found to be an effective numerical method for the calculation of engineering problems involving granular materials. However, the representation of irregular particles using the DEM is a very challenging issue, leading to different geometrical approaches. This document presents a new insight in the application of one of those simplifications known as rolling friction, which avoids excessive rotation when irregular shaped materials are simulated as spheric particles. This new approach, called the Bounded Rolling Friction model, was applied to reproduce a ballast resistance test.
A meaningful contribution to the evaluation of heterogeneous public investments is described in this article. The proposed methodology provides a step towards sustainable urban planning in which decisions are taken according to clear, consistent and transparent criteria assisted by the MIVES multi-criteria analysis framework. The MIVES methodology combines multi-criteria decision making (MCDM) and multi-attribute utility theory (MAUT), incorporating the value function (VF) concept and assigning weights through the analytic hierarchy process (AHP). First, a homogenization coefficient is calculated to develop the Prioritization Index for Heterogeneous Urban Investments (PIHUI), so that non-homogenous alternatives may be comparable. This coefficient measures the need of society to invest in each public project through the consideration of its contribution to the regional balance, the scope of its investment, the evaluation of the current situation and the values of the city. Then, the MIVES multi-criteria framework is used to evaluate the degree to which each investment would contribute to sustainable development. Different economic, environmental and social aspects were considered through a decision framework, constructed with the three aforementioned requirements, five criteria and eight indicators. The case study conducted for the Ecology, Urban Planning and Mobility Area of Barcelona municipal council is presented in this article, showing how this method performs accurate, consistent, and repeatable evaluations.
Montero-Chacón, F.; Zaghi, S.; Rossi, R.; García-Pérez, E.; Heras, I.; Martinez, X.; Oller, S.; Doblaré, M. Finite elements in analysis and design Vol. 127, p. 31-43 DOI: 10.1016/j.finel.2016.12.006 Data de publicació: 2017-05 Article en revista
Solar selective coatings can be multi-layered materials that optimize the solar absorption while reducing thermal radiation losses, granting the material long-term stability. These layers are deposited on structural materials (e.g., stainless steel, Inconel) in order to enhance the optical and thermal properties of the heat transfer system. However, interesting questions regarding their mechanical stability arise when operating at high temperatures. In this work, a full thermo-mechanical multiscale methodology is presented, covering the nano-, micro-, and macroscopic scales. In such methodology, fundamental material properties are determined by means of molecular dynamics simulations that are consequently implemented at the microstructural level by means of finite element analyses. On the other hand, the macroscale problem is solved while taking into account the effect of the microstructure via thermo-mechanical homogenization on a representative volume element (RVE). The methodology presented herein has been successfully implemented in a reference problem in concentrating solar power plants, namely the characterization of a carbon-based nanocomposite and the obtained results are in agreement with the expected theoretical values, demonstrating that it is now possible to apply successfully the concepts behind Integrated Computational Materials Engineering to design new coatings for complex realistic thermo-mechanical applications.
Under general seismic loading, reinforced concrete columns may be subjected to lateral loads in more than one direction. Available experimental data on columns subjected to bidirectional forces indicate that higher levels of damage and a higher loss of ductility and strength have been observed compared to similar tests under unidirectional shear forces. In this study, an experimental program was conducted in which six lightly reinforced concrete columns were subjected to unidirectional and bidirectional cyclic shear forces. This observation was used to identify the mechanisms and parameters governing the behavior of columns subjected to cyclic bidirectional lateral loads. Hence, a new conceptual model was developed to obtain the capacity of member. The shear forces were analyzed and an analytical formulation was derived to account for the effects in the concrete stress-strain relationship, the moment-curvature diagram and the plastic hinge length. These equations were used along with a structural model with concentrated plastic hinges to obtain the capacity curve of the column. The results of the formulations developed were verified using the results of the experiments performed on columns subjected to unidirectional and bidirectional cyclic lateral forces.
The paper presents a constitutive model for argillaceous rocks, developed within the framework of elastoplasticity, that includes a number of features that are relevant for a satisfactory description of their hydromechanical behaviour: anisotropy of strength and stiffness, behaviour nonlinearity and occurrence of plastic strains prior to peak strength, significant softening after peak, time-dependent creep deformations and permeability increase due to damage. Both saturated and unsaturated conditions are envisaged. The constitutive model is then applied to the simulation of triaxial and creep tests on Callovo-Oxfordian (COx) claystone. Although the main objective has been the simulation of the COx claystone behaviour, the model can be readily used for other argillaceous materials. The constitutive model developed is then applied, via a suitable coupled hydromechanical formulation, to the analysis of the excavation of a drift in the Meuse/Haute-Marne Underground Research Laboratory. The pattern of observed pore water pressures and displacements, as well as the shape and extent of the damaged zone, are generally satisfactorily reproduced. The relevance and importance of rock anisotropy and of the development of a damaged zone around the excavations are clearly demonstrated.
