The cavity characteristics in liquid-filled containers caused by high-velocity impacts represent an important area of research in hydrodynamic ram phenomena.The dynamic expansion of the cavity induces liquid pressure ...The cavity characteristics in liquid-filled containers caused by high-velocity impacts represent an important area of research in hydrodynamic ram phenomena.The dynamic expansion of the cavity induces liquid pressure variations,potentially causing catastrophic damage to the container.Current studies mainly focus on non-deforming projectiles,such as fragments,with limited exploration of shaped charge jets.In this paper,a uniquely experimental system was designed to record cavity profiles in behind-armor liquid-filled containers subjected to shaped charge jet impacts.The impact process was then numerically reproduced using the explicit simulation program ANSYS LS-DYNA with the Structured Arbitrary Lagrangian-Eulerian(S-ALE)solver.The formation mechanism,along with the dimensional and shape evolution of the cavity was investigated.Additionally,the influence of the impact kinetic energy of the jet on the cavity characteristics was analyzed.The findings reveal that the cavity profile exhibits a conical shape,primarily driven by direct jet impact and inertial effects.The expansion rates of both cavity length and maximum radius increase with jet impact kinetic energy.When the impact kinetic energy is reduced to 28.2 kJ or below,the length-to-diameter ratio of the cavity ultimately stabilizes at approximately 7.展开更多
Shaped charge has been widely used for penetrating concrete.However,due to the obvious difference between the propagation of shock waves and explosion products in water and air,the theory governing the formation of sh...Shaped charge has been widely used for penetrating concrete.However,due to the obvious difference between the propagation of shock waves and explosion products in water and air,the theory governing the formation of shaped charge jets in water as well as the underwater penetration effect of concrete need to be studied.In this paper,we introduced a modified forming theory of an underwater hemispherical shaped charge,and investigated the behavior of jet formation and concrete penetration in both air and water experimentally and numerically.The results show that the modified jet forming theory predicts the jet velocity of the hemispherical liner with an error of less than 10%.The underwater jets exhibit at least 3%faster and 11%longer than those in air.Concrete shows different failure modes after penetration in air and water.The depth of penetration deepens at least 18.75%after underwater penetration,accompanied by deeper crater with 65%smaller radius.Moreover,cracks throughout the entire target are formed,whereas cracks exist only near the penetration hole in air.This comprehensive study provides guidance for optimizing the structure of shaped charge and improves the understanding of the permeability effect of concrete in water.展开更多
Unlike conventional spherical charges,a shaped charge generates not only a strong shock wave and a pulsating bubble,but also a high strain rate metal jet and a ballistic wave during the underwater explosion.They show ...Unlike conventional spherical charges,a shaped charge generates not only a strong shock wave and a pulsating bubble,but also a high strain rate metal jet and a ballistic wave during the underwater explosion.They show significant characteristic differences and couple each other.This paper designs and conducts experiments with shaped charges to analyze the complicated process.The effects of liner angle and weight of shaped charge on the characteristics of metal jets,waves,and bubbles are discussed.It is found that in underwater explosions,the shaped charge generates the metal jet accompanied by the ballistic wave.Then,the shock wave propagates and superimposes with the ballistic wave,and the generated bubble pulsates periodically.It is revealed that the maximum head velocity of the metal jet versus the liner angle a and length-to-diameter ratio k of the shaped charge follows the laws of 1/(α/180°)^(0.55)andλ^(0.16),respectively.The head shape and velocity of the metal jet determine the curvature and propagation speed of the initial ballistic wave,thus impacting the superposition time and region with the shock wave.Our findings also reveal that the metal jet carries away some explosion products,which hinders the bubble development,causing an inward depression of the bubble wall near the metal jet.Therefore,the maximum bubble radius and pulsation period are 5.2%and 3.9%smaller than the spherical charge with the same weight.In addition,the uneven axial energy distribution of the shaped charge leads to an oblique bubble jet formation.展开更多
In this study,the potential application of shaped charge jets as transient antennas for electromagnetic signal transmission was explored and an electromagnetic pulse radiation system with a shaped charge jet as a tran...In this study,the potential application of shaped charge jets as transient antennas for electromagnetic signal transmission was explored and an electromagnetic pulse radiation system with a shaped charge jet as a transient antenna was proposed.During the research,crucial characteristics of the transient antenna formed by a shaped charge with a 30 mm diameter,such as resonant frequency,radiation pattern,and radiation efficiency,were evaluated.The typical shaped charge jet morphology was obtained based on the simulations,in which it could insight the dynamic behavior of the shaped charge jet selected.An equivalent model experiment was employed to test the radiation efficiency,and it showed that a shorting pin loading method could increase the relative bandwidth of the jet antenna to 32.8%,and the experimental results correlate with the theoretical predictions for half-wave dipole antennas reasonably well.Additionally,variations in the diameter of the shaped charge jet were found to affect the input impedance and impedance bandwidth,while the length of the jet influenced the resonant frequency of the antenna.This suggests that altering these parameters can achieve reconfigurability of the jet antenna.展开更多
The impact of high-velocity penetrators into liquid-filled containers can generate hydrodynamic ram effects,potentially causing catastrophic structural damage to the container.Previous studies have primarily focused o...The impact of high-velocity penetrators into liquid-filled containers can generate hydrodynamic ram effects,potentially causing catastrophic structural damage to the container.Previous studies have primarily focused on undeformed penetrators,such as fragments or bullets,with limited attention directed toward shaped charge jets.This study investigates the penetration characteristics of shaped charge jets impacting behind-armor liquid-filled containers,with particular emphasis on jet-liquid interactions.A theoretical penetration model incorporating material compressibility and jet stretching was developed based on the virtual origin theory.A high-speed imaging experimental system was designed to capture the jet motion within the container.The impact process was numerically reproduced using ANSYS/LSDYNA,and the effects of standoff and overmatch on jet penetration were analyzed.The results reveal that jet stretching induced by increased standoff enhances the penetration velocity of the jet.A proportional relationship between the stretching factor(λ)and the overmatch parameter(I)was identified,withλranging from approximately 1.22 to 1.38 times I across the studied standoff range(80-220 mm).The findings offer a basis for future studies on the pressure distribution in the liquid and the structural response of containers.展开更多
