Documents published in 2019 : Scipedia

Carles-Jordi Guardiola, «Carles Riba. Retrat de grup. Protagonistes de la cultura catalana del segle XX», València, Edicions 3i4, 2017, 271 pp.
J. Veny-Mesquida

Caplletra. Revista Internacional de Filologia (2019). Vol. 34, (1), 13

Abstract
Book review: Carles-Jordi Guardiola, Carles Riba. Retrat de grup. Protagonistes de la cultura catalana del segle XX, València, Edicions 3i4, 2017, 271 pp., ISBN: 978-84-16789-69-6.
Abstract
Book review: Carles-Jordi Guardiola, Carles Riba. Retrat de grup. Protagonistes de la cultura catalana del segle XX, València, Edicions 3i4, 2017, 271 pp., ISBN: 978-84-1[...]
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Emili Samper, ed. (2016), «The Myths of the Republic: Literature and Identity», Kassel, Edition Reichenberger, 242 pp.
M. Llombart Huesca

Caplletra. Revista Internacional de Filologia (2019). Vol. 34, (1), 12

Abstract
Book review: Emili Samper, ed. (2016), The Myths of the Republic: Literature and Identity, Kassel, Edition Reichenberger, 242 pp., ISBN 978-3-944244-53-2.
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Francesc Foguet i Boreu, «El teatro catalán en el exilio republicano de 1939», Biblioteca del Exilio (Anejos 28), Sevilla, Renacimiento, 2016, 203 pp.
H. Buffery

Caplletra. Revista Internacional de Filologia (2019). Vol. 34, (1), 11

Abstract
Book review: Francesc Foguet i Boreu, El teatro catalán en el exilio republicano de 1939, Biblioteca del Exilio (Anejos 28), Sevilla, Renacimiento, 2016, 203 pp., ISBN: 9788416685646.
Abstract
Book review: Francesc Foguet i Boreu, El teatro catalán en el exilio republicano de 1939, Biblioteca del Exilio (Anejos 28), Sevilla, Renacimiento, 2016, 203 pp., ISBN: [...]
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Aspects of transitivity at the beginning of Modern Catalan
A. Pineda

Caplletra. Revista Internacional de Filologia (2019). Vol. 34, (1), 10

Abstract
In this corpus study we make a first approach to different aspects of transitivity, understood as a phenomenon with multiple faces, in the texts corresponding to the beginning of Modern Catalan (17th century, with a especial emphasis on the first half of the century). In particular, we deal with the case of several verbs showing an hesitating behaviour between the transitive and the intransitive use, and we undertake the study of this aspect from the point of view of differential object marking, since the alternations in these verbs may be confusing when analysing the pervasiveness of direct object introduced by a (see § 2). Next, also taking differential object marking as the reference point, we focus on the constructions that favour significantly the use of this marking in front of direct objects (see § 3). Finally, we briefly deal with some other interesting aspects of transitivity in the texts of the beginning of Modern Catalan, such as the use of unergative verbs in transitive patterns including a cognate direct object, or the causativization of intransitive verbs of motion (see § 4).
Abstract
In this corpus study we make a first approach to different aspects of transitivity, understood as a phenomenon with multiple faces, in the texts corresponding to the beginning [...]
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«Que ja·s parla different que·sparlava deu anys ha esta part». Modern Catalan: The indispensable link in the chain of linguistic history of Catalan
M. Massanell i Messalles

Caplletra. Revista Internacional de Filologia (2019). Vol. 34, (1), 9

Abstract
In this paper we review the causes that have led to the long-established underestimation of Catalan texts from the seventeenth and eighteenth centuries and the first third of the nineteenth, which is why the linguistic study of Modern Catalan has received less attention than the study of Catalan language from other periods. Despite this situation, we point out some linguistic innovations of Modern Catalan that make its study very attractive and, at the same time, very necessary to achieve a complete knowledge of the evolutionary phases of Catalan from its origin to our days and, especially, to understand the linguistic changes that turned Old Catalan into a modern language very close to the one used today. Finally, because of the next culmination of the Computerized Corpus of Modern Catalan, that will allow researchers to introduce corpus linguistics into the study of Catalan from 1601 to 1833, we refer to the advantages that corpus linguistics, combined with the philological method, brings to diachronic linguistics.
Abstract
In this paper we review the causes that have led to the long-established underestimation of Catalan texts from the seventeenth and eighteenth centuries and the first third [...]
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The analysis of lexical change in specialized discourse
M. Lorente Casafont

Caplletra. Revista Internacional de Filologia (2019). Vol. 34, (1), 8

Abstract
This text explores the incipient approach to the analysis of language change in specialized communicative contexts. From history of science and terminology, incursions have been made in the subject of the evolution of the specialized discourse, but neither the theory of change nor the methodology of the analysis of variation have been applied. In this first work we expose briefly the main items which regulate the study of language change and a synthesis of the main lexical changes (neology, loanwords, lexicalization and minor grammaticalization), to conclude what theoretical and methodological adjustments should be introduced and what kind of analysis that should be done with the purpose of analyzing initiated and stabilized changes in specialized discourses. This first approach focuses on the topic of change towards medical discourse, due to the relevance of the intersection between communication and health in the current research.
Abstract
This text explores the incipient approach to the analysis of language change in specialized communicative contexts. From history of science and terminology, incursions have [...]
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Beyond grammaticalization: The evolution of «no obstant això» in Catalan
M. Garachana

Caplletra. Revista Internacional de Filologia (2019). Vol. 34, (1), 7

Abstract
The aim of this piece of work is to analyse the emergence of the discursive marker no obstant això ‘however’ in Catalan. This evolution allows us to emphasize that not every change in grammar should be studied from the point of view of Theory of Grammaticalization. At the same time, the grammatical history of no obstant això highlights the need to analyse the syntactic changes within the social and cultural context in which they occurred. In the case of no obstant això, a careful study of its first occurrences in Catalan shows that, far from being the result of a grammaticalization, this marker arose as a result of the grammatical loaning of a particle originating in Medieval Latin.
Abstract
The aim of this piece of work is to analyse the emergence of the discursive marker no obstant això ‘however’ in Catalan. This evolution allows us to emphasize that not [...]
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From Petrés to Bigastre: an excursion through the language of Valencian settlement letters from 17th century
F. Feliu, J. Ferrer

Caplletra. Revista Internacional de Filologia (2019). Vol. 34, (1), 6

Abstract
The town charters of modern period, very abundant in the Valencian Country, mainly as a result of the repopulations that followed the expulsion of the Moriscos (1609), have not been studied so far from a linguistic point of view to a large extent because until a few years ago we did not have a significant repertoire of this type of documents. These are texts of legal linguistic variety that directly affected the life of an important part of the population —also, indirectly, the idea that people could have of their native language. This paper attempts to make a first approach to the study of Valencian town charters from the 17th century, evaluating the degree of persistence of the use of Valencian in these texts, as well as the persistence of traditional linguistic models.
Abstract
The town charters of modern period, very abundant in the Valencian Country, mainly as a result of the repopulations that followed the expulsion of the Moriscos (1609), have [...]
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Presentation of the monograph «La gramàtica del català de l’edat moderna. Un avanç»
J. Martines

Caplletra. Revista Internacional de Filologia (2019). Vol. 34, (1), 5

Abstract
Presentation of the monograph «La gramàtica del català de l’edat moderna. Un avanç», number 66 (Spring 2019) of Caplletra. Revista Internacional de Filologia.
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Analysis of the morphological and semantic specifitity of the Andorran neology
R. Muñoz-Espí, C. Bastida-Serra

Caplletra. Revista Internacional de Filologia (2019). Vol. 34, (1), 4

Abstract
The study of neology is not only important from a metalinguistic point of view, but also from the perspective of language planning, because monitoring the lexical creation allows for new lexicographic and terminological proposals. Taking into account the singularity of Andorra within the Catalan language domain, in terms of demography and geography but also regarding politics and culture, the language can have lexicographic and terminological needs that are different from other territories. This work analyzes the patterns in morphology and formation processes of the Andorran neology, comparing them with the rest of the language domain. Furthermore, the Andorran specific neologisms (so-called hapax legomena) have been classified and analyzed semantically, which has led to the observation that specific lexical creation is determined by the social, cultural, political, and economic environment of Andorra.
Abstract
The study of neology is not only important from a metalinguistic point of view, but also from the perspective of language planning, because monitoring the lexical creation [...]
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The position of clitics and presuppositional negative markers in restructuring contexts
A. Llop Naya, A. Paradís Pérez

Caplletra. Revista Internacional de Filologia (2019). Vol. 34, (1), 3

Abstract
This paper aims to explore syntactic microvariation in Catalan dialects as a source of insight into the nature of restructuring contexts and long-distance dependencies. We claim that restructuring involves a bi-clausal structure with a defective embedded domain. We provide evidence for this analysis by exploring the positions of clitics and presuppositional negative markers in restructuring contexts in Catalan varieties. On the one hand, the data collected highlights that, although clitic climbing and embedded presuppositional negation are independent phenomena, they can both be explained by the transparency of the embedded clausal boundary. On the other hand, dialectal data evince the existence of an ongoing syntactic change in the restructuring nature of some verbs. Furthermore, data collected confirms the validity of long-distance licensing as a transparency effect. This hypothesis is corroborated by the exploration of the same phenomena in subjunctive contexts.
Abstract
This paper aims to explore syntactic microvariation in Catalan dialects as a source of insight into the nature of restructuring contexts and long-distance dependencies. We [...]
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Testimony, updating and storytelling: the historical memory of Spanish Civil War in contemporary Catalan literature
J. Espinós Felipe

Caplletra. Revista Internacional de Filologia (2019). Vol. 34, (1), 2

Abstract
Since the mid-nineties onwards, the theme of the Civil War and Franco’s Dictatorship has generated in Spain an enormous number of novels, newspaper articles, historical research papers and audiovisual production that highlight the problematic relevance of the theme in the present time. This article focuses on one aspect of this production: those narrations that within Catalan literature have addressed it. It is an extensive body of works in which some of the most outstanding writers have been involved. Our approach aims to study this vast and diverse production, trying to figure out the motivations and narrative approaches that govern these proposals. We’ve discerned three basic models: the testimonial, the updater and the storyteller, and we have exemplified them with the works that we have considered the most representative. Likewise, we have identified a change regarding the model of representation of historical characters and events, which tends towards multiperspectivism and a more critical vision. This change is related to the public debate that the movement of recovery of historical memory has generated throughout Spain.
Abstract
Since the mid-nineties onwards, the theme of the Civil War and Franco’s Dictatorship has generated in Spain an enormous number of novels, newspaper articles, historical [...]
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Some notes on the influence of Joan Roís de Corella’s mythological fables in Francesc Alegre’s «Transformacions»
G. Pellissa Prades

Caplletra. Revista Internacional de Filologia (2019). Vol. 34, (1), 1

Abstract
This article establishes a comparison between Joan Roís de Corella’s mythological fables and Francesc Alegre’s translation of Ovid’s Metamorphoses into Catalan. The author proves by means of examples that Alegre drew on Corella’s Lamentacions and Parlament en casa de Berenguer Mercader while translating his work between circa 1472 and 1492. Further, he may have also known Corella’s Raonament de Telamó i Ulisses. Thus, even if Alegre based his text on the Latin poem, he surely completed the translation with the aid of other sources that are not made explicit, such as Bonsignori and Corella. In addition, the author suggests that Corella might have known and used Bonsignori’s Italian compilation or another version of Ovid’s poem which depended on it.
Abstract
This article establishes a comparison between Joan Roís de Corella’s mythological fables and Francesc Alegre’s translation of Ovid’s Metamorphoses into Catalan. The [...]
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Assessment of a Lagrangian Incompressible Flow Code
R. Aubry, R. Lohner, E. Oñate, S. Idelsohn

American Institute of Aeronautics and Astronautics Paper (AIAA) (2007). 2007-0715

Abstract
An incompressible Finite Element Lagrangian code is presented and validated against classical experimental and numerical Eulerian results. The main distinction between an Eulerian and a Lagrangian approach is due to the convection of the mesh with the computed velocity. On one hand, the convective term is taken into account in the total derivative of the velocity, which greatly simplifies its numerical treatment. On the other hand, a constant remeshing must be performed to maintain a good element quality due to the large deformations undergone by the fluid. The classical cylinder and the thermally coupled cavity benchmarks have been chosen to perform a detailed comparison with an Eulerian code, FEFLO, and experimental results.
Abstract
An incompressible Finite Element Lagrangian code is presented and validated against classical experimental and numerical Eulerian results. The main distinction between an [...]
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Simple Model of Nonlinear Spin Waves in Graphene Structures
D. Kulyabov, K. Lovetskiy, L. Nhat, A. Nhat

(2018). Вестник Российского университета дружбы народов. Серия: Математика …, 2018

