一种优化的频率域三维声波有限差分模拟方法   总被引：1，自引：1，他引：0       下载免费PDF全文

范娜  成景旺  秦雷  赵连锋  谢小碧  姚振兴 《地球物理学报》2018,61(3):1095-1108

为提高频率域有限差分（FD，finite-difference）正演模拟技术的计算精度和效率，基于旋转坐标系统的优化差分格式被广泛应用，但是只应用于正方形网格的情况.基于平均导数法（ADM）的优化差分格式，应用于正方形和长方形网格模拟.这些频率域有限差分算子，各自具有不同的差分格式和对应的优化系数求解表达式.本文基于三维声波方程发展了一种新的优化方法，只要给定FD模板形式，可直接构造频散方程，求取FD模板上各节点的优化系数.此方法的优点在于频率域FD算子的优化系数对应各个节点，可扩展优化其他格式.运用此优化方法，计算得到了不同空间采样间距比情况下27点和7点格式的优化系数.数值实验表明，优化27点格式与ADM 27点格式具有相同的精度，优化7点格式比经典的7点格式具有更小的数值频散.  相似文献   

基于改进的BP神经网络构建区域精密对流层延迟模型   总被引：4，自引：0，他引：4       下载免费PDF全文

肖恭伟  欧吉坤  刘国林  张红星 《地球物理学报》2018,61(8):3139-3148

利用神经网络算法挖掘海量数据的规律已成为科技发展的一种趋势，本文针对卫星信号的天顶对流层延迟进行建模.对流层延迟是影响卫星定位精度的重要因素之一，建立精密区域对流层模型对高精度定位有着重要的意义.对区域测站对流层延迟数据的分析，考虑到实时建模中传统BP（Back Propagation）神经网络计算量大，易出现"过拟合"现象、不稳定等因素，通过改进的BP神经网络建立了区域精密对流层模型.详细介绍了新模型的建立过程，并与常用的对流层区域实时模型进行了对比.还讨论了建模测站数目对预报精度的影响.相比现有的其他对流层延迟模型，基于改进的BP神经网络构建的区域精密对流层延迟模型无论在拟合和预报方面都有较好的精度，且随着测站数目的增加模型精度趋于平稳.改进的模型参数较少，可以进行实时的区域精密对流层延迟改正；需要播发的信息量小，适用于连续运行参考站系统（Continuously Operating Reference Stations，CORS）的应用.研究表明：改进的BP神经网络模型能够更好的充分利用大规模历史数据描述卫星信号对流层延迟的空间分布情况，适用于实时大区域精密对流层建模.基于日本地区2005年近1000多个测站的NCAR（National Center Atmospheric Research）对流层数据进行区域对流层延迟建模，结果表明改进的BP神经网络模型在拟合和预报精度上都有较大提升，RMSE（Root Mean Square Error）分别为：7.83 mm和8.52 mm，而四参数模型拟合、预报RMSE分别18.03 mm和16.60 mm.  相似文献   

一种卫星重力梯度数据的ARMA最优滤波模型构建方法          下载免费PDF全文

朱广彬  常晓涛  付兴科  瞿庆亮 《地球物理学报》2018,61(12):4729-4736

由于卫星重力梯度观测的有色噪声特性和海量观测特征，在利用直接法进行重力场模型的最小二乘求解时，观测值的协方差阵为超大型的非对角阵，这给数值求解带来了极大困难.本文提出了一种基于先验误差功率谱密度的最优ARMA滤波模型构建方法，结合法方程的分块求解策略，可实现对卫星重力梯度观测值的高效滤波处理.数值仿真结果表明，利用最优ARMA滤波器进行时域滤波后，法方程的态性得到了明显改善，重力梯度观测值中的有色噪声得到了有效的"白化"处理，大地水准面精度得到了显著提升.  相似文献   

基于波形拟合的中国东海地区410 km间断面附近速度结构研究          下载免费PDF全文

李文兰  魏荣强  崔清辉  高雅健  周元泽 《地球物理学报》2018,61(1):150-160

410 km间断面是地幔转换带的顶界面，对其速度结构和起伏形态开展地震学探测有助于认识地球内部物质组成和相关的地球动力学过程.本文选取了由中国数字地震台网记录到的位于琉球俯冲区的一个中源地震P波宽频带波形资料，利用三重震相波形拟合研究了中国东海地区410 km间断面附近的精细速度结构.结果表明：中国东海地区下方410 km间断面整体表现为一尖锐的速度界面且有8~15 km的小幅抬升；该间断面之上存在52~62 km厚的低速层，其P波速度降低0.5%~1.6%；440 km深度以下存在1.0%~3.0%的P波高速异常.结合前人在该地区的层析成像结果，我们推测该高速异常体与西太平洋俯冲板片在中国东海地区地幔转换带内的滞留有关；板片内水相E分解使得转换带内水含量增加，这引发了410 km间断面的抬升；410 km间断面之上的低速层应与含水矿物脱水导致的地幔橄榄岩部分熔融有关.  相似文献   

