共查询到19条相似文献，搜索用时 171 毫秒
1.
基于ABAQUS的粘弹性边界单元及在重力坝抗震分析中的应用 总被引：2，自引：0，他引：2
考虑了2种不同的地震输入模型,即无质量地基模型和考虑辐射阻尼的粘弹性边界模型。以大型非线性有限元程序ABAQUS为平台,采用FORTRAN语言开发了用户单元子程序VSB_UEL.for,将粘弹性边界有效地嵌入到ABAQUS中。在尽量避免求解自由场的前提下,将离散的地震荷载转化为等效结点荷载,编写的计算程序可以方便地将等效荷载施加到人工边界结点上,并通过数值算例验证了粘弹性边界单元及波动输入程序的正确性,其求解效率和计算精度均令人满意,最后将该程序应用到在建的某水电站厂房坝段的抗震分析中。结果表明,与传统的固定边界无质量地基相比,考虑了粘弹性人工边界后,坝体的动力响应峰值减小了20%~40%;在进行结构动力响应分析时,考虑无限域地基的辐射阻尼影响是很有必要的。文中的用户子程序及波动输入程序很容易扩展至三维,为同类工程的抗震分析提供了简洁、合理的计算模式。 相似文献
2.
3.
本文围绕大跨度斜拉桥结构的地震动输入方式、土-结相互作用以及桥梁动水作用问题展开了如下研究:(1)固定地基地震动输入方式下,采用引入一个‘时差’的方式考虑了行波效应对一座七跨全漂浮结构体系斜拉桥结构的影响,比较了地震行波激励与一致激励作用下桥梁结构关键部位动力响应,分析了两种激励方式下桥梁结构关键部位动力响应的差异,阐明了行波激励作用对桥梁结构动力响应的影响规律,给出了相应抗震措施的建议和方法。(2)针对多跨径大跨度斜拉桥等多波源问题,分别基于刘晶波考虑柱面衰减波和杜修力考虑平面波与远场散射波叠加的单点源粘弹性人工边界,利用波场叠加原理推导出一种多源加权集中粘弹性人工边界条件,给出了其弹簧系数、阻尼系数的计算公式,并通过二维偏心单点源、偏心多点源以及多散射源算例讨论了本文多源加权集中粘弹性人工边界的计算精度 相似文献
4.
5.
6.
7.
《世界地震工程》2017,(2)
基于粘弹性人工边界相关理论和地震动输入方法的有关理论,推导并建立了既具有粘弹性人工边界特性,同时可以将地震动转化为施加在人工边界上等效荷载的三维粘弹性人工边界,并利用二次开发工具UPFs将其成功地嵌入至通用有限元分析软件ANSYS中。通过Lamb表面源问题以及内源问题对上述二次开发单元进行了验证。算例表明,该单元可以很好地对无限地基辐射阻尼进行模拟。随后通过对自由场波动输入问题的验证,表明该单元可以实现在有限元单元级别上准确有效地施加地震动等效荷载。与传统的粘弹性边界施加方式相比,该单元有着更简单的使用性以及更强的操作性,同时又不增加计算模型的规模等优势,因而计算效率更高。同时,结合通用有限元分析软件ANSYS强大的建模和计算分析能力,使粘弹性边界有着更广泛的应用,并可适用于各种结构-地基动力相互作用问题的分析。 相似文献
8.
9.
结构阻尼与材料阻尼的关系 总被引：5，自引：1，他引：4
针对固体材料在弹性阶段的内阻尼,采用材料粘弹性本构关系,通过有限单元法建立了考虑剪切变形影响的杆单元阻尼矩阵,得到了材料拉压粘滞系数和剪切粘滞系数之间的关系。我们可以通过实验测试材料的损耗因子或粘滞阻尼系数(材料阻尼),像结构质量矩阵、刚度矩阵一样通过比较确切的计算得到弹性阶段结构内阻尼的阻尼矩阵(结构阻尼),而且此阻尼矩阵既基于材料阻尼实验测试,又便于数学处理,且物理意义明确。其次,本文分析了材料阻尼对结构阻尼比影响,得到了材料损耗因子与结构模态阻尼比间的关系,并通过10层钢筋混凝土剪切型框架结构进一步给出了具体的数值结果。 相似文献
10.
