一种低机械噪声弱耦合的微机电陀螺敏感结构

研究了一种能够在大气压下达到较高性能的微机电陀螺敏感结构。设计了一种用于敏感垂直于结构平面方向的角速度的、驱动轴和检测轴相似的线振动微机电陀螺敏感结构。用U形梁隔离驱动器、敏感质量块和检测器以降低机械耦合,检测轴采用变面积式检测电容以降低阻尼。推导了振动速率陀螺的机械频率响应特性,分析了机械热噪声和在调谐及非调谐模式下检测电路噪声等效的角速度噪声,分析了梁的刚度矩阵和机械耦合特性,测试了结构的驱动-检测耦合频率响应。在大气压下陀螺检测轴品质因数达到66,机械热噪声为1.89((°)·h-1)/√Hz,理论耦合刚度比大于800。     

Dynamic buckling of partially-sway frames with varying stiffness using catastrophe theory

This work deals with the static and dynamic stability analysis of imperfect partially-sway frames with non-uniform columns. The examined two-bar frames are elastically supported and subjected to an eccentrically vertical load at their joint. Through a linear stability analysis, the effect of the taper ratio of the column cross-section on the buckling capacity of the partially-sway frame is thoroughly discussed. Using a non-linear method an accurate formula has been established for determining the exact asymmetric bifurcation point associated with the maximum load carrying capacity. These findings have been re-derived more readily using Catastrophe Theory (CT) and considering the frame as a one degree-of-freedom (1-DOF) system through an efficient technique. A local analysis allows us to classify, after reduction, the total potential energy (TPE) function of the system to one of the seven elementary Thom׳s catastrophes (with known properties) and to obtain static and dynamic singularity as well as bifurcational sets. It has been found that geometrical and loading imperfections, which are always present in structural engineering problems, have a significant effect on the dynamic buckling loads. The efficiency of the present approach is illustrated via several examples, while results from finite element analyses are in good agreement with the analytical solution presented herein.     

Buckling analysis of nanobeams with exponentially varying stiffness by differential quadrature method

We present the application of differential quadrature(DQ) method for the buckling analysis of nanobeams with exponentially varying stiffness based on four different beam theories of Euler-Bernoulli, Timoshenko, Reddy, and Levison.The formulation is based on the nonlocal elasticity theory of Eringen. New results are presented for the guided and simply supported guided boundary conditions. Numerical results are obtained to investigate the effects of the nonlocal parameter,length-to-height ratio, boundary condition, and nonuniform parameter on the critical buckling load parameter. It is observed that the critical buckling load decreases with increase in the nonlocal parameter while the critical buckling load parameter increases with increase in the length-to-height ratio.     

可能的原子核形状及硬度演化性质:基于能量面计算的系统分析(英文)

基于（β₂,γ,β₄）形变空间下对-形变自洽的原子核能量面计算方法,系统研究分析了50 < Z < 82区偶偶核的形状及硬度演化特征。计算的平衡形变与其它理论预言及存在的实验值进行了对比。从相应的形变势能曲线提取了与β₂及γ相关的硬度参数C_β,C_γ,这与实验观测到的低位β及γ振动带信息相符。还简要讨论了转动情况下的硬度演化,例如基于蜈蚣型E-GOS曲线,表明存在不可忽略的振动效应。Nuclear shape and stiffness evolutions in even-even nuclei with 50 < Z < 82 are systematically analyzed in terms of the pairing-deformation self-consistent nuclear-energy-surface calculation in (β₂,γ,β₄) deformation space. Calculated equilibrium deformations are presented and compared with other theoretical predictions and available experimental data. The stiffness parameters C_β and C_γ respectively related to quadrupole deformations β₂ and γ are determined from the deformation energy curves, which are consistent with the observed low-lying β and/or γ bands. The stiffness evolution under rotation along the yrast line is briefly discussed, e.g., on the basis of the centipidelike E-GOS curves, showing an unnegligible vibration effect.     

Static lateral stiffness of wire rope isolators

This paper presents an analytical model for the static lateral stiffness of Wire Rope Isolators (WRI). The wire rope isolator, which is a passive isolation device, has been widely adopted as a shock and vibration isolation for many types of equipment and lightweight structures. The major advantage of the WRI is its ability to provide isolation in all three planes and in any orientation. The WRI in the lateral roll mode, is required to possess the required lateral stiffness to support and isolate the equipment effectively. The static lateral stiffness of WRI depends mainly on the geometrical characteristics and wire rope properties. The model developed in this paper is validated experimentally using a series of monotonic loading tests. The flexural rigidity of the wire ropes, which is required in the model, was determined from the transverse bending test on several wire rope cables. It was observed that the lateral stiffness is significantly influenced by the wire rope diameter and height of the isolator. The proposed analytical model can be used for the evaluation of lateral stiffness and in the preliminary design of the WRI.     

齿轮箱非线性耦合系统的动力学分析

分别建立了啮合齿轮子系统弯扭耦合振动模型、弹性轴子系统的弯曲振动和扭转振动模型以及齿轮箱弹性箱板子系统的横向振动模型,通过轴承多维刚度矩阵和子结构之间的受力变形协调关系将各子结构的振动模型联立起来,从而得到整个齿轮箱耦合系统的动力学模型。结合相图和庞加莱映射图分析了系统的运动特性,采用功率流方法研究了系统振动能量传递特性及其影响因素,揭示了外部激励和轴承刚度等因素对系统特性的影响,为齿轮箱系统的振动控制与结构设计提供了新的分析方法和理论依据。     

六边形桥墩柔性抗船撞装置抗弯刚度

针对中国自主研发的桥梁柔性抗船撞装置,构建该装置模型:由两个相似的六边形梁为内外钢围以及均布且垂直于六边形各边的防撞圈构成。分析该模型得到在冲击载荷作用下六边形梁的控制方程及相应的初边值条件。利用Laplace变换和数值Laplace逆变换对该方程进行求解,揭示六边形梁在冲击载荷作用下的动态响应。并进一步分析外钢围等效抗弯刚度对抗船撞装置动态响应的影响,发现外刚围结构在冲击载荷作用下存在临界等效抗弯刚度。当外钢围等效抗弯刚度达到该临界值后,该外钢围在冲击载荷作用下可以近似为刚性。     

A Comment on the Low Speed Impact of a Clamped Beam by a Heavy Striker∗

ABSTRACT

An approximate theoretical analysis is presented for a rigid, perfectly plastic clamped beam struck transversely at the mid-span by a mass which produces Finite transverse displacements. An alternative quasi-static procedure is proposed for estimating the dynamic plastic response of a beam when struck by a heavy mass that travels at a low speed. The theoretical basis of this method is explained and the accuracy is examined by an error analysis. Finally, it is suggested that this quasi-static procedure could be used for estimating the dynamic plastic response of other structures that are struck by a heavy mass traveling at a low speed,     

表面织构对界面接触参数影响的实验研究

机械接触表面的接