This paper uses the bibliometric analysis software CiteSpace to examine the current status and evolution of cold-chain logistics vehicle routing problems(CCVRP).7381 relevant articles published in the Web of Science c...
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This paper uses the bibliometric analysis software CiteSpace to examine the current status and evolution of cold-chain logistics vehicle routing problems(CCVRP).7381 relevant articles published in the Web of Science core collection from 2008 to 2024 were analyzed,an in-depth understanding of the publication trends and category distribution were ***,CiteSpace was used to create a scientific knowledge graph and perform visualization *** analysis includes collaboration among authors,countries,and institutions;co-citation analysis of authors,journals,and references;citation burst detection of keywords;and co-citation cluster analysis of *** on a deep understanding of current research hotspots,an in-depth discussion of existing research was conducted from three perspectives:optimization objectives,distribution scenarios,and solution *** results show that CCVRP involves complex factors such as temperature requirements,time window constraints,and multi-objective *** intricate constraints are causing research to become increasingly interdisciplinary and *** evolution of hot topics shows that the research directions span multiple fields,from algorithm design to logistics *** review helps researchers better understand the history,current status,and future development directions of CCVRP research,and provides valuable references and inspiration for academia and practice.
This paper investigates a formation control technique for low-Earth-orbit nanosatellites based on the differential aerodynamic drag and lift. An innovative method of using only the yaw angle deviation, instead of the ...
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This paper investigates a formation control technique for low-Earth-orbit nanosatellites based on the differential aerodynamic drag and lift. An innovative method of using only the yaw angle deviation, instead of the three-axis attitude rotation, is proposed to simultaneously control the in-plane and out-of-plane relative motions. This method can be used for the formation control of the Earth-pointing satellite. A control scheme consisting of four steps is designed considering complex input constraints. In this scheme, two control inputs are defined based on the predicted atmospheric density, and the explicit expressions of their time-varying feasible regions are analyzed. To obtain the yaw angle of each nanosatellite, a yaw angle solution algorithm based on the grid interpolation method is designed with online solving nonlinear optimization avoided. A dynamic surface control algorithm based on the hyperbolic tangent function and a linear model predictive control algorithm are, respectively, used to limit two control inputs within their feasible regions. In addition, a nonlinear finite-time disturbance observer is used to track the total system disturbance. Numerical simulations are carried out for along-track and circular formations, in which the uncertainties of aerodynamic forces, the attitude dynamics, and the unknown perturbation are taken into account.
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 t...
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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.
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 correl...
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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.
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 decide...
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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.
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 ...
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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.
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 i...
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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.
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)...
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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
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 ...
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