Hierarchical production control for a flow shop with dynamic setup changes and random machine breakdowns

In this paper, we study a manufacturing system consisting of two machines separated by two intermediate buffers, and capable of producing two different products. Each product requires a constant processing time on each of the machines. Each machine requires a constant non-negligible setup change time from one product to the other. The demand rate for each product is considered to be piecewise constant. Each machine undergoes failure and repair. The time-to-failure and time-to-repair are exponentially distributed random variables. The setup change and processing operations are resumable. We model our system as a continuous time, continuous flow process. An optimal control problem is formulated for the system to minimize the total expected discounted cost over an infinite horizon. To determine the optimal control policy structure, a discrete version of the problem is solved numerically using a dynamic programming formulation with a piecewise linear penalty function. A real-time control algorithm is then developed with the objective of maintaining low work-in-process inventory and keeping the production close to the demand. The algorithm uses a hierarchical control structure to generate the loading times for each product on each machine in real time and to respond to random disruptions in the system. The system is simulated using this algorithm to study its performance. The performance of the algorithm is also compared to alternative policies.     

Dynamic elastic-plastic buckling phenomena in a rod due to axial impact

Dynamic elastic-plastic buckling phenomena which might develop in a rod from an axial impact loading are studied in order to identify the conditions for quasi-static behaviour. A discrete model for dynamic elastic-plastic buckling, which retains the axial and the lateral inertia forces, is proposed, and the relationship between the model parameters and the characteristics of an actual structure is given. Examples of different external loadings and boundary conditions are considered in order to clarify the influence of elastic-plastic axial wave propagation on the buckling process. The critical time for the initiation of buckling is obtained and the post-buckling behaviour of the model is analysed. Particular attention is paid to the role of the striking mass on the characteristics of the buckling process and on the development of the buckling shape. The numerical study reveals that the inertia of the striking mass affects considerably the development of the buckling shape causing different patterns of axial strain distributions at the initiation of buckling. The comparisons which are made between the model predictions and some previously published experimental data show that the buckling process is governed by the impact velocity as well as by the external loading history provided by the experimental technique.     

The effect of temperature on the dynamic characteristics of heat-resistant thermoplastic composites

Two thermoplastic and two thermosetting fibrereinforced plastic composites were subjected to dynamic tests over a wide range of temperature, covering both cryogenic and hot environments. The thermal behaviour of each composite, as indicated by its dynamic mechanical properties, was assessed individually, and was compared collectively with that of the other composites.     

底敞口充气浮箱研究和试验

提出底敞口充气浮箱的结构和概念。经模型模拟试验研究分析，经典浮力定律可用于这种浮箱的浮力计算；其动充气状况还具有一定的允许伤损面积。它的研究将为水陆两用车辆增大浮力，缩小外形，提高水上自下而上能力和潜驶潜伏提供具有诱惑力的工程应用前景。     

催化裂化装置动态机理模型 Ⅱ.再生器部分

建立了前置烧焦罐式高效再生器动态机理模型。烧焦罐再生段采用轴向扩散模型，包括催化剂上碳含量、氢含量和再生温度动态分布参数方程、气体中氧含量拟稳态分布参数方程和催化剂藏量动态方程。二密相床气速低，采用气固全返混模型，并考虑了气体外扩散对烧碳速率的影响。二密相床数学模型包括再生剂碳含量和催化剂藏量的动态集中参数方程和烟气中氧含量的拟稳态代数方程。     

How to Control Robots Interacting with Dynamic Environment

The goal of this paper is to shed light on the control problem of constrained robot motion from the aspect of the dynamical nature of the environment with which the robot is in contact. Therefore, the criticism of traditional hybrid control which allows position/force feedback loops to split into independent control with respect to position and force, is not the main point we want to make. Reference to the papers written by the founders of hybrid control and their numerous followers served only to better understand the reason and motivation for suggesting a different approach to control of robots interacting with environment.The paper has a predominantly review character, based on recently published work. It also contains some new, unpublished results in the framework of the unified approach to the position/force control of robots, proposed by the present author and his co-workers. By pointing to the possibility of introducing an environment dynamics in the contact tasks of the machining type, the author emphasizes that the proposed dynamically interactive control can be applied to a completely different class of tasks, in which a contact is made between the system (constructions or structure) and very specific kinds of dynamic environments.     

A new approach to the mechanism of chlorine evolution: Separate examination of the kinetic steps using ac impedance on a rotating thin ring electrode

In the absence of a bulk diffusion effect, it is shown for the first time that the impedance spectra for the chlorine evolution reaction on a rotating thin ring electrode comprise three consecutive semicircles in the capacitive half of the complex plane. The first (highest frequency) semicircle is due to the charge-transfer resistance for chloride discharge and the simultaneous chlorine adsorption coupled to the double-layer capacitance. The second semicircle (around 5 Hz) is due to the adsorption and desorption of a chlorine intermediate. The third (lowest frequency, around 0.5 Hz) semicircle is due to the relaxation of surface oxygen species. The impedance data allow the steps of the overall reaction to be examined individually. On a Pt surface the rate of chloride discharge and simultaneous chlorine adsorption (the admittance of the first semicircle) is first order with respect to chloride concentration and has a potential-dependence close to 58 mV/decade. The rate of the adsorption and desorption process (the admittance of the second semicircle) is second order with respect to chloride concentration, and has a potential dependence close to 30 mV/decade. The time constant for the adsorption/desorption processes is ca 20 ms, independent of electrode potential in the range studied. These features are consistent with a mechanism in which a faster discharge reaction (Cl⁻ Cl_ad + e) is followed by a slower surface combination reaction (2Cl_ad → Cl₂), but inconsistent with mechanisms in which ion + atom desorption is predominant, the initial chloride discharge is slow, or a unipositively charged chlorine species is involved.     

叠后地震剖面的线性化波阻抗反演

本文提出了由井旁道出发逐道进行的叠后地震剖面的线性化波阻抗反演方法。每一道反演采用逐次线性化对波阻抗进行修正，反演的纵向分辨率为一个采样时间间隔，并以合成记录道与实际地震道的相似系数作为迭代收敛准则，已处理的地震道波阻抗作为下一道反演初始值。实际资料处理表明，该方法具有较高的分辨率和运算速度快的优点。     

转子叶片在非均匀来流条件下的流体激振特性

该文通过研究得出非均匀来流对转子叶片流体激振的三个重要特征 :非均匀来流相对于转子叶片的非定常流中主频分量是产生叶片动应力的决定因素 ;非均匀来流的非均匀度 (相当于非定常流的波幅 )大小和叶片流体激振的动应力大小成正比 ;转子叶片流体的定常压力水平与叶片动应力的水平密切相关。图 4表 2     

泡沫铝的动态压缩性能和吸能性研究

通过测量泡沫铝在动态和准静态压缩条件下的应力 -应变曲线 ,研究了泡沫铝的准静态和动态压缩行为以及不同应变条件下的吸能性 ,并对其应变率效应进行了分析。结果表明 ,在高应变速率和准静态压缩下 ,泡沫铝的σ -ε曲线均表现出弹性变形段、平缓段和密实段三阶段特征 ;泡沫铝的压缩性能具有明显的应变速率敏感性 ,随应变速率的提高 ,流动应力上升 ,吸能性升高