S波由饱和土入射于弹性土时在界面上的反射与透射

从地震工程实际出发，借助Biot多孔介质中的波动方程，根据各种界面条件导出了S波从饱和土入射于弹性土时在交界面上反射与透射的一般计算公式。作为算例，数值计算分析了S波从饱和土入射于饱和土与弹性土交界面时，饱和土中P1、P2和S波的反射系数以及弹性土中P波、SV射系数与界面排水条件、入射角以及频率之间的关系。结果表明：各种波的反射、透射系数与入射角、入射频率以及界面排水条件有关系。     

Nonstationary Rayleigh waves on the thermally-insulated surfaces of some thermoelastic bodies of revolution

Summary The influence of heat conduction and thermal relaxation on the propagation of the surface waves polarized in the sagittal plane along the heat-insulated surfaces of the following thermoelastic bodies of revolution: a cylinder, a sphere, a torus, and a cone is investigated. The modified Maxwell law is used as the law of heat conduction, which allows one to take a finite speed of heat propagation into account. The nonstationary surface waves are interpreted as lines (a straight line or a diverging or converging circumference) on which the temperature and the components of the stress and strain tensors experience a discontinuity. Each of the discontinuity lines propagates with a constant normal velocity across the free from stresses and thermally-insulated surface of the body of revolution along the corresponding lines of curvature and is obtained by coming onto the body's surface of the three strong discontinuity complex wave surfaces which intersect along this line: quasi-thermal, quasi-longitudinal and quasi-transverse volume waves. By applying the theory of discontinuities, the velocities and the intensities of the surface waves have been found. It has been shown that the attenuation of the surface wave intensity is determined by the two factors: the coupling between the related strain and temperature fields and the change in curvature of the surface wave with time if the wave is a curvilinear one.     

Propagation properties of longitudinal leaky surface waves on lithium tetraborate

Theoretical and experimental results of longitudinal leaky surface waves with a higher phase velocity than that of ordinary leaky surface waves and a low propagation loss on lithium tetraborate (LBO) are investigated in detail. They propagate along the surface with a phase velocity close to that of longitudinal bulk wave, slightly radiating two kinds of shear bulk waves (or one shear bulk wave in the case that one of two shear wave terms is uncoupled) into the solid. Most surface components of the mode consist of a longitudinal wave term and an electromagnetic wave term. The detailed propagation properties of the longitudinal leaky surface waves on LBO with the Euler angles (phi, theta, 90 degrees ) are investigated theoretically and experimentally. The (011) cut of LBO was found to be desirable for higher frequency SAW devices. One of the reasons why that mode on LBO has a low propagation loss is also discussed.     

Condition assessment of concrete in hydraulic structures by surface wave non-destructive testing

Maintenance and rehabilitation of concrete structures affected by alkali-aggregate reaction (AAR) require conducting detailed assessment of the concrete conditions, mainly close to the surface where the damage is more severe. This paper presents in situ investigations by surface wave testing of near-surface AAR damage in two hydraulic structures. The survey was carried out using a non-intrusive multi-sensor method that involves frequency–wavenumber analysis of surface waves. The method allows solving Rayleigh surface wave propagation modes required for the determination of the shear wave velocity in terms of depth. The variation of Young’s modulus with concrete depth can be estimated from the obtained shear wave velocity profile. Two different cases of surface wave propagation, typical of concrete structures, are discussed in this paper. The tests were conducted from the concrete surface only and the subsurface quality was mapped up to a depth of 1.50 m. The applications show that the proposed surface wave method is a potential non-destructive evaluation method that can be used to detect and locate near surface damage in concrete structures.

