Adaptive nonlinear guidance law considering control loop dynamics

A new adaptive nonlinear guidance law is proposed here. The fourth order state equation for integrated guidance and control loop is formulated taking into consideration the target uncertainties and control loop dynamics. The state equation is further changed into the normal form by nonlinear coordinate transformation. Using the normal form of state equation, an adaptive nonlinear guidance law is proposed to compensate for the uncertainties in both target acceleration and control loop dynamics. The proposed law adopts the sliding mode control approach with adaptation for unknown bound of uncertainties. The present approach can effectively solve the existing guidance problem against target maneuver and the limited performance of control loop. We have provided the stability analyses and performed simulations comparing favorably our approach to the state of the art.     

GNSS-Reflectometry: Forest canopies polarization scattering properties and modeling

Nowadays, GNSS-Reflectometry (GNSS-R) can be a new promising remote sensing tool in the ocean, snow/ice and land surfaces, e.g., vegetation biomass monitoring. Although GNSS-R provides a potentially special L-band multi-angular and multi-polarization measurement, the theoretical vegetation scattering properties and mechanisms for GNSS-R are not understood clearly. In this paper, the GNSS-R vegetation polarization scattering properties are studied and modeled at different incidence angles (specular direction). The bistatic scattering model Bi-mimics is employed, which is the first-order radiative transfer equation. As a kind of forest stand, the Aspen’s crown layer is composed of entire leaves, and its parameters in Mimics handbook are used as model input. The specular circular polarizations (co-polarization RR and cross-polarization LR) are simulated. For cross-polarization, the received polarization is assumed as a linear (horizontal and vertical) polarizations and ±45° linear polarizations. Therefore, the HR VR, +45R and −45R polarizations are simulated here. Contributions from different scattering components at RR, LR and VR polarization are also presented. For co-polarization, it is large in the whole specular angles (10–80°). The scattering trends of the other cross polarization (HR, LR, +45R and −45R) are a little similar when compared to the RR and RV. Therefore, the RHCP and V polarizations are more favorable to collect the reflected signals. The trunk heights and crown depths do not affect the scattering trends of RR, RV and RL, while the trunk height has some effect on the scattering amplitude of different polarizations. The azimuth angle has more effects on RR, RL and RV scattering, especially in lower than 50°. The observation angles and polarization combinations are extremely important for GNSS-R remote sensing.     

服从任意分布的部件可用度快速计算方法

工程中通常认为电子产品故障密度和修复服从指数分布，但是现代的航空和航天系统使用部件，并不总是指数分布，指数分布部件构成的系统也并不一定服从指数分布。文中提出了故障密度和修复密度任意分布的部件可用度快速计算方法，并且以故障密度和修复密度服从常用分布情形，即指数分布、正态分布、对数正态分布和威布尔分布情形，分析了任意分布部件可用度的变化规律，所提出的方法，便于工程实际应用。     

液体火箭发动机钎焊、扩散焊质量检测技术研究

现代液体火箭发动机的推力室钎焊身部、发生器钎焊身部及游机推力室钎焊身部均是在高温、高压环境下工作，采用波纹板和铣槽式结构，而这种结构的钎焊和扩散焊的焊接质量直接关系到产品的承压强度及冷却效果。因此，对钎焊和扩散焊的质量检测尤为重要。着重讨论了对波纹板结构和铣槽结构的钎焊、扩散焊质量采用不同无损检测方法进行检测时，方法的可行性和存在的问题，并给出不同方法对产品的可检测性结论。     

产业转移与江西承接基地建设

纵观世界各国和地区的经济发展,产业梯度转移是一个普遍存在的客观经济规律,这种梯度推进规律为欠发达国家或地区发挥比较和后发优势、实现跨越式发展提供了机遇.从现实性考察,江西近年在招商引资中也开创出崭新的局面.但尽快制订相应对策,促进产业转移承接基地建设仍然是实现江西在中部率先崛起的一条有效路径.     

发动机舱门及后机身结构一体化综合设计

针对某型机后机身并列配置两台发动机的特点,提出了一种腹部大开口结构及发动机承力快卸舱门一体化综合设计方案,通过合理划分舱门、设计专利钩形快卸锁、优化布置钩锁-插销锁,以及采取一系列设计、工艺措施保证快卸锁与机体的可靠连接等创新技术,使该设计方案达到了既定目标。     

被动式电磁阻尼器对磁悬浮转子系统不平衡响应的影响

采用被动式电磁阻尼器控制磁悬浮轴承转子系统振动.首先,设计了一个被动式电磁阻尼器,可以通过电流变化控制阻尼力.然后,基于通用有限元软件NASTRAN,对磁悬浮轴承转子系统分析了不同阻尼下的不平衡响应仿真.最后通过系统高速旋转实验,研究了不同阻尼器控制参数下该系统的不平衡响应.仿真与试验结果表明,增加被动式电磁阻尼器能够改善系统的动态性能并降低转子的不平衡振动,使转子成功越过一阶弯曲临界转速15 600 r/min,稳定运行在21 000 r/min.     

瞬时热曝露对BTi-62421S钛合金组织和性能影响研究

BTi-62421S是一种先进的近α型耐温钛合金,以1.5mm轧制板材为例,开展了瞬时热曝露试验。运用金相显微镜和力学性能试验机对组织和性能进行了分析和测试。结果表明,合金由片状α组织和极少量β转变组织组成,随热曝露温度变化,合金呈现出明显不同的温色特征。在热曝露参数600℃/5h条件下,合金组织较稳定,氧化膜致密度下降,并有富氧α层产生,随着曝露温度的提高,β转变组织开始积聚粗化,次生α相增多,组织稳定性开始下降,氧向基体扩散加剧,富氧α层厚度呈倍数增加,组织变化对合金强度无明显影响,但富氧α层严重降低合金塑性。     

Adaptive control for feedback-linearized missiles withuncertainties

A robust adaptive control scheme is proposed that can be applied to a practical autopilot design for feedback-linearized skid-to-turn (STT) missiles with aerodynamic uncertainties. The approach is to add a robust adaptive controller to a feedback-linearizing controller in order to reduce the influence of the aerodynamic uncertainties. The proposed robust adaptive control scheme is based on a sliding mode control technique with an adaptive law for estimating the unknown upper bounds of uncertain parameters. A feature of the proposed scheme is that missile systems with aerodynamic uncertainties can be controlled effectively over a wide operating range of flight conditions. It is shown, using Lyapunov stability theory, that the proposed scheme can give sufficient tracking capability and stability for a feedback-linearized STT missile with aerodynamic uncertainties. The six-degree-of-freedom nonlinear simulation results also show that good performance for several uncertainty models and engagement scenarios can be achieved by the proposed scheme in practical night conditions     

飞航导弹变结构过载控制方案研究

对飞航导弹的变结构过载控制进行了研究,提出了以过载、角加速度和角速度构造滑模面的工程易实现的方案。同时,应用根轨迹方法,进行了控制参数的优化设计。最后,针对两类典型飞航导弹模型,将"过载 角加速度 角速度"方案与"过载 角加速度"方案进行仿真比较。结果表明"过载 角加速度 角速度"方案适用范围更广、控制效果更好。