Abstract
A series of theoretical and experimental works are known which investigated the magnetic properties of graphene structures. This is due, among other things, to the prospects of using graphene as a material for the needs of the future nanoelectronics and spintronics. In particular, it is known about the presence of ferromagnetic properties at temperatures up to 200 C and above in single-layer graphene films that are free from impurities. Previously there was proposed a quantum field theoretical model describing the possible mechanism of ferromagnetism in graphene as a result of the spontaneous breaking of spin symmetry of the surface density of valence electrons. The possible spatial configurations of the localized spin density were described. In this paper, we investigate such spatially localized nonlinear spin configurations of the valence electron density on the graphene surface such as kinks, and their interactions, as well as quasibound metastable states of the interacting kinks and antikinks, that are breathers. The spectrum of such breathers is investigated. It is shown that under certain conditions, this spectrum has a discrete sector, which, in turn, allows us to speak about the possibility of coherent quantum generation of spin waves in graphene structures, which is important in terms of practical applications in nanoelectronics and spintronics.
Abstract
A series of theoretical and experimental works are known which investigated the magnetic properties of graphene structures. This is due, among other things, to the prospects [...]
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On load interaction in the non linear buckling analysis of cylindrical shells
L. Godoy, S. Idelsohn, E. Barbero

Advances in Engineering Software and Workstations (1991). Vol. 13 (1), pp. 46-50

Abstract
The elastic stability of shells or shell-like structures under two independent load parameters is considered. One of the loads is associated to a limit point form of buckling, whereas the second is a bifurcation. A simple one degree of freedom mechanical system is first investigated, for which an analytical solution is possible. Next, a cylindrical shell under the combined action of axial load and localised lateral pressure is studied via a non linear, two-dimensional, finite element discretization. It is shown that both problems display the same general behaviour, with a stability boundary in the load space which is convex towards the region of stability. The results show the need of performing a full non-linear analysis to evaluate the stability boundary for the class of interaction problems considered.
Abstract
The elastic stability of shells or shell-like structures under two independent load parameters is considered. One of the loads is associated to a limit point form of buckling, [...]
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Upwind parameters for the numerical solution of the compressible flow Euler equations
S. Idelsohn

Advances in Engineering Software and Workstations (1991). Vol. 13 (2), pp. 58-67

Abstract
The present work generalises the earlier work in which a variational principle technique was presented in order to evaluate the magnitude of upwind required to solve the compressible flow equations. The technique proposed allows the choice of nodes where upwind is required in each of the relevant equations. It is a simple and mathematically consistent way of evaluating the amount of upwind or artificial viscosity to be introduced at every node and every equation involved.
Abstract
The present work generalises the earlier work in which a variational principle technique was presented in order to evaluate the magnitude of upwind required to solve the compressible [...]
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Numerical implementation of a discontinuous finite element algorithm for phase-change problems
M. Storti, L. Crivelli, S. Idelsohn

Advances in Engineering Software (1987). Vol. 9 (2), pp. 66-73

Abstract
This paper is devoted to the numerical solution of phase-change problems in two dimensions. The technique of finite elements is employed. The discretization is carried out using linear isoparametric elements and special attention is given to the accurate integration of functions presenting discontinuities at arbitrarily curved interfaces. This type of function arises in a natural way when dealing with phase-change problems because the enthalpy attains a discontinuity at the phase change temperature. To integrate the discontinuous functions in the phase-changing elements a second mapping is performed from the master element onto a new one for which the interface iis a straight line. The integrals are calculated using the Gaussian technique applied to each part of the divided element, which may be triangular or quadrilateral. The discontinuous integration technique improves the behaviour of the numerical method avoiding any possible loss of latent heat due to an inaccurate evaluation of the residual vector. Some important aspects of the solution of the nonlinear system of equations are discussed and several numerical examples are presented together with the details of the computational implementation of the algorithm.
Abstract
This paper is devoted to the numerical solution of phase-change problems in two dimensions. The technique of finite elements is employed. The discretization is carried out [...]
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A simple hidden line algorithm for a structural model of planar elements
E. Laitano, S. Idelsohn

Advances in Engineering Software (1986). Vol. 8 (1), pp. 2-7

Abstract
A simple and efficient hidden line algorithm for finite element models is described here. The algorithm runs quickly, it has low computer storage and core size requirements. The method does not require any calculation of trigonometric functions and is able to treat planar quadrilateral polygons without subdividing them into triangles. Detailed flowcharts are presented for a better understanding.
Abstract
A simple and efficient hidden line algorithm for finite element models is described here. The algorithm runs quickly, it has low computer storage and core size requirements. [...]
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Reduction methods and explicit time integration technique in structural dynamics
S. Idelsohn, A. Cardona

Advances in Engineering Software (1984). Vol. 6 (1), pp. 36-44

Abstract
A computer procedure for economically time-integrating large structural dynamics problems is presented. The main process is described as a two-step discretisation, the first one being performed by the finite element method. An error measure is proposed in order to check the validity of the results. The reduced system of equations is integrated by using the central differences explicit scheme. Linear and physical nonlinear examples of applications are shown. The entire procedure seems to be particularly well-suited to be programmed in small computers, where the core and velocity characteristics impose severe restrictions on the problems to be directly solved.
Abstract
A computer procedure for economically time-integrating large structural dynamics problems is presented. The main process is described as a two-step discretisation, the first [...]
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A Finite Element Model for the Simulation of the UL-94 Burning Test
J. Marti, S. Idelsohn, E. Oñate

Fire Technology (2018). Vol. 54 (6), pp. 1783–1805

Abstract
The tendency of the polymers to melt and drip when they are exposed to external heat source play a very important role in the ignition and the spread of fire. Numerical simulation is a promising methodology for predicting this behaviour. In this paper, a computational procedure that aims at analyzing the combustion, melting and flame spread of polymer is presented. The method models the polymer using a Lagrangian framework adopting the particle finite element method framework while the surrounding air is solved on a fixed Eulerian mesh. This approach allows to treat naturally the polymer shape deformations and to solve the thermo-mechanical problem in a staggered fashion. The problems are coupled using an embedded Dirichlet–Neumann scheme. A simple combustion model and a radiation modeling strategy are included in the air domain. With this strategy the burning of a polypropylene specimen under UL-94 vertical test conditions is simulated. Input parameters for the modelling (density, specific heat, conductivity and viscosity) and results for the validation of the numerical model has been obtained from different literature sources and by IMDEA burning a specimen of dimensions of 148×13×3.2mm3. Temperature measurements in the polymer have been recorder by means of three thermocouples exceeding the 1000 K. Simultaneously a digital camera was used to record the burning process. In addition, thermal decomposition of the material (Arrhenius coefficient A=7.14×1016 min−1 and activation energy E=240.67kJ/mol) as and changes in viscosity (μ) as a function of temperature were obtained. Finally, a good agreement between the experimental and the numerical can be seen in terms of shape of the polymer as well as in the temperature evolution inside the polymer.
Abstract
The tendency of the polymers to melt and drip when they are exposed to external heat source play a very important role in the ignition and the spread of fire. Numerical simulation [...]
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Global-local HROM for non-linear thermal problems with irreversible changes of material states
A. Cosimo, A. Cardona, S. Idelsohn

C. R. Mecanique (2018). Vol. 346 (7), pp. 539-555

Abstract
Highly concentrated moving nonlinearities are extremely difficult to solve numerically. The Selective Laser Melting Additive Manufacturing process is a problem of this kind. A material global-local scheme is proposed, which consists in describing the neighbourhood of the heat source by a moving local domain while the material phase fractions are represented in a global domain. The equations of the non-linear thermal problem are defined on the local domain only, assuming that the local domain is large enough to capture the most important variations of the temperature field. Additionally, a Hyper-Reduced-Order Model (HROM) is proposed for the local domain problem. The performance is studied by solving a SLM problem taken from the literature.
Abstract
Highly concentrated moving nonlinearities are extremely difficult to solve numerically. The Selective Laser Melting Additive Manufacturing process [...]
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Reduced order models for thermally coupled low Mach flows
R. Reyes, R. Codina, J. Baiges, S. Idelsohn

Adv. Model. and Simul. in Eng. Sci. (2018). Vol. 5, art. 28

Abstract
In this paper we present a collection of techniques used to formulate a projection-based reduced order model (ROM) for zero Mach limit thermally coupled Navier–Stokes equations. The formulation derives from a standard proper orthogonal decomposition (POD) model reduction, and includes modifications to improve the drawbacks caused by the inherent non-linearity of the used Navier–Stokes equations: a hyper-ROM technique based on mesh coarsening; an implicit ROM subscales formulation based on a variational multi-scale (VMS) framework; and a Petrov–Galerkin projection necessary in the case of non-symmetric terms. At the end of the article, we test the proposed ROM formulation using 2D and 3D versions of the same example: a differentially heated cavity.
Abstract
In this paper we present a collection of techniques used to formulate a projection-based reduced order model (ROM) for zero Mach limit thermally coupled Navier–Stokes [...]
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On the issue that Finite Element discretizations violate, nodally, Clausius’s postulate of the second law of thermodynamics
A. Limache, S. Idelsohn

Adv. Model. and Simul. in Eng. Sci. (2016). Vol. 3, art 13

Abstract
Discretization processes leading to numerical schemes sometimes produce undesirable effects. One potentially serious problem is that a discretization may produce the loss of validity of some of the physical principles or mathematical properties originally present in the continuous equation. Such loss may lead to uncertain results such as numerical instabilities or unexpected non-physical solutions. As a consequence, the compatibility of a discrete formulation with respect to intrinsic physical principles might be essential for the success of a numerical scheme. This paper addresses such type of issue. Its main objective is to demonstrate that standard Finite Element discretizations of the heat conduction equation violate Clausius’s postulate of the second law of thermodynamics, at nodal level. The problem occurs because non-physical, reversed nodal heat-fluxes arise in such discretizations. Conditions for compatibility of discrete nodal heat-fluxes with respect to Clausius’s postulate are derived here and named discrete thermodynamic compatibility conditions (DTCC). Simple numerical examples are presented to show the undesirable consequences of such failure. It must be pointed out that such DTCCs have previously appeared in the context of the study of the conditions that make discrete solutions to satisfy the discrete maximum principle (DMP). However, the present article does not put attention on such mathematical principle but on the satisfaction of a fundamental physical one: the second law of thermodynamics. Of course, from the presented point of view, it is clear that the violation of such fundamental law will cause, among different problems, the violation of the DMP.
Abstract
Discretization processes leading to numerical schemes sometimes produce undesirable effects. One potentially serious problem is that a discretization may produce the loss [...]
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General treatment of essential boundary conditions in reduced order models for non-linear problems
A. Cosimo, A. Cardona, S. Idelsohn

Adv. Model. and Simul. in Eng. Sci. (2016). Vol. 3, art 7

Abstract
Inhomogeneous essential boundary conditions must be carefully treated in the formulation of Reduced Order Models (ROMs) for non-linear problems. In order to investigate this issue, two methods are analysed: one in which the boundary conditions are imposed in an strong way, and a second one in which a weak imposition of boundary conditions is made. The ideas presented in this work apply to the big realm of a posteriori ROMs. Nevertheless, an a posteriori hyper-reduction method is specifically considered in order to deal with the cost associated to the non-linearity of the problems. Applications to nonlinear transient heat conduction problems with temperature dependent thermophysical properties and time dependent essential boundary conditions are studied. However, the strategies introduced in this work are of general application.
Abstract
Inhomogeneous essential boundary conditions must be carefully treated in the formulation of Reduced Order Models (ROMs) for non-linear problems. In order to investigate this [...]
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A semi-analytical model for droplet dynamics on the GDL surface of a PEFC electrode
A. Jarauta, M. Secanell, J. Pons Prats, P. Ryzhakov, S. Idelsohn, E. Oñate

Int. J. Hydrogen Energy (2015). Vol. 40 (15), pp. 5375-5383

Abstract
Water management is one of the key factors in Proton Exchange Fuel Cell (PEFC) performance. The water produced within the fuel cell is evacuated through the gas channels, but at high current densities water can block the channel, thus limiting the current density generated in the fuel cell. A semi-analytical model of a water droplet emerging from a gas diffusion layer pore in a PEFC channel is developed. The transient model contains a detailed adhesion and drag force estimation model. Results show that the predicted values for both drag and surface tension force are higher than the results found in literature. The results for the detachment force are consistent with the experimental data available. Higher air velocity values lead to more deformation of the droplet and oscillation with lower frequency but higher amplitude. Similar effects have been identified when the liquid mass flow is increased, leading to faster detachment of the droplet.
Abstract
Water management is one of the key factors in Proton Exchange Fuel Cell (PEFC) performance. The water produced within the fuel cell is evacuated through the gas channels, [...]
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GPGPU implementation of the BFECC algorithm for pure advection equations
S. Costarelli, M. Storti, R. Paz, L. Dalcin, S. Idelsohn

Cluster computing (2014). Vol. 17 (2), pp. 243-254

Abstract
In the present work an implementation of the Back and Forth Error Compensation and Correction (BFECC) algorithm specially suited for running on General-Purpose Graphics Processing Units (GPGPUs) through Nvidia’s Compute Unified Device Architecture (CUDA) is analyzed in order to solve transient pure advection equations. The objective is to compare it to a previous explicit version used in a Navier-Stokes solver fully written in CUDA. It turns out that BFECC could be implemented with unconditional stable stability using Semi-Lagrangian time integration allowing larger time steps than Eulerian ones.
Abstract
In the present work an implementation of the Back and Forth Error Compensation and Correction (BFECC) algorithm specially suited for running on General-Purpose Graphics Processing [...]
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An assessment of the potential of PFEM-2 for solving long real-time industrial applications
J. Gimenez, D. Ramajo, S. Damián, N. Nigro, S. Idelsohn