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钢管混凝土单圆管拱结构振动台阵试验研究

为了研究钢管混凝土拱桥地震响应特性,以某钢管混凝土拱桥为原型,通过采用人工质量一致相似律设计制作1∶10缩尺比例的钢管混凝土拱结构模型,利用福州大学地震模拟振动台台阵系统,采用正弦波激励、Taft波以及当地场址生成的人工波等,进行了纵向、横向、横向+纵向地震动试验。试验结果表明,不同的地震波激励使结构产生不同的地震响应。Taft波横向激励产生的响应小于纵向激励的,人工波正好相反。拱顶的加速度相对于拱脚的有放大作用,放大倍数与输入波形的卓越周期相关;多维激励和行波激励使结构的加速度、位移和应变响应显著增大,其对结构的影响比一致激励时更为不利。不过,试验过程中模型均未出现开裂和破坏现象,表明钢管混凝土拱结构具有良好的抗震性能。     

Anomalous propagation of elastic waves through a boundary between liquid and magnetoacoustic material

We consider a longitudinal acoustic wave incident onto a plane boundary between a liquid and a magnetoacoustic medium representing an antiferromagnetic material with anisotropy of the easy plane type, occurring in the vicinity of an orientational phase transition with respect to magnetic field. The directions of propagation and the amplitudes of reflected and transmitted longitudinal and transverse waves are determined. The possibility of an effective field control for the refraction angle and the wave type transformation is demonstrated. Beginning with a certain critical angle of incidence, the longitudinal and, eventually, the transverse waves in the magnetic medium become inhomogeneous and slide along the interface. If the magnetic material is sufficiently close to the phase transition point, the waves can be reirradiated into the liquid medium.     

Mechanical evolution of concrete during setting

This paper deals with the rheological behaviour of fresh concrete during setting. An experimental non-destructive device based on the propagation of acoustic waves (compression and shear waves) at low frequency (20Hz–800Hz) is used to continuously characterise the setting and hardening of hydraulic concrete. The results are presented for various concrete formulations involving various initial temperatures and water/cement ratios. The characteristics of wave propagation (velocities, damping coefficients,...) enable to monitor material setting and hardening phases. By means of an inverse analysis, the evolution of rheological parameters is presented from the fluid to the solid state. It is shown that the mechanical evolution of fresh concrete exhibits a characteristic time (τ). The wave velocity presented as a function of normalized time (t/τ) follows a master curve which depends only slightly on the formulations tested.     

既有临空面对采空区上覆岩体爆破振速场的影响研究

采空区边界条件影响其上覆岩体爆破地震效应.基于弹性波动理论,借助动力有限元算法,研究了采空区临空面、地表自由面及两种边界耦合作用下爆破地震波的传播机制与上覆岩体振速场的空间分布规律,以此为理论依据提出了上覆岩体分区准则.结果表明:采空区临空面改变爆破地震波传播路径,拐点对爆破地震效应具有显著衰减作用,可根据波传播途径拐...     

Non-contact imaging for surface-opening cracks in concrete with air-coupled sensors

Rapid and accurate non-destructive evaluation (NDE) techniques are needed to assess the in-place condition of concrete structures. However the time and effort required to perform NDE tests using conventional surface-mounted contact sensors hinder rapid evaluation of large full-scale structures. The suitability of surface waves and non-contact sensing techniques to detect the presence of concrete defects is examined here. First, the ability to detect leaky surface waves in concrete with air-coupled sensors is demonstrated. Surface waves in a concrete slab specimen are generated by an electrically-controlled impact source. Next, the data and signal processing needed to improve leaky surface wave data, with respect to eventual application to velocity and attenuation images, are demonstrated. Finally velocity and wave attenuation data collected from a concrete slab specimen that exhibits surface cracking are presented. Test results show that the proposed energy ratio (attenuation) criterion is more sensitive to existence of cracks than the velocity criterion.     

地应力对岩石爆破开裂及爆炸地震波的影响研究

深部岩体爆破开挖是高地应力和炸药爆炸产生的动应力共同作用的结果。采用SPH-FEM耦合数值模拟方法,研究了地应力场对岩石爆破开裂及开裂区外地震波能量的影响。结果表明:随着地应力水平的提高,岩石爆破破碎区的范围缩小、裂纹扩展速度降低,非静水地应力场中破碎区内裂纹主要沿最大主应力方向扩展,但地应力对爆破粉碎区的形成几乎没有影响;地应力作用下爆破开裂区形态改变影响了爆炸地震波的能量及传播特性,随着地应力的增大,更多的炸药爆炸能转化为地震波能量,产生的高频地震波随距离衰减更快,且小主应力方向上的爆炸地震波能量更大。研究成果可为深部岩体爆破优化设计提供理论参考。     

