查看更多>>摘要：Global navigation satellite system-reflection(GNSS-R)sea surface altimetry based on satellite constel-lation platforms has become a new research direction and inevitable trend,which can meet the alti-metric precision at the global scale required for underwater navigation.At present,there are still research gaps for GNSS-R altimetry under this mode,and its altimetric capability cannot be specifically assessed.Therefore,GNSS-R satellite constellations that meet the global altimetry needs to be designed.Meanwhile,the matching precision prediction model needs to be established to quantitatively predict the GNSS-R constellation altimetric capability.Firstly,the GNSS-R constellations altimetric precision under different configuration parameters is calculated,and the mechanism of the influence of orbital altitude,orbital inclination,number of satellites and simulation period on the precision is analyzed,and a new multilayer feedforward neural network weighted joint prediction model is established.Secondly,the fit of the prediction model is verified and the performance capability of the model is tested by calculating the R2 value of the model as 0.9972 and the root mean square error(RMSE)as 0.0022,which indicates that the prediction capability of the model is excellent.Finally,using the novel multilayer feedforward neural network weighted joint prediction model,and considering the research results and realistic costs,it is proposed that when the constellation is set to an orbital altitude of 500 km,orbital inclination of 75° and the number of satellites is 6,the altimetry precision can reach 0.0732 m within one year simulation period,which can meet the requirements of underwater navigation precision,and thus can provide a reference basis for subsequent research on spaceborne GNSS-R sea surface altimetry.
查看更多>>摘要：This study focuses on the improvement of path planning efficiency for underwater gravity-aided navi-gation.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 be-tween an ancestor and its descendants was derived,and the ancestors were filtered accordingly.Sec-ondly,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.
查看更多>>摘要：In order to improve the detonation characteristics of RDX,a RDX-based composite explosive with TiH2 powders was prepared.The effects of content and particle size of TiH2 powders on thermal safety,shock wave parameters and thermal damage effects of RDX-based composite explosive were studied with the C80 microcalorimeter,air blast experiment system and colorimetric thermometry method.Experimental results showed that TiH2 powders could enhance the thermal stability of RDX-based composite explosive and increase its ultimate decomposition heat.The content and particle size of TiH2 powders also had significant effects on the thermal safety,detonation velocity,shock wave parameters,fireball tempera-ture and duration of RDX-based composite explosives.Furthermore,the differences of TiH2 and Ti powders on the detonation energy output rules of RDX-based composite explosives were also compared,showing that TiH2 powders had better influences on improving the explosion power and thermal damage effect of RDX-based composite explosives than Ti powders,for the participation of free H2 released by TiH2 powders in the detonation process.TiH2 powders have important research values as a novel energetic additive in the field of military composite explosives.
查看更多>>摘要：Copper-based azide(Cu(N3)2 or CuN3,CA)chips synthesized by in-situ azide reaction and utilized in miniaturized explosive systems has become a hot research topic in recent years.However,the advan-tages of in-situ synthesis method,including small size and low dosage,bring about difficulties in quantitative analysis and differences in ignition capabilities of CA chips.The aim of present work is to develop a simplified quantitative analysis method for accurate and safe analysis of components in CA chips to evaluate and investigate the corresponding ignition ability.In this work,Cu(N3)2 and CuN3 components in CA chips were separated through dissolution and distillation by utilizing the difference in solubility and corresponding content was obtained by measuring N3-concentration through spectro-photometry.The spectrophotometry method was optimized by studying influencing factors and the recovery rate of different separation methods was studied,ensuring the accuracy and reproducibility of test results.The optimized method is linear in range from 1.0-25.0 mg/L,with a correlation coefficient R2=0.9998,which meets the requirements of CA chips with a milligram-level content test.Compared with the existing ICP method,component analysis results of CA chips obtained by spectrophotometry are closer to real component content in samples and have satisfactory accuracy.Moreover,as its application in miniaturized explosive systems,the ignition ability of CA chips with different component contents for direct ink writing CL-20 and the corresponding mechanism was studied.This study provided a basis and idea for the design and performance evaluation of CA chips in miniaturized explosive systems.
