共查询到19条相似文献，搜索用时 150 毫秒
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在地学中广泛应用的偏微分方程数值解法有两种:有限差分法及有限单元法。对于定常态问题两种方法完全等价,对于非定常态问题有限单元法形成的代数方程归根到底仍是有限差分方程,但在一定条件下会引起反常问题,原因是与代数组相容的不是原来的热传导方程,而是反热传导方程。 相似文献
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我们利用初至时距改正非线性波动方程反演方法中的相位畸变问题，从而改善了大变量速度层析射线重精度，并帮助解决了波动方程反演的不适当问题，当速度分布变化较大时，普通的非线性波动方程反演严重不适定，对于这样严重的非线性问题，不能获得正确的反结果。 相似文献
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利用反问题新算法—时间域正演反演法研究非线性抛物型方程的逆时反问题。该方法处理反问题的主要思路是先求解相对应的正问题,获得解在特定时间网格处的近似值;然后构造一个合适的全纯映射,在象空间中获得解在时间网格对应点处的近似值;最后利用解析函数的唯一延拓性质实现反问题的逆时间反演。数值模拟例子说明了方法的有效性。 相似文献
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《物探化探计算技术》2021,(2)
各向异性梯度可以预测裂缝型储层,利用宽方位地震数据可以更好地反演各向异性梯度。为了克服地震反演方程条件数太大、反演结果不稳定的难题,常规反演都是对反演方程做加法,如加入高斯分布、柯西分布等数学约束和测井低频约束,但是各向异性梯度测井信息不易获取,难以对反演方程做加法。因此这里提出了对反演方程做减法的反演方法,该方法分为两步:(1)认为地震数据是反射系数序列,据此消除导致最小二乘反演方程不稳定的子波项,得到自激自收地震记录和各向异性梯度地震记录;(2)基于最少反射层假设搜索准确的地下界面位置,建立反演方程,以降低反褶积方程维数。模型试算和实际工区应用表明,该方法能够增强反演方程稳定性,并能得到准确的地层各向异性梯度,为预测高角度裂缝型地层提供借鉴。 相似文献
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谢靖 《吉林大学学报(地球科学版)》1987,(4)
本文利用脉冲技术研究了地震勘探反问题的算法。同时还应用积分方程的解核表出示了正演问题的解。从而得到了点距、频率、反射层深度之间的级数关系,对于反演问所导出的第一类积分方程,文中指出了应用作者在位场反演中所采用的方法,这就保证了反问题解的稳定性。 相似文献
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电阻率三维反演稳定性和可靠性研究 总被引：1，自引：0，他引：1
电阻率三维反演参数太多,将导致反演不稳定性和高度非唯一性等诸多方面的问题。比较传统的最小二乘反演方法,利用共轭梯度的电阻率三维最小构造反演显示了更好的效果。讨论了初始模型选择及数据误差对三维反演结果的影响,说明了反演方法的稳定性和可靠性。 相似文献
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Wu Zhishan Lin Junqin 《吉林大学学报(地球科学版)》1989,(4)
本文用加权剩余法导出点源二维地电断面的边界单元法积分方程。通过付氏反变换,可获得三维空间的电位。若干模型上正演计算结果与解析解完全一致。对实测的ρ_s曲线进行了地形攻正及选择法反演拟合,解释结果与实际地质断面符合得很好。 相似文献
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根据逆边界逆动态控制理论,将河流水污染动态控制问题提为逆边界逆动态混合控制问题。针对多个或单个污染源排放浓度和排放总量计算,提出了一维对流-扩散方程逆控制的精确算法。该方法与现行最优控制方法相比,其优点是充分考虑了河流沿程的稀释混合容量,并能充分考虑水质动态标准和社会经济变化等因素,可获得动态控制精确解的近似解。 相似文献
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The thermoelastic response due to a time-dependent rectangular heat source in a semi-infinite medium is analyzed. The problem originates from studies of nuclear waste repositories in rock. Canisters containing heat-emitting nuclear waste are deposited over a large rectangular area deep below the ground surface. The solution for a time-dependent heat source is obtained from the corresponding instantaneous heat source by superposition. The thermoelastic problem for the instantaneous rectangular heat source in a infinite surrounding is solved exactly. An important step is the introduction of so-called quadrantal heat sources. The solution for the rectangle is obtained from four quadrantal solutions. The solution for the quadrantal heat source depends on the three dimelasionless coordinates only. Time occurs in the scale factors only. The condition of zero normal and shear stresses at the ground surface is fulfilled by using a mirror heat source and a boundary solution. The boundary solution accounts for the residual normal stress at the ground surface. Using a Hertzian potential, a surprisingly simple solution is obtained. The final analytical solution is quite tractable considering the complexity of the initial problem. The solution may be used to test numerical models for coupled thermoelastic processes. It may also be used in more detailed numerical simulations of the process near the heat sources as boundary conditions to account for the three-dimensional global process. 相似文献
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探讨了孔隙与单裂隙双重介质中的一类核素迁移数学模型及其反演问题。该核素迁移模型是一个耦合的抛物型方程组定解问题。若已知排污点的核素浓度变化规律,利用Laplace变换及其逆变换方法,求得了核素迁移模型正问题的解析解;反之,由下游裂隙中某个点的实测核素浓度,利用偏微分方程的叠加原理和反问题的拟解法,反求出核素迁移模型反问题的解,即排污点的核素状态。最后,给出核素迁移模型的正问题和反问题的数值模拟。数值结果表明,正问题的解析解能够刻画核素的迁移规律,也显示出所提反问题方法能有效地反演核素污染源。 相似文献
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以BG理论为基础,首先在重磁异常线性反演中将该理论与吉洪诺夫正则化方法相结合求解地下密度源(或磁源)分布及质心(或磁质心)位置;在重磁非线性反演中结合应用正则化方法和马奎特思想给出一种确定地下密度(或磁性)界面的稳定迭代算法:正则—马奎特法其次研究一种综合多和磁两种异常联合反演既是磁界面也是密度界面的方法。最后,以判断重磁异常是否同源的对应分析为先导,将上述方法综合于一起建立了重磁异常广义线性人机交互式综合反演系统。实际地区的应用已取得较好效果。 相似文献
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《Physics and Chemistry of the Earth, Part A: Solid Earth and Geodesy》1999,24(3):231-234
We study some effects that produce 3D topographical irregularities under incoming elastic waves from point sources using the indirect boundary element method. This technique is based on the representation of elastic waves in terms of single-layer boundary sources. In this way reflected and diffracted waves are constructed at the boundaries from where they are radiated by means of boundary sources. The field emited from the point source is computed with the moment tensor for a shear dislocation and analytical expressions of the elastodynamic 3D Green's functions. In this way we can construct a double couple with variable orientation. We compare the technique with that of Bouchon, who used the discrete wave number method for a shear dislocation in a halfspace with a triangular source function. We subsequently apply our method to simulate the seismic response of a mountain of ellipsoidal geometry. The source function that we have considered is a triangular pulse and we show results corresponding to the velocity registered over the surface of the irregularity and that of the halfspace. This motion is presented by means of snapshots showing the evolution of the wavefields that are present in the problem. 相似文献
