Scipedia: Documents published in 2019

All‐hexahedral mesh smoothing with a node‐based measure of quality

María Jesús Samper — Mon, 18 Feb 2019 12:40:35 +0100

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.

Non‐reflective planar boundary condition based on Gauss filter

María Jesús Samper — Mon, 18 Feb 2019 12:32:47 +0100

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.

Transient analysis of tube rolling processes by a semi‐analytical formulation

María Jesús Samper — Mon, 18 Feb 2019 11:53:18 +0100

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

A preconditioning mass matrix to accelerate the convergence to the steady Euler solutions using explicit schemes

María Jesús Samper — Mon, 18 Feb 2019 11:38:26 +0100

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

Improving the convergence rate of the Petrov‐Galerkin techniques for the solution of transonic and supersonic flows

María Jesús Samper — Mon, 18 Feb 2019 10:57:53 +0100

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

Upwind techniques via variational principles

María Jesús Samper — Mon, 18 Feb 2019 10:51:22 +0100

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.

Making curved interfaces straight in phase‐change problems

María Jesús Samper — Mon, 18 Feb 2019 10:44:05 +0100

This paper presents a method for straightening curved interfaces arising in phase‐change problems. The method works on isoparametric finite elements, performing a second transformation which maps the master element onto a new one in which the interface looks like a straight line. This allows using the current Gaussian integration technique for squares to evaluate the integrals over each phase. The method provides a better estimation of the contribution of latent heat effects to the residual vector, compared to those obtained by using the assumption that the interface is straight. Appropriate guidelines for solving the non‐linear system of equations arising in this kind of problem are also given. Several numerical examples are presented to show the performance of the method.

Solution of non‐linear thermal transient problems by a reduction method

María Jesús Samper — Fri, 15 Feb 2019 13:41:19 +0100

A new algorithm for solving transient thermal problems in a reduced subspace of the original space of discretization is described. The basis of the subspace is formed by using the system response at the first time step (or an approximation to it) and a set of orthogonal vectors obtained by the algorithm of Lanczos. Derivatives of these vectors are included when treating non‐linear cases. The method allows one to handle the sharp gradients that appear in thermally loaded structures, and the response is accurately predicted by using only a small number of degrees of freedom in the reduced system. The algorithm is specially well suited for treating large‐scale problems. Examples dealing with one‐, two‐ and three‐dimensional cases of linear and non‐linear conduction problems are presented.

A temperature‐based finite element solution for phase‐change problems

María Jesús Samper — Fri, 15 Feb 2019 12:15:37 +0100

A finite element procedure for solving multidimensional phase change problems is described. The algorithm combines a temperature formulation with a finite element treatment of the differential equation and discontinuous integration within the two‐phase elements to avoid the necessity of regularization. A new criterion for the computation of the iteration matrix is proposed. It is based on a quasi‐Newton correction of the Jacobian matrix for conduction problems without change of phase. A set of test problems with exact solution is analysed and demonstrates that the procedure can accurately evaluate the front position and temperature history with a reasonable computational effort.

A family of conforming finite elements for deep shell analysis

María Jesús Samper — Fri, 15 Feb 2019 11:36:30 +0100

The problem related to the derivation of conforming deep shell finite elements is examined in the light of the thin shell theory and using the classical Loves strain energy formulation. A family of quadrangular finite elements allowing for variable curvature is developed. It is shown how an exact conformity of the displacements can be ensured in a large number of cases.

Various static and dynamic applications are used to illustrate the advantages of these elements.

Elemental enriched spaces for the treatment of weak and strong discontinuous fields

María Jesús Samper — Fri, 15 Feb 2019 10:40:55 +0100

This paper presents a finite element that incorporates weak, strong and both weak plus strong discontinuities with linear interpolations of the unknown jumps for the modeling of internal interfaces. The new enriched space is built by subdividing each triangular or tetrahedral element in several standard linear sub-elements. The new degrees of freedom coming from the assembly of the sub-elements can be eliminated by static condensation at the element level, resulting in two main advantages: first, an elemental enrichment instead of a nodal one, which presents an important reduction of the compunting time when the internal interface is moving all around the domain and second, an efficient implementation involving minor modifications allowing to reuse existing finite element codes. The equations for the internal interface are constructed by imposing the local equilibrium between the stresses in the bulk of the element and the tractions driving the cohesive law, with the proper equilibrium operators to account for the linear kinematics of the discontinuity. To improve the continuity of the unknowns on both sides of the elements on which a static condensation is done, a contour integral has been added. These contour integrals named inter-elemental forces can be interpreted as a “do nothing” boundary condition (Coppola-Owen and Codina, 2011) published in another context, or as the usage of weighting functions that ensure convergence of the approach as proposed by J.C. Simo (Simo and Rifai, 1990). A series of numerical tests for scalar unknowns as a simple representation of more general numerical simulations are presented to illustrate the performance of the enriched elemental space.

Objectivity tests for Navier–Stokes simulations: The revealing of non-physical solutions produced by Laplace formulations

María Jesús Samper — Thu, 14 Feb 2019 12:48:20 +0100

Laplace formulations are weak formulations of the Navier–Stokes equations commonly used in computational fluid dynamics. In these schemes, the viscous terms are given as a function of the Laplace diffusion operator only. Despite their popularity, recently, it has been proven that they violate a fundamental principle of continuum mechanics, the principle of objectivity. It is remarkable that such flaw has not being noticed before, neither detected in numerical experiments. In this work, a series of objectivity tests have been designed with the purpose of revealing such problem in real numerical experiments. Through the tests it is shown how, for slip boundaries or free-surfaces, Laplace formulations generate non-physical solutions which widely depart from the real fluid dynamics. These tests can be easily reproduced, not requiring complex simulation tools. Furthermore, they can be used as benchmarks to check consistency of developed or commercial software. The article is closed with a discussion of the mathematical aspects involved, including the issues of boundary conditions and objectivity.

All-hexahedral element meshing: Generation of the dual mesh by recurrent subdivision

María Jesús Samper — Thu, 14 Feb 2019 12:39:12 +0100

The domain geometry is defined by means of a closed all-quadrilateral mesh. The outer mesh imposes very strong restrictions on the possible connectivities between the inner hexahedral elements. Following the guidelines of the outer topology, the inner one is almost entirely defined. Several ways may be decided for certain configurations, some of them requiring special considerations in order to achieve a valid FEM mesh. The process is entirely performed by constructing the (graph theoretical) dual of the hexahedral mesh, this means no metric information is handled until the final (positioning and smoothing) steps. The essential steps of this scheme are described by means of examples.

The DNL absorbing boundary condition: applications to wave problems

María Jesús Samper — Thu, 14 Feb 2019 12:29:58 +0100

A general methodology for developing absorbing boundary conditions is presented. For planar surfaces, it is based on a straightforward solution of the system of block difference equations that arise from partial discretization in the directions transversal to the artificial boundary followed by discretization on a constant step 1D grid in the direction normal to the boundary. This leads to an eigenvalue problem of the size of the number of degrees of freedom in the lateral discretization. The eigenvalues are classified as right- or left-going and the absorbing boundary condition consists in imposing a null value for the ingoing modes, leaving free the outgoing ones. Whereas the classification is straightforward for operators with definite sign, like the Laplace operator, a virtual dissipative mechanism has to be added in the mixed case, usually associated with wave propagation phenomena, like the Helmholtz equation. The main advantage of the method is that it can be implemented as a black-box routine, taking as input the coefficients of the linear system, obtained from standard discretization (FEM or FDM) packages and giving on output the absorption matrix. We present the application of the DNL methodology to typical wave problems, like Helmholtz equations and potential flow with free surface (the ship wave resistance and sea-keeping problems).

Physics based GMRES preconditioner for compressible and incompressible Navier-Stokes equations

María Jesús Samper — Thu, 14 Feb 2019 12:23:26 +0100

This paper presents the implementation of a local physics preconditioning mass matrix [8] for an unified approach of 3D compressible and incompressible Navier-Stokes equations using an SUPG finite element formulation and GMRES implicit solver. During the last years a lot of effort has been dedicated to finding a unified approach for compressible and incompressible flow in order to treat fluid dynamic problems with a very wide range of Mach and Reynolds numbers [10,26,37]. On the other hand, SUPG finite element formulation and GMRES implicit solver is one of the most robust combinations to solve state of the art CFD problems [1,6,9,22,29,30,31].

The selection of a good preconditioner and its performance on parallel architecture is another open problem in CFD community. The local feature of the preconditioner presented here means that no communication among processors is needed when working on parallel architectures. Due to these facts we consider that this research can make some contributions towards the development of a unified fluid dynamic model with high rates of convergence for any combination of Mach and Reynolds numbers, being very suitable for massively parallel computations.

Finally, it is important to remark that while this kind of preconditioning produces stabilized results in nearly incompressible regimes the standard version exhibits some numerical drawbacks that lead to solutions without physical meaning.

Equal-order interpolations: a unified approach to stabilize the incompressible and advective effects

María Jesús Samper — Thu, 14 Feb 2019 12:16:28 +0100

In this paper we present a new SUPG formulation for compressible and near incompressible Navier-Stokes equations [5]. It introduces an extension of the exact solution for one-dimensional systems to the multidimensional case, in a similar way to that arising in the scalar problem. It is important to note that this formulation satisfies both the one-dimensional advective-diffusive system limit case and the advection-dominated multidimensional system case presented by Mallet et al. Another interesting feature of this formulation is that it introduces naturally a stabilizing term for the incompressibility condition, in a similar way to that found by other authors [1–4]. However, in our formulation the stabilization is introduced to the whole system of equations, while other authors introduce a term to stabilize the incompressibility condition and another one for the advective term.

In Section 1 we present Navier-Stokes equations for compressible flow and, then, we pass to detail several topics related to the numerical discretization of such advective-diffusive multidimensional systems of PDEs, in the Petrov-Galerkin context. The method is applicable and described for the general Re > 0 laminar flow, but the nature of the stabilizing effect of the artificial diffusion matrix introduced is discussed in depth for the simpler Stokes (Re = 0) flow.

