接触问题的增广拉格朗日块体粘接模型

在弹性接触数值模拟研究中,建立了一种新的块体粘接模型:通过将原模型所求解的问题归结成以粘接弹簧应变能为罚函数项的最小化问题.新模型引入拉格朗日乘子作为粘接弹簧拉力,从而将作为目标函数的系统总势能构造成增广拉格朗日函数.为求解该模型,提出一种新算法,在每个时间步引入一层增广拉格朗日迭代过程取得模型的最优解.数值算例验证了所提出模型和算法的精确性和有效性.

复合绝缘子交界面非线性力学模型及弱粘接缺陷无损检测方法

复合绝缘子交界面缺陷是造成绝缘子异常发热、断裂的主要原因。现有的无损检测方法主要基于电磁波或机械波在内部空气间隙处的折反射实现无损探伤,对更加普遍存在的弱粘接缺陷无能为力。针对无明显空气间隙的弱粘接缺陷,从粘接机理出发,根据氢键弹簧假设与迟滞摩擦模型,分别建立了完好粘接与弱粘接交界面的本构模型;并利用本构模型的数值仿真,初步证明了当界面粘接性能下降时,机械波的非线性畸变程度将会增加;之后搭建了非线性声学平台,并分别制备了含弱粘接缺陷的平板与绝缘子短样,并测试了其非线性畸变程度。根据试验结果,提出了弱粘接缺陷的无损识别方法。

DNA粘接计算模型及其应用

DNA计算是应用分子生物技术进行计算的新方法。应用形式语言及自动机理论技术研究DNA计算理论,有利于推动理论计算科学的发展。本文根据DNA分子的结构及特点给出了DNA分子的形式化描述,介绍了DNA粘接计算模型的文法结构和计算能力,并应用DNA计算方法求解3-SAT问题。

DNA分子计算模型

The field of practical DNA computing opened in 1994 with Adleman's paper,in which a laboratory experi-ment involving DNA molecules was used to solve a small instance of the Hamiltonian Path problem. The characteris-tic of this computation is its powerful ability in parallelism, its huge storage and high energy efficiency. This papermainly introduces the principles of DNA computing and the sticker computing model.

加速度计的粘接工艺与迟滞仿真分析

本文以某型加速度计为研究对象,开展了胶层固化工艺、固化应力等方面的研究,建立了粘接工艺模型,并在此基础上进行了加速度计迟滞仿真分析,确定了胶层粘弹效应对加速度计迟滞输出的影响。

非连续变形分析的MLS后处理方法

非连续变形分析(discontinuous deformatrion analysis,DDA)通过引入虚拟节理网格将块体离散成子块体系统进行断裂扩展数值模拟.针对这种方法难以获得精确块体应力分布的问题,提出一种基于无网格法移动最小二乘(moving least squares,MLS)插值的应力恢复算法.利用DDA计算得到的节点位移,通过恰当构造MLS形函数及其导数,推导了块体任意点应力的计算公式.数值算例将基于MLS后处理的结果与解析解及平均值法后处理结果进行比较,验证了所提出方法的精确性和有效性.

伸缩溜筒下料仿真分析及其结构优化

针对块状颗粒在伸缩溜筒下料过程中的破碎问题,运用离散元Hertz-Mindlin with bonding粘结接触理论,建立煤炭颗粒破碎模型,基于岩石破碎的能量学说,采用虚拟标定法确定粘结参数。根据离散元仿真研究煤炭颗粒在伸缩溜筒中的输送及破碎情况,对伸缩溜筒系统提出结构优化建议。结果表明,改进后的伸缩溜筒系统能够有效降低下料过程中的块煤破碎情况,降低运输折损。

计算科学的新领域:DNA计算(Ⅱ)

DNA 计算是应用分子生物技术进行计算的新方法。从理论上研究 DNA 计算方法,有利于推动理论计算科学的发展。本系列文章应用形式语言及自动机理论技术,系统地探讨了 DNA 分子的可计算性及其计算能力。本文主要介绍 DNA 分子粘接计算模型的文法结构和计算方法,探讨了不同粘接计算模型的计算能力,并证明了 DNA 有穷自动机与正规文法的等价性。

Discrete element method for adhesion properties evaluation of deep-sea sediment from macro and micro perspectives

