利用Taylor展开结合Pade逼近求解Volterra人口模型

Volterra人口模型是在Logistic模型的基础上加入积分表达式,以表示毒素积累对种群的影响.利用Taylor级数结合Pade逼近的方法求解Volterra模型,得到模型的解析近似解,并分析模型参数的影响.

Application of Synthetic Meteorological Time Series in BROOK90:A Case Study for the Tharandt Forest in Saxony,Germany

This study presents an extended version of a single site daily weather generator after Richardson. The model is driven by daily precipitation series derived by a first-order two-state Markov chain and considers the annual cycle of each meteorological variable. The evaluation of its performance was done by deploying its synthetic time series into the physical based hydrological model BROOK90. The weather generator was applied and tested for data from the Anchor Station at the Tharandt Forest, Germany. Additionally its results were compared to the output of another weather generator with spell-length approach for the precipitation series (LARS-WG). The comparison was distinguished into a meteoro-logical and a hydrological part in terms of extremes, monthly and annual sums and averages. Extreme events could be preserved adequately by both models. Nevertheless a general underestimation of rare events was observed. Natural correlations between vapour pressure and minimum temperature could be conserved as well as annual cycles of the hydro-logical and meteorological regime. But the simulated spectrums of extremes, especially, of precipitation and temperature, are more limited than the observed spectrums. While LARS-WG already finds application in practice, the results show that the data derived from the presented weather generator is as useful and reliable as those from the established model for the simulation of the water balance.

基于Volterra级数改进的混合遗传算法在谐波平衡中的应用

针对遗传算法在谐波平衡仿真中经常出现随机性大、迭代过程慢、局部搜索能力弱等问题,提出一种改进的混合遗传算法。该算法将Volterra级数、拟牛顿算法与遗传算法相结合,利用Volterra级数的记忆特性估算频域初始值,通过遗传算法进行全局优化,最后利用拟牛顿算法进行局部优化。基于对MRF281的谐波平衡仿真结果表明,该算法与遗传算法相比,迭代次数减少了40%左右,同时仿真数据与实测数据拟合较好。改进算法兼备了全局优化和局部优化的特点,明显提高了精度和收敛速度,并克服了遗传算法随机性大、局部搜索能力弱等缺点,对非线性电路分析具有较大的参考价值。

非线性振荡器频率占据现象的Volterra级数分析

本文应用Volterra级数和谐波平衡技术分析了一个互感耦合非线性振荡电路在外电动势作用下的频率占据现象。导出了占据带宽表达式。这种方法在建立好系统模型后只需进行代数运算,从而避开了求解非线性微分方程的复杂过程。

微波功率放大器非线性失真分析

功率放大器非线性失真产生的交调失真、邻道干扰等直接影响通信系统的性能 ,在放大器模型的基础上 ,如何定量地描述和分析其非线性具有重要意义。文中讨论了放大器非线性失真的泰勒级数分析法、Volterra级数分析法和谐波平衡分析法 ,给出相应的仿真和实验结果。结果表明 :根据非线性的强弱采用不同的分析方法 ,结果具有较大的参考意义。

利用高阶径向导数带限模型进行重力向下延拓计算

泰勒级数展开是实施位场向下延拓解算的主要方法之一。该方法的有效性主要取决于位场延拓参量各阶垂向(或径向)偏导数的求取精度及其可靠性。为了避免使用封闭解析核函数在球边界面出现奇异性带来的不确定性问题,依据各类重力观测经滤波处理后均表现为一类有限频谱带宽信号的特点,提出将地球外部重力异常泊松积分式的核函数表示为球谐级数展开式,并将其截断为与重力观测值频谱范围相一致的带限求和式,进而通过直接求导方法,推导得到一组与带限核函数相对应的重力异常高阶径向导数带限计算公式,同时对该组公式进行了实用性改化,并将其应用于重力异常向下延拓泰勒级数展开式计算。使用超高阶地球位模型EGM2008设计两个阶段的数值计算检验方案,分别对重力异常高阶径向偏导数带限模型及其泰勒级数展开向下延拓模型的计算精度进行了检核评估,表明新模型具有良好的可靠性和有效性,在解算稳定性和计算精度两个方面都优于其他同类模型。