An analysis of the interaction mechanisms between a Shaped Charge Jet(SCJ) and a single Moving Plate(MP) is proposed in this article using both experimental and numerical approaches. First, an experimental set-up is p...An analysis of the interaction mechanisms between a Shaped Charge Jet(SCJ) and a single Moving Plate(MP) is proposed in this article using both experimental and numerical approaches. First, an experimental set-up is presented. Four collision tests have been performed: two tests in Backward Moving Plate(BMP) configuration, where the plate moves in opposition to jet, and two tests in Forward Moving Plate(FMP) configuration, where the plate moves alongside the jet. Based on the virtual origin approximation,a methodology(the Virtual Origin Method, VOM) is developed to extract quantities from the X-ray images, which serve as comparative data. γSPH simulations are carried out to complete the analysis, as they well capture the disturbance dynamics observed in the experiments. Based on these complementary experimental and numerical results, a new physical description is proposed through a detailed analysis of the interaction. It is shown that the SCJ/MP interaction is driven at first order by the contact geometry. Thus, BMP and FMP configurations do not generate the same disturbances because their local flow geometries are different. In the collision point frame of reference, the BMP flows in the same direction as the jet, causing its overall deflection. On the contrary, the FMP flow opposes that of the jet leading to an alternative creation of fragments and ligaments. An in-depth study, using the VOM shows that deflection angles, fragment-ligament creation frequencies, and deflection velocities evolve as the interaction progresses through slower jet elements.展开更多
A scheme based on irregular V-shaped silicon nanoantennas is proposed to optimize transverse unidirectional scattering under plane wave irradiation.Traditional methods of designing regular shapes offer fewer parameter...A scheme based on irregular V-shaped silicon nanoantennas is proposed to optimize transverse unidirectional scattering under plane wave irradiation.Traditional methods of designing regular shapes offer fewer parameters and higher search efficiency.However,due to the limitations of regular shapes,it is challenging to meet high-precision design requirements.Irregular shape design allows for a broader range of adjustments,but the complexity of shape parameters leads to lower search efficiency and a higher likelihood of converging to local optima.展开更多
The Explosive Reactive Armors(ERA)are really efficient at reducing Shaped Charge Jet(SCJ)performance.The main destabilizing mechanism is the transverse movement of the front and rear moving plates(MP)on the SCJ.Theref...The Explosive Reactive Armors(ERA)are really efficient at reducing Shaped Charge Jet(SCJ)performance.The main destabilizing mechanism is the transverse movement of the front and rear moving plates(MP)on the SCJ.Therefore,a good understanding of the interaction SCJ/MP is essential for improving both weapon and armor systems.In a previous article,we have shown that interaction regimes are mainly influenced by the local collision geometry.Thus,in the collision point frame,the angle of collision be-tween the continuous SCJ and the MP is a key parameter.This flow angle is acute for the Backward Moving plate(BMP)moving against the SCJ and obtuse for the Forward Moving Plate(FMP)moving alongside it.In the former,the jet is simply deflected,which is the regime 1 of deflection.In the latter,the interaction turns on an alternative creation of fragment and ligament,which is the regime 2.Fragments are parts of the jet that are only slightly deflected while ligaments are the curved material bridges that connect two consecutive fragments.When stretching,the jet is systematically subject to instabilities that disturb its surface,creating necks along it.Their growth finally leads to the jet fragmentation.In this article,we focus on this jet distur-bance and its consequences on the SCJ/MP interaction.An experimental set-up was built to implement the interaction between a SCJ and a moving plate for different collision points,at different stand-off distances.The plate can interact with a smooth SCJ or a disturbed SCJ at a close and a far stand-off distance,respectively.One of the main results is the visualization of a regime change in SCJ/BMP interaction.A regime 1(deflection)interaction changes into a ligament regime interaction(similar to a FMP regime 2)when the collision point stand-off is increased.It is proposed that this change can be attributed as the increase of the amplitude of the jet surface disturbances.This phenomenon is well captured by the gSPH simula-tions.Finally,using both experimental and numerical approaches,we propose a new detailed analysis of the different phenomena occurring during the interaction between a disturbed-surface jet and a moving plate.Interaction regime changes are linked to jet local geometry changes.The interactions of a BMP with a smooth SCJ or with a disturbed surface SCJ are geometrically not the same and,thus,generate different local flows and interaction mechanisms.However,some other simulations have been carried out with constant velocity jet whose surface has been previously disturbed.These simulations underline the influence of both disturbance wavelength l and amplitude A on the interaction regimes.Surface disturbances of the SCJ,linked to its stretching,have a major influence on its interaction with a moving plate.展开更多
The attosecond extreme ultraviolet(XUV) pulse pump and femtosecond infrared(IR) pulse probe scheme is commonly used to study the dynamics and attosecond transient absorption(ATA) spectra of microscopic systems. In a r...The attosecond extreme ultraviolet(XUV) pulse pump and femtosecond infrared(IR) pulse probe scheme is commonly used to study the dynamics and attosecond transient absorption(ATA) spectra of microscopic systems. In a recent report [Proc. Natl. Acad. Sci. USA 121 e2307836121(2024)], we showed that shaped XUV pulses with spectral minima can significantly alter the absorption line shape of helium's 2s2p doubly excited state within a few tens of attoseconds.However, it remains unclear if similar effects could be observed in a singly excited state. In this study, we use shaped XUV pulses to excite helium's 2p singly excited state and couple the 2p and 3d states with a delayed IR pulse. Comparing these results with those from Gaussian XUV pulses, we find that the ATA spectra for the shaped XUV pulses exhibit more pronounced changes with delay, while the changes for the Gaussian pulses are gradual. We also explain these differences through population changes and analytical models. Our findings show that shaped XUV pulses can regulate the dynamics and absorption spectra of a singly excited state.展开更多
