共查询到18条相似文献，搜索用时 203 毫秒
1.
ABAQUS动力无限元人工边界研究 总被引：2，自引：0，他引：2
针对动力场天然无限地基的数值模拟与地震波输入问题进行了一些有意义的研究,评述了现有动力计算常用无限元的优缺点,详细阐述了ABAQUS无限元理论体系框架,并加以改进,提出一种考虑外域地震动影响的ABAQUS动力无限元人工边界。采用等效边界力的叠加原理,对入射波和散射波分开处理,视入射波和散射波在边界上互不影响,将输入地震动转化为作用于有限元无限元交界面上的等效应力的方法来解决外源波的入射问题。算例验证结果表明：内源振动和固定边界会出现失真和扰动现象,同时该计算结果与黏弹性边界的计算结果对比可知,该方法对外行散射波的过滤作用优于黏弹性边界。因此,改进的ABAQUS动力无限元人工边界理论方法有效且具有一定的稳定性。 相似文献
2.
根据饱和土Biot理论,在频域内提出了一种适用于弹性波波动问题的有限元-无限元解法,其中有限单元用于近场介质的模拟,而形函数基于一维解析解答的无限单元则被用于人工边界,它可反映波传递到无限远处的特性;应用该法计算算例,以证明其有效性与正确性。在此基础上,对饱和地基中空沟主动隔振效果进行了详细的数值分析,结果表明,空沟深度是影响隔振效果的主要因素,一般沟深越大,隔振效果越好;当沟深一定时,空沟到振源的距离不宜超过1.5倍饱和土剪切波长;空沟的宽度对隔振效果的影响相对较小。 相似文献
3.
在土-结构动力相互作用分析中,黏性人工边界条件和黏弹性人工边界条件虽具有计算效率和精度较高的优点,但施加边界单元的工作量较大;远置边界虽然具有处理技术简单、精度高等优点,但又存在计算成本高的问题。为克服黏性人工边界和黏弹性人工边界施加边界黏弹性单元工作量大、远置边界计算成本高的缺点,基于波的传播理论和波在介质交界面上的反射、透射原理,通过设置完全透射层并大大降低波在透射层的传播速度的方法,提出了一种等效远置动力人工边界条件并对其进行数值验证分析。研究结果表明,所提出的等效远置动力人工边界条件仅需通过合理选取透射层的参数,即可实现反射波向无限地基传播的模拟,具有精度和效率较好、不需施加边界单元工作量等优点,可应用到土-结构动力相互作用分析当中。 相似文献
4.
煤系地层为成层分布的沉积岩,煤层的开采会引起地表大规模的沉陷,发展适应此类介质的分析方法一直是本领域的研究热点。本文发展了一种新型的边界元方法来分析煤层开采引起的地表移动。该边界元方法基于层状材料基本解,采用4～8变结点单元离散边界,并采用有效的数值方法计算各类奇异积分。然后,用有解析解的算例验证建议数值方法。最后,采用新型边界元方法分析煤层开采引起的地表移动。本文所建议的方法在分析煤层开采引起的地表沉陷时具有较高的计算精度和效率。 相似文献
5.
将排桩对平面SH波的隔振简化为弹性波散射的二维平面问题,基于全空间中无限周期结构的周期特性,给出了一种求解无限周期分布桩体对平面SH波隔振效应的解析方法。该方法采用波函数展开法并结合Graf加法定理,利用全空间中相邻周期单元的散射波场在频域内相差一个相位的特性,仅选取一个周期单元,将入射波场和所有散射波场的贡献叠加后,根据边界条件求解待定系数,从而求得整个散射波场。该解析解能够精确求解无限周期分布桩体的散射问题,分析周期分布桩体数量较多时的隔振规律,弥补了以往理论分析中桩体个数较多时难以求解的不足。重点讨论了桩体个数、桩体刚度、桩体间距和桩体类型等因素对隔振效果的影响,结果表明：（1）该方法显著降低了求解大量桩体问题时的存储量和计算量,有限周期模型计算结果随桩体个数增多收敛于无限周期模型,反映了该方法的正确性;（2）整体上桩体刚度增大有利于提高隔振效果,但桩体刚度对隔振效果的提升有限,桩体剪切波速为土体5倍时已具有足够的隔振效果;（3）桩间距对隔振效果有着直接影响,间距越小则低频禁带宽度越大;（4）桩体类型对隔振效果有着显著影响,实心桩有着良好的隔振效果,而具有柔性内填充的管桩在低频段有着更佳的隔振效果。 相似文献
6.
7.
