On the Numerical Prediction of Interfacial Instabilities in Shear Flows (Keynote)

2007 ◽  
Author(s):  
Robert Nourgaliev ◽  
Meng-Sing Liou ◽  
Theo Theofanous
Keyword(s):  
State Of The Art ◽  
Numerical Prediction ◽  
Viscous Fluids ◽  
Convergence Properties ◽  
Interfacial Instabilities ◽  
Diffuse Interfaces ◽  
Sharp Interfaces ◽  
Interface Treatment ◽  
Layered Flows ◽  
Resolution Requirements

We assess the state of the art in numerical prediction of interfacial instabilities due to shear in layered flows of viscous fluids. Basic ingredients of this assessment include linear stability analysis results for both miscible (diffuse) and immiscible (sharp) interfaces, the physics and resolution requirements of the critical layer, and convergence properties of the relevant numerical schemes. Behaviors of physically and numerically diffuse interfaces are contrasted and the case for a sharp interface treatment for reliable predictions of this class of flows is made.

scholarly journals Synthesis and catalytic applications of combined zeolitic/mesoporous materials

2011 ◽  
Vol 2 ◽  
pp. 785-801 ◽  
Author(s):  
Jarian Vernimmen ◽  
Vera Meynen ◽  
Pegie Cool
Keyword(s):  
Catalytic Activity ◽  
Mesoporous Materials ◽  
State Of The Art ◽  
Nanoporous Materials ◽  
The State ◽  
Viscous Fluids ◽  
Formation Mechanisms ◽  
Enhanced Diffusion ◽  
Redox Catalysts ◽  
Catalytic Applications

In the last decade, research concerning nanoporous siliceous materials has been focused on mesoporous materials with intrinsic zeolitic features. These materials are thought to be superior, because they are able to combine (i) the enhanced diffusion and accessibility for larger molecules and viscous fluids typical of mesoporous materials with (ii) the remarkable stability, catalytic activity and selectivity of zeolites. This review gives an overview of the state of the art concerning combined zeolitic/mesoporous materials. Focus is put on the synthesis and the applications of the combined zeolitic/mesoporous materials. The different synthesis approaches and formation mechanisms leading to these materials are comprehensively discussed and compared. Moreover, Ti-containing nanoporous materials as redox catalysts are discussed to illustrate a potential implementation of combined zeolitic/mesoporous materials.

scholarly journals Hybrid Selection Based Multi/Many-Objective Evolutionary Algorithm

2021 ◽  
Author(s):  
Saykat Dutta ◽  
Rammohan Mallipeddi ◽  
Kedar Nath Das
Keyword(s):  
Pareto Front ◽  
State Of The Art ◽  
Superior Performance ◽  
Selection Strategy ◽  
Convergence Properties ◽  
Pareto Dominance ◽  
Advantages And Disadvantages ◽  
Environmental Selection ◽  
Hybrid Selection ◽  
Test Suites

Abstract In the last decade, numerous Multi/Many-Objective Evolutionary Algorithms (MOEAs) have been proposed to handle Multi/Many-Objective Problems (MOPs) with challenges such as discontinuous Pareto Front (PF), degenerate PF, etc. MOEAs in the literature can be broadly divided into three categories based on the selection strategy employed such as dominance, decomposition, and indicator-based MOEAs. Each category of MOEAs have their advantages and disadvantages when solving MOPs with diverse characteristics. In this work, we propose a Hybrid Selection based MOEA, referred to as HS-MOEA, which is a simple yet effective hybridization of dominance, decomposition and indicator-based concepts. In other words, we propose a new environmental selection strategy where the Pareto-dominance, reference vectors and an indicator are combined to effectively balance the diversity and convergence properties of MOEA during the evolution. The superior performance of HS-MOEA compared to the state-of-the-art MOEAs is demonstrated through experimental simulations on DTLZ and WFG test suites with up to 10 objectives.

scholarly journals On a nonlocal Cahn–Hilliard model permitting sharp interfaces

2021 ◽  
pp. 1-38
Author(s):  
Olena Burkovska ◽  
Max Gunzburger
Keyword(s):  
Inequality Constraints ◽  
Coupled System ◽  
Energy Functional ◽  
Sharp Interface ◽  
Nonlocal Model ◽  
Weak Formulation ◽  
Diffuse Interfaces ◽  
Spatial Dimensions ◽  
Pure Phases ◽  
Sharp Interfaces

A nonlocal Cahn–Hilliard model with a non-smooth potential of double-well obstacle type that promotes sharp interfaces in the solution is presented. To capture long-range interactions between particles, a nonlocal Ginzburg–Landau energy functional is defined which recovers the classical (local) model as the extent of nonlocal interactions vanish. In contrast to the local Cahn–Hilliard problem that always leads to diffuse interfaces, the proposed nonlocal model can lead to a strict separation into pure phases of the substance. Here, the lack of smoothness of the potential is essential to guarantee the aforementioned sharp-interface property. Mathematically, this introduces additional inequality constraints that, in a weak formulation, lead to a coupled system of variational inequalities which at each time instance can be restated as a constrained optimization problem. We prove the well-posedness and regularity of the semi-discrete and continuous in time weak solutions, and derive the conditions under which pure phases are admitted. Moreover, we develop discretizations of the problem based on finite element methods and implicit–explicit time-stepping methods that can be realized efficiently. Finally, we illustrate our theoretical findings through several numerical experiments in one and two spatial dimensions that highlight the differences in features of local and nonlocal solutions and also the sharp interface properties of the nonlocal model.

Linear Stability of Sharp and Diffuse Interfaces Under Shear

2007 ◽  
Author(s):  
Theo Theofanous ◽  
Svetlana Sushchikh ◽  
Robert Nourgaliev
Keyword(s):  
Shear Flow ◽  
Linear Stability ◽  
Immiscible Fluids ◽  
Diffuse Interfaces ◽  
Sharp Interfaces

We show that diffuse interfaces in shear flow are prone to instabilities that are of the same origin and character as the Yih-instability (for sharp interfaces between immiscible fluids). We also show that the development of these “Yih-like” instabilities towards “Yih” is monotonic, and that the agreement with Yih becomes quantitative as the limits of zero thickness and no-diffusion are approached.

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