Picolo, R.; Pialarissi Cavalaro, S.H.; Monte, R.; de Figueiredo, A.D. Cement & concrete composites Vol. 79, p. 117-132 DOI: 10.1016/j.cemconcomp.2017.02.002 Data de publicació: 2017-05 Article en revista
Cement and accelerator compatibility is critical for achieving proper mechanical performance in sprayed matrices. Few studies in the literature focus on establishing relationships between accelerated chemical reactions and the resulting mechanical properties of these matrices. The objective of this study is to evaluate the correlation between the chemical processes occurring in accelerated matrices and their mechanical strength development from a quantitative standpoint, elucidating the main mechanisms governing their performance. Hydration kinetics were analyzed by XRD and isothermal calorimetry, while mechanical properties were evaluated by needle and pin penetration resistance and compressive strength of extracted cores. Results showed the influence of the accelerated hydration and the evolution of phase composition on the development of mechanical properties of the matrices. Based on an extensive statistical analysis, multivariate linear regressions were established between the mechanical strength of sprayed mortars and the main chemical parameters influencing its development at early and late ages.
This paper shows new possibilities of using novel, open-source, low-cost platforms for the structural health monitoring of heritage structures. The objective of the study is to present an assessment of increasingly available open-source digital modeling and fabrication technologies in order to identify the suitable counterparts of the typical components of a continuous static monitoring system for a historical construction. The results of the research include a simple case-study, which is presented with low-cost, open-source, calibrated components, as well as an assessment of different alternatives for deploying basic structural health monitoring arrangements. The results of the research show the great potential of these existing technologies that may help to promote a widespread and cost-efficient monitoring of the built cultural heritage. Such scenario may contribute to the onset of commonplace digital records of historical constructions in an open-source, versatile and reliable fashion.
Sole, M.; Cucina, M.; Folch, M.; Tapias, J.; Gigliotti, G.; Marianna Garfi'; Ferrer, I. Science of the total environment Vol. 586, p. 1-9 DOI: 10.1016/j.scitotenv.2017.02.006 Data de publicació: 2017-05 Article en revista
Microalgae anaerobic digestion produces biogas along with a digestate that may be reused in agriculture. However, the properties of this digestate for agricultural reuse have yet to be determined. The aim of this study was to characterise digestates from different microalgae anaerobic digestion processes (i.e. digestion of untreated microalgae, thermally pretreated microalgae and thermally pretreated microalgae in co-digestion with primary sludge). The main parameters evaluated were organic matter, macronutrients and heavy metals content, hygenisation, potential phytotoxicity and organic matter stabilisation. According to the results, all microalgae digestates presented suitable organic matter and macronutrients, especially organic and ammonium nitrogen, for agricultural soils amendment. However, the thermally pretreated microalgae digestate was the least stabilised digestate in comparison with untreated microalgae and co-digestion digestates. In vivo bioassays demonstrated that the digestates did not show residual phytotoxicity when properly diluted, being the co-digestion digestate the one which presented less phytotoxicity. Heavy metals contents resulted far below the threshold established by the European legislation on sludge spreading. Moreover, low presence of E. coli was observed in all digestates. Therefore, agricultural reuse of thermally pretreated microalgae and primary sludge co-digestate through irrigation emerges a suitable strategy to recycle nutrients from wastewater.
Sanchez-Arcilla, A.; Carniel, S.; Badger, M.; Bidlot, J.; Hansen, L.B.; Bolaños, R.; Cipollini, P.; Espino, M.; Miglietta, M.; Saulter, A.; Staneva, J. European Geosciences Union General Assembly p. 1 Data de presentació: 2017-04-28 Presentació treball a congrés
The increasing quality and quantity (resolution in space, coverage in time, combinations of sensors in the Sentinel family) of information provided by Copernicus offer the possibility to analyse and predict coastal meteo-oceanography at an unprecedented level. This is a unique opportunity to develop the Copernicus coastal dimension to tackle the pressures of increasing population and activities.