Several numerical results are shown in Section 5, taking the well-known test problem of the square-cavity and a variant of this, namely a multiply connected square-cavity, as a validation for this code

A Petrov-Galerkin formulation for advection-reaction-diffusion problems

María Jesús Samper — Thu, 14 Feb 2019 12:09:01 +0100

In this work we present a new method called (SU + C)PG to solve advection-reaction-diffusion scalar equations by the Finite Element Method (FEM). The SUPG (for Streamline Upwind Petrov-Galerkin) method is currently one of the most popular methods for advection-diffusion problems due to its inherent consistency and efficiency in avoiding the spurious oscillations obtained from the plain Galerkin method when there are discontinuities in the solution. Following this ideas, Tezduyar and Park treated the more general advection-reaction-diffusion problem and they developed a stabilizing term for advection-reaction problems without significant diffusive boundary layers. In this work an SUPG extension for all situations is performed, covering the whole plane represented by the Peclet number and the dimensionless reaction number. The scheme is based on the extension of the super-convergence feature through the inclusion of an additional perturbation function and a corresponding proportionality constant. Both proportionality constants (that one corresponding to the standard perturbation function from SUPG, and the new one introduced here) are selected in order to verify the ‘super-convergence’ feature, i.e. exact nodal values are obtained for a restricted class of problems (uniform mesh, no source term, constant physical properties). It is also shown that the (SU + C)PG scheme verifies the Discrete Maximum Principle (DMP), that guarantees uniform convergence of the finite element solution. Moreover, it is shown that super-convergence is closely related to the DMP, motivating the interest in developing numerical schemes that extend the super-convergence feature to a broader class of problems.

Steady state incompressible flows using explicit schemes with an optimal local preconditioning

María Jesús Samper — Thu, 14 Feb 2019 12:02:13 +0100

Solving large systems of equations from CFD problems by the explicit pseudo-temporal scheme requires a very low amount of memory and is highly parallelizable, but the CPU time largely depends on the conditioning of the system. For advective systems it is shown that the rate of convergence depends on a condition number defined as the ratio of the maximum and the minimum group velocities of the continuum system. If the objective is to reach the steady state, the temporal term can be modified in order to reduce this condition number. Another possibility consists in the addition of a local preconditioning mass matrix. In this paper an optimal preconditioning for incompressible flow is presented, also applicable to compressible ones with locally incompressible zones, like stagnation points, in contrast with the artificial compressibility method. The preconditioned system has a rate of convergence independent from Mach number. Moreover, the discrete solution is highly improved, eliminating spurious oscillations frequently encountered in incompressible flows.

A Petrov-Galerkin technique for the solution of transonic and supersonic flows

María Jesús Samper — Thu, 14 Feb 2019 11:57:02 +0100

This paper is both the description of a streamline-upwind/Petrov-Galerkin (SUPG) formulation and the documentation of the development of a code for the finite element solution of transonic and supersonic flows. 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. 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. The theoretical background of the SUPG formulation is described briefly. How the foregoing formulation was used in the finite element code and which are the appropriate boundary conditions to be used are also described. Finally some results obtained with this code are discussed.

Multigrid methods and adaptive refinement techniques in elliptic problems by finite element methods

María Jesús Samper — Thu, 14 Feb 2019 11:42:34 +0100

Multigrid and adaptive refinement techniques are powerful tools in the resolution of problems arising from computational mechanics. In structured grids the number of numerical operations needed in the resolution via the multigrid method is of order N, the number of degrees of freedom, regardless the dimensionality of the problem. In this work a multigrid technique, which works on unstructured meshes, is described. These meshes are obtained from a user defined tesselation through bisection refinement upon any element. Original techniques for nodes numbering, irregular nodes detection and nodes classification are developed in view of multigrid method implementation. The error indicator used in the refinement process is based on truncation error estimates. The refinement strategy is oriented toward error reduction at constant computational effort. Finally several numerical examples are presented.

An efficient tangent scheme for solving phase-change problems

María Jesús Samper — Thu, 14 Feb 2019 11:36:17 +0100

Using weak formulations and finite elements to solve heat-conduction problems with phase change finally leads to the solution, at each time step, of a nonlinear system of equations in the nodal temperatures. The Newton-Raphson scheme is an effective procedure to cope with this type of problems; however, the choice of a good approximation to the tangent matrix is critical when the latent heat is comparatively large. In this work we derive an exact expression for the tangent matrix and analyze the behavior of its terms for different values of the physical parameters of the system. We demonstrate that this method has good convergence properties. In fact, the rate of convergence is quadratic when the trial approximation is sufficiently close to the solution. Finally, several numerical examples are given.

A reduction method for nonlinear structural dynamic analysis

María Jesús Samper — Thu, 14 Feb 2019 10:41:30 +0100

A computational algorithm for predicting the nonlinear dynamic response of a structure is presented. The nonlinear system of ordinary differential equations resulting from the finite element discretization is highly reduced by means of a Rayleigh-Ritz analysis. The basis vectors are chosen to be the current tangent eigenmodes together with some modal derivatives that indicate the way in which the spectrum is changing. Only a few basis updatings are required during the whole time integration.

The truncation error introduced at every change of basis is pointed out as the cause for a divergence-type behaviour, and some means for eliminating it are discussed.

Results for examples involving large displacements are shown and compared to the results obtained by integrating the complete system of equations.

Pre- and post-degradation analysis of composite materials with different moduli in tension and compression

María Jesús Samper — Wed, 13 Feb 2019 14:17:59 +0100

An isoparametric finite element tor the analysis of multi-layer composite materials is presented. Several linear and nonlinear stress-strain relations are discussed. Special attention is given to the composite materials with different moduli in tension and compression, for which a new mathematical model is presented and tested.

Different failure criteria for the matrix degradation are incorporated in the element and several post-degradation behaviors are also considered.

Finally we discuss the role of the Newton-Raphson method in composite materials, especially in the presence of geometrical nonlinearities.

On the use of deep, shallow or flat shell finite elements for the analysis of thin shell structures

María Jesús Samper — Wed, 13 Feb 2019 12:43:41 +0100

This paper is confined to the study of thin shells. The aim is to summarize the different theories used and to examine the assumptions upon which each of them is based. The intention is to show when it is more suitable to use a particular approximation and to indicate the errors it introduces. Beginning with the general deep shell theory, some simplifications are introduced to obtain the shallow shell theories. The special implications of this theory for the finite element method are also examined. Finally the particular case of flat elements is discussed.

Triangular element for two-dimensional elasticity with z stress and z strain constant and different from zero.

Francisco Zarate — Fri, 08 Feb 2019 15:35:03 +0100

This paper describes how to obtain a two-dimensional element of three nodes from a prismatic solid element of six nodes, assuming that the normal voltage to the triangular faces is constant and different from zero.

A numerical example is also presented where the results obtained are compared with the developed element and with three-dimensional elements, showing the good behavior of the developed element.

HPC-SHEAKS brief description

Clara García — Mon, 04 Feb 2019 16:33:11 +0100

Compass IS is a consulting services company specialized in engineering design, as well as in development of software for engineering analysis and information management in technology. Civil and industrialengineering, naval architecture and ICT areas are the main focus of Compass IS activities.

The HPC-Sheaks experiment aimed to increase the efficiency of the design, engineering and building processes of a marine structure, by offering to the market added-value tools that, thanks to high performance computing, can be used further down from the final design phase, and allowing its integration in the design cycle to develop more competitive designs.

Presentation of HPC-SHEAKS in the Digital Innovation Hub Annual Event (Warsaw)

Clara García — Mon, 04 Feb 2019 16:33:09 +0100

Presentation made during the DIH2018 Annual Event that took place in Warsaw, from November 27 to 28, 2018. During the DIH2018 Annual Event, Compass IS has been honored the I4MS Disruptors Award 2018, by the European Commissioner Mariya Gabriel and Jadwiga Emilewicz, Minister of Entrepreneurship and Technology of Poland.

During the event, Compass had the opportunity to show a stand to present its technological capabilities and the solution of the experiment.

HPC-SHEAKS in the Fortissimo Success Story Booklet (4th edition)

Clara García — Mon, 04 Feb 2019 16:33:08 +0100

Seakeeping is the study of a ship or marine structure that is subject to the action of waves. WAVEC is a private non-profit association active in applied research and consulting. VICUSDT operates in the shipbuilding and shipping industries, providing hydrodynamic engineering services. It also provides hydrodynamic analysis capabilities to the offshore and marine energy sector, carrying out advanced simulations of structures for the oil and gas industry. COMPASSIS is an SME ISV which provides simulation software for a variety of different engineering fields including multiphysics simulations and structural and seakeeping analysis. In this experiment COMPASSIS will enable and evaluate simulations that require intense computational and data storage resources.

Presentation of HPC-SHEAKS Experiment in the kick-off meeting

Clara García — Mon, 04 Feb 2019 16:33:06 +0100

Presentation of the "HPC-SHEAKS" experiment during the kick-off meeting which took place on July 2015, in the frame of the Fortissimo Forum in Amsterdam. The Forum was a platform for Independent Software Vendors (ISVs), Service Providers, Small & Medium Enterprises (SMEs) and technical experts around the theme of HPC applications in the cloud.

SeaFEM features and system requirements

Clara García — Mon, 04 Feb 2019 16:33:04 +0100

SeaFEM is a suite of tools for the computational analysis of the effect of waves, wind and currents on naval and offshore structures, as well as for maneuvering studies. SeaFEM applications include ships, spar platforms, FPSO systems, semi- submersibles, TLPs, marine wind turbines and ocean energy harnessing devices.

SeaFEM offers a state of the art solver developed for the most realistic seakeeping simulations of 3D multi-body radiation and diffraction problems, by solving potential flow equations in the time domain, using the finite element method on unstructured meshes. SeaFEM features the latest technology for solving first and second order diffraction-radiation equations with real sea spectra.

SeaFEM has been developed in collaboration with the International Center for Numerical Methods in Engineering, and is completely integrated in the comprehensive simulation environment, Tdyn, developed by Compass.

HPC-SHEAKS Success Story

Clara García — Mon, 04 Feb 2019 16:33:02 +0100

The ultimate goal of the "HPC-enabled system for enhanced seakeeping and station-keeping design" (HPC-SHEAKS) experiment was the efficient and easy-to-use integration of available HPC infrastructures with the most advanced seakeeping software. As a result of the experiment, an effective interface between the end-user and the HPC resources was implemented. The relevant seakeeping software packages were ported to the HPC infrastructure and integrated into an overall simulation package. This solution enables the simulations to be run from a familiar desktop system whilst using the full capabilities of the HPC system.

Decision support system for cardiovascular problems

María Jesús Samper — Fri, 01 Feb 2019 15:05:46 +0100

The two main lines of medical research in this project are vascular anatomy (large vessels around
the heart, coronaries and peripheral arteries) and heart chambers. Geometric models will be
constructed to aid clinical diagnosis or multiphysical modelling and simulation. Two levels of
complexity will be considered. For heart modelling, the first level will concentrate on models of the
left and right ventricular cavities for robust and efficient extraction of simple clinical indexes of
geometry, volume, mass, and wall kinetics. The second level will aim at more complex, fourchambered
models, which will be important in developing comprehensive solid and fluid models to
assist the design of medical devices.

