An approach to constructing mathematical models of moving mechanical systems under uncertainty

The paper outlines an approach to constructing a mathematical model of moving mechanical systems under uncertainty. Generalized fuzzy differential equations are used to prove that the model is mathematically correct. The motion of a control oscillator under uncertainty is considered as an example __________ Translated from Prikladnaya Mekhanika, Vol. 43, No. 10, pp. 108–119, October 2007.     

On stability of moving autonomous mechanical systems under uncertainty

Conditions of stability with respect to two measures of autonomous mechanical systems under uncertainty are established by decomposing the phase space of the system, a space of fuzzy sets, and using the natural monotonicity of fuzzy differential equations __________ Translated from Prikladnaya Mekhanika, Vol. 44, No. 2, pp. 119–131, February 2008.     

Conditions for the feasibility of multiple rolling for mechanical systems with multiple contact points

We illustrate a theoretical procedure determining necessary conditions for which simultaneous pure rolling kinetic constraints acting on a mechanical system can be fulfilled. We also analyze the sufficiency of these conditions by generalizing to this case a well known and usually accepted assumption on the behavior of pure rolling constraint. We present in detail the application of the procedure to some significative mechanical systems.     

锻造操作机机构受力性能的多目标优化设计

考虑到锻造操作机的重载特性,为避免因受力不均造成局部受力过大而危及机械结构的安全性,本文以某DDS锻造操作机为例,进行操作机的机构受力性能优化设计。通过灵敏度分析,以关键的机构受力构件在整个工作空间上的平均受力作为优化目标,基于多目标遗传算法NSGA II对操作机的主运动机构进行尺寸优化设计,以合理分配机构受力。与原设计相比,优化后的操作机具有更为良好的整体受力性能。本文的研究工作有助于操作机的机构设计。     

Continuous contact force models for impact analysis in multibody systems

One method for predicting the impact response of a multibody system is based on the assumption that the impacting bodies undergo local deformations and the contact forces are continuous. In a continuous analysis, the integration of the system equations of motion is carried out during the period of contact; therefore, a model for evaluating the contact forces is required. In this paper, two such contact force models are presented, both Hertzian in nature and based upon the direct-central impact of two solid particles.At low impact velocities, the energy dissipation during impact can be represented by material damping. A model is constructed based on the general trend of the Hertz contact law in conjuction with a hysteresis damping function. The unknown parameters are determined in terms of a given coefficient of restitution and the impact velocity. When local plasticity effects are the dominant factor accounting for the dissipation of energy at high impact velocities, a Hertzian contact force model with permanent indentation is constructed. Utilizing energy and momentum considerations, the unknown parameters in the model are again evaluated. The two particle models are generalized to an impact analysis between two bodies of a multibody system.     

Integrated mechanical and control design of underactuated multibody systems

Multibody systems are called underactuated if they have less control inputs than degrees of freedom, e.g. due to passive joints or body flexibility. For trajectory tracking of underactuated multibody systems often advanced modern nonlinear control techniques are necessary. The analysis of underactuated multibody systems might show that they possess internal dynamics. Feedback linearization is only possible if the internal dynamics remain bounded, i.e. the system is minimum phase. Also feed-forward control design for minimum phase systems is much easier to realize than for non-minimum phase systems. However, often the initial design of an underactuated multibody system is non-minimum phase. Therefore, in this paper a procedure for integrated mechanical and control design is proposed such that minimum phase underactuated multibody systems are obtained. Thereby an optimization-based design process is used, whereby the geometric dimensions and mass distribution of the multibody systems are altered.     

Gauss optimization method for the dynamics of unilateral contact of rigid multibody systems

Acta Mechanica Sinica - The discontinuous dynamical problem of multi-point contact and collision in multi-body system has always been a hot and difficult issue in this field. Based on the...     

Cooperative game-oriented optimal design in constraint-following control of mechanical systems

Nonlinear Dynamics - This paper proposes a cooperative game-oriented optimal design problem of robust control for uncertain mechanical systems. State of the concerned system is affected by...     

A NEW STATIC MECHANICS MODEL TO SOLVE CONTACT PROBLEMS IN MECHANICAL SYSTEMS

The coupling of the local contact problems between the components and the deformation of the components in the mechanical system were discovered. A series of coordinate systems have been founded to describe the mechanical system with the contact proble.ms. The method of isolating the boundary of contact body from others has been used to describe the constraint between the contacting points. A more generalized static mechanics model of the mechanical system with the contact problems has been founded through the principle of virtual work, As an application, the model was used to study the multi-teeth engagement problems in the inner meshed planet gear systems. The stress distribution of contact gears was got. A test has verified that the static contact model and the computational method are right.     

