The Experts below are selected from a list of 2011536 Experts worldwide ranked by ideXlab platform
Bernard Larrouturou - One of the best experts on this subject based on the ideXlab platform.
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Partitioned procedures for the transient solution of coupled aroelastic Problems Part I: Model Problem, theory and two-dimensional application
Computer Methods in Applied Mechanics and Engineering, 1995Co-Authors: S. Piperno, Charbel Farhat, Bernard LarrouturouAbstract:In order to predict the dynamic response of a flexible structure in a fluid flow, the equations of motion of the structure and the fluid must be solved simultaneously. In this paper we present several partitioned procedures for time-integrating this focus coupled Problem and discuss their merits in terms of accuracy, stability, heterogeneous computing, I/O transfers, subcycling and parallel processing. All theoretical results are derived for a one-dimensional piston Model Problem with a compressible flow, because the complete three-dimensional aeroelastic Problem is difficult to analyze mathematically. However, the insight gained from the analysis of the coupled piston Problem and the conclusions drawn from its numerical investigation are confirmed with the numerical simulation of the two-dimensional transient aeroelastic response of a flexible panel in a transonic non-linear Euler flow regime. © 1995.
Paola Testa - One of the best experts on this subject based on the ideXlab platform.
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the solar Model Problem solved by the abundance of neon in nearby stars
Nature, 2005Co-Authors: J J Drake, Paola TestaAbstract:One of the successes of modern astrophysics has been the ability of standard solar Models to predict the structure of the Sun in agreement with inference from solar oscillations. At least that was the idea. Recent revisions of the solar abundances of a number of elements meant that chemical composition no longer matched oscillation measurements. Drake and Testa have taken a novel approach to this ‘solar Model Problem’, measuring the relative abundance of neon and oxygen in a number of nearby Sun-like stars. The Ne/O ratios are all very similar and higher than the recently revised solar value. Take this value instead of the difficult-to-pin-down direct measurement of the Sun and the Model is rescued. The interior structure of the Sun can be studied with great accuracy using observations of its oscillations, similar to seismology of the Earth. Precise agreement between helioseismological measurements and predictions of theoretical solar Models1 has been a triumph of modern astrophysics. A recent downward revision by 25–35 per cent of the solar abundances of light elements such as C, N, O and Ne (ref. 2) has, however, broken this accordance: Models adopting the new abundances incorrectly predict the depth of the convection zone, the depth profiles of sound speed and density, and the helium abundance1,3. The discrepancies are far beyond the uncertainties in either the data or the Model predictions4. Here we report neon-to-oxygen ratios measured in a sample of nearby solar-like stars, using their X-ray spectra. The abundance ratios are all very similar and substantially larger than the recently revised solar value. The neon abundance in the Sun is quite poorly determined. If the Ne/O abundance in these stars is adopted for the Sun, the Models are brought back into agreement with helioseismology measurements5,6.
Thierry Lanz - One of the best experts on this subject based on the ideXlab platform.
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neon abundances in b stars of the orion association solving the solar Model Problem
The Astrophysical Journal, 2006Co-Authors: Katia Cunha, Ivan Hubeny, Thierry LanzAbstract:We report on non-LTE Ne abundances for a sample of B-type stellar members of the Orion association. The abundances were derived by means of non-LTE fully metal-blanketed Model atmospheres and extensive Model atoms with updated atomic data. We find that these young stars have a very homogeneous abundance of A(Ne) = 8.11 ± 0.04. This abundance is higher by ~0.3 dex than the currently adopted solar value, A(Ne) = 7.84, which is derived from lines produced in the corona and active regions. The general agreement between the abundances of C, N, and O derived for B stars with the solar abundances of these elements derived from three-dimensional hydrodynamical Models atmospheres strongly suggests that the abundance patterns of the light elements in the Sun and B stars are broadly similar. If this hypothesis is true, then the Ne abundance derived here will help to reconcile solar Models with helioseismological observations.
M.p. Errera - One of the best experts on this subject based on the ideXlab platform.