A model of material failure for reinforced concrete via continuum strong discontinuity approach and mixing theory

María Jesús Samper — Fri, 01 Feb 2019 14:46:53 +0100

In this work a two-dimensional formulation describing the fracture process in reinforced
concrete is developed, implemented and validated. The cracks in the material are captured
by means of continuum strong discontinuity approach (CSDA) (Oliver 1996) and the constitutive
model of composite material is defined through mixing theory (Truesdell & Toupin
1960).

The composite material consists of one or two groups of long fibers or steel bars embedded
within a concrete matrix. Likewise, each component is characterized by a constitutive
model. The concrete is described by a damage model with degradation in tension and compression
(Oliver, Cervera et al. 1990). A uniaxial plasticity model (Simó & Hughes 1998) is
used for the steel. Also, phenomena as bond-slip and dowel action (Park & Paulay 1975)
are included and represented by additional models of interaction between concrete and steel.
The initiation and propagation of cracks are understood as a strain localization process
described by means of CSDA. A bifurcation analysis of composite material is proposed to
establish the bifurcation time and direction of the crack.

The model has been implemented in a two-dimensional analysis program using the finite
element method (FEM), where it is assumed material non-linearity and infinitesimal strains.
An implicit-explicit integration scheme for the constitutive equation (Oliver, Huespe et al.
2004; Oliver, Huespe et al. 2006) ensures a positive defined stiffness matrix of the problem
and increases the robustness and stability of the solution. On the other hand, a strategy to
tracking discontinuity paths (Samaniego 2002; Oliver & Huespe 2004), allows that the discontinuity
paths correspond among the elements.

According to the proposed formulation, on each point of solid, the strain and stress fields
of the reinforced concrete are described as a composite material. This has the following
advantages: first, the model facilitates the implementation on the finite element method,
since many ingredients of standard numerical process remain, and secondly, the macroscopic scale of analysis avoids the discretization of each component material and the interaction
effects, and consequently the computational cost is reduced.

The model can reproduce two different stages of cracking in the reinforced concrete.
Initially, the steel capacity and the adherence in the interface produce a stable stage of distributed
cracking, where appear many cracks with constant spacing and opening. Afterward,
a localization cracking stage is characterized by few cracks while the structural response decreases.
Reinforced concrete members subjected to tension, bending and shear are simulated.
The numerical results, mainly the structural response and the crack pattern, are compared
with experimental test (Leonhardt 1965; Collins, Vecchio et al. 1985; Ouyang & Shah 1994;
Ruiz, Elices et al. 1998). The correlation between numerical results using the proposed
formulation and actual results is quantitative and qualitatively satisfactory.

Contribuciones a la simulación numérica del fallo material en medios tridimensionales mediante la metodología de discontinuidades fuertes de continuo

María Jesús Samper — Fri, 01 Feb 2019 14:21:46 +0100

La metodología de discontinuidades fuertes de continuo [50]-[51] es una aproximación
numérica al fenómeno de la localización de deformaciones por ablandamiento.
Al contrario de las aproximaciones discretas, utiliza un formato continuo
tensión-deformación para describir todo el proceso de agotamiento del material.
Gracias a una regularización (reinterpretación) de la cinemática del problema y del
módulo de ablandamiento se garantiza que la disipación del modelo venga dada por
la densidad superficial de energía de fractura [52]. Adicionalmente, la utilización de
un algoritmo tipo térmico de captura y gestión de las superficies de localización de
deformaciones permite abordar el análisis de problemas con multifisuración [57].

La mejora en la robustez del análisis numérico se ha conseguido adoptando la
formulación simétrica cinemáticamente consistente y formulando un nuevo esquema
de integración, denominado IMPL-EX, que garantiza la definición positiva de los
operadores algorítmicos que intervienen en el problema.

La confiabilidad en el resultado numérico se asegura mediante un algoritmo
de control del error cometido y mediante un nuevo esquema de limitación de la
longitud de arco. Estos dos algoritmos han sido desarrollados específicamente para
el esquema de integración IMPL-EX.

La formulación así definida ha sido aplicada en el estudio de dos fenómenos
propios de la mecánica de la fractura: el estudio de la influencia del tamaño de una
estructura en su resistencia nominal (efecto tamaño) y el estudio/medición de la
longitud de procesamiento de fractura.

Por último se presentan una serie de ensayos numéricos del fallo material en
estructuras tridimensionales. Estos ensayos se dividen en tres grupos: ensayos donde
el modo de fallo predominante es en modo I, ensayos donde el modo de fallo
predominante es de deslizamiento (análisis de taludes) y ensayos donde el modo de
fallo moviliza mecanismos resistentes tridimensionales (análisis del efecto arco en
presas con simple y doble curvatura).

A finite element method for solving the incompressible Navier-Stokes equations at low and high Reynolds numbers using finite calculus. Application to fluid-structure interaction

María Jesús Samper — Fri, 01 Feb 2019 14:04:16 +0100

The main objective of this monograph is to develop a stabilized finite element
method (FEM) for solving the incompressible Navier-Stokes equations. Using Finite Calculus (FIC),
which is a methodology developed by E. On˜ate and co-workers at CIMNE (International Center for
Numerical Methods in Engineering), flows with a wide range of Reynolds numbers can be modeled. The
secondary objective is to test the applicability of the FIC/FEM model to fluid-structure
interaction (FSI) emphasizing aero-elasticity. The implementation of the model is carried out
within KRATOS, a finite element code for solving multi-physics problems developed at
CIMNE.

Formulaciones tangentes y secantes en análisis no lineal de vigas Cosserat

María Jesús Samper — Fri, 01 Feb 2019 13:59:03 +0100

En este trabajo se han dedicado cinco capítulos a la exposición y discretización de un modelo clásico no
lineal de viga Cosserat por medio del método de elementos finitos, utilizando las
formulaciones Tangente y Secante.

Análisis estructural de edificios históricos mediante modelos localizados de fisuración

María Jesús Samper — Fri, 01 Feb 2019 13:42:44 +0100

En este trabajo se plantea un objetivo principal: formular un modelo numérico
capaz de estudiar el comportamiento estructural de edificios históricos de obra de fábrica.
Para ello se estudian en primer lugar las características de este material, así como las particularidades que presentan las construcciones antiguas. Como referencia se toma la Catedral de
Mallorca, de la que se dispone de información proveniente de una campaña de monitorización llevada
a cabo recientemente, así como de diversos análisis estructurales elaborados por diferentes
autores.

Un modelo del fallo material en el hormigón armado, mediante la metodologia de discontinuidades fuertes de continuo y la teoría de mezclas

María Jesús Samper — Fri, 01 Feb 2019 13:32:57 +0100

Esta monografía presenta una reformulación de la metodología de discontinuidades fuertes de continuo para la simulación numérica del fallo material de estructuras.
Los objetivos buscados han sido mejorar la robustez de este tipo de análisis numérico y proporcionar una serie de herramientas que garanticen la confiabilidad de los resultados obtenidos.
La metodología de discontinuidades fuertes de continuo [50]-[51] es una aproximación numérica al fenómeno de la localización de deformaciones por ablandamiento.
Al contrario de las aproximaciones discretas, utiliza un formato continuo tensión-deformación para describir todo el proceso de agotamiento del material.
Gracias a una regularización (reinterpretación) de la cinemática del problema y del módulo de ablandamiento se garantiza que la disipación del modelo venga dada por la densidad superficial de energía de fractura [52]. Adicionalmente, la utilización de un algoritmo tipo térmico de captura y gestión de las superficies de localización de deformaciones permite abordar el análisis de problemas con multifisuración [57].
La mejora en la robustez del análisis numérico se ha conseguido adoptando la formulación simétrica cinemáticamente consistente y formulando un nuevo esquema de integración, denominado IMPL-EX, que garantiza la definición positiva de los operadores algorítmicos que intervienen en el problema.
La confiabilidad en el resultado numérico se asegura mediante un algoritmo de control del error cometido y mediante un nuevo esquema de limitación de la longitud de arco. Estos dos algoritmos han sido desarrollados específicamente para el esquema de integraciónn IMPL-EX. La formulación así definida ha sido aplicada en el estudio de dos fenómenos propios de la mecánica de la fractura: el estudio de la influencia del tamaño de una
estructura en su resistencia nominal (efecto tamaño) y el estudio/medición de la longitud de procesamiento de fractura.

Por último se presentan una serie de ensayos numéricos del fallo material en estructuras tridimensionales. Estos ensayos se dividen en tres grupos: ensayos donde el modo de fallo predominante es en modo I, ensayos donde el modo de fallo predominante es de deslizamiento (análisis de taludes) y ensayos donde el modo de fallo moviliza mecanismos resistentes tridimensionales (análisis del efecto arco en presas con simple y doble curvatura).

Modelización numérica de la no-linealidad constitutiva de laminados compuestos

María Jesús Samper — Fri, 01 Feb 2019 13:24:06 +0100

La respuesta mecánica de los materiales compuestos depende del comportamiento de los
materiales componentes y de su micro‐estructura.

Para mejorar y optimizar el diseño de piezas estructurales de materiales compuestos, la industria
requiere herramientas informáticas que reproduzcan de manera apropiada el comportamiento de estos
materiales incluso en el rango no lineal. Por tanto, es muy importante la investigación y
desarrollo de modelos numéricos para compuestos que tengan en cuenta la morfología o estructura
del material de forma adecuada y eficiente, además de ser necesario contar con un entorno gráfico
específico para este tipo de problemas que facilite la entrada de datos al código de cálculo y
posteriormente permita visualizar los resultados deseados.

El objetivo principal del presente trabajo es el desarrollo, formulación e implementación
computacional, de un modelo numérico para el tratamiento de la no linealidad constitutiva de
laminados reforzados con fibras, en el contexto de la mecánica de los medios continuos. Esta
formulación plantea combinar (o componer) los comportamientos de materiales simples (homogéneos)
con el objetivo de obtener la respuesta mecánica del material compuesto (heterogéneo). Para ello,
propone una gestión adecuada de los modelos constitutivos (homogéneos), actualmente disponibles, de
cada uno de los materiales componentes; aprovechándose de esta manera el gran desarrollo conseguido
en el campo de la modelización constitutiva de materiales simples, y permitiendo la transferencia
de toda esta tecnología al campo de los materiales compuestos. Teniendo en cuenta la estructura
interna del material compuesto, se desarrolla una estrategia de desacoplamiento e interacción de
estas fases; de una manera novedosa. Esta metodología, denominada “composición de comportamientos”,
permite tener en cuenta muchos fenómenos locales de degradación que tienen lugar en las fases
componentes, tales como plasticidad, daño, fatiga, envejecimiento, fluencia, etc., de una manera
acoplada, lo cual también es novedoso en este tipo de enfoque. Las aplicaciones del presente
trabajo se centran en los tres primeros fenómenos mencionados, dado que su combinación permite
simular el comportamiento de una extensa variedad de materiales compuestos empleados en la
industria.