Compressed air energy storage(CAES)caverns transformed from horseshoe-shaped roadways in abandoned coal mines still face unclear mechanisms of force transfer,especially in the presence of initial damage in the surroun...Compressed air energy storage(CAES)caverns transformed from horseshoe-shaped roadways in abandoned coal mines still face unclear mechanisms of force transfer,especially in the presence of initial damage in the surrounding rock.The shape and size of the initial damage area as well as their effect on cavern stability remain unclear.Due to the complex geometry and multiphysical couplings,traditional numerical algorithms encounter problems of nonconvergence and low accuracy.These challenges can be addressed through numerical simulations with robust convergence and high accuracy.In this study,the damage area shapes of a CAES cavern are first computed using the concept of damage levels.Then,an iteration algorithm is improved using the generalization a method through the error control and one-way coupling loop for fully coupling equations.Finally,the stability of the CAES cavern with different damage zone shapes is numerically simulated in the thermodynamic process.It is found that this improved algorithm can greatly enhance numerical convergence and accuracy.The nonuniformity of the elastic modulus has a significant impact on the mechanical responses of the CAES cavern.The cavern shape with different damage zones has significant impacts on cavern stability.The initial damage area can delay the responses of temperature and stress.It induces variations of temperature in the range of approximately 1.2 m and variations of stress in the range of 1.5 m from the damage area.展开更多
A numerical investigation and experimental validation is performed to address deeper insights into the combined effect of shaped holes and Sand-Dune-shaped upstream Ramp(SDR)on enhancing the film cooling effectiveness...A numerical investigation and experimental validation is performed to address deeper insights into the combined effect of shaped holes and Sand-Dune-shaped upstream Ramp(SDR)on enhancing the film cooling effectiveness,under a wide blowing ratio range(M=0.25–1.5).Three kinds of holes(Cylindrical Hole(CH),Fan-Shaped Hole(FSH),and Crater-Shaped Hole(CSH))are taken into consideration.The SDR shows an inherent affecting mechanism on the mutual interaction of jet-in-crossflow.It aggravates the lateral spreading of cooling jet and thus improves the film cooling uniformity significantly,regardless of film-hole shape and blowing ratio.When the blowing ratio is beyond 1.0,the combined effect of shaped holes and SDR on improving film cooling effectiveness behaves more significantly.It is suggested that FSH-SDR is a most favorable film cooling scheme.For FSH-SDR case,the spatially-averaged film cooling effectiveness is increased monotonously with the increase of blowing ratio,among the present bowing ratio range.展开更多
To investigate the seismic behavior of specially shaped column joints with X-shaped reinforcement,two groups of specimens with or without X-shaped reinforcement in joint core region were tested under constant axial co...To investigate the seismic behavior of specially shaped column joints with X-shaped reinforcement,two groups of specimens with or without X-shaped reinforcement in joint core region were tested under constant axial compression load and low reversed cyclic loading,which imitated low to moderate earthquake force.The seismic behavior of specially shaped column joints with X-shaped reinforcement in terms of bearing capacity,displacement,ductility,hysteretic curve,stiffness degradation and energy dissipation was studied and compared to that without Xshaped reinforcement in joint core region.With the damage estimation model,the accumulated damage was analyzed.The shearing capacity formula of specially shaped column joints reinforced by X-shaped reinforcement was proposed with a simple form.The test results show that X-shaped reinforcement is an effective measure for improving the seismic behavior of specially shaped column joints including deformation behavior,ductility and hysteretic characteristic.All specimens were damaged with gradual stiffness degeneration.In addition,X-shaped reinforcement in the joint core region is an effective way to lighten the degree of cumulated damage.The good seismic performance obtained from the specially shaped column joint with X-shaped reinforcement can be used in engineering applications.The test value is higher than the calculated value,which indicates that the formula is safe for the design of specially shaped column joints.展开更多
Based on experiments, a computer program is developed. The calculated results agree well with the experimental results. The flexural behavior of T shaped high strength concrete members subjected to axial compression ...Based on experiments, a computer program is developed. The calculated results agree well with the experimental results. The flexural behavior of T shaped high strength concrete members subjected to axial compression and biaxial bending is studied. The main factors affecting the flexural behavior of T shaped high strength concrete members are loading angle, axial compression ratio and reinforcement ratio.展开更多
The linear shaped charge cutting technology is an effective technology for aircraft separation.It can separate invalid components from aircrafts timely to achieve light-weight.Magnesium alloy is the lightest metal mat...The linear shaped charge cutting technology is an effective technology for aircraft separation.It can separate invalid components from aircrafts timely to achieve light-weight.Magnesium alloy is the lightest metal material,and can be used to cast effective light-weight components of an aircraft construction.However,the application study of the linear shaped charge cutting technology on magnesium alloy components is basically blank.In response to the demand for the linear separation of magnesium alloys,the Mg-12Gd-0.5Y-0.4Zn alloy is selected to carry out the target shaped charge cutting test.The effects of the shaped charge line density,cutting thickness,and mechanical properties on the cutting performance of the alloy are studied.The shaped charge cutting mechanism is analyzed through the notch structure.The results show that the linear shaped charge cutting performance is significantly affected by the penetration and the collapse.The higher the linear density is,the stronger the ability of the linear shaped charge cutter is,and the greater the penetration depth is,which is advantageous.However,the target structure will be damaged when it is too large(e.g.,4.5 g·m^(-1)).Within 12 mm,when the cutting thickness of the target increases,the penetration depth increases.The lower the tensile strength is,the greater the penetration depth is,and the more conducive the penetration depth to the shaped charge cutting is.When the elongation(EL)increases to 12%,the collapse of the target is incomplete and the target cannot be separated.When the tensile strength of the Mg-Gd-Y-Zn alloy is less than 350 MPa,the EL is less than 6.5%,the cutting thickness is less than 12 mm,and the linear shaped charge cutting of the magnesium alloy can be achieved stably.展开更多
