In this paper,a wideband true time delay line for X-band is designed to overcome the beam dispersion problem in a high-resolution spaceborne synthetic aperture radar phased array antenna system.The delay line loads th...In this paper,a wideband true time delay line for X-band is designed to overcome the beam dispersion problem in a high-resolution spaceborne synthetic aperture radar phased array antenna system.The delay line loads the electromagnetic bandgap structure on the upper surface of the substrate integrated waveguide.This is equivalent to including an additional inductance-capacitance for energy storage,which realizes the slow-wave effect.A microstrip line-SIW tapered transition structure is introduced to achieve a low loss and a large bandwidth.In the frequency band between 8-12 GHz,the measured results show that the delay multiplier of the delay line reaches 4 times,i.e.,delay line’s delay time is 4 times larger than 50Ωmicrostrip line with same length.Furthermore,the delay fluctuation,i.e.,the difference between the maximum and minimum delay as a percentage of the standard delay is only 2.5%,the insertion loss is less than-2.5 dB,and the return loss is less than-15 dB.Compared with the existing delay lines,the proposed delay line has the advantages of high delay efficiency,low delay error,wide bandwidth and low loss,which has good practical value and application prospects.展开更多
In order to accurately forecast the main engine fuel consumption and reduce the Energy Efficiency Operational Indicator(EEOI)of merchant ships in polar ice areas,the energy transfer relationship between ship-machine-p...In order to accurately forecast the main engine fuel consumption and reduce the Energy Efficiency Operational Indicator(EEOI)of merchant ships in polar ice areas,the energy transfer relationship between ship-machine-propeller is studied by analyzing the complex force situation during ship navigation and building a MATLAB/Simulink simulation platform based on multi-environmental resistance,propeller efficiency,main engine power,fuel consumption,fuel consumption rate and EEOI calculation module.Considering the environmental factors of wind,wave and ice,the route is divided into sections,the calculation of main engine power,main engine fuel consumption and EEOI for each section is completed,and the speed design is optimized based on the simulation model for each section.Under the requirements of the voyage plan,the optimization results show that the energy efficiency operation index of the whole route is reduced by 3.114%and the fuel consumption is reduced by 9.17 t.展开更多
The National Independent Innovation Demonstration Zone has been assigned the unique mission of demonstrating and leading national innovation and playing a key supportive role in enhancing green innovation.Based on the...The National Independent Innovation Demonstration Zone has been assigned the unique mission of demonstrating and leading national innovation and playing a key supportive role in enhancing green innovation.Based on the sample data of A-share listed companies in China from 2007 to 2021,we apply a multi-period difference-in-differences model to analyze whether the implementation of the National Independent Innovation Demonstration Zone policies plays a leverage effect or a crowd out effect on the green innovation efficiency of enterprises and systematically test the regulatory mechanism of government grants and media attention in the process of this influence.The empirical results show that the imple-mentation of the National Independent Innovation Demonstration Zone policies has a positive impact on the green innovation efficiency of enterprises and that the green innovation induced by this reform is not the leverage effect of additional R&D investment on the basis of the existing innovation activities of enterprises but rather the result of the reallocation of resources to crowd out existing non-green innovation.It is further found that government grants and media attention positively moderate the positive driving effect of National Independent Innovation Demonstration Zone policies on the green innovation efficiency of enterprises.展开更多
The contact characteristics of the rough tooth surface during the meshing process are significantly affected by the lubrication state.The coupling effect of tooth surface roughness and lubrication on meshing character...The contact characteristics of the rough tooth surface during the meshing process are significantly affected by the lubrication state.The coupling effect of tooth surface roughness and lubrication on meshing characteristics of planetary gear is studied.An improved three-dimensional(3 D)anisotropic tooth surface roughness fractal model is proposed based on the experimental parameters.Considering asperity contact and elastohydrodynamic lubrication(EHL),the contact load and flexibility deformation of the tooth surface are derived,and the deformation compatibility equation of the 3 D loaded tooth contact analysis(3 D-LTCA)method is improved.The asperity of the tooth surface changes the system from EHL to mixed lubrication and reduces the stiffness of the oil film.Compared with the sun planet gear,the asperity has a greater effect on the meshing characteristics of the ring-planet gear.Compared with the proposed method,the comprehensive stiffness obtained by the traditional calculation method considering the lubrication effect is smaller,especially for the ring-planet gear.Compared with roughness,speed and viscosity,the meshing characteristics of planetary gears are most sensitive to torque.展开更多
