基于迭代法的同轴法X射线相衬成像的相位复原

相位复原问题是指在只有强度可以测量的情况下,从强度数据中提取出物体的相位信息。相位复原是同轴法X射线相衬成像的关键问题之一。本文采用误差递减法,通过限制物体的空间大小,结合测量到的强度数据,在物体的空域和频域都进行约束。通过反复迭代,进行带宽外推,最终实现物面和像面的相位复原。仿真实验证明了此迭代算法的收敛性,并且以塑料管为样品,在上海光源采集到同轴法X射线相衬成像的实验数据,对上述算法进行了验证。     

地幔上涌引起的破裂危险性

本文用二维非线性有限元方法,计算了一个地堑剖面因地幔上涌引起的破裂危险。在两侧边界挤压应力小于岩石静压力条件下,破裂危险增长区主要集中于地堑内部及地堑断层附近     

Damage detection of 3D structures using nearest neighbor search method

An innovative damage identification method using the nearest neighbor search method to assess 3 D structures is presented. The frequency response function was employed as the input parameters to detect the severity and place of damage in 3 D spaces since it includes the most dynamic characteristics of the structures. Two-dimensional principal component analysis was utilized to reduce the size of the frequency response function data. The nearest neighbor search method was employed to detect the severity and location of damage in different damage scenarios. The accuracy of the approach was verified using measured data from an experimental test; moreover, two asymmetric 3 D numerical examples were considered as the numerical study. The superiority of the method was demonstrated through comparison with the results of damage identification by using artificial neural network. Different levels of white Gaussian noise were used for polluting the frequency response function data to investigate the robustness of the methods against noise-polluted data. The results indicate that both methods can efficiently detect the damage properties including its severity and location with high accuracy in the absence of noise, but the nearest neighbor search method is more robust against noisy data than the artificial neural network.     

Significance of ichnofossils to genetic stratigraphy--Examples from the Cretaceous of Alberta, Canada

Trace fossils represent both sedimentological and paleontological entities, representing a unique blending of potential environmental indicators in the rock record. Trace fossils and trace fossil suites can be employed effectively to aid in the recognition of various discontinuity types and to assist in their genetic interpretation. Ichnology may be employed to resolve surfaces of stratigraphic significance in two main ways: 1) through the identification of discontinuities using substrate-controlled ichnofacies, and 2) through careful analysis of vertical softground (penecontemporaneous) ichnologic successions (analogous to facies successions). Ichnological analysis is a valuable tool in genetic stratigraphic studies. Integrating the data derived from substrate-controlled ichnofacies with paleoecological data from vertical ichnologic successions greatly enhances the recognition and interpretation of a wide variety of stratigraphic surfaces. When this is coupled with conventional facies analysis and sequence stratigraphy, a powerful approach to the interpretation of the rock record is generated.     

高密度电法数值模拟及其在寻找北京人头盖骨化石中的应用

为寻找埋藏在地下两米以内深度装有文物的木箱,采用高密度电阻率方法进行了探测.在完成三维正演与二维反演数值模拟的基础上进行了野外数据的反演解释工作,利用三维局部异常体的正演响应特征及二维反演结构与真实模型的对应关系,对实际的数据进行了认识解释,得到了目的层的异常体可能是地道而不是木箱的初步结论.实际表明,利用高密度电法来进行浅层的探测是可行的.     

基于瞬变电磁矩变换的快速三维反演方法

瞬变电磁法的严格三维反演计算复杂、占用资源多,在普通计算机上难以实现.本文引入瞬变电磁矩变换的概念,提出一种快速三维反演方法.该方法基于阻性限制(resistive limit)特性,建立包含异常体的三维大地的一阶矩响应正演算法,根据不同约束条件,选择优化的最速下降法实现瞬变电磁快速三维反演.文中通过含异常体的三维大地正演一阶矩与仿真数据一阶矩的对比,验证了快速三维正演算法的有效性,之后在不同约束条件下,利用优化的最速下降法实现了对含噪声的仿真瞬变电磁数据的快速三维反演.结果表明,该方法能够在普通计算机上短时间内较为准确地反演出地下异常体的体积和位置,在瞬变电磁数据的实时解释工作中具有良好的应用前景.     

Study on the feature selection and classifica－tion effect of precursory data of ground tilt

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三维电阻率测深数据Zohdy近似反演方法

Zohdy方法近似反演三维电阻率测深数据。正演计算采用有限单元法。反演初始模型由测量视电阻率数据给出。通过比较实测视电阻率值和预测模型计算的视电阻率值对数差来修改模型网格电阻率．为了解决任意电极距测深数据的反演,采用大、小双网格剖分。大网格反映地下电性分布情况。小网格用于实际有限元正演计算．在电阻率调整公式中加入一个迭代系数,能够加快收敛速度．并对加5％随机噪声的模型理论视电阻率测深断面数据进行反演,得到的电阻率分布与模型电阻率基本一致．     

