常吸力下非饱和土水-力耦合循环塑性的模拟

为描述非饱和黏性土在静、动态荷载作用下的应力-应变特征及水-力耦合效应,在塑性增量流动理论的框架内建立一个描述常吸力条件下非饱和黏性土水-力耦合效应的弹塑性双面模型.基于BBM(Barcelona basic model)及Li和Meissner提出的一种塑性硬化准则,并考虑非饱和土的典型土水特征,通过边界面和加载面在...     

非饱和原状膨胀土平面应变剪切试验性状

介绍了非饱和土孔隙压力的测试技术和轴平移技术,利用改装的土工真三轴仪,模拟膨胀土边坡开挖过程的应力状态,对河南南阳原状膨胀土进行了平面应变等应力比卸荷试验,试验中同时测定了土中孔隙压力值,分析了膨胀土中吸力在剪切过程中的变化.试验表明,非饱和土原状膨胀土的吸力状态不仅与土的应力状态有关,还与土体的变形有关,其稳定表现出明显的滞后现象.土体吸力不仅取决于σ1、σ3,还与土中偏应力状态(σ1-σ3)有关.     

Triaxial creep tests of weak sandstone from fracture zone of high dam foundation

The lithology of fracture zone which was developed at the dam foundation ofa hydropower station is weak sandstone with poor integrity and pore cementation contact.Its creep properties have a significant impact on the deformation and stability of the dam.Based on the characteristics of loose organizational structure,high moisture content and poor mechanical properties,the triaxial compression tests and creep tests were carried out,respectively.The results show significant non-linear,low strength and no obvious strength peaks.Both axial and lateral strains are achieved more than 3％ when the tests are failed.The weak sandstone has a significant creep property,but only transient and steady state appear under low stress.Increased stress causes creep intensified and lateral strain gradually exceeds axial strain.In the failure stage,it has characteristics of large axial plastic deformation,obvious volumetric ductility dilation and large steady creep rate.The accelerated creep appears shortly after transient loading under confining of pressures 1.0 MPa and 1.5 MPa.Therefore,an improved Burgers creep model considering the non-linear characteristics of weak sandstone is built based on hyperbolic equation and the creep parameters are identified.This model can well describe the creep properties of weak sandstone.     

A computational method for post-construction settlement of high-speed railway bridge pile foundation considering soil creep effect

Based on reasonable assumptions that simplified the calculational model,a simple and practical method was proposed to calculate the post-construction settlement of high-speed railway bridge pile foundation by using the Mesri creep model to describe the soil characteristics and the Mindlin-Geddes method considering pile diameter to calculate the vertical additional stress of pile bottom.A program named CPPS was designed for this method to calculate the post-construction settlement of a high-speed railway bridge pile foundation.The result indicates that the post-construction settlement in 100 years meets the requirements of the engineering specifications,and in the first two decades,the post-construction settlement is about 80% of its total settlement,while the settlement in the rest eighty years tends to be stable.Compared with the measured settlement after laying railway tracks,the calculational result is closed to that of the measured,and the results are conservative with a high computational accuracy.It is noted that the method can be used to calculate the post-construction settlement for the preliminary design of high-speed railway bridge pile foundation.     

非饱和土等效时间流变模型

为了理论分析流变速率效应力学特性,需要建立非饱和土流变模型.首先把非饱和土屈服面分为LC和SI屈服面。其次根据LC屈服面的压缩蠕变公式,利用等效时间法建立相应的黏塑性体应变速率公式,结合巴塞罗那屈服方程和相关联流动法则,获得LC屈服面的三维流变速率方程,揭示了本文与Gennaro-Pereira提出的LC后继屈服面方程的异同。再次,根据SI屈服面的吸力压缩蠕变公式,利用等效时间法建立相应的黏塑性体应变速率方程.最后,把LC和SI屈服面的流变速率方程与弹性方程相结合,建立非饱和土等效时间三维弹黏塑性模型.当不考虑流变速率效应时,LC和SI流变屈服方程可以退化到巴塞罗那模型的塑性屈服方程.理论分析了非饱和土一维流变特性,并与土工试验数据进行对比,两者较为吻合。三轴加载条件下的流变特性数值分析结果表明,按不同方式施加到同一恒载时,随着恒载维持时间的增长,不同加载方式引起的体积流变趋向一致,但剪切流变有较明显的差别.     

考虑抗拉强度时非饱和土的干燥裂缝深度

根据弹性理论和增量理论，应用非饱和土的双应力状态变量表示方法和饱和度与基质吸力之间的关系．建立了非饱和土在考虑抗拉强度和密度随基质吸力改变而变化情况下干燥裂缝深度的方程。研究表明裂缝深度不仅与内因即众多土参数有关而且与外因如地下水位有关；地下水位下降到某一深度时并不引起裂缝，这比文献[1]方法即认为只要地下水位低于地表就存在裂缝更符合实际。以上结是的原因在于合理考虑了土的抗拉强度和密度变化。     

Coupled model of consolidation and creep for consolidation test

For most soft soil,the consolidation process and the creep process were coupled and the character of settlement time curve was obtained by the consolidation test at the same time.A simple and continuous function was presented to express the whole process of consolidation including immediate settlement stage,the primary consolidation stage and the secondary consolidation stage.And the features of the continuous function were analyzed.The results of the long-term(duration to 18 months) consolidation test on clays from the Chek Lap Kok formation proved the rightness of the method.In the end,the parameter meanings of the continuous function were discussed.     

