A brief concept study of a modular research aircraft with potential applications to Mars exploration is conducted.Considered are dimensional and mass constraints of a launch vehicle payload compartment,mission radius ...A brief concept study of a modular research aircraft with potential applications to Mars exploration is conducted.Considered are dimensional and mass constraints of a launch vehicle payload compartment,mission radius extension applying ground mobility and overall flight envelope extension using fixed-wing aerodynamics.Also,some lessons learned from NASA Mars Ingenuity flights are considered and addressed with few solutions.The modular system includes a fixed-wing design along with a number of smaller autonomous quadcopter UAVs,encapsulated inside a geodesic spherical support through a gimbal mechanism for ground mobility.Analyzed is the feasibility of allocating to these mini drones both scout and mapping tasks of complex terrain such as crater walls,canyons and cave systems that might hold key insights into the planet's geologic history.Once docked with the mothership fixed wing,the mini drones serve as a distributed propulsion system,for vertical take-off and landing and control,completely replacing control surfaces on the flying wing itself,its engine and landing gear.CFD and structural simulations have demonstrated the flight-ability in Mars conditions of a flying wing design along with scout drone prototypes with a pentagon-hexagon geodesic shell.Also demonstrated is the great flexibility of the suggested modular approach for various research applications and mission profiles on Mars and other planets or moons,improving overall reliability and mission radius.展开更多
The article considers the impact of forestry machines on the soil of the cutting areas and presents the results of the impact of harvesters of different classes(middlesmall,middle and heavy)and configurations of wheel...The article considers the impact of forestry machines on the soil of the cutting areas and presents the results of the impact of harvesters of different classes(middlesmall,middle and heavy)and configurations of wheeled equipment and additional equipment on the soil of the cutting areas in the conditions of Kronoberg County(South of Sweden).Methods to reduce negative impact of wheeled harvesters on the soil of forests are proposed.The aim of the research is to assess the effect of the structural parameters of the wheel harvesters of different class on the soil of the cutting areas.Wheeled harvesters were loaded with 60 kN force.The results of experimental studies of the impact of wheeled harvesters on the forest soil are presented.Recommendations on the possibility of testing the results of research in the conditions of the rental base of the Western part of the North-Western Federal District of the Russian Federation are given.展开更多
When an aircraft passes through a rainy area at high speed,the coating on the front edge of the fuselage will be continuously eroded by raindrops,causing the coating to wear,crack or even peel off.This paper uses carb...When an aircraft passes through a rainy area at high speed,the coating on the front edge of the fuselage will be continuously eroded by raindrops,causing the coating to wear,crack or even peel off.This paper uses carbon fiber T300 material as the base material,and at the different impact speeds and impact numbers,water cutting equipment was used to simulate the erosion of the coating caused by the continuous impact of water droplets.The damage morphology of samples at different damage stages was observed by digital microscope and Scanning Electron Microscope(SEM),and the damage evolution curve was established to analyze and reveal the damage behavior and damage mechanism of rain erosion.The results show that the degree of damage experienced an increasing trend with the increase of impact numbers and speed,until circular peel damage was formed;no damage occurred during the incubation period,and the curvature of the damage evolution curve increased significantly after the expansion period and eventually showed a stable expansion trend.The mechanical properties of the coating material were the main influencing factors of its rain corrosion resistance.Moreover,the axially symmetric unsteady contact problem of droplets impacting the surface of a solid deformable body was studied.And the contact area was determined based on the iterative algorithm boundary positioning method.A mathematical model and closed mathematical formula describing the unsteady interaction between a droplet and a solid deformable obstacle were proposed.展开更多
The use of dynamic programming(DP)algorithms to learn Bayesian network structures is limited by their high space complexity and difficulty in learning the structure of large-scale networks.Therefore,this study propose...The use of dynamic programming(DP)algorithms to learn Bayesian network structures is limited by their high space complexity and difficulty in learning the structure of large-scale networks.Therefore,this study proposes a DP algorithm based on node block sequence constraints.The proposed algorithm constrains the traversal process of the parent graph by using the M-sequence matrix to considerably reduce the time consumption and space complexity by pruning the traversal process of the order graph using the node block sequence.Experimental results show that compared with existing DP algorithms,the proposed algorithm can obtain learning results more efficiently with less than 1%loss of accuracy,and can be used for learning larger-scale networks.展开更多
