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边坡振动台模型实验动位移的加速度时程积分探讨 总被引：3，自引：0，他引：3
受数据采集条件限制,振动台模型实验的速度和动位移时程一般由实测加速度时程信号进行积分得到。通过理论分析和实验实测数据计算,认为动位移的频域积分法误差来源是低频截止频率的选取,特别当低频频率接近零时,传统二阶频域积分可产生较大的动位移低频振荡和峰值误差。提出利用时域与频域混合的方法,即频域一时域混合积分法,来克服积分过程带来的误差,其在对加速度两次积分中,分别进行一次频域积分和一次时域积分。地震模拟振动实验的台面实测加速度数据积分与台面动位移计实测数据的对比表明,较之传统的二阶频域积分,采用频域一时域混合积分时误差可明显减小。 相似文献
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本文比较详细地讨论和分析了均匀介质中零偏移距散射曲面拓扑奇性和相应回波解析奇性之间的关系和分类.其基础是衍射理论的Kirchhoff积分,原理是通过曲面几何函数的解析奇性和距离函数的拓扑奇性之间的联系.基本的数学工具是Morse理论和突变理论. 相似文献
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本文就非弹性地震反应谱的计算问题（运动方程的形式，谱参量的选取，方程解算中恢复力模型上拐折点的处理和时间积分方法），给出了几点理论考虑，介绍了一个改进的算法。这一算法具有精度好和效率高的优点，这对做好结构抗震设计和其它地震工程问题中需要处理大量强震动数据的分析研究工作是有利的。文中还就双线型恢复力模型具体计算了2个例子（一个为屈服强化情形，另一个为理想弹塑性情形）。最后联系计算工作和计算结果，对非弹性反应谱计算中的其它有关事项做了补充讨论和说明。 相似文献
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Pi2地磁脉动的理论进展 总被引：1，自引：1，他引：1
目前，国内外在Ｐｉ２脉动的理论研究上取得了很大进展，现在问题的焦点是如何完整地解释Ｐｉ２脉动的全球特征和激发机制。解释Ｐｉ２脉动的理论主要有三种，即瞬态响应机制，亚暴电流楔理论和磁层空腔振荡理论。本文介绍了这三种理论的由来和发展，分析了每种理论在Ｐｉ２脉动研究中的贡献，并对Ｐｉ２脉动理论研究的进一步发展提出一些看法。 相似文献
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本文给出了从沿球面上大圆的积分值直接反推球面上函数分布的关系式,即得到了球面上大圆的积分变换和反变换对。如利用的是整个大圆的积分,得到的是球面上任何点及其对蹠点上函数的平均值,或者说得到的是球面上函数的偶对称部分。如果进行积分的球面域小于半球面,反演将是唯一的。所得结果可应用于从地震表面波资料反演三维地球内部构造的地球物理问题。 相似文献
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Seismic diffracted waves carry valuable information for identifying geological discontinuities. Unfortunately, the diffraction energy is generally too weak, and standard seismic processing is biased to imaging reflection. In this paper, we present a dynamic diffraction imaging method with the aim of enhancing diffraction and increasing the signal‐to‐noise ratio. The correlation between diffraction amplitudes and their traveltimes generally exists in two forms, with one form based on the Kirchhoff integral formulation, and the other on the uniform asymptotic theory. However, the former will encounter singularities at geometrical shadow boundaries, and the latter requires the computation of a Fresnel integral. Therefore, neither of these methods is appropriate for practical applications. Noting the special form of the Fresnel integral, we propose a least‐squares fitting method based on double exponential functions to study the amplitude function of diffracted waves. The simple form of the fitting function has no singularities and can accelerate the calculation of diffraction amplitude weakening coefficients. By considering both the fitting weakening function and the polarity reversal property of the diffracted waves, we modify the conventional Kirchhoff imaging conditions and formulate a diffraction imaging formula. The mechanism of the proposed diffraction imaging procedure is based on the edge diffractor, instead of the idealized point diffractor. The polarity reversal property can eliminate the background of strong reflection and enhance the diffraction by same‐phase summation. Moreover,the fitting weakening function of diffraction amplitudes behaves like an inherent window to optimize the diffraction imaging aperture by its decaying trend. Synthetic and field data examples reveal that the proposed diffraction imaging method can meet the requirement of high‐resolution imaging, with the edge diffraction fully reinforced and the strong reflection mostly eliminated. 相似文献
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本文讨论一项用以研究折射绕射波的三度空间超声波模拟实验的结果。实验说明,在三度空间中,在某一点观测到的绕射波包含着来自无穷个绕射源的波涟,这些绕射源沿着绕射楔或断层而分布。这点在观测点位于垂直绕射楔或断层的方向上也是同样真实。 结果也指出绕射波的动力学性质随着绕射楔或断层的几何形状而变化,因此根据这种结果可以设想,若详细研究绕射波的动力学特性,可以对绕射楔或断层的几何形状得出有用的证据。 此外,根据模拟实验的结果,可用“最小走程原理”来解释波涟到达观测点的行程和求得绕射点的位置。 相似文献
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Roman Teisseyre 《Acta Geophysica》2006,54(3):225-238
We present a relation between stress moments and antisymmetric part of stresses and the related constitutive law joining those
stresses with the particle/point rotations. Correspondence of the asymmetric continuum theory to the micromorphic theory is
