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Sensitivity of mixed subsonic-supersonic turbulent mixing layers

JOURNAL OF PROPULSION AND POWER 2001年第4期17卷 823-835页

作者： Cottrell, DC Plesniak, MW Purdue Univ Sch Mech Engn Maurice J Zucrow Labs W Lafayette IN 47907 USA

Numerical predictions of compressible turbulent mixing layers have been performed for convective Mach numbers up to 0.7 (M-C less than or equal to0.7), This flow is particularly challenging to compute because the mixing layer consists of one supersonic stream and one subsonic stream, resulting in a mixed hyperbolic/elliptic solution. The FLUENT (C) computational fluid dynamics code, which incorporates a renormalization group k-is an element of turbulence model and the SIMPLEC solution algorithm, was used to perform the computations. Initially, predictions were performed for several different convective Mach numbers (M-C = 0.2, 0.5, and 0.7), and the computed results (mixing layer thickness, mean velocity, and turbulence parameters) were compared with experiments to benchmark the code. Following this qualification procedure, the sensitivity of the Me = 0.7 case to disturbances was further investigated by introducing small perturbations to the boundary conditions and recomputing the mixing layer. Specifically, effects of perturbations to the secondary stream stagnation pressure and test section wall adjustment angle were investigated, It was found that the compressible mixing layer growth rate was significantly altered by small changes (<4%) in the secondary stream stagnation pressure. In addition, divergence or convergence of the test section walls of less than 3 deg resulted in appreciable changes in the streamwise pressure gradient and mixing layer development.

关键词： Turbulent Mixing Adverse Pressure Gradient SIMPLE algorithm Kinematic Viscosity Freestream Velocity Kinetic Energy Stress Distribution solution algorithm Turbulence Models Turbulent Boundary Layer

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Series load flow: A novel non-iterative load flow method

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IEE PROCEEDINGS-GENERATION TRANSMISSION AND DISTRIBUTION 1998年第3期145卷 251-256页

作者： Xu, W Liu, Y Salmon, JC Le, T Chang, GWK Univ Alberta Dept Elect & Comp Engn Edmonton AB T6G 2G7 Canada Virginia Polytech Inst & State Univ Dept Elect Engn Blacksburg VA 24061 USA ABB Power T&D Co Inc Raleigh NC 27606 USA Siemens Power T&D LLC Brooklyn Pk MN 55428 USA

A noniterative method for solving load flow equations is presented in the paper. The method is based on the Taylor series expansion of the inverse load flow function. Formulas to compute the Taylor series are derived and associated solution algorithms are developed, Load flow results can be obtained by simply calculating and summing the significant terms of the series. The proposed method is evaluated using four test systems. Potential applications of the method are discussed.

关键词： load flow Taylor series solution algorithm evaluation test systems

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NONITERATIVE PARABOLIC GRID GENERATION FOR PARABOLIZED EQUATIONS

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AIAA JOURNAL 1987年第4期25卷 542-549页

作者： HODGE, JK LEONE, SA MCCARTY, RL Air Force Institute of Technology Wright-Patterson Air Force Base Ohio

Three-dimensional generalized curvilinear grids are generated for Cartesian, cylindrical, and spherical shaped bodies using parabolic partial differential equations. Elliptic grid equations are parabolized in an axial direction consistent with the Parabolized Navier Stokes (PNS) equations or the boundary-layer equations. The parabolized grid equations are solved in a noniterative fashion by marching in two directions. Any limitations of parabolic grid generation are investigated on convex and concave corners. Even though body surfaces are not smooth, the grid between axial stations is smoothed. Highly stretched and optimized grids for high Reynold's number are accurately and efficiently generated for the first time using parabolic grid equations with a difference approximation based on exponentials. The grid can also be adapted easily based on a flow solution at the previous axial station using this approach. © 1987 American Institute of Aeronautics and Astronautics, Inc., All rights reserved.

关键词： Boundary Layer Equations Poisson's Equation Turbulent Flow Velocity Profiles Finite Difference Approximation Cartesian Coordinate System solution algorithm Iterative solution Computer Memory Flow Equations

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Applications of Generalized Zero-Effort-Miss/Zero-Effort-Velocity Feedback Guidance algorithm

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JOURNAL OF GUIDANCE CONTROL AND DYNAMICS 2013年第3期36卷 810-820页

作者： Guo, Yanning Hawkins, Matt Wie, Bong Iowa State Univ Ames IA 50010 USA Iowa State Univ Dept Aerosp Engn Ames IA 50010 USA Iowa State Univ Asteroid Deflect Res Ctr Dept Aerosp Engn Ames IA 50010 USA

The performance of the zero-effort-miss/zero-effort-velocity feedback guidance algorithm is evaluated through practical space application examples. The zero-effort-miss/zero-effort-velocity feedback guidance algorithm is, in general, not an optimal solution;however, it is an optimal solution in a uniform gravitational environment. It is also conceptually simple and easy to implement and, thus, has great potential for autonomous onboard implementation. It is shown dim, for some classic ballistic missile intercept and asteroid intercept scenarios, the zero-effort-miss/zero-effort-velocity algorithm can even compete with corresponding open-loop optimal solutions, while its feedback characteristics make it more suitable to deal with uncertainties and perturbations. By employing the zero-effort-miss/zero-effort-velocity algorithm in the highly nonlinear orbital transfer and raising problems and comparing with corresponding open-loop optimal solutions, its simplicity and near-optimality are further verified.

