AC losses in a composite tubular superconductor for power transmission

AC losses have been measured as a function of current and temperature in a 63.5 mm diameter niobium/copper composite tube, forming the inner conductor of a co-axial superconducting transmission line. The conductor has a 2.6 mm thick substrate of high-conductivity copper with a 50 μm thick niobium surface layer bonded by co-extrusion and cold-drawing. Closed-cycle refrigeration allowed losses to be measured as a continuous function of temperature between 4.4 and 8.0 K for surface current densities between 23 and 89 A mm^?1. Losses were less than 0.1 W m^?2 at 5 K for surface current densities less than 50 A mm^?1, and obeyed approximately the empirical relation: loss ∝ h⁷ where h is the ratio of surface current density to H_c2 for the superconductor.     

On the problem of modelling for parameter identification in distributed structures

Structures are often characterized by parameters, such as mass and stiffness, that are spatially distributed. Parameter identification of distributed structures is subject to many of the difficulties involved in the modelling problem, and the choice of the model can greatly affect the results of the parameter identification process. Analogously to control spillover in the control of distributed-parameter systems, identification spillover is shown to exist as well and its effect is to degrade the parameter estimates. Moreover, as in modelling by the Rayleigh–Ritz method, it is shown that, for a Rayleigh–Ritz type identification algorithm, an inclusion principle exists in the identification of distributed-parameter systems as well, so that the identified natural frequencies approach the actual natural frequencies monotonically from above.     

基于R-SOBI的结构模态参数辨识方法

提出了一种基于稳健SOBI算法提取结构/系统的频率、阻尼比及模态振型的方法。运用该法提取系统/结构模态参数的步骤为:首先利用稳健SOBI的盲源分离方法采集的信号进行分离,然后将分离矩阵作为结构/系统的模态振型矩阵,最后再对各个分离后的单自由度信号提取频率、阻尼比参数。研究结果表明,提出的方法可以准确提取出结构/系统的模态参数,尤其是即使噪声环境下仍然能准确提取出系统的模态振型矩阵。     

Size effects in polyurethane bonds: experiments, modelling and parameter identification

In this study we examine polyurethane bonds of varying thickness between anodised aluminium substrates. The performed shear tests showed an intriguing size effect of the kind “thinner equals softer”. This size effect occurs not only in the basic elasticity (relaxed state), but also in the viscoelastic behaviour of the tested material. The cause of such size effects is supposed to be found in the existence of so-called interphases or boundary layers, which may differ considerably from the bulk in terms of mechanical behaviour, thus having an enormous impact on thin bonds. In thick bonds, however, these interphases or boundary layers have a minor effect on the overall mechanical behaviour. To account for these experimental results in bond modelling, an extended phenomenological continuum mechanics-based model, which explicitly includes such size effects in its calculation, is developed and presented. For this purpose, an abstract structure parameter with its corresponding balance equation is established describing the formation of the interphases by means of a phase transition. This makes it possible to define the bond stiffness at a macroscopic level, without entering into the microstructure. The extended model brings up a set of model parameters, which are determined efficiently by an ES (evolution strategy). The study concludes with a summary and an outlook on our further research work.

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A novel method of reducing iron losses in power transformer cores

A method is described in which the iron loss of single phase transformer cores constructed from grain-oriented silicon-iron can be reduced. It is shown in two different sized cores that by assembling the limbs with laminations cut at small angles to the rolling direction (RD) of the steel, and stacked in a certain way, the loss can be reduced. Reductions of up to 6 percent were achieved in cores assembled from high permeability steel.     

