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Papers by pascal galon

The Proceedings of the International Conference on Nuclear Engineering (ICONE)

HAL (Le Centre pour la Communication Scientifique Directe), May 16, 2022

On développe un élément fini de type poutre enrichi permettant de prendre en compte l'ovalisation... more On développe un élément fini de type poutre enrichi permettant de prendre en compte l'ovalisation de la section droite d'un tube. La cinématique retenue est une cinématique de coque, dont le mouvement de la section est développée en séries de Fourier. Le modèle décrit est alors discrétisé et implémenté dans le code de calcul Europlexus. Les résultats numériques de traction simple et de flexion pure sont comparés aux solutions analytiques. Mots clés-poutre enrichie, ovalisation de section, séries de Fourier.

Journal of Computational Physics, 2018

A Finite-Volume scheme for the numerical computations of compressible single-and two-phase flows ... more A Finite-Volume scheme for the numerical computations of compressible single-and two-phase flows in flexible pipelines is proposed based on an approximate Godunov-type approach. The spatial discretization is here obtained using the HLLC scheme. In addition, the numerical treatment of abrupt changes in area and network including several pipelines connected at junctions is also considered. The proposed approach is based on the integral form of the governing equations making it possible to tackle general equations of state. A coupled approach for the resolution of fluid-structure interaction of compressible fluid flowing in flexible pipes is considered. The structural problem is solved using Euler-Bernoulli beam finite elements. The present Finite-Volume method is applied to ideal gas and twophase steam-water based on the Homogeneous Equilibrium Model (HEM) in conjunction with a tabulated equation of state in order to demonstrate its ability to tackle general equations of state. The extensive application of the scheme for both shock tube and other transient flow problems demonstrates its capability to resolve such problems accurately and robustly. Finally, the proposed 1-D fluid-structure interaction model appears to be computationally efficient.

Applied Mathematics and Computation

HAL (Le Centre pour la Communication Scientifique Directe), Nov 18, 2015

International audienceThis paper is dedicated to the comparison between experimental data and num... more International audienceThis paper is dedicated to the comparison between experimental data and numerical results in multi-phase flows involving high pressure ratios such as water hammer transients. A two-fluid seven equation model has been selected due to its ability to take into account all phasic desequilibria as well as vanishing phases. Theoretical properties of the model are underlined. A mono-dimensional finite volume implementation of the two-fluid model is then compared to the experimental data of the Simpson and Canon experiment. Differences with the classical Baer and Nunziato model are also pointedout

Journal of Fluids and Structures, 2021

Abstract A 1D/3D Finite-Volume coupling is proposed for the Euler/Homogeneous Equilibrium Model e... more Abstract A 1D/3D Finite-Volume coupling is proposed for the Euler/Homogeneous Equilibrium Model equations. The present approach is based on the Finite-Volume framework making it possible to tackle general equations of state. A special attention is given to the conservation of mass, momentum and energy at the common 1D/3D interface. For fluid–structure interaction induced by fast-transient phenomena occurring in pipelines, the present 1D/3D fluid coupling is also associated with a beam/shell elements coupling to deal with the mechanical pipe behavior. A series of test-cases involving both purely fluid, purely structural and coupled fluid–structure problems with available analytical or experimental references is considered to demonstrate the performance of the present 1D/3D coupling.

Computer Methods in Applied Mechanics and Engineering, 2019

A novel Finite-Volume scheme for the numerical computations of compressible two-phase flows in pi... more A novel Finite-Volume scheme for the numerical computations of compressible two-phase flows in pipelines is proposed for the fully non-equilibrium Baer-Nunziato model. The present FV approach is the extension of the method proposed in [1] in the context of the Euler equations to the Baer-Nunziato model. In addition, proper approximations of the non-conservative terms are proposed to consider jumps of volume fraction as well as jumps of cross-section in order to respect uniform pressure and velocity profiles preservation. In particular, focus is given to the numerical treatment of abrupt changes in area and to networks wherein several pipelines are connected at junctions. The proposed method makes it possible to avoid the use of an iterative procedure for the solution of the junction problem. The present approach can also deal with general Equations Of State. In addition, the fluid-structure interaction of compressible fluid flowing in flexible pipes is also considered. The proposed scheme is then assessed on a variety of shock-tubes and other transient flow problems and experiments demonstrating its capability to resolve such problems efficiently, accurately and robustly.

Journal of Fluids and Structures, 2018

Water-hammer with column-separation induced by cavitation is investigated numerically. The vapor-... more Water-hammer with column-separation induced by cavitation is investigated numerically. The vapor-water flow is modeled using the Homogeneous Equilibrium Model in conjunction with the 1984 NBS/NRC Steam Tables. The discretization is done with the quasi 1-D Finite-Volume approach recently developed by the authors for compressible flows in pipelines. The ability of the present approach to tackle cavitating flows is first assessed. Then, comparisons with experimental results of water-hammer with column-separation demonstrate consistency with the present computations. Based on the obtained numerical results, focus is given to the dynamics of the liquid column-separation and to the associated physics such as cavitation, vapor growth and collapse, generation of the secondary waterhammer peak and the interaction of the primary and secondary pressure waves. The influence of the initial flow velocity before valve closure on the duration and size of the cavity and on the magnitude of the secondary water-hammer is examined.

