The Experts below are selected from a list of 234 Experts worldwide ranked by ideXlab platform
Serafim Kalliadasis - One of the best experts on this subject based on the ideXlab platform.
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Boundary Layer Approximation
2012Co-Authors: Serafim Kalliadasis, Christian Ruyerquil, Benoit Scheid, Manuel G VelardeAbstract:We derive the Boundary-Layer equations for falling liquid films. The assumptions used in their derivation are similar in spirit to those in the classical Boundary-Layer theory in aerodynamics. The key in their derivation is the elimination of the pressure by integrating the y-component of the momentum equation where the inertia terms are neglected while at the same time maintaining the inertia terms in the x- and z-components of the momentum equation. We introduce the “Shkadov scaling,” which makes apparent the balance between all forces necessary to sustain strongly nonlinear waves, and we show that the speed of single-hump solitary waves for an isothermal film shows a steep increase as a function of the Shkadov parameter δ, precisely at δ≃1 which then demarcates two distinct flow regimes: the “drag-gravity regime” where δ is small and the “drag-inertia” regime where δ=O(1). Finally, we summarize the different levels of Approximations utilized in the description of the falling film problem and the different scalings.
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dynamics of a reactive falling film at large peclet numbers ii nonlinear waves far from criticality integral Boundary Layer Approximation
Physics of Fluids, 2004Co-Authors: P M J Trevelyan, Serafim KalliadasisAbstract:We consider the dynamics of a reactive falling film far from criticality. Our analysis is based on the integral-Boundary-Layer (IBL) Approximation of the equations of motion, energy and concentration, and associated free-surface Boundary conditions. We develop a hierarchy of IBL models starting from a simplified Shkadov approach to large IBL systems based on high-order Galerkin projections. We show that these high-order models correct the deficiencies of Shkadov’s approach and predict correctly all relevant quantities including the critical Reynolds number. We also numerically construct nonlinear solutions of the solitary wave type for a simplified Shkadov Approximation and we show that unlike the long-wave theory in Paper I which leads to branch multiplicity and limit points as well as points where the solitary wave solution branches terminate, the IBL model predicts the existence of solitary waves for all Reynolds numbers.
Igorm Boiko - One of the best experts on this subject based on the ideXlab platform.
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chattering in sliding mode control systems with Boundary Layer Approximation of discontinuous control
International Journal of Systems Science, 2013Co-Authors: Igorm BoikoAbstract:It has been a widely accepted notion that Approximation of discontinuous control by certain continuous function in a Boundary Layer results in chattering elimination in sliding mode control systems. It is shown through three different types of analysis that in the presence of parasitic dynamics, this approach to chattering elimination would work only if the slope of the continuous nonlinear function within the Boundary Layer is low enough, which may result in the deterioration of performance of the system. A few examples are provided. An approach to robust stability of linear systems from the consideration of the saturating control is proposed.
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ACC - Analysis of chattering in sliding mode control systems with continuous Boundary Layer Approximation of discontinuous control
Proceedings of the 2011 American Control Conference, 2011Co-Authors: Igorm BoikoAbstract:It has been a widely accepted notion that Approximation of discontinuous control by certain continuous function in a Boundary Layer results in chattering elimination in sliding mode (SM) control systems. It is shown through three different types of analysis that in the presence of parasitic dynamics, this approach to chattering elimination would work only if the slope of the continuous nonlinear function within the Boundary Layer is low enough, which may result in the deterioration of performance of the system. A few examples are provided.
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Analysis of chattering in sliding mode control systems with continuous Boundary Layer Approximation of discontinuous control
Proceedings of the 2011 American Control Conference, 2011Co-Authors: Igorm BoikoAbstract:It has been a widely accepted notion that Approximation of discontinuous control by certain continuous function in a Boundary Layer results in chattering elimination in sliding mode (SM) control systems. It is shown through three different types of analysis that in the presence of parasitic dynamics, this approach to chattering elimination would work only if the slope of the continuous nonlinear function within the Boundary Layer is low enough, which may result in the deterioration of performance of the system. A few examples are provided.
