舰艇的雷达散射特性对反舰导弹捕捉概率的影响分析

通过对舰艇有效散射截面计算方法的引入,得出弹上雷达在不同目标特性下对舰艇的探测能力及最大探测距离,进而提出雷达最大探测距离与导弹捕捉概率在俯仰、距离和航向三个通道内的函数关系,为不同舰艇的雷达散射特性对反舰导弹捕捉概率的影响研究提供理论依据．最后得出结论,对于反舰导弹而言,舰艇的雷达散射特性对雷达捕捉概率的大小有着重大的影响,寻求舰艇的目标特性与导弹捕捉概率之间的关系值得研究．     

基于体征变化修正的火控雷达RCS仿真方法

复杂目标RCS数值计算难度高,计算机资源消耗大,在实时仿真上的应用较为困难.结合空袭兵器RCS仿真的实际情况和需求,采用部件分解法建立运算模型,并用高精度算法计算其RCS,然后通过分析体征变化对RCS的影响,推演经典算法公式提取体征修正系数;使用简单的系数运算代替复杂的算法求解,进一步得出其他不同体征空袭兵器的RCS,从而减小计算量,缩短运算周期.这种方法建模简单、物理概念清晰并能满足仿真实时性要求.     

可重复使用运载器的RCS姿态控制技术研究

反作用控制系统作为可重复使用运载器高空的姿态控制手段,其力矩特性不同于常规的气动操纵面,因此设计适合高空姿态控制特点与要求的控制系统是非常必要的。文中采用了一种带死区的乒乓控制方式,设计了俯仰、滚转和偏航的反馈控制律,采用描述函数法在频率上分析了控制系统的稳定性。仿真结果表明,设计的控制系统能较好的满足高空姿态控制要求,最后对姿态控制效果和反作用控制系统喷量之间的关系进行了分析。     

雷达散射截面对反舰导弹生存能力的影响研究

建立了反舰导弹对由预警雷达和舰空导弹武器系统组成的现代化反导系统的突防概率的计算方法,其中包括探测概率和拦截概率的计算.通过仿真计算,分析反舰导弹的RCS对生存能力的影响.研究结果表明,减缩反舰导弹的RCS可以显著降低反舰导弹被探测的概率,从而可以缩短舰空导弹的发射区远界,缩短反导的作战准备时间,提高反舰导弹的生存能力.     

一种低频外露机载天线隐身设计

针对低成本准隐身飞机,探讨了一种低频外露机载天线的隐身设计,提出了一系列的隐身设计措施(例如优化天线外形、改变安装方式、在天线罩表面涂敷吸波材料等);经过隐身仿真、隐身测试等手段,获取了天线在不同频点、不同极化下的RCS均值,并通过仿真、测试数据对比,验证了隐身改进设计的有效性,并为其他外露物隐身设计提供了设计依据和手段.     

全数字雷达仿真系统中恒虚警率模型的参数分析及设计

在实际的工程实践中,全数字雷达仿真系统建模中通常存在着设计参数输入不充分和客观环境模型建立的复杂度高两个问题,而这两个问题严重增加雷达系统仿真建模的难度。在此,以雷达仿真系统中的恒虚警率模型设计为例,提出对雷达模型中未知参数的推演及估算和复杂模型的替代模型结合,进行参数分析及设计思路。通过模型的边设计边验证的过程,分析并确认设计模型是否能够达到已知的关键性能指标要求,进而反向调整并确定设计的合理性。这种将模型建立和模型验证同步进行的设计方法,指导了某型号反潜直升机飞行模拟器的全数字多普勒搜索雷达的仿真实现。通过该实例应用,证明该仿真方法具备严谨性及实用性。     