无限域地基有限元分析的简化粘弹性边界 总被引：4，自引：0，他引：4
本文提出一种能用于无限域地基动、静力有限元分析的简单人工边界——粘弹边界，采用一层边界单元来实现。该边界弹簧部分采用弹性半空间Mindlin解计算，边界单元采用具有粘性阻尼的粘弹材料，通过确定合理的弹性模量、泊松比和粘性阻尼系数，不仅可以使边界单元能够模拟无限域远场的弹性恢复力，同时可以模拟粘性边界。通过算例分析，验证了该边界的有效性，它可用于土-结构动力相互作用分析。 相似文献
11.
黏弹性人工边界以其概念清晰,稳定性高,精度良好的优点,在地下结构抗震的研究中已经得到了较为广泛的应用。在使用黏弹性边界进行地震动的输入时,需要把地震波转化为模型网格节点上的等效节点力,这个过程就要涉及到波场分解的问题。波场分解的方式可以不同,但不同的波场分解方式会得出精度不同的计算结果,而学界目前尚未就此达成一致。本文在前人研究的基础上,总结了3种地震波斜入射的波场分解方法,编制了相应的Python脚本来实现黏弹性边界和等效节点力的批量施加,并且以不同角度的地震波斜入射为例在同一有限元模型中计算以进行比较研究。结果表明计算精度与波场分解的方式密切相关:在模型边界上考虑的自由场波动叠加越完整,计算结果越精确。 相似文献
12.
Earth medium is not completely elastic, with its viscosity resulting in attenuation and dispersion of seismic waves. Most viscoelastic numerical simulations are based on the finite-difference and finite-element methods. Targeted at viscoelastic numerical modeling for multilayered media, the constant-Q acoustic wave equation is transformed into the corresponding wave integral representation with its Green’s function accounting for viscoelastic coefficients. An efficient alternative for full-waveform solution to the integral equation is proposed in this article by extending conventional frequency-domain boundary element methods to viscoelastic media. The viscoelastic boundary element method enjoys a distinct characteristic of the explicit use of boundary continuity conditions of displacement and traction, leading to a semi-analytical solution with sufficient accuracy for simulating the viscoelastic effect across irregular interfaces. Numerical experiments to study the viscoelastic absorption of different Q values demonstrate the accuracy and applicability of the method. 相似文献
13.
After reviewing the studies on the lateral artificial boundaries in dynamic soil-structure interactions, the free field boundary was theoretically analyzed in asymmetric- and symmetric-matrix forms. First, the lumped mass system was combined with viscous or viscoelastic elements to obtain a lumped mass-free field boundary. Second, typical examples were implemented using the finite element software ABAQUS. The incident shear wave was taken to be perpendicular to the bottom to verify the effectiveness of the lumped mass-free field under various sites: underground structures, uniform sites, and layered sites. Finally, the accuracy of the lumped mass-free field boundary was compared with those of the viscoelastic and roller boundaries on different calculation scales, soil damping ratios, structure sizes, and ground motion characteristics. Subsequently, the engineering design values for different damping ratios are given. The results show that the precision of the lumped mass-free field boundary was reasonable, and the operation was simple within the same engineering application.
相似文献14.
结合均匀场地模型和分层均匀场地模型,采用数值试验的方法研究了场地地震反应分析中侧向人工边界距离的选取问题。分析了各主要因素对人工边界距离选取的影响,得到了如下结论:单侧人工边界距离与土层深度之比L/h是影响人工边界距离选取的主要参数;随着侧向人工边界距离的增加,有限元模型的计算误差并不一直减小,在局部范围内,会出现计算误差随着边界距离的增加而增大的现象;场地硬度、阻尼比和激振频率等因素不会影响计算误差随边界距离的变化规律,但采用自由场边界时受输入地震动频谱特性的影响较为明显;对水平激振下的一维场地模型来说,采用结合自由度边界时所需边界距离最短,自由场边界次之,采用粘性边界达到收敛时所需边界距离最长;无论哪种边界条件,当边界距离大于某一范围后,都能得到稳定的计算结果;相对于均质场地模型来说,实际的分层均匀场地建模时可适当减小侧向人工边界距离。 相似文献
15.