Shaped charge liner(SCL)has been extensively applied in oil recovery and defense industries.Achieving superior penetration capability through optimizing SCL structures presents a substantial challenge due to intricate...Shaped charge liner(SCL)has been extensively applied in oil recovery and defense industries.Achieving superior penetration capability through optimizing SCL structures presents a substantial challenge due to intricate rate-dependent processes involving detonation-driven liner collapse,high-speed jet stretching,and penetration.This study introduces an innovative optimization strategy for SCL structures that employs jet penetration efficiency as the primary objective function.The strategy combines experimentally validated finite element method with machine learning(FEM-ML).We propose a novel jet penetration efficiency index derived from enhanced cutoff velocity and shape characteristics of the jet via machine learning.This index effectively evaluates the jet penetration performance.Furthermore,a multi-model fusion based on a machine learning optimization method,called XGBOOST-MFO,is put forward to optimize SCL structure over a large input space.The strategy's feasibility is demonstrated through the optimization of copper SCL implemented via the FEM-ML strategy.Finally,this strategy is extended to optimize the structure of the recently emerging CrMnFeCoNi high-entropy alloy conical liners and hemispherical copper liners.Therefore,the strategy can provide helpful guidance for the engineering design of SCL.展开更多
Due to the strong unsteadiness of pulse detonation,large flow losses are generated when the detonation wave interacts with the turbine blades,resulting in low turbine efficiency.Considering that the flow losses are di...Due to the strong unsteadiness of pulse detonation,large flow losses are generated when the detonation wave interacts with the turbine blades,resulting in low turbine efficiency.Considering that the flow losses are dissipated into the gas as heat energy,some of them can be recycled during the expansion process in subsequent stages by the reheat effect,which should be helpful to improve the detonationdriven turbine efficiency.Taking this into account,this paper developed a numerical model of the detonation chamber coupled with a two-stage axial turbine,and a stoichiometric hydrogen-air mixture was used.The improvement in turbine efficiency attributable to the reheat effect was calculated by comparing the average efficiency of the stages with the efficiency of the two-stage turbine.The research indicated that the first stage was critical in suppressing the flow unsteadiness caused by pulse detonation,which stabilized the intake condition of the second stage and consequently allowed much of the flow losses from the first stage to be recycled,so that the efficiency of the two-stage turbine was improved.At a 95%confidence level,the efficiency improvement was stable at 4.5%—5.3%,demonstrating that the reheat effect is significant in improving the efficiency of the detonation-driven turbine.展开更多
This study focuses on the improvement of path planning efficiency for underwater gravity-aided navigation.Firstly,a Depth Sorting Fast Search(DSFS)algorithm was proposed to improve the planning speed of the Quick Rapi...This study focuses on the improvement of path planning efficiency for underwater gravity-aided navigation.Firstly,a Depth Sorting Fast Search(DSFS)algorithm was proposed to improve the planning speed of the Quick Rapidly-exploring Random Trees*(Q-RRT*)algorithm.A cost inequality relationship between an ancestor and its descendants was derived,and the ancestors were filtered accordingly.Secondly,the underwater gravity-aided navigation path planning system was designed based on the DSFS algorithm,taking into account the fitness,safety,and asymptotic optimality of the routes,according to the gravity suitability distribution of the navigation space.Finally,experimental comparisons of the computing performance of the ChooseParent procedure,the Rewire procedure,and the combination of the two procedures for Q-RRT*and DSFS were conducted under the same planning environment and parameter conditions,respectively.The results showed that the computational efficiency of the DSFS algorithm was improved by about 1.2 times compared with the Q-RRT*algorithm while ensuring correct computational results.展开更多
Shock wave caused by a sudden release of high-energy,such as explosion and blast,usually affects a significant range of areas.The utilization of a uniform fine mesh to capture sharp shock wave and to obtain precise re...Shock wave caused by a sudden release of high-energy,such as explosion and blast,usually affects a significant range of areas.The utilization of a uniform fine mesh to capture sharp shock wave and to obtain precise results is inefficient in terms of computational resource.This is particularly evident when large-scale fluid field simulations are conducted with significant differences in computational domain size.In this work,a variable-domain-size adaptive mesh enlargement(vAME)method is developed based on the proposed adaptive mesh enlargement(AME)method for modeling multi-explosives explosion problems.The vAME method reduces the division of numerous empty areas or unnecessary computational domains by adaptively suspending enlargement operation in one or two directions,rather than in all directions as in AME method.A series of numerical tests via AME and