双重流动法则下地基黏塑性随机有限元方法

针对地基工程复杂的随机非线性力学增益,基于黏塑性非线性随机有限元优势,借助Mohr Coulomb破坏准则下的黏性拟时间步,推导在三维及平面应变条件下黏塑性非线性随机有限元的本构关系式,建立基于全量理论的黏塑性非线性随机有限元列式.在Naylor孔隙水压理论基础上,提出考虑各向同性及各向异性孔压条件的土体介质黏塑性非线性随机本构模型.以施工期三层复合地基为例,分别针对关联及非关联流动法则2种工况,研究地基在增量加载条件下的位移、应力、黏塑性应变、孔隙水压等矢量场的随机数字特征,以及地基在各个加载时期的可靠度情况.结果表明,在复杂工况下复合地基中有效应力及孔隙水压的数字特征与可靠指标分布的内在联系紧密;由非关联到关联流动法则,有效应力增加,孔压减小,同时随着孔压变异下降、可靠指标显著提高,由此形成在随机数学覆盖下完整的非线性数学模型.     

从耗散率函数看黏性与塑性间的内在联系

利用热力学的基本定律和内应变率空间中的最大Homilton耗散率原理,建立了黏性和塑性相统一的广义黏弹性本构理论.利用凸分析数学理论,阐明了内应变率空间中的最大Homilton耗散率原理等价于内应力空间中的最大Lagrange耗散率原理.当Homilton耗散率函数为内应变速率的一次欧拉齐次函数时,材料的黏性特性退化为塑性特性,最大Lagrange耗散率原理退化为Hill最大塑性功原理,因此,塑性是材料广义黏性的一种特例.选取不同的自由能函数和耗散率函数,利用最大Homilton耗散率原理和最大Lagrange耗散率原理,建立了准Maxwell模型、准Kelvin模型和准临界状态黏弹性模型,证明了广义Von Mises屈服准则、广义Von Mises线性运动硬化屈服准则和魏汝龙临界状态屈服准则是准Maxwell模型、准Kelvin模型和准临界状态黏弹性模型当耗散率函数为一次欧拉齐次函数时的特例.通过数值算例和图可以直观地验证上述结论的可靠性.     

粒状体流动法则的微观机制

粒状体力学方法为散粒体建立了一种理想化的数值计算模型,可以模拟粒状体的力学表现.本研究认为粒状体力学方法不是缩尺模型而是一种"几率场模拟",所依据的不是相似理论而是接触点附近的微观机制的一致性,所计算的每个结果只是该机率场的一个"样本",其可靠性服从统计规律.因此本研究用粒状单元法对于一组平面的圆盘的集合作了单向的探针试验,发现粒状体的塑性应变在某些条件下几乎符合非关联流动法则,另一些条件下不符合.即使符合该法则的场合,也稍有偏差,使得理论上认为非关连流动法则应该导致的Hill失稳现象实际上不会发生.以此证明了该方法的价值和适用性.     

金属塑性流动过程界面阻尼特性对系统动力学的影响

测试平整机的振动结果表明,其振动的主要成分是自激振动;对平整机轧制界面的摩擦学、阻尼特性及自激振动机理进行了理论建模与分析,自激振动的根源在于轧制界面的负阻尼特性,而负阻尼的产生则源于轧制界面的粘滑状态与部分弹流膜作用的存在。轧制界面的阻尼特性对系统动力学有重要的影响。     

利用全息双曝光法和有限元分析对铝板裂纹尖端塑性流动状况的研究

本文利用全息双曝光法,连续观察和分析了在拉伸载荷作用下LF21铝板试件裂纹尖端塑性区的产生和扩展过程,并按表面塑性区的形状划分了三个不同阶段,同时利用有限元程序对此进行了计算,并将两者的结果进行了对比分析。     

损伤力学中耗散势的物理意义及正交法则的证明

根据不可逆热力学的原理,得出了损伤力学中耗散势的物理意义,并证明了相应的正交法则。     

砂土的剪胀方程及其塑性势(Ⅰ):发展现状

以能量守恒原理为主线,在各向同性前提下,对Taylor剪胀方程、Cam-clay剪胀方程、修正Cam-clay剪胀方程、Rowe剪胀方程和扩展的Rowe剪胀方程等进行了较全面的综述.论证了剪胀方程和塑性势函数之间的相互转化关系.指出了Lade-Kim塑性势函数和Nova塑性势函数的缺陷之处,即这两个塑性势函数均没有合理耦合临界状态这一概念.     

Influences of nonassociated flow rules on three-dimensional seismic stability of loaded slopes

The influences of soil dilatancy angle on three-dimensional (3D) seismic stability of locally-loaded slopes in nonassociated flow rule materials were investigated using a new rotational collapse mechanism and quasi-static coefficient concept. Extended Bishop method and Boussinesq theorem were employed to establish the stress distribution along the rupture surfaces that are required to obtain the rate of internal energy dissipation for the nonassociated flow rule materials in rotational collapse mechanisms. Good agreement was observed by comparing the current results with those obtained using the translational or rotational mechanisms and numerical finite difference method. The results indicate that the seismic stability of slopes reduces by decreasing the dilatancy angle for nonassociated flow rule materials. The amount of the mentioned decrease is more significant in the case of mild slopes in frictional soils. A nearly infinite slope under local loading, whether its critical failure surface is 2D or 3D, not only depends on the magnitude of the external load, but also depends on the dilatancy angle of soil and the coefficient of seismic load.     

