声波测井仪器的等效理论及其应用(英文)   总被引：3，自引：0，他引：3  

苏远大  唐晓明  黑创  庄春喜 《应用地球物理》2011,8(1):69-78

在处理实际声波测井模式波数据或用模式波的反演地层参数时,必须考虑测井仪器对频散模式波传播的影响。本文介绍了一种用具有等效弹性模量的圆柱体来模拟声波测井仪器的等效理论,并将该理论推广应用到电缆、随钻多极子声波测井。在波长大于仪器半径的前提下,将井中的多极子声场与该等效仪器模型进行声导纳/阻抗匹配,便可导出这一理论。通过数值模拟和现场资料对该理论的有效性和实用性进行了验证,验证结果证明该理论既简单又足够精确。利用该理论模型处理实际资料时,通过调整仪器等效弹性模量和半径在给定频段标定仪器的影响,而不必考虑仪器的具体材料和结构。本文以电缆偶极子声波测井现场资料的频散校正为例,进一步证明了该等效理论处理现场资料的准确性和高效性。  相似文献   

用强震记录检验深厚土层小应变下一维等效线性化土层地震反应     

刘峥  徐永林  王绍博  李斌  胡俊  熊里军  徐海云 《震灾防御技术》2011,6(4):372-383

本文以强震记录为基础,通过土层地震反应计算得到了地表加速度与加速度反应谱,对比研究了由强震记录得到的地表加速度以及由地表加速度得到的与土层地震反应相同阻尼下的加速度反应谱.结果表明:在高频段与中频段,用一维等效线性化计算得到的土层地震反应加速度值与反应谱值比地表实测得到的加速度记录值与加速度反应谱值偏低;但在低频段,计...  相似文献   

Numerical analysis of permafrost effects on the seismic site response     

Zhaohui Yang  Utpal Dutta  Gang Xu  Kenan Hazirbaba  Elmer E. Marx 《Soil Dynamics and Earthquake Engineering》2011

Some of the damage to the infrastructure observed in past earthquakes occurred in Alaska could be related to the existence of permafrost. However, only limited research has been carried out so far to investigate the effects of permafrost on the seismic site response. Permafrost with relatively high shear wave velocity (1000–1500 m/s) extensively exists in the interior of Alaska and causes anomaly in the shear wave velocity profile that may alter the site response. In current design practices, permafrost has been treated as bedrock and its potential effects on site response are ignored. A systematic investigation was conducted to understand the effects of permafrost on the ground motion characteristics using one-dimensional equivalent linear analysis for the MCE, AASHTO and IBC Design Earthquake level hazards. The average surface displacement, velocity and acceleration response spectra for a typical permafrost site were obtained and the worst case scenario was identified. The results show that the presence of permafrost can significantly alter the ground motion characteristics and it may not be conservative to ignore the effects of permafrost in the seismic design of civil structures.  相似文献   

Dynamics of steel offshore platforms under ship impact     

《Applied Ocean Research》2014

This paper deals with the prediction of the dynamic response of steel offshore platforms to high energy impacts from typical supply vessels. The contribution of the high modes of a cantilever beam type structure with a concentrated top mass subjected to transverse impact from rigid and deformable strikers is analysed. A procedure to develop simplified equivalent systems for efficient structural response analysis is presented and its reliability tested by comparing the results from the explicit non-linear FE simulations. Effects such as the overall rotation of the installation, plastic deformations in the contact area, different impact locations and different hinge mechanisms are taken into account. It is shown that the use of the proposed equivalent systems with a reduced number of DOF's can provide accurate results at significantly less computational efforts as compared to the FE simulations. The derivation of some parameters of the equivalent dynamic elastic–plastic SDOF/2SDOF systems, however, needs to consider the complexity of the analysed steel frames and perform preliminary non-linear static analyses. Therefore, further studies of different impact scenarios on platforms with different configurations are recommended to augment the results presented here.  相似文献   

非球形气溶胶粒子散射特性及其等效Mie散射误差分析   总被引：3，自引：2，他引：1  

胡帅  高太长  刘磊 《气象科学》2014,34(6):612-619

为分析形状对气溶胶粒子散射特性的影响,采用T矩阵法计算了0.633μm波段(自然光)不同种类、形状的气溶胶单粒子与体散射的散射相函数,并讨论了气溶胶粒子形状畸变与等效Mie散射误差的变化规律。结果表明:粒子形状畸变对气溶胶粒子散射能量空间分布影响较大。对于单粒子,各散射角上的等效Mie散射误差并不随粒子形状畸变程度单调变化。从相对误差量级上看,形状畸变对180°散射的影响强于0°,对35°的散射影响相对较弱。对于两种非球形粒子等效方法,等表面积法优于等体积法。不同类型的非球形气溶胶粒子体散射存在显著差异,沙尘性与海洋性的等效Mie散射误差明显大于煤烟性与可溶性粒子;对于同一种气溶胶,形状的改变对侧向与后向散射影响显著,对前向散射影响不大。  相似文献   

