环境激励下冷却塔结构模态测试与阻尼比特性研究

现行冷却塔结构阻尼比均借鉴荷载规范中钢筋混凝土的5%取值,考虑到冷却塔结构自身构型和材料属性,在理论上其真实阻尼比应小于规范值;阻尼比作为风与地震动力分析的重要输入参数,其取值大小将直接影响冷却塔抗风及抗震安全性,然而,现阶段国内外均缺乏大型冷却塔的现场实测和阻尼比取值研究。选取国内8座典型塔高和塔型的冷却塔进行现场测试,获取了环境激励下塔筒典型部位的加速度响应振动信号。首先采用随机减量法和自然激励技术对实测信号进行预处理,然后结合ARMA,ITD和STD三种模态识别方法获得冷却塔前10阶结构自振频率和阻尼比,并将实测值与有限元结果进行对比和误差分析,再借鉴振型组合的思路推荐了8座测试塔的等效综合阻尼比,最后给出了以基频为目标函数的前10阶模态阻尼比和等效综合阻尼比的估算公式。研究表明,8座冷却塔实测频率与有限元分析结果较为一致,基频最大相差为4.4%;阻尼比识别结果分布较为离散,前10阶模态阻尼比最大为2.86%;8座测试塔的综合等效阻尼比范围均在1.13%-2.16%,误差分析结果表明本文提出的阻尼比拟合公式精度高、稳定性好。     

Entanglement sudden birth and sudden death in a system of two distant atoms coupled via an optical element

An investigation is reported of the collective effects and the dynamics of atom–atom entanglement in a system of two distant two-level atoms which are coupled via an optical element. In the system under consideration, the two atoms, which are trapped in the foci of a lens, are coupled to a common environment being in the vacuum state and they emit photons spontaneously. A fraction of the emitted photons from each atom is thus focused on the position of the other atom. The presence of optical element between two distant atoms leads to the occurrence of delayed collective effects, such as delayed dipole–dipole interaction and delayed collective spontaneous emission, which play the crucial role in the dynamical behaviour of the entanglement. We discuss the phenomena of entanglement sudden birth, entanglement sudden death, and revival of entanglement for both cases of initial one-photon and initial two-photon unentangled atomic states. We show that the evolution of the entanglement is sensitive not only to the interatomic distance but also to the initial state of the system as well as to the properties of the optical element.     

燕子掌微弱电信号的计量研究

利用自制的屏蔽室和屏蔽箱以及自制的铂金传感器接触式微弱电信号测试仪,初次获得了燕子掌(Crassula portulacea)自适应微弱电信号特性.采用小波软阈值消噪法对测试电信号进行消噪,并进行了时间序列的高斯径向基函数(RBF)神经网络预测.结果表明,采用RBF人工神经网络对植物微弱电信号进行短期预测是可行的.实现预测是在温室和/或塑料大棚生产中建立植物自适应智能化自动控制系统的关键环节.     

Kalman filter-based force estimation in a clamped plate using reduced order model and noisy measurements

Deterministic techniques are available for force estimation in dynamic systems in time, frequency, and modal domain. But, these techniques are susceptible to measurement noise and require an accurate model of the system, hence, are not suitable for precise force estimation. Some combined deterministic-stochastic approaches are available in the literature for unknown input force estimations, where force estimations are performed by considering the model uncertainty and measurement noise. In the present work, one such technique is extended by incorporating reduced-order model to estimate forces in of plate structures. Kalman filter and a recursive least-squares (KF-RLSE)-based technique which uses displacement and/or velocity measurements for force estimation is used in the present work with a reduced-order model. Time-varying unknown forces acting at single/multiple locations are reconstructed using the measured responses from the plate. Numerical simulation followed by experimental verification is presented. The effect of error in model parameters on the force estimation is presented, and robustness of the input estimation technique is tested for different levels of measurement noise.     