It has been known that the lack of excellent corrosion resistance is the key problem restricting the wide application of Mg−Li alloys.Based on a quantity of literature about corrosion behavior of Mg−Li alloys,this rev...It has been known that the lack of excellent corrosion resistance is the key problem restricting the wide application of Mg−Li alloys.Based on a quantity of literature about corrosion behavior of Mg−Li alloys,this review elaborates the factors affecting the corrosion behavior of Mg−Li alloys and the processing methods for improving corrosion resistance.The corrosion characteristics of Mg−Li alloys are described firstly.Then,it is explained that the grain size,orientation,second phase,and surface film strongly influence corrosion performance,which can be tailored by alloying,plastic deformation,and heat treatment.Further in-depth discussion about the corrosion mechanisms for Mg−Li alloys was also presented.Finally,important points of improving corrosion resistance are suggested.展开更多
Calcium phosphate(CaP) coatings were prepared on Mg–8Li–2Ca magnesium alloy by micro-arc oxidation(MAO) in an alkaline Na_3PO_4–Ca[C_3H_7O_6P] base solution at the different applied voltages. Scanning electron micr...Calcium phosphate(CaP) coatings were prepared on Mg–8Li–2Ca magnesium alloy by micro-arc oxidation(MAO) in an alkaline Na_3PO_4–Ca[C_3H_7O_6P] base solution at the different applied voltages. Scanning electron microscope and X-ray diffraction were employed to characterize the microstructure and phase composition of the coatings, respectively. The corrosion resistance of the coatings was assessed by potential dynamic polarization curves, electrochemical impedance spectroscopy and hydrogen evolution experiment in simulated body fluids solution. The friction and wear properties were evaluated by friction and wear testing machine. The results demonstrate that the coating surface is porous and mainly composed of MgO, Ca_5(PO_4)_3(OH) and CaH_2P_2O_5. With the increase in voltage, the corrosion resistance and wear resistance of the MAO coating are both enhanced. The corrosion current density of the MAO coating decreases about two orders of the magnitude compared to the substrate. Additionally, wear and corrosion mechanisms are discussed.展开更多
The original free vortex wake model was used for numerical investigation.Calculation of the aerodynamic characteristics in hover and vertical descent modes in the range of vertical descent speed of 0–30 m/s including...The original free vortex wake model was used for numerical investigation.Calculation of the aerodynamic characteristics in hover and vertical descent modes in the range of vertical descent speed of 0–30 m/s including the Vortex Ring State(VRS)area was performed.The calculations were carried out under the condition of variable blade pitch angle values providing a fixed timeaverage thrust value.Visualization data of free vortex wake shapes,flow structures,and velocity fields were obtained and analyzed.The time-dependences of the rotor’s thrust and torque coefficients were obtained and analyzed.The obtained data allows determining the boundaries of the VRS area by various criteria such as rotor thrust and torque pulsations,growth of rotor power consumption relative to the hover,growth of rotor induced velocities relative to the hover,and growth of the required rotor blade pitch angles values.The results of the study are compared with experimental and calculated data of other authors and can significantly supplement the available results of experimental and computational studies in this area.展开更多
Carbonate was added to the silicate system electrolyte to improve the corrosion resistance of the plasma electrolytic oxidation coating on Mg-9Li-3Al(wt%,LA93)alloy.The influences of carbonate on the morphology,struct...Carbonate was added to the silicate system electrolyte to improve the corrosion resistance of the plasma electrolytic oxidation coating on Mg-9Li-3Al(wt%,LA93)alloy.The influences of carbonate on the morphology,structure,and phase composition of the coating were investigated by scanning electron microscopy,energy dispersive spectrometry,X-ray diffraction,and X-ray photoelectron spectroscopy.The corrosion resistance of the coating was evaluated by electrochemical experiment,hydrogen evolution,and immersion test.The results showed that the addition of carbonate resulted in a denser coating with increased hardness,and the corrosion-resistant Li_(2)CO_(3) phase was formed.Electrochemical experiments showed that compared with the coating without carbonate,the corrosion potential of the carbonate coating positively shifted(24 mV),and the corrosion current density was reduced by approximately an order of magnitude.The coating with carbonate addition possessed a high corrosion resistance and long-term protection capability.展开更多
Aiming at addressing the problem of manoeuvring decision-making in UAV air combat,this study establishes a one-to-one air combat model,defines missile attack areas,and uses the non-deterministic policy Soft-Actor-Crit...Aiming at addressing the problem of manoeuvring decision-making in UAV air combat,this study establishes a one-to-one air combat model,defines missile attack areas,and uses the non-deterministic policy Soft-Actor-Critic(SAC)algorithm in deep reinforcement learning to construct a decision model to realize the manoeuvring process.At the same time,the complexity of the proposed algorithm is calculated,and the stability of the closed-loop system of air combat decision-making controlled by neural network is analysed by the Lyapunov function.This study defines the UAV air combat process as a gaming process and proposes a Parallel Self-Play training SAC algorithm(PSP-SAC)to improve the generalisation performance of UAV control decisions.Simulation results have shown that the proposed algorithm can realize sample sharing and policy sharing in multiple combat environments and can significantly improve the generalisation ability of the model compared to independent training.展开更多
