基于热力学定律的土体动力Hardin-Drnevich模型再认识

从Masing二倍法构造的Hardin—Drnevich模型的卸荷再加荷滞回曲线出发,以热力学定律为基础,考虑了塑性中心的移动为直线和骨架曲线两种情况下的耗散函数表达形式,应用Ziegler正交条件,通过对耗散函数求一阶偏导,得到耗散应力空间中的屈服函数表达式,并引入耗散应力和真实应力之间的差别项即转移应力,从而得到真实应力空间中的屈服函数。屈服曲线的绘制表明了对于塑性中心的不同转移规律,屈服曲线遵循同样的变化规律：应变在某一范围内,剪切形的屈服曲线是直线形式;当应变超过某一阈值时,剪切形的屈服曲线呈现弯曲。此外,还给出了应变的阈值。     

混凝土混合硬化黏塑性损伤统本构模型

传统的黏塑性统一本构模型只能用于金属类材料的本构分析,而不适用于混凝土的本构分析.基于此,以不可逆热力学理论为基础,选定了涉及混合硬化参量的Helmholtz自由能函数,推导出混凝土的黏塑性损伤耦合本构模型.通过对混凝土硬化模型的分析,构造了含运动硬化和等向硬化内变量的非相关流动势函数,又推导出流动方程以及内变量演化方程.所建模型对混凝土试验曲线的数值模拟显示,其能够正确描述混凝土的率相关性、非弹性体积膨胀特性、加载过程的软硬化特性以及由断裂和损伤引起的应力软化现象.     

Comparison of different numerical approaches to the 1D sea-ice thermodynamics problem

The vertical one-dimensional sea-ice thermodynamic problem using the principle of conservation of enthalpy is revisited here using (1) the Bitz and Lipscomb (1999) finite-difference approach (FD), (2) a reformulation of the sigma-level transformation of Huwald et al. (2005b) (FV) and (3) a Finite Element approach also in sigma coordinates (FE). These three formulations are compared in terms of physics, numerics, and performance, in order to identify the best choice for large-scale climate models. The BL99 formulation sequentially treats the diffusion of heat and the changes in the vertical position of the ice-snow layers. In contrast, the FV sigma-level transformation elegantly treats both simultaneously. The original FV formulation suffers however from slow convergence. The convergence can nonetheless be improved significantly with a few simple modifications to the original code. The three formulations are compared following the experimental protocol of the Sea Ice Model Intercomparison Project for ice thermodynamics (SIMIP2). It is found that all formulations converge to the same solution. The FD approach, however, suffers from the added cost of the remapping step at large number of ice layers (we include in the appendix an optimized version of the FD code–written by one of the reviewer–that resolves this issue). Finally the FE formulation results in a sub-surface temperature over-estimation at low resolution, a problem which disappears at high resolution. Hence, only FD and FV are found suitable for climate models.     

Cyclic shakedown of piles subjected to two‐dimensional lateral loading

Pile foundations are frequently subjected to cyclic lateral loads. Wave and wind loads on offshore structures will be applied in different directions and times during the design life of a structure. Therefore, the magnitude and direction of these loads in conjunction with the dead loads should be considered. This paper investigates a loading scenario where a monotonic lateral load is applied to a pile, followed by two‐way cycling in a direction perpendicular to the initial loading. This configuration is indicative of the complexity of loading that may be considered and is referred to in the paper as ‘T‐shaped’ loading. The energy‐based numerical model employed considers two‐dimensional lateral loading in an elasto‐plastic soil, with coupled behaviour between the two perpendicular directions by local yield surfaces along the length of the pile. The behaviour of the soil–pile system subjected to different loading combinations has been divided into four categories of shakedown previously proposed for cyclic loading of structures and soils. A design chart has been created to illustrate the type of pile behaviour for a given two‐dimensional loading scenario. Copyright © 2009 John Wiley & Sons, Ltd.     

针铁矿和蒙脱石对菲的吸附解吸行为与热力学研究

采用批量振荡吸附平衡法设计针铁矿和蒙脱石对菲的吸附解吸试验,对比研究了针铁矿和蒙脱石对菲的吸附解吸行为,并考察了不同K＋浓度的溶液对蒙脱石吸附菲的影响,比较分析了线性吸附模型和Freundlich吸附模型描述矿物吸附等温线的准确性,并从吸附热力学角度探讨了矿物的吸附机理。结果表明：针铁矿和蒙脱石对菲的吸附解吸均表现出明显的非线性和解吸滞后现象;相对于线性吸附模型来说,针铁矿和蒙脱石对菲的吸附解吸更符合Freundiich吸附模型;与蒙脱石相比,针铁矿对菲的吸附更为显著,且具有更好的稳定性;溶液中软阳离子K＋的存在使蒙脱石对菲的吸附能力得到显著提高;菲在蒙脱石和针铁矿上的吸附过程是一个自发放热,同时伴随着熵值减小的过程;随着温度的升高,蒙脱石和针铁矿对菲的吸附能力均减弱。     

有机质碳同位素热力学分馏与天然气碳同位素组成

干酪根中不同结构和官能团具有不同的碳同位素组成,这种差异可以用有机质碳同位素热力学同位素因子（β因子）进行预测。煤岩模拟实验产物中,δ13CCO2相对烃类气体而言明显偏重,这与干酪根中羧基的β13C较大有关。含水实验产物的δ13CCO2轻于无水实验产物的δ13CCO2是由于含水实验中所增加CO2的碳同位素组成相对较轻造成的,含水实验增加的CO2产率是由β13C相对较小的部分亚甲基碳通过断裂、氢转移、以及与水反应转变而来。模拟实验低温阶段（≤300℃）,甲氧基中的甲基断裂可能的甲烷形成的主要方式。而甲氧基的β13C大于甲基,所以低温阶段出现了甲烷碳同位素组成先较重后变轻的现象。     

Solid–liquid–air coupling in multiphase porous media

This paper addresses various issues concerning the modelling of solid–liquid–air coupling in multiphase porous media with an application to unsaturated soils. General considerations based on thermodynamics permit the derivation and discussion of the general form of field equations; two cases are considered: a three phase porous material with solid, liquid and gas, and a two phase porous material with solid, liquid and empty space. Emphasis is placed on the presentation of differences in the formulation and on the role of the gas phase. The finite element method is used for the discrete approximation of the partial differential equations governing the problem. The two formulations are then analysed with respect to a documented drainage experiment carried out by the authors. The merits and shortcomings of the two approaches are shown. Copyright © 2003 John Wiley & Sons, Ltd.     

1970-2000年中国近地层大气热力增强的气候效应

中国区域1970-2000年622个气象观测台站资料EOF分析显示,气温的上升导致中国大部分地区饱和水汽压差呈上升趋势,大气热力强度增加,风动力明显减弱.内蒙中部以南至长江中游以北区域是大气热力增强最为敏感的地区.气温升高导致这一区域大气"干燥力"增强,区域蒸发潜力下降速度低于其他地区,气温的上升对低云覆盖产生一定程度...     

热力学方法在土体动力Ramberg—Osgood模型中的应用研究

从Ramberg—Osgood模型的骨架曲线和滞回曲线出发,假定塑性中心的移动为直线,构造土体动力耗散函数,从热力学基本定律出发研究了土体动力耗散特性及动力变形机理．提出了反映筑坝堆石料动力特性的第1阌值应变和第2阈值应变,两个阈值应变主要受最大动剪切模量系数、指数及无黏性土的内摩擦角的影响．第1和第2阈值应变间屈服面...