DFIG rotor voltage control for system dynamic performance enhancement

This article develops a model of a doubly fed induction generator system including the detailed dynamics of the converter circuitry. The order of the converter controls in terms of providing damping to the system is identified through residue principles. Supplementary damping controller has been incorporated so as to compensate for the phase lag introduced by the rotor voltage input, which was observed to have the largest residue contribution at the lightly damped mode. The improvement in damping profile was verified by simulating the system for a number of disturbance conditions. While the power oscillation damping (POD) controller was observed to enhance the system damping generally, it was also able to ride through low voltage conditions arising out of severe fault conditions thus averting total system collapse.     

低能离子注入过程中真空和注入对小麦过氧化物酶同工酶的影响

本文报道了真空处理和低能离子束注入处理对小麦过氧化物酶同工酶的影响。研究发现,经真空处理后的样品,其酶活随着培养时间的延长呈增加的趋势,与对照样保持一致;而且相同取样时间不同样品之间的酶活性随真空时间的延长呈现略为增加的趋势;各剂量的N^ 注入处理后,种子的发芽率未受影响,而剂量较大时种子的芽长增长速度受到了明显的抑制;低剂量处理能刺激过氧化物酶酶活升高,而较高剂量处理则使酶活降低。     

A POD reduced‐order model for eigenvalue problems with application to reactor physics

A reduced‐order model based on proper orthogonal decomposition (POD) has been presented and applied to solving eigenvalue problems. The model is constructed via the method of snapshots, which is based upon the singular value decomposition of a matrix containing the characteristics of a solution as it evolves through time. Part of the novelty of this work is in how this snapshot data are generated, and this is through the recasting of eigenvalue problem, which is time independent, into a time‐dependent form. Instances of time‐dependent eigenfunction solutions are therefore used to construct the snapshot matrix. The reduced order model's capabilities in efficiently resolving eigenvalue problems that typically become computationally expensive (using standard full model discretisations) has been demonstrated. Although the approach can be adapted to most general eigenvalue problems, the examples presented here are based on calculating dominant eigenvalues in reactor physics applications. The approach is shown to reconstruct both the eigenvalues and eigenfunctions accurately using a significantly reduced number of unknowns in comparison with ‘full’ models based on finite element discretisations. The novelty of this paper therefore includes a new approach to generating snapshots, POD's application to large‐scale eigenvalue calculations, and reduced‐order model's application in reactor physics.Copyright © 2013 John Wiley & Sons, Ltd.     

A stable Galerkin reduced order model for coupled fluid–structure interaction problems

A stable reduced order model (ROM) of a linear fluid–structure interaction (FSI) problem involving linearized compressible inviscid flow over a flat linear von Kármán plate is developed. Separate stable ROMs for each of the fluid and the structure equations are derived. Both ROMs are built using the ‘continuous’ Galerkin projection approach, in which the continuous governing equations are projected onto the reduced basis modes in a continuous inner product. The mode shapes for the structure ROM are the eigenmodes of the governing (linear) plate equation. The fluid ROM basis is constructed via the proper orthogonal decomposition. For the linearized compressible Euler fluid equations, a symmetry transformation is required to obtain a stable formulation of the Galerkin projection step in the model reduction procedure. Stability of the Galerkin projection of the structure model in the standard L² inner product is shown. The fluid and structure ROMs are coupled through solid wall boundary conditions at the interface (plate) boundary. An a priori energy linear stability analysis of the coupled fluid/structure system is performed. It is shown that, under some physical assumptions about the flow field, the FSI ROM is linearly stable a priori if a stabilization term is added to the fluid pressure loading on the plate. The stability of the coupled ROM is studied in the context of a test problem of inviscid, supersonic flow past a thin, square, elastic rectangular panel that will undergo flutter once the non‐dimensional pressure parameter exceeds a certain threshold. This a posteriori stability analysis reveals that the FSI ROM can be numerically stable even without the addition of the aforementioned stabilization term. Moreover, the ROM constructed for this problem properly predicts the maintenance of stability below the flutter boundary and gives a reasonable prediction for the instability growth rate above the flutter boundary. Copyright © 2013 John Wiley & Sons, Ltd.     