Peter A. Taylor - One of the best experts on this subject based on the ideXlab platform.
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Development of a non-linear mixed spectral finite difference model for turbulent Boundary-Layer flow over topography
Boundary-Layer Meteorology, 1994Co-Authors: Dapeng Xu, Keith W. Ayotte, Peter A. TaylorAbstract:Further development of the non-linear mixed spectral finite difference (NLMSFD) model of turbulent Boundary-Layer flow over topography is documented. This includes modifications and refinements to the solution procedure, the incorporation of second-order turbulence closures to the model and the three-dimensional extension of the model. Based on these higher order closures, linear limitations, Boundary-Layer Approximation and non-linear effects are discussed. The impact of different turbulence closures on the prediction of the NLMSFD model is also demonstrated. Furthermore, sample results for 3D idealized topography (sinusoidal) are presented. The parameterization of drag over small-scale topography is also addressed.
Syed Tauseef Mohyuddin - One of the best experts on this subject based on the ideXlab platform.
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effect of joule heating and mhd in the presence of convective Boundary condition for upper convected maxwell fluid through wall jet
Journal of Molecular Liquids, 2017Co-Authors: Zulfiqar Ali Zaidi, Syed Tauseef MohyuddinAbstract:Abstract In the present study, the Boundary-Layer flow of an incompressible upper convected Maxwell fluid through a vertical slit is considered. In addition, the convected Boundary condition is applied for the analysis of heat transfer. To attain more insight of the heat transfer problem, the effect of joule heating is also taken into account. Also, for controlled type of flow, a magnetic field is applied along the y -axis. A reduced form of ordinary differential equations is obtained by applying the Boundary-Layer Approximation theory and similarity transformation. The results are obtained using the numerical Runge–Kutta method coupled with the shooting method. From the investigation, we conclude that the Biot number, magnetic parameter, and β values play important roles in increasing the temperature and controlling the fluid velocity through a wall jet, whereas, higher values of local Eckert number to increase the thickness of thermal Boundary Layer.
Olaf Deutschmann - One of the best experts on this subject based on the ideXlab platform.
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Optimization of Reactive Flows in a Single Channel of a Catalytic Monolith: Conversion of Ethane to Ethylene
Reactive Flows Diffusion and Transport, 2007Co-Authors: H. G. Bock, S. Körkel, Hai Do Minh, Johannes P. Schlöder, Lubow Maier, Olaf Deutschmann, Steffen TischerAbstract:We discuss the modeling, simulation, and, for the first time, optimization of the reactive flow in a channel of a catalytic monolith with detailed chemistry. We use Boundary Layer Approximation to model the process and obtain a high dimensional PDE. We discuss numerical methods based on the efficient solution of high dimensional stiff DAEs arising from spatial semi-discretization and SQP method for the optimal control problem parameterized by the direct approach. We have investigated the application of conversion of ethane to ethylene which involves a complex reaction scheme for gas phase and surface chemistry. Our optimization results show that the maximum yield, an improvement of a factor of two, is achieved for temperatures around 1300 K.
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transient three dimensional simulations of a catalytic combustion monolith using detailed models for heterogeneous and homogeneous reactions and transport phenomena
Catalysis Today, 2001Co-Authors: Steffen Tischer, Chrys Correa, Olaf DeutschmannAbstract:Abstract The application of a newly developed computational tool, DETCHEMMONOLITH, for the transient two- and three-dimensional simulation of catalytic combustion monoliths is presented. The simulation is based on the coupling of a transient 2D/3D heat balance of the solid monolith structure with steady-state calculations of the reactive flow in a representative number of channels. The two-dimensional single-channel model uses a Boundary-Layer Approximation including detailed models for heterogeneous and homogeneous reactions as well as transport phenomena. As an example, the computational tool is applied to study the hydrogen-assisted catalytic combustion of methane in a platinum-coated honeycomb monolith.
