层状弹性场地基岩斜入射地震动二维反演

提出了层状弹性场地基岩斜入射地震动二维反演的一个方法,方法利用土层和半空间的精确动力刚度矩阵,根据地表某一点的水平和竖向两个地震加速度记录,进行基岩地震加速度时程和入射角的反演,并以SV波二维斜入射为例对方法进行了验证。研究表明,根据水平和竖向两个地震加速度记录可以进行基岩地震加速度时程和入射角的准确反演。同时,对文献中仅根据地表水平加速度记录进行基岩面水平地震动的一维反演方法进行了误差分析,研究表明,一维反演因忽略了波型转换,在模型上存在一定的误差,且误差随着实际地震动斜入射角的增大而显著增大。     

主余震序列作用下结构增量损伤比研究

强震过后短时间内发生的余震会对主震损伤结构产生重要影响,目前针对地下结构抗震性能的研究多是基于单次主震作用,对余震作用的认识有待进一步提高。为研究主余震作用下地下结构的性能劣化及增量损伤,以2层3跨地铁车站为原型建立土–地下结构相互作用模型,选取14次真实地震中的85组天然主震记录和对应的主余震序列为输入,对比研究了地下结构的地震响应特征。结果表明：考虑主余震作用时地下结构的地震损伤程度一般要比仅考虑主震作用时严重,但其增量幅度及扩展范围与主余震序列峰值加速度比ξ、地震动特性和主余震“极性”等因素有关;由于地下结构的损伤累计效应,在相近主余震峰值强度作用下(ξ≈1.0),地铁车站在余震时的层间位移反应较主震更大;当主震与余震的峰值加速度相差较大时(ξ≥1.4),余震对结构造成的附加损伤十分有限。

     

Boundary integral equation analysis for radiation and scattering of elastic waves in three dimensions

Abstract

In this paper, the boundary integral equation (BIE) method is employed to investigate the radiation and scattering of time‐harmonic elastic waves by obstacles of arbitrary shape embedded in an infinite medium. Based on the vector BIE, entirely free of Cauchy principal value integrals, an efficient numerical scheme using quadratic isoparametric boundary elements is proposed. Furthermore, the difficulty of non‐uniquess of a solution inherent with BIE formulations for exterior elastodynamic problems is studied numerically and analytically. The counterparts of the combined Helmholtz integral formulation method for elastodynamics together with the least‐square or Lagrange‐multiplier technique are derived and applied to overcome this difficulty successfully. In addition, the elastic‐wave fields radiated or scattered by either a spherical cavity or a rigid sphere in an infinite medium are calculated and the results are compared with the analytical solutions to demonstrate the accuracy and versatility of the proposed numerical scheme.     

轴向时变冲击载荷作用下直杆弹性动力屈曲研究

基于应力波理论,用半解析半数值方法对轴向时变冲击载荷作用下的直杆进行研究,给出了一种利用压应力波前附加约束条件求解轴向时变载荷作用下直杆弹性动力屈曲问题的方法。以三角脉冲载荷作用下的直杆为例,对其临界屈曲长度、初始屈曲模态和动力特征参数进行了求解,探讨了脉冲载荷峰值和载荷持续时间对临界屈曲长度和屈曲模态的影响。总结了三角脉冲载荷作用下直杆弹性动力屈曲的规律,并与阶跃载荷作用下的情况进行对比分析,结果与之前文献研究结果吻合良好。     

Propagation of Love waves in an elastic layer with void pores

The paper presents a study of propagation of Love waves in a poroelastic layer resting over a poro-elastic half-space. Pores contain nothing of mechanical or energetic significance. The study reveals that such a medium transmits two types of love waves. The first front depends upon the modulus of rigidity of the elastic matrix of the medium and is the same as the love wave in an elastic layer over an elastic half-space. The second front depends upon the change in volume fraction of the pores. As the first front is well-known, the second front has been investigated numerically for different values of void parameters. It is observed that the second front is many times faster than the shear wave in the void medium due to change in volume fraction of the pores and is significant     

Photoelastic analysis of stress waves in building subjected to vertical impact under laboratory earthquake experiments

In an earthquake occurring directly under a city, the vertical impact induced from the source may cause a large amount of damage to a column and beam of the building. Model-based simulations are carried out with photoelastic material in order to examine the effect of a vertical impact on the building in the case of a near-field type earthquake. The dynamic photoelastic method combined with strain gages is utilized to conduct direct full field and real time observations of stress waves in a building due to vertical impact in laboratory earthquake experiments. The conditions under which vertical impact loading is applied to the model building in a controlled laboratory environment are derived from the data recorded for the 1995 Hanshin-Awaji earthquake in Japan. The experimental apparatus with which an impact of a longitudinal stress pulse is able to be applied to a model of a real building is shown. It is estimated from our earthquake simulations that large dynamic stress concentrations are produced in the beam–column joints of the building by the vertical impact arising from a seismic source located directly below a surface.     

