渗流水压力分级加载岩石蠕变模型

采用RLW-2000M微机控制煤岩流变仪,以细粒砂岩为研究对象,对三轴压缩条件下岩石孔隙水压力分级加载蠕变试验进行了蠕变特性及模型研究.重点分析了孔隙水压力分级加载时蠕变条件下岩石的应变、渗流体积演化曲线,同时对不同渗流水压力分级加载条件下的岩石蠕变演化曲线进行了模型分析和对比.试验结果表明,逐级加载孔隙水压作用下细粒砂岩的蠕变曲线符合蠕变演化三阶段特征;利用西原体模型进行理论与实验蠕变曲线对比,蠕变方程曲线与实验曲线的演化规律吻合.     

考虑塑性效应的岩石蠕变Maxwall模型的改进

岩石蠕变是工程中常见的问题,蠕变岩体往往具有粘性、弹性、塑性三大基本特性,文章对现有岩石蠕变模式进行了改进,即根据前人的实验结果,在Maxwall模型基础上对虎克体、牛顿体、圣文南体三种基本元件进行合理重组,并运用基本微分方程演绎新模型下蠕变本构方程。将得到的方程拟合曲线与前人试验数据进行比较,结果表明改进的模型能够反映软弱岩石的粘弹特性。     

成都裂隙性黏土流变特性试验

以成都裂隙性黏土为对象,进行一系列室内试验,探讨了成都裂隙性黏土的流变特性。通过三轴固结不排水蠕变试验,得到不同围压下各级偏应力水平的全过程蠕变曲线和应力—应变等时曲线,对试验结果做了讨论,并建立了蠕变方程。其中应变—时间关系采用伯格斯模型,应力—应变关系采用指数函数的蠕变方程,拟和曲线与试验曲线很好的吻合,较好地表达了土体的应力—应变—时间关系。     

孔隙水压力作用下岩石蠕变及损伤特性实验

采用RLW-2000M煤岩流变仪,以细粒砂岩为研究对象,进行孔隙水压力作用下岩石三轴压缩蠕变试验,并研究其蠕变及损伤特性,重点分析不同轴向应力时蠕变条件下岩石的体应变(应变速率)和等效孔隙体积(体积速率)演化曲线,同时对其孔隙率的损伤变量演化规律进行分析.试验结果表明:利用孔压水体积揭示了蠕变过程孔隙率演化规律且符合蠕变三阶段规律;利用Rabotnov模型蠕变损伤演化方程的损伤变量,对比宏观标量(蠕变时间)和细观标量(孔隙率)的损伤变量演化规律,克服传统的蠕变损伤定量分析的缺陷,弥补传统蠕变试验研究的不足.     

成都黏土蠕变试验及其蠕变模型研究

以成都黏土为研究对象,通过三轴固结不排水蠕变试验,得到了不同围压下各级偏应力水平的全过程蠕变曲线和应力-应变等时曲线,探讨了成都黏土的流变特性,并建立了蠕变模型。     

低应力水平下时间效应对岩石蠕变模型参数的影响

在岩石蠕变实验数据基础上,通过拟合分析,得到了蠕变模型的相关参数。通过对比理论计算数据与实验数据,结果发现:不考虑参数受时间尺度的影响将引起较大的误差,对于蠕变模型来说,其参数不是常数,而是随时间变化的量,时间尺度对模型参数影响较为明显;如考虑参数的时间相关性,建立非定常参数的蠕变模型方程,将比定常蠕变模型更能准确地反映岩石的蠕变变形特征。     

八种典型岩石力学流变组合模型的教学研究

岩石流变模型的学习和研究不仅在教学研究中具有重要意义,而且在工程应用中也具有指导意义.对岩石流变模型进行分析,发现岩石流变模型本构方程和蠕变方程的推导过程以及八种典型的岩石力学模型、本构方程、蠕变曲线、松弛曲线及其特性,了解各个流变模型所适用的范围,并通过对八种岩石流变模型比较,加深对岩石流变模型的认识和了解。     