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A coupling approach to Modeling heat transfer during a full transient flight cycle
International Journal of Heat and Mass Transfer, 2017Co-Authors: M.p. Errera, M. Lazareff, J.d. Garaud, T. Soubrié, C. Douta, T. FedericiAbstract:The purpose of the present study is to describe novel numerical coupling schemes to analyze the transient temperature field in a solid via a conjugate heat transfer procedure. Emphasis is put on the interfacial treatment based on two complementary treatments: Dirichlet-Robin and Neumann-Robin transmission conditions. The numerical methods are first presented on the basis of a stability analysis in an aerothermal Model Problem. Stability conditions are expressed and the mathematical expression of the most relevant coupling parameters are provided for the first time. Furthermore, an overview of all the coefficients that can be used in a transient thermally-coupled procedure are given and a unified approach for steady and unsteady ramps is proposed. Then, these interfacial schemes are applied to the Problem of convective heat transfer over, and transient conduction heat transfer within, a flat plate. A comparative study with realistic operating conditions is carried out, at low and large Biot numbers. It is shown that certain choices of coupling coefficients, even if physically reasonable, may result in non-converging algorithms. This confirms that a Model Problem provides insight to the behavior of complicated heat transfer cases and constitutes an invaluable aid for generating efficient interfacial schemes. Indeed, the numerical computations demonstrate the efficiency of the numerical schemes based on the main theoretical results. The trends predicted by the Model Problem are recovered and excellent convergence properties are observed in all cases.
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Numerical study of two optimized coupling interface treatments for steady conjugate heat transfer Problems
2016Co-Authors: M.p. Errera, R. El KhouryAbstract:This paper presents two transmission interface treatments, Dirichlet-Robin and Neumann-Robin procedures, that may be employed for conjugate heat transfer Problems. These conditions are analyzed on the basis of a 1D simplified Model Problem. In the first part of the paper, the Dirichlet-Robin procedure is presented. This interface treatment is the most widely employed in the literature. The same analysis is then performed with a Neumann-Robin procedure. On the basis of the Model Problem, the general expression of the amplification factor, the stability bounds and the optimal coefficients are provided. It is shown that the two interface treatments are opposite and complementary. Moreover, the so-called optimal coefficient provides the best results in terms of stability and convergence in the Dirichlet-Robin procedure. A criterion is expressed to choose the most appropriate transmission procedure and its importance is underlined by a test case.
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Comparative study of coupling coefficients in Dirichlet–Robin procedure for fluid–structure aerothermal simulations
Journal of Computational Physics, 2016Co-Authors: M.p. Errera, F. DuchaineAbstract:This paper tests the performance of coupling coefficients of a Dirichlet–Robin transmission procedure in the context of steady conjugate heat transfer (CHT). Particular emphasis is put on the optimal coefficients highlighted recently in a theoretical study based on a normal mode stability analysis. This work can be seen as the logical continuation of that study in order to assess the relevance of the coefficients provided by the Model Problem in a realistic aerothermal computation. First, the numerical and physical CHT Modeling methodologies are presented. Then, the optimal procedure applied to a Dirichlet–Robin algorithm (one-coefficient method) is briefly described. In order to gauge the ability of this Model to predict the stability and convergence properties of a realistic case, it is compared on a heated cylinder in a flowfield test case. A series of five coupling coefficients and three Fourier numbers are considered. These parameters are introduced into the Model Problem as data to compute the amplification factor and the stability limits. The stability and convergence properties predicted by the Model Problem are then compared to those obtained in the CHT computation. This comparison shows an excellent overall agreement. Moreover, for all the Fourier numbers considered, the numerical solution is stable and oscillation-free when the optimal coefficient of the Model Problem is used. This would suggest that the one-dimensional normal mode analysis can provide relevant coefficients directly applicable to real CHT Problems.
S. Piperno - One of the best experts on this subject based on the ideXlab platform.
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Partitioned procedures for the transient solution of coupled aroelastic Problems Part I: Model Problem, theory and two-dimensional application
Computer Methods in Applied Mechanics and Engineering, 1995Co-Authors: S. Piperno, Charbel Farhat, Bernard LarrouturouAbstract:In order to predict the dynamic response of a flexible structure in a fluid flow, the equations of motion of the structure and the fluid must be solved simultaneously. In this paper we present several partitioned procedures for time-integrating this focus coupled Problem and discuss their merits in terms of accuracy, stability, heterogeneous computing, I/O transfers, subcycling and parallel processing. All theoretical results are derived for a one-dimensional piston Model Problem with a compressible flow, because the complete three-dimensional aeroelastic Problem is difficult to analyze mathematically. However, the insight gained from the analysis of the coupled piston Problem and the conclusions drawn from its numerical investigation are confirmed with the numerical simulation of the two-dimensional transient aeroelastic response of a flexible panel in a transonic non-linear Euler flow regime. © 1995.