Material selection for the torque tubes of large superconducting rotating machinery

This report identifies properties to be considered when selecting materials used in construction of torque tubes for rotating superconducting field windings in electrical machinery.The main design requirements are stated and the groups of material properties that influence directly the mechanical and thermal performance of a torque tube are derived. Most desirable is a low thermal conductivity to modulus of elasticity ratio which governs the refrigeration expenses and the tube wall aspect ratio (thickness/length). Numerical examples point out that fibre-reinforced plastics are potential candidates for use in torque tubes.     

Modified Roebuck compression device for cryogenic refrigeration system of superconducting rotating machine

Cryogenic refrigeration system installed on superconducting rotor has the merit that it can eliminate cryogen transfer between rapidly revolving rotor and stationary part and, therefore, the loss generated by it. Nevertheless, such an on-board cryogenic refrigeration system has not been realized yet because of the absence of compression device that can work reliably on rapidly revolving rotor. This paper presents the idea of modified Roebuck compression device as a potential on-board compression device. Although it has the disadvantage that it requires large radial space and external cooling and heating, a modified Roebuck compression device of 14 stages with diameter of 0.80 m mounted on a rotor revolving at 3600 rpm can produce substantially high compression ratio. J-T neon refrigeration system equipped with such a compression device can produce low temperature of 30 K and be useful for cooling superconducting rotor windings made of high temperature superconductor.     

Optimization of refrigeration machinery

This paper reports the application of thermoeconomics to the optimization of a heat pump. The method is suited for application to thermodynamic processes and yields exergy losses. The marginal cost of an arbitrary variable can also be calculated. The efficiencies of the compressor, condenser, evaporator and electric motor are chosen as variables to be optimized. Parameters such as the price of electricity and the temperature of the delivered heat may vary between optimizations, and results are presented for different parameter values. The results show that the efficiency of the electric motor is the most important variable.     

Design considerations for refrigeration cycles

The Carnot COP, which assumes a thermodynamically ideal cycle in which no irreversibilities exist, is often considered to be a design goal for actual cycles. However, the Carnot COP does not consider heat transfer mechanisms. Heat transfer at a finite rate is necessarily an irreversible process and unavoidable in a refrigeration cycle. The lack of consideration of rate processes reduces the usefulness of the Carnot COP as a realistic design goal. In this paper, the limitations of both thermodynamics and heat transfer are considered to identify a more realistic design goal for the COP of refrigeration cycles. The consideration of heat transfer limitations leads to a design rule for the optimum distribution of heat exchange area between the low- and high-temperature heat exchangers.     

Thermodynamic properties of superconducting iridium

The superconducting transition temperature of pure Ir is found to be 0.1125 K (±0.0005 K). The critical magnetic field as a function of temperatureH _c(T) has also been measured. From these data it is determined thatH _c(0) is 16.00 G (1 G corresponds to 10^–4 T), (dH _c/dT)_T=Tc is 235 G/K, the linear coefficient of normal state electronic specific heat is 3.19 mJ/mole-K², and the energy gap anisotropy parameter a ² is 0.048. This value for a ² is the largest of any superconducting element so far observed, and its significance in determining the superconducting properties of Ir is discussed. By using the large supercooling effects noticed nearT _c, the Ginzburg-Landau parameter x₀ is found to be 8.6×10^–3. The effects of impurities onT _c and on the magnetic behavior of Ir are also discussed.     

Thermodynamic properties of superconducting niobium

The thermodynamic properties of superconducting Nb are calculated numerically from the solution of the Eliashberg equations on the imaginary axis for several possible electron-phonon spectral densities ²()F(). Comparison with experiment is made in order to see which spectrum gives the best agreement, and functional derivatives with respect to ²()F() are used to estimate how this agreement might be improved by small changes in ²()F(). Possible gap anisotropy effects are also considered with the help of a simple model anisotropy for the interaction.Research supported by Natural Science and Engineering Research Council of Canada.     

