Documents published in 2019 : Scipedia

Métodos avanzados para el cálculo de la resistencia de la última de estructuras de hormigón
E. Oñate, A. Hanganu

(1999). Research Report, Nº PI176

Abstract
Se presenta en el trabajo una panorámica de los modelos más recientes para evaluar la resistencia última de estructuras de hormigón en masa y armado. Se presta especial atención al modelo de daño, descubriéndose varios ejemplos de aplicación de este modelo.
Abstract
Se presenta en el trabajo una panorámica de los modelos más recientes para evaluar la resistencia última de estructuras de hormigón en masa y armado. [...]
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Desarrollando la abstracción en adultos emergentes: Primer año de ingeniería
M. Jimenez, C. Astudillo, J. Reveco, M. González

Revista Iberoamericana de Educación en Ingeniería (RIEI) (2019). Vol. 1, 3

Abstract
Contexto: El primer año de universidad representa un momento de transición para jóvenes que se encuentran en una etapa vital, caracterizada por una adultez emergente. Desde esta manera, la docencia en estos cursos suele estar marcada por una tensión entre una tradición escolarizada y la expectativa de lo que constituye la educación superior. Con el proceso de masificación, las instituciones y en especial los profesores han debido dirigir sus prácticas de aula, para alcanzar niveles de pensamiento superior. En el caso de ingeniería, el pensamiento abstracto representa un desafío pedagógico en generaciones donde la tradición escolar, ha marcado en exceso la respuesta hacia la contingencia. Objetivo: El objetivo del presente artículo es identificar las variables que participan de este proceso a partir de un caso de aula en un curso de primer año. Metodología: Para el diseño del presente estudio se usó una investigación de tipo descriptiva. Se escoge este tipo pues permite llegar a conocer las situaciones, costumbres y actitudes predominantes a través de la descripción exacta de las actividades, objetos, procesos y personas. Resultados: Los estudiantes de primer año requieren estrategias de aula que favorezcan la adaptación hacia los cursos superiores, ya que son proclives a abandonar los estudios e interpretar las dificultades como problemas vocacionales.
Abstract
Contexto: El primer año de universidad representa un momento de transición para jóvenes que se encuentran en una etapa vital, caracterizada por una adultez [...]
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A large strain plasticity model for anisotropic composite materials
E. Car, S. Oller, E. Oñate

(1999). Research Report, Nº PI179
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Evaluación de competencias en management para la formación de ingenieros civiles
M. Gómez, F. Muñoz La Rivera, E. Atencio

Revista Iberoamericana de Educación en Ingeniería (RIEI) (2019). Vol. 1, 2

Abstract
La industria de la arquitectura, ingeniería y construcción (AIC) se caracteriza por estar fragmentada en varias especialidades, generando un alto nivel de especialización y una interacción más compleja. Los directores de proyectos en la industria de la AIC deben tener un conjunto integral de competencias alineadas con management. En la formación de ingenieros, estas competencias son ampliamente recomendadas por acuerdos internacionales y exigidas por las entidades de acreditación especializada, sin embargo, éstas tienen un alto foco en lo técnico. El objetivo de este estudio es identificar las competencias más relevantes en management para la formación de ingenieros civiles. Para ello, se realizaron 2 fases: (1) revisión de literatura; y (2) focus group de practitioners ingenieros civiles. La clasificación de competencias se realizó en tres grupos: administrativas, técnicas y conductuales. Existió una alta convergencia entre las competencias descritas en la literatura con la mencionada por los profesionales, en donde las que destacaron fueron: liderazgo, comunicación eficaz, inteligencia emocional, proactividad, planificación y control de presupuesto y cronograma, uso de plataformas tecnológicas, gestión de compromisos y resolución de problemas y conflictos.
Abstract
La industria de la arquitectura, ingeniería y construcción (AIC) se caracteriza por estar fragmentada en varias especialidades, generando un alto nivel de especialización [...]
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Higher-order simulations: Strategic investment under model-induced market structures
G. Peffer, B. Llacay

(2004). Research Report, Nº PI261

Abstract
The trading and investment decision processes in financial markets becomes ever more dependent on the use of valuation and risk models. In certain, cases such as risk management, modelling practice has become so homogeneous that one is led to ask about the effect this has on the price formation process. Furthermore, should stable price patterns emerge from this, can sophisticated investors who have private information about the use and characteristics of these models make superior gains? The aim of this article is to test this hypothesis in a stylised market environment, where a strategic trader who trades on information about the valuation and risk management models used by competitors. Results show that for our particular market setting, such a strategy has an advantage over those that do not use this information.
Abstract
The trading and investment decision processes in financial markets becomes ever more dependent on the use of valuation and risk models. In certain, cases such as risk management, [...]
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Smeared crack approach: Back to the original track
M. Cervera, M. Chiumenti

(2006). Research Report, Nº PI295

Abstract
This paper reviews briefly the formulations used over the last 40 years for the solution of problems involving tensile cracking, both with the discrete and smeared crack approaches. The paper focuses in the smeared approach, identifying as its main drawbacks the observed mesh-size and mesh-bias spurious dependence when the method is applied “straightly”. A simple isotropic local damage constitutive model is considered, and the (exponential) softening modulus is regularized according to the material fracture energy and the element size. The continuum and discrete mechanical problems corresponding to both the weak discontinuity (smeared cracks) and strong discontinuity (discrete cracks) approaches are analyzed and the question of propagation of the strain localization band (crack) is identified as the main difficulty to be overcome in the numerical procedure. A tracking technique is used to ensure uniqueness of the solution, attaining the necessary stability and convergence properties of the corresponding discrete finite element formulation. Numerical examples show that the formulation derived is well posed, stable and remarkably robust. As a consequence, the results obtained do not suffer from spurious meshsize or mesh-bias dependence, comparing very favorably with those obtained with other fracture and continuum mechanics approaches.
Abstract
This paper reviews briefly the formulations used over the last 40 years for the solution of problems involving tensile cracking, both with the discrete and smeared crack [...]
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Single Arm Dislocation Source mechanism-based flow stress and computation of crystal plasticity at submicron scale
Z. Zhuang

Videos of Plenary Lectures presented at the XV International Conference on Computational Plasticity (COMPLAS 2019) (2019). 10
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Exploration of predictive disaster simulations by FEM and MPM
K. Terada

Videos of Plenary Lectures presented at the XV International Conference on Computational Plasticity (COMPLAS 2019) (2019). 9
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The Finite Cell Method: A high order immersed boundary method for large scale nonlinear problems
E. Rank

Videos of Plenary Lectures presented at the XV International Conference on Computational Plasticity (COMPLAS 2019) (2019). 8
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Multiscale modelling and analysis of multi-phase alloys
F. Pires

Videos of Plenary Lectures presented at the XV International Conference on Computational Plasticity (COMPLAS 2019) (2019). 7
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Model-free data-driven computational mechanics (and III): Analysis, solvers, data identification and data management
M. Ortiz

Videos of Plenary Lectures presented at the XV International Conference on Computational Plasticity (COMPLAS 2019) (2019). 6
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Variational approach to topological optimization problems: closed-form solutions in a pseudo-time framework
J. Oliver

Videos of Plenary Lectures presented at the XV International Conference on Computational Plasticity (COMPLAS 2019) (2019). 5
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Computational nonlinear solid mechanics for complex loading histories
P. Ladevèze

Videos of Plenary Lectures presented at the XV International Conference on Computational Plasticity (COMPLAS 2019) (2019). 4
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The isogeometric approach to phase field modeling of fracture
T. Hughes

Videos of Plenary Lectures presented at the XV International Conference on Computational Plasticity (COMPLAS 2019) (2019). 3
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Semi-Lagrangian and Eulerian RKPM shock algorithms with application to explosive welding simulation
J. Chen

Videos of Plenary Lectures presented at the XV International Conference on Computational Plasticity (COMPLAS 2019) (2019). 2
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Simulation of fracture processes using the Virtual Element Method
P. Wriggers

Videos of Plenary Lectures presented at the XV International Conference on Computational Plasticity (COMPLAS 2019) (2019). 1
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Possibilities of the finite element viscous shell approach for analysis of sheet metal forming problems
E. Oñate, R. Lama

(1986). Simulation of Metal Forming Processes by the Finite Element Method (SIMOP-I). Lange K. (eds). Berichte aus dem Institut für Umformtechnik der Universität Stuttgart, vol 85. Springer, Berlin, Heidelberg

Abstract
The viscous shell approach combines the use of visco-plastic flow and classical shell theories. The paper presents the general aspects of the viscous shell formulation for axisymmetric and general 3-D shell problems using finite elements. Details of treatment of coordenate updating, friction effects, strain hardening and extensions to include the elastic deformations are also given together with some examples of application to the forming of axisymmetrical thin sheets of metal under hemispherical punches.
Abstract
The viscous shell approach combines the use of visco-plastic flow and classical shell theories. The paper presents the general aspects of the viscous shell formulation for [...]
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Applying multi-objective robust design optimization procedure to the route planning of a commercial aircraft
J. Pons Prats, G. Bugeda, F. Zarate, E. Oñate, J. Periaux

(2018). Computational Methods and Models for Transport. Computational Methods in Applied Sciences. Diez, P. Neittaanmäki, P., Periaux, J., Tuovinen, T., Bräysy, O. (Eds.), Vol. 45, pp. 147-167, Springer, Cham

Abstract
Aircraft emission targets worldwide and their climatic effects have put pressure in government agencies, aircraft manufacturers and airlines to reduce water vapour, carbon dioxide (CO2CO2) and oxides of nitrogen (NOxNOx) resulting from aircraft emissions. The difficulty of reducing emissions including water vapor, carbon dioxide (CO2CO2) and oxides of nitrogen (NOxNOx) is mainly due to the fact that a commercial aircraft is usually designed for a particular optimal cruise altitude but may be requested or required to operate and deviate at different altitudes and speeds to archive a desired or commanded flight plan, resulting in increased emissions. This is a multi- disciplinary problem with multiple trade-offs such as optimizing engine efficiency, minimizing fuel burnt and emissions while maintaining prescribed aircraft trajectories, altitude profiles and air safety. There are possible attempts to solve such problems by designing new wing/aircraft shape, new efficient engine, ATM technology, or modifying the aircraft flight plan. Based on the rough data provided by an air carrier company, who was willing to assess the methodology, this paper will present the coupling of an advanced optimization technique with mathematical models and algorithms for aircraft emission, and fuel burnt reduction through flight plan optimization. Two different approaches are presented; the first one describes a deterministic optimization of the flight plan and altitude profile in order to reduce the fuel consumption while reducing time and distance. The second approach presents the robust design optimization of the previous case considering uncertainties on several parameters. Numerical results will show that the methods are able to capture a set of useful trade-offs solutions between aircraft range and fuel consumption, as well as fuel consumption and flight time.
Abstract
Aircraft emission targets worldwide and their climatic effects have put pressure in government agencies, aircraft manufacturers and airlines to reduce water vapour, carbon [...]
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Advances in the DEM and coupled DEM and FEM techniques in non linear solid mechanics
E. Oñate, F. Zárate, M. Celigueta, J. González, J. Canet, J. Carbonell, F. Garcia, S. Latorre, M. Santasusana

(2018). (Preprint) Advances in Computational Plasticity. Computational Methods in Applied Sciences. Oñate, E., Peric, D., de Souza Neto, E., Chiumenti, M., (Eds.), Vol. 46, pp. 309-335, Springer

Abstract
In this chapter we present recent advances on the Discrete Element Method (DEM) and on the coupling of the DEM with the Finite Element Method (FEM) for solving a variety of problems in non linear solid mechanics involving damage, plasticity and multifracture situations.
Abstract
In this chapter we present recent advances on the Discrete Element Method (DEM) and on the coupling of the DEM with the Finite Element Method (FEM) for solving a variety of [...]
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REVISIÓN DE LAS TENDENCIAS INNOVADORAS EN LA ESTRUCTURACIÓN DE PAVIMENTOS COMO PARTE DEL DESARROLLO SUSTENTABLE
R. DE, . renemora1121

Journal of Energy, Engineering Optimization and Sustainability (2018). ISSN 2448-8186

Abstract
Currently, worldwide, many nations are paying close attention to the improvement and optimization of the usage of recycled materials in the building sector. The increase in the raw materials and the increased environmental awareness have gained considerable importance on a global scale. In road engineering, the waste material is used for the design and construction of pavements. Ecology, energy efficiency, profitability and significant reduction of the construction time are the primary drivers of this proposal. However, social and legislative aspects have prevented these types of procedures are implemented successfully in most developing countries. In this article, we analyze some of the main trends in the use of waste materials for the design and construction of pavements.
Abstract
Currently, worldwide, many nations are paying close attention to the improvement and optimization of the usage of recycled materials in the building sector. The increase in [...]
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Effect of the Suction on the Stability of a Silty Sand Slope
E. Slope, . renemora1121