The combination of ocean/atmosphere/land observations from the Sentinel (S) 1/2/3, aligned with the availability of an increasing number of high-resolution numerical simulations (e.g. wave and current fields) in the Copernicus Marine Environment Monitoring Service (CMEMS) catalogue, should allow users to access proven representations of the coastal environment at a new level of understanding (e.g. wave diffraction at coastal “obstacles”), coupling (e.g. incorporating the land discharge into the coastal sea) and reliability for applications (e.g. hazards for coastal navigation). By adding periodic bathymetric up-dating and incorporating new assimilation routines it will be possible to achieve a new level of analysis for coastal seas.
In the paper we shall present the CEASELESS project that addresses the multiple scales coexisting in littoral areas by developing new shallow water parameterizations, introducing them into coupled model suites (wind-wave-surge-current-land discharge) and producing new standards for coastal simulations and analyses. This will demonstrate the technical feasibility of an operational coastal service. The set of derived products will be ingested into the users’ work routines, proving the economic feasibility of such a coastal extension. The level of conflicts in squeezed coastal zones, expected to grow in the face of climate change, will, thus, benefit directly from CEASELESS, establishing tangible contributions for a wide range of economic sectors. The mutual validation of satellite data, numerical results and in-situ observations will generate reciprocal profit for enhanced competiveness of coastal oceanographic products and their future evolution.
The coupling between waves, ocean and atmospheric models has been one of the main topics in the physical oceanography community for the last decade. The resulting challenge is more difficult and relevant in coastal areas, where the interaction between wind, waves and currents fields is far from negligible, and therefore some sort of model coupling is required. However, it is important to remark that it is only during energetic “enough” events that the coupling becomes quantitatively significant. The Western Mediterranean sea is an area characterised by calm periods most of the year. However, coastal areas
often present highly variable and heterogeneous wind, wave and current conditions, which make the numerical prediction of meteo-oceanographic processes difficult and with large associated local errors. Specifically, the Catalan coast is frequently affected by offshore wind intensifications channel by river valleys and by local current intensifications associated to coastal “bulges” (e.g. deltaic forms) that can reach up to 1 m/s in the surface. In this study we present different coupling strategies applied to both calm periods and energetic events, represented by the wind jets or current intensifications mentioned before, with the objective to quantify the effect of model coupling on the resulting wave fields off the Catalan coast. The SWAN wave model is used to model the wave fields, together with the ROMS oceanic model and the WRF atmospheric model. Two different types of coupling are considered: the first is a one-way coupling consisting in introducing the current field as an input for the SWAN wave model; the second one, consists in running in parallel the ROMS circulation model, the WRF atmospheric model and the SWAN wave model. The second methodology is more complex and should better reproduce the physics involved in the interactions, but requires an important computational capacity, not always available, so a critical comparison between the two methodologies, balancing costs and benefits will be presented and analysed. From the results obtained from a set of typical synoptic situations, it can be concluded that during most of the time, with the calm conditions typical of the Mediterranean coast, it is not necessary to consider the coupling in any of its forms to provide accurate wave simulations. However, when a wind or current intensification occurs, the results improve considerably with the coupled model and the robustness of predictions greatly improves. Because of that an “intelligent” modelling sequence that activates the coupling in terms of the expected meteo-oceanography is proposed for operational applications.
Ràfols, L.; Grifoll, M.; Espino, M.; Cerralbo, P.; Sairouni, A.; Bravo, M.; Sanchez-Arcilla, A. European Geosciences Union General Assembly p. 1 Data de presentació: 2017-04-28 Presentació treball a congrés
The Wave-Current Interactions (WCI) are investigated examining the influences of coupling two numerical models. The Regional Ocean Model System (ROMS; Shchepetkin and McWilliams, 2005) and the Simulating
Waves Nearshore (SWAN; Booij et al. 1999) are used in a high resolution domain (350 m). For the initial and boundary conditions, data from the IBI-MFC products have been used and the atmospheric forcing fields have been obtained from the Catalan Meteorological Service (SMC). Results from uncoupled numerical models are compared with one-way and two-way coupling simulations. The study area is located at the northern margin of the Ebro Shelf (NW Mediterranean Sea), where episodes of strong cross-shelf wind occur. The results show that during these episodes, the water currents obtained in the two-way simulation have better agreement with the observations compared with the other simulations. Additionally, when the water currents are considered, the wave energy (and thus the significant wave heigh)
decrease when the current flows in the same direction as waves propagate. The relative importance of the different terms of the momentum balance equation is also analyzed.