The tailored nanoparticles with a complex core/shell structure can satisfy a variety of demands, such as lattice misfit, shearability and coarsening resistance. In this research, core-shell nanoscale Al3(Yb, Er, Sc,Zr...The tailored nanoparticles with a complex core/shell structure can satisfy a variety of demands, such as lattice misfit, shearability and coarsening resistance. In this research, core-shell nanoscale Al3(Yb, Er, Sc,Zr, Li) composite particles were precipitated in Al-2 Li-0.1 Yb-0.1 Er-0.1 Sc-0.1 Zr(wt%) alloy through the double-aging treatment, in which the core was(Yb, Er, Sc, Zr)-rich formed at 300°C and the shell was Li-rich formed at 150°C. The coarsening kinetics and precipitate size distributions(PSDs) of Al3(Yb, Er, Sc,Zr, Li) particles aged at 150°C previously aged at 300°C for 24 h showed a better fit to the relation of 2∝ kt and normal distribution, indicating that the coarsening of precipitates was controlled by interface reaction, not diffusion. The Orowan bypass strengthening was operative mechanism at 150°C.展开更多
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: thrus...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.展开更多
As an advanced combat weapon,Unmanned Aerial Vehicles(UAVs)have been widely used in military wars.In this paper,we formulated the Autonomous Navigation Control(ANC)problem of UAVs as a Markov Decision Process(MDP)and ...As an advanced combat weapon,Unmanned Aerial Vehicles(UAVs)have been widely used in military wars.In this paper,we formulated the Autonomous Navigation Control(ANC)problem of UAVs as a Markov Decision Process(MDP)and proposed a novel Deep Reinforcement Learning(DRL)method to allow UAVs to perform dynamic target tracking tasks in large-scale unknown environments.To solve the problem of limited training experience,the proposed Imaginary Filtered Hindsight Experience Replay(IFHER)generates successful episodes by reasonably imagining the target trajectory in the failed episode to augment the experiences.The welldesigned goal,episode,and quality filtering strategies ensure that only high-quality augmented experiences can be stored,while the sampling filtering strategy of IFHER ensures that these stored augmented experiences can be fully learned according to their high priorities.By training in a complex environment constructed based on the parameters of a real UAV,the proposed IFHER algorithm improves the convergence speed by 28.99%and the convergence result by 11.57%compared to the state-of-the-art Twin Delayed Deep Deterministic Policy Gradient(TD3)algorithm.The testing experiments carried out in environments with different complexities demonstrate the strong robustness and generalization ability of the IFHER agent.Moreover,the flight trajectory of the IFHER agent shows the superiority of the learned policy and the practical application value of the algorithm.展开更多
The demand for autonomous motion control of unmanned aerial vehicles in air combat is boosted as taking the initiative in combat appears more and more crucial.Unmanned aerial vehicles inability to manoeuvre autonomous...The demand for autonomous motion control of unmanned aerial vehicles in air combat is boosted as taking the initiative in combat appears more and more crucial.Unmanned aerial vehicles inability to manoeuvre autonomously during air combat that features highly dynamic and uncertain manoeuvres of the enemy;however,limits their combat capabilities,which proves to be very challenging.To meet the challenge,this article proposes an autonomous manoeuvre decision model using an expert actor-based soft actor critic algorithm that reconstructs empirical replay buffer with expert experience.Specifically,the algorithm uses a small amount of expert experience to increase the diversity of the samples,which can largely improve the exploration and utilisation efficiency of deep reinforcement learning.And to simulate the complex battlefield environment,a one-toone air combat model is established and the concept of missile's attack region is introduced.The model enables the one-to-one air combat to be simulated under different initial battlefield situations.Simulation results show that the expert actor-based soft actor critic algorithm can find the most favourable policy for unmanned aerial vehicles to defeat the opponent faster,and converge more quickly,compared with the soft actor critic algorithm.展开更多
Ultrafine-grain and high-strength Mg-SLi-1Al sheets were prepared by accumulative roll bonding （ARB） process. Evolution of microstructure and mechanical properties of ARB-processed Mg-5Li-1Al sheets was investigated...Ultrafine-grain and high-strength Mg-SLi-1Al sheets were prepared by accumulative roll bonding （ARB） process. Evolution of microstructure and mechanical properties of ARB-processed Mg-5Li-1Al sheets was investigated. Results show that, during ARB process, the evolution of deformation mechanism oft Mg-5Li-1Al alloy is as follows： twinning deformation, shear deformation, forming macro shear zone, and finally dynamic recrystallization （DRX）. The grain refining mechanism changes from twin DRX to rotation DRX. With the increase in ARB cycles, strength of the Mg-5Li-1Al sheets is enhanced, whilst elongation varies slightly. With the increase in rolling cycles, anisotropy of mechanical properties decreases. It is conclusive that strain hardening and grain refinement dominate the strengthening mechanism of Mg-5Li-1Al alloy.展开更多
Evolution of geometric forms of antenna coils for radiofrequency(RF)inductively coupled plasma(ICP)sources is analyzed.Top effectiveness of flat ICPSs generating plasma"tablet"is shown.Especially effective a...Evolution of geometric forms of antenna coils for radiofrequency(RF)inductively coupled plasma(ICP)sources is analyzed.Top effectiveness of flat ICPSs generating plasma"tablet"is shown.Especially effective are ICPSs using antenna coils enhanced with ferromagnetic cores(FMICPS).It is found that the design of flat ICPSs is simpler and more convenient for the arrangement of plasma diagnostics in comparison with ICPSs of other geometries.Effective flat FMICPS models of different diameters ranging from 10 cm to 100cm are considered.Recommendations are given for development engineers dealing with ICPS devices in general and with radio frequency ion thrusters(RITs)in particular.展开更多
