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1.
研究含梯度残余应力的弹性半无限体的平面应变型表面波,即广义Rayleigh波。将该结构等效为含梯度初应力的弹性覆盖层和无初应力的弹性基底构成的半无限体结构。求得覆盖层中位移函数的幂级数解与均质基底位移函数的解析解,并代入边界条件,得到频散方程。针对拉、压残余应力,分别讨论了其随厚度方向均匀分布、线性变化和指数变化情况下广义Rayleigh波的一阶模态频散特性。数值结果表明:随着拉应力增大,广义Rayleigh波波速会增加,反之,压应力的增大会导致波速的降低;残余应力均匀分布时波速的改变量较大,线性变化次之;当残余应力按照指数函数变化时,梯度参数越趋近于零,其结果越趋近于线性变化情况,随着梯度参数的减小,波速改变量也随之减小。当使用广义Rayleigh波频散特性实现残余应力无损检测时,如果采用与实际梯度渐变残余应力不符的均匀残余应力模型将会低估表面残余应力。本文所得结论可为利用广义Rayleigh波实现梯度残余应力无损检测提供理论基础。  相似文献   

2.
基于现场位移收敛计监测数据,利用FLAC3D研究了拱桥铺山岭隧道在底部爆破作用下锚固壁动态响应及衬砌的影响。研究结果表明:通过静载下位移对比及应力波传播规律分析,说明数值分析结果比较可靠;由于衬砌能够很好地限制隧道动态位移,所以使隧道拱底正下方1.42m范围内的垂直压应力峰值明显增大,在与拱脚同一水平方向9.51m范围内的垂直压应力峰值也明显增大,并且离拱脚越近增大越明显;隧道衬砌对锚固壁拱底位移、振动速度、振动加速度的运动规律没有影响,都是先向隧道中心方向运动;而其它监测点由于衬砌的"拱作用"使锚固壁位移、振动速度、振动加速度的运动规律相反,并且衬砌能使隧道锚固壁振动最强烈位置(拱底)的位移峰值、振动速度峰值、振动加速度峰值分别减小76.6%、9.4%和5.0%。  相似文献   

3.
半圆形河谷场地可构造为包含河谷的广义子结构和具有规则边界的开挖场地两部分,基于土-结构相互作用SSI原理,建立子结构控制方程。利用比例边界有限元SBFEM求解开挖场地动刚度,解析求解各向异性介质自由场qP波波动,将两者代入控制方程,可求得广义结构的动力响应。与文献中各向同性半空间中半圆形河谷在P波入射下的位移结果对比,验证了方法的精度和有效性。进一步分析了椭圆各向异性和非椭圆各向异性对半圆形河谷在qP波入射下位移分布的影响。数值算例显示,介质的各向异性改变了半圆形河谷散射位移的空间分布,增大了水平向位移的峰值;同时,介质的各向异性加剧了入射角对散射波场位移分布的影响。  相似文献   

4.
半圆形河谷场地可构造为包含河谷的广义子结构和具有规则边界的开挖场地两部分,基于土-结构相互作用SSI原理,建立子结构控制方程。利用比例边界有限元SBFEM求解开挖场地动刚度,解析求解各向异性介质自由场qP波波动,将两者代入控制方程,可求得广义结构的动力响应。与文献中各向同性半空间中半圆形河谷在P波入射下的位移结果对比,验证了方法的精度和有效性。进一步分析了椭圆各向异性和非椭圆各向异性对半圆形河谷在qP波入射下位移分布的影响。数值算例显示,介质的各向异性改变了半圆形河谷散射位移的空间分布,增大了水平向位移的峰值;同时,介质的各向异性加剧了入射角对散射波场位移分布的影响。  相似文献   