查看更多>>摘要：In order to study the dynamic and electrical coupling response characteristics of Metal Oxide Semi-conductor Controlled Thyristor(MCT)high-voltage switch under the synergic action of mechanical load and high voltage,the separated Hopkinson pressure bar(SHPB)test system was used to simulate different impact load environments,and combined with the multi-layer high-voltage ceramic capacitor charging and discharging system,the instantaneous electrical signals of MCT high-voltage switch were collected.Combined with numerical simulation and theoretical analysis,the failure mode and stress wave propagation characteristics of MCT high voltage switch were determined.The mechanical and electrical coupling response characteristics and failure mechanism of MCT high voltage switch under dynamic load were revealed from macroscopic and microscopic levels.The results show that the damage modes of MCT high-voltage switches can be divided into non-functional damage,recoverable functional damage,non-recoverable damage and structural damage.Due to the gap between the metal gate and the oxide layer,the insulating oxide layer was charged.After placing for a period of time,the elastic deformation of the metal gate partially recovered and the accumulated charge disappeared,which induced the recoverable functional damage failure of the device.In addition,obvious cracks appeared on both sides of the monocrystalline silicon inside the MCT high-voltage switch,leading to unrecoverable damage of the device.
查看更多>>摘要：Investigating the ignition response of nitrate ester plasticized polyether(NEPE)propellant under dy-namic extrusion loading is of great significant at least for two cases.Firstly,it helps to understand the mechanism and conditions of unwanted ignition inside charged propellant under accident stimulus.Secondly,evaluates the risk of a shell crevice in a solid rocket motor(SRM)under a falling or overturning scene.In the present study,an innovative visual crevice extrusion experiment is designed using a drop-weight apparatus.The dynamic responses of NEPE propellant during extrusion loading,including compaction and compression,rapid shear flow into the crevice,stress concentration,and ignition re-action,have been firstly observed using a high-performance high-speed camera.The ignition reaction is observed in the triangular region of the NEPE propellant sample above the crevice when the drop weight velocity was 1.90 m/s.Based on the user material subroutine interface UMAT provided by finite element software LS-DYNA,a viscoelastic-plastic model and dual ignition criterion related to plastic shear dissipation are developed and applied to the local ignition response analysis under crevice extrusion conditions.The stress concentration occurs in the crevice location of the propellant sample,the shear stress is relatively large,the effective plastic work is relatively large,and the ignition reaction is easy to occur.When the sample thickness decreases from 5 mm to 2.5 mm,the shear stress increases from 22.3 MPa to 28.6 MPa,the critical value of effective plastic work required for ignition is shortened from 1280 μs to 730 µs,and the triangular area is easily triggering an ignition reaction.The propellant sample with a small thickness is more likely to stress concentration,resulting in large shear stress and effective work,triggering an ignition reaction.
查看更多>>摘要：Al/Ni reactive multilayer foil(RMF)possesses excellent comprehensive properties as a promising sub-stitute for traditional Cu bridge.A theoretical resistivity model of Al/Ni RMF was developed to guide the optimization of EFIs.Al/Ni RMF with different bilayer thicknesses and bridge dimensions were prepared by MEMS technology and electrical explosion tests were carried out.According to physical and chemical reactions in bridge,the electrical explosion process was divided into 5 stages:heating of condensed bridge,vaporization and diffusion of Al layers,intermetallic combination reaction,intrinsic explosion,ionization of metal gases,which are obviously shown in measured voltage curve.Effects of interface and grain boundary scattering on the resistivity of film metal were considered.Focusing on variations of substance and state,the resistivity was developed as a function of temperature at each stage.Electrical explosion curves were calculated by this model at different bilayer thicknesses,bridge dimensions and capacitor voltages,which showed an excellent agreement with experimental ones.
