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A Paradoxical Consistency Between Dynamic and Conventional Derivatives on Hybrid Grids
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作者 Qin Sheng 《Numerical Mathematics(Theory,Methods and Applications)》 SCIE 2008年第2期198-213,共16页
It has been evident that the theory and methods of dynamic derivatives are playing an increasingly important role in hybrid modeling and computations. Being constructed on various kinds of hybrid grids, that is, tim... It has been evident that the theory and methods of dynamic derivatives are playing an increasingly important role in hybrid modeling and computations. Being constructed on various kinds of hybrid grids, that is, time scales, dynamic derivatives offer superior accuracy and flexibility in approximating mathematically important natural processes with hard-to-predict singularities, such as the epidemic growth with unpredictable jump sizes and option market changes with high uncertainties, as compared with conventional derivatives. In this article, we shall review the novel new concepts, explore delicate relations between the most frequently used second-order dynamic derivatives and conventional derivatives. We shall investigate necessary conditions for guaranteeing the consistency between the two derivatives. We will show that such a consistency may never exist in general. This implies that the dynamic derivatives provide entirely different new tools for sensitive modeling and approximations on hybrid grids. Rigorous error analysis will be given via asymptotic expansions for further modeling and computational applications. Numerical experiments will also be given. 展开更多
关键词 Dynamic derivatives conventional derivatives time scale theory APPROXIMATIONS error estimates hybrid grids uniform and nonuniform grids asymptotic expansions
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COMPUTATION OF TURBULENCE FLOW ON HYBRID GRIDS USING k-ω TURBULENCE MODEL AND OSHER SCHEME
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作者 LIUXue-qiang WUYi-zhao 《Transactions of Nanjing University of Aeronautics and Astronautics》 EI 2004年第2期94-97,共4页
An unstructured Reynolds-averaged Navier-Stokes flow solver using the finite volume method is studied. The spatial discretisation is based on the Osher approximate Riemann solvers. A two-equation turbulence model (k-... An unstructured Reynolds-averaged Navier-Stokes flow solver using the finite volume method is studied. The spatial discretisation is based on the Osher approximate Riemann solvers. A two-equation turbulence model (k-ω model) is also developed for hybrid grids to compute the turbulence flow. The turbulence flow past NACA0012 airfoil and the double ellipsolids are computed, and the numerical results show that the above methods are very efficient. 展开更多
关键词 turbulence model hybrid grids AIRFOIL Navier-Stokes equations
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Navier-Stokes Computation of Grid Fin Missile Using Hybrid Structured-Unstructured Grids 被引量:3
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作者 邓有奇 马明生 +1 位作者 郑鸣 周乃春 《Chinese Journal of Aeronautics》 SCIE EI CAS CSCD 2006年第4期304-308,共5页
Viscous CFD computations are performed to predict the aerodynamic coefficients and flowfield for a missile with grid fins by using hybrid grids. The computations arc made at Math numbvrs of 0.7 and 2.0. Full N-S equat... Viscous CFD computations are performed to predict the aerodynamic coefficients and flowfield for a missile with grid fins by using hybrid grids. The computations arc made at Math numbvrs of 0.7 and 2.0. Full N-S equations arc discretized into finite volume form and solved by an algorithm in LU-SGS. The comparisons between computation and experimental data are made, and the detailed flow structure near grid fin is shown and examined. 展开更多
关键词 computational fluid dynamics steady flow Navier-Stokes equation hybrid structureunstructured grid finite volume grid fin missile
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Hybrid Grid DSMC Method for Chemical Nonequilibrium with Rarefied Flow Heating 被引量:1
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作者 屈程 王江峰 《Transactions of Nanjing University of Aeronautics and Astronautics》 EI CSCD 2015年第4期408-414,共7页
The influence of chemical nonequilibrium on the thermal characteristics is explored by using the 2Dhybrid grid direct simulation Monte Carlo(DSMC)parallel method.An improved molecule search algorithm is proposed,which... The influence of chemical nonequilibrium on the thermal characteristics is explored by using the 2Dhybrid grid direct simulation Monte Carlo(DSMC)parallel method.An improved molecule search algorithm is proposed,which can preserve the high efficiency of area search algorithm.This method can overcome the defects of area search algorithm,and give all information about molecules hitting surface.The heat flux calculation method for a rarefied hypersonic flow is established.In addition,the testing methods of chemical reaction probability for five species of mixed gas with limited speed chemical reactions are also selected.To validate the effectiveness of the present method,hypersonic flow around a cylinder is firstly simulated,and subsequently numerical simulations of the heat flux and flow field characteristics around the blunt body at different heights are carried out in two different cases:the thermal nonequilibrium condition and the thermochemical nonequilibrium condition.Numerical results demonstrate the validity and reliability of the proposed methods. 展开更多
关键词 hybrid grid chemical nonequilibrium heat flux search algorithm DSMC parallel algorithm
