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1.
运用作者推导的动量积分关系式,分析了向有积水的斜置管道中分别吹入轴向气流和螺旋气流时积水的运动情况。结果表明:在大多数情况下,螺旋气流能除去斜置管道中积水;而轴向气流不能除去积水,一段时间后会出现逆流。这一结果与Horii和赵耀华等人在这个问题上所做的实验结果一致。此外,还讨论了不同的实始条件对排水情况的影响。  相似文献   

2.
紧急网络中的最小饱和流问题   总被引:8,自引:0,他引:8  
网络N中的一个流,如果沿前向已无法再增流,则称为饱和流,在交通拥挤或紧急疏散时,网络往往被一饱和流所堵塞。显然,这饱和流的值越小,网络的性能就越差。于是从网络分析的观点就提出最小饱和流问题。本文首先证明此问题NP-困难的。然后给出关于最小饱和流与最大流的关系及算法方面的结果。  相似文献   

3.
本文研究幂律非牛顿流体在环管内的不定常旋转流,该方程是一非线性方程,在部分因子的稳态近拟假设之下,方程被线性化,用Laplace积分变换法我们获得了问题的解,文中给出了几组解曲线,它反映了角向速度的时间深浅伦规律与空间分布特征。另外我们专门研究了幂律指数对流场的影响,该参数的敏感性具有一定的数值界限。这一结果,在有关的工程设计中具有重要的意义。  相似文献   

4.
纤维悬浮槽流空间模式稳定性分析   总被引:1,自引:1,他引:0  
采用扰动的空间发展模式而非通常的时间发展模式,对含有悬浮纤维的槽流进行了线性稳定性分析。建立了适用于纤维悬浮流的稳定性方程并针对较大范围的流动Re数及扰动波角频率进行了数值求解.计算结果表明,纤维轴向抗拉伸力与流体惯性力之比H可以反映纤维对流动稳定性的影响.H增大使临界Re数升高,对应的扰动波数减小,扰动空间衰减率增加,扰动速度幅值的峰值降低,不稳定扰动区域缩小,长波扰动所受影响相对较大.纤维的存在抑制了流场的失稳.  相似文献   

5.
本文分析了一种非定常振荡的不稳定性问题。其特点是,应用偏微分方程特征理论以及O-S方程特征值的展开,求解扰动波的相函数而不是预先给定扰动波的波动形式。本文研究平面Poisettille流与其垂向振荡流的组合流动系统,对于连续振荡源导致的波包演化,该系统存在不稳定性。  相似文献   

6.
本文考虑的问题是二维粘性渠流,对0到2000之间的雷诺数,计算了平稳扰动的Couette-Poiseuille流的下游特征值,其特征方程类似于Orr-Sommerfeld方程,所用的方法是谱方法和初值方法(复合矩阵方法),就几种有趣的流量,给出了相应的特征值的计算结果,这些特征值确定了扰动的衰减率。  相似文献   

7.
彭位炳 《工科数学》1998,14(1):50-53
本文考虑在有两个发点x1和x2,两个收点y1和y2的网络中,求把商品1从x1运送到y1,把商品2从x2运送到y2的最大流问题,给出一个充分必要条件,指出在一般情况下无最大流,但可以得到满意流,最后给出一个算例。  相似文献   

8.
拟牛顿流的一种三变量域模型的有限元方法的数值分析   总被引:1,自引:0,他引:1  
周磊  周天孝 《计算数学》1997,19(3):305-312
0.引言目前,涉及高温条件下材料蠕变性质的粘弹性流动问题已引起人们广泛的研究兴趣,不少文章讨论了如何对其进行数值求解(见[1]--[41),首先,人们研究了较简单的仅以速度,压力两个变量来表述此现象的模型问题(如[1,2])等.鉴于应力变量在材料性质方面的特殊重要性,最近J.Baxanzer等人在[3]中首次对应力满足幂函数规律的蠕变流研究了包含应力、速度和压力三种变量的模型问题的有限元逼近,当粘性的牛顿部分为零时(详见下述)在假定速度与应力、速度与压力有限元空间之间同时满足两种**B条件以后,证明了有限元解…  相似文献   

