共查询到20条相似文献,搜索用时 187 毫秒
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Because of the presence of corner eddies that change in number and pattern the lid-driven cavity problem has been found suitable to study various aspects of the performance of solution algorithms for incompressible viscous flows. It retains all the difficult flow physics and is characterized by a large primary eddy at the centre and secondary eddies located near the cavity corners. In this work, lid-driven cavity flow is simulated by lattice Boltzmann method with single-relaxation-time and it is compared with those by lattice Boltzmann method with multi-relaxation-time and finite difference method. The effects of the Reynolds number on the size, centre position and number of vortices are studied in detail together with the flow pattern in the cavity. The close agreement of the results bears testimony to the validity of this relatively new approach. However lattice Boltzmann method with multi-relaxation-time model is seen to remove the difficulties faces by the lattice Boltzmann method with single-relaxation-time at higher Reynolds numbers. 相似文献
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S. P. Nair P. M. Pardalos V. A. Yatsenko 《Journal of Optimization Theory and Applications》2007,134(3):533-547
In this paper, we analyze various control algorithms that have been proposed for controlling spatiotemporal chaos in a globally
coupled map lattice (CML) system. We reformulate the choice of feedback parameters in such systems as a constrained optimization
problem and provide numerical and experimental results on the choice of optimal parameters for controlling the mean global
Lyapunov exponent of a lattice. Finally, we propose a scheme to use this optimization technique to solve a learning problem
in which such a CML system can be used to emulate the dynamics of an epileptic brain.
This work was supported by NIH-NIBIB and CRDF grants. 相似文献
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In a work by L. Fuchs, W. Heinzer and B. Olberding, a decomposition of ideals in a commutative ring as intersections of primal
isolated component ideals is investigated. In subsequent work by L. Fuchs and R. Reis, these ideas are developed in multiplicative
lattices. The object of this note is to point out that, when specialized to the lattice of ideals of a commutative ring, the
decomposition of L. Fuchs and R. Reis does not give the decomposition obtained in the paper by Fuchs, Heinzer and Olberding,
and to give two variations of the decomposition of Fuchs and Reis. One of these variations, when specialized to the lattice
of ideals of a ring, does give the decomposition obtained by Fuchs, Heinzer and Olberding, and the other one gives a decomposition
which is superior in some ways.
Received December 2, 2004; accepted in final form February 17, 2005. 相似文献
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We consider the problem of increasing the threshold parameter of a secret-sharing scheme after the setup (share distribution) phase, without further communication between the dealer and the shareholders. Previous solutions to this problem require one to start off with a non-standard scheme designed specifically for this purpose, or to have secure channels between shareholders. In contrast, we show how to increase the threshold parameter of the standard CRT secret-sharing scheme without secure channels between the shareholders. Our method can thus be applied to existing CRT schemes even if they were set up without consideration to future threshold increases.Our method is a positive cryptographic application for lattice reduction algorithms, and we also use techniques from lattice theory (geometry of numbers) to prove statements about the correctness and information-theoretic security of our constructions. 相似文献
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Lattice Boltzmann method for slip flow heat transfer in circular microtubes: Extended Graetz problem
Sheng Chen 《Applied mathematics and computation》2010,217(7):3314-3320
Slip flow heat transfer in circular microtubes is of fundamental interest and practical importance. However, to the best knowledge of the present author, there is no open publication of developing simple and efficient lattice Boltzmann (LB) models on such topic. To bridge the gap, in this paper a simple LB model, which is based on our recent work [S. Chen, J. Tölke, M. Krafczyk, Simulation of buoyancy-driven flows in a vertical cylinder using a simple lattice Boltzmann model, Phys. Rev. E 79 (2009) 016704], is designed. In addition, the recently developed Langmuir slip model [S. Chen, Z.W. Tian, Simulation of thermal micro-flow using lattice Boltzmann method with Langmuir slip model, Int. J. Heat Fluid Flow 31 (2010) 227-235], which possesses a clear physical picture and keeps the Reynolds analogy, is extended to capture velocity slip as well as temperature jump in microtubes. The feasibility and capability of the present model are validated by the extended Graetz problem, which is a benchmark prototype for forced convection heat transfer in circular microtubes. 相似文献
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《Communications in Nonlinear Science & Numerical Simulation》2014,19(10):3570-3590