Comp. Part. Mech. (2016). Vol. 4 (3), pp. 251-267

Abstract
The latest generation of the particle finite element method (PFEM-2) is a numerical method based on the Lagrangian formulation of the equations, which presents advantages in terms of robustness and efficiency over classical Eulerian methodologies when certain kind of flows are simulated, especially those where convection plays an important role. These situations are often encountered in real engineering problems, where very complex geometries and operating conditions require very large and long computations. The advantages that the parallelism introduced in the computational fluid dynamics making affordable computations with very fine spatial discretizations are well known. However, it is not possible to have the time parallelized, despite the effort that is being dedicated to use space–time formulations. In this sense, PFEM-2 adds a valuable feature in that its strong stability with little loss of accuracy provides an interesting way of satisfying the real-life computation needs. After having already demonstrated in previous publications its ability to achieve academic-based solutions with a good compromise between accuracy and efficiency, in this work, the method is revisited and employed to solve several nonacademic problems of technological interest, which fall into that category. Simulations concerning oil–water separation, waste-water treatment, metallurgical foundries, and safety assessment are presented. These cases are selected due to their particular requirements of long simulation times and or intensive interface treatment. Thus, large time-steps may be employed with PFEM-2 without compromising the accuracy and robustness of the simulation, as occurs with Eulerian alternatives, showing the potentiality of the methodology for solving not only academic tests but also real engineering problems.
Abstract
The latest generation of the particle finite element method (PFEM-2) is a numerical method based on the Lagrangian formulation of the equations, which presents advantages [...]
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Evaluating the performance of the particle finite element method in parallel architectures
J. Gimenez, N. Nigro, S. Idelsohn

Comp. Part. Mech. (2014). Vol. 1 (1), pp. 103-116

Abstract
This paper presents a high performance implementation for the particle-mesh based method called particle finite element method two (PFEM-2). It consists of a material derivative based formulation of the equations with a hybrid spatial discretization which uses an Eulerian mesh and Lagrangian particles. The main aim of PFEM-2 is to solve transport equations as fast as possible keeping some level of accuracy. The method was found to be competitive with classical Eulerian alternatives for these targets, even in their range of optimal application. To evaluate the goodness of the method with large simulations, it is imperative to use of parallel environments. Parallel strategies for Finite Element Method have been widely studied and many libraries can be used to solve Eulerian stages of PFEM-2. However, Lagrangian stages, such as streamline integration, must be developed considering the parallel strategy selected. The main drawback of PFEM-2 is the large amount of memory needed, which limits its application to large problems with only one computer. Therefore, a distributed-memory implementation is urgently needed. Unlike a shared-memory approach, using domain decomposition the memory is automatically isolated, thus avoiding race conditions; however new issues appear due to data distribution over the processes. Thus, a domain decomposition strategy for both particle and mesh is adopted, which minimizes the communication between processes. Finally, performance analysis running over multicore and multinode architectures are presented. The Courant–Friedrichs–Lewy number used influences the efficiency of the parallelization and, in some cases, a weighted partitioning can be used to improve the speed-up. However the total cputime for cases presented is lower than that obtained when using classical Eulerian strategies.
Abstract
This paper presents a high performance implementation for the particle-mesh based method called particle finite element method two (PFEM-2). It consists of a material derivative [...]
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A compressible Lagrangian framework for modeling the fluid-structure interaction in the underwater implosion of an aluminum cylinder
K. Kamran, R. Rossi, E. Oñate, S. Idelsohn

Mathematical Models and Methods in Applied Sciences (2013). Vol. 23 (2), pp. 339–367

Abstract
We propose a fully Lagrangian monolithic system for the simulation of the underwater implosion of cylindrical aluminum containers. A variationally stabilized form of the Lagrangian shock hydrodynamics is exploited to deal with the ultrahigh compression shock waves that travel in both air and water domains. The aluminum cylinder, which separates the internal atmospheric-pressure air from the external high-pressure water, is modeled by a three-node rotation-free shell element. The cylinder undergoes fast transient deformations, large enough to produce self-contact along it. A novel elastic frictionless contact model is used to detect contact and compute the non-penetrating forces in the discretized domain between the mid-planes of the shell. Mesh quality in the vicinity of the cylinder is guaranteed by regenerating the mesh in the air and water domains when large displacements occur. A monolithic fluid–structure interaction (FSI) system is then solved. Two schemes are tested, implicit using the predictor/multi-corrector Bossak scheme, and explicit, using the forward Euler scheme. The results of the two simulations are compared with experimental data.
Abstract
We propose a fully Lagrangian monolithic system for the simulation of the underwater implosion of cylindrical aluminum containers. A variationally stabilized form of the Lagrangian [...]
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Flow behaviour of negatively buoyant jets in immiscible ambient fluid
A. Geyer, J. Phillips, M. Mier-Torrecilla, S. Idelsohn, E. Oñate

Experiments in Fluids (2011). Vol 52 (1), pp. 261-257

Abstract
In this paper we investigate experimentally the injection of a negatively buoyant jet into a homogenous immiscible ambient fluid. Experiments are carried out by injecting a jet of dyed fresh water through a nozzle in the base of a cylindrical tank containing rapeseed oil. The fountain inlet flow rate and nozzle diameter were varied to cover a wide range of Richardson Ri(8 × 10−4 < Ri < 1.98), Reynolds Re (467 < Re < 5,928) and Weber We (2.40 < We < 308.56) numbers. Based on the Re, Ri and We values for the experiments, we have determined a regime map to define how these values may control the occurrence of the observed flow types. Whereas Ri plays a stronger role when determining the maximum penetration height, the effect of the Reynolds number is stronger predicting the flow behaviour for a specific nozzle diameter and injection velocity.
Abstract
In this paper we investigate experimentally the injection of a negatively buoyant jet into a homogenous immiscible ambient fluid. Experiments are carried out by injecting [...]
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Fluid flows around turbomachinery using an explicit pseudo‐temporal Euler FEM
N. Nigro, M. Storti, S. Idelsohn

Commun. Numer. Meth. Engng (1995). Vol. 11 (3), pp. 199-211

Abstract
This work is devoted to the simulation by finite elements of nearly incompressible inviscid flows in real 3D geometries, by means of an Euler code based on the SUPG (streamline upwind Petrov–Galerkin) method, explicit forward Euler pseudo‐temporal time integration and periodic and absorbing boundary conditions, among other features. The main goal is the application to flow around turbomachinery, with special emphasis on the performance analysis of a given machine, that involves several numerical computations at different operation points. Finally, these results are summarized in the form of characteristic curves.
Abstract
This work is devoted to the simulation by finite elements of nearly incompressible inviscid flows in real 3D geometries, by means of an Euler code based on the SUPG (streamline [...]
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Comparative accuracy and performance assessment of the finite point method in compressible flow problems
E. Ortega, E. Oñate, S. Idelsohn, R. Flores

Computers and Fluids (2014). Vol. 89, pp. 53-65

Abstract
A comparative assessment of the Finite Point Method (FPM) is presented. Using a wing-fuselage configuration under transonic inviscid flow conditions as reference test case, the performance of the FPM flow solver is compared with an equivalent edge-based Finite Element (FEM) implementation. Efficiency issues have discouraged practical application of meshless methods in the past. Thus, a simplification of the basic FPM technique is proposed in order to reduce the performance gap with respect to classical grid-based algorithms. A comparative evaluation of the accuracy, computational cost and parallel performance of the meshless implementation is carried out with the objective to assess the level of maturity of the technique and identify improvements still required to tackle practical applications. The results obtained show accuracy and performance of the core algorithm comparable to a conventional FEM implementation, thus removing a major obstacle for further developments of the FPM.
Abstract
A comparative assessment of the Finite Point Method (FPM) is presented. Using a wing-fuselage configuration under transonic inviscid flow conditions as reference test case, [...]
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A portable OpenCL-based unstructured edge-based finite element Navier–Stokes solver on graphics hardware
R. Rossi, F. Mossaiby, S. Idelsohn

Computers & Fluids (2013). Vol. 81, pp. 134-144

Abstract
The rise of GPUs in modern high-performance systems increases the interest in porting portion of codes to such hardware. The current paper aims to explore the performance of a portable state-of-the-art FE solver on GPU accelerators. Performance evaluation is done by comparing with an existing highly-optimized OpenMP version of the solver. Code portability is ensured by writing the program using the OpenCL 1.1 specifications, while performance portability is sought through an optimization step performed at the beginning of the calculations to find out the optimal parameter set for the solver. The results show that the new implementation can be several times faster than the OpenMP version.
Abstract
The rise of GPUs in modern high-performance systems increases the interest in porting portion of codes to such hardware. The current paper aims to explore the performance [...]
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Migration of a generic multi-physics framework to HPC environments
P. Dadvand, R. Rossi, M. Gil, X. Martorell, J. Cotela, E. Juanpere, S. Idelsohn, E. Oñate

Computers and Fluids (2013). Vol. 80, pp. 301-309

Abstract
Creating a highly parallelizable code is a challenge specially for Distributed Memory Machines (DMMs). Moreover, algorithms and data structures suitable for these platforms can be very different from the ones used in serial code. For this reason, many programmers in the field prefer to start their own code from scratch. However, for an already existing framework supported by a long-time expertise the idea of transformation becomes attractive in order to reuse the effort done during years of development. In this presentation we explain how a relatively complex framework but with modular structure can be prepared for high performance computing with minimum modification. Kratos Multi-Physics is an open source generic multi-disciplinary platform for solution of coupled problems consist of fluid, structure, thermal and electromagnetic fields. The parallelization of this framework is performed with objective of enforcing the less possible changes to its different solver modules and encapsulate the changes as much as possible in its common kernel. This objective is achieved thanks to the Kratos design and also innovative way of dealing with data transfers for a multi-disciplinary code. This work is completed by the migration of the framework from the 86× architecture to the Marenostrum Supercomputing platform. The migration has been verified by a set of benchmarks which show high scalability, from which we present the Telescope problem in this paper.
Abstract
Creating a highly parallelizable code is a challenge specially for Distributed Memory Machines (DMMs). Moreover, algorithms and data structures suitable for these platforms [...]
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Parallel adaptive mesh refinement for incompressible flow problems
R. Rossi, J. Cotela, N. Lafontaine, P. Dadvand, S. Idelsohn

Computers and Fluids (2013). Vol. 80, pp. 342-355

Abstract
The present article describes a simple element-driven strategy for the conforming refinement of simplicial finite element meshes in a distributed environment. The proposed algorithm is effective both for local adaptive refinement and for the division of all the elements within an existing mesh. We aim to provide sufficient detail to allow the practical implementation of the algorithm, which can be coded with minimal effort provided that a distributed linear algebra library is available. The proposed refinement strategy is composed of three basic components: a global splitting strategy, an elemental splitting procedure and an error estimation technique, which are combined so to guarantee obtaining a conformant refined mesh. A number of benchmark examples show the capabilities of the proposed method. Error is estimated for the incompressible fluid-flow benchmarks using a novel indicator based on the computation of the sub-scale velocity.
Abstract
The present article describes a simple element-driven strategy for the conforming refinement of simplicial finite element meshes in a distributed environment. The proposed [...]
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A FFT preconditioning technique for the solution of incompressible flow on GPUs
M. Storti, R. Paz, L. Dalcin, S. Costarelli, S. Idelsohn

Computers and Fluids (2013). Vol. 74, pp. 44-57

Abstract
Graphic processing units have received much attention in last years. Compute-intensive algorithms operating on multidimensional arrays that have nearest neighbor dependency and/or exploit data locality can achieve massive speedups. Simulation of problems modeled by time-dependent Partial Differential Equations by using explicit time-stepping methods on structured grids is an instance of such GPU-friendly algorithms. Solvers for transient incompressible fluid flow cannot be developed in a fully explicit manner due to the incompressibility constraint. Segregated algorithms like the fractional step method require the solution of a Poisson problem for the pressure field at each time level. This stage is usually the most time-consuming one. This work discuss a solver for the pressure problem in applications using immersed boundary techniques in order to account for moving solid bodies. This solver is based on standard Conjugate Gradients iterations and depends on the availability of a fast Poisson solver on the whole domain to define a preconditioner. We provide a theoretical and numerical evidence on the advantages of our approach versus classical techniques based on fixed point iterations such as the Iterated Orthogonal Projection method.
Abstract
Graphic processing units have received much attention in last years. Compute-intensive algorithms operating on multidimensional arrays that have nearest neighbor dependency [...]
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The ALE/Lagrangian Particle Finite Element Method: A new approach to computation of free-surface flows and fluid–object interactions
F. Del Pin, S. Idelsohn, E. Oñate, R. Aubry

Computers and Fluids (2007). Vol. 36 (1), pp. 27-38

Abstract
The Particle Finite Element Method (PFEM) is a well established numerical method [Aubry R, Idelsohn SR, Oñate E, Particle finite element method in fluid mechanics including thermal convection–diffusion, Comput Struct 2004;83:1459–75; Idelsohn S, Oñate E, Del Pin F, A Lagrangian meshless finite element method applied to fluid–structure interaction problems, Comput Struct 2003;81:655–71; Idelsohn SR, Oñate E, Del Pin F, The particle finite element method a powerful tool to solve incompressible flows with free-surfaces and breaking waves, Int J Num Methods Eng 2004;61:964–84] where critical parts of the continuum are discretized into particles. The nodes treated as particles transport their momentum and physical properties in a Lagrangian way while the rest of the nodes may move in an Arbitrary Lagrangian–Eulerian (ALE) frame. In order to solve the governing equations that represent the continuum, the particles are connected by means of a Delaunay Triangulation [Idelsohn SR, Oñate E, Calvo N, Del Pin F, The meshless finite element method, Int J Num Methods Eng 2003;58(4)]. The resulting partition is a mesh where the Finite Element Method is applied to solve the equations of motion. The application of a fully Lagrangian formulation on the particles provides a natural and simple way to track free surfaces as well as to compute contacts in an accurate and robust fashion. Furthermore, the usage of an ALE formulation allows large mesh deformation with larger time steps than the full Lagrangian scheme.
Abstract
The Particle Finite Element Method (PFEM) is a well established numerical method [Aubry R, Idelsohn SR, Oñate E, Particle finite element method in fluid mechanics [...]
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Modeling bed erosion in free surface flows by the particle finite element method
E. Oñate, M. Celigueta, S. Idelsohn

