并行遗传算法对硅藻软岩本构关系的求解

利用并行遗传算法,基于不同条件下软岩三轴压缩实验的实验数据,对正常固结领域和超固结领域硅藻软岩的本构关系进行了拟合,建立了一种新的考虑时间效应的应力-应变-时间本构模型。预测结果分析表明,所建模型很好地反映了硅藻软岩的本构关系,从而验证了该模型并行遗传算法解的合理性和可行性。研究成果在地下空间的利用和开发中具有良好的应用前景,对介于岩石和土之间复杂软岩材料力学特性研究的进一步发展具有重要的参考价值。     

Calibration of an elasto-plastic constitutive model by a constrained optimisation procedure

The presented paper deals with a constrained optimisation technique for the calibration of elasto-plastic model parameters in a rational and objective manner. The procedure consists in finding a set of model parameters which minimise the difference between the experimental data and the numerical simulations defined by an objective function. For this purpose, an optimisation routine, termed ParaID, has been developed which combines the quasi-Newton and stochastic methods. The optimisation technique was employed to calibrate a multi-mechanism elasto-plastic constitutive model. Using the results of three isotropically consolidated drained triaxial compression tests, a comparison between numerical and experimental results clearly shows the capability of the optimisation procedure to determine the model parameters correctly.     

Calibration of a constitutive model for volcanic sands under simple shear conditions

Acta Geotechnica - The simple shear response of air-fall volcanic (pyroclastic) soils under both saturated and unsaturated conditions is interpreted through an elastoplastic constitutive model with...     

基于多目标遗传算法的巨型水库群发电优化调度

低碳时代,水电作为清洁可再生能源,节能发电调度为梯级水电联合调度运行带来了难得的历史机遇,如何有效地开展梯级水库群优化调度,充分合理利用水能资源,是流域梯级电站管理迫切需要解决的问题。文章在对清江梯级与三峡梯级径流特征分析的基础上,建立了以水库群整体发电量最大和弃能最小为目标的梯级调度模型。根据电力系统对三峡、葛洲坝、水布垭、隔河岩、高坝洲水电站的要求,用1951—2002年的月径流资料和典型年的日径流资料进行长期和短期优化调度,采用多目标遗传算法得到清江3个电站、三峡-葛洲坝2电站单独运行和联合优化调度发电指标,5库联合优化调度系统多年平均发电量增加约21亿kW.h;短期(日)优化调度较长期(月时间尺度)优化调度发电效益有进一步提升,增发电量约9.68亿kW.h。研究表明,充分利用清江和三峡梯级实际运行位置相近、水力联系紧密、互补性强的特点,统一安排电站机组运行模式,合理分配机组出力,可在来水量相同的条件下获得更大的效益。     

Numerical modeling of changes in anisotropy during liquefaction using a generalized constitutive model

A constitutive model with rotation hardening was generalized from the triaxial compression state to a general stress state. With the generalized model, numerical simulations of cyclic and monotonic undrained triaxial tests were conducted to reproduce the phenomenon of continuous, orderly and rapid changes in anisotropy during liquefaction. The simulated results demonstrated that when sand enters the liquefaction stage, the yield surface in the stress space rotates quickly, causing continuous and rapid changes in anisotropy. Through comparison of the simulated and experimental results, the generalized constitutive model was shown to be able to capture the fundamental behaviors of sand demonstrated by the experimental data, and the rotational hardening rule adopted in the generalized model was proven suitable for describing the continuous, orderly and rapid changes in anisotropy that occur during liquefaction.     

基于统计损伤本构模型的改进桩-土接触面模型研究

建立准确合理的接触面本构模型是研究桩基承载力、沉降及变形等问题的前提。考虑桩-土界面初始剪切刚度的深度效应,提出基于统计损伤本构模型的无厚度接触面本构模型,根据剪切试验的数据对改进的接触面本构模型参数进行拟合,得到了不同法向应力下的模拟曲线。利用FLAC3D软件内嵌的FISH语言,对桩-土界面进行改进本构模型的二次开发,提出的无厚度接触面模型合理地模拟出桩-土界面刚度的非线性,成功实现了桩-土剪切试验过程的数值模拟。计算结果表明：提出的无厚度接触面本构模型能够合理地模拟桩-土界面的力学行为,可以描述接触面刚度的非线性变化,也适于程序化计算,拓展了接触面统计损伤本构模型的应用领域,为深入探讨桩基承载变形性状奠定了基础。     

Estimating aquifer recharge in Mission River watershed, Texas: model development and calibration using genetic algorithms

Soil moisture balance studies provide a convenient approach to estimate aquifer recharge when only limited site-specific data are available. A monthly mass-balance approach has been utilized in this study to estimate recharge in a small watershed in the coastal bend of South Texas. The developed lumped parameter model employs four adjustable parameters to calibrate model predicted stream runoff to observations at a gaging station. A new procedure was developed to correctly capture the intermittent nature of rainfall. The total monthly rainfall was assigned to a single-equivalent storm whose duration was obtained via calibration. A total of four calibrations were carried out using an evolutionary computing technique called genetic algorithms as well as the conventional gradient descent (GD) technique. Ordinary least squares and the heteroscedastic maximum likelihood error (HMLE) based objective functions were evaluated as part of this study as well. While the genetic algorithm based calibrations were relatively better in capturing the peak runoff events, the GD based calibration did slightly better in capturing the low flow events. Treating the Box-Cox exponent in the HMLE function as a calibration parameter did not yield better estimates and the study corroborates the suggestion made in the literature of fixing this exponent at 0.3. The model outputs were compared against available information and results indicate that the developed modeling approach provides a conservative estimate of recharge.     