5.
采用复变函数的保角映射方法和波函数展开法,根据孔洞与内部流体在界面上的应力和位移连续的边界条件,得到了充满流体的任意形状的孔洞对入射平面P波的散射问题的理论解,以椭圆形孔洞为例,着重分析了椭圆的长短轴之比、流体的存在与否以及入射频率对散射幅值的影响,结果表明:(1)圆形孔洞的分波波谱的峰值分布均匀,而椭圆形孔洞则不均匀;(2)散射P波的波谱主要集中于前进方向和背向一侧,而散射S波的波谱主要集中于与传播方向垂直的一侧;(3)入射波与孔洞的作用面积越大,散射P波的波谱也越大,而散射S波的波谱也越小;(4)当孔洞为圆形时,流体对散射P波和S波的波谱影响最小,即此时流体与孔壁的动力相互作用最小.  相似文献   

6.
含松软覆盖层峡谷地形对地震动具有放大效应已被多次地震观测所证实。本文对Rayleigh波入射下V形覆盖层峡谷的地震反应进行宽频模拟,讨论了V形峡谷深度、覆盖层软硬程度、倾角以及波的频率等因素对地表位移幅值的影响。数值结果表明:在中低频段(量纲为一的频率η5.0),含覆盖层峡谷地形对地震波的放大效应显著。在高频波段(η10.0),覆盖层放大效应减弱甚至出现缩幅效应;随覆盖层深度增加,位移放大频段的带宽逐渐减小,第一峰值频率降低,且在低频段频谱曲线振荡剧烈;覆盖层越软,位移越大,峡谷表面位移空间变化越剧烈;峡谷右边界与水平面夹角不同,导致地表位移幅值的空间分布相差较大,在中低频时峡谷右侧的图线差异比较明显,在高频时变化差异不大。由此可见覆盖层软硬程度和形状对地震波聚焦特征也具有重要影响。  相似文献   

7.
孙晓剑  刘中宪  赵延喜  张海 《应用力学学报》2020,(1):91-97,I0006,I0007
采用间接边界元法,求解了饱和半空间裂隙对平面PI波的二维衍射问题。基于单层位势理论,将边界离散并直接在边界单元上施加虚拟荷载(水平作用力、竖向作用力和流量源的叠加)以构造散射波场,并由边界条件确定虚拟荷载密度,总波场由自由波场和散射波场共同组成。通过参数分析研究了入射波频率、入射倾角、埋深、孔隙率、边界渗透条件等因素对饱和半空间中裂隙对平面PI波衍射的影响规律。结果表明:裂隙随埋深增大,地表位移谱振荡加剧,峰值有所降低;随着入射频率增加,孔隙率影响逐渐增大;垂直入射时,水平位移的放大区域主要分布在裂隙两端,斜入射时,主要集中在裂隙正上方地表附近;透水和不透水两种情况下的地表位移幅值和相位差别较小,但干土情况与饱和情况下的位移幅值相差较大。  相似文献   

8.
在直剪试验过程中,随着剪切位移的增大,试样的剪切面积不断减小,如果以恒定的剪切面积来计算,所得的剪应力是不真实的,为了克服以上缺点,通过理论推导,得到了不同剪切位移下的剪应力表达式。研究表明,本文所得剪应力比恒定剪切面积法所得剪应力大,其差值随剪切位移的增大而增大,随剪切面直径或边长的增大而变小。当试样的直径或剪切边长为6.18~50 cm,剪切位移为2~60 mm时,本文所得的土的粘聚力提高了4.9%~14.6%,内摩擦角提高了3.9%~13.4%。建议尽量使用剪切面积大的试样进行直剪试验。  相似文献   

9.
曲面曲率对Rayleigh波传播特性的影响   总被引:2,自引:1,他引:1  
王子昆  金峰 《力学学报》2002,34(6):895-903
对任意形状的均匀各向同性线弹性曲面物体,用 WKB~(1)方法求解了沿曲面传播的Rayleigh表面波的运动微分方程,同时考虑了波传播方向及其垂直方向曲面曲率对波的穿透性的影, 所获波动方程的势函数解答表明,在一般情况下垂直波传播方向的曲面曲率对波的穿透深度的影响是不容忽视的.进而以同种介质平面表面情况下的Rayleigh面波的传播特性为基准,给出了曲面曲率引起波数或波速变化的解析表达式.通过理论分析和数值算例,描述了曲面上Rayleigh面波传播行为的一些基本特征.  相似文献   

