Evaluation of Two Momentum Control Variable Schemes and Their Impact on the Variational Assimilation of Radar Wind Data:Case Study of a Squall Line

Different choices of control variables in variational assimilation can bring about different influences on the analyzed atmospheric state. Based on the WRF model＇s three-dimensional variational assimilation system, this study compares the be- havior of two momentum control variable options-streamfunction velocity potential （ψ-χ） and horizontal wind components （U-V）-in radar wind data assimilation for a squall line case that occurred in Jiangsu Province on 24 August 2014. The wind increment from the single observation test shows that the ψ-χ control variable scheme produces negative increments in the neighborhood around the observation point because streamfunction and velocity potential preserve integrals of velocity. On the contrary, the U-V control variable scheme objectively reflects the information of the observation itself. Furthermore, radial velocity data from 17 Doppler radars in eastern China are assimilated. As compared to the impact of conventional observation, the assimilation of radar radial velocity based on the U-V control variable scheme significantly improves the mesoscale dynamic field in the initial condition. The enhanced low-level jet stream, water vapor convergence and low-level wind shear result in better squall line forecasting. However, the ψ-χ control variable scheme generates a discontinuous wind field and unrealistic convergence/divergence in the analyzed field, which lead to a degraded precipitation forecast.

Bias Momentum Attitude Control System Using Energy/Momentum Wheels

The integrated power and attitude control for a bias momentum attitudecontrol system is investigated. A pair of counter-spinning wheels is used to provide the biasangular momentum and store/ discharge energy for power requirement of the devices on the spacecraft.The roll/yaw motion is controlled by pitch magnetic dipole moment. The torque-based control law ofthe wheels is designed, so that the desired pitch control torque is provided and the operation ofcharging/discharging energy is carried out based on the given power. System singularity in thecontrol law of wheels is fully avoided by keeping the wheels counter-spinning. A power managementscheme using kinetic energy feedback is proposed to keep energy balance, which can avoid wheelsaturation caused by superfluous energy. The minimum moment of inertia of the wheels is limited bythe maximum bias angular momentum and the minimum energy, such constrains are analyzed incombination with the geometrical method. Numerical simulation results are presented to demonstratethe effectiveness of the control scheme.

一种适应卫星姿态侧摆机动的混合轮系控制方法

针对高稳定度轮控大型卫星因动量轮力矩小而难以满足侧摆成像任务需求问题,开展了混合轮系配置方案及控制方法研究。首先,提出常规轮系配置卫星滚动轴方向串联大力矩飞轮的混合配置方案,并设计飞轮开环前馈与常规动量轮闭环反馈相结合的控制策略;其次,设计以容许角动量最大量为权重的飞轮组前馈力矩分配律和具有角动量反馈的飞轮力矩跟踪控制方法,实现飞轮力矩合理分配及其模型不确定性导致输出力矩偏差抑制;然后,设计估计器对星体内外扰动力矩进行估计与补偿,以确保卫星高稳定度性能实现;最后,给出在轨应用情况,验证所提出方案及方法的有效性。在轨应用表明,采用该控制方法,有效缩短了整星侧摆稳定时间达100 s以上,且非机动期间姿态稳定度优于3.75×10-5(°)/s。

无陀螺偏置动量微纳卫星的姿态控制方案研究

针对低成本微纳卫星的姿态控制问题进行了研究,提出了一种无陀螺条件下的偏置动量姿态控制方案,控制部件仅包含磁强计、磁力矩器和一个动量轮,配置精简.使用磁强计实现了卫星姿态确定,通过磁力矩器与动量轮的组合控制实现了三轴稳定的对地定向姿态控制,并具备了由任意初始姿态条件恢复至三轴稳定对地定向姿态的能力.仿真结果表明:姿态确定精度优于2°,姿态控制精度优于3°,姿态稳定度优于0003(°)/s.

Numerical Investigation of Flow Separation Control over an NACA0018 Airfoil Using Sweeping Jet Actuator

As an active flow control technology and with the advantages of no moving components, the Sweeping jet actuator has become a hotspot in the field of flow control. However, the linear relationship between oscillation frequency and momentum coefficient in a sweeping jet actuator makes it difficult to determine the dominant factors that affect control effectiveness. Decoupling the oscillation frequency and momentum coefficient, as well as determining the control mechanism, is the focus of studying the sweeping jet actuator. In this study, a novel sweeping jet actuator is designed using synthetic jets instead of feedback channels and applied to the flow separation control of NACA0018 airfoil. This article studies the control effect under three oscillation frequencies of F+ = f × c/U∞ = 1, 10, 100 and three momentum coefficients of Cμ = 0.45%, 0.625%, 0.9%. The numerical results indicate that all three oscillation frequencies have good control effects on flow separation, and the control effect is best when F+ = 1, with the maximum lift coefficient increasing by approximately 14% compared to the other two cases. And the sweeping jet actuator has a better ability to control flow separation as the momentum coefficient increases. By decoupling the characteristics of the sweeping jet actuator and conducting numerical analysis of the flow control effect, it will promote its better engineering application in the field of flow control. .