Acta Geotechnica (2006). Vol. 1 (4), pp. 237-252

Abstract
We present a general formulation for modeling bed erosion in free surface flows using the particle finite element method (PFEM). The key feature of the PFEM is the use of an updated Lagrangian description to model the motion of nodes (particles) in domains containing fluid and solid subdomains. Nodes are viewed as material points (called particles) which can freely move and even separate from the fluid and solid subdomains representing, for instance, the effect of water drops or soil/rock particles. A mesh connects the nodes defining the discretized domain in the fluid and solid regions where the governing equations, expressed in an integral form, 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 nonlinear transient coupled fluid-structure problem is described. The erosion mechanism is modeled by releasing the material adjacent to the bed surface according to the frictional work generated by the fluid shear stresses. The released bed material is subsequently transported by the fluid flow. Examples of application of the PFEM to solve a number of bed erosion problems involving large motions of the free surface and splashing of waves are presented.
Abstract
We present a general formulation for modeling bed erosion in free surface flows using the particle finite element method (PFEM). The key feature of the PFEM is the use of [...]
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A multiresolution strategy for solving landslides using the Particle Finite Element Method
P. Becker, S. Idelsohn

Acta Geotechnica (2016). Vol. 11 (3), pp. 643-657

Abstract
We present an approach for the simulation of landslides using the Particle Finite Element Method of the second generation. In this work, the multiphase nature (granular phase and water) of the phenomenon is considered in a staggered fashion using a single, indeformable Finite Element mesh. A fractional step and a monolithic strategy are used for the water flow and granular phase, respectively. In this way, the maximum accuracy with minimal computational times is reached. The method is completed by adding the interaction terms due to drag and pressure forces, together with a moving mesh strategy to reduce the size of the computational domain.
Abstract
We present an approach for the simulation of landslides using the Particle Finite Element Method of the second generation. In this work, the multiphase nature (granular phase [...]
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Numerical Simulation of the 3D Laminar Viscous Flow on a Horizontal-axis Wind Turbine Blade
R. Prado, M. Storti, S. Idelsohn

Int. J. Computational Fluid Dynamics (2002). Vol. 16 (4), pp. 283-295

Abstract
The aim of this paper is to describe the methodology followed in order to determine the viscous effects of a uniform wind on the blades of small horizontal-axis wind turbines that rotate at a constant angular speed. The numerical calculation of the development of the three-dimensional boundary layer on the surface of the blades is carried out under laminar conditions and considering flow rotation, airfoil curvature and blade twist effects. The adopted geometry for the twisted blades is given by cambered thin blade sections conformed by circular are airfoils with constant chords. The blade is working under stationary conditions at a given tip speed ratio, so that an extensive laminar boundary layer without flow separation is expected. The boundary layer growth is determined on a non-orthogonal curvilinear coordinate system related to the geometry of the blade surface. Since the thickness of the boundary layer grows from the leading edge of the blade and also from the tip to the blade root, a domain transformation is proposed in order to solve the discretized equations in a regular computational 3D domain. The non-linear system of partial differential coupled equations that governs the boundary layer development is numerically solved applying a finite difference technique using the Krause zig-zag scheme. The resulting coupled equations of motion are linearized, leading to a tridiagonal system of equations that is iteratively solved for the velocity components inside the viscous layer applying the Thomas algorithm, procedure that allows the subsequent numerical determination of the shear stress distribution on the blade surface.
Abstract
The aim of this paper is to describe the methodology followed in order to determine the viscous effects of a uniform wind on the blades of small horizontal-axis wind turbines [...]
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A Panel-Fourier Method for Free-Surface Flows
J. D'ELIA, M. Storti, S. Idelsohn

Journal of Fluids Engineering (1999). Vol. 122 (2), 309-317

Abstract
A panel Fourier method for ship-wave flow problems is considered here. It is based on a three-dimensional potential flow model with a linearized free surface condition, and it is implemented by means of a low order panel method coupled to a Fourier series. The wave resistance is computed by pressure integration over the static wet hull and the wave pattern is obtained by a post-processing procedure. The strategy avoids the use of numerical viscosity, in contrast with the Dawson-like methods, widely used in naval panel codes, therefore a second centered scheme can be used for the discrete operator on the free surface. Numerical results including the wave pattern for a ferry along fifteen ship lengths are presented.
Abstract
A panel Fourier method for ship-wave flow problems is considered here. It is based on a three-dimensional potential flow model with a linearized free surface condition, and [...]
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An unstructured grid-based, parallel free surface solver
R. Löhner, C. Yang, E. Oñate, S. Idelsohn

Applied Numerical Mathematics (1999). Vol. 31 (3), pp. 271-293

Abstract
An unstructured grid-based, parallel-free surface solver is presented. The overall scheme combines a finite-element, equal-order, projection-type 3-D incompressible flow solver with a finite element, 2-D advection equation solver for the free surface equation. For steady-state applications, the mesh is not moved every timestep, in order to reduce the cost of geometry recalculations and surface repositioning. A number of modifications required for efficient processing on shared-memory, cache-based parallel machines are discussed, and timings are shown that indicate scalability to a modest number of processors. The results show good quantitative comparison with experiments and the results of other techniques. The present combination of unstructured grids (enhanced geometrical flexibility) and good parallel performance (rapid turnaround) should make the present approach attractive to hydrodynamic design simulations.
Abstract
An unstructured grid-based, parallel-free surface solver is presented. The overall scheme combines a finite-element, equal-order, projection-type 3-D incompressible flow solver [...]
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A second-order in time and space particle-based method to solve flow problems on arbitrary meshes
J. Gimenez, H. Aguerre, S. Idelsohn, N. Nigro

Journal of Computational Physics (2018). Vol. 380, pp. 295-310

Abstract
This work presents a novel proposal of a second-order accurate (in time and space) particle-based method for solving transport equations including incompressible flows problems within a mixed Lagrangian–Eulerian formulation. This methodology consists of a symmetrical operator splitting, the use of high-order operators to transfer data between the particles and the background mesh, and an improved version of the eXplicit Integration Following the Streamlines (X–IVS) method. In the case of incompressible flows, a large time-step iterative solver is employed where the momentum equation is split to improve the numerical approximation of the convective term. New interpolation and projection operators are evaluated and quadratically accurate solutions of scalar transport tests are presented. Then, incompressible flow problems are solved where the rate of convergence of the method is assessed using both structured and unstructured background grids. The method is implemented in the open source platform OpenFOAM®allowing employing arbitrary meshes and obtaining reliable computing time comparisons with standardized solvers. The results obtained reveal that the current method is able to obtain a lower level of error than a fast Eulerian alternative, without increasing the total computing time.
Abstract
This work presents a novel proposal of a second-order accurate (in time and space) particle-based method for solving transport equations including incompressible [...]
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Algebraic Discrete Nonlocal (DNL) Absorbing Boundary Condition for the Ship Wave Resistance Problem
M. Storti, J. D'ELIA, S. Idelsohn

Journal of Computational Physics (1998). Vol. 146 (2), pp 570-602

Abstract
An absorbing boundary condition for the ship wave resistance problem is presented. In contrast to the Dawson-like methods, it avoids the use of numerical viscosities in the discretization, so that a centered scheme can be used for the free surface operator. The absorbing boundary condition is “completely absorbing,” in the sense that the solution is independent of the position of the downstream boundary and is derived from straightforward analysis of the resulting constant-coefficients difference equations, assuming that the mesh is 1D-structured (in the longitudinal direction) and requires the eigen-decomposition of a matrix one dimension lower than the system matrix. The use of a centered scheme for the free surface operator allows a full finite element discretization. The drag is computed by a momentum flux balance. This method is more accurate and guarantees positive resistances.
Abstract
An absorbing boundary condition for the ship wave resistance problem is presented. In contrast to the Dawson-like methods, it avoids the use of numerical viscosities in the [...]
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Applied hydrodynamic wave-resistance computation by Fourier transform
J. D'ELIA, M. Storti, S. Idelsohn

Ocean Engng. (2002). Vol. 29 (3), p. 261-278

Abstract
An applied Fourier transform computation for the hydrodynamic wave-resistance coefficient is shown, oriented to potential flows with a free surface and infinity depth. The presence of a ship-like body is simulated by its equivalent pressure disturbance imposed on the un-perturbed free surface, where a linearized free surface condition is used. The wave-resistance coefficient is obtained from the wave-height downstream. Two examples with closed solutions are considered: a submerged dipole, as a test-case, and a parabolic pressure distribution of compact support. In the three dimensional case, a dispersion relation is included which is a key resource for an inexpensive computation of the wave pattern far downstream like fifteen ship-lengths.
Abstract
An applied Fourier transform computation for the hydrodynamic wave-resistance coefficient is shown, oriented to potential flows with a free surface and infinity depth. The [...]
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Buckling of circular, annular plates of non-uniform thickness
P. Laura, R. Gutiérrez, V. Sonzogni, S. Idelsohn

Ocean Engng. (1997). Vol. 24 (1), pp. 51-62

Abstract
This paper deals with the solution of the title problem in the case where the outer boundary is subjected to uniform, hydrostatic pressure while the inner edge of the plate is free. It is assumed that the plate thickness varies (a) in a discontinuous fashion and (b) linearly. An approximate approach is proposed using polynomial coordinate functions which identically satisfy the boundary conditions at the outer edge, only. The eigenvalues are determined using the optimized Rayleigh-Ritz method and good engineering agreement is shown to exist with buckling parameters obtained by means of a finite element code.
Abstract
This paper deals with the solution of the title problem in the case where the outer boundary is subjected to uniform, hydrostatic pressure while the inner edge of the plate [...]
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CVBEM Formulation for Multiple Profiles and Cascades
M. Storti, J. D'ELIA, S. Idelsohn

Appl. Mech. Rev. (1995). Vol. 48 (11), pp. 203-210

Abstract
A numerical algorithm based on the CVBEM (from Complex Variable Boundary Element Method) for plane incompressible potential flow around aerofoils and cascades is described. The method is based on the representation of the complex disturbance velocity by means of a Cauchy-type integral around the foil. The Cauchy density function is approximated piecewise linearly and a linear system on the nodal values is obtained by collocation at the nodes. The Kutta condition is imposed via a Lagrange multiplier, in contrast with the least-squares formulation used in a previous work. For cascades, the problem is conformally mapped by a simple hyperbolic function (exponential or hyperbolic tangent) to a related problem with only one profile and one or two poles. Thus, the cascade problem is accurately solved with minor modifications to the single profile code and at the same cost of a single profile computation. Finally, several numerical examples are shown: single Joukowski and NACA profiles, interference coefficients for the flat plate cascade and a plane cascade at the external cylindrical section of an industrial fan.
Abstract
A numerical algorithm based on the CVBEM (from Complex Variable Boundary Element Method) for plane incompressible potential flow around aerofoils and cascades is described. [...]
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A general algorithm for compressible and incompressible flow. Stability analysis and explicit time integration
N. Nigro, M. Storti, S. Idelsohn

Int. J. of Num. Meths. for Heat and Fluid Flow (1997). Vol. 7 (2/3), pp. 141-168

Abstract
Addresses two difficulties which arise when using a compressible code with equal order interpolation (non‐staggered grids in the finite‐difference nomenclature) to capture a steady‐state solution in the incompressible limit, i.e. at low Mach numbers. Explains that, first, numerical instabilities in the form of spurious oscillations in pressure pollute the solution and, second, the convergence to the steady state becomes extremely slow owing to bad conditioning of the different speeds of propagation. By using a stabilized method, allows the use of equal‐order interpolations in a consistent (weighted‐residual) formulation which stabilizes both the convection and the continuity terms at the same time. On the other hand, by using specially devised preconditioning, assures a rate of convergence independent of Mach number.
Abstract
Addresses two difficulties which arise when using a compressible code with equal order interpolation (non‐staggered grids in the finite‐difference nomenclature) to capture [...]
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An improved enrichment method for weak discontinuities for thermal problems
J. Marti, E. Ortega, S. Idelsohn