Se desarrolla el algoritmo de resolución del modelo propuesto que permite conseguir convergencia
cuadrática, tanto local como global, de los problemas no‐ lineales al ser implementado como modelo
constitutivo en un código de elementos finitos, proveyendo rapidez y precisión al análisis de
estructuras de
materiales compuestos en muchas aplicaciones industriales.

La simulación del laminado se logra mediante la combinación del modelo
propuesto con una teoría de laminado aplicada en cada punto de integración. Se
emplean elementos 3D sólidos isoparamétricos para discretizar estructuras
laminadas gruesas; mientras que para estudiar estructuras laminares de pequeño
espesor, se desarrolla un elemento de lámina laminado en capas de material
compuesto, sobre la base de un elemento de lámina más simple (Discrete Kirchoff
Triangle).

La validación del modelo muestra el cumplimiento de las ecuaciones de cierre
(equilibrio de tensiones y compatibilidad de deformaciones entre componentes),
tanto en la dirección de las fibras (comportamiento en paralelo) como en
direcciones ortogonales (comportamiento en serie). Además, se ilustran diversas
envolventes de fallo para lámina/laminados generadas con el modelo propuesto y
se las compara con otros criterios de fallo global para compuestos y resultados
experimentales disponibles en la literatura.

La aplicabilidad del modelo se demuestra mediante simulaciones numéricas
realizadas sobre geometrías de mayor complejidad para modelar la respuesta
mecánica de piezas industriales. Los resultados numéricos contrastados con los
experimentales indican la capacidad del modelo propuesto para describir el
comportamiento no‐lineal de laminados reforzados con fibras en diferentes
orientaciones sometidos a estados de carga multiaxial tanto estática como cíclica.

Implementación de algoritmos numéricos en una tarjeta gráfica

María Jesús Samper — Fri, 01 Feb 2019 13:19:44 +0100

Se definirán los objetivos de la monografía que consistirá en valorar las herramientas existentes
para usar estas tarjetas como coprocesador y desarrollar una librería para usarlas. Se establecerá un
plan de desarrollo y el entorno de trabajo.

Se contrastarán las herramientas existentes para programar estas tarjetas gráficas desde un punto de
vista de un profano en el ámbito de gráficos, su facilidad de uso y se definirán las líneas maestras
de la librería y la implementaremos.

Finalmente se analizán los resultados obtenidos y sev enumerarán futuras líneas de trabajo.

Pulse fracture simulation in shale rock reservoirs. DEM and FEM-DEM approaches

María Jesús Samper — Fri, 01 Feb 2019 13:00:02 +0100

In this paper we analyze the capabilities of two numerical techniques based on DEM and FEM-DEM approaches for the simulation of fracture in shale rock caused by a pulse of pressure. We have studied the evolution of fracture in several fracture scenarios related to the initial stress state in the soil or the pressure pulse peak. Fracture length and type of failure have been taken as reference for validating the models. The results obtained show a good approximation to FEM results from the literature.

On the application of Particle Finite Element Method (PFEM) to problems in civil engineering

María Jesús Samper — Thu, 31 Jan 2019 16:19:11 +0100

Current chapter tries to give an overview of theoretic background necessary to deal with fluid dynamic problems with Finite Element Method (PFEM) approach. Starting form a brief summary of the principle steps of the development of the theory, we analyze the differences between the classical world of fluids, finding out finally the principle equations that control these problems.

Modelación del flujo en lámina libre sobre cauces naturales. Análisis integrado en una y dos dimensiones

María Jesús Samper — Thu, 31 Jan 2019 16:05:39 +0100

En esta monografía se presenta un trabajo de desarrollo de herramientas de modelación numérica realizado dentro del grupo de investigación FLUMEN, en la E.T.S. de Ingenieros de Caminos, Canales y Puertos de Barcelona, destacando la integración de esquemas numéricos en una y dos dimensiones. El objetivo principal es la puesta a punto de una herramienta para la modelación matemática del flujo de agua en lámina libre, en régimen variable, con geometrías irregulares como son los cauces naturales (programa CARPA).

Stabilized pressure segregation methods and their application to fluid-stucture interaction problems

María Jesús Samper — Thu, 31 Jan 2019 15:48:27 +0100

In this work we design and analyze pressure segregation methods in order to approximate
the Navier-Stokes equations. Pressure correction methods are widely used because they
allow the decoupling of velocity and pressure computation, decreasing the computational
cost. We have analyzed some of these schemes, obtaining inherent pressure stability.
However, for second order accurate methods (in time) this inherent stability is too weak,
requiring the introduction of a stabilized finite element methodology for the space dis-
cretization. Moreover, we have carried out a complete convergence analysis of a first order
pressure segregation method.

We have used a stabilization technique justified from a multiscale approach that allows
the use of equal velocity-pressure interpolation spaces and convection dominated °ows.
A new kind of methods has been motivated from an alternative version of the mono-
lithic fluid solver where the continuity equation is replaced by a discrete pressure Poisson
equation. These methods belong to the family of velocity correction schemes, where it
is the velocity instead of the pressure the extrapolated unknown. Some stability bounds
have been proved, revealing that their inherent pressure stability is too weak. Further,
predictor corrector schemes easily arise from the new monolithic system. Numerical ex-
perimentation shows the good behavior of these methods.

We have introduced the ALE framework in order for the fluid governing equations to
be formulated on moving domains. Taking as the model equation the convection-di®usion
equation, we have analyzed the blend of the ALE framework and a stabilized finite element
method.

We suggest a coupling procedure for the fluid-structure problem taking benefit from
the ingredients previously introduced: pressure segregation methods, a stabilized finite
element formulation and the ALE framework. The final algorithm, using one loop, tends
to the monolithic (fluid-structure) system.

This method has been applied to the simulation of bridge aerodynamics, obtaining a
good convergence behavior.

We end with the simulation of wind turbines. The fact that we have a rotary body
surrounded by the fluid (air) has motivated the introduction of a remeshing strategy. We
consider a selective remeshing procedure that only affects a tiny portion of the domain,
with little impact on the overall CPU time.

Incompressible lagrangian fluid flow with thermal coupling

María Jesús Samper — Thu, 31 Jan 2019 15:40:39 +0100

A method is presented for the solution of an incompressible viscous fluid flow
with heat transfer and solidification using a fully Lagrangian description of the
motion. The originality of this method consists in assembling various concepts
and techniques which appear naturally due to the Lagrangian formulation.
First of all, the Navier-Stokes equations of motion coupled with the Boussinesq
approximation must be reformulated in the Lagrangian framework, whereas
they have been mostly derived in an Eulerian context. Secondly, the Lagrangian
formulation implies to follow the material particles during their motion, which
means to convect the mesh in the case of the Finite Element Method (FEM), the
spatial discretisation method chosen in this work. This provokes various difficulties
for the mesh generation, mainly in three dimensions, whereas it eliminates
the classical numerical difficulty to deal with the convective term, as much in
the Navier-Stokes equations as in the energy equation. Even without the discretization
of the convective term, an efficient iterative solver, which constitutes
the only viable alternative for three dimensional problems, must be designed for
the class of Generalized Stokes Problems (GSP), which could be able to behave
well independently of the mesh Reynolds number, as it can vary greatly for
coupled fluid-thermal analysis.
Moreover, it offers a natural framework to treat free-surface problems like
wave breaking and rough fluid-structure contact. On one hand, the convection
of the mesh during one time step after the resolution of the non-linear system
provides explicitly the locus of the domain to be considered. On the other hand,
fluid-to-fluid and fluid-to-wall contact, as well as the update of the domain due
to the remeshing, must be accurately and efficiently performed. Finally, the
solidification of the fluid coupled with its motion through a variable viscosity is
considered

An efficient overall algorithm must be designed to bring the method effective,
particularly in a three dimensional context, which is the ambition of this
monograph. Various numerical examples are included to validate and highlight
the potential of the method.

A three dimensional FEM-DEM technique for predicting the evolution of fracture in geomaterials and concrete

María Jesús Samper — Thu, 31 Jan 2019 13:02:05 +0100

This paper extends to three dimensions (3D) the computational technique developed by the authors in 2D for predicting the onset and evolution of fracture in a finite element mesh in a simple manner based on combining the finite element method (FEM) and the discrete element method (DEM) approach Zarate2D. Once a crack is detected at an element edge, discrete elements are generated at the adjacent element vertexes and a simple DEM mechanism is considered in order to follow the evolution of the crack. The combination of the DEM with simple 4-noded linear tetrahedron elements correctly captures the onset of fracture and its evolution, as shown in several 3D examples of application.

An accurate nonlocal bonded discrete element method for non linear analysis of solids. Application to concrete fracture tests (preprint)

María Jesús Samper — Thu, 31 Jan 2019 12:56:56 +0100

We present a numerical procedure for elastic and non linear analysis (including fracture situations) of solid materials and structures using the Discrete Element Method (DEM). It can be applied to strongly cohesive frictional materials such as concrete and rocks. The method consists on defining the non-local constitutive equations at the contact interfaces between discrete particles using the information provided by the stress tensor over the neighbour particles. The method can be used with different yield surfaces and in the paper it is applied to the analysis of fracture of concrete samples. Good comparison with experimental results is obtained.

A coupled fluid FEM-DEM technique for predicting blasting operations in tunnels

María Jesús Samper — Thu, 31 Jan 2019 12:56:03 +0100

We present recent developments in the coupling of the finite element method (FEM) and the discrete element method (DEM) for analysis of rock blasting operations in tunnels. The coupled FEM-DEM technique has proven to be an efficient procedure for predicting the multi-fracture of rock induced by the loads generated in blasting situations. The coupled FEM-DEM procedure is applied in the tunnel construction, as well as to gas pressure blasting pyrotechnics situations to break rock for excavation of the tunnel front. In the latter case the effect of gas explosion is modelled by solving with the FEM the equations of gas dynamics in the analysis domain. The effect of the gas forces in the underlying rock mass is modelled via an embedded fluid-structure interaction method. The efficiency of the coupled FEM-DEM technique is demonstrated in several examples of fracture tests and rock blasting problems related to tunnel engineering. The examples presented show that the combination of the DEM with simple 3-noded linear triangular elements (for 2D problems) correctly captures the onset of fractures and their evolution accounting for the penetration of the gas in the failure domain [[#cite-1|[1,2]]].