Aiming at intelligent decision-making of unmanned aerial vehicle(UAV)based on situation information in air combat,a novelmaneuvering decision method based on deep reinforcement learning is proposed in this paper.The a...Aiming at intelligent decision-making of unmanned aerial vehicle(UAV)based on situation information in air combat,a novelmaneuvering decision method based on deep reinforcement learning is proposed in this paper.The autonomous maneuvering model ofUAV is established byMarkovDecision Process.The Twin DelayedDeep Deterministic Policy Gradient(TD3)algorithm and the Deep Deterministic Policy Gradient(DDPG)algorithm in deep reinforcement learning are used to train the model,and the experimental results of the two algorithms are analyzed and compared.The simulation experiment results show that compared with the DDPG algorithm,the TD3 algorithm has stronger decision-making performance and faster convergence speed and is more suitable for solving combat problems.The algorithm proposed in this paper enables UAVs to autonomously make maneuvering decisions based on situation information such as position,speed,and relative azimuth,adjust their actions to approach,and successfully strike the enemy,providing a new method for UAVs to make intelligent maneuvering decisions during air combat.展开更多
The purpose of this study is to develop chitosan/phosphate composite films on magnesium alloys to improve their corrosion resistance and broaden their applications in aerospace.Phosphate/chitosan composite films were ...The purpose of this study is to develop chitosan/phosphate composite films on magnesium alloys to improve their corrosion resistance and broaden their applications in aerospace.Phosphate/chitosan composite films were successfully prepared by adding ultra-high deacetylated chitosan in a phosphate bath.The chemical composition of the prepared composite film was investigated by X-ray photoelectron spectroscopy(XPS)and Fourier trans-form infrared spectroscopy(FT-IR),and the morphology and fracture of the composite film were characterized by scanning electron microscope(SEM).Potentiodynamic polarization curves and electrochemical impedance spec-troscopy were used to study the corrosion behavior of the coated alloys.The results showed that when pH=2.5 and the chitosan concentration was 5.0 g/L,chitosan was deposited in the phosphate coating in the form of inclusions.In addition,the potentiodynamic polarization curves of the composite films show that the corrosion potential is positively shifted by 0.6 V compared to the monolayer phosphate coating,indicating improved corro-sion resistance.This work shows that highly deacetylated chitosan can be co-deposited with phosphate to form a dense composite film on the surface of magnesium alloys in one step,thereby improving the corrosion resistance of the alloy.展开更多
Experiments have been carried out to study the anomalous passage of laboratory-produced ball lightning through solid-state sheets. The passing of the ball lightning within the standard model can be explained by cascad...Experiments have been carried out to study the anomalous passage of laboratory-produced ball lightning through solid-state sheets. The passing of the ball lightning within the standard model can be explained by cascading generation of particles at entering of high-energetic protons of the ball lightning into a dense matter. The process of energy conversion of its own poloidal magnetic field of the ball lightning into the kinetic energy of its charged particles occurs in this case. The energy of protons becomes sufficient for the generation of charged pions and their subsequent cascade decay. The decay of pions leads to the appearance of negative and positive muons, as well as muon antineutrino and muon neutrino. This fact is confirmed by the presence of a passed ball lightning and a high potential of variable polarity in the region above the solid-state sheet after the ball lightning passing through it. The dark ball lightning also found was in the experiments. The laboratory ball lightning opens up new perspectives in many areas of research and applications and may have a positive impact on attempts to solve the energy problem based on muon-catalyzed nuclear fusion.展开更多
基金funded by the Russian Science Foundation(No.22–49-02047)。
文摘A brief concept study of a modular research aircraft with potential applications to Mars exploration is conducted.Considered are dimensional and mass constraints of a launch vehicle payload compartment,mission radius extension applying ground mobility and overall flight envelope extension using fixed-wing aerodynamics.Also,some lessons learned from NASA Mars Ingenuity flights are considered and addressed with few solutions.The modular system includes a fixed-wing design along with a number of smaller autonomous quadcopter UAVs,encapsulated inside a geodesic spherical support through a gimbal mechanism for ground mobility.Analyzed is the feasibility of allocating to these mini drones both scout and mapping tasks of complex terrain such as crater walls,canyons and cave systems that might hold key insights into the planet's geologic history.Once docked with the mothership fixed wing,the mini drones serve as a distributed propulsion system,for vertical take-off and landing and control,completely replacing control surfaces on the flying wing itself,its engine and landing gear.CFD and structural simulations have demonstrated the flight-ability in Mars conditions of a flying wing design along with scout drone prototypes with a pentagon-hexagon geodesic shell.Also demonstrated is the great flexibility of the suggested modular approach for various research applications and mission profiles on Mars and other planets or moons,improving overall reliability and mission radius.
