Abstracts:Thermodynamic calculation is the theoretical basis for the study of initiation and detonation, as well as the prerequisite for forecasting the detonation performance of unknown explosives. Based on the VLWR(Virial-Wu) thermodynamic code, this paper introduced the universal solid equation of state (EOS) VINET. In order to truly reflect the compressibility of nanocarbon under the extremely high-temperature and high-pressure environment in detonation, an SVM (support vector machine) was utilized to optimize the input parameters of carbon. The detonation performance of several explosives with different densities was calculated by the optimized universal EOS, and the results show that the thermodynamic code coupled with the universal solid EOS VINET can predict the detonation performance parameters of explosives well. To investigate the application of the thermodynamic code with the improved VINET EOS in the working capacity of explosives, the interrelationship between pressure P-particle velocity u and pressure P-volume V were computed for the detonation products of TNT and HMX-based PBX (HMX: binder: insensitive agent = 95:4.3:0.7) in the CJ isentropic state. A universal curve proposed by Cooper was used to compared the computed isentropic state, where the ratio of pressure to CJ state were plotted against the ratio of velocity to CJ state. The parameters of the JWL(Jones-Wilkins-Lee) EOS for detonation products were obtained by fitting the P–V curve. The cylinder tests of TNT and HMX-based PBX were numerically simulated using the LS-DYNA, it is verified that, within a certain range, the improved algorithm has superiority in describing the working capacity of explosives.

Abstracts:With the increasing number of vehicles, manual security inspections are becoming more laborious at road checkpoints. To address it, a specialized Road Checkpoints Robot (RCRo) system is proposed, incorporated with enhanced You Only Look Once (YOLO) and a 6-degree-of-freedom (DOF) manipulator, for autonomous identity verification and vehicle inspection. The modified YOLO is characterized by large objects’ sensitivity and faster detection speed, named “LF-YOLO”. The better sensitivity of large objects and the faster detection speed are achieved by means of the Dense module-based backbone network connecting two-scale detecting network, for object detection tasks, along with optimized anchor boxes and improved loss function. During the manipulator motion, Octree-aided motion control scheme is adopted for collision-free motion through Robot Operating System (ROS). The proposed LF-YOLO which utilizes continuous optimization strategy and residual technique provides a promising detector design, which has been found to be more effective during actual object detection, in terms of decreased average detection time by 68.25% and 60.60%, and increased average Intersection over Union (IoU) by 20.74% and 6.79% compared to YOLOv3 and YOLOv4 through experiments. The comprehensive functional tests of RCRo system demonstrate the feasibility and competency of the multiple unmanned inspections in practice.

Abstracts:In this paper, we propose a compressive sampling and reconstruction system based on the shift-invariant space associated with the fractional Gabor transform. With this system, we aim to achieve the sub-Nyquist sampling and accurate reconstruction for chirp-like signals containing time-varying characteristics. Under the proposed scheme, we introduce the fractional Gabor transform to make a stable expansion for signals in the joint time-fractional-frequency domain. Then the compressive sampling and reconstruction system is constructed under the compressive sensing and shift-invariant space theory. We establish the reconstruction model and propose a block multiple response extension of sparse Bayesian learning algorithm to improve the reconstruction effect. The reconstruction error for the proposed system is analyzed. We show that, with considerations of noises and mismatches, the total error is bounded. The effectiveness of the proposed system is verified by numerical experiments. It is shown that our proposed system outperforms the other systems state-of-the-art.