9.
两相流中柱状固粒对流体湍动特性影响的研究   总被引:7,自引:2,他引:5  
对含柱状固粒的两相流场,建立了包含柱状固粒对流场影响的流体脉动速度方程,在求解脉动速度方程的基础上,经平均得到流体的湍流强度和雷诺应力。将该方法用于槽流湍流场的求解,并与单相流实验结果进行了比较。计算中变化柱状固粒的参数,给出了固粒的体积分数,长径比,松驰时间对流场湍动特性的影响,说明粒子对流场的湍动特性起着抑制作用,其抑制的程度与粒子的体积分数,长径比成正比,与粒子的松弛时间成反比。  相似文献   

10.
本文详细阐述了旋风分离器内流动在球坐标系中的数学表述和结果,应用质量守恒定律和定常流动的运动定律,在轴对称的考虑下,用流函数方法详尽推导了流动的三个速度分量。此讨论是从三维的整体观点来全面分析流动状况的。此外,对文[1]中的一些结果作了必要的修正。  相似文献   

11.
Linear Fuzzy constraints are linear constraints where coefficients are fuzzy numbers. This paper demonstrates that two points of view can be considered to extend classical linear constraints: either tolerance constraints, or approximate (in)equality constraints can be obtained. Resolution of systems of linear fuzzy constraints is shown to be made easier by the use of fuzzy numbers analytically represented through a given type of membership function and three parameters. Solution methods are provided in the case of non fuzzy variables; as an illustration, some numerical examples are presented. The fuzzy variable case is also evoked.This paper is part of Purdue University Electrical Engineering technical report TR-EE 78-13.  相似文献   

12.
模糊数的相等、同一与等式限定运算   总被引:2,自引:1,他引:1  
讨论了在模糊数运算中相等与同一的区别,在Klir的模糊数限定运算基础上提出了模糊数的等式限定运算以及等式限定运算的结构元表示方法,解决了传统模糊数运算的不可逆问题.通过模糊数的结构元表示方法,将其等式限定运算转换为两个同序单调函数的运算,这不仅仅给出等式限定运算的可操作形式,同时对于求解模糊数方程也给出了具体的计算方法.  相似文献   

13.
We consider fuzzy stochastic programming problems with a crisp objective function and linear constraints whose coefficients are fuzzy random variables, in particular of type L-R. To solve this type of problems, we formulate deterministic counterparts of chance-constrained programming with fuzzy stochastic coefficients, by combining constraints on probability of satisfying constraints, as well as their possibility and necessity. We discuss the possible indices for comparing fuzzy quantities by putting together interval orders and statistical preference. We study the convexity of the set of feasible solutions under various assumptions. We also consider the case where fuzzy intervals are viewed as consonant random intervals. The particular cases of type L-R fuzzy Gaussian and discrete random variables are detailed.  相似文献   

14.
A note on chance constrained programming with fuzzy coefficients   总被引:17,自引:0,他引:17  
This paper deals with nonlinear chance constrained programming as well as multiobjective case and goal programming with fuzzy coefficients occurring in not only constraints but also objectives. We also present a fuzzy simulation technique for handling fuzzy objective constraints and fuzzy goal constraints. Finally, a fuzzy simulation based genetic algorithm is employed to solve a numerical example.  相似文献   

15.
In this paper, we propose a method of solving the fully fuzzified linear fractional programming problems, where all the parameters and variables are triangular fuzzy numbers. We transform the problem of maximizing a function with triangular fuzzy value into a deterministic multiple objective linear fractional programming problem with quadratic constraints. We apply the extension principle of Zadeh to add fuzzy numbers, an approximate version of the same principle to multiply and divide fuzzy numbers and the Kerre’s method to evaluate a fuzzy constraint. The results obtained by Buckley and Feuring in 2000 applied to fractional programming and disjunctive constraints are taken into consideration here. The method needs to add extra zero-one variables for treating disjunctive constraints. In order to illustrate our method we consider a numerical example.  相似文献   

