On the stable exact model matching problem

The stable exact model matching problem (SEMMP) is investigated. We state and prove a number of equivalent necessary and sufficient conditions for the existence of proper solutions to the exact model matching problem that are also Ω-stable, i.e. have no poles inside a symmetric ‘forbidden’ subset Ω of the finite complex plane . These results can be viewed as the counterpart of the results in [3] and [9] for the case of the ring of proper and Ω-stable rational functions.     

Analysis of dominant flow structures and their flow dynamics in chemical process equipment using snapshot proper orthogonal decomposition technique

Snapshot proper orthogonal decomposition (POD) technique has been applied to reveal the dominant flow structures, their dynamics and length scales in six widely used industrial equipments (stirred tank, bubble column, Taylor-Couette flow (annual contactor), ultrasonic reactor, jet reactor, and channel flow). The variation in length scale of structures within an equipment, with change in its operating conditions (Reynolds number and power input) or change in its geometric configuration (sparger and impeller designs), has been brought out in this work. The planar data set for POD analysis was obtained from particle image velocimetry (PIV) and large eddy simulation (LES) studies. The dominant spatial topology was analyzed by using the velocity and vorticity POD modes. The modes have revealed the following flow structures: the ascending streaks and bursts in channel flow, the vortex tube and leading edge vortices in jets, the irregular small chaotic vortices in Taylor-Couette flow, the variation in plume oscillation and flow structures in the vortical region of bubble column resulting from changes in sparger design, the high intensity vortices near the source of ultrasound in the ultrasonic reactor and the effect of impeller designs on dominant flow structures and near blade vortices in the stirred tank. The length scales of structures are obtained by applying image processing on the spatial modes. The dynamics of these flow structures in each of the items of equipment is captured by reconstructing the flow field using appropriate spatial and temporal modes that contribute to these structures. Further, a unique attempt has been made to correlate the length scale distribution with the mixing time.     

中石化国际化经营人才英语培训的实践与思考

国际化经营人才英语培训有其自身的特点和规律。不断探索和总结其规律,形成符合实际的由能力模块、培训方式和教学管理构成的培训模式对增强培训效果十分重要。能力模块的构建必须以听说为主,满足受训者出国后工作和生活的需要。培训方式要满足个性发展需要,营造英语环境,帮助学员度过平台期。管理上应体现以人为本、厂校结合、适度施压的原则,打造中石化国际化经营人才英语培训品牌。     

On the propagation of uncertainty in inflow turbulence to wind turbine loads

When stochastic simulation of inflow turbulence random fields is employed in the analysis or design of wind turbines in normal operating states, it is common to use well-established standard spectral models represented in terms of parameters that are usually treated as fixed or deterministic values. Studies have suggested, though, that many of these spectral parameters can exhibit some degree of variability. It is not unreasonable to expect, then, that derived flow fields based on simulation with such spectral models can be in turn highly variable for different realizations. Turbine load and performance variability would also be expected to result if response simulations are carried out with these variable flow fields. The aim here is to assess the extent of variability in derived inflow turbulence fields that arises from the noted variability in spectral model parameters. Simulation of these parameters as random variables forms the basis of this study. A commercial-sized 1.5 MW concept wind turbine is considered in the numerical studies. Variability in turbulence power spectra at field points on the rotor plane and in turbulence coherence functions for separations on the order of a rotor diameter and smaller is studied. Using time domain simulations, variability in various wind turbine response measures is also studied where the focus is on statistics such as response root-mean-square and 10-min extreme estimates. It is seen that while variability in inflow turbulence spectra can be great, the variability in turbine loads is generally considerably lower. One exception is for turbine yaw loads whose larger variability arises due to sensitivity to a coherence decay parameter that is itself highly variable. Finally, because reduced-order representations of turbulence random fields using empirical orthogonal decomposition techniques allow useful physical insights into spatial patterns of flow, variability in the energy distribution and the shapes of such empirical eigenmodes is studied and a simplified model is proposed that retains key variability sources in a limited number of modes and that accurately preserves overall inflow turbulence field uncertainty.     

