低轨星座对静止轨道卫星同频干扰指标研究

随着全球低轨星座系统的快速部署及应用,非静止轨道卫星对静止轨道卫星系统的同频干扰问题日益凸显。为保护静止轨道卫星系统不受有害干扰,国际电联现行无线电规则中规定了非静止轨道卫星系统应满足的等效功率通量密度限值或干扰噪声比限值,但所适用频段及限值标准仍在不断修订完善中。为了精确定量评估低轨星座对静止轨道卫星的同频干扰,通过对等效功率通量密度限值和干扰噪声比限值的确定方法及演进历程进行研究,分析了上述限值与静止轨道卫星实际被干扰的对应关系,并以典型倾斜轨道星座和极地轨道星座为例,分析了不同干扰指标对卫星系统间干扰判定结果的影响,当静止轨道卫星系统的实际被干扰门限低于国际电联制定等效功率通量密度限值选用的参考门限时,建议低轨星座选择干扰噪声比限值作为开展频率干扰分析与判定的依据。     

充气卸荷开关泄漏机理分析

某发射场进行火箭发动机气瓶充气时出现充气卸荷开关关闭后泄漏故障,分解卸荷开关后发现卸荷开关阀芯导向部位存在异常磨损,且阀芯非金属密封面周向密封压痕深度不均匀,结合故障形貌,采用有限元仿真计算压痕深度,对泄漏故障的根本原因进行深入剖析。分析结果表明:卸荷开关阀芯导向部位存在微小原始缺陷,多次动作后在阀芯与壳体导向部位产生粘着磨损,阀芯在壳体导向孔中回位发生偏斜,造成阀芯非金属密封面出现不均匀压痕,最终导致卸荷开关在测试时漏率超标。     

面向电容式微机电加速度计的接口噪声分析和数字闭环技术研究

优化电容检测接口并采用力反馈控制方案能够在不影响表头敏感结构的情况下,通过改变环路参数提高加速度计的信噪比,改善加速度计性能。基于一款阵列式差分电容的加速度计敏感结构,在等效电容模型的基础上,通过电容检测接口电路的搭建与输出信号的频谱分析,验证了单载波电容检测电路具有更出色的输出信噪比。后级采用STM32H743VIT6微处理器实现调幅信号的数字解调,经PI控制算法调节后作为反馈电压施加于可动极板,实现了加速度计的数字闭环控制。实测结果显示,闭环状态下加速度计的速度随机游走（VRW）为57 μg/Hz1/2,与开环状态相当,而零偏稳定性则从开环状态的184 μg改善至58 μg,验证了单载波调制型电容检测接口和力反馈控制技术对提升加速度计静态性能的具体效果。     

基于模态匹配和正交抑制的微机电陀螺闭环控制技术研究

模态匹配和力反馈控制可以在不牺牲检测带宽的情况下,利用机械谐振放大特性有效提高微机电陀螺信噪比、改善陀螺性能。结合一款高Q值对称式四质量敏感结构的陀螺表头,在陀螺动力学平均模型基础上,通过对检测模态同相分量和正交分量的控制,实现陀螺的闭环检测控制。基于静电负刚度原理,通过改变陀螺敏感结构梳齿与质量块之间的电压,构建实时正交抑制系统和精确模态匹配环节,推导出陀螺的静电刚度矩阵,完成了对正交耦合信号的实时抑制和驱动、检测模态的精确模态匹配并且实现对两环节的解耦控制。实测结果显示,陀螺频差由24 Hz缩小到0.05 Hz以内,全温条件下,陀螺的正交耦合量由3(°)/s抑制到0.01(°)/s,陀螺全温零偏稳定性由初始的11.48(°)/h改善到1.95(°)/h,验证了实时正交抑制和模态匹配等技术对提升陀螺性能的具体效果。     

纳米颗粒SiCp/Al复合材料车削特性试验研究

针对纳米颗粒增强铝基(SiCp/Al)复合材料在航空航天领域的应用需求,采用试验的方法,研究不同刀具材料和不同刀具几何参数对切削加工纳米SiCp/Al复合材料加工表面粗糙度和切屑形貌的影响。试验结果表明,相同切削参数下,PCD刀具比硬质合金刀具能获得更低的已加工工件表面粗糙度,微崩刃的存在是导致硬质合金刀具加工时工件表面粗糙度升高的主要原因之一;增加刀具的锋利度能够获得较低的工件表面粗糙度,较大的主偏角表面粗糙度变化较剧烈;由于纳米颗粒增强相的不均匀分布和材料内部存在微裂纹,在切削时导致切屑呈不规则的锯齿状,基体的断裂模式是该现象产生的主要原因。文中的研究成果将为进一步分析纳米SiCp/Al复合材料的切削机理提供必要的试验基础。     

光纤光子纠缠增强陀螺的现状与认知

1996年,Bollinger等指出利用光子纠缠态NOON态可使干涉仪的相位测量精度相对于散粒噪声极限提高N倍,达到海森堡极限(Heisenberg Limit Measurement).2019年5月8日,奥地利科学家马蒂亚斯·芬克(Matthias Fink)团队在《New Journal of Physics》上报道了纠缠增强光子陀螺,其利用纠缠光源降低光子de-Broglie波长,实现了超过散粒噪声极限的相位测量.马蒂亚斯·芬克团队的研究成果在业界引起较大反响,并聚焦为光纤光子纠缠陀螺的研究热点.基于新型光纤光子纠缠增强陀螺的相关概念,对光纤光子纠缠增强陀螺的工作原理、理论可实现精度、国内外研究基础和现状等进行了收集梳理、学习分析、认知提升,进而在此基础上针对相关技术,如光子纠缠源、光子纠缠通量的增强抑衰、信息的逻辑采集处理解算、光子纠缠增强陀螺集成技术、光子纠缠陀螺系统验证技术等的创新推进提出了一些浅显看法以商榷.通过上述工作也期望能"抛砖引玉",为我国光纤光子纠缠增强陀螺技术的起步和未来的发展推广应用奠定基础,并激励广大研究者继续深入探索.     

