A MATHEMATICAL MODEL FOR THE DYNAMIC PARTICIPATE FILTRATION IN DIESEL FOAM FILTERS

Diesel Particulate Filters (DPFs) are probably the most effective means for trapping the exhaust-emitted participate from diesel engines. Foam type filters become a promising alternative to the common wall flow filters, since they are effective in filtering small size particles and provide a larger specific surface area for catalytic coatings. A mathematical model taking into account the significant phenomena during the dynamic filtration of foam filters is developed. The model predicts the filtration efficiency and the induced backpressure as function of the geometric filter properties and operating conditions. Due to the particular structure properties of the foam filters it is necessary to employ a tunable parameter, which accounts for the influence of non-Stokes flow in foam filters. This parameter is easily derived by simple measurements. The model is employed to identify and understand the critical parameters of the filtration in foam filters. Indicative parametric runs are presented, which illustrate the applicability of the model in system optimization procedures.     

THE DEVELOPMENT OF A MATHEMATICAL MODEL FOR PREDICTING THE DEPTH OF PLASTIC DEFORMATION IN A MACHINED SURFACE

The development and verification of a mathematical model for the prediction of plastic deformation in a machined surface are presented. The main assumption for developing this model is that there is a linear relation between plastic strain and the depth to which it extends. The model relates the work required to shear the workpiece material to the work needed to compress the workpiece material ahead of the cutting tool. The resulting depth of plastic deformation in the machined surface is a function of the true stress-strain characteristics of the workpiece material, the shear stress and shear strain on the shear plane, and the distribution of plastic strain. Results of the model agree well with data found in the literature. An improvement of the model is suggested through application of actual distribution data of plastic strain and calculation of frictional behavior on the rake face of the tool.     

COMPARISONS OF MECHANICAL MELT-BLOWN FILTERS AND ELECTROSTATICALLY ENHANCED SPLIT-FIBER FILTERS FOR CABIN AIR FILTRATION APPLICATIONS

In this paper, compared are filtration characteristics of two different filters made from uncharged melt-blown media and electrostatically charged split-fiber media. The split-fiber filters have stronger electrostatic charges in the media than the melt-blown filter, which in turn enhances the initial fractional efficiency. The compared parameters are fractional efficiencies, dust holding capacities, incremental fractional efficiencies, and pressure drop. The advantages and disadvantages of these filters for cabin air filtration applications are discussed based on the experimental results obtained using SAE-fine dust and sodium chloride test aerosol. The optimization process of the filter selection is also discussed.     

非直纤维的细观动态拔出模型分析

在Chanvillard关于非直纤维静态拔出模型基础上,建立非直纤维的细观动态模型。此模型通过纤维与基体接触界面剪应力的传递考虑纤维的动态拔出过程,并考虑应变率效应。同时,适当选取阈值,建立基于细观损伤演化的纤维脱粘和拔出动态模型。此模型可以很好地模拟Chanvillard关于非直纤维的静态实验结果,并能反映复合材料的应变率影响。      

微振动力学系统模型构造微分方程系数矩阵方法

对于多自由度定常约束微振力学系统的数学建模有许多方法，但这些方法不是受到使用条件限制就是计算繁琐，并且不适合于计算机建模。根据系统的动能、势能、耗散能量与运动方程决定的动能、势能、耗散能量分别相等的原理，提出了构造微分方程系数矩阵方法（下称能量偏导法）。论证了直接法^[1]、视察法^[2,7]是能量偏导法的特例。能量偏导法的优点是；在建立运动方程的过程,没有对时间求异的过程，也没有对方程整理和化简的过程。该方法既适用于单自由度系数又适合于多自由度系统，既适用于手工建模又方便于计算机建模。在该方法的基础上，本文又提出了运动方程解耦的数学条件，为广义坐标的选取指明了方向。文中也给出了能量偏导法的应用和结论。     