Parameter estimations of a storm surge model using a genetic algorithm

A genetic algorithm was used to optimize the parameters of the two-dimensional Storm Surge/Tide Operational Model (STORM) to improve sea level predictions of storm surges. The model was then tested using data from Typhoon Maemi, which landed on the Korean Peninsula in 2003. The following model parameters were used: the coefficients for bottom drag, background horizontal diffusivity, Smagorinsky’s horizontal viscosity, and sea level pressure scaling. The simulation results using the optimized parameters improved sea level predictions. This study demonstrates that parameter optimizations and their adequate applications are essential for improving model performance.     

Calibration of cyclic constitutive models by oscillating functions

Most structures are subjected to more cyclic loads during their life time than static loads. These cyclic action could be a result of either natural or man-made activities and may lead to soil failure. In order to understand the response of the foundation and its interaction with these complex cyclic loadings, various researchers have over the years developed different constitutive models. Although a lot of research is being carried out on these relatively new models, little or no details exist in literature about the model-based identification of the cyclic constitutive parameters which to a large extent govern the quality of the model output. This could be attributed to the difficulties and complexities of the inverse modeling of such complex phenomena. A variety of optimisation strategies are available for the solution of the sum of least-squares problems as usually done in the field of model calibration. However, for the back analysis (calibration) of the soil response to oscillatory load functions, this article gives insight into the model calibration challenges and also puts forward a method for the inverse modeling of cyclic loaded foundation response such that high-quality solutions are obtained with minimum computational effort.     

Simulating the effects of induced anisotropy on liquefaction potential using a new constitutive model

The effects of induced anisotropy on the undrained behaviour of very loose and saturated sands have been a subject of intensive investigation, both experimentally and theoretically, by several authors in the past few years. This paper proposes an original constitutive model well‐adapted to simulate the behaviour of sands subject to complex stress histories, in particular, the preloading cycle along the classical drained stress path in compression. The developed model belongs to the family of critical state models. Its construction is based on a few theoretical concepts taken from the theory of ‘Bounding Surface Plasticity’ developed among others by Y. Dafalias and Popov (1975), the ‘Clay And Sand Model’ (CASM) of H. Yu (2006), the CJS model (B. Cambou and K. Jafari (1988)) and the hyperelastic isotropic model of P. Lade (1987). To accurately simulate volume changes, which represent a key element in soil behaviour, a state‐dependent dilatancy rule is proposed, which can account for the influences of stress and void ratio. The current void ratio depends implicitly on the irreversible strains already accumulated hence the strain history. A kinematic hardening is combined with an isotropic hardening, involving rotation and distortion of the bounding surface, in order to capture correctly the experimental observations. Comparisons of experimental results to numerical simulations show that the model is able to simulate with a good precision the major trends of undrained responses of loose and presheared sands. It predicts correctly rapid static liquefaction at small or null drained preloading, as well as the progressive transition to a completely stable behaviour typical of dense sands, while the sample is loose in reality. At intermediate to large amplitudes of preloadings, the model also predicts correctly the temporary stage of instability when the deviatoric stress decreases slightly before rising up again. Copyright © 2013 John Wiley & Sons, Ltd.     

A pressuremeter-based evaluation of structure in London Clay using a kinematic hardening constitutive model

Acta Geotechnica - The self-boring pressuremeter (SBP) test was designed to measure in situ engineering properties of the ground with a relatively small amount of disturbance. The properties that...     

Probabilistic analyses of a strip footing on horizontally stratified sandy deposit using advanced constitutive model

An advanced hypoplastic constitutive model is used in probabilistic analyses of a typical geotechnical problem, strip footing. Spatial variability of soil parameters, rather than state variables, is considered in the study. The model, including horizontal and vertical correlation lengths, was calibrated using a comprehensive set of experimental data on sand from horizontally stratified deposit. Some parameters followed normal, whereas other followed lognormal distributions. Monte-Carlo simulations revealed that the foundation displacement u_y for a given load followed closely the lognormal distribution, even though some model parameters were distributed normally. Correlation length in the vertical direction θ_v was varied in the simulation. The case of infinite correlation length was used for evaluation of different approximate probabilistic methods (first order second moment method and several point estimate methods). In the random field Monte-Carlo analyses with finite θ_v, the vertical correlation length was found to have minor effect on the mean value of u_y, but significant effect on its standard deviation. As expected, it decreased with decreasing θ_v due to spatial averaging of soil properties.     