为研究综合管廊动力边界条件对地震动力响应的影响,以厦门地区的代表性土层为例,建立动力有限元数值模型,土体本构采用小应变硬化模型,分别设定固定边界、黏性边界和自由场3种人工边界条件,进行Rayleigh波和地震底部剪切波作用下的场地响应研究;并根据变形特征及拟绝对加速度反应谱（PSA）评价3种边界的有效性,提出综合管廊地震动力分析的优化动力边界组合方法。研究表明：在地震波（底部水平加速度时程）及Rayleigh波的作用下,由于考虑了黏性边界对外行波的吸收,但未考虑地震动的输入问题及边界外半无限介质的弹性恢复性能,边界会对模型内部土体的水平位移产生限制作用,使得场地内水平位移响应偏小,而采用自由场边界则基本不存在这种限制作用,表现出强烈的振荡;采用激励侧固定边界、远离激励侧黏性边界、其余侧自由场边界的优化组合动力边界,在Rayleigh波和底部加速度时程共同作用下,二者引起的动力响应交叉干扰较少,可按线性叠加处理;同时,黏性边界对地震波引起的动力响应有一定范围的吸收,自由场边界对Rayleigh波引起的动力响应也有一定范围的变形限制影响。研究成果可供地下综合管廊结构地震响应精细化数值模拟及抗震设计参考。 相似文献
8.
岩土工程中经常会遇到无穷域问题,而采用无限单元可以实现对其有效地模拟。弱形式求积元法是一个有效的数值工具,它常通过提高积分阶次来提高计算精度。建立了无限弱形式求积单元并被应用于求解岩土工程中的无穷域问题,该单元基于坐标映射,将无穷域变换到标准域,在标准域上进行数值积分和数值微分,保留了传统弱形式求积元的积分点坐标和权系数。求解了瞬态渗流、固结和静力分析等数值算例,并与解析解或截断方法进行了对比。结果表明:基于坐标映射的无限弱形式求积单元使用简单,可以模拟各种类型的无穷域问题,仅需要将感兴趣的范围进行有限域划分并通过提高积分阶次来减小对极点位置的依赖,极大地节省了计算资源,提高了计算精度。 相似文献
9.
公路黄土暗穴临界稳定埋深回归的预测方法及其程序实现 总被引：1，自引：0，他引：1
基于动力学基本方程,运用有限单元法（FEM）和NEWMARK隐式积分方法,对动荷载（FWD荷载）作用下路基下伏黄土暗穴动力稳定的临界埋深进行了弹塑性数值分析,考虑到人工截断边界上波反射对计算结果的影响,分别用传递边界和半无限单元来处理侧面和底面边界。在此基础上,对利用有限个数值分析结果进行不同洞径及位置暗穴临界稳定埋深的预测方法和步骤进行了分析,提出了一种基于洞径和中心距的双变量临界稳定埋深计算方法,并用VB6.0编制了计算程序LDMC。为验证程序的有效性,用3 m和5 m洞径的暗穴进行了对比分析,表明计算结果具有较高的精度,完全可满足实际工程的要求,同时指出了使用时应注意的问题。 相似文献
10.
针对半无限长多孔介质柱体,一端为定浓度边界的水动力弥散反求参数问题,先用数值方法求解补余误差函数erfc（x）的反函数,再根据该问题的解析解,通过变量代换,构造一个基于解析解的最小二乘模型来反求水动力弥散系数。最后将该方法应用于一个实例,计算结果表明该方法比erfc（x）近似公式法、配线法、正态分布函数法等传统方法要好。 相似文献
11.
This paper presents a model for the analysis of plane waves diffraction at a cavity in an infinite homogeneous poroelastic saturated medium, lined by a lining composed of four equal segments. An elastic boundary layer is placed between the cavity lining and the infinite porous medium. The boundary layer is simulated by ‘elastic boundary conditions’ in which the bulk matrix stress is proportional to the relative displacement between the lining and the surrounding medium matrix boundary. In addition, fluid impermeability through the intermediate layer is assumed. For the frequencies, that differ from the pseudoresonanse frequencies, the problem was reduced to the problem of an ideal elastic medium. A closed‐form analytical solution of the problem was obtained using Fourier–Bessel series, the convergence of which was proven. It was shown that the number of series terms required to obtain a desired level of accuracy can be determined in advance. The influence of the medium porosity on the medium dynamic stress concentration was studied. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
12.
《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
13.
M. A. Hicks 《国际地质力学数值与分析法杂志》2000,24(5):453-476
An adaptive mesh refinement algorithm has been developed for non‐linear computations in geomechanics, based on a smoothed stress–strain finite element formulation. This uses estimates of error in the incremental shear strain invariant to guide the regeneration of unstructured meshes at regular intervals during loading. Following each mesh‐update, no re‐analysis of previous increments with the new mesh is necessary. Algorithm performance has been investigated by analysing a passive earth pressure problem using a linear elastic‐perfectly plastic Mohr–Coulomb soil model. Perfectly drained behaviour has been considered, as have partially drained situations using hydromechanical coupling, while undrained behaviour has been approximated using time steps close to zero. In all cases, mesh adaptivity has been successful in capturing regions of high strain gradient. The results have been compared with analytical solutions. Accurate computations of limit load and shear band orientation have been obtained for a wide range of material dilation angles. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
14.
