一个改进的混凝土非线性双剪切强度准则

通过对混凝土、岩石等材料强度理论的分析研究,基于普遍形式强度理论及双剪切强度理论,考虑混凝土在多轴荷载作用下材料强度性质在π平面和拉伸压缩子午线上不同的变化规律,将混凝土的强度准则定义为两个较大主剪切应力平方和的函数;并考虑其对应剪切应力作用面上的正应力和静水压力的影响,推导了一个考虑中间主应力效应和复杂极限面情况的非线性双剪切强度准则;通过实验数据获得了相关参数。结果表明该强度准则可以较好地描述混凝土材料的破坏特性。     

影响函数与有限元应力计算

用有限元法得到位移场后,总要计算应力场。通常的做法是对位移进行微商计算应变,再根据应力-应变关系计算应力。有限元位移计算的精度比较高,但通过用位移微商来计算应力,精度会大大降低。本文利用Hamilton对偶体系的已有成果,解析求解位移和应力的影响函数,利用有限元法计算得到的位移和节点力,通过功的互等定理,可以求得一点的应力值。因影响函数是分析解,而且计算应力时不必进行微商,应力精度大幅提高。数值结果表明该方法是可行的和有效的。由该方法编制成的计算程序,可作为有限元通用程序应力计算的一个模块,将较大地提高有限元应力计算的精度和稳定性。     

二维边界层方程的迭代求解

针对二维边界层方程,提出了分析积分迭代法.首先将该方法应用于Blasius方程和Falkner-Skan方程的求解,数值计算结果稳定,计算精度高;然后对外部有势流不能达到自相似要求、必须二维求解的二维层流边界层问题,在分析积分迭代法中加上计算力学的松弛迭代法,形成了一套有效的算法.数值结果表明该方法用于层流边界层的计算是很有效的.     

STOCHASTIC OPTIMAL VIBRATION CONTROL OF PARTIALLY OBSERVABLE NONLINEAR QUASI HAMILTONIAN SYSTEMS WITH ACTUATOR SATURATION

An optimal vibration control strategy for partially observable nonlinear quasi Hamiltonian systems with actuator saturation is proposed. First,a controlled partially observable non-linear system is converted into a completely observable linear control system of finite dimension based on the theorem due to Charalambous and Elliott. Then the partially averaged It stochastic differential equations and dynamical programming equation associated with the completely observable linear system are derived by using the stochastic averaging method and stochastic dynamical programming principle,respectively. The optimal control law is obtained from solving the final dynamical programming equation. The results show that the proposed control strategy has high control effectiveness and control effciency.     

Hybrid and multi-field variational principles for geometrically exact three-dimensional beams

This paper addresses the development of several alternative novel hybrid/multi-field variational formulations of the geometrically exact three-dimensional elastostatic beam boundary-value problem. In the framework of the complementary energy-based formulations, a Legendre transformation is used to introduce the complementary energy density in the variational statements as a function of stresses only. The corresponding variational principles are shown to feature stationarity within the framework of the boundary-value problem. Both weak and linearized weak forms of the principles are presented. The main features of the principles are highlighted, giving special emphasis to their relationships from both theoretical and computational standpoints.     

Finite dynamic deformations of a hyperelastic,anisotropic, incompressible and prestressed tube. Applications to in vivo arteries

In this paper, we study the mechanical behavior of a prestressed tube subjected to finite dynamic deformations. The tube is assumed to be made of a hyperelastic, anisotropic and incompressible material. The analysis is carried out by using a Mooney–Rivlin stored energy function augmented with fiber reinforcements in four unidimensional orientations. A semi-analytical solution is proposed to study the radial dynamic mechanical response of an artery by using in vivo data. The optimal model parameters describing the mechanical characteristics of arterial wall microconstituents are obtained by minimizing the difference between computed and measured inner pressures over the cardiac cycle using a nonlinear regression. Theoretical and experimental results on rat carotid elastic arteries are compared in order to assess the validity of the approach by estimating differences of the model parameters and wall stresses with aging.     

岩石脆性破坏临界信息综合识别

岩石脆性破坏导致的各种现象可以分为两类:①与物理力学参数和结构特征改变有关,表现为岩石本身变得破碎,承载力降低,变形速率增大,模量变小,渗透率增大,波速参数与电阻率值突变;②与能量释放及物理场参数变化有关,体现在声发射信号激增,电磁辐射强度增加,红外辐射加大.试验和理论分析表明:单轴条件下岩石破裂前临界特征点所对应的应力和岩石峰值应力比值约在70%-80%之间.论文通过分析得出,岩石脆性破坏的各种信息与岩石微破裂发展存在特定的关联性,利用综合信息源可以很好的进行脆性破坏临界点的识别.     

改进SPH方法在陶瓷材料层裂数值模拟中的应用

为了探讨铝飞片撞击陶瓷材料时的层裂现象,采用改进SPH方法模拟应力波在陶瓷材料中的传播。结果表明,当离散粒子分布不均匀时,数值模拟计算的自由面速度时程曲线与实测曲线吻合良好。对比CSPM方法,改进SPH方法的精度更高。提出适用于数值模拟的陶瓷材料损伤演化方程,对脉冲载荷下陶瓷/钢层合板层裂的破坏过程进行数值模拟,结果表明,由于陶瓷的波阻抗高于钢的,且抗压强度远高于抗拉强度,因此拉应力引起的层裂破坏是主要的。即使在材料内部传播的只是弹性压缩波,当弹性波到达材料界面时,由界面反射引起的卸载波也能导致陶瓷发生层裂破坏。     

高速铁路连续箱型梁桥的动力响应与减振分析

根据列车具体的轴距和轴重,建立了和谐号动车组CRH380AL型列车简化模型;对高速铁路两跨连续梁桥采用多自由度欧拉伯努利梁单元进行主梁的模拟,并将液体黏滞阻尼器模拟为有限元阻尼单元;采用Newmark直接积分方法求解了高速列车作用下的连续梁桥运动方程,数值分析了列车车速以及液体黏滞阻尼器的阻尼系数对于高速铁路连续梁桥振动响应的影响。结果表明:黏滞阻尼器对于桥梁具有明显的减振效果,阻尼力不仅与阻尼系数有关还与列车时速有关;同一黏滞阻尼器条件下,桥梁的最大加速度并不随列车速度的增加而单调增加,而是在某些特定列车车速下桥梁的最大加速度出现了峰值,且随着黏滞阻尼器的阻尼系数增大,桥梁振动响应峰值处的最大加速度减幅不同;同一列车时速的条件下,桥梁的减振效果并不是随着阻尼系数的递增呈正比递增,而是随着阻尼系数的增大,阻尼器的减振效果增幅在减小。