台风激发的第二类地脉动特征及激发模式分析

0.003~1 Hz频段的地脉动主要来源于海浪运动与固体地球的耦合作用,台风引起的强烈海浪运动往往可使地脉动能量显著增强.由于涉及大气-海洋-固体地球三个圈层之间的复杂动量传递与耦合过程,迄今为止,关于台风激发地脉动的具体源区位置及激发机制尚存在争议.本文选取日本、中国东南沿海及台湾地区的地震台站波形连续记录,研究了2008年台风“森拉克”和“黑格比”激发地脉动的时频特征,开展相应数值模拟,并与观测数据进行了对比分析研究.结果表明台风激发第二类地脉动存在两种主要模式：（1）近岸源区激发,即台风引起波浪入射至海岸反射并与后续来波相互作用形成驻波作用于海底而激发;（2）台风中心附近源区激发,即台风中心移动过程中不同时期激发的同频率波浪相向传播、相互作用产生驻波作用于海底而激发,源区位置主要集中于台风中心左后方.此外,结合波浪再分析数据、台风风场特征,我们进一步对第二类地脉动激发过程中的影响因素进行了分析,发现：第一种模式激发的地脉动与近岸源区波浪场强度、观测点至源区距离及台风中心至海岸线距离等因素相关;而第二种模式激发的地脉动则主要受台风中心附近波浪场的频率成分与传播方向影响.

     

有限差分的时间和空间频散及其对逆时偏移和全波形反演的影响

有限差分是最常用的地震波方程数值模拟方法,但时间和空间离散会产生数值频散.正演是逆时偏移和全波形反演的基本单元,成像和反演的精度很大程度依赖于所采用的数值模拟算法.本文研究了有限差分的时间和空间频散特性及其对逆时偏移和全波形反演的影响.通过时间有限差分+伪谱法、时间频散校正+空间有限差分、时间频散校正+伪谱法获取时间频散、空间频散和无频散数据;发展了抗时间频散、抗空间频散、抗时间+空间频散的逆时偏移和全波形反演方法;采用理论模型和实际资料对提出的方法进行了测试.数值结果表明：逆时偏移同时受时间和空间频散影响,时间频散导致同相轴不聚焦、成像位置偏离,空间频散会产生高频噪声和虚假反射界面;全波形反演在低频大尺度反演中几乎不受时间和空间频散影响,高频精细反演中时间频散引起波形相移、降低反演精度,空间频散增加多解性、导致反演不收敛;抗频散方法可以有效缓解时间和空间频散影响,获得高质量的偏移剖面和反演结果.

     

Nonlinear behavior of high-damping rubber bearings under horizontal bidirectional loading: full-scale tests and analytical modeling

Horizontal bidirectional loading tests are conducted for real-sized high-damping rubber (HDR) bearings with diameters of 700 mm (HDR700) and 1300 mm (HDR1300). The hysteresis loops of these bearings under bidirectional horizontal loadings are compared with those under unidirectional loadings. The results show that the bearing force measurement in the primary direction of loading increases when there is displacement in the orthogonal direction. Unusually, the maximum restoring force in the orthogonal direction to the primary loading direction occurs near zero displacement. On the basis of the observations of the restoring forces, a rate-independent model is proposed. This model simulates well the test results under both bidirectional loading and unidirectional loading. It can reproduce the irregular restoring forces characteristics around zero displacement as described above. Bidirectional loading induced twist deformation in the HDR bearings that increased local shear strains. This phenomenon results in an early failure as observed in HDR700. The additional shear strain is estimated based on the twist deformation measured by video image analysis. The comparison of the nominal total shear stress demonstrates that the increase of shear stress because of bidirectional loading occurs when the average shear strain is larger than about 200%. The larger the shear strain, the greater the bidirectional effect. It is shown that the nominal total shear stress of average strain of 350% under bidirectional circular loading pattern is approximately the same as the average shear strain of 400% under unidirectional loading. This means that the average shear strain of 350% under a bidirectional circular loading corresponds to a local shear strain of 400%. Copyright © 2012 John Wiley & Sons, Ltd.     

Understanding and managing the morphology of branches incising into sand-clay deposits in the Dutch Rhine Delta

In the Rhine-Meuse delta in the south-western part of the Netherlands,the morphology of the river branches is highly dependent on the erodibility of the subsoil.Erosion processes that were initiated after closure of the Haringvliet estuary branch by a dam(in 1970),caused a strong incision of several connecting branches.Due to the geological evolution of this area the lithology of the subsoil shows large variations in highly erodible sand and poorly erodible peat and clay layers.This study shows how the geological information can be used to create 3D maps of the erodibility of the sub-soil, and how this information can be used to schematize the sub-soil in computational models for morphological simulations.Local incisement of sand patches between areas with poorly erodible bed causes deep scour holes,hence increasing the risk on river-bank instability(flow slides) and damage to constructions such as groynes,quays,tunnels, and pipelines.Various types of mathematical models,ranging from 1D(SOBEK) to quasi-3D(Delft3D) have been applied to study the future development of the river bed and possible management options.The results of these approaches demonstrate that models require inclusion of a layer-bookkeeping approach for sub-soil schematization, non-uniform sediment fractions(sand-mud),tidal and river-discharge boundary conditions,and capacity-reduction transport modeling.For risk-reducing river management it has been shown how the development of the river bed can be addressed on a large scale and small scale.For instance,the use of sediment feeding and fixation of bed can be proposed for large-scale management,while monitoring and interventions at initiation of erosion can be proposed as response to small-scale developments that exceed predefined intervention levels.     

