The Marginal Density of a TMA(1) Process

This note reconsiders the marginal density of a threshold moving average process and proposes a simple yet effective numerical algorithm to implement that by solving an associated integral equation. This algorithm can also be applied to calculate stationary probability density or distribution functions of a few other types of nonlinear stationary stochastic processes numerically.     

State feedback integral control for a rotary direct drive servo valve using a Lyapunov function approach

This paper concerns a state feedback integral control using a Lyapunov function approach for a rotary direct drive servo valve (RDDV) while considering parameter uncertainties. Modeling of this RDDV servovalve reveals that its mechanical performance is deeply influenced by friction torques and flow torques; however, these torques are uncertain and mutable due to the nature of fluid flow. To eliminate load resistance and to achieve satisfactory position responses, this paper develops a state feedback control that integrates an integral action and a Lyapunov function. The integral action is introduced to address the nonzero steady-state error; in particular, the Lyapunov function is employed to improve control robustness by adjusting the varying parameters within their value ranges. This new controller also has the advantages of simple structure and ease of implementation. Simulation and experimental results demonstrate that the proposed controller can achieve higher control accuracy and stronger robustness.     

Improving CNC contouring accuracy by robust digital integral sliding mode control

Integral sliding mode control (ISMC) has been employed and shown to improve contouring accuracy in the presence of external disturbances and model uncertainties. An ISMC controller directly reduces the tracking errors of each individual axis, thereby reducing the overall contour errors indirectly. An ISMC controller drives the system dynamics back onto the sliding surface if there exists a deviation from the predefined surface. In the design of an ISMC controller, it is crucial to choose an appropriate sliding surface as this has a great impact on system performance and on chattering. In current approaches, the sliding surface is chosen largely based on a rule of thumb which is only applicable for systems with open-loop poles having imaginary parts. In this paper, an approach is presented to design the sliding surface using principles of robust digital control so that both the regulation and robustness requirements can be satisfied. The natural frequency of the dominant closed-loop poles is chosen such that the modulus of the output sensitivity function lies within the robustness bounds. Resonant pole-zero filters are then used to reshape the output sensitivity function in specific frequency regions. Experiments showed that when the modulus of the output sensitivity function is kept within the robustness bounds, chattering can be avoided and the contour errors resulting from vibrations can be reduced. The introduction of a resonant pole-zero filter also allowed the attenuation band to be expanded so that the low frequency components of the contour errors are attenuated.     

单晶/多晶镍轴向拉伸力学性能的分子动力学模拟

为提高航空发动机推重比采用整体叶盘新技术却带来了盘叶连接区域高风险失效问题。本文采用分子动力学对连接区单晶/多晶镍(SPSNi)的力学性能进行模拟,首先通过对比了不同晶态镍拉伸原子图。发现,由于单晶/多晶界面的存在使得拉伸后界面处的非晶化程度加剧,易于孔洞萌生,加剧了SPSNi突然断裂的风险。最后重点研究了单晶/多晶镍的应变率效应与温度效应。当应变率大于1í10_⁸s_^-1小于2í10_¹⁰s_^-1时,SPSNi对加载应变率几乎不敏感,屈服强度小幅上升。超过2í10_¹⁰s_^-1之后,其屈服强度随着应变率的增加而迅速下降。这是因为在高应变率下,SPSNi的FCC原子大规模迅速转变为无序的非晶结构,导致了晶体镍承载能力迅速下降。可以将应变率2í10_¹⁰s_^-1作为SPSNi拉伸变形的阈值。不同温度下,SPSNi屈服强度随温度的增大而线性下降。这是由于在温度的影响下,位错网络的初始镶嵌结构逐渐变得不规则,初始失配应力随着温度的升高而下降。     

加速金属尾矿综合利用途径的探讨

金属尾矿数量大，占地广，污染严重，通过综合利用，除回收有用金属外，还可供建材原料，矿井充填料和复垦造田，均有利于节约资源和改善环境，是贯彻可持续发展方针的有效措施，文章介绍了综合利用现状并提出了改进建议。     

Experimental measurements,integral modeling and smoke detection of early fire in thermally stratified environments

Building fires go through a series of stages. They start with a fire plume period during which buoyant fire smoke rises to the ceiling. A second stage is the following enclosure smoke-filling period. In this paper, the first stage is the subject, especially for the fire plume behavior in thermally stratified environments in large volume spaces. In NFPA 92B, Morton's integral equation was introduced for calculating the maximum plume rise, and beam smoke detectors were recommended for smoke detection design. In this work, experiments and CFD simulations were conducted in a small-scale enclosure and a large space to investigate early fire movements in temperature-stratified ambients. The results show that in a thermally stratified environment, the axial temperature and velocity of a fire plume decrease more quickly along the vertical axis than in uniform environment, and in some cases the fire plume ceases to rise. The previous integral equation was shown to underestimate the actual maximum height of a fire smoke plume, and also was unable to explain the differences of the maximum heights of low-density and high-density smoke plumes with the same stratification and outlet conditions. The integral equation was improved by introducing two correction factors, and extended for non-linear temperature stratified environments. A light section smoke detection method with three space-protected area was suggested and discussed.     

中心区高密度协调单元的构建--一种整体适应的城市设计策略

通过对协调单元概念的回顾,探讨现代城市中心协调单元的新内涵.并分析其对中心区城市设计理论研究和实践操作的意义,强调运用整体适应的城市设计策略构建中心区高密度协调单元.     

历史城市中心景观的价值重塑与再生

本文着重研究了狭义遗产保护范畴之外的非新建城市中心,它们与现实生活有丝丝入扣的关联,却成为学界容易忽视的研究领域。通过分析历史城市中心的景观特质及其面临的困境,构建了历史城市中心的整体景观系统并提出了价值重塑的原则与途径。     

城市设计的载体──城市景观规划新探──以秀屿市区景观规划为例

城市设计应该融于城市规划的全过程，因此，城市总体规划阶段也应该进行相应的城市设计，即整体城市设计。城市景观规划是实现整体城市设计的主要手段，是整体城市设计内容的载体。文章结合莆田市秀屿市区景观规划实践，对城市总体规划阶段如何创造高质量的城市空间环境进行粗略的探索。