变系数紧耦合波动方程组的非线性边界镇定

利用黎曼几何方法和乘子技巧,讨论了带变系数和非线性边界扩散反馈项的紧耦合波动方程组的镇定,得到了解能量的衰减估计.     

Nelder-Mead单纯形算法改进及在气象上的应用

Nelder-Mead Simplex (NMS)算法是一种查找多元函数局地最小值的无微分算法,在现代科学计算中得到广泛应用,该文提出了一种对NMS算法的改进方法.改进后,大大简化了其计算过程,提高了该算法的收敛速度.利用改进后的算法对陆面过程参数进行了拟合计算,结果表明:改进的NMS算法对非线性公式具有非常高的拟合精...     

固定式海洋平台极限强度试验研究

根据墨西哥湾某海域一典型固定式海洋平台为原型,按照几何相似准则和刚度相似准则设计并制作海洋平台试验模型,开展极限强度模型试验研究,观察并记录其破坏过程。并采用非线性有限元方法(ANSYS)对试验模型进行极限强度数值计算,将计算结果与试验结果对比,结果表明计算结果与试验结果吻合较好,验证非线性有限元方法的有效性。     

非线性VAD反演低层风廓线拟合阶数优化方法

结合理论和SoWMEX试验 (西南气流试验,Southwest Monsoon Experiment) 的连续多普勒天气雷达观测资料和广东省阳江雷达资料, 对非线性速度方位显示 (非线性VAD) 方法反演低层低于2 km垂直风廓线精度和能力进行定量分析。结果表明:非线性VAD基本能反演出低层风廓线在空间和时间上的演变。但当雷达径向速度数据在方位存在较大的连续性缺测、体积扫描仰角较少时,因传统非线性VAD采用的速度方位显示 (VAD) 方法拟合阶数和垂直拟合阶数过高,反演的低层风廓线会存在较大误差,造成不合理高风速区和风廓线不连续。通过实际观测资料统计分析反演参数对非线性VAD的影响,提出基于连续性数据缺测间隔和不同仰角的多少的VAD和垂直拟合阶数动态调整方法。同锋面降水和台风降水两典型个例的实际探空比对显示,调整后的非线性VAD显著改进低层风廓线反演精度,反演的风廓线结构和变化与实况相符,反演平均误差小于2 m·s-1。     

改进遗传算法在变形监测网平差中的应用

遗传算法在处理非线性最小二乘问题上具有其独到的优势。文中通过对遗传算法的理论性研究,对常规遗传算法的选择交叉策略、变异步长及变异率都作了改进。并将改进的遗传算法应用到变形监测网平差中,实现变形监测网在不同基准下的非线性平差计算,并通过实例证明其实用性及优越性。     

基准站非线性变化的成因及消除或减弱的方法与途径

近20年累积的全球IGS基准站位置时间序列呈现显著的非线性变化,尤其是高程方向的季节性变化。随着各研究领域对大地测量成果所要求的精度越来越高,大地点位的非线性时变越来越受到关注。本文详细阐述了造成基准站非线性变化的成因,包括与GPS相关的技术类系统误差、地球物理效应、接收机及天线变化、地震引起的突变、噪声影响等,研究了消除或减弱各种非线性变化的方法及途径。     

浮体自由衰减运动阻尼识别方法误差分析

讨论了使用Froude法和Faltinsen法识别线性和非线性阻尼系数时的系统误差。通过回顾两种方法的推导过程,论证了方法的内在假设,并量化两种方法的系统误差。为减少识别过程误差,文中提出了直接积分法,并依据数值与试验数据,讨论了3种识别方法识别结果。结果表明,Froude法相比于Faltinsen法能更好地预报线性和非线性阻尼系数。对于低阻尼浮体问题,Froude法和Faltinsen法可以给出相对准确的预测,而对于强阻尼浮体问题,Froude法与Faltinsen法在确定的线性和非线性阻尼系数中会给出大于5%的系统误差,而直接积分法展示了较高的识别精度。     

Mean-field equations for weakly nonlinear two-scale perturbations of forced hydromagnetic convection in a rotating layer

We consider stability of regimes of hydromagnetic thermal convection in a rotating horizontal layer with free electrically-conducting boundaries, to perturbations involving large spatial and temporal scales. Equations governing the evolution of weakly nonlinear mean perturbations are derived under the assumption that the α-effect is insignificant in the leading-order (e.g. due to a symmetry of the system). The mean-field equations generalise the standard equations of hydromagnetic convection: New terms emerge – a second-order linear operator representing the combined eddy diffusivity and quadratic terms associated with the eddy advection. If the perturbed CHM regime is nonsteady and insignificance of the α-effect in the system does not rely on the presence of a spatial symmetry, the combined eddy diffusivity operator also involves a nonlocal pseudodifferential operator. If the perturbed CHM state is almost symmetric, α-effect terms appear in the mean-field equations as well. Near a point of a symmetry-breaking bifurcation, cubic nonlinearity emerges in the equations. All the new terms are in general anisotropic. A method for evaluation of their coefficients is presented; it requires solution of a significantly smaller number of auxiliary problems than in a straightforward approach.     

Hydrological implications of the Southern Oscillation: variability of the rainfall-runoff relationship

Abstract

A connection between El Niño Southern Oscillation (ENSO) and weather phenomena in eastern Australia has been recognized for several decades. However, little work has been devoted to addressing how this correlation affects hydrological system behaviour within regional-scale catchments. In this study, spatially distributed ENSO effects are evaluated in terms of monthly rainfall, evaporation, streamflow and runoff characteristics for a 1300 km² catchment. The catchment is located in southeastern Australia where previous studies have indicated only modest ENSO influences on rainfall variability. Spatial and temporal analysis indicates that strongest ENSO-induced rainfall variability occurs during summer months. Additionally, the strength of the relationship is variable in space indicating that topographic controls may affect ENSO influences on rainfall totals and intensities. However, analysis of runoff shows substantially magnified ENSO-induced variability in comparison to the induced variability in rainfall. This may be attributable to the nonlinearity of runoff generation. Differences in antecedent moisture storage conditions will exist but may also be enhanced by complementary ENSO influences on daily rainfall intensities and mean monthly evaporation and temperature totals. The degree of the nonlinearity displayed by the hydrometeorological processes presented demonstrates that the significance of ENSO forecasts for surface water resource management should be assessed with direct regard to streamflow generation rather than on the basis of rainfall totals alone.     

Demand modulation of water scarcity sensitivities to secular climatic variation: theoretical insights from a computational maquette

ABSTRACT

Increased demand associated with population or economic growth, and decreased supply under some climatic shifts, obviously contribute to water scarcity. As a fresh perspective, we offer a generic theoretical treatment using a computational “maquette”, employing parameterizations to avoid assumptions about the origin and scale of climate and demand changes. The results suggest a distinct (and more subtle) point: the sensitivities of water stress to changes in both the mean and the variance of hydroclimate are modulated by demand level. Theoretical behaviours generated by the reduced-complexity model are surprisingly intricate, including profound nonlinearities and bifurcations. These may form a lower bound on the dynamical complexity of the demand–supply–scarcity nexus. Overall, the outcomes suggest that demand growth substantially intensifies and nonlinearizes water stress sensitivities to secular climate variation, and, in particular, that the interactions between demand changes and second-order hydroclimatic non-stationarity may produce non-intuitive water scarcity impacts requiring much closer study.

EDITOR A. Castellarin; ASSOCIATE EDITOR N. Ilich