We present a coupled lattice Boltzmann method (LBM) to solve a set of model equations for electrokinetic flows in micro-/nano-channels. The model consists of the Poisson equation for the electrical potential, the Nernst–Planck equation for the ion concentration, and the Navier–Stokes equation for the flows of the electrolyte solution. In the proposed LBM, the electrochemical migration and the convection of the electrolyte solution contributing to the ion flux are incorporated into the collision operator, which maintains the locality of the algorithm inherent to the original LBM. Furthermore, the Neumann-type boundary condition at the solid/liquid interface is then correctly imposed. In order to validate the present LBM, we consider an electro-osmotic flow in a slit between two charged infinite parallel plates, and the results of LBM computation are compared to the analytical solutions. Good agreement is obtained in the parameter range considered herein, including the case in which the nonlinearity of the Poisson equation due to the large potential variation manifests itself. We also apply the method to a two-dimensional problem of a finite-length microchannel with an entry and an exit. The steady state, as well as the transient behavior, of the electro-osmotic flow induced in the microchannel is investigated. It is shown that, although no external pressure difference is imposed, the presence of the entry and exit results in the occurrence of the local pressure gradient that causes a flow resistance reducing the magnitude of the electro-osmotic flow. 相似文献
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Ralph Freese 《Order》1987,3(4):331-344
In the late 1930s Phillip Whitman gave an algorithm for deciding for lattice terms v and u if vu in the free lattice on the variables in v and u. He also showed that each element of the free lattice has a shortest term representing it and this term is unique up to commutivity and associativity. He gave an algorithm for finding this term. Almost all the work on free lattices uses these algorithms. Building on the work of Ralph McKenzie, J. B. Nation and the author have developed very efficient algorithms for deciding if a lattice term v has a lower cover (i.e., if there is a w with w covered by v, which is denoted by w) and for finding them if it does. This paper studies the efficiency of both Whitman's algorithm and the algorithms of Freese and Nation. It is shown that although it is often quite fast, the straightforward implementation of Whitman's algorithm for testing vu is exponential in time in the worst case. A modification of Whitman's algorithm is given which is polynomial and has constant minimum time. The algorithms of Freese and Nation are then shown to be polynomial. 相似文献
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A lattice Boltzmann model for blood flows is proposed. The lattice Boltzmann Bi-viscosity constitutive relations and control dynamics equations of blood flow are presented. A non-equilibrium phase is added to the equilibrium distribution function in order to adjust the viscosity coefficient. By comparison with the rheology models, we find that the lattice Boltzmann Bi-viscosity model is more suitable to study blood flow problems. To demonstrate the potential of this approach and its suitability for the application, based on this validate model, as examples, the blood flow inside the stenotic artery is investigated. 相似文献
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Chaos,transport and mesh convergence for fluid mixing 总被引:1,自引:0,他引:1
Chaotic mixing of distinct fluids produces a convoluted structure to the interface separating these fluids. For miscible fluids (as considered here), this interface is defined as a 50% mass concentration isosurface. For shock wave induced (Richtmyer-Meshkov) instabilities, we find the interface to be increasingly complex as the computational mesh is refined. This interfacial chaos is cut off by viscosity, or by the computational mesh if the Kolmogorov scale is small relative to the mesh. In a regime of converged interface statistics, we then examine mixing, i.e. concentration statistics, regularized by mass diffusion. For Schmidt numbers significantly larger than unity, typical of a liquid or dense plasma, additional mesh refinement is normally needed to overcome numerical mass diffusion and to achieve a converged solution of the mixing problem. However, with the benefit of front tracking and with an algorithm that allows limited interface diffusion, we can assure convergence uniformly in the Schmidt number. We show that different solutions result from variation of the Schmidt number. We propose subgrid viscosity and mass diffusion parameterizations which might allow converged solutions at realistic grid levels. 相似文献
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《Journal of Complexity》1988,4(1):73-85
The paper presents some extensions of the optimality results obtained in previous work on algorithms used in the field of system identification in the light of information-based complexity. In particular, a class of conditional algorithms is defined by means of a restriction on the space of solution elements and a corresponding conditional worst case error is introduced. We define conditional central algorithms and show their optimality. A conditional central algorithm is then constructed by modifying a projection algorithm and obtaining in this way a conditional projection algorithm. This algorithm is shown to enjoy local optimality properties with reference to the problem element space within the class of conditionally correct algorithms. Finally, it is shown how these results can be used to handle the problem of reduced order model estimation. 相似文献
