The demands of aircraft quality design criterion on main control system failure and subsequently instantaneous response were analyzed.According to the simulation,the flight characteristics of an aircraft were studied ...The demands of aircraft quality design criterion on main control system failure and subsequently instantaneous response were analyzed.According to the simulation,the flight characteristics of an aircraft were studied in different angle of rudder seizure.It demonstrated that when rudder seizure with high angle and pilot could not take action immediately,the flight parameters would change sharply.The yaw angle increased 50 degrees in 5 minutes,side velocity could attain 40 meters per-second,the angle of attack and sideslip would surpass 30 degrees,roll rate would reach -20 degrees per second,side load would arrive 0.6g.Simultaneity the angle of attack exceeded the limited angle,the aircraft would stall.If control wasn't working,the disaster would happen.These phenomena supply the sufficient information of the rudder malfunction. The validity of correcting yaw moment by asymmetry thrust was testified,the simulation results showed that even rudder seizure in most serious conditions,adopting asymmetry thrust can correct yaw moment caused by the rudder seizure.The judgment standards of flight safety level for the state of malfunction were given.The safety level was assessed caused by the rudder seizure.For an aircraft with two engines on one side,the pilots need to adjust the 4 engines to balance the asymmetric moment,the work load is increased enormously.According the flight safety standards,the safety level is level Ⅲ.展开更多
The influence of dihedral layout on lateral–directional dynamic stability of the tailless flying wing aircraft is discussed in this paper. A tailless flying wing aircraft with a large aspect ratio is selected as the ...The influence of dihedral layout on lateral–directional dynamic stability of the tailless flying wing aircraft is discussed in this paper. A tailless flying wing aircraft with a large aspect ratio is selected as the object of study, and the dihedral angle along the spanwise sections is divided into three segments. The influence of dihedral layouts is studied. Based on the stability derivatives calculated by the vortex lattice method code, the linearized small-disturbance equations of the lateral modes are used to determine the mode dynamic characteristics. By comparing 7056 configurations with different dihedral angle layouts, two groups of stability optimized dihedral layout concepts are created. Flight quality close to Level 2 requirements is achieved in these optimized concepts without any electric stability augmentation system.展开更多
The effects of shot peening（SP） and plasma electrolytic oxidation（PEO） on the intergranular corrosion behavior of the novel high strength aluminum alloy 7A85（AA 7A85） were investigated by electrochemical polariz...The effects of shot peening（SP） and plasma electrolytic oxidation（PEO） on the intergranular corrosion behavior of the novel high strength aluminum alloy 7A85（AA 7A85） were investigated by electrochemical polarization and electrochemical impedance tests.The intergranular corrosion mechanism of SP,PEO and PEO combined with sealingtreated AA 7A85 was studied by the metallographic analysis,residual stress testing,X-ray diffractometer analysis and scanning electron microscopy.The results show that AA 7A85-T7452 is very sensitive to intergranular corrosion.SP would significantly improve its intergranular corrosion resistance.This is attributed to the combination action of residual compressive stress and grain refinement.PEO would reduce the largest corrosion depth by 41.6%.Moreover,PEO without sealing did not eliminate the intergranular corrosion due to the existence of the micropores and microcracks in the oxide coating.However,PEO combined with the SiO2sol–gel sealing treatment could effectively protect the AA 7A85-T7452 from intergranular corrosion because of the good corrosion resistance and barrier function of the sealed coating.展开更多
Wind tunnel test is an important way to test the performance of Gust Load Alleviation(GLA).At present,some component-level wind tunnel tests have been carried out in big aviation countries,but there is a lack of full ...Wind tunnel test is an important way to test the performance of Gust Load Alleviation(GLA).At present,some component-level wind tunnel tests have been carried out in big aviation countries,but there is a lack of full aircraft model GLA tests.In this study,a set of large-scale GLA test system in low-speed wind tunnel is developed,which includes a gust generator,a five-degree-of-freedom suspension system,a full elastic aircraft model with control system,and gust load measuring devices.Two control schemes based on closed-loop feedback control and open-loop feed forward control are respectively designed and verified by the full-model GLA tests in the wind tunnel.The experimental results show that the designed gust generator can generate a stable wideband,wide-area gust wind field;the suspension support system can sustain static and dynamic stability during wind tunnel test,and enables the model moving in the horizontal,vertical,pitching,rolling and yawing directions.The results show that the closed-loop feedback control can obtain good control performance of reducing the peak values of elastic vibration response induced by gust excitation,but has little effect on suppressing the rigid body motion excited by low-frequency gust,while the open-loop feed forward control presents superior performance in allevi-ating the high-frequency elastic vibration as well as the low-frequency rigid body motion with more than 40%overall reduction rate.展开更多
The phase transition of titanium alloys is sensitive to the heat-treatment procedure,accompanied with the latent heat induced by phase transition.However,the latent heat during phase transition of titanium alloy has n...The phase transition of titanium alloys is sensitive to the heat-treatment procedure,accompanied with the latent heat induced by phase transition.However,the latent heat during phase transition of titanium alloy has not been systematically studied,which may result in the gap between designed and actual temperature of the sample and affect the final mechanical properties.In this work,DSC(differential scanning calorimetry)and first-principles simulate methods were used to study theβ→αphase transition process of TB18(Ti–Al-Mo-V-Cr-Nb-Fe system)metastableβtitanium alloy,especially to reveal the influence of the heating rate on latent heat.The ratio of latent heat to endothermic heat of the sample during temperature rising was introduced to interpret the effect of latent heat to actual temperature.The ratio of latent heat to endothermic heat at 1℃/min is about 15 to 20 times higher than that at 10℃/min.The higher ratio indicates that the latent heat of phase transition has a more significant effect on the temperature,which is related to the temperature range of phase transition and theαvolume fraction.Compared with the heating rate of 1℃/min,theβ→αphase transition takes place at higher temperature and the volume fraction ofαis smaller at 10℃/min.Meanwhile,there is a precipitation free zone between grain boundaryαand intragranularαand the distribution ofαlamellae is heterogeneous when the heating rate is 10℃/min.Both of the experimental and theoretical results suggest that the latent heat of phase transition is the main cause of the temperature fluctuation during heat-treatment process.This work has guiding significance for microstructure optimization affected by temperature,to achieve the desired mechanical properties.展开更多
