Optimizing accuracy of a parabolic cylindrical deployable antenna mechanism based on stiffness analysis

Accuracy of the fitted surface is of great importance to the performance of deployable antennas utilized in space. This paper proposes a stiffness analysis based fitting accuracy optimization method for achieving the optimal parameters of the parabolic cylindrical deployable antenna mechanism. The stiffness matrix of the proposed cylindrical antenna mechanism is established by assembling the stiffness of beams and tension cables. Structural deformations of the mechanism are calculated where the tensioned cable is substituted by a 2-node truss element and an equivalent force acting on the joint. Consideration of the tensity of tension cables, namely tensioned or slack, is transformed into a typical linear complementarity problem. Comparison between structural deformations of the mechanism fixed at different points is performed. Sensitivities of the geometric and structural parameters on fitting accuracy are investigated. Influence of force of the driven cable on structural deformations of antenna operated in different orbits is conducted. A fitting optimization method is proposed to minimize the structural deformations subject to constraints on volume and mass. Simulation result shows that the fitting accuracy of the antenna mechanism is improved significantly through the optimization. The proposed method can be utilized for the optimal design of other deployable mechanisms constructed by joining rigid links.     

舰载直升机系留座的布置优化

本文根据舰载直升机系留索的受力特点,推导出系留索的张力计算表达式,利用遗传算法对系留点的位置进行优化,得到了各海况下系留点的优化布局形式和系留索的张力值,最后对得到的结果进行综合分析比较,确定了最佳的系留座布局形式。     

基于刚度优化的绳牵引并联支撑系统力/位混合控制

针对应用于风洞试验的八绳牵引并联支撑系统高性能运动控制问题,开展绳索张力实时优化与力/位混合控制技术研究。基于动态试验需求和系统刚度矩阵,选择主刚度加权和最大为目标函数,将其转化为线性规划问题,采用二维凸多边形张力可行域顶点法进行实时求解,并根据绳索张力变化约束进一步提出连续可行域,确保解的连续性,实现其优化分布;设计一种基于电机转角和绳索张力反馈的力/位混合控制策略,其中位姿控制环采用计算力矩法,并利用实际绳索张力补偿惯性力和非线性力等,进而开展稳定性分析。以风洞试验中典型的推力模拟、俯仰振荡等线位移和角运动轨迹为例,在原理样机上开展控制验证实验。研究结果表明该控制策略能够实现对末端飞行器模型位姿和绳索张力的有效跟踪,且具有较高的精度和良好的稳定性,可以为绳牵引并联支撑在风洞动态试验中的应用提供技术支持。     

全模颤振风洞试验三索悬挂系统多体动力学分析

全模颤振风洞试验需要通过软支撑系统模拟飞行器的自由飞行状态并调整模型姿态达到配平状态。参考NASA双索悬挂方案,提出了一种两电机驱动的三索悬挂系统,利用后方两索的同向/反向联动实现模型俯仰和滚转姿态的调整,利用弹簧刚度以及钢绳张力设计实现支撑频率要求。基于柔性多体动力学方法,建立了包括飞行器刚体模型、柔性索、滑轮、弹簧、气动力模型、伺服电机控制在内的复杂系统动力学模型,其中,利用任意拉格朗日-欧拉（ALE）变长度索单元描述钢绳,利用不约束物质坐标的索结点约束描述钢绳与滑轮相互作用,利用索结点物质输运速度约束描述伺服电机绞盘,利用飞行力学的气动力模型描述吹风下的气动力。基于该模型,通过小扰动响应辨识研究了弹簧刚度、钢绳张力、连接点位置等因素对支撑频率的影响规律,并分析了系统姿态调整能力,俯仰调整范围达到-12.5°~12.5°,滚转调整范围达到-45°~45°。采用滑轮处电位计测量的钢绳相对位移作为反馈信号,基于设计的控制律利用多体动力学求解器与Simulink对风洞吹风下的姿态调整过程进行仿真,模型达到配平状态,获得了吹风下的索拉力和伺服电机功率,为系统设计提供基础。     

Surrogate role of machine learning in motor-drive optimization for more-electric aircraft applications

