Multi-scale modeling of fatigue crack propagation applied to random sequence of clustered loading

Fatigue crack propagation in marine structures is obviously governed by mechanics of the considerably different four levels of multi-scale problems. Problems of structural response to environmental loads have length scale of several hundred meters, whereas possible detectable size of cracks from initial defects in a weld is of the order of millimeters. Once a fatigue crack initiates, crack tip plasticity is of the order of several grain sizes, while the resulting fatigue crack growth in each load cycle is of the order of nanometers. In our previous work, the first author and their associates have developed the so-called CP-System, which can treat the first two multi-level problems as an integrated system. Furthermore, we have incorporated the third level of mechanics by using the stress intensity range corresponding to the repeated tensile plastic deformation ahead of the crack tip. In the present paper, we shall discuss a more rational integral equation-based formulation in order to integrate the third and fourth levels of micro-mechanics to the first two levels of continuum mechanics.The method is then applied to fatigue crack propagation under the effects of random sequence of clustered loading. As an example of the random sequence of clustered load, we shall use the so-called “storm model”. In the crack propagation simulation, we have to take into account of the plastic wake on the crack surfaces, whose thicknesses are influenced by the material parameters involved in the crack growth model. These parameters are first identified by the fatigue tests under combined constant and random loading using a CT specimen. Then, fatigue crack growth is investigated by numerical simulation and fatigue tests for various random sequences of clustered loading. The experimental and numerical results agree quite well with each other, and fatigue crack propagation is found to be considerably retarded under random sequence loading, so that the conventional equivalent stress approach may provide rather conservative results to the real seaway loading.     

Multi-resolution modeling and simulation for urban rail transit network planningEI北大核心

Research purposes: Simulation technology plays an important role in the urban rail transit network planning and analysis. With the enlargement of the urban rail network scale, the complexity and difficulty in the development of simulation system for urban rail transit network planning increase. To develop the simulation system with high efficiency, an approach to multi-resolution modeling and simulation of urban rail transit system is presented. Research conclusions: (1) An approach to build a multi-resolution simulation system of urban rail transit is presented, by building and integrating transit network architecture models and passenger models in different resolutions. (2) Ahierarchical model of rail transit network topology is built to resolve the problem of spatial consistency in multi-resolution modeling. (3) A polymerization based station simulation model is built to resolve the problem of state consistency. (4) To meet the needs of extensibility and flexibility of the simulation system, an agent-based integration method is applied to develop the simulation system of urbanrail transit network. (5) Arealized example on the application of the simulation model is introduced, which is used to analyze and evaluate a transit network planning.     

基于ObjectARX的船舶快速分舱程序设计

舰船舱室形状复杂、数量众多,给船舶初步设计阶段的舰船分舱工作带来很大困难。文章提出基于有向分舱线的舱室定义方法,以降低舰船舱室定义阶段的复杂性,同时提高直观性。基于有向分舱线的概念,结合船型曲线的有序化组织,对AutoCAD进行二次开发,完成软件编制。在实际应用中,不仅极大减少了舱室定义的时间和复杂性.同时为舰船舱室划分提供结构化的组织和管理方法。     

基于MasterCAM的后置处理技术研究与实现

本文基于MasterCAM通用后置处理系统,应用数控代码导向技术,通过修改其数据库模型,较好地开发配置西门子810D数控系统的专用后置处理程序,解决了该系统处理孔加工固定循环的难题,并成功地应用于实际加工。     

汽车虚拟试验场中整车的建模技术与要点

通过对某型商务车白车身、悬架系统、轮胎、非结构质量进行有限元模型的建立、联接装配,直至完成整车的有限元模型的过程,并对该模型进行简单的验证,来说明在汽车虚拟试验场中整车的建模技术与要点。     

民用飞机维修成本评估

近年来, 航空公司的经营状况持续低迷, 为解决这一现实问题, 从民用飞机维修成本入手, 提出了对民用飞机进行经济性评估的方法和策略, 介绍了用于民用飞机维修成本经济性评估的方法、步骤以及参数化建模的数学工具, 最后以发动机本体送修为例, 运用介绍的理论作了实例分析。实证表明, 对民用飞机的维修成本进行合理的评估, 对改善航空公司经营状况是非常必要和有益的     

A system dynamics modeling for urban air pollution: A case study of Tehran,Iran

Development of strategies to control urban air pollution is a complex process involving a wide range of sciences. In this study a system dynamics model is proposed in order to estimate the behavior of parameters affecting air pollution in Tehran. The proposed model includes two subsystems: (1) urban transportation, (2) air polluting industries. In this paper, several policies are proposed to mitigate air pollution. The proposed model is simulated under several scenarios using historical data of transportation and industrial sectors in Tehran. Policies are categorized as: (1) road construction, (2) technology improvement in fuel and automotive industries, (3) traffic control plans, (4) development of public transportation infrastructures. The results show effectiveness of the proposed policies. In this case, technology improvement in fuel and automotive industries and development of public transportation infrastructures are more effective policies in order to reduce air pollution.     

基于计划行为理论的竞争驾驶行为建模0

为获取竞争驾驶行为的潜变量因子,分析驾驶员竞争驾驶行为的产生动机.对 225 名驾驶员进行了网上问卷调查,通过主成分分析和验证性因子分析提取竞争驾驶行 为的4 个潜变量因子：速度领先、空间占用、路权争夺和空间领先争夺.基于计划行为理 论,构建了竞争驾驶意图与行为关系结构方程模型.研究表明,驾驶员的竞争驾驶态度、主 观标准、知觉行为控制等心理因素和社会环境外界因素,通过行为意向能够很好地对竞 争驾驶行为进行预测.社会环境因素对竞争驾驶意图有显著影响,为驾驶员竞争驾驶行为 的矫正提供了有效途径.     

潜艇居住舱室计算机辅助设计研究

将ＣＡＤ技术应用于潜艇居住舱室设计，研究在微机上利用ＡｕｔｏＣＡＤ软件进行三维舱室立体模型的设计，并提出了一种由三维实体模型转换成二维工程设计图样的新方法。     

随轴系做复杂空间运动的船舶 螺旋桨水动性能计算

船舶航行时,附在转轴上的螺旋桨通常做复杂的空间运动。这是因为一方面螺旋桨和转轴不可避免地存在偏心,使得在不平衡激励下转轴在绕自身中心线旋转的同时又发生空间涡动(又称为进动);另一方面,螺旋桨通常工作在不均匀的流场中(即使来流均匀,轴系涡动亦会导致流场的不均匀),桨叶表面的脉动力也会导致转轴的空间振动。对具有复杂三维运动的螺旋桨的水动性能预报是一个难点。本文建立了螺旋桨在流场中随轴系做复杂空间运动时的水动力预报数学模型,并利用不定常面元法求解了这一问题。该方法按时间步顺序求解,考虑了不均匀流场、轴系振动、尾涡的非线性运动及卷曲等因素。利用本文提出的方法并结合结构动力学模型,可以方便地研究流体-螺旋桨-轴系双向流固耦合等问题。同时该方法也可以用来预报船舶转弯、船舶升沉及纵摇振荡、螺旋桨启停及加速等复杂工况下的螺旋桨水动性能。文中通过一个算例验证了算法的有效性。最后,预报了轴系纵向振动幅值为1 mm,振动频率为3 Hz并伴有微量回旋振动时所引起的4381螺旋桨的脉动力。研究表明推力脉动分量大约为其静态分量的4.5/1 000,扭矩脉动分量大约为其静态分量的4/1 000。