Heading control strategy assessment for coaxial compound helicopters

The coaxial compound helicopter has two possible strategies for heading control: collective differential and rudder deflection. A flight dynamics model is developed to assess the effect of different heading control strategies. This includes the trim characteristics, steady flight performance,controllability, and manoeuvrability. The trim study demonstrates that heading control strategies are less influential on trim results, and the steady flight performance is also not significantly affected by the heading control strategy adopted. The controllability analysis shows although heading bandwidth and phase delay results at various speeds with different heading control strategies are all satisfied, the control derivative of the collective differential decreases as speed increases, and its heading aggressive agility is degraded into Level 3 in high-speed flight. In addition, using collective differential would lead to severe heading-rolling coupling as forward speed increases. On the contrary, the control derivative and aggressive agility of the rudder deflection is improved with forward speed, and there is no evidence of heading-rolling coupling. Finally, the transient turn MissionTask-Element(MTE) is utilized to investigate the heading manoeuvre characteristics in different heading control strategies, which indicates that the collective differential would add the amplitude of control input and the power consumption during this MTE.     

Multi-objective Optimization of Differential Steering System of Electric Vehicle with Motorized Wheels

A differential steering system is presented for electric vehicle with motorized wheels and a dynamic model of three-freedom car is built. Based on these models, the quantitative expressions of the road feel, sensitivity, and operation stability of the steering are derived. Then, according to the features of multi-constrained optimization of multi-objective function, a multi-island genetic algorithm （MIGA） is designed. Taking the road feel and the sensi- tivity of the steering as optimization objectives and the operation stability of the steering as a constraint, the system parameters are optimized. The simulation results show that the system optimized with MIGA can improve the steering road feel, and guarantee the operation stability and steering sensibility.     

Focus Reflective Shock Wave Interaction with Flame

An experiment on deformation of flame under the effect of focusing shock wave reflection is performed with the help of multiple-spark camera to understand the flame instability of the deformation process. Methane and oxygen are mixed stoichiometrically to be used in the experiment. Based on Navier-Strokes equations, two-dimen- sional axisymmetric elementary reactions are numerically simulated. And the simulation results are solved by opti- cal calculation. Shaded pictures by simulation fit well with experimental photos. Focusing reflecton shock waves can affect the flame, which accelerates the deformation of flame and renders violent burning in high-energy flam- mable gases behind waves. Therefore anticlockwise whirlpool appears. It clusters around the external surface of flame and has a tendency to develop toward the right. Finally, the whirlpool focuses on the right side of the flame, which involves the fresh unfired gases into the whirlpool circle, and consequently the head of mushroom cloud is formed. Meanwhile, when shock wave passes through the flame, the intensity of the shock waves on the axis is strengthened.     

一种高斯型ASE光源研究

简单介绍了掺铒光纤的光放大原理,分析了四种ASE光源的光路结构。针对双通前向结构,设计了一种适用高精度光纤陀螺仪的高斯型ASE光源,并进行了试验研究。试验结果表明,掺铒光纤的掺杂浓度、光纤长度都对ASE光源的输出特性具有很大的影响。此外,根据试验结论,研制出高斯型ASE光源,其性能稳定,已在多个高精度光纤陀螺仪型号上实现了实际应用,并取得了良好的效果。     

边界层抽吸对超燃冲压发动机流场特性的影响研究

为了解边界层抽吸对超燃冲压发动机流场的影响,采用风洞试验和数值计算对隔离段激波串特性以及燃烧室燃烧特性进行了研究。结果表明,在发动机入口马赫数2.0,总温950K,总压0.82MPa的来流条件下,当量比为0.18先锋氢气与不同当量比煤油共同燃烧呈不稳定状态,激波串在隔离段内前后振荡传播。当煤油当量比为0.29时,激波串振荡前缘远离抽吸位置,边界层抽吸对发动机流场基本没有影响。随着煤油当量比逐渐增大,激波串前缘位置到达抽吸区附近,边界层抽吸开始产生影响,改变了隔离段内的激波串动态演化过程、形态结构以及位置分布,同时有效提高了隔离段抗反压特性,使得煤油最大当量比可以由0.38增大至0.42。此外,边界层抽吸对发动机内的亚燃/超燃区域分布也会产生影响。     

纤维金属层板的开发和应用现状

随着我国航空航天领域器械的飞速发展,对该领域中结构件所用材料的综合性能及轻量化提出了新的要求。在过去几十年里,大型客机的市场需求不断扩大,刺激了新型材料的兴起,使材料向着高性能,轻质量发展。纤维金属层板是由铝合金与纤维预浸料交替铺层固化而成的层间混杂复合材料。纤维金属层板结合了金属与复合材料的优良特性,具有密度小、损伤容限优良、抗冲击和疲劳性能,越来越受到航天航空和轨道交通领域的关注。目前用于商业生产的金属纤维层压板(FMLs)多以基于芳纶纤维(ARALL)与基于高强玻璃纤维(GLARE)的层板为主。概括了纤维金属层板的制备前表面处理工艺,对其弯曲测试、拉伸测试、冲击测试和疲劳测试等力学性能的测试方法进行综述,同时对未来新型纤维金属层板的开发进行探究,为纤维金属层板的开发提供参考信息。     

煤油燃料超燃冲压发动机燃烧特性实验研究

为研究空气节流时序对超燃冲压发动机点火和火焰稳定的影响,本文通过实验方法研究了13个状态的煤油燃料超燃冲压发动机的燃烧特性,煤油燃烧通过先锋氢气和节流空气增强稳定性。通过两个固定位置的压力传感器来监测火焰稳定状态,采用纹影和OH-PLIF相结合的测量手段,获得了流场结构和火焰发展信息。发动机入口来流条件为Ma = 2.0,总温950 K,总压0.82 MPa。在空气节流的作用下,煤油被先锋火焰引燃;在先锋氢撤除后,煤油仍然可以稳定燃烧。在扩张段中,空气节流和燃烧共同作用产生的激波串移动速度约为52 m/s,但在凹槽内其速度仅为3.7 m/s。通过监测点压力变化情况可以区分所研究状态的火焰稳定与否,通过对13个研究状态的考察,获得了火焰稳定临界曲线。当所研究状态点在临界曲线右上方区域时,火焰状态稳定;当所研究状态点在临界曲线左下方区域时,火焰将被吹熄;当所研究状态点在临界曲线上时,火焰不稳定,在空气节流撤除之前将被吹熄。     

光纤陀螺惯导在航海领域的发展与应用

针对航海导航领域对惯性技术发展的新需求,从系统精度、旋转调制技术、陀螺性能等方面出发,梳理了国外航海惯导技术的发展脉络。由此总结出了航海惯导三点新的发展需求,包括定位精度、研制成本、使用维护性,同时给出了满足当前发展需求的一个研究方向,那就是采用超高精度的光纤陀螺研制航海惯导。最后从陀螺精度极限、温控、全阻尼等几个方面进行简要的可行性论证,并给出了部分验证试验结果,试验结果表明光纤陀螺惯导在航海领域具有广阔的发展前景。     

稳定环境下的高精度光纤捷联惯导精度探索研究

在分析法国MARINS光纤惯导方案及温度试验的基础上,论证提出了一种带温控高精度光纤陀螺捷联惯导设计方法,并在温箱稳定环境下进行了试验验证。试验表明,在温箱温控精度为0.1℃的条件下,惯导系统精度可以达到1nmile/10d;若实装,温控精度将优于0.02℃,光纤惯导精度还可进一步提高。