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Multi-Mesh-Scale Approximation of Thin Geophysical Mass Flows on Complex Topographies

Communications in Computational Physics 2021年第1期29卷 148-185页

作者： Yih-Chin Tai Jeaniffer Vides boniface nkonga Chih-Yu Kuo Department of Hydraulic and Ocean Engineering National Cheng Kung UniversityTainanTaiwan LEMMA R&D Services Sophia AntipolisBiotFrance&Maison de la SimulationGif-sur-YvetteFrance Universit́e Cˆote d’Azur(UCA) LJAD Nice&Inria Sophia Antipolis–ḾediterrańeeFrance Research Center for Applied Sciences Academia SinicaTaipeiTaiwan

This paper is devoted to a multi-mesh-scale approach for describing the dynamic behaviors of thin geophysical mass flows on complex *** the topographic surfaces are generally non-trivially curved,we introduce an appropriate local coordinate system for describing the flow behaviors in an efficient *** complex surfaces are supposed to be composed of a finite number of triangle *** to the unequal orientation of the triangular elements,the distinct flux directions add to the complexity of solving the Riemann problems at the boundaries of the triangular ***,a vertex-centered cell system is introduced for computing the evolution of the physical quantities,where the cell boundaries lie within the triangles and the conventional Riemann solvers can be ***,there are two mesh scales:the element scale for the local topographic mapping and the vertex-centered cell scale for the evolution of the physical *** final scheme is completed by employing the HLL-approach for computing the numerical flux at the *** numerical examples and one application to a large-scale landslide are conducted to examine the performance of the proposed approach as well as to illustrate its capability in describing the shallow flows on complex topographies.

关键词： Multi-mesh-scale approach complex topography shallow flows unstructured mesh vertex-centered formulation

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Sharpening Diffuse Interfaces with Compressible Flow Solvers

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Open Journal of Fluid Dynamics 2014年第1期4卷 44-68页

作者： Nicolas Favrie Sergey Gavrilyuk boniface nkonga Richard Saurel Aix-Marseille University Marseille France J.A. Dieudonné Mathematics Lab. University Nice-Sophia Antipolis Nice France

Diffuse interfaces appear with any Eulerian discontinuity capturing compressible flow solver. When dealing with multifluid and multimaterial computations, interfaces smearing results in serious difficulties to fulfil contact conditions, as spurious oscillations appear. To circumvent these difficulties, several approaches have been proposed. One of them relies on multiphase flow modelling of the numerically diffused zone and is based on extended hyperbolic systems with stiff mechanical relaxation (Saurel and Abgrall, 1999 [4], Saurel et al., 2009 [6]). This approach is very robust, accurate and flexible in the sense that many physical effects can be included: surface tension, phase transition, elastic-plastic materials, detonations, granular effects etc. It is also able to deal with dynamic appearance of interfaces. However it suffers from an important drawback when long time evolution is under interest as the interface becomes more and more diffused. The present paper addresses this issue and provides an efficient way to sharpen interfaces. A sharpening flow model is used to correct the solution after each time step. The sharpening process is based on a hyperbolic equation that produces a steady shock in finite time at the interface location. This equation is embedded in a “sharpening multiphase model” redistributing volume fractions, masses, momentum and energy in a consistent way. The method is conservative with respect to the masses, mixture momentum and mixture energy. It results in diffused interfaces sharpened in one or two mesh points. The method is validated on test problems having exact solutions.

关键词： Material Interfaces Multifluid Multiphase Multimaterial Shocks Non-Conservative Hyperbolic Equations

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A Godunov-Type Solver for the Numerical Approximation of Gravitational Flows

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Communications in Computational Physics 2014年第1期15卷 46-75页

作者： J.Vides B.Braconnier E.Audit C.Berthon B.nkonga Inria Maison de la SimulationUSR 3441Gif-sur-YvetteFrance IFP Energies Nouvelles 1-4 avenue de Bois-Préau92852 Rueil-MalmaisonFrance CEA Maison de la SimulationUSR 3441Gif-sur-YvetteFrance. Univ.of Nantes Lab.J.LerayUMR CNRS 6629NantesFrance. Univ.of Nice-Sophia Antipolis Lab.J.A.DieudonnéUMR CNRS 7351NiceFrance. Inria Sophia Antipolis BP.93F-06902 Sophia Antipolis CedexFrance.

We present a new numerical method to approximate the solutions of an Euler-Poisson model,which is inherent to astrophysical flows where gravity plays an important *** propose a discretization of gravity which ensures adequate coupling of the Poisson and Euler equations,paying particular attention to the gravity source term involved in the latter *** order to approximate this source term,its discretization is introduced into the approximate Riemann solver used for the Euler equations.A relaxation scheme is involved and its robustness is *** method has been implemented in the software HERACLES[29]and several numerical experiments involving gravitational flows for astrophysics highlight the scheme.

关键词： Euler-Poisson equations approximate Riemann solver relaxation scheme source terms gravitational effects.

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Determination of Major Carotenoids in Processed Tropical Leafy Vegetables Indigenous to Africa

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Food and Nutrition Sciences 2011年第8期2卷 793-802页

作者： Viviane nkonga Djuikwo Djuikwo Richard Aba Ejoh Inocent Gouado Carl Moses Mbofung Sherry A. Tanumihardjo 不详

Tropical leafy-vegetables (n = 21) indigenous to Cameroon, Africa, were collected, processed, and analyzed for carotenoids by HPLC. The processing techniques used were oven drying;sun-drying;squeeze-washing and boiling;and a combination of boiling in alkaline salt and squeeze-washing. Carotenoids included lutein, α-carotene, zeaxanthin, β-cryptoxanthin, and β-carotene (all-trans, 13-cis, and 9-cis), which varied by species (P 40% of total carotenoids. Traditional preparation and processing procedures led to significant losses of carotenoids and β-carotene was most affected during sun-drying with a maximum of 73.8% loss observed in A. acanthochiton.

关键词： Carotenoids Processing Vegetables Vitamin A Component

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