762 research outputs found


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    京都大学新制・課程博士博士(医学)甲第24832号医博第5000号新制||医||1067(附属図書館)京都大学大学院医学研究科医学専攻(主査)教授 武藤, 学, 教授 今中, 雄一, 教授 阪上, 優学位規則第4条第1項該当Doctor of Medical ScienceKyoto UniversityDGA

    On the sets of maximum points for generalized Takagi functions

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    Let φ be a continuous and periodic function on ℝ with period 1 and φ(0)=0. We consider the generalized Takagi function ƒφ defined by ƒφ(x)=Σ[n=0,∞]1/2ⁿφ(2ⁿx) and the set Mᵩ of maximum points of ƒᵩ in the interval [0,1]. When φ₀(x) is the function defined by the distance from x to the nearest integer, ƒᵩ₀ is just the Takagi function. Our aim is to seek a condition on φ in order that Mᵩ⊂Mᵩ₀

    Fast Marching Method with Multiphase Flow and Compositional Effects

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    In current petroleum industry, there is a lack of effective reservoir simulators for modeling shale and tight sand reservoirs. An unconventional resource modeling requires an accurate flow characterization of complex transport mechanisms caused by the interactions among fractures, inorganic matrices, and organic rocks. Pore size in shale and tight sand reservoirs typically ranges in nanometers, which results in ultralow permeability (nanodarcies) and a high capillary pressure in the confined space. In such extremely low permeability reservoirs, adsorption/desorption and diffusive flow processes play important roles for a fluid flow behavior in addition to heterogeneity-driven convective flow. In this study, the concept of “Diffusive Time of Flight” (DTOF) is generalized for multiphase and multicomponent flow problems on the basis of the asymptotic theory. The proposed approach consists of two decoupled steps – (1) calculation of well drainage volumes along a propagating ‘peak’ pressure front, and (2) numerical simulation based on the transformed 1-D coordinates. Geological heterogeneities distributed in 3-D space are integrated by tracking the propagation of ‘peak’ pressure front using a “Fast Marching Method” (FMM), and subsequently, the drainage volumes are evaluated along the outwardly propagation contours. A DTOF-based numerical simulation is performed by treating a series of the DTOF as a spatial coordinate. This approach is analogous to streamline simulation, whereby a multidimensional simulation is transformed into 1-D coordinates resulting in substantial savings in computational time, thus allowing for high resolution simulation. However, instead of using a convective time of flight (CTOF), a diffusive time of flight is introduced in the modeling of a pressure front propagation. The overall workflow, which consist of the FMM and numerical simulation, is described in detail for single-phase, two-phase, blackoil, and compositional cases. The model validation is firstly performed on single-porosity systems with and without geological heterogeneity, then extended to multi-continuum domains including dual-porosity fractured reservoir and triple-continuum system. The large-scale unconventional models are finally demonstrated in consideration of the permeability correction for shale gas system and capillarity incorporation for confined phase behavior in multiphase shale oil system

    Flame spread over thin hollow cylindrical fuels in microgravity

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    This work presents experimental study on opposed flow flame spread over thin hollow cylindrical cellulosic fuel of diameters varying from 10 mm to 49 mm in microgravity environment. To understand the effect of flow and geometry on flame spread, experiments are conducted in low convective opposed flow conditions ranging from 10 cm/s to 30 cm/s for both hollow cylindrical and planar fuels at oxygen concentration of 21% and 1 atm pressure. In the microgravity environment the flame length and the flame spread rate are seen to increase with increase in hollow cylindrical fuel diameter over the flow range studied here. The flame spread rate exhibited a non-monotonic trend with flow speed, for flow of large diameter whereas a monotonic increasing trend is noted for small diameters. The flame spread rate over hollow cylindrical fuel is noted to be higher or at most equal compared to planar fuels over the matrix of experiments conducted in this study. A simplified analysis is carried out to arrive at an expression for flame spread rate over thin hollow cylindrical fuels. The analysis shows that the radiation heat transfer from the hot char to the inner surface of hollow virgin fuel dictates flame spread rate trend with fuel diameter of the hollow cylindrical fuels. Higher overall equivalence ratio in the inner section of the hollow fuels is responsible for higher char length in hollow fuels and also influence the flame spread rate for smaller fuel diameters.Comment: 40 pages, 14 figure