高轨卫星角动量管理的太阳电池阵转角控制

为了延长高轨卫星的角动量卸载周期,提出一种用于高轨卫星角动量管理的太阳电池阵转角控制方法。首先,构建出太阳电池阵转角控制作用模型,并将用于卫星角动量管理的太阳电池阵转角控制转化为约束优化问题。然后,从工程实用的角度出发,根据常用的两翼太阳电池阵对称布局的特点,简化用于角动量管理的太阳电池阵转角控制问题,提出简单实用的太阳电池阵转角控制律。最后,通过数值仿真和某遥感卫星的在轨环境干扰数据对所提方法进行验证。结果表明,所提方法可以显著降低卫星角动量的积累,延长角动量卸载周期。

基于超表面的涡旋波束控制技术研究综述

轨道角动量(Orbital Angular Momentum,OAM)复用技术因OAM模式间的正交性和模式的无限性,能极大程度地提升信道容量与频谱效率,对解决当前无线通信频谱拥挤问题具有重大潜力。然而,OAM波束的衍射特性和发散角问题严重限制了通信质量。对OAM通信的技术的难点进行了介绍,并对比分析了现有OAM波束控制天线的优势与不足,其中超表面天线因其结构简单、成本低和优异的电磁调控能力,在OAM波束控制中具有独特优势。其次重点梳理了基于超表面实现OAM波束控制的不同实现方式以及发展现状,最后综述了未来发展方向,为OAM波束控制相关技术的发展和未来大容量通信的实现提供了一定指导。

一种机械臂驱动电推力器的角动量卸载方法

为利用电推力器实现地球静止轨道卫星的飞轮角动量卸载和位置保持,提出了一种利用机械臂动态调整电推力器位置以及推力方向的方案,并给出了机械臂指令关节角的求解方法。首先设计了基于三自由度机械臂和单电推进器的构型方案,之后利用机械臂运动学关系建立了电推力器的推力模型以及相对系统质心的力矩模型。以飞轮角动量卸载效率为最优指标,以机械臂各关节转角范围和电推力器推力方向角的限制为约束条件,建立了系统的优化问题模型,并通过粒子群算法对该优化问题进行求解,得到机械臂指令关节角。位置保持的功能通过推力方向角的约束实现。基于地球静止轨道卫星的三轴对地姿态稳定控制数值仿真结果表明,所提出的方案和算法可有效对飞轮组三轴角动量进行卸载,且优化结果满足给定的约束条件。

液压支架大流量换向阀稳态液动力计算与补偿方法

针对液压支架换向阀元件复杂结构形成不规则流道,传统一次动量定理不能精确求得阀芯所受液动力,以及因液动力过大或不稳定使换向阀动静态特性降低的问题,以支架换向阀主阀为研究对象,在分析其结构组成与工作原理基础上,提出一种全流域控制体积划分方式。运用多次动量定理,分别分析了每个控制体积内动量变化量,考虑阀芯上下游元件结构参数对阀芯液动力数值的影响,较为精确的推导出阀芯所受稳态液动力公式,并进行理论计算。通过分析公式,得出对阀内元件结构参数进行优化的方法来补偿稳态液动力并用CFD方法模拟了稳态液动力随阀芯开度变化规律。结果表明:结构参数优化后阀芯所受液动力峰值与变化幅度均较原结构低,将阀套内径结构优化后,液动力峰值与变化幅度较原结构降低了56.25%与48.12%;将回液阀芯顶杆直径优化后,液动力峰值与变化幅度较原结构降低了28.79%与32.71%;将回液阀芯端面倾角优化后,液动力峰值与变化幅度较原结构降低了31.87%与37.16%,有效缓解了支架换向阀阀芯所受稳态液动力使阀动静态性能降低的问题。

公转和自转协同下绕包机转速自动控制研究

绕包机公转和自转过程中可能会产生非线性影响,为了实现转速有效控制,该文提出一种公转和自转协同下绕包机转速自动控制方法。构建神经网络控制模型,将公转速度和自转速度作为输入,通过输出层输出控制规律;利用反向传播算法,通过调节网络权值和引入动量权值对神经网络模型进行改进,以此提升公转和自转协同控制效果;利用双馈定向矢量方法实施绕包机转速自动控制,在满足绕包机定子和转子对应电压矢量和磁链矢量条件的基础上,完成最终的转速自动控制。在不同实验条件下,所提方法对输入信号的实际跟踪效果较好,且不易受影响因素干扰。

