3D forward modeling and response characteristics of low-resistivity overburden of the CFS-PML absorbing boundary for ground-well transient electromagnetic method

This study used the stable and convergent Dufort-Frankel method to differentially discretize the diffusion equation of the ground-well transient electromagnetic secondary field.The absorption boundary condition of complex frequency-shifted perfectly matched layer(CFS-PML)was used for truncation so that the low-frequency electromagnetic wave can be better absorbed at the model boundary.A typical three-dimensional(3D)homogeneous half-space model was established and a low-resistivity cube model was analyzed under the half-space condition.The response patterns and drivers of the low-resistivity cube model were discussed under the influence of a low-resistivity overburden.The absorption boundary conditions of CFS-PML significantly affected the low-frequency electromagnetic waves.For a low-resistivity cube around the borehole,its response curve exhibited a single-peak,and the extreme point of the curve corresponded to the center of the low-resistivity body.When the low-resistivity cube was directly below the borehole,the response curve showed three extreme values(two high and one low),with the low corresponding to the center of the low-resistivity body.The total field response of the low-resistivity overburden was stronger than that of the uniform half-space model due to the low-resistivity shielding effect of electromagnetic waves.When the receiving-transmitting distance gradually increased,the effect of the low-resistivity overburden was gradually weakened,and the response of the low-resistivity cube was strengthened.It was affected by the ratio of the overburden resistivity to the resistivity of the low-resistivity body.

基于Forward-Modeling方法的黑河流域水储量变化特征研究

黑河流域陆地水储量变化对流域下游等周边区域水资源的合理利用以及经济和社会发展等有着重要的意义.本文利用2003年1月至2013年12月的GRACE RL05数据反演了黑河流域陆地水储量长时间序列的变化,并针对重力场模型和数据处理中产生的信号泄漏问题,采用Forward-Modeling方法进行了改正并恢复泄漏信号;将GRACE获得的泄漏信号恢复前后的黑河流域水储量变化结果与全球水文模型GLDAS和CPC进行比较分析,结果表明泄漏信号改正后的结果与水文模型结果的时间序列相关性均有明显提高,从其空间分布结果可以看出Forward-Modeling方法有效地恢复初始信号、增强被湮没的信号,泄漏信号误差减小;通过分析黑河流域水储量变化的长时间序列结果,发现其具有明显的阶段性变化特征,即2003—2006年呈明显下降趋势,约为-0.86cm·a-1,在2007—2010年趋于平衡状态,而2011—2013年则呈现缓慢上升趋势约为0.14cm·a-1;联合GRACE数据和GLDAS数据反演了黑河流域地下水储量变化,并与全球降雨数据GPCC进行了比较分析,两者相关性可达到0.88以上.

A Gravity Forward Modeling Method based on Multiquadric Radial Basis Function

It is one of the most important part to build an accurate gravity model in geophysical exploration.Traditional gravity modelling is usually based on grid method,such as difference method and finite element method widely used.Due to self-adaptability lack of division meshes and the difficulty of high-dimensional calculation.

Real-time forward modeling and inversion of logging-while-drilling electromagnetic measurements in horizontal wells

Based on the pseudo-analytical equation of electromagnetic log for layered formation,an optimal boundary match method is proposed to adaptively truncate the encountered formation structures.An efficient integral method is put forward to significantly accelerate the convergence of Sommerfeld integral.By asymptotically approximating and subtracting the first reflection/transmission waves from the scattered field,the new Sommerfeld integral method has addressed difficulties encountered by the traditional digital filtering method,such as low computational precision and limited operating range,and realized the acceleration of the computation speed of logging-while-drilling electromagnetic measurements(LWD EM).By making use of the priori information from the offset/pilot wells and interactively adjusting the formation model,the optimum initial guesses of the inversion model is determined in order to predict the nearby formation boundaries.The gradient optimization algorithm is developed and an interactive inversion system for the LWD EM data from the horizontal wells is established.The inverted results of field data demonstrated that the real-time interactive inversion method is capable of providing the accurate boundaries of layers around the wellbore from the LWD EM,and it will benefit the wellbore trajectory optimization and reservoir interpretation.