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ADAPTIVE HYBRID CARTESIAN GRID METHOD FOR VORTEX-DOMINATED FLOWS
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作者 胡偶 赵宁 +1 位作者 刘剑明 吴杰 《Transactions of Nanjing University of Aeronautics and Astronautics》 EI 2013年第3期221-226,共6页
An efficient compressible Euler equation solver for vortex-dominated flows is presented based on the adaptive hybrid Cartesian mesh and vortex identifying method.For most traditional grid-based Euler solvers,the exces... An efficient compressible Euler equation solver for vortex-dominated flows is presented based on the adaptive hybrid Cartesian mesh and vortex identifying method.For most traditional grid-based Euler solvers,the excessive numerical dissipation is the great obstruction for vortex capturing or tracking problems.A vortex identifying method based on the curl of velocity is used to identify the vortex in flow field.Moreover,a dynamic adaptive mesh refinement(DAMR)process for hybrid Cartesian gird system is employed to track and preserve vortex.To validate the proposed method,a single compressible vortex convection flow is involved to test the accuracy and efficiency of DAMR process.Additionally,the vortex-dominated flow is investigated by the method.The obtained results are shown as a good agreement with the previous published data. 展开更多
关键词 hybrid Cartesian grid adaptive mesh vortex identification vortex-dominated compressible flows
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Hybrid Cartesian Grid Method for Moving Boundary Problems
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作者 Shen Zhiwei Zhao Ning 《Transactions of Nanjing University of Aeronautics and Astronautics》 EI CSCD 2016年第1期37-44,共8页
A hybrid Cartesian structured grid method is proposed for solving moving boundary unsteady problems. The near body region is discretized by using the body-fitted structured grids, while the remaining computational dom... A hybrid Cartesian structured grid method is proposed for solving moving boundary unsteady problems. The near body region is discretized by using the body-fitted structured grids, while the remaining computational domain is tessellated with the generated Cartesian grids. As the body moves, the structured grids move with the body and the outer boundaries of inside grids are used to generate new holes in the outside adaptive Cartesian grid to facilitate data communication. By using the alternating digital tree (ADT) algorithm, the computational time of hole-cutting and identification of donor cells can be reduced significantly. A compressible solver for unsteady flow problems is developed. A cell-centered, second-order accurate finite volume method is employed in spatial discreti- zation and an implicit dual-time stepping low-upper symmetric Gauss-Seidei (LU-SGS) approach is employed in temporal discretization. Geometry-based adaptation is used during unsteady simulation time steps when boundary moves and the flow solution is interpolated from the old Cartesian grids to the new one with inverse distance weigh- ting interpolation formula. Both laminar and turbulent unsteady cases are tested to demonstrate the accuracy and efficiency of the proposed method. Then, a 2-D store separation problem is simulated. The result shows that the hybrid Cartesian grid method can handle the unsteady flow problems involving large-scale moving boundaries. 展开更多
关键词 hybrid Cartesian grid l moving boundary alternating digital tree (ADT) algorithm unsteady flow
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Characteristic Analysis of UHVAC/DC Hybrid Power Grids and Construction of Power System Protection 被引量:15
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作者 Yinbiao Shu Guoping Chen +3 位作者 Zhao Yu Jianyun Zhang Chao Wang Chao Zheng 《CSEE Journal of Power and Energy Systems》 SCIE 2017年第4期325-333,共9页
Strong DC coupling with weak AC and large-scale renewable energy integration are the two significant characteristics of ultra-high-voltage AC/DC(UHVAC/DC)hybrid power grids in China.Strong coupling between AC and DC g... Strong DC coupling with weak AC and large-scale renewable energy integration are the two significant characteristics of ultra-high-voltage AC/DC(UHVAC/DC)hybrid power grids in China.Strong coupling between AC and DC grids and the different integration performance of renewable energy sources have profoundly changed the stability characteristics of the power system.The traditional stability control system is inadequate for the stability control of UHVAC/DC power grids.This paper analyzes the requirements for constructing an integrated defense system in a UHVAC/DC hybrid power grid(i.e.power system protection).The definition,connotation,and designing principles of power system protection are put forward.The relationship between the power system protection and the traditional three-defense lines is investigated.The design principles,general hardware structure and main functions of a power system protection are presented.Key problems and technologies are specified in the construction of the power system protection. 展开更多
关键词 Design scheme general structure power system protection key technology renewable energy integration security and stability strong DC coupling with weak AC UHVAC/DC hybrid power grid
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Aerodynamic Characteristics of Projectile with Exotic Wraparound Wings Configuration
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作者 Fu Zhang Wen-Jun Ruan +2 位作者 Hao Wang Chen-Guang Zhu Meng-Hua Zhang 《Journal of Harbin Institute of Technology(New Series)》 EI CAS 2014年第3期30-37,共8页
