First order sensitivity analysis of flexible multibody systems using absolute nodal coordinate formulation

Design sensitivity analysis of flexible multibody systems is important in optimizing the performance of mechanical systems. The choice of coordinates to describe the motion of multibody systems has a great influence on the efficiency and accuracy of both the dynamic and sensitivity analysis. In the flexible multibody system dynamics, both the floating frame of reference formulation (FFRF) and absolute nodal coordinate formulation (ANCF) are frequently utilized to describe flexibility, however, only the former has been used in design sensitivity analysis. In this article, ANCF, which has been recently developed and focuses on modeling of beams and plates in large deformation problems, is extended into design sensitivity analysis of flexible multibody systems. The Motion equations of a constrained flexible multibody system are expressed as a set of index-3 differential algebraic equations (DAEs), in which the element elastic forces are defined using nonlinear strain-displacement relations. Both the direct differentiation method and adjoint variable method are performed to do sensitivity analysis and the related dynamic and sensitivity equations are integrated with HHT-I3 algorithm. In this paper, a new method to deduce system sensitivity equations is proposed. With this approach, the system sensitivity equations are constructed by assembling the element sensitivity equations with the help of invariant matrices, which results in the advantage that the complex symbolic differentiation of the dynamic equations is avoided when the flexible multibody system model is changed. Besides that, the dynamic and sensitivity equations formed with the proposed method can be efficiently integrated using HHT-I3 method, which makes the efficiency of the direct differentiation method comparable to that of the adjoint variable method when the number of design variables is not extremely large. All these improvements greatly enhance the application value of the direct differentiation method in the engineering optimization of the ANCF-based flexible multibody systems.     

δ/γ Interface bondary sliding as a mechanism for strain accommodation during hot deformation in a duplex stainless steel

In the present work, the mechanical properties and the microstructural evolution of a duplex stainless steel in the as-cast and wrought conditions during deformation under hot-working conditions have been studied. Hot torsion tests, at strain rates of = 1 s⁻¹, have been carried out using prepolished samples on which surface parallel scratches have been practiced. The observation of the surface of the samples shows a large displacement of the scratches produced by two different mechanisms, sliding on the δ/γ interface, and shearing of the ferrite. The displacements in the as-cast condition have been found to concentrate in a reduced set of ferrite/austenite interfaces leading to the formation of cracks along them. In the wrought material, the distribution of the sliding is more homogeneous over all the ferrite/austenite interfaces, and no damage has been produced. These behavioral differences between both materials have been related in the present work, to the characteristics of the corresponding microstructures, to the spatial phase distribution, and to the nature of the ferrite/austenite interface, among others.     

Socio-Cultural Connections and Ruptures: Social Roles of Older Adults in Chile

This research focused on determining the sociocultural factors that build the social perception of the social roles of senior citizens in Chile in the 2002–2012 period. For this purpose, public opinion was studied in newspapers El Mercurio and La Cuarta. Specialized opinion included the Senior Citizen Program of Pontificia Universidad Católica de Chile, the National Service for Senior Citizens, the Social Observatory for Aging and Old Age of Universidad de Chile, and the Society of Geriatrics and Gerontology of Chile. A comprehensive methodology was used, along with a bibliographical four-stage design. The following ten sociocultural factors were identified: Health and Quality of Life, Studies and Data, Social Images of Aging, Gerontological Concepts and Sociopolitical Participation, Gerontological Policies, Plans and Principles, Aging, Production and Gender, Institutionalization, Demographic Growth, Gerontological Training, and Exclusion and Old Age. This work suggests modifying the conceptual premise that emphasizes the inexistence of a social role for elderly people with a vision centered on the heterogeneity of social roles under permanent sociocultural construction.     

基于SWARM的虚拟社会经济系统建模与仿真

经济系统是虚拟社会中的重要组成部分,通过研究虚拟社会中政治、军事、外交等危机事件对经济系统整体及内部组成因素的影响,为决策者提供一种近似实际的较为逼真的训练环境,达到在不同条件下进行战略决策综合演练,提高战略决策者处理危机事件能力的目的.主要阐述了一种基于SWARM的经济建模与仿真方法,概括总结了该方法的建模思路与仿真步骤,运用该方法对虚拟社会的经济系统进行了建模,重点描述了模型的结构及各类Agent的属性和行为,并给出了虚拟社会经济系统的仿真框架,最后以某一地区的宏观经济情况为研究背景做了初步实验,得到了初步的实验结果.     

Modal parameter identification using Z-transforms

A method for the time domain identification of modal parameters of a vibrating structure using Z-transformation sequences is presented in this paper. This identification proceeds using the Z-transfer function of a vibrating structure from which an auto-regressive and moving-average (ARMA) model of the vibrating structure is derived. From this ARMA model and time domain data, the modal parameters can be identified. The time domain data can be obtained from single point or multiple shaker excitation modal testing. To demonstrate the application and efficiency of the method, a test on a simulated cantilever beam is presented.     

石油模型研究综述

针对石油能源开发综合研究问题,从时间序列、灰色理论、神经网络以及组合预测等不同的角度,对石油产量、价格、需求等单一模型的成果进行研究,并对各类模型优缺点进行比较.为进一步开展与石油问题相关的复杂系统建模提供参考,针对国家能源政策和能源政策分析的需要,与目前国际上比较具有代表性的综合能源模型系统,从复杂系统分析与建模的角度,介绍了各系统的建模方法、功能、应用.综合以上各类研究成果和现实需求,为今后石油以及能源模型的开发提出设想和展望.     

A statistical evaluation of the free energy of Fe-base ternary ordering alloys

The free energy of the Fe-base ternary ordering alloys whereB2 andD0₃ ordered structures are formed is evaluated. The statistical theory is employed using a pairwise interaction approximation taking into account not only the atomic interaction but also the magnetic interaction, based upon the Bragg-Williams-Gorsky model. The application of this model on Fe-Si-Co ordering alloys are demonstrated. The propriety of the calculation results are performed by comparing the experimental results. The influences of the magnetic energy to the stability of ordered structures are also demonstrated.     

铅、银对活性碳分离富集-原子吸收法测金的干扰及消除

本文针对电鲜阳极泥、冰铜、铅、锌精矿、炉砖四种含金样品中铅银对活性碳富集－AAS测Au的干扰,提出了消除干扰的具体措施,提高了分析结果的准确性。     

Acute endocarditis of the native aortic valve caused by Propionibacterium acnes

Propionibacterium acnes is often considered to be a contaminant but it has also been found to be the principal pathogen in serious infections. P. acnes is a rare cause of infective endocarditis. It has been suggested that aortic root abscesses are caused by bacteria that are particularly virulent. The strongest risk factor for serious infections by this bacteria is the presence of foreign bodies. A case is presented in which endocarditis of a native aortic valve caused by P. acnes was associated with an aortic root abscess. Transesophageal echocardiography is particularly helpful in the diagnosis of this severe complication of infective endocarditis. The literature for P. acnes endocarditis is reviewed.     

热冲压成形后22MnB5钢的组织与拉伸性能以及拉伸时的微观形貌演变

对比研究了22MnB5钢经890℃热冲压成形前后的显微组织与拉伸性能,采用原位拉伸试验观察了热冲压成形后试验钢在单向拉伸过程中微观形貌的演变.结果表明:热冲压成形前试验钢的显微组织为铁素体和珠光体,热冲压成形后组织转变为马氏体,试验钢的强度和强塑积提高,塑性下降;在拉伸过程中,试验钢先发生颈缩,随后原奥氏体晶界破坏,微...