vAME with varying nonintegral enlargement ratios and different mesh numbers are simulated to verify the efficiency and order of accuracy.An estimate of speedup ratio is analyzed for further efficiency comparison.Several large-scale near-ground explosion experiments with single/multiple explosives are performed to analyze the shock wave superposition formed by the incident wave,reflected wave,and Mach wave.Additionally,the vAME method is employed to validate the accuracy,as well as to investigate the performance of the fluid field and shock wave propagation,considering explosive quantities ranging from 1 to 5 while maintaining a constant total mass.The results show a satisfactory correlation between the overpressure versus time curves for experiments and numerical simulations.The vAME method yields a competitive efficiency,increasing the computational speed to 3.0 and approximately 120,000 times in comparison to AME and the fully fine mesh method,respectively.It indicates that the vAME method reduces the computational cost with minimal impact on the results for such large-scale high-energy release problems with significant differences in computational domain size.展开更多
Gear assembly errors can lead to the increase of vibration and noise of the system,which affect the stability of system.The influence can be compensated by tooth modification.Firstly,an improved three-dimensional load...Gear assembly errors can lead to the increase of vibration and noise of the system,which affect the stability of system.The influence can be compensated by tooth modification.Firstly,an improved three-dimensional loaded tooth contact analysis(3D-LTCA)method which can consider tooth modification and coupling assembly errors is proposed,and mesh stiffness calculated by proposed method is verified by MASTA software.Secondly,based on neural network,the surrogate model(SM)that maps the relationship between modification parameters and mesh mechanical parameters is established,and its accuracy is verified.Finally,SM is introduced to establish an optimization model with the target of minimizing mesh stiffness variations and obtaining more even load distribution on mesh surface.The results show that even considering training time,the efficiency of gear pair optimization by surrogate model is still much higher than that by LTCA method.After optimization,the mesh stiffness fluctuation of gear pair with coupling assembly error is reduced by 34.10%,and difference in average contact stresses between left and right regions of the mesh surface is reduced by 62.84%.展开更多
The aim of this paper is to simulate and study the early moments of the reactive ballistics of a large caliber projectile fired from a gun,combining 0D and 2D axisymmetric Computational Fluid Dynamics(CFD)approaches.F...The aim of this paper is to simulate and study the early moments of the reactive ballistics of a large caliber projectile fired from a gun,combining 0D and 2D axisymmetric Computational Fluid Dynamics(CFD)approaches.First,the methodology is introduced with the development of an interior ballistics(IB)lumped parameter code(LPC),integrating an original image processing method for calculating the specific regression of propellant grains that compose the gun propellant.The ONERA CFD code CEDRE,equipped with a Dynamic Mesh Technique(DMT),is then used in conjunction with the developed LPC to build a dedicated methodology to calculate IB.First results obtained on the AGARD gun and 40 mm gun test cases are in a good agreement with the existing literature.CEDRE is also used to calculate inter-mediate ballistics(first milliseconds of free flight of the projectile)with a multispecies and reactive approach either starting from the gun muzzle plane or directly following IB.In the latter case,an inverse problem involving a Latin hypercube sampling method is used to find a gun propellant configuration that allows the projectile to reach a given exit velocity and base pressure when IB ends.The methodology developed in this work makes it possible to study the flame front of the intermediate flash and depressurization that occurs in a base bleed(BB)channel at the gun muzzle.Average pressure variations in the BB channel during depressurization are in good agreement with literature.展开更多
基金Supported by the National Natural Science Foundation of China(61971401)。
文摘In this paper,a wideband true time delay line for X-band is designed to overcome the beam dispersion problem in a high-resolution spaceborne synthetic aperture radar phased array antenna system.The delay line loads the electromagnetic bandgap structure on the upper surface of the substrate integrated waveguide.This is equivalent to including an additional inductance-capacitance for energy storage,which realizes the slow-wave effect.A microstrip line-SIW tapered transition structure is introduced to achieve a low loss and a large bandwidth.In the frequency band between 8-12 GHz,the measured results show that the delay multiplier of the delay line reaches 4 times,i.e.,delay line’s delay time is 4 times larger than 50Ωmicrostrip line with same length.Furthermore,the delay fluctuation,i.e.,the difference between the maximum and minimum delay as a percentage of the standard delay is only 2.5%,the insertion loss is less than-2.5 dB,and the return loss is less than-15 dB.Compared with the existing delay lines,the proposed delay line has the advantages of high delay efficiency,low delay error,wide bandwidth and low loss,which has good practical value and application prospects.