关键词： Guidance algorithms Asteroids Closed Loop Hohmann Transfer Ballistic Missile Pseudospectral Optimal Control Earth Numerical Simulation Terminal Velocity solution algorithm

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Optimal Inventory Level Control and Replenishment Plan for Retailers

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NETWORKS & SPATIAL ECONOMICS 2021年第1期21卷 57-83页

作者： Lin, Chih-Kang Yan, Shangyao Hsiao, Fei-Yen Feng Chia Univ Coll Construct & Dev Innovat Ctr Intelligent Transportat & Logist Taichung 40724 Taiwan Natl Cent Univ Dept Civil Engn Chungli 32001 Taiwan

In vendor managed inventory (VMI) operations, it is necessary for both the suppliers and the customers to reach an agreement on the maximal and minimal inventory level. In practice, in VMI, inventory levels are decided manually by planning personnel, based on their experience and past operating records. From a system optimization point of view, the determination of the upper and lower inventory levels in storage areas is complicated, necessitating analysis of many factors. Consequently, it may not be possible to obtain the best planning results, to determine and maintain the optimum levels of inventory. In this study, we utilize network flow techniques to build a replenishment model to deal with the upper-and-lower inventory level control problem, with the objective of minimizing the total cost in short-term operations, subject to inventory level control and other operating constraints. The model is formulated as an integer network flow problem with side constraints and is characterized as NP-hard in terms of optimization. To efficiently and effectively solve the large-scale problems that occur in the real world, a solution algorithm is also developed. Finally, numerical tests are conducted using real data from a major retail company in northern Taiwan. The results demonstrate the usefulness of the proposed model and solution algorithm for replenishment planning in actual practice.

关键词： Replenishment planning Vendor managed inventory Upper-and-lower inventory level Network flow solution algorithm

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Enhanced-interval linear programming

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EUROPEAN JOURNAL OF OPERATIONAL RESEARCH 2009年第2期199卷 323-333页

作者： Zhou, Feng Huang, Gordon H. Chen, Guo-Xian Guo, Huai-Cheng Peking Univ Coll Environm Sci & Engn Beijing 100871 Peoples R China Univ Regina Fac Engn Environm Syst Engn Program Regina SK S4S 0A2 Canada Peking Univ LMAM Beijing 100871 Peoples R China Peking Univ CCSE Sch Math Sci Beijing 100871 Peoples R China

An enhanced-interval linear programming (EILP) model and its solution algorithm have been developed that incorporate enhanced-interval uncertainty (e.g., A(+/-), B-+/- and C-+/-) in a linear optimization framework. As a new extension of linear programming, the EILP model has the following advantages. Its solution space is absolutely feasible compared to that of interval linear programming (ILP), which helps to achieve insight into the expected-value-oriented trade-off between system benefits and risks of constraint violations. The degree of uncertainty of its enhanced-interval objective function (EIOF) would be lower than that of ILP model when the solution space is absolutely feasible, and the EIOF's expected value could be used as a criterion for generating the appropriate alternatives, which help decision-makers obtain non-extreme decisions. Moreover, because it can be decomposed into two submodels. EILP's computational requirement is lower than that of stochastic and fuzzy LP models. The results of a numeric example further indicated the feasibility and effectiveness of EILP model. In addition, El nonlinear programming models, hybrid stochastic or fuzzy EILP models as well as risk-based trade-off analysis for El uncertainty within decision process can be further developed to improve its applicability. (C) 2008 Elsevier B.V. All rights reserved.

关键词： Linear programming Optimization Uncertainty Feasibility solution algorithm Risk-based decision making

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MULTIPERIOD SECURE ECONOMIC-DISPATCH FOR LARGE-SCALE POWER-SYSTEMS

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IEE PROCEEDINGS-C GENERATION TRANSMISSION AND DISTRIBUTION 1989年第3期136卷 130-136页

作者： HINDI, KS GHANI, MRA Decision Technologies Group Department of Computation UMIST Manchester UK

Dynamic multi-period economic dispatch for large-scale power systems is considered; the formulation presented provides for loading and deloading rates, limits on generator outputs, spinning-reserve requirements and group power import-export limits. It is also suitable for implementation within a constraint relaxation strategy. The solution algorithm is based on a Dantzig-Wolfe decomposition, which yields a capacitated transshipment subproblem along with a master problem solved by the revised simplex method. The computational efficiency of the algorithm renders it suitable for on-line dispatch.