10.
为探讨高温花岗岩经水冷却后的细观结构损伤及动态力学性能,对水冷却后高温花岗岩开展波速和核磁共振测试,分离式霍普金森压杆冲击试验,以及冲击破碎试样的扫描电镜观察,分析比较不同状态下花岗岩波速、孔隙度和动力学参数的变化规律。研究发现:随着温度升高,经水冷却处理后高温花岗岩波速非线性下降,大孔径孔隙度分量增大,且水冷却后试样的孔隙孔径尺寸和数量均大于自然冷却;水冷却后高温花岗岩动力学参数呈现出随着温度升高,峰值应力减小,峰值应变增大,弹性模量则先增大后减小的规律;由于水冷却使高温花岗岩表面温度急剧降低,产生额外的温度应力,花岗岩内部损伤加剧,表现出更低的波速与峰值应力;而水的冷淬作用一定程度上提高了表层花岗岩的硬度,降低了高温后花岗岩的塑性能力,与自然冷却相比水冷却后花岗岩的峰值应变减小,弹性模量增大,表现出脆性破坏特征。在温度低于400 ℃时,冷却方式对冲击裂纹影响不大,随着温度升高到800 ℃,自然冷却后花岗岩冲击断面呈蜂窝状,而水冷却后冲击断面则相对平整。  相似文献   

11.
By introducing the equivalent stiffness of an elastic half-space interacting with a Timoshenko beam, the displacement solution of the beam resting on an elastic half-space subjected to a moving load is presented. Based on the relative relation of wave velocities of the half-space and the beam, four cases with the combination of different parameters of the half-space and the beam, the system of soft beam and hard half-space, the system of sub-soft beam and hard half-space, the system of sub-hard beam and soft half-space, and the system of hard beam and soft half-space are considered. The critical velocities of the moving load are studied using dispersion curves. It is found that critical velocities of the moving load on the Timoshenko beam depend on the relative relation of wave velocities of the half-space and the beam. The Rayleigh wave velocity in the half-space is always a critical velocity and the response of the system will be infinite when the load velocity reaches it. For the system of soft beam and hard half-space, wave velocities of the beam are also critical velocities. Besides the shear wave velocity of the beam, there is an additional minimum critical velocity for the system of sub-soft beam and hard half-space. While for systems of (sub-) hard beams and soft half-space, wave velocities of the beam are no longer critical ones. Comparison with the Euler-Bernoulli beam shows that the critical velocities and response of the two types of beams are much different for the system of (sub-) soft beam and hard half-space but are similar to each other for the system of (sub-) hard beam and soft half space. The largest displacement of the beam is almost at the location of the load and the displacement along the beam is almost symmetrical if the load velocity is smaller than the minimum critical velocity (the shear wave velocity of the beam for the system of soft beam and hard half-space). The largest displacement of the beam shifts behind the load and the asymmetry of the displacement along the beam increases with the increase of the load velocity due to the damping and wave radiation. The displacement of the beam at the front of the load is very small if the load velocity is larger than the largest wave velocity of the beam and the half space. The results of the present study provide attractive theoretical and practical references for the analysis of ground vibration induced by the high-speed train.  相似文献   

12.
We perform wave experiments using a vertical shock tube setup. Shock waves are generated by the rupture of a thin membrane. In the test section, the incident pressure waves generate borehole-guided waves along water-saturated samples. The tube is equipped with side wall gages and a mobile pressure probe, so that the attenuation and reflection of the wave can be measured. The computation for a single horizontal fracture intersecting a vertical borehole gives a quantitative prediction of reflection and transmission of borehole-guided waves. Three different fracture apertures are used for the calculation. Fracture aperture significantly affects both reflection and transmission coefficients. Large fractures increase reflectivity and decrease transmissivity. In the experiment, we found that both pressures above and below the fracture are influenced by the fracture aperture indeed, thus indicating the potential for fracture detection by borehole waves.  相似文献   