基态位涡径向分布对浅水涡旋系统动力稳定性的影响分析          下载免费PDF全文

刘爽  钟玮  刘宇迪 《地球物理学报》2018,61(6):2207-2219

本文基于正压浅水模型，分析基态位涡（Potential Vorticity：PV）结构对热带气旋（Tropical Cyclone：TC）类涡旋系统稳定性及其波动特征的影响.通过引入基态PV结构参数：宽度δ（眼墙内外边界涡度发生陡变的半径长度之比）和中空度γ（眼心相对涡度与内核区域平均相对涡度之比），设计具有相同基流最大切向风速和最大风速半径的170组不同基态PV环结构的敏感性试验，并讨论了不同基态PV结构下涡旋系统最不稳定波数（the most unstable wavenumber：MUWN）和系统最不稳定模态（the most unstable mode of System：MUMS）的特征频率及其不稳定增长率的大小.结果指出：当PV环较宽，系统表现为低波数最不稳定，相应的MUMS为低频波且增长率小；当PV环较窄，系统表现为高波数不稳定，且PV环越实最不稳定波数越高；当PV环窄且空时，MUMS均为中高频波动，且不稳定增长率随PV环的宽度变窄和中空度变空而明显增大.分析典型PV结构下系统演变特征可知，当PV环较宽，MUMS表现为具有平衡约束的低频波动的线性不稳定特征；当PV环趋向窄且空时，MUMS的平衡性约束趋向弱化，同时不稳定增长表现为明显的指数型增长.进一步讨论系统内部非对称结构的形成和传播机制发现，对于弱不稳定的PV环来说，低波数波最不稳定的特征波动具有典型涡旋Rossby波特征；而对于强不稳定的PV环来说，高波数不稳定的特征波动混合波性质明显.  相似文献   

A new method for establishing hydrologic fidelity of snow depth measurements based on snowmelt–runoff hydrographs     

Daeryong Park 《水文科学杂志》2018,63(3):369-385

For snowmelt-driven flood studies, snow water equivalent (SWE) is frequently estimated using snow depth data. Accurate measurements of snow depth are important in providing data for continuous hydrologic simulations of such watersheds. A new hydrologic fidelity metric is proposed in this study to evaluate the potential contribution of particular snow depth datasets to flow characteristics using observed data and hydrologic modeling using the Variable Infiltration Capacity (VIC) model. Data-based hydrologic fidelity of snow depth measurements is defined as a categorical skill score between the snow depth in the watershed and the hydrograph peak or volume at the watershed outlet. Similarly, model-based hydrologic fidelity is defined as a categorical skill score between the model-simulated snow depth and the model-simulated hydrograph peak or volume. The proposed framework is illustrated using the Pecatonica River watershed in the USA, indicating which sites have a higher hydrologic fidelity, which is preferred in hydrologic studies.  相似文献   

Wetland hydroperiod classification in the western prairies using multitemporal synthetic aperture radar          下载免费PDF全文

Joshua S. Montgomery  Chris Hopkinson  Brian Brisco  Shane Patterson  Stewart B. Rood 《水文研究》2018,32(10):1476-1490