Dynamics of mechanical systems involving impact and friction using an efficient contact detection algorithm

In this work, some new results are presented on the dynamics of a class of multibody mechanical systems, involving contact and friction. The main contribution refers to the development of a systematic, accurate and efficient method for detecting contact among the components of a system of solid bodies. For some simple geometries, this task is achieved by employing analytical means. For systems possessing components with complex geometric shapes a more involved numerical methodology is developed. In both cases, once a potential contact point is detected, the common tangent plane and normal vector are located and the penetration depth is calculated, leading to determination of the force arising between the contacting bodies. This information is then passed to a solver, providing the full dynamic response of the system. The validity and numerical efficiency of the methodology developed is first demonstrated by considering a number of examples with relatively small geometric complexity but large traditional value and interesting dynamic response. Some new results are obtained and presented on the dynamics of these systems. Finally, the same methodology is also tested in a more complicated and demanding mechanical application.     

力学环境约束下剪切销可靠性分析及优化设计

剪切销是火工装置关键部件,其可靠性不仅表现为点火作用下可靠剪断,还表现为受力学环境激励不发生断裂。本文中以多项式混沌展开方法为基础,建立了力学环境约束下的剪切销分析模型,结合序贯优化与可靠性分析方法,提出了剪切销可靠性优化设计的思路。以某型火工作动装置为应用实例,依据实用的力学环境,进行了剪切销可靠性分析及优化设计,揭示了设计参数与力学环境之间的关系,并获得了影响可靠性的关键参数。最后,开展了优化后的火工作动装置实验测试,结果佐证了优化设计的有效性。     

水平井分段采油优化模型

考虑水平井的分段采油,研究了封闭油藏、定压油藏、底水油藏三类油藏的渗流模型,建立了以水平段每段长度和中心点位置为研究对象的新优化模型,并对水平井分段数、每一段的长度及距离跟端位置等待优化的问题利用遗传算法最终给出了一套具有实际应用价值的最优分段方案。     

A critical review of microscale mechanical testing methods used in the design of microelectromechanical systems

Microelectromechanical systems (MEMS) technologies are evolving at a rapid rate with increasing activity in the design, fabrication, and commercialization of a wide variety of microscale systems and devices. The importance of accurate mechanical property measurement for successful design was realized early on in the development of this field. Consequently, there exist many different techniques to measure quantities such as the Young's modulus (E), yield strength (σ _Y ), fracture strength (σ _F ), residual stress (σ _F ), and residual stress gradient (∇σ _R ) of microscale structures and materials. We review and critically compare several of the important techniques including the microtension test, axisymmetric plate bend test, microbeam bend test, M-test, wafer curvature measurements, dynamic (resonant) tests, fabrication of passive strain sensors, and Raman spectroscopy. We discuss the characteristics of typical test structures, and the common sources of structure-related errors in measurement. A rational approach for the selection of test techniques for the design of microsystems is suggested.     

Constrained mechanical systems and gradient systems with strong Lyapunov functions

The characteristics of stationary and non-stationary gradient systems with strong Lyapunov functions are studied. The conditions under which holonomic mechanical systems, generalized Birkhoff systems and generalized Hamilton systems can be considered as gradient systems are given. The characteristics of the gradient systems can be used to study the stability of the mechanical systems. Some examples are given to illustrate the application of the results.     

The Bauschinger effect and its role in mechanical anisotropy

A new relationship has been obtained experimentally between the amount of pre-strain and the decrease of yield stress due to the Bauschinger effect. From this relation, the yield criterion including the concept of kinematical hardening has been derived. This criterion has been successfully applied to the strain-induced mechanical anisotropy of isotropic materials.     

Intelligent design of waste heat recovery systems using thermoelectric generators and optimization tools

Optimal design of thermal systems that effectively use energy resources is one of the foremost challenges that researchers almost confront. Until now, several researches have been made to enhance the performance of major thermal systems. In this investigation, the authors try to make a conceptual design to maximize the electricity demand of Damavand power plant as the biggest thermal system in Middle East sited in Iran. The idea of designing is laid behind applying a number of thermoelectric modules within the condenser in order to recover the waste heat of the thermal systems. Besides, the authors have developed some intelligent tools to elaborate on the performance of their proposed model. Firstly, an artificial neural network has been utilized to estimate the potential power generation of the thermoelectric modules. At the second step, computational fluid dynamic solver, FLUENT is used to determine the variation of the temperature through the length of the thermoelectric module assembly. Based on the gained results, an intelligent multi-objective optimization algorithm called Pareto based mutable smart bee is developed to optimize the properties of the thermoelectric component.