Numerical simulation of cone penetration testing using a new critical state constitutive model for sand

A new perspective on the numerical simulation of cone penetration in sand is presented, based on an enhanced critical state model implemented in an explicit-integration finite element code. Its main advantage, compared to similar studies employing simpler soil models, is that sand compressibility can be described with a single set of model parameters, irrespective of the stress level and the sand relative density. Calibration is based on back-analysis of published centrifuge experiments, while results of the methodology are also compared against independent tests. Additional analyses are performed to investigate sand state effects on cone penetration resistance, in comparison with empirical expressions from the literature.     

基于广义塑性理论的尾砂本构模型在ABAQUS中的二次开发

建立尾砂的本构模型是开展尾矿坝数值模拟和安全评价的重要基础,而目前尾砂的本构模型研究多集中于非线性弹性模型,如Duncan-Chang模型,关于弹塑性模型的研究较少。结合尾砂的应力-应变特性,提出了一种适用于描述尾砂力学特性的改进广义塑性模型。基于用户自定义材料子程序UMAT,将提出的模型在ABAQUS中二次开发实现,应力积分采用Runge-Kutta显式积分。通过三轴试验模拟验证,偏差应力曲线表明,有限元计算结果可以反映围压对应力-应变关系的影响,抗剪强度随应变逐渐硬化,达到峰值强度,随后发生应变软化,抗剪强度有所下降。体应变曲线结果表明,广义塑性模型可以很好地描述体应变曲线的体缩-体胀发展过程,与试验曲线吻合较好。同时有限元数值模拟结果和理论值误差很小,且和试验结果拟合较好。该研究成果可进一步用于尾矿坝的应力变形计算和安全评价。     

Predicting flow liquefaction,a constitutive model approach

In this paper, flow liquefaction criterion for contractive loose sands is analytically extracted based on the fundamental definition of flow liquefaction. In order to obtain the closed form of this criterion, Dafalias–Manzari constitutive model is employed; so the stress ratio at the onset of flow liquefaction is presented as a function of model parameters, state parameter and void ratio. Flow liquefaction line, as a graphical form of suggested criterion in stress space, shows that the peak points of undrained stress paths with same void ratios are not necessarily in a straight line. In order to validate the reliability of proposed flow liquefaction line to predict the onset of instability, it has been compared with the results of experimental tests performed on Toyoura, Ottawa and Leighton Buzzard sands. The verification results show that the present criterion can satisfactorily predict the onset of flow liquefaction in monotonic and cyclic undrained tests of saturated sands as well as the structural collapse in constant deviatoric stress tests of loose dry sands.     

Simulation of long-term thermo-mechanical response of clay using an advanced constitutive model

Acta Geotechnica - There is extensive data to show that heating and cooling produces irrecoverable deformations in clays under fully drained conditions. The effects are most pronounced for normally...     

Three‐dimensional modelling of differential railway track settlement using a cycle domain constitutive model

A method for simulation of differential (spatially varying) track settlement in a ballasted railway track is presented. It employs a cycle domain constitutive model to determine accumulated plastic (permanent) deformation of the granular layers supporting the track. The constitutive model is adopted for both the ballast and the sub‐ballast but with different parameter sets. The proposed framework can be used to predict differential track settlement accounting for heterogeneous (space‐variant) track characteristics and loading conditions. Here, it is demonstrated for three‐dimensional continuum modelling of a railway crossing panel subjected to a large number of axle passages. Because of the design of the crossing panel and the transient character of the impact loads on the crossing, the load transferred into the track bed is not uniform along the track, and the resulting differential settlement leads to vertical irregularities in track geometry. The spatial variation of track settlement is calculated both along the sleepers and along the rails. The influences of the number of adjacent sleepers accounted for in the model and the stiffness of the subgrade on the predicted settlement at the crossing are studied. Copyright © 2016 John Wiley & Sons, Ltd.     

一种岩石统计损伤本构模型的研究

基于岩石的非均质性,假设岩石微元粘聚力服从Weibull分布,微元破坏后其粘聚力降为0,结合统计理论和岩石剪切面上剪力平衡方程,建立了岩石发生剪切破坏时的损伤演化方程。该损伤演化方程考虑了破坏微元的抗压和抗剪能力,能够反映岩石峰后强度逐步丧失过程和残余强度。将该模型编入有限元程序,数值计算了不同围压下岩石应力-应变全过程曲线,与试验曲线比较取得了很好的一致性。     

Implementation of a general constitutive model for geological materials

A generalized constitutive model is described with particular attention to determination of material constants, and its implementation. The model involves use of only a single function to characterize the complete range of plastic yielding, and employs a special function to describe plastic hardening. Laboratory behaviour of an artificial soil is used to iliustrate the determination of the constants and verification of the model.     

混凝土损伤塑性本构模型研究

提出了一种新的损伤塑性本构模型,强调了应力三轴比对塑性屈服的影响.采用本研究设计的专门用于本构校验的计算机软件,对上述模型的应力应变加载曲线进行了数值模拟,数值结果与实验结果吻合得比较好.