Correcting for the influence of frozen lakes in satellite microwave radiometer observations through application of a microwave emission model

The spatial resolution of passive microwave observations from space is of the order of tens of kilometers with currently available instruments, such as the Special Sensor Microwave/Imager (SSM/I) and Advanced Microwave Scanning Radiometer (AMSR-E). The large field of view of these instruments dictates that the observed brightness temperature can originate from heterogeneous land cover, with different vegetation and surface properties.In this study, we assess the influence of freshwater lakes on the observed brightness temperature of AMSR-E in winter conditions. The study focuses on the geographic region of Finland, where lakes account for 10% of the total terrestrial area. We present a method to mitigate for the influence of lakes through forward modeling of snow covered lakes, as a part of a microwave emission simulation scheme of space-borne observations. We apply a forward model to predict brightness temperatures of snow covered sceneries over several winter seasons, using available data on snow cover, vegetation and lake ice cover to set the forward model input parameters. Comparison of model estimates with space-borne observations shows that the modeling accuracy improves in the majority of examined cases when lakes are accounted for, with respect to the case where lakes are not included in the simulation. Moreover, we present a method for applying the correction to the retrieval of Snow Water Equivalent (SWE) in lake-rich areas, using a numerical inversion method of the forward model. In a comparison to available independent validation data on SWE, also the retrieval accuracy is seen to improve when applying the influence of snow covered lakes in the emission model.     

三维几何约束系统的等价性分析

针对过约束、完整约束和欠约束三维几何约束系统的求解问题,提出了等价性分析方法.该方法基于三维几何约束系统的内在等价性,充分挖掘几何领域知识,依据拆解约束闭环、缩减约束闭环和析出约束闭环等原则,采用等价约束替换来处理几何约束闭环问题,优化几何约束图的结构,实现几何约束系统的优化分解.最后用多个实例验证了该方法的正确性和有...     

基于改进纤维模型的RC剪力墙静力弹塑性分析

为了使纤维模型能够有效模拟剪切效应,提出了一种基于塑性理论和虚拟单元法的改进纤维模型RC剪力墙全过程静力弹塑性分析方法.推导出等效单轴应力和等效单轴应变的计算公式,在纤维层面建立考虑剪切效应的应力和应变关系,将纤维由多轴受力状态等效为单轴受力状态,引入虚拟单元法来解决有限元数值计算过程中遇到的负刚度问题.利用自编程序及ABAQUS软件对一片钢筋混凝土剪力墙进行静力弹塑性分析,结果表明,自编程序计算曲线与试验曲线及ABAQUS软件计算曲线吻合较好,能够反映出剪切效应的影响.改进的分析方法简便有效,便于编程,可用于分析剪切效应明显的钢筋混凝土剪力墙构件.     

基于几何线形的立交噪声计算方法

为定量评价道路几何线形对立交噪声的影响,研究了基于几何线形计算立交噪声的方法,以车辆行驶速度为切入点,拟合噪声级和车速之间的关系.对于匝道噪声的计算,根据等效声级的定义给出了相对等效声能量的含义及计算方法,采用将匀速运动段与变速运动段噪声能量相加的方法求出总的噪声能量,建立了相对等效声能量与匝道长度之间函数关系,用对匝道长度进行积分的方法,根据等效声级的定义式推导出左、右转匝道的噪声级.根据主线设计速度、噪声级和车速之间的关系推导出主线噪声级计算公式.立交总噪声通过对各条主线和匝道的噪声级叠加求得.通过对黑龙江省鹤大立交的实例分析表明,该方法能够解决立交匝道变速运动段的噪声计算问题,能够将车辆在立交行驶产生的噪声与道路几何线形联系起来.当道路立交的几何设计条件已知,可以根据几何线形参数进行噪声污染计算,为定量评价立交噪声污染程度提供依据.     