Forward modeling to improve seismic reflection energy of a protective coal seam based on Zoeppritz equation

In seismic exploration for coal, seismic waves are very difficult to transmit downward because of high velocity protective layers, making the reflection information very hard to receive above ground. Based on the Snell law and the Zoeppritz equation, we studied the relationship between the incidence angle and reflection seismic wave energy using a forward model of level media. The result shows that the seismic wave energy has a sudden increase at the critical angle. Based on the energy propagation rule, using big offset to receive the seismic wave energy under a protective layer can effectively reduce its protection effect.

The parallel 3D magnetotelluric forward modeling algorithm

3D 磁电机的工作量碲的向前当模特儿的算法那么大传统的连续算法花费一极其大计算时间。然而，向前为算法建模的 3D 能在频率域处理数据，它对平行计算很合适。与 MPI 并且基于 3D 磁电机的流动的分析的优点碲的连续前面的算法，我们建议平行计算的想法并且使用它。三个理论模型被测试，实行效率处于不同状况被比较。结果显示向前为计算建模的平行 3D 是正确的，效率极大地被改进。这个方法对大尺寸合适地球物理的计算。

One-way wave equation seismic prestack forward modeling with irregular surfaces

数学地震检波器(MG )(et ) 并且相等时间的叠原则被用来实现向前用单程的声学的波浪方程与不规则的表面当模特儿的地震 prestack。这个方法从表面下的使用受到地震主要思考一套虚拟 MG。接收装置能位于在任何地方不规则的观察表面。而且， ETS 方法利用单程的声学的波浪方程到容易并且快速想象并且外推地震思考数据。方法用普通射击集合由二个简单模型，的数字前面的建模计算了的高单个噪音的比率被说明有扁平的表面的和有不规则的表面的，和复杂正常指责模型。为不规则的表面地形学的一个 prestack 深度迁居方法被用来与高精确性复制正常差错模型。

Forward modeling for “earth-ionosphere” mode electromagnetic field

A fixed artificial source(greater than 200 kW) was used and the source location was selected at a high resistivity region to ensure high emission efficiency. Some publications used the "earth-ionosphere" mode in modeling the electromagnetic(EM) fields with the offset up to a thousand kilometer, and such EM fields still have a signal/noise ratio of 10-20 dB. This means that a new EM method with fixed source is feasible, but in their calculation, the displacement in air was neglected. In this work, some three-layer modeling results were presented to illustrate the basic EM fields' characteristics in the near, far and waveguide areas under "earth-ionosphere" mode, and a standard is given to distinguish the boundary of near, far and waveguide areas. Due to the influence of the ionosphere and displacement current in the air, the "earth-ionosphere" mode EM fields have an extra waveguide zone, where the fields' behavior is very different from that of the far field zone.

Three-dimensional forward modeling for magnetotelluric sounding by finite element method

A finite element algorithm combined with divergence condition was presented for computing three-dimensional(3D) magnetotelluric forward modeling. The finite element equation of three-dimensional magnetotelluric forward modeling was derived from Maxwell's equations using general variation principle. The divergence condition was added forcedly to the electric field boundary value problem, which made the solution correct. The system of equation of the finite element algorithm was a large sparse, banded, symmetric, ill-conditioned, non-Hermitian complex matrix equation, which can be solved using the Bi-CGSTAB method. In order to prove correctness of the three-dimensional magnetotelluric forward algorithm, the computed results and analytic results of one-dimensional geo-electrical model were compared. In addition, the three-dimensional magnetotelluric forward algorithm is given a further evaluation by computing COMMEMI model. The forward modeling results show that the algorithm is very efficient, and it has a lot of advantages, such as the high precision, the canonical process of solving problem, meeting the internal boundary condition automatically and adapting to all kinds of distribution of multi-substances.

Estimation of Displacement and Extension due to Reverse Drag of Normal Faults: Forward Method

In the case of reverse drag of normal faulting, the displacement and horizontal extension are determined based on the established equations for the three mechanisms: rigid body, vertical shear and inclined shear. There are three sub-cases of basal detachment for the rigid body model: horizontal detachment, antithetic detachment and synthetic detachment. For the rigid body model, the established equations indicate that the total displacement on the synthetic base (Dt2) is the largest, that on the horizontal base (Dt1) is moderate, and that on the antithetic base (Dt3) is the smallest. On the other hand, the value of (Dt1) is larger than the displacement for the vertical shear (Dt4). The value of (Dt1) is larger than or less than the displacement for the inclined shear (Dt5) depending on the original fault dip δ0, bedding angle θ, and the angle of shear direction β. For all original parameters, the value of Dt5 is less than the value of Dt4. Also, by comparing three rotation mechanisms, we find that the inclined shear produces largest extension, the rigid body model with horizontal detachment produces the smallest extension, and the vertical shear model produces moderate extension.

