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The dynamic response of composite sandwich structures with honeycomb-foam hybrid cores subjected to underwater shock waves was investigated by numerical simulations. The deformation process, core compression, momentum transmitting characteristics, and energy absorbing properties of sandwich structures subjected to underwater shock waves with different initial pressures were analyzed. The dynamic responses of the composite sandwich with different core configurations were also compared. The results show that the composite sandwich structures can provide superior protection from underwater shock waves than mass equal laminate plates and the sandwich structures with hybrid cores have better performance than that with empty honeycomb cores when subjected to underwater shock waves. The research can provide reference for the lightweight design and optimization of protective structures against underwater blast loading.

The aerodynamic characteristics are vital for short cylindrical Terminal Sensitive Bullets (TSB) with low aspect ratio, especially in terminal trajectory. Currently, there is little research in terms of the TSB and short cylinder with two free ends, and particularly in this trajectory, where the scanning angle β and roll angle α vary over a broad range between 0° and 180°. In this work, wind tunnel experiments are first conducted to learn the effects of Reynolds number and scanning angle on aerodynamic parameters for short cylinder with aspect ratio L / D = 1 . Similar to infinite cylinder, for the short cylinder with two free ends, the drag crisis phenomenon still exists in the critical regime 1.7 × 10 5 ≤ R e ≤ 6.8 × 10 5 . Then 3D simulations are performed to demonstrate the aerodynamic characteristics of short cylinder and TSB over a broad range of R e , L / D , α and β . The sensitivity analysis of time step and grid are presented as well. When β = 0 ° , for short cylinder, the drag crisis phenomenon was also observed in the simulation, but not as obvious as in the wind tunnel test. In some attitudes, there is an obvious Karman vortex in the wake of short cylinder and TSB. The correlation between time-averaged aerodynamic coefficients and L / D , R e , α & β is discussed. The vortex shedding frequency and shear layer behavior are obtained for quasi-steady and unsteady flow. Finally, the effect of end’s shape on drag reduction and vortex shedding frequency is analyzed.

A novel polymethacrylimide foam-filled square carbon fiber reinforced composite honeycomb core was proposed and prepared. Numerical simulations and theoretical predictions were conducted to study the quasi-static compressive strength of the hybrid core. The effects of material and structural parameters on the compressive strength of the core were analyzed. The results show that the failure modes of the core under quasi-static compression include elastic buckling and plastic fracture failure. The change law of the compressive strength of the core with the increase in the relative density can be divided into three phases, including post-buckling load bearing stage, buckling failure stage, and fracture stage. The failure modes of the core and the change law of the compressive strength with the increase of the relative density vary with the material and structural parameters. The research provides an accurate method to predict the compressive strength of the foam-filled composite honeycomb, which can help to guide the design and optimization of light weight and energy-efficient sandwich cores.

A type of high-voltage pulse source technology generating double-exponential waveform pulse group was introduced. In this approach, the pulse interval could be adjusted with the step length of 100 μs, and the amplitude would reach up to 35 kV. This pulse source could be used to test the sensitivity of electric vehicle (EV) piles under electrical fast transient (EFT) interference. The theory of obtaining double-exponential wave and its generating circuit was analyzed, and then the influencing factors of the rising edge were expounded. A method of pulse insertion was adopted to generate a fast transient pulse group due to the limitation of the repeated operating frequency of switching devices. This method could be summarized as a common load fed by several parallel pulse sources, which were controlled and triggered in time sequence. Thus, a set of timing pulse could be obtained from the load ending. The feasibility of this method was also demonstrated. The electromagnetic interference cannot be avoidable because the load was fed by different timing sources. The high-voltage pulse generated initially causes the latter sources to be false-triggered with serious influence to the entire system. The interference generated by the couple circuit composed by distributed parameters, such as distributed capacitance and inductance, was also analyzed. A coupled model was established, analyzed, and simulated to prove the existence of the conducted interference and false triggering for other sources. The measure of conducted interference suppression was also presented. A set of experiments was carried out to show that different numbers of double-exponential pulse groups with different time intervals could be obtained.

