A Taylor basis for kinematic nonlinear real-time simulations. Part II: The Taylor basis

Real-time simulations are used to a significant extent in many engineering fields. However, if nonlinearities are included, the real-time requirement significantly limits the size and complexity of numerical models. The present work constitutes the second of two papers where a general basis method to simulate kinematic nonlinear structures more efficiently is introduced. The advantage of the basis formulation is that it enables the number of basis vectors to be increased without increasing the number of unknown basis co-ordinates. This allows for larger numerical kinematically nonlinear models to run in real time. The basis is organized from a Taylor series that includes the system mode shapes and their complete first-order modal derivatives derived in Part I. The Taylor series predicts fixed linear relations between the modal co-ordinates of the system mode shapes and the modal derivatives, respectively. Thus, the full solution is known solely by determining the modal co-ordinates of the mode shapes, which significantly minimizes the computational costs. Furthermore, it is illustrated that the stability of the Taylor basis formulation is dependent on the mode shape frequencies only, allowing the applied time steps to be significantly larger than in standard nonlinear basis analysis. An example illustrates a case where the computational time can be decreased by one order of magnitude using a Taylor basis formulation compared with a standard basis formulation including identical basis vectors.     

Projections of wind changes for 21st century in China by three regional climate models

This paper examines the capability of three regional climate models(RCMs),i.e.,RegCM3(the International Centre for Theoretical Physics Regional Climate Model),PRECIS(Providing Regional Climates for Impacts Studies)and CMM5(the fifth-generation Pennsylvania State University-the National Center for Atmospheric Research of USA,NCAR Mesoscale Model)to simulate the near-surface-layer winds(10 m above surface)all over China in the late 20th century.Results suggest that like global climate models(GCMs),these RCMs have the certain capability of imitating the distribution of mean wind speed and fail to simulate the greatly weakening wind trends for the past 50 years in the country.However,RCMs especially RegCM3 have the better capability than that of GCMs to simulate the distribution and change feature of mean wind speed.In view of their merits,these RCMs were used to project the variability of near-surface-layer winds over China for the 21st century.The results show that 1)summer mean wind speed for 2020-2029 will be lower compared to those in 1990-1999 in most area of China; 2)annual and winter mean wind speed for 2081-2100 will be lower than those of 1971-1990 in the whole China; and 3)the changes of summer mean wind speed for 2081-2100 are uncertain.As a result,although climate models are absolutely necessary for projecting climate change to come,there are great uncertainties in projections,especially for wind speed,and these issues need to be further explored.     

A projection of future changes in summer precipitation and monsoon in East Asia

The future potential changes in precipitation and monsoon circulation in the summer in East Asia are projected using the latest generation of coupled climate models under Intergovernmental Panel on Climate Change (IPCC) Special Report on Emission Scenarios (SRES) A1B scenario (a medium emission scenario).The multi-model ensemble means show that during the period of 2010-2099,the summer precipitation in East Asia will increase and experience a prominent change around the 2040s,with a small increase (～1%) before the end of the 2040s and a large increase (～9%) afterward.This kind of two-stage evolution characteristic of precipitation change can be seen most clearly in North China,and then in South China and in the mid and lower Yangtze River Valley.In 2010-2099,the projected precipitation pattern will be dominated by a pattern of "wet East China" that explains 33.6% of EOF total variance.The corresponded time coefficient will markedly increase after the 2040s,indicating a great contribution from this mode to the enhanced precipitation across all East China.Other precipitation patterns that prevail in the current climate only contribute a small proportion to the total variance,with no prominent liner trend in the future.By the late 21st century,the monsoon circulation will be stronger in East Asia.At low level,this is due to the intensification of southwesterly airflow north of the anticyclone over the western Pacific and the SCS,and at high level,it is caused by the increased northeasterly airflow east of the anticyclone over South Asia.The enhanced monsoon circulation will also experience a two-stage evolution in 2010-2099,with a prominent increase (by ～0.6 m s-1) after the 2040s.The atmospheric water vapor content over East Asia will greatly increase (by ～9%) at the end of 21st century.The water vapor transported northward into East China will be intensified and display a prominent increase around the 2040s similar to other examined variables.These indicate that the enhanced precipitation over East Asia is caused by the increases in both monsoon circulation and water vapor,which is greatly different from South Asia.Both the dynamical and thermal dynamic variables will evolve consistently in response to the global warming in East Asia,i.e.,the intensified southwesterly monsoon airflow corresponding to the increased water vapor and southwesterly moisture transport.     