Ingeniería Investigación y Tecnología. (2012). volumen XIII, (número 3), julio-septiembre 2012: 271-281; ISSN 1405-7743 FI-UNAM

Abstract
This paper presents a revision of some of the models that have been proposed to estimate the strength of unsaturated soils. The theoretical results obtained from these models are compared with the experimental results of controlled suction triaxial tests made on silty sand. The model that resulted in the best prediction was used to determine the stability of a slope of highly compressive clay subjected to changes in its water content. It is well known that the water content of soil is directly related with suction and that suction is an independent variable of the stress state that modifies the shear strength of unsaturated soils. Therefore, when the water content of a slope is modified, the safety factor of the slope is also modified. This exercise allows drawing some important conclusions over the stability of slopes related to the safety factor.
Abstract
This paper presents a revision of some of the models that have been proposed to estimate the strength of unsaturated soils. The theoretical results obtained from these models [...]
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The Effect of Saturation on the Slope Sliding in the San Juan de Grijalva Comunity, Chiapas
T. Sliding, . renemora1121

Ingeniería Investigación y Tecnología. (2012). Vol. XIII, Núm. 1, 2012, 55-68; ISSN 1405-7743 FI-UNAM

Abstract
A number of slopes that have been stable during many years may fail when an extraordinary rain period occurs. This phenomenon involves not only the lithology, the geometric and the mechanical characteristics of the slope but also the rain-evaporation-infi ltration regime of the site. In this paper, the stability of a slope in the comunity of San Juan de Grijalva, Ostuacán, Chiapas (Mexico) that failed during an intense raining period is analyzed. The volume of this slide was over 5 millions of cubics meters of soil and it produced the obstruction of the Grijalva river. The stratigraphic and geometric properties of the slope were determined and undisturbed samples were obtained in the site to determine the mechanical properties of the material. The stability analysis considered the variation of the cohesion of the soil caused by we ing and it was possible to observe the evolution of the safety factor with the water content of the material. Through the analysis of the rain infi ltration and the stability of the slope, it has been possible to reproduce the failure process.
Abstract
A number of slopes that have been stable during many years may fail when an extraordinary rain period occurs. This phenomenon involves not only the lithology, the geometric [...]
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ANÁLISIS DEL EFECTO DEL HUMEDECIMIENTO EN LA ESTABILIDAD DE UN BORDO DEL RÍO GRIJALVA, EN EL ESTADO DE TABASCO
A. OF, . renemora1121

ESPACIO I+D, Innovación más Desarrollo (2019). Vol. viii, N° 21, Octubre 2019 • ISSN: 2007-6703

Abstract
Durante la época de lluvias se presentan en el estado de Tabasco (México) deslizamientos en los bordos de los ríos que atraviesan la entidad, siendo los de la zona conocida como La Manga de los más afectados. Este artículo presenta el análisis de la evolución de la estabilidad de uno de estos bordos debido a los cambios en el grado de saturación del suelo (Sr) que lo conforma. El objetivo fue determinar el Sr del suelo para el cual el bordo pasa de una condición de seguridad a una de falla. Para lograrlo, primero se realizó una campaña de exploración de campo y ensayos de laboratorio, lo que permitió obtener las características geométricas del bordo, así como las propiedades del suelo que lo constituye. De las muestras inalteradas obtenidas en campo se realizaron ensayos de compresión triaxial variando solo el grado de saturación del suelo. Con los datos obtenidos y mediante el software GeoSlope 2016 se realizaron diversos análisis de la estabilidad. Los resultados muestran que conforme el grado de saturación crece la estabilidad del bordo disminuye. Se comprobó que para el bordo en estudio sobrepasar un grado de saturación de 70 % implica una condición de peligro de deslizamiento. Por lo tanto, el monitoreo del grado de saturación del suelo que constituye a los bordos permite anticipar su falla y, en consecuencia, hace posible establecer acciones de prevención.
Abstract
Durante la época de lluvias se presentan en el estado de Tabasco (México) deslizamientos en los bordos de los ríos que atraviesan la entidad, siendo los [...]
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COMPARACIÓN DEL RENDIMIENTO DE DOS AGENTES QUÍMICOS EN LA ESTABILIZACIÓN DE UN SUELO ARCILLOSO
. —, . renemora1121

ESPACIO I+D, Innovación más Desarrollo (2019). Vol. viii, N° 20, Junio 2019 • ISSN: 2007-6703

Abstract
Durante la ejecución de obras de ingeniería es común que el suelo que se desea utilizar no cumpla con los criterios de calidad que la normativa correspondiente exige para garantizar la estabilidad estructural de la obra. Para aquellos casos en los que el valor del índice de plasticidad del suelo excede el máximo permitido, la estabilización química ha demostrado los mejores resultados. En esta investigación se realizó un análisis comparativo del rendimiento del óxido de calcio (CaO) o cal viva, y el cloruro de sodio (NaCl) o sal de mesa, como agentes estabilizadores. Se agregaron estos agentes químicos en distintas proporciones al suelo en estudio y se monitorizaron las variaciones del límite líquido, límite plástico y el índice de plasticidad. Los resultados demostraron, contrario a lo que tradicionalmente se espera, que para el caso del suelo en estudio el mejor agente estabilizador es el cloruro de sodio o sal de mesa, debido a que no solo es más efectivo en disminuir el índice de plasticidad, sino que además es más barato que la cal.
Abstract
Durante la ejecución de obras de ingeniería es común que el suelo que se desea utilizar no cumpla con los criterios de calidad que la normativa correspondiente [...]
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A framework for developing finite element codes for multi- disciplinary applications
P. Dadvand, E. Oñate

Monograph CIMNE (2008). M109

Abstract
The world of computing simulation has experienced great progresses in recent years and requires more exigent multidisciplinary challenges to satisfy the new upcoming demands. Increasing the importance of solving multi-disciplinary problems makes developers put more attention to these problems and deal with difficulties involved in developing software in this area. Conventional finite element codes have several difficulties in dealing with multi-disciplinary problems. Many of these codes are designed and implemented for solving a certain type of problems, generally involving a single field. Extending these codes to deal with another field of analysis usually consists of several problems and large amounts of modifications and implementations. Some typical difficulties are: predefined set of degrees of freedom per node, data structure with fixed set of defined variables, global list of variables for all entities, domain based interfaces, IO restriction in reading new data and writing new results and algorithm definition inside the code. A common approach is to connect different solvers via a master program which implements the interaction algorithms and also transfers data from one solver to another. This approach has been used successfully in practice but results duplicated implementation and redundant overhead of data storing and transferring which may be significant depending to the solvers data structure. The objective of this work is to design and implement a framework for building multi-disciplinary finite element programs. Generality, reusability, extendibility, good performance and memory efficiency are considered to be the main points in design and implementation of this framework. Preparing the structure for team development is another objective because usually a team of experts in different fields are involved in the development of multi-disciplinary code. Kratos, the framework created in this work, provides several tools for easy implementation of finite element applications and also provides a common platform for natural interaction of its applications in different ways. This is done not only by a number of innovations but also by collecting and reusing several existing works. In this work an innovative variable base interface is designed and implemented which is used at different levels of abstraction and showed to be very clear and extendible. Another innovation is a very efficient and flexible data structure which can be used to store any type of data in a type-safe manner. An extendible IO is also created to overcome another bottleneck in dealing with multi-disciplinary problems. Collecting different concepts of existing works and adapting them to coupled problems is considered to be another innovation in this work. Examples are using an interpreter, different data organizations and variable number of dofs per node. The kernel and application approach is used to reduce the possible conflicts arising between developers of different fields and layers are designed to reflect the working space of different developers also considering their programming knowledge. Finally several technical details are applied in order to increase the performance and efficiency of Kratos which makes it practically usable. This work is completed by demonstrating the framework’s functionality in practice. First some classical single field applications like thermal, fluid and structural applications are implemented and used as benchmark to prove its performance. These applications are used to solve coupled problems in order to demonstrate the natural interaction facility provided by the framework. Finally some less classical coupled finite element algorithms are implemented to show its high flexibility and extendibility.
Abstract
The world of computing simulation has experienced great progresses in recent years and requires more exigent multidisciplinary challenges to satisfy the new upcoming demands. [...]
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Ship hydrodynamics
E. Oñate, J. García-Espinosa, S. Idelsohn, B. Servan Camas

(2018). Encyclopedia of Computational Mechanics Second Edition, E. Stein, R. de Borst and T.J.R. Hughes (Eds.), John Wiley & Sons Ltd, Vol. 6, Chapter 24, pp. 1091 - 1137

Abstract
This chapter presents an overview of some computational methods for the analysis of problems in ship hydrodynamics. Attention is focused on the description of stabilized finite element formulations derived via a finite increment calculus (FIC) procedure. Both arbitrary Lagrangian–Eulerian (ALE) and fully Lagrangian forms are presented. Details of the treatment of the free‐surface waves and the interaction between the ship structure and the sea water are given. Potential flow formulations for seakeeping analysis and calculation of the added resistance in waves are also described. Examples of application of the computational methods presented to a variety of ship hydrodynamics and related problems are given.
Abstract
This chapter presents an overview of some computational methods for the analysis of problems in ship hydrodynamics. Attention is focused on the description of stabilized finite [...]
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A Particle Finite Element Method (PFEM) for coupled thermal analysis of quasi and fully incompressible flows and fluid-structure interaction
E. Oñate, A. Franci, J. Carbonell

(2014). (preprint) Numerical simulation of coupled problems in engineering. S. R. Idelsohn (Eds.), pp. 129-156, Springer

Abstract
We present a Lagrangian formulation for coupled thermal analysis of quasi and fully incompressible flows and fluid-structure interaction (FSI) problems that has excellent mass preservation features. The success of the formulation lays on a residual-based stabilized expression of the mass balance equation obtained using the Finite Calculus (FIC) method. The governing equations are discretized with the FEM using simplicial elements with equal linear interpolation for the velocities, the pressure and the temperature. The merits of the formulation in terms of reduced mass loss and overall accuracy are verified in the solution of 2D and 3D adiabatic and thermally-coupled quasi-incompressible free-surface flow problems using the Particle Finite Element Method (PFEM). Examples include the sloshing of water in a tank and the falling of a water sphere and a cylinder into a tank containing water.
Abstract
We present a Lagrangian formulation for coupled thermal analysis of quasi and fully incompressible flows and fluid-structure interaction (FSI) problems that has excellent [...]
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GiD 2008. 4th Conference on advances and applications of GiD
A. Coll, M. Pasenau, E. Escolano, J. Pérez, A. Melendo

Monograph CIMNE (2008). M110

Abstract
The extended use of simulation programs has leaned on the advances in user-friendly interfaces and in the capability to generate meshes for any generic complex geometry. More than ten years of development have made Gid grow to become one of the more popular pre ans postprocessing systems at international level. The constant dialogue between the GiD development team and the users has guided the development of giD to cover the pre-post needs of many disciplines in science and engineering. Following gthis philosophy, the biannual GiD Conference has become an important forum for discussion and interchange of experiences among the GiD community. This monograph includes the contributions of the participants to the fourth edition of the GiD Conference held in the island of Ibiza from 8-9 May 2008.
Abstract
The extended use of simulation programs has leaned on the advances in user-friendly interfaces and in the capability to generate meshes for any generic complex geometry. More [...]
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Shear band localization via local J2 continuum damage mechanics
M. Cervera, M. Chiumenti, C. Agelet de Saracibar

Monograph CIMNE (2003). M78

Abstract
This paper describes a novel formulation for the solution of problems involving shear band localization using a local isotropic J2 continuum damage model and mixed linear simplex (triangles and tetrahedra). Stabilization methods are used to ensure existence and uniquess of the solution, attaining global and local stability of the corresponding discrete finite element formulation. Consistent residual viscosity is used to enhance robustness and convergence of the formulation. Implementation and computational aspects are also discussed. A simple isotropic local J2 damage constitutive model is considered, either with linear or exponential softening. The softening modulus is regularized according to the material mode II fracture energy and the element size. Numerical examples show that the formulation derived is fully stable and remarkably robust, totally free of volumetric locking and spurious oscillations of the pressure. As a consequence, the results obtained do not suffer from spurious mesh-size or mesh-bias dependence, comparing very favorably with those obtained with the ill-posed standard approaches.
Abstract
This paper describes a novel formulation for the solution of problems involving shear band localization using a local isotropic J2 continuum damage model and mixed linear [...]
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A new approach in computational contact mechanics: The contact domain method
J. Oliver, S. Hartmann, J. Cante, R. Weyler, J. Hernández

