Sensitivity analysis of stamping processes using various friction models appropriate for non-stationary contact problems

This paper looks at the sensitivity of thickness to variation of friction. The models of friction used are: the classic Amontons-Coulomb; a nonlinear pressure-dependent model proposed by Wriggers, vu Van and Stein; and a velocity-dependent model proposed by Molinari, Estrin and Mercier. They are coded in FORTRAN for use with finite element program ABAQUS. The contact problem is then formulated in the total Lagrangian formulation for contact between an elastic-plastic body and rigid tools. The variational (weak) form of the formulation is given and this is discretized by finite element method. To test and compare the models, one common metal forming processes is simulated: deep drawing of a square-cup. The sensitivity graphs showing each of the three friction models together is given at the end. One other conclusion although not major part of this work is that Amonton-Coulomb is not the best model suited for contact conditions in metal forming processes, because Wriggers et al. model and Molinari et al. model provide better results for modelling bends and corners.     

On the least time suboptimal control of nonlinear processes

A design procedure is presented leading to a least time suboptimal feedback control law for nonlinear systems in the presence of “small disturbances”. The proposed method is based on the theory developed for a small-deviation suboptimal control law for the case of linear systems. To clarify the method, a problem of guiding an aircraft to a terminal take-off area in the least time is given as a simulation example.     

同行评议制──方法、理论、功能、指标

同行评议作为决策的一种辅助手段，在我国以及美英等国已被许多部门广泛采用。同行评议往往与一个国家科学资源的分配以及不同层次科技决策有关，因而受到人们的极大关注。为对同行评议制的机制有更深入的认识，更好地发挥其在科技管理中的作用，本文在给出同行评议可操作的定义及方法的一般描述后，着重从政策科学与科学社会学角度探讨了同行评议的本质及其社会功能，进而提出一套评价同行评议制运作的定性指标体系。     

On the set-valued approach to optimal control of sliding mode processes

This paper is devoted to a theoretic framework for a general optimal control problem (OCP) associated with the classic sliding mode process. The sliding dynamic behavior is interpreted here as a special kind of additional constraints related to the main optimization problem. We are specially interested in the development of some adequate constructive approximations of the original OCPs. The mathematical approach based on the set-valued analysis allows to study the discontinuity of sliding mode dynamics in the abstract setting. Moreover, we also establish some sensitivity properties of the optimal solutions. The obtained results provide an universal analytical tool for the corresponding conceptual approximation schemes related to the original OCPs. The constructive approximations proposed in this paper are numerically stable and can be applied to various classes of optimal control processes governed by the affine control systems.     

科学道德建设要“四管齐下”

在两院院士大会即将召开之际,中科院院长、中科院学部主席团执行主席路甬祥院士就科学道德建设问题对记者发表了谈话,现摘要如下:在当前科技环境下,科学不端行为已经成为一个不容忽视的社会问题。仅仅依靠科学家的自律是远远不够的,还要高度重视道德教育、社会监督和科研机构内部的制度建设。尽管近年来我国一些科学组织和科学研究机构已经制定了一些针对科学工作者行为的规范性文件,但必须认识到,我国目前还缺乏具体有力的监督、约束和惩戒机制,对科学不端行为的社会监督与控制缺乏相应的制度保障。近年来,由于市场经济大潮的冲击,以及科技…