Shear waves in a fluid saturated elastic plate

In the present context, we consider the propagation of shear waves in the transverse isotropic fluid saturated porous plate. The frequency spectrum for SH-modes in the plate has been studied. It is observed that the frequency of the propagation is damped due to the two-phase character of the porous medium. The dimensionless phase velocities of the shear waves have also been calculated and presented graphically. It is interesting to note that the frequency and phase velocity of shear waves in porous media differ significantly in comparison to that in isotropic elastic media.     

饱和土中管桩对倾斜入射弹性波的隔离

在Biot饱和土波动方程的基础上,分析了全空间均质饱和土体中单排空心管桩对倾斜入射弹性波的隔离效果。将倾斜入射波和散射波的势函数展开成Fourier-Bessel函数的无穷级数的形式,利用一组圆柱坐标系统和Graff加法转换定理,通过施加桩土界面处的应力和位移连续的边界条件,求解出散射波势函数的待定系数,进而得到饱和土体中任意点的位移和应力。数值算例分析了饱和土体的渗透性和管桩的壁厚等参数对管桩隔离效果的影响。结果表明：空心管桩的隔离效果要好于实心排桩;随着饱和土体渗透性的降低,管桩的隔离效果越好,但当渗透性降低到一定程度后,再减小土体渗透性对管桩的隔离效果影响不大。     

Transient waves in plates of functionally graded materials

A numerical method is proposed for analysing transient waves in plates of functionally graded material (FGM) excited by impact loads. The material properties of the FGM plate have a gradient in the thickness direction and are anisotropic in the plane of the plate. In the present method, the FGM plate is divided into layer elements in the thickness direction. For an accurate modelling of the variation of the material property of FGM plates, it is expressed by second‐order polynomials in the thickness direction within an element. This can further reduce the number of elements to obtain more accurate results effectively. The principle of virtual work is used to develop approximate dynamic equilibrium equations. The displacement response is determined by employing the Fourier transformation and the modal analysis. As examples, the displacement response of FGM plates excited by line, point and distributed loads is calculated. The computations have shown the efficiency of the present method. Copyright © 2001 John Wiley & Sons, Ltd.     

Investigation of the scattering of harmonic elastic antiplane shear waves by a finite crack using the non-local theory

In this paper, the scattering of harmonic antiplane shear waves by a finite crack is studied using the non-local theory. The Fourier transform is applied and a mixed boundary value problem is formulated. Then a set of dual integral equations is solved using the Schmidt method instead of the first or the second integral equation method. Contrary to the classical elasticity solution, it is found that no stress singularity is presented at the crack tip. The non- local dynamic elastic solutions yield a finite hoop stress at the crack tip, thus allowing for a fracture criterion based on the maximum dynamic stress hypothesis. The finite hoop stress at the crack tip depends on the crack length. This revised version was published online in July 2006 with corrections to the Cover Date.     

Dynamic stress intensity factors due to scattering of harmonic waves by a crack in an infinite medium

An analytical method for calculating dynamic stress intensity factors in the mixed mode (combination of opening and sliding modes) using complex functions theory is presented. The crack is in infinite medium and subjected to the plane harmonic waves. The basis of the method is grounded on solving the two‐dimensional wave equations in the frequency domain and complex plane using mapping technique. In this domain, solution of the resulting partial differential equations is found in the series of the Hankel functions with unknown coefficients. Applying the boundary conditions of the crack, these coefficients are calculated. After solving the wave equations, the stress and displacement fields, also the J‐integrals are obtained. Finally using the J‐integrals, dynamic stress intensity factors are calculated. Numerical results including the values of dynamic stress intensity factors for a crack in an infinite medium subjected to the dilatation and shear harmonic waves are presented.     

基于支持向量机的现地地震预警地震动峰值预测

以0.1-10 Hz带通滤波后三分向矢量合成地震动峰值PGA 与PGV 为预测目标参数,利用日本K-net 强震台网P波触发后3 s数据,基于人工智能中的经典机器学习方法-支持向量机,选取加速度幅值Pa、速度幅值Pv、位移幅值Pd、傅里叶谱幅值AMmax、速度平方积分IV2、破坏烈度DI、累积绝对速度CAV、阿里亚斯烈...     