基于梯度下降算法和动量因子的醇基燃料锅炉燃烧温度非线性控制方法

醇基燃料锅炉燃烧温度与控制参数之间的关系不是简单的线性关系,增加了控制的难度,提出基于梯度下降算法和动量因子的醇基燃料锅炉燃烧温度非线性控制方法。建立醇基燃料锅炉的气流三维流动方程,确定燃烧速率、实际温度与期望温度之间的差值以及差值变化率等温度非线性控制参数。搭建燃烧温度控制的模糊神经PID控制器,采用梯度下降算法和动量因子对PID神经网络的权值展开训练,将所得温度非线性控制参数输入训练后的模糊神经PID控制器,实现醇基燃料锅炉燃烧温度非线性控制。实验结果表明,所提方法对于燃烧速率、实际温度与期望温度之间的差值以及差值变化率计算结果精准,温度控制精度高,温度变化率低,燃料能源利用率高,实际应用效果好。

Design of a Three-Dimensional Centrifugal Fan with Controlled Blade Loading Approach

The high flow-rate centrifugal fan needs a three-dimensional impeller to achieve a high efficiency. In this paper, the design procedure of a high-efficiency three-dimensional centrifugal fan is presented. First, the main dimensions of the fan were calculated by using the conventional one-dimensional method. Then, the blade loading or the angular momentum distribution along the meridional streamline on the blade surfaces is prescribed. After that, the three-dimensional blade is determined by using the streamline curvature method. With the aid of numerical simulations, the performance of the three-dimensional fan was improved and some of the key influence factors were investigated. The analyses indicate that, as to the high flow-rate centrifugal fan, the Stanitz modified formula is recommended to calculate the separation radius, rb. A proper increase in the separation radius is beneficial for the fan’s performance. It is also indicated that a decrease in the angular momentum on the hub leads to an increase in total pressure efficiency, under the condition of a given constant mean angular momentum at the outlet of the blade. In addition, the installation of a fairing on the hub plate can improve the fan’s efficiency evidently when the streamline curvature method is adopted to design the three-dimensional impeller.

基于控制力矩陀螺的航天器功率最优姿态控制

本文研究基于控制力矩陀螺利用零子空间的航天器姿态控制功率优化问题.航天器采用4个为一组的控制力矩陀螺(CMG)作为姿态控制执行机构.对于N-CMG(N≥4)组而言,如非进入奇异构型,控制的解空间存在一维自由度的零运动.利用该自由度,根据设定的功率函数,可通过局部优化算法在零运动空间求解功率最优解.将该功率最优化算法分别应用于姿态跟踪任务与姿态稳定任务,仿真结果表明,这种功率最优算法对姿态稳定任务具有更好的功率优化效果.

电推进在航天器姿态控制中的研究综述

本文首先对电推进技术进行了简要的介绍,根据目前已有的电推进姿态控制应用,分析了适用于航天器姿态控制的不同类型的电推力器特性,之后分别对电推力器在姿态控制中的在轨应用现状和研究现状进行了综述和分析。在研究现状综述中,针对航天器姿态控制、姿轨联合控制和角动量卸载三个任务类型,分析总结了电推力器在布局、控制策略和算法等方面的研究成果和结论。最后,针对未来电推进技术在航天器姿态控制应用所面临的挑战,提出了相应的发展建议。

Dynamics and nonlinear control of space electromagnetic docking

Space electromagnetic docking technology, free of propellant and plume contamination, offers continuous, reversible and synchronous controllability, which is widely applied in the future routine on-orbit servicing missions. Due to the inherent nonlinearities, couplings and uncertainties of an electromagnetic force model, the dynamics and control problems of them are difficult. A new modeling approach for relative motion dynamics with intersatellite force is proposed. To resolve these control problems better, a novel nonlinear control method for soft space electro-magnetic docking is proposed, which combines merits of artificial potential function method, Lyapunov theory and extended state observer. In addition, the angular momentum management problem of space electromagnetic docking and approaches of handling it by exploiting the Earth＇s magnetic torque are investigated. Finally, nonlinear simulation results demonstrate the feasibility of the dynamic model and the novel nonlinear control method.