Int. J. of Num. Meths. for Heat and Fluid Flow (2017). Vol. 27 (8), pp.1748-1764

Abstract
Purpose The purpose of this paper is to propose a new elemental enrichment technique to improve the accuracy of the simulations of thermal problems containing weak discontinuities. Design/methodology/approach The enrichment is introduced in the elements cut by the materials interface by means of adding additional shape functions. The weak form of the problem is obtained using Galerkin approach and subsequently integrating the diffusion term by parts. To enforce the continuity of the fluxes in the “cut” elements, a contour integral must be added. These contour integrals named here the “inter-elemental heat fluxes” are usually neglected in the existing enrichment approaches. The proposed approach takes these fluxes into account. Findings It has been shown that the inter-elemental heat fluxes cannot be generally neglected and must be included. The corresponding method can be easily implemented in any existing finite element method (FEM) code, as the new degrees of freedom corresponding to the enrichment are local to the elements. This allows for their static condensation, thus not affecting the size and structure of the global system of governing equations. The resulting elements have exactly the same number of unknowns as the non-enriched finite element (FE). Originality/value It is the first work where the necessity of including inter-elemental heat fluxes has been demonstrated. Moreover, numerical tests solved have proven the importance of these findings. It has been shown that the proposed enrichment leads to an improved accuracy in comparison with the former approaches where inter-elemental heat fluxes were neglected.
Abstract
Purpose The purpose of this paper is to propose a new elemental enrichment technique to improve the accuracy of the simulations of thermal problems [...]
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Variational Framework for FIC Formulations in Continuum Mechanics: High Order Tensor-Derivative Transformations and Invariants
C. Felippa, E. Oñate, S. Idelsohn

Archives of Comp. Meths. Engng. (2017). Vol. 25 (4), pp. 919–963

Abstract
This is part of an article series on a variational framework for continuum mechanics based on the Finite Increment Calculus (FIC). The formulation utilizes high order derivatives of the classical fields of continuum mechanics integrated over control regions to construct stabilizing modification terms. Fields may include displacements, body forces, strains, stresses, pressure and volumetric strains. To support observer-invariant FIC formulations, we have catalogued field transformation equations as well as sets of linear and quadratic invariants of fields and of their derivatives up to appropriate order. Attention is focused on the two-dimensional case of a body in plane strain under the drilling-rotation transformation group. Results are presented for displacement and body-force derivatives of orders up to 4, and for stress, strain, pressure and volumetric strain derivatives of order up to 3. The material assembled here is self-contained because this catalog is believed to be useful beyond FIC applications; for example gradient-based, nonlocal constitutive models of multiscale mechanics and physics that involve finite characteristic dimensions analogous to FIC steplengths.
Abstract
This is part of an article series on a variational framework for continuum mechanics based on the Finite Increment Calculus (FIC). The formulation utilizes high order derivatives [...]
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Numerical methods in phase-change problems
S. Idelsohn, M. Storti, L. Crivelli

Archives of Comp. Meths. Engng. (1994). Vol. 1 (1), pp. 49-74

Abstract
This paper summarizes the state of the art of the numerical solution of phase-change problems. After describing the governing equations, a review of the existing methods is presented. The emphasis is put mainly on fixed domain techniques, but a brief description of the main front-tracking methods is included. A special section is devoted to the Newton-Raphson resolution with quadratic convergence of the non-linear system of equations.
Abstract
This paper summarizes the state of the art of the numerical solution of phase-change problems. After describing the governing equations, a review of the existing methods is [...]
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A discrete non‐local (DNL) outgoing boundary condition for diffraction of surface waves
R. Bonet Chaple, N. Nigro, M. Storti, S. Idelsohn

Commun. Numer. Meth. Engng (1998). Vol. 14 (9), pp. 849-861

Abstract
A discrete non‐local (DNL) boundary condition is used to solve the water waves propagation problem over variable depth. This condition is obtained by means of full solution of the discrete Helmholtz operator in a structured network. We consider a simulation of wave propagation around a circular island located on either a paraboloidal shoal or constant depth bathymetry. Such examples confirm the important improvement in accuracy for the DNL method over standard conditions in the near field.
Abstract
A discrete non‐local (DNL) boundary condition is used to solve the water waves propagation problem over variable depth. This condition is obtained by means of full solution [...]
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Computing ship wave resistance from wave amplitude with a non‐local absorbing boundary condition
M. Storti, J. D'ELIA, S. Idelsohn

Commun. Numer. Meth. Engng (1998). Vol. 14 (11), pp. 997-1012

Abstract
A method for computing ship wave resistance from a momentum flux balance is presented. It is based on computing the momentum flux carried by the gravity waves that exit the computational domain through the outlet plane. It can be shown that this method ensures a non‐negative wave‐resistance, in contrast with straightforward integration of the normal pressure forces. However, this calculation should be performed on a transverse plane located far behind the ship. Traditional Dawson‐like methods add a numerical viscosity that dampens the wave pattern so that some amount of momentum flux is lost, and resulting in an error in the momentum balance. The flow field is computed, then, with a centred scheme with absorbing boundary conditions.
Abstract
A method for computing ship wave resistance from a momentum flux balance is presented. It is based on computing the momentum flux carried by the gravity waves that exit the [...]
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Fluid flows around turbomachinery using an explicit pseudo‐temporal Euler FEM
N. Nigro, M. Storti, S. Idelsohn

Commun. Numer. Meth. Engng (1995). Vol. 11 (3), pp. 199-211

Abstract
This work is devoted to the simulation by finite elements of nearly incompressible inviscid flows in real 3D geometries, by means of an Euler code based on the SUPG (streamline upwind Petrov–Galerkin) method, explicit forward Euler pseudo‐temporal time integration and periodic and absorbing boundary conditions, among other features. The main goal is the application to flow around turbomachinery, with special emphasis on the performance analysis of a given machine, that involves several numerical computations at different operation points. Finally, these results are summarized in the form of characteristic curves.
Abstract
This work is devoted to the simulation by finite elements of nearly incompressible inviscid flows in real 3D geometries, by means of an Euler code based on the SUPG (streamline [...]
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Multifluid flows with weak and strong discontinuous interfaces using an elemental enriched space
S. Idelsohn, J. Gimenez, N. Nigro

Int. J. Numer. Meth. Fluids (2018). Vol. 86 (12), pp. 750–769

Abstract
In a previous paper, the authors presented an elemental enriched space to be used in a finite‐element framework (EFEM) capable of reproducing kinks and jumps in an unknown function using a fixed mesh in which the jumps and kinks do not coincide with the interelement boundaries. In this previous publication, only scalar transport problems were solved (thermal problems). In the present work, these ideas are generalized to vectorial unknowns, in particular, the incompressible Navier‐Stokes equations for multifluid flows presenting internal moving interfaces. The advantage of the EFEM compared with global enrichment is the significant reduction in computing time when the internal interface is moving. In the EFEM, the matrix to be solved at each time step has not only the same amount of degrees of freedom (DOFs) but also the same connectivity between the DOFs. This frozen matrix graph enormously improves the efficiency of the solver. Another characteristic of the elemental enriched space presented here is that it allows a linear variation of the jump, thus improving the convergence rate, compared with other enriched spaces that have a constant variation of the jump. Furthermore, the implementation in any existing finite‐element code is extremely easy with the version presented here because the new shape functions are based on the usual finite‐element method shape functions for triangles or tetrahedrals, and once the internal DOFs are statically condensed, the resulting elements have exactly the same number of unknowns as the nonenriched finite elements.
Abstract
In a previous paper, the authors presented an elemental enriched space to be used in a finite‐element framework (EFEM) capable of reproducing kinks and jumps in an unknown [...]
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Analysis of multifluid flows with large time steps using the particle finite element method
S. Idelsohn, J. Marti, P. Becker, E. Oñate

Int. J. Numer. Meth. Fluids (2014). Vol. 75 (9), pp. 621-644

Abstract
Multifluids are those fluids in which their physical properties (viscosity or density) vary internally and abruptly forming internal interfaces that introduce a large nonlinearity in the Navier–Stokes equations. For this reason, standard numerical methods require very small time steps in order to solve accurately the internal interface position. In a previous paper, the authors developed a particle‐based method (named particle finite element method (PFEM)) based on a Lagrangian formulation and FEM for solving the fluid mechanics equations for multifluids. PFEM was capable of achieving accurate results, but the limitation of small time steps was still present. In this work, a new strategy concerning the time integration for the analysis of multifluids is developed allowing time steps one order of magnitude larger than the previous method. The advantage of using a Lagrangian solution with PFEM is shown in several examples. All kind of heterogeneous fluids (with different densities or viscosities), multiphase flows with internal interfaces, breaking waves, and fluid separation may be easily solved with this methodology without the need of small time steps.
Abstract
Multifluids are those fluids in which their physical properties (viscosity or density) vary internally and abruptly forming internal interfaces that introduce a large nonlinearity [...]
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Application of the finite point method to high‐Reynolds number compressible flow problems
R. Ortega, E. Oñate, S. Idelsohn, R. Flores

Int. J. Numer. Meth. Fluids (2014). Vol. 74 (10), pp. 732-748

Abstract
In this work, the finite point method is applied to the solution of high‐Reynolds compressible viscous flows. The aim is to explore this important field of applications focusing on two main aspects: the easiness and automation of the meshless discretization of viscous layers and the construction of a robust numerical approximation in the highly stretched clouds of points resulting in such domain areas. The flow solution scheme adopts an upwind‐biased scheme to solve the averaged Navier–Stokes equations in conjunction with an algebraic turbulence model. The numerical applications presented involve different attached boundary layer flows and are intended to show the performance of the numerical technique. The results obtained are satisfactory and indicative of the possibilities to extend the present meshless technique to more complex flow problems.
Abstract
In this work, the finite point method is applied to the solution of high‐Reynolds compressible viscous flows. The aim is to explore this important field of applications [...]
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A meshless finite point method for three‐dimensional analysis of compressible flow problems involving moving boundaries and adaptivity
R. Ortega, E. Oñate, S. Idelsohn, R. Flores

Int. J. Numer. Meth. Fluids (2013). Vol. 73 (4), pp. 323-343

Abstract
A finite point method for solving compressible flow problems involving moving boundaries and adaptivity is presented. The numerical methodology is based on an upwind‐biased discretization of the Euler equations, written in arbitrary Lagrangian–Eulerian form and integrated in time by means of a dual‐time steeping technique. In order to exploit the meshless potential of the method, a domain deformation approach based on the spring network analogy is implemented, and h‐adaptivity is also employed in the computations. Typical movable boundary problems in transonic flow regime are solved to assess the performance of the proposed technique. In addition, an application to a fluid–structure interaction problem involving static aeroelasticity illustrates the capability of the method to deal with practical engineering analyses. The computational cost and multi‐core performance of the proposed technique is also discussed through the examples provided.
Abstract
A finite point method for solving compressible flow problems involving moving boundaries and adaptivity is presented. The numerical methodology is based on an upwind‐biased [...]
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Explicit reduced‐order models for the stabilized finite element approximation of the incompressible Navier–Stokes equations
J. Baiges, R. Codina, S. Idelsohn

Int. J. Numer. Meth. Fluids (2013). Vol. 72 (12), pp. 1219-1243

Abstract
In this paper, we present an explicit formulation for reduced‐order models of the stabilized finite element approximation of the incompressible Navier–Stokes equations. The basic idea is to build a reduced‐order model based on a proper orthogonal decomposition and a Galerkin projection and treat all the terms in an explicit way in the time integration scheme, including the pressure. This is possible because the reduced model snapshots do already fulfill the continuity equation. The pressure field is automatically recovered from the reduced‐order basis and solution coefficients. The main advantage of this explicit treatment of the incompressible Navier–Stokes equations is that it allows for the easy use of hyper‐reduced order models, because only the right‐hand side vector needs to be recovered by means of a gappy data reconstruction procedure. A method for choosing the optimal set of sampling points at the discrete level in the gappy procedure is also presented. Numerical examples show the performance of the proposed strategy
Abstract
In this paper, we present an explicit formulation for reduced‐order models of the stabilized finite element approximation of the incompressible Navier–Stokes equations. [...]
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A new enrichment space for the treatment of discontinuous pressures in multi‐fluid flows
R. Ausas, G. Buscaglia, S. Idelsohn

Int. J. Numer. Meth. Fluids (2011). Vol. 70 (7), pp. 829-850

Abstract
In this work, a new enrichment space to accommodate jumps in the pressure field at immersed interfaces in finite element formulations, is proposed. The new enrichment adds two degrees of freedom per element that can be eliminated by means of static condensation. The new space is tested and compared with the classical P1 space and to the space proposed by Ausas et al (Comp. Meth. Appl. Mech. Eng., Vol. 199, 1019–1031, 2010) in several problems involving jumps in the viscosity and/or the presence of singular forces at interfaces not conforming with the element edges. The combination of this enrichment space with another enrichment that accommodates discontinuities in the pressure gradient has also been explored, exhibiting excellent results in problems involving jumps in the density or the volume forces.
Abstract
In this work, a new enrichment space to accommodate jumps in the pressure field at immersed interfaces in finite element formulations, is proposed. The new enrichment adds [...]
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Numerical simulations of negatively buoyant jets in an immiscible fluid using the Particle Finite Element Method
M. Mier-Torrecilla, A. Geyer, J. Phillips, S. Idelsohn, E. Oñate

Int. J. Numer. Meth. Fluids (2011). Vol. 69 (5), pp. 1016-1030

Abstract
Negatively buoyant jets consist in a dense fluid injected vertically upward into a lighter ambient fluid. The numerical simulation of this kind of buoyancy‐driven flows is challenging as it involves multiple fluids with different physical properties. In the case of immiscible fluids, it requires, in addition, to track the motion of the interface between fluids and accurately represent the discontinuities of the flow variables. In this paper, we investigate numerically the injection of a negatively buoyant jet into a homogenous immiscible ambient fluid using the Particle Finite Element Method and compare the two‐dimensional numerical results with experiments on the injection of a jet of dyed water through a nozzle in the base of a cylindrical tank containing rapeseed oil. In both simulations and experiments, the fountain inlet flow velocity and nozzle diameter have been varied to cover a wide range of Froude Fr and Reynolds Re numbers ( 0.1 < Fr < 30, 8 < Re < 1350), reproducing both weak and strong laminar fountains. The flow behaviors observed for the different numerical simulations fit in the regime map based on the Re and Fr values of the experiments, and the maximum fountain height is in good agreement with the experimental observations, suggesting that particle finite element method is a useful tool for the study of immiscible two‐fluid systems.
Abstract
Negatively buoyant jets consist in a dense fluid injected vertically upward into a lighter ambient fluid. The numerical simulation of this kind of buoyancy‐driven flows [...]
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A family of residual‐based stabilized finite element methods for Stokes flows
E. Oñate, P. Nadukandi, S. Idelsohn, J. García-Espinosa, C. Felippa