伴随2000年9月30日sawtooth事件地磁变化和电流楔特征研究          下载免费PDF全文

林悯惠  邓晓华  袁志刚  王敬芳 《地球物理学报》2010,53(10):2280-2290

为了解极光电集流在sawtooth事件期间的响应情形,本文利用北半球高纬地磁台站的磁场数据,建立了以球元基本电流系反演法求得大尺度电离层水平等效电流系分布的方法,以此研究了2000年9月30日同步轨道LANL卫星观测到的sawtooth事件期间极光电集流的变化.本文将sawtooth注入事件后极区电离层夜侧西向电集流增长的特征,与中低纬地基磁场北向分量正弯扰的特征做比较分析.两者的观测结果都表明在本sawtooth注入事件期间有电流楔的形成,且电流楔约有11 h磁地方时(MLT)的宽度.此外,中低纬磁弯扰达到最大扰动值的时间一般比高纬电集流达到最大扰动值的时间长,说明影响中低纬磁弯扰变化的电流源较丰富.  相似文献   

Assessing Mongolian snow disaster risk using livestock and satellite data   总被引：3，自引：0，他引：3  

K. Tachiiri  M. Shinoda  B. Klinkenberg  Y. Morinaga   《Journal of Arid Environments》2008,72(12):2251-2263

In Mongolia, several record-breaking disastrous dzuds (mass livestock loss directly induced by harsh winter conditions but often influenced by drought in the previous summer) occurred from 1999 to 2003. To understand the mechanism of this climatic disaster, we conducted a tree regression analysis. The predictor variables included two indices developed from remote sensing data—the Normalized Difference Vegetation Index (NDVI) and the Snow Water Equivalent (SWE)—as well as the previous year's livestock numbers and mortality rates. According to the model, serious livestock mortality was associated with low NDVI values (i.e., poor vegetation) in August of the previous year, high SWE values (i.e., significant snow accumulation) in December of the previous year, a high previous year's mortality, and high previous year's livestock population. This result suggests that for dzud risk assessment, we need to monitor snowfall in winter, the vegetation condition in the previous summer, and the density and health condition of the livestock. The tree-based model developed in this study is effective only for a white dzud (deep snow), the most common type of dzud. The large cross-validation error indicates that more data are needed before using the model in order to make predictions.  相似文献   

煤层陷落柱散射波数值模拟与成像   总被引：1，自引：1，他引：0       下载免费PDF全文

曹志勇  王伟  王赟 《地球物理学报》2012,55(5):1749-1756

煤层陷落柱是煤田勘探开发中常见的一种典型的非均匀地质体.由于来自陷落柱的反射信号少、反射能量弱,使得基于反射波原理的常规地震成像方法难以有效识别陷落柱.本文以散射波理论为基础,采用数值模拟方法,研究了陷落柱的散射波场特征,研究表明地面接收的波场中含有来自陷落柱陡倾角界面的散射波场.通过共散射点道集波场的模拟,可以清晰地识别散射波,获得地下散射点和非均匀地质体的信息,判断散射点的位置,从而勾画出不均匀地质体的形态.采用等效偏移距假设抽取共散射点道集,在此基础上进行叠前偏移,对陷落柱成像;模拟与实际数据成像结果对比表明此方法能够合理地提取散射点的散射波场信息,对陷落柱形态及内部结构准确成像,是一种有效的煤田陷落柱成像方法.  相似文献   

设定场源参数的区域重力微变化特征与模型实验     

郑秋月  陈石  李晓一  徐伟民 《地震》2016,36(4):186-195

流动重力测量作为地震前兆监测手段之一, 所得到的区域重力场微变化信号反映地壳内部密度变化、 地壳变形、 流体运移等信息。 采用定量化和模型化方法研究与地震孕育相关的重力场变化信号时空特征, 对于构建地震预报定量化指标体系具有重要意义。 通过设定场源参数构建了数值模型, 正演得到了多组不同场源条件下的重力场变化模型; 通过模型对比, 分析了重力变化与重力梯度变化对不同类型场源参数的关系。 研究结果表明: 重力垂直梯度变化对异常体边界比较敏感, 特对浅部异常更为敏感, 适用于圈定异常体范围。 以此为基础提出了观测系统的优化测量方案, 以及对观测精度的需求。 研究结果对于构建地震预报指标参数, 优化流动重力观测系统具有一定参考意义。  相似文献   

Binary upscaling on complex heterogeneities: The role of geometry and connectivity     

《Advances in water resources》2014

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