Neural Network Based Diagnostics of Actuator for an Attitude Control System

The objective of this paper is to develop a neural network-based residual generator to detect the fault in the actuators for a specific communication satellite in its attitude control system （ACS）. First, a dynamic multilayer perceptron network with dynamic neurons is used, these neurons correspond to a second order linear Infinite Impulse Response （IIR） filter and a nonlinear activation function with adjustable parameters. Second, the parameters from the network are adjusted to minimize a performance index specified by the output estimated error, with the given input-output data collected from the specific ACS. Then, the proposed dynamic neural network is trained and applied for detecting the faults injected to the wheel, which is the main actuator in the normal mode for the communication satellite. Then the performance and capabilities of the proposed network were tested and compared with a conventional model-based observer residual, showing the differences between these two methods, and indicating the benefit of the proposed algorithm to know the real status of the momentum wheel. Finally, the application of the methods in a satellite ground station is discussed.

Geometric Analysis of Singularity for Single-Gimbal Control Moment Gyro Systems

This research is focused on the singularity analysis for single-gimbal control moment gyros systems （SCMGs） which include two types, with constant speed （CSCMG） or variable speed （VSCMG） rotors. Through angular momentum hypersurfaces of singular states, the passable and impassable singular points are discriminated easily, meanwhile the information about how much the angular momentum workspace as well as the steering capability available is provided directly. It is obvious that the null motions of steering laws are more effective for the five pyramid configuration（FPC） than for the pyramid configuration（PC） from the singular plots. The possible degenerate hyperbolic singular points of the preceding configurations are calculated and the distinctness of them is denoted by the Gaussian curvature. Furthermore, failure problems to steer integrated power and attitude control system （IPACS） are also analyzed. A sufficient condition of choosing configurations of VSCMGs to guarantee the IPACS steering is given. The angular momentum envelops of VSCMGs, in a given energy and a limited range of rotor speeds, are plotted. The connection and distinctness between CSCMGs and VSCMGs are obtained from the point of view of envelops.

Optimum Duty Cycle of Unsteady Plasma Aerodynamic Actuation for NACA0015 Airfoil Stall Separation Control

Unsteady dielectric barrier discharge（DBD） plasma aerodynamic actuation technology is employed to suppress airfoil stall separation and the technical parameters are explored with wind tunnel experiments on an NACA0015 airfoil by measuring the surface pressure distribution of the airfoil.The performance of the DBD aerodynamic actuation for airfoil stall separation suppression is evaluated under DBD voltages from 2000 V to 4000 V and the duty cycles varied in the range of 0.1 to 1.0.It is found that higher lift coefficients and lower threshold voltages are achieved under the unsteady DBD aerodynamic actuation with the duty cycles less than 0.5as compared to that of the steady plasma actuation at the same free-stream speeds and attack angles,indicating a better flow control performance.By comparing the lift coefficients and the threshold voltages,an optimum duty cycle is determined as 0.25 by which the maximum lift coefficient and the minimum threshold voltage are obtained at the same free-stream speed and attack angle.The non-uniform DBD discharge with stronger discharge in the positive half cycle due to electrons deposition on the dielectric slabs and the suppression of opposite momentum transfer due to the intermittent discharge with cutoff of the negative half cycle are responsible for the observed optimum duty cycle.

基于LQR的动量轮单摆起摆及平衡控制仿真研究

单摆作为一个简单非线性系统常被高校师生用于非线性控制理论的教学和研究。根据角动量守恒定律,在摆杆末端添加一个由电机驱动的飞轮组成带动量轮的欠驱动单摆系统,通过驱动动量轮转动,间接实现单摆的平衡和起摆控制。应用拉格朗日方程建立系统的动力学模型,在竖直向上平衡位置线性化,得到系统的状态空间方程,使用MATLAB编写线性二次型调节器(LQR)控制程序,进行初始偏离竖直向上位置的平衡控制仿真,采用Simulink和ADAMS联合仿真的方法进行摆杆的起摆及平衡控制的虚拟样机仿真实验。仿真结果表明,基于LQR控制动量轮转动的控制方法对于摆杆的平衡稳定性和起摆有较好的控制效果,这可为类似的系统提供一个基于动量轮的间接控制方法。

基于模糊PID控制的空间吊装物姿态控制

针对在装配式房屋建造过程中,房屋构件及其姿态只能依靠人力才能够准确地调整到目标位置,不仅工作效率低且容易造成人员伤亡的问题。对空间吊装物姿态位置控制进行了研究。将角动量交换原理运用到空间吊装物姿态控制上,通过改变飞轮速度与加速度达到控制空间吊装物绕吊装线水平旋转角度姿态的目的。介绍了飞轮动力系统,推导了整个实验装置的动力学方程和运动学方程。考虑到被控对象吊装物负载经常改变,设计了模糊PID(proportional integral derivative)控制器,使控制效果达到最佳。首先对控制算法进行了Simulink仿真研究,然后在搭建的实验装置上进行了实验。实验结果表明,能够实现空间吊装物姿态位置控制,且模糊PID控制更适合于实际控制。