共查询到20条相似文献,搜索用时 15 毫秒
1.
2.
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 Hc2 for the superconductor. 相似文献
3.
Mark A. Norris Leonard Meirovitch 《International journal for numerical methods in engineering》1989,28(10):2451-2463
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. 相似文献
4.
5.
Michael Johlitz Stefan Diebels Jan Batal Holger Steeb Wulff Possart 《Journal of Materials Science》2008,43(14):4768-4779
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.
相似文献
Holger SteebEmail: |
6.
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. 相似文献
7.
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。 相似文献
8.
Wieslaw J. Oledzki 《中国工程学刊》2018,41(4):333-341
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. 相似文献
9.
10.
11.
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。 相似文献
12.
13.
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。 相似文献
14.
15.
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 相似文献
16.
Yun Mei Luo Luc Chevalier Eric Monteiro 《International Journal of Material Forming》2014,7(3):359-367
The mechanical response of Polyethylene Terephthalate (PET) in elongation is strongly dependent on temperature, strain and strain rate. Near the glass transition temperature Tg, 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. 相似文献
17.
结构振动台模型模态参数识别新方法研究 总被引:3,自引:0,他引:3
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。 相似文献
18.
19.
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. 相似文献