16.
Constraint programming models appear in many sciences including mathematics, engineering and physics. These problems aim at optimizing a cost function joint with some constraints. Fuzzy constraint programming has been developed for treating uncertainty in the setting of optimization problems with vague constraints. In this paper, a new method is presented into creation fuzzy concept for set of constraints. Unlike to existing methods, instead of constraints with fuzzy inequalities or fuzzy coefficients or fuzzy numbers, vague nature of constraints set is modeled using learning scheme with adaptive neural-fuzzy inference system (ANFIS). In the proposed approach, constraints are not limited to differentiability, continuity, linearity; also the importance degree of each constraint can be easily applied. Unsatisfaction of each weighted constraint reduces membership of certainty for set of constraints. Monte-Carlo simulations are used for generating feature vector samples and outputs for construction of necessary data for ANFIS. The experimental results show the ability of the proposed approach for modeling constrains and solving parametric programming problems.  相似文献   

17.
In this paper, possibility and necessity representations of fuzzy inequality constraints are presented and then crisp versions of the constraints are derived. Here analogous to chance constraints, real-life necessity and possibility constraints in the context of two warehouse multi-item dynamic production-inventory control system are defined and defuzzified following fuzzy relations. Hence, a realistic two warehouse multi-item production-inventory model with fuzzy constraints has been formulated for a finite period of time and solved for optimal production with the objective of having maximum profit. The rate of production is unknown, assumed to be a function of time and considered as a control variable. Also the present system produces some defective units alongwith the perfect ones and the rate of produced defective units is stochastic in nature. Demand of the good units is stock dependent and known and the defective units are sold at a reduced price. The space required per unit item and available storage space are assumed to be imprecise. The inequality of budget constraints is also imprecise. The space and budget constraints are expressed as necessity and/or possibility types. The model is reduced to an equivalent deterministic model using fuzzy relations and solved for optimum production function using Pontryagin’s optimal control policy, the Kuhn–Tucker conditions and generalized reduced gradient (GRG) technique. The model is illustrated numerically and values of demand, optimal production function and stock level are presented in both tabular and pictorial forms.  相似文献   

18.
Multi-item inventory model with stock-dependent demand and two-storage facilities is developed in fuzzy environment (purchase cost, investment amount and storehouse capacity are imprecise) under inflation and time value of money. Joint replenishment and simultaneous transfer of items from one warehouse to another is proposed using basic period (BP) policy. As some parameters are fuzzy in nature, objective (average profit) function as well as some constraints are imprecise in nature. Model is formulated as to optimize the possibility/necessity measure of the fuzzy goal of the objective function and constraints are satisfied with some pre-defined necessity. A genetic algorithm (GA) is developed with roulette wheel selection, binary crossover and mutation and is used to solve the model when the equivalent crisp form of the model is available. In other cases fuzzy simulation process is proposed to measure possibility/necessity of the fuzzy goal as well as to check the constraints of the problem and finally the model is solved using fuzzy simulation based genetic algorithm (FSGA). The models are illustrated with some numerical examples and some sensitivity analyses have been done.  相似文献   

19.
Model predictive control (MPC) has been used in process control systems with constraints, however, the constrained optimization problem involved in control systems has generally been solved in practice in a piece-meal fashion. To solve the problem systemically, in this paper, the Multi-Objective Fuzzy-Optimization (MOFO) is used in the constrained predictive control for online applications as a means of dealing with fuzzy goals and fuzzy constraints in control systems. The conventional model predictive control is integrated with the techniques from fuzzy multicriteria decision making, translating the goals and the constraints to predictive control in a transparent way. The information regarding the fuzzy goals and the fuzzy constraints of the control problem is combined by using a decision function from the fuzzy theory, so it is possible to aggregate the fuzzy goals and the fuzzy constraints using fuzzy operators, e.g. t-norms, s-norms or the convex sum. It is shown that the model predictive controller based on MOFO allows the designers a more flexible aggregation of the control objectives than the usual weighting sum of squared errors in MPC. The efficiency of the presented algorithm is validated by the visual robot path planning.  相似文献   

20.
Lotfi et al. [Solving a full fuzzy linear programming using lexicography method and fuzzy approximate solution, Appl. Math. Modell. 33 (2009) 3151–3156] pointed out that there is no method in literature for finding the fuzzy optimal solution of fully fuzzy linear programming (FFLP) problems and proposed a new method to find the fuzzy optimal solution of FFLP problems with equality constraints. In this paper, a new method is proposed to find the fuzzy optimal solution of same type of fuzzy linear programming problems. It is easy to apply the proposed method compare to the existing method for solving the FFLP problems with equality constraints occurring in real life situations. To illustrate the proposed method numerical examples are solved and the obtained results are discussed.  相似文献   

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