Structural topology optimization under stationary random base acceleration excitations

Structural topology optimization subjected to stationary random base acceleration excitations is investigated in this paper. In the random response analysis, the Large Mass Method(LMM) which attributes artificial large mass values at each driven nodal Degree Of Freedom(DOF) to transforming the base acceleration excitations into force excitations is proposed. The Complete Quadratic Combination(CQC) which is commonly used to calculate the random responses in previous optimization has been proven to be computationally expensive especially for large-scale problems. In order to conquer this difficulty, the Pseudo Excitation Method(PEM) and the combined method of PEM and Mode Acceleration Method(MAM) are adopted into the dynamic topology optimization, and random responses are calculated using these two methods to ascertain a high efficiency over the CQC. A density-based topology optimization method minimizing dynamic responses is then formulated based on the integration of LMM and PEM or the combined method of PEM and MAM. Numerical examples are presented to verify the accuracy of the proposed schemes in dynamic response analysis and the quality of the optimized design in improving dynamic performance.     

高温化学非平衡湍流边界层脉动量象限分析

高超声速飞行器在较低空域以极高马赫数飞行时，表面会同时存在湍流与化学非平衡流动，但目前针对此类高温化学非平衡湍流边界层流动特性的研究工作还比较有限，对不同湍流特征的主导流动机制的认识还有待于进一步深入。选取高超声速楔形体头部斜激波后的流动状态，设置3种不同的壁面温度，通过直接数值模拟对比了不同壁温条件下的边界层参数分布特性，并采用象限分解技术分析了边界层不同象限流动事件对雷诺剪切应力、湍流热流、湍流质量扩散的贡献。结果显示：在整个边界层中上抛和下扫运动对雷诺剪切应力的贡献占优；冷壁效应会使得流向和法向湍流热流通量的主导流动事件在温度峰值两侧发生改变。O原子组分流向湍流组分扩散主要受到高质量分数流体慢速运动事件和低质量分数流体快速运动事件的影响，而法向湍流组分扩散则主要受到高质量分数流体向上运动事件和低质量分数流体向下运动事件的影响。     

Satellite availability and positioning performance of uncombined precise point positioning using BeiDou-2 and BeiDou-3 multi-frequency signals

To realize the smooth transition from regional BeiDou Navigation Satellite System (BDS-2) to the global one (BDS-3), the integration of BDS-2 and BDS-3 is important for providing continuous, stable and reliable positioning, navigation and timing (PNT) services for global users. This work used 154 globally distributed multi-GNSS (Global Navigation Satellite System) experiment stations spanning 30 days to analyze the satellite availability and positioning performance of uncombined precise point positioning (UC-PPP) under current BDS-2 and BDS-3 constellations. We focused on three issues: the influence of BDS-3 receiver tracking abilities, the positioning performance among different areas, and the benefit of multi-frequency observations. The results show that the elliptical zone caused by poor BDS-2 satellite visibility is disappeared when the evenly distributed BDS-3 medium earth orbit satellites are introduced. When BDS-3 are integrated with BDS-2, the area with the Position Dilution of Precision (PDOP) less than 2 can be expanded to 75° S-75° N and 30° E-150° W. The positioning performance of BDS-3 and BDS-2/BDS-3 UC-PPP are seriously affected by the receiver tracking abilities of BDS-3 signals. When the maximum pseudo-random noise sequences (PRNs) of BDS-3 satellites tracked by stations are within 30 or 37, the positioning accuracy of static UC-PPP can be improved by 22.94% or 8.27% due to the integration of BDS-2 and BDS-3. Besides, the most improvement of BDS-2 and BDS-3 integration is achieved in Asia-Pacific regions, especially for the kinematic UC-PPP or the poor receiver tracking abilities of BDS-3. Similar to the multi-frequency BDS-2 UC-PPP, the benefit of multi-frequency signals for BDS-3 or BDS-2/BDS-3 UC-PPP is also non-vital. The three-dimensional positioning accuracy of BDS-2/BDS-3 multi-frequency UC-PPP in static mode and kinematic mode are 2.24 cm and 5.39 cm, while the corresponding convergence time are 49.62 min and 73.80 min, respectively. Compared with BDS-2, both the positioning accuracy and the convergence time of BDS-2/BDS-3 joint UC-PPP are improved by approximately over 50%, which indicates that BDS-3 has a great potential to provide high-quality PNT services as other global navigation satellite systems.     

Dynamic performance of a C/C composite finger seal in a tilting mode

The complex operating state of aeroengines has an impact on the performance of finger seals.However,little work has been focused on the issue and the dynamic performance of finger seals is also rarely studied.Therefore,a distributed mass equivalent model considering working conditions is proposed in this paper for solving the existing problems.The effects of the fiber bundle density and the preparation direction of the fiber bundle of a C/C composite on the dynamic performance of a finger seal are investigated in rotor tilt based on the proposed model.The difference between the C/C composite finger seal performances under the rotor precession and nutation tilt cases is also investigated.The results show that the fiber bundle density and the preparation direction of the fiber bundle have an influence on the dynamic performance of the finger seal as rotor tilt is considered,and the dynamic performance of the finger seal is different in the two kinds of tilting modes.In addition,a novel method for design of finger seals is presented based on the contact pressure between finger boots and the rotor.Finger seals with good leakage rates and low wear can be acquired in this method.