Minimum time‐step criteria for the Galerkin finite element methods applied to one‐dimensional parabolic partial differential equations

The finite element method has been well established for numerically solving parabolic partial differential equations (PDEs). Also it is well known that a too large time step should not be chosen in order to obtain a stable and accurate numerical solution. In this article, accuracy analysis shows that a too small time step should not be chosen either for some time‐stepping schemes. Otherwise, the accuracy of the numerical solution cannot be improved or can even be worsened in some cases. Furthermore, the so‐called minimum time step criteria are established for the Crank‐Nicolson scheme, the Galerkin‐time scheme, and the backward‐difference scheme used in the temporal discretization. For the forward‐difference scheme, no minimum time step exists as far as the accuracy is concerned. In the accuracy analysis, no specific initial and boundary conditions are invoked so that such established criteria can be applied to the parabolic PDEs subject to any initial and boundary conditions. These minimum time step criteria are verified in a series of numerical experiments for a one‐dimensional transient field problem with a known analytical solution. The minimum time step criteria developed in this study are useful for choosing appropriate time steps in numerical simulations of practical engineering problems. © 2005 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2006     

弯纵复合超声直线马达的研究

本文研究了一种利用一阶纵振动和二阶弯曲振动的弯纵直线超声马达，采用加粗两端金属块的方法达到频率简并。实验测量得出一阶纵振动为36．6kHz，二阶弯曲振动频率为37．3kHz。利用该马达设计研制了一套驱动装置，经实验测得，当马达的预压力14．3N时，该装置无承载且无负载速度大于6cm／s；该装置承载196N的重物且负载l-2kgf时，仍能正常运行。     

应用微机数模转换接口控制小直流电机的转速

介绍了采用微机数模转换器接口技术实现对小直流电机转速控制的实验方案，并对实验结果进行了讨论．     

The precision improvement of the scanner in optical scanning imaging system

A disadvantage of using a galvanometer as the horizontal scanner in CSOM and OCT is its nonlinear distortion caused by the rotational inertial. This is inevitable even if a closed loop is equipped. Here, a second closed loop is introduced to provide pixel clocks to reduce the pincushion distortion of the images. A subdivided step motor is employed to be the vertical scanner as the result of price consideration. Nonetheless, the conventional linearity model of the peck torque with a winding current relationship is no longer in agreement with the experiment when the winding current is low, while a parabolic model is more likely to be reasonable. Relational treatment is proposed in the paper. Both methods have proved to be good enough to meet the requirement of a super resolution scanning imaging.     

一种纵扭复合换能器型超声马达的原理及实验研究

本文从纵扭振动换能器理论出发，计算了一种新的复合换能器型超声马达，并进行了实验研究，测出了其主要性能参数。     

机、电、微机控制一体化

通过平面电机绘图机系统的设计,描述了机、电、微机控制技术一体化的优越性。一个重要的优点是机械、电气技术的结合将会大大地简化平面电机绘图系统的结构和制造工艺,因而降低了成本。另一个重要优点是微机控制技术将会大大地扩大机电产品的功能。最后结论:机、电、微机控制技术一体化是机电产品今后的发展趋势。     

斯特林制冷机直线电机磁性材料模拟分析与应用

直线电机磁性材料的选择对斯特林制冷机的性能具有重要影响。应用电机电磁场理论和有限元分析方法,建立动磁式直线电机的电磁场模型,基于Ansoft Maxwell软件对几种常用磁性材料的电磁场进行有限元分析,得到了相应的电磁推力和磁感应强度分布。经过分析比较,选择铷铁硼、铁钴钒和硅钢作为电机磁性材料,研制的斯特林制冷机应用于5L深冷冰箱,获得了-150℃的低温环境,对应温度的制冷量为7W。     

Current reversal and mass separation of inertial Brownian motors in a two-noise ratchet

Transport of an inertial Brownian motor moving in an asymmetric periodic potential driven by an external force and correlated noises is investigated. Using the numerical algorithm, the asymptotic mean velocity (AMV) for characterizing directed transport is obtained. The effects of the external driving force f and the correlation λ between the two noises on the AMV are discussed. The results manifest: (1) the external driving force and the correlation between the two noises can lead to the phenomena like current reversal. (2) The competitions among the external driving force and the correlation between the two noises are necessary for current reversal, i.e., fλ>0. (3) Different directions of transport are found for different masses of the Brownian particles under the condition fλ>0. Therefore a theoretical study is suggested for separating Brownian particles according to their different masses in the ratchet system.     

离散式任意充磁角度Halbach永磁电机解析模型研究

Halbach电机因其自身优势在新型船舶推进、海洋洋流发电等方面受到广泛关注. 本文在假设铁磁材料线性和定子内表面光滑的条件下, 通过将任意充磁角度Halbach阵列等效为两组90° Halbach(或180° Halbach)阵列的矢量合成, 提出了一种分析离散式任意充磁角度Halbach永磁电机气隙磁场的解析方法; 通过对电机中磁标量势的傅里叶级数进行计算, 推导出了最简单的90° Halbach永磁电机在极坐标系下的气隙磁密表达式, 并在此基础上, 给出了任意充磁角度Halbach电机永磁体磁化强度在一个极下的表达式, 进而得出任意充磁角度Halbach电机气隙磁密的分布, 并分析了气隙磁密与电机极对数、永磁体厚度和充磁角度间的关系. 最后通过有限元和试验结果验证了本文方法的正确性. 关键词： 离散式Halbach电机 任意充磁角度 矢量等效 解析模型