应变功率谱密度传递比与工作应变模态参数识别EI北大核心CSCD

选取一个应变响应测点作为参考点,定义了响应应变功率谱密度传递比(Strain Power Spectrum Density Transmissibility,SPSDT),从理论上证明了SPSDT在系统的极点处为应变振型系数之比。利用这一性质,选取一系列不同的参考点构造响应应变功率谱密度传递比矩阵,在系统的极点处对该矩阵进行奇异值分解,分解所得左奇异矩阵的第一列向量即为应变振型,从而实现结构工作应变模态参数的识别。与传统的工作模态分析方法相比,SPSDT方法不需要对激励做白噪声假定,不需要多种激励类型,仅在一种激励下即可识别出结构的工作应变模态参数。通过数值模拟算例和实验室模型试验验证了所提出方法的有效性,并与传统的频域分解法和随机子空间识别方法进行了比较,验证了所提出方法是有效的。最后分析了采样时长对识别结果的影响,结果表明该方法仅用1min时长数据即可达到稳定的识别精度,具有较好的鲁棒性。     

Split power hydro-mechanical transmission with power circulation

This paper presents a novel hydrodynamic-mechanical split power transmission (US patent application No. 15695671, and PL patent application No. P.422664) with an exceptionally large torque ratio and torque ratio growth rate, and a potentially wide range of (continuous and naturally automatic) torque ratio variation. The transmission features a strong positive feedback between rotors of the impeller and turbine, and makes a systematic use of power circulation (which is present in all transmissions using a hydrodynamic torque converter). The transmission is particularly suitable for vehicles and working machines operating in a start–stop mode and those subjected to heavy, fast-changing external loads, like city buses, wheel and track loaders, dozers, farm tractors, and small earth-moving machines, and most of all for emergency, military, and sports vehicles, where good acceleration is of the highest priority.     

结构物理参数识别的贝叶斯估计马尔可夫蒙特卡罗方法

从结构动力特征方程出发,以结构主模态参数为观测量,推得结构物理参数线性回归模型。对该模型应用贝叶斯估计理论得到物理参数后验联合分布,再结合马尔可夫蒙特卡罗抽样方法给出各个物理参数的边缘概率分布和最优估计值,而提出了基于结构主模态参数的结构物理参数识别贝叶斯估计马尔可夫蒙特卡罗方法。对五层剪切型结构的数值研究表明,此方法能够利用少数主模态参数给出结构质量和刚度参数的概率分布和最优识别值,而且在主模态参数较准确时识别误差很小。     

基于改进确定-随机子空间算法的桥梁结构模态参数识别

为了实现桥梁结构模态参数的智能化在线跟踪识别,提出了一种基于滑窗技术、模糊C均值聚类算法与确定-随机子空间算法的时域识别(SC-CDSI)算法.对桥梁结构的输入信号和输出信号进行加窗划分处理,分析了窗函数、窗口大小及窗口步长的确定标准;将频率、阻尼比及模态振型作为模糊C均值聚类算法的聚类元素完成对稳定图中有效模态的智能...     

改进的受力状态映射法在结合部动力学参数辨识中应用

针对受力状态映射法作为辨识非线性结合部参数重要方法具有物理意义明确、辨识准确等特点,而实际辨识试验时结构某些参数难以测定、致辨识过程困难等问题,提出结合子结构模态综合法的受力状态映射法,可有效解决该问题。参数辨识过程中对模型易出现的缺失项及冗余项,利用基于TSVD(Truncated Singular Value Decomposition)正则化方法的模型迭代修正法。仿真模型表明,修正模型较精确模型误差小、辨识精度高。通过对导轨结合部进行参数辨识实验研究,证明辨识方法的有效性及准确性。     

迟滞非线性系统参数识别方法的研究

迟滞非线性既是非线性的,又是非解析的,关于它的参数识别一直是人们关注却又难以解决的问题,本文提出 了一种较好的识别迟滞非线性系统参数的方法,就是根据实测得到的系统输入－输出数据来直接识别系统的物理参数。     

基于粒子群算法的改进模态参数识别方法

针对一类多模态振动衰减信号的模态参数识别,结合奇异值分解(singular value decomposition,SVD)、解析模态分解(analytical mode decomposition,AMD)、自回归功率谱和粒子群优化(particle swarm optimization,PSO)算法,提出了一种改进...     