Monograph CIMNE (2009). M112

Abstract
This first part of the work presents the theoretical aspects of a new approach to solve two-dimensional large-strain problems in computational contact mechanics. The basic elements of the proposed metod are: 1) the use of an updated Lagrangean approach to describe the motion of the contacting bodies, 2) consideration of a two-dimensional aontact domain, where the contact/friction restrictions are imposed, and construction of a one layer triangulation in this domain, 3) resorting to a Lagrange multiplier method to impose the contact/friction contraints, 4) an interior penaltyprocedure, allowing condensation of the Lagrange multipliers, ensuring the stability of the discretized problem and 5) an active set strategy, for determining the subsets of the contact domain were contact/friction conditions have to be applied, based on the concept domain were contact/friction conditions have to be aaplied, based on the concept of effective gaps as suitable entities for extrapolation and prediction purposes.
Abstract
This first part of the work presents the theoretical aspects of a new approach to solve two-dimensional large-strain problems in computational contact mechanics. The basic [...]
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Freak Edge Waves
F. WAVES, A. Lechuga

Antonio Lechuga's personal collection (2019). 13

Abstract
The nonlinear and unsteady dynamics of the edge waves is discussed. Two physical processes: dispersive focusing and nonlinear modulational instability, are studied. Both mechanisms can induce the appearance of the short-living large-amplitude isolated waves and intense wave packets (“freak edge waves”).
Abstract
The nonlinear and unsteady dynamics of the edge waves is discussed. Two physical processes: dispersive focusing and nonlinear modulational instability, are studied. Both mechanisms [...]
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Aplicación del método PFEM a la simulación de procesos de transferencia propios de la industria pulvimetalúrgica
C. González, J. Cante, J. Oliver

Monograph CIMNE (2010). M117

Abstract
El objetivo primario del trabajo es desarrollar desde el enfoque de la ingeniería la metodología PFEM, la cual se fundamenta en una reinterpretación alternativa los métodos clásicos masivamente aceptados. Como objetivos adicionales de la monografía se tienen aplicar el PFEM a problemas complejos pertenecientes a la pulvimetalurgia, exhibir sus potencialidades en otros campos de la ingeniería y vislumbrar algunas líneas de investigación y desarrollo futuros.
Abstract
El objetivo primario del trabajo es desarrollar desde el enfoque de la ingeniería la metodología PFEM, la cual se fundamenta en una reinterpretación [...]
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Flood. An open source neural networks C++ library
R. López

Monograph CIMNE (2010). M120

Abstract
The multilayer perceptron is an important model of neural network, and much of the literature in the eld is referred to that model. The multilayer perceptron has found a wide range of applications, which include function re- gression, pattern recognition, time series prediction, optimal control, optimal shape design or inverse problems. All these problems can be formulated as variational problems. That neural network can learn either from databases or from mathematical models. Flood is a comprehensive class library which implements the multilayer perceptron in the C++ programming language. It has been developed follow- ing the functional analysis and calculus of variations theories. In this regard, this software tool can be used for the whole range of applications mentioned above. Flood also provides a workaround for the solution of function opti- mization problems.
Abstract
The multilayer perceptron is an important model of neural network, and much of the literature in the eld is referred to that model. The multilayer perceptron has found a [...]
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Numerical modelling of crack formation in powder compaction processes
J. Hernández, J. Oliver, J. Cante

Monograph CIMNE (2009). M114

Abstract
The primary objective of this work is precisely to fill this gap by developing a constitutive model that attempts to describe the mechanical behavior of the powder during both pressing and ejection phases, with special emphasis on the representation of the cracking phenomenon. The constitutive relationships are derived within the general framework of rate-independent, isotropic, finite strain elastoplasticity. The yield function is defined in stress space by three surfaces intersecting nonsmoothly, namely, an elliptical cap and two classical Von Mises and Drucker-Prager yield surfaces. The distinct irreversible processes occurring at the microscopic level are macroscopically described in terms of two internal variables: an internal hardening variable, associated with accumulated compressive (plastic) strains, and an internal softening variable, linked with accumulated (plastic) shear strains. The innovative part of our modeling approach is connected mainly with the characterization of the latter phenomenological aspect: strain softening. Incorporation of a softening law permits the representation of macroscopic cracks as high gradients of inelastic strains (strain localization). Motivated by both numerical and physical reasons, a parabolic plastic potential function is introduced to describe the plastic flow on the linear Drucker-Prager failure surface. A thermodynamically consistent calibration procedure is employed to relate material parameters involved in the softening law to fracture energy values obtained experimentally on Distaloy AE specimens.
Abstract
The primary objective of this work is precisely to fill this gap by developing a constitutive model that attempts to describe the mechanical behavior of the powder during [...]
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Regularized maxwell equations and nodal finite elements for electromagnetic field computations in frequency domain
R. Otín, E. Oñate

Monograph CIMNE (2011). M123

Abstract
In this work we present an alternative approach to the usual finite element formulation based on edge elements and double-curl Maxwell equations. This alternative approach is based on nodal elements and regularized Maxwell equations. The advantages are that, without adding extra unknowns (such as Lagrange multipliers), it provides spurious-free solutions and well-conditioned matrices. Besides, its integral representation involves a less singular kernel (order 1 instead of 3), which makes this approach best suited to hybridization with integral numerical techniques. On the other hand, a new set of difficulties arises that were not present in the classical formulation. The main drawback is that a globally wrong solution is obtained when the electromagnetic field has a singularity in the problem domain. Also, boundary conditions and field discontinuities are more laborious to implement. This work explains how to overcome these difficulties and demonstrates that accurate solutions can be obtained with nodal elements and the regularized formulation. We also present ERMES, the C++ implementation of the finite element approach depicted above and the main deliverable of this work. We compute with ERMES the scattering parameters of microwave filters and the specific absorption rate induced in a body when exposed to electromagnetic fields. ERMES is also the computational tool used in two novel numerical models introduced in this work. The first one characterizes electromagnetic metal forming processes and the second one the transfer impedance of cable shields. The electromagnetic metal forming model calculates the driving Lorentz force and estimates the optimum frequency at which it is attained the maximum workpiece deformation. The main advantage of the approach is that it provides an explicit relation between the capacitance of the capacitor bank and the frequency of the discharge, which is a key parameter in the design of an electromagnetic forming system. The successful application of the regularized formulation in this model reveals its excellent behavior in the low-frequency (quasi-static) regime. The second numerical model introduced in this work computes the transfer impedance of cable shields. The model reproduces the high frequency behavior of the transfer impedance more accurately than the approaches found in the literature and, moreover, it is able to analyze a wider variety of geometries and materials.
Abstract
In this work we present an alternative approach to the usual finite element formulation based on edge elements and double-curl Maxwell equations. This alternative approach [...]
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The Particle Finite Element Method. An effective numerical technique for fluid-soil-structure interaction problems
E. Oñate, M. Celigueta, S. Idelsohn, F. Salazar, B. Suarez

(2012). Issues on Mechanical and Civil Engineering. A Symposium to honour Prof. Enrique Alarcón. M. Doblaré, Ja. Domínguez, Jo. Domínguez, A. Fraile, F. García, S. Gómez, A. Martín, F. París (Eds.)

Abstract
We present some developments in the Particle Finite Element Method (PFEM) for analysis of complex coupled problems in mechanics involving fluid-soil-structure interaction (FSSI). The PFEM uses an updated Lagrangian description to model the motion of nodes (particles) in both the fluid and the solid domains (the later including soil/rock and structures). A mesh connects the particles (nodes) defining the discretized domain where the governing equations for each of the constituent materials are solved as in the standard FEM. The stabilization for dealing with an incompressibility continuum is introduced via the finite calculus (FIC) method. An incremental iterative scheme for the solution of the non linear transient coupled FSSI problem is described. The procedure to model frictional contact conditions and material erosion at fluid-solid and solid-solid interfaces is described. We present several examples of application of the PFEM to solve FSSI problems such as the motion of rocks by water streams, the erosion of a river bed adjacent to a bridge foundation, the stability of breakwaters and constructions sea waves and the study of landslides.
Abstract
We present some developments in the Particle Finite Element Method (PFEM) for analysis of complex coupled problems in mechanics involving fluid-soil-structure interaction [...]
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Possibilities of the Particle Finite Element Method in computational mechanics
E. Oñate, S. Idelsohn, M. Celigueta, R. Rossi, S. Latorre

(2010). Computer Methods in Mechanics, M. Kuzma, K. Wilmanski (Eds.), Chapter 15, pp. 271-310., Springer-Verlag, Berlin, Heidelberg

Abstract
We present some developments in the formulation of the Particle Finite Element Method (PFEM) for analysis of complex coupled problems in fluid and solid mechanics accounting for fluid-structure interaction and coupled thermal effects. The PFEM uses an updated Lagrangian description to model the motion of nodes (particles) in both the fluid and the structure domains. Nodes are viewed as material points which can freely move and even separate from the main analysis domain representing, for instance, the effect of water drops. A mesh connects the nodes defining the discretized domain where the governing equations are solved as in the standard FEM. The necessary stabilization for dealing with the incompressibility of the fluid is introduced via the finite calculus (FIC) method. An incremental iterative scheme for the solution of the non linear transient coupled fluid-structure problem is described. Extensions of the PFEM to allow for frictional contact conditions at fluid-solid and solid-solid interfaces via mesh generation are described. A simple algorithm to treat erosion in the fluid bed is presented. Examples of application of the PFEM to solve a number of coupled problems such as the effect of large wave on structures, the large motions of floating and submerged bodies, bed erosion situations and melting and dripping of polymers under the effect of fire are given.
Abstract
We present some developments in the formulation of the Particle Finite Element Method (PFEM) for analysis of complex coupled problems in fluid and solid mechanics accounting [...]
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Posibilidades de los métodos numéricos en obras subterráneas
E. Oñate, B. Suarez, J. Canet

(2007). Avances en Mecánica de Medios Continuos. Simposium en honor al Profesor J. A. Garrido García. E. Alarcon, A. Forces, F. París (Eds.), pp. 195-210

Abstract
Se presenta un resumen de las posibilidades de diversos métodos numéricos basados en la combinación de técnicas de elementos finitos y de partículas para la simulación de problemas típicos de obras subterráneas, tales como la excavación de túneles y la inundación de cavidades.
Abstract
Se presenta un resumen de las posibilidades de diversos métodos numéricos basados en la combinación de técnicas de elementos finitos y de partículas [...]
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Finite elements versus finite volumes. Is there really a choice?
O. Zienkiewicz, E. Oñate

(1992). Non linear computational mechanics. State of the art. P. Wriggers and R. Wagner (eds.), Springer Verlag

Abstract
The finite volume method appears to be a particular case of finite elements with a non Galerkin weighting. It is course less accurate for self adjoint problems but has some computationally useful features for first order equations involving only surface integrals. For certain problems this is a substational economy and leads to computationally useful approximations.
Abstract
The finite volume method appears to be a particular case of finite elements with a non Galerkin weighting. It is course less accurate for self adjoint problems but has some [...]
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Possibilities of the finite element viscous shell approach for analysis of sheet metal forming problems
E. Oñate, R. Lama

(1986). In Lange K. (eds), Simulation of Metal Forming Processes by the Finite Element Method (SIMOP-I). Berichte aus dem Institut für Umformtechnik der Universität Stuttgart, vol 85. Springer, Berlin, Heidelberg

Abstract
The viscous shell approach combines the use of visco-plastic flow and classical shell theories. The paper presents the general aspects of the viscous shell formulation for axisymmetric and general 3-D shell problems using finite elements. Details of treatment of coordenate updating, friction effects, strain hardening and extensions to include the elastic deformations are also given together with some examples of application to the forming of axisymmetrical thin sheets of metal under hemispherical punches.
Abstract
The viscous shell approach combines the use of visco-plastic flow and classical shell theories. The paper presents the general aspects of the viscous shell formulation for [...]
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Numerical simulation of industrial sheet forming processes
E. Oñate

Monograph CIMNE (1993). M23

Abstract
This monograph presents different finite element based mathematical models and computational methods for numerical simulation of industrial sheet metal forming processes.
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II International Workshop. Information Technologies and Computing Techniques for the Agro-Food Sector
E. Balsa, J. Mora, J. Banga, E. Oñate

Monograph CIMNE (2003). M86

Abstract
This monographs of proceedings includes all extended abstracts, which will be presented during the AfoT. These presentations will cover a wide range of topics: - Modelling and simulation operations and process plants. - Food process optimisation, scheduling and control. - Food properties measurements and quality control. - Simulation of complex processes, for example those requiring computational fluid dynamics, CFD. - The use of new information technologies to develop decision support sytems.
Abstract
This monographs of proceedings includes all extended abstracts, which will be presented during the AfoT. These presentations will cover a wide range of topics: - [...]
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Métodos avanzados de cálculo de estructuras de materiales compuestos
E. Oñate, S. Oller, S. Botello, J. Miquel