预制混凝土管组合柱-钢梁连接节点抗震性能试验研究

为研究预制混凝土管组合柱-钢梁连接节点的抗震性能,以轴压比、钢套箍延伸高度、芯部混凝土强度以及钢套箍厚度为主要参数,进行了6个1/2缩尺节点的拟静力试验。研究了各节点的破坏形态、滞回特性、承载能力、耗能能力以及节点域受剪性能。试验结果表明：各节点主要破坏模式均为节点域剪切破坏;滞回曲线呈典型弓形,耗能能力较好;芯部混凝土强度和钢套箍厚度是影响节点抗震性能的关键参数,对承载能力和耗能性能影响较大;破坏时节点域极限剪切变形介于0.0482 ~0.100 rad之间;节点域受剪承载力降低系数介于0.86~1.00之间,承载力退化性能稳定。建立了预制混凝土管组合柱-钢梁连接节点受剪承载力计算式,计算值与试验值吻合较好且偏于安全。     

Compound fault-tolerant attitude control for hypersonic vehicle with reaction control systems in reentry phase

In this paper, a novel compound fault-tolerant attitude control (FTC) scheme is proposed for reentry hypersonic vehicles with aerodynamic surfaces and reaction control systems (RCS) in the presence of parameter uncertainties, external disturbances and aerodynamic surfaces faults. Aerodynamic surfaces work as the primary actuators and RCS serve as auxiliary actuators. When aerodynamic surfaces cannot provide the required attitude control torque due to low dynamic pressure or faults, RCS are activated to assist aerodynamic surfaces to generate the residual torque. A nonlinear disturbance observer-based sliding mode controller is designed to calculate the required attitude control torque which can handle the parametric uncertainties and external disturbances together. The quadratic programming method is applied to obtain the optimal aerodynamic surfaces deflections from the required control torque. An innovative fuzzy rule-based decision-making system is design to solve the RCS control allocation problem, which is conceptually easy to understand and computationally efficiently compared with existing approaches. Based on quantized control theory, the closed-loop control system stability is rigorously analyzed. Simulation results are given to demonstrate the effectiveness and efficiency of developed FTC scheme.     

Zero reflection from metamaterial sphere

In this study spherical structure is considered and analyzed with full wave method. The plane wave radiates to the structure and the zero reflection condition is deduced as a closed formula. Two theorems and ideas are proofed mathematically, and finally some examples are presented for validating these theorems. Theorems indicate if the double negative metamaterial sphere (DNG) with an arbitrary radius and parameters (Re(ɛ₂) < 0, Re(μ₂) < 0) situate within conventional space with parameters (ɛ₁, μ₁), and ɛ₂/ɛ₁ = μ₂/μ₁ then backscattering radar cross section (RCS) of this metamaterial sphere equals zero whiles the same situation with cylindrical structure has noticeable backscattering. In addition, the bistatic radar cross section of this metamaterial sphere is constant by changing the angle φ. Both theorems are generalized to spherical multilayer structure.     

Guidelines and recommendations for indoor use of fuel cells and hydrogen systems

Hydrogen energy applications often require that systems are used indoors (e.g., industrial trucks for materials handling in a warehouse facility, fuel cells located in a room, or hydrogen stored and distributed from a gas cabinet). It may also be necessary or desirable to locate some hydrogen system components/equipment inside indoor or outdoor enclosures for security or safety reasons, to isolate them from the end-user and the public, or from weather conditions.Using of hydrogen in confined environments requires detailed assessments of hazards and associated risks, including potential risk prevention and mitigation features. The release of hydrogen can potentially lead to the accumulation of hydrogen and the formation of a flammable hydrogen-air mixture, or can result in jet-fires. Within Hyindoor European Project, carried out for the EU Fuel Cells and Hydrogen Joint Undertaking safety design guidelines and engineering tools have been developed to prevent and mitigate hazardous consequences of hydrogen release in confined environments. Three main areas are considered: Hydrogen release conditions and accumulation, vented deflagrations, jet fires and including under-ventilated flame regimes (e.g., extinguishment or oscillating flames and steady burns). Potential RCS recommendations are also identified.