Int. J. Numer. Meth. Fluids (2010). Vol. 65 (1-3), pp. 106-134

Abstract
We present a collection of stabilized finite element (FE) methods derived via first‐ and second‐order finite calculus (FIC) procedures. It is shown that several well known existing stabilized FE methods such as the penalty technique, the Galerkin Least Square (GLS) method, the Pressure Gradient Projection (PGP) method and the orthogonal sub‐scales (OSS) method are recovered from the general residual‐based FIC stabilized form. A new family of stabilized Pressure Laplacian Stabilization (PLS) FE methods with consistent nonlinear forms of the stabilization parameters are derived. The distinct feature of the family of PLS methods is that they are residual‐based, i.e. the stabilization terms depend on the discrete residuals of the momentum and/or the incompressibility equations. The advantages and disadvantages of the different stabilization techniques are discussed and several examples of application are presented.
Abstract
We present a collection of stabilized finite element (FE) methods derived via first‐ and second‐order finite calculus (FIC) procedures. It is shown that several well known [...]
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A finite point method for adaptive three‐dimensional compressible flow calculations
E. Ortega, E. Oñate, S. Idelsohn

Int. J. Numer. Meth. Fluids (2008). Vol. 60 (9), pp. 937-971

Abstract
The finite point method (FPM) is a meshless technique, which is based on both, a weighted least‐squares numerical approximation on local clouds of points and a collocation technique which allows obtaining the discrete system of equations. The research work we present is part of a broader investigation into the capabilities of the FPM to deal with 3D applications concerning real compressible fluid flow problems. In the first part of this work, the upwind‐biased scheme employed for solving the flow equations is described. Secondly, with the aim of exploiting the meshless capabilities, an h‐adaptive methodology for 2D and 3D compressible flow calculations is developed. This adaptive technique applies a solution‐based indicator in order to identify local clouds where new points should be inserted in or existing points could be safely removed from the computational domain. The flow solver and the adaptive procedure have been evaluated and the results are encouraging. Several numerical examples are provided in order to illustrate the good performance of the numerical methods presented.
Abstract
The finite point method (FPM) is a meshless technique, which is based on both, a weighted least‐squares numerical approximation on local clouds of points and a collocation [...]
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The violation of objectivity in Laplace formulations of the Navier–Stokes equations
A. Limache, S. Idelsohn, R. Rossi, E. Oñate

Int. J. Numer. Meth. Fluids (2007). Vol. 54 (6-8), pp. 639-664

Abstract
The Navier–Stokes equations written in Laplace form are often the starting point of many numerical methods for the simulation of viscous flows. Imposing the natural boundary conditions of the Laplace form or neglecting the viscous contributions on free surfaces are traditionally considered reasonable and harmless assumptions. With these boundary conditions any formulation derived from integral methods (like finite elements or finite volumes) recovers the pure Laplacian aspect of the strong form of the equations. This approach has also the advantage of being convenient in terms of computational effort and, as a consequence, it is used extensively. However, we have recently discovered that these resulting Laplacian formulations violate a basic axiom of continuum mechanics: the principle of objectivity. In the present article we give an accurate account about these topics. We also show that unexpected differences may sometimes arise between Laplace discretizations and divergence discretizations.
Abstract
The Navier–Stokes equations written in Laplace form are often the starting point of many numerical methods for the simulation of viscous flows. Imposing the natural [...]
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Iterative solution of panel method discretizations for potential flow problems. The modal multipolar preconditioning
J. D'ELIA, M. Storti, S. Idelsohn

Int. J. Numer. Meth. Fluids (2000). Vol. 32 (1), pp. 1-22

Abstract
The iterative solution of linear systems arising from panel method discretization of three‐dimensional (3D) exterior potential problems coming mainly from aero‐hydrodynamic engineering problems, is discussed. An original preconditioning based on an approximate eigenspace decomposition is proposed, which corrects bad conditioning arising from a pair of surfaces that are very close to each other, which is a very common situation in slender wings and other aerodynamic profiles. This preconditioning has been tested with the standard Bi‐conjugate gradient (Bi‐CG) and conjugate gradient squared (CGS) iterative methods.
Abstract
The iterative solution of linear systems arising from panel method discretization of three‐dimensional (3D) exterior potential problems coming mainly from aero‐hydrodynamic [...]
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Discrete non‐local absorbing boundary condition for exterior problems governed by Helmholtz equation
R. Bonet Chaple, N. Nigro, M. Storti, S. Idelsohn

Int. J. Numer. Meth. Fluids (1999). Vol. 29 (5), pp. 605-621

Abstract
The finite element method is employed to approximate the solutions of the Helmholtz equation for water wave radiation and scattering in an unbounded domain. A discrete, non‐local and non‐reflecting boundary condition is specified at an artificial external boundary by the DNL method, yielding an equivalent problem that is solved in a bounded domain. This procedure formulates a boundary value problem in a bounded region by imposing a relation in the discrete medium between the nodal values at the two last layers. For plane geometry, this relation can be found by straightforward eigenvalue decomposition. For circular geometry, the plane condition is applied at the external layer and this condition is condensed through a structured annular region, resulting in a condition at an inner radius. Exterior problems with a bounded internal physical obstacle are considered. It is well‐known that these kind of problems are well‐posed, and have a unique solution. Numerical studies based on standard Galerkin methodology examine the dependence of the DNL condition with respect to the circular annular region width. The DNL condition is compared with local boundary conditions of several orders. Numerical examples confirm the important improvement in accuracy obtained by the DNL method over standard conditions.
Abstract
The finite element method is employed to approximate the solutions of the Helmholtz equation for water wave radiation and scattering in an unbounded domain. A discrete, non‐local [...]
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GMRES physics‐based preconditioner for all Reynolds and Mach numbers: numerical examples
N. Nigro, M. Storti, S. Idelsohn

Int. J. Numer. Meth. Fluids (1997). Vol. 25 (12), pp. 1347-1371

Abstract
This paper presents several numerical results using a vectorized version of a 3D finite element compressible and nearly incompressible Euler and Navier–Stokes code. The assumptions were set on laminar flows and Newtonian fluids. The goal of this research is to show the capabilities of the present code to treat a wide range of problems appearing in laminar fluid dynamics towards the unification from incompressible to compressible and from inviscid to viscous flow codes. Several authors with different approaches have tried to attain this target in CFD with relative success. At the beginning the methods based on operator splitting and perturbation were preferred, but lately, with the wide usage of time‐marching algorithms, the preconditioning mass matrix (PMM) has become very popular. With this kind of relaxation scheme it is possible to accelerate the rate of convergence to steady state solutions with the modification of the mass matrix under certain restrictions. The selection of the mass matrix is not an easy task, but we have certain freedom to define it in order to improve the condition number of the system. In this paper we have used a physics‐based preconditioner for the GMRES implicit solver developed previously by us and an SUPG formulation for the semidiscretization of the spatial operator. In sections 2 and 3 we present some theoretical aspects related to the physical problem and the mathematical model, showing the inviscid and viscous flow equations to be solved and the variational formulation involved in the finite element analysis. Section 4 deals with the numerical solution of non‐linear systems of equations, with some emphasis on the preconditioned matrix‐free GMRES solver. Section 5 shows how boundary conditions were treated for both Euler and Navier–Stokes problems. Section 6 contains some aspects about vectorization on the Cray C90. The performance reached by this implementation is close to 1 Gflop using multitasking. Section 7 presents several numerical examples for both models covering a wide range of interesting problems, such as inviscid low subsonic, transonic and supersonic regimes and viscous problems with interaction between boundary layers and shock waves in either attached or separated flows.
Abstract
This paper presents several numerical results using a vectorized version of a 3D finite element compressible and nearly incompressible Euler and Navier–Stokes code. [...]
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Stability analysis of mixed finite element formulations with special mention of equal‐order interpolations
S. Idelsohn, M. Storti, N. Nigro

Int. J. Numer. Meth. Fluids (1995). Vol. 20 (8-9), pp. 1003-1022

Abstract
We present a method to assess the stability of pairs of interpolation spaces for mixed formulations. The method is based on a straightforward calculation of the eigenvalues of the discrete matrices through Fourier decomposition in plane waves and is intended to give, via straightforward numerical computations, a sharper determination of stability than the well‐known ‘patch test’ of Zienkiewicz et al. Special attention is devoted to the study of stability and accuracy of equal‐order interpolations
Abstract
We present a method to assess the stability of pairs of interpolation spaces for mixed formulations. The method is based on a straightforward calculation of the eigenvalues [...]
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Fractures prediction in concrete structures combining the finite and discrete element methods
F. Zarate, E. Oñate

Hormigón y Acero (2018). (prepint) 69, Supl 1, pp. 53-69

Abstract
This paper presents the basic concepts and application of the strategy that combines finite element methods (FEM) and discrete elements (DEM)for the study of the propagation of fractures in concrete structures. The calculation of the structure, modeled as a continuum, begins with the FEMand the DEM is used to start and grow the cracks that may appear in the structure. This methodology has been proposed by the authors in two andthree dimensions. Recently, the use of one-dimensional steel elements embedded in the continuum has been added to model the reinforcement inconcrete structures. The work presents different examples of application to the study of the breakage of parts and structures of concrete in massand armed, as well as the multiple breakage of a historic structure of masonry due to an earthquake.
Abstract
This paper presents the basic concepts and application of the strategy that combines finite element methods (FEM) and discrete elements (DEM)for the study of the propagation [...]
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Two‐phase flow modelling in gas‐stirred liquid vessels with SUPG‐stabilized equal‐order interpolations
N. Nigro, M. Storti, S. Idelsohn

Int. J. Numer. Meth. Fluids (1994). Vol. 19 (1), pp. 1-22

Abstract
The modelling of liquid flow in gas‐stirred vessels is described. A simple two‐phase model accounts for the buoyancy effect of bubbles. Friction between liquid and gas is modelled with the hypothesis of independent bubbles. The resulting PDE system is discretized with an original version of the SUPG‐FEM technique which stabilizes both the convection term and equal‐order interpolations for velocity and pressure, which are known to be unstable for incompressible flows. The resulting steady state discrete system is solved via pseudotemporal explicit iteration with a local time step and a preconditioning to homogenize the temporal scales for liquid and gas.
Abstract
The modelling of liquid flow in gas‐stirred vessels is described. A simple two‐phase model accounts for the buoyancy effect of bubbles. Friction between liquid and gas [...]
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Adaptive refinement criterion for elliptic problems discretized by FEM
M. Storti, N. Nigro, S. Idelsohn

Commun. Numer. Meth. Engng (1993). Vol. 9 (9), pp. 729-743

Abstract
In a recent paper we presented a data structure to be used with multigrid techniques on non‐homogeneously refined FEM meshes. This paper focuses on the adaptive refinement techniques used there. The error estimate is obtained from standard Taylor series. For each element we compute its efficiency in terms of the size, the norm of the second derivatives of the unknown and the parameter p, where Lp is the chosen norm. The way the norm influences the optimal mesh is studied. The number of elements to be refined at each step is such to produce a fast convergence to the optimal mesh, followed by successive homogeneous refinements. We hope that the analysis of these two subjects could be of value for people working with other (perhaps very dissimilar) adaptive refinement techniques (error estimate and data structure, for instance).
Abstract
In a recent paper we presented a data structure to be used with multigrid techniques on non‐homogeneously refined FEM meshes. This paper focuses on the adaptive refinement [...]
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A fast and accurate method to solve the incompressible Navier‐Stokes equations
S. Idelsohn, N. Nigro, J. Gimenez, R. Rossi, J. Marti

Engineering Computations (2013). Vol. 30 (2), pp. 197-222

Abstract
Purpose – The purpose of this paper is to highlight the possibilities of a novel Lagrangian formulation in dealing with the solution of the incompressible Navier‐Stokes equations with very large time steps. Design/methodology/approach – The design of the paper is based on introducing the origin of this novel numerical method, originally inspired on the Particle Finite Element Method (PFEM), summarizing the previously published theory in its moving mesh version. Afterwards its extension to fixed mesh version is introduced, showing some details about the implementation. Findings – The authors have found that even though this method was originally designed to deal with heterogeneous or free‐surface flows, it can be competitive with Eulerian alternatives, even in their range of optimal application in terms of accuracy, with an interesting robustness allowing to use large time steps in a stable way. Originality/value – With this objective in mind, the authors have chosen a number of benchmark examples and have proved that the proposed algorithm provides results which compare favourably, both in terms of solution time and accuracy achieved, with alternative approaches, implemented in in‐house and commercial codes.
Abstract
Purpose – The purpose of this paper is to highlight the possibilities of a novel Lagrangian formulation in dealing with the solution [...]
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Using pseudo-concentrations in the analysis of transient forming processes
H. Antúnez, S. Idelsohn