Multi-scale correlation analyses of two lateral profiles of full-scale downburst wind speeds

Lateral correlation analyses are carried out in different scales for two sets of full-scale thunderstorm downburst full wind speed time series. These two sets of data were recorded at the TTU field site, Texas, USA, on June 4 and 15, 2002, respectively. The same data sets were also used in the authors’ previous paper [L. Chen, C.W. Letchford, Proper orthogonal decomposition of two vertical profiles of full-scale nonstationary correlated downburst wind speeds, J. Wind Eng. Ind. Aerodyn., 93(3)(2005) 187-266.], which presents a methodology to model downburst vertical profiles. The statistical procedures utilized in [7], such as the POD technique, the wavelet shrinkage for time-varying mean inference, the two-stage weighted moving-average method for time-varying variance inference and the Priestley's EPSD estimator, are also employed in this paper and their details are thus omitted. While in [7] the authors employed the proper orthogonal decomposition (POD) to reduce the dimensions, POD in this article is employed to measure the degree of the correlation between two deterministic time series. Conventionally, wind speeds are decomposed to a time-varying mean speed and a nonstationary fluctuating speed by virtue of wavelet shrinkage [7]. Time-varying mean speeds are in the largest scale, which are essentially due to translations of storms and radial velocities of spreading flow. It was observed that the time-varying standard deviations [7] of fluctuating speeds are basically driven by time-varying mean speeds other than small-scale turbulence. Therefore, time-varying standard deviations are considered in the medium scale. Finally, the modulated fluctuating speeds are viewed in the smallest scale and due to small-scale turbulence. It is found that (1) the two lateral profiles are fully correlated and almost evenly spatially distributed in the largest and medium scales with more than 96% of the total energy; (2) they are uncorrelated in the smallest scale since the measurement locations are at least 263 m apart.     

集值优化问题全局真有效解集的连通性

在局部凸空间中给出了集值向量优化问题全局真有效解的连通性定理,该定理是在可行域为弧连通紧的,目标函数为C-弧连通的集值映射的条件下得到的.     

三思而行——记四川省雅安市名山县涌泉村抗震小学设计

为推广有效适用的抗震建造技术和有益经验,中国四川省雅安市名山县涌泉村试点建立一所抗震示范小学.建筑师试图运用抽象化的建筑语言隐喻儿童记忆中的折纸游戏,创建一个童真的卡片模型.     

Proper orthogonal decomposition based algorithm for detecting damage location and severity in composite beams

A damage detection algorithm based on the proper orthogonal decomposition technique that can be used for structural health monitoring is presented in this study. The proper orthogonal modes are employed as dynamical invariants to filter out the influence of operational/environmental variation in the dynamic response of the structure. Finite element models of a healthy and damaged carbon/epoxy composite beam are used to generate vibration data. Varying levels of stiffness reduction for the elements in the damaged zone of the structure are used to simulate impact damage. Three damage locations (center of beam, fixed end, and free end) with three damage cases for each location are investigated. Different random force inputs are used to introduce variations in the loading conditions of the beam. The results show that the developed algorithm is capable of detecting both location and severity of damage even under changing loading conditions, with a high level of confidence.     

Assessment of a composite beam finite element based on the proper generalized decomposition

In this paper, a finite element based on the Proper Generalized Decomposition (PGD) is presented for the analysis of bi-dimensional laminated beams. The displacement field is approximated as a sum of separated functions of x (axial coordinate) and z (transverse coordinate). This choice yields to an iterative process that consists of computing a product of two one-dimensional functions at each iteration. The capability and the behavior of the PGD approach are shown on isotropic beam with different slenderness ratios. A second and fourth-order expansion with respect to the thickness are considered. Mechanical tests for thin/thick laminated and sandwich beams are presented in order to evaluate the two approaches. They are compared with elasticity and 2D finite element reference solutions.     

基于POD-RBF降阶模型的超高温气冷堆DLOFC事故温度时空分布计算方法

超高温气冷堆（VHTR）具有核能制氢等广泛的应用领域,失冷失压（DLOFC）事故是VHTR后果最严重的设计基准事故之一,而利用全阶模型（FOM）进行大量不同参数下的DLOFC事故特性分析需要消耗大量的计算资源。对设计参数范围内的不同方案进行基于降阶模型（ROM）的DLOFC事故的快速、准确计算具有重要需求和意义。本文利用TINTE程序建立了VHTR的FOM,基于本征正交分解-径向基函数插值（POD-RBF）方法实现了一个快速计算VHTR-DLOFC事故的ROM,并给出了两种方法来实现ROM的瞬态过程计算,方法1将时间等同于入口温度等输入参数;方法2对于同一参数下的不同时间步的系数整体进行计算。结果表明,两种ROM方法的计算结果最大相对误差均低于1%,且ROM计算效率远高于FOM;同时方法2的计算效率是方法1的40倍。因此,ROM可以为VHTR设计参数的优化工作提供快速计算程序。