超声调制电加工振动系统工具优化设计及试验

用有限元方法分析超声调制电加工振动系统,探讨有、无负载时振动工具的动力学特性,通过ANSYS分析结果与理论计算值的比较,表明用有限元方法分析超声特性有较高精度;用ANSYS参数化方法设计、优化超声振动工具设计,通过振动系统的振动特性测试,验证了振动系统设计的合理性;通过微结构超声复合电解加工试验,证明超声调制电解方式加工难加工材料、异型面的技术优势.     

动态压力校准技术现状分析

动态压力校准技术是确保航天型号压力测试数据准确可靠、量值统一的关键。介绍了动态压力校准的 必要性和特殊性,分别从阶跃压力校准法、周期压力校准法以及脉冲压力校准法三个方面,系统总结了国内外动态 压力校准技术的研究现状,提出目前仍存在的问题并对未来动态压力校准技术的发展提出改进措施。     

基于非线性神经网络的摆式列车检测系统动态补偿方法研究

针对零极点匹配动态补偿方法的不足 ,提出基于非线性神经网络的摆式列车检测系统动态补偿方法。根据陀螺平台实测超高数据 ,采用LM算法对所设计的非线性神经网络进行训练。仿真结果表明 ,所设计的神经网络动态补偿器能有效改善陀螺平台系统的动态特性 ,满足摆式列车倾摆控制实时性的要求。     

考虑动态控制分配的空天飞行器再入姿态复合控制设计

针对空天飞行器再入大气层阶段的直接力/气动力复合控制分配问题,设计了一种基于改进指标函数的动态控制分配律,兼顾了反作用控制系统燃料消耗和闭环控制系统响应速度需求.此外,针对空天飞行器面对称大攻角再入引发的横侧向气动强耦合问题,在预测控制律中引入了通道间交叉耦合反馈项,对姿控过程进行增稳.对比仿真结果表明,动态分配算法在...     

固体燃料热分解特性分析

为了认清固液火箭发动机混合燃烧过程,采用热平板导热方式对固体燃料进行热分解实验,得到了固体燃料的化学动力学参数。在热平板导热实验中,观察了固体燃料在不同温度条件下的热分解残药情形,绘制了典型的燃料表面热分解温度-时间曲线,进一步得到Arrhenius类型的燃面退移速率-燃料表面温度关系曲线,并得出固体燃料的活化能强烈依赖于燃料的表面温度,"燃速-温度"曲线明显地展现了2个活化能区域,为固液火箭发动机燃料表面退移速率理论计算提供实验依据。     

Flame features and oscillation characteristics in near-blowout swirl-stabilized flames using high-speed OH-PLIF and mode decomposition methods

Flame features and dynamics are important to the explanation and prediction of a lean blowout (LBO) phenomenon. In this paper, recognition of near-LBO flame features and oscillation characterization methods were proposed based on flame spectroscopic images. High-speed planar laser-induced fluorescence measurements of OH were used to capture unique dynamic features such as the local extinction and reignition feature and entrained reactant pockets. The Zernike moment demonstrated a good performance in recognition of stability and near-LBO conditions, though the geometric moment had more advantages to characterize frequency characteristics. Low-frequency oscillations, especially at the obvious self-excited oscillation frequency around 200 Hz, were found when approaching an LBO condition, which can be expected to be used as a novel prediction characteristic parameter of the flameout limit. Proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD) were used to conduct dynamic analysis of near-LBO flames. POD modes spectra showed the unique frequency characteristics of stable and near-LBO flames, which were basically in line with those at the heat-release frequency. The primary POD modes demonstrated that the radial vibration mode dominated in a stable flame, while the rotation mode was found to exist in a near-LBO flame. Analysis of modal decomposition showed that flame shedding and agminated entrained reactant pockets were responsible for generating self-excited flame oscillations.     

Real-time modular dynamic modeling for compression system of altitude ground test facilities

Modeling of a centrifugal compressor is of great significance to surge characteristics and fluid dynamics in the Altitude Ground Test Facilities (AGTF). Real-time Modular Dynamic System Greitzer (MDSG) modeling for dynamic response and simulation of the compression system is introduced. The centrifugal compressor, pipeline network, and valve are divided into pressure output type and mass flow output type for module modeling, and the two types of components alternate when the system is established. The pressure loss and thermodynamics of the system are considered. An air supply compression system of AGTF is modeled and simulated by the MDSG model. The simulation results of mass flow, pressure, and temperature are compared with the experimental results, and the error is less than 5%, which demonstrates the reliability, practicability, and universality of the MDSG model.     

Dynamic neighborhood genetic learning particle swarm optimization for high-power-density electric propulsion motor

To maximize the power density of the electric propulsion motor in aerospace application, this paper proposes a novel Dynamic Neighborhood Genetic Learning Particle Swarm Optimization (DNGL-PSO) for the motor design, which can deal with the insufficient population diversity and non-global optimal solution issues. The DNGL-PSO framework is composed of the dynamic neighborhood module and the particle update module. To improve the population diversity, the dynamic neighborhood strategy is first proposed, which combines the local neighborhood exemplar generation mechanism and the shuffling mechanism. The local neighborhood exemplar generation mechanism enlarges the search range of the algorithm in the solution space, thus obtaining high-quality exemplars. Meanwhile, when the global optimal solution cannot update its fitness value, the shuffling mechanism module is triggered to dynamically change the local neighborhood members. The roulette wheel selection operator is introduced into the shuffling mechanism to ensure that particles with larger fitness value are selected with a higher probability and remain in the local neighborhood. Then, the global learning based particle update approach is proposed, which can achieve a good balance between the expansion of the search range in the early stage and the acceleration of local convergence in the later stage. Finally, the optimization design of the electric propulsion motor is conducted to verify the effectiveness of the proposed DNGL-PSO. The simulation results show that the proposed DNGL-PSO has excellent adaptability, optimization efficiency and global optimization capability, while the optimized electric propulsion motor has a high power density of 5.207 kW/kg with the efficiency of 96.12%.     

Impact of aperture on dynamic response of sandwich plates with aluminium face-sheets and PMI core based on an alternative finite element formulation and experiments

Apertures generally exist in the sandwich structures attributing to mechanical connection and lightweight, which might induce failure of such structures. Thus, it is required to realize the impact of aperture on mechanical behaviors of sandwich structures. If transverse shear deformations are unable to be described accurately, the reasonable prediction of dynamic behaviors of the form-core sandwich plates with apertures will meet severe challenges due to a large difference of transverse shear mo...     

Investigation of flow unsteadiness in a highly-loaded compressor cascade using a dynamic mode decomposition method

Unsteady flow in the hub endwall region has long been a hot topic in the turbomachinery community. However important it is to the performance of the whole engine, the coherent unsteady flow phenomena are still not well understood. In this paper, the complex flow field in the hub endwall of a cantilevered compressor cascade has been investigated through numerical approach. The predicted results were validated by experimental data. To highlight the dominant flow structures among irregular and chao...