In this work,a tacticity strategy is proposed to adjust the mechanical properties of chiral mechanical metamaterials for vibration isolation.By applying the finite element method,the impact of tacticity on tensile def...In this work,a tacticity strategy is proposed to adjust the mechanical properties of chiral mechanical metamaterials for vibration isolation.By applying the finite element method,the impact of tacticity on tensile deformations,band structures,and vibration transmission spectra of chiral metamaterials is investigated.The axial deformations of isotactic configuration and syndiotactic configuration are similar under tensile loads,but rotational deformation occurs in the isotactic configuration.With the same geometric and material parameters,the first band gap of the syndiotactic configuration is lower than that of the isotactic configuration.The vibration suppression performance of chiral mechanical metamaterials is verified by numerical simulations and experiments.Parametric analysis of the band gap provides valuable insights for the manipulation and expansion of vibration reduction.Gradient design based on parametric analysis achieves an extended range of vibration suppression.展开更多
In this research,we introduce an innovative approach that combines the Continuum Damage Mechanics-Finite Element Method(CDM-FEM)with the Particle Swarm Optimization(PSO)-based technique,to predict the Medium-Low-Cycle...In this research,we introduce an innovative approach that combines the Continuum Damage Mechanics-Finite Element Method(CDM-FEM)with the Particle Swarm Optimization(PSO)-based technique,to predict the Medium-Low-Cycle Fatigue(MLCF)life of perforated structures.First,fatigue tests are carried out on three center-perforated structures,aiming to assess their fatigue life under various strengthening conditions.These tests reveal significant variations in fatigue life,accompanied by an examination of crack initiation through the analysis of fatigue fracture surfaces.Second,an innovative fatigue life prediction methodology is applied to perforated structures,which not only forecasts the initiation of fatigue cracks but also traces the progression of damage within these structures.It leverages an elastoplastic constitutive model integrated with damage and a damage evolution model under cyclic loads.The accuracy of this approach is validated by comparison with test results,falling within the three times error band.Finally,we explore the impact of various strengthening techniques,including cross-sectional reinforcement and cold expansion,on the fatigue life and damage evolution of these structures.This is achieved through an in-depth comparative analysis of both experimental data and computational predictions,which provides valuable insights into the behavior of perforated structures under fatigue conditions in practical applications.展开更多
A series of computations is conducted for many multi-hole arrangements at several blowing ratios to further investigate the evolution of the film from multi-holes. The influence of multi-hole arrangement on effusion f...A series of computations is conducted for many multi-hole arrangements at several blowing ratios to further investigate the evolution of the film from multi-holes. The influence of multi-hole arrangement on effusion film cooling is analyzed and a preliminary relationship evaluating the film development from developing state to developed state is brought forward. Results show that the coolant jets from front rows of multi-holes merge rapidly and the strength of the kidney vortices due to mainstream-coolant jet interaction in the downstream region are mitigated under super-long-diamond arrangement where the streamwise hole-to-hole pitch is bigger than spanwise hole-to-hole pitch. The holes array arranged in super-long-diamond mode is not only in favor of obtaining developed film layer, but also improving averaged adiabatic film cooling effectiveness.展开更多
This paper develops a low-diffusion robust flux splitting scheme termed TVAP to achieve the simulation of wide-ranging Mach number flows.Based on Toro-Vazquez splitting approach,the new scheme splits inviscid flux int...This paper develops a low-diffusion robust flux splitting scheme termed TVAP to achieve the simulation of wide-ranging Mach number flows.Based on Toro-Vazquez splitting approach,the new scheme splits inviscid flux into convective system and pressure system.This method introduces Mach number splitting function and numerical sound speed to evaluate advection system.Meanwhile,pressure diffusion term,pressure momentum flux,interface pressure and interface velocity are constructed to measure pressure system.Then,typical test problems are utilized to systematically assess the robustness and accuracy of the resulting scheme.Matrix stability analysis and a series of numerical cases,such as double shear-layer problem and hypersonic viscous flow over blunt cone,demonstrate that TVAP scheme achieves excellent low diffusion,shock stability,contact discontinuity and low-speed resolution,and is potentially a good candidate for wide-ranging Mach number flows.展开更多
It is imperative to develop a novel matching of metallic substrate and self-lubricating coating for aircraft spherical plain bearing in a wide range of service conditions.As a new type of superelastic material,60NiTi ...It is imperative to develop a novel matching of metallic substrate and self-lubricating coating for aircraft spherical plain bearing in a wide range of service conditions.As a new type of superelastic material,60NiTi alloy meets the performance requirements of aerospace bearing materials,but exhibits poor tribological performance,especially under the conditions of dry sliding friction.A Hydrogenated Diamond-Like Carbon(H-DLC)coating was deposited on the 60NiTi alloy to improve its tribological performance.The microstructure and mechanical behavior of the 60NiTi alloy and its H-DLC coating were explored.Results show that improvement of friction and wear performance of the H-DLC coating deposited on the 60NiTi substrate is mainly achieved by graphitization at the friction interface and the transfer film produced on the counterpart ball.The increased friction load leads to intensification of graphitization at the friction interface and formation of continuous and compact transfer film on the surface of the counterpart ball.展开更多
Highly accurate positioning is a crucial prerequisite of multi Unmanned Aerial Vehicle close-formation flight for target tracking,formation keeping,and collision avoidance.Although the position of a UAV can be obtaine...Highly accurate positioning is a crucial prerequisite of multi Unmanned Aerial Vehicle close-formation flight for target tracking,formation keeping,and collision avoidance.Although the position of a UAV can be obtained through the Global Positioning System(GPS),it is difficult for a UAV to obtain highly accurate positioning data in a GPS-denied environment(e.g.,a GPS jamming area,suburb,urban canyon,or mountain area);this may cause it to miss a tracking target or collide with another UAV.In particular,UAV close-formation control in GPS-denied environments faces difficulties owing to the low-accuracy position,close distance between vehicles,and nonholonomic dynamics of a UAV.In this paper,on the one hand,we develop an innovative UAV formation localization method to address the formation localization issues in GPS-denied environments;on the other hand,we design a novel reinforcement learning based algorithm to achieve the high-efficiency and robust performance of the controller.First,a novel Lidar-based localization algorithm is developed to measure the localization of each aircraft in the formation flight.In our solution,each UAV is equipped with Lidar as the position measurement sensor instead of the GPS module.The k-means algorithm is implemented to calculate the center point position of UAV.A novel formation position vector matching method is proposed to match center points with UAVs in the formation and estimate their position information.Second,a reinforcement learning based UAV formation control algorithm is developed by selecting the optimal policy to control UAV swarm to start and keep flying in a close formation of a specific geometry.Third,the innovative collision risk evaluation module is proposed to address the collision-free issues in the formation group.Finally,a novel experience replay method is also provided in this paper to enhance the learning efficiency.Experimental results validate the accuracy,effectiveness,and robustness of the proposed scheme.展开更多