Since the mass distribution of behind-armor debris (BAD) is an important measurement to evaluate the level of destruction caused by BAD, this work proposes a new approach for predicting the mass distribution of BAD generated during the normal penetration of variable cross-section explosive formed projectile (EFP) on rolled homogeneous armor (RHA) steel. Few papers considered the variable cross-section characteristic of EFP, and it is an important influencing factor on number of BAD from target and EFP. In this paper, the variable cross-section characteristic of EFP, the strength of EFP, the axial length of mushroom of EFP, the nose shape of the EFP are all considered, besides, the fit factor of the average strain rate and the fit factor of Mott formula are introduced. The number of BAD from target and EFP as well as the mass distribution of BAD from target and EFP, could both be predicted by modified formula on the base of theoretical analysis and numerical simulation, then it is verified by the experiment. The results indicate that: 1) compared with ignoring the variable cross-section characteristic of EFP, the accuracy of the number of BAD from target and EFP could be improved as the variable cross-section characteristic of EFP is considered; 2) the modified Mott formula can describe the mass distribution of more than 90% BAD from target and EFP.

Analyzing the mass of behind-armor debris (BAD) generated by Rolled Homogeneous Armor (RHA) subjected to normal penetration of variable cross-section Explosively Formed Projectile (EFP) is the purpose of this paper. So theoretical analysis, numerical simulation and experimental data are combined to analyze the influence of variable cross-section characteristic on the time history of crater radius. Moreover the relationships between time history of crater radius (as well as mass of BAD) and the thickness of RHA (from 30 mm to 70 mm) and the impact velocity of EFP (1650 m/s to 1860 m/s) are also investigated. The results indicate that: 1) being compared to the variable cross-section characteristic is ignored, the theoretical time history of crater radius is in better agreement with the simulation results when the variable cross-section characteristic is considered; 2) being compared to the other three conditions of plug, the theoretical mass of BAD is in the best agreement with the simulation results when the shape of plug is frustum of a cone and the angle between generatrix and bottom is 45° and the axial length of mushroom is considered. Keywords: Explosively formed projectile, Behind-armor debris, Variable cross-section characteristic, Shape of plug, Axial length of mushroom, Theoretical model

The dynamic response of freestanding carbon fiber reinforced composite sandwich plates with square honeycomb cores of different relative densities subjected to water blast is investigated by numerical simulations. The constitutive models are validated by quasi-static compression response comparisons of numerical simulations and theoretical calculations. The deformation process, core compression and momentum transmitting characteristics are analyzed and the regulations of the core compression and momentum transmitting for sandwich plates with different core relative densities are revealed. Dynamic response and protection property of composite sandwich plates and mass-equal laminate plates are compared, which indicates that the composite sandwich plates can provide superior protection from water blast than laminate plates.

The flow-induced lateral vibration phenomenon of the terminal sensitive bullets (TSB) when it is dispersed by the airborne distributor is taken as the research background. Based on the Fluent, the flow around a rotating short cylindrical TSB (L/D < 1) is simulated and analyzed varying with relative rotation velocity at high Re number (1×105 ≤ Re ≤ 3×106). The simulation results show that the flow field structure of the short cylinder with two free ends is different from the symmetry of the short cylindrical flow field with one free end, and there is no horseshoe vortex. Compared to the long cylinder with double free ends, the Cd of the short cylinder is more sensitive to the change of Re. With the increase of Re, the Cd of the short cylinder decreases, and the value is between the infinite cylinder and the sphere in the non-critical region. When the short cylinder rotates at the angular velocity ω, the top vortex bends and deforms to a ‘C’ shape on the leeward side where the fluid is accelerated. Due to the periodic disturbance of the detector, the aerodynamic coefficient of the rotating TSB is periodically vibrated. In a single cycle, the waveform of the cd shows a ‘W’ shape, and the waveform of the cl is ‘M’.

