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1.
Soil models based on kinematic hardening together with elements of bounding surface plasticity, provide a means of introducing some memory of recent history and stiffness variation in the predicted response of soils. Such models provide an improvement on simple elasto‐plastic models in describing soil behaviour under non‐monotonic loading. Routine use of such models requires robust numerical integration schemes. Explicit integration of highly non‐linear models requires extremely small steps in order to guarantee convergence. Here, a fully implicit scheme is presented for a simple kinematic hardening extension of the Cam clay soil model. The algorithm is based on the operator split methodology and the implicit Euler backward integration scheme is proposed to integrate the rate form of the constitutive relations. This algorithm maintains a quadratic rate of asymptotic convergence when used with a Newton–Raphson iterative procedure. Various strain‐driven axisymmetric triaxial paths are simulated in order to demonstrate the efficiency and good performance of the proposed algorithm. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
2.
In this paper a new methodology to simulate saturated soils subjected to dynamic loadings under large deformation regime (locally up to 40% in equivalent plastic strain) is presented. The coupling between solid and fluid phases is solved through the complete formulation of the Biot’s equations. The additional novelty lies in the employment of an explicit time integration scheme of the \(u-w\) (solid displacement–relative fluid displacement) formulation which enables us to take advantage of such explicit schemes. Shape functions based on the principle of maximum entropy implemented in the framework of Optimal Transportation Meshfree schemes are utilized to solve both elastic and plastic problems. 相似文献
3.
Error-controlled implicit time integration of elasto-visco-plastic constitutive models for rock salt
The mechanical behavior of rock salt is rate-dependent at different time scales. Using caverns in rock salt formations for renewable energy storage implies that the underground structures are subjected to both short-term and long-term loads, increasing robustness and flexibility requirements for numerical simulators used to assess the safety of such structures. So far, explicit time integration with model-specific heuristics for time-step size determination dominate in application studies. In this paper, the suitability of error-controlled adaptive time-integration schemes of the diagonally implicit Runge-Kutta type is investigated in comparison with the Backward Euler and Crank-Nicolson schemes when applied to the integration of typical elasto-visco-plastic constitutive models of rock salt. The comparison is made both for monotonic and for cyclic loads as well as taking account of thermo-mechanical coupling. Analyses of the time-integration errors and the time step-size evolution show the suitability of the integration scheme for these material models. The automatic adjustment of the time-step size was found to be robust across all material models and boundary conditions as well as for non-isothermal situations for a single algorithmic parameter set. 相似文献
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In this study, the time-dependent damage process of granite is investigated utilizing two numerical simulation schemes based on continuous method and discontinuous method. Numerical creep tests are carried out with both simulation schemes and mechanical responses and fracture patterns of rock specimens are analyzed. The calibrated numerical models can successfully reflect the typical creep stages observed in the laboratory. The predicted lifetime is in accordance with the laboratory test data. Comparisons are made between the two simulation schemes. It is found that both schemes have unique features that can promote a genuine reflection of the time-dependent damage process of the brittle rocks. 相似文献
6.
声波散射数值模拟的两种新方案 总被引：4，自引：0，他引：4
孙建国 《吉林大学学报(地球科学版)》2006,36(5):863-868
声波散射的数值模拟问题一般用网格法或积分方程法解决。当模型的尺度很大时,两种方法都会遇到计算机资源不足所造成的困难。另外,在网格法中,场源的位置和场源附近的波场奇异性逼近精度都受网格点的控制,因此难以满足实际问题所提出的要求。针对这些问题,提出了两种处理声波散射问题的新方案。一种主要针对网格法,另外一种针对积分方程法。在针对网格法的方案中,通过模型分解和波场分裂,将原始的总场计算问题转化为散射场计算问题。由于背景场是由解析公式给出的,所以可以将场源放置在数值网格的任意位置,不一定非得在网格点上。基于同样的原因,场源附近的波场奇异性可以精确地算出。在针对积分方程法的方案中,通过引入拟线性近似,使得散射场的数值求解不必再借助于代数方程组,只要进行数值积分即可。所建立的数值计算方案具有普遍的适用性,其基本思想可以直接用于解决弹性波散射的数值模拟问题并用于反演密度和速度。 相似文献
7.