The Reynolds Averaged Navier-Stokes(RANS) models are still the workhorse in current engineering applications due to its high efficiency and robustness. However, the closure coefficients of RANS turbulence models are d...The Reynolds Averaged Navier-Stokes(RANS) models are still the workhorse in current engineering applications due to its high efficiency and robustness. However, the closure coefficients of RANS turbulence models are determined by model builders according to some simple fundamental flows, and the suggested values may not be applicable to complex flows, especially supersonic jet interaction flow. In this work, the Bayesian method is employed to recalibrate the closure coefficients of Spalart-Allmaras(SA) turbulence model to improve its performance in supersonic jet interaction problem and quantify the uncertainty of wall pressure and separation length. The embedded model error approach is applied to the Bayesian uncertainty analysis. Firstly, the total Sobol index is calculated by non-intrusive polynomial chaos method to represent the sensitivity of wall pressure and separation length to model parameters. Then, the pressure data and the separation length are respectively served as calibration data to get the posterior uncertainty of model parameters and Quantities of Interests(Qo Is). The results show that the relative error of the wall pressure predicted by the SA turbulence model can be reduced from 14.99% to 2.95% through effective Bayesian parameter estimation. Besides, the calibration effects of four likelihood functions are systematically evaluated. The posterior uncertainties of wall pressure and separation length estimated by different likelihood functions are significantly discrepant, and the Maximum a Posteriori(MAP) values of parameters inferred by all functions show better performance than the nominal values. Finally, the closure coefficients are also estimated at different jet total pressures. The similar posterior distributions of model parameters are obtained in different cases, and the MAP values of parameters calibrated in one case are also applicable to other cases.展开更多
The S–N curves of 7A85-T7452 aluminum alloy in laboratory air and in neutral 3.5 wt% NaCl solution were obtained by axial fatigue tests. Results show that the detrimental effect of the aggressive solution was not not...The S–N curves of 7A85-T7452 aluminum alloy in laboratory air and in neutral 3.5 wt% NaCl solution were obtained by axial fatigue tests. Results show that the detrimental effect of the aggressive solution was not noticeable at high-cyclic-stress regions, but the effect was significant at low-stress region. Corrosion fatigue mechanism was discussed by corrosion morphology analysis, fracture surface analysis and microstructure characterization. It was found that the corrosion fatigue crack commonly initialed at the localized intergranular corrosion site. TEM analysis showed that the microstructures of 7A85-T7452 aluminum alloy were characterized by fine and homogeneously distributed matrix precipitates, as well as continually distributed anodic grain boundary precipitates. The types of microstructures are the reason for its intergranular corrosion susceptibility. The corrosion fatigue process of 7A85 aluminum alloy in 3.5 wt% NaCl solution can be divided into four stages： the crack initiation stage, the stable growth stage with low and high growth rate and the final rupture stage. The sodium chloride solution mainly affected the crack initiation stage and the stable growth stage with low growth rate, and when the crack growth rate reached a threshold, the effect was reduced.展开更多
The microstructures and crystallization behavior of Ti-47 at% Ni-3 at% Fe shape memory alloy wire under the condition of severe cold drawing at room temperature and different post-deformation annealing processes were ...The microstructures and crystallization behavior of Ti-47 at% Ni-3 at% Fe shape memory alloy wire under the condition of severe cold drawing at room temperature and different post-deformation annealing processes were intensively investigated using transmission electron microscope（TEM） and differential scanning calorimetry（DSC）. It is indicated that the amorphous phase is dominant in the Ti50Ni47Fe3 wire after the cold drawing of 78 % areal reduction. The critical temperature for recrystalization is determined at about 300 °C. The average grain size grows from 7 up to 125 nm when annealing temperature rises from300 to 500 °C. Post-deformation annealing process exerts significant influence on the crystallization temperature which climbs up with the increase of annealing temperature.展开更多
There is a lack of quantitative flying qualities assessment requirements for unmanned combat aerial vehicles.The mission-oriented flying qualities evaluation approach can make up for the deficiencies of existing flyin...There is a lack of quantitative flying qualities assessment requirements for unmanned combat aerial vehicles.The mission-oriented flying qualities evaluation approach can make up for the deficiencies of existing flying qualities specifications.Considering the control characteristics and mission requirements of autonomous control unmanned combat aerial vehicles,flying qualities assessment tasks are designed and performance standards are developed on the basis of manned aircraft flying qualities assessment tasks.Multiple sets of mathematical simulations are performed by varying the control law parameters to investigate the relationship between the control law parameter values,closed-loop aircraft system characteristics and flying qualities levels.The simulation results and closed-loop frequency domain analysis show that the existing flying qualities guidelines for manned aircraft are not fully applicable to the flying qualities assessment of autonomous control unmanned combat aerial vehicles.It is found that the combination of the bandwidth and the phase at the bandwidth frequency can define the flying qualities requirements of autonomous control unmanned aerial vehicles.The criterion boundaries of different levels are given,and the physical reasons for the formation of boundary are analysed.Our results can be applied to flying qualities assessment and design of flight control laws for autonomous control unmanned combat aerial vehicles.展开更多