Monograph CIMNE (1991). M3

Abstract
Se presenta una panorámica del estado del arte de los métodos más actuales para análisis de estructuras con materiales compuestos, incidiendo particularmente en los métodos para análisis de vehículos industriales como materiales compuestos
Abstract
Se presenta una panorámica del estado del arte de los métodos más actuales para análisis de estructuras con materiales compuestos, incidiendo particularmente [...]
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Simulación numérica de la aerodinámica de vehículos
J. Miquel, G. Bugeda, E. Oñate

Monograph CIMNE (1991). M2

Abstract
Este trabajo analiza las posibilidades de simulación numérica del flujo aerodinámico alrededor de vehículos automotores, desde un doble punto de vista: metodología a utilizar y desarrollo de las aplicaciones que tal tipo de estudios tienen en los vehículos automotores. A lo largo del desarrollo del mismo, quedan patentes una serie de herramientas mediante las cuales es posible realizar tal tipo de simulación numérica. Dichos estudios revisten una gran importancia si se quiere conocer el comportamiento de los vehículos automotores en condiciones de operación, afectando a aspectos tan importantes como seguridad, ruido, estabilidad, consumo de combustible, ventilación, etc.
Abstract
Este trabajo analiza las posibilidades de simulación numérica del flujo aerodinámico alrededor de vehículos automotores, desde un doble punto de [...]
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CFD analysis of the roll movement of a container ship
J. García-Espinosa, E. Oñate, J. Helmers, M. Chakkor

Revista de Ingeniería Naval (2004). Vol. 814, pp. 104-108

Abstract
In the present work a novel approach has been developed for the resolution of this problem of analysis of the movement of roll of a ship. The methodology used for this is based on the modification of the differential equations of the fluid dynamics (RANSE equations), including the movement of the free surface, by applying the finite calculus method. The modified equations are solved using an implicit predictor-corrector scheme and the finite element method (FEM). This resolution scheme is considered optimal for these types of problems, both in accuracy and in calculation time. As an example, it should be noted that for typical problems (more than 1,000,000 finite elements) less than 4 hours of CPU are required to solve several cycles of ship movement (Pentium IV). This allows the analysis of an array of tests in a few days or even hours, having a computer network or sufficient computing power.
Abstract
In the present work a novel approach has been developed for the resolution of this problem of analysis of the movement of roll of a ship. The methodology used for this is [...]
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Desarrollos y aplicaciones de modelos de fractura en la escuela de ingenieros de caminos de Barcelona
E. Oñate

Anales de Mecánica de Fractura (2000). Vol. 17, pp. 127-154

Abstract
El artículo es una panorámica de los aspectos teóricos y algunas aplicaciones prácticas de los modelos de fractura desarrollados por diversos grupos en la Escuela de Ingenieros de Caminos de Barcelona (EICB) durante los últimos quince años para el análisis no lineal de estructuras. La motivación fundamental para el desarrollo de estos modelos se centra en el análisis de la seguridad de estructuras de hormigón en masa y armado. La mayor parte de los modelos se basan en la teoría de daño continuo y utilizan el método de los elementos finitos para la solución numérica. Los modelos de daño se han extendido y aplicado también con éxito al análisis de diversas estructuras de edificios históricos. Los desarrollos más recientes de estos modelos en la EICB incluyen la predicción de fenómenos de localización en estructuras de hormigón y el análisis del comportamiento no lineal de estructuras con materiales compuestos. De todos estos modelos se presentan en el artículo unas breves pinceladas, las aplicaciones más relevantes y las referencias donde pueden encontrarse los detalles sobre cada caso.
Abstract
El artículo es una panorámica de los aspectos teóricos y algunas aplicaciones prácticas de los modelos de fractura desarrollados por diversos grupos [...]
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A finite element model for fluid–structure interaction problems involving closed membranes, internal and external fluids
P. Ryzhakov, E. Oñate

Comput. Methods Appl. Mech. Engrg., (2017). Vol. 326, pp. 422-445

Abstract
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.
Abstract
In this paper we propose a Finite Element model for analyzing closed membranes (“bags”) interacting with internal and external (surrounding) fluids. The approach [...]
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Cool steam method for desalinating seawater
P. Arnau, N. Navarro, J. Soraluce, J. Martínez-Iglesias, J. Illas, E. Oñate

Water (2019). Vol. 11 (11), 16 pp.

Abstract
Cool steam is an innovative distillation technology based on low-temperature thermal distillation (LTTD), which allows obtaining fresh water from non-safe water sources with substantially low energy consumption. LTTD consists of distilling at low temperatures by lowering the working pressure and making the most of low-grade heat sources (either natural or artificial) to evaporate water and then condensate it at a cooler heat sink. To perform the process, an external heat source is needed that provides the latent heat of evaporation and a temperature gradient to maintain the distillation cycle. Depending on the available temperature gradient, several stages can be implemented, leading to a multi-stage device. The cool steam device can thus be single or multi-stage, being raw water fed to every stage from the top and evaporated in contact with the warmer surface within the said stage. Acting as a heat carrier, the water vapor travels to the cooler surface and condensates in contact with it. The latent heat of condensation is then conducted through the conductive wall to the next stage. Net heat flux is then established from the heat source until the heat sink, allowing distilling water inside every parallel stage.
Abstract
Cool steam is an innovative distillation technology based on low-temperature thermal distillation (LTTD), which allows obtaining fresh water from non-safe water sources with [...]
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PFEM formulation for thermo-coupled FSI analysis. Application to nuclear core melt accident
A. Franci, E. Oñate, J. Carbonell, M. Chiumenti

Comput. Methods Appl. Mech. Engrg., (2017). Vol. 325, pp. 711-732

Abstract
The aim of this paper is to present a Lagrangian formulation for thermo-coupled fluid–structure interaction (FSI) problems and to show its applicability to the simulation of hypothetical scenarios of a nuclear core melt accident. During this emergency situation, an extremely hot and radioactive lava-like material, the corium, is generated by the melting of the fuel assembly. The corium may induce collapse of the nuclear reactor devices and, in the worst case, breach the reactor containment and escape into the environment. This work shows the capabilities of the proposed formulation to reproduce the structural failure mechanisms induced by the corium that may occur during a meltdown scenario. For this purpose, a monolithic method for FSI problems, the so-called Unified formulation, is here enhanced in order to account for the thermal field and to model phase change phenomena with the Particle Finite Element Method (PFEM). Several numerical examples are presented. First, the convergence of the thermo-coupled method and phase change algorithm is shown for two academic problems. Then, two complex simulations of hypothetical nuclear meltdown situations are studied in 2D as in 3D.
Abstract
The aim of this paper is to present a Lagrangian formulation for thermo-coupled fluid–structure interaction (FSI) problems and to show its applicability [...]
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A FIC-based stabilized finite element formulation for turbulent flows
J. Cotela-Dalmau, R. Rossi, E. Oñate

Comput. Methods Appl. Mech. Engrg., (2017). (preprint) Vol. 315, pp. 607-631

Abstract
We present a new stabilized finite element (FEM) formulation for incompressible flows based on the Finite Increment Calculus (FIC) framework (Oñate, 1998). In comparison to existing FIC approaches for fluids, this formulation involves a new term in the momentum equation, which introduces non-isotropic dissipation in the direction of velocity gradients. We also follow a new approach to the derivation of the stabilized mass equation, inspired by recent developments for quasi-incompressible flows (Oñate et al., 2014). The presented FIC-FEM formulation is used to simulate turbulent flows, using the dissipation introduced by the method to account for turbulent dissipation in the style of implicit large eddy simulation.
Abstract
We present a new stabilized finite element (FEM) formulation for incompressible flows based on the Finite Increment Calculus (FIC) framework (Oñate, [...]
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A shallow water model by finite point method
C. Bouchart, W. Kanok-Nukulschai, E. Ortega, E. Oñate

International Journal of Computational Methods (2014). Vol. 11 (1), 27 pp., Paper N: 1350047

Abstract
In this paper, "finite point method" (FPM) is presented for modeling 2D shallow water flow problem. The method is based on the use of a weighted least-square approximation procedure, incorporating QR factorization and an iterative adjustment of local approximation parameters. The stabilization of the convective term in this present work is derived from the approximate Riemann solver proposed by Roe. The present method is shown to produce competitive accuracy in the comparisons with the analytical solutions and the well-known Galerkin characteristic-based split (CBS) algorithm.
Abstract
In this paper, "finite point method" (FPM) is presented for modeling 2D shallow water flow problem. The method is based on the use of a weighted least-square approximation [...]
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Advances in the development of a FEM model for evaluation of a Surface-Effect Ship (SES) including skirt dynamics
J. García-Espinosa, B. Camas, D. Di Capua, P. Ubach de Fuentes, E. Oñate

Ingeniería Naval (2013). Vol. 1 (920), pp. 68-91

Abstract
El “Innovative Naval Prototype Transformable Craft” (T-Craft) es un nuevo concepto de buque desarrollado por la marina de los Estados Unidos de América para la conexión de una base en alta mar con tierra. El TCraft puede operar en múltiple modos, usándose para conectar una base intermedia de soporte con la principal, y luego ser utilizado como conexión de alta velocidad con la costa, transportando vehículos y otros equipos y carga pesada hasta la playa. El T-Craft se ha concebido como un buque de efecto superficie (Surface-Effect Ship, SES) con un colchón de aire activo entre dos cascos rígidos, que permite al buque operar a desplazamiento completo, con soporte parcial del colchón o con el colchón plenamente activo. Este artículo presenta el trabajo reciente de los autores en el desarrollo de un modelo de evaluación del comportamiento en la mar y la maniobrabilidad del T-Craft, incluyendo la interacción del faldón. Este modelo está basado en la resolución de las ecuaciones de flujo potencial en el dominio del tiempo, mediante el método de los elementos finitos, integrando la superficie libre a lo largo de las líneas de corriente. Este artículo revisa el algoritmo de interacción fluido estructura desarrollado para la simulación de la compleja dinámica de los sellos, en la interfaz entre el colchón de aire y el agua. El algoritmo se basa, por una parte, en un algoritmo explícito alternado que permite la comunicación entre los solvers fluido-dinámico y estructural mediante TCP-IP sockets, intercambiando fuerzas de presión y desplazamientos en los sellos durante la ejecución, y por otra parte, en un innovador esquema de secado-mojado que permite predecir la interacción del agua con los sellos. Se incluyen varios casos de aplicación de la metodología desarrollada sobre el modelo l XR-1B.
Abstract
El “Innovative Naval Prototype Transformable Craft” (T-Craft) es un nuevo concepto de buque desarrollado por la marina de los Estados Unidos de América [...]
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Analysis of the melting, burning and flame spread of polymers with the particle finite element method
E. Oñate, J. Marti, P. Ryzhakov, R. Rossi, S. Idelsohn

Computer Assisted Methods in Engineering and Sciences (2013). Vol. 20 (3), pp. 165-184

Abstract
A computational procedure for analysis of the melting, burning and flame spread of polymers under fire conditions is presented. The method, termed particle finite element method (PFEM), combines concepts from particle-based techniques with those of the standard finite element method (FEM). The key feature of the PFEM is the use of an updated Lagrangian description to model the motion of nodes (particles) in the thermoplastic material. Nodes are viewed as material points which can freely move and even separate from the main analysis domain representing, for instance, the effect of melting and dripping of polymer particles. A mesh connects the nodes defining the discretized domain where the governing equations are solved using the FEM. An incremental iterative scheme for the solution of the nonlinear transient coupled thermal-flow problem, including radiation, loss of mass by gasification and combustion is used. Examples of the possibilities of the PFEM for the modelling and simulation of the melting, burning and flame spread of polymers under different fire conditions are described.
Abstract
A computational procedure for analysis of the melting, burning and flame spread of polymers under fire conditions is presented. The method, termed particle finite element [...]
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Analysis of the discharge capacity of radial-gated spillways using CFD and ANN – Oliana Dam case study
F. Salazar, R. Morán Moya, R. Rossi, E. Oñate

Journal of Hydraulic Research (2013). (preprint) Vol. 51 (3), pp. 244-252

Abstract
The paper focuses on the analysis of radial-gated spillways, which is carried out by the solution of a numerical model based on the finite element method (FEM). The Oliana Dam is considered as a case study and the discharge capacity is predicted both by the application of a level-set-based free-surface solver and by the use of traditional empirical formulations. The results of the analysis are then used for training an artificial neural network to allow real-time predictions of the discharge in any situation of energy head and gate opening within the operation range of the reservoir. The comparison of the results obtained with the different methods shows that numerical models such as the FEM can be useful as a predictive tool for the analysis of the hydraulic performance of radial-gated spillways.
Abstract
The paper focuses on the analysis of radial-gated spillways, which is carried out by the solution of a numerical model based on the finite element method (FEM). The Oliana [...]
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Olgierd Cecil Zienkiewicz obituary
M. Kleiber, E. Oñate

