一种有限元并行计算前处理方法

本文研究一种有限元并行计算前处理方法,只需将各子结构的超单元信息发送给各处理机,就可并行自动剖分各子结构和并行优化各子结构单元编号,以达到极小最大波宽和波宽的均主根,算例表明,该方法可大大减少有限元并行计算前处理时间。     

Finite element analysis of tire traveling performance using anisotropic frictional interaction model

The traveling performance of off-the-road vehicles, such as construction machinery and exploration rovers, significantly depends on the interaction between the ground and the traveling mechanism, since inelastic ground deformation and frictional sliding phenomena are induced by the vehicle’s movement. In general, a tread surface causes anisotropic frictional interaction behavior on a macroscopic scale. In this study, an acceptable frictional interaction model was implemented to finite element method to rationally examine the anisotropic frictional interaction behavior between the tire and the ground. Finite element analysis of the single tire traveling performance, including certain slippage and side slip (skid), was then carried out to examine the effect of the anisotropic frictional interaction on the numerical results for the drawbar-pull and side force.     

现场实测结构温度对半刚性沥青路面性能的影响

针对中国特色的半刚性基层沥青路面,在广韶高速公路瓮城段进行为期一个月高温期的现场温度观测。运用三维有限元方法,结合现场实测温度,分析了半刚性沥青路面结构的最大拉应力、最大剪应力和最大路表弯沉在荷载和荷载耦合作用下的变化情况。结果表明,随着路面深度增加,温度波动的幅度逐渐减小;路面内的最高温度相对大气和路表温度滞后约1小时;沥青路面内部温度高于表面温度;大气、路表和路面内部温度变化基本同步,温度波峰与波谷的出现频率相同;在温度和荷载综合作用下,路表以下2cm深度范围内易出现因拉应力不足造成的开裂破坏;路表以下10cm深度范围内,较易出现剪切破坏;高温温度场的存在虽不会明显增大路面结构各层的拉应力与剪应力,但会明显增大路表弯沉,故易产生车辙破坏。     

PZT-4紧凑拉伸试样的断裂分析

基于线性压电材料的复势理论,通过解析分析,导出了一种分析有限压电板裂纹问题的解析数值方法. 首先,计算了含中心裂纹有限板的断裂参数,与Woo和Wang的解析数值法(Int J Fract, 1993, 62: 203$\sim$218)相比较,表明该方法具有很高的精度和很好的计算效率. 随后,采用该方法和有限元法计算了PZT-4紧凑拉伸试样在绝缘裂纹面边界条件下断裂时的断裂参数,发现各断裂参数的临界值分散性很大,不能作为压电材料的单参数断裂准则. 进而,针对试样真实的裂隙形状,采用有限元法计算了裂隙尖端的应力、电位移场,比较了裂隙内介质的介电性能对裂隙尖端场的影响,计算了带微裂纹的真实裂隙模型的断裂参数并进行了理论分析.      

高边坡结构可靠度的二次处理有限元分析

本文依据强度折减理论,利用MIDAS/GTS有限元软件,分析计算了高边坡结构的安全系数K,找到边坡滑裂带的位置。在此基础上,对有限元输入数据和输出结果进行二次处理,建立基本随机变量c,f与滑裂带中单元的最大(和最小)主应力σ1(和σ3)的拟合关系f1(和f3),将其代入高边坡结构的功能函数Z中,使Z由隐式形式变为显式。基于该显式表示的Z,利用Monte Carlo法计算滑裂带中所有失效单元的可靠指标β1,并将其单元面积A1作为权重系数,经过加权平均得到边坡结构的整体可靠指标β。上述方法使得结合有限元软件计算边坡结构的整体可靠度得以简化。经实例分析可知,本文提出的方法是合理可行的,可使边坡结构整体可靠性分析得以简化,也可为高边坡结构整体可靠性分析提供理论参考。     