Electromagnetic synergy and porous characteristics are two dominant factors in realizing light-weight and high-efficient microwave absorption performance.In this paper,a formaldehydeassisted metal-ligand crosslinking ...Electromagnetic synergy and porous characteristics are two dominant factors in realizing light-weight and high-efficient microwave absorption performance.In this paper,a formaldehydeassisted metal-ligand crosslinking strategy and a subsequent pyrolysis process are employed to synthesize magnetic porous carbon spheres with the electromagnetic synergy and porous characteristics,in which metal ions are tightly anchored in poly-(tannin acid)spheres because of the strong chelation coordination between them.The chemical composition of magnetic particles and the microwave absorption performance of the derived magnetic porous carbon spheres can be manipulated by adjusting the metal ions.Benefiting from the cooperative effects of porous structure,matched impedance,the electromagnetic synergistic enhancement between magnetic particles and carbon matrix,as well as the improved interfacial polarization caused by the large number of hetero-interfaces,both the microwave absorption intensity and the effective absorption bandwidths are significantly enhanced for magnetic porous carbon spheres,such as Co-PCSs and CoNi-PCSs,compared with PCSs.With 15 wt.%filler loading,the maximum reflection loss of CoNi-PCSs is -51 dB at 2.2 mm and the effective bandwidth is 7.2 GHz at 2.9 mm.Furthermore,this study provides the theoretical theory for the design and development of light-weight and highly efficient microwave absorption materials.展开更多
Conduction and/or polarization loss play a key role in improving electromagnetic wave(EMW)absorption.In this work,a combined polymerization and high-heat treatment process was utilized to efficiently fabricate core@sh...Conduction and/or polarization loss play a key role in improving electromagnetic wave(EMW)absorption.In this work,a combined polymerization and high-heat treatment process was utilized to efficiently fabricate core@shell structure SiO_(2)@C adopting SiO_(2)nanospheres as a hard template.The acquired SiO_(2)@C nanocomposites displayed unsatisfied EMW absorption performances with minimum reflection loss value of-34.92 dB at 6.35 mm,and effective absorption bandwidth value of 3.20 GHz at 4.83 mm,respectively.In order to further comprehensively boost its microwave absorption performances(MAPs),a facile self-assembly strategy was adopted to load Au nanoparticles on the outer surface of SiO_(2)@C nanospheres,constructing core@shell SiO_(2)@C-Au multicomponent nanocomposites(MCNCs).By regulating the volume of Au nanoparticles,different Au contents of SiO_(2)@C-Au MCNCs could be selectively produced in high efficiencies.The obtained outcomes demonstrated that the SiO_(2)@C-Au MCNCs presented improved properties including EMW attenuation,impedance matching,conduction loss and polarization loss with increasing the content of Au nanoparticles.Thanks to the introduction of conductive Au nanoparticles and excellent interfacial effects,the SiO_(2)@C-Au MCNCs presented the greatly improved antimicrobial and EMW absorption performances including strong absorption,wide bandwidth and small thicknesses.Consequently,this finding offered a novel strategy to construct core@shell SiO_(2)@C-Au MCNCs,which simultaneously boosted conduction and polarization loss capabilities for EMW absorption.展开更多
Piezoelectric filler-based composite fiber sensors have emerged as promising candidates for wearable textiles due to their self-powered capability and excellent sensing performance.However,current spinning fabrication...Piezoelectric filler-based composite fiber sensors have emerged as promising candidates for wearable textiles due to their self-powered capability and excellent sensing performance.However,current spinning fabrication methods face significant challenges in achieving uniform distribution and optimal orientation of piezoelectric fillers within polymer matrices,which limits their sensing performance.To address these issues,an innovative electric-assisted coaxial wet spinning method is developed to fabricate piezoelectric composite fiber(denoted as P-B fiber),which was composed of boron nitride nanosheets(BNNSs)as piezoelectric fillers and polyvinylidene fluoride(PVDF)as a piezoelectric polymer matrix.The radial electric field applied during spinning promotes the radial orientation of BNNSs,leading to enhanced stress transfer efficiency and,as a result,improved piezoelectricity.Moreover,the radial electric field enables the simultaneous in-situ polarization of BNNSs and PVDF during spinning process,further improving the piezoelectric performance.As a result,the P-B fiber exhibits an exceptional piezoelectric sensitivity of(186.4±1.1)mV/N,approximately sixfold higher than that of fibers produced without electric field assistance.Accordingly,the P-B fiber demonstrates remarkable capability in detecting tiny mechanical loads,such as pulse waves and respiration,making it particularly suitable for wearable physiological monitoring textiles,providing a promising strategy for developing high-performance piezoelectric fiber sensors.展开更多
Mitigating the sonic boom to an acceptable stage is crucial for the next generation of supersonic transports.The primary way to suppress sonic booms is to develop a low sonic boom aerodynamic shape design.This paper p...Mitigating the sonic boom to an acceptable stage is crucial for the next generation of supersonic transports.The primary way to suppress sonic booms is to develop a low sonic boom aerodynamic shape design.This paper proposes an inverse design approach to optimize the near-field signature of an aircraft,making it close to the shaped ideal ground signature after propagation in the atmosphere.By introducing the Deep Neural Network(DNN)model for the first time,a predicted input of Augmented Burgers equation is inversely achieved.By the K-fold cross-validation method,the pre-dicted ground signature closest to the target ground signature is obtained.Then,the corresponding equivalent area distribution is calculated using the classical Whitham’s F-function theory from the optimal near-field signature.The inversion method is vali-dated using the classic example of the C608 vehicle provided by the Third Sonic Boom Prediction Workshop(SBPW-3).The results show that the design ground signature is consistent with the target signature.The equivalent area distribution of the design result is smoother than the baseline distribution,and it shrinks significantly in the rear section.Finally,the robustness of this method is verified through the inverse design of sonic boom for the non-physical ground signature target.展开更多
文摘The demands of aircraft quality design criterion on main control system failure and subsequently instantaneous response were analyzed.According to the simulation,the flight characteristics of an aircraft were studied in different angle of rudder seizure.It demonstrated that when rudder seizure with high angle and pilot could not take action immediately,the flight parameters would change sharply.The yaw angle increased 50 degrees in 5 minutes,side velocity could attain 40 meters per-second,the angle of attack and sideslip would surpass 30 degrees,roll rate would reach -20 degrees per second,side load would arrive 0.6g.Simultaneity the angle of attack exceeded the limited angle,the aircraft would stall.If control wasn't working,the disaster would happen.These phenomena supply the sufficient information of the rudder malfunction. The validity of correcting yaw moment by asymmetry thrust was testified,the simulation results showed that even rudder seizure in most serious conditions,adopting asymmetry thrust can correct yaw moment caused by the rudder seizure.The judgment standards of flight safety level for the state of malfunction were given.The safety level was assessed caused by the rudder seizure.For an aircraft with two engines on one side,the pilots need to adjust the 4 engines to balance the asymmetric moment,the work load is increased enormously.According the flight safety standards,the safety level is level Ⅲ.