Computers & Fluids, 2020

A low-diffusion self-adaptive flux-vector splitting method is presented for the Euler equations. ... more A low-diffusion self-adaptive flux-vector splitting method is presented for the Euler equations. The flux-vector is here split into convective and acoustic parts following the formulation recently proposed by the authors. This procedure is based on the Zha-Bilgen (or previously Baraille et al. for the Euler barotropic system) approach enriched by a dynamic flow-dependent splitting parameter based on the local Mach number. As a consequence, in the present self-adaptive splitting, the convective and acoustic parts decouple in the low-Mach number regime whereas the complete Euler equations are considered for the sonic and highly subsonic regimes. The low diffusive property of the present scheme is obtained by adding anti-diffusion terms to the momentum and the energy components of the pressure flux in the acoustic part of the present splitting. This treatment results from a formal invariance principle preserving the discrete incompressible phase space through the pressure operator. Numerical results for several carefully chosen one-and two-dimensional test problems are finally investigated to demonstrate the accuracy and robustness of the proposed scheme for a wide variety of configurations from subsonic to highly subsonic flows.

Journal of Computational and Applied Mathematics, 2018

The method presented below focuses on the numerical approximation of the Euler compressible syste... more The method presented below focuses on the numerical approximation of the Euler compressible system. It pursues a twofold objective: being able to accurately follow slow material waves as well as strong shock waves in the context of low Mach number flows. The resulting implicit-explicit fractional step approach leans on a dynamic splitting designed to react to the time fluctuations of the maximal flow Mach number. When the latter rises suddenly, the IMEX scheme, so far driven by a material-wave Courant number, turn into a time-explicit approximate Riemann solver constrained by an acoustic-wave Courant number. It is also possible to enrich the dynamic splitting in order to capture high pressure jumps even when the flow Mach number is low. One-dimensional low Mach number test cases involving single or multiple waves confirm that the present approach is as accurate and efficient as an IMEX Lagrange-Projection method. Besides, numerical results suggest that the stability of the present method holds for any Mach number if the Courant number related to the convective subsystem arising from the splitting is of order unity.

Finite Volumes for Complex Applications VIII - Hyperbolic, Elliptic and Parabolic Problems, 2017

In steady-state regimes, water circulating in the nuclear power plants pipes behaves as a low Mac... more In steady-state regimes, water circulating in the nuclear power plants pipes behaves as a low Mach number flow. However, when steep phenomena occur, strong shock waves are produced. Herein, a fractional step approach allowing to decouple the convective from the acoustic effects is proposed. The originality is that the splitting between these two parts of the physics evolves dynamically in time according to the Mach number. The first one-dimensional explicit and implicit numerical results on a wide panel of Mach numbers show that this approach is as accurate and CPU-consuming as a state of the art Lagrange-Projection-type method.

The computation of compressible two-phase flows with the Baer-Nunziato model is addressed. Only t... more The computation of compressible two-phase flows with the Baer-Nunziato model is addressed. Only the convective part of the model that exhibits non-conservative products is considered and the source terms of the model that represent the exchange between phases are neglected. Based on the solver proposed by Tokareva & Toro [42], a new HLLC-type Riemann solver is built. The key idea of this new solver lies in an approximation of the two-phase contact discontinuity of the model. Thus the Riemann invariants of the wave are approximated in the "subsonic" case. A major consequence of this approximation is that the resulting solver can deal with any Equation of State. It also allows to bypass the resolution of a non-linear equation based on those Riemann invariants. We assess the solver and compare it with others on 1D Riemann problems including grid convergence and efficiency studies. The ability of the proposed solver to deal with complex Equations Of State is also investigated....

Small Specimen Test Techniques: Fourth Volume

Claude Sainle Catherine,&#x27;Christophe Poussard,&#x27;Julie Vodinh,&#x2... more Claude Sainle Catherine,&#x27;Christophe Poussard,&#x27;Julie Vodinh,&#x27;Roland Schill, 1 Nicolas Hourdequin, 1 Pascal Galon2 and Pierre Forget1 Finite Element Simulations and Empirical Correlation for Charpy-V and Subsize Charpy Tests on an Unirradiated Low-Alloy RPV Ferritic Steel ...

ESAIM: Mathematical Modelling and Numerical Analysis, 2018

Herein, a Mach-sensitive fractional step approach is proposed for Euler-like systems. The key ide... more Herein, a Mach-sensitive fractional step approach is proposed for Euler-like systems. The key idea is to introduce a time-dependent splitting which dynamically decouples convection from acoustic phenomenon following the fluctuations of the flow Mach number. By doing so, one seeks to maintain the accuracy of the computed solution for all Mach number regimes. Indeed, when the Mach number takes high values, a time-explicit resolution of the overall Euler-like system is entirely performed in one of the present splitting step. On the contrary, in the low-Mach number case, convection is totally separated from the acoustic waves production. Then, by performing an appropriate correction on the acoustic step of the splitting, the numerical diffusion can be significantly reduced. A study made on both convective and acoustic subsystems of the present approach has revealed some key properties as hyperbolicity and positivity of the density and internal energy in the case of an ideal gas thermody...

Journal of Fluids and Structures

Abstract The present paper is dedicated to the simulation of fast transient phenomena involving m... more Abstract The present paper is dedicated to the simulation of fast transient phenomena involving multi-component flows with fluid–structure interaction and ALE grid motion, where the fluid interfaces are tracked using the VOFIRE anti-dissipative scheme for unstructured meshes. It introduces an extension of the existing scheme in EUROPLEXUS software, written for liquid–gas flows only, to handle a combination of stiffened gases as equations of state for the fluid components, thus increasing its genericity and overcoming some limitations, at the cost of significantly modifying its implementation. The proposed methodology is proven to achieve its goals through validation examples with fluid only, such as the sloshing of a liquid in a decelerated tank or a gas–gas interaction with Richtmyer–Meshkov instability. Two large scale three-dimensional examples with full fluid–structure interaction are then provided to fully demonstrate the capabilities and the robustness of the complete proposed computational framework.