Decisin support system for risk assessment and management of floods

María Jesús Samper — Thu, 31 Jan 2019 12:09:18 +0100

The objective of the RAMFLOOD project is to develop and validate a new decision support system (DSS) for the risk assessment and management of emergency scenarios due to severe floods. The DSS combines environmental and geo-physical data from earth observation, with advanced computer simulation and graphical visualisation methods and artificial intelligence techniques, for generating knowledge contributing to the risk prevention of floods and the design of effective response actions maximising the safety of infrastructures and human life.

Diseño de tanques cilíndricos de ferrocemento para construir en comunidades rurales de países en desarrollo

María Jesús Samper — Thu, 31 Jan 2019 11:07:10 +0100

En este documento se presenta un estudio sobre el diseño y la construcción de depósitos de
ferrocemento para países en vías de desarrollo. Se le da un especial énfasis al hecho de que los depósitos
que se plantean están pensados para países en vías de desarrollo, porque la tecnología empleada así como
los materiales tendrá una calidad notablemente inferior a la que se podría esperar de países desarrollados.
Asimismo, la participación de los usuarios (a través de la supervisión de un técnico) en la construcción
del depósito hace que se tienda a simplificar lo máximo posible el montaje de la estructura así como la
cantidad de cálculos necesarios.
En primer lugar se introduce el concepto de ferrocemento, se analizan sus propiedades, se
describen sus componentes (tipo de refuerzo, proporciones de mezcla,…), se detallan algunos elementos
empleados para su ejecución (encofrado, herramientas, equipo necesario,…) y se hace un breve repaso, a
continuación, a las aplicaciones que hasta la fecha se le han dado al ferrocemento como material de
construcción. También se incluyen los resultados correspondientes a unos ensayos realizados en un
estudio sobre el diseño de tanques para países en vías de desarrollo (llevados a cabo en otra universidad)
y obtenidos a través de Internet.
A continuación se plantea una formulación específica para el dimensionamiento de la pared del
depósito y se acompaña con algunos ejemplos de aplicación práctica en base a la formulación planteada
que recogen capacidades bien diferenciadas: 10, 50 y 150m3. De este modo se recogen los diseños tipo
para un depósito pequeño, mediano y grande (considerando el ámbito en el que nos encontramos y el
rango en el que se mueven este tipo de estructuras). En éstos se resuelve el diseño de la solera a través de
un exhaustivo análisis por Elementos Finitos de diversos modelos de solera, considerando como forma
básica el casquete esférico y variando a partir de aquí la curvatura de éste así como la unión con la base
de la pared. Al final de cada ejemplo propuesto se muestra un croquis detallado de la estructura, el
refuerzo y las cotas correspondientes.
Se incluye también un capítulo con ejemplos reales sobre depósitos de ferrocemento
(concretamente se comentan la construcción de un depósito de 10m3, uno de 150m3, un depósito
enterrado y el montaje de una cubierta para un tanque de ferrocemento) fruto del trabajo de investigación
bibliográfica llevado a cabo a lo largo del estudio y que se ha creído conveniente incluir por su alto
interés técnico. Los ejemplos además se acompañan de los detalles y mediciones de las obras.
En una segunda parte, se generalizan los resultados para un rango de depósitos acotado entre un
cierto valor de alturas y radios del depósito. El rango adoptado es bastante amplio, variando el radio desde
50cm hasta 10m, mientras que las alturas consideradas van de 1m hasta 3m. Se abarca, de esta manera
cualquier posibilidad de dimensionamiento, por muy remota que sea. El criterio adoptado a la hora de
acotar el rango de los resultados ha sido el de proporcionar alturas razonables para facilitar la
construcción y diámetros no mayores de los que parece ser que este material llega a resultar más viable
que otro como por ejemplo el hormigón (aunque este tema es discutible). Estos resultados se han
resumido a modo de tablas organizadas según las variables estudiadas sean variables de
dimensionamiento (capacidad, espesores, cuantías de armadura, flecha de solera) o de cuantificación de
materiales (peso de acero, volumen de arena, peso de cemento), dando lugar en total a 12 tablas, cuyo
método de empleo se describe en el propio capítulo. Además para tener una idea comparativa de los
resultados ofrecidos por las tablas se analizan diversos ejemplos comparando las cantidades propuestos
por diversos autores y los obtenidos a partir del empleo de las tablas. Cabe destacar que estas tablas no
pretenden ser un método estricto, sino más bien orientativo (en fase experimental), en el que se
recomienda al menos la presencia de un técnico para valorar los resultados y apreciar los detalles
necesarios que lógicamente no se incluyen en las tablas como herramientas, elementos de atado,
encofrado, personal necesario, etc.

An overlay J2 viscoelastic viscoplastic viscodamage model for stable shear localization problems

María Jesús Samper — Wed, 30 Jan 2019 13:23:34 +0100

This work formulates a relatively simple isotropic local Overlay J2-Viscoelastic-Viscoplastic-Viscodamage constitutive model (O-J2-VVV) which encompasses the merits of both the plastic and continuum damage formulations.

The plastic component of the model account for inelastic permanent
strains, while the damage component account for loss of stiffness. The plas- tic and damage
softening moduli are regularized according to the material mode II fracture energy and the element
size. The Orthogonal SubGrid Stabilization Method (OSGS ) is used to ensure existance and uniquess
of the solution for strain shear strain localization processes, attaining global and local
stability of the corresponding discrete finite element formulation. Consistent residual viscosity
is used to enhance robustness and convergence of the formulation. Numerical examples show that the
formulation derived is versatily, fully stable and remarkably robust, The solutions obtained are
completely mesh independent, unlike those obtained with the ill-posed
standard approaches.

Viscoelasticity and rate-dependent continuum damage

María Jesús Samper — Wed, 30 Jan 2019 12:59:44 +0100

A mixed Finite Element formulation for incompressibility using linear displacement and pressure interpolations

María Jesús Samper — Wed, 30 Jan 2019 12:35:31 +0100

In this work shall be presented a stabilized finite element method to deal with incompressibility
in solid mechanics. A mixed formulation involving pressure and displacement fields
is used and a continuous linear interpolation is considered for both fields. To overcome
the Ladyzhenskaya-Babuska-Brezzi condition, a stabilization technique based on the orthogonal
sub-grid scale method is introduced. The main advantage of the method is the
possibility of using linear triangular finite elements, which are easy to generate for real
industrial applications. Results are compared with several improved formulations, as the
enhanced assumed strain method (EAS) and the Q1P0-formulation, in nearly incompressible
problems and in the context of linear elasticity and J2-plasticity.

Simulation of temperature and stress during and after RCC dams construction

María Jesús Samper — Wed, 30 Jan 2019 10:55:03 +0100

The aim of this monograph is to verify the prediction of temperature and stress evolution of the finite element program COMET including the constitutive model using 1-D model. It includes the analysis of the Rialb RCC dam during and after its construction.

Simulación numérica del comportamiento mecánico de los materiales compuestos

María Jesús Samper — Tue, 29 Jan 2019 16:33:41 +0100

El presente trabajo resume la tarea de investigación llevada a cabo por el autor en el área
de los materiales compuestos durante los últimos doce años (desde 1990). El mismo
refleja la actividad realizada personalmente, junto a otros investigadores y también a través
de los estudiantes de fin de carrera y doctorado que he dirigido en esta línea de trabajo.

Los temas que aquí se incluyen están orientados fundamentalmente a la modelización
constitutiva y evaluación de estructuras construidas en materiales compuestos. Los mismos
han sido y muchos de ellos siguen siendo originales, por lo que no representan una mera
continuidad de las corrientes investigadoras que estaban en desarrollo en cada momento.

Mecánica de daño continuo

María Jesús Samper — Tue, 29 Jan 2019 16:24:41 +0100

En esta monografía se intenta presentar un marco teórico general que permita
analizar la gran cantidad de modelos de daño continuo existentes, no sólo desde el punto
de vista de su formulación sino también teniendo en cuenta su capacidad para
reproducir las evidencias experimentales correspondientes a un amplio rango de
materiales y su implementación numérica en códigos de elementos finitos. La
monografía se restringe al tratamiento del daño en pequeñas deformaciones y dentro del
marco de la Mecánica de Medios Continuos.

Topics on failure mechanics

María Jesús Samper — Tue, 29 Jan 2019 15:57:08 +0100

Desarrollo sostenible del cemento y del hormigón

María Jesús Samper — Tue, 29 Jan 2019 15:48:16 +0100

Esta monografía contiene algunas de las comunicaciones presentadas al Seminario Internacional CANMET/ACI/UPC sobre Desarrollo Sostenible del Cemento y del Hormigón celebrado los días 4 y 5 de noviembre de 2002 en Barcelona, España.

Dinámica no-lineal

María Jesús Samper — Tue, 29 Jan 2019 15:34:09 +0100

Esta monografía trata la “dinámica no-lineal” de los sistemas estructurales. Existen diversos
enfoques para esta materia y por ello intento que este trabajo aporte un punto de vista más
al estudio dinámico no-lineal.
La motivación para escribir estas páginas se basa en la necesidad de contar con un material
de estudio para la asignatura de “Dinámica no-lineal” que dicto en doctorado del
departamento de “Resistencia de Materiales y Estructuras en la Ingeniería” de la
Universidad Politécnica de Cataluña.
Espero que estas notas ayuden a la mejor comprensión de la dinámica e incentiven a lector
a una mayor profundización.

On the strong discontinuity approach in finite deformation settings. Theoretical aspects and numerical simulation

María Jesús Samper — Tue, 29 Jan 2019 14:57:11 +0100

Taking the strong discontinuity approach as a framework for modeling displacement discontinuities and strain localization phenomena, this Part 1 extends previous results of the authors, for infinitesimal strain settings, to finite deformation scenarios.

By means of the strong discontinuity analysis, and for both damage and elastoplasticity continuum (stress-strain) constitutive models, projected discrete (tractions-displacement jumps) constitutive models are derived, together with the strong discontinuity conditions that restrict the stress states at the discontinuous regime. Also a variable bandwidth model, to automatically induce those strong discontinuity conditions, and a discontinuous bifurcation procedure, to determine the initiation and propagation of the discontinuity, are briefly sketched. Numerical simulation issues are tackled in Part 2 of the work.