脉冲频率调制LLC串联谐振X光机电源

为了满足X光机电源输出电压调节范围宽的要求,提出了一种全桥LLC串联谐振高频高压电源,并利用仿真软件设计其控制电路,使设计方法更加简单.主电路采用全桥LLC串联谐振、高压变压器、单相双向对称倍压整流电路,从理论上分析系统的工作原理,并建立了LLC谐振变换器的基波等效模型,对主电路的参数进行了设计;在控制电路设计中,借助仿真软件得到补偿前系统近似的开环传递函数,再进行控制器的设计.仿真结果表明,输出电压可以在40~120 kV范围内连续可调,输出电压上升时间短、纹波小,在输出电压跳变过程中,动态调节时间很短,证明了所提出的拓扑和控制电路设计方法的正确性和可靠性.     

非线性体系动力可靠性分析的等效Duffing体系法

等效线性化法是非线性结构体系的随机反应分析最常用的方法,但使用等效线性化法给出的反应结果进行结构动力可靠性分析会带来很大的误差.将一般非线性体系通过均方最小误差原则等效为Duffing非线性体系来进行结构动力可靠性分析.Duffing非线性体系可以通过FPK方程求得其稳态精确解析解,所以使用该等效非线性法进行结构动力可靠性分析不仅计算上方便可行而且精度较高.算例分析表明了等效非线性法分析结果可靠,且比等效线性化法的计算精度有明显提高.     

Scattering loss in optical waveguide with trapezoidal cross section

To get the scattering loss of the trapezoidal core waveguide, a new analysis model is presented based on the perturbation equivalent method and modified effective-index method. Firstly, the trapezoidal core waveguide is successfully equivalent to the rectangular one with both restricting the same optical field energy by adopting the perturbation method. Then, the equivalent rectangular core waveguide is decomposed into two slab waveguides by employing the modified effective-index method. The trapezoidal core waveguide scattering theory model is established based on the slab waveguide scattering theory. With the sidewalls surface roughness in the range from 0 to 100 nm in the single model trapezodial core waveguide, optical simulation shows excellent agreement with the results from the scattering loss model presented. The relationship between the dimension and side-wall roughness with the scattering loss can be determined in the trapezoidal core waveguide by the scattering loss model.     

基于ANSYS的500kV电力变压器端部绝缘电场分析及结构优化

采用ANSYS软件对500kV电力变压器高压绕组端部电场进行仿真计算,得到了端部电场和电位分布图,指出了端部电场最大电场强度值及其所在位置.通过改变静电环的曲率半径,减小了绝缘层表面的最大场强值,以优化电场分布并确定500kV变压器主绝缘的结构尺寸,为变压器的设计和改进提供了参考依据.     

水管冷却热传导计算模型能量分析

对水管冷却有限元法和水管冷却等效热传导法的相关性进行了研究,采用同一套有限元网格,仿真分析了混凝土浇筑仓的非稳定温度场和徐变应力场,对比分析了两种水管冷却计算模型计算的混凝土浇筑仓平均温度和弹性应变能及黏性应变能.水管冷却等效热传导法计算的混凝土平均温度与水管冷却有限元法计算的平均温度接近,前者是后者的等效平均,但两者的同一节点温度不一样,且差异有时还比较大.由于前者是后者温度的等效平均,所以前者和后者的弹性应变能和黏性应变能接近,但两者的同一节点的应力不一样,因此其差异有时也比较大.     

考虑填充墙作用的框架结构Pushover分析

通过对"汶川地震"中框架填充墙的破坏情况进行调查分析,给出了框架填充墙的主要破坏形式,并总结发生破坏的原因;针对砌体填充墙框架结构在地震作用下的受力特点,提出结构简化计算模型(框架-斜撑模型),利用等效轴向刚度推导出斜撑宽度;结合实际工程,采用框架-斜撑模型对已建的框架填充墙结构进行Pushover分析,对结构的抗震能力做出评估。结果表明:①填充墙消耗了大量的地震能量,对周边部分构件起到了保护作用;②填充墙的参与,改变了结构的受力状态,结构薄弱部位也发生了变化。