;requency domain wave equation forward modeling using gaussian elimination with static pivoting

频率域波动方程正演是求解一个大型线性稀疏方程组问题,其受到计算效率和内存存储问题的限制。常规的高斯消元法不能满足大型数据的并行计算,本文提出基于静主元消元法(GESP)进行稀疏矩阵LU分解和多炮有限差分正演,该方法不仅提高了稳定性,更有利于单频点内LU分解的分布式并行计算。通过Marmousi模型模拟试验,单频波场和转化到时间域地震剖面的试验表明模拟精度和计算效率得到提高,节约并充分利用内存,为波形反演奠定基础。

High Precision Time Domain Forward Modeling for Crosshole Electromagnetic Tomography

To improve the resolution of crosshole electromagnetic tomography, high precision of forward modeling is necessary. A pseudo-spectral time domain （PSTD） forward modeling was used to simulate electromagnetic wave propagation between two boreholes. The PSTD algorithm is based on the finite difference time domain （FDTD） method and uses the fast Fourier transform （FFT） algorithm for spatial derivatives in Maxwell＇s equations. Besides having the strongpoint of the FDTD method, the calculation precision of the PSTD algorithm is higher than that of the FDTD method under the same calculation condition. The forward modeling using the PSTD method will play an important role in enhancing the resolution of crosshole electromagnetic tomography.

A study on Parallel Computation Based on Finite Element Forward Modeling of 2D Magnetotelluric

Magnetotelluric sounding method based on the difference of the rock’s resistivity is an exploration method about doing research in earth’s resistivity and phase using the native electromagnetic field. The paper adopts 2D finite element method as the magnetotelluric forward method and calculates the total field by primary field (also named background field) plus secondary field. We can?get more accurate forward result through the finite element method and we can get the result effected by the dense degree of grid slightly by the total field. But the method is not effective?enough when the model is divided into relative big grid. When the frequency changes, program solves relevant equation separately. According to the feature of the algorithm, we apply MPI parallel method in the algorithm. Every process solves relevant equation. The account of frequency?that a process needs to solve in parallel computation is less than the account that the process?needs to solve in serial algorithm. We can see that the forward result is the same with the serial algorithm and proves the correctness of algorithm. We do statistics about the efficiency of the parallel algorithm. When the account of processes is from 2 to 8, the speedup is from 1.63 to 2.64. It proves the effectiveness of the parallel algorithm.

Forward Modeling Research of Gravity Data Offset in North China Region

Due to the complexity and overlap effects of gravity anomalies,the gravity high point always deviates from the real position of the target.Researching the offset characteristics is helpful to determine the right location of gravity anomalies.In this paper,a series of forward models were designed to calculate the offset features under different assumptions.Different density models were established based on the measured gravity data in north China Sunhu area and a variety of methods were tried to eliminate offset effects under different conditions.The results indicate that the gravity anomalies of different density bodies can be separated effectively and the real position of target can be correctly located by using the“layer stripping method”.

Multi-wave forward modeling of a reservoir and AVO analysis

In the process of accurate interpretation of multi-wave seismic data,we wanted to solve the problem of multi-wave information recognition.Based on techniques of elastic wave forwarding,targeting the geological model of a reservoir of an oil field exploration area,we used a high-order staggered-grid difference technology to simulate many shots of seismic records of nonzero offset shots,implemented multi-wave seismic data processing to acquire the CMP of P waves and converted waves,NMO traces of CCP pre stacks,including AVA information and superposition profiles.Based on the AVA calculation of the model,the layer parameters of the model and the forwarding wave field relations of the P-S wave,we also compared and studied the correspondence between P waves and converted waves.The results of our analysis show that the results from simulation and from the AVO analysis are consistent.Significant wave field differences between P waves and converted waves in the same reservoir were found,which are helpful in recognizing and interpreting the multi-wave information in this area.We made use of the multi-wave data to provide the important guidelines for reservoir prediction.

