一类非自治单种群模型的持久性

在这篇文章里，我们利用微分方程比较原理以及一些精细的分析方法，研究了具有无限时滞和反馈控制的非自治单种群模型的持久性，得到了一些新的结论。     

伺服系统速度环控制器参数的自整定及优化

针对交流伺服系统速度环控制器参数自整定及优化的需求,为使工程技术人员避免繁琐的调参过程,提出了一种基于转动惯量辨识的速度环控制器参数自整定及优化方法。首先,采用频率法分析伺服系统速度环控制器参数的设计规则;随后,采用遗忘因子递推最小二乘法,对控制器参数设计所需的系统转动惯量进行辨识;最后,在此基础上利用设计的变步长迭代算法,完成控制器参数寻优过程。仿真结果表明,采用遗忘因子递推最小二乘法,能够有效辨识出电机轴端的转动惯量。提出算法进行整定及优化后,速度环控制器参数能使系统具有良好的动态响应和鲁棒性。     

Adaptive sliding mode control of modular self-reconfigurable spacecraft with time-delay estimation

The reconstruction control of modular self-reconfigurable spacecraft (MSRS) is addressed using an adaptive sliding mode control (ASMC) scheme based on time-delay estimation (TDE) technology. In contrast to the ground, the base of the MSRS is floating when assembled in orbit, resulting in a strong dynamic coupling effect. A TED-based ASMC technique with exponential reaching law is designed to achieve high-precision coordinated control between the spacecraft base and the robotic arm. TDE technology is used by the controller to compensate for coupling terms and uncertainties, while ASMC can augment and improve TDE’s robustness. To suppress TDE errors and eliminate chattering, a new adaptive law is created to modify gain parameters online, ensuring quick dynamic response and high tracking accuracy. The Lyapunov approach shows that the tracking errors are uniformly ultimately bounded (UUB). Finally, the on-orbit assembly process of MSRS is simulated to validate the efficacy of the proposed control scheme. The simulation results show that the proposed control method can accurately complete the target module’s on-orbit assembly, with minimal perturbations to the spacecraft’s attitude. Meanwhile, it has a high level of robustness and can effectively eliminate chattering.     

基于频率补偿的时延估计方法

由于2个测量站的通道幅相不一致而导致送给时延估计器的两路信号的频率有差异,继而影响时延估计和系统定位精度。首先理论推导了频率差异是如何影响广义相关时延估计的,接着应用频域相关函数对频率差异做准确估计和补偿,最后给出了频差补偿后的时延估计方法。以4种常用通信信号为例,仿真验证了不同信噪比下所提出方法的正确性和有效性。     

Benders decomposition with alternative multiple cuts for a multi‐product closed‐loop supply chain network design model

In this article, we consider a multi‐product closed‐loop supply chain network design problem where we locate collection centers and remanufacturing facilities while coordinating the forward and reverse flows in the network so as to minimize the processing, transportation, and fixed location costs. The problem of interest is motivated by the practice of an original equipment manufacturer in the automotive industry that provides service parts for vehicle maintenance and repair. We provide an effective problem formulation that is amenable to efficient Benders reformulation and an exact solution approach. More specifically, we develop an efficient dual solution approach to generate strong Benders cuts, and, in addition to the classical single Benders cut approach, we propose three different approaches for adding multiple Benders cuts. These cuts are obtained via dual problem disaggregation based either on the forward and reverse flows, or the products, or both. We present computational results which illustrate the superior performance of the proposed solution methodology with multiple Benders cuts in comparison to the branch‐and‐cut approach as well as the traditional Benders decomposition approach with a single cut. In particular, we observe that the use of multiple Benders cuts generates stronger lower bounds and promotes faster convergence to optimality. We also observe that if the model parameters are such that the different costs are not balanced, but, rather, are biased towards one of the major cost categories (processing, transportation or fixed location costs), the time required to obtain the optimal solution decreases considerably when using the proposed solution methodology as well as the branch‐and‐cut approach. © 2007 Wiley Periodicals, Inc. Naval Research Logistics, 2007     

具有leakage时滞与传输时滞的神经网络的分支

研究一类具有leakage时滞与传输时滞的两神经元神经网络的分支,分别以leakage时滞和传输时滞为分支参数,通过对模型对应的特征方程进行分析,得到出现Hopf分支的临界性条件,并通过数值例子验证该理论结果.     

具有时滞的比率型Chemostat模型的全局稳定性

研究一类具有时滞的比率型功能性反应的Chemostat模型。研究了模型的边界平衡点和正平衡点的局部稳定性以及Hopf分支的存在性;利用比较定理证明了边界平衡点的全局稳定性;通过构造Liapunov泛函给出了保证系统正平衡点全局稳定的充分条件;并通过数值模拟验证了理论结果。     

BDS导航信号抗电离层闪烁载波跟踪的自适应卡尔曼滤波算法

电离层闪烁会引起导航信号幅度和相位的快速衰落,严重影响跟踪环路的精度和稳健性,而相比频率跟踪和伪码跟踪,载波跟踪环路更易受电离层闪烁的影响而失锁。因此,提出一种基于相位锁定指示自适应扩展卡尔曼滤波的北斗导航信号抗电离层闪烁载波跟踪算法,其以同相与正交支路的积分结果估计相位锁定指示值,并采用该指示作为控制参数对不同闪烁场景下扩展卡尔曼滤波的观测向量进行自适应调整,这不仅能够提高跟踪环路的精度和稳健性,而且能够降低扩展卡尔曼滤波发散的概率。实验结果验证了相关分析和所提跟踪算法的有效性。     

Optimal policies for stochastic clearing systems with time-dependent delay penalties

We study stochastic clearing systems with a discrete-time Markovian input process, and an output mechanism that intermittently and instantaneously clears the system partially or completely. The decision to clear the system depends on both quantities and delays of outstanding inputs. Clearing the system incurs a fixed cost, and outstanding inputs are charged a delay penalty, which is a general increasing function of the quantities and delays of individual inputs. By recording the quantities and delays of outstanding inputs in a sequence, we model the clearing system as a tree-structured Markov decision process over both a finite and infinite horizon. We show that the optimal clearing policies, under realistic conditions, are of the on-off type or the threshold type. Based on the characterization of the optimal policies, we develop efficient algorithms to compute parameters of the optimal policies for such complex clearing systems for the first time. We conduct a numerical analysis on the impact of the nonlinear delay penalty cost function, the comparison of the optimal policy and the classical hybrid policy (ie, quantity and age thresholds), and the impact of the state of the input process. Our experiments demonstrate that (a) the classical linear approximation of the cost function can lead to significant performance differences; (b) the classical hybrid policy may perform poorly (as compared to the optimal policies); and (c) the consideration of the state of the input process makes significant improvement in system performance.     

坦克底盘角振动对火炮射击精度影响机理研究

实车试验表明,在行进间射击试验时,当车辆超过一定车速(行进间射击车速)时,射击精度或射击命中率会发生大幅度的下降。针对这个问题,建立了坦克底盘角振动导致的射击偏差的数学模型;并结合实车试验数据,对射击延迟时间内底盘角振动造成的火炮射击偏差进行了全面分析。分析研究表明:在相同的行驶车速条件下,车辆底盘角速度、姿态角变化量随着射击延迟时间的增大而增大;在相同的射击延迟时间内,车辆底盘角速度、姿态角变化量与射角偏差随着行驶车速的增大而增大;其中射角偏差引起的目标距离偏差是弹丸横向速度导致的目标距离偏差的3倍~5倍。因此,随着行驶车速增加而增加的射角偏差增大是行进间射击车速受限的主要原因。