The Numerical Simulation of Flow Field of Jet System

In this paper, the internal fluid motion of a jet system is described by the Navier Stokes mechanics equations. For the simulation of the motion, the penalty function finite element method is used, and the velocity vectors and stream function curves are obtained. Using the Prandtl theory, this paper derives the free jet velocity and the jet bunch width in a half-space, the latter of which is amended by experiment. The results obtained in this paper are applied to micro-type high pressure water jet cleaner and the ejector of rocket engine.     

串联随进战斗部前后级影响数值仿真

利用Autodyn进行了破爆型串联随进攻坚战斗部爆炸场数值仿真,得到了装药的爆炸压力、速度和温度分布,获得了作用在随进子弹头部和子弹装药炸药内的爆炸响应冲击波压力-时间历程,得到了爆炸过载及其对随进后级的速度降。仿真结果表明,子弹装药炸药具有不被前级爆炸所殉爆的安定性和足够的随进速度,爆炸过载满足子弹引信解除保险要求。对比静爆实验结果,数值仿真与实验基本相吻合,这种方法可以为随进战斗部设计提供依据。

Abstract：

Using Autodyn software,the explosive field of demolition-blast traveling hard structural tandem warhead was investigated by numerical simulation. The blast pressure,velocity and temperature distributions were gained. The response blast shock wave pressures varied against time of sub-munition fore-body and charge were calculated. The explosive overload and velocity drop-off of sub-munition were obtained. Simulation results show that sub-munition charge has sympathetic detonation security and enough traveling velocity,and explive overload can meet sub-munition fuze arming demand. Numerations agree with test results,which can support the base for this type warhead design.     

Wentzel-Kramer-Brillouin and finite-difference time-domain analysis of Terahertz band electromagnetic characteristics of target coated with unmagnetized plasma

We investigate computationally the attenuation and reflection of Terahertz （THz） wave using targets coated with plasmas. The simulators are the Wentzel-Kramer-Brillouin （WKB） method and finite-difference timedomain （FDTD） method. The relation between the frequency of the incident electromagnetic （EM） wave and the attenuation caused by unmagnitized plasma is analyzed. The results demonstrate that the amount of absorbed power is a decreasing function of the EM wave frequency and the plasma collision frequency. For THz band incident wave, the attenuation that is caused by plasma is small when the plasma has common density and the collision frequency. This conclusion has fine applying foreground for plasma anti stealth.     

Exact Controllability of Wave Equations with Interior Degeneracy and One-Sided Boundary Control

In this paper, the authors mainly consider the exact controllability for degenerate wave equation, which degenerates at the interior point, and boundary controls acting at only one of the boundary points. The main results are that, it is possible to control both the position and the velocity at every point of the body and at a certain time T for the wave equation with interior weakly degeneracy.Moreover, it is shown that the exact controllability fails for the wave equation with interior strongl...     

Universal FRFT-based algorithm for parameter estimation of chirp signals

The realization of the parameter estimation of chirp signals using the fractional Fourier transform (FRFT) is based on the assumption that the sampling duration of practical observed signals would be equal to the time duration of chirp signals contained in the former. However, in many actual circumstances, this assumption seems unreasonable. On the basis of analyzing the practical signal form, this paper derives the estimation error of the existing parameter estimation method and then proposes a novel and universal parameter estimation algorithm. Furthermore, the proposed algorithm is developed which allows the estimation of the practical observed Gaussian windowed chirp signal. Simulation results show that the new algorithm works well.     

