Rapid identification technique for virtual CNC drives

This paper presents a technique for rapid identification of machine tool drives by conducting a short G-code test. The proposed strategy uses commanded and measured axis profiles and requires minimal intervention to the servo control loop. The drive system is identified as a whole, including the feed mechanism, motor, amplifier, and the control law. The methodology is fairly general and applicable to linear or ball screw drives, controlled with commonly used controllers like P, PI, PID, P–PI Cascade or Adaptive Sliding Mode Control; with or without feedforward dynamic or friction compensation. In order to guarantee the stability of identified dynamics, bounds are imposed on the pole locations. The identified models can be used in a Virtual CNC system for predicting the contouring and tracking errors to different part programs. Simulation and experimental case studies are presented, where tracking and contour errors are successfully predicted using drive models identified with the proposed strategy.     

Participatory landscape analysis to guide restoration of ponderosa pine ecosystems in the American Southwest

Over the past 5 decades, stand-replacing crown fires have increased in size and frequency throughout the long-needled pine forests of the American Southwest. Suppression of frequent, low-intensity ground fires has resulted in dense stands of fire-prone trees over large areas. Efforts to restore forest structure to conditions that would permit a return to historical fire regimes, characterized by frequent ground fire, are hindered by the inability of managers and the public to compare the effects of alternative forest management practices on fire behavior and a host of other issues. Currently, forest management is mired in controversy, endangering ecosystem function, biodiversity, public safety, and municipal watersheds. Our research program, motivated by the need to examine cumulative effects of many independent management decisions over large planning areas, focuses on the development of spatial data and modeling tools that enable diverse stakeholders to work together to guide landscape-scale planning efforts. Data layers describing forest composition and structure facilitate modeling of fire threat and wildlife habitat over areas of several hundred thousand hectares. Modeling alternative forest management scenarios via a collaborative, public process fosters informed discourse and helps conflicting parties forge appropriate policy and identify management responses that meet restoration objectives.     

Multiresolution Representation of 2D CSG Models

Multiresolution is currently one of the main schemes used in CAD modeling for representing objects, particularly when large-scale geometric data must be transferred interactively over a network, as in the case of collaborative design. Increasingly complex products and growing competition have turned design into a collaborative team effort. Furthermore, the widespread development of Internet viewers has also necessitated the transfer and display of large-scale CAD models over networks. In order to reduce the volume of transferred data, efforts have been made to transfer CSG (Constructive Solid Geometry) models rather than those based on B_rep (Boundary Representation). This paper presents an original new method for speeding up data transfer by using multiresolution CSG models at different levels of details (LOD). The multiresolution CSG algorithm generates a hierarchy of multiresolution CSG trees; at each level, the shape is further approximated and represented by a smaller number of CSG primitives. The paper analyzes the proposed algorithm, and demonstrates its feasibility.     

150t RH装置内钢液的流动和混合特性及吹气管直径的影响

在几何相似比为1∶4的水模型上研究了150tRH装置内钢液的流动和混合特性及吹气管直径的影响。模型的吹气管内径分别为0.10、0.15和0.2cm。所得结果表明,该装置的环流量计算式为：Qlp=0.0291Qg0.323Du0.65Dd0.84（t/min）,式中Qg—提升气体流量,Nl/min;Du和Dd—上升管和下降管内径,cm。在给定的Qg、Du和Dd下,吹气管直径din的变化对液体的流态没有显著影响,环流量则略有改变,在（0.40~0.80）cm的范围内,Qlp=0.0304Qg0.322Du0.651Dd0.839din0.07。在Du和Dd均为53cm、din为0.60cm的情况下,该装置内钢液的最大（“饱和”）环流量约为135.1t/min,相应的Qg为2500Nl/min。钢包内钢液的混合效果随Qg的增大迅速提高。增大din使混合时间τm（s）略有缩短,对应于0.10,0.15和0.20cm的孔径,τm与搅拌功率密度ε（W/t）的关系分别为：τm∞ε-0.497,τm∞ε-0.493和Tm∞ε-0.476。     

气动肌肉驱动仿生关节的理论分析

根据气动肌肉的简化模型,通过引入关节的刚度和力矩-压力系数等概念,建立了由一对对抗性气动肌肉驱动仿生关节的理论模型.研究了关节的刚度和位置独立控制时对气动肌肉输入压力的要求,并对气动肌肉驱动关节运动时的几种压力变化方式进行了分析.研究表明,两个气动肌肉的压力的不同变化方式对于关节动态的刚度、转矩有很大的影响.     