Un método de elementos finitos para análisis hidrodinámico de estructuras navales

María Jesús Samper — Tue, 29 Jan 2019 14:35:44 +0100

En este trabajo se presenta una metodología basada en el método de los elementos finitos para el análisis de problemas de flujo incompresible en fluidodinámica naval. Esta metodología se basa en la obtención de unas nuevas ecuaciones diferenciales, basadas en criterios discretos, alternativas a las tradicionales ecuaciones de Navier-Stokes.

El punto más novedoso del presente trabajo es la aplicación del método de análisis de flujo incomprensible mencionado a problemas navales.

Nuevos elementos finitos para el anaálisis dinámico elastoplástico no lineal de estructuras laminares

María Jesús Samper — Tue, 29 Jan 2019 13:15:14 +0100

Los objetivos de este trabajo se enmarcan en el análisis de estructuras laminares delgadas sometidas a un régimen dinámico de cargas, que dan origen a grandes cambios de forma sobre la estructura. Se consideran dos nuevas formulaciones de elementos finitos de lámica delgada, siendo una de ellas una nueva formulación que solo considera los desplazamientos de la superficie media del elemento como variables cinemáticas, independizándose de los grados rotacionales de libertad.

El método de desplazamiento crítico para la predicción de puntos límite y de bifurcación en estructuras

María Jesús Samper — Tue, 29 Jan 2019 13:00:25 +0100

Se presenta la descripción Lagrangiana Generalizada para el análisis estático de sólidos con no linealidad geométrica. Se describen las relaciones incrementales básicas de la cinemática, de la estática y del modelo constitutivo. Se obtiene la forma incremental completa de las ecuaciones de equilibrio no lineales a través del principio de los trabajos visuales. La discretización de dichas ecuaciones por el método de los elementos finitos conduce a la obtención de una expresión paramétrica general y no simétrica de la matriz de rigidez secante incremental. Se obtienen formas simétricas de dicha matriz asignando determinados valores a los parámetros. A partir de la matriz de rigidez secante incremental se deduce, de forma directa, la clásica expresión de la matriz de rigidez tangente empleada en problemas no lineales.

Se formula, de manera incremental, la matriz de rigidez secante a través de la descripción Lagrangiana Generalizada, de tal modo que se pueda obtener una relación entre incrementos finitos de fuerzas y desplazamientos. Se discuten las posibilidades de aplicación de la matriz secante en el análisis no lineal de estabilidad, de bifurcación y de carga límite en sistemas estructurales.

Se presenta una nueva técnica de predicción de puntos críticos para el análisis de inestabilidad estructural. Este método se basa en la determinación de un campo de desplazamiento crítico que aproxima el modo de bifurcación o el modo de deformación crítico del sistema estructural. Se determinan estos desplazamientos críticos imponiendo la condición de singularidad en una expresión aproximada de la matriz de rigidez tangente en el punto crítico. La carga crítica se obtiene a posteriori, de modo directo, utilizando la relación secante entre carga y desplazamiento. Se detalla este procedimiento y las formas explícitas de las matrices secante y tangente para elementos de barra y de sólido en dos y tres dimensiones. Se muestra la eficiencia y la buena aproximación de los resultados en la simulación numérica de varios ejemplos.

A contribution to adaptive numerical solution of compressible flow problems

María Jesús Samper — Tue, 29 Jan 2019 12:43:58 +0100

The monograph presents recent developments on the solution of high speed compressible flow problems using finite element and finite point (meshless) methods with adaptive refinement, techniques.

This work treats two of the main problems of today's problems related to computational fluid dynamics. One problem dealt with is the assured accuracry of a numerical model, at least for the problems which are presented. The other problem which is addressed is the vast amount of time spent in generating (or regenerating) a mes in the design process.

Current trends in qualitative reasoning and applications

María Jesús Samper — Tue, 29 Jan 2019 12:21:22 +0100

In June 1994 the ARCA group was founded in order to enhance communication between Spanish professionals either directly on indirectly related to Qualitative Reasoning. Thus we are talking about a new-born group which tries to follow mainly the working pattern of the French QR group, established in 1987 and closely partner of ARCA, both in research and organization matters. Our group maintains also important relationship with other European clusters and is a integrated in the now in progress European QR Network.

ARCA is structured around five research lines; the members of each one contact each other on a personal and non programmed basis, but two general meetings a year are scheduled so as to, in the one hand letting every “ARCher” learn about every other’s activities and, on the other hand, starting up projects involving the whole group.

Technology transfer of the new trends in concrete

María Jesús Samper — Tue, 29 Jan 2019 12:16:34 +0100

The international RILEM Workshop on Technology Transfer of the New Trends in Concrete (ConTech’94) was held at the Universitat Politècnica de Catalunya (UPC). It was organized by the UPC, the International Center for Numerical Methods in Engineering (CIMNE, Barcelona), and the NSF Center for the Science & Technology of Advanced Cement-Based Materials (ACBM, Northwestern University, Evanston,USA). ConTech’94 was sponsored by the International Union of the Testing and Research Laboratories for Materials and Structures (RILEM), the Commission of the European Communities, the Centro i Desenvolupament Empresarial de Generalitat de Catalunya (CIDEM, Barcelona).
The workshop had to two primary objectives. First, to discuss the incorporation of recent developments and research results in the concrete technology for the present and the future. Secondly, to help bridge the gaps between research and practice, and between more and less developed sectors in the field of concrete. 100 participants attended the workshop, 88 of whom were from the European Union (including 11 young researchers whose participation was partially funded by the European Commission). The official language of the workshop was English, and simultaneous translation between Spanish and English was provided. In all, 23 lectures were presented by experts form Europe, America and Japan, on topics covering the important aspects of concrete technology. The papers corresponding to the lectures are included in a book published by E & FN SPON.

Nonlinear finite element techniques using and object-oriented code

María Jesús Samper — Tue, 29 Jan 2019 12:08:51 +0100

When treating nonlinear problems with the Finite Element formulation, the need to solve nonlinear sets of equations arises. Classically, those nonlinear sets of equations were solved by performing an incremental / iterative analysis with a full Newton-Raphson method.

Today, one can chose from a wide range of methods. The modifications to the original fNR method use tangent stiffness matrices, which are updated at most once per increment. Quasi-Newton methods use secant matrices instead of tangent matrices. Secant-Newton methods are simplifications of the Quasi-Newton.

This work deals, in particular, with the implementation of these methods in an object-oriented code and with the comparison between them on several tests. The expected behavior of the methods is observed from the results.
Also, an acceleration line-search technique is implemented to improve the results supplied by the previous methods.

Evaluation of existing highway bridge systems

María Jesús Samper — Tue, 29 Jan 2019 11:58:41 +0100

Evaluation, repair and rehabilitation of bridges are increasingly important topic in current efforts to deal with the deteriorating infrastructure of developed countries. In fact, after several years of large scale construction projects to build new highway networks, the number of existing bridges is so large that current administrations need to invest increasingly large amounts of funds on the maintenance, diagnostic and repair of these bridges

Comportamiento térmico de presas de hormigón en servicio

María Jesús Samper — Tue, 29 Jan 2019 11:47:26 +0100

Este trabajo se enmarca en el ámbito de las presas de hormigón en fase de explotación y, dentro de este ámbito, se centra en el análisis de la respuesta térmica de la presa frente a la actuación de la acción térmica
ambiental.

Retention of Mechanical Properties After Water Immersion for Glass-Fibre Polymer Composite Laminates with Thermoset & Thermoplastic Infusible Resins

Niamh H Nash — Mon, 28 Jan 2019 14:05:03 +0100

In this work, we conducted an extensive comparative study of the water absorption behavior and retention of mechanical properties of a group of GRP composite laminates manufactured with a range of infusible thermosetting and thermoplastics resins. All laminates were manufactured by Vacuum-Assisted Resin Transfer Moulding (VARTM; the most relevant manufacturing technique in shipbuilding) with a range of state-of-the-art thermosetting resins (Urethane acrylate Crestapol 1210, Epoxy SR1125, Bio-epoxy Supersap CLR, Phenolic Cellobond J2027X) and a novel infusible acrylic thermoplastic resin (Acrylic Elium 150). The reinforcement of choice for each laminate was a unidirectional glass fabric of 996 gsm. Sample preparation for water immersion studies was according to ASTM D5229. This study was part of a comprehensive down-selection of commercially available resins in terms of their suitability for shipbuilding applications, as part of the EU H2020 project FIBRESHIP2 . A selection of relevant properties of the laminates with different resin systems is presented in this paper including fibre volume fraction, apparent interlaminar shear strength (dry and wet condition), flexural strength (dry and wet condition) and flexural modulus (dry and wet condition).

Thermoplastic infusible resin systems: candidates for the marine sector?

Niamh H Nash — Mon, 28 Jan 2019 13:56:02 +0100

This work investigated the feasibility of the use of a novel infusible thermoplastic resin (Elium 150 from Arkema) for composite laminate manufacture by resin infusion methods and possible application in the shipbuilding sector. We compared the properties of Elium glass-fibre laminates with those of laminates infused with state-of-the-art thermosetting epoxy and urethane acrylate resins. The Elium laminates matched the mechanical performance (flexure and interlaminar shear strength) of the epoxy and surpassed that of the urethane acrylate counterpart. However, the mechanical performance of the Elium laminates after immersion in water at 35 oC for 28 days deteriorated compared to urethane acrylate, but was comparable in flexural properties to that of the epoxy. The combination of superior mechanical performance coupled with acceptable environmental resistance and comparable composite laminate manufacturing conditions makes the infusible thermoplastic a possible future candidate matrix over commercial thermosetting resin options.

Modelling strong discontinuities in solid mechanics via strain softening constitutive equations

María Jesús Samper — Wed, 23 Jan 2019 16:14:19 +0100

This part addresses some fundamental aspects about the use of standard constitutive equations to model strong discontinuities (cracks, shear bands, slip lines, etc.) in solid mechanics analyzes. The so called strong discontinuity analysis is introduced as a basic tool to derive a general framework, in which different families of constitutive equations can be inscribed, then allowing to extract relevant aspects for the intended analysis. In particular, a ling between continuum ad discrete approaches to the strain localization phenomena is obtained. Applications to standard continuum damage and elasto-plastic constitutive equations are presented. Relevant aspects to be considered in the numerical simulation of the problem are alo presented.

Utilización de la información histórica en el análisis regional de las avenidas.