Archives of Comp. Meths. Engng. (2009). Vol. 16, pp. 465
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Control of the finite element discretization error during the convergence of structural shape optimization algorithms
G. Bugeda, J. Ródenas, J. Albelda, E. Oñate

Int. J. Simul. Multidisci. Des. Optim. (2009). Vol. 3 (3), pp. 363-369

Abstract
This work analyzes the influence of the discretization error contained in the Finite Element (FE) analyses of each design configuration proposed by structural shape optimization algorithms over the behaviour of the algorithm. If the FE analyses are not accurate enough, the final solution will neither be optimal nor satisfy the constraints. The need for the use of adaptive FE analysis techniques in shape optimum design will be shown. The paper also proposes the use of the algorithm described in [1] in order to reduce the computational cost associated to the adaptive FE analysis of each geometrical configuration when evolutive optimization algorithms are used.
Abstract
This work analyzes the influence of the discretization error contained in the Finite Element (FE) analyses of each design configuration proposed by structural shape optimization [...]
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Advances in the particle finite element method for fluid-structure interaction problems
E. Oñate, S. Idelsohn, M. Celigueta, R. Rossi

Computational Mechanics (2006). Vol. 6, pp. 41-62

Abstract
We present a general formulation for analysis of fluid-structure interaction problems using the particle finite element method (PFEM). The key feature of the PFEM is the use of a Lagrangian description to model the motion of nodes (particles) in both the fluid and the structure domains. Nodes are thus viewed as particles which can freely move and even separate from the main analysis domain representing, for instance, the effect of water drops. A mesh connects the nodes defining the discretized domain where the governing equations, expressed in an integral from, are solved as in the standard FEM. The necessary stabilization for dealing with the incompressibility of the fluid is introduced via the finite calculus (FIC) method. A fractional step scheme for the transient coupled fluid-structure solution is described. Examples of application of the PFEM to solve a number of fluid-structure interaction problems involving large motions of the free surface and splashing of waves are presented.
Abstract
We present a general formulation for analysis of fluid-structure interaction problems using the particle finite element method (PFEM). The key feature of the PFEM is the use [...]
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The rotation-free BST shell element for linearized buckling analysis of steel structures
A. Agüero, F. Pallarés, E. Oñate

Int. J. Computational Methods in Engineering Science and Mechanics (2006). Vol. 7 (3), pp. 209-215

Abstract
In this paper the ability of the basic shell triangular (BST) element to perform linearized buckling analysis is evaluated. The results have been compared with analytical solutions and other finite elements in the literature, such as ANDES3, ANDES4, QSEL, FFQC and BCIZ. This type of analysis is applied to the design of steel structures to obtain the collapse load of panels using the effective width of the plate. In this approach, which is currently recommended by most of the design standards, a semi-empirical/analytical method is used to take into account the nonlinear geometric and material behavior, geometric imperfections and residual stresses. To obtain the critical loads two methods have been mainly applied: the finite strip method and the finite element method, which is more appropriate to deal with any boundary condition and loading pattern. In practice, to obtain the local and distortional buckling, some assumptions related to the interaction between plates are made in order to obtain practical formulae that can be applied; these simplifications can lead to unsafe results, so the linearized buckling analysis must be carried out in a proper way, taking into account the interactions. It is concluded that the BST element presents an excellent behavior to predict the critical loads in compression and shear, and therefore this element must be utilized in future codes when this type of analysis turn out to be mandatory.
Abstract
In this paper the ability of the basic shell triangular (BST) element to perform linearized buckling analysis is evaluated. The results have been compared with analytical [...]
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Simulación de problemas de desgaste, en la interacción herramienta de corte terreno, empleando el método de los elementos discretos
C. Recarey Morfa, E. Oñate, J. Canet, J. Rojek, F. Zarate, S. Burrel

Ingeniería Civil (2006). Vol. 141, pp. 19-34

Abstract
Se presenta un modelo numérico que emplea elementos discretos esféricos o también denominados elementos distintos. Este modelo se aplica en la simulación de problemas de desgaste. El movimiento de elementos esféricos se describe por medio de las ecuaciones de Newton-Euler. Se emplea en la formulación una integración explícita, la cual, brinda una buena eficiencia computacional. Los elementos esféricos interactúan recíprocamente entre sí a través de las fuerzas de contacto. El esquema de búsqueda de contacto es muy eficaz, y está basado en las estructuras de oct-tree. El modelo constitutivo de contacto presenta una singularidad muy especial, ya que puede simular las fuerzas de cohesión que permiten modelar la fractura y descohesión de los materiales. El estudio de desgastes se realiza a partir de una formulación termoacoplada que se aplica a nivel experimental, o escala reducida, y además in-situ o escala real.
Abstract
Se presenta un modelo numérico que emplea elementos discretos esféricos o también denominados elementos distintos. Este modelo se aplica en la simulación [...]
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Posibilidades de los métodos numéricos en el mundo industrial
E. Oñate

Col·lecció Aula de Ciència i Cultura (2002). Nº 13, pp. 9-33

Abstract
Se presentan en el artículo las ideas básicas de qué son los métodos numéricos, cuáles son los métodos numéricos más populares, cómo se aplican para resolver ecuaciones diferenciales de interés práctico en ingeniería y qué posibilidades y limitaciones tienen para ayudarnos a entender mejor el mundo que nos rodea. El contenido del artículo se completa con diversas aplicaciones prácticas del método de elementos finitos a diversos problemas de ingeniería.
Abstract
Se presentan en el artículo las ideas básicas de qué son los métodos numéricos, cuáles son los métodos numéricos más [...]
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ECONOMIA DEL COMPORTAMIENTO APLICADA A LAS TELECOMUNICACIONES
F. Legaspe, F. Legaspe Gabrielli

Collection of Articles on Economics, Econometrics and Finance (2019). 1

Abstract
A nivel mundial, el mercado de servicios de telefonía móvil es un mercado relativamente nuevo que presenta un gran dinamismo. Generalmente su estructura es oligopólica, dando lugar a ineficiencias asignativas, esto es, el consumidor paga un precio superior al costo marginal de provisión y por lo tanto su excedente es menor que el que obtendría en situaciones de competencia perfecta. El mercado argentino no es la excepción. El objetivo de esta investigación es sugerir, un conjunto de medidas que, sin alterar el cuadro tarifario de los prestadores, refuercen el régimen de protección de los consumidores e incrementen el nivel de satisfacción de los mismos. En particular, la investigación se focalizará en tres problemáticas que son consideradas de especial relevancia: los problemas de información, los errores en la toma de decisiones y la baja calidad de los servicios de atención al cliente. El marco teórico utilizado para el análisis es el de economía del comportamiento que, al revalorizar aspectos sociológicos y psicológicos del consumidor, dota de un mayor realismo al análisis económico convencional. Se proponen diversas medidas para cada una de las problemáticas. Para resolver los problemas de información se propone que se presente la información en formatos simplificados y en momentos críticos. En cuanto a los errores en la toma de decisiones se sugiere disminuir los costos de traspaso, eliminar las opciones predeterminadas y crear un sistema que indique a los usuarios su plan mensual óptimo. Se propone también generar incentivos para que las empresas aumenten la calidad de los servicios de atención al cliente, para lograr esto se recomienda unificar las plataformas de reclamos de las compañías y crear un sistema de recompensas para incentivas feedback de los usuarios.
Abstract
A nivel mundial, el mercado de servicios de telefonía móvil es un mercado relativamente nuevo que presenta un gran dinamismo. Generalmente su estructura es oligopólica, [...]
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A large strain plasticity model for anisotropic materials - composite material application
E. Car, S. Oller, E. Oñate

International Journal of Plasticity (2001). Vol. 17 (11), pp. 1437-1463

Abstract
In this work a generalized anisotropic model in large strains based on the classical isotropic plasticity theory is presented. The anisotropic theory is based on the concept of mapped tensors from the anisotropic real space to the isotropic fictitious one. In classical orthotropy theories it is necessary to use a special constitutive law for each material. The proposed theory is a generalization of classical theories and allows the use of models and algorithms developed for isotropic materials. It is based on establishing a one-to-one relationship between the behavior of an anisotropic real material and that of an isotropic fictitious one. Therefore, the problem is solved in the isotropic fictious space and the results are transported to the real field. This theory is applied to simulate the behavior of each material in the composite. The whole behavior of the composite is modeled by incorporating the anisotropic model within a model based on a modified mixing theory.
Abstract
In this work a generalized anisotropic model in large strains based on the classical isotropic plasticity theory is presented. The anisotropic theory is based on the concept [...]
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Optimización de embarcaciones de recreo mediante la utilización de un código CFD
M. López-Rodríguez, J. García-Espinosa, E. Oñate

Ingeniería Naval (2001). Vol. 784, pp. 122-130

Abstract
En la actualidad las más avanzadas técnicas para diseño naval ya no se restringen sólo a proyectos de alto coste; si no que también ahora son de aplicación en el campo de las embarcaciones de recreo y turísticas, dando con ello un valor añadido al proyecto final. La utilización de un código CFD para el mayor conocimiento del comportamiento hidrodinámico de las embarcaciones de recreo y turísticas es de una gran utilidad debido a las complejidades que en el diseño de estas se presentan. Estas herramientas nos van a proporcionar una serie de datos como sustentación lateral en las embarcaciones de vela o interacción entre cascos en catamaranes con deriva lateral, que de otra forma nunca pudieran conocerse. Los resultados hidrodinámicos obtenidos nos sirven para comparar las diferentes alternativas, y para además obtener unos valores que directamente son usados para la predicción de velocidad de la embarcación, que más tarde se verán refrendadas por las pruebas de mar. La utilización de técnicas CFD, basadas en el método de los elementos finitos, para la resolución de las ecuaciones de Reynolds (RANSE), incluyendo efectos de superficie libre, hace que todo esto sea posible. En este trabajo se presentan diversos resultados de aplicación del código CFD SHYNE a varias embarcaciones deportivas y de recreo. SHYNE está basado en la técnica del Cálculo Finitesimal para la integración de las ecuaciones de Reynolds.
Abstract
En la actualidad las más avanzadas técnicas para diseño naval ya no se restringen sólo a proyectos de alto coste; si no que también ahora [...]
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ED-Elas2D: An Educational Program for Computer-aided Training in Structural Analysis Using the Finite Element Method
B. Suarez, E. Blanco, L. Gil, P. Zapata, E. Oñate

European Journal of Engineering Education (1998). Vol. 23 (2), pp. 243-254

Abstract
In this paper, a methodology for computer-aided training of structural problems by the finite element method is presented. The resulting educational program, named ED-Elas2D, has been developed by a group of researchers at the School of Civil Engineering at the Technical University of Catalonia (UPC) in Barcelona, UPC. The program combines the standard concept which appears in the traditional teaching of finite element methods for structural analysis, such as the introduction to the basic structural theory, data definition (pre-processor), description of the analysis procedure (processor) and interpretation of results (post-processor). The program is addressed to both students who enrol in the study on finite element methods and to academic and technical staff in universities and companies who wish to update their knowledge of finite element techniques. The educational program ED-Elas2D works in the Windows system and it is characterized by its interactivity and graphic utilities.
Abstract
In this paper, a methodology for computer-aided training of structural problems by the finite element method is presented. The resulting educational program, named ED-Elas2D, [...]
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A finite element model for thermomechanical analysis in casting processes
D. Celentano, S. Oller, E. Oñate

Journal of Physique IV (1993). Vol. 3 (C7), pp. 1171-1180

Abstract
This paper summarizes the recent work of the authors in the numerical simulation of casting processes. In particular, a coupled thermomechanical model to simulate the solidification problem in casting has been developed [7,8,9]. The model, based on a general isotropic thermoelasto-plasticity theory and formulated in a macroscopical point of view, includes generalized phase-change effects and considers the different thermomechanical behaviour of the solidifying material during its evolution from liquid to solid. For this purpose, a phase-change variable, plastic evolution equations and a temperature-dependent material constitutive law have been defined. Some relevant aspects of this model are presented here. Full thermomechanical coupling terms have been considered as well as variable thermal and mechanical boundary conditions : the first are due to air gap formation, while the second involve a contact formulation. Particular details concerning the numerical implementation of this model are also mentioned. An enhanced staggered scheme, used to solve the highly non-linear fully coupled finite element equations, is proposed. Furthermore, a proper convergence criterion to stop the iteration process is adopted and, although the quadratic convergence of Newton-Rapshon's method is not achieved, several numerical experiments demonstrate reasonable convergence rates [9]. Finally, an experimental cylindrical casting test problem, including phase-change phenomena, temperature-dependent constitutive properties and contact effects, is analyzed. Numerical results are compared with some laboratory measurements.
Abstract
This paper summarizes the recent work of the authors in the numerical simulation of casting processes. In particular, a coupled thermomechanical model to simulate the solidification [...]
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Análisis no lineal de tanques criogénicos bajo cargas térmicas
J. Oliver, E. Oñate, J. Peraire, R. Chueca

Hormigón y Acero (1985). Vol. 155, pp. 99-123
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La formulación del flujo viscoplástico y sus diversas aplicaciones prácticas por el método de los elementos finitos
E. Oñate

Revista de Obras Públicas (1980). Vol. 127 (3178), pp. 115-129
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Diseño óptimo de vasijas de presión usando el método de los elementos finitos y un optimizador no lineal
J. Middleton, E. Oñate

ETSIIT (1977). Vol. 11, pp. 309-325

Abstract
Se presenta un esquema de diseño para vasijas de presión metálicas de manera que se minimice la tensión tangencial en la vasija . La geometría final se establece mediante un procedimiento iterativo que optimiza un modelo matemático que expresa la variación de la tensión tangencial en la vasija. Los parámetros del modelo se calculan para cada interacción a partir de los valores de las tensiones tangenciales en la vasija, determinados por el método de los elementos finitos.
Abstract
Se presenta un esquema de diseño para vasijas de presión metálicas de manera que se minimice la tensión tangencial en la vasija . La geometría [...]
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ExaQUte Leaflet
C. Soriano

Open Access Repository of the ExaQUte project (2019). 2

Abstract
ExaQUte Leaflet
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ExaQUte_4_Everyone
C. Soriano

Open Access Repository of the ExaQUte project (2019). 1

Abstract
ExaQUte Description for the general public
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J. Garcia de la Santa
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Detection of highly pathogenic avian inﬂuenza A(H5N6) viruses in waterfowl in Bangladesh
A. Virology, . May, S. Ghosh

(Select a year).