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The strong motion displacement records available during an earthquake can be treated as the response of the earth as the a
structural system to unknown forces acting at unknown locations. Thus, if the part of the earth participating in ground motion
is modelled as a known finite elastic medium, one can attempt to model the source location and forces generated during an
earthquake as an inverse problem in structural dynamics. Based on this analogy, a simple model for the basic earthquake source
is proposed. The unknown source is assumed to be a sequence of impulses acting at locations yet to be found. These unknown
impulses and their locations are found using the normal mode expansion along with a minimization of mean square error. The
medium is assumed to be finite, elastic, homogeneous, layered and horizontal with a specific set of boundary conditions. Detailed
results are obtained for Uttarkashi earthquake. The impulse locations exhibit a linear structure closely associated with the
causative fault. The results obtained are shown to be in good agreement with reported values. The proposed engineering model
is then used to simulate the acceleration time histories at a few recording stations. The earthquake source in terms of a
sequence of impulses acting at different locations is applied on a 2D finite elastic medium and acceleration time histories
are found using finite element methods. The synthetic accelerations obtained are in close match with the recorded accelerations. 相似文献
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基于导数换算的边界检测技术在位场数据处理与解释中具有重要应用,但是高阶导数算法极易受到干扰噪声的影响,稳定性较差。鉴于此,本文提出利用水平导数与垂向导数标准偏差的相关系数进行边界检测,该方法是基于水平导数与垂向导数的标准偏差在地质体边界位置处呈现负相关性实现的。理论模型试验表明:该方法不仅可以识别出不同深度的异常体的边界位置,而且受噪声影响较小,计算稳定性更强。将本文方法应用于海拉尔盆地实测航磁数据,检测结果与实际资料有着较好的对应关系。 相似文献
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Based on the governing equations of the thermo-elastic problem, the analytical layer-elements of a finite layer and an underlying half-space are obtained using the Laplace-Hankel transform and the characteristic value method. The cylindrical heat source is divided into several micro cylindrical heat sources, which can be approximately simulated by plane heat sources. Then, the global stiffness matrix for the problem is assembled and solved in the transformed domain, and a Laplace-Hankel transform inversion is taken to obtain the real solution. Finally, the influence of heat source types, division numbers, embedded depths and layered properties on the thermo-mechanical coupling response is investigated. 相似文献
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Iran is a developing country, and nowadays, a demand to establish a time transfer system can be sensed more than anytime. On the other hand, global positioning system (GPS) is one of the most efficient and accurate systems in precise time estimation and dissemination domain. This study aims to investigate the different accuracy limiting effects of a time transfer system in a geodetic point of view. For this purpose, a simulation study is performed in which pseudo-range and carrier phase observations are simulated for some GPS stations in Iran. The baselines for time transfer have been chosen in a way that the maximum effect of each bias source can be analyzed. Therefore, the results of this study can be used in order to design the absolute and relative locations of the GPS stations equipped with external atomic frequencies in Iran considering a specific application. As a result, the most prominent bias source is the site-specific troposphere parameters which produce a variation of more than 1 ns in the time transfer results. Other bias sources including bias in the coordinate components and orbital information have a considerable impact only for time keeping purposes. Additionally, the influence of noise of the carrier phase and pseudo-range observations is analyzed. Variations of clock estimations between consecutive epochs up to 70 ps and day boundary discontinuities up to 0.6 ns, respectively, are the results of measurement errors. On the other hand, a time transfer between H-masers located at US Naval Observatory and National Resources Canada has been conducted to pursue a standard and efficient algorithm to deal with the problem of day boundary jumps. The method of overlapping batches with 12 h coverage of each of the involved days is applied to overcome this problem. The results of this method show a considerable decrease in the magnitude of the day boundary jumps. 相似文献