查看更多>>摘要：Introducing Neutral Polymeric bonding agents(NPBA)into the Nitrate Ester Plasticized Polyether(NEPE)propellant could improve the adhesion between filler/matrix interface,thereby contributing to the development of new generations of the NEPE propellant with better mechanical properties.Therefore,understanding the effects of NPBA on the deformation and damage evolution of the NEPE propellant is fundamental to material design and applications.This paper studies the uniaxial tensile and stress relaxation responses of the NEPE propellant with different amounts of NPBA.The damage evolution in terms of interface debonding is further investigated using a cohesive-zone model(CZM).Experimental results show that the initial modulus and strength of the NEPE propellant increase with the increasing amount of NPBA while the elongation decreases.Meanwhile,the relaxation rate slows down and a higher long-term equilibrium modulus is reached.Experimental and numerical analyses indicate that interface debonding and crack propagation along filler-matrix interface are the dominant damage mechanism for the samples with a low amount of NPBA,while damage localization and crack advancement through the matrix are predominant for the ones with a high amount of NPBA.Finally,crosslinking density tests and simulation results also show that the effect of the bonding agent is interfacial rather than due to the overall crosslinking density change of the binder.
查看更多>>摘要：In this work,a Cu-10Ta alloy with a copper to tantalum mass ratio of 9∶1 is prepared using powder metallurgy technology.Physical properties of the alloy,including density,microstructure,melting point,and constant-volume specific heat,are tested.Via the split Hopkinson pressure bar(SHPB)and flyer-plate impact experiments,the relationship between equivalent stress and equivalent plastic strain of the material is studied at temperatures of 298-823 K and under strain rates of 1 × 10-3-5.2 × 103 s-1,and the Hugoniot relationship at impact pressures of 1.46-17.25 GPa and impact velocities of 108-942 m/s is obtained.Evolution of the Cu-10Ta microstructure that occurs during high-strain-rate impact is analyzed.Results indicate that the Cu-10Ta alloy possesses good thermal stability,and at ambient temperatures of up to 50％its melting point,stress softening of less than 15％of the initial strength is observed.A modified J-C constitutive model is employed to accurately predict the variation of yield strength with strain rate.Under strong impact,the copper phase is identified as the primary source of plastic deformation in the Cu-10Ta alloy,while significant deformation of the high-strength tantalum particles is less pronounced.Furthermore,the longitudinal wave speed D is found to correlate linearly with the particle velocity u upon strong impact.Analysis reveals that the sound speed and spallation strength of the alloy increase with increasing impact pressure.
查看更多>>摘要：To enhance the catalytic activity of copper ferrite(CuFe2O4)nanoparticle and promote its application as combustion catalyst,a low-cost silicon dioxide(SiO2)carrier was employed to construct a novel CuFe2O4/SiO2 binary composites via solvothermal method.The phase structure,morphology and catalytic activity of CuFe2O4/SiO2 composites were studied firstly,and thermal decomposition,combustion and safety performance of ammonium perchlorate(AP)and 1,3,5-trinitroperhydro-1,3,5-triazine(RDX)with it affecting were then systematically analyzed.The results show that CuFe2O4/SiO2 composite can remarkably either advance the decomposition peak temperature of AP and RDX,or reduce the apparent activation energy at their main decomposition zone.Moreover,the flame propagation rate of RDX was promoted by about 2.73 times with SiO2 content of 3 wt％,and safety property of energetic component was also improved greatly,in which depressing the electrostatic discharge sensitivity of pure RDX by about 1.89 times.In addition,the effective range of SiO2 carrier content in the binary catalyst is found to be 3 to 5 wt％.Therefore,SiO2 opens a new insight on the design of combustion catalyst carrier and will promote the application of CuFe2O4 catalyst in solid propellant.
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