开放式柔性材料力学实验平台的建设与实践

提出建设以机器编号为标识,以计算机网络通信技术为支撑的柔性力学实验平台,在这个平台上,学生自主进行实验,而教师在后台监控学生实验,既提高了学生实验的积极性,也减轻了教师的工作量,使实验设备得到很好的保护和利用.     

Numerical modelling of viscous non-Newtonian effects in lubricating systems

Modern lubricants often exhibit shear-thinning due to the presence of high molecular weight polymers as additives. Therefore the influence of such non-Newtonian effects on the performances of lubricating systems must be predicted. The corresponding fluid film flow is governed by a non-linear partial differential equation, which generalizes the classical Reynolds equation. Having prescribed adequate boundary conditions, this equation is solved by a finite element method with optimal control. The problem of the square slider bearing lubricated by the Rabinowitsch fluid is solved in order to test the accuracy of the numerical scheme. The pressure and velocity fields are given and compared with the corresponding ones obtained for the Newtonian fluid.     

A second-order Lagrangian condition for restricted control problems

We derive a second-order condition for optimal control problems defined by ordinary differential equations with time-varyingconvex restrictions on controls and with endpoint constraints. This condition generalizes theaccessory minimum problem of the calculus of variations.This research was partially supported by Grant No. MCS 76-06756 of the National Science Foundation.     

Stabilization of neutral functional differential equations

In this paper, we prove a necessary and sufficient condition for feedback stabilization of neutral functional differential equations.This paper follows the program of the Gruppo Nazionale per l'Analisi Funzionale e le Sue Applicazioni, Consiglio Nazionale delle Ricerche (CNR), Rome, Italy.     

Vibration reduction in a flexible-link mechanism through synthesis of an optimal controller

In this paper, reduction of vibration of a flexible planar mechanism is achieved through synthesis of an optimal controller. A finite element model, based on the equivalent rigid-link system theory, is used to accurately describe the dynamic behavior of the system. The model, which accounts for geometric and inertial nonlinearities of the mechanism, has been fully validated through experimental tests. In order to be able to employ the classical optimal control theory, a suitable linear model has been derived from the original one by means of a suitable linearization procedure. Vibration reduction can then be obtained by first defining an adequate performance index, which accounts for vibration amplitude, then by solving Riccati’s equation in order to find the controller that minimizes the performance index, i.e. the optimal controller. The results of several tests that have been carried out are also reported, to show the effectiveness of the synthesized control system.     

Response probability density functions of strongly non-linear systems by the path integration method

The paper discusses challenges in numerical analysis and numerical/analytical results for strongly non-linear systems—systems with “signum”-type non-linearities. Such non-linearities are implemented for instantaneous variations of the systems’ parameters, to reduce their mean energy response when subjected to random excitations. Numerical results for displacement and velocity response probability density functions (PDFs), energy response PDFs and various order moments are obtained by the path integration technique. Attention is also given to evaluation of mean upcrossing rate, related to the system's half period, via Rice's formula informally applied to discontinuous response PDFs.