高地应力断裂破碎隧道爆破开挖振动效应

为确定关角隧道高地应力断裂破碎带地层的爆破地震波传播规律及其对邻近围岩(混凝土衬砌)的影响,对隧道开挖中的爆破振动进行了监测。通过现场测试数据回归分析,得到了该地层爆破地震波的传播规律。在此基础上,提出了断裂破碎带地层爆破振动速度的安全控制标准及减少振动危害的措施。     

高地应力断裂破碎隧道爆破开挖振动效应

为确定关角隧道高地应力断裂破碎带地层的爆破地震波传播规律及其对邻近围岩(混凝土衬砌)的影响,对隧道开挖中的爆破振动进行了监测。通过现场测试数据回归分析,得到了该地层爆破地震波的传播规律。在此基础上,提出了断裂破碎带地层爆破振动速度的安全控制标准及减少振动危害的措施。     

Scanning electron microscopy observation of surface acoustic wavepropagation in the LiNbO3 crystals with regular domainstructures

This paper reports a scanning electron microscopy investigation of surface acoustic wave propagation in the LiNbO₃ crystals with regular domain structures. The regular domain structures in the LiNbO ₃ crystals were formed by the method of the thermo-electric treatment after growth. We investigated two modes of the interaction between the surface acoustic waves and regular domain structures in the LiNbO₃ crystals: excitation of the surface acoustic waves by the curved regular domain structure, and propagation of the surface acoustic waves along and across the regular domain structures. It is shown that the regular domain structure in the first case can be used as an interdigital transducer for excitation of the surface acoustic waves through the longitudinal piezoelectric effect. In the second mode of the interaction we observed that the regular domain structure can be used as an acoustic wave-guide in the process of the propagation of the traveling surface acoustic waves along the regular domain structure. Also, we demonstrate the reflection of the surface acoustic waves from the domain walls in the process of surface acoustic wave propagation across the regular domain structure     

爆破地震波穿越不同介质结构面的衰减效应

为探索爆破地震波穿越不同充填介质结构面的振动速度、频率和能量分布的衰减规律,采用混凝土边坡相似模型进行爆破振动试验。通过分析爆破地震波的峰值振动速度、边际能量谱和各频带能量百分比,获得了爆破地震波穿越无结构面与结构面充填泥、细沙、水和空气的衰减规律。结果表明:当充填介质波阻抗越小,地震波的峰值能量和峰值振动速度衰减越快,频率上表现出高频滤波作用越强,在频带间能量分布变窄,主频带有往低频带0～20 Hz聚集的趋势;值得注意的是,当水作为充填介质时,不仅水的波阻抗会影响地震波的衰减,而且水的微压缩连续性也会使峰值能量和峰值振动速度衰减更慢,能量在频带间分布更广,水的流动性则会造成爆破地震波的主频带在各传播方向上分布不一。在相同充填介质条件下,随着结构面倾角增大,峰值振动速度在各传播方向上均减小。     

Stress waves in layered rocks

Summary In this paper two problems will be solved analytically: the reflection of plane stress waves at a free boundary and the reflection and refraction of plane stress waves at a welded interface separating two dissimilar materials. In particular, stress reflection and refraction coefficients will be derived and the superimposed state of stress in regions of wave interference will be calculated. The solutions are visualized in a series of examples by means of computer-generated isochromatic fringe patterns. They show the partition of stress between reflected and refracted waves, stress distribution in regions of wave interference and demonstrate stress wave propagation in laycred structures.     

Nonlinear wave propagation and run-up generated by subaerial landslides modeled using meshless method

The focus of present study is on water waves generated by landslides. Because such problems involve moving boundaries and large deformation of the computational domain, a 2-D numerical model is established with a meshless method and a fully nonlinear Lagrangian time marching scheme. The method chosen in this study is a RBF collocation method developed in the way that the collocations of both the governing equation and boundary conditions are applied at each of the boundary points. This guarantees the accuracies of the partial derivatives of the velocity potential near the free surface, which results in the precise prediction of the free surface. A very effective treatment is proposed for the landslide boundary in this study. Present model is verified by comparing the numerical results of waves generated by a submerged landslide with other numerical solutions, including those obtained using the BIEM and Boussinesq-type models. Fairly good agreements are observed. Present model is then applied to simulate subaerial landslide-induced waves. Various slopes are considered. The landslide-induced wave propagation and shoreline motions are examined. The effects of sliding horizontal distance along a given slope on the induced wave are also discussed.     