Performance of a QAM/FSO communication system employing spatial diversity in weak and saturation turbulence channels

In this paper, the bit error rate (BER) performance and outage probability of quadrature amplitude modulation free space optical (QAM/FSO) communications with spatial diversity in turbulent environments are investigated. The equal-gain combining (EGC) and selection combining (SelC) diversity techniques are considered to mitigate turbulence-induced signal fading in the proposed system. The average BER and outage probability expressions are derived for EGC diversity in weak and saturation turbulence channels. The results indicate that using EGC diversity can significantly improve the system performance compared to employing the SelC diversity or single monolithic aperture schemes. Specifically, approximately 4 and 9?dB lower signal-to-noise power ratios are required for the 1?×?4 EGC diversity system than for the 1?×?4 SelC and non-diversity systems at a BER of 10^?10. In addition, the use of diversity techniques also significantly decreases the outage probability. The proposed scheme can be helpful for establishing a spatial diversity FSO system with a low error rate and high transmission rate.     

An extended Galerkin weak form and a point interpolation method with continuous strain field and superconvergence using triangular mesh

A point interpolation method (PIM) with continuous strain field (PIM-CS) is developed for mechanics problems using triangular background mesh, in which PIM shape functions are used to construct both displacement and strain fields. The strain field constructed is continuous in the entire problem domain, which is achieved by simple linear interpolations using locally smoothed strains around the nodes and points required for the interpolation. A general parameterized functional with a real adjustable parameter α are then proposed for establishing PIM-CS models of special property. We prove theoretically that the PIM-CS has an excellent bound property: strain energy obtained using PIM-CS lies in between those of the compatible FEM and NS-PIM models of the same mesh. Techniques and procedures are then presented to compute the upper and lower bound solutions using the PIM-CS. It is discovered that an extended Galerkin (x-Galerkin) model, as special case resulted from the extended parameterized functional with α = 1, is outstanding in terms of both performance and efficiency. Intensive numerical studies show that upper and lower bound solutions can always be obtained, there exist α values at which the solutions of PIM-CS are of superconvergence, and the x-Galerkin model is capable of producing superconvergent solutions of ultra accuracy that is about 10 times that of the FEM using the same mesh.     

Tripartite entanglement generation using cavity-QED and its dynamics in dissipative environments

We investigate the generation of tripartite field states inside the high-Q cavities using the cavity QED. The main goal is to successfully generate the entanglement in tripartite systems by passing two-level atoms through three identical high-Q cavities. Our scheme gives the successful generation of entangled tripartite W and GHZ states for pre-determined interaction times of atoms with the cavity fields. The dynamics of initial entangled states is studied as the system evolves in the dissipative environments.     

Comparisons of Kt/V evaluated using an online method and calculated from urea measurements in patients on intermittent hemodialysis

Kt/V(urea) (Kt/V) depends on the method applied for its evaluation. Our aim was to compare Kt/V obtained using the conductivity online method and that calculated from urea measurements. Studies were carried out in 40 patients. A stable dialysis schedule was maintained during the study. Online Kt/V was measured every week or 4 consecutive months. Single pool Kt/V (spKt/V) was calculated from urea estimations in the fourth week of the first month and in the last week of the fourth month of studies, using the formulas: (1)spKt/V = -ln(Ct/Co), where Ct is the postdialysis urea concentration obtained at the end of dialysis, Co the predialysis urea concentration obtained before the start of the blood pump; (2)spKt/V = -ln(R - 0.008 x t - f x UF/W), where R is the Ct/Co, t the duration of HD session, f=1.0, UF is the ultrafiltration volume (l), W is the body weight after the HD session; and (3)spKt/V + -ln(R - 0.008 x t) + (4 - 3.5 x R) x UF/W. The equilibrated Kt/V (eKt/V) was calculated as (3)spKt/V - {0.47 x [(3)spKt/V]/t} + 0.02. Correlation analysis was performed between all obtained Kt/V. Weekly online Kt/V was stable during 4 months of studies. In the first month, the respective values of online Kt/V, (1)spKt/V, (2)spKt/V, (3)spKt/V, and eKt/V were 1.15+/-0.14, 1.16+/-0.14, 1.38+/-0.17, 1.36+/-0.20, and 1.22+/-0.13. In the fourth month, these values were 1.17+/-0.14, 1.16+/-0.17, 1.38+/-0.22, 1.35+/-0.20, and 1.22+/-0.18. The respective values of Kt/V, estimated in the first and fourth month, were not different and showed a positive correlation: the highest one occurred between online Kt/V estimated at the indicated study periods (r=0.713, p=0.0000). Online Kt/V was significantly lower than (2)spKt/V, (3)spKt/V, and eKt/V. Correlation coefficients between online Kt/V, spKt/V, and urea reduction ratio did not exceed 0.490. Our studies show that Kt/V obtained using online monitoring indicates a lower intermittent hemodialysis adequacy that those calculated from urea measurements. This difference has to be remembered in application of results to clinical practice.     