纤维素黏度测量结果的统一方程拟合

在Lyocell纤维生产过程中，需要用溶解木浆作为纤维素原液，由于纤维素原液的黏度极高，在生产设备内部流动过程中产生的流阻极大。大量实验研究证实，纤维素原液黏度主要与流体剪切速率及温度有关。为研究纤维素原液的黏度随温度变化关系，为纤维素生产设备的工艺设计提供依据，对某型纤维素原液黏度在5组温度下与应变速率的关系进行测量，并将测量结果回归为黏度—应变速率方程，将方程中的系数和指数视为温度参变数，对方程进行拟合，为编制纤维素冷却器自动设计程序提供算法基础。     

最小二乘法求作拟合直线

静态测试中,检测系统可以在一定的区间内用一个线性函数表达测试数据的变化规律,确定此线性函数即拟合直线的方法常采用最小二乘法.机械工程中,通过对应变测试可以分析与研究零件或结构的受力状况以及工作状态.根据实验输入输出测试数据,用最小二乘法求解拟合直线方程,以此计算的测量误差,均未超出测试数据的极限偏差.     

震级·烈度·灾度

一个地方发生了地震,它的强度有多大？破坏程度如何？灾情严重不严重？损失大不大……这一切,都需要有一个衡量和界定的标准。这标准,就是“震级”、“烈度”和“灾度”。“震级”指的是地震的强度,它跟地震释放的能量有关。一次地震,震级只能是一个。释放能量相同的...     

蛋白质水解度测定及其标准曲线绘制研究

应用茚三酮显色法对蛋白质水解度的测定及其标准曲线生成进行了分析。进而,基于一元线性回归分别在Excell和Matlab平台上对标准曲线的生成进行了研究,并给出了相应的标准曲线生成源代码,为蛋白质水解度的控制及工业分析中各标准曲线的绘制提供了必要的手段和方法。     

施工过程中混凝土徐变对结构竖向变形影响的有限元模拟

通过有限元模拟及算例验证,分析了高层建筑考虑施工过程中混凝土材料徐变对结构竖向变形的影响。分析表明,混凝土的徐变变形作用对柱的轴力影响不大,但对柱端弯矩影响较大;考虑徐变变形的柱端弯矩计算结果较没有考虑徐变变形的情况有显著减小。在考虑徐变影响的情况下,各层位移均有所增加,且两者的最大差值相差较大,很可能会影响结构的正常使用,在设计过程中不应忽视。该研究结果可为考虑高层建筑结构在施工过程中材料的徐变性能对结构内力的影响提供理论依据及分析方法。     

半刚性连接节点的类型及其受力性能

半刚性连接是目前常用的一种梁柱连接形式,以其施工方便、抗震性能好而得到推广.但是此类节点受力复杂,而且目前国内对此类节点的设计方法缺乏具体规范.本文给出了几种半刚性连接的类型以及梁柱连接的弯矩.转角曲线,考虑节点半刚性连接的线性模型,介绍了初始刚度的计算公式,从而为半刚性节点的设计和应用提供参考.     

气相色谱法分析喹啉及其加氢脱氮产物

采用气相色谱分析法测定喹啉及其加氢脱氮产物含量。实验中,通过峰高增加法定性确定喹啉加氢脱氮产物。采用外标法对喹啉加氢脱氮产物进行定量,该方法线性关系良好,各产物的校正曲线相关系数都在0.99以上;相对标准偏差〈0.23%,加标回收率在93%到104%范围内变化。该方法能在14分钟内完成各产物的定量分析,并进而可以得出喹啉脱氮率,适合于喹啉加氢脱氮率的考察。     

测量絮团分维数的新方法

描述絮团分形结构的定量参数分维数可用沉降法、图像法等进行测量。本文提出了一种测量絮团分维数的新方法,即通过测量絮凝体系的表观粘度而获得絮团的分维数(文中名之为粘度分维数)。为此,将絮团依据其空间特征分成四类:分散的单体颗粒、线状絮团、面状絮团及体状絮团,类比说明体系粘度为分散相及各类絮团对体系粘度贡献的线性叠加。通过颗粒碰撞理论及絮团的绕流阻力分析殊途同归地得出了体系粘度与各类絮团分维数的数学模型。依据该模型,可以同时测量不同类型絮团的分维数,并使定量分析絮团的相对组成成为可能。     