Developing and testing the Automated Post-Event Earthquake Loss Estimation and Visualisation (APE-ELEV) technique

An automated, real-time, multiple sensor data source relying and globally applicable earthquake loss model and visualiser is desirable for post-event earthquake analysis. To achieve this there is a need to support rapid data ingestion, loss estimation and integration of data from multiple data sources and rapid visualisation at multiple geographic levels. In this paper, the design and development of the Automated Post-Event Earthquake Loss Estimation and Visualisation (APE-ELEV) system for real-time estimation and visualisation of insured losses incurred due to earthquakes is presented. A model for estimating ground up and net of facultative losses due to earthquakes in near real-time is implemented. Since post-event data is often available immediately from multiple disparate sources, a geo-browser is employed to facilitate the visualisation and integration of earthquake hazard, exposure and loss data. The feasibility of APE-ELEV is demonstrated using a test case earthquake that occurred in Tohoku, Japan (2011). The APE-ELEV model is further validated for ten global earthquakes using industry loss data.     

电缆地层测试器在渗透率各向异性地层中的响应

为正确地设计仪器和解释电缆地层测试器的测量结果,文中建立了渗透率各向异性地层中电缆地层测试器响应的数学模型,并利用三维有限元方法得到其数值,解得到了压力场随时间、距离变化及等压面等的各种结果。     

用佘山地震台观测资料进行中长期地震趋势异常分析

通过对上海观测的形变资料,运用EIS 2000软件,分析余山地震台倾斜记录资料的中期趋势.在排除干扰的前提下,结合差分、一阶差分等各种分析方法来分析这一区域的形变资料.发现强震发生前,余山地震台的倾斜仪器从中期趋势上出现了明显的趋势转折、加速、变化现象.在差分异常频次累加等分析方法中,也找到了类似的大震前的能量异常现象,值得关注.     

Non-linear buffeting response analysis of long-span suspension bridges with central buckle

The rigid central buckle employed in the Runyang Suspension Bridge (RSB) was the first time it was used in a suspension bridge in China. By using a spectral representation method and FFT technique combined with measured data,a 3D fluctuating wind field considering the tower wind effect is simulated. A novel FE model for buffeting analysis is then presented,in which a specific user-defined Matrix27 element in ANSYS is employed to simulate the aeroelastic forces and its stiffness or damping matrices are parameterized by wind velocity and vibration frequency. A nonlinear time history analysis is carried out to study the influence of the rigid central buckle on the wind-induced buffeting response of a long-span suspension bridge. The results can be used as a reference for wind resistance design of long-span suspension bridges with a rigid central buckle in the future.     

Inverse analysis of weak and strong motion downhole array data from the Mw7.0 Sanriku-Minami earthquake

A hybrid optimization scheme, comprising a genetic algorithm in series with a local least-squares fit operator, is used for the inversion of weak and strong motion downhole array data obtained by the Kik-Net Strong Motion Network during the M_w7.0 Sanriku-Minami Earthquake. Inversion of low-amplitude waveforms is first employed for the estimation of low-strain dynamic soil properties at five stations. Successively, the frequency-dependent equivalent linear algorithm is used to predict the mainshock site response at these stations, by subjecting the best-fit elastic profiles to the downhole-recorded strong motion. Finally, inversion of the mainshock empirical site response is employed to extract the equivalent linear dynamic soil properties at the same locations. The inversion algorithm is shown to provide robust estimates of the linear and equivalent linear impedance profiles, while the attenuation structures are strongly affected by scattering effects in the near-surficial heterogeneous layers. The forward and inversely estimated equivalent linear shear wave velocity structures are found to be in very good agreement, illustrating that inversion of strong motion site response data may be used for the approximate assessment of nonlinear effects experienced by soil formations during strong motion events.     

反插值法实现地球物理数据快速网格化

本文借鉴反演理论，采用反插值法实现地球物理数据的快速网格化.首先由已知点与未知网格点的反距离拓扑关系建立反演方程，用已知点值直接计算出其所在网格的未知网格点值，再利用Laplacian算子滤波，使得模型光滑，且能量最小化.利用预条件共轭梯度法求解网格化方程组，并结合螺旋坐标系思想和Wilson\|Burg谱分解法，将二维数据的滤波处理转换到一维空间进行处理，实现二维数据快速滤波.另外，引入了阻尼约束，保证求解稳定、迭代收敛.最后，应用该方法对合成数据和实际资料进行了试验.     