considered. An extension of the asymmetric continuum theory for the case of 2D anisotropy for antisymmetric stresses leads
us to the problems of friction anisotropy and fracture pattern. 相似文献
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We derive exact time-domain solutions for scattering of acoustic waves by a half plane by inverse Fourier transforming the frequency-domain integral solutions. The solutions consist of a direct term, a reflected term and two diffraction terms. The diffracting edge induces step function discontinuities in the direct and reflected, terms at two shadow boundries. At each boundary, the associated diffraction term reaches a maximum amplitude of half the geometrical optics term and has a signum function discontinuity so that the total field remains continuous. We evaluate solutions for practical point source configurations by numerically convolving the impulse diffraction responses with a wavelet. We solve the associated problems of convolution with a singular, truncated diffraction operator by analytically derived correction techniques. We produce a zero offset section and compare it to a Kirchhoff integral solution. Our exact diffraction hyperbola exhibits noticeable asymmetry, with higher amplitudes on the reflector side of the edge. Near the apex of the hyperbola the Kirchhoff solution approximates the exact diffraction term symmetric in amplitude about the reflection shadow boundary, but omits the other low amplitude term necessary to ensure continuity at the direct shadow boundary. 相似文献
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Oscillatory pumping tests—in which flow is varied in a periodic fashion—provide a method for understanding aquifer heterogeneity that is complementary to strategies such as slug testing and constant‐rate pumping tests. During oscillatory testing, pressure data collected at non‐pumping wells can be processed to extract metrics, such as signal amplitude and phase lag, from a time series. These metrics are robust against common sensor problems (including drift and noise) and have been shown to provide information about aquifer heterogeneity. Field implementations of oscillatory pumping tests for characterization, however, are not common and thus there are few guidelines for their design and implementation. Here, we use available analytical solutions from the literature to develop design guidelines for oscillatory pumping tests, while considering practical field constraints. We present two key analytical results for design and analysis of oscillatory pumping tests. First, we provide methods for choosing testing frequencies and flow rates which maximize the signal amplitude that can be expected at a distance from an oscillating pumping well, given design constraints such as maximum/minimum oscillator frequency and maximum volume cycled. Preliminary data from field testing helps to validate the methodology. Second, we develop a semi‐analytical method for computing the sensitivity of oscillatory signals to spatially distributed aquifer flow parameters. This method can be quickly applied to understand the “sensed” extent of an aquifer at a given testing frequency. Both results can be applied given only bulk aquifer parameter estimates, and can help to optimize design of oscillatory pumping test campaigns. 相似文献
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The paper addresses the issue of upward acceleration of ions along geomagnetic field lines. It has been shown that ion acceleration by electric field oscillations (formerly known as magnetic moment “pumping” or MMP) may be treated as a centrifugal acceleration mechanism. More precisely, the case in point is oscillatory centrifugal acceleration; this brings up the question on comparing the MMP with the centrifugal acceleration caused by the quasi-static magnetospheric convection field. It has been found that at high geomagnetic latitudes, the oscillatory centrifugal force is weaker or stronger than the centrifugal force of magnetospheric convection if the ratio of the electric field oscillation amplitude to the mean field is correspondingly lower or higher than \(\sqrt 2 \). Analysis of data from measurements and calculations of magnetospheric electric fields suggests that, contrary to current opinion, the oscillatory centrifugal force may be comparable to the centrifugal force of magnetospheric convection and even exceed it when strong global Pc5 pulsations are excited in the magnetosphere. 相似文献