文摘In order to accurately forecast the main engine fuel consumption and reduce the Energy Efficiency Operational Indicator(EEOI)of merchant ships in polar ice areas,the energy transfer relationship between ship-machine-propeller is studied by analyzing the complex force situation during ship navigation and building a MATLAB/Simulink simulation platform based on multi-environmental resistance,propeller efficiency,main engine power,fuel consumption,fuel consumption rate and EEOI calculation module.Considering the environmental factors of wind,wave and ice,the route is divided into sections,the calculation of main engine power,main engine fuel consumption and EEOI for each section is completed,and the speed design is optimized based on the simulation model for each section.Under the requirements of the voyage plan,the optimization results show that the energy efficiency operation index of the whole route is reduced by 3.114%and the fuel consumption is reduced by 9.17 t.
基金supported by the National Natural Science Foundation of China(72474034)the Young Elite Scientists Sponsorship Program by SAST(20240123)+1 种基金Humanities and Social Science Fund of Ministry of Education of China(21YJC630037,21YJC630057)Social Science Foundation of Xi’an(25JX218).
文摘The National Independent Innovation Demonstration Zone has been assigned the unique mission of demonstrating and leading national innovation and playing a key supportive role in enhancing green innovation.Based on the sample data of A-share listed companies in China from 2007 to 2021,we apply a multi-period difference-in-differences model to analyze whether the implementation of the National Independent Innovation Demonstration Zone policies plays a leverage effect or a crowd out effect on the green innovation efficiency of enterprises and systematically test the regulatory mechanism of government grants and media attention in the process of this influence.The empirical results show that the imple-mentation of the National Independent Innovation Demonstration Zone policies has a positive impact on the green innovation efficiency of enterprises and that the green innovation induced by this reform is not the leverage effect of additional R&D investment on the basis of the existing innovation activities of enterprises but rather the result of the reallocation of resources to crowd out existing non-green innovation.It is further found that government grants and media attention positively moderate the positive driving effect of National Independent Innovation Demonstration Zone policies on the green innovation efficiency of enterprises.
基金Project(2024A1515240020)supported by the Guangdong Basic and Applied Basic Research Foundation,China。
文摘The contact characteristics of the rough tooth surface during the meshing process are significantly affected by the lubrication state.The coupling effect of tooth surface roughness and lubrication on meshing characteristics of planetary gear is studied.An improved three-dimensional(3 D)anisotropic tooth surface roughness fractal model is proposed based on the experimental parameters.Considering asperity contact and elastohydrodynamic lubrication(EHL),the contact load and flexibility deformation of the tooth surface are derived,and the deformation compatibility equation of the 3 D loaded tooth contact analysis(3 D-LTCA)method is improved.The asperity of the tooth surface changes the system from EHL to mixed lubrication and reduces the stiffness of the oil film.Compared with the sun planet gear,the asperity has a greater effect on the meshing characteristics of the ring-planet gear.Compared with the proposed method,the comprehensive stiffness obtained by the traditional calculation method considering the lubrication effect is smaller,especially for the ring-planet gear.Compared with roughness,speed and viscosity,the meshing characteristics of planetary gears are most sensitive to torque.
