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541.
为了提高线式爆炸分离装置的安全性,本研究基于扩展有限元法,通过创建二维和三维动态裂纹扩展模型,探索了线式爆炸分离装置在爆轰波作用过程中的动态裂纹扩展和止裂机理。研究表明,分离壳体的裂纹扩展路径独立于裂纹初始角度;不考虑载荷时序时,二维和三维动态裂纹扩展的主方向分别沿着分离壳体的径向和环向;考虑载荷时序时,受不同区域应力波的联合作用,三维裂纹沿环向扩展的同时会沿着轴向扩展,但裂纹的扩展均不会影响到止裂槽以外的结构。所提方法和相应结论可为线式爆炸分离装置设计提供参考。  相似文献   
542.
为满足导弹拦截机动目标时交会角约束和有限时间收敛的需求,建立了考虑弹体一阶动态特性的制导模型。把目标加速度视为有界外界干扰,同时结合非线性反步设计法中的动态面法,设计一种考虑弹体动态延迟的非奇异滑模制导律,并且证明了基于Lyapunov稳定性理论制导系统状态可渐进收敛到零。在所设计的制导律下,对单侧机动的低空高速目标进行仿真。仿真结果表明所设计的非奇异制导律可以有效降低弹体动态延迟带来的影响,而且具有较低的脱靶量与交会角误差;与考虑弹体动态特性和交会角约束的最优导引律相比,其具有更高的制导精度。  相似文献   
543.
针对INS/GNSS组合导航仿真中,捷联惯导系统陀螺、加速度计信号高精度模拟问题,提出了基于实际飞行数据插值的动态轨迹解析生成仿真算法。对转换到地心惯性坐标系中的载体姿态、位置和重力场数据进行关于时间的样条函数插值,得到载体坐标系下陀螺角速率、角增量以及加速度计比力积分增量的高精度分段解析表达式。使生成的陀螺、加速度计信号符合载体运动学和动力学特性,反映杆臂效应影响,同时与经事后处理的实测GNSS伪距、伪距率等数据特征保持一致。提出了四元数约束插值算法,可满足四元数解析插值时范数为1的约束限制条件。基于某实际无人机飞行数据,验证了所提出算法的有效性,完全满足组合导航动态仿真精度要求。该算法也适用于其他高精度高动态导航系统和刚体运动控制仿真中的角运动、线运动传感器信号模拟。  相似文献   
544.
In many applications, managers face the problem of replenishing and selling products during a finite time horizon. We investigate the problem of making dynamic and joint decisions on product replenishment and selling in order to improve profit. We consider a backlog scenario in which penalty cost (resulting from fulfillment delay) and accommodation cost (resulting from shortage at the end of the selling horizon) are incurred. Based on continuous‐time and discrete‐state dynamic programming, we study the optimal joint decisions and characterize their structural properties. We establish an upper bound for the optimal expected profit and develop a fluid policy by resorting to the deterministic version of the problem (ie, the fluid problem). The fluid policy is shown to be asymptotically optimal for the original stochastic problem when the problem size is sufficiently large. The static nature of the fluid policy and its lack of flexibility in matching supply with demand motivate us to develop a “target‐inventory” heuristic, which is shown, numerically, to be a significant improvement over the fluid policy. Scenarios with discrete feasible sets and lost‐sales are also discussed in this article.  相似文献   
545.
为使大口径舰炮制导炮弹在打击近岸机动目标的末制导段满足落角约束,现考虑自动驾驶仪动态特性,基于自适应RBF逼近网络与动态面滑模提出一种空间末制导律。构建空间弹目相对运动模型,通过带改进微分跟踪器的扩张状态观测器估计目标加速度。为零化视线角跟踪误差与视线角速率,采用自适应指数趋近律设计非奇异终端滑模动态面,并运用自适应RBF逼近网络削弱控制指令抖振。通过Lyapunov第二法证明了全系统中视线角跟踪误差与视线角速率均最终一致有界。仿真实验表明:该末制导律使制导炮弹在空间中打击具有不同机动形式的近岸目标时,均具备良好的末制导性能。  相似文献   
546.
