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Effect of Insulations and Coatings on Hypersonic Heat Flux Reconstruction

JOURNAL OF THERMOPHYSICS AND HEAT TRANSFER 2021年第1期35卷 63-79页

作者： Nguyen, Nhat M. Ruda, Mathew L. Massa, Luca Virginia Polytech Inst & State Univ Kevin T Crofton Dept Aerosp & Ocean Engn 460 Old Turner St Blacksburg VA 24061 USA

The present study investigates the effects of material discontinuities and thermal resistances on the temperature reconstruction and heat flux evaluation via an inverse heat transfer method in hypersonic wind-tunnel tests. Thin coating layers and adhesive interfaces support a localized multidimensional temperature perturbation that alters the near-surface field. A technique is developed for the real-time evaluation of the heat transfer based on approximating the Green's function of the heat conduction equation in bounded complex domains and resolving the heat flux on a B-spline basis, leading to an efficient and robust algorithm. Evaluating the Green's function for three-dimensional problems with material discontinuities is generally difficult. A new approach is developed in which the Green's function is evaluated independently for the regular partitions of the domain, and appropriate connection conditions are derived to determine the full "system" Green's function. This paper describes the verification, validation, and application of the approach to the heat flux reconstruction for a nonaxisymmetric flat-faced article with coating and potting interfaces. The article was tested at Mach 6 in the Virginia Tech Hypersonic wind tunnel using four temperature sensors arranged in a cross pattern on the flat face. Good agreement was obtained between computational fluid dynamics predictions and the heat flux deduced from the experiments using the new data analysis method.

关键词： Heat Flux Distribution Green's Function Inverse Heat Conduction Hypersonic Wind Tunnels Heat Flow CFD Simulation Temperature Sensors Conduction Equation solution algorithm Data Analysis

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Smooth Local Correlation-Based Transition Model for the Spalart-Allmaras Turbulence Model

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AIAA JOURNAL 2021年第2期59卷 474-492页

作者： Piotrowski, Michael G. H. Zingg, David W. NASA Ames Res Ctr Moffett Field CA 94035 USA Univ Toronto Computat Aerodynam & Sustainable Aviat Inst Aerosp Studies Toronto ON M3H 5T6 Canada Univ Toronto NASA Computat Aerosci Branch Toronto ON Canada Univ Toronto Inst Aerosp Studies N York ON M3H 5T6 Canada

A smooth version of the gamma-R similar to e theta t local correlation-based transition model (LM2015) for the Spalart-Allmaras (SA) turbulence model is presented. The LM2015 model with helicity-based crossflow correlations is modified and coupled to the SA turbulence model, designated SA-LM2015. The LM2015 and SA-LM2015 transition models include source terms that contain stiff and nonsmooth functions. Approximations to these functions are introduced to eliminate discontinuities and improve the numerical behavior of the model, with the smooth model designated SA-sLM2015. Deep convergence is achieved using a fully coupled, implicit Newton-Krylov algorithm globalized using an efficient pseudotransient continuation strategy. Modifications to the Newton-Krylov algorithm are introduced, including a source-term time stepping strategy, to address the large sources introduced by the turbulence and transition model equations. Two- and three-dimensional transition test cases demonstrate that both models, SA-LM2015 and SA-sLM2015, are able to predict transition due to a variety of mechanisms accurately, with the smooth variant displaying significantly improved numerical behavior. Several of the strategies presented, including the smoothing techniques and source-term time stepping, could be useful in the context of other transition models as well.

关键词： Spalart Allmaras Turbulence Model solution algorithm Angle of Attack Reynolds Averaged Navier Stokes Aerodynamic Shape Optimization Laminar Turbulent Transition Swept Wing Freestream Turbulence Natural Laminar Flow Low Turbulence Pressure Tunnel

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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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Warm Start for Low-Thrust Trajectory Optimization via Switched System

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JOURNAL OF GUIDANCE CONTROL AND DYNAMICS 2021年第9期44卷 1700-1706页

作者： Wu, Di Jiang, Fanghua Li, Junfeng Tsinghua Univ Sch Aerosp Engn Beijing 100084 Peoples R China

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Experimental and Numerical Study of Methane-Oxygen Combustion Inside a Low Pressure Rocket Motor

Experimental and Numerical Study of Methane-Oxygen Combustio...