基金supported by the NSFC Basic Science Center Program for"Multi-scale Problems in Nonlinear Mechanics" (Grant No.11988102)the NSFC (Grant Nos.U2141204,12172367)+2 种基金the Key Research Program of the Chinese Academy of Sciences (Grant No.ZDRW-CN-2021-2-3)the National Key Research and Development Program of China (Grant No.2022YFC3320504-02)the opening project of State Key Laboratory of Explosion Science and Technology (Grant No.KFJJ21-01 and No.KFJJ18-14 M)。
文摘Shaped charge liner(SCL)has been extensively applied in oil recovery and defense industries.Achieving superior penetration capability through optimizing SCL structures presents a substantial challenge due to intricate rate-dependent processes involving detonation-driven liner collapse,high-speed jet stretching,and penetration.This study introduces an innovative optimization strategy for SCL structures that employs jet penetration efficiency as the primary objective function.The strategy combines experimentally validated finite element method with machine learning(FEM-ML).We propose a novel jet penetration efficiency index derived from enhanced cutoff velocity and shape characteristics of the jet via machine learning.This index effectively evaluates the jet penetration performance.Furthermore,a multi-model fusion based on a machine learning optimization method,called XGBOOST-MFO,is put forward to optimize SCL structure over a large input space.The strategy's feasibility is demonstrated through the optimization of copper SCL implemented via the FEM-ML strategy.Finally,this strategy is extended to optimize the structure of the recently emerging CrMnFeCoNi high-entropy alloy conical liners and hemispherical copper liners.Therefore,the strategy can provide helpful guidance for the engineering design of SCL.
基金financially supported by the National Natural Science Foundation of China through Grant Nos.12372338 and U2241272the Natural Science Foundation of Shaanxi Province of China through Grant Nos.2023-JC-YB-352 and 2022JZ-20+1 种基金the Guangdong Basic and Applied Basic Research Foundation through Grant No.2023A1515011663the Practice and Innovation Funds for Graduate Students of Northwestern Polytechnical University through Grant No.PF2023010。
文摘Due to the strong unsteadiness of pulse detonation,large flow losses are generated when the detonation wave interacts with the turbine blades,resulting in low turbine efficiency.Considering that the flow losses are dissipated into the gas as heat energy,some of them can be recycled during the expansion process in subsequent stages by the reheat effect,which should be helpful to improve the detonationdriven turbine efficiency.Taking this into account,this paper developed a numerical model of the detonation chamber coupled with a two-stage axial turbine,and a stoichiometric hydrogen-air mixture was used.The improvement in turbine efficiency attributable to the reheat effect was calculated by comparing the average efficiency of the stages with the efficiency of the two-stage turbine.The research indicated that the first stage was critical in suppressing the flow unsteadiness caused by pulse detonation,which stabilized the intake condition of the second stage and consequently allowed much of the flow losses from the first stage to be recycled,so that the efficiency of the two-stage turbine was improved.At a 95%confidence level,the efficiency improvement was stable at 4.5%—5.3%,demonstrating that the reheat effect is significant in improving the efficiency of the detonation-driven turbine.
基金the National Natural Science Foundation of China(Grant No.42274119)the Liaoning Revitalization Talents Program(Grant No.XLYC2002082)+1 种基金National Key Research and Development Plan Key Special Projects of Science and Technology Military Civil Integration(Grant No.2022YFF1400500)the Key Project of Science and Technology Commission of the Central Military Commission.
文摘This study focuses on the improvement of path planning efficiency for underwater gravity-aided navigation.Firstly,a Depth Sorting Fast Search(DSFS)algorithm was proposed to improve the planning speed of the Quick Rapidly-exploring Random Trees*(Q-RRT*)algorithm.A cost inequality relationship between an ancestor and its descendants was derived,and the ancestors were filtered accordingly.Secondly,the underwater gravity-aided navigation path planning system was designed based on the DSFS algorithm,taking into account the fitness,safety,and asymptotic optimality of the routes,according to the gravity suitability distribution of the navigation space.Finally,experimental comparisons of the computing performance of the ChooseParent procedure,the Rewire procedure,and the combination of the two procedures for Q-RRT*and DSFS were conducted under the same planning environment and parameter conditions,respectively.The results showed that the computational efficiency of the DSFS algorithm was improved by about 1.2 times compared with the Q-RRT*algorithm while ensuring correct computational results.