Stable pitting corrosion of stainless steel as diffusion-controlled dissolution process with a sharp moving electrode boundary

This paper is devoted to explanation and prediction of pit propagation or stable pit growth, governed by ion transport properties in electrolytic solutions. Therefore, we vigorously derive the (3D) mass conservation law for a body hosting a sharp metal/solution interface separating the solid electrode from liquid electrolyte. The model for stable pitting corrosion is completed by Fick’s law of diffusion, governing the behavior of the dissolved metal ions. There are only three model input values, which are directly accessible from experiments, namely the ion concentration in the solid metal, as well as the diffusion coefficient and the saturation concentration of the dissolved metal ions in the electrolyte. The partial differential equations describing stable pitting corrosion as diffusion-controlled dissolution process are solved for boundary conditions related to 1D pencil electrode tests as well as to 2D foil electrode tests. The mathematical solution functions (model predictions) are related to pit growth in terms of depth and width, and to electric current evolution. Such model predictions reasonably agree with corresponding experiments, which shows the relevance of the proposed approach. In the case of pits with lacy covers, the boundary conditions for the ionic flux probably depend on complex depassivation-repassivation phenomena. However, once the extent of perforation of the lacy cover is known, the entire pit propagation characteristics, in particular the pit shape, can be predicted by the proposed model, relating to a classical Stefan problem.     

Effects of blending on surface characteristics of copper corrosion products in drinking water distribution systems

Copper scales formed over 6-months during exposure to ground, surface and saline waters were characterized by EDS, XRD and XPS. Scale color and hardness were light red-brown-black/hard for high alkalinity and blue-green/soft for high SO₄ or Cl waters. Cl was present in surface or saline copper scales. The Cu/Cu₂O ratio decreased with time indicating an e transfer copper corrosion mechanism. Cu₂O, CuO, and Cu(OH)₂ dominated the top 0.5-1 A° scale indicating continuous corrosion. Cu₂O oxidation to CuO increased with alkalinity, and depended on time and pH. Total copper release was predicted using a Cu(OH)₂ model.     

液压传动CAI三维动画设计

分析了三维动画在液压传动CAI中的重要作用以及AutoCAD和3DS MAX的特点,介绍了将二者结合起来进行液压传动元件和液压回路的三维建模及其工作原理、组装动画设计的方法,给出了液压传动CAI三维动画实例,最后介绍了使用3DS MAX进行动画设计的技巧。     

Higher alcohol and paraffin synthesis on cobalt based catalysts: Comparison of mechanistic aspects

Syngas reaction mechanism studies on cobalt based catalysts suggested that the CO dissociation step and the (alcohol and/or hydrocarbon) chain growth can be well mimicked by CO disproportionation and temperature programmed desorption (TPD) of acetaldehyde. Correlation between C₂₊ hydrocarbon selectivity and CO disproportionation on the one hand, C₂₊ alcohol selectivity and TPD after acetaldehyde adsorption on the other hand could be evidenced.     

不锈钢AOD转炉精炼过程数学模拟初探

对不锈钢AOD转炉精炼过程数学模拟作了初步研究,注意到该侧顶复吹精炼过程的物理和化学特性,考虑体系的质量和热量衡算,以及添加渣料、废钢、合金料等操作、精炼过程的不等温状态、钢液和熔渣质量的变化等因素的影响,提出了一个针对整个精炼过程的数学模型。基于设计的操作模式,以该模型对120 t AOD转炉内奥氏体不锈钢的整个精炼过程,包括氧化（脱碳）和还原过程作了模拟和估算,与工艺设计给出的参照数据作了比较。