The adhesion between the mining machine and the deep-sea sediments will significantly affect the driving performance of the mining machine in the deep-sea environment.When the mining machine and the deep-sea sediment interaction simulation was carried out,the accuracy of the particle interaction parameters will directly affect the simulation results.This study proposed a method to systematically calibrate the interaction parameters between deep-sea sediment and grouser through the combination of experiment and simulation.The uniaxial compression test and macro adhesion test and corresponding discrete element numerical simulation were carried out,modifying the contact parameters until the simulation results are close to the experimental results.Then the micro-parameters of the JKR adhesion contact model were back calibrated with the test results,and the contact parameters between soil particle-soil particle and soil particle-metal are calibrated.Besides,the adhesion test shows that the adhesion forces were ranked in the order of 5052<STi80<TA2<TC4 under the same surface roughness,which indicates the aluminum alloy 5052 has the best anti-adhesion performance.The relationship between surface adhesion force and microscopic contact parameters was studied by discrete element numerical simulation,and the result shows that the coefficient of static friction and the coefficient of rolling friction has little effect on adhesion force.While it is mainly affected by the coefficient of restitution and surface energy,the surface adhesion force tends to decrease with the increase of the coefficient of restitution and increase with the growth of surface energy.The obtained parameters of soil particle to soil particle and soil particle to metal affecting the adhesion can contribute to the design optimization for the grouser of mining machines to decrease surface adhesion and enhance its movability and mining efficiency.

An Analytical Approach for Assessing the Collapse Strength of an Unbonded Flexible Pipe

This paper presents an analytical scheme for predicting the collapse strength of a flexible pipe, which considers the structural interaction between relevant layers. The analytical results were compared with a FEA model and a number of test data, and showed reasonably good agreement. The theoretical analysis showed that the pressure armor layer enhanced the strength of the carcass against buckling, though the barrier weakened this effect. The collapse strength of pipe was influenced by many factors such as the inner radius of the pipe, the thickness of the layers and the mechanical properties of the materials. For example, an increase in the thickness of the barrier will increase contact pressure and in turn reduce the critical pressure.

Evaluation of Adhesive Joints for Combined Load Test-Fixtures

Abstract： In a test-fixture that the authors were using, steel tabs adhesively bonded to an aluminum panel debonded before the design load on the real test panel was fully applied. Therefore, studying behavior of adhesive joints for joining dissimilar materials was deemed to be necessary. To determine the failure load responsible for debonding of adhesive joints of two dissimilar materials, stress distributions in adhesive joints as obtained by a nonlinear finite element model of the test-fixture were studied under a gradually increasing compression-shear load. It was observed that in-plane stresses were responsible for the debonding of the steel tabs. To achieve a better understanding of adhesive joints of dissimilar materials, finite element models of adhesive lap joints and ADCB （asymmetric double cantilever beam） were studied, under loadings similar to the loading faced by the test-fixture. The analysis was performed using ABAQUS, a commercially available software, and the cohesive zone modeling was used to study the debonding growth.

On the fracture resistance of adhesively jointing structures

The interface toughness of adhesively bonded structural members is one of the critical parameters for adhesive joint design. It is often assumed that the joint toughness is a material constant so that its value can be obtained from fracture tests of simple geometries such as DCB for Mode-Ⅰ, ENF for Mode-Ⅱ, using linear elastic fracture mechanics （LEFM）. However, the LEFM assumption of point-wise crack-tip fracture process is overly simplistic and may cause significant error in interpreting fracture test data. In this paper, the accuracy and applicability of various traditional beam-bending-theory based methods for fracture toughness evaluation, such as simple beam theory （SBT）, corrected beam theory （CBT） and experimental compliance method （ECM）, were assessed using the cohesive zone modelling （CZM） approach. It was demonstrated that the fracture process zone （FPZ） size has profound influence on toughness calculation and unfortunately, all the classic beam-bending theories based methods fail to include this important element and are erroneous especially when the ratio of crack length to FPZ size is relatively small （〈5.0）. It has also been demonstrated that after the FPZ size is incorporated into simple beam formulations, they provide much improved evaluation for fracture toughness. Formulation of first order estimate of FPZ size is aIso given in this paper.