基于倾斜摄影测量的大比例尺三维测图技术

目前,城市大比例尺地形图更新主要采用全野外的测量方法,不仅耗费大量的劳动力,并且效率低下。旋翼机和倾斜摄影测量技术的快速发展,为城市大比例尺地形图的测绘与更新提供了全新的技术手段。本文以滕州市城区约10 km2的1∶500地形图测绘项目为例,采用大疆精灵4 Pro旋翼机进行数据获取,Smart 3D软件进行空三加密及三维建模,最后在EPS软件中进行三维测图,并对地形图成果进行了精度检核,验证了技术方案的可行性,为同类项目提供了有益参考。     

塔河油田6~7区孔洞型碳酸盐岩储层建模

塔河油田6~7区奥陶系碳酸盐岩储层受岩溶作用影响,非均质性极强。因此,准确地刻画储集体的形态及三维空间展布对油气田的勘探开发至关重要。在对研究区奥陶系缝洞型碳酸盐岩储层纵向发育规律的认识的基础上,首次提出采用"多点统计学"进行储集相建模的基本思路。根据地震属性与孔洞型储层之间的对应关系优选"特征属性",建立基于"特征属性"的"训练图像";以钻井、地震识别以及测井解释成果作为硬数据,地震波阻抗的溶洞发育概率体作为软数据,进行"储集相"模拟。结果表明:该方法不仅实现了对孔洞型储集体形态的模拟,而且再现了孔洞型储集体的复杂结构及空间分布,同时模拟结果与该类型储集体的纵向发育规律相符。     

离心模拟技术中运动学的物理意义

研究离心模拟中的运动学,有助于提高对离心模型试验结果的认识。笔者推导了描述离心模型中任一质点运动的整体速度和加速度的数学表达式。按照牛顿第二定律,在离心模拟中的加速度是连接运动学与动力学的重要因素。笔者描述了整体加速度表达式中各项的物理意义,指出了离心机稳定运转时的向心加速度、由角加速度效应引起的切向加速度、互补(复合向心)加速度分量、径向(原型的竖向)、环向和轴向(原型的两个水平方向)振动效应以及离心机臂伸长效应对整体加速度的贡献。分析结果表明,对于单向振动的动力离心模拟试验,选轴向(平行于转轴)为振动方向便于理解试验结果。另外,仔细检查了Schofield[1]对离心模拟中运动学的描述并发现其混淆之处。     

Modeling Methane Emissions from Paddy Rice Fields under Elevated Atmospheric Carbon Dioxide Conditions

Methane(CH4 ) emissions from paddy rice fields substantially contribute to the dramatic increase of this greenhouse gas in the atmosphere.Due to great concern about climate change,it is necessary to predict the effects of the dramatic increase in atmospheric carbon dioxide(CO2 ) on CH4 emissions from paddy rice fields.CH4MOD 1.0 is the most widely validated model for simulating CH4 emissions from paddy rice fields exposed to ambient CO2(hereinafter referred to as aCO2 ).We upgraded the model to CH4MOD 2.0 b...     

Multi-physics modeling of flow and transport in porous media using a downscaling approach

Multi-phase flow and transport processes generally occur on different spatial and temporal scales. Very often also, within a physical system, they vary in space meaning that different kinds of processes might take place in different parts of the system. In order to account for the variety of processes and to take their scale-dependence into account, the development of multi-scale multi-physics techniques can be envisaged.     

Parametric study for optimal design of large piled raft foundations on sand

In designing piled raft foundations, controlling the total and differential settlements as well as the induced bending moments of the raft is crucial. The majority of piled raft foundations have been designed by placing piles uniformly. In such a design method, the settlements of the piled rafts are likely to be large, which leads to an increase of the pile length and/or number of piles required to reduce the settlements. However, this increase does not satisfy the requirement for economical design. On the basis of a parametric study, this paper contributes a framework for considering an economical design methodology in which piles are placed more densely beneath the column positions when the piled raft is subjected to column loads. The analysis uses PLAXIS 3D software, and the validity of the parametric study is examined through the results of centrifuge model tests conducted by the authors. The study shows that the concentrated pile arrangement method can help to considerably reduce the total and differential settlements as well as the induced bending moments of the raft. Moreover, the effects of parameters, such as pile length, pile number, raft thickness and load types, on the piled raft behavior are investigated. This study can help practicing engineers choose pile and raft parameters in combination with the concentrated pile arrangement method to produce an economical design.