In this contribution we investigate the observed resuspension events in Alfacs Bay (semi-enclosed bay in The Ebro Delta, NW Mediterranean Sea) using a wave-current coupled model. This bay is characterized by a micro-tidal environment and a relevant seiche activity which may lead velocities more than 50 cm s-1. A set of ADCP and OBS moored at sea bottom were used to acquire hydrodynamic and optical information. The time-series observations showed an evident relation between seiche activity and the sediment resuspension events. The implementation of
a wave-current coupled model shows a strong spatial variability in terms of combined bottom stress. Significant wave hight of 0.4 m are modeled during energetic wind events. A significant correlation between the resuspension events and the combined bottom stress are observed. The numerical results reveal two different mechanism to
explain the resuspension events observed: during the Seiche episodes the combined bottom stresses are controlled by the current-induced bottom stress. Otherwise during strong winds the combined bottom stress are controlled by the wave-induced bottom stress.
Flash floods induced by heavy rain are one of the hazardous natural events that significantly affect human lives. Because flash floods are characterized by their rapid onset, forecasting flash flood to lead an effective response requires accurate rainfall predictions with high spatial and temporal resolution and adequate representation of the hydrologic and hydraulic processes within a catchment that determine rainfall-runoff accumulations.
We present extreme flash flood cases which occurred throughout Europe in 2015-2016 that were identified and forecasted by two real-time approaches: 1) the European Rainfall-Induced Hazard Assessment System (ERICHA) and 2) the European Runoff Index based on Climatology (ERIC). ERICHA is based on the nowcasts of accumulated precipitation generated from the pan-European radar composites produced by the EUMETNET project OPERA. It has the advantage of high-resolution precipitation inputs and rapidly updated forecasts (every 15 minutes), but limited forecast lead time (up to 8 hours). ERIC, on the other hand, provides 5-day forecasts based on the COSMO-LEPS NWP simulations updated 2 times a day but is only produced at a ~7 km resolution.
We compare the products from both systems and focus on showing the advantages, limitations and com- plementarities of ERICHA and ERIC for seamless high-resolution flash flood forecasting.
The Portainé catchment is situated at the south flank of the Pyrenees and drains a total area of 5.72 km2. Its altitude ranges from 950 m to 2439 m asl and the Melton ratio is 0.62. Bedrock consists of folded and largely fractured Cambro-Ordovician metapelite, sandstone and greywackes and is covered by colluvium. A ski resort is located in the upper part of the catchment and the access roads cross the drainage network at various points. Since 2006, ten important torrential processes (debris floods and debris flows) have occurred and caused considerable damages along the road. Previous to 2006, no evidences of important torrential activity have been found. Herein, the critical rainfall conditions of the recent debris floods and debris flows were analysed. A common drawback of precipitation analysis for torrential flows in mountainous areas is the fact that no meteorological station
is situated inside the affected catchment. This was also the case at Portainé, where rainfall measurements in the basin are only available since 2012. Previous to 2012, the data of nearby meteorological stations were used and different techniques were applied to estimate the rainfall amounts in the catchment. Moreover, measurements of
the weather radar were used for selected events to study the effect of spatial variability. Finally, historic trends on the precipitation amount of a nearby meteorological station were investigated. The results show that most torrential flows occurred in summer (June to September) due to rather short and intense storms. Only one small event in November was triggered by a long-lasting rainfall. Values of the peak hour precipitation for the different events mostly exceeded 10 mm/h (a minor torrential flow was triggered by 5.1 mm/h) and total accumulated rainfall ranged from 19 to 113 mm. Strong spatial variability was detected in most events comparing the measurements of the nearby raingauges and specially the radar observations. In spite of this fact,
overplotting the triggering rainfalls in the standard intensity-duration plot shows a good correlation. Moreover, the intensity-duration values fit rather well with other published threshold lines (specially the well-known Caine 1980 threshold). Analysis of historic rainfall time series showed that no significant increase of important rainstorms has been observed during the last decades. This fact, together with the lack of observed events prior to 2006, supports the hypothesis that the construction and enlargement of the ski resort may have played a significant role in the occurrence of the torrential flows in the catchment. However, further investigation is necessary to assess the different governing factors.
Ribe, M.; Castelltort, X.; Blade, E.; Balasch, J.; Ruiz, J.; Tuset, J.; Barriendos, M.; Pino, D.; Mazon, J. European Geosciences Union General Assembly p. 1 Data de presentació: 2017-04-24 Presentació treball a congrés
The backwater effect influences the flood routing in a significant way by introducing water storage upstream from a channel disturbance. Water storage attenuates the peak of the flood wave. The backwater effect forces the stream to create room for the backing up water. This process can be formative. The end point of the backwater effect is the place where the rise in water begins to cause damage. A lithologic constriction into the channel is one of the cases of backwater effect occurrence. This effect has been studied in the Barrufemes Gorge, in the Ebro River, just few kilometers before its flowing into the Mediterranean Sea.