Abstracts:Cocrystallization integrates the merits of high energy and insensitivity between energetic molecules to obtain energetics with satisfying performance. However, how to obtain supramolecular synthons accurately and rapidly for predicting the structure and property of cocrystal remains a challenging problem. In this research, an efficient systematic search approach to predict CL-20/2,4-DNI cocrystal has been proposed that 2,4-DNI revolves around CL-20 with a stoichiometric ratio of 1:1 in accordance with the specified rules (hydrogen bond length: 2.2–3.0 Å; search radius: 6.5 Å; the number of hydrogen bond: 1–3). Eight possible supramolecular synthons were obtained by combining quantum chemistry with molecular mechanics. Crystal structure prediction indicated that there are four structures in cocrystal, namely P21/c, P212121, Pbca and Pna21, and CL-20/2,4-DNI cocrystal is likely to be P21/c and the corresponding cell parameters are Z = 4, a = 8.28 Å, b = 12.17 Å, c = 20.42 Å, α = 90°, β = 96.94°, γ = 90°, and ρ = 1.9353 g/cm3. To further study the intermolecular interaction of CL-20/2,4-DNI cocrystal, a series of theoretical analyses were employed including intermolecular interaction energy, electrostatic potential (ESP), Density of State (DOS), Hirshfeld surface analysis. The C–H⋯O hydrogen bonds are demonstrated as the predominant driving forces in the cocrystal formation. The mechanical properties and detonation properties of CL-20/2,4-DNI cocrystal implies that the cocrystal shows better ductility and excellent detonation performances (9257 m/s, 39.27 GPa) and can serve as a promising energetic material. Cocrystal structure predicted was compared with the experimental one to verify the accuracy of systematic search approach. There is a less than 8.8% error between experiment and predict results, indicating the systematic search approach has extremely high reliability and accuracy. The systematic search approach can be a new strategy to search supramolecular synthons and identify structures effectively and does have the potential to promote the development of energetic cocrystal by theoretical design.

Abstracts:Recent advances in on-board radar and missile capabilities, combined with individual payload limitations, have led to increased interest in the use of unmanned combat aerial vehicles (UCAVs) for cooperative occupation during beyond-visual-range (BVR) air combat. However, prior research on occupational decision-making in BVR air combat has mostly been limited to one-on-one scenarios. As such, this study presents a practical cooperative occupation decision-making methodology for use with multiple UCAVs. The weapon engagement zone (WEZ) and combat geometry were first used to develop an advantage function for situational assessment of one-on-one engagement. An encircling advantage function was then designed to represent the cooperation of UCAVs, thereby establishing a cooperative occupation model. The corresponding objective function was derived from the one-on-one engagement advantage function and the encircling advantage function. The resulting model exhibited similarities to a mixed-integer nonlinear programming (MINLP) problem. As such, an improved discrete particle swarm optimization (DPSO) algorithm was used to identify a solution. The occupation process was then converted into a formation switching task as part of the cooperative occupation model. A series of simulations were conducted to verify occupational solutions in varying situations, including two-on-two engagement. Simulated results showed these solutions varied with initial conditions and weighting coefficients. This occupation process, based on formation switching, effectively demonstrates the viability of the proposed technique. These cooperative occupation results could provide a theoretical framework for subsequent research in cooperative BVR air combat.

Abstracts: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 m3. 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-3D 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.

Abstracts:High velocity ballistic impact deformation behaviour of Titanium/GFRP Fiber Metal Laminates (FML) has been explored. Both single and multiple projectiles impact conditions were considered. Ti/GFRP FML targets were fabricated with addition of 5% and 10% weight percentage of boron carbide (B4C) particles. Mechanical properties of Ti/GFRP FML targets were determined as per ASTM standards. High velocity ballistic experiments were conducted using Armour Piercing Projectile (APP) of diameter 7.62 mm and velocity ranging between 350 and 450 m/s. Depth of penetration of the projectile into the target was measured. The deformation behaviour of Ti/GFRP targets with and without the presence of ceramic powder (B4C) was investigated. “Ductile hole growth” failure mode was observed for pure GFRP target when subjected to single projectile impact whereas “plugging” failure mode was noted for Ti/GFRP targets. The presence of B4C (5% by weight) particles has significantly improved the ballistic resistance of the Ti/GFRP FML target by offering frictional resistance to the projectile penetration. Further addition (10% by weight) of B4C has reduced the ballistic performance due to agglomeration. None of the targets showed ‘brittle cracking’ or ‘fragmentation’ failures. When compared to the published results of Aluminium (Al 1100/GFRP and Al 6061/GFRP) FMLs, Ti/GFRP FML showed lesser DoP which increases its potential application to aerospace industry.