R. G. Wan 《Computers and Geotechnics》1992,14(3):149-177
A realistic strength criterion often used to describe the yielding behaviour of a jointed rock mass at a continuum level is the well-known Hoek and Brown criterion. This paper is concerned with a 3-D stress generalization of the Hoek-Brown failure criterion by means of an elliptical functional which leads to a smooth deviatoric trace in the stress space. For its incorporation into a finite element analysis involving plasticity calculations, the formulation of an implicit stress integration algorithm is presented. The key computational methodology alludes to the notion of consistent tangent modulus and implicit return mapping schemes (radial and closest point return) for stress integration in a finite element analysis. Within the context of non-linear elastoplastic analysis, it is found that formulation of such consistent modulus and success into achieving numerical efficiency are closely intertwined. Indeed, the procedure results into accurate and rapid convergence of the displacement finite element scheme during the search for equilibrium. This means that considerable savings in computational time can be achieved for large scale problems. Numerical examples which focus on the Hoek-Brown plasticity model are presented in order to fully appreciate the robustness of the algorithm, and hence the viability of such method to practical problems. 相似文献
8.
The Advanced Research WRF (ARW) model is used to simulate Very Severe Cyclonic Storms (VSCS) Hudhud (7–13 October, 2014), Phailin (8–14 October, 2013) and Lehar (24–29 November, 2013) to investigate the sensitivity to microphysical schemes on the skill of forecasting track and intensity of the tropical cyclones for high-resolution (9 and 3 km) 120-hr model integration. For cloud resolving grid scale (<5 km) cloud microphysics plays an important role. The performance of the Goddard, Thompson, LIN and NSSL schemes are evaluated and compared with observations and a CONTROL forecast. This study is aimed to investigate the sensitivity to microphysics on the track and intensity with explicitly resolved convection scheme. It shows that the Goddard one-moment bulk liquid-ice microphysical scheme provided the highest skill on the track whereas for intensity both Thompson and Goddard microphysical schemes perform better. The Thompson scheme indicates the highest skill in intensity at 48, 96 and 120 hr, whereas at 24 and 72 hr, the Goddard scheme provides the highest skill in intensity. It is known that higher resolution domain produces better intensity and structure of the cyclones and it is desirable to resolve the convection with sufficiently high resolution and with the use of explicit cloud physics. This study suggests that the Goddard cumulus ensemble microphysical scheme is suitable for high resolution ARW simulation for TC’s track and intensity over the BoB. Although the present study is based on only three cyclones, it could be useful for planning real-time predictions using ARW modelling system. 相似文献
9.
Stress‐driven integration strategies and m‐AGC tangent operator for Perzyna viscoplasticity and viscoplastic relaxation: application to geomechanical interfaces 
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下载免费PDF全文 The paper proposes a stress‐driven integration strategy for Perzyna‐type viscoplastic constitutive models, which leads also to a convenient algorithm for viscoplastic relaxation schemes. A generalized trapezoidal rule for the strain increment, combined with a linearized form of the yield function and flow rules, leads to a plasticity‐like compliance operator that can be explicitly inverted to give an algorithmic tangent stiffness tensor also denoted as the m‐AGC tangent operator. This operator is combined with the stress‐prescribed integration scheme, to obtain a natural error indicator that can be used as a convergence criterion of the intra‐step iterations (in physical viscoplasticity), or to a variable time‐step size in viscoplastic relaxation schemes based on a single linear calculation per time step. The proposed schemes have been implemented for an existing zero‐thickness interface constitutive model. Some numerical application examples are presented to illustrate the advantages of the new schemes proposed. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
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Many studies have proven that the dynamic control of flood-limited water level (DC-FLWL) is an effective methodology to balance flood control and water conservation for reservoir operations during the flood season. However, these studies have focused on determining the bound of FLWL; few studies have investigated the implementation of real-time DC-FLWL, which actually is the core of DC-FLWL. To implement real-time DC-FLWL, a new method for considering rain forecast is presented in the present study. The proposed method includes two procedures: prerelease and prefill, which constitute the prerelease–refill and the prefill–prerelease schemes. For each scheme, the categorical rain forecast with a lead time of 24 h is used as the trigger for different actions, while hydrological forecast and discharge are used to calculate the action details, including the water level reserved and the amount of discharge water. The method is examined via the operation of the flood event “19960810,” which occurred in the catchment of the Biliuhe reservoir in China. The results show that although the maximum water level and the maximum discharge of the three schemes have the same value, the water level at the end of both the prerelease–refill and the prefill–prerelease schemes of DC-FLWL is 68.8 and 68.5 m, which are both higher than the planning scheme, i.e., 68.1 m. These findings further confirm the effectiveness of DC-FLWL and also prove that the proposed method is suitable for implementing real-time DC-FLWL. 相似文献
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The numerical integration of the stress–strain relationship is an important part of many finite element code used in geotechnical engineering. The integration of elasto-plastic models for unsaturated soils poses additional challenges associated to the presence of suction as an extra constitutive variable with respect to traditional saturated soil models. In this contribution, a range of explicit stress integration schemes are derived with specific reference to the Barcelona Basic Model (BBM), which is one of the best known elasto-plastic constitutive models for unsaturated soils. These schemes, however, do not address possible non-convexity of the loading collapse (LC) curve and neglect yielding on the suction increase (SI) line. The paper describes eight Runge–Kutta methods of various orders with adaptive substepping as well as a novel integration scheme based on Richardson extrapolation. The algorithms presented also incorporate two alternative error control methods to ensure accuracy of the numerical integration. Extensive validation and comparison of different schemes are presented in a companion paper. Although the algorithms presented were coded for the Barcelona Basic Model, they can be easily adapted to other unsaturated elasto-plastic models formulated in terms of two independent stress variables such as net stress and suction. 相似文献
12.