Engineering Computations (1992). Vol. 9 (5), pp. 547-559

Abstract
The pseudo‐concentration method is applied to the analysis of transient processes. A simple, easy‐to‐handle model is obtained by keeping an Eulerian description: it does not require remeshing after a certain amount of plastic deformation. The range of applicability of the method is extended to non‐confined (even with several free surfaces) processes. It is shown the need of distinct handling of free surfaces according to their orientation to the direction of the flow. A seamless tube rolling process, a cylinder upsetting and a backward extrusion are modelled. Experimental data and results obtained by other methods are used to compare and discuss the performance of the model.
Abstract
The pseudo‐concentration method is applied to the analysis of transient processes. A simple, easy‐to‐handle model is obtained by keeping an Eulerian description: it [...]
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Fracture analysis of a surface-coated ceramic by speckle photography and finite elements
E. Barbero, G. Kaufmann, S. Idelsohn

Optics & Laser Technology (1990). Vol. 22 (1), pp. 17-22

Abstract
The fracture behaviour of a four-point bend surface-coated ceramic specimen with a through-the-thickness crack was experimentally investigated. Speckle photography was used to measure opening displacements over the specimen surface and across the crack line. For a glazed and unglazed specimen, stress-intensity factors were experimentally determined by means of a method that uses data not restricted to the singularity-dominated zone. Stress-intensity factors were numerically calculated using a three-dimensional finite element analysis and their variations along the crack front were also evaluated. Experimental results agree reasonably well with the numerical results. Results show the influence of the glaze on the fracture behaviour of the composite material.
Abstract
The fracture behaviour of a four-point bend surface-coated ceramic specimen with a through-the-thickness crack was experimentally investigated. Speckle photography was used [...]
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Evaluation of finite-element calculations in a part-circular crack by coherent optics techniques
G. Kaufmann, A. Lopergolo, S. Idelsohn, E. Barbero

Experimental Mechanics (1987). Vol. 27 (2), pp. 154-157

Abstract
Two techniques, speckle photography and holographic interferometry, were used to test three-dimensional finite-element calculations in an internally pressurized cylinder with an external part-circular crack. Opening displacements along the crack line were measured by speckle photography. Radial displacements were obtained from holographic fringe patterns. Good agreement between experimental and numerical data is obtained. Stress-intensity factor variations along the crack front are calculated from numerical results.
Abstract
Two techniques, speckle photography and holographic interferometry, were used to test three-dimensional finite-element calculations in an internally pressurized cylinder with [...]
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Inelastic seismic analysis of a building structure designed by argentine codes
V. Sonzogni, A. Cardona, S. Idelsohn

Earthquake Engineering Structural Dynamics (1984). Vol. 12 (6), pp. 721-736

Abstract
A reinforced concrete frame‐wall structure of a building designed in accordance to standard practice in Argentina was analysed by the procedures prescribed by current Argentine Codes. In addition, the inelastic step‐by‐step response of the structure to design spectrum‐compatible accelerograms was studied by means of a special element for inelastic dynamic analysis of reinforced concrete frames. Results obtained by the different methods of analysis are presented
Abstract
A reinforced concrete frame‐wall structure of a building designed in accordance to standard practice in Argentina was analysed by the procedures prescribed by current Argentine [...]
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A comparative computational study of blood flow through prosthetic heart valves using the finite element method
S. Idelsohn, L. Costa, R. Ponso

Journal of Biomechanics (1985). Vol. 18 (2), pp. 97-115

Abstract
The steady flow of blood through three common types of prosthetic heart valves was simulated numerically using the finite element method. The velocity, pressure and stress fields were obtained for the disk-type, tilting-disk and ball-type prosthetic heart valves in aortic position, for increasing Reynolds numbers up to 900, 1500 and 2000 respectively. Computer graphics of calculated velocities are presented, showing in detail the accelerated flow, recirculation and stagnation areas developed in the prosthesis. Maximum wall shear stresses were found at 0.5, 1.4, and 1.2 diameters from the sewing ring downstream for the disk, tilting-disk and ball valves being the values of 55, 18 and 33 dyn cm−2 respectively. In the vicinity of the occluder, maximum shear stresses of 38, 30 and 47 dyn cm−2 respectively were computed. The flow characteristics and performance for each valve are compared, the results are presented in terms of energy loss and maximum shear stress. The velocity and stress fields are compared with in vitro evaluations found in the literature
Abstract
The steady flow of blood through three common types of prosthetic heart valves was simulated numerically using the finite element method. The velocity, pressure and stress [...]
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Smoothed surface gradients for panel methods
J. D'Elía, M. Storti, S. Idelsohn

Advances in Engineering Software (2000). Vol. 31 (5), pp. 339-346

Abstract
A weak form to compute the dipolar and monopolar surface gradients, related to a low-order panel method, is shown. The flow problem is formulated by means of a three-dimensional potential model and the discretization is based on Morino's formulation for the perturbation velocity potential. On the body surface, this representation reduces to a boundary integral equation with the source (or monopolar) and the doublet (or dipolar) densities. The first of the two is found by application of the boundary flow condition, and the second one is the unknown over the body surface. A lower panel method is used for the analytic integrations of both the monopolar and dipolar influence coefficients. The surface velocity field is computed after solving the linear system, with a strong and a weak form of the Stokes theorem, which is oriented to fairly non-structured panel meshes. The proposed method is validated by comparing the numerical results with analytical ones for an isolated sphere and includes a prediction over a car-like configuration.
Abstract
A weak form to compute the dipolar and monopolar surface gradients, related to a low-order panel method, is shown. The flow problem is formulated by means of a three-dimensional [...]
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A closed form for low-order panel methods
J. D'Elía, M. Storti, S. Idelsohn

Advances in Engineering Software (2000). Vol. 31 (5), pp. 347-353

Abstract
A closed form for the computation of the dipolar and monopolar influence coefficients related to a low-order panel method is shown. The flow problem is formulated by means of a three-dimensional potential model; the method of discretization is based on the Morino formulation for the perturbation velocity potential. On the body surface this representation reduces to an integral equation with the source (or monopolar) and the doublet (or dipolar) densities. The former is found by application of the boundary condition, and the latter is the unknown over the surface of the body. The lower panel method is used for the analytical integrations of the monopolar and dipolar influence coefficients, with special attention to avoid a logarithmic singularity in the monopolar matrix when flat fairly structured meshes that are common in ship-wave calculations are used.
Abstract
A closed form for the computation of the dipolar and monopolar influence coefficients related to a low-order panel method is shown. The flow problem is formulated by means [...]
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Evaluation of Finite Element Calculations in a Cracked Cylinder Under Internal Pressure by Speckle Photography
G. Kaufmann, A. Lopergolo, S. Idelsohn

J. Appl. Mech (1983). Vol. 50 (4a), pp. 896-897

Abstract
The usefulness of using the speckle photography technique in fracture mechanics to check numerical calculations is demonstrated for an internally pressurized cylinder with a surface flaw. A pointwise technique was utilized to measure the opening displacements along the crack line and the Mode I stress-intensity factor was determined by extrapolating these results to the crack tip. Finite element calculations were performed to be compared with experimental data and good agreement was obtained.
Abstract
The usefulness of using the speckle photography technique in fracture mechanics to check numerical calculations is demonstrated for an internally pressurized cylinder with [...]
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Transverse vibrations of an isotropic, simply supported rectangular plate with an orthotropic inclusion
L. Ercoli, V. Sonzogni, S. Idelsohn, P. Laura

Journal of Sound and Vibration (1992). Vol. 135 (2), pp. 217-221

Abstract
An approximate analytical solution is obtained for the title problem by using a Navier-type solution. It is shown that the fundamental frequency coefficient obtained by means of this procedure is in reasonably good agreement with the result obtained by using a finite element algorithmic methodology. Obviously the type of material disturbance considered introduces considerable change in the dynamic behavior of the structural element and this fact is clearly shown in the variation of the fundamental frequency value.
Abstract
An approximate analytical solution is obtained for the title problem by using a Navier-type solution. It is shown that the fundamental frequency coefficient obtained by means [...]
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Free vibrations of rectangular plates of exponentially varying thickness and with a free edge
V. Sonzogni, S. Idelsohn, P. Laura, V. Cortínez

Journal of Sound and Vibration (1990). Vol. 140 (3), pp. 513-522

Abstract
Transverse vibrations of the structural system described in the title are analyzed by using classical plate theory and employing two different methodologies: the recently developed “optimized Kantorovich approach”; and a finite element algorithmic procedure. It is shown that the fundamental frequency coefficients obtained by using both techniques for a rather wide variation of the governing geometric parameters are in very good agreement. Lower frequency coefficients of the plate system determined by means of the finite element method are also presented.
Abstract
Transverse vibrations of the structural system described in the title are analyzed by using classical plate theory and employing two different methodologies: the recently [...]
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On the self-stressing modes in free vibration analysis
S. Idelsohn, M. Geradin

Journal of Sound and Vibration (1982). Vol. 83 (2), pp. 143-155

Abstract
The type of convergence to the eigenspectrum of a structure calculated from a finite element analysis is examined in light of the variational properties of the Rayleigh quotient and of Courant's maximum-minimum principle. The influence of the self-stressing modes on the solution is firt demonstrated theoretically and then shown practically on the results obtained via a family of equilibrium elements in which the number of self-stressing modes relative to the number of vibration modes may be varied as a parameter.
Abstract
The type of convergence to the eigenspectrum of a structure calculated from a finite element analysis is examined in light of the variational properties of the Rayleigh quotient [...]
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Fast fluid–structure interaction simulations using a displacement-based finite element model equipped with an explicit streamline integration prediction
P. Ryzhakov, J. Miquel, S. Idelsohn, E. Oñate

Comput. Methods Appl. Mech. Engrg., (2017). Vol. 315, pp. 1080-1097

Abstract
We propose here a displacement-based updated Lagrangian fluid model developed to facilitate a monolithic coupling with a wide range of structural elements described in terms of displacements. The novelty of the model consists in the use of the explicit streamline integration for predicting the end-of-step configuration of the fluid domain. It is shown that this prediction considerably alleviates the time step size restrictions faced by the former Lagrangian models due to the possibility of an element inversion within one time step. The method is validated and compared with conventional approaches using three numerical examples. Time step size and corresponding Courant numbers leading to optimal behavior in terms of computational efficiency are identified.
Abstract
We propose here a displacement-based updated Lagrangian fluid model developed to facilitate a monolithic coupling with a wide range of structural elements [...]
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Metal forming analysis by fourier series expansion and further uses of pseudo-concentrations
H. Antúnez, S. Idelsohn, E. Dvorkin

Computers and Structures (1992). Vol. 44 (1-2), pp. 435-451

Abstract
An analysis of metal forming processes with axial geometry is performed by an expansion in Fourier series on the circumferential direction. For that purpose, an incremental form is presented on the basis of the flow formulation. For every increment of the non-null imposed boundary conditions an algebraic system is formed in which the non-linearity due to the visco-plastic properties of the material is placed as part of the load term. In this way, the global stiffness matrix is block diagonal, the coupling due to material non-linearity being included on the right-hand side. Free surfaces are treated as an interface inside the elements, as an extension of the pseudo-concentration method.
Abstract
An analysis of metal forming processes with axial geometry is performed by an expansion in Fourier series on the circumferential direction. For that purpose, an incremental [...]
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An effective automatic incremental/iterative method for static nonlinear structural analysis
J. Jeusette, G. Laschet, S. Idelsohn

Computers and Structures (1989). Vol. 32 (1), pp. 125-135

Abstract
In the prebuckling range of the complete nonlinear response of a structure submitted to destabilizing loads, a linearized stability analysis is generally an interesting tool. Used in conjunction with an arc-length algorithm, incremental bifurcation analyses are able to give optimal definition for the increment predictor size. When the associated eigenvalue problem is solved by minimizing the finite element discretized form of the Rayleigh quotient via a preconditioned conjugate gradient technique, it can be very easily inserted in an automatic nonlinear equations solver. Such a procedure is presented in this paper after a review of existing arc-length schemes and step-size control methods. Moreover, for tracing the postbuckling range of the nonlinear response automatically, a new recurrence formula is proposed to control the step-size. The well behaviour of this algorithm is illustrated in two classical structural applications.
Abstract
In the prebuckling range of the complete nonlinear response of a structure submitted to destabilizing loads, a linearized stability analysis is generally an interesting tool. [...]
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A load-dependent basis for reduced nonlinear structural dynamics
S. Idelsohn, A. Cardona

Computers and Structures (1985). Vol. 20 (1-3), pp. 203-210

Abstract
A computational algorithm for predicting the dynamical response of a nonlinear structure by means of a reduction scheme is described. In it, the nonlinear system of ordinary differential equations obtained from the finite element discretization is reduced, by employing a Rayleigh-Ritz technique. A new criterion for the computation of the basis vectors is proposed. It is based on a sequence of basis vectors proposed by Wilson et al. for linear dynamics problems, which was augmented by adding derivatives of these vectors with respect to the generalized displacement amplitudes. The later vectors allow the treatment of nonlinear problems.
Abstract
A computational algorithm for predicting the dynamical response of a nonlinear structure by means of a reduction scheme is described. In it, the nonlinear system of ordinary [...]
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Computational strategies for the solution of large nonlinear problems via quasi-newton methods
M. Geradin, S. Idelsohn, M. Hogge