Temperature determination by solubility measurements and a study of evaporation of volatile components in LPE

When growing different structures by LPE it is necessary to know exactly the temperature on the boundary between the liquid and solid phases. That temperature can not be measured directly by a thermocouple because normally it is located at some distance from this boundary and in any LPE system there are always unknown temperature gradients. However the interface temperature and its distribution along the LPE boat can be determined by solubility measurements. The accuracy of such measurements will be affected by several factors and phenomena. One of such effects is related to the evaporation of volatile components. In this work we have used In–P liquid solutions and its phase diagram to determine the temperature distribution along an LPE boat and have also studied the effect of phosphorus evaporation. It is shown that phosphorus evaporation can be neglected for temperatures under 650°C but at higher temperatures it is significant.     

The relationship between yield and flow time in a production system under inspection

This work studies the relationship between Yield and Flow Time (FT) in a production system monitored by in-line inspection. It originates in the known semiconductors Yield vs. FT trade-off premise, but can be adapted to other industries. We challenge the common premise, and suggest an alternate analytical model to demonstrate this relationship. The model relies on a simplified production system that represents a repetitive segment in a production line. It illustrates that rising inspection rate increases both Yield and FT while exhibiting a trade-off. However with further growing inspection rate the Yield reaches a maximum and then starts to decline, while FT continues to increase. The Yield decline is explained by longer delay of inspection results which trigger the repair of an out-of-control machine. Clearly, lower Yield performance and higher FT are undesired. Our work defines this relationship with the analytical model and validates it with simulation. The model can be embedded in a decision support tool to pre-determine the inspection policy, while simultaneously considering Yield and FT.     

Performance evaluation and capacity planning in a metallurgical job-shop system using open queueing network models

In this paper, we apply performance evaluation and capacity allocation models to support decisions in the design (or redesign) and planning of a job-shop queueing network of a metallurgical plant. Approximate parametric decomposition methods are used to evaluate system performance measures, such as the expected work-in-process (WIP) and production leadtimes. Based on these methods, optimisation models are then applied for the allocation (or reallocation) of capacity to the stations of the job-shop network. These models are also used to generate approximate trade-off curves between capacity investment and WIP or leadtime, which are valuable for a production manager to estimate how much capacity should be allocated to the stations to reach some targeted performance measures. These curves are also useful for the sensitivity analysis of the solutions to changes in the input parameters, such as the variability of the product demands, the mix of the production and the throughput rate of the network.     

On the diagnostics of regular and chaotic motion regimes in a dynamic system using the number of states function

A method for determining the type of dynamic behavior is suggested. The method, based on constructing a function of the number of states of a system, is intended for diagnostics of the laminar and turbulent phases of motion in a system.     

Fatigue crack growth in a structural steel under single and multiple periodic overload cycles

Preliminary results of a research program on fatigue crack growth in a low-carbon steel under a variable amplitude loading are presented. First, test results are reported on crack growth under simple loading sequences containing single and multiple tensile overloads applied periodically between smaller, constant amplitude cycles. Next, the observed crack growth behaviour is compared to predictions from a theoretical model developed by the authors.     