Viscoelastoplastic constitutive model for creep deformation behavior of asphalt sand

A uniaxial viscoelastoplastic model that can describe whole creep behaviors of asphalt sand at different temperatures was presented.The model was composed of three submodels in series,which describe elastoplastic,viscoelastic and viscoplastic characteristics respectively.The constitutive equation was established for uniaxial loading condition,and the creep representation was also obtained.The constitutive parameters were determined by uniaxial compression tests under controlled-stress of 0.1 MPa with five different test temperatures of 20,40,45,50 and 60 ℃.Expressions of the model parameters in terms of temperatures were also given.The model gave prediction at various temperatures consistent with the experimental results,and can reflect the total deformation characterization of asphalt sands.     

一种改进的纤维素热解动力学模型

纤维素热解是生物质能利用技术中的一个重要领域，而热解动力学又是其中的关键内容，为了更好地研究该过程，基于Broido-Shafizadeh热解动力学模型进行了验证计算和分析比较，讨论了竞争反应动力学参数、“活性纤维素“的存在与状态以及热解产物二次反应等几个方面的问题，并在此基础上提出了一种改进的纤维素热解动力学模型。改进后的动力学模型采用了新的竞争反应动力学参数，克服了B-S模型中由于试验样品较大，样品颗粒内部存在传热限制而导致的动力学参数偏差；另一方面，计算表明，在快速加热条件下，纤维素热解过程中的活性纤维素相变过程可以影响热解的传热、传质过程，改进后的动力学模型特别强调了该过程的重要性；最后，为了体现 挥发分二次分解对纤维素热解反应的影响，改进模型在反应途径中包含了该过程。经过改进完善后的热解动力学模型更中贴近于客观事实，这将有利于对纤维素热解这一复杂过程展开进一步研究。     

改进遗传算法在水文模型参数优选中的应用

为改善传统水文模型参数优选算法的性能,针对遗传算法的寻优效果明显依赖于模型参数的初始变化区间的大小,并且局部搜索能力较差、可能会出现过早收敛等问题,在遗传算法中加入局部搜索算子和加速算子,并引入了生物学中的小生境概念,提出了基于小生境技术的混合加速遗传算法(HAGA).该算法在广西合浦水库流域的洪水预报中得到成功应用.结果表明:基于小生境技术的混合加速遗传算法不仅有较好的全局优化性能而且精度较高,是一种既可以较大概率搜索全局最优解,又能进行局部细致搜索的优秀非线性优化方法.     

语音多带激励模型基音搜索算法的一种改进

深入分析了ＭＢＥ模型分析算法的复杂度,认为原算法中的双闭环基音搜索结构有很大的改进余地,提出了一种基于Ｂ－样条二进离散子波变换（Ｂ－ＳＤｙＷＴ）基音检测法的改进ＭＢＥ模型分析算法．其关键在于利用Ｂ－ＳＤｙＷＴ 基音检测原理将这种双闭环搜索算法改造成先开环后闭环的结构．理论分析说明,这种改造可以大幅度地降低基音搜索的复杂度,而不降低其性能．通过仿真实验对改进前、后的ＭＢＥ模型基音搜索算法的复杂度、准确度以及抗噪声能力等方面进行了全面的对比分析．得出的结论是改进算法与原算法相比各项性能均不低于原算法甚至有所改善,特别是证实了理论分析中的复杂度降低作用．     

一种可检测类型缺陷攻击的SAT改进模型

针对现有SAT模型检测器不能检测类型缺陷攻击的问题,提出了一种新的SAT#改进模型.该模型通过在匹配模式下引入无类型变量,并利用无类型消息的概念,解除了SAT模型检测器对未知消息的类型限制,并且在诚实主体重写规则中用无类型消息替换了原来的强类型限制消息.通过增加消息匹配算法,使诚实主体能够接受带有类型缺陷的消息,从而实现类型缺陷攻击的检测.通过对Otway Rees协议进行检测,不仅发现了已有的针对发起者A的类型缺陷攻击,而且发现了新的针对响应者B的类型缺陷攻击,其实验结果证明了SAT#模型具有一定的可靠性.     

An improved neural network model for prediction of mechanical properties of magnesium alloys

An improved neural network model was developed for prediction of mechanical properties in the de-sign and development of new types of magnesium alloys by refining the types of input variables and using a more reasonable algorithm. The results showed that the improved model apparently decreased the prediction errors, and raised the accuracy of the prediction results. Better preprocessing parame-ters were found to be [0.15, 0.90] for the tensile strength, [0.1, 0.9] for the yield strength, and [0.15, 0.90] for the elongation. When the above parameters were used, the relativity for predicition of strength was bigger than 0.95. By using improved ANN analysis, more reasonable process parameters and compo- sition could be obtained in some magnesium alloys without addition of strontoum.     

考虑梳齿动态特性的微加速度计敏感结构等效电学模型

为确保Σ△(sigma-delta)微加速度计系统仿真的正确性,提出一种改进的敏感结构等效电学模型.在分析传统敏感结构等效电学模型局限性的基础上,研究了结构梳齿在外力作用下发生弯曲对闭环系统的影响和使∑△闭环反馈失效的机理,分析了梳齿弯曲对质量块所受静电合力的影响,结合传统电学模型,建立了包含梳齿弯曲因素的改进的等效电学模型.在微加速度计系统仿真中,利用敏感结构的传统模型并不能反映出调制器失效特性,输出显示调制器仍然正常工作,而利用所建立的敏感结构电学模型能够准确的表现出∑△反馈失效现象,为电路仿真的准确性提供了保障.