San Carlos de Bariloche, Argentina
San Carlos de Bariloche, Argentina

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Grillo S.,Instituto Balseiro | Marsden J.,California Institute of Technology | Nair S.,UTRC - United Technologies Research Center
Journal of Geometric Mechanics | Year: 2011

In this paper, we develop a method for stabilizing underactuated mechanical systems by imposing kinematic constraints (more precisely Lyapunov constraints). If these constraints can be implemented by actuators, i.e., if there exists a related constraint force exerted by the actuators, then the existence of a Lyapunov function for the system under consideration is guaranteed. We establish necessary and sufficient conditions for the existence and uniqueness of constraint forces. These conditions give rise to a system of PDEs whose solution is the required Lyapunov function. To illustrate our results, we solve these PDEs for certain underactuated mechanical systems of interest such as the inertia wheel-pendulum, the inverted pendulum on a cart system and the ball and beam system. © American Institute of Mathematical Sciences.

Leiva J.S.,Instituto Balseiro | Blanco P.J.,Laboratorio Nacional Of Computacao Cientifica | Buscaglia G.C.,University of Sao Paulo
International Journal for Numerical Methods in Engineering | Year: 2010

In this article we address decomposition strategies especially tailored to perform strong coupling of dimensionally heterogeneous models, under the hypothesis that one wants to solve each submodel separately and implement the interaction between subdomains by boundary conditions alone. The novel methodology takes full advantage of the small number of interface unknowns in this kind of problems. Existing algorithms can be viewed as variants of the 'natural' staggered algorithm in which each domain transfers function values to the other, and receives fluxes (or forces), and vice versa. This natural algorithm is known as Dirichlet-to-Neumann in the Domain Decomposition literature. Essentially, we propose a framework in which this algorithm is equivalent to applying Gauss-Seidel iterations to a suitably defined (linear or nonlinear) system of equations. It is then immediate to switch to other iterative solvers such as GMRES or other Krylov-based method, which we assess through numerical experiments showing the significant gain that can be achieved. Indeed, the benefit is that an extremely flexible, automatic coupling strategy can be developed, which in addition leads to iterative procedures that are parameter-free and rapidly converging. Further, in linear problems they have the finite termination property. © 2009 John Wiley & Sons, Ltd.

Blanco P.J.,Laboratorio Nacional Of Computacao Cientifica | Blanco P.J.,Instituto Nacional Of Ciencia E Tecnologia | Leiva J.S.,Instituto Balseiro | Feijoo R.A.,Laboratorio Nacional Of Computacao Cientifica | And 3 more authors.
Computer Methods in Applied Mechanics and Engineering | Year: 2011

Increasing efforts exist in integrating different levels of detail in models of the cardiovascular system. For instance, one-dimensional representations are employed to model the systemic circulation. In this context, effective and black-box-type decomposition strategies for one-dimensional networks are needed, so as to: (i) employ domain decomposition strategies for large systemic models (1D-1D coupling) and (ii) provide the conceptual basis for dimensionally-heterogeneous representations (1D-3D coupling, among various possibilities). The strategy proposed in this article works for both of these two scenarios, though the several applications shown to illustrate its performance focus on the 1D-1D coupling case.A one-dimensional network is decomposed in such a way that each coupling point connects two (and not more) of the sub-networks. At each of the M connection points two unknowns are defined: the flow rate and pressure. These 2. M unknowns are determined by 2. M equations, since each sub-network provides one (non-linear) equation per coupling point. It is shown how to build the 2 M× 2. M non-linear system with arbitrary and independent choice of boundary conditions for each of the sub-networks. The idea is then to solve this non-linear system until convergence, which guarantees strong coupling of the complete network. In other words, if the non-linear solver converges at each time step, the solution coincides with what would be obtained by monolithically modeling the whole network. The decomposition thus imposes no stability restriction on the choice of the time step size. Effective iterative strategies for the non-linear system that preserve the black-box character of the decomposition are then explored. Several variants of matrix-free Broyden's and Newton-GMRES algorithms are assessed as numerical solvers by comparing their performance on sub-critical wave propagation problems which range from academic test cases to realistic cardiovascular applications. A specific variant of Broyden's algorithm is identified and recommended on the basis of its computer cost and reliability. © 2010 Elsevier B.V.

