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981.
A.J. Giacomin A.J. Hade L.M. Johnson A.W. Mix Yi-Chang ChenHui-Chen Liao Shi-Chang Tseng 《ournal of non Newtonian Fluid Mechanics》2011,166(16):908-914
Core bending often complicates the injection molding of thin slender parts. Here, a fifth order nonlinear ordinary differential equation is derived for core deflection caused by a Newtonian liquid race tracking through the slit between the core and the rigid cavity wall. Solving this numerically, a universal graph is produced to help engineers predict core deflection. For small core deflections, explicit analytical solutions for these deflections and for the pressure developed in the race tracking fluid are also derived. We find that core deflection is governed by a single dimensionless group called core deflectability. Core deflection measurements agree closely with predictions of this fifth order nonlinear theory. 相似文献
982.
Second order Stochastic Dominance (SSD) has a well recognised importance in portfolio selection, since it provides a natural interpretation of the theory of risk-averse investor behaviour. Recently, SSD-based models of portfolio choice have been proposed; these assume that a reference distribution is available and a portfolio is constructed, whose return distribution dominates the reference distribution with respect to SSD. We present an empirical study which analyses the effectiveness of such strategies in the context of enhanced indexation. Several datasets, drawn from FTSE 100, SP 500 and Nikkei 225 are investigated through portfolio rebalancing and backtesting. Three main conclusions are drawn. First, the portfolios chosen by the SSD based models consistently outperformed the indices and the traditional index trackers. Secondly, the SSD based models do not require imposition of cardinality constraints since naturally a small number of stocks are selected. Thus, they do not present the computational difficulty normally associated with index tracking models. Finally, the SSD based models are robust with respect to small changes in the scenario set and little or no rebalancing is necessary. 相似文献
983.
Numerical simulation of dispersion and deposition of aerosol particles in a channel flow over two square cylinders in tandem are performed. A Lagrangian particle tracking computational procedure is developed and is used to simulate particles transport and deposition. Drag, gravity, and buoyancy forces are included in the computational model. Ensembles of particles in asterisk arrangement are released from different source points to calculate their capture efficiency on walls and obstructions. The effects of source point location, gravity direction, size and density of released particles and the gap between obstructions on capture efficiency are discussed. Time evolution of dispersion of four different clusters of particles representing the worst possible situation, issuing from maximum obstruction capture efficiency, are also illustrated. 相似文献
984.
985.
986.
987.
考虑子系统的时空耦合作用及模型的不确定性,实现模型不确定的耦合时空混沌的 跟踪控制非常困难.然而耦合时空混沌的每个子系统用一系列模糊逻辑模型逼近,同时考虑子 系统状态的不可测性,采用模糊观测器来估计子系统的状态.由于混沌模型的很多参数和动态 特性很难准确地确定即模型具有不确定性,因此在用模糊模型逼近的同时定会产生建模误差. 基于模糊模型及状态观测器,考虑混沌模型的不确定性,提出一种H∞ 模糊跟踪控制方法,实现模型不确定性的耦合时空混沌的鲁棒跟踪控制.将控制方 案表征为求解线性矩阵不等式问题,并用凸优化方法
关键词:
耦合时空混沌
模糊模型
模糊观测器
H∞模糊跟踪控 制
线性矩阵不等式 相似文献
988.
J. N. Juang J. D. Turner H. M. Chun 《Journal of Optimization Theory and Applications》1986,51(2):307-320
Feedback control laws are derived for a class of optimal finite time tracking problems with terminal constraints. Analytical solutions are obtained for the feedback gain and the closed-loop response trajectory. Such formulations are expressed in recursive forms so that a real-time computer implementation becomes feasible. An example involving the feedback slewing of a flexible spacecraft is given to illustrate the validity and usefulness of the formulations. 相似文献
989.
The paper describes the application of front tracking to the polymer system, an example of a nonstrictly hyperbolic system. Front tracking computes piecewise constant approximations based on approximate Riemann solutions and exact tracking of waves. It is well known that the front tracking method may introduce a blowup of the initial total variation for initial data along the curve where the two eigenvalues of the hyperbolic system are identical. It is demonstrated by numerical examples that the method converges to the correct solution after a finite time, and that this time decreases with the discretization parameter.For multidimensional problems, front tracking is combined with dimensional splitting, and numerical experiments indicate that large splitting steps can be used without loss of accuracy. Typical CFL numbers are in the range 10–20, and comparisons with Riemann free, high-resolution methods confirm the high efficiency of front tracking.The polymer system, coupled with an elliptic pressure equation, models two-phase, three-component polymer flooding in an oil reservoir. Two examples are presented, where this model is solved by a sequential time stepping procedure. Because of the approximate Riemann solver, the method is non-conservative and CFL numbers must be chosen only moderately larger than unity to avoid substantial material balance errors generated in near-well regions after water breakthrough. Moreover, it is demonstrated that dimensional splitting may introduce severe grid orientation effects for unstable displacements that are accentuated for decreasing discretization parameters. 相似文献
990.
A meta-control algorithm for generating approximate solutions to binary integer programming problems
Kathrine von Haartman Wolf Kohn Zelda B. Zabinsky 《Nonlinear Analysis: Hybrid Systems》2008,2(4):1232-1244
Binary integer program problems, which are known to be difficult to solve, have long been an important research area. We use a new approach with continualization techniques to find approximate solutions to binary integer programming problems. The algorithm constructs a sequence of approximations to a solution using a meta-control approach that has low polynomial time complexity. The algorithm is illustrated with a BIP example. 相似文献