Effect of voids on the propagation of waves in an elastic layer

The present paper investigates the propagation of waves in an elastic layer containing voids. Numerical calculations and discussions indicate that the velocity of the propagation of waves decreases due to the presence of voids in the material medium of the layer and the voids cause dispersion of the general waveform.     

梁结构耦合点的纵向弹性波传播

采用波动分析法研究了纵向弹性波在两半无限梁耦合点的传播。应用梁的一维波动方程，耦合点模拟为质量弹簧系统，根据耦合点的连续条件和平衡条件，计算得到了纵向波传输至耦合点的振动功率传播效率和反射效率。传播效率和反射效率确定为梁纵向波阻抗和耦合点阻抗的函数，分析了梁纵向波阻抗和耦合点阻抗对纵向波传播效率和反射效率的影响。研究表明通过合理的选择激励梁、耦合梁和耦合点阻抗之间的匹配关系，可有效控制耦合点的纵向波传播。本研究对于振动控制和结构优化设计具有重要的意义。     

Numerical modelling of the scattering of elastic waves in plates

This paper describes the application of finite difference methods to the calculation of the scattering of elastic waves. The emphasis is on cracklike defects in plates, and it is shown that a common numerical technique can span a range of wavelengths from Lamb waves to ultrasonic waves with many reflections from the surfaces of the plate. Quantitative results are given for the scattering of Lamb waves and ultrasonic shear waves from surface-breaking cracks.     

弹性压应力波作用下直杆动力失稳的差分解

以受载端简支、远端固支弹性直杆为例，通过对直杆微元的动力平衡分析导出了直杆动力失稳的控制方程，这与用哈密顿原理得出的方程完全一致。利用差分方法求解了动力屈曲方程，解出了动力失稳模态以及临界力参数和动力特征参数的值。特别分析了随着动力特征参数由零增加到一定值后，由静力失稳模态过渡到动力失稳模态的过程。结果表明，对于等效长度直杆，动力失稳临界压力要远大于静力失稳的临界压力。     

延时叠加震源激发地震波能量的研究

根据弹性波动理论,分析了装药爆炸时冲击波转换成地震波的能量关系,对多级小药量垂向延时震源地震波能量叠加的原理进行了研究,建立了简化模型.试验结果表明,垂向延时叠加震源可在保证一定的信噪比的前提下,提高地震波的主频率,是高分辨率地震勘探的较理想的激发震源.     

A fractional equation to approximate wave dispersion relation in elastic rods

The Kolsky‐Hopkinson bar technique is widely used to test materials at high strain rates. When large‐diameter bars have to be used, the processing of experimental signals needs to take into account wave dispersion effects. Such effects are either characterised experimentally, mostly using spectral techniques, or modelled analytically, using the Pochhammer‐Chree equation. In this paper, a phenomenological fractional approximation is proposed to model the wave dispersion relation in elastic bars. It involves the Poisson's ratio as a parameter. The proposed new equation approximates well the wave dispersion relation obtained by the Pochhammer‐Chree equation for Poisson's ratio ranging from 0.25 to 0.4 and for wavelengths 4 times higher than the radius of the bar. This roughly corresponds to frequencies up to 75 kHz. Thus, the proposed fractional equation is useful for processing signals obtained in Kolsky‐Hopkinson bar experiments. The approximate fractional equation is as simple as Love's equation; however, the former outperforms the latter equation.     

非轴对称多元载荷条件下管道中纵向模态导波激励

轴对称载荷是管道中轴对称模态导波激励的有效方法。然而,受换能器安装误差等因素的影响,激励载荷多会变为非轴对称载荷,进而使激励出的导波模态变得复杂。对非轴对称多元载荷条件下纵向模态导波的激励问题进行了深入研究。考虑两种典型的非轴对称载荷,采用简正模态展开技术,建立了导波激励声场与边界载荷的量化关系,进而分析了各模态导波的产生机理及载荷阵列对纵向导波激励的影响。采用有限元数值模拟验证了理论预测结果。考虑实际管道检测中出现的非轴对称载荷,提出了一种载荷补偿策略并进行了实验验证。结果表明,该方法能够有效抑制弯曲模态导波的产生,同时也有助于改善导波信号的噪声水平。