In urban rail transit systems of large cities, the headway and following distance of successive trains have been compressed as much as possible to enhance the corridor capacity to satisfy extremely high passenger demand during peak hours. To prevent train collisions and ensure the safety of trains, a safe following distance of trains must be maintained. However, this requirement is subject to a series of complex factors, such as the uncertain train braking performance, train communication delay, and driver reaction time. In this paper, we propose a unified mathematical framework to analyze the safety‐oriented reliability of metro train timetables with different corridor capacities, that is, the train traffic density, and determine the most reliable train timetable for metro lines in an uncertain environment. By employing a space‐time network representation in the formulations, the reliability‐based train timetabling problem is formulated as a nonlinear stochastic programming model, in which we use 0‐1 variables to denote the time‐dependent velocity and position of all involved trains. Several reformulation techniques are developed to obtain an equivalent mixed integer programming model with quadratic constraints (MIQCP) that can be solved to optimality by some commercial solvers. To improve the computational efficiency of the MIQCP model, we develop a dual decomposition solution framework that decomposes the primal problem into several sets of subproblems by dualizing the coupling constraints across different samples. An exact dynamic programming combined with search space reduction strategies is also developed to solve the exact optimal solutions of these subproblems. Two sets of numerical experiments, which involve a relatively small‐scale case and a real‐world instance based on the operation data of the Beijing subway Changping Line are implemented to verify the effectiveness of the proposed approaches.  相似文献   
547.
This paper considers optimal staffing in service centers. We construct models for profit and cost centers using dynamic rate queues. To allow for practical optimal controls, we approximate the queueing process using a Gaussian random variable with equal mean and variance. We then appeal to the Pontryagin's maximum principle to derive a closed form square root staffing (SRS) rule for optimal staffing. Unlike most traditional SRS formulas, the main parameter in our formula is not the probability of delay but rather a cost‐to‐benefit ratio that depends on the shadow price. We show that the delay experienced by customers can be interpreted in terms of this ratio. Throughout the article, we provide theoretical support of our analysis and conduct extensive numerical experiments to reinforce our findings. To this end, various scenarios are considered to evaluate the change in the staffing levels as the cost‐to‐benefit ratio changes. We also assess the change in the service grade and the effects of a service‐level agreement constraint. Our analysis indicates that the variation in the ratio of customer abandonment over service rate particularly influences staffing levels and can lead to drastically different policies between profit and cost service centers. Our main contribution is the introduction of new analysis and managerial insights into the nonstationary optimal staffing of service centers, especially when the objective is to maximize profitability. © 2016 Wiley Periodicals, Inc. Naval Research Logistics 63: 615–630, 2017  相似文献   
548.
为高精度模拟高动态条件下GNSS信号的多普勒特性,本文提出一种任意阶DDS信号合成器的设计方法。设计了任意阶DDS信号合成器的结构;通过理论分析,推导了各级累加器相位初值的计算公式;给出了字长选择方法;经仿真与验证,该方法能精确模拟GNSS信号的多普勒特性。此外,本文提出的DDS设计方法不受阶数的限制,可普遍应用于各类信号模拟器的设计。  相似文献   
549.
针对电磁轨道发射器动态发射过程的数值模拟问题,基于矢量磁位A和时间积分标量电位V,采用节点单元法,并选择运动坐标系描述运动问题,推导出动态发射下的电磁轨道发射器三维涡流场有限元离散方程。结合温度场控制方程,建立电磁轨道发射器的三维电磁-温度耦合有限元模型。针对一个电磁轨道发射器动态发射问题,对模型进行数值模拟,得到了动态发射下轨道及电枢的温度场分布特点及发射器电感梯度随时间的变化规律。计算结果表明,模型计算出的脉冲电流峰值、出口电流大小、出口速度等参数均与试验结果吻合较好,验证了所开发的有限元程序代码的正确性。  相似文献   
550.
为充分利用高超声速飞行器在俯冲段的质心运动与绕质心运动之间的耦合作用和飞行过程中的不确定性,基于模糊干扰观测器提出三维一体化制导与控制问题。根据飞行器的动力学方程以及飞行器-目标的视线角相对运动方程,推导出适用于倾斜转弯控制的一体化制导控制模型。针对模型中的不确定性采用模糊干扰观测器进行补偿,并使用块动态面方法设计一种一体化制导控制律。通过选取适当的李雅普诺夫函数证明闭环系统状态的一致毕竟有界性。仿真结果验证了该一体化制导控制方法的有效性和鲁棒性。  相似文献   
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