In order to develop a tandem warhead that can effectively destroy concrete targets, this paper explores the penetration performance of shaped charges with different cone angles and liner materials into concrete target...In order to develop a tandem warhead that can effectively destroy concrete targets, this paper explores the penetration performance of shaped charges with different cone angles and liner materials into concrete targets by means of experiments. The penetration process and the destruction mechanism of concrete targets by shaped charges and kinetic energy projectiles are analyzed and compared. Experimental results suggest that both kinetic energetic projectile and shaped charge are capable of destroying concrete targets, but the magnitudes of damage are different. Compared with a kinetic energy projectile, a shaped charge has more significant effect of penetration into the target, and causes very large spalling area. Hence, a shaped charge is quite suitable for first-stage charge of tandem warhead. It is also found that, with the increase of shaped charge liner cone angle, the depth of penetration decreases gradually while the hole diameter becomes larger. Penetration depth with copper liner is larger than of aluminum liner but hole diameter is relatively smaller, and the shaped charge with steel liner is between the above two cases. The shaped charge with a cone angle of 100° can form a jet projectile charge （JPC）. With JPC, a hole with optimum depth and diameter on concrete targets can be formed, which guarantees that the second-stage warhead smoothly penetrates into the hole and explodes at the optimum depth to achieve the desired level of destruction in concrete targets.展开更多
With the development of two-stage munitions(a precursor shaped charge(SC)and a following kinetic energy projectile)to attack the hard concrete targets,as well as the increasing applications of ultra-high performance c...With the development of two-stage munitions(a precursor shaped charge(SC)and a following kinetic energy projectile)to attack the hard concrete targets,as well as the increasing applications of ultra-high performance concrete(UHPC)in both civil and military protective structures,a comparative study on the impact performance of SC formed jet on UHPC target is performed experimentally and numerically at present.Firstly,a series of jet penetration/perforation test on the UHPC,45# steel and UHPC/45# steel composite targets are conducted.By assessing the penetration depth and borehole(crater and tunnel)diameter,the influences of target material and configuration as well as the standoff distance of SC on the impact performance of jet are experimentally discussed.Then,by adopting the 2 D multi-material Arbitrary Lagrange-Euler(ALE)algorithm,Fluid-Structure Interaction(FSI)method and erosion algorithm implemented in the finite element code LS-DYNA,the formation and impact performance of jet in the present test are well reproduced.Finally,based on the validated numerical algorithms,constitutive models and the corresponding parameters,the influences of target material(UHPC,NSC and 45# steel),standoff distance,target configuration(stacked and spaced)and weight efficiency on the impact performance of jet are further discussed.The derived conclusions could provide helpful references for evaluating the ballistic performance of jet and designing the protective structures.展开更多
To improve the grinding quality of robotic belt grinding systems for the workpieces with complex shaped surfaces, new concepts of the dexterity grinding point and the dexterity grinding space are proposed and their ma...To improve the grinding quality of robotic belt grinding systems for the workpieces with complex shaped surfaces, new concepts of the dexterity grinding point and the dexterity grinding space are proposed and their mathematical descriptions are defined. Factors influencing the dexterity grinding space are analyzed. And a method to determine the necessary dexterity grinding space is suggested. Based on particle swarm optimization （PSO） method, a strategy to optimize the grinding robot structural dimensions and position with respect to the grinding wheel is put forward to obtain the necessary dexterity grinding space. Finally, to grind an aerial engine blade, a dedicated PPPRRR （P： prismatic R： rotary） grinding robot structural dimensions and position with respect to the grinding wheel are optimized using the above strategy. According to simulation results, if the blade is placed within the dexterity grinding space, only one gripper and one grinding machine are needed to grind its complex shaped surfaces.展开更多
Penetration and internal blast behavior of reactive liner enhanced shaped charge against concrete space were investigated through experiments and simulations.The volume of the enclosed concrete space is about 15 m^(3)...Penetration and internal blast behavior of reactive liner enhanced shaped charge against concrete space were investigated through experiments and simulations.The volume of the enclosed concrete space is about 15 m^(3).The reactive liner enhanced shaped charge utilizes reactive copper double-layered liner,which is composed of an inner copper liner and an outer reactive liner,while the reactive material liner is fabricated by PTFE/Al(Polytetrafluoroethylene/Aluminum)powders through cold-pressing and sintering.Static explosion experiments show that,compared with the shaped charge which utilizes copper liner,the penetration cavity diameter and spalling area of concrete by the novel shaped charge were enlarged to 2 times and 4 times,respectively.Meanwhile,the following reactive material had blast effect and produced significant overpressure inside the concrete closed space.Theoretical analysis indicates concrete strength and detonation pressure of reactive material both affect the penetration cavity diameter.To the blast behavior of reactive material inside the concrete space,developing TNT equivalence model and simulated on AUTODYN-3 D for analysis.Simulation results reproduced propagation process of the shock wave in concrete space,and revealed multi-peaks phenomenon of overpressure-time curves.Furthermore,the empirical relationship between the peak overpressure and relative distance for the shock wave of reactive material was proposed.展开更多
Experiments on shaped charge penetration into high and ultrahigh strength steel-fiber reactive powder concrete(RPC) targets were performed in this paper.Results show that the variation of penetration depth and crater ...Experiments on shaped charge penetration into high and ultrahigh strength steel-fiber reactive powder concrete(RPC) targets were performed in this paper.Results show that the variation of penetration depth and crater diameter with concrete strength is different from that of shaped charge penetration into normal strength concrete(NSC).The crater diameter of RPC is smaller than that of NSC penetrated by the shaped charge.The jet particles are strongly disturbed and hardly reach the crater bottom because they pass through the narrow channel formed by jet penetration into the RPC.The effects of radial drift velocity and gap effects of jet particles for a shaped charge penetration into RFC target are discussed.Moreover,a theoretical model is presented to describe the penetration of shaped charge into RPC target.As the concrete strength increases,the penetration resistance increases and the entrance crater diameter decreases.Given the drift velocity and narrow crater channel,the low-velocity jet particles can hardly reach the crater bottom to increase the penetration depth.Moreover,the narrow channel has a stronger interference to the jet particles with increasing concrete strength;hence,the gap effects must be considered.The drift velocity and gap effects,which are the same as penetration resistance,also have significant effects during the process of shaped charge penetration into ultrahigh-strength concrete,The crater profiles are calculated through a theoretical model,and the results are in good agreement with the experiments.展开更多
基金financial support from the National Natural Science Foundation of China(Grant No.11572159).
