检索结果-南通市图书馆

THE GENERALIZED RIEMANN PROBLEM FOR A SCALAR NONCONVEX COMBUSTION MODEL-THE PERTURBATION ON INITIAL BINDING ENERGY

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Acta Mathematica Scientia 2012年第3期32卷 1262-1280页

作者：潘丽君盛万成 department of Mathematics Nanjing University of Aeronautics and Astronautics department of Mathematics Shanghai University

In this article, we study the generalized Riemann problem for a scalar non- convex Chapman-Jouguet combustion model in a neighborhood of the origin （t 〉 0） on the （x, t） plane. We focus our attention to the perturbation on initial binding energy. The solutions are obtained constructively under the entropy conditions. It can be found that the solutions are essentially different from the corresponding Riemann solutions for some cases. Especially, two important phenomena are observed： the transition from detonation to deflagration followed by a shock, which appears in the numerical simulations [7, 27]; the transition from deflagration to detonation （DDT）, which is one of the core problems in gas dynamic combustion.

关键词： Scalar nonconvex Chapman-Jouguet combustion model binding energy perturbation detonation deflagration

Performance comparison of aero-ramp and transverse injector based on gas-pilot flame

在线全文

学校读者我要写书评

暂无评论

航空动力学报 2014年第2期29卷 405-419页

作者： SONG Gang-lin ZHANG Yan WEI Bao-xi TIAN Liang XU Xu School of astronautics Beijing University of Aeronautics and Astronautics Xichang Satellite Launch Center Chinese People's Liberation Amry General Armament Department department of Civil Engineering Nanyang Institute of Technology

A direct performance comparison between the four-hole aero-ramp injector and single transverse injector in a dual-mode scramjet combustor was *** mixing characteristics of two injectors were calculated by solving the three-dimensional(3-D)compressible Reynolds-averaged Navier-Stokes equations(RANS),with the help of the shear-stress-transport(SST)k-ωturbulence *** numerical results show that the far field mixing efficiency of the aero-ramp injector is higher than that of the single transverse *** enthalpy vitiated air was heated to a total temperature of 1 200Kby hydrogen-oxygen combustion, entering the isolator entrance at a Mach number of ***-reacting experimental conditions involved sonic injection of nitrogen to safely simulate ethylene injected into the combustor at a jet-to-free stream momentum flux ratio of *** photographs were obtained to analyze the shock structure around the *** test conditions involved sonic injection of ethylene at the jet-to-free stream momentum flux ratios ranging from 0.5to *** speed camera was used to capture the flame structures in the near-field combustion. The experimental results show that the aero-ramp injector produce sustained combustion over a wider range of fuel-air ratios than the single transverse *** the identical jet-to-free stream momentum flux ratio,the aero-ramp has a larger isolator margin than the single transverse injector,demonstrating a better ability for avoiding ***,the air specific impulse and total temperature recovery of two injectors,which are calculated by the one-dimensional(1-D)performance analysis code,are almost identical.

关键词： dual-mode scramjet aero-ramp injector transverse injector gas-pilot flame mixing and combustion performance

Stability of the Equilibrium to the Boltzmann Equation with Large Potential Force

在线全文

学校读者我要写书评

暂无评论

Chinese Annals of Mathematics,Series B 2018年第5期39卷 805-816页

作者： Xiuhui YANG department of Mathematics College of Science Nanjing University of Aeronautics and Astronautics

The Boltzmann equation with external potential force exists a unique equilibrium—local Maxwellian. The author constructs the nonlinear stability of the equilibrium when the initial datum is a small perturbation of the local Maxwellian in the whole space R^3. Compared with the previous result [Ukai, S., Yang, T. and Zhao, H.-J.,Global solutions to the Boltzmann equation with external forces, Anal. Appl.(Singap.), 3,2005, 157–193], no smallness condition on the Sobolev norm H^1 of the potential is needed in our arguments. The proof is based on the entropy-energy inequality and the L^2-L~∞ estimates.

