MONTE CARLO SIMULATION OF THE ION BEAM ENHANCED DEPOSITION OF SILICON NITRIDE FILMS

In this paper, the growth process of silicon nitride films by ion beam enhanced depo-sition (IBED) is investigated by using the dynamic Monte Carlo simulation, which is based on the binary collision approximation. The effects of the incident angles, energies of the bombarded ions and the interaction potentials on the composition of the films are discussed. The successive and alternate deposition process of silicon and implantation of nitrogen ions have been applied to simulate the actual continuous and synchronous process of IBED. The relationship between the calculated composition of the films and the ion/atom arrival ratio of implanted nitrogen ions to deposited silicon atoms has been established. The composition profile obtained by computer simulation is in good agreement with the experimental results.     

吊片法动态湿润实验系统

流体动态湿润是非常普遍的自然现象并在各工程领域有重要应用.湿润动力学研究仍面临诸多困难和挑战:该领域的核心问题,即接触线的真实移动机制目前仍未被很好地解决;已有实验结果以牛顿流体为主,对于更常见、更复杂的非牛顿流体的研究近几年刚刚开始,研究成果非常有限.高精度实验测量是湿润动力学研究的基础.本文组建了一套基于Wilhelmy吊片法的动态湿润实验系统,以动态接触角与接触线移动速度测量为核心,兼备流体表面张力和流变性等动态湿润重要影响因素的测量功能,辅以样品密封配置、超声波清洗和精密控温等装置.通过对实际测量校验,证明了系统的可靠性和高精度.     

Impulsive dynamics of a flexible arm: analytical and numerical solutions

Impulsive motion of a flexible, beam-like arm is investigated in this paper. The arm is attached to an inertial system through a revolute joint. A modelling approach and an analytical solution are outlined for this problem. Comparisons are presented between analytical and numerical solutions. Finite motion due to an impulsive event is also considered by simulations, and the results are compared to experimental data.     

一类含时变间隙的强非线性相对转动系统分岔和混沌

建立一类具有时变间隙的两质量相对转动系统的强非线性动力学方程.应用MLP方法求解出变换参数,并运用多尺度法求解该系统发生1/2亚谐共振时的分岔响应方程,采用奇异性理论分析得到系统稳态响应的转迁集,并且得到系统在非自治情形下的分岔特性以及系统的分岔形态.最后通过数值仿真得到系统在间隙和阻尼参数变化下的分岔和混沌行为,发现随着系统参数变化系统将出现周期运动、倍周期运动以及混沌等多种不同的运动形态.     

THE DYNAMIC ANALYSIS OF A BEAM-MASS SYSTEM DUE TO THE OCCURRENCE OF TWO-COMPONENT PARAMETRIC RESONANCE

The objective of this paper is an analytical and numerical study of the dynamics of a beam--mass system. Special attention is given to the phenomena arising due to the motion of the attached mass and modal interactions produced by the existence of multi-component, specifically two-component, parametric resonance under primary resonance. The two-component parametric resonance occurs when the sums or the differences among internal frequencies are the same, or close, as the dimensionless speed parameter of the moving mass. The effects of two-component parametric resonance post on dynamic condition are investigated. Resonance generated by more than two-component modes are neglected due to its remote probability of occurrence in nature.The mechanics of the problem is Newtonian. Based on the assumption that when the moving mass is set in motion the mass is assumed to be rolling on the beam, the mechanics, including the effects due to friction and convective accelerations, of the interface between the moving mass and the beam are determined.Based on the Bernoulli-Euler beam theory, the coupled non-linear equations of motion of an inextensible beam with an attached moving mass are derived. By employing Galerkin procedure, the partial differential equations which describe the motion of a beam-mass system are reduced to an initial-value problem with finite dimensions. The method of multiple time scales is applied to consider the solutions and the occurrence of internal resonance of the resulting multi-degree-of-freedom beam--mass system with time dependent coefficients.     

