空间机械的摩擦学设计探讨

本文对空间机械的摩擦学设计进行了探讨,指出要确保空间机械工作的可靠性,就应当根据摩擦学知识在进行空间机械摩擦副结构、强度及动力学设计的同时,合理地选择润滑方式和润滑材料。作者认为,系统地积累空间摩擦学基础知识和各类润滑材科的基本性能数据,以及建立材科的基本性能与实际应用性能之间的数学关系式,都是进行空间机械摩擦学设计所需要具备的条件,并且提出应当根据摩擦副的使用环境和操作条件选择润滑方式利润滑材料,以及根据润滑材科的性能确定摩擦副的结构、强度和动力学设计的摩擦学设计之方法与步骤。 作者在举例说明对空间机械进行摩擦学设计的重要性后强调指出,为了提高我国空间机械的设计水平,应当加强研究部门与设计部门的密切合作,加速建立以材料之基本性能为基础的摩擦学数据库,并逐步建立空间机械摩擦学设计方面的专家系统。     

基于设计空间调整的结构拓扑优化方法

提出了一种基于设计空间调整的结构拓扑优化方法,以求解有限元网格规模大的问题,且获得0/1拓扑解. 首先, 借鉴有理分式材料模型, 建立了材料刚度性质与拓扑变量的关系. 为了解决分析计算量大和需要解释得到的材料分布等问题,给出了一种不影响数学规划求解算法收敛特性的设计空间调整手段. 其次,当优化迭代求解接近结构最佳拓扑邻域后,采用了加速收敛求解的策略,并给出了一种加速收敛的启发式算法. 然后, 结合基于倒设计变量的位移函数的非完整二阶近似式,建立了一种基于设计空间调整的结构拓扑优化算法. 该方法能获得较好0--1分布特征的优化拓扑,能较好地处理多载荷和多约束的结构拓扑优化问题. 给出的算例表明通过结构分析模型规模的减小和传统的位移迭代求解法的采用,方法效率明显提高. 算例验证了该方法的正确性和有效性.      

第三届深空轨道设计竞赛冠军团队方法与结果

介绍了2011 年第3 届全国深空轨道设计竞赛冠军团队中科院空间应用工程与技术中心(筹) 的设计方法与结果.设计方法包括总体设计思路、小推力转移轨道优化方法、小推力轨道简化模型、行星引力辅助序列设计、小行星搜索方法等. 给出了具体设计步骤以及初步和最终的设计结果. 最后, 总结了从此次设计过程中获得的若干经验与启示.     

计及气动和隐身约束结构综合优化的并行子空间优化方法

通过分析基于响应面的并行子空间优化算法的特点指出并行子空间优化算法学科级优化的作用在于向系统级优化响应面提供性能优良的设计点.在此基础上,建立了不要求学科级优化的改进的并行子空间优化算法,进一步降低了设计优化的计算量,解决了分析模块与优化模块间的接口困难.依据该算法建立了结构、气动和隐身一体化设计优化框架,实现了某无人机机翼计及气动和隐身约束的结构综合优化.     

纤维增强复合材料热隐身斗篷设计

基于变换热动力学原理可获得具有热隐身性能的隐身结构(隐身斗篷)所需要的材料性质的空间分布。但这种材料性质的复杂分布形式以及局部热传导性能无限大等极值性质需求,使得隐身斗篷设计的实现非常困难,需要研究基于常规材料的隐身斗篷设计。本文基于常规材料的热隐身结构实现问题,提出了基于纤维增强复合材料圆环结构的实现热隐身的结构形式。首先,基于变换热动力学原理获得热隐身所需的热传导系数沿半径方向的变化规律;进而,通过设计复合材料不同位置的纤维铺设方式(含量和铺设方向)实现热隐身对材料性能的需求。选择金属银作为纤维,空气作为基体,设计出了具有热隐身性能的复合材料圆环结构纤维含量和铺设方向沿径向的分布方案。对该设计方案进行数值仿真,结果显示所设计的隐身结构具有良好的热隐身性能。由于设计方案基于常规材料,因此具有容易实现的优点。     

