Discrete Methods Based on First Order Reversal Curves to Identify Preisach Model of Smart Materials

Preisach model is widely used in modeling of smart materials. Although first order reversal curves (FORCs) have often found ap- plications in the fields of physics and geology, they are able to serve to identify Preisach model. In order to clarify the relationship be- tween the Preisach model and the first order reversal curves, this paper is directed towards: (1) giving the reason a first order reversal curve is introduced; (2) presenting, for identifying Preisach model, two discrete methods, which are analytically based on first order reversal curves. Herein also is indicated the solution’s uniqueness of these two identifying methods. At last, the validity of these two methods is verified by simulating a real smart actuator both methods have been applied to.     

液氧／甲烷气液喷注器试验研究

介绍了液氧／甲烷气液喷注器热试验情况,试验燃烧室压力7．1～7．4MPa,混合比3．5～3．9。研究了不同的喷嘴结构参数对燃烧性能和流量特性的影响。获得了燃烧效率、流量系数、振动、点火性能以及积炭特性等重要参数。     

基于试验气动力的飞机副翼效率优化

针对弹性后掠翼飞机在使用试验气动力分析时所出现的副翼反效问题,利用遗传算法对机翼结构进行优化.弹性飞机副翼效率计算采用试验气动力.重点针对一个发生副翼反效的严重飞行状态点进行了机翼结构优化,对比分析了优化前后副翼效率、相同副翼偏度下所产生的滚转率随飞行动压的变化及颤振特性的变化.并比较了基于试验气动力的情况下只针对单一飞行攻角的优化结果和同时考虑多个飞行攻角的优化结果,分析了飞行攻角对优化结果的影响.结果证明:利用结构优化方法可有效在详细设计阶段解决弹性飞机严重飞行状态点副翼反效问题,并且优化结果对飞机颤振特性基本无影响.     

方形同轴线色散特性的研究

文章研究了一种横截面为方形结构的同轴线，采用有限差分原理^[1]分析方同轴线中TM波的两个最低模式的色散特性及横截面电磁场分布的问题，理论分析了该模式下的色散方程；利用Matlab编程得到方同轴线中TM波的两个最低模式的色散曲线，然后利用CST模拟了该结构的场分布^[2]和色散曲线；将CST仿真结果与理论数值模拟结果进行比较，二者的结果基本一致。     

Specific features of the high-speed plasma stream cycles

The high-speed plasma streams in the solar wind are investigated during the solar cycles nos. 20–22 (1964–1996), separately on the two types of streams according to their solar origin: the HSPS produced by coronal holes (co-rotating) and the flare-generated, in keeping with the classification made in different catalogues. The analysis is performed taking into account the following high-speed stream parameters: the durations (in days), the maximum velocities, the velocity gradients and, the importance of the streams. The time variation of these parameters and the high-speed plasma streams occurrence rate show an 11-year periodicity with some differences between the solar cycles considered. A detailed analysis of the high-speed stream 11-year cycles is made by comparison with the “standard” cycles of the sunspot relative number (Wolf number). The different behaviour of the high-speed stream parameters between even and odd solar cycles could be due to the 22-year solar magnetic cycle. The increased activity of the high-speed plasma streams on the descendant phases of the cycles, regardless of their solar sources, proves the existence of some special local conditions of the solar plasma and the magnetic field on a large scale that allow the ejection of the high energy plasma streams. This fact has led us to the analysis the stream parameters during the different phases of the solar cycles (minimum, ascendant, maximum and, descendant) as well as during the polar magnetic field reversal intervals. The differences between the phases considered are pointed out. The solar cycles 20 and 22 reveal very similar dynamics of the flare-generated and also co-rotating stream parameters during the maximum, descendant and reversal intervals. This fact could be due to their position in a Hale Cycle (the first component of the 22-year solar magnetic cycle). The 21st solar cycle dominance of all co-rotating stream parameters against the 20th and 22nd solar cycle ones, during almost all phases, could be due to the same structure of a Hale Cycle – solar cycle 21 is the second component in a 22-year SC. During the reversal intervals, all high-speed stream parameters have comparable values with the ones of the maximum phases of the cycles even if this interval contains a small part of the descendant branch (solar cycles 20 and 22).     

