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以连续介质不可逆热力学为基础,采用了Mohr-Coulomb屈服准则,提出混凝土塑性损伤耦合的新的本构方程。在该模型中采用了塑性应变 、各向同性损伤标量D作为内变量。这个新的本构关系模型严格满足热力学的基本方程。以不同围压作用下混凝土试件的单轴压缩行为为例,采用开发的程序进行了局部水平上本构模型数值验证。结果表明,模型损伤演化数值结果符合试验趋势。 相似文献
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从热力学定律出发,利用自由能函数和耗散函数,通过严格的理论推导得到屈服函数、流动法则和硬化规律。在临界状态模型的框架内,将基于热力学基础的各向异性模型和特定的旋转硬化规律结合起来,提出了一种新的处理方法用来模拟密砂在三轴试验中的变形曲线。给定多组模型参数,计算排水和不排水三轴试验,并简单讨论了模型参数对曲线规律的影响,结果表明这种方法是有效的。通过屈服面在变形不同阶段采用不同的旋转方向,能够考虑密砂的复杂试验曲线特征,又由模型的热力学基础保证了屈服面和剪胀函数的协调。这种方法确定的模型结构严密,适应性强,可以描述大范围土体的特性,且简单易于使用。 相似文献
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定量恢复高大地形的古高程是地质学家一直以来追求的目标，将自生矿物中氢氧同位素用作古高程计的历史不长，这种方法还有很大的应用潜力，可用到比新生代更古老的时期。根据与气团上升和水汽凝结的热动力学性质相关的瑞利平衡分馏原理，建立了这种古高程计的热动力模型，这个模型应用简便，适用于纬度小于35°的地区。区域性经验关系的方法误差较小，但也有计算繁琐、适用区域有限的不足。以上两种方法的计算精度均有待于提高。研究中使用方解石作为样品最普遍，在方解石、高岭石、蒙脱石和针铁石等矿物中,究竟使用哪种推算古高程产生的误差更小，还需进一步研究。 相似文献
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Non-equilibrium thermodynamics and Biot poro-elasticity have been combined to give a coupled hydro-mechanical formulation for unsaturated rock. Darcy’s law for unsaturated flow has been derived from the dissipation process by using standard arguments of non-equilibrium thermodynamics, whereas Helmholtz free energy has been used to derive the relationship between stress and pore pressure changes. The resulting general framework accommodates both large and small deformation theories. When small deformations are assumed, the formulation is comparable with coupled equations derived using an alternative approach. For illustrative purposes, the formulation has been used to analyse a seasonally affected tunnel model. Numerical results for the desaturation in winter and resaturation in summer, of the zone near the tunnel wall, have been evaluated and compared with the findings of other researchers. 相似文献
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冻融循环作用下砂岩孔隙体积变形模型的建立与分析 总被引：2，自引：1，他引：1
为研究冻融作用下砂岩内部孔隙的扩展机制,基于弹性力学和热力学理论,建立了饱水孔隙内水结冰的体积变形计算模型。结合基于核磁共振技术的冻融循环作用下饱和砂岩的孔隙度变化和T2谱分布的试验结果,通过建立的孔隙体积变形计算模型,分析了冻融作用下砂岩的孔隙体积变形规律。结果表明：冻融作用下饱和砂岩的体积膨胀系数大于8.69%;单次冻融作用对砂岩试样的损伤较小,孔隙体积的变化范围在0.80%~1.03%之间;砂岩的孔隙收缩系数和孔隙弹性变形体积占比的变化规律一致,均为先增大后减小;砂岩试样的孔隙收缩系数在7.92%~8.04%之间,其孔隙弹性变形体积占比平均为97.79%;在冻融过程中大孔隙的弹性变形比小孔隙的弹性变形更小。 相似文献
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模拟土体本构特性的热力学方法 总被引：4，自引：1，他引：3
简要介绍了建立岩土材料弹塑性本构模型的热力学方法。它不仅具有紧凑的数学结构,而且自动满足热力学定律,仅从两个热力学势函数,即自由能函数与耗散增量函数出发,就足以导出弹塑性理论必须的屈服条件,流动法则,硬化定律和弹性定律。通过理论证明指出,只要耗散增量函数依赖于当前应力,流动法则必然是非关联的,岩土材料的摩擦特性与非关联流动法则密不可分。介绍该方法在三维模型,岩土材料的微细观力学特性,应力应变的均匀化以及剪胀和各向异性方面应用的主要研究进展,并对一些重要的概念,诸如“储存的塑性功”,“Reynolds-Taylor状态”等,进行分析与解释。最后给出近期需进一步深入研究的几点建议。 相似文献
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A bounding surface model is formulated to simulate the behavior of clays that are subject to an anisotropic consolidation stress history. Conventional rotational hardening is revisited from the perspective of thermodynamics. As the free energy cannot be accumulated infinitely upon critical state failure, the deviatoric back stress must vanish. This requires the rotated yield surface to be turned back to eventually align on the hydrostatic axis in the stress plane. Noting that most of the previous propositions violate this restriction, an innovative rotational hardening rule is formulated that is thermodynamically admissible. The bounding surface framework that employs the modified yield surface is applied to simulate elastoplastic deformations for overconsolidated clays, with which the overprediction of strength on the “dry” side can be greatly improved with reasonable results. Other important features, including contractive or dilative response and hardening or softening behavior, can also be well-captured. It has been shown that the model can simulate three types of reconstituted clays that are sheared with initial conditions over a wide range of anisotropic consolidation stress ratios and overconsolidation ratios under both triaxial undrained and drained conditions. Limitations and potential improvement of the model regarding the fabric anisotropy at critical state have been discussed. 相似文献
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PengGang FanJian LiLi TanJiaxiang 《中国地质大学学报(英文版)》2003,14(2):169-174