María Jesús Samper — Wed, 23 Jan 2019 15:52:16 +0100

Bio-based epoxy resin systems as potential alternatives to petroleum based epoxy matrices in marine fibre-reinforced polymer composites

Niamh H Nash — Tue, 22 Jan 2019 17:03:02 +0100

Fibre-reinforced polymers (FRP) are extensively used in the marine industry for the manufacture of lightweight hull structures for vessels up to 50m in length, and for secondary structures and components in larger vessels. The main benefits resulting in the application of FRP in shipbuilding include: significant weight reduction resulting in substantial fuel saving, increase in cargo capacity and subsequent reduction of greenhouse gas emissions, improved life cycle performance and reduced maintenance costs due to corrosion resistance. As the use of thermoset polymers in shipbuilding increases, so too does the interest in finding suitable alternatives to the use of petroleum-based raw materials. Much work has been published on bio-based epoxy resin systems from natural raw materials, such as vegetable oils, however, the mechanical performance of the bio-based resin systems in comparison to equivalent petroleum-based systems is not widely documented. This research focusses on the comparison of petroleum-based and bio-based two-part commercial epoxy resin systems to manufacture glass fibre reinforced polymers (GFRP) for marine applications. Laminates were manufactured using the Vacuum Assisted Resin Transfer Moulding (VARTM) manufacturing process. Specimens were mechanically characterised in order to evaluate fibre volume fraction, density, apparent inter-laminar shear strength, flexural modulus and strength. The effect of water ingress on the mechanical properties of laminates was also studied by soaking samples in water at 35°C for 28 days. Specimen quality and fracture surfaces were assessed using optical and scanning electron microscopy. Initial results have shown that the average apparent inter-laminar shear strength of the petroleum-based samples was almost identical to the bio-based samples (within 1%), while the flexural strength and modulus of the petroleum-based samples was only 6% and 7% higher than the bio-based samples. Despite the comparatively good mechanical performance of the bio-based laminate, the high viscosity of the resin resulted in higher infusion temperatures and longer infusion times than for the petroleum-based epoxy.

Variability in uncertainty cost for micro-Wind Energy Generation (WEG)

Sergio Rivera — Sat, 19 Jan 2019 05:56:02 +0100

Faced with the problem of wind speed in generation and the difficulty that this entails in the economic future of electric power, mathematical formulations (functions), called uncertainty costs, have been developed. The term is used in a model composed of two parts, an implication of penalization costs for overestimation and the other due to the underestimation of a programmed power. Through analytical mathematics and Monte Carlo simulations, we have found the expected value of the costs of uncertainty, the stability of primary resources through the distribution of probability. However, the results can not be evaluated accurately from an analytical point of view, without taking into account the variability around the average value. In this article we calculate the analytical function of the variance, we understand as a measure of dispersion of the expected values of uncertainty costs for the specific case of wind operators; Likewise, this formulation has been validated through Monte Carlo simulations. The function found is used to observe the dispersion of the data around its expected average value, by applying the standard deviation.

Study of the influence of protuberances in the trailing edge of airfoils and determination of their aerodynamic efficiency through CFD using Ansys Fluent

Jorge Hinojosa — Fri, 18 Jan 2019 20:46:03 +0100

In the present research, the effect of incorporating protuberances in the leading edge to the aerofoil NACA-0012 was studied. For the simulations, two profiles were designed: parametric profile (NACA 0012) and modified profile (0012-MOD), with help of CAD Program Inventor Professional 2016. The 0012-MOD profile incorporates modifications in the leading edge, whose inspiration comes from malformations present on the flippers of the humpback whale (Megaptera novaeangliae). The computational simulations were performed in Ansys Fluent, using the turbulent viscosity model k-ε realizable, with SIMPLE calculation algorithm. The study fluid is air in the incompressible range with Ma: 0.11. To obtain the lift and drag curves for both profiles, they were simulated for angles of attack α: between 0° and 40°, this way it will be possible to compare the profiles and determine their aerodynamic behaviour.

Real-time micro-modelling of city evacuations

María Jesús Samper — Tue, 15 Jan 2019 14:06:42 +0100

A methodology to integrate geographical information system (GIS) data with large-scale pedestrian simulations has been developed. Advances in automatic data acquisition and archiving from GIS databases, automatic input for pedestrian simulations, as well as scalable pedestrian simulation tools have made it possible to simulate pedestrians at the individual level for complete cities in real time. An example that simulates the evacuation of the city of Barcelona demonstrates that this is now possible. This is the first step towards a fully integrated crowd prediction and management tool that takes into account not only data gathered in real time from cameras, cell phones or other sensors, but also merges these with advanced simulation tools to predict the future state of the crowd.

Virtual modeling of polycrystalline structures of materials using particle packing algorithms and Laguerre cells

María Jesús Samper — Tue, 15 Jan 2019 13:08:36 +0100

The influence of the microstructural heterogeneities is an important topic in the study of materials. In the context of computational mechanics, it is therefore necessary to generate virtual materials that are statistically equivalent to the microstructure under study, and to connect that geometrical description to the different numerical methods. Herein, the authors present a procedure to model continuous solid polycrystalline materials, such as rocks and metals, preserving their representative statistical grain size distribution. The first phase of the procedure consists of segmenting an image of the material into adjacent polyhedral grains representing the individual crystals. This segmentation allows estimating the grain size distribution, which is used as the input for an advancing front sphere packing algorithm. Finally, Laguerre diagrams are calculated from the obtained sphere packings. The centers of the spheres give the centers of the Laguerre cells, and their radii determine the cells’ weights. The cell sizes in the obtained Laguerre diagrams have a distribution similar to that of the grains obtained from the image segmentation. That is why those diagrams are a convenient model of the original crystalline structure. The above-outlined procedure has been used to model real polycrystalline metallic materials. The main difference with previously existing methods lies in the use of a better particle packing algorithm.

Systemic characterization and evaluation of particle packings as initial sets for discrete element simulations

María Jesús Samper — Mon, 14 Jan 2019 10:41:56 +0100

A methodology that comprises several characterization properties for particle packings is proposed in this paper. The methodology takes into account factors such as dimension and shape of particles, space occupation, homogeneity, connectivity and isotropy, among others. This classification and integration of several properties allows to carry out a characterization process to systemically evaluate the particle packings in order to guarantee the quality of the initial meshes in discrete element simulations, in both the micro- and the macroscales. Several new properties were created, and improvements in existing ones are presented. Properties from other disciplines were adapted to be used in the evaluation of particle systems. The methodology allows to easily characterize media at the level of the microscale (continuous geometries—steels, rocks microstructures, etc., and discrete geometries) and the macroscale. A global, systemic and integral system for characterizing and evaluating particle sets, based on fuzzy logic, is presented. Such system allows researchers to have a unique evaluation criterion based on the aim of their research. Examples of applications are shown.

General advancing front packing algorithm for the discrete element method

María Jesús Samper — Fri, 11 Jan 2019 13:44:19 +0100

A generic formulation of a new method for packing particles is presented. It is based on a constructive advancing front method, and uses Monte Carlo techniques for the generation of particle dimensions. The method can be used to obtain virtual dense packings of particles with several geometrical shapes. It employs continuous, discrete, and empirical statistical distributions in order to generate the dimensions of particles. The packing algorithm is very flexible and allows alternatives for: 1—the direction of the advancing front (inwards or outwards), 2—the selection of the local advancing front, 3—the method for placing a mobile particle in contact with others, and 4—the overlap checks. The algorithm also allows obtaining highly porous media when it is slightly modified. The use of the algorithm to generate real particle packings from grain size distribution curves, in order to carry out engineering applications, is illustrated. Finally, basic applications of the algorithm, which prove its effectiveness in the generation of a large number of particles, are carried out.

Computation of the stabilization parameter for the finite element solution of advective–diffusive problems

Eugenio Oñate — Fri, 11 Jan 2019 12:14:02 +0100

In a previous paper a general procedure for deriving stabilized finite element schemes for advective type problems based on invoking higher order balance laws over finite size domains was presented. This provides an expression for the element stabilization parameter in terms of the solution residual and its first derivatives in a kind of iterative or adaptative manner. Details of the application of this procedure to 1D and 2D advective- diffusive problems are given. Some examples of applications showing the potential of the new approach are presented.

A Comparison of two objective stress rates in object-oriented codes

María Jesús Samper — Fri, 11 Jan 2019 12:03:21 +0100

An object-oriented code, CASTEM2000, has provided the framework for algorithmic development and numerical testing. In these codes, information is stored and manipulated as objects which represent the entitiesrelevant to a finite element method computation.

A rate dependent plastic-damage constitutive model for large scale computational in concrete structures

María Jesús Samper — Fri, 11 Jan 2019 10:54:58 +0100

Integration methodology of different softwares for constrained tubular truss size optimization problems

Carmem Miranda Lage — Thu, 10 Jan 2019 20:35:07 +0100

Practical size structural optimization problems can involve a large number of variables and constraints that meet regulatory requirements for safety and structural performance. Most optimization problems tend to find the minimum value of the objective function within a feasible set that satisfies the constraints. Among evolutionary computation techniques, genetic algorithms (GAs) have been successfully used for the optimization of structures, including lattice systems. This article proposes an automated interactive methodology for the optimization of structures based on the integration of two commercial programs: Ansys and Matlab. The developed script uses the Finite Element Method for the analysis of the structure, together with the Genetic Algorithms for the optimization. The objective of the article is to evaluate the applicability, precision and efficiency of the proposed methodology. Two numerical examples of trusses were solved with the proposed methodology, classic truss of the literature and truss with normative restrictions. The results show that the methodology is adequate for the solution of size structural optimization problems with a good precision of the results.

Análisis de problemas de choque e impacto entre sólidos deformables por el Método de los Elementos Finitos.

María Jesús Samper — Thu, 10 Jan 2019 16:21:33 +0100

El trabajo que se expone ha hecho uso de los últimos avances en mecánica computacional, métodos numéricos, visualización y algoritmos de cálculo para obtener un programa de ordenador para simulación de problemas de choque e impacto de interés práctico para una amplia variedad de sectores industriales. En particular, el objetivo del proyecto SIMPACT ha sido el desarrollo de un paquete de software para análisis de problemas de dinámica rápida y análisis no lineal procesable en una amplia variedad de ordenadores, con aplicación a choques de vehículos, impacto en estructuras aeroespaciales, defensa y problemas de conformado, entre otros.

Estructuras de edificación con aislaminto antisísmico

María Jesús Samper — Thu, 10 Jan 2019 15:34:53 +0100

Estimación y corrección del error en el análisis estructural por el MEF

María Jesús Samper — Thu, 10 Jan 2019 15:29:21 +0100

En los últimos años se han desarrollado diversas técnicas para resolver el problema de la estimación y la
corrección del error. De hecho, la mayoría de los avances que se han realizado dentro del campo de los
elementos finitos se pueden entender como formas distingas de minimizar el error existente en las soluciones.