腐蚀磨损数学模型

测试了化学镀Ｎｉ－Ｐ合金静腐蚀、动腐蚀和腐蚀磨损试验结果。通过对试验结果的处理，建立了动腐蚀速率和腐蚀磨损速率与冲击速度Ｖ、介质浓度Ｃ的数学模型：Ｖ＝Ｋ１Ｖ＾ｎ１＋Ｋ２Ｖ＾ｎ２Ｃ＾ａ（ａ＝Ｋ３Ｖ＾ｎ３）。建立了腐蚀磨损速率Ｖｗｃ与纯磨损速率Ｖｗｏ、纯腐蚀速率Ｖｐｃ及动腐蚀速率Ｖｏｃ之间数学模型：Ｖｗｃ＝Ｖｗｏ＋Ｖｐｃ＋ＫｗｃＶｗｏ，Ｖｐｃ＝Ｖｗｏ＋（１＋Ｋｗ）Ｖｏｃ＋Ｋｗｃ（１＋Ｋｗ）ＶｗｃＶｏｃ     

高速柴油机曲轴动态特性研究

本文利用ＳＵＰＥＲ ＳＡＰ９１微机版工程分析软件，对某高速柴油机曲轴进行了有限元计算模态分析，获得了其前五阶模态参数；利用随机信号与振动分析系统ＣＲＡＳ４．１版对该曲轴进行了试验模态分析，其固有频率与计算结果的相对误差在５．７％之内，验证了计算结果的正确性，为结构的动态特性分析提供了可靠的数据。     

圆环斜二测投影数学模型的建立

本文建立了圆环斜二测投影的数学模型，并对投影中轮廓线的可视性进行了分析，导出了可见轮廓线端点坐标的计算公式，为计算机辅助绘较提供了依据。     

Nb,Ti微合金钢热变形的动态模拟变形抗力模型

本文报道 Nb,Ti 微合金钢的热变形动态模拟变形抗力模型。在试验中用热加工模拟试验机进行高温压缩试验,其变形温度为1123—1423K,变形速率为0.1—60s~(-1)。结果表明,在峰值以前该钢种的流变应力数学模型为:σ=5.99.ε~(0.167)·(?)~(6.47×10~(-5)·T)·exp(4064/T)。形变激活能(Q)为444 kJ/mol,β系数为0.080。峰值应力(σ_p),临界应变(ε_c)和温度补偿应变速率参数(Z)之间的关系分别为:σ_p=12.56·lnZ-391.8;lnε_c=0.157·lnZ-7.39。     

残余应力平板表面裂纹的线弹簧模型

建立了残余应力平板表面裂纹的线弹簧模型,利用边裂纹权函数得到了裂纹表面上沿厚度非线性分布残余应力向线性分布转化的公式;基于Reissner板理论和连续分布位错思想,通过积分变换方法,推导了问题的控制方程和应力强度因子表达式;利用Gauss-Chebyshev方法给出了数值计算结果,并与现有的有限元解进行了比较,结果表明:该模型简单有效,而且精度较高。     

现有结构抗震维修动态规划决策

本文基于大地震发生的半马尔可夫过程模型,建立了服役结构抗震维修动态规划决策模型。文中考虑了钢筋锈蚀对结构抗力的影响,利用“分枝限界法”计算结构系统可靠度,并进行安全性等级划分,在此离散状态及离散时间的基础上,运用技术经济评价法,建立了动态规划决策模型。最后以一简单框架验证了上述方法的可行性     

A CONTINUUM MODEL FOR DYNAMIC DAMAGE EVOLUTION OF ANISOTROPIC BRITTLE MATERIALS

This paper is concerned with the development of a computational model for the damage evolution of brittle materials under dynamic loading. Two models for dynamic damage evolution of brittle materials with or without microflaws in general anisotropic damage state are presented; the first one is based on power function of principal tensile stress and the second one is based on damage strain energy release rate. A second-order tensor based elastic–brittle damage model is formulated which is efficient computationally and consistent in its treatment of damage evolution. Measured Weibull strength distribution may be employed to account for flaw size distribution effects on the damage accumulation rate. Methods of computing the accumulated damage of a structural component and their implementation in a finite element program together with some numerical results are presented. Finally, a comparison has been made between the two damage models.     

