Defence Technology(防务技术)最新文献

The main goal of this study is to use higher-order isogeometric analysis (IGA) to study the dynamic response of sandwich shells with an auxetic honeycomb core and two different functionally graded materials (FGM) skin layers (namely honeycomb-FGS shells) subjected to dynamic loading. Touratier's non-polynomial higher-order shear deformation theory (HSDT) is used due to its simplicity and performance. The governing equation is derived from Hamilton's principle. After verifying the present approach, the effect of input parameters on the dynamic response of honeycomb-FGS shells is carried out in detail.

In this research, a Multidisciplinary Design Optimization approach is proposed for the dual-spin guided flying projectile design considering external and internal parts of the body as design variables. In this way, a parametric formulation is developed. All related disciplines, including structure, aerodynamics, guidance, and control are considered. Minimum total mass, maximum aerodynamic control effectiveness, minimum miss distance, maximum yield stress in all subsystems, controllability and gyroscopic stability constraints are some of objectives/constraints taken into account. The problem is formulated in All-At-Ones Multidisciplinary Design Optimization approach structure and solved by Simulated Annealing and minimax algorithms. The optimal configurations are evaluated in various aspects. The resulted optimal configurations have met all design objectives and constraints.

Aiming at the problem of shadow interference in UAV's ground reconnaissance, a color and polarization synergistic target detection method is proposed for anti-shadow interference, based on the influence of two physical characteristics (wavelength and polarization) under different illuminations. A valid fusion strategy is proposed via integrating two separate detection results on color and polarization images. Moreover, a local enhancement and recognition module (LER) is introduced to boost the performance. Based on our built dataset, experimental results show that our method achieves m_AP of 87.76%, and 12.37% higher than that of color image and 14.68% higher than that of polarization image.

In order to study the blast damage effects of aviation kerosene storage tanks, the out-field explosion experiments of 8 m³ fixed-roof tanks were carried out. The fragments, shock wave and fireball thermal radiation of the tank in the presence of bottom oil, half oil and full oil, as well as empty tank, were investigated under internal explosion by various TNT charge contents (1.8 kg, 3.5 kg and 6.2 kg). The results showed that the tank roof was the only fragment produced, and the damage forms could be divided into three types. The increase of TNT charge content and oil volume enlarged the deformation of the tank, while the hole ratio presented a trend of increase first and then decrease. The H_{r, max} and V_max values positively increased as increasing the TNT charge content and oil volume (from empty to half oil), but decreased in full oil. The P_max values had a progressive increase with the increment of TNT charge content, but not the case with the increase in oil volumes. The development of fireball was divided into three stages: tank roof ‘towed’ flame, jet flow flame tumbling and rising, and jet flow flame extinguishing. The D_max and H_{f, max} values both increased as increasing TNT charge content and oil volumes. The oscillation phenomenon of fireball temperature was observed in the cooling process. The average temperature of fireball surface was positively correlated with TNT charge content, and negatively correlated with oil volumes.

To achieve the controllable release of energy of nitrocellulose-based propellants, this paper combines the cellulose-based nanocomposites aqueous coating (Surelease®-NC) with fluidized bed coating equipment to successfully prepare the coated spherical propellant for the first time. The effects of fluidized bed coating temperature, air velocity, flow speed and atomization pressure on the adhesion rate, coating integrity and coating uniformity of the coated spherical propellant were investigated, and the preparation of coated spherical propellant with homogeneous size and structural integrity was achieved for the first time. The microscopic morphology, chemical structure, water vapor adsorption behavior, combustion performance, and ageing resistance property of the coated spherical propellant were systematically investigated by, Fourier transforms infrared spectroscopy (FTIR), Micro confocal raman spectrometer, field scanning electron microscopy (SEM), dynamic vapor adsorption techniques, and closed bomb test, confirming the surface core-shell structure and the tightly bonded interfacial structure of coated spherical propellant. Meanwhile, the coated spherical propellant has good hygroscopic, excellent progressive burning and long storage stability.

The Disc Acceleration eXperiment (DAX) is one of the most recent experimental methods of performance characterization of new energetic materials. A cylindrical explosive charge accelerates a thin metallic disc and its velocity is measured continuously using photonic Doppler velocimetry. The detonation velocity is measured simultaneously. The DAX test can be used to obtain the Chapman-Jouguet (CJ) detonation pressure and to describe detonation products expansion using reduced amount of explosive. A series of DAX tests was performed at various charge diameters and disc thicknesses with Semtex 1 A plastic bonded explosive and sensitized nitromethane. The DAX-like evaluation was also applied to previously measured data of Semtex 1A and A-IX-1 explosives. The optimum disc thickness is determined by the disc to explosive mass ratio of 0.01–0.08. The repeatability of the Semtex 1 A detonation pressure results is about four times lower compared to the pressed and liquid explosives.