In this article, mechanics model of SMA center tension from damper is developed. According to the theory of Brinson constitutive model and thermodynamics first law, damper thermodynamics non-linear equation has been developed. Dynamics non-linear equation of frame structure under operation of SMA damper and its solution have been worked out; the software of seismic response analysis for frame structure and of damper characteristic analysis have been compiled with MATLAB software, andthe examples have been computed with it. The result indicates that SMA damper has obvious damp characteristics and it can provide with obvious restraint effect for seismic response of frame structure. Decreasing rate of displacement and velocity on top of frame structure reaches 50％-60％. The result is in accordance with other pundits experimentation results, which indicates that the above methods are correct and useful. 相似文献
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An existing dual-porosity finite element model has been extended to include thermo-hydro-mechanical coupling in both media. The model relies on overlapping distinct continua for the fluid and solid domains. In addition, conductive and convective heat transfers are incorporated using a single representative thermodynamics continuum. The model is applied to the problem of an inclined borehole drilled in a fractured formation subjected to a three-dimensional state of stress and, a temperature gradient between the drilling fluid and the formation. A sensitivity analysis has been carried out to study the impact of thermal loading, effect of heat transport by pore fluid flow and, the effect of parameters of the secondary medium used to represent the fractures. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
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A large number of constitutive models for geomaterials, such as soils and rocks, have been proposed over the last three decades. Those models have been implemented into computer codes and have been successfully used to solve practical engineering problems particularly under monotonic loading conditions. Compared with the models for monotonic loadings, more improvements for cyclic models are necessary in order to obtain more accurate predictions for the dynamic behavior of geomaterials, e.g., the behavior during earthquakes. A cyclic elastoplastic model has been developed in this study for sandy soils; it is based on the kinematical hardening rule with a yield function that includes the changes in the stress ratio and the mean effective stress considering the degradation of the yield surface. From a simulation with the present model, it has been found that strong non-associativity leads to a large decrease in the mean effective stress during cyclic deformations under undrained conditions, while the model with the associated flow rule does not. This result is quite important because the mean effective stress becomes almost zero at the state of full liquefaction. Compared with the experimental results, the model can accurately reproduce the cyclic behavior of soil. 相似文献
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石油包裹体显微测温和体积分析已经被广泛应用于重构石油包裹体组分和压力-温度(P-T)捕获条件, 然而, 其P-T捕获条件准确预测除精确的均一温度(Thoil)和气泡充填度(Fv)测试外, 还依赖于石油饱和压力和体积预测能力.基于改进石油流体饱和压力和气、液相摩尔体积预测精度, 建立了石油流体C7+组分摩尔含量与其Thoil和室温(20 ℃)下Fv之间的定量关系.尽管利用该定量关系可以极大地简化石油包裹体热动力学模拟过程, 还是不能避免Fv对热动力学模拟精度的影响.因此, 根据大量已知组分石油流体建立了甲烷摩尔含量约束的新的石油包裹体捕获压力预测模型.新模型中唯一变量即为石油包裹体甲烷摩尔含量, 并且不再依赖于专业的热动力学模拟软件(PVTsim、VTflinc、PIT和FIT-OIL), 从而极大地简化了传统石油包裹体捕获压力重构过程.最终, 新模型捕获压力预测精度得到评价, 石油包裹体甲烷摩尔含量对捕获压力重构具有重要控制作用, 单个石油包裹体甲烷含量定量化是未来石油包裹体捕获压力重构的主要研究方向. 相似文献
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Normal and lognormal data distribution in geochemistry: death of a myth. Consequences for the statistical treatment of geochemical and environmental data 总被引：13，自引：0，他引：13
All variables of several large data sets from regional geochemical and environmental surveys were tested for a normal or
lognormal data distribution. As a general rule, almost all variables (up to more than 50 analysed chemical elements per data
set) show neither a normal or a lognormal data distribution. Even when different transformation methods are used more than
70 % of all variables in every single data set do not approach a normal distribution. Distributions are usually skewed, have
outliers and originate from more than one process. When dealing with regional geochemical or environmental data normal and/or
lognormal distributions are an exception and not the rule. This observation has serious consequences for the further statistical
treatment of geochemical and environmental data. The most widely used statistical methods are all based on the assumption
that the studied data show a normal or lognormal distribution. Neglecting that geochemcial and environmental data show neither
a normal or lognormal distribution will lead to biased or faulty results when such techniques are used.