Thermodynamic stability of superconducting magnetic states

The different magnetic states of superconductors are characterized by extensive and intensive parameters. The elements of the entropy matrix are determined from the derived total entropy density, which contains all possible interactions. The element of the conductivity matrix characterizing the vortex motion is also evaluated. Stability criteria for the Meissner, flux creep, and flux flow states and the value of the needed external generation are given, as are the nonequilibrium deviations, thermodynamical forces, currents and entropy productions for the different cases. The nature of the unstable flux jump state is discussed.     

旋转机械系统碰摩故障的失效灵敏度研究

针对仅考虑质量偏心的Jeffcott转子碰摩故障的动力学方程,进行了旋转机械系统的碰摩失效灵敏度分析,应用Kronecker代数,矩阵微分理论,四阶矩技术,矩阵摄动理论,概率统计方法,可靠性理论和灵敏度技术系统地发展了转子系统碰摩的可靠性灵敏度分析方法,研究了转轴刚度和阻尼、偏心距和定子的刚度对可靠度和可靠性灵敏度的影响,并给出了数值分析解。     

Refrigeration for rotating superconducting windings of large ac electric machines

The rotating superconducting windings of large ac machines must be supplied with enough refrigeration at an adequate temperature. The problems associated with bringing liquid helium to the rotating winding structure are analysed. Existing designs as well as newly proposed systems are used to draw the general guidelines for the design concepts of cooling systems for rotating superconducting windings.     

无转速计的旋转机械Vold-Kalman阶比跟踪研究

结合旋转机械升降速阶段振动信号的特点,提出了一种无转速计的旋转机械Vold-Kalman阶比跟踪方法。该方法利用能量重心法对振动信号进行频谱校正,估计瞬时频率,获得参考轴转速信号,再对振动信号进行Vold-Kalman阶比跟踪,提取阶比分量。与需要转速计的经典Vold-Kalman阶比跟踪方法相比,该方法无需鉴相装置,完全用软件方式实现,算法精度高。仿真和应用实例分析结果表明此方法能够在时域中准确地提取幅值和频率变化的阶比分量。     

Thermodynamic modelling and parameter determination of ejector for ejection refrigeration systems

This paper presents a detailed thermodynamic modelling method of an ejector for ejection refrigeration system. In this model, the primary flow in the ejector was assumed to fan out from the nozzle without mixing with the secondary flow in a certain downstream distance, so that a hypothetical throat was formed where the secondary flow reached the sound speed. However, the area of this hypothetical throat remained unknown. Therefore, based on several sets of experimental results, the present study developed empirical correlations of the hypothetical throat area to aid further modelling. The ratio of the hypothetical throat area to the mixing area was correlated with two dimensionless variables: one was the ratio of nozzle throat area to the mixing area, and the other one was the primary and secondary flow pressure ratio. The model has been validated by the measured primary mass flow rates and the critical back pressures.     

旋转机械非平稳振动信号的时频分析比较

信号分析与处理是机械故障监测与诊断中故障提取的常用方法,传统的振动故障分析方法难以满足频率随时间变化的非平稳信号的要求,联合时频分析是非平稳信号比较有力的分析工具。以转子实验台的典型振动故障信号为研究对象,分析研究了几种时频分析方法如STFT、Wigner-Ville分布、小波变换和Hilbert-Huang变换。对比结果表明:STFT和Wigner-Ville分布的时频分辨率是矛盾的,易出交叉项或使信号变得微弱;小波分解会出现多余信号;Hilbert-Huang变换的时频分析能够直观检测信号中的微弱奇异成分,清楚给出时频分布情况,为旋转机械状态监测和故障诊断提供了新的手段。     

基于ASEGMF的旋转机械振动信号降噪方法研究

针对实测振动信号易受噪声污染而淹没有用信息的问题,提出一种基于自适应结构元素广义形态滤波(ASEGMF)方法对旋转机械振动信号进行降噪处理。首先,根据待分析信号的性质,选择正弦形结构元素,并定义了结构元素的长度尺度和高度尺度。其次,根据信号局部峰值特征,定义了峰值间隔和峰值高度,结合自适应方法得到了正弦结构元素的长度尺度和高度尺度。最后,采用一小一大自适应结构元素级联而成的广义形态滤波器对振动信号进行降噪处理。该方法克服了以往形态滤波器结构元素尺寸选择的随机性,完全根据信号局部峰值特征自适应地确定结构元素,消除了人为因素的影响。仿真和实例分析结果表明,自适应结构元素广义形态滤波具有更强的降噪性能,非常适合旋转机械故障的在线监测和诊断。     