Based on Detached Eddy Simulation (DES) technique, the flow around a columnar projectile with different cross-section shapes in the supercritical and extremely supercritical region is simulated by the Fluent. The cross-section of the projectile is regular polygon, which number of edges is 4, 6, 8, 10, 12, 24 and ∞, where ∞ means a circle. The vortex shedding pattern and flow field characteristics are analyzed at Reynolds number 2.5×105 to 2×107. Regarding circular cylinder projectile, when the flow velocity changes from 25 m/s to 200 m/s, the average drag coefficient decreases, and the St Number increases. Regarding regular polygon, when the number of edges for polygon changes from 4 to ∞ at flow velocity 50 m/s, the average drag coefficient decreases, and the St Number increases. The average lift coefficient is almost equal to zero and does not change with the flow velocity and the cross-section. The pressure coefficient Cp of 4-prism, 6-prism, 8-prism, 12-prism and 24-prism has multiple local minimum values at the polygon vertices of the cross section. According to the spectrum analysis, the vortex shedding frequency of 4-prism, 24-prism and cylindrical is single and fixed, so the projectile may cause resonance and deviates from a predetermined trajectory. But for the 6-prism and 8-prism and 12-prism, the cl and cd is multi-periodic vibration. So, considering the flow induced structural vibrations, drag, the power of shrapnel and manufacturing cost, the 8-prism are better choices for cluster warhead underwater in engineering design.

The stuffed corrugated sandwich structure was proposed for the application in the protection of the spacecraft against orbital debris. In order to investigate the protection properties of the stuffed corrugated sandwich structure under hypervelocity impact, numerical simulations were carried out to analyze the impact characteristics. The hypervelocity impact process was presented and the properties such as shock waves propagation, energy absorption, and expansion of the debris cloud were discussed; corresponding properties of mass equal Whipple structure under impact were analyzed for comparison. The results illustrate the protection mechanism of the stuffed corrugated sandwich subject to hypervelocity impact and show that it has superior protection performance to monolithic plate, which prove that the stuffed corrugated sandwich structure has potentially broad application prospect in the field of spacecraft protection against the orbital debris. The research can provide reference for the design of protection shield of the spacecraft.

In order to investigate compressive and tensile mechanical properties of HTPB CBBG, split Hopkinson bar experiments were conducted. The strain rate varied from 1100 to 8000 s-1 at temperatures of 323 to 233 K. Non-linear true stress-true strain curves show that yielding is more significant at high strain rates or low temperatures. All true stress-true strain curves under compression have characteristics of strain hardening after yield point. The obvious stress drop after yield point of true stress-true strain curves under tension at high strain rates and low temperatures indicates that serious damage occurs and evolves. Based on the sensitivity analysis of yield stress to temperature and strain rate, it is found that the former has a more significant influence on compressive mechanical behaviors while temperature and strain rate have an evenly effect on tensile mechanical behaviors. According to the time-temperature superposition principle, the master curve of compressive initial modulus was built at reference temperature of 301 K and it matches well with experimental data.

In order to study the mechanism of initiation of solid rocket motors under the impact of shaped charge jets, a shaped charge jet initiation test was experimentally studied to evaluate the safety of the motor under attack in the battlefield environment. The ex-perimental results indicated that the motor had a detonation reaction under the shaped charge jet impact. The response of the mo-tor was recorded by a high-speed camera. In addition, the mechanism of initiation of the propellant charge was evaluated using by numerical simulations. Pressure-time and reaction-time curves of propellants were analyzed in this paper.

The purpose of this study is to analyse how the thickness of Rolled Homogeneous Armor (RHA) and impact velocity of an Explosively Formed Projectile (EFP) influence the middle mass behind-armor debris (BAD) when a variable cross-section EFP penetrates RHA normally. Numerical simulation is adopted, the thickness of RHA varies from 10mm to 70mm, and the impact velocity of the EFP varies from 1650m/s to 1860m/s. The results indicate that: (1) when the impact velocity of the EFP is 1650m/s and the thickness of RHA varies from 10mm to 70mm, p1g of the RHA and EFP decreases with increasing H0. The thin target could be used to produce a large proportion of the middle mass BAD from RHA (including BAD from the EFP and BAD from the RHA and EFP). (2) When the impact velocity of the EFP varies from 1650m/s to 1860m/s and the thickness of the RHA is 40mm, p1g of the RHA is less than 50%, p1g of the EFP is more than 70%, and p1g of the RHA and EFP is more than 50%.