缝合复合材料层板低速冲击损伤研究

通过三维动力学有限元法,以空间杆单元模拟缝线的增强作用,建立了缝合复合材料层板在横向低速冲击载荷作用下的渐近损伤分析模型.该模型考虑了缝合层板受低速冲击时的纤维断裂、基体开裂及分层等五种典型损伤形式,采用基于应变描述的Hashin失效准则和Yeh分层失效准则,并将其嵌入ABAQUs/Explicit用户子程序以实现相应损伤类型的判断及其材料性能退化.针对相同铺层的缝合与未缝合层板,模拟了低速冲击作用下的冲击响应和渐进损伤过程,数值结果与试验吻合较好,证明了该方法的合理有效性.同时探讨了冲击速度、缝合密度等对缝合层板冲击响应和损伤的影响.     

Mathematical modelling of rate-independent pseudoelastic SMA material

The paper presents a procedure for the formulation of constitutive equations for rate-independent pseudoelastic SMA material models. The procedure applies a rheological scheme representing mechanical properties of the material. An additive decomposition of strains into two parts is proposed. The first part describes strains of a perfectly elastic body while the second part may be represented by a combination of a rigid perfectly elastic body and a rigid perfectly plastic body. It is demonstrated that the key problem of formulation of constitutive relationships is to derive the 1st order differential equation with respect to the tensor describing the second part of the strain field. This equation may be obtained in explicit form starting from the variational inequalities defining non-elastic parts of rheological model. The uniqueness of the obtained differential equation has been proved. A numerical implementation of the constitutive relationships of SMA material was done through the user subroutine module VUMAT within the FE commercial code ABAQUS/Explicit. As an example we analyzed the problem of vibration of a simple 3D structure made of SMA.     

表面活性物质对液体晃动阻尼影响分析及计算

对表面活性物质对液体晃动阻尼的影响进行了理论分析, 针对液体小幅自由晃动对表面活性物质耗散阻尼计算公式进行了推导. 在此基础上提出了结合液体晃动有限元计算的表面活性物质耗散阻尼的数值计算方法.通过将算例结果与实验值和理论分析结果进行比较, 数值方法的有效性得到了验证.     

铁中Ⅰ型裂纹裂尖场与裂尖形变机制分析

应用有限元及连续介质力学计算了平面应交条件下体心立方铁中不同取向裂纹的裂尖应力场和弹性应变能密度分布,从宏微观相结合角度分析了裂尖场分布与裂尖微结构演化的相互关联.指出裂尖塑性变形的具体形式与裂尖滑移面上分切应力的大小密切相关,并从能量角度解释了裂尖相变产生的原因,最后结合相关分子动力学研究成果探讨了裂尖奇异性区域.     

Simulation of oscillatory flow in an aortic bifurcation using FVM and FEM: A comparative study of implementation strategies

Cardiovascular diseases are one of the major causes of long‐term morbidity and mortality in human beings. The nearly epidemic increase in prevalence of such diseases poses a serious threat to public health and calls for efficient methods of diagnosis and treatment. Non‐invasive diagnostic procedures such as MRI are often used in this context; however, these are limited in terms of spatial and temporal resolution and do not provide information on time‐dependent pressures and wall shear stresses—key quantities considered to be partially responsible for the formation and development of related pathologies. The present study is concerned with the numerical simulation of oscillatory flow through the abdominal aortic bifurcation. Computational fluid dynamics simulation of oscillatory flow in a branched geometry at high Reynolds numbers poses considerable challenges. The present study reports a detailed comparison of simulations performed with a finite volume and a finite element method, two approaches with significant differences in their discretization strategy, treatment of boundary conditions and other numerical aspects. Both solvers were parallelized, using loop parallelization of the BiCGStab linear solver for the finite volume and domain decomposition based on the Schur complement method for the finite element technique. The experience gained with these two approaches for the solution of flow in a bifurcation forms the focus of this study. Although similar results were obtained for both methods, the computation time required for convergence was found to be significantly smaller for the finite element approach. Copyright © 2010 John Wiley & Sons, Ltd.