Thermodynamic stability of the superconducting phase diagram of UPt3

The superconducting phase diagram ofUPt ₃, as determined by accurate dilatometry as function of temperature and magnetic field (Bc andBc), exhibits three superconducting phases which meet in a tetracritical point. We show that the measured phase diagrams are thermodynamically stable and that all four phase lines are of second order. Via Ehrenfest relations the pressure dependence of the various phases has been determined. The so-calledC phase is the most stable phase under uniaxial pressure along the c-axis (p _c>2.5 kbar). The resulting phase diagram in thep _c -T plane yields stringent constraints on the fourth order coupling constants in the Ginzburg-Landau scenario of a vector superconducting order parameter coupled to a symmetry breaking field.     

旋转机械故障诊断的多小波分析法

本文选择 Daubechies、Coiflets、Symlets、Biorthogonal等多小波 ,对叠加有白噪声的典型旋转机械故障信号进行多分辨分析、比较 ,给出了不同分辨率下的离散近似 ,结果表明多小波比单一小波较容易而准确地获得故障特征信息     

Thermodynamic and spectral properties of ultrasmall superconducting grains

We study the problem of superconductivity in the canonicalensemble which applies to recent experiments on metallicnanoparticles. Spectral properties which can be expressed asuniversal functions allow a quantitative characterization ofthe crossover to superconductivity in finite metallicsystems. Parity effects in the ground state and excitationspectrum are discussed. We discuss the thermodynamicquantities as well. The susceptibility for odd grains shows areentrant behavior with temperature. This behavior may be anobservable signature of superconducting correlations inultrasmall grains.     

Underground production scheduling with ventilation and refrigeration considerations

Underground mine production scheduling determines when, if ever, activities associated with the extraction of ore should be executed. The accumulation of heat in the mine where operators are working is a major concern. At the time of this writing, production scheduling and ventilation decisions are not made in concert. Correspondingly, heat limitations are largely ignored. Our mixed-integer program maximizes net present value subject to constraints on precedence, and mill and extraction capacities with the consideration of heat using thermodynamic principles, while affording the option of activating refrigeration to mitigate heat accumulation. In seconds to hours, depending on the problem size (up to thousands of activities and 900 daily time periods), a corresponding methodology that exploits the mathematical problem structure provides schedules that maintain a safe working environment for mine operators; optimality gaps are no more than 15% and average less than half that for otherwise-intractable instances.

     

旋转机械故障诊断的图形识别方法研究

以旋转机械振动三维参数图形为研究对象,提出了基于图形识别技术的旋转机械故障诊断方法。该方法用表征纹理的统计法、结构法及图形纹理方向的梯度法形成描述图形纹理特征的灰度-梯度-基元三维共生矩阵。该矩阵精确地反映了图形纹理的粗糙程度、重复方向和空间复杂度及纹理方向,准确地描述了图形灰度空间分布特性(概率)、空间统计相关性和图形内各像素点梯度的分布规律。描述了灰度统计和空间结构的纹理特征,有效地提取旋转机械状态参数图形中纹理特征信息。最后,利用RBF人工神经网络实现旋转机械故障诊断。在汽轮机转子试验台上进行了6种状态试验研究,诊断结果表明该方法具有较高的诊断准确率,为旋转机械故障诊断探索了一条新路。     

旋转机械转速计算及键相脉冲处理方法

旋转机械的转速是旋转机械故障诊断中重要的参数,为了准确地获取旋转机械的转速,有效地对旋转机械进行阶次分析和计算转速谱阵,根据光电传感器采集转速信号的特点,提出了如何判断键相脉冲是否缺失,并利用线性插值方法对其修正.详细介绍了两种常见的转速计算方法,并对采集的转速键相信号进行了转速计算.经实验表明,该方法准确可行,可以准确地计算出在脉冲丢失情况下的转速,尤其是低采样率情况下,可以避免因脉冲丢失而引起的转速剧烈波动,获取准确的转速曲线.