Motor drives form an essential part of the electric compressors, pumps, braking and actuation systems in the More-Electric Aircraft (MEA). In this paper, the application of Machine Learning (ML) in motor-drive design and optimization process is investigated. The general idea of using ML is to train surrogate models for the optimization. This training process is based on sample data collected from detailed simulation or experiment of motor drives. However, the Surrogate Role (SR) of ML may vary for different applications. This paper first introduces the principles of ML and then proposes two SRs (direct mapping approach and correction approach) of the ML in a motor-drive optimization process. Two different cases are given for the method comparison and validation of ML SRs. The first case is using the sample data from experiments to train the ML surrogate models. For the second case, the joint-simulation data is utilized for a multi-objective motor-drive optimization problem. It is found that both surrogate roles of ML can provide a good mapping model for the cases and in the second case, three feasible design schemes of ML are proposed and validated for the two SRs. Regarding the time consumption in optimizaiton, the proposed ML models can give one motor-drive design point up to 0.044 s while it takes more than 1.5 mins for the used simulation-based models.     

Dynamics,stability, and control of a four-cable mount system for wind tunnel test

A four-cable mount system is proposed for full-model wind tunnel flutter tests, which may adjust the pitch and roll attitude of the aircraft scaled model and ensure that the model is not subjected to cable tension. The system provides sufficient support to simulate the free flight of the aircraft by applying appropriate spring stiffness and cable tensions. The proposed four-cable mount system is modeled based on Lagrange mechanics, and its dynamics equations consider aerodynamic effects. The singularity of the system and its bifurcation characteristics under flow conditions are analysed to determine the supercritical bifurcation phenomenon for different tension levels and distances from the front suspension point to the mass centre of the model. The mathematical expressions of the longitudinal flight stability of the cable mount system are derived by linearising the system dynamics equations using small perturbations. The influence of the cable tension, spring stiffness, suspension point position, and other factors on the flight stability of the aircraft are analysed. A feedforward control algorithm is proposed to minimize the total elastic potential energy of the system. The results show that the model is in the level flight state when the elastic potential energy of the four-cable mount system is minimized. A feedback control design method is proposed based on the Lyapunov stability theory to derive the closed-loop stability conditions. The system dynamics model that includes the aircraft rigid body model, flexible cables, pulleys, springs, aerodynamic model, and servo motor control is established using the flexible multibody dynamics method. A multibody dynamics solver and Simulink are used to simulate the attitude adjustment of the model in the wind tunnel and verify the supercritical bifurcation characteristics of the system and the effectiveness of the feedback and feedforward control.     

基于CST软件仿真的线束隔离研究

在民用飞机电气线路互联系统(EWIS)设计中,通过物理隔离防止电弧和电磁干扰(EMI)是适航审定的重要内容。以隔离距离为研究对象,基于电磁仿真软件CST,构建多种模型,对不同类型线缆间、不同电信号线路进行了仿真,证明了物理隔离不但是防止电弧产生的有效方式,而且能够极大地降低电磁干扰,同时使用屏蔽线缆和多芯扭绞等防护方法,也是降低电磁干扰的有效措施。     

航空拖曳诱饵系统的动态特性研究简

 为准确预测航空拖曳诱饵系统能否干扰成功,建立了系统的物理数学模型并对其动态特性进行了仿真研究。应用集中质量法,将柔性拖曳缆绳离散为一系列由阻尼弹簧连接的节点,建立了缆绳的动态模型;对诱饵进行受力分析,建立了诱饵的六自由度模型;提出了缆绳与诱饵的耦合条件,使模型更加精确。分别对诱饵释放过程中,以及释放完成后载机机动时系统的动态特性进行了仿真研究,给出并分析了缆绳的形状、张力和诱饵的姿态角等参数的变化规律。结果表明：为避免出现“鱼钩”现象,应尽可能减小释放诱饵的初速度与载机空速的夹角;应按梯形速度释放诱饵,以使缆绳中拉力的最大值较小。释放完成后,应控制载机最大飞行速度,以避免缆绳进入载机的高温尾喷流区;载机作盘旋时,缆绳在载机的圆形轨迹之外,且载机飞行速率一定时,角速度越大,缆绳向外趋势越大,越有利于避开载机的尾喷流区。     