文摘The influence of dihedral layout on lateral–directional dynamic stability of the tailless flying wing aircraft is discussed in this paper. A tailless flying wing aircraft with a large aspect ratio is selected as the object of study, and the dihedral angle along the spanwise sections is divided into three segments. The influence of dihedral layouts is studied. Based on the stability derivatives calculated by the vortex lattice method code, the linearized small-disturbance equations of the lateral modes are used to determine the mode dynamic characteristics. By comparing 7056 configurations with different dihedral angle layouts, two groups of stability optimized dihedral layout concepts are created. Flight quality close to Level 2 requirements is achieved in these optimized concepts without any electric stability augmentation system.
基金financially supported by the National Natural Science Foundation of China (No.51171154)
文摘The effects of shot peening（SP） and plasma electrolytic oxidation（PEO） on the intergranular corrosion behavior of the novel high strength aluminum alloy 7A85（AA 7A85） were investigated by electrochemical polarization and electrochemical impedance tests.The intergranular corrosion mechanism of SP,PEO and PEO combined with sealingtreated AA 7A85 was studied by the metallographic analysis,residual stress testing,X-ray diffractometer analysis and scanning electron microscopy.The results show that AA 7A85-T7452 is very sensitive to intergranular corrosion.SP would significantly improve its intergranular corrosion resistance.This is attributed to the combination action of residual compressive stress and grain refinement.PEO would reduce the largest corrosion depth by 41.6%.Moreover,PEO without sealing did not eliminate the intergranular corrosion due to the existence of the micropores and microcracks in the oxide coating.However,PEO combined with the SiO2sol–gel sealing treatment could effectively protect the AA 7A85-T7452 from intergranular corrosion because of the good corrosion resistance and barrier function of the sealed coating.
基金co-supported by the National Natural Science Foundation of China(No.11972296)the Major Project Foundation of China(No.2017-F-08).
文摘Wind tunnel test is an important way to test the performance of Gust Load Alleviation(GLA).At present,some component-level wind tunnel tests have been carried out in big aviation countries,but there is a lack of full aircraft model GLA tests.In this study,a set of large-scale GLA test system in low-speed wind tunnel is developed,which includes a gust generator,a five-degree-of-freedom suspension system,a full elastic aircraft model with control system,and gust load measuring devices.Two control schemes based on closed-loop feedback control and open-loop feed forward control are respectively designed and verified by the full-model GLA tests in the wind tunnel.The experimental results show that the designed gust generator can generate a stable wideband,wide-area gust wind field;the suspension support system can sustain static and dynamic stability during wind tunnel test,and enables the model moving in the horizontal,vertical,pitching,rolling and yawing directions.The results show that the closed-loop feedback control can obtain good control performance of reducing the peak values of elastic vibration response induced by gust excitation,but has little effect on suppressing the rigid body motion excited by low-frequency gust,while the open-loop feed forward control presents superior performance in allevi-ating the high-frequency elastic vibration as well as the low-frequency rigid body motion with more than 40%overall reduction rate.
基金the Strategic Priority Research Program of the Chinese Academy of Sciences(XDA22010101)the National Key Research and Development Program of China(2021YFC2801801)+1 种基金the CAS Project for Young Scientists in Basic Research(YSBR-025),the Natural Science Foundation of China(51871225)the Youth Innovation Promotion Association CAS and Liaoning Revitalization Talents Program(XLYC1907005).
文摘The phase transition of titanium alloys is sensitive to the heat-treatment procedure,accompanied with the latent heat induced by phase transition.However,the latent heat during phase transition of titanium alloy has not been systematically studied,which may result in the gap between designed and actual temperature of the sample and affect the final mechanical properties.In this work,DSC(differential scanning calorimetry)and first-principles simulate methods were used to study theβ→αphase transition process of TB18(Ti–Al-Mo-V-Cr-Nb-Fe system)metastableβtitanium alloy,especially to reveal the influence of the heating rate on latent heat.The ratio of latent heat to endothermic heat of the sample during temperature rising was introduced to interpret the effect of latent heat to actual temperature.The ratio of latent heat to endothermic heat at 1℃/min is about 15 to 20 times higher than that at 10℃/min.The higher ratio indicates that the latent heat of phase transition has a more significant effect on the temperature,which is related to the temperature range of phase transition and theαvolume fraction.Compared with the heating rate of 1℃/min,theβ→αphase transition takes place at higher temperature and the volume fraction ofαis smaller at 10℃/min.Meanwhile,there is a precipitation free zone between grain boundaryαand intragranularαand the distribution ofαlamellae is heterogeneous when the heating rate is 10℃/min.Both of the experimental and theoretical results suggest that the latent heat of phase transition is the main cause of the temperature fluctuation during heat-treatment process.This work has guiding significance for microstructure optimization affected by temperature,to achieve the desired mechanical properties.