Damage-induced strain softening is of vital importance for the modeling of localized failure in frictional-cohesive materials. This paper addresses strain localization of damaging solids and the resulting consistent frictional-cohesive crack models. As a supplement to the framework recently established for stress-based continuum material models in rate form (Wu and Cervera 2015, 2016), several classical strain-based damage models, expressed usually in total and secant format, are considered. Upon strain localization of such damaging solids, Maxwell's kinematics of a strong (or regularized) discontinuity has to be reproduced by the inelastic damage strains, which are defined by a bounded characteristic tensor and an unbounded scalar related to the damage variable. This kinematic constraint yields a set of nonlinear equations from which the discontinuity orientation and damage-type localized cohesive relations can be derived. It is found that for the "Simó and Ju 1987" isotropic damage model, the localization angles and the resulting cohesive model heavily depend on lateral deformations usually ignored in classical crack models for quasi-brittle solids. To remedy this inconsistency, a modified damage model is proposed. Its strain localization analysis naturally results in a consistent frictional-cohesive crack model of damage type, which can be regularized as a classical smeared crack model. The analytical results are numerically verified by the recently-proposed mixed stabilized finite element method, regarding a singly-perforated plate under uniaxial tension. Remarkably, for all of the damage models discussed in this work, the numerically-obtained localization angles agree almost exactly with the closed-form results. This agreement, on the one hand, consolidates the strain localization analysis based on Maxwell's kinematics and, on the other hand, illustrates versatility of the mixed stabilized finite element method.
Many systems of partial differential equations governing physical phenomena have some underlying structure, e.g., positivity or some maximum principle. However, to inherit at the discrete level such structure is not an obvious task. We are particularly interested in finite element schemes that preserve at the discrete level maximum principles, especially for steady problems and transient problem with implicit time integration. In order to attain such objective, we consider nonlinear stabilization techniques based on a judiciously chosen artificial viscosity. A complete numerical analysis shows that the resulting schemes are discrete maximum princple (DMP) preserving and Lipschitz continuous.
Unfortunately, these additional terms come with a price. The artificial viscosity term is based on a shock capturing detector, which is highly nonlinear and non-differentiable, make extremely hard the nonlinear convergence, and drastically increase the computational cost with respect to nonstabilized formulations. In order to make these algorithms more applicable to real applications, we propose smoothing techniques that lead to differentiable nonlinear viscosity terms, which combined with Newton’s method, allows us to clearly improve nonlinear convergence.
The framework has been originally developed for linear and continuous finite element spaces on accute meshes , and recently extended to discontinuous Galerkin methods  and arbitrary meshes [3, 4]. Since the schemes rely on the convex hull, they loose the DMP property at the discrete level. Finally, in order to go to high order, we will explore the use of B-spline based discretizations.
An a-posteriori error estimate with application to inviscid compressible flow problems is presented. The estimate is a surrogate measure of the discretization error, obtained from an approximation to the truncation terms of the governing equations. This approximation is calculated from the discrete nodal differential residuals using a reconstructed solution field on a modified stencil of points. Both the error estimation methodology and the flow solution scheme are implemented using the Finite Point Method, a meshless technique enabling higher-order approximations and reconstruction procedures on general unstructured discretizations. The performance of the proposed error indicator is studied and applications to adaptive grid refinement are presented.
Aliguer, I.; Carol, I.; Sture, S. International journal for numerical and analytical methods in geomechanics Vol. 41, num. 6, p. 918-939 DOI: 10.1002/nag.2654 Data de publicació: 2017-04 Article en revista
The paper proposes a stress-driven integration strategy for Perzyna-type viscoplastic constitutive models, which leads also to a convenient algorithm for viscoplastic relaxation schemes. A generalized trapezoidal rule for the strain increment, combined with a linearized form of the yield function and flow rules, leads to a plasticity-like compliance operator that can be explicitly inverted to give an algorithmic tangent stiffness tensor also denoted as the m-AGC tangent operator. This operator is combined with the stress-prescribed integration scheme, to obtain a natural error indicator that can be used as a convergence criterion of the intra-step iterations (in physical viscoplasticity), or to a variable time-step size in viscoplastic relaxation schemes based on a single linear calculation per time step. The proposed schemes have been implemented for an existing zero-thickness interface constitutive model. Some numerical application examples are presented to illustrate the advantages of the new schemes proposed.