热端部件低温热腐蚀疲劳损伤机理、寿命模型和抗腐蚀设计方法

对于沿海地区或海洋环境中使用的航空发动机来说,由于高温、机械载荷和盐雾环境的共同作用,热腐蚀疲劳破坏是影响其热端部件服役寿命的主要因素.本文对热端部件低温热腐蚀疲劳损伤机理、寿命模型和防腐蚀设计方法进行了总结、归纳及评述,提出了未来的研究趋势与发展方向.首先介绍航空发动机热端部件的热腐蚀疲劳故障案例、损伤演化机理;其次,重点分析了低温腐蚀疲劳寿命的唯象模型、损伤力学模型、断裂力学模型以及机器学习模型;再次,对几种代表性的考虑腐蚀演化不同阶段的分段式腐蚀疲劳全寿命模型进行综述,还分析指出了腐蚀疲劳全寿命模型的发展趋势;从次,对航空发动机材料选择、零件制造、结构强度设计和外场运行维护不同阶段的抗腐蚀方法进行了综述.最后,对增材制造零部件的热腐蚀疲劳问题以及无损检测技术、人工智能等与热腐蚀疲劳研究的结合进行了展望.     

开展深空轨道设计研究, 促进青年创新人才成长

今天, 在航天城举办了深空轨道设计竞赛活动和学术研讨会. 特别是, 这次活动适逢我们国家的空间实验室"天宫一号"与"神舟8号"飞船交会对接成功之际, 适逢钱学森先生诞辰100周年之日, 这是一件非常有意义的事情.     

基于虚拟中心引力场方法的航天器转移轨道设计

空间机动技术是实现空间操作任务的基础,具有重要的研究价值. 研究了连续推力作用下航天器转移轨道设计问题,提出了一种基于虚拟中心引力场的轨道设计方法. 该方法有两大特点:(1) 能够将机动轨道设计问题转化为虚拟中心引力场参数的优化问题,简化了设计过程;(2) 对轨道形状或推力方向、大小不做任何假定,能够应用于一般情况下的机动轨道设计. 将该方法应用于航天器二维和三维的转移轨道设计,并和形状方法进行了对比分析. 仿真结果分析表明,采用该方法简化了轨道设计过程,为航天器快速轨道设计提供了新思路.      

双臂空间机器人关节空间的补偿学习控制

在载体位置与姿态均不受控制情况下,结合动量(矩)守恒关系对系统进行了运动学、动力学的分析,得到了漂浮基双臂空间机器人的系统动力学方程. 采用PD控制的计算力矩法,得到了系统的闭环动态误差方程,在此基础上设计了针对不确定性的自由漂浮空间机器人的控制方案,提出了一种基于遗传算法的补偿学习控制方法. 将补偿学习控制与计算力矩法相结合,利用遗传算法的进化学习消除不确定因素的影响,实现机器人轨迹跟踪的良好控制.     

搭载实践十号卫星的蒸发液滴空间实验研究

实践十号蒸发对流实验以微重力环境中的蒸发相变流体界面过程为主要研究内容,利用空间微重力条件下浮力对流消失和热毛细对流起主导作用的特殊环境,实验研究置于加热底板的蒸发液滴相变过程中表面蒸发与表面张力驱动对流的耦合机理.利用研制的空间蒸发对流装置完成了在轨工况的科学匹配实验,得到了不同工况(温度、液滴大小、加热底板材料)下蒸发液滴形貌和热流量、蒸发速率等变化规律.为后续空间实验结果的比对分析提供了前期结果.     

基于深度学习的跨分辨率结构拓扑优化设计方法

在传统拓扑优化设计中,随着结构单元增加,迭代计算过程消耗了大量的时间.本文提出了一种基于深度学习的方法来加速拓扑优化设计过程,缩短了结构拓扑优化设计的迭代过程,并生成了高分辨率拓扑优化结构.利用深度学习方法,在低分辨率中间构型与高分辨率拓扑构型之间创建高维映射关系,利用独立、连续和映射(ICM)方法建立深度学习网络所需...     