A fuzzy multiresolution wavelet neural network (FMWNN) controller with dynamic compensation (DC) is proposed to address the complexities of the electric load simulator (ELS). The FMWNN acts as a main torque tracking controller, which takes full advantage of the merits of an ideal sliding mode, fuzzy rules, and multiresolution WNN. The fuzzy algorithm is used to dynamically adjust the weights of the WNN and effectively accelerate the convergence rate. In addition, the DC controller is designed to greatly decrease the effect of the approximation error and guarantee the system stability in the sense of the Lyapunov theory. Finally, the proposed algorithms are carried out on the semiphysical simulation platform, the precision and superiority of which are comparatively verified based on the simulation results.

Due to requests on high rotary velocity of novel smart empennage-stable projectiles, the rolling characteristics under wide-angle oblique angles are studied. Since the wind tunnel tests performed verify numerical simulation, so that the latter method can be applied to study the rolling characteristics widely combining theoretical models. In the theoretical part, the rolling dynamics equations are established considering the span, taper ratio and oblique angle of the empennages, and are further solved combing ballistic equations. For the simulation, the rolling moment coefficients under various rotary velocities are solved based on rotating coordinate system methods, so that the balance rotary velocity can be obtained using interpolation. The results indicate that shorter span, higher taper ratio and especially larger oblique angle can bring higher projectile rotary velocity; the balance rotary velocity is approximately linear to the oblique angle in a certain range.

In order to improve the identification probability of the parachute terminal sensitive projectile in complex battlefield environment, which can recognize armor targets from camouflaged targets and conventional vehicle targets with high probability, and to meet high real-time requirements of algorithm in the terminal sensitive projectile detection system, the method based on Multiple linear array Laser Radar is proposed to achieve 3D Ground Object Automatic Target Recognition. Firstly the OTSU algorithm bounded by 3-D point cloud was used to obtain the height binary image and then morphology filter processing was performed on the binary image from the previous step to get the suspected target. Finally, the target was identified based on the target height features and the enclosing rectangle features. The results of the simulation of the target model show that the proposed method can realize the accurate ground target extraction.

Template matching is a basic algorithm for image processing, and real-time is a crucial requirement of object tracking. For real-time tracking, a fast template matching algorithm based on grey prediction is presented, where computation cost can be reduced dramatically by minimizing search range. First, location of the tracked object in the current image is estimated by Grey Model (GM). GM(1,1), which is the basic model of grey prediction, can use some known information to foretell the location. Second, the precise position of the object in the frame is computed by template matching. Herein, Sequential Similarity Detection Algorithm (SSDA) with a self-adaptive threshold is employed to obtain the matching position in the neighborhood of the predicted location. The role of threshold in SSDA is important, as a proper threshold can make template matching fast and accurate. Moreover, a practical weighted strategy is utilized to handle scale and rotation changes of the object, as well as illumination changes. The experimental results show the superior performance of the proposed algorithm over the conventional full-search method, especially in terms of executive time.

To improve the damage efficiency of the compact terminal sensitive projectile with EFP warhead, it is vital to understand how the embedded structure (ES) affects the EFP forming performance. In this paper, the corresponding numerical investigation is focused on, where the fluid-structure interaction (FSI) method is applied and the experimental verification is employed. Based on the obtained quantitative relations between the formation performance and α (the ratio of the height to the maximum radius of the ES), the optimal design is further provided. The results indicate that: At a fixed volume, when the embedded structural length and width range 0.1-0.3D and 0.1-0.2D respectively (D: diameter of the EFP warhead) EFP forming velocity nearly keeps as a constant, 1760m/s; the height of ES can affect the detonation wave propagating range dramatically resulting in significant influences on the EFP aerodynamic shape and length-diameter ratio; under the given constraints, the EFP length-diameter ratio can reach the optimal value, 2.76 at height of ES 0.22D.

Through the research and analysis of tube-rod extended penetrator vertically penetrating limited thick target, a simplified model of tube-rod extended penetrator vertically penetrating semi-infinite thick target is proposed based on hydrodynamics and penetration mechanics. At the speed ​​of 1470-1770m/s, numerical simulation of tube-rod extended penetrator vertically penetrating limited thick target is conducted with the usage of LS-DYNA. The theoretical calculations and numerical simulation results agree with each other greatly. The tube-rod extended structure has been optimized through numerical simulation. The extended structure with connectors forms lateral drift reflux in penetration, which reduces the penetration efficiency. This adverse effect is alleviated by connectors plus plug plan, with a maximum efficiency gain of 18.1%