1,299 research outputs found
Fluctuation splitting Riemann solver for a non-conservative modeling of shear shallow water flow
No full textInternational audienceIn this paper we propose a fluctuation splitting finite volume scheme for a non-conservative modeling of shear shallow water flow (SSWF). This model was originally proposed by Teshukov (2007) in [14] and was extended to include modeling of friction by Gavrilyuk et al. (2018) in [7]. The directional splitting scheme proposed by Gavrilyuk et al. (2018) in [7] is tricky to apply on unstructured grids. Our scheme is based on the physical splitting in which we separate the characteristic waves of the model to form two different hyperbolic subsystems. The fluctuations associated with each subsystems are computed by developing Riemann solvers for these subsystems in a local coordinate system. These fluctuations enables us to develop a Godunov-type scheme that can be easily applied on mixed/unstructured grids. While the equation of energy conservation is solved along with the SSWF model in Gavrilyuk et al. (2018)[7], in this paper we solve only SSWF model equations. We develop a cell-centered finite volume code to validate the proposed scheme with the help of some numerical tests. As expected, the scheme shows first order convergence. The numerical simulation of 1D roll waves shows a good agreement with the experimental results. The numerical simulations of 2D roll waves show similar transverse wave structures as observed by Gavrilyuk et al. (2018) in [7]
Plotinus on Divine Simplicity
No full textGavrilyuk attends to divine simplicity according to the third-century AD pagan philosopher Plotinus. He shows that Plotinus draws his doctrine of divine simplicity from the earlier Greco-Roman philosophical tradition, in which the nature of the “first principle” was highly contested. Aristotle offers a history of the early debate, with Anaxagoras being the first to glimpse the first principle’s simplicity. The Platonist philosophers conceived of the first principle as incorporeal, and on these grounds linked the first principle to simplicity. For his part, Aristotle associated simplicity with the absoluteness of pure actuality. The Stoics, with their essentially material understanding of the divine, ignored or denied divine simplicity. Plotinus draws upon the reception of Aristotle that is found in Alexander of Aphrodisias, Numenius, and Ammonius. According to Gavrilyuk, the signal contribution of Plotinus consists in setting forth the strongest possible doctrine of divine simplicity. Indeed, for Plotinus God’s utter simplicity means that God cannot even be thought, because thinking requires the duality of subject-object. Plotinus conceives of the divine One as above divine Mind (nous), since the latter contains a unified plurality but not the perfect simplicity that marks the unknowable One. Gavrilyuk ends his essay with an account of the qualifications made to divine simplicity by philosophers and theologians who are less radical in their doctrine than is Plotinus. He emphasizes that the Enneads\u27 key metaphysical insight, utterly ruling out any kind of composition from the One, has the benefit of being supremely intellectually coherent and elegant
Modelling rollers for shallow water flows
No full textHydraulic jumps, roll waves or bores in open channel flows are often treated as singularities by hydraulicians while slowly varying shallow water flows are described by continuous solutions of the Saint-Venant equations. Richard & Gavrilyuk (J. Fluid Mech., vol. 725, 2013, pp. 492–521) have enriched this model by introducing an equation for roller vorticity in a very elegant manner. This new model matches several experimental results that have resisted theoretical approaches for decades. This is the case of the roller of a stationary hydraulic jump as well as the oscillatory instability that the jump encounters when the Froude number is increased. The universality of their approach as well as its convincing comparisons with experimental results open the way for significant progress in the modelling of open channel flows
Rigorous justification of the Favrie-Gavrilyuk approximation to the Serre-Green-Naghdi model
No full textIn v2, minor corrections and additional explanations on the strategy of the proof. To appear in Nonlinearity.International audienceThe (Serre-)Green-Naghdi system is a non-hydrostatic model for the propagation of surface gravity waves in the shallow-water regime. Recently , Favrie and Gavrilyuk (Nonlinearity, 30(7) (2017)) proposed an efficient way of numerically computing approximate solutions to the Green-Naghdi system. The approximate solutions are obtained through solutions of an augmented quasilinear system of balance laws, depending on a parameter. In this work, we provide quantitative estimates showing that any sufficiently regular solution to the Green-Naghdi system is the limit of solutions to the Favrie-Gavrilyuk system as the parameter goes to infinity, provided the initial data of the additional unknowns is well-chosen. The problem is therefore a singular limit related to low Mach number limits with additional difficulties stemming from the fact that both order-zero and order-one singular components are involved
Modern Orthodox Thinkers
No full textThis chapter discusses four general features of modern Orthodox epistemology of theology—ontologism, apophaticism, integral knowledge, and the noetic implications of theosis—and the contributions of individual Orthodox authors, including Berdyaev, Bulgakov, Florensky, Florovsky, Frank, Khomiakov, Lossky, Solovyov, and Zizioulas. Ontologism is a philosophical stance that subordinates epistemology to metaphysics; apophaticism is an attitude towards the mystery of God with implications for theories of religious language, religious experience, and metaphysics; a theory of integral knowledge challenges one-sided epistemologies developed in modernity; and the idea of theosis indicates human participation in the life of God, which has implications for the process of coming to know God. Gavrilyuk highlights the retrieval by Orthodox neopatristic theologians of important pre-modern epistemological insights as well as their contributions to personalism, reliabilism, and social and virtue epistemology that remain unknown in Western scholarly literature.</p
A modular equality for m‐ovoids of elliptic quadrics
No full textAn m-ovoid of a finite polar space P is a set O of points such that every maximal subspace of P contains exactly m points of O. In the case when P is an elliptic quadric Q(-)(2r+ 1, q) of rank r in F-q(2r+2), we prove that an m-ovoid exists only if m satisfies a certain modular equality, which depends on q and r. This condition rules out many of the possible values of r. Previously, only a lower bound on m was known, which we slightly improve as a byproduct of our method. We also obtain a characterization of them-ovoids of Q(-)(7, q) for q = 2 and (m, q) = (4, 3)
Anastasia Semenivna Horbenko, a researcher of the rodent fauna of the Middle Dnipro Region
No full textAnastasia Horbenko (23.05.1937–18.07.2017) was a Ukrainian mammalogist and researcher of rodent ecology. She was born in Cherkasy Oblast. She graduated from
Cherkasy Pedagogical Institute in 1960 and worked there in 1962 to 2011. She earned a degree of Candidate of Biological Sciences. Her main scientific interests were the fauna and ecology of rodents of the Middle Dnipro Region. The topic of her dissertation was the ecology of the little ground squirrel (Spermophilus pygmaeus) and the speckled ground squirrel (S. suslicus) at the intersection of their geographic ranges. She authored nearly forty scientific works
Mathematical and numerical study of hyperelastic and visco-plastic models : applications to hypervelocity impact.