文摘The cavity characteristics in liquid-filled containers caused by high-velocity impacts represent an important area of research in hydrodynamic ram phenomena.The dynamic expansion of the cavity induces liquid pressure variations,potentially causing catastrophic damage to the container.Current studies mainly focus on non-deforming projectiles,such as fragments,with limited exploration of shaped charge jets.In this paper,a uniquely experimental system was designed to record cavity profiles in behind-armor liquid-filled containers subjected to shaped charge jet impacts.The impact process was then numerically reproduced using the explicit simulation program ANSYS LS-DYNA with the Structured Arbitrary Lagrangian-Eulerian(S-ALE)solver.The formation mechanism,along with the dimensional and shape evolution of the cavity was investigated.Additionally,the influence of the impact kinetic energy of the jet on the cavity characteristics was analyzed.The findings reveal that the cavity profile exhibits a conical shape,primarily driven by direct jet impact and inertial effects.The expansion rates of both cavity length and maximum radius increase with jet impact kinetic energy.When the impact kinetic energy is reduced to 28.2 kJ or below,the length-to-diameter ratio of the cavity ultimately stabilizes at approximately 7.
基金supported by the National Science Foundation of China(Grant Nos.12372361,12102427,12372335 and 12102202)the Fundamental Research Funds for the Central Universities(Grant No.30923010908)Postgraduate Research&Practice Innovation Program of Jiangsu Province(Grant No.KYCX23_0520).
文摘Shaped charge has been widely used for penetrating concrete.However,due to the obvious difference between the propagation of shock waves and explosion products in water and air,the theory governing the formation of shaped charge jets in water as well as the underwater penetration effect of concrete need to be studied.In this paper,we introduced a modified forming theory of an underwater hemispherical shaped charge,and investigated the behavior of jet formation and concrete penetration in both air and water experimentally and numerically.The results show that the modified jet forming theory predicts the jet velocity of the hemispherical liner with an error of less than 10%.The underwater jets exhibit at least 3%faster and 11%longer than those in air.Concrete shows different failure modes after penetration in air and water.The depth of penetration deepens at least 18.75%after underwater penetration,accompanied by deeper crater with 65%smaller radius.Moreover,cracks throughout the entire target are formed,whereas cracks exist only near the penetration hole in air.This comprehensive study provides guidance for optimizing the structure of shaped charge and improves the understanding of the permeability effect of concrete in water.
基金funded by the National Natural Science Founda-tion of China(52071109).
文摘Unlike conventional spherical charges,a shaped charge generates not only a strong shock wave and a pulsating bubble,but also a high strain rate metal jet and a ballistic wave during the underwater explosion.They show significant characteristic differences and couple each other.This paper designs and conducts experiments with shaped charges to analyze the complicated process.The effects of liner angle and weight of shaped charge on the characteristics of metal jets,waves,and bubbles are discussed.It is found that in underwater explosions,the shaped charge generates the metal jet accompanied by the ballistic wave.Then,the shock wave propagates and superimposes with the ballistic wave,and the generated bubble pulsates periodically.It is revealed that the maximum head velocity of the metal jet versus the liner angle a and length-to-diameter ratio k of the shaped charge follows the laws of 1/(α/180°)^(0.55)andλ^(0.16),respectively.The head shape and velocity of the metal jet determine the curvature and propagation speed of the initial ballistic wave,thus impacting the superposition time and region with the shock wave.Our findings also reveal that the metal jet carries away some explosion products,which hinders the bubble development,causing an inward depression of the bubble wall near the metal jet.Therefore,the maximum bubble radius and pulsation period are 5.2%and 3.9%smaller than the spherical charge with the same weight.In addition,the uneven axial energy distribution of the shaped charge leads to an oblique bubble jet formation.
基金supported by the"Fundamental Research Funds for the Central Universities"(Grant No.30924010801).
文摘In this study,the potential application of shaped charge jets as transient antennas for electromagnetic signal transmission was explored and an electromagnetic pulse radiation system with a shaped charge jet as a transient antenna was proposed.During the research,crucial characteristics of the transient antenna formed by a shaped charge with a 30 mm diameter,such as resonant frequency,radiation pattern,and radiation efficiency,were evaluated.The typical shaped charge jet morphology was obtained based on the simulations,in which it could insight the dynamic behavior of the shaped charge jet selected.An equivalent model experiment was employed to test the radiation efficiency,and it showed that a shorting pin loading method could increase the relative bandwidth of the jet antenna to 32.8%,and the experimental results correlate with the theoretical predictions for half-wave dipole antennas reasonably well.Additionally,variations in the diameter of the shaped charge jet were found to affect the input impedance and impedance bandwidth,while the length of the jet influenced the resonant frequency of the antenna.This suggests that altering these parameters can achieve reconfigurability of the jet antenna.
基金the financial support from the National Natural Science Foundation of China(Grant No.11572159)。
文摘The impact of high-velocity penetrators into liquid-filled containers can generate hydrodynamic ram effects,potentially causing catastrophic structural damage to the container.Previous studies have primarily focused on undeformed penetrators,such as fragments or bullets,with limited attention directed toward shaped charge jets.This study investigates the penetration characteristics of shaped charge jets impacting behind-armor liquid-filled containers,with particular emphasis on jet-liquid interactions.A theoretical penetration model incorporating material compressibility and jet stretching was developed based on the virtual origin theory.A high-speed imaging experimental system was designed to capture the jet motion within the container.The impact process was numerically reproduced using ANSYS/LSDYNA,and the effects of standoff and overmatch on jet penetration were analyzed.The results reveal that jet stretching induced by increased standoff enhances the penetration velocity of the jet.A proportional relationship between the stretching factor(λ)and the overmatch parameter(I)was identified,withλranging from approximately 1.22 to 1.38 times I across the studied standoff range(80-220 mm).The findings offer a basis for future studies on the pressure distribution in the liquid and the structural response of containers.