关键词： online dispatch spinning-reserve requirements power systems loading rates constraint relaxation strategy large-scale power systems economics Dantzig-Wolfe decomposition Power system management, operation and economics group power import-export limits computational efficiency deloading rates generator output limits solution algorithm secure economic dispatch load dispatching capacitated transshipment subproblem dynamic multiperiod dispatch revised simplex method

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Fuzzy analysis of queueing systems with an unreliable server: A nonlinear programming approach

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APPLIED MATHEMATICS AND COMPUTATION 2006年第1期175卷 330-346页

作者： Ke, Jau-Chuan Lin, Chuen-Horng Natl Taichung Inst Technol Dept Stat Taichung 404 Taiwan Natl Taichung Inst Technol Dept Informat Management Taichung 404 Taiwan

This work constructs the membership functions of the system characteristics of a queuing model with an unreliable server, in which the arrival rate and the service rate of customers, as well as the breakdown rate and repair rate of server are all fuzzy numbers. The alpha-cut approach is used to transform a fuzzy queue with an unreliable server into a family of conventional crisp queues with an unreliable server. By means of the membership functions of the system characteristics, a set of parametric nonlinear programs is developed to describe the family of crisp queues with an unreliable server. An efficient algorithm is provided to find the optimal solutions at a different possibility level a. Three numerical examples are solved successfully to illustrate the validity of the proposed approach. Due to the system characteristics being expressed and governed by the membership functions, more information is provided for use by management. By extending the fuzzy environment, the fuzzy queues with an unreliable server can be represented more accurately by using the proposed approach, and the analysis results for such queuing model will be useful and significant for system designers and practitioners. (c) 2005 Elsevier Inc. All rights reserved.

关键词： fuzzy sets nonlinear programming queue solution algorithm unreliable server

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IMPLICIT CONSERVATIVE SCHEMES FOR THE EULER EQUATIONS

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AIAA JOURNAL 1986年第2期24卷 215-223页

作者： WORNOM, SF HAFEZ, MM UNIV CALIF DAVIS DEPT MECH ENGNDAVISCA 95616

A new approach to a characteristic modeling scheme is presented that does not require the governing equations to be written in characteristic variables or the flux terms to be split into positive and negative parts. The method is based on the observation that, for certain finite volume schemes, the upwind influence can be accounted for through the conditions applied at the boundaries of individual cells instead of flux differencing. The method is developed and applied to the one-dimensional nozzle flow equations for subsonic, transonic, and supersonic flows and is then extended to two dimensions using an approximate factorization. For the problem of a shock wave reflecting from a flat plate, the present solution algorithm reduces the computational work per time step by 40% of that required by standard, central difference, implicit, calculations. © 1986 American Institute of Aeronautics and Astronautics, Inc., All rights reserved.

关键词： Continuity Equation One Dimensional Flow solution algorithm Mach Cones Finite Volume Scheme Aerodynamics Computational Fluid Dynamics Central Processing Unit Implicit Methods Conservation of Mass

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DETERMINING A FORCE ACTING ON A PLATE - AN INVERSE PROBLEM

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AIAA JOURNAL 1991年第3期29卷 464-470页

作者： DCRUZ, J CRISP, JDC RYALL, TG DEF SCI & TECHNOL ORG AERONAUT RES LABDIV AIRCRAFT STRUCTMELBOURNEVIC 3001AUSTRALIA

It is traditional in the study of elasticity to determine the response of a structure to a known force. Such problems may be described as direct problems as they involve the determination of the unknown effects of a known cause. The problem of determining the force acting on a structure from measurements of the response of the structure to the force is the inverse problem. Presented here is a method for determining the location and magnitude of a static point force acting on a simply-supported elastic rectangular plate from a number of displacement readings at discrete points on the plate. This problem reduces to a nonlinear least-squares one. It is solved by calculating an approximate solution from a simplified set of equations that is then used as an initial estimate in an iterative procedure for a solution of the actual nonlinear least-squares problem. Results of numerical simulations illustrate the use of the method, and a confidence criterion is supplied. Presented also is a demonstration of the robustness of the algorithm to the effects of measurement noise, as well as a means by which the method may be extended to problems of a more general nature.

关键词： Inverse Problems Numerical Simulation Poisson's Ratio Finite Element Formulation Aspect Ratio Newton's Method Electromagnetic Radiation solution algorithm Aircraft Structures Aerodynamic Force

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