基于移动目标的DOA估计偏差校正

针对移动目标的波达方向估计容易出现偏差的问题,提出一种利用频移信息修正方位估计偏差的算法,解决了传统方位估计算法不能适用于高速移动目标或平台的问题。该方法利用基阵平台与目标的径向移动速度,估计中心频率偏移,然后利用频移信息修正传统的方位估计结果。仿真结果表明,该算法可以极大地提高移动目标的方位估计精度。此外,该算法对阵列的阵型和方位估计算法没有任何限制,因此具有广泛的适用性和较强的工程实用价值。     

色噪声环境下MIMO雷达相干目标角度估计算法

针对色噪声环境下的MIMO雷达相干目标角度估计问题,提出一种基于目标信息矢量重构的角度估计算法.算法对MIMO雷达的接收数据进行了低复杂度改进,通过计算四阶累积量,得到一组矢量并证明该矢量包含所有目标的角度信息,通过重构Toeplitz矩阵,结合MUSIC算法实现了色噪声环境下MIMO雷达相干目标的角度估计.算法保留了MIMO雷达的阵元扩展能力和目标分辨力,具有自动抑制加性高斯白噪声和色噪声的能力,实现了相干目标的有效估计,更利于在实际中应用.最后计算机仿真结果证实了算法的有效性和可行性.     

稀薄气体动理论中介观尺度数值模拟的加速方法

针对滑移流、早期过渡流区域采用离散速度法(discrete velocity method, DVM)求解Boltzmann方程收敛速度极慢、计算资源消耗大的难题,提出全流场耦合介观/宏观方程加速方法。在介观层面基于有限差分的DVM求解Boltzmann方程,在宏观层面基于有限体积的压力耦合方程组半隐式方法求解矩方程,充分利用纳维-斯托克斯-傅里叶/R26矩方程在低克努森数下的快速收敛特性,对介观方程进行加速。基于高阶Hermite多项式重构分布函数,完成宏观方程与介观方程之间的数据传输。仿真结果表明:全流场耦合介观/宏观方程的加速方法在滑移流、早期过渡流区域具有显著加速性能,最大降低了95.28%的计算时长;但对中、大克努森数流域,加速性能大幅度下降。     

Investigations on influence of rifle automatics system action on values of energetic efficiency coefficient of muzzle brakes

The objective of the paper was to compare values of the muzzle brake efficiency coefficient for a rifle with active or inactive automatics systems. Special laboratory stand designed for investigating the recoil process was used. The motion of the rifle was detected by the use of the laser interferometer and the optical camera. The recoil velocity time courses were determined by smoothing and differentiation of experimental position records. The results of the experiments indicated that in the case of an active automatics system two values of the recoil velocity can be used for calculation of the energetic efficiency coefficient: the maximum recoil velocity and the final recoil velocity at the end of the automatics action cycle. The values of the coefficient, calculated using these two values of the recoil velocity, distinctly differ. However, it was shown that their values indicate the same relation between the efficiency of various muzzle brakes. The value of the efficiency coefficient, determined on the basis of the final recoil velocity value, is practically the same as that determined on the basis of the final recoil velocity value for the rifle with an inactive automatics system.     

钢管在冲击荷载作用下的变形与失效破坏

为研究钢管在弹体侵彻过程中的变形特点,基于ANSYS/LS-DYNA软件,采用Johnson-Cook模型,模拟了半球形弹体以不同速度正向冲击钢管时的非线性动力响应情况。结果表明：弹体速度越小,钢管的抗侵彻性能越好;弹体速度越接近临界破坏速度,钢管降低弹体速度的能力就越明显;弹体冲击钢管时,钢管上表面比下表面更容易产生大变形,消耗更多的弹体动能,并在抗侵彻过程中伴有局部凹陷、蝶形变形和贯穿现象。实验结果可为圆柱壳结构钢管在冲击荷载作用下的耗能分析提供参考。     