基金supported by the national natural science foundation of China(Grant No.12172297)the open foundation of state key laboratory of structural analysis for industrial equipment(GZ22106)the fundamental research funds for the central universities.
文摘In this work,a tacticity strategy is proposed to adjust the mechanical properties of chiral mechanical metamaterials for vibration isolation.By applying the finite element method,the impact of tacticity on tensile deformations,band structures,and vibration transmission spectra of chiral metamaterials is investigated.The axial deformations of isotactic configuration and syndiotactic configuration are similar under tensile loads,but rotational deformation occurs in the isotactic configuration.With the same geometric and material parameters,the first band gap of the syndiotactic configuration is lower than that of the isotactic configuration.The vibration suppression performance of chiral mechanical metamaterials is verified by numerical simulations and experiments.Parametric analysis of the band gap provides valuable insights for the manipulation and expansion of vibration reduction.Gradient design based on parametric analysis achieves an extended range of vibration suppression.
基金support from the National Natural Science Foundation of China(No.12472072)the Fundamental Research Funds for the Central Universities,China.
文摘In this research,we introduce an innovative approach that combines the Continuum Damage Mechanics-Finite Element Method(CDM-FEM)with the Particle Swarm Optimization(PSO)-based technique,to predict the Medium-Low-Cycle Fatigue(MLCF)life of perforated structures.First,fatigue tests are carried out on three center-perforated structures,aiming to assess their fatigue life under various strengthening conditions.These tests reveal significant variations in fatigue life,accompanied by an examination of crack initiation through the analysis of fatigue fracture surfaces.Second,an innovative fatigue life prediction methodology is applied to perforated structures,which not only forecasts the initiation of fatigue cracks but also traces the progression of damage within these structures.It leverages an elastoplastic constitutive model integrated with damage and a damage evolution model under cyclic loads.The accuracy of this approach is validated by comparison with test results,falling within the three times error band.Finally,we explore the impact of various strengthening techniques,including cross-sectional reinforcement and cold expansion,on the fatigue life and damage evolution of these structures.This is achieved through an in-depth comparative analysis of both experimental data and computational predictions,which provides valuable insights into the behavior of perforated structures under fatigue conditions in practical applications.
基金National Natural Science Foundation of China (50876041)
文摘A series of computations is conducted for many multi-hole arrangements at several blowing ratios to further investigate the evolution of the film from multi-holes. The influence of multi-hole arrangement on effusion film cooling is analyzed and a preliminary relationship evaluating the film development from developing state to developed state is brought forward. Results show that the coolant jets from front rows of multi-holes merge rapidly and the strength of the kidney vortices due to mainstream-coolant jet interaction in the downstream region are mitigated under super-long-diamond arrangement where the streamwise hole-to-hole pitch is bigger than spanwise hole-to-hole pitch. The holes array arranged in super-long-diamond mode is not only in favor of obtaining developed film layer, but also improving averaged adiabatic film cooling effectiveness.
基金supported by the Space Science and Technology Fund Project of China(No.2020-HT-XG-14)。
文摘This paper develops a low-diffusion robust flux splitting scheme termed TVAP to achieve the simulation of wide-ranging Mach number flows.Based on Toro-Vazquez splitting approach,the new scheme splits inviscid flux into convective system and pressure system.This method introduces Mach number splitting function and numerical sound speed to evaluate advection system.Meanwhile,pressure diffusion term,pressure momentum flux,interface pressure and interface velocity are constructed to measure pressure system.Then,typical test problems are utilized to systematically assess the robustness and accuracy of the resulting scheme.Matrix stability analysis and a series of numerical cases,such as double shear-layer problem and hypersonic viscous flow over blunt cone,demonstrate that TVAP scheme achieves excellent low diffusion,shock stability,contact discontinuity and low-speed resolution,and is potentially a good candidate for wide-ranging Mach number flows.
基金co-supported by the National Natural Science Foundation of China(No.51905466)the Aeronautical Science Foundation of China(No.201945099002)+1 种基金the Natural Science Foundation of Hebei Province,China(Nos.E2021203191 and E2020203184)the Youth Top Talent Project of Hebei Province Higher Education,China(No.BJ2019058).
文摘It is imperative to develop a novel matching of metallic substrate and self-lubricating coating for aircraft spherical plain bearing in a wide range of service conditions.As a new type of superelastic material,60NiTi alloy meets the performance requirements of aerospace bearing materials,but exhibits poor tribological performance,especially under the conditions of dry sliding friction.A Hydrogenated Diamond-Like Carbon(H-DLC)coating was deposited on the 60NiTi alloy to improve its tribological performance.The microstructure and mechanical behavior of the 60NiTi alloy and its H-DLC coating were explored.Results show that improvement of friction and wear performance of the H-DLC coating deposited on the 60NiTi substrate is mainly achieved by graphitization at the friction interface and the transfer film produced on the counterpart ball.The increased friction load leads to intensification of graphitization at the friction interface and formation of continuous and compact transfer film on the surface of the counterpart ball.
基金This work was co-funded by the National Natural Science Foundation of China(No.52072309)Key Research and Development Program of Shaanxi,China(No.2019ZDLGY14-02-01)+5 种基金Shenzhen Fundamental Research Program,China(No.JCYJ20190806152203506)Aeronautical Science Foundation of China(No.ASFC-2018ZC53026)Funding Project with Beijing Institute of Spacecraft System Engineering,China(No.JSZL2020203B004)the Basic Research Program of Taicang,China(No.TC2021JC09)the Natural Science Foundation of Shaanxi Province,China(No.2023-JC-QN-0003)Innovation Foundation for Doctor Dissertation of Northwestern Polytechnical University,China(No.CX2021033).