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Jianguo Sun 《Geophysical Prospecting》1996,44(3):351-374
Conventionally, the Fresnel zone and the geometrical spreading factor are investigated separately, because they belong to different theories of wave propagation. However, if the paraxial ray method is used for establishing the Fresnel–Kirchhoff diffraction formula for a laterally inhomogeneous multilayered medium, it can be shown that the normalized geometrical spreading factor is inversely proportional to the area of the first Fresnel zone associated with the reflection point. Therefore, if no diffracting edge cuts the first Fresnel zone, the geometrical optics approximation represents the principal part of the wavefield obtained by Fresnel–Kirchhoff diffraction theory. Otherwise, the geometrical optics approximation has to be corrected by adding edge diffractions. It is also shown that Kirchhoff-type migration and geometrical spreading factor correction both reduce the first Fresnel zone to a zone with unit area. 相似文献
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As an ideal carrier of high-resolution information, seismic diffraction can be used to clarify and locate small-scale discontinuities or inhomogeneities in the subsurface. However, a diffraction is weak and thus be suppressed by the specular reflection. Furthermore, a diffraction would be destroyed by the conventional imaging method due to the polarity reversal of diffraction. In this paper, we analyse the behaviour of diffraction and reflection. For the image point on a horizontal or oblique reflector, the zone on both sides of the stationary point has the same energy after using a cosine weight function. Based on the behaviour, we propose the adaptive phase filter to adjust the polarity of the energy on both sides, and calculate it through the illumination angle and the reflector dip angle. This method avoids the calculation of the Fresnel zones and can further suppress residual reflection that disturb the diffraction images. Synthetic and field data applications show that the desired imaging results can be obtained by the proposed method. The test results demonstrate that the method is efficient in detecting small-scale discontinuities or inhomogeneities in the subsurface and can provide high-resolution information for seismic interpretation. 相似文献
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Numerical simulation of an unsaturated flow equation 总被引：1，自引：1，他引：0
A numerical model for an unsaturated flow problem by using the finite element method is established in order to simulate liquid
moisture flow In an unsaturated zone with homogeneous soil and deep subsurface water, and with different initial and boundary
conditions. For infiltration or evaporation problems, a traditional method usually yields oscillatory non-physics profiles.
However, nonoscillatory solutions are obtained and non-physics solutions for these problems are evaded by using the mass-lumped
finite element method. Moreover, the kind of boundary condition is handled very well.
Project supported by the National Key Project of Fundamental Research ”Climate Dynamics and Climate Prediction Theory“ and
China Postdoctoral Science Foundation. 相似文献
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本文在文献[1]、[2]的基础上,进一步应用耗散理论中的多重选择和岔区外敏概念来讨论地震预报问题。指出,在断层平面组合中,由于始裂点的位置不同,会导致后果的重大差异。在立交模式中,深部剪切蠕滑线在哪里发生有一定的随机性,即上部岩石圈中某一发震断层在某一时间内是否有深部剪切蠕滑线与其相交,具有随机选择的性质。关于岔区外敏问题,耗散理论认为,分岔点上外界因素对系统变成新态的途径选择具有很大影响。外界因素的作用会有利于某种途径的选择,特别在分岔点处这种选择的作用要显著放大。对于一个地震,在震源区处于不稳定状态时,外因对震源地方的调制和触发作用是很大的。如果外因的时间规律、空间规律和方向规律是已知的,则可对多重选择进行实际选择,使其可能性范围缩小,进而进行相对确定的地震预报。 相似文献