文摘The article considers the impact of forestry machines on the soil of the cutting areas and presents the results of the impact of harvesters of different classes(middlesmall,middle and heavy)and configurations of wheeled equipment and additional equipment on the soil of the cutting areas in the conditions of Kronoberg County(South of Sweden).Methods to reduce negative impact of wheeled harvesters on the soil of forests are proposed.The aim of the research is to assess the effect of the structural parameters of the wheel harvesters of different class on the soil of the cutting areas.Wheeled harvesters were loaded with 60 kN force.The results of experimental studies of the impact of wheeled harvesters on the forest soil are presented.Recommendations on the possibility of testing the results of research in the conditions of the rental base of the Western part of the North-Western Federal District of the Russian Federation are given.
基金Supported by the National Natural Science Foundation of China(Nos.12261131505,62005172)the Russian Science Fund(No.23-49-00133)+1 种基金the Fundamental Research Funds for the Central Universities,China(No.D5000210517)the Basic Research Programs of Taicang,China(No.TC2021JC21).
文摘When an aircraft passes through a rainy area at high speed,the coating on the front edge of the fuselage will be continuously eroded by raindrops,causing the coating to wear,crack or even peel off.This paper uses carbon fiber T300 material as the base material,and at the different impact speeds and impact numbers,water cutting equipment was used to simulate the erosion of the coating caused by the continuous impact of water droplets.The damage morphology of samples at different damage stages was observed by digital microscope and Scanning Electron Microscope(SEM),and the damage evolution curve was established to analyze and reveal the damage behavior and damage mechanism of rain erosion.The results show that the degree of damage experienced an increasing trend with the increase of impact numbers and speed,until circular peel damage was formed;no damage occurred during the incubation period,and the curvature of the damage evolution curve increased significantly after the expansion period and eventually showed a stable expansion trend.The mechanical properties of the coating material were the main influencing factors of its rain corrosion resistance.Moreover,the axially symmetric unsteady contact problem of droplets impacting the surface of a solid deformable body was studied.And the contact area was determined based on the iterative algorithm boundary positioning method.A mathematical model and closed mathematical formula describing the unsteady interaction between a droplet and a solid deformable obstacle were proposed.
基金Shaanxi Science Fund for Distinguished Young Scholars,Grant/Award Number:2024JC-JCQN-57Xi’an Science and Technology Plan Project,Grant/Award Number:2023JH-QCYJQ-0086+2 种基金Scientific Research Program Funded by Education Department of Shaanxi Provincial Government,Grant/Award Number:P23JP071Engineering Technology Research Center of Shaanxi Province for Intelligent Testing and Reliability Evaluation of Electronic Equipments,Grant/Award Number:2023-ZC-GCZX-00472022 Shaanxi University Youth Innovation Team Project。
文摘The use of dynamic programming(DP)algorithms to learn Bayesian network structures is limited by their high space complexity and difficulty in learning the structure of large-scale networks.Therefore,this study proposes a DP algorithm based on node block sequence constraints.The proposed algorithm constrains the traversal process of the parent graph by using the M-sequence matrix to considerably reduce the time consumption and space complexity by pruning the traversal process of the order graph using the node block sequence.Experimental results show that compared with existing DP algorithms,the proposed algorithm can obtain learning results more efficiently with less than 1%loss of accuracy,and can be used for learning larger-scale networks.
基金financial supports from the Natural Science Foundation of China (Nos. 51771060, 51871068, 51971071, 52011530025)the Domain Foundation of Equipment Advance Research of the 13th Fiveyear Plan, China (No. 61409220118)+2 种基金the National Key Research and Development Program, China (No. 2021YFE0103200)the Zhejiang Province Key Research and Development Program, China (No. 2021C01086)the Open Foundation of Key Laboratory of Superlight Materials & Surface Technology of Ministry of Education, China (No. HEU10202104)。
文摘It has been known that the lack of excellent corrosion resistance is the key problem restricting the wide application of Mg−Li alloys.Based on a quantity of literature about corrosion behavior of Mg−Li alloys,this review elaborates the factors affecting the corrosion behavior of Mg−Li alloys and the processing methods for improving corrosion resistance.The corrosion characteristics of Mg−Li alloys are described firstly.Then,it is explained that the grain size,orientation,second phase,and surface film strongly influence corrosion performance,which can be tailored by alloying,plastic deformation,and heat treatment.Further in-depth discussion about the corrosion mechanisms for Mg−Li alloys was also presented.Finally,important points of improving corrosion resistance are suggested.