The Trauzl lead block test allows the determination of the approximate performance of explosives in blasting applications by measuring the volume increase (expansion) that is produced by the detonation of an explosive charge in the cavity of a lead block. In this paper, we reconsider the possibility of interpreting the Trauzl test results in terms of detonation parameters or quantities. The detonation parameters used in the analysis are calculated using the thermochemical code EXPLO5, while the hydrocode AUTODYN is used to simulate the effect of explosive charge density and reaction rate on the results of the Trauzl test. The increase in the volume of the lead block cavity was found to correlate best with the product of the detonation heat and the root of the volume of detonation products. Hydrocode simulation showed that the density of explosive charge and the rate of explosive decomposition affect the dynamics of the interaction of the detonation product and the lead block, and consequently the lead block cavity volume increase.

A direct comparison is made between the effectiveness of Al, Mg, and Be powders as additional fuels in model thermobaric compositions containing 20% fuel, 20% ammonium perchlorate, and 60% RDX (1,3,5-Trinitro-1,3,5-triazacyclohexane) passivated with wax. Experimentally determined calorimetric measurements of the heat of detonation, along with the overpressure histories in an explosion chamber filled with nitrogen, were used to determine the quasi-static pressure (QSP) under anaerobic conditions. Overpressure measurements were also performed in a semi-closed bunker, and all blast wave parameters generated after the detonation of 500 g charges of the tested explosives were determined. Detonation calorimetry results, QSP values, and blast wave parameters (pressure amplitude, specific and total impulses) clearly indicate that Be is much more effective as an additional fuel than either Al or Mg in both anaerobic post-detonation reactions as well as the subsequent aerobic combustion. The heat of detonation of the RDXwax/AP/Be explosive mixture is over 40% and 50% higher than that of the mixture containing aluminum and magnesium instead of beryllium, respectively. Moreover, the TNT equivalent of the Be-containing composition due to the overpressure in the nitrogen-filled explosion chamber is 1.66, while the equivalent calculated using an air shock wave-specific impulse at a distance of 2.5 m is equal to 1.69. The high values of these parameters confirm the high reactivity of beryllium in both the anaerobic and aerobic stages of the thermobaric explosion.

Swarm robot systems are an important application of autonomous unmanned surface vehicles on water surfaces. For monitoring natural environments and conducting security activities within a certain range using a surface vehicle, the swarm robot system is more efficient than the operation of a single object as the former can reduce cost and save time. It is necessary to detect adjacent surface obstacles robustly to operate a cluster of unmanned surface vehicles. For this purpose, a LiDAR (light detection and ranging) sensor is used as it can simultaneously obtain 3D information for all directions, relatively robustly and accurately, irrespective of the surrounding environmental conditions. Although the GPS (global-positioning-system) error range exists, obtaining measurements of the surface-vessel position can still ensure stability during platoon maneuvering. In this study, a three-layer convolutional neural network is applied to classify types of surface vehicles. The aim of this approach is to redefine the sparse 3D point cloud data as 2D image data with a connotative meaning and subsequently utilize this transformed data for object classification purposes. Hence, we have proposed a descriptor that converts the 3D point cloud data into 2D image data. To use this descriptor effectively, it is necessary to perform a clustering operation that separates the point clouds for each object. We developed voxel-based clustering for the point cloud clustering. Furthermore, using the descriptor, 3D point cloud data can be converted into a 2D feature image, and the converted 2D image is provided as an input value to the network. We intend to verify the validity of the proposed 3D point cloud feature descriptor by using experimental data in the simulator. Furthermore, we explore the feasibility of real-time object classification within this framework.

Honeycomb sandwich structures are widely used in lightweight applications. Usually, these structures are subjected to extreme loading conditions, leading to potential failures due to delamination and debonding between the face sheet and the honeycomb core. Therefore, the present study is focused on the mechanical characterisation of honeycomb sandwich structures fabricated using advanced 3D printing technology. The continuous carbon fibres and ONYX-FR matrix materials have been used as raw materials for 3D printing of the specimens needed for various mechanical characterization testing; ONYX-FR is a commercial trade name for flame retardant short carbon fibre filled nylon filaments, used as a reinforcing material in Morkforged 3D printer. Edgewise and flatwise compression tests have been conducted for different configurations of honeycomb sandwich structures, fabricated by varying the face sheet thickness and core cell size, while keeping the core cell thickness and core height constant. Based on these tests, the proposed structure with face sheet thickness of 3.2 mm and a core cell size of 12.7 mm exhibited the highest energy absorption and prevented delamination and debonding failures. Therefore, 3D printing technology can also be considered as an alternative method for sandwich structure fabrication. However, detailed parametric studies still need to be conducted to meet various other structural integrity criteria related to the lightweight applications.