En esta monografía se hablará de dos técnicas distintas para la corrección de errores: Técnicas de
refinamiento y técnicas de remallado.

Modelización numérica de materiales friccionales

María Jesús Samper — Thu, 10 Jan 2019 15:26:34 +0100

La presente monografía trata el problema del comportamiento de los materiales friccionales,
especialmente del hormigón, más allá de su límite elástico. Estudia los problemas de aplastamiento y
fractura y describe un modelo constitutivo amplio que permite una muy adecuada simulación de estos
fenómenos.

A Finite Element formulation for the numerical solution of the convection-diffusion equation

María Jesús Samper — Thu, 10 Jan 2019 15:19:49 +0100

In this work we present several finite element techniques to solve the convection-diffusion equation when the Péclet number is high, tha is, when diffusion is very small. The basic finite element formulation employed here is the Streamline-Upwind-Petrov-Galerkin (SUPG). A thorough description of this approach is presented in Chapter 1. Chapter 2 deals with the application of the generalized trapezoidal rule to advance in time for the transient equation. A complete stability and accuracy analysis is performed for the explicit Euler scheme, both using linear and quadratic finite elements. Chapter 3 is concerned with the problem of removing the localized oscillations that remain about abrupt layers of the solution.

Mechanics of a continuum medium. Vol. III

María Jesús Samper — Thu, 10 Jan 2019 15:11:35 +0100

This work presents the fundamental assumptions and the successive mathematical developments which allow to establish the complete field equations of a continuum. The aim is to be sufficiently general and self-content using, however, mathematical procedures which can be always understook by an engineer with a common background of Linear Algebra and elementary Differential Calculus.

A Finite Element formulation for viscous incompressible flows

María Jesús Samper — Thu, 10 Jan 2019 14:52:59 +0100

Modelado de la fisuración en estructuras de hormigón

María Jesús Samper — Thu, 10 Jan 2019 14:27:02 +0100

En este trabajo, se presenta una perspectiva general de los modelos de fisuración existentes y de algunas aportaciones de la línea de investigación que se desarrollan, tanto en el dominio de la formulación teórica de dichos modelos como de su aplicación práctica.

Lectures on nonlinear finite element analysis of concrete shells

María Jesús Samper — Thu, 10 Jan 2019 13:32:38 +0100

This monograph presents 4 lectures on non linear analysis of concrete shells by the finite element method. The lectures were prepared by the author for the course on "Non linear analysis of shells by finite elements" held at the International Center for Mechanics Sciences in Udine, Italy on June 24-28th 1991.

The content of the lectures presents an overview of the different aspects involved in the analysis of concrete shells by finite elements. Thus, Lecture 1 introdeuces the basic concepts of the analysis of reinforced concrete shell structures using flat shell and curved degenerated layered shell finite elements. Both the geometric and kinematic assumptions are described in detail together with the respective finite element formulation and the numerical algorithm for non linear elasto-plastic analysis including the effect of moderately large displacements.

Lecture 2 presents an overview of the constitutive behaviour of concrete and steel in a form suitable for numerical computations using the finite element models described in previous lecture. The reinforcing steel bars are modelled with a simple elasto-plastic model. Hovewer, two conceptualy different concrete models are presented. The first model is based on elasto-plastic theory to describe the compressive behaviour of concrete, whereas a linear orthotropic elasto-brittle model is used for modelling the cracking behaviour under tensile conditions. This ``elasto-platic-brittle model has been extensively used by Owen and Figueiras and most of the concepts presented emanate from reference [18] of this chapter.

The second model is based on the assumptions that both the tensile and compressive behaviour of concrete can be treated under the unified framework of elasto-plasticity theory. This model termed ``plastic-damage model has ben proposed by Lubliner, Oller, Oliver and O\~nate in different publications which main concepts are summarized in the lecture (see refs. [33-38] of this chapter).

In Lecture 3 the basic finite element formulation for the analysis of stiffened concrete shells via the use of eccentric beams is described.

Finally, in Lecture 4 some examples of applications of the finite element formulations presented to the non-linear analysis of different reinforced concrete shell structures analyzed by different authors are described. Examples included range from the analysis of plain and pre-stressed concrete deep beams, to more sophisticated shell type structures including the nonlinear behaviour of a composite steel-concrete girder bridge and a cryogenic concrete liquid gas tank under severe thermal conditions.

This monograph has been written exclusively with didactic purposes. Most of the ideas included in the text have been extracted from research publications by the author and many others. The interested reader will be able to find details on the different subjects treated in the many references included at the end of each chapter.

Análisis dinámico de presas

María Jesús Samper — Thu, 10 Jan 2019 10:32:02 +0100

Se desarrolla en este trabajo un estudio numérico-experimental acerca del comportamiento dinámico de las presas bóvedas considerando su interacción con el agua del embalse. Para ello, se ha realizado un análisis de los factores que inciden más directamente en el comportamiento dinámico de tales tipos de estructuras. Dicho análisis se realiza mediante e lmétodo de los elementos finitos, estudiando distintas alternativas de formulación. Asimismo, se ha realizado un esayo a escala real de una presa bóveda existente, mediante una serie de explosiones y midiendo la respuesta obtenida.

Simulación Numérica de Patologías en Presas de Hormigón

María Jesús Samper — Wed, 09 Jan 2019 16:58:02 +0100

A stabilized mixed implicit Material Point Method for non-linear incompressible solid mechanics

María Jesús Samper — Thu, 03 Jan 2019 12:47:47 +0100

In this work a stabilized mixed formulation for the solution of non-linear solid mechanics problems in nearly-incompressible conditions is presented. In order to deal with high material deformation, an implicit Material Point Method is chosen. Such choice allows avoiding the classical limitations of the Finite Element Method, e.g., element tangling and extreme mesh distortion. The proposed mixed formulation, with displacement and pressure as primary variables, is tested through classical benchmarks in solid and geo-mechanics where a Neo-Hookean, a J2 and a Mohr-Coulomb plastic law are employed. Further, the stabilized mixed formulation is compared with a displacement-based formulation to demonstrate how the proposed approach gets better results in terms of accuracy, not only when incompressible materials are simulated, but also in the case of compressible ones.

Determining the micro film of hexyl alcohol in laminar condition on a rotating drum

Christ Trang — Tue, 18 Dec 2018 04:17:03 +0100

In this research, the free surface of micro film of hexyl alcohol on a partially submerged rotating drum has been predicted using CFD (computational fluid dynamics) and compared with experimental data and analytical solution. The trend of has been found very comparable with experimental and analytical solution. A Matlab code was used to model the flow and film dynamics. Computationally it was an unsteady state problem and semi-steady state was achieved. No surfactant was present on the surface. The speed of the moving rotating drum was set a ''rpm''. With the increase of rotating drum, the minimum film thickness increases with ''rpm'' (for \alpha _o = 47^{0} and for \alpha _o = 58^{0}).

Numerical analysis of particulate flows with the finite element method

María Jesús Samper — Tue, 11 Dec 2018 12:54:14 +0100

In this work we study the numerical simulation of particle-laden fluids, with an emphasis on Newtonian fluids and spherical, rigid particles. Our general strategy consists in using the discrete element method (DEM) to model the particles and the finite element method (FEM) to discretize the continuous phase, such that the fluid is not resolved around the particles, but rather averaged over them. The effect of the particles on the fluid is taken into account by averaging (filtering) their individual volumes and particle-fluid interaction forces. In the first part of the work we study the Maxey–Riley equation of motion for an isolated particle in a nonuniform flow; the equation used to calculate the trajectory of the DEM particles. In particular, we perform a detailed theoretical study of its range of applicability, reviewing the initial effects of breaking its fundamental hypotheses, such as small Reynolds number, sphericity of the particle, isolation etc. The output of this study is a set of tables containing order-of-magnitude inequalities to assess the validity of the method in practice. The second part of the work deals with the numerical discretization of the MRE and, in particular, the study of different techniques for the treatment of the history-dependent term, which is difficult to calculate efficiently. We provide improvements on an existing method, proposed by van Hinsberg et al. (2011), and demonstrate its accuracy and efficiency in a sequence of tests of increasing complexity. In the final part of the work we give three application examples representative of different regimes that may be encountered in the industry, demonstrating the versatility of our numerical tool. For that, we describe necessary generalizations to the MRE to cover problems outside its range of applicability. Furthermore, we give a detailed account of the stabilized FEM algorithm used to discretize the fluid phase and compare several derivative recovery tools necessary to calculate some of the interphase coupling terms. Finally, we generalize the algorithm to include the backward-coupling effects according to the theory of multicomponent continua, allowing the code to deal with arbitrarily dense flow regimes.

Application of optimization techniques to the determination of modal parameters in civil structures by the identification method

LUIS MANUEL VILLA GARCIA — Tue, 04 Dec 2018 20:36:08 +0100

In the present paper, the application of optimization techniques –via FRF– is developed for determining modal parameters by means of the identification method that are exclusively limited to: systems with viscous damping, low levels of damping, and methods that work within the frequency domain. Decomposition techniques are proposed for working with complex magnitudes that allow the real and imaginary parts to be treated separately (which can, in this way, be implemented in commercial optimization programs), even in matrix product operations. The influence of high and low modes is rigorously taken into consideration via the selfsame optimization algorithm. To illustrate this work we have analyzed a structure unique in its slenderness, La Cartuja Bridge (Seville, Spain), which also constitutes a very light structure with very little damping. Its design contributed in its day a new structural framework of complicated geometries through the use of a new material: high yield strength steel.

Comparison of Wind Loads on Flat and Gabled Roofs calculated with the Colombian Building Code and Numerical Results using CFD

Martha Elena Delgado Osorio — Mon, 03 Dec 2018 23:33:03 +0100

The Colombian building code, NSR-10, specifies three methods for estimating wind loads on structures: a) a Simplified Method, b) an Analytical Method and c) Wind Tunnel Testing. The first two of these methods are widely used by structural engineers in Colombia, as wind tunnel testing is comparatively expensive and time consuming, and only mandatory in special cases. Although the Simplified Method is only valid for buildings with regular shaped roofs and overall heights less than 18 m, the Analytical Method can be used for any regular building, regardless of the height. However, when these two methods are used to estimate wind loads for buildings with heights less than 18 m, they often produce very different results and, at times, contradictory values. In this study, Computational Fluids Dynamic (CFD) analyses were performed on flat and gabled roofed building models in order to compare the pressures on the roofs with those calculated using the standard design methods specified by the Colombian building code. The results illustrate the significant differences produced from the Simplified and Analytical methods of the NSR-10 and highlight the need of conducting wind tunnel tests in order to propose a more consistent method for estimating design wind loads in Colombia