Abstracts:In this paper, a novel method of ultra-lightweight convolution neural network (CNN) design based on neural architecture search (NAS) and knowledge distillation (KD) is proposed. It can realize the automatic construction of the space target inverse synthetic aperture radar (ISAR) image recognition model with ultra-lightweight and high accuracy. This method introduces the NAS method into the radar image recognition for the first time, which solves the time-consuming and labor-consuming problems in the artificial design of the space target ISAR image automatic recognition model (STIIARM). On this basis, the NAS model's knowledge is transferred to the student model with lower computational complexity by the flow of the solution procedure (FSP) distillation method. Thus, the decline of recognition accuracy caused by the direct compression of model structural parameters can be effectively avoided, and the ultra-lightweight STIIARM can be obtained. In the method, the Inverted Linear Bottleneck (ILB) and Inverted Residual Block (IRB) are firstly taken as each block's basic structure in CNN. And the expansion ratio, output filter size, number of IRBs, and convolution kernel size are set as the search parameters to construct a hierarchical decomposition search space. Then, the recognition accuracy and computational complexity are taken as the objective function and constraint conditions, respectively, and the global optimization model of the CNN architecture search is established. Next, the simulated annealing (SA) algorithm is used as the search strategy to search out the lightweight and high accuracy STIIARM directly. After that, based on the three principles of similar block structure, the same corresponding channel number, and the minimum computational complexity, the more lightweight student model is designed, and the FSP matrix pairing between the NAS model and student model is completed. Finally, by minimizing the loss between the FSP matrix pairs of the NAS model and student model, the student model's weight adjustment is completed. Thus the ultra-lightweight and high accuracy STIIARM is obtained. The proposed method's effectiveness is verified by the simulation experiments on the ISAR image dataset of five types of space targets.

Abstracts:An adaptive wheel-legged shape reconfigurable mobile robot, based on a scissor-like mechanism, is proposed for an obstacle detecting and surmounting robot, moving on complex terrain. The robot can dynamically adjust its own shape, according to the environment, realizing a transformation of wheel shape into leg shape and vice versa. Each wheel-legged mechanism has one degree of freedom, which means that only the relative motion of the inner and outer discs is needed to achieve the transformation of the shape into a wheel or a leg. First, the force analysis of the conversion process of the wheel-legged mechanism is carried out, while the relationship between the driving torque and the friction factor in the non-conversion trigger stage and in the conversion trigger stage is obtained. The results showed that the shape conversion can be better realized by increasing the friction factor of the trigger point. Next, the kinematics analysis of the robot, including climbing the obstacles, stairs and gully, is carried out. The motion of the spokes tip is obtained, in order to derive the folding ratio and the surmountable obstacle height of the wheel-legged mechanism. The parameters of the wheel-legged structure are optimized, to obtain better stability and obstacle climbing ability. Finally, a dynamic simulation model is established by ADAMS, to verify the obstacle climbing performance and gait rationality of the robot, in addition to a prototype experiment. The results showed that the surmountable obstacle height of the robot is about 3.05 times the spoke radius. The robot has the stability of a traditional wheel mechanism and the obstacle surmount performance of a leg mechanism, making it more suitable for field reconnaissance and exploration missions.

Abstracts:Ballistic impact response of resistance-spot-welded (RSW) double-layered (2 × 1.6 mm) plates (190 mm × 150 mm) for Q&P980 steel impacted by a round-nosed steel bullet (12 mm diameter and 30 mm length) was investigated by using gas gun and high-speed camera system. The RSW specimens were spot welded using a 6 mm diameter electrode face producing a 7.2 mm diameter fusion zone of the spot weld. The ballistic curve and energy balance for the tests of the spot weld of the RSW specimens at different velocity were analyzed to characterize the ballistic behavior of the RSW specimens under bullet impact. The fracture mechanisms of the RSW specimens under bullet impact were presented. For the tests below the ballistic limit, the cracks initiated from the notch-tip and propagated along the faying surface or obliquely through the thickness depending on the impact velocity. For the tests above the ballistic limit, the plug fracture in the front plate of the RSW specimen could be caused by the thinning-induced necking in the BM near the HAZ, while the plug fracture in the rear plate of the RSW specimens may be consist of the circumferential cracking from the rear surface and the bending fracture of the hinged part of material. The effects of the electrode indentation and the weld interfaces on deformation and fracture of the RSW specimens under bullet impact were revealed. For the tests above the ballistic limit, the circumferential fracture from the rear surface of the RSW specimens was always initiated along the interior periphery of the electrode indentation and the crack paths were along the FZ/CGHAZ or CGHAZ/FGHAZ interface. When the circumferential crack also formed outside the electrode indentation, the fracture on the BM/HAZ interface could be found. On the front plate of the RSW specimens, the shear/bending induced cracking from the notch-tip were observed and the crack paths were along the FZ/CGHAZ or CGHAZ/FGHAZ interface.