Blanco P.J.,Laboratorio Nacional Of Computacao Cientifica | Leiva J.S.,Instituto Balseiro | Buscaglia G.C.,University of Sao Paulo
International Journal for Numerical Methods in Biomedical Engineering | Year: 2013

This work presents a generic and efficient black-box approach for the strong iterative coupling of dimensionally heterogeneous flow models in computational hemodynamics. A heterogeneous model of the cardiovascular system is formed by several vascular black-box components, which are connected through coupling equations. The associated system of equations is solved using the Broyden algorithm. In addition, a multiple time-stepping strategy is introduced to meet different component requirements. The proposed algorithm is employed to split a 3D-1D-0D closed-loop model of the cardiovascular system into corresponding black-box components standing for the 3D (specific vessels), 1D (systemic arteries/peripheral vessels), and 0D (venous/cardiac/pulmonary circulation) components. Examples of application are presented showing the robustness and suitability of this novel approach. © 2012 John Wiley & Sons, Ltd.

Leiva J.S.,Instituto Balseiro | Blanco P.J.,Laboratorio Nacional Of Computacao Cientifica | Buscaglia G.C.,University of Sao Paulo
Multiscale Modeling and Simulation | Year: 2011

In this work an iterative strategy is developed to tackle the problem of coupling dimensionally- heterogeneous models in the context of fluid mechanics. The procedure proposed here makes use of a reinterpretation of the original problem as a nonlinear interface problem for which classical nonlinear solvers can be applied. Strong coupling of the partitions is achieved while dealing with different codes for each partition, each code in black-box mode. The main application for which this procedure is envisaged arises when modeling hydraulic networks in which complex and simple subsystems are treated using detailed and simplified models, correspondingly. The potentialities and the performance of the strategy are assessed through several examples involving transient flows and complex network configurations. © 2011 Society for Industrial and Applied Mathematics.

Bubach D.,Bariloche Atomic Center | Perez Catan S.,Bariloche Atomic Center | Arribere M.,Bariloche Atomic Center | Arribere M.,Instituto Balseiro | Guevara S.R.,Bariloche Atomic Center
Chemosphere | Year: 2012

The emission of volatile pollutants from the volcanic eruption of the Puyehue-Cordón Caulle complex (North Patagonia Andean Range) that started in June 4th, 2011, was investigated by bioindication means with the epyphytic fruticose lichen Usnea sp. The elemental composition of pooled samples made up with 10 lichen thalli were analysed by Instrumental Neutron Activation Analysis. Eleven sampling sites were selected within the impacted region at different distance from the volcanic source. Five sites were selected as they were already sampled in a previous study prior to the eruption. Two other new sampling sites were selected from outside the impacted zone to provide non-impacted baseline sites.The elements associated with the lichen incorporation of particulate matter (PM) of geological origin were identified by linear correlation with a geochemical tracer (Sm concentrations). The elements associated with PM uptake were Ce, Eu, Fe, Hf, La, Lu, Na, Nd, Sb, Sc, Se, Ta, Tb, Th, U, and Yb. Arsenic and Cs concentrations showed contributions exceeding the PM fraction in sites near the volcanic centre, also higher than the baseline concentrations, which could be associated with permanent emissions from the geothermal system of the Puyehue-Cordón Caulle complex. The lichen concentrations of Ba, Ca, Co, Hg, K, Rb, Sr, and Zn were not associated with the PM, not showing higher concentrations in the sites nearby the volcanic source or respect to the baseline values either. Therefore, there is no indication of the emission of volatile forms of these elements in the lichen records. The lichen records only identified Br volatile emissions associated with the Puyehue-Cordón Caulle complex eruption in 2011. © 2012 Elsevier Ltd.