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AIAA Propulsion and Energy Forum / IEEE Electric Aircraft Technologies Symposium (EATS)

作者： Kaya, Mine Akyuzlu, Kazim M. Univ New Orleans Dept Mech Engn New Orleans LA 70148 USA Texas A&M Univ College Stn TX 77843 USA

ISBN: (数字)9781624106118

ISBN: (纸本)9781624106118

An experimental and numerical study was conducted to gain insight to the thermal-fluid characteristics of methane fueled combustion inside a laboratory scale, low pressure, rocket motor. The combustion chamber of the motor has a square cross section and is equipped with quartz side windows to enable visual observation of the flame. The thermocouples placed along the axial direction of the motor provides measurement of temperature inside the flame. Hot tests were conducted for various methane-oxygen ratios and at different chamber pressures. A numerical study was also conducted using a commercial CFD code to predict the temperature and velocity distribution inside combustion chamber. The CFD predicted temperatures at the thermocouple locations fair well with the experimentally measured values.

关键词： Hybrid Rocket Engines Combustion Chambers Thermocouples CFD Codes Combustion Products Mass Flow Rate Numerical Simulation solution algorithm Data Acquisition System Pressure Transducers

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Optimal Deployment of Flood Emergency Response Materials under Stochastic Demands

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JOURNAL OF MARINE SCIENCE AND TECHNOLOGY 2022年第2期30卷 86-101页

作者： Yan, Shangyao Lin, Jenn-Rong Ku, Chia-Fu Natl Cent Univ Dept Civil Engn Taoyuan 32001 Taiwan Natl Taiwan Ocean Univ Dept Transportat Sci Keelung 20224 Taiwan

This study aims to develop a planning model for the deployment of flood emergency response materials under stochastic demands. For ease of modeling, a deterministic demand model is first proposed, from which the stochastic model is further extended. These models are used to determine the allocation of materials the transport truck routes and distribution of the stockpiled materials to emergency sites. The models are formulated as multiple integer network flow problems with special side constraints which are characterized as NP-hard in terms of optimization. To solve the complicated stochastic model efficiently, we also develop a solution algorithm based on a problem decomposition technique coupled with a variable fixing technique. Finally, to preliminarily evaluate the proposed models and solution algorithm, we perform numerical tests using data related to a Taiwan flood emergency response system. The test results are good, indicating the potential usefulness of the models and solution algorithm in practice.

关键词： Flood emergency response Material deployment Time-space network Stochastic demand solution algorithm

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Multi-Agent Passive Safe Optimal Control using Integration Constants as State Variables

Multi-Agent Passive Safe Optimal Control using Integration C...

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AIAA Science and Technology Forum and Exposition (AIAA SciTech Forum)

作者： Guffanti, Tommaso D'Amico, Simone Stanford Univ Aeronaut & Astronaut 496 Lomita Mall Stanford CA 94305 USA

ISBN: (数字)9781624106095

ISBN: (纸本)9781624106095

This paper presents a new algorithm that provides optimal control profiles that drive a multi-agent system to a desired state at a desired time, with the guarantee of no collision, for a specified time horizon, even in case of control input application failure. The algorithm is applicable to multi-agent systems governed by nonlinear control-affine dynamics. First, the paper defines the problem of passive safe optimal control, which adds an important layer of safety to the traditional collision avoidance between agents. A multi-agent system is defined passive safe if the agents maintain safe separation even in the case any agent loses control at any time on the trajectory towards the final condition. Second, the paper shows that using the integration constants of an integrable portion of the multi-agent system dynamics as state variables is the key for including efficiently passive safety into an algorithmic framework. In particular, the number of constraints to be enforced reduces from cubic to quadratic in the number of time samples. Finally, using the integration constants, a solution algorithm based on convex programming is formalized and tested on the challenging problem of passive safe optimal control of multi-spacecraft systems in closed orbits of arbitrary eccentricity.