关键词： Boltzmann equation Large potential force Stability Entropy-energyinequality L^2 - L^∞ method

Long-term semi-autonomous orbit determination supported by a few ground stations for navigation constellation

在线全文

学校读者我要写书评

暂无评论

Science China(Physics,Mechanics & Astronomy) 2011年第7期54卷 1342-1353页

作者： YI Hang XU Bo GAO YouTao WANG JiaSong State Key Laboratory of astronautics Dynamics Xi'an 710043 China College of astronautics Nanjing University of Aeronautics and astronautics Nanjing 210016 China Astronomy department of Nanjing University Nanjing 210093 China

In view of the present technology of autonomous orbit determination for navigation satellite constellation(NSC) and the geographical conditions of China,we propose a long-term semi-autonomous orbit determination scheme supported by a few ground stations for NSC in this *** the effect of rotation and translation of the entire constellation relative to the inertial reference frame can bring large errors to the autonomous orbit determination using only cross-link range measurement,a few ground stations(such as 1-3) are supposed to construct the connection between the NSC and the *** by such a few ground stations,the NSC can realize long-term orbit determination called semi-autonomous orbit *** simulation results based on the IGS ephemeris indicate that,for a certain degree of measurement errors,the NSC can maintain its semi-autonomous orbit determination in a period of 240 days within 5 meters of URE.

关键词： navigation constellation cross-link range measurement semi-autonomous orbit determination a few ground stations

Thermal state calculation of chamber in small thrust liquid rocket engine for steady state pulsed mode

在线全文

学校读者我要写书评

暂无评论

Chinese Journal of Aeronautics 2019年第2期32卷 253-262页

作者： Alexey Gennadievich VOROBYEV Svatlana Sergeevna VOROBYEVA Lihui ZHANG Evgeniy Nikolaevich BELIAEV department of Rocket Engines Moscow Aviation Institute School of astronautics Beihang University

This paper presents a method of thermal state calculation of combustion chamber in small thrust liquid rocket engine. The goal is to predict the thermal state of chamber wall by using basic parameters of engine: thrust level, propellants, chamber pressure, injection pattern, film cooling parameters, material of wall and their coating, etc. The difficulties in modeling the startup and shutdown processes of thrusters lie in the fact that there are the conjugated physical processes occurring at various parameters for non-design conditions. A mathematical model to predict the thermal state of the combustion chamber for different engine operation modes is developed. To simulate the startup and shutdown processes, a quasi-steady approach is applied by replacing the transient process with time-variant operating parameters of steady-state processes. The mathematical model is based on several principles and data commonly used for heat transfer modeling: geometry of flow part, gas dynamics of flow, thermodynamics of propellants and combustion spices, convective and radiation heat flows, conjugated heat transfer between hot gas and wall, and transient approach for calculation of thermal state of construction. Calculations of the thermal state of the combustion chamber in single-turn-on mode show good convergence with the experimental results. The results of pulsed modes indicate a large temperature gradient on the internal wall surface of the chamber between pulses and the thermal state of the wall strongly depends on the pulse duration and the interval.

关键词： Combustion chamber Film cooling Mathematical model Nonstationary thermal mode Small thrust liquid rocket engine Steady pulse mode Thermal state

A molecular dynamics-based comparison of defect production in collision cascades during the bombardment of iron with different ions

在线全文

学校读者我要写书评

暂无评论

Science China(Technological Sciences) 2014年第1期57卷 29-34页

作者： YANG YaHui TANG XiaoBin CHEN FeiDa HUANG Hai LIU Jian department of Nuclear Science and Engineering Nanjing University of Aeronautics and Astronautics

We present a computer simulation study on the influence of incident ions on the energy transferred to primary knock-on atoms(PKAs)and defects produced in the cascade collision of *** types of ions(H,Fe,and Xe,which are frequently used in irradiation experiments)with an energy of 3 MeV were *** to the calculation results of SRIM,the average energy transferred to PKAs by Fe ions was the highest among the three ***,cascade collisions induced by PKAs with different energies were simulated by the molecular dynamics *** maximum number of defects produced during irra-diation increased,and the time taken by defect number peak formation was extended with the increased energy of *** difference in radial distribution function between pre-and post-irradiation irons showed that a higher energy of PKA transferred resulted in a flatter ***,the law of defects varying in temperature was also *** the researches imply that heavy ions can substitute for neutrons in irradiation experiments which is a practicable way,but the influence of conditions must be taken into account.