基金supported by the Ministère des Armées,and the Agence de l'Innovation de Défense(AID).
文摘An analysis of the interaction mechanisms between a Shaped Charge Jet(SCJ) and a single Moving Plate(MP) is proposed in this article using both experimental and numerical approaches. First, an experimental set-up is presented. Four collision tests have been performed: two tests in Backward Moving Plate(BMP) configuration, where the plate moves in opposition to jet, and two tests in Forward Moving Plate(FMP) configuration, where the plate moves alongside the jet. Based on the virtual origin approximation,a methodology(the Virtual Origin Method, VOM) is developed to extract quantities from the X-ray images, which serve as comparative data. γSPH simulations are carried out to complete the analysis, as they well capture the disturbance dynamics observed in the experiments. Based on these complementary experimental and numerical results, a new physical description is proposed through a detailed analysis of the interaction. It is shown that the SCJ/MP interaction is driven at first order by the contact geometry. Thus, BMP and FMP configurations do not generate the same disturbances because their local flow geometries are different. In the collision point frame of reference, the BMP flows in the same direction as the jet, causing its overall deflection. On the contrary, the FMP flow opposes that of the jet leading to an alternative creation of fragments and ligaments. An in-depth study, using the VOM shows that deflection angles, fragment-ligament creation frequencies, and deflection velocities evolve as the interaction progresses through slower jet elements.
基金supported by the National Natural Science Foundation of China(Nos.62475121 and 62335012)。
文摘A scheme based on irregular V-shaped silicon nanoantennas is proposed to optimize transverse unidirectional scattering under plane wave irradiation.Traditional methods of designing regular shapes offer fewer parameters and higher search efficiency.However,due to the limitations of regular shapes,it is challenging to meet high-precision design requirements.Irregular shape design allows for a broader range of adjustments,but the complexity of shape parameters leads to lower search efficiency and a higher likelihood of converging to local optima.
基金supported by the Ministère des Arméesthe Agence de l'Innovation de Défense (AID)
文摘The Explosive Reactive Armors(ERA)are really efficient at reducing Shaped Charge Jet(SCJ)performance.The main destabilizing mechanism is the transverse movement of the front and rear moving plates(MP)on the SCJ.Therefore,a good understanding of the interaction SCJ/MP is essential for improving both weapon and armor systems.In a previous article,we have shown that interaction regimes are mainly influenced by the local collision geometry.Thus,in the collision point frame,the angle of collision be-tween the continuous SCJ and the MP is a key parameter.This flow angle is acute for the Backward Moving plate(BMP)moving against the SCJ and obtuse for the Forward Moving Plate(FMP)moving alongside it.In the former,the jet is simply deflected,which is the regime 1 of deflection.In the latter,the interaction turns on an alternative creation of fragment and ligament,which is the regime 2.Fragments are parts of the jet that are only slightly deflected while ligaments are the curved material bridges that connect two consecutive fragments.When stretching,the jet is systematically subject to instabilities that disturb its surface,creating necks along it.Their growth finally leads to the jet fragmentation.In this article,we focus on this jet distur-bance and its consequences on the SCJ/MP interaction.An experimental set-up was built to implement the interaction between a SCJ and a moving plate for different collision points,at different stand-off distances.The plate can interact with a smooth SCJ or a disturbed SCJ at a close and a far stand-off distance,respectively.One of the main results is the visualization of a regime change in SCJ/BMP interaction.A regime 1(deflection)interaction changes into a ligament regime interaction(similar to a FMP regime 2)when the collision point stand-off is increased.It is proposed that this change can be attributed as the increase of the amplitude of the jet surface disturbances.This phenomenon is well captured by the gSPH simula-tions.Finally,using both experimental and numerical approaches,we propose a new detailed analysis of the different phenomena occurring during the interaction between a disturbed-surface jet and a moving plate.Interaction regime changes are linked to jet local geometry changes.The interactions of a BMP with a smooth SCJ or with a disturbed surface SCJ are geometrically not the same and,thus,generate different local flows and interaction mechanisms.However,some other simulations have been carried out with constant velocity jet whose surface has been previously disturbed.These simulations underline the influence of both disturbance wavelength l and amplitude A on the interaction regimes.Surface disturbances of the SCJ,linked to its stretching,have a major influence on its interaction with a moving plate.
基金Project supported by the National Natural Science Foundation of China (Grant No. 12274230)the Funding of Nanjing University of Science and Technology (Grant No. TSXK2022D005)。
文摘The attosecond extreme ultraviolet(XUV) pulse pump and femtosecond infrared(IR) pulse probe scheme is commonly used to study the dynamics and attosecond transient absorption(ATA) spectra of microscopic systems. In a recent report [Proc. Natl. Acad. Sci. USA 121 e2307836121(2024)], we showed that shaped XUV pulses with spectral minima can significantly alter the absorption line shape of helium's 2s2p doubly excited state within a few tens of attoseconds.However, it remains unclear if similar effects could be observed in a singly excited state. In this study, we use shaped XUV pulses to excite helium's 2p singly excited state and couple the 2p and 3d states with a delayed IR pulse. Comparing these results with those from Gaussian XUV pulses, we find that the ATA spectra for the shaped XUV pulses exhibit more pronounced changes with delay, while the changes for the Gaussian pulses are gradual. We also explain these differences through population changes and analytical models. Our findings show that shaped XUV pulses can regulate the dynamics and absorption spectra of a singly excited state.