关键词： Trajectory Optimization Multi Agent System solution algorithm Nonlinear Control Spacecraft System Highly Eccentric Orbit Orbital Period Model Predictive Control Saturn Numerical Integration

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Unsteady Preconditioned Characteristic Boundary Conditions for Direct Numerical Simulation of Incompressible Flows

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AIAA JOURNAL 2020年第4期58卷 1476-1489页

作者： Parseh, Kaveh Hejranfar, Kazem Sharif Univ Technol Dept Aerosp Engn Tehran 11365 Iran

The unsteady preconditioned characteristic boundary conditions (UPCBCs) based on the artificial compressibility (AC) method are formulated and applied at artificial boundaries for the direct numerical simulation (DNS) of incompressible flows. The compatibility equations including the unsteady terms are mathematically derived in the generalized curvilinear coordinates and then incorporated as boundary conditions (BCs) in a high-order accurate incompressible flow solver. The spatial derivative terms of the system of equations are discretized using the fourth-order compact finite difference (FD) scheme, consistent with the high-order accuracy required for the DNS. The time integration is carried out using an implicit dual time-stepping method, and the robustness and performance of the numerical algorithm are enhanced by applying the preconditioning technique and calculating the automated AC parameter based on the local flow conditions. At first, the steady viscous incompressible flow for a two-dimensional plane jet is computed to assess the accuracy and performance of the solution method by applying the UPCBCs in comparison with the simplified BCs. Then, the simulation of the unsteady incompressible viscous flow around a two-dimensional NACA0012 airfoil at the Reynolds number 800 and the angle of attack 20 degrees is performed, and it is indicated that the computational cost of the solution is considerably decreased by implementing the UPCBCs at the artificial far-field boundary compared with the simplified BCs, which is remarkably valuable for the DNSs. Finally, the computation of the transition to unsteady for the incompressible flow around a three-dimensional NACA0012 wing at the same conditions of the two-dimensional case is successfully performed, and the results obtained are compared with those of previous studies that exhibit good agreement. Indications are that the present solution method by applying the UPCBCs at the artificial far-field boundary can be effect

关键词： Incompressible Viscous Flow Direct Numerical Simulation Lift Coefficient Airfoil Freestream Conditions Flow Characteristics Numerical algorithms Curvilinear Coordinates Strouhal Number solution algorithm

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Evaluation Model of Leadership Competency Based on Fuzzy Information and Its algorithm Implementation 2

Evaluation Model of Leadership Competency Based on Fuzzy Inf...

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2nd International Conference on Big Data Economy and Information Management, BDEIM 2021

作者： Cui, Yan Qi, Jun Mao, Hongtao Hu, Nan Liu, Jingfeng Li, Zhenyu Zhang, Yushi Liu, Yubo State Grid Liaoning Electric Power Supply Company Limited Shenvang China

ISBN: (纸本)9781665482882

Competency model is widely used in enterprises, and effective evaluation of leadership competency is the basis and prerequisite for their selection, training, performance management and personal development. Based on a systematic review of relevant literatures, this study proposed a leadership competency evaluation model based on fuzzy information, and designed a solution algorithm. Taking the leadership competency evaluation of A company as a case, this study carried out the identification of individual advantage characteristics of leadership competency, and performed its individual agent evaluation and democratic agent evaluation. The results show that the algorithm can effectively identify the advantage characteristics of leaders. It also helps to explore the inherent strength structure of leadership competency and provides technical methods for individual growth and improvement. © 2021 IEEE.

关键词： component evaluation model fuzzy information leadership competency solution algorithm

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Combining the advantages of discrete-and continuous-time scheduling models: Part 3. General algorithm

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COMPUTERS & CHEMICAL ENGINEERING 2020年 139卷 106848-106848页

作者： Lee, Hojae Maravelias, Christos T. Univ Wisconsin Dept Chem & Biol Engn 1415 Engn Dr Madison WI 53706 USA

One of the main challenges in applying optimization-based scheduling techniques in process industries stems from the different process characteristics and constraints that need to be taken into account when generating a schedule. For instance, consideration of sequence-dependent changeovers may easily make the resulting optimization model computationally expensive. Accordingly, building upon the recently pro-posed Discrete-Continuous algorithm (Lee and Maravelias, 2018), we propose generalized algorithm that enables accurate and fast solution of difficult instances while efficiently handling a wide range of process characteristics. The algorithm combines modeling versatility with computational tractability while guar-anteeing the feasibility and accuracy of the final solution. Through a case study inspired by a real-world brewing process, we show that our algorithm provides accurate and high quality solutions to industrial-scale instances in reasonable time. (C) 2020 Elsevier Ltd. All rights reserved.

关键词： Chemical production scheduling solution algorithm Mixed-integer programming Process operations

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