The implementation of an improved NPML absorbing boundary condition in elastic wave modeling

在向前当模特儿的有弹性的波浪，吸收边界条件(ABC ) 被用来从模型截断边界减轻不希望得到的思考。完美地匹配的层(PML ) 证明了是最好的可得到的 ABC。然而，传统的切开 PML (SPML ) ABC 有一些严肃的劣势：例如，全球 SPML ABC 要求更多计算记忆，尽管实现是容易的。本地 SPML ABC 的实现也有一些困难，自从边和角落必须被考虑。因为卷绕旋转，传统的非切开的完美地匹配的层(NPML ) ABC 有复杂计算。在这篇论文，基于 ABC 与复杂转移频率的拉长函数(CFS ) 相结合的非切开的完美地匹配的层(NPML ) ，我们为与简单计算方程，小存储器要求，和容易的编程吸收边界条件的 PML 介绍一个新奇数字实现方法。

Damage-Monitoring Forward Equivalent-model Construction of Rosette Eddy Current Sensors

结构损伤监测对于保证结构安全是极其重要的。针对金属螺栓连接结构中螺栓孔位置处的裂纹损伤定量监测需求,在Goldfine等人的基础之上,该文提出一种花萼状涡流传感器,构建了传感器损伤监测正向等效模型并通过搭建实验装置验证损伤监测正向等效模型准确性并进行误差分析。相对于传统的多层导电结构谐波涡流场的积分/级数解析模型,构建的损伤监测正向等效模型考虑了在高频激励下导线电流密度分布的集肤效应,并可用于互感式涡流传感器建模。实验结果表明：对测量结果经空气标定后,传感器贴于2A12-T4标准试件表面时的模型计算结果和实验结果较为吻合,第1、2和3感应通道的幅值比量模型计算结果误差随频率变化均在10%以内,第4感应通道的幅值比量模型计算结果误差随频率变化在15%以内。

Forward and backward models for fault diagnosis based on parallel genetic algorithms

In this paper, a mathematical model consisting of forward and backward models is built on parallel genetic algorithms (PGAs) for fault diagnosis in a transmission power system. A new method to reduce the scale of fault sections is developed in the forward model and the message passing interface (MPI) approach is chosen to parallel the genetic algorithms by global sin-gle-population master-slave method (GPGAs). The proposed approach is applied to a sample system consisting of 28 sections, 84 protective relays and 40 circuit breakers. Simulation results show that the new model based on GPGAs can achieve very fast computation in online applications of large-scale power systems.

Physical model of acoustic forward scattering by cylindrical shell and its experimental validation

Research on the underwater target scattering can provide important theoretical support for target detection. The scattering model of cylindrical shell is established in this paper. It is found that the forward target strength is much stronger and varies with angles of incident wave less significantly than backward target strength. The received forward signal strength fluctuates with the target moving due to the interference between direct signal and scattering signal, which is most significant when the target approaches the baseline. An experiment is carried out in an anechoic tank to validate the scattering model. The method of acquisiting forward scattering in the tank is proposed. The forward and the backward target strengths are achieved by using the pulse compression technology, and they axe about 3dB less than the modeling results. The forward scattering phenomena of quiescent and moving targets are measured, which are similar to modeling results with different target types.

The application of a gravimetric forward modelling of the lithospheric structure for an estimate of the average density of the upper asthenosphere

The average density of 3300 kg m-3 is often attributed for the asthenosphere. In this study, we inspect this value by estimating the average value of the(upper) asthenosphere based on applying the gravimetric forward modelling of major known lithospheric density structures. The LITHO1.0 global seismic model of the lithospheric density structure is used for this purpose, while considering that the lithosphere-asthenosphere boundary(LAB) is rheological, conventionally taken at the 1300C isotherm,above which the mantle behaves in a rigid fashion and below which it behaves in a ductile fashion.According to our result, the average density of the upper asthenosphere is roughly 3400 kg m-3. This density value closely agrees with the corresponding average value 3371 kg m-3 computed based on an empirical density model provided in the Preliminary Reference Earth Model(PREM), while using the LITHO1.0 LAB depth data. We also demonstrate that the sub-lithospheric mantle gravity map exhibits mainly a thermal signature. The most prominent features in this gravity map are mid-oceanic spearing ridges marked by gravity lows, while oceanic subductions in the West Pacific are characterized by the most pronounced gravity highs.