航空拖曳诱饵系统的动态特性研究

为准确预测航空拖曳诱饵系统能否干扰成功,建立了系统的物理数学模型并对其动态特性进行了仿真研究。应用集中质量法,将柔性拖曳缆绳离散为一系列由阻尼弹簧连接的节点,建立了缆绳的动态模型;对诱饵进行受力分析,建立了诱饵的六自由度模型;提出了缆绳与诱饵的耦合条件,使模型更加精确。分别对诱饵释放过程中,以及释放完成后载机机动时系统的动态特性进行了仿真研究,给出并分析了缆绳的形状、张力和诱饵的姿态角等参数的变化规律。结果表明：为避免出现“鱼钩”现象,应尽可能减小释放诱饵的初速度与载机空速的夹角;应按梯形速度释放诱饵,以使缆绳中拉力的最大值较小。释放完成后,应控制载机最大飞行速度,以避免缆绳进入载机的高温尾喷流区;载机作盘旋时,缆绳在载机的圆形轨迹之外,且载机飞行速率一定时,角速度越大,缆绳向外趋势越大,越有利于避开载机的尾喷流区。     

系留气球系统三拉索收放状态建模与仿真

系留气球是一种依靠气囊内的浮升气体获得浮力,并用缆索拴系固定的浮空器。系留气球、三根机械拉索、地面转动梁等构成系留气球三拉索收放系统,综合考虑收放系统中三拉索的运动特性,采用Matlab/Sim-ulink工具对近地三拉索收放运动进行系统建模,建立了整体的三拉索收放运动状态的仿真模型,仿真结果表明：仿真计算结果与实际飞...     

Form-finding methods for deployable mesh reflector antennas

Deployable high-frequency mesh reflector antennas for future communications and obser- vations are required to obtain high gain and high directivity. In order to support these new missions, reflectors with high surface accuracy are widely required. The form-finding analysis of deployable mesh reflector antennas becomes more vital which aims to determine the initial surface profile formed by the equilibrium prestress distribution in cables to satisfy the surface accuracy requirement. In this paper, two form-finding methods for mesh reflector antennas, both of which include two steps, are pro- posed. The first step is to investigate the prestress design only for the cable net structure as the circum- ferential nodes connected to the supporting truss are assumed fixed. The second step is to optimize the prestress distribution of the boundary cables connected directly to the supporting truss considering the elastic deformation of the antenna structure. Some numerical examples are carried out and the simulation results demonstrate the proposed form-finding methods can warrant the deformed antenna reflector surface matches the one by design and the cable tension forces fall in a specified range.     

A modified forward and backward reaching inverse kinematics based incremental control for space manipulators

Forward and backward reaching inverse kinematics(FABRIK) is an efficient two-stage iterative solver for inverse kinematics of spherical-joint manipulator without the calculation of Jacobian matrix. Based on FABRIK, this paper presents an incremental control scheme for a free-floating space manipulator consists of revolute joints and rigid links with the consideration of joint constraints and dynamic coupling effect. Due to the characteristics of FABRIK, it can induce large angular movements on s...     

Design and analysis of a novel hinged boom based on cable drive

Hinged booms are widely used in astrophysics missions; however, the trajectory and deployment velocity are difficult to control because they are usually driven by springs, which limits their application in narrow spaces. Thus, a novel hinged boom is highly required to achieve motion controllability. Through an equivalent substitution between the cable drive loop and the binary link in topology, a type synthesis method for the cable-driven single-degree-of-freedom chain is proposed based on the s...     

Stifness modeling and analysis of a novel 4-DOF PKM for manufacturing large components

Faster response to orientation varying is one of the outstanding abilities of a parallel kinematic machine（PKM）.It enables such a system to act as a reconfgurable module employed to machine large components effciently.The stiffness formulation and analysis are the beforehand key tasks for its parameters design.A novel PKM with four degrees of freedom（DOFs）is proposed in this paper.The topology behind it is 2PUS-2PRS parallel mechanism.Its semianalytical stiffness model is frstly obtained,where the generalized Jacobian matrix of 2PUS-2PRS is formulated with the help of the screw theory and the stiffness coeffcients of complicated components are estimated by integrating fnite element analysis and numerical ftting.Under the help of the model,it is predicted that the property of system stiffness distributes within the given workspace,which features symmetry about a certain plane and is also verifed by performing fnite element analysis of the virtual prototype.Furthermore,key parameters affecting the system stiffness are identifed through sensitivity analysis.These provide insights for further optimization design of this PKM.     