基金supported by the National Natural Science Foundation of China(Nos.51671063,51771060 and51871068)the Key Laboratory of Lightweight and high strength structural materials of Jiangxi Province(No.20171BCD40003)+4 种基金the Research Fund for the Doctoral Program of Higher Education(No.20132304110006)Heilongjiang Province Natural Science Foundation(No.ZD2017010)the Fundamental Research Funds for the Central Universities(No.HEUCFG201834)the Harbin City Application Technology Research and Development Project(Nos.2015RQXXJ001 and 2017RAQXJ032)the Science and Technology Innovation Project(No.009-031-001)
文摘Calcium phosphate(CaP) coatings were prepared on Mg–8Li–2Ca magnesium alloy by micro-arc oxidation(MAO) in an alkaline Na_3PO_4–Ca[C_3H_7O_6P] base solution at the different applied voltages. Scanning electron microscope and X-ray diffraction were employed to characterize the microstructure and phase composition of the coatings, respectively. The corrosion resistance of the coatings was assessed by potential dynamic polarization curves, electrochemical impedance spectroscopy and hydrogen evolution experiment in simulated body fluids solution. The friction and wear properties were evaluated by friction and wear testing machine. The results demonstrate that the coating surface is porous and mainly composed of MgO, Ca_5(PO_4)_3(OH) and CaH_2P_2O_5. With the increase in voltage, the corrosion resistance and wear resistance of the MAO coating are both enhanced. The corrosion current density of the MAO coating decreases about two orders of the magnitude compared to the substrate. Additionally, wear and corrosion mechanisms are discussed.
文摘The original free vortex wake model was used for numerical investigation.Calculation of the aerodynamic characteristics in hover and vertical descent modes in the range of vertical descent speed of 0–30 m/s including the Vortex Ring State(VRS)area was performed.The calculations were carried out under the condition of variable blade pitch angle values providing a fixed timeaverage thrust value.Visualization data of free vortex wake shapes,flow structures,and velocity fields were obtained and analyzed.The time-dependences of the rotor’s thrust and torque coefficients were obtained and analyzed.The obtained data allows determining the boundaries of the VRS area by various criteria such as rotor thrust and torque pulsations,growth of rotor power consumption relative to the hover,growth of rotor induced velocities relative to the hover,and growth of the required rotor blade pitch angles values.The results of the study are compared with experimental and calculated data of other authors and can significantly supplement the available results of experimental and computational studies in this area.
基金the Natural Science Foundation of China (Nos.51771060,51871068,51971071,and 52011530025)the Domain Foundation of Equipment Advance Research of 13th Five-year Plan,China(No.61409220118)+1 种基金the Zhejiang Province Key Research and Development Program,China (No.2021C01086)the Open Foundation of Key Laboratory of Superlight Materials&Surface Technology of Ministry of Education,China (No.HEU10202104)
文摘Carbonate was added to the silicate system electrolyte to improve the corrosion resistance of the plasma electrolytic oxidation coating on Mg-9Li-3Al(wt%,LA93)alloy.The influences of carbonate on the morphology,structure,and phase composition of the coating were investigated by scanning electron microscopy,energy dispersive spectrometry,X-ray diffraction,and X-ray photoelectron spectroscopy.The corrosion resistance of the coating was evaluated by electrochemical experiment,hydrogen evolution,and immersion test.The results showed that the addition of carbonate resulted in a denser coating with increased hardness,and the corrosion-resistant Li_(2)CO_(3) phase was formed.Electrochemical experiments showed that compared with the coating without carbonate,the corrosion potential of the carbonate coating positively shifted(24 mV),and the corrosion current density was reduced by approximately an order of magnitude.The coating with carbonate addition possessed a high corrosion resistance and long-term protection capability.
基金National Natural Science Foundation of China,Grant/Award Number:62003267Fundamental Research Funds for the Central Universities,Grant/Award Number:G2022KY0602+1 种基金Technology on Electromagnetic Space Operations and Applications Laboratory,Grant/Award Number:2022ZX0090Key Core Technology Research Plan of Xi'an,Grant/Award Number:21RGZN0016。
文摘Aiming at addressing the problem of manoeuvring decision-making in UAV air combat,this study establishes a one-to-one air combat model,defines missile attack areas,and uses the non-deterministic policy Soft-Actor-Critic(SAC)algorithm in deep reinforcement learning to construct a decision model to realize the manoeuvring process.At the same time,the complexity of the proposed algorithm is calculated,and the stability of the closed-loop system of air combat decision-making controlled by neural network is analysed by the Lyapunov function.This study defines the UAV air combat process as a gaming process and proposes a Parallel Self-Play training SAC algorithm(PSP-SAC)to improve the generalisation performance of UAV control decisions.Simulation results have shown that the proposed algorithm can realize sample sharing and policy sharing in multiple combat environments and can significantly improve the generalisation ability of the model compared to independent training.