逆散射级数法去除自由表面多次波

压制多次波是地震资料处理过程中的重要环节之一,多次波去除的效果直接影响到最后成像的质量．本文研究的逆散射级数法以波动方程和Born级数为基础,构造一个与自由表面多次波相关的子序列来预测并消除多次波,该方法不需要知道地下的速度结构信息,适用于各种复杂的地下情况．在逆散射级数法的实现过程中,地震子波和近道波场是必不可少的信息,本文采用能量最低法则和带限抛物Radon变换法来弥补原始地震资料中所缺失的这些信息．合成资料和实际地震资料的处理结果表明,逆散射级数法能够在去除自由表面多次波的同时保留有效波的信息,对于地下复杂结构的情况同样有效．     

Comparison of global geopotential models from the champ and grace missions for regional geoid modelling in Turkey

The continuous efforts on establishment and modernization of the geodetic control in Turkey include a number of regional geoid models that have been determined since 1976. The recently released gravimetric Geoid of Turkey, TG03, is used in geodetic applications where GPS-heights need to be converted to the local vertical datum. To reach a regional geoid model with improved accuracy, the selection of the appropriate global geopotential model is of primary importance. This study assesses the performance of a number of recent satellite-only and combined global geopotential models (GGMs) derived from CHAMP and GRACE missions’ data in comparison to the older EGM96 model, which is the underlying reference model for TG03. In this respect, gravity anomalies and geoid heights from the global geopotential models were compared with terrestrial gravity data and low-pass filtered GPS/levelling data, respectively. Also, five new gravimetric geoid models, computed by the Fast Fourier Transform technique using terrestrial gravity data and the geopotential models, were validated at the GPS/levelling benchmarks. The findings were also compared with the validation results of the TG03 model. The tests showed that as it was expected any of the high-degree combined models (EIGEN-CG03C, EIGEN-GL04C, EGM96) can be employed for determining the gravity anomalies over Turkey. In the west of Turkey, EGM96 and EIGEN-CHAMP03S fit the GPS/levelling surface better. However, all the tested GGMs revealed equal performance when they were employed in gravimetric geoid modelling after de-trending the gravimetric geoid model with corrector surface fitting. The new geoid models have improved accuracy (after fit) compared to TG03.     

土-结构相互作用对结构监测与辨识结果的影响

通过对一个现有建筑的结构动态参数的辨识讨论了土与结构的相互作用.目标建筑是建于1998年的8层的型钢混凝土结构.在此研究中,8自由度的模型被建立以分析微震观测数据,随即,非参数和参数技巧以辨识此结构的自然频率,阻尼率和层硬度等.在考虑土-结构相互作用和不考虑土-结构相互作用的两种情况下,分别辨识结构的参数并对比结果以证...     

UK 1-D regional velocity models by analysis of variance of P-wave travel times from local earthquakes

A method is presented for deriving 1-D velocity depth models from earthquake bulletin data. The models can be used as initial models for more advanced modelling techniques such as tomographic inversion. The method is useful when there is little or no refraction and long-range reflection survey data. The bulletin travel times are subjected to an analysis of variance, where they are separated into source, distance, and receiving station terms. The distance terms describe the variation of travel time with distance, and the associated trend lines allow 1-D velocity models for the crustal layers to be determined. The velocity models provide an average crustal model for the region derived from local data. This does not include superficial layers which are necessarily poorly determined. Earthquake bulletin P-wave data from propagation paths across three different regions of the UK are employed to illustrate the use of the technique.     

Least-squares modification of extended Stokes’ formula and its second-order radial derivative for validation of satellite gravity gradiometry data

The gravity anomalies at sea level can be used to validate the satellite gravity gradiometry data. Validation of such a data is important prior to downward continuation because of amplification of the data errors through this process. In this paper the second-order radial derivative of the extended Stokes’ formula is employed and the emphasis is on least-squares modification of this formula to generate the second-order radial gradient at satellite level. Two methods in this respect are proposed: (a) modifying the second-order radial derivative of extended Stokes’ formula directly, and (b) modifying extended Stokes’ formula prior to taking the second-order radial derivative. Numerical studies show that the former method works well but the latter is very sensitive to the proper choice of the cap size of integration and degree of modification.     

A Genetic Algorithm Variational Approach to Data Assimilation and Application to Volcanic Emissions

Variational data assimilation methods optimize the match between an observed and a predicted field. These methods normally require information on error variances of both the analysis and the observations, which are sometimes difficult to obtain for transport and dispersion problems. Here, the variational problem is set up as a minimization problem that directly minimizes the root mean squared error of the difference between the observations and the prediction. In the context of atmospheric transport and dispersion, the solution of this optimization problem requires a robust technique. A genetic algorithm (GA) is used here for that solution, forming the GA-Variational (GA-Var) technique. The philosophy and formulation of the technique is described here. An advantage of the technique includes that it does not require observation or analysis error covariances nor information about any variables that are not directly assimilated. It can be employed in the context of either a forward assimilation problem or used to retrieve unknown source or meteorological information by solving the inverse problem. The details of the method are reviewed. As an example application, GA-Var is demonstrated for predicting the plume from a volcanic eruption. First the technique is employed to retrieve the unknown emission rate and the steering winds of the volcanic plume. Then that information is assimilated into a forward prediction of its transport and dispersion. Concentration data are derived from satellite data to determine the observed ash concentrations. A case study is made of the March 2009 eruption of Mount Redoubt in Alaska. The GA-Var technique is able to determine a wind speed and direction that matches the observations well and a reasonable emission rate.