传热结构的多目标拓扑优化设计研究

深入分析了传热结构多目标拓扑优化设计中的几个关键问题。提出了基于结构柔度最小化和结构散热弱度最小化的多目标拓扑优化设计方法,建立了传热结构的多目标拓扑优化设计模型,推导了传热结构多目标拓扑优化中用于迭代分析求解的优化准则算法和敏度分析方程。通过数值计算验证了理论和算法的有效性。     

模具冷却通道截面拓扑优化设计

本文提出一种模具冷却通道截面设计的拓扑优化方法。根据直通道的特性建立等效的温度场模型,用均匀流体速度场代替湍流流速场,构建对流换热方程,并用第三类边界条件对流道入口温度边界进行描述。建立考虑热应力的热-力耦合模型,对模具结构的热机械性能进行描述。通过引入离散体过滤法得到含圆形通道的截面拓扑,并加入几何约束解决离散体法导致的相混问题。分别以模具表面的平均温度和位移均匀性为优化目标及约束条件,构建拓扑优化列式。通过平顶模具与U型模具设计实例,验证了本文方法的可行性。设计结果表明,本文方法能够得到清晰的拓扑结构,而且优化结果满足给定的管径、管间距及管到模面距离等尺寸约束。     

Flow and Heat Transfer in a High-Aspect-Ratio Rib-Roughed Cooling Channel with Longitudinal Intersecting Ribs

This paper describes a detailed numerical investigation of a stationary high-aspect-ratio rib-roughed rectangular cooling channel with longitudinal intersecting ribs near the gas turbine blade trailing edge region. In order to overcome the heat transfer performance degeneration in the highaspect- ratio channel, longitudinal intersecting ribs are arranged on the channel bottom surface. The effect of the number of longitudinal intersecting ribs on the flow and heat transfer is systematically studied in the Reynolds number range Re = 10 000–30 000. The results show that a heat transfer augmentation region exists just downstream the junction between the longitudinal rib and the angled rib due to additional secondary flows. With more longitudinal intersecting ribs, the heat transfer distributions on the channel surfaces are more uniform. Though the pressure loss is also enlarged with an increase in the number of longitudinal intersecting ribs, the overall thermal efficiency increases in the entire range of Reynolds numbers investigated. The configuration with two sets of longitudinal intersecting ribs shows the best overall thermal efficiency.     

Periodic oscillations in a horizontal single boiling channel with thermal wall capacity

The dynamic behavior of a horizontal boiling channel with a surge tank is investigated through nonlinear analysis. The model involves a surge tank that is subject to inlet mass flow rate and a constitutive model containing a cubic nonlinearity is used to describe the outlet pressure-flow rate relation of the downstream boiling regime. The model also includes boiling heat transfer process and incorporates the effect of the wall thermal capacity which allows the temperature and heat transfer coefficient of the heater wall to vary with time. Within certain operating regimes, the model exhibits self-excited periodic oscillations, which can be identified with pressure-drop oscillations. In this study, these oscillations are described as relaxation oscillation and the qualitative features of the response can be understood in terms of the underlying model. Finally, the present model is compared with the experimental data available in literature to investigate that transient effects of temperature heater walls, pressure, and mass flow rate.     

Topology optimization and heat dissipation performance analysis of a micro-channel heat sink

Junction temperature in the electronic packaging process is one of the critical factors affecting the service life of electronic devices. A micro-channel heat sink is a common heat dissipating device used to reduce the thermal resistance between components and substrate. In order to maximize the heat dissipation while minimizing the pressure drop, this paper adopts a topology optimization method. A material interpolation method based on variable density principle is used together with a moving asymptote algorithm for the optimization. The physics is governed by the heat and mass transfer, coupled with the momentum conservation in the fluid. Four parameters are varied in order to investigate their influence on the optimization process. A three-dimensional geometry has been constructed to study the flow field and the results are compared to a reference case to verify the temperature uniformity and thermal performance of the model. It is demonstrated that the optimized design of the micro-channel heat sink is reliable and effective.     

