带有输入死区的航天器姿态有限时间控制

死区非线性是航天器姿态控制系统中一种普遍存在的执行机构非线性,它的存在会降低姿态控制系统的性能,甚至可能破坏系统的稳定性.为了解决带有输入死区非线性的航天器的高精度姿态控制问题,给出了一种有限时间控制方法,并且考虑航天器姿态控制模型中含有有界的不确定性且输入死区非线性仅部分信息已知.通过引入一个在指定时间内收敛到零的期望姿态变化曲线,并基于时变滑模控制理论设计鲁棒控制算法使得实际姿态和期望姿态之间的偏差始终保持足够小,从而保证实际姿态在指定的时间内收敛到原点附近.严格的理论分析表明,所设计控制律不仅可以保证闭环系统的信号有界而且可以使得实际姿态在指定的时间内收敛到并以指定的精度保持在原点附近.数值仿真结果表明,所提控制方法是有效的,该方法不仅能够保证系统状态具有很快的收敛速度、很高的控制精度,而且对于系统的不确定性具有很强的鲁棒性和抗干扰能力,因而在航天器的姿态控制中具有良好的潜在应用价值.     

Finite-time State Feedback Stabilization Method for a Class of Flexible Manipulators

Aimed at the finite-time stabilization problem of a class of flexible manipulators,a finite-time state feedback stabilization controller was proposed in this paper.Firstly,the nonlinear model of flexible manipulators was transformed into linear system through the exact state feedback linearization,and then using the finite time stabilization control method of the linear system,a finite-time state feedback stabilization controller was designed for the flexible manipulators.Furthermore,it was proved that all ...     

太阳能驱动闭式不可逆布雷顿循环性能解析式

在计入换热器阻和压气机，涡轮中不可逆损失后，导出太阳能驱动变温热源闭式简单布雷顿循环功率，效率与循环压比关系的解析公式。     

考虑运动受限的履带式移动机器人轨迹跟踪控制

针对履带式移动机器人的轨迹跟踪控制问题进行研究,首先,建立了履带式移动机器人的运动学模型和跟踪误差模型;其次,设计了转速有限时间控制和线速度滑模控制的轨迹跟踪控制律,并给出了考虑运动受限作用下的控制律修正表达式;最后,基于MATLAB对所提控制律进行仿真,对比分析了不考虑运动受限情况下跟踪控制效果;结果表明,设计的跟踪控制律能够实现履带式移动机器人对圆轨迹的有效跟踪,且考虑运动受限作用的控制律更加符合实际;文章研究分析了运动受限作用对于移动机器人轨迹跟踪控制的影响,分析结果对其他移动机器人的运动控制研究具有参考价值。     

Second Order Sliding Mode Control for Robot Arms with Time Base Generators for Finite-Time Tracking

A novel chattering-free dynamic sliding mode controller for a class of uncertain mechanical systems is proposed in order to account globally for a time-varying sliding regime for all time and for any initial condition. The new sliding surface, parametrized by a time base generator, plays the role of moving, and rotating continuously the nominal sliding surface, while shifting is done through a known, state-independent, vanishing vector to eliminate the reaching phase for any initial condition, a weaker assumption in comparison to some moving sliding surface designs. In this way, the closed-loop system yields finite-time convergence of tracking errors, whose convergence time can be fixed independently of initial conditions, in contrast to terminal sliding mode wherein convergence time depends on initial conditions. To implement the controller, the upper bound of the derivative of the sliding surface is required, a weaker assumption in contrast to some dynamic sliding mode controllers. The performance of the closed-loop system is visualized through simulation.     

不同结构微反应器下甲烷水蒸气重整制氢性能对比

微通道反应器是便携式制氢领域目前最有发展前景的技术之一。为了提高甲烷水蒸气重整在微反应器内制氢的效果,设计了三种不同结构的微反应器几何模型,分别为直管(Pipe)模型、平板圆弧弯道(FCC)模型和三纹内螺旋枪管(Tri-g ISB)模型,利用Ansys Fluent流体仿真软件结合甲烷水蒸气重整制氢的CHEMKIN反应机理文件对三种不同结构的微反应器进行了数值模拟分析。通过研究不同条件下微反应器出口气体组分变化可知,入口速度越小,CH₄转化率和H₂体积分数越高;S/C>3时,CH₄转化率增大至80%以上、H₂含量增加至73vol%以上;壁面温度越大,CH₄转化率可稳定在99.9%,几乎完全转化,H₂含量增大到77vol%以上,但温度过高会降低H₂产量,增加CO含量。通过计算不同条件下微反应器达到稳定所需时间可知,随入口速度和S/C增加稳定时间均逐渐减小并趋于稳定,随壁面温度增加,稳定时间先减小后增加。通过对比三种微反应器可知,复...     