刺葡萄对霜霉病的抗性机理初探

本试验通过室内接种与田间接种的方法鉴定了刺葡萄对霜霉病的抗病性,并通过测定刺葡萄叶片结构特征与叶片内相关抗病物质的含量研究了刺葡萄对霜霉病的抗性机理。试验结果表明:刺葡萄对霜霉病的抗病性与其叶片蜡质含量、木质素含量、单宁含量、接种后PPO、POD酶活性升高幅度成正相关,与叶背气孔密度成负相关;刺葡萄对霜霉病的抗性较低,这与其感染霜霉病菌后叶片内PPO、POD活性降低有重要关系。     

Peroxidase activity of germinating Sorghum bicolor grains: effect of some cations

We investigated some properties of the major ionic peroxidase (POD) from germinating Sorghum bicolor var Fara Fara. Peroxidase activity increased eightfold during the first 36 h of germination and declined thereafter to four times the value in the dry grain after 144 h. Gel filtration followed by ion exchange chromatography resolved the major peroxidase into two forms. The predominant POD had an optimum temperature of 55 °C, two pH optima at 5.0 and 7.0, with a sharp decline in activity below pH 4.5, an apparent activation energy of 463 kJ mol^?1, an apparent molecular weight of 63.1 kDa and was relatively heat‐stable up to 70 °C. The enzyme was strongly inhibited by dithiothreitol and sodium metabisulphite. Calcium chloride and magnesium chloride below 2 mM enhanced POD activity without any adverse effect on germination, while ammonium chloride and ferric chloride inhibited the enzymatic activity of both forms. At 5 mM , magnesium chloride inhibited POD activity by 50% with only a 14% reduction in germination, while calcium chloride achieved the same effect at 10 mM . These results are pertinent to controlling the undesirable activity of peroxidase in a typical malting or brewing process. © 2002 Society of Chemical Industry     

超高压与热处理对荔枝汁品质影响的研究

对比分析了热处理和高压处理达到商业杀菌要求的基础上分别对荔枝汁感官品质的影响,同时探讨分析处理后果汁理化性质和感官品质的变化。结果表明,热处理和高压处理均使果汁总糖含量增加,而总酸含量有所下降,超高压处理后果汁总酸含量相对下降更大。不同杀菌方式处理后果汁中可溶性固形物变化不显著(P>0.05),超高压处理(450MPa,5min)能显著降低单宁的含量,从感官评价角度看,超高压杀菌处理后果汁品质相对于热处理效果更佳,当超高压达到450MPa,保压5min处理后的果汁样品总体评价优于其他条件处理的果汁样品。     

大空间柱壳结构爆炸动力响应的Ritz-POD数值模拟

应用ANSYS/LS-DYNA建立大空间柱壳结构在内爆炸荷载作用下的数值模拟实验,在验证模型及参数选取的正确性及可靠性的基础上,建立了大空间柱壳结构在内爆炸作用下进行动力响应计算的合适模型。将Ritz振型叠加法与POD法结合,解决了冲击波荷载的时空差异性和结构表面压力场分布问题,大大减少了大空间结构爆炸动力响应分析的计算量。对大空间柱面网壳结构在内爆炸冲击荷载作用下的动力响应进行了数值模拟计算与分析,研究了矢跨比和爆炸点位置等因素对结构动力响应的影响。结果表明,计算模型适合于大空间柱壳结构的爆炸动力响应分析,矢跨比大的结构防(抗)爆炸冲击波的能力较强。偏心爆炸比中心爆炸对大空间结构构件的损害大,对结构的边跨构件最为不利,设计中应更注重支座附近和边跨结构的防爆能力。     

平衡特征正交分解及其在机翼气弹模型降阶中的应用

将平衡特征正交分解方法(Balanced Proper Orthogonal Decomposition, BPOD)应用于气弹控制系统降阶。该方法是平衡截断(balance truncation theory)与特征正交分解 (Proper Orthogonal Decomposition, POD)的结合,可以克服高阶系统为控制方法应用所带来的局限性。首先给出了BPOD方法的理论推导与降阶过程,然后以三元大展弦比机翼的 有限元模型为例进行仿真验证。根据仿真结果分析,BPOD方法可以有效减少系统阶数,计算开销较小并保留输入输出关系,非常适用于气弹控制系统。