Super-resolution processing of passive millimeter-wave images based on adaptive projected Landweber algorithm

Passive millimeter wave （PMMW） images inherently have the problem of poor resolution owing to limited aperture dimension. Thus, efficient post-processing is necessary to achieve resolution improvement. An adaptive projected Landweber （APL） super-resolution algorithm using a spectral correction procedure, which attempts to combine the strong points of all of the projected Landweber （PL） iteration and the adaptive relaxation parameter adjustment and the spectral correction method, is proposed. In the algorithm, the PL iterations are implemented as the main image restoration scheme and a spectral correction method is included in which the calculated spectrum within the passband is replaced by the known low frequency component. Then, the algorithm updates the relaxation parameter adaptively at each iteration. A qualitative evaluation of this algorithm is performed with simulated data as well as actual radiometer image captured by 91.5 GHz mechanically scanned radiometer. From experiments, it is found that the super-resolution algorithm obtains better results and enhances the resolution and has lower mean square error （MSE）. These constraints and adaptive character and spectral correction procedures speed up the convergence of the Landweber algorithm and reduce the ringing effects that are caused by regularizing the image restoration problem.     

Differently implicational α-universal triple I restriction method of （1,2, 2） type

From the viewpoints of both fuzzy system and fuzzy reasoning, a new fuzzy reasoning method which contains the α-triple I restriction method as its particular case is proposed. The previous α-triple I restriction principles are improved, and then the optimal restriction solutions of this new method are achieved, especially for seven familiar implications. As its special case, the corresponding results of α-triple I restriction method are obtained and improved. Lastly, it is found by examples that this new method is more reasonable than the α-triple I restriction method.     

Multi-criteria linguistic interval group decision-making approach

For group decision-making problems with linguistic assessment information, a new method based on two-tuple and WC-OWA operator is proposed, in which the criteria＇s weights and the decision-makers＇ preference information might take the form of linguistic grade, or might be between two continuous linguistic grades, or might be linguistic interval, or might be default. In this method, all linguistic values are transformed into two-tuple, and an aggregative decision-making matrix is obtained by using interval operation. The group aggregative values of each criterion on alternatives are computed by using a WC-OWA operator, the aggregative values on alternatives are worked out, and transformed into two-tuple. And the rank of the alternatives is obtained by using the order property of two-tuple. An example shows the feasibility and effectiveness of the proposed method.     

Modelling of a Class of Nonstationary Time Series with Kalman Filter Using Moving Window

In this paper a method for modelling and forecasting of a class of nonstationary time series with Kalmnan filter using moving window is proposed. The procedure of the method is as follows: in terms of parameter estimation during recursive process by using LSM, the state space equation is constructed, then the Kahnan filter using moving window is made to get the data with reduced level of observation noise. Finally, the precise parameter estimation can be obtained by using the LSM again. The algorithm is carried on recursively. Good results for estimating and forecasting are shown by simulation, examples. The algorithm of Kalman filter using moving window proposed by us is introduced in this paper, which can guarantee the precision and convergence of Kalman filter.     

垂直热发射流场研究与计算机仿真

本文着重分析了垂直热发射单喷管流场自由双限制射流流场及其多组分流场参数的计算方法和复杂激波系的数值解,运用Godunov方法在386微机上进行了数学仿真,编制了CAD软件包。     

非轴对称装药对杆式射流初速影响的数值仿真

为了增加杆式射流的威力,采用LS-DYNA研究了非轴对称装药对杆式射流初速的影响规律,并提出用装药的非轴对称度表征非轴对称装药。通过分析可知:长轴起爆半径对爆轰波波形和压力的影响较大,长轴装药半径则决定了长轴起爆半径的选择范围。随着长轴起爆半径的增加,爆轰波的相互作用区域增大,压力峰值提高。得到了起爆半径非轴对称度对杆式射流初速的影响规律:随着起爆半径非轴对称度的增加,杆式射流的初速开始增加较快,后来增加变慢。所研究的非轴对称杆式射流头部初速最高可以达到3510m/s。     

一种新的计算周期表面电磁散射算法

利用数值方法研究周期表面的电磁散射问题。应用矩量法研究周期表面的电磁散射可以获得较为精确的数值结果。对于表面散射 ,应用矩量法时表面未知变量的数目非常大 ,即使对于一维表面也需要几千个未知变量 ;当求解矩阵方程时 ,计算机对求解的问题有内存和速度的限制。为了克服内存的限制 ,采用了一种新的迭代数值算法。对周期表面的电磁散射问题进行了研究 ,并与矩阵反演方法作了比较。所得结果表明 ,这种新的迭代法具有很好的收敛性。最后对散射结果进行了讨论     

