基于广义哈密顿系统理论的汽轮调速器分散无源控制

提出了一种预置功角反馈的方法，推导出多机系统汽轮机调速系统的广义受控哈密顿系统模型，进而在哈密顿结构的基础上进行无源化控制器的设计。控制策略的所有变量都是本地可量测的，只与本机组的状态量有关，与其他机组的状态量和输电网络的参数无关，因而具有分散性。4机系统仿真结果表明，该控制规律可以提高电力系统的暂态稳定性和动态性能。     

聚丙烯在国际纺织品市场上的拓展

10年前把尼龙挤到市场份额的第四位后,聚丙烯持续进行着有条不紊的拓展。在回顾聚丙烯成功的潜在原因后,用图表对市场份额最大的国家和产品进行说明。     

Internal Flow Simulation of High-Performance Solid Rockets using a k-ω Turbulence Model

For technological reasons many high-performance solid rocket motors are made from segmented propellant grains with non-uniform port geometry. In this paper parametric studies have been carried out to examine the geometric dependence of transient flow features in solid rockets with non-uniform ports. Numerical computations have been carried out in an inert simulator of solid propellant rocket motor with the aid of a standard k-ωturbulence model. It was seen that the damping of the temperature fluctuation is faster in solid rocket with convergent port than with divergent port geometry. We inferred that the damping of the flow fluctuations using the port geometry is a meaningful objective for the suppression and control of the instability and/or pressure/thrust oscillations during the starting transient of solid rockets.     

AN ATTRIBUTION OF CAVITATION RESONANCE： VOLUMETRIC OSCILLATIONS OF CLOUD

In order to further verify the proposed theory of cavitation resonance, as well as to proceed the investigations into microscopic level, a series of studies are being carried out on the Warwick venturi. The analysis of the oscillation characteristics of the cavitation resonance has conclusively verified the macro-mechanism proposed through previous studies on other cavitating flows by the authors. The initial observations using high-speed photographic approach have revealed a new attribution of cavitation resonance. That is, the volumetric oscillation of cavitation cloud is associated with the cavitation resonance, which is a collective behaviour of the bubbles in the cloud.     

Turbopump Condition Monitoring Using Incremental Clustering and One-class Support Vector Machine

Turbopump condition monitoring is a significant approach to ensure the safety of liquid rocket engine (LRE).Because of lack of fault samples,a monitoring system cannot be trained on all possible condition patterns.Thus it is important to differentiate abnormal or unknown patterns from normal pattern with novelty detection methods.One-class support vector machine (OCSVM) that has been commonly used for novelty detection cannot deal well with large scale samples.In order to model the normal pattern of the turbopump with OCSVM and so as to monitor the condition of the turbopump,a monitoring method that integrates OCSVM with incremental clustering is presented.In this method,the incremental clustering is used for sample reduction by extracting representative vectors from a large training set.The representative vectors are supposed to distribute uniformly in the object region and fulfill the region.And training OCSVM on these representative vectors yields a novelty detector.By applying this method to the analysis of the turbopump’s historical test data,it shows that the incremental clustering algorithm can extract 91 representative points from more than 36 000 training vectors,and the OCSVM detector trained on these 91 representative points can recognize spikes in vibration signals caused by different abnormal events such as vane shedding,rub-impact and sensor faults.This monitoring method does not need fault samples during training as classical recognition methods.The method resolves the learning problem of large samples and is an alternative method for condition monitoring of the LRE turbopump.     

Urease from Staphylococcus saprophyticus: purification, characterization and comparison to Staphylococcus xylosus urease

Urease from Staphylococcus saprophyticus was purified more than 800-fold by liquid chromatography reaching homogeneity, as shown by isoelectric focussing, at a maximum specific activity of 1979 U/mg. The molecular weight of the native enzyme was 420,000; it consisted of subunits with molecular weights of 72,400 (alpha), 20,400 (beta), 13,900 (gamma) in an estimated (alpha beta gamma)4 stoichiometry. In native gradient polyacrylamide gel electrophoresis urease exhibited a multiple activity band pattern with molecular weights ranging from 420,000 to 100,000. In the native enzyme, 4.09 (+/- 0.25) atoms of nickel per molecule were detected. The N-terminal amino acids of the urease subunits were identical to those from Staphylococcus xylosus, and amino acid analysis revealed high similarities in both enzymes; no cysteine was detected after acid hydrolysis of vinylpyridinylated urease. Electron micrographs of negatively stained urease specimens from both staphylococci showed identical size and structure.