Abstract
Bangladesh has reported repeated outbreaks of highly pathogenic avian inﬂuenza (HPAI) A(H5) viruses in poultry since 2007. Because of the large number of live poultry markets (LPM) relative to the population density of poultry throughout the country, these markets can serve as sentinel sites for HPAI A(H5) detection. Through active LPM surveillance during June 2016–June 2017, HPAI A(H5N6) viruses along with 14 other subtypes of inﬂuenza A viruses were detected. The HPAI A(H5N6) viruses belonged to clade 2.3.4.4 and were likely introduced into Bangladesh around March 2016. Human infections with inﬂuenza clade 2.3.4.4 viruses in Bangladesh have not been identiﬁed, but the viruses had several molecular markers associated with potential human infection. Vigilant surveillance at the animal-human interface is essential to identify emerging avian inﬂuenza viruses with the potential to threaten public and animal health.
Abstract
Bangladesh has reported repeated outbreaks of highly pathogenic avian inﬂuenza (HPAI) A(H5) viruses in poultry since 2007. Because of the large number of live poultry markets [...]
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Awareness of rabies and response to dog bites in a Bangladesh community
S. Ghosh

(Select a year).

Abstract
Community awareness regarding rabies and treatment seeking behaviours are critical both for the prevention and control of the disease in human and animals. We conducted a study to explore people’s awareness about rabies, their attitudes towards dogs and practices associated with treating dog bites in Satkhira Sadar, a southwestern sub-district of Bangladesh. Of the total 3200 households (HHs) surveyed, the majority of the respondents have heard about rabies (73%) and there was a high level of awareness that dog bite is the main cause of rabies (86%), and that rabies can be prevented by vaccination (85%). However, 59% of the dog bite victims first seek treatment from traditional healers instead of visiting the hospitals, 29% received the rabies vaccine, 2% practiced proper wound washing with soap and water, while 4.8% have not taken any measures. None of the victims have received rabies immunoglobulin (RIG). Of the respondents, 5.2% reported a history of dog bite in at least one family member, and 11.8% reported a history of dog bite in domestic animals during the previous year. The HHs having a higher number of family members (OR: 1.13, 95% CI: 1.07–1.2), having a pet dog (OR: 2.1, 95% CI: 1.4–3.2) and caring or feeding a community dog (OR: 2.1, 95% CI: 1.4–2.9) showed an increased risk of getting a dog bite. Among the bite victims, 3.6% (n= 6) humans and 15.8% (n = 60) animals died. As a measure for dog population management (DPM), 56% preferred sterilization while the rest preferred killing of dogs. The current treatment seeking behaviours of the respondents should be improved through additional education and awareness programme and better availability for the provision of post-exposure prophylaxis in Bangladesh. We recommend scaling up national mass dog vaccination and DPM to reduce the burden of rabies cases and dog bites in Bangladesh.
Abstract
Community awareness regarding rabies and treatment seeking behaviours are critical both for the prevention and control of the disease in human and animals. We conducted a [...]
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A Proper Generalized Decomposition (PGD) approach to crack propagation in brittle materials: with application to random field material properties
H. Garikapati, S. Zlotnik, C. Verhoosel, E. Brummelen, P. Diez

Computational Mechanics (2019). (Preprint) pp. 1-23

Abstract
Understanding the failure of brittle heterogeneous materials is essential in many applications. Heterogeneities in material properties are frequently modeled through random fields, which typically induces the need to solve finite element problems for a large number of realizations. In this context, we make use of reduced order modeling to solve these problems at an affordable computational cost. This paper proposes a reduced order modeling framework to predict crack propagation in brittle materials with random heterogeneities. The framework is based on a combination of the Proper Generalized Decomposition (PGD) method with Griffith’s global energy criterion. The PGD framework provides an explicit parametric solution for the physical response of the system. We illustrate that a non-intrusive sampling-based technique can be applied as a postprocessing operation on the explicit solution provided by PGD.We first validate the framework using a global energy approach on a deterministic two-dimensional linear elastic fracture mechanics benchmark. Subsequently, we apply the reduced order modeling approach to a stochastic fracture propagation problem.
Abstract
Understanding the failure of brittle heterogeneous materials is essential in many applications. Heterogeneities in material properties are frequently modeled through random [...]
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A new 3D equilibrated residual method improving accuracy and efficiency of flux‐free error estimates
N. Parés, P. Diez

Comput. Methods Appl. Mech. Engrg., (2019). (Preprint) Vol. 120, pp. 391-432

Abstract
The paper presents a novel strategy providing fully computable upper bounds for the energy norm of the error in the context of three‐dimensional linear finite element approximations of the reaction‐diffusion equation. The upper bounds are guaranteed regardless the size of the finite element mesh and the given data, and all the constants involved are fully computable. The upper bound property holds if the shape of the domain is polyhedral and the Dirichlet boundary conditions are piecewise‐linear. The new approach is an extension of the flux‐free methodology introduced by Parés and Díez in the paper “A new equilibrated residual method improving accuracy and efficiency of flux‐free error estimates”, which introduces a guaranteed, low‐cost, and efficient flux‐free method substantially reducing the computational cost of obtaining guaranteed bounds using flux‐free methods while retaining the good quality of the bounds. Besides extending the 2D methodology, specific new modifications are introduced to further reduce the computational cost in the three‐dimensional setting. The presented methodology also provides a new strategy to obtain equilibrated boundary tractions, which improves the quality of standard techniques while having a similar computational cost.
Abstract
The paper presents a novel strategy providing fully computable upper bounds for the energy norm of the error in the context of three‐dimensional linear finite element approximations [...]
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Sampling-based stochastic analysis of the PKN model for hydraulic fracturing
H. Garikapati, C. Verhoosel, E. Brummelen, S. Zlotnik, P. Diez

Computational Geosciences (2019). (Preprint) Vol. 23 (1), pp. 81-105

Abstract
Hydraulic fracturing processes are surrounded by uncertainty, as available data is typically scant. In this work, we present a sampling-based stochastic analysis of the hydraulic fracturing process by considering various system parameters to be random. Our analysis is based on the Perkins-Kern-Nordgren (PKN) model for hydraulic fracturing. This baseline model enables computation of high fidelity solutions, which avoids pollution of our stochastic results by inaccuracies in the deterministic solution procedure. In order to obtain the desired degree of accuracy of the computed solution, we supplement the employed time-dependent moving-mesh finite element method with two new enhancements: (i) global conservation of volume is enforced through a Lagrange multiplier; (ii) the weakly singular behavior of the solution at the fracture tip is resolved by supplementing the solution space with a tip enrichment function. This tip enrichment function enables the computation of the tip speed directly from its associated solution coefficient. A novel incremental-iterative solution procedure based on a backward-Euler time-integrator with sub-iterations is employed to solve the PKN model. Direct Monte-Carlo sampling is performed based on random variable and random field input parameters. The presented stochastic results quantify the dependence of the fracture evolution process—in particular the fracture length and fracture opening—on variations in the elastic properties and leak-off coefficient of the formation, and the height of the fracture.
Abstract
Hydraulic fracturing processes are surrounded by uncertainty, as available data is typically scant. In this work, we present a sampling-based stochastic analysis of the hydraulic [...]
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Algebraic and parametric solvers for the power flow problem: towards real-time and accuracy-guaranteed simulation of electric systems
R. García-Blanco, P. Diez, D. Borzacchiello, F. Chinesta

Archives of Comp. Meths. Engng. (2018). (Preprint) Vol. 25 (4), pp. 1003-1026

Abstract
The power flow model performs the analysis of electric distribution and transmission systems. With this statement at hand, in this work we present a summary of those solvers for the power flow equations, in both algebraic and parametric version. The application of the Alternating Search Direction method to the power flow problem is also detailed. This results in a family of iterative solvers that combined with Proper Generalized Decomposition technique allows to solve the parametric version of the equations. Once the solution is computed using this strategy, analyzing the network state or solving optimization problems, with inclusion of generation in real-time, becomes a straightforward procedure since the parametric solution is available. Complementing this approach, an error strategy is implemented at each step of the iterative solver. Thus, error indicators are used as an stopping criteria controlling the accuracy of the approximation during the construction process. The application of these methods to the model IEEE 57-bus network is taken as a numerical illustration.
Abstract
The power flow model performs the analysis of electric distribution and transmission systems. With this statement at hand, in this work we present a summary of those solvers [...]
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Algebraic PGD for tensor separation and compression: An algorithmic approach
P. Diez, S. Zlotnik, A. García-González, A. Huerta

Comptes Rendus Mécanique (2018). (Preprint) Vol. 346 (7), pp. 501-514

Abstract
Proper Generalized Decomposition (PGD) is devised as a computational method to solve high-dimensional boundary value problems (where many dimensions are associated with the space of parameters defining the problem). The PGD philosophy consists in providing a separated representation of the multidimensional solution using a greedy approach combined with an alternated directions scheme to obtain the successive rank-one terms. This paper presents an algorithmic approach to high-dimensional tensor separation based on solving the Least Squares approximation in a separable format of multidimensional tensor using PGD. This strategy is usually embedded in a standard PGD code in order to compress the solution (reduce the number of terms and optimize the available storage capacity), but it stands also as an alternative and highly competitive method for tensor separation.
Abstract
Proper Generalized Decomposition (PGD) is devised as a computational method to solve high-dimensional boundary value problems (where many dimensions are associated [...]
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Numerical estimation of the bearing capacity of resistance spot welds in martensitic boron steels using a J-integral fracture criterion
D. Dorribo, L. Greve, P. Diez, I. Arias, X. Larráyoz-Izcara

Theoretical and Applied Fracture Mechanics (2018). (Preprint) Vol. 96, pp. 497-508

Abstract
Predicting the bearing capacity of resistance spot welds (RSW) during vehicle crash tests has become a crucial task for the automotive industry, since the recent introduction of advanced high strength steels (AHSS) such as martensitic boron steels (e.g. 22MnB5). The spot weld joints of these steels exhibit relatively low bearing strengths, compared to those of more ductile high strength steels. Currently, the bearing capacity of spot weld joints is characterized through extensive experimental campaigns. In this article, a model for quantification of the bearing capacity of RSW using a finite-element J-integral fracture criterion is presented. The model takes into account geometric and mechanical features of the spot weld, namely the weld diameter and the mechanical properties distribution resulting from the welding process. An experimental loading test campaign is carried out for calibration and validation purposes, considering multiple sheet thickness combinations, loading angles and weld sizes. Experimental observations of the failed spot welds and preliminary simulations show that failure is caused mostly by stress concentration around the sharp weld notch. Consequently, the J-integral obtained from detailed finite element simulations is used to asses the stress/strain concentration along the first crack advance direction predicted by the acoustic tensor. The computed J-integral values are compared to the material toughness to obtain the joint’s maximum force. The resulting simulated and experimental bearing capacities show a good agreement for all tested configurations.
Abstract
Predicting the bearing capacity of resistance spot welds (RSW) during vehicle crash tests has become a crucial task for the automotive industry, since the recent introduction [...]
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Método Numérico Basado en Cálculo Exterior Discreto Para la Discretización de la Ecuación de Convección - Difusión
M. Noguez, S. Botello, R. Herrera