文摘Highly accurate positioning is a crucial prerequisite of multi Unmanned Aerial Vehicle close-formation flight for target tracking,formation keeping,and collision avoidance.Although the position of a UAV can be obtained through the Global Positioning System(GPS),it is difficult for a UAV to obtain highly accurate positioning data in a GPS-denied environment(e.g.,a GPS jamming area,suburb,urban canyon,or mountain area);this may cause it to miss a tracking target or collide with another UAV.In particular,UAV close-formation control in GPS-denied environments faces difficulties owing to the low-accuracy position,close distance between vehicles,and nonholonomic dynamics of a UAV.In this paper,on the one hand,we develop an innovative UAV formation localization method to address the formation localization issues in GPS-denied environments;on the other hand,we design a novel reinforcement learning based algorithm to achieve the high-efficiency and robust performance of the controller.First,a novel Lidar-based localization algorithm is developed to measure the localization of each aircraft in the formation flight.In our solution,each UAV is equipped with Lidar as the position measurement sensor instead of the GPS module.The k-means algorithm is implemented to calculate the center point position of UAV.A novel formation position vector matching method is proposed to match center points with UAVs in the formation and estimate their position information.Second,a reinforcement learning based UAV formation control algorithm is developed by selecting the optimal policy to control UAV swarm to start and keep flying in a close formation of a specific geometry.Third,the innovative collision risk evaluation module is proposed to address the collision-free issues in the formation group.Finally,a novel experience replay method is also provided in this paper to enhance the learning efficiency.Experimental results validate the accuracy,effectiveness,and robustness of the proposed scheme.
基金supported by the National Numerical Windtunnel Project,China(No.NNW2019ZT1-A03)the National Natural Science Foundation of China(No.11721202)。
文摘The Reynolds Averaged Navier-Stokes(RANS) models are still the workhorse in current engineering applications due to its high efficiency and robustness. However, the closure coefficients of RANS turbulence models are determined by model builders according to some simple fundamental flows, and the suggested values may not be applicable to complex flows, especially supersonic jet interaction flow. In this work, the Bayesian method is employed to recalibrate the closure coefficients of Spalart-Allmaras(SA) turbulence model to improve its performance in supersonic jet interaction problem and quantify the uncertainty of wall pressure and separation length. The embedded model error approach is applied to the Bayesian uncertainty analysis. Firstly, the total Sobol index is calculated by non-intrusive polynomial chaos method to represent the sensitivity of wall pressure and separation length to model parameters. Then, the pressure data and the separation length are respectively served as calibration data to get the posterior uncertainty of model parameters and Quantities of Interests(Qo Is). The results show that the relative error of the wall pressure predicted by the SA turbulence model can be reduced from 14.99% to 2.95% through effective Bayesian parameter estimation. Besides, the calibration effects of four likelihood functions are systematically evaluated. The posterior uncertainties of wall pressure and separation length estimated by different likelihood functions are significantly discrepant, and the Maximum a Posteriori(MAP) values of parameters inferred by all functions show better performance than the nominal values. Finally, the closure coefficients are also estimated at different jet total pressures. The similar posterior distributions of model parameters are obtained in different cases, and the MAP values of parameters calibrated in one case are also applicable to other cases.
基金the National Natural Science Foundation of China (No. 51171154)the National Defense Key Disciplines Laboratory of Light Alloy Processing Science and Technology, Nanchang Hangkong University (No. gf 201401001)
文摘The S–N curves of 7A85-T7452 aluminum alloy in laboratory air and in neutral 3.5 wt% NaCl solution were obtained by axial fatigue tests. Results show that the detrimental effect of the aggressive solution was not noticeable at high-cyclic-stress regions, but the effect was significant at low-stress region. Corrosion fatigue mechanism was discussed by corrosion morphology analysis, fracture surface analysis and microstructure characterization. It was found that the corrosion fatigue crack commonly initialed at the localized intergranular corrosion site. TEM analysis showed that the microstructures of 7A85-T7452 aluminum alloy were characterized by fine and homogeneously distributed matrix precipitates, as well as continually distributed anodic grain boundary precipitates. The types of microstructures are the reason for its intergranular corrosion susceptibility. The corrosion fatigue process of 7A85 aluminum alloy in 3.5 wt% NaCl solution can be divided into four stages： the crack initiation stage, the stable growth stage with low and high growth rate and the final rupture stage. The sodium chloride solution mainly affected the crack initiation stage and the stable growth stage with low growth rate, and when the crack growth rate reached a threshold, the effect was reduced.
基金financially the National Natural Science Foundation of China (Nos. 50835002 and 51105102)the Industry, Education and Research Projects of the China Aviation Industrial (No. cxy2012BH04)
文摘The microstructures and crystallization behavior of Ti-47 at% Ni-3 at% Fe shape memory alloy wire under the condition of severe cold drawing at room temperature and different post-deformation annealing processes were intensively investigated using transmission electron microscope（TEM） and differential scanning calorimetry（DSC）. It is indicated that the amorphous phase is dominant in the Ti50Ni47Fe3 wire after the cold drawing of 78 % areal reduction. The critical temperature for recrystalization is determined at about 300 °C. The average grain size grows from 7 up to 125 nm when annealing temperature rises from300 to 500 °C. Post-deformation annealing process exerts significant influence on the crystallization temperature which climbs up with the increase of annealing temperature.
文摘There is a lack of quantitative flying qualities assessment requirements for unmanned combat aerial vehicles.The mission-oriented flying qualities evaluation approach can make up for the deficiencies of existing flying qualities specifications.Considering the control characteristics and mission requirements of autonomous control unmanned combat aerial vehicles,flying qualities assessment tasks are designed and performance standards are developed on the basis of manned aircraft flying qualities assessment tasks.Multiple sets of mathematical simulations are performed by varying the control law parameters to investigate the relationship between the control law parameter values,closed-loop aircraft system characteristics and flying qualities levels.The simulation results and closed-loop frequency domain analysis show that the existing flying qualities guidelines for manned aircraft are not fully applicable to the flying qualities assessment of autonomous control unmanned combat aerial vehicles.It is found that the combination of the bandwidth and the phase at the bandwidth frequency can define the flying qualities requirements of autonomous control unmanned aerial vehicles.The criterion boundaries of different levels are given,and the physical reasons for the formation of boundary are analysed.Our results can be applied to flying qualities assessment and design of flight control laws for autonomous control unmanned combat aerial vehicles.