AN ANALYTICAL DESIGN METHODOLOGY FOR AN ANNULAR COMBUSTOR

SUMMARY

This paper describes a computational procedure for the optimization of the performance parameters of a simulated annular combustor. This method has been applied to analyze the influence of the performance parameters and geometries on the annular combustor characteristics and provide a good understanding of combustor internal flow fields, and therefore it can be used for guiding the combustor design process. The approach is based on the solution of governing nonlinear, elliptic partial differential equations for 3-D axisymmetric recirculating turbulent reacting swirling flows and the modelling of turbulence, combustion, thermal radiation and pollutant formation. The turbulence effects are introduced via the modified two-equation κ-ε model. Turbulent combustion is modelled using the κ-ε-g model and a two-step turbulent combustion model is employed for the excess emission of carbon monoxide CO. For the evaluation of the NO pollutant formation rate, the NO pollutant formation model, which takes into account the influence of turbulence, presented here. The radiative heat transfer is handled by the heat flux model. The predictions of the combustor character-istics and performance parameters are made using the present approach.

Predictions of velocity, length of the recirculation zone, combustion efficiency and wall temperature are compared with measurements. Agreement between the predictions and experimental data is very satisfactory.     

Transformational-zone method of calculation of complex heat exchange during flow of optically active medium inside tube of diffuse grey surface

The paper presents analytical and experimental investigations of influence of radiative heat transfer on complex heat exchange during flow of optically active gas inside a pipe of diffusegrey properties. It was assumed that the pipe is heated from the outside by a constant heat flux and gas flowing inside is both absorbing and emitting and of small optical density. The influence of length and radiative properties of the pipe surface and of the gas temperature distribution on the wall and in the gas were analysed. The influence of radiative energy transfer on overall heat transfer coefficient was estimated. Mathematical model of radiative convective heat exchange in a system of one-dimensional temperature field, based on zone division method of Hottel and surface transformation, was verified numerically and experimentally. The results of numerical calculations were compared with experimental results obtained during carbone dioxide (CO₂) flow inside electrically heated ceramic tube. The set of nonlinear differential equations was solved by Runge-Kutta method with Hamming modification and with the use of separable-kernel method.     

Turbulent forced convective heat transfer in two-phase evaporating droplet flow through a vertical pipe

A physical model was developed to study heat transfer in turbulent dispersed flow at very high vapor quality in a vertical pipe by numerically solving the coupling governing differential equations for both phases. Major heat transfer mechanisms included in the model were the thermal nonequilibrium effects, droplet vaporization, droplet deposition on the duct wall and thermal radiative transfer. The predicted results indicated that vapor superheating is dominant for the cases with high wall superheat, otherwise droplet vaporization dominates the energy transport processes. Heat transfer during the droplet-wall interaction only exists at low wall superheat but in small amounts.     

Chemically reactive and radiative von Kármán swirling flow due to a rotating disk

A new mathematical model is presented to study the heat and mass transfer characteristics of magnetohydrodynamic (MHD) Maxwell fluid flow over a convectively heated stretchable rotating disk. To regulate the fluid temperature at the surface, a simple isothermal model of homogeneous-heterogeneous reactions is employed. The impact of nonlinear thermal radiative heat flux on thermal transport features is studied. The transformed nonlinear system of ordinary differential equations is solved numerically with an efficient method, namely, the Runge-Kutta-Felberg fourth-order and fifth-order (RKF45) integration scheme using the MAPLE software. Achieved results are validated with previous studies in an excellent way. Major outcomes reveal that the magnetic flux reduces the velocity components in the radial, angular, and axial directions, and enhances the fluid temperature. Also, the presence of radiative heat flux is to raise the temperature of fluid. Further, the strength of homogeneous–heterogeneous reactions is useful to diminish the concentration of reaction.