A projectile with exotic wraparound wings( WAW) configuration is designed to improve the finstabilized projectile shooting quality. Two fin-stabilized projectiles with the same body with and without exotic WAW configu... A projectile with exotic wraparound wings( WAW) configuration is designed to improve the finstabilized projectile shooting quality. Two fin-stabilized projectiles with the same body with and without exotic WAW configuration are simulated numerically by applying the Roe scheme. The shear-stress transport turbulence models and the lower-upper symmetric Gauss-Seidel implicit method are used to solve 3D Reynoldsaveraged Navier—Stokes equations. The differences in aerodynamic coefficients and aerodynamic characteristics of the projectiles when the Mach number varies from 0. 35 to 0. 95 are obtained,and the cause of these differences is analyzed. The calculation results indicate that the lift-to-drag ratio of the projectile significantly increases,the rolling moment decreases,and the position of the pressure center of the projectile shows relatively small changes when the exotic WAW configuration is used. Therefore,this projectile can obviously reduce rolling effect,enlarge range and improve flying stability. 展开更多
关键词 exotic WAW configuration aerodynamic characteristic hybrid structure-unstructured grid overlapping grid
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An efficient large-scale mesh deformation method based on MPI/Open MP hybrid parallel radial basis function interpolation 被引量:4
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作者 Zhong ZHAO Rong MA +2 位作者 Lei HE Xinghua CHANG Laiping ZHANG 《Chinese Journal of Aeronautics》 SCIE EI CAS CSCD 2020年第5期1392-1404,共13页
An efficient MPI/OpenMP hybrid parallel Radial Basis Function (RBF) strategy for both continuous and discontinuous large-scale mesh deformation is proposed to reduce the computational cost and memory consumption.Unlik... An efficient MPI/OpenMP hybrid parallel Radial Basis Function (RBF) strategy for both continuous and discontinuous large-scale mesh deformation is proposed to reduce the computational cost and memory consumption.Unlike the conventional parallel methods in which all processors use the same surface displacement and implement the same operation,the present method employs different surface points sets and influence radius for each volume point movement,accompanied with efficient geometry searching strategy.The deformed surface points,also called Control Points (CPs),are stored in each processor.The displacement of spatial points is interpolated by using only 20-50 nearest control points,and the local influence radius is set to 5-20 times the maximum displacement of control points.To shorten the searching time for the nearest control point clouds,an Alternating Digital Tree (ADT) algorithm for 3D complex geometry is designed based on an iterative bisection technique.Besides,an MPI/OpenMP hybrid parallel approach is developed to reduce the memory cost in each High-Performance Computing (HPC) node for large-scale applications.Three 3D cases,including the ONERA-M6 wing and a commercial transport airplane standard model with up to 2.5 billion hybrid elements,are used to test the present mesh deformation method.The robustness and high parallel efficiency are demonstrated by a wing deflection case with a maximum bending angle of 450 and more than 80% parallel efficiency with 1024 MPI processors.In addition,the availability for both continuous and discontinuous surface deformation is verified by interpolating the projecting displacement with opposite directions surface points to the spatial points. 展开更多
关键词 Mesh deformation Moving mesh generation MPI/Open MP hybrid parallel computing Parallel radial basis function interpolation Unstructured hybrid grid
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Pilot protection of hybrid MMC DC grid based on active detection 被引量:21
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作者 Guobing Song Junjie Hou +1 位作者 Bing Guo Zhehong Chen 《Protection and Control of Modern Power Systems》 2020年第1期82-96,共15页
Considering the advantages and limitations of traditional identification method,combined with the strategy of active detection,the principle of DC grid pilot protection based on active detection is proposed to improve... Considering the advantages and limitations of traditional identification method,combined with the strategy of active detection,the principle of DC grid pilot protection based on active detection is proposed to improve the sensitivity and reliability of hybrid MMC DC grid protection,and to ensure the accurate identification of fault areas in DC grid.By using the DC fault ride-through control strategy of the hybrid sub-module MMC,the fault current at the converter station DC terminal is limited.Based on the high controllability of hybrid MMC,sinusoidal fault detection signals with the same frequency are injected into the line at each converter station.Based on model recognition,the capacitance model condition is satisfied by the detected signals at both ends during external faults whereas not satisfied during internal faults.The Spearman correlation coefficients is then introduced,and the correlation discriminant of capacitance model is constructed to realize fault area discrimination of DC grid.The simulation results show that the active detection protection scheme proposed in this paper can accurately identify the fault area of DC grid,and is not affected by fault impedance and has low sampling rate requirement. 展开更多