The method of fundamental solution for 3‐D wave scattering in a fluid‐saturated poroelastic infinite domain 
下载免费PDF全文
下载免费PDF全文 Zhongxian Liu Zhikun Wang Alexander H.D. Cheng Jianwen Liang Chuchu Wang 《国际地质力学数值与分析法杂志》2018,42(15):1866-1889
By using a complete set of poroelastodynamic spherical wave potentials (SWPs) representing a fast compressional wave PI, a slow compressional wave PII, and a shear wave S with 3 vectorial potentials (not all are independent), a solution scheme based on the method of fundamental solution (MFS) is devised to solve 3‐D wave scattering and dynamic stress concentration problems due to inhomogeneous inclusions and cavities embedded in an infinite poroelastic domain. The method is verified by comparing the result with the elastic analytical solution, which is a degenerated case, as well as with poroelastic solution obtained using other numerical methods. The accuracy and stability of the SWP‐MFS are also demonstrated. The displacement, hoop stress, and fluid pore pressure around spherical cavity and poroelastic inclusion with permeable and impermeable boundary are investigated for incident plane PI and SV waves. The scattering characteristics are examined for a range of material properties, such as porosity and shear modulus contrast, over a range of frequency. Compared with other boundary‐based numerical strategy, such as the boundary element method and the indirect boundary integral equation method, the current SWP‐MFS is a meshless method that does not need elements to approximate the geometry and is free from the treatment of singularities. The SWP‐MFS is a highly accurate and efficient solution methodology for wave scattering problems of arbitrary geometry, particularly when a part of the domain extends to infinity. 相似文献
15.
A local artificial boundary for transient seepage problems with unsteady boundary conditions in unbounded domains 下载免费PDF全文
下载免费PDF全文 Numerical analysis of transient seepage in unbounded domains with unsteady boundary conditions requires a more sophisticated artificial boundary approach to deal with the infinite character of the domain. To that end, a local artificial boundary is established by simplifying a global artificial boundary. The global artificial boundary conditions (ABCs) at the truncated boundary are derived from analytical solutions for one‐dimensional axisymmetric diffusion problems. By applying Laplace transforms and introducing some specially defined auxiliary variables, the global ABCs are simplified to local ABCs to significantly enhance the computational efficiency. The proposed local ABCs are implemented in a finite element computer program so that the solutions to various seepage problems can be calculated. The proposed approach is first verified by the computation of a one‐dimensional radial flow problem and then tentatively applied to more general two‐dimensional cylindrical problems and planar problems. The solutions obtained using the local ABCs are compared with those obtained using a large element mesh and using a previously proposed local boundary. This comparison demonstrates the satisfactory performance and obvious superiority of the newly established boundary to the other local boundary. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
16.
M. E. Duncan Fama 《国际地质力学数值与分析法杂志》1989,13(3):331-337
It is shown that a finite element calculation which approximates an ‘infinite medium’; problem by a mesh with finite boundaries will yield greater accuracy when stress boundary conditions are applied on the far-field boundary than is obtainable with displacement boundary conditions. In particular, with Poisson's ratio close to 0.5, the accuracy of the latter model is severely impaired, whereas the stress boundary condition model is unaffected for Poisson's ratio of 0.49 and a reasonable mesh. The eight-node quadratic isoparametric element displays superb accuracy for the axisymmetric thick cylinder with either type of boundary condition. 相似文献
17.
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
18.
Moche Ziv 《国际地质力学数值与分析法杂志》2003,27(3):207-232
The response of an ideal elastic half‐space to a line‐concentrated impulsive vector shear force applied momentarily is obtained by an analytical–numerical computational method based on the theory of characteristics in conjunction with kinematical relations derived across surfaces of strong discontinuities. The shear force is concentrated along an infinite line, drawn on the surface of the half‐space, while being normal to that line as well as to the axis of symmetry of the half‐space. An exact loading model is introduced and built into the computational method for this shear force. With this model, a compatibility exists among the prescribed applied force, the geometric decay of the shear stress component at the precursor shear wave, and the boundary conditions of the half‐space; in this sense, the source configuration is exact. For the transient boundary‐value problem described above, a wave characteristics formulation is presented, where its differential equations are extended to allow for strong discontinuities which occur in the material motion of the half‐space. A numerical integration of these extended differential equations is then carried out in a three‐dimensional spatiotemporal wavegrid formed by the Cartesian bicharacteristic curves of the wave characteristics formulation. This work is devoted to the construction of the computational method and to the concepts involved therein, whereas the interpretation of the resultant transient deformation of the half‐space is presented in a subsequent paper. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献