基金supported financially by the National Natural Science Foundation of China(Nos.51671063,51771060,51871068 and 51971071)the Domain Foundation of Equipment Advance Research of 13th Five-year Plan(No.61409220118)+2 种基金the Fundamental Research Funds for the Central Universities(No.HEUCFG201834)the Harbin City Application Technology Research and Development Project(Nos.2015RQXXJ001 and 2017RAQXJ032)the Ph.D.Student Research and Innovation Fund of the Fundamental Research Funds for the Central Universities(No.3072019GIP1013)。
文摘The tailored nanoparticles with a complex core/shell structure can satisfy a variety of demands, such as lattice misfit, shearability and coarsening resistance. In this research, core-shell nanoscale Al3(Yb, Er, Sc,Zr, Li) composite particles were precipitated in Al-2 Li-0.1 Yb-0.1 Er-0.1 Sc-0.1 Zr(wt%) alloy through the double-aging treatment, in which the core was(Yb, Er, Sc, Zr)-rich formed at 300°C and the shell was Li-rich formed at 150°C. The coarsening kinetics and precipitate size distributions(PSDs) of Al3(Yb, Er, Sc,Zr, Li) particles aged at 150°C previously aged at 300°C for 24 h showed a better fit to the relation of 2∝ kt and normal distribution, indicating that the coarsening of precipitates was controlled by interface reaction, not diffusion. The Orowan bypass strengthening was operative mechanism at 150°C.
文摘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.
基金co-supported by the National Natural Science Foundation of China(Nos.62003267 and 61573285)the Natural Science Basic Research Plan in Shaanxi Province of China(No.2020JQ-220)+1 种基金the Open Project of Science and Technology on Electronic Information Control Laboratory,China(No.JS20201100339)the Open Project of Science and Technology on Electromagnetic Space Operations and Applications Laboratory,China(No.JS20210586512).
文摘As an advanced combat weapon,Unmanned Aerial Vehicles(UAVs)have been widely used in military wars.In this paper,we formulated the Autonomous Navigation Control(ANC)problem of UAVs as a Markov Decision Process(MDP)and proposed a novel Deep Reinforcement Learning(DRL)method to allow UAVs to perform dynamic target tracking tasks in large-scale unknown environments.To solve the problem of limited training experience,the proposed Imaginary Filtered Hindsight Experience Replay(IFHER)generates successful episodes by reasonably imagining the target trajectory in the failed episode to augment the experiences.The welldesigned goal,episode,and quality filtering strategies ensure that only high-quality augmented experiences can be stored,while the sampling filtering strategy of IFHER ensures that these stored augmented experiences can be fully learned according to their high priorities.By training in a complex environment constructed based on the parameters of a real UAV,the proposed IFHER algorithm improves the convergence speed by 28.99%and the convergence result by 11.57%compared to the state-of-the-art Twin Delayed Deep Deterministic Policy Gradient(TD3)algorithm.The testing experiments carried out in environments with different complexities demonstrate the strong robustness and generalization ability of the IFHER agent.Moreover,the flight trajectory of the IFHER agent shows the superiority of the learned policy and the practical application value of the algorithm.
基金acknowledge the National Nature Science Foundation of China(Grant No.62003267)Fundamental Research Funds for the Central Universities(Grant No.G2022KY0602)+1 种基金Technology on Electromagnetic Space Operations and Applications Laboratory(Grant No.2022ZX0090)key core technology research plan of Xi'an(Grant No.21RGZN0016)to provide fund for conducting experiments.
文摘The demand for autonomous motion control of unmanned aerial vehicles in air combat is boosted as taking the initiative in combat appears more and more crucial.Unmanned aerial vehicles inability to manoeuvre autonomously during air combat that features highly dynamic and uncertain manoeuvres of the enemy;however,limits their combat capabilities,which proves to be very challenging.To meet the challenge,this article proposes an autonomous manoeuvre decision model using an expert actor-based soft actor critic algorithm that reconstructs empirical replay buffer with expert experience.Specifically,the algorithm uses a small amount of expert experience to increase the diversity of the samples,which can largely improve the exploration and utilisation efficiency of deep reinforcement learning.And to simulate the complex battlefield environment,a one-toone air combat model is established and the concept of missile's attack region is introduced.The model enables the one-to-one air combat to be simulated under different initial battlefield situations.Simulation results show that the expert actor-based soft actor critic algorithm can find the most favourable policy for unmanned aerial vehicles to defeat the opponent faster,and converge more quickly,compared with the soft actor critic algorithm.