Robust finite-time tracking control of nonholonomic mobile robots without velocity measurements

The problem of robust finite-time trajectory tracking of nonholonomic mobile robots with unmeasurable velocities is studied. The contributions of the paper are that: first, in the case that the angular velocity of the mobile robot is unmeasurable, a composite controller including the observer-based partial state feedback control and the disturbance feed-forward compensation is designed, which guarantees that the tracking errors converge to zero in finite time. Second, if the linear velocity as well as the angular velocity of mobile robot is unmeasurable, with a stronger constraint, the finite-time trajectory tracking control of nonholonomic mobile robot is also addressed. Finally, the effectiveness of the proposed control laws is demonstrated by simulation.     

一类扩展结构大系统的分散有限时间鲁棒关联镇定

研究一类扩展结构大系统分散有限时间鲁棒关联镇定问题. 扩展结构大系统是在原结构系统上增加新子系统而构成的, 在原系统分散控制律确定不变的情况下, 设计新加入子系统的鲁棒分散控制律, 使扩展后的系统仍能保持有限时间关联稳定. 利用LMI 方法推导此类系统基于状态反馈和输出反馈的分散有限时间关联镇定的充分条件, 并给出扩展子系统的相应控制器的设计方法. 最后通过仿真实验表明了所提出方法的可行性和有效性.

     

带落角约束的有限时间收敛末制导律研究

针对导弹末制导过程中的终端落角约束的问题,基于滑模控制和有限时间控制理论,设计了一种有限时间收敛末制导律。利用终端滑模控制中滑模面上的跟踪误差能够有限时间收敛到0的特点,选取终端滑模面,引入落角约束项,采用有限时间稳定性理论对导引律的有限时间收敛特性进行了证明,并给出了收敛时间的数学表达式。将该末制导律与其他2种带落角约束的导引律进行了对比仿真。结果表明,利用该制导律,制导武器能以更高的命中精度和更小的落角偏差命中目标。     

Ecogeomorphic interactions of Russian olives (Elaeagnus angustifolia) and point-bar morphology along Powder River,Montana, USA

Point bars are crucial alluvial features that help sustain meandering river ecosystems. They are influenced by interactions among physical processes and biological components, such as riparian vegetation. Understanding the mechanisms underlying these interactions can inform management decisions. The meandering Powder River in southeastern Montana, USA, provides a valuable study system for fluvial interactions because it has no major human alterations. Riparian stands of non-native Russian olive trees (Elaeagnus angustifolia) became noticeable after  ~50-year flood in 1978. Fortuitously, 20 channel cross-sections had been established in 1975 and 1977 and have been surveyed periodically ever since. This temporally extensive dataset was coupled with a spatially extensive dataset of 85 point-bar cross-sections derived from high-resolution LiDAR that enabled evaluation of interactions between Russian olives and point-bar morphology through time and space. Based on published literature and field observations, we hypothesised that an increase in the width of Russian olive stands would result in (1) a decrease in the overall point-bar slope, (2) an increase in point-bar heights and (3) in point-bar toe-slopes. The results indicated that point-bar slopes did decrease with an increase in stand width, supporting the first hypothesis (R² = 0.87). However, point-bar heights decreased with an increase in stand width (R² = 0.63), contradicting the second hypothesis and there was no relation between point-bar toe-slopes and stand width (R² < 0.1). The reverse hypothesis that point-bar morphology controls Russian olive stand widths makes more biophysical sense. Thus, Russian olive stand width increases as the point-bar slope and height decrease (R² = 0.79 and 0.50), which provide a greater area of inundation for colonisation. This study demonstrates that geomorphology is controlling non-native vegetation colonisation along Powder River, but that the subsequent stabilisation associated with Russian oliveexpansion may in turn upset the critical geomorphic balance between bank erosion and point-bar aggradation necessary for a stable meandering system.