雷达目标识别的滤波器法

本文讨论了基于高分辨率距离像提取不敏感于方位角变化的特征矢量的方法和利用特征矢量间的相关性进行目标识别的问题，并对一些目标进行了识别实验，识别结果验证了本文所提出的利用相关滤波器法进行目标识别的有效性和可行性。     

基于物理力学机制的黄土震陷数学估算模型

通过分析黄土震陷物理力学机制,将影响震陷的主导因素归纳为粘聚力与内摩擦角(土体强度特征)、孔隙比(土体沉降特征)和外部动荷载特性(能量输入特征)等3方面。在此基础上,推导了应用孔隙比描述震陷系数的定量关系;利用摩尔-库伦破坏准则,提出了考虑动应力和固结应力的应力比概念,用以刻画动载输入对土体结构强度的影响;结合室内动三轴试验数据,给出了孔隙比压缩量与应力比之间的定量统计关系。耦合以上分析结果,建立了基于物理力学机制的求算地震动作用下黄土残余应变(震陷系数)的数学估算模型。     

开放系统悬臂类结构的动力特性计算方法

结构总是修建在一定的场地而形成土-结构相互作用的开放系统。为解决开放体系下悬臂类结构的自振频率、振型和考虑辐射阻尼下模态阻尼比的计算问题,提出了脉冲荷载响应模态分析法。该方法采用直接有限元法建立土-结构相互作用有限元模型,对结构施加脉冲荷载得到结构动力反应后,由模态识别方法计算结构的动力特性。随后,以一个悬臂类五层框架结构为例研究了计算动力特性随土体计算范围变化的规律和脉冲荷载激励点位置对计算结果的影响。在此基础上,讨论了土体材料阻尼对模态阻尼比的影响,并与集总参数模型和直接模态分析法进行对比,说明不同方法的计算精度。计算结果表明,随着土域计算范围的增加,脉冲荷载响应模态分析法所得的动力特性将逐渐收敛到精确解;当土体计算范围大于结构基频所对应的波长的2倍时,结构自振频率的误差小于1%,模态阻尼比的误差小于5%;以非模态节点作为激励点都可以得到比较精确的结果;三参数集总参数模型所得模态阻尼比存在显著误差,直接模态分析法所得模型的基频随土域范围增大而趋向于零;相比于辐射阻尼,土体材料阻尼对结构的各阶模态阻尼比的影响较小。     

广义逆特征值方法在动力模型修正中的应用

本文针对土木工程中理论计算的要求和特点,基于逆特征值理论给出了一种适合有限元动力模型修正的广义逆特征值方法,该方法在给出修正解的表达式基础上,要求修正解满足动力模型的力学特征,且仅需要少量试验数据,是一种简单、实用的有限元模型修正方法。     

动载荷识别的时间有限元模型理论及其应用

本文利用广义正交多项式作为时间有限元的形函数,推导了基于时间有限元的动载荷识别模型.成功地将时域下动载荷识别的复杂逆卷积关系转变为广义正交域的线性算子逆运算,这种模型识别精度高,抗干扰能力强,具有良好的计算稳定性,尤其适用于具有短时间样本的冲击类型动载荷识别,使该类问题在工程应用时的复杂程度大大降低,具有较高的工程应用价值.该方法为结构动力学逆问题的研究提供了一种新的技术途径.     

基于贝叶斯更新的深水桥墩波浪动力响应概率模型

海洋环境中的深水桥墩长期受到不规则随机波浪动力作用。传统设计规范中采用的特征波浪计算方法,虽然简单高效,但是无法充分考虑波浪随机性和动力效应对结构的影响。该文以深水桥墩在波浪作用下的动力响应与静力响应之间的概率关系为研究对象,应用贝叶斯更新理论建立简单有效的深水桥墩波浪动力响应概率模型。通过对比深水桥墩动力时程分析结果,验证模型的有效性,并对样本数量和模型形式进行讨论。研究表明：基于贝叶斯更新理论的深水桥墩波浪动力响应概率模型可以快速准确地计算波浪作用下深水桥墩的动力响应,能够有效修正传统静力方法存在的偏差,并可在样本数据非常有限的情况下对深水桥墩的动力响应进行较好估计。     

A HEURISTIC FOR THE DYNAMIC FACILITY LAYOUT PROBLEM

This paper presents a heuristic for the dynamic facility layout problem. All existing methods for solving this problem require the use of a dynamic programming model, the optimal solution of the quadratic assignment problem, or both. The proposed heuristic is based on the steepest-descent pairwise-interchange procedure to develop layouts utilizing material handling cost data from varying lengths of forecast windows as well as the explicit consideration of the corresponding rearrangement costs. Numeric results indicate that it typically performs as well as any existing methodology and only slightly worse than optimal.