An implicit material point method (MPM), a variant of the finite element method (FEM), is presented in this paper. The key feature of MPM is that the spatial discretisation uses a set of material points, which are allowed to move freely through the background mesh. All history-dependent variables are tracked on the material points and these material points are used as integration points similar to the Gaussian points. A mapping and re-mapping algorithm is employed, to allow the state variables and other information to be mapped back and forth between the material points and background mesh nodes during an analysis. In contrast to an explicit time integration scheme utilised by most researchers, an implicit time integration scheme has been utilised here. The advantages of such an approach are twofold: firstly, it addresses the limitation of the time step size inherent in explicit integration schemes, thereby potentially saving significant computational costs for certain types of problems; secondly, it enables an improved algorithm accuracy, which is important for some constitutive behaviours, such as elasto-plasticity. The main purpose of this paper is to provide a unified MPM framework, in which both quasi-static and dynamic analyses can be solved, and to demonstrate the model behaviour. The implementation closely follows standard FEM approaches, where possible, to allow easy conversion of other FEM codes. Newton’s method is used to solve the equation of motion for both cases, while the formation of the mass matrix and the required updating of the kinematic variables are unique to the dynamic analysis. Comparisons with an Updated Lagrangian FEM and an explicit MPM code are made with respect to the algorithmic accuracy and time step size in a couple of representative examples, which helps to illustrate the relative performance and advantages of the implicit MPM. A geotechnical application is then considered, illustrating the capabilities of the proposed method when applied in the geotechnical field. 相似文献
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碎屑沉积地质体构型分级方案探讨 总被引：4，自引：0，他引：4
沉积体的层次结构是复杂地质体的内在特征。针对现有碎屑沉积体层次结构分级中的不足,按照构型规模及包含关系,
以最大自旋回与最小异旋回为衔接点,采用倒序分级原则,将已有的岩性体构型与层序构型分级整合为一体化的沉积体构
型分级方案,并与我国的沉积相分级体系进行了比较分析。在沉积盆地内划分了12 级构型单元,其中1~6 级单元为层序构型,
7~9 级单元为相构型,10~12 级单元为层理构型。这一方案有利于勘探开发一体化的地下地质研究。油气田勘探阶段构型分
布的研究级别主要为1~4 级,油气田开发阶段构型分布研究的级别主要为5~9 级。我国现有的沉积相分级体系为自成因沉积
体的分级体系,但并非层次结构分级体系,且存在相单元级次不统一的问题。微相单元一般具有层次结构意义,可作为构
型单元,而亚相一般不能作为构型单元。 相似文献
14.
Giancarlo Gioda 《国际地质力学数值与分析法杂志》1982,6(1):21-46
An analysis is presented of the non-linear creep effects around a deep circular tunnel driven in ‘squeezing’ ground. The time-dependent behaviour of the geotechnical medium is described by means of a simple viscoplastic rheological model capable of approximating primary, secondary and tertiary creep behaviours. It is shown that tertiary creep can be allowed for by providing a suitable law governing the variation of some material parameters (such as viscosity) with stresses and strains. The basic operations of the ‘evolutive’ procedure adopted for time integration are outlined. Along each time integration step, quadratic variations of the stress and strain fields and linear variations of the material parameters are assumed. The results of various finite element analyses are presented concerning both lined and unlined cases. For the lined cases, the influence of the liner stiffness and of the time elapsed between the end of excavation and the liner installation is considered. 相似文献
15.