Wetlands represent one of the world's most biodiverse and threatened ecosystem types and were diminished globally by about two‐thirds in the 20th century. There is continuing decline in wetland quantity and function due to infilling and other human activities. In addition, with climate change, warmer temperatures and changes in precipitation and evapotranspiration are reducing wetland surface and groundwater supplies, further altering wetland hydrology and vegetation. There is a need to automate inventory and monitoring of wetlands, and as a study system, we investigated the Shepard Slough wetlands complex, which includes numerous wetlands in urban, suburban, and agricultural zones in the prairie pothole region of southern Alberta, Canada. Here, wetlands are generally confined to depressions in the undulating terrain, challenging wetlands inventory and monitoring. This study applied threshold and frequency analysis routines for high‐resolution, single‐polarization (HH) RADARSAT‐2, synthetic aperture radar mapping. This enabled a growing season surface water extent hyroperiod‐based wetland classification, which can support water and wetland resource monitoring. This 3‐year study demonstrated synthetic aperture radar‐derived multitemporal open‐water masks provided an effective index of wetland permanence class, with overall accuracies of 89% to 95% compared with optical validation data, and RMSE between 0.2 and 0.7 m between model and field validation data. This allowed for characterizing the distribution and dynamics of 4 marsh wetlands hydroperiod classes, temporary, seasonal, semipermanent, and permanent, and mapping of the sequential vegetation bands that included emergent, obligate wetland, facultative wetland, and upland plant communities. Hydroperiod variation and surface water extent were found to be influenced by short‐term rainfall events in both wet and dry years. Seasonal hydroperiods in wetlands were particularly variable if there was a decrease in the temporary or semipermanent hydroperiod classes. In years with extreme rain events, the temporary wetlands especially increased relative to longer lasting wetlands (84% in 2015 with significant rainfall events, compared with 42% otherwise).  相似文献   

A multiscaling‐based intensity–duration–frequency model for extreme precipitation          下载免费PDF全文

Hans Van de Vyver 《水文研究》2018,32(11):1635-1647

Rainfall intensity–duration–frequency (IDF) curves are a standard tool in urban water resources engineering and management. They express how return levels of extreme rainfall intensity vary with duration. The simple scaling property of extreme rainfall intensity, with respect to duration, determines the form of IDF relationships. It is supposed that the annual maximum intensity follows the generalized extreme value (GEV) distribution. As well known, for simple scaling processes, the location parameter and scale parameter of the GEV distribution obey a power law with the same exponent. Although, the simple scaling hypothesis is commonly used as a suitable working assumption, the multiscaling approach provides a more general framework. We present a new IDF relationship that has been formulated on the basis of the multiscaling property. It turns out that the GEV parameters (location and scale) have a different scaling exponent. Next, we apply a Bayesian framework to estimate the multiscaling GEV model and to choose the most appropriate model. It is shown that the model performance increases when using the multiscaling approach. The new model for IDF curves reproduces the data very well and has a reasonable degree of complexity without overfitting on the data.  相似文献   

Model for multiblock columns subjected to base excitation     

Tamás Ther  László P. Kollár 《地震工程与结构动力学》2018,47(2):418-437

A new model is presented for multiblock columns subjected to earthquakes, which contains an impact and an opening model. Both in the impact and in the opening model, all the possible opening configurations are investigated because it was found that in many practical cases, unexpected patterns may occur. The model is purely mechanical: assuming rigid blocks and classical (inelastic) impact. The effect of energy dissipation during impact was investigated. Using our model in accordance with the literature, it was found that monolithic blocks are more vulnerable to overturning than multiblock systems.  相似文献   

Validation of the SCEC Broadband Platform simulations for tall building risk assessments considering spectral shape and duration of the ground motion     

Nenad Bijelić  Ting Lin  Greg G. Deierlein 《地震工程与结构动力学》2018,47(11):2233-2251

Earthquake simulation technologies are advancing to the stage of enabling realistic simulations of past earthquakes as well as characterizations of more extreme events, thus holding promise of yielding novel insights and data for earthquake engineering. With the goal of developing confidence in the engineering applications of simulated ground motions, this paper focuses on validation of simulations for response history analysis through comparative assessments of building performance obtained using sets of recorded and simulated motions. Simulated ground motions of past earthquakes, obtained through a larger validation study of the Southern California Earthquake Center Broadband Platform, are used for the case study. Two tall buildings, a 20‐story concrete frame and a 42‐story concrete core wall building, are analyzed under comparable sets of simulated and recorded motions at increasing levels of ground motion intensity, up to structural collapse, to check for statistically significant differences between the responses to simulated and recorded motions. Spectral shape and significant duration are explicitly considered when selecting ground motions. Considered demands include story drift ratios, floor accelerations, and collapse response. These comparisons not only yield similar results in most cases but also reveal instances where certain simulated ground motions can result in biased responses. The source of bias is traced to differences in correlations of spectral values in some of the stochastic ground motion simulations. When the differences in correlations are removed, simulated and recorded motions yield comparable results. This study highlights the utility of physics‐based simulations, and particularly the Southern California Earthquake Center Broadband Platform as a useful tool for engineering applications.  相似文献