关键词 hybrid MMC DC grid Fault ride-through control strategy Active detection Model recognition Pilot protection
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Sizing of hybrid PMSG-PV system for battery charging of electric vehicles
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作者 M. M. RAJAN SINGARAVEL S. ARUL DANIEL 《Frontiers in Energy》 SCIE CSCD 2015年第1期68-74,共7页
The number of electric vehicles are increasing in the society as they are considered as zero emission vehicles and also because conventional fuels are becoming expensive. Additional electrical power should be produced... The number of electric vehicles are increasing in the society as they are considered as zero emission vehicles and also because conventional fuels are becoming expensive. Additional electrical power should be produced to meet the energy requirement of this increase in electric vehicle population. To use the existing grid infrastructure without any failure, installing distributed generator at secondary distribution network is essential. In this work, sizing of wind-driven permanent magnet synchronous generator photovoltaic hybrid distributed generating system has been attempted to meet the energy demand of electric vehicles of a particular residential area. Different feasible combinations for wind generator capacity and photovoltaic capacity are obtained to satisfy the additional energy requirement. Results are analyzed based on energy, financial payback periods and daily power profile of the hybrid system. Based on this analysis, the sizes of wind generator and photovoltaic array have been chosen to meet the energy demand of electric vehicles of that particular residential locality. 展开更多
关键词 electric vehicles hybrid PMSG-PV system smart grid
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Differential Formulation of Discontinuous Galerkin and Related Methods for the Navier-Stokes Equations
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作者 Haiyang Gao Z.J.Wang H.T.Huynh 《Communications in Computational Physics》 SCIE 2013年第4期1013-1044,共32页
A new approach to high-order accuracy for the numerical solution of conservation laws introduced by Huynh and extended to simplexes by Wang and Gao is renamed CPR(correction procedure or collocation penalty via recons... A new approach to high-order accuracy for the numerical solution of conservation laws introduced by Huynh and extended to simplexes by Wang and Gao is renamed CPR(correction procedure or collocation penalty via reconstruction).The CPR approach employs the differential form of the equation and accounts for the jumps in flux values at the cell boundaries by a correction procedure.In addition to being simple and economical,it unifies several existing methods including discontinuous Galerkin,staggered grid,spectral volume,and spectral difference.To discretize the diffusion terms,we use the BR2(Bassi and Rebay),interior penalty,compact DG(CDG),and I-continuous approaches.The first three of these approaches,originally derived using the integral formulation,were recast here in the CPR framework,whereas the I-continuous scheme,originally derived for a quadrilateral mesh,was extended to a triangular mesh.Fourier stability and accuracy analyses for these schemes on quadrilateral and triangular meshes are carried out.Finally,results for the Navier-Stokes equations are shown to compare the various schemes as well as to demonstrate the capability of the CPR approach. 展开更多
关键词 Discontinuous Galerkin lifting collocation penalty flux reconstruction Navier-Stokes equations correction procedure via reconstruction unstructured hybrid grids
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A CFD-based numerical virtual flight simulator and its application in control law design of a maneuverable missile model 被引量:6
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作者 Laiping ZHANG Xinghua CHANG +2 位作者 Rong MA Zhong ZHAO Nianhua WANG 《Chinese Journal of Aeronautics》 SCIE EI CAS CSCD 2019年第12期2577-2591,共15页
A CFD-based Numerical Virtual Flight(NVF)simulator is presented,which integrates an unsteady flow solver on moving hybrid grids,a Rigid-Body Dynamics(RBD)solver and a module of the Flight Control System(FCS).A techni... A CFD-based Numerical Virtual Flight(NVF)simulator is presented,which integrates an unsteady flow solver on moving hybrid grids,a Rigid-Body Dynamics(RBD)solver and a module of the Flight Control System(FCS).A technique of dynamic hybrid grids is developed to control the active control surfaces with body morphing,with a technique of parallel unstructured dynamic overlapping grids generating proper moving grids over the deflecting control surfaces(e.g.the afterbody rudders of a missile).For the flow/kinematic coupled problems,the 6 Degree-Of-Freedom(DOF)equations are solved by an explicit or implicit method coupled with the URANS CFD solver.The module of the control law is explicitly coupled into the NVF simulator and then improved by the simulation of the pitching maneuver process of a maneuverable missile model.A nonlinear dynamic inversion method is then implemented to design the control law for the pitching process of the maneuverable missile model.Simulations and analysis of the pitching maneuver process are carried out by the NVF simulator to improve the flight control law.Higher control response performance is obtained by adjusting the gain factors and adding an integrator into the control loop. 展开更多
关键词 Dynamic hybrid grid generation Flight control law Flow/kinematic coupling method Maneuverable missile pitching Nonlinear dynamic inversion Numerical virtual?ight
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