基金supported by the National Natural Science Foundation of China (51671063)Research Fund for the Doctoral Program of Higher Education (20132304110006)+1 种基金the Fundamental Research Funds for the Central Universities (HEUCF20161016)Harbin City Application Technology Research and Development Project (2015AE4AE005, 2015RQXXJ001, 2016AB2AG013)
文摘Ultrafine-grain and high-strength Mg-SLi-1Al sheets were prepared by accumulative roll bonding （ARB） process. Evolution of microstructure and mechanical properties of ARB-processed Mg-5Li-1Al sheets was investigated. Results show that, during ARB process, the evolution of deformation mechanism oft Mg-5Li-1Al alloy is as follows： twinning deformation, shear deformation, forming macro shear zone, and finally dynamic recrystallization （DRX）. The grain refining mechanism changes from twin DRX to rotation DRX. With the increase in ARB cycles, strength of the Mg-5Li-1Al sheets is enhanced, whilst elongation varies slightly. With the increase in rolling cycles, anisotropy of mechanical properties decreases. It is conclusive that strain hardening and grain refinement dominate the strengthening mechanism of Mg-5Li-1Al alloy.
基金Project supported by the Frames of the Russian Federation Government’s Grant for StateSupport of Scientific Research Headed by High Rank Foreign Scientists(11.G34.31.0022)
文摘Evolution of geometric forms of antenna coils for radiofrequency(RF)inductively coupled plasma(ICP)sources is analyzed.Top effectiveness of flat ICPSs generating plasma"tablet"is shown.Especially effective are ICPSs using antenna coils enhanced with ferromagnetic cores(FMICPS).It is found that the design of flat ICPSs is simpler and more convenient for the arrangement of plasma diagnostics in comparison with ICPSs of other geometries.Effective flat FMICPS models of different diameters ranging from 10 cm to 100cm are considered.Recommendations are given for development engineers dealing with ICPS devices in general and with radio frequency ion thrusters(RITs)in particular.
基金acknowledge National Natural Science Foundation of China(Grant No.61573285,No.62003267)Open Fund of Key Laboratory of Data Link Technology of China Electronics Technology Group Corporation(Grant No.CLDL-20182101)Natural Science Foundation of Shaanxi Province(Grant No.2020JQ220)to provide fund for conducting experiments.
文摘Aiming at intelligent decision-making of unmanned aerial vehicle(UAV)based on situation information in air combat,a novelmaneuvering decision method based on deep reinforcement learning is proposed in this paper.The autonomous maneuvering model ofUAV is established byMarkovDecision Process.The Twin DelayedDeep Deterministic Policy Gradient(TD3)algorithm and the Deep Deterministic Policy Gradient(DDPG)algorithm in deep reinforcement learning are used to train the model,and the experimental results of the two algorithms are analyzed and compared.The simulation experiment results show that compared with the DDPG algorithm,the TD3 algorithm has stronger decision-making performance and faster convergence speed and is more suitable for solving combat problems.The algorithm proposed in this paper enables UAVs to autonomously make maneuvering decisions based on situation information such as position,speed,and relative azimuth,adjust their actions to approach,and successfully strike the enemy,providing a new method for UAVs to make intelligent maneuvering decisions during air combat.
基金supported by the National Natural Science Founda-tion of China(52075112,51971071,52011530025)Natural Science Foundation of Heilongjiang Province(JJ2019LH1520).
文摘The purpose of this study is to develop chitosan/phosphate composite films on magnesium alloys to improve their corrosion resistance and broaden their applications in aerospace.Phosphate/chitosan composite films were successfully prepared by adding ultra-high deacetylated chitosan in a phosphate bath.The chemical composition of the prepared composite film was investigated by X-ray photoelectron spectroscopy(XPS)and Fourier trans-form infrared spectroscopy(FT-IR),and the morphology and fracture of the composite film were characterized by scanning electron microscope(SEM).Potentiodynamic polarization curves and electrochemical impedance spec-troscopy were used to study the corrosion behavior of the coated alloys.The results showed that when pH=2.5 and the chitosan concentration was 5.0 g/L,chitosan was deposited in the phosphate coating in the form of inclusions.In addition,the potentiodynamic polarization curves of the composite films show that the corrosion potential is positively shifted by 0.6 V compared to the monolayer phosphate coating,indicating improved corro-sion resistance.This work shows that highly deacetylated chitosan can be co-deposited with phosphate to form a dense composite film on the surface of magnesium alloys in one step,thereby improving the corrosion resistance of the alloy.
文摘Experiments have been carried out to study the anomalous passage of laboratory-produced ball lightning through solid-state sheets. The passing of the ball lightning within the standard model can be explained by cascading generation of particles at entering of high-energetic protons of the ball lightning into a dense matter. The process of energy conversion of its own poloidal magnetic field of the ball lightning into the kinetic energy of its charged particles occurs in this case. The energy of protons becomes sufficient for the generation of charged pions and their subsequent cascade decay. The decay of pions leads to the appearance of negative and positive muons, as well as muon antineutrino and muon neutrino. This fact is confirmed by the presence of a passed ball lightning and a high potential of variable polarity in the region above the solid-state sheet after the ball lightning passing through it. The dark ball lightning also found was in the experiments. The laboratory ball lightning opens up new perspectives in many areas of research and applications and may have a positive impact on attempts to solve the energy problem based on muon-catalyzed nuclear fusion.