海洋涡旋地震成像的时域有限差分仿真

传统的水声建模方法只考虑水中声波的折射影响,忽略了水层间的声反射,因此不能对反射波地震勘探的海水分层结构成像结果进行分析。文章首先建立了基于时域有限差分的低频宽带脉冲信号传输预报模型,该模型考虑海水分层结构的声反射影响,通过数值求解波动方程计算低频宽带脉冲信号近距离传播过程中的时域波形;其次将某次海上多道地震测量的水文条件作为输入环境参数,计算了近海面地震勘探接收阵所接收的气枪低频脉冲信号时域波形;最后按照反射波地震勘探处理流程,对接收阵信号在共反射点进行相干累加和地震成像,所得到的海水分层结构成像结果与海上多道测量成像结果符合较好。仿真结果验证了水层声反射对海水分层结构反射波地震成像的影响。     

爆破地震波穿越不同介质结构面的衰减效应

为探索爆破地震波穿越不同充填介质结构面的振动速度、频率和能量分布的衰减规律,采用混凝土边坡相似模型进行爆破振动试验。通过分析爆破地震波的峰值振动速度、边际能量谱和各频带能量百分比,获得了爆破地震波穿越无结构面与结构面充填泥、细沙、水和空气的衰减规律。结果表明:当充填介质波阻抗越小,地震波的峰值能量和峰值振动速度衰减越快,频率上表现出高频滤波作用越强,在频带间能量分布变窄,主频带有往低频带0~20 Hz聚集的趋势;值得注意的是,当水作为充填介质时,不仅水的波阻抗会影响地震波的衰减,而且水的微压缩连续性也会使峰值能量和峰值振动速度衰减更慢,能量在频带间分布更广,水的流动性则会造成爆破地震波的主频带在各传播方向上分布不一。在相同充填介质条件下,随着结构面倾角增大,峰值振动速度在各传播方向上均减小。     

Size-dependent effective dynamic properties of unidirectional nanocomposites with interface energy effects

This article studies the size effect on wave propagation characteristics of plane longitudinal and transverse elastic waves in a two-phase nanocomposite consisting of transversely isotropic and unidirectionally oriented identical cylindrical nanofibers embedded in a transversely isotropic homogeneous matrix. The surface elasticity theory is employed to incorporate the interfacial stress effects. The effect of random distribution of nanofibers in the composite medium is taken into account via a generalized self-consistent multiple scattering model. The phase velocities and attenuations of longitudinal and shear waves along with the associated dynamic effective elastic constants are calculated for a wide range of frequencies and fiber concentrations. The numerical results reveal that interface elasticity at nanometer length scales can significantly alter the overall dynamic mechanical properties of nanofiber-reinforced composites. Limiting cases are considered and excellent agreements with solutions available in the literature have been obtained.     

Imaging of the Elastic Wave Propagation in Concrete Using Scanning Techniques: Application for Impact-Echo and Ultrasonic Echo Methods

Acoustic NDT methods like ultrasonic echo and impact-echo are successfully used for NDT of concrete structures. This paper describes useful techniques for a detailed experimental study of the elastic wave propagation, which is highly relevant for the interpretation of the results obtained from practical measurement applications. By using a scanning laser vibrometer it becomes possible to obtain a 2D visualization of the elastic waves propagating along the surfaces of concrete specimens. Time slices are prepared so that the wave field becomes apparent. In order to visualize especially the surface wave propagation a similar technique using a scanning system with a piezoelectric sensor is applied. The results obtained provide an appropriate basis for the comparison with numerical results from 3-D Elastodynamic finite integration technique (EFIT) calculations, which is demonstrated here. Examples are presented for the application with phased array ultrasonic echo, air-coupled ultrasonic echo and impact-echo.