Diffusion measurements on a liquid monotectic alloy PbGa using the shear cell technique under µg in the foton-M2 mission and under 1G

Diffusion experiments of a liquid monotectic alloy PbGa were performed under 1g-conditions at 623, 773 and 903K, and under µg-conditions at 903K. As a measurement tool the shear cell specially designed for Russian satellite Foton missions within the AGAT-furnace was used to have a homogenization time before the diffusion and to avoid the influence of decomposition into two liquid phases during cooling-down. The experiment type was diffusion from a thick layer of PbGa5at% into pure Pb. The liquid sample in the capillary was pressurized using a reservoir system in order to minimize Marangoni convection. In 1g-experiments the diffusion axis was arranged vertically and the sample was set such that the density increases monotonously parallel to the gravity vector in order to suppress buoyancy convection. Four experiments were performed simultaneously for each set-up. The µg-experiment was performed in the AGAT facility during the Foton-M2 mission (June 2005) where one capillary was assigned for the PbGa-Pb experiment (PbGa was containing an enriched Pb-isotope tracer). The concentration profiles were obtained by AAS (1g) and by ICP-MS (µg). The diffusion coefficients were evaluated by fitting with the thick layer solution. For the evaluation a correction method was used for the shear convection and the averaging effect inside each cell. As a result, the obtained concentration curves agreed well with the fitting function. The reproducibility of the diffusion coefficients among four parallel 1g-experiments was good with a standard deviation among four capillaries smaller than 5.5% including the standard temperature deviation. The diffusion coefficients agreed well between 1g- and µg-experiments. The temperature dependence of the diffusion coefficients could be fitted well to a power law with an exponent about 2.4. From these results we conclude that the 1g-experimental method in this study for diffusion measurement is effective also for monotectic systems.     

Forward and backward risk assessment throughout a system life cycle using dynamic Bayesian networks: A case in a petroleum refinery

In this paper, risk modeling was conducted based on the defined risk elements of a conceptual risk framework. This model allows for the estimation of a variety of risks, including human error probability, operational risk, financial risk, technological risk, commercial risk, health risk, and social and environmental risks. Bayesian network (BN) structure learning techniques were used to determine the relationships among the model variables. By solving a bi-objective optimization problem applying the genetic algorithm (GA) with the Pareto ranking approach, the network structure was learned. Then, risk modeling was performed for a petroleum refinery focusing on HydroDeSulfurization (HDS) technology throughout its life cycle. To extend the model horizontally and make it possible to evaluate the risk trend throughout the technology life cycle, we developed a dynamic Bayesian network (DBN) with three-time slices. A two-way forward and backward approach was used to analyze the model. The model validation was performed by applying the leave-one-out cross-validation method.     

Mathematical and methodological principles in using a constructive residue theorem in processing measurements

New methods in computational mathematics are considered in application to personal computers and microprocessor computing. Advantages are demonstrated in the nontraditional theory of finite fields, which is based on a constructive theorem on residues. __________ Translated from Izmeritel’naya Tekhnika, No. 10, pp. 18–21, October, 2006.     

Non‐weak/strong solutions in gas dynamics: a C11 p‐version STLSFEF in Lagrangian frame of reference using ρ, u,p primitive variables

In this paper, we present computations of the non‐weak solutions of class C¹¹ of transient Navier–Stokes equations for compressible flow in Lagrangian frame of reference using space‐time least squares finite element formulation with primitive variables ρ, u, p. For high speed compressible flows the solutions reported here possess the same orders of continuity as the governing differential equations. The role of diffusion i.e. viscosity (physical or artificial) and thermal conductivity on shock structure is demonstrated. Compression of air in a rigid cylinder by a rigid, massless and frictionless piston is used as a model problem. True time evolutions of class C¹¹ are reported beginning with the first time step until steady shock conditions are achieved. Comparisons with analytical solutions are presented when possible. Copyright © 2001 John Wiley & Sons, Ltd.     

Residual stress measurements in a cruciform welded joint using hole drilling and strain gauges

Residual stress measurements were made close to the toe of each fillet weld on a load carrying cruciform welded specimen by the hole drilling technique. A standard milling guide with high speed air turbine was used in conjunction with bonded resistance strain gauge rosettes. Experimental calibrations of the method were conducted under known uniform uniaxial tension loads.
A simple incremental drilling technique was used to determine the stress gradient with hole depth. Measurements were also made both at zero load and known tensile loads in order to study the interaction between residual stresses and the applied loads.