Design and experimental verification of a new multi-functional bridge seismic isolation bearing

A new multi-functional bridge seismic isolation bearing (MFBSIB) is designed and its mechanical model is developed in this paper. Combining an upper sliding device and a lower energy dispassion isolation device effectively, the new MFBSIB can adjust the deformation caused by temperature, vehicle breaks, and concrete creep, etc., in addition to dissipating energy. The switch of ??slide-isolation?? is achieved and the efficiency of both upper and lower parts is validated through experiment with a model. The shear performance curve established in this paper is verified to be efficient in describing the mechanical characteristics of the bearing through experiment. It is proved through both numerical calculation and experimental analysis that the new MFBSIB is endowed with enough vertical rigidity, good energy dissipation ability, stable overall performance, and good realization in expected goals. Its performance is slightly influenced by shear stress, while affected by vertical pressure, loading frequency, slide limit, etc., diversely. The results could provide reference for study and application of the new MFBSIB.     

Comparison of Inverse Wishart and Separation-Strategy Priors for Bayesian Estimation of Covariance Parameter Matrix in Growth Curve Analysis

Growth curve modeling provides a general framework for analyzing longitudinal data from social, behavioral, and educational sciences. Bayesian methods have been used to estimate growth curve models, in which priors need to be specified for unknown parameters. For the covariance parameter matrix, the inverse Wishart prior is most commonly used due to its proper and conjugate properties. However, many researchers have pointed out that the inverse Wishart prior might not work as expected. The purpose of this study is to investigate the influence of the inverse Wishart prior and compare it with a class of separation-strategy priors on the parameter estimates of growth curve models. In this article, we illustrate the use of different types of priors with 2 real data analyses, and then conduct simulation studies to evaluate and compare these priors in estimating both linear and nonlinear growth curve models. For the linear model, the simulation study shows that both the inverse Wishart and the separation-strategy priors work well for the fixed effects parameters. For the Level 1 residual variance estimate, the separation-strategy prior performs better than the inverse Wishart prior. For the covariance matrix, the results are mixed. Overall, the inverse Wishart prior is suggested if the population correlation coefficient and at least 1 of the 2 marginal variances are large. Otherwise, the separation-strategy prior is preferred. For the nonlinear growth curve model, the separation-strategy priors work better than the inverse Wishart prior.     

Failure Modes for Single-Layer Reticulated Domes Under Impact Loads

The paper presents the theory of Hamilton variation principle which is the current method for impact problem,central difference method which is efficient solution of finite element (FE)method for impact problem and adapts to solve non-linear dynamic problem.And it introduces the ANSYS/LS-DYNA which is the popular FE software for impact problem both at home and abroad.Then it gives solutions for one simple model by analytical method and ANSYS/LS-DYNA respectively to validate function of software,and they are consistent.Afterward,it gives model of singlelayer Kiewitt reticulated dome with a span of 60 m,and the cylinder impactor,and introduces the contact interface arithmetic,especially the material model of steel (piecewise linear plasticity model) which takes stain rate into account and makes steel failure stress higher under impact loads.The vertical displacement,stress in main members,and the plastic deformation for dome under impact loads were obtained.Then four failure modes (no failure,moderate failure,global failure and slight failure) were summarized according to the rules of dynamic response.And the characteristics of dynamic response for each failure mode were shown.     

A SAS Interface for Bayesian Analysis With WinBUGS

Bayesian methods are becoming very popular despite some practical difficulties in implementation. To assist in the practical application of Bayesian methods, we show how to implement Bayesian analysis with WinBUGS as part of a standard set of SAS routines. This implementation procedure is first illustrated by fitting a multiple regression model and then a linear growth curve model. A third example is also provided to demonstrate how to iteratively run WinBUGS inside SAS for Monte Carlo simulation studies. The SAS codes used in this study are easily extended to accommodate many other models with only slight modification. This interface can be of practical benefit in many aspects of Bayesian methods because it allows the SAS users to benefit from the implementation of Bayesian estimation and it also allows the WinBUGS user to benefit from the data processing routines available in SAS.