Received: 21 June 1999 · Accepted: 14 August 1999 相似文献
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A new constitutive law for the behaviour of undrained sand subjected to dynamic loading is presented. The proposed model works for small and large strain ranges and incorporates contractive and dilative properties of the sand into the unified numerical scheme. These features allow to correctly predict liquefaction and cyclic mobility phenomena for different initial relative densities of the soil. The model has been calibrated as an element test, by using cyclic simple shear data reported in the literature. For the contractive sand behaviour a well‐known endochronic densification model has been used, whereas a plastic model with a new non‐associative flow rule is applied when the sand tends to dilate. Both dilatancy and flow rule are based on a new state parameter, associated to the stiffness degradation of the material as the shaking goes on. Also, the function that represents the rearrangement memory of the soil takes a zero value when the material dilates, in order to easily model the change in the internal structure. Proceeding along this kind of approach, liquefaction and cyclic mobility are modelled with the same constitutive law, within the framework of a bi‐dimensional FEM coupled algorithm developed in the paper. For calibration purposes, the behaviour of the soil in a cyclic simple shear test has been simulated, in order to estimate the influence of permeability, frequency of loading, and homogeneity of the shear stress field on the laboratory data. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
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Fernando Saboya Jr. Maria da Glória Alves Wendell Dias Pinto 《Engineering Geology》2006,86(4):211-224
Generally, the process of land occupation in urban areas involves spaces that are not suitable for construction. In most cases these areas are subject to landslides. Therefore it is mister the development of models to evaluate the susceptibility of occurrence of landslides in these areas. For this, Fuzzy Logic is used herein for modeling such areas where landslides are susceptible to occur and, therefore, a direct evaluation is important. The possibility of capturing the judgment and the modeling of linguistic variables are the main advantages of using Fuzzy Logic. These models are capable to capture the factors directly affecting the slope stability and also the inter-relationship amongst them. These factors were chosen by experts to whom a questionnaire was sent. Fuzzy Logic was then used to transform the linguistic variables into fuzzy number, allowing thus, the calculation of failure potential index (FPI). Herein the MAX-MIN Mamdani strategy for the inference of the rule base was used. This methodology has been applied to identify the susceptibility of landslides in a chaotic occupied urban area of Itaperuna City in northeastern of Rio de Janeiro, Brazil, where some occurrences have been reported. 相似文献
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J C JOSHI TANKESHWAR KUMAR SUNITA SRIVASTAVA DIVYA SACHDEVA 《Journal of Earth System Science》2017,126(1):3
Maximum and minimum temperatures are used in avalanche forecasting models for snow avalanche hazard mitigation over Himalaya. The present work is a part of development of Hidden Markov Model (HMM) based avalanche forecasting system for Pir-Panjal and Great Himalayan mountain ranges of the Himalaya. In this work, HMMs have been developed for forecasting of maximum and minimum temperatures for Kanzalwan in Pir-Panjal range and Drass in Great Himalayan range with a lead time of two days. The HMMs have been developed using meteorological variables collected from these stations during the past 20 winters from 1992 to 2012. The meteorological variables have been used to define observations and states of the models and to compute model parameters (initial state, state transition and observation probabilities). The model parameters have been used in the Forward and the Viterbi algorithms to generate temperature forecasts. To improve the model forecasts, the model parameters have been optimised using Baum–Welch algorithm. The models have been compared with persistence forecast by root mean square errors (RMSE) analysis using independent data of two winters (2012–13, 2013–14). The HMM for maximum temperature has shown a 4–12% and 17–19% improvement in the forecast over persistence forecast, for day-1 and day-2, respectively. For minimum temperature, it has shown 6–38% and 5–12% improvement for day-1 and day-2, respectively. 相似文献
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引言戈斯（Ghose,S.）在测定斜方辉石的结构时,首次发现Fe2+离子择优占据M2晶位,而Mg2+离子择优占据M1晶位。这一事实,引起了矿物学家的极大注意。 相似文献
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非饱和土的应力状态变量研究 总被引：1，自引：0，他引：1
以热力学和连续介质力学的应力理论为基础,从非饱和土的土骨架平衡方程出发,导出了一系列应力状态变量,目前文献中所使用的应力状态变量都在其中。研究发现：非饱和土的应力状态变量有多种组合形式（5组以上）,不是惟一的;大多数应力状态变量与土的孔隙率、饱和度等物性指标孪生相伴;所有应力状态变量都具有应力的量纲,单纯孔隙率或饱和度及其组合都不构成应力状态变量;简化的Bishop有效应力公式和Fredlund倡导的两个应力状态变量都是简化了的应力状态变量,前者忽略了孔隙率的影响,而后者忽略了与孔隙率及饱和度的关联性。在选择应力状态变量时应考虑理论合理、应用方便、逻辑关系正确的原则,还应做一定的验证工作。 相似文献