This paper presents a coupling technique for integrating the element-free Galerkin method (EFGM) with the fractal finite element method (FFEM) to analyze unbounded problems in the half-space. FFEM is adopted to model the far field of an unbounded domain and EFGM is used in the near field. In the transition region interface elements are employed. The shape functions of interface elements which comprise both the element-free Galerkin and the finite element shape functions, satisfy the consistency condition thus ensuring convergence of the proposed coupled EFGM–FFEM. The proposed method combines the best features of EFGM and FFEM, in the sense that no structured mesh or special enriched basis functions are necessary. The numerical results show that the proposed method performs extremely well converging rapidly to the analytical solution. Also a parametric study is carried out to examine the effects of the integration order, the similarity ratio, the weight function, the scaling parameter and the number of transformation terms, on the quality of the numerical solutions. 相似文献
16.
Hypo-elastic relations are often adopted to simulate the recoverable non-linear behaviour of soils within elasto-plastic constitutive models. In reality, they are unable to reproduce the elastic, ie, recoverable, response of materials; hence, they introduce severe inconsistencies in models based on the decomposition of the total strain tensor into its recoverable and permanent parts. Hyper-elasticity should then be used. However, existing models developed within this framework do not satisfy a number of fundamental theoretical requirements. A new hyper-elastic model is proposed, which is rigourously formulated by integrating some of the main relations which emerge from experimental results. The model satisfies all theoretical requirements and also possesses features that are fundamental for its numerical integration. The model can be considered as the correct hyper-elastic version of the classical hypo-elastic constitutive relation adopted in models based on the Critical State framework, such as the Modified Cam-Clay, with a constant Poisson's ratio. 相似文献
17.
Assessment of groundwater resources in India is guided by National Water Policy (1987, 2002) which states that groundwater resources can be exploited only up to its recharge limit. The methodology for groundwater resources assessment in India is broadly based on Ground Water Resources Estimation Methodology, 1997 and it involves assessment of annual replenishable groundwater resources (recharge), annual groundwater draft (utilization) and the percentage of utilization with respect to recharge (stage of development). The assessment units (blocks/watersheds) are categorized based on stage of groundwater development (utilization) and the long term water level trend. The present methodology though useful in identification and prioritization of areas for groundwater management, falls short of addressing several critical issues like spatial and temporal variation of groundwater availability within the aquifer, accessibility of groundwater resources and quality of groundwater. This paper introduces a new categorisation scheme considering the above issues. The proposed scheme takes into account four criteria, viz. (i) stage of exploitation, (ii) extractability factor, (iii) temporal availability factor and (iv) quality factor. In comparison to the existing method used for categorisation, the proposed approach is more inclusive. The methodology is also equally suitable for both alluvial and hard rock terrain since it takes into consideration the variable characteristics of different types of aquifers and convergence of quantitative and qualitative assessment. The categorisation proposed here involves GIS based integration of different parameters/ themes. This allows better representation of spatial variability. The proposed methodology is demonstrated in this paper taking a case study from a hard rock terrain in central India. 相似文献
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某深大基坑位于长江下游岸边,场地地层为典型的二元结构,基坑开挖涉及的两层承压含水层间的弱透水层局部缺失,之间水力联系密切,基坑场地地质条件极为复杂,基坑施工降水直接关系到基坑工程的安全。这里将基坑分3个区,分别进行降水设计。具体降水方案:Ⅰ区两层承压含水层和Ⅱ区第一承压含水层被围护结构隔断内外水力联系,采用疏干井降水;Ⅱ区第二承压含水层未被围护结构隔断,Ⅲ区两层承压含水层水力联系密切,针对这两个区域设计了两套降水方案,方案一在Ⅱ区和Ⅲ区均布置有降水井,在Ⅱ区对第二承压含水层降水,在Ⅲ区对第一承压含水层降水;方案二仅在Ⅲ区布置降水井对第一承压含水层降水。为了更好地对降水方案进行对比分析,验证方案的可行性,对此进行了数值模拟分析,计算结果显示,两种方案均能满足降水要求,不过方案二布井数量少,基坑外水位降深较小,对周边环境影响更小,优于方案一。 相似文献
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