《模拟电路》教学中的几种典型方法

本文作者从自己教学的角度出发，介绍了《模拟电路》教学中的几种典型方法，并以具体实例辅以印证说明。以最终达到以点带面，提高教学质量和教学效果的目的。     

基于记忆的类比联想

类比联想——怎样发现合适的类似物,是类比推理的核心和难点。本文首先简介我们设计的一种支持类比推理的联想记忆模型,它包括语义层、具体层和抽象层。本文将类比联想分为诱发和初步确认两个阶段,其中诱发阶段遵从语义诱发原则、突出相似原则、熟悉优先原则和相似优先原则;初步确认准则包括全面相似性、目的性和差别。最后简介了我们用于实现这一原理的系统ARE(Analogical Reminding Engine)。     

A CONCISE M-METRIC LEAST SQUARE FORMULA FOR POLYNOMIAL ANALOGY

ＡＣＯＮＣＩＳＥＭ－ＭＥＴＲＩＣＬＥＡＳＴＳＱＵＡＲＥＦＯＲＭＵＬＡＦＯＲＰＯＬＹＮＯＭＩＡＬＡＮＡＬＯＧＹ￥ＰａｎＸｉａｏｓｕ（ＣｏｌｌｅｎｇｏｆＳｃｉｅｎｃｅ，ＮＵＡＡ２９ＹｕｄａｏＳｔｒｅｅｔ，Ｎａｎｊｉｎｇ２１００１６，Ｐ．Ｒ．Ｃｈｉｎａ）Ａ...     

Spatio-temporal structure of the wave packets generated by the solar terminator

Using long-term (1998--2009) total electron content (TEC) measurements from the GPS global network including dense network of GPS sites in USA and Japan, we have obtained the first data regarding the spatio-temporal structure and the statistics of medium-scale traveling wave packets (MS TWPs) excited by the solar terminator (ST). Total amount of the detected TWPs exceeds 565,000. There is no correlation between TWPs occurrence and geomagnetic and solar activity. We found that the diurnal, seasonal and spectral MS TWPs characteristics are specified by the solar terminator (ST) dynamics. MS TWPs are the chains of narrow-band TEC oscillations with single packet’s duration of about 1–2 h and oscillation periods of 10–20 min. The total duration of chain is about 4–6 h. The MS TWPs spatial structure is characterized by a high degree of anisotropy and coherence at the distance of more than 10 wavelengths. Occurrence rate of daytime MS TWPs is high in winter and during equinoxes. Occurrence rate of nighttime MS TWPs has its peak in summer. These features are consistent with previous MS travelling ionosphere disturbance (TID) statistics obtained from 630-nm airglow imaging observations in Japan. In winter, MS TWPs in the northern hemisphere are observed 3–4 h after the morning ST passage. In summer, MS TWPs are detected 1.5–2 h before the evening ST appearance at the point of observations, but at the moment of the evening ST passage in the magneto-conjugate point. The obtained results are the first experimental evidence for the hypothesis of the ST-generated ion sound waves.     

声波激振破坏的机理及条件研究

从微观层面而言,物体在声波激励共振中发生了失效破坏,显然是因为出现了破坏物质微观粒子之间结合力的因素。在大气中运动传播的声波进入物质体后转换为应力波,这种应力波(能量)的传导、扩散和聚集交合方式会对物质微观粒子结合薄弱之处的结合力产生影响。这是因为当声波作为外激励源能量作用于物质粒子并大到一定程度时,特别是在两个纵波对撞或在变向结构交汇处出现回波激振效应时,会使粒子间出现异常的能量变化,从而破坏了粒子间相对稳定的平衡状态。如果物体中的粒子大量失衡,就会对物体产生整体结构性破坏作用,使物体结构强度下降、出现裂纹,甚至完全失效。     

利用“交叉类比”学习法掌握基本放大电路特性

在模拟电子技术课程的教学中,分立器件构成的基本放大电路的静态和动态特性分析,是掌握放大电路工作原理中的一个基本知识点.作者经过多年的教学探索和实践,通过“交叉类比”的学习方法,能有效地帮助学生更快更深入地理解由各类分立器件构成的不同组态的放大电路特性.本文以晶体三极管和场效应管构成的基本放大电路特性的授课为例,从不同的...     

Analytic estimation and numerical modeling of actively cooled thermal protection systems with nickel alloys

Actively cooled thermal protection system has great influence on the engine of a hypersonic vehicle, and it is significant to obtain the thermal and stress distribution in the system. So an analytic estimation and numerical modeling are performed in this paper to investigate the behavior of an actively cooled thermal protection system. The analytic estimation is based on the electric analogy method and finite element analysis（FEA） is applied to the numerical simulation. Temperature and stress distributions are obtained for the actively cooled channel walls with three kinds of nickel alloys with or with no thermal barrier coating（TBC）. The temperature of the channel wall with coating has no obvious difference from the one with no coating, but the stress with coating on the channel wall is much smaller than that with no coating. Inconel X-750 has the best characteristics among the three Ni-based materials due to its higher thermal conductivity, lower elasticity module and greater allowable stress. Analytic estimation and numerical modeling results are compared with each other and a reasonable agreement is obtained.     

一种基于有限元/边界元耦合方法的管道进口声传播及声辐射模型

本文发展了一种基于有限元和边界元耦合方法的管道进口声传播及声辐射计算模型。该模型将整个声场分为内部有限域和外部无界域,分别用有限元和边界元方法求解控制方程,在二者之间的界面上使用具有物理意义的声阻抗参数进行匹配,并通过一种快速迭代方法实现全声场求解。这种迭代方法可以保证有限元刚度矩阵等带宽以及对称的特性不被破坏,有助于提高计算效率。该模型先得到了Levine and Schwinger标准解的检验,进而在无流动情况下对于简化的航发短舱进口管道模型进行了噪声辐射现象的数值模拟,最后基于计算结果分析了声衬对远场声辐射的影响。     

基于非结构背景网格的动网格方法研究

借鉴弹簧动网格方法和Delaunay背景图方法,提出一种基于非结构背景网格的动网格生成方法。先用少量的物面控制点生成相对较粗的非结构背景网格,再用弹簧法将动边界的变化量作用到该背景网格,然后利用计算网格与背景网格的映射关系插值生成对应的动网格,最后对物面网格点及其附近受影响的密网格点进行局部网格修正,获得最终计算所需的动网格。所提方法与直接弹簧法比较,由于弹簧法作用的背景网格远粗于实际的计算网格,提高了计算效率,此外,由于网格的运动受控于受弹簧法作用的背景网格,边界变形或运动能较为均匀地传递到内部网格上,使网格单元过渡光滑,提高了动网格的质量。给出若干算例,展示了方法的效率和可行性。     

考虑地面影响的半空间气动噪声数值计算方法

含非紧致边界的半空间气动噪声问题普遍存在于航空领域,在数值计算过程中不仅要考虑非紧致边界的散射效应,还需要考虑地面对声波的反射。基于Lighthill声模拟理论和广义格林函数方法,引入边界声压积分项和可压缩修正项可以考虑非紧致边界以及流体可压缩性对声波散射的影响。然而在半空间声场的计算过程中,包含沿无限大地面的积分项,为了克服沿地面积分所带来的巨大工作量,根据无穷大平板对声波的反射特性,推导得出频域下基于半空间格林函数的声学积分方程。同时开展了半空间中应力源噪声与圆柱绕流噪声的数值预测与分析,验证了该方法的准确性与高效性。