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We study a system composed of a nonlinear Stokes flow in one subdomain coupled with a nonlinear porous medium flow in another subdomain. Special attention is paid to the mathematical consequence of the shear-dependent fluid viscosity for the Stokes flow and the velocity-dependent effective viscosity for the Darcy flow. Motivated by the physical setting, we consider the case where only flow rates are specified on the inflow and outflow boundaries in both subdomains. We recast the coupled Stokes–Darcy system as a reduced matching problem on the interface using a mortar space approach. We prove a number of properties of the nonlinear interface operator associated with the reduced problem, which directly yield the existence, uniqueness and regularity of a variational solution to the system. We further propose and analyze a numerical algorithm based on mortar finite elements for the interface problem and conforming finite elements for the subdomain problems. Optimal a priori error estimates are established for the interface and subdomain problems, and a number of compatibility conditions for the finite element spaces used are discussed. Numerical simulations are presented to illustrate the algorithm and to compare two treatments of the defective boundary conditions. 相似文献
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In this paper we develop a new multi-dimensional continued fraction algorithm and three known multi-dimensional continued fraction algorithms from the lattice basis reduction multisequence synthesis (LBRMS) algorithm with respect to the different choice of a parameter and so a continued fraction expansion is associated with a basis transformation. The new algorithm is similar to Dai's continued fraction algorithm [Z.D. Dai, K.P. Wang, D.F. Ye, m-Continued fraction algorithm on multi-Laurent series, Acta Arith. (2006) 1–21] but improves the latter effectively. 相似文献
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A groundwater management problem is presented involving pumping cost minimization with both well discharges and well locations as decision variables. A grid of candidate well locations is set up and optimal arrangements of wells are sought within this discrete space. A genetic algorithm approach is presented with the following particular features: (a) A suitable scaling is applied to the objective function in order to alleviate its regionally flat behavior. (b) No penalty functions are involved in constraint handling. Instead, the feasible region is transformed into a rectangular domain. The transformation introduced is proved to be bijective. (c) A binary representation of well configurations is presented and compared to a combinatorial one. The binary representation necessitates the introduction of specially designed genetic operators. Besides purely genetic algorithms, the concept of cellular automaton is introduced as the basis of an alternative formulation of the optimization problem. The lattice of the cellular automaton provides the discrete set of candidate well positions. The well configuration is represented by a group of agents occupying an equal number of lattice sites. The agents change positions as dictated by the structure of the automaton and, also, by an associated genetic algorithm, which directs the evolution of the whole scheme toward an optimal configuration. An improved performance of this approach is noted and discussed in comparison to the purely genetic algorithm schemes of the present work. A simulated annealing approach is also applied to the same problem for comparison purposes. Finally, a new and more efficient hybrid annealing–genetic approach is introduced and discussed. 相似文献
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Galois lattices and formal concept analysis of binary relations have proved useful in the resolution of many problems of theoretical or practical interest. Recent studies of practical applications in data mining and software engineering have put the emphasis on the need for both efficient and flexible algorithms to construct the lattice. Our paper presents a novel approach for lattice construction based on the apposition of binary relation fragments. We extend the existing theory to a complete characterization of the global Galois (concept) lattice as a substructure of the direct product of the lattices related to fragments. The structural properties underlie a procedure for extracting the global lattice from the direct product, which is the basis for a full-scale lattice construction algorithm implementing a divide-and-conquer strategy. The paper provides a complexity analysis of the algorithm together with some results about its practical performance and describes a class of binary relations for which the algorithm outperforms the most efficient lattice-constructing methods. 相似文献
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《Operations Research Letters》1997,20(3):119-127
This paper reports a fast local search (FLS) algorithm which helps to improve the efficiency of hill climbing and a guided local search (GLS) algorithm which was developed to help local search to escape local optima and distribute search effort. To illustrate how these algorithms work, this paper describes their application to British Telecom's workforce scheduling problem, which is a hard real life problem. The effectiveness of FLS and GLS are demonstrated by the fact that they both outperform all the methods applied to this problem so far, which include simulated annealing, genetic algorithms and constraint logic programming. 相似文献