No full textUn modèle mathématique d'interfaces diffuses pour l'interaction de N solides élasto-plastiques a été construit. C'est une extension du modèle développé par Favrie & Gavrilyuk (2012) pour l'interaction d'un fluide et d'un solide. En dépit du grand nombre d'équations présentes dans ce modèle, deux propriétés remarquables ont été démontrées : ce modèle est hyperbolique (quelles que soient les déformations admissibles) et il vérifie le second principe de la thermodynamique. En dépit du grand nombre d'équations présentes dans ce modèle, deux propriétés remarquables ont été démontrées: ce modèle est hyperbolique (quelles que soient les déformations admissibles) et il vérifie le second principe de la thermodynamique. L'énergie interne de chaque solide est prise sous forme séparable: c'est la somme d'une énergie hydrodynamique qui ne dépend que de la densité et de l'entropie, et d'une énergie de cisaillement. L'équation d'état de chaque solide est telle que si nous prenons le module de cisaillement du solide égale à zéro, on retrouve les équations de la mécanique des fluides. Ce modèle permet, en particulier, de:- prédire les déformations de solides élasto-plastiques en petites déformations et en très grandes déformations.- prédire l'interaction d'un nombre arbitraire de solides élasto-plastiqueset de fluides. L'aptitude de ce modèle à résoudre des problèmes complexes a été démontrée. Sans être exhaustif, on peut citer:-le phénomène d'écaillage dans les solides.- La fracturation et la fragmentation dynamique dans les solides.A mathematical model of diffuse interface for the interaction of N elasto-plastic solidS was built. It is an extension of the model developed by Favrie & Gavrilyuk (2012) for a fluid-solid interaction. Despite the large number of equations present in this model, two remarkable properties have been demonstrated: it is hyperbolic for any admissible deformations and satisfies the second principle of thermodynamics. In this model, the internal energy of each solid is taken in separable form: it is the sum of a hydrodynamic energy (which depends only on the density and entropy) and shear energy. The equation of state of each solid is such that if we take the shear modulus of the solid vanishes, we find the equations of fluid mechanics. This model allows, in particular:- predict the deformation of elastic-plastic solids in small and very large deformations.- predict the interaction of an arbitrary number of elasto-plastic solids and fluids.The ability of this model to solve complex problems has been demonstrated. Without being exhaustive, one can mention:- the spall phenomenon in solids.- fracturing and fragmentation in solids
Existence and Stability of Hydraulic Shock Profiles of the Richard-Gavrilyuk Model for Inclined Shallow Water Flow
No full textThis is work in progress. Shared for grant application purposes.We study by a combination of numerical computation and rigorous analysis the existence and stability of hydraulic shock solutions of the Richard-Gavrilyuk model (RG) for inclined shallow water flow, a recently introduced refinement of the industry standard Saint Venant equations (SV) in hydraulic engineering and related fields, obtaining existence and stability diagrams similar to those obtained by Johnson-Noble-Rodrigues-Yang-Zumbrun and Faye-Rodrigues-Yang-Zumbrun for (SV). Under a natural rescaling, the regions of existence are similar, though the demonstration of this fact is surprisingly complicated. On the other hand, the wave profiles can be quite different. The (RG) equations were shown by Richard and Gavrilyuk to correct "overshoot" errors in periodic (SV) traveling-wave profiles, or roll waves, improving practically important estimates on maximum wave height. We show that a similar phenomenon occurs for nonmonotone hydraulic shocks, and give a simple practical method for computing the corrector in the smallbottom vorticity limit relevant to experiments of Brock and others. Similarly, the stability regions agree on most of the parameter domain; however, we find for (RG) an interesting new region of oscillatory instability in the ultra-low bottom vorticity limit, associated with Hopf bifurcation and unstable point spectra rather than convective instability and unstable essential spectra as for (SV)
Paul L. Gavrilyuk, Histoire du catéchuménat dans l’Église ancienne. Trad. du russe par F. Lhoest, N. Mojaïsky et A.-M. Gueit, (Initiations aux Pères de l’Église) Paris, Cerf, 2007
No full textGounelle Rémi. Paul L. Gavrilyuk, Histoire du catéchuménat dans l’Église ancienne. Trad. du russe par F. Lhoest, N. Mojaïsky et A.-M. Gueit, (Initiations aux Pères de l’Église) Paris, Cerf, 2007. In: Revue d'histoire et de philosophie religieuses, 88e année n°3, Juillet-Septembre 2008. pp. 406-407
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