失谐叶栅的受迫振动响应特性分析

采用基于计算流体力学(CFD)方法的降阶气动力模型并耦合结构运动方程,实现了存在外激励载荷时失谐叶栅受迫振动响应的快速分析。针对典型的跨声速叶栅,通过求解其位移响应幅值较系统地研究了失谐方式、失谐强度和叶片质量比对失谐叶栅受迫振动响应幅值的影响。研究表明文中刚度失谐形式可以改善叶栅振动的稳定性,同时导致系统受迫振动响应局部化程度的增加,并且受迫响应的最大振幅放大因子随失谐强度增加或者质量比降低存在先增大后减小的一个峰值,不同失谐形式则对这个峰值的大小有着明显的影响。由于该方法可高效地分析失谐叶栅受迫振动各参数对模态局部化的影响,在工程上有一定的应用价值。     

An efficient aerodynamic shape optimization of blended wing body UAV using multi-fidelity models

This paper presents a novel optimization technique for an efficient multi-fidelity model building approach to reduce computational costs for handling aerodynamic shape optimization based on high-fidelity simulation models. The wing aerodynamic shape optimization problem is solved by dividing optimization into three steps—modeling 3D(high-fidelity) and 2D(lowfidelity) models, building global meta-models from prominent instead of all variables, and determining robust optimizing shape associated with tuning local meta-models. The adaptive robust design optimization aims to modify the shape optimization process. The sufficient infilling strategy—known as adaptive uniform infilling strategy—determines search space dimensions based on the last optimization results or initial point. Following this, 3D model simulations are used to tune local meta-models. Finally, the global optimization gradient-based method—Adaptive Filter Sequential Quadratic Programing(AFSQP) is utilized to search the neighborhood for a probable optimum point. The effectiveness of the proposed method is investigated by applying it, along with conventional optimization approach-based meta-models, to a Blended Wing Body(BWB) Unmanned Aerial Vehicle(UAV). The drag coefficient is defined as the objective function, which is subjected to minimum lift coefficient bounds and stability constraints. The simulation results indicate improvement in meta-model accuracy and reduction in computational time of the method introduced in this paper.     

透平级通流部分全设计变量多目标优化设计

采用优化设计方法优化某轴流透平级通流部分造型,利用基于非均匀有理B样条(NURBS)曲线技术的参数化造型方法提取包括叶片和端壁造型的全设计变量,选取级效率最大化和动叶根部最高温度最小化进行多目标优化设计.引入基于并行子空间的组合优化策略,缩短了优化设计周期.优化设计后的透平级效率提高了0.664%,动叶根部最高温度下降达透平级内温度变化范围的1.5%.该工作表明该优化设计方法在透平级设计上具有重大应用价值.      

基于小生境遗传算法和RANS方程的平面叶栅气动优化设计

发展了一种将小生境遗传算法与RANS方程数值求解相结合的平面叶栅全局优化设计方法.该方法针对遗传算法的搜索原理和平面叶栅的气动外形特点, 提出了与之相适应的Bezier曲线参数化表达, 构造了用于优化设计的适应度函数.优化设计变量是平面叶栅的参数化Bezier曲线特征多边形控制点坐标, 目标函数为极大化叶栅的升阻比, 约束条件综合考虑了叶栅的进出口几何安装角及叶片强度和性能等要求, 约束条件的处理采用松紧罚函数法.优化得到的叶栅升阻比比初始叶栅提高了8.3%.      

大展弦比机翼总体刚度的气动弹性优化设计

针对大展弦比机翼总体刚度设计问题,提出了梁架模型气动弹性优化和三维优化模型折算两种设计方法,并以大展弦比机翼为例对两种方法的合理性进行了验证.前者基于机翼梁架式模型,利用气动弹性优化方法对其主梁刚度进行设计,其特点是建模简单、计算效率较高,可以在设计信息较少的概念和初步设计阶段使用,但由于约束条件考虑较少,设计结果相对...     

基于全局敏度方程方法的飞机方案优化设计

针对飞机方案分析模块之间存在耦合关系,从而使方案分析需要迭代求解这一特点,采用全局敏度方程方法计算参数之间的敏度,以克服差分方法所带来的高费用和不精确问题。该方法本身具有递归和并行特点,使得其与数值优化方法结合起来特别适合于像飞机这类复杂的内部耦合系统的优化。给出了该方法与约束变尺度法结合,用于某假想的喷气教练机方案优化的简单算例以及用于某4座公务机方案优化的实例。