Revista Mexicana de Métodos Numéricos (2019). Vol. 3, 4

Abstract
Mientras que la discretización con Cálculo Exterior Discreto (DEC) del término elíptico de la ecuación de Transporte, también conocida como la Ecuación de Convección - Difusión, está bien documentada y establecida, la discretización del término convectivo, así como su estabilización siguen siendo un tema de investigación. En este trabajo se propone una discretización local de la Ecuación de Transporte homogénea, isótropa y con flujo incompresible, basada en DEC y fundamentada en argumentos geométricos. Debido a que el método numérico obtenido para el termino convectivo es similar al de Elemento Finito con funciones de interpolación lineales (FEML), se pueden aprovechar algunas técnicas conocidas para la estabilización de la ecuación. Empleando esta característica, las pruebas numéricas se llevan a cabo en mallas que varían de gruesas a finas para comparar los resultados obtenidos con DEC y FEML, y para mostrar convergencia numérica en problemas estacionarios. La estabilización de la ecuación es llevada a cabo mediante Difusión Artificial.
Abstract
Mientras que la discretización con Cálculo Exterior Discreto (DEC) del término elíptico de la ecuación de Transporte, también conocida [...]
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A non-intrusive proper generalized decomposition scheme with application in biomechanics
X. Zou, M. Conti, P. Diez, F. Auricchio

Int. J. Numer. Meth. Engng. (2018). (Preprint) Vol. 113 (2), pp. 230-251

Abstract
Proper generalized decomposition (PGD) is often used for multi-query and fast-response simulations. It is a powerful tool alleviating the curse of dimensionality affecting multi-parametric partial differential equations. Most implementations of PGD are intrusive extensions based on in-house developed finite element (FE) solvers. In this work, we propose a non-intrusive PGD scheme using off-the-shelf FE codes (such as certified commercial software) as an external solver. The scheme is implemented and monitored by in-house flow-control codes. A typical implementation is provided with downloadable codes. Moreover, a novel parametric separation strategy for the PGD resolution is presented. The parametric space is split into two- or three-dimensional subspaces, to allow PGD technique solving problems with constrained parametric spaces, achieving higher convergence ratio. Numerical examples are provided. In particular, a practical example in biomechanics is included, with potential application to patient-specific simulation.
Abstract
Proper generalized decomposition (PGD) is often used for multi-query and fast-response simulations. It is a powerful tool alleviating the curse of dimensionality affecting [...]
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Explicit parametric solutions of lattice structures with proper generalized decomposition (PGD)
A. Sibileau, A. García-González, F. Auricchio, S. Morganti, P. Diez

Computational Mechanics (2018). (Preprint) Vol. 62 (4), pp. 871-891

Abstract
Architectured materials (or metamaterials) are constituted by a unit-cell with a complex structural design repeated periodically forming a bulk material with emergent mechanical properties. One may obtain specific macro-scale (or bulk) properties in the resulting architectured material by properly designing the unit-cell. Typically, this is stated as an optimal design problem in which the parameters describing the shape and mechanical properties of the unit-cell are selected in order to produce the desired bulk characteristics. This is especially pertinent due to the ease manufacturing of these complex structures with 3D printers. The proper generalized decomposition provides explicit parametic solutions of parametric PDEs. Here, the same ideas are used to obtain parametric solutions of the algebraic equations arising from lattice structural models. Once the explicit parametric solution is available, the optimal design problem is a simple post-process. The same strategy is applied in the numerical illustrations, first to a unit-cell (and then homogenized with periodicity conditions), and in a second phase to the complete structure of a lattice material specimen.
Abstract
Architectured materials (or metamaterials) are constituted by a unit-cell with a complex structural design repeated periodically forming a bulk material with emergent mechanical [...]
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Numerical Modelling of Multi-Phase Multi-Component. Reactive Transport in the Earth’s interior
B. Oliveira, J. Afonso, S. Zlotnik, P. Diez

Geophysical Journal International (2018). (Preprint) Vol. 212 (1), pp. 345-388

Abstract
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 multicomponent in the sense that the compositions of the system and its constituent phases are expressed by a full set of fundamental chemical components (e.g. SiO2, Al2O3, MgO, etc.) rather than proxies. These chemical components evolve, react with and partition into different phases according to an internally consistent thermodynamic model. We combine concepts from Ensemble Averaging and Classical Irreversible Thermodynamics to obtain sets of macroscopic balance equations that describe the evolution of systems governed by multiphase multicomponent reactive transport (MPMCRT). Equilibrium mineral assemblages, their compositions and physical properties, and closure relations for the balance equations are obtained via a ‘dynamic’ Gibbs free-energy minimization procedure (i.e. minimizations are performed on-the-fly as needed by the simulation). Surface tension and surface energy contributions to the dynamics and energetics of the system are taken into account. We show how complex rheologies, that is, visco-elasto-plastic, and/or different interfacial models can be incorporated into our MPMCRT ensemble-averaged formulation. The resulting model provides a reliable platform to study the dynamics and nonlinear feedbacks of MPMCRT systems of different nature and scales, as well as to make realistic comparisons with both geophysical and geochemical data sets. Several numerical examples are presented to illustrate the benefits and limitations of the model.
Abstract
We present a conceptual and numerical approach to model processes in the Earth’s interior that involve multiple phases that simultaneously interact thermally, mechanically [...]
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Generalized parametric solutions in Stokes flow
P. Diez, S. Zlotnik, A. Huerta

Comput. Methods Appl. Mech. Engrg. (2017). (Preprint) Vol. 326, pp. 223-240

Abstract
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.
Abstract
Design optimization and uncertainty quantification, among other applications of industrial interest, require fast or multiple queries of some parametric model. The Proper [...]
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A semi‐analytical scheme for highly oscillatory integrals over tetrahedra
R. Hospital-Bravo, J. Sarrate, P. Diez

Comput. Methods Appl. Mech. Engrg., (2017). (Preprint) Vol. 111 (8), pp. 703-723

Abstract
This paper details a semi‐analytical procedure to efficiently integrate the product of a smooth function and a complex exponential over tetrahedral elements. These highly oscillatory integrals appear at the core of different numerical techniques. Here, the partition of unity method enriched with plane waves is used as motivation. The high computational cost or the lack of accuracy in computing these integrals is a bottleneck for their application to engineering problems of industrial interest. In this integration rule, the non‐oscillatory function is expanded into a set of Lagrange polynomials. In addition, Lagrange polynomials are expressed as a linear combination of the appropriate set of monomials, whose product with the complex exponentials is analytically integrated, leading to 16 specific cases that are developed in detail. Finally, we present several numerical examples to assess the accuracy and the computational efficiency of the proposed method, compared with standard Gauss–Legendre quadratures.
Abstract
This paper details a semi‐analytical procedure to efficiently integrate the product of a smooth function and a complex exponential over tetrahedral elements. These highly [...]
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Monitoring a PGD solver for parametric power flow problems with goal-oriented error assessment
R. García-Blanco, D. Borzacchiello, F. Chinesta, P. Diez

Int. J. Numer. Meth. Engng. (2017). Vol. 111 (6), pp. 529-552

Abstract
The parametric analysis of electric grids requires carrying out a large number of Power Flow computations. The different parameters describe loading conditions and grid properties. In this framework, the Proper Generalized Decomposition (PGD) provides a numerical solution explicitly accounting for the parametric dependence. Once the PGD solution is available, exploring the multidimensional parametric space is computationally inexpensive. The aim of this paper is to provide tools to monitor the error associated with this significant computational gain and to guarantee the quality of the PGD solution. In this case, the PGD algorithm consists in three nested loops that correspond to 1) iterating algebraic solver, 2) number of terms in the separable greedy expansion and 3) the alternated directions for each term. In the proposed approach, the three loops are controlled by stopping criteria based on residual goal-oriented error estimates. This allows one for using only the computational resources necessary to achieve the accuracy prescribed by the end- user. The paper discusses how to compute the goal-oriented error estimates. This requires linearizing the error equation and the Quantity of Interest to derive an efficient error representation based on an adjoint problem. The efficiency of the proposed approach is demonstrated on benchmark problems.
Abstract
The parametric analysis of electric grids requires carrying out a large number of Power Flow computations. The different parameters describe loading conditions and grid properties. [...]
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Enhanced goal-oriented error assessment and computational strategies in adaptive reduced basis solver for stochastic problems
K. Serafin, B. Magnain, E. Florentin, N. Parés, P. Diez

Int. J. Numer. Meth. Engng. (2017). (Preprint) Vol. 110 (5), pp. 440-466

Abstract
This work focuses on providing accurate low-cost approximations of stochastic finite elements simulations in the framework of linear elasticity. In [E. Florentin, P. Diez, Adaptive reduced basis strategy based on goal oriented error assessment for stochastic problems, Comput. Methods Appl. Mech. Engrg. 225-228 (2012) 116-127], an adaptive strategy has been 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 cost gain. Technical insight of these two topics are presented in details and numerical examples show the interest of these new developments.
Abstract
This work focuses on providing accurate low-cost approximations of stochastic finite elements simulations in the framework of linear elasticity. In [E. Florentin, P. Diez, [...]
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Proper generalized decomposition solution of the parameterized Helmholtz problem: application to inverse geophysical problems
M. Signorini, S. Zlotnik, P. Diez

Int. J. Numer. Meth. Engng. (2017). (Preprint) Vol. 109, (8), pp. 1085-1102

Abstract
The identification of the geological structure from seismic data is formulated as an inverse problem. The properties and the shape of the rock formations in the subsoil are described by material and geometric parameters, which are taken as input data for a predictive model. Here, the model is based on the Helmholtz equation, describing the acoustic response of the system for a given wave length. Thus, the inverse problem consists in identifying the values of these parameters such that the output of the model agrees the best with observations. This optimization algorithm requires multiple queries to the model with different values of the parameters. Reduced order models are especially well suited to significantly reduce the computational overhead of the multiple evaluations of the model. In particular, the proper generalized decomposition produces a solution explicitly stating the parametric dependence, where the parameters play the same role as the physical coordinates. A proper generalized decomposition solver is devised to inexpensively explore the parametric space along the iterative process. This exploration of the parametric space is in fact seen as a post‐process of the generalized solution. The approach adopted demonstrates its viability when tested in two illustrative examples.
Abstract
The identification of the geological structure from seismic data is formulated as an inverse problem. The properties and the shape of the rock formations in the subsoil are [...]
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A new equilibrated residual method improving accuracy and efficiency of flux-free error estimates
N. Parés, P. Diez

Comput. Methods Appl. Mech. Engrg., (2017). (Preprint) Vol. 313 (1), pp. 785-816

Abstract
This paper presents a new methodology to compute guaranteed upper bounds for the energy norm of the error in the context of linear finite element approximations of the reaction-diffusion equation. The new approach revisits the ideas in [20, 18] with the goal of substantially reducing the com- putational cost of the flux-free method while retaining the good quality of the bounds. The new methodology provides also a technique to compute equilibrated boundary tractions improving the quality of standard equilibration strategies. The zeroth-order equilibration conditions are imposed using an alternative less restrictive form of the first-order equilibration conditions, along with a new efficient minimization criterion. This new equilibration strategy provides much more accurate up- per bounds for the energy and requires only doubling the dimension of the local linear systems of equations to be solved.
Abstract
This paper presents a new methodology to compute guaranteed upper bounds for the energy norm of the error in the context of linear finite element approximations of the reaction-diffusion [...]
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A reduced order modeling approach for optimal allocation of Distributed Generation in power distribution systems
R. García-Blanco, P. Diez, D. Borzacchiello, F. Chinesta

International Energy Conference (ENERGYCON) (2016). (preprint) pp, 1-6

Abstract
This paper presents an “offline-online” strategy for optimal allocation and sizing of Distributed Generation. In traditional optimization approaches, each function evaluation requires the solution of a power flow problem, which makes global optimality a computationally challenging goal. In the proposed strategy the power flow solver is invoked only once and a parametric solution is constructed with a monolithic solver. Despite the fact that the parametrized power flow equations result in a high-dimensional problem, the proposed algorithm is specifically designed to circumvent the curse of dimensionality. This is achieved through the application of Model Reduction, in particular the Proper Generalized Decomposition combined with a nonlinear solver. Numerical examples are carried out for showing the validity of the proposed method.
Abstract
This paper presents an “offline-online” strategy for optimal allocation and sizing of Distributed Generation. In traditional optimization approaches, each function [...]
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Unified formulation of a family of iterative solvers for power system analysis
F. Chinesta, P. Diez, D. Borzacchiello, M. Malik, R. García-Blanco