基金National Key Research and Development Program of China,Grant/Award Number:2022YFE0129100National Natural Science Foundation of China,Grant/Award Number:51674246+1 种基金Graduate Innovation Program of China University of Mining and Technology,Grant/Award Number:2023WLJCRCZL046Postgraduate Research&Practice Innovation Program of Jiangsu Province,Grant/Award Number:KYCX23_2660。
文摘Compressed air energy storage(CAES)caverns transformed from horseshoe-shaped roadways in abandoned coal mines still face unclear mechanisms of force transfer,especially in the presence of initial damage in the surrounding rock.The shape and size of the initial damage area as well as their effect on cavern stability remain unclear.Due to the complex geometry and multiphysical couplings,traditional numerical algorithms encounter problems of nonconvergence and low accuracy.These challenges can be addressed through numerical simulations with robust convergence and high accuracy.In this study,the damage area shapes of a CAES cavern are first computed using the concept of damage levels.Then,an iteration algorithm is improved using the generalization a method through the error control and one-way coupling loop for fully coupling equations.Finally,the stability of the CAES cavern with different damage zone shapes is numerically simulated in the thermodynamic process.It is found that this improved algorithm can greatly enhance numerical convergence and accuracy.The nonuniformity of the elastic modulus has a significant impact on the mechanical responses of the CAES cavern.The cavern shape with different damage zones has significant impacts on cavern stability.The initial damage area can delay the responses of temperature and stress.It induces variations of temperature in the range of approximately 1.2 m and variations of stress in the range of 1.5 m from the damage area.
基金financial support for this project from the National Natural Science Foundation of China(No.U1508212)National Science and Technology Major Projects(Nos.2017-Ⅲ-0011-0025 and 2017-Ⅲ0011-0037)。
文摘A numerical investigation and experimental validation is performed to address deeper insights into the combined effect of shaped holes and Sand-Dune-shaped upstream Ramp(SDR)on enhancing the film cooling effectiveness,under a wide blowing ratio range(M=0.25–1.5).Three kinds of holes(Cylindrical Hole(CH),Fan-Shaped Hole(FSH),and Crater-Shaped Hole(CSH))are taken into consideration.The SDR shows an inherent affecting mechanism on the mutual interaction of jet-in-crossflow.It aggravates the lateral spreading of cooling jet and thus improves the film cooling uniformity significantly,regardless of film-hole shape and blowing ratio.When the blowing ratio is beyond 1.0,the combined effect of shaped holes and SDR on improving film cooling effectiveness behaves more significantly.It is suggested that FSH-SDR is a most favorable film cooling scheme.For FSH-SDR case,the spatially-averaged film cooling effectiveness is increased monotonously with the increase of blowing ratio,among the present bowing ratio range.
基金Supported by National Natural Science Foundation of China (No. 50878141)Hebei Natural Science Foundation,China (No. E2011202013)High School of Hebei Science and Technology Research Youth Foundation,China(No. Q2012083)
文摘To investigate the seismic behavior of specially shaped column joints with X-shaped reinforcement,two groups of specimens with or without X-shaped reinforcement in joint core region were tested under constant axial compression load and low reversed cyclic loading,which imitated low to moderate earthquake force.The seismic behavior of specially shaped column joints with X-shaped reinforcement in terms of bearing capacity,displacement,ductility,hysteretic curve,stiffness degradation and energy dissipation was studied and compared to that without Xshaped reinforcement in joint core region.With the damage estimation model,the accumulated damage was analyzed.The shearing capacity formula of specially shaped column joints reinforced by X-shaped reinforcement was proposed with a simple form.The test results show that X-shaped reinforcement is an effective measure for improving the seismic behavior of specially shaped column joints including deformation behavior,ductility and hysteretic characteristic.All specimens were damaged with gradual stiffness degeneration.In addition,X-shaped reinforcement in the joint core region is an effective way to lighten the degree of cumulated damage.The good seismic performance obtained from the specially shaped column joint with X-shaped reinforcement can be used in engineering applications.The test value is higher than the calculated value,which indicates that the formula is safe for the design of specially shaped column joints.
文摘Based on experiments, a computer program is developed. The calculated results agree well with the experimental results. The flexural behavior of T shaped high strength concrete members subjected to axial compression and biaxial bending is studied. The main factors affecting the flexural behavior of T shaped high strength concrete members are loading angle, axial compression ratio and reinforcement ratio.
基金the National Natural Science Foundation of China(No.U2037601)。
文摘The linear shaped charge cutting technology is an effective technology for aircraft separation.It can separate invalid components from aircrafts timely to achieve light-weight.Magnesium alloy is the lightest metal material,and can be used to cast effective light-weight components of an aircraft construction.However,the application study of the linear shaped charge cutting technology on magnesium alloy components is basically blank.In response to the demand for the linear separation of magnesium alloys,the Mg-12Gd-0.5Y-0.4Zn alloy is selected to carry out the target shaped charge cutting test.The effects of the shaped charge line density,cutting thickness,and mechanical properties on the cutting performance of the alloy are studied.The shaped charge cutting mechanism is analyzed through the notch structure.The results show that the linear shaped charge cutting performance is significantly affected by the penetration and the collapse.The higher the linear density is,the stronger the ability of the linear shaped charge cutter is,and the greater the penetration depth is,which is advantageous.However,the target structure will be damaged when it is too large(e.g.,4.5 g·m^(-1)).Within 12 mm,when the cutting thickness of the target increases,the penetration depth increases.The lower the tensile strength is,the greater the penetration depth is,and the more conducive the penetration depth to the shaped charge cutting is.When the elongation(EL)increases to 12%,the collapse of the target is incomplete and the target cannot be separated.When the tensile strength of the Mg-Gd-Y-Zn alloy is less than 350 MPa,the EL is less than 6.5%,the cutting thickness is less than 12 mm,and the linear shaped charge cutting of the magnesium alloy can be achieved stably.