从Maxwell方程组出发,推导了探地雷达(GPR)有限元波动方程.阐述了透射边界条件和Sarma边界条件的原理,推导了这两种边界条件的理论公式;通过在衰减层内加入过渡带优化了Sarma边界条件的加载方法,压制了介质区和衰减层交界面处的人为反射.考虑到透射边界条件与Sarma边界条件不同的理论机制,提出了一种结合透射边界条件和Sarma边界条件的混合边界条件,它利用Sarma边界条件对到达边界区域的GPR波能量衰减功能和透射边界对GPR波能量的透射功能,使GPR波经过Sarma边界条件的衰减吸收后,再通过透射边界条件将剩余能量透射出去,集成了二者的优势.并以二维均匀模型中的中心脉冲激励源方式为例,通过Matlab程序实现,以GPR的全波场快照的直观方式,对比了有、无边界条件及不同边界条件对人工截断边界的处理效果,说明了该混合边界条件对到达截断边界处的GPR波的处理优于单一边界条件.最后,以基于混合边界条件的有限单元法对两个典型的GPR地电模型进行了正演模拟,指导了GPR数据处理与工程实践. 相似文献
16.
R. Betti 《地震工程与结构动力学》1997,26(10):1005-1019
A boundary element formulation of the substructure deletion method is presented for the seismic analysis of the dynamic cross-interaction between multiple embedded foundations. This approach is particularly suitable for three-dimensional foundations of any arbitrary geometrical shape and spatial location, since it requires only the discretization of the foundations’ surfaces. The surrounding soil is represented by a homogeneous viscoelastic half-space while the foundations are assumed to be rigid and subjected to incoming SH-, P-, and SV-waves arbitrarily inclined in both the horizontal and vertical planes. The proposed methodology is tested for the case of two identical embedded square foundations for different values of the foundations’ embedment and distance. The effects of the cross-interaction are outlined in the components of the impedance matrix and of the foundation input motion. © 1997 John Wiley & Sons, Ltd. 相似文献
17.
用三维半解析边界元的子结构法分析凸起山包对地震波的散射 总被引：7，自引：0，他引：7
本文建立了一种三维半解析边界元子结构法。这种方法可在频域就三维轴对称凸起山包对地震波的散射进行分析。这种方法节省存储空间、计算工作量小。另外还叙述了拐角的处理方法。 相似文献
18.
Apart from some special cases, calculating the dynamic stiffness matrix of foundations on a layered half-space, especially for embedded foundations, is computationally expensive. An efficient method for two-dimensional foundations in a horizontally layered soil media is presented in this paper. This method is based on indirect boundary element methods and uses discrete wave number solution methods for calculating Green's functions for displacements and analytical methods for the integrations over the boundary. For surface foundations, the present method applies at all frequencies. For embedded foundations or for constructing energy transmitting boundaries, because the free-field part is modelled by boundary elements and the excavated part is modelled by finite elements, the present method applies only at low frequencies for the spring coefficients (the real parts of the dynamic stiffness matrix) but applies at all frequencies for the damping coefficients (the imaginary part of the dynamic stiffness matrix) for undamped sites. The novelty of the method can be used for three-dimensional foundations. © 1997 by John Wiley & Sons, Ltd. 相似文献
19.
Michel Bouchon 《Pure and Applied Geophysics》1996,148(1-2):3-20
We review the application of the discrete wave number method to problems of scattering of seismic waves formulated in terms of boundary integral equation and boundary element methods. The approach is based on the representation of the diffracting surfaces and interfaces of the medium by surface distributions of sources or by boundary source elements, the radiation from which is equivalent to the scattered wave field produced by the diffracting boundaries. The Green's functions are evaluated by the discrete wave number method, and the boundary conditions yield a linear system of equations. The inversion of this system allows the calculation of the full wave field in the medium. We investigate the accuracy of the method and we present applications to the simulation of surface seismic surveys, to the diffraction of elastic waves by fractures, to regional crustal wave propagation and to topographic scattering. 相似文献