Electric Power Systems Research (2016). (Preprint) Vol. 140, pp. 201-208

Abstract
This paper illustrates the construction of a new class of iterative solvers for power flow calculations based on the method of Alternating Search Directions. This method is fit to the particular algebraic structure of the power flow problem resulting from the combination of a globally linear set of equations and nonlinear local relations imposed by power conversion devices, such as loads and generators. The choice of the search directions is shown to be crucial for improving the overall robustness of the solver. A noteworthy advantage is that constant search directions yield stationary methods that, in contrast with Newton or Quasi-Newton methods, do not require the evaluation of the Jacobian matrix. Such directions can be elected to enforce the convergence to the high voltage operative solution. The method is explained through an intuitive example illustrating how the proposed generalized formulation is able to include other nonlinear solvers that are classically used for power flow analysis, thus offering a unified view on the topic. Numerical experiments are performed on publicly available benchmarks for large distribution and transmission systems.
Abstract
This paper illustrates the construction of a new class of iterative solvers for power flow calculations based on the method of Alternating Search Directions. This method is [...]
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Numerical modeling of undersea acoustics using a partition of unity method with plane waves enrichment
R. Hospital-Bravo, J. Sarrate, P. Diez

Computational Mechanics (2016). (Preprint) Vol. 57 (5), pp. 717-732

Abstract
A new 2D numerical model to predict the underwater acoustic propagation is obtained by exploring the potential of the Partition of Unity Method (PUM) enriched with plane waves. The aim of the work is to obtain sound pressure level distributions when multiple operational noise sources are present, in order to assess the acoustic impact over the marine fauna. The model takes advantage of the suitability of the PUM for solving the Helmholtz equation, especially for the practical case of large domains and medium frequencies. The seawater acoustic absorption and the acoustic reflectance of the sea surface and sea bottom are explicitly considered, and perfectly matched layers (PML) are placed at the lateral artificial boundaries to avoid spurious reflexions. The model includes semi-analytical integration rules which are adapted to highly oscillatory integrands with the aim of reducing the computational cost of the integration step. In addition, we develop a novel strategy to mitigate the ill-conditioning of the elemental and global system matrices. Specifically, we compute a low-rank approximation of the local space of solutions, which in turn reduces the number of degrees of freedom, the CPU time and the memory footprint. Numerical examples are presented to illustrate the capabilities of the model and to assess its accuracy.
Abstract
A new 2D numerical model to predict the underwater acoustic propagation is obtained by exploring the potential of the Partition of Unity Method (PUM) enriched with plane waves. [...]
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Adaptividade e estimativas de erro orientadas por metas aplicadas a um benchmark test de propagação de onda
L. Steffens, P. Diez, M. Alves

Tendências em Matemática Aplicada e Computacional (2016). (preprint) Vol. 17 (1), pp. 35-53

Abstract
O objetivo deste artigo é estudar a eficiência e a robustez de técnicas adaptativas e estimativas de erro orientadas por metas para um benchmark test. As técnicas utilizadas aqui são baseadas em um simples pós-processo das aproximações de elementos finitos. As estimativas de erro orientadas por metas são obtidas por analisar o problema direto e um problema auxiliar, o qual está relacionado com a quantidade de interesse específico. O procedimento proposto é válido para quantidades lineares e não-lineares. Além disso, são discutidas diferentes representações para o erro e é analisada a influência do erro de dispersão. Os resultados numéricos mostram que as estimativas de erro fornecem boas aproximações ao erro real e que a técnica de refino adaptativo proposta conduz a uma redução mais rápida do erro.
Abstract
O objetivo deste artigo é estudar a eficiência e a robustez de técnicas adaptativas e estimativas de erro orientadas por metas para um benchmark test. [...]
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An error estimator for real-time simulators based on model order reduction
I. Alfaro, D. Gonzalez, S. Zlotnik, P. Diez, E. Cueto, F. Chinesta

Adv. Model. and Simul. in Eng. Sci. (2015). Vol. 2 (1), pp. 1-30

Abstract
Model order reduction (MOR) is one of the most appealing choices for real-time simulation of non-linear solids. In this work a method is presented in which real time performance is achieved by means of the o-line solution of a (high dimensional) parametric problem that provides a sort of response surface or computational vademecum. This solution is then evaluated in real-time at feedback rates compatible with haptic devices, for instance (i.e., more than 1kHz). This high dimensional problem can be solved without the limitations imposed by the curse of dimensionality by employing Proper Generalized Decomposition (PGD) methods. Essentially, PGD assumes a separated representation for the essential eld of the problem. Here, an error estimator is proposed for this type of solutions that takes into account the non-linear character of the studied problems. This error estimator allows to compute the necessary number of modes employed to obtain an approximation to the solution within a prescribed error tolerance in a given quantity of interest.
Abstract
Model order reduction (MOR) is one of the most appealing choices for real-time simulation of non-linear solids. In this work a method is presented in which real time performance [...]
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Effect of the separated approximation of input data in the accuracy of the resulting PGD solution
S. Zlotnik, P. Diez, D. Gonzalez, E. Cueto, A. Huerta

Adv. Model. and Simul. in Eng. Sci. (2015). Vol. 2, art. 28

Abstract
The Proper Generalized Decomposition (PGD) requires separability of the input data (e.g. physical properties, source term, boundary conditions, initial state). In many cases the input data is not expressed in a separated form and it has to be replaced by some separable approximation. These approximations constitute a new error source that, in some cases, may dominate the standard ones (discretization, truncation…) and control the nal accuracy of the PGD solution. In this work the relation between errors in the separated input data and the errors induced in the PGD solution is discussed. Error estimators proposed for homogenized problems and oscillation terms are adapted to asses the behaviour of the PGD errors resulting from approximated input data. The PGD is stable with respect to error in the separated data, with no critical amplification of the perturbations. Interestingly, we identified a high sensitiveness of the resulting accuracy on the selection of the sampling grid used to compute the separated data. The separation has to be performed on the basis of values sampled at integration points: sampling at the nodes defining the functional interpolation results in an important loss of accuracy. For the case of a Poisson problem separated in the spatial coordinates (a complex diffusivity function requires a separable approximation), the final PGD error is linear with the truncation error of the separated data. This relation is used to estimate the number of terms required in the separated data, that has to be in good agreement with the truncation error accepted in the PGD truncation (tolerance for the stoping criteria in the enrichment procedure). A sensible choice or the prescribed accuracy of the PGD solution has to be kept within the limits set by the errors in the separated input data.
Abstract
The Proper Generalized Decomposition (PGD) requires separability of the input data (e.g. physical properties, source term, boundary conditions, initial state). In many cases [...]
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Real time parameter identification and solution reconstruction from experimental data using the Proper Generalized Decomposition
E. Nadal Soriano, F. Chinesta, P. Diez, F. Fuenmayor, F. Denia

Comput. Methods Appl. Mech. Engrg., (2015). (preprint) Vol. 296 (1), pp. 113-128

Abstract
Some industrial processes are modelled by parametric partial differential equations. Integrating computational modelling and data assimilation into the control process requires obtaining a solution of the numerical model at the characteristic frequency of the process (real-time). This paper introduces a computational strategy allowing to efficiently exploit measurements of those industrial processes, providing the solution of the model at the required frequency. This is particularly interesting in the framework of control algorithms that rely on a model involving a set of parameters. For instance, the curing process of a composite material is modelled as a thermo-mechanical problem whose corresponding parameters describe the thermal and mechanical behaviours. In this context, the information available (measurements) is used to update the parameters of the model and to produce new values of the control variables (data assimilation). The methodology presented here is devised to ensure the possibility of having a response in real-time of the problem and therefore the capability of integrating it in the control scheme. The Proper Generalized Decomposition is used to describe the solution in the multi-parametric space. The real-time data assimilation requires a further simplification of the solution representation that better fits the data (reconstructed solution) and it provides an implicit parameter identification. Moreover, the analysis of the assimilated data sensibility with respect to the points where the measurements are taken suggests a criterion to locate the sensors.
Abstract
Some industrial processes are modelled by parametric partial differential equations. Integrating computational modelling and data assimilation into the control process [...]
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An efficient and general approach for implementing thermodynamic phase equilibria information in geophysical and geodynamic studies
J. Alfonso, S. Zlotnik, P. Diez

Geochmistry, geophysics, geosystems (2015). (preprint) Vol. 16 (10), pp. 3767-3777

Abstract
We present a flexible, general, and efficient approach for implementing thermodynamic phase equilibria information (in the form of sets of physical parameters) into geophysical and geodynamic studies. The approach is based on Tensor Rank Decomposition methods, which transform the original multidimensional discrete information into a separated representation that contains significantly fewer terms, thus drastically reducing the amount of information to be stored in memory during a numerical simulation or geophysical inversion. Accordingly, the amount and resolution of the thermodynamic information that can be used in a simulation or inversion increases substantially. In addition, the method is independent of the actual software used to obtain the primary thermodynamic information, and therefore, it can be used in conjunction with any thermodynamic modeling program and/or database. Also, the errors associated with the decomposition procedure are readily controlled by the user, depending on her/his actual needs (e.g., preliminary runs versus full resolution runs). We illustrate the benefits, generality, and applicability of our approach with several examples of practical interest for both geodynamic modeling and geophysical inversion/modeling. Our results demonstrate that the proposed method is a competitive and attractive candidate for implementing thermodynamic constraints into a broad range of geophysical and geodynamic studies. MATLAB implementations of the method and examples are provided as supporting information and can be downloaded from the journal's website.
Abstract
We present a flexible, general, and efficient approach for implementing thermodynamic phase equilibria information (in the form of sets of physical parameters) into geophysical [...]
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Fast r-adaptivity for multiple queries of heterogeneous stochastic material fields
R. Cottereau, P. Diez

Computational Mechanics (2015). (preprint) Vol. 56 (4), pp. 601-612

Abstract
We present an r-adaptivity approach for boundary value problems with randomly fluctuating material parameters solved through the Monte Carlo or stochastic collocation methods. This approach tailors a specific mesh for each sample of the problem. It only requires the computation of the solution of a single deterministic problem with the same geometry and the average parameter, whose numerical cost becomes marginal for large number of samples. Starting from the mesh used to solve that deterministic problem, the nodes are moved depending on the particular sample of mechanical parameter field. The reduction in the error is small for each sample but sums up to reduce the overall bias on the statistics estimated through the Monte Carlo scheme. Several numerical examples in 2D are presented.
Abstract
We present an r-adaptivity approach for boundary value problems with randomly fluctuating material parameters solved through the Monte Carlo or stochastic collocation [...]
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Proper generalized decomposition of a geometrically parametrized heat problem with geophysical applications
S. Zlotnik, P. Diez, D. Modesto, A. Huerta

Int. J. Numer. Meth. Engng. (2015). (preprint) Vol. 103 (10), pp. 737-758

Abstract
The solution of a steady thermal multiphase problem is assumed to be dependent on a set of parameters describing the geometry of the domain, the internal interfaces and the material properties. These parameters are considered as new independent variables. The problem is therefore stated in a multidimensional setup. The proper generalized decomposition (PGD) provides an approximation scheme especially well suited to preclude dramatically increasing the computational complexity with the number of dimensions. The PGD strategy is reviewed for the standard case dealing only with material parameters. Then, the ideas presented in [Ammar et al., “Parametric solutions involving geometry: A step towards efficient shape optimization.” Comput. Methods Appl. Mech. Eng., 2014; 268:178–193] to deal with parameters describing the domain geometry are adapted to a more general case including parametrization of the location of internal interfaces. Finally, the formulation is extended to combine the two types of parameters. The proposed strategy is used to solve a problem in applied geophysics studying the temperature field in a cross section of the Earth crust subsurface. The resulting problem is in a 10‐dimensional space, but the PGD solution provides a fairly accurate approximation (error ≤1%) using less that 150 terms in the PGD expansion.
Abstract
The solution of a steady thermal multiphase problem is assumed to be dependent on a set of parameters describing the geometry of the domain, the internal interfaces and the [...]
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A time-domain second-order FEM model for the wave diffraction-radiation problem. Validation with a semisubmersible platform
B. Servan Camas, J. Gutiérrez Romero, J. García-Espinosa

Marine Structures (2018). Volume 58, Pages 278-300

Abstract
A finite element method for the solution of the up-to-second-order wave diffraction-radiation problem in the time-domain is proposed. The solver has been verified against available analytical solutions, and validated against experimental data available for the HiPRWind semisubmersible platform (designed for floating wind turbines). To perform the validation, the wave diffraction-radiation solver is coupled to a body dynamics and mooring solvers in the time-domain. The HiPRWind movements and mooring forces have been compared for a large number of test cases, including decay tests, monochromatic waves, and bichromatic waves obtaining good agreement for both, body movements and mooring forces.
Abstract
A finite element method for the solution of the up-to-second-order wave diffraction-radiation problem in the time-domain is proposed. The solver has been verified against [...]
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