Influences of nonassociated flow rules on seismic bearing capacity factors of strip footing on soil slope by energy dissipation method

Seismic bearing capacity factors of a strip footing placed on soil slope were determined with both associated and nonassociated flow rules. Quasi-static representation of earthquake effects using a seismic coefficient concept was adopted for seismic bearing capacity calculations. A multi-wedge translational failure mechanism was used to obtain the seismic bearing capacity factors for different seismic coefficients and various inclined angles. Employing the associated flow rule, numerical results were compared with the published solutions. For bearing capacity factors related to cohesion and equivalent surcharge load, the maximum difference approximates 0.1%. However, the difference of bearing capacity factor related to unit weight is larger. With the two flow rules, the seismic bearing capacity factors were presented in the form of design charts for practical use. The results show that seismic bearing capacity factors related to the cohesion, the equivalent surcharge load and the unit weight increase greatly as the dilatancy angle increases, and that the nonassociated flow rule has important influences on the seismic bearing capacity.     

塑性增量理论的变分原理和广义变分原理

自弹塑性力学的广义变分原理问世以来,如何将塑性增量理论(塑性流动理论)的变分原理和广义变分原理写成更加规范的形式,一直是塑性力学专家和变分原理专家努力的方向.该文借助弹塑性本构关系研究的新进展,按照广义力和广义位移之间的对应关系,将塑性增量理论的基本方程乘上相应的虚量,然后积分,并代数相加,进而推导出了形式规范的塑性增量理论的变分原理和广义变分原理.     

应变空间塑性余位势理论的力学基础研究

岩土材料的力学试验表明在应变空间中Iliushin塑性公设不适用于岩土材料，为了克服这一
理论缺陷，依照Caratheodory定理，建构了应变空间的广义塑性公设。根据广义塑性公设，证明了塑性余
位势函数在应变空间塑性区的存在性。研究表明，塑性余位势函数的物理含义是超余功增量为零面；
Iliushin塑性公设存在的条件是塑性余位势函数正定且可逆；在应变空间塑性区必须采用分部塑性应力而
不能采用总塑性应变来建构屈服面方程和塑性余位势函数，否则与热力学第二定理相矛盾。最后给出了考
虑塑性应力相互耦合的应变空间弹塑性模量的普遍表达式。     

新型射流消能的流态演变与极限临底流速研究

本文列举了多个水电站采用挑流及底流消能的应用情况及泄洪雾化特点。针对向家坝水电站所采用的多股多层水平淹没射流的消能型式,分析了影响其效率效果的17个物理参数。表孔单独泄洪条件下,消力池内分别呈自由射流、半潜射流、淹没射流及回复底流的流态演变;中孔单独泄洪条件下,随下游水位的变化,其出现偏流,并随下游水位的升高而消失,同时空间扩散比对其流态演变影响明显;联合泄洪,下游水位对其流态演变影响明显,同时表孔适当收缩对流态改变影响明显。研究表明：表孔单独泄洪,影响其最大临底流速的参数为出口跌坎高程和水流弗氏数;中孔单独泄洪,影响最大临底流速的参数主要为出口跌坎高程和跌坎底坡比;联合泄洪,影响其最大临底流速的为表孔收缩比、表孔侧收缩比、表中孔出口高程差、表中孔出口水流弗氏数及中孔跌坎底坡比。本文展望了高水头大流量低雾化泄洪消能的研究前景。     

二元属性文法及汉语的句法规则体系

本文在全面分析汉语语言特点的基础上,采用了二元属性文法作为描述形式用于汉语的计算机处理。对汉语短语句法规则进行符号化形式化的分析,给出了句法模型,定义了一整套汉语的句法规则体系及相应的语义处理方案。该文法体系已成功应用于本人设计的汉语句法分析器中。     

零屈服应力下混凝土三轴受压塑性模型

为了模拟混凝土真三轴压缩的力学性质,在分析混凝土真三轴和常规三轴压缩试验结果基础上,以经典塑性力学为理论基础,建立了混凝土的真三轴本构模型.模型考虑了混凝土初始屈服强度为0的实验特性,采用4参数的Hsieh-Ting-Chen作为破坏准则,假定材料强化和软化符合各向同性和非相关联的塑性流动法则,并将混凝土压缩实验中的扩容和塑性功相联系起来,把lode角引入塑性势函数中.模型与两种不同配比的混凝土立方体试件分别在6组不同加载路径下的试验结果进行了验证.     

Seismic failure mechanisms for loaded slopes with associated and nonassociated flow rules

Seismic failure mechanisms were investigated for soil slopes subjected to strip load with upper bound method of limit analysis and finite difference method of numerical simulation, considering the influence of associated and nonassociated flow rules. Quasi-static representation of soil inertia effects using a seismic coefficient concept was adopted for seismic failure analysis. Numerical study was conducted to investigate the influences of dilative angle and earthquake on the seismic failure mechanisms for the loaded slope, and the failure mechanisms for different dilation angles were compared. The results show that dilation angle has influences on the seismic failure surfaces, that seismic maximum displacement vector decreases as the dilation angle increases, and that seismic maximum shear strain rate decreases as the dilation angle increases.     

基于最大均值似然判决规则的说话人辨认研究

在基于统计模型的说话人识别中，需要对说话人的数据进行训练，依据某种准则确定模型的参数，用某种判决规则将未知语音参数序列分配给具有最大概率似然度的说话人模型，常用的判决规则是最大似然判决规则。但这种规则不是很灵活，有一定的局限性，该文提出一种最大均值似然判决规则，通过理论分析以及实验结果表明，在说话人辨认中MAL规则比ML规则更加有效。