THE NON-LINEAR DYNAMIC BEHAVIOR OF AN ELASTIC LINKAGE MECHANISM WITH CLEARANCES

In terms of Newton two-state model, by choosing two sets of generalized co-ordinates, this paper develops a unified dynamic model between the separation and collision process for the elastic linkage mechanism. This model incorporates the effects of rigidity and elasticity coupling and the angular velocity of crank is assumed to be variable in the operation. In addition, this paper provides a more simple and practical numerical solution method for convenient analysis. Through an example, the dynamic responses of the elastic linkage mechanism with clearances are analyzed, both the effects of elasticity and clearance on the dynamic behaviors of the mechanism are analyzed simultaneously and the non-linear behaviors caused by the clearance joints are analyzed by the dynamic model of rigid mechanism.     

Dynamic analysis of clamp band joint system subjected to axial vibration

Clamp band joints are commonly used for connecting circular components together in industry. Some of the systems jointed by clamp band are subjected to dynamic load. However, very little research on the dynamic characteristics for this kind of joint can be found in the literature. In this paper, a dynamic model for clamp band joint system is developed. Contact and frictional slip between the components are accommodated in this model. Nonlinear finite element analysis is conducted to identify the model parameters. Then static experiments are carried out on a scaled model of the clamp band joint to validate the joint model. Finally, the model is adopted to study the dynamic characteristics of the clamp band joint system subjected to axial harmonic excitation and the effects of the wedge angle of the clamp band joint and the preload on the response. The model proposed in this paper can represent the nonlinearity of the clamp band joint and be used conveniently to investigate the effects of the structural and loading parameters on the dynamic characteristics of this type of joint system.     

A SIMPLE MODEL TO ESTIMATE THE IMPACT FORCE INDUCED BY PISTON SLAP

The dynamics of piston's secondary motion (lateral and rotational motion) across the clearance between piston and cylinder inner wall of reciprocating machines are analyzed. This paper presents an analytical model, which can predict the impact forces and vibratory response of engine block surface induced by the piston slap of an internal combustion engine. A piston is modelled on a three-degree-of-freedom system to represent its planar motion. When slap occurs, the impact point between piston skirt and cylinder inner wall is modelled on a two-degree-of-freedom vibratory system. The equivalent parameters such as mass, spring constant, and damping constant of piston and cylinder inner wall are estimated by using measured (driving) point mobility. Those parameters are used to calculate the impact force and for estimating the vibration level of engine block surfaces. The predicted results are compared with experimental results to verify the model.     

叶顶间隙大小和壁面相对运动对低速轴流压气机孤立转子性能的影响

本文针对一低速轴流压气机孤立转子,利用数值方法分析了不同叶顶间隙大小、机匣和叶顶之间相对运动对其总体性能的影响。 结果表明存在着最佳顶部间隙,原因是顶部区域吸力面边界层引起的损失由于叶顶间隙流的作用而减少,虽然存在泄漏损失,但总损失却小于无顶部间隙时的损失。壁面相对静止和相对运动时的顶部区域二次流和损失分布有着明显的区别,因此某些没有考虑壁面相对运动的平面叶栅实验或计算结果在用于压气机转子设计时,需要经过一定的修正。     

CHAOS AND MULTIPLE PERIODS IN AN UNSYMMETRICAL SPRING AND DAMPING SYSTEM WITH CLEARANCE

Chaos and multiple periods are presented for the harmonically excited unsymmetrical spring and damping system with clearance. This paper demonstrates the non-linear behaviour of the motion through simulation and experiment. Intensive care and caution are taken in the experiments to observe the chaos and the multiple periods properly. The focus in this paper is mainly on the change of the bilinear spring stiffness ratio as a prime factor by which chaotic motions occur from quasi-periodic motion. Other investigations and effects on motion are also discussed for the changing of the extent of clearance. The investigations are based on frequency response curves. To understand the dynamics of the non-linearity of this model, all possible data processing and displaying techniques are taken into account. To observe the overall phenomena of this bilinear system, the resonance curves and the bifurcation diagrams are taken thoroughly for a wide frequency region.