喷孔前置式膨胀波枪炮发射过程数值仿真与分析

喷孔前置式膨胀渡枪炮是一种结合了喷气反推式低后坐力枪炮和膨胀波火炮性能优点的新型低后坐力武器.提出了其发射过程的四阶段物理模型,运用准一维准两相流理论建立了其内弹道过程的动力学模型,针对其特殊的减后坐组件结构提出了身管--反作用导气管双流场耦合计算的边界务件和计算方法,以14.5mm喷孔前置式膨胀波弹道枪为例进行了数值仿真,并将仿真结果与普通14.5mm机枪的内弹道过程进行了对比.结果表明,在结构参数匹配合理的情况下14.5mm喷孔前置式膨胀波弹道枪能在不减小弹丸初速的前提下减少40.56%的后坐动量.     

基于Prewitt算子的X波段雷达有效波高反演研究

在X波段雷达有效波高获取的工程应用中,无现场仪器校准获取波高的方法一直是人们所致力研究的。基于雷达阴影调制特性无校准有效波高反演的方法是一种可进行工程应用的方法,但该方法采用差分算子获取的雷达图像阴影阈值的准确度和稳定性不高,影响有效波高的反演精度。本文针对这一问题,采用Prewitt算子对雷达图像的边缘检测算法进行了改进,该算子能更加精准地定位雷达图像阴影区与非阴影区的边缘。通过两次不同地点和不同时间获得的试验数据进行验证,结果表明Prewitt算子能够提高图像阈值选取的准确度和有效波高的反演精度,两次反演结果与浮标数据相比平均绝对误差在15%以内。     

复杂背景中的运动目标回波仿真计算

针对窄带相参体制的脉冲雷达波形,建立了杂波干扰反射复杂背景环境下直线飞行的空中目标机体反射信号和二次调制信号的模型,研究了发射波形同目标与环境相互作用的电磁散射机理。该模型中的复杂背景包括地杂波下垫面的干扰反射信号和空间分布反射体的干扰反射信号。根据给定的目标建模算法和干扰反射杂波模型,模拟了不同信杂比下螺旋桨飞机和喷气式飞机的雷达回波,仿真结果表明,这两种目标具有不同的频谱结构,证明了给出的模型是有效的,为雷达系统提供了实用的回波仿真信号。     

渐变微波吸收体散射截面计算

针对二维周期渐变微波吸收体尺寸大、结构较复杂、锥齿间耦合强,很难直接精确计算出雷达散射截面(RCS)的问题,采用矩量法和天线阵分析技术相结合的方法对渐变吸收体进行分析和计算,解决了计算量大、锥齿间耦合强而难以计算的难题,且能保证计算的精度。在线极化平面波入射情况下,给出单个和两个涂敷二面角的散射截面以及多个渐变吸收体的散射截面,计算结果与商用软件HFSS(high-frequency structure simulator)计算得到的结果基本吻合,计算速度明显快于HFSS,且克服了因吸收体大而无法用HFSS计算的难题,结果表明所提方法在工程运用上是可行的。     

脉冲力末端修正追踪制导律稳定性分析

脉冲力控制的离散性和弹体动力学的连续性使得脉冲力控制制导控制系统成为难于分析的混杂控制系统。鉴于此,建立了脉冲力控制弹体和制导回路动力学模型,通过将脉冲力控制制导系统等价为幅值式脉冲调制(amplitude pulse frequency modulator,APF-M)系统,解决了脉冲力控制制导回路的变周期离散化建模问题。进一步利用滑模理论分析了制导回路的稳定性,得出脉冲冲量、喷管点火等待时间及重力对制导回路稳定性的影响。提出了偏置阈值法进行重力补偿,并对脉冲力控制制导回路进行了仿真分析。仿真结果验证了偏置阈值法重力补偿的有效性,并得出加大脉冲冲量,减小喷管点火等待时间能有效减缓失调角发散的结论。