13.
We perform wave experiments using a vertical shock tube setup. Shock waves are generated by the rupture of a thin membrane. In the test section the incident pressure waves generate borehole-guided waves along water-saturated samples. The tube is equipped with side wall gages and a mobile pressure probe, so that the attenuation and reflection of the wave can be measured. The computation for a single horizontal fracture intersecting a vertical borehole gives a quantitative prediction of reflection and transmission of borehole-guided waves. Three different fracture apertures are used for the calculation. Fracture aperture significantly affects both reflection and transmission coefficients. Large fractures increase reflectivity and decrease transmissivity. In the experiment, we found that both pressures above and below the fracture are influenced by the fracture aperture indeed, thus indicating the potential for fracture detection by borehole waves.  相似文献   

14.
The probability distributions of sand particles' lift-off and incident velocities in a wind-blown sand flux play very important roles in the simulation of the wind-blown sand movement. In this paper, the vertical and the horizontal speeds of sand particles located at 1.0 mm above a sand-bed in a wind-blown sand flux are observed with the aid of Phase Doppler Anemometry (PDA) in a wind tunnel. Based on the experimental data, the probability distributions of not only the vertical lift-off speed but also the lift-off velocity as well as its horizontal component and the incident velocity as well as its vertical and horizontal components can be obtained by the equal distance histogram method. It is found, according to the results of the χ 2-test for these probability distributions, that the probability density functions (pdf's) of the sand particles' lift-off and incident velocities as well as their vertical components are described by the Gamma density function with different peak values and shapes and the downwind incident and lift-off horizontal speeds, respectively, can be described by the lognormal and the Gamma density functions. These pdf's depend on not only the sand particle diameter but also the wind speed.  相似文献   

15.
Experimental-stress-analysis techniques were used to study wave and fracture propagation in rock media. Marble and granite plates were loaded explosively. Wave propagation was observed through isochromatic-fringe patterns on bonded photoelastic coatings and moiré-fringe patterns. These patterns were recorded with a Beckman and Whitley camera operating at rates from 250,000 to 1,000,000 frames per second. Dilatational, shear and Rayleigh wave velocities were determined. The leading part of the pulse is compressive and shows appreciable attenuation. The trailing part goes into tension, causing widespread tensile fracture. The velocity of propagation of this fracture zone in marble was nearly equal to the theoretical terminal velocity. In the case of induced cracks in marble and granite, the velocities of crack propagation were appreciably lower than the theoretical terminal values. Experimental results obtained were discussed and interpreted for their relevance to the rapid-excavation process in rock.  相似文献   

16.
5.12汶川Ms8.0级地震沿龙门山中央断裂带形成长度约270km的地表破裂带,破裂带垂直和水平位移一般为1.0~5.0m,最大可达9.8m。在地表破裂带附近,建筑物破坏严重。笔者系统调查了龙门山中央断裂带地表破裂的垂直和水平位移以及地震地表破裂影响带宽度,并采用物探测试方法对部分影响带宽度进行了验证。统计结果表明,汶川地震地表破裂影响带宽度主要集中在16~60m,影响带宽度(D)与垂直位移(H)具有较好的线性关系,即D=10.11H+16.0。对于逆冲性质为主的地震地表破裂而言,上盘影响带宽度与下盘的比值一般为3:1~2:1,据此可确定地表破裂带上、下盘的避让带宽度。笔者根据现场调查并借鉴国外经验提出,上盘避让宽度下限一般不应低于15m,下盘避让宽度下限不应低于10m。本项研究对于汶川地震灾后重建场地选址具有重要的实际意义。
  相似文献   

17.
The probability distributions of sand particles' lift-off and incident velocities in a wind-blown sand flux play very important roles in the simulation of the wind-blown sand movement. In this paper, the vertical and the horizontal speeds of sand particles located at 1.0 mm above a sand-bed in a wind-blown sand flux are observed with the aid of Phase Doppler Anemometry (PDA) in a wind tunnel. Based on the experimental data, the probability distributions of not only the vertical lift-off speed but also the lift-off velocity as well as its horizontal component and the incident velocity as well as its vertical and horizontal components can be obtained by the equal distance histogram method. It is found, according to the results of the χ2-test for these probability distributions, that the probability density functions (pdf's) of the sand particles' lift-off and incident velocities as well as their vertical components are described by the Gamma density function with different peak values and shapes and the downwind incident and lift-off horizontal speeds, respectively, can be described by the lognormal and the Gamma density functions. These pdf's depend on not only the sand particle diameter but also the wind speed. The project supported by the National Natural Science Foundation of China (10532040) and the Hundred Talents Project, the Knowledge Innovation Project of Chinese Academy of Sciences (KZCX2-304). The English text was polished by Keren Wang.  相似文献   