高同轴度精密零件的加工方法

高同轴度精密零件在精密加工中,用普通方法很难保证其同轴度精度要求。本文采用增加径向辅助定位面的方法,从而使被加工零件的轴向和径向定位误差得到误差补偿,较好地满足了同轴度要求。     

一种低副瓣波纹喇叭天线的设计与实现

文章设计了一种高斯分布的波纹喇叭天线,具有增益高、转换效率高、交叉极化低、相位中心不随频率变化的特点。该天线采用正交馈电,结构简单紧凑,以双线极化或圆极化方式工作。根据天线设计参数,建立了天线模型,进行了优化设计。仿真和实测结果表明,天线在频率34～36 GHz范围内,增益大于20dBi,方向图在E面和H面具有良好对称性,副瓣电平不大于-26 d B,驻波比小于1.5,整体性能满足工程应用要求。     

复合式共轴直升机飞行动力学数学模型研究

建立了复合式共轴直升机的飞行动力学数学模型。根据复合式共轴直升机的构型特点,计入上下旋翼,旋翼与机翼之间的相互气动干扰,建立了旋翼、机翼等部件的气动计算模型。以某小型复合式共轴直升机为例,运用牛顿迭代法完成了3种飞行模式下的配平计算,得到了从悬停到高速前飞各种飞行状态下的操纵量和状态量,分析了复合式共轴直升机飞行的物理...     

共轴式直升机地面共振机理分析

为理解共轴式直升机上下旋翼与机体之间的耦合作用,提出了一种分析共轴式直升机地面共振物理机理的时-频分析方法。考虑上下旋翼周期型摆振与机体俯仰和滚转自由度(DOF),建立了具有结构阻尼的共轴铰接式旋翼直升机地面共振分析模型。通过特征值计算和扰动运动方程的数值积分,获得了共轴式直升机地面共振的模态特性及时域响应特性,根据各自由度的响应特性揭示了旋翼与机体之间的相互作用。分析表明,具有上旋翼特征的摆振后退型模态是最不稳定模态。在动不稳定区内,上旋翼周期摆振与机体滚转自由度之间相互输入能量,是造成共轴式直升机地面共振的主要原因;对于该不稳定模态,下旋翼的周期摆振与机体滚转自由度之间也构成相互输入能量的相位关系,增加了直升机地面共振的动不稳定性。     

悬停状态共轴刚性双旋翼非定常流动干扰机理

基于运动嵌套网格方法,建立了一套适合于悬停状态下共轴刚性双旋翼非定常干扰流场分析的计算流体力学(CFD)方法。首先,基于高效的运动嵌套网格技术,采用积分形式的可压雷诺平均Navier-Stokes(RANS)方程作为双旋翼非定常流场求解控制方程,湍流模型选用Baldwin-Lomax模型,时间推进采用双时间方法。在CFD方法的验证基础之上,对干扰过程中的桨尖涡涡核位置及强度演变规律进行了细致分析,揭示了共轴双旋翼非定常干扰流场中上、下旋翼桨尖涡与双旋翼桨叶之间的贴近干扰、碰撞现象,以及上、下旋翼桨尖涡之间的相互干扰机理。然后,进一步研究了不同总距角下的共轴旋翼系统中上、下旋翼的非定常气动特性以及影响规律。计算结果表明:上旋翼桨叶的桨尖涡会直接与下旋翼桨叶发生碰撞,导致下旋翼桨叶拉力损失;上旋翼桨叶的桨尖涡和下旋翼桨叶的桨尖涡相互干扰,改变了桨尖涡的强度和轨迹;上、下旋翼桨叶相互靠近时,上、下旋翼桨叶的拉力均会上升,之后相互远离时上、下旋翼桨叶拉力均会先下降再上升。