基金supported by the National Natural Science Foundation of China(Grant Nos.12302435 and 12221002)。
文摘Shock wave caused by a sudden release of high-energy,such as explosion and blast,usually affects a significant range of areas.The utilization of a uniform fine mesh to capture sharp shock wave and to obtain precise results is inefficient in terms of computational resource.This is particularly evident when large-scale fluid field simulations are conducted with significant differences in computational domain size.In this work,a variable-domain-size adaptive mesh enlargement(vAME)method is developed based on the proposed adaptive mesh enlargement(AME)method for modeling multi-explosives explosion problems.The vAME method reduces the division of numerous empty areas or unnecessary computational domains by adaptively suspending enlargement operation in one or two directions,rather than in all directions as in AME method.A series of numerical tests via AME and vAME with varying nonintegral enlargement ratios and different mesh numbers are simulated to verify the efficiency and order of accuracy.An estimate of speedup ratio is analyzed for further efficiency comparison.Several large-scale near-ground explosion experiments with single/multiple explosives are performed to analyze the shock wave superposition formed by the incident wave,reflected wave,and Mach wave.Additionally,the vAME method is employed to validate the accuracy,as well as to investigate the performance of the fluid field and shock wave propagation,considering explosive quantities ranging from 1 to 5 while maintaining a constant total mass.The results show a satisfactory correlation between the overpressure versus time curves for experiments and numerical simulations.The vAME method yields a competitive efficiency,increasing the computational speed to 3.0 and approximately 120,000 times in comparison to AME and the fully fine mesh method,respectively.It indicates that the vAME method reduces the computational cost with minimal impact on the results for such large-scale high-energy release problems with significant differences in computational domain size.
基金Project(11972112)supported by the National Natural Science Foundation of ChinaProject(N2103024)supported by the Fundamental Research Funds for the Central Universities,ChinaProject(J2019-IV-0018-0086)supported by the National Science and Technology Major Project,China。
文摘Gear assembly errors can lead to the increase of vibration and noise of the system,which affect the stability of system.The influence can be compensated by tooth modification.Firstly,an improved three-dimensional loaded tooth contact analysis(3D-LTCA)method which can consider tooth modification and coupling assembly errors is proposed,and mesh stiffness calculated by proposed method is verified by MASTA software.Secondly,based on neural network,the surrogate model(SM)that maps the relationship between modification parameters and mesh mechanical parameters is established,and its accuracy is verified.Finally,SM is introduced to establish an optimization model with the target of minimizing mesh stiffness variations and obtaining more even load distribution on mesh surface.The results show that even considering training time,the efficiency of gear pair optimization by surrogate model is still much higher than that by LTCA method.After optimization,the mesh stiffness fluctuation of gear pair with coupling assembly error is reduced by 34.10%,and difference in average contact stresses between left and right regions of the mesh surface is reduced by 62.84%.
基金the French Defense Innovation Agency (AID)the French Procurement Agency for Armament (DGA)ONERA's scientific direction for funding and supporting the present work
文摘The aim of this paper is to simulate and study the early moments of the reactive ballistics of a large caliber projectile fired from a gun,combining 0D and 2D axisymmetric Computational Fluid Dynamics(CFD)approaches.First,the methodology is introduced with the development of an interior ballistics(IB)lumped parameter code(LPC),integrating an original image processing method for calculating the specific regression of propellant grains that compose the gun propellant.The ONERA CFD code CEDRE,equipped with a Dynamic Mesh Technique(DMT),is then used in conjunction with the developed LPC to build a dedicated methodology to calculate IB.First results obtained on the AGARD gun and 40 mm gun test cases are in a good agreement with the existing literature.CEDRE is also used to calculate inter-mediate ballistics(first milliseconds of free flight of the projectile)with a multispecies and reactive approach either starting from the gun muzzle plane or directly following IB.In the latter case,an inverse problem involving a Latin hypercube sampling method is used to find a gun propellant configuration that allows the projectile to reach a given exit velocity and base pressure when IB ends.The methodology developed in this work makes it possible to study the flame front of the intermediate flash and depressurization that occurs in a base bleed(BB)channel at the gun muzzle.Average pressure variations in the BB channel during depressurization are in good agreement with literature.