18.
This paper presents the results of experimental and numerical investigations of the problem of turbulent natural convection in a converging-plate vertical channel. The channel has two isothermally heated inclined walls and two adiabatic vertical side walls. The parameters involved in this study are the channel geometry represented by the channel width at exit, the inclination of the heated walls and the temperature difference between the heated walls and the ambient. The investigation covered modified Rayleigh numbers up to 108 in the computational study and up to 9.3 × 106 in the experimental work. The experimental measurements focused on the velocity field and were carried out using a PIV system and included measurements of the mean velocity profiles as well as the root-mean-square velocity and shear stress profiles. The experiments were conducted for an inclination angle of 30°, a gap width of 10 mm and two temperature differences (∆T=25.4°C and 49.8°C). The velocity profiles in the lower part of the channel indicated the presence of two distinct layers. The first layer is adjacent to the heated plate and driven by buoyancy forces while the second layer extends from the point of maximum velocity to the channel center plane and driven mainly by shear forces. The velocity profile at the upper portion of the channel has shown the merging of the two boundary layers growing over the two heated walls. The measured values of the Reynolds shear stress and root mean square of the horizontal and vertical velocity fluctuation components have reached their maximum near the wall while having smaller values in the core region. The computational results have shown that the average Nusselt number increases approximately linearly with the increase of the modified Rayleigh number when plotted on log–log scale. The variation of the local Nusselt number indicated infinite values at the channel inlet (leading edge effect) and high values at the channel exit (trailing edge effect). For a fixed value of the top channel opening, the increase of the inclination angle tended to reduce flow velocity at the inlet section while changing the flow structure near the heated plates in such a way to create boundary-layer type flow. The maximum value of the average Nusselt number occurs when θ = 0 and decreases with the increase of the inclination angle. On the other hand, the increase of the channel width at exit for the same inclination angle caused a monotonic increase in the flow velocity at the channel inlet.  相似文献   

19.
高速荷载下多孔饱和地基的动力响应   总被引:8,自引:0,他引:8  
金波 《力学季刊》2004,25(2):168-174
研究高速荷载作用下梁与多孔饱和半空间的动力响应。由Fourier变换求解多孔饱和固体的动力基本方程,根据梁与半空间的接触条件得出多孔饱和半空间上梁的垂直位移的表达式。文中的数值算例考虑了荷载移动速度对梁的动力位移的影响,并与相应的弹性半空间问题作了对比。从算例中可以发现荷载移动速度对动力位移有很大的影响,当移动速度与半空间的表面波速相近时,地面会当产生很大的振动,同时还发现当速度大于介质的剪切波速时,多孔饱和半空间上梁的动力响应与弹性半空间上梁的动力响应有很大的差别。  相似文献   

20.
砂岩岩石力学参数各向异性研究   总被引:2,自引:0,他引:2       下载免费PDF全文
俞然刚  田勇 《实验力学》2013,28(3):368-375
对胜利油田不同深度的四口井的砂岩岩芯进行了三轴压缩试验和动态岩石力学参数试验。根据获得的垂直地层方向和平行地层方向的试验数据,计算了各岩石力学参数的各向异性系数。通过分析围压以及深度对各向异性系数的影响,给出了砂岩峰值强度各项异性系数、静泊松比各向异性系数、纵波波速各向异性系数、纵横波速比和动泊松比各向异性系数与深度的拟合公式。发现峰值强度、纵波波速和纵横波速比的各向异性系数都随着深度的增加而减小,而泊松比各向异性系数随着深度的增加而增大。动、静弹性模量各向异性系数与深度相关性都很差,动弹性模量各向异性较弱,静弹性模量相对较强。  相似文献   

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