Finite-element method for power losses calculation in longrectangular conductors located in transverse harmonic magneticfield

A method is presented for calculation of the Joule power losses in a long linear isotropic nonferromagnetic rectangular conductor located in a harmonic transverse magnetic field that is situated in a homogeneous environment. The method links two others: the method of finite elements (for the internal region) and the separation of variables method (for the external region). On the basis of the obtained relationships, numerical calculations were performed, and plots of Joule power losses for the rectangular conductors were made     

Basis for viscoelastic modelling of polyethylene terephthalate (PET) near Tg with parameter identification from multi-axial elongation experiments

The mechanical response of Polyethylene Terephthalate (PET) in elongation is strongly dependent on temperature, strain and strain rate. Near the glass transition temperature T_g, the stress vs strain curves present a strain hardening effect vs strain under conditions of large deformations. At a given strain value, the strain rate has also an increasing influence on the stress value. The main goal of this work is to propose a visco-elastic model to predict the PET behaviour when subjected to large deformations and to determine the material properties from the experimental data. The visco-elastic model is written in a Leonov like way and the variational formulation is carried out for the numerical simulation using this model. To represent the non–linear effects, an elastic part depending on the elastic equivalent strain and a non-Newtonian viscous part depending on both viscous equivalent strain rate and cumulated viscous strain are tested. The model parameters can then be accurately obtained through the comparison with the experimental uniaxial and biaxial tests.     

结构振动台模型模态参数识别新方法研究

提出了一种结构振动台模型模态参数识别方法,利用结构模型试验过程中地震反应记录,识别结构模型模态参数。首先判断结构模型在地震动激励下发生的是非时变反应还是时变反应,当结构模型发生非时变反应时,采用整个反应记录数据识别模型参数;当结构模型发生时变反应时,则识别模型进入和退出时变反应的时刻点,将整个记录时程分为3段,采用模型退出时变反应后第三段数据识别参数。该方法可以识别试验中每一次地震动输入之后的结构模态参数,得到整个试验过程中结构模型动力特性变化情况。利用所提方法识别了一座12层钢筋混凝土框架结构模型模态参数,并将识别结果和白噪声输入下模态分析结果进行了对比,验证了方法的实用性、可靠性和准确性。结果发现:结构模型自振频率在整个试验过程中呈阶梯状下降,模型发生破坏后,频率降低,阻尼比增加,传递函数幅值随着输入地震动峰值增加而降低。     

基于非线性振动的斜拉索参数识别无模型方法

基于非线性振动理论提出了斜拉索参数识别的无模型方法.该方法以由奇异摄动法所获得的斜拉索自振频率解析表达式为依据,根据斜拉索频率测试结果和计算值之差构建目标函数,将斜拉索索力、索长等关键参数作为待识别参数,采用最优化方法实现参数识别.通过试验验证了方法的有效性并和有模型方法的识别结果进行了对比.研究表明,所提出的方法可以显著提高斜拉索动力响应分析结果的准确性;无模型方法和有模型方法精度相当.而无模型方法在求解效率、方法的易用性等方面更具优越性,更便于实际工程应用.     

Hysteresis parameter identification with limited experimental data

The Preisach operator and its variants have been successfully used in the modeling of hysteresis observed in ferromagnetic, magnetostrictive, and piezoelectric materials. However, in designing with these "smart" materials, one has to determine a density function for the Preisach operator by using the input-output behavior of the material at hand. In this paper, we describe a method for numerically determining an approximation of the density function when there is not enough experimental data to uniquely solve for the actual density function by Mayergoyz's method. We present theoretical justification for our method by establishing links to regularization methods for ill-posed problems. We also present numerical results where we estimate an approximate density function from data published in the literature for a magnetostrictive actuator and two electroactive polymers.     

多点激励模态参数识别方法研究进展

在回顾多点激励模态参数识别方法理论和应用的最新进展基础上,重点针对基于响应数据的多点激励参数识别法在模态参数识别中的应用进行了分析和总结。按对激励信号模型假设不同:基于白噪声的平稳随机激励假设和非平稳随机激励假设下多点激励模态参数识别技术分别进行深入的讨论。最后,对多点激励参数识别方法的发展前景进行了探讨和展望。