Computers and Structures (1981). Vol. 13 (1-3), pp. 73-81

Abstract
The usefulness of quasi-Newton methods for the solution of nonlinear systems of equations is demonstrated. After a review of the Newton iterative method, several quasi-Newton updates are presented and tested. Special attention is devoted to the solution of large sparse systems of equations such as those issued from spatial discretization of continua by finite elements. The numerical examples presented comprise static and dynamic analyses of geometrical, material and combined nonlinear structural problems and a model fluid flow problem with different levels of nonlinearity. All the results are assorted with a complete discussion of the different methods used, of the convergence rates and of the associated computer costs. From the present studies, it can be concluded that computational costs for the solution of large nonlinear systems of equations can be reduced drastically by using convenient quasi-Newton updates or by adequate combined Newton/quasi-Newton strategies.
Abstract
The usefulness of quasi-Newton methods for the solution of nonlinear systems of equations is demonstrated. After a review of the Newton iterative method, several quasi-Newton [...]
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Failure internal pressure of spherical steel containments
G. Sarmiento, S. Idelsohn, A. Cardona, V. Sonzogni

Nuclear Engineering and Desing (1985). Vol. 90 (2), pp. 209-222

Abstract
An application of the British CEGB's R6 Failure Assessment Approach to the determination of failure internal pressure of nuclear power plant spherical steel containments is presented. The presence of hypothetical cracks both in the base metal and in the welding material of the containment, with geometrical idealizations according to the ASME Boiler and Pressure Vessel Code (Section XI), was taken into account in order to analyze the sensitivity of the failure assessment with the values of the material fracture properties. Calculations of the elastoplastic collapse load have been performed by means of the Finite Element System SAMCEF. The clean axisymmetric shell (neglecting the influence of nozzles and minor irregularities) and two major penetrations (personnel and emergency locks) have been taken separately into account. Large-strain elastoplastic behaviour of the material was considered in the Code, using lower bounds of true stress—true strain relations obtained by testing a collection of tensile specimens. Assuming the presence of cracks in non-perturbed regions, the reserve factor for test pressure and the failure internal pressure have been determined as a function of the flaw depth.
Abstract
An application of the British CEGB's R6 Failure Assessment Approach to the determination of failure internal pressure of nuclear power plant spherical steel containments [...]
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Nonlinear structural dynamics via Newton and quasi-Newton methods
M. Geradin, S. Idelsohn, M. Hogge

Nuclear Engineering and Design (1980). Vol. 58 (3), pp. 339-348;

Abstract
This paper is an attempt to compare Newton and quasi-Newton methods in nonlinear structural dynamics. After a review of the classical iterative methods, several quasi-Newton updates are presented and tested. Special attention is devoted to the solution of large sparse systems for which two original procedures are described: a substructure correction and a vectorial correction. The numerical examples presented include the dynamic analyses of geometrical, material and combined nonlinearities. All the results are assorted with a complete discussion of the different methods used, of the convergence rates and of the associated computer costs. From the present results, Newton's methods appear to exhibit the best convergence rates when an efficient computational strategy is adopted. Nevertheless computational costs for the solution of large systems can be reduced drastically by using convenient quasi-Newton updates.
Abstract
This paper is an attempt to compare Newton and quasi-Newton methods in nonlinear structural dynamics. After a review of the classical iterative methods, several quasi-Newton [...]
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OpenCL‐based implementation of an unstructured edge‐based finite element convection‐diffusion solver on graphics hardware
F. Mossaiby, R. Rossi, P. Dadvand, S. Idelsohn

Int. J. Numer. Meth. Engng. (2012). Vol. 89 (13), pp. 1635-1651

Abstract
The solution of problems in computational fluid dynamics (CFD) represents a classical field for the application of advanced numerical methods. Many different approaches were developed over the years to address CFD applications. Good examples are finite volumes, finite differences (FD), and finite elements (FE) but also newer approaches such as the lattice‐Boltzmann (LB), smooth particle hydrodynamics or the particle finite element method. FD and LB methods on regular grids are known to be superior in terms of raw computing speed, but using such regular discretization represents an important limitation in dealing with complex geometries. Here, we concentrate on unstructured approaches which are less common in the GPU world. We employ a nonstandard FE approach which leverages an optimized edge‐based data structure allowing a highly parallel implementation. Such technique is applied to the ‘convection‐diffusion’ problem, which is often considered as a first step towards CFD because of similarities to the nonconservative form of the Navier–Stokes equations. In this regard, an existing highly optimized parallel OpenMP solver is ported to graphics hardware based on the OpenCL platform. The optimizations performed are discussed in detail. A number of benchmarks prove that the GPU‐accelerated OpenCL code consistently outperforms the OpenMP version.
Abstract
The solution of problems in computational fluid dynamics (CFD) represents a classical field for the application of advanced numerical methods. Many different approaches were [...]
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All‐hexahedral element meshing: automatic elimination of self‐intersecting dual lines
N. Calvo, S. Idelsohn

Int. J. Numer. Meth. Engng. (2002). Vol. 55 (12), pp. 1439-1449

Abstract
There has been some degree of success in all‐hexahedral meshing. Standard methods start with the object geometry defined by means of an all‐quadrilateral mesh, followed by the use of the combinatorial dual to the mesh in order to define the internal connectivities among elements. For all of the known methods using the dual concept, it is necessary to first prevent or eliminate self‐intersecting (SI) dual lines of the given quadrilateral mesh. The relevant features of SI lines are studied, giving a method to remove them, which avoids deforming the original geometry. Some examples of resulting meshes are shown where the current meshing method has been successfully applied.
Abstract
There has been some degree of success in all‐hexahedral meshing. Standard methods start with the object geometry defined by means of an all‐quadrilateral mesh, followed [...]
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All‐hexahedral mesh smoothing with a node‐based measure of quality
N. Calvo, S. Idelsohn

Int. J. Numer. Meth. Engng. (2001). Vol. 50 (8), pp. 1957-1967

Abstract
This research work deals with the analysis and test of a normalized‐Jacobian metric used as a measure of the quality of all‐hexahedral meshes. Instead of element qualities, a measure of node quality was chosen. The chosen metric is a bound for deviation from orthogonality of faces and dihedral angles. We outline the main steps and algorithms of a program that is successful in improving the quality of initially invalid meshes to acceptable levels. For node movements, the program relies on a combination of gradient‐driven and simulated annealing techniques. Some examples of the results and speed are also shown.
Abstract
This research work deals with the analysis and test of a normalized‐Jacobian metric used as a measure of the quality of all‐hexahedral meshes. Instead of element qualities, [...]
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Non‐reflective planar boundary condition based on Gauss filter
R. Bonet Chaple, N. Nigro, M. Storti, S. Idelsohn

Int. J. Numer. Meth. Engng. (2000). Vol. 47 (5), pp. 969-983

Abstract
A non‐reflecting boundary condition based on the Gauss filter is employed for the determination of scattered potential governed by the equation. A filtering layer is used for closing infinite domain calculations. An expression for the reflection coefficient is derived and an optimal filtering layer is designed. Numerical results validate the performance of this method for unbounded wave guide problems.
Abstract
A non‐reflecting boundary condition based on the Gauss filter is employed for the determination of scattered potential governed by the equation. A filtering layer is used [...]
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A finite point method in computational mechancis. Applications to convective transport and fluid flow.
E. Oñate, S. Idelsohn, O. Zienkiewicz, R. Taylor

Int. J. Numer. Meth. Engng. (1996). Vol. 39 (22), pp. 3839-3866

Abstract
The paper presents a fully meshless procedure fo solving partial differential equations. The approach termed generically the ‘finite point method’ is based on a weighted least square interpolation of point data and point collocation for evaluating the approximation integrals. Some examples showing the accuracy of the method for solution of adjoint and non‐self adjoint equations typical of convective‐diffusive transport and also to the analysis of compressible fluid mechanics problem are presented.
Abstract
The paper presents a fully meshless procedure fo solving partial differential equations. The approach termed generically the ‘finite point method’ is based on [...]
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Transient analysis of tube rolling processes by a semi‐analytical formulation
H. Antúnez, S. Idelsohn

Int. J. Numer. Meth. Engng. (1994). Vol. 37 (21), pp. 3621-3632

Abstract
A semi‐analytical formulation is presented for transient metal‐forming processes which, being axisymmetric in geometry, are subjected to non‐axisymmetric loads and boundary conditions. The problems are described in terms of the flow formulation, and the pseudo‐concentration method (two material based) is used to account for time integration and non‐axisymmetric free surfaces. Proper Fourier series expansion of both the scalar fields defined to identify the free surfaces and of all the variables of the mechanical problem allows the performance of an advective transport–corresponding to time integration–for a non‐axisymmetric velocity field. A block diagonal matrix is obtained for each harmonic component, as it has been achieved for the constant time solution. The new configuration found as a result of this analysis is taken to calculate the velocity field for the incremented time, which in turn is used to perform the following time step
Abstract
A semi‐analytical formulation is presented for transient metal‐forming processes which, being axisymmetric in geometry, are subjected to non‐axisymmetric loads and boundary [...]
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A preconditioning mass matrix to accelerate the convergence to the steady Euler solutions using explicit schemes
M. Storti, C. Baumann, S. Idelsohn

Int. J. Numer. Meth. Engng. (1992). Vol. 34 (2), pp. 519-541

Abstract
When explicit time marching algorithms are used to reach the steady state of problems governed by the Euler equations, the rate of convergence is strongly impaired both in the zones with low Mach number and in the zones with transonic flow, e.g. Mach ⩽ α and | Mach − 1| ⩽ α, with α ⩽ 0·2. The rate of convergence becomes slower as α diminishes. We show in this paper, with analytical and numerical results, how the use of a preconditioning mass matrix accelerates the convergence in the aforementioned ranges of Mach numbers. The preconditioning mass matrix (PMM) we advocate in this paper can be applied to any FEM/FVM that uses an explicit time marching scheme to find the steady state. The method's rate of convergence to the steady state is studied, and results for the one‐ and two‐dimiensional cases are presented. In Sections 1‐3, using the one‐dimensional Euler equations, we first explain why there exists a slow rate of convergence when the plain lumping of mass is used. Then the convergence rate to steady solutions is analysed from its two constituents, that is, convergence by absorption at the boundaries and by damping in the domain. Next we give the natural solution to this problem, and with several examples we show the effectiveness of the proposed mass matrix when compared with the plain scheme. In Sections 4‐8 we give the multidimensional version of the preconditioning mass matrix. We make a stability analysis and compare the group velocities and damping with and without the new mass matrix. To finish, we show the velocity of convergence for a common test problem
Abstract
When explicit time marching algorithms are used to reach the steady state of problems governed by the Euler equations, the rate of convergence is strongly impaired both in [...]
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Improving the convergence rate of the Petrov‐Galerkin techniques for the solution of transonic and supersonic flows
C. Baumann, M. Storti, S. Idelsohn

Int. J. Numer. Meth. Engng. (1992). Vol. 34 (2), pp. 453-568

Abstract
This paper report progress on a technique to accelerate the convergence to steady solutions when the streamline‐upwind/Petrov‐Galerkin (SUPG) technique is used. Both the description of a SUPG formulation and the documentation of the development of a code for the finite element solution of transonic and supersonic flows are reported. The aim of this work is to present a formulation to be able to treat domains of any configuration and to use the appropriate physical boundary conditions, which are the major stumbling blocks of the finite difference schemes, together with an appropriate convergence rate to the steady solution. The implemented code has the following features: the Hughes' SUPG‐type formulation with an oscillation‐free shock‐capturing operator, adaptive refinement, explicit integration with local time‐step and hourglassing control. An automatic scheme for dealing with slip boundary conditions and a boundary‐augmented lumped mass matrix for speeding up convergence. It is shown that the velocities at which the error is absorbed in and ejected from the domain (that is damping and group velocities respectively) are strongly affected by the time step used, and that damping gives an O(N2) algorithm contrasting with the O(N) one given by absorption at the boundaries. Nonetheless, the absorbing effect is very low when very different eigenvalues are present, such as in the transonic case, because the stability condition imposes a too slow group velocity for the smaller eigenvalues. To overcome this drawback we present a new mass matrix that provides us with a scheme having the highest group velocity attainable in all the components. In Section 1 we will describe briefly the theoretical background of the SUPG formulation. In Section 2 it is described how the foregoing formulation was used in the finite element code and which are the appropriate boundary conditions to be used. Finally in Section 3 we will show some results obtained with this code
Abstract
This paper report progress on a technique to accelerate the convergence to steady solutions when the streamline‐upwind/Petrov‐Galerkin (SUPG) technique is used. Both the [...]
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Upwind techniques via variational principles
S. Idelsohn

Int. J. Numer. Meth. Engng. (1989). Vol. 28 (4), pp. 769-784

Abstract
The amount of upwind or magnitude of off‐centering needed in the numerical solution of second order differential equations with significant first derivatives is justified more rigorously in this paper by requiring the satisfaction of a variational principle. It will be shown that, for a discrete solution, a set of variational principles can be found which allow the problem to be solved as a self‐adjoint system. The technique presented here will give a clear indication of those regions where (i) upwind techniques are not required, (ii) upwind techniques are necessary and sufficient and (iii) upwind techniques are insufficient and artificial viscosity is required.
Abstract
The amount of upwind or magnitude of off‐centering needed in the numerical solution of second order differential equations with significant first derivatives is justified [...]
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