scholarly journals Robin fractional problems with symmetric variable growth

2020 ◽  
Vol 61 (10) ◽  
pp. 101503
Author(s):  
Anouar Bahrouni ◽  
Vicenţiu D. Rădulescu ◽  
Patrick Winkert
Keyword(s):  
Symmetric Variable

scholarly journals Variable-Order Fractional Models for Wall-Bounded Turbulent Flows

Entropy ◽  
2021 ◽  
Vol 23 (6) ◽  
pp. 782
Author(s):  
Fangying Song ◽  
George Em Karniadakis
Keyword(s):  
Fractional Derivative ◽  
Turbulent Flows ◽  
Fractional Order ◽  
Variable Order ◽  
Universal Curve ◽  
Reynolds Stresses ◽  
Continuous Change ◽  
Mean Velocity ◽  
Symmetric Variable ◽  
Fractional Models

Modeling of wall-bounded turbulent flows is still an open problem in classical physics, with relatively slow progress in the last few decades beyond the log law, which only describes the intermediate region in wall-bounded turbulence, i.e., 30–50 y+ to 0.1–0.2 R+ in a pipe of radius R. Here, we propose a fundamentally new approach based on fractional calculus to model the entire mean velocity profile from the wall to the centerline of the pipe. Specifically, we represent the Reynolds stresses with a non-local fractional derivative of variable-order that decays with the distance from the wall. Surprisingly, we find that this variable fractional order has a universal form for all Reynolds numbers and for three different flow types, i.e., channel flow, Couette flow, and pipe flow. We first use existing databases from direct numerical simulations (DNSs) to lean the variable-order function and subsequently we test it against other DNS data and experimental measurements, including the Princeton superpipe experiments. Taken together, our findings reveal the continuous change in rate of turbulent diffusion from the wall as well as the strong nonlocality of turbulent interactions that intensify away from the wall. Moreover, we propose alternative formulations, including a divergence variable fractional (two-sided) model for turbulent flows. The total shear stress is represented by a two-sided symmetric variable fractional derivative. The numerical results show that this formulation can lead to smooth fractional-order profiles in the whole domain. This new model improves the one-sided model, which is considered in the half domain (wall to centerline) only. We use a finite difference method for solving the inverse problem, but we also introduce the fractional physics-informed neural network (fPINN) for solving the inverse and forward problems much more efficiently. In addition to the aforementioned fully-developed flows, we model turbulent boundary layers and discuss how the streamwise variation affects the universal curve.

scholarly journals Regional Competitiveness in Fresh Produce Markets: Exploring Seasonal Dynamics and the Role of Energy Costs in Apple Markets

2014 ◽  
Vol 43 (3) ◽  
pp. 357-372
Author(s):  
Wenjing Hu ◽  
Dawn Thilmany McFadden ◽  
Dustin L. Pendell
Keyword(s):  
Fresh Produce ◽  
Key Factors ◽  
Regional Competitiveness ◽  
Market Conditions ◽  
Variable Threshold ◽  
Threshold Autoregressive ◽  
Threshold Autoregressive Model ◽  
Regional Markets ◽  
Symmetric Variable ◽  
The Impact

The fresh produce sector is subject to season-specific market conditions so understanding differential impacts of various factors across marketing periods is important. We analyze the market structure, key factors influencing shipments, and seasonal price relationships in regional apple markets at the shipping-point and terminal-market levels using a symmetric variable threshold autoregressive model that allows threshold bands (which define price ranges considered in shipping decisions) to vary seasonally. We find that transportation costs and seasonality have a significant impact on threshold bands of market pairs and that the impact varies seasonally. This varying band across seasons may represent suppliers who perceive more or less opportunities to adjust their supply between regional markets and gain advantage by being responsive to market conditions.

Isospectral sets for transmission eigenvalue problem

2020 ◽  
Vol 28 (1) ◽  
pp. 63-69 ◽  
Author(s):  
Chuan-Fu Yang ◽  
Sergey A. Buterin
Keyword(s):  
Wave Equation ◽  
Eigenvalue Problem ◽  
Wave Speed ◽  
Spherically Symmetric ◽  
Variable Speed ◽  
Transmission Eigenvalues ◽  
Constructive Methods ◽  
Transmission Eigenvalue ◽  
Symmetric Variable ◽  
Transmission Eigenvalue Problem

AbstractWe consider the boundary value problem {R(a,q)}: {-y^{\prime\prime}(x)+q(x)y(x)=\lambda y(x)} with {y(0)=0} and {y(1)\cos(a\sqrt{\lambda})=y^{\prime}(1)\frac{\sin(a\sqrt{\lambda})}{\sqrt{% \lambda}}}. Motivated by the previous work [T. Aktosun and V. G. Papanicolaou, Reconstruction of the wave speed from transmission eigenvalues for the spherically symmetric variable-speed wave equation, Inverse Problems 29 2013, 6, Article ID 065007], it is natural to consider the following interesting question: how does one characterize isospectral sets corresponding to problem {R(1,q)}? In this paper applying constructive methods we answer the above question.

Global bounded variation solutions describing Fanno–Rayleigh fluid flows in nozzles

2018 ◽  
Vol 28 (06) ◽  
pp. 1135-1169 ◽  
Author(s):  
Shih-Wei Chou ◽  
John M. Hong ◽  
Bo-Chih Huang ◽  
Reyna Quita
Keyword(s):  
Global Existence ◽  
Bounded Variation ◽  
Wave Interaction ◽  
Initial Boundary ◽  
Initial Boundary Value Problem ◽  
Quantitative Relation ◽  
Riemann Solutions ◽  
Glimm Scheme ◽  
Symmetric Variable ◽  
Initial Boundary Value

In this paper, we investigate the initial-boundary value problem of compressible Euler equations including friction and heating that model the transonic Fanno–Rayleigh flows through symmetric variable area nozzles. In particular, the case of contracting nozzles is considered. A new version of a generalized Glimm scheme (GGS) is presented for establishing the global existence of entropy solutions with bounded variation. Modified Riemann and boundary Riemann solutions are applied to design this GGS, which is constructed using the contraction matrices acting on the homogeneous Riemann (or boundary-Riemann) solutions. The extended Glimm–Goodman’s type of wave interaction estimates are investigated to determine the stability of the scheme and the positivity of gas velocity that results in the existence of the weak solution. The limit of approximation solutions serves as an entropy solution. Moreover, a quantitative relation between the shape of the nozzle, friction, and heat is proposed for the global existence result in the contracting nozzle. Numerical simulations of the contraction-expansion and expansion-contraction nozzles are presented to validate the scheme.

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