基金The project supported by the National Natural Science Foundation of China(10625208)
文摘In order to develop a tandem warhead that can effectively destroy concrete targets, this paper explores the penetration performance of shaped charges with different cone angles and liner materials into concrete targets by means of experiments. The penetration process and the destruction mechanism of concrete targets by shaped charges and kinetic energy projectiles are analyzed and compared. Experimental results suggest that both kinetic energetic projectile and shaped charge are capable of destroying concrete targets, but the magnitudes of damage are different. Compared with a kinetic energy projectile, a shaped charge has more significant effect of penetration into the target, and causes very large spalling area. Hence, a shaped charge is quite suitable for first-stage charge of tandem warhead. It is also found that, with the increase of shaped charge liner cone angle, the depth of penetration decreases gradually while the hole diameter becomes larger. Penetration depth with copper liner is larger than of aluminum liner but hole diameter is relatively smaller, and the shaped charge with steel liner is between the above two cases. The shaped charge with a cone angle of 100° can form a jet projectile charge （JPC）. With JPC, a hole with optimum depth and diameter on concrete targets can be formed, which guarantees that the second-stage warhead smoothly penetrates into the hole and explodes at the optimum depth to achieve the desired level of destruction in concrete targets.
基金supported by the National Natural Science Foundation of China (51438003,51878507)
文摘With the development of two-stage munitions(a precursor shaped charge(SC)and a following kinetic energy projectile)to attack the hard concrete targets,as well as the increasing applications of ultra-high performance concrete(UHPC)in both civil and military protective structures,a comparative study on the impact performance of SC formed jet on UHPC target is performed experimentally and numerically at present.Firstly,a series of jet penetration/perforation test on the UHPC,45# steel and UHPC/45# steel composite targets are conducted.By assessing the penetration depth and borehole(crater and tunnel)diameter,the influences of target material and configuration as well as the standoff distance of SC on the impact performance of jet are experimentally discussed.Then,by adopting the 2 D multi-material Arbitrary Lagrange-Euler(ALE)algorithm,Fluid-Structure Interaction(FSI)method and erosion algorithm implemented in the finite element code LS-DYNA,the formation and impact performance of jet in the present test are well reproduced.Finally,based on the validated numerical algorithms,constitutive models and the corresponding parameters,the influences of target material(UHPC,NSC and 45# steel),standoff distance,target configuration(stacked and spaced)and weight efficiency on the impact performance of jet are further discussed.The derived conclusions could provide helpful references for evaluating the ballistic performance of jet and designing the protective structures.
基金National Natural Science Foundation of China （51075013） Beijing Natural Science Foundation （4102035）+1 种基金 Fundamental Research Funds for the Central Universities （YWF-10-01-A09） Research Foundation of State Key Laboratory for Manufacturing Systems Engineering （Xi＇an Jiaotong University）
文摘To improve the grinding quality of robotic belt grinding systems for the workpieces with complex shaped surfaces, new concepts of the dexterity grinding point and the dexterity grinding space are proposed and their mathematical descriptions are defined. Factors influencing the dexterity grinding space are analyzed. And a method to determine the necessary dexterity grinding space is suggested. Based on particle swarm optimization （PSO） method, a strategy to optimize the grinding robot structural dimensions and position with respect to the grinding wheel is put forward to obtain the necessary dexterity grinding space. Finally, to grind an aerial engine blade, a dedicated PPPRRR （P： prismatic R： rotary） grinding robot structural dimensions and position with respect to the grinding wheel are optimized using the above strategy. According to simulation results, if the blade is placed within the dexterity grinding space, only one gripper and one grinding machine are needed to grind its complex shaped surfaces.
基金supported by National Natural Science Foundation of china[grant number:U1730112]。
文摘Penetration and internal blast behavior of reactive liner enhanced shaped charge against concrete space were investigated through experiments and simulations.The volume of the enclosed concrete space is about 15 m^(3).The reactive liner enhanced shaped charge utilizes reactive copper double-layered liner,which is composed of an inner copper liner and an outer reactive liner,while the reactive material liner is fabricated by PTFE/Al(Polytetrafluoroethylene/Aluminum)powders through cold-pressing and sintering.Static explosion experiments show that,compared with the shaped charge which utilizes copper liner,the penetration cavity diameter and spalling area of concrete by the novel shaped charge were enlarged to 2 times and 4 times,respectively.Meanwhile,the following reactive material had blast effect and produced significant overpressure inside the concrete closed space.Theoretical analysis indicates concrete strength and detonation pressure of reactive material both affect the penetration cavity diameter.To the blast behavior of reactive material inside the concrete space,developing TNT equivalence model and simulated on AUTODYN-3 D for analysis.Simulation results reproduced propagation process of the shock wave in concrete space,and revealed multi-peaks phenomenon of overpressure-time curves.Furthermore,the empirical relationship between the peak overpressure and relative distance for the shock wave of reactive material was proposed.
基金supported by the Natural Science Foundation of China through Grant No.11702144。
文摘Experiments on shaped charge penetration into high and ultrahigh strength steel-fiber reactive powder concrete(RPC) targets were performed in this paper.Results show that the variation of penetration depth and crater diameter with concrete strength is different from that of shaped charge penetration into normal strength concrete(NSC).The crater diameter of RPC is smaller than that of NSC penetrated by the shaped charge.The jet particles are strongly disturbed and hardly reach the crater bottom because they pass through the narrow channel formed by jet penetration into the RPC.The effects of radial drift velocity and gap effects of jet particles for a shaped charge penetration into RFC target are discussed.Moreover,a theoretical model is presented to describe the penetration of shaped charge into RPC target.As the concrete strength increases,the penetration resistance increases and the entrance crater diameter decreases.Given the drift velocity and narrow crater channel,the low-velocity jet particles can hardly reach the crater bottom to increase the penetration depth.Moreover,the narrow channel has a stronger interference to the jet particles with increasing concrete strength;hence,the gap effects must be considered.The drift velocity and gap effects,which are the same as penetration resistance,also have significant effects during the process of shaped charge penetration into ultrahigh-strength concrete,The crater profiles are calculated through a theoretical model,and the results are in good agreement with the experiments.