三维锥束代数重建算法的投影排序方案

代数重建算法中的投影访问顺序对重建图像的收敛速度和精度有很大的影响。针对三维锥束代数重建算法,比较了几种投影序列排序方案的重建图像收敛速度:顺序访问方案,多水平级排序方案,素数分解排序方案,加权距离排序方案。通过仿真实验得到的实验结果表明:在三维锥束ART算法中按照后三种投影序列排序方案排序后的图像重建比顺序访问方案的收敛速度快,并且WDS排序方案的收敛速度最好。     

边坡位移预测的非线性组合模型及应用

通过边坡现场监测位移序列来预测未来时间边坡的位移,可以有效地评价和判断边坡的稳定性。多种非线性分析方法的组合可以有效提高预测精度,将灰色理论与投影寻踪回归各自的优缺点的基础上,提出了将二者相结合的一种新的预测模型--时序投影寻踪回归模型。新模型既发挥了灰色预测方法中“累加生成”的优点,弱化了原始序列中随机扰动因素的影响,增强了数据的规律性,又充分利用了投影寻踪回归方法易于描述非线性关系的优良特性,避免了灰色预测方法及模型存在的理论缺陷。同时,对模型的可靠性进行了验证。将文中提出的时序投影寻踪回归方法应用到 2 个工程实例,研究结果表明该模型预测值与实测值吻合较好,具有较高的精度,可为边坡位移的预测提供一条新的途径。     

Back‐projection stacking of P‐ and S‐waves to determine location and focal mechanism of microseismic events recorded by a surface array

We present an automatic method of processing microseismic data acquired at the surface by a star‐like array. The back‐projection approach allows successive determination of the hypocenter position of each event and of its focal mechanisms. One‐component vertical geophone groups and three‐component accelerometers are employed to monitor both P‐ and S‐waves. Hypocenter coordinates are determined in a grid by back‐projection stacking of the short‐time‐average‐to‐long‐time‐average ratio of absolute amplitudes at vertical components and polarization norm derived from horizontal components of the P‐ and S‐waves, respectively. To make the location process more efficient, calculation is started with a coarse grid and zoomed to the optimum hypocenter using an oct‐tree algorithm. The focal mechanism is then determined by stacking the vertical component seismograms corrected for the theoretical P‐wave polarity of the focal mechanism. The mechanism is resolved in the coordinate space of strike, dip, and rake angles. The method is tested on 34 selected events of a dataset of hydraulic fracture monitoring of a shale gas play in North America. It was found that, by including S‐waves, the vertical accuracy of locations improved by a factor of two and is equal to approximately the horizontal location error. A twofold enhancement of horizontal location accuracy is achieved if a denser array of geophone groups is used instead of the sparse array of three‐component seismometers. The determined focal mechanisms are similar to those obtained by other methods applied to the same dataset.     

未来气候变化对天津市办公建筑制冷采暖能耗的影响

利用能耗模拟软件（TRNSYS）模拟了1971—2010年天津市办公建筑制冷和采暖能耗,结合未来不同排放情景（低排放：B1;中等排放：A1B）下气候预估数据,定量评估了未来（2011—2100年）气候变化对办公建筑能耗的影响。结果表明,2011—2100年热负荷呈显著的下降趋势,而冷负荷显著上升,冷负荷的上升幅度高于热负荷的下降,导致总能耗呈微弱的上升趋势;低排放情景下热负荷的下降和冷负荷的上升幅度低于中等排放情景,总能耗的变化在两种排放情景下没有明显差异;与1971—2010年相比,低排放和中等排放两种情景下2011—2050年热负荷下降10%左右,而冷负荷上升约12%,总能耗增加超过2%;2051—2100年热负荷的下降和冷负荷的上升更为明显,尤其是冷负荷上升（约30%）,总能耗增加8%左右,冷负荷变化率在两种情景下相差较大。     

等面积可伸缩地球网格投影分析与应用

详细介绍了等面积可伸缩地球网格(EASE-Grid)投影,包括参数设置、特征以及如何定义该投影。选择南半球的海洋环境数据——海表面温度进行了研究分析。结合常用的地图投影软件ArcGIS,实现了海表面温度基于等面积可伸缩地球网格投影的显示和应用,为我国捕捞南极磷虾提供数据支撑。     

锥束CT散射抑制方法综述

锥束CT严重的散射伪影极大地降低图像质量,成为限制其发展和应用的关键因素。国内外学者对散射抑制或校正方法已做了很多综述性的报道,但是随着锥束CT系统散射抑制研究的进一步推进,出现了一些新的技术。本文分析了X射线散射对CT成像的影响,对常用的散射抑制方法进行归纳总结,梳理散射校正框架,详细介绍基于投影补偿的散射校正技术和常用的散射估计方法,对目前散射校正的问题进行总结,重点讨论了散射校正对噪声的放大作用,为散射抑制的研究和发展提供借鉴作用。      

抗投影变换的矢量地理数据水印算法

在矢量地理数据水印算法研究中,以往研究较多考虑增删点、裁剪、平移、旋转等攻击方式,而对抗投影变换的攻击方式研究较少。由于投影变换在GIS中具有重要意义,故本文提出了一种抗投影变换的矢量地理数据水印算法。水印嵌入前,对待嵌矢量地理数据利用道格拉斯算法进行压缩,使用四叉树分块选取特征点,提取并保存特征点及其属性信息;水印嵌入采用坐标映射和量化机制以增强水印算法的鲁棒性;检测水印时,将待检测数据与原始特征点进行属性信息匹配,匹配成功的同名点采用二元三次多项式进行最小二乘法拟合,根据拟合的多项式系数对待检测数据进行投影变换,最终实现水印信息的提取。实验结果表明,本方法能抵抗投影变换攻击、增删点、几何变换以及它们的复合攻击,具有较好的可行性和实用性。