关键词： molecular dynamics cascade collision defect production Radial Distribution Function (RDF)

An actor-critic based learning method for decision-making and planning of autonomous vehicles

在线全文

学校读者我要写书评

暂无评论

Science China(Technological Sciences) 2021年第5期64卷 984-994页

作者： XU Can ZHAO WanZhong CHEN QingYun WANG ChunYan department of Vehicle Engineering Nanjing University of Aeronautics and AstronauticsNanjing 210016China

In order to improve the agility and applicability of trajectory planning algorithm for autonomous vehicles, this paper proposes a novel actor-critic based learning method for decision-making and planning in multi-vehicle complex traffic. It is the coupling planning of vehicle’s path and speed thus to make the trajectory more flexible. First, generations from the decided action to the planned trajectory are described by the end-point of the trajectory. Then, the actor-critic based learning method is built to learn an optimal policy for the decision process. It can update the policy by the gradient of the current policy’s advantage. In this process,features of the real traffic are carefully extracted by time headway(TH) and speed distribution. Reward function is built by the safety, efficiency and driving comfort. Furthermore, to make the policy network have better convergency, the policy network is modularized in two parts: the lane-changing network and the lane-keeping network, which decide the optimal end-point of the path and speed candidates respectively. Finally, the curved overtaking scenario and the interaction process with human driver are conducted to illustrate the feasibility and superiority. The results show that the proposed method has better real-time performance and can make the planned coupling trajectory more continuous and smoother than the existing rule-based method.

关键词： trajectory planning decision-making actor-critic feature extraction autonomous driving

QUASI-NEUTRAL LIMIT OF THE BIPOLAR NAVIER-STOKES-POISSON SYSTEM

在线全文

学校读者我要写书评

暂无评论

Acta Mathematica Scientia 2011年第4期31卷 1272-1280页

作者：杨秀绘 department of Mathematics College of Science Nanjing University of Aeronautics and Astronautics

This paper is concerned with the quasi-neutral limit of the bipolar NavierStokes-Poisson system. It is rigorously proved, by introducing the new modulated energy functional and using the refined energy analysis, that the strong solutions of the bipolar Navier-Stokes-Poisson system converge to the strong solution of the compressible NavierStokes equations as the Debye length goes to zero. Moreover, if we let the viscous coefficients and the Debye length go to zero simultaneously, then we obtain the convergence of the strong solutions of bipolar Navier-Stokes-Poisson system to the strong solution of the compressible Euler equations.

关键词： bipolar Navier-Stokes-Poisson system compressible Navier-Stokes equations compressible Euler equations modulated energy functional

The Feasibility of Applying AC Driven Low-Temperature Plasma for Multi-Cycle Detonation Initiation

在线全文

学校读者我要写书评

暂无评论

Plasma Science and Technology 2016年第11期18卷 1110-1115页

作者： ZHENG Dianfeng department of Aeronautics and astronautics School of Engineering Peking University Beijing 100871 China

Ignition is a key system in pulse detonation engines （PDE）. As advanced ignition methods, nanosecond pulse discharge low-temperature plasma ignition is used in some combustion systems, and continuous alternating current （AC） driven low-temperature plasma using dielectric barrier discharge （DBD） is used for the combustion assistant. However, continuous AC driven plasmas cannot be used for ignition in pulse detonation engines. In this paper, experimental and numerical studies of pneumatic valve PDE using an AC driven low-temperature plasma igniter were described. The pneumatic valve was jointly designed with the low-temperature plasma igniter, and the numerical simulation of the cold-state flow field in the pneumatic valve showed that a complex flow in the discharge area, along with low speed, was beneficial for successful ignition. In the experiments ethylene was used as the fuel and air as oxidizing agent, ignition by an AC driven low-temperature plasma achieved multi-cycle intermittent detonation combustion on a PDE, the working frequency of the PDE reached 15 Hz and the peak pressure of the detonation wave was approximately 2.0 MPa. The experimental verifications of the feasibility in PDE ignition expanded the application field of AC driven low-temperature plasma.

关键词： pulse detonation engine low-temperature plasma ignition detonation combustion