Gennari F.C.,CONICET | Gennari F.C.,Instituto Balseiro | Gennari F.C.,Bariloche Atomic Center
International Journal of Hydrogen Energy | Year: 2012

In the present study, the synthesis of two different LiBH 4-Y(BH4)3 and LiBH4-YH3 composites was performed by mechanochemical processing of the 4LiBH 4-YCl3 mixture and as-milled 4LiBH4-YCl 3 plus 3LiH. It was found that Y(BH4)3 and YH3 formed in situ during milling are effective to promote LiBH 4 destabilization but differ substantially from each other in terms of the dehydrogenation pathway. During LiBH4-Y(BH4) 3 dehydriding, Y(BH4)3 decomposes first generating in situ freshly YH3 and subsequently, it destabilizes LiBH4 with the formation of minor amounts of YB4. About 20% of the theoretical hydrogen storage was obtained via the rehydriding of YB4-4LiH-3LiCl at 400 °C and 6.5 MPa. As a novel result, a compound containing (B12H12)2- group was identified during dehydriding of Y(BH4)3. In the case of 4LiBH4-YH3 dehydrogenation, the increase of the hydrogen back pressure favors the formation of crystalline YB4, whereas a reduction to ≤0.1 MPa induces the formation of minor amounts of Li 2B12H12. Although for hydrogen pressures ≤0.1 MPa direct LiBH4 decomposition can occur, the main dehydriding pathway of 4LiBH4-YH3 composite yields YB 4 and LiH. The nanostructured composite obtained by mechanochemical processing gives good hydrogen storage reversibility (about 80%) regardless of the hydrogen back pressure. Copyright © 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Gennari F.C.,CONICET | Gennari F.C.,Instituto Balseiro | Gennari F.C.,Bariloche Atomic Center
International Journal of Hydrogen Energy | Year: 2011

Destabilization of LiBH4 by addition of metal hydrides or borohydrides is a powerful strategy to develop new promising hydrogen storage systems. In this study, we compare the destabilization behavior of the LiBH 4 by addition of MH2 (M = La, Ce). A notable improvement in the hydrogen desorption temperature, the rate and the weight percentage of hydrogen released is observed for LiBH4-MH2 with respect to LiBH4. Formation of LaB6 and CeB6 after dehydriding of the composites is proved by PXRD. Remarkable hydrogen storage reversibility of LiBH4-MH2 composites is confirmed under moderate conditions: 400 °C and 6.0 MPa of hydrogen pressure for 4 h without catalyst. The LiBH4-LaH2 composite exhibits improved hydrogen desorption performance compared with LiBH4-CeH2 composite, but the hydrogen storage reversibility is inferior. Notably, the LiBH4-CeH2 nanocomposite produced by in situ formation of CeH2 from Ce(BH4)3-LiH displays excellent hydrogen storage properties. The addition of ZrCl4 as a catalyst improves dehydriding kinetics. The mechanism underlying the enhancement in the LiBH4-MH2 composites is also discussed. Our study is the first work about reversible hydrogen storage in LiBH4-LaH 2. © 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Alessi M.,Instituto Balseiro | Alessi M.,Bariloche Atomic Center | Otranto S.,CONICET | Focke P.,Bariloche Atomic Center
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2011

In this work we have measured single-electron capture in collisions of He32+ projectiles incident on a helium target for energies of 13.3-100 keV/amu with the cold-target recoil-ion momentum spectroscopy setup implemented at the Centro Atómico Bariloche. State-selective single-capture cross sections were measured as a function of the impact energy. They were found to agree with previous existing data from the Frankfurt group, starting at the impact energy of 60 keV/amu; as well as with recent data, at 7.5 keV/amu, from the Lanzhou group. The present experimental results are also contrasted to the classical trajectory Monte Carlo method with dynamical screening. © 2011 American Physical Society.

Guozden T.M.,Instituto Balseiro | Clausse A.,National University of Central Buenos Aires
International Journal of Heat and Mass Transfer | Year: 2016

Species separation can be produced by imposing a pressure gradient in gaseous mixtures, which induces different molecular velocities depending on the molar weight. Pressure gradients can be achieved by centrifugal forces brought about by the passage of the gas through a curved nozzle at supersonic velocity. The efficiency of this process depends on the geometry of the nozzle as well as the flow operating conditions. The numerical solver Fluent was used in order to produce a model of the aerodynamics and the oxygen diffusion of a steady-state flow of air in a curved nozzle. The development of the pressure and O2 concentration profiles along the nozzle were analyzed for different pressure boundary conditions at the inlet and the exit, testing several nozzle sizes. Optimum values of the cut and the inlet pressure were found which maximize the separation efficiency. The effect of the exit pressure was associated with the axial pressure distribution along the inner wall of the nozzle. The results were compared with measurements showing good agreement. © 2016 Elsevier Ltd. All rights reserved.

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