新型舰炮使用测速雷达后观测距离偏差射击校正方法

针对测速雷达精确校正初速后的观测距离偏差校正方法进行研究,建立不同校正方法校正量计算模型,对比分析不同校正方法校正精度,得出了使用测速雷达精确校正初速后观测距离偏差应采用折合空气密度校正精度高的结论,为中大口径舰炮部队作战与训练和装备的研制改进提供依据。     

Study of nano-nitramine explosives: preparation,sensitivity and application

Nano-nitramine explosives (RDX, HMX, CL-20) are produced on a bi-directional grinding mill. The scanning electron microscope (SEM) observations show that the prepared particles are semi-spherical, and the narrow size distributions are characterized using the laser particle size analyzer. Compared with the micron-sized samples, the nano-products show obvious decrease in friction and impact sensitivities. In the case of shock sensitivities, nano-products have lower values by 59.9% (RDX), 56.4% (HMX), and 58.1% (CL-20), respectively. When nano-RDX and nano-HMX are used in plastic bonded explosives (PBX) as alternative materials of micron-sized particles, their shock sensitivities are significantly decreased by 24.5% (RDX) and 22.9% (HMX), and their detonation velocities are increased by about 1.7%. Therefore, it is expected to promote the application of nano-nitramine explosives in PBXs and composite modified double-based propellants (CMDBs) so that some of their properties would be improved.     

Long-rod penetration: the transition zone between rigid and hydrodynamic penetration modes

Long-rod penetration in a wide range of velocity means that the initial impact velocity varies in a range from tens of meters per second to several kilometers per second. The long rods maintain rigid state when the impact velocity is low, the nose of rod deforms and even is blunted when the velocity gets higher, and the nose erodes and fails to lead to the consumption of long projectile when the velocity is very high due to instantaneous high pressure. That is, from low velocity to high velocity, the projectile undergoes rigid rods, deforming non-erosive rods, and erosive rods. Because of the complicated changes of the projectile, no well-established theoretical model and numerical simulation have been used to study the transition zone. Based on the analysis of penetration behavior in the transition zone, a phenomenological model to describe target resistance and a formula to calculate penetration depth in transition zone are proposed, and a method to obtain the boundary velocity of transition zone is determined. A combined theoretical analysis model for three response regions is built by analyzing the characteristics in these regions. The penetration depth predicted by this combined model is in good agreement with experimental result.     

Theoretical study of an energetic material di-1H-1,3,4-triazole derivatives

Computations by density functional theory (DFT) method are performed on a series of di-1H-1,3,4-triazole derivatives with different substituents and linkages. The heat of formation (HOF) is predicted by the designed isodesmic reactions. The predicted results reveal that –N₃ and –NN– groups are effective structural units for increasing the HOF values of the di-1H-1,3,4-triazole derivatives. The HOMO–LUMO gap is affected by the substituents and linkage groups. Detonation performance is evaluated using the Kamlet–Jacobs approach based on the calculated density and HOF. The results indicate that –NO₂, –NF₂, –NH–, –NH–NH– and –NN– groups are helpful for enhancing the detonation properties of di-1H-1,3,4-triazole derivatives. The bond dissociation energy and bond order of the weakest bonds are analyzed to investigate their stability. It is observed that the –CH₂–, –CH₂–CH₂– and –CHCH– groups are effective structural units for improving the stabilities of these derivatives. Considering the detonation performance and the stability, five compounds are screened as the potential candidates for high energy density materials.     

Analysis of parameter estimation using the sampling-type algorithm of discrete fractional Fourier transform

Parameter estimation is analyzed using two kinds of common sampling-type DFRFT (discrete fractional Fourier transform) algorithm. A model of parameter estimation is established. The factors which influence estimation accuracy are analyzed. And the simulation is made to verify the conclusions. From the theoretic analysis and simulation verification, it can be drawn that, for the estimation of chirp-rate and initial frequency, Pei's method [10] is more suitable if the absolute value of chirp-rate is small relatively; Ozaktas' method [9] is more suitable if the absolute value of chirp-rate is large relatively; and the two methods are both workable if the absolute value of chirp-rate is moderate. The scope of moderate chirp-rate can be approximately determined as [40 Hz/s, 110 Hz/s].