基金financially supported by the National Natural Science Foundation of China(No.52373271).
文摘Electromagnetic synergy and porous characteristics are two dominant factors in realizing light-weight and high-efficient microwave absorption performance.In this paper,a formaldehydeassisted metal-ligand crosslinking strategy and a subsequent pyrolysis process are employed to synthesize magnetic porous carbon spheres with the electromagnetic synergy and porous characteristics,in which metal ions are tightly anchored in poly-(tannin acid)spheres because of the strong chelation coordination between them.The chemical composition of magnetic particles and the microwave absorption performance of the derived magnetic porous carbon spheres can be manipulated by adjusting the metal ions.Benefiting from the cooperative effects of porous structure,matched impedance,the electromagnetic synergistic enhancement between magnetic particles and carbon matrix,as well as the improved interfacial polarization caused by the large number of hetero-interfaces,both the microwave absorption intensity and the effective absorption bandwidths are significantly enhanced for magnetic porous carbon spheres,such as Co-PCSs and CoNi-PCSs,compared with PCSs.With 15 wt.%filler loading,the maximum reflection loss of CoNi-PCSs is -51 dB at 2.2 mm and the effective bandwidth is 7.2 GHz at 2.9 mm.Furthermore,this study provides the theoretical theory for the design and development of light-weight and highly efficient microwave absorption materials.
基金support from Guizhou Provincial Basic Research Program(Natural Science)(No.ZD[2025]Key 086)Platform of Science and Technology and Talent Team Plan of Guizhou province(No.GCC[2023]007)Innovation Group of Guizhou University(No.[2024]08)for financial support.
文摘Conduction and/or polarization loss play a key role in improving electromagnetic wave(EMW)absorption.In this work,a combined polymerization and high-heat treatment process was utilized to efficiently fabricate core@shell structure SiO_(2)@C adopting SiO_(2)nanospheres as a hard template.The acquired SiO_(2)@C nanocomposites displayed unsatisfied EMW absorption performances with minimum reflection loss value of-34.92 dB at 6.35 mm,and effective absorption bandwidth value of 3.20 GHz at 4.83 mm,respectively.In order to further comprehensively boost its microwave absorption performances(MAPs),a facile self-assembly strategy was adopted to load Au nanoparticles on the outer surface of SiO_(2)@C nanospheres,constructing core@shell SiO_(2)@C-Au multicomponent nanocomposites(MCNCs).By regulating the volume of Au nanoparticles,different Au contents of SiO_(2)@C-Au MCNCs could be selectively produced in high efficiencies.The obtained outcomes demonstrated that the SiO_(2)@C-Au MCNCs presented improved properties including EMW attenuation,impedance matching,conduction loss and polarization loss with increasing the content of Au nanoparticles.Thanks to the introduction of conductive Au nanoparticles and excellent interfacial effects,the SiO_(2)@C-Au MCNCs presented the greatly improved antimicrobial and EMW absorption performances including strong absorption,wide bandwidth and small thicknesses.Consequently,this finding offered a novel strategy to construct core@shell SiO_(2)@C-Au MCNCs,which simultaneously boosted conduction and polarization loss capabilities for EMW absorption.
基金support from the National Natural Science Foundation of China(Grant Numbers:52175544,52172098)Key R&D Program of Gansu province(Grant Number:25YFGA076)Key R&D Program of Guangdong province(Grant Number:2023A0505010019)。
文摘Piezoelectric filler-based composite fiber sensors have emerged as promising candidates for wearable textiles due to their self-powered capability and excellent sensing performance.However,current spinning fabrication methods face significant challenges in achieving uniform distribution and optimal orientation of piezoelectric fillers within polymer matrices,which limits their sensing performance.To address these issues,an innovative electric-assisted coaxial wet spinning method is developed to fabricate piezoelectric composite fiber(denoted as P-B fiber),which was composed of boron nitride nanosheets(BNNSs)as piezoelectric fillers and polyvinylidene fluoride(PVDF)as a piezoelectric polymer matrix.The radial electric field applied during spinning promotes the radial orientation of BNNSs,leading to enhanced stress transfer efficiency and,as a result,improved piezoelectricity.Moreover,the radial electric field enables the simultaneous in-situ polarization of BNNSs and PVDF during spinning process,further improving the piezoelectric performance.As a result,the P-B fiber exhibits an exceptional piezoelectric sensitivity of(186.4±1.1)mV/N,approximately sixfold higher than that of fibers produced without electric field assistance.Accordingly,the P-B fiber demonstrates remarkable capability in detecting tiny mechanical loads,such as pulse waves and respiration,making it particularly suitable for wearable physiological monitoring textiles,providing a promising strategy for developing high-performance piezoelectric fiber sensors.
基金the National Key Research and Development Program of China(No.2020YFB1709500)Natural Science Basic Research Program of Shaanxi province(No.2021JQ-076)Fundamental Research Funds for the Central Universities.
文摘Mitigating the sonic boom to an acceptable stage is crucial for the next generation of supersonic transports.The primary way to suppress sonic booms is to develop a low sonic boom aerodynamic shape design.This paper proposes an inverse design approach to optimize the near-field signature of an aircraft,making it close to the shaped ideal ground signature after propagation in the atmosphere.By introducing the Deep Neural Network(DNN)model for the first time,a predicted input of Augmented Burgers equation is inversely achieved.By the K-fold cross-validation method,the pre-dicted ground signature closest to the target ground signature is obtained.Then,the corresponding equivalent area distribution is calculated using the classical Whitham’s F-function theory from the optimal near-field signature.The inversion method is vali-dated using the classic example of the C608 vehicle provided by the Third Sonic Boom Prediction Workshop(SBPW-3).The results show that the design ground signature is consistent with the target signature.The equivalent area distribution of the design result is smoother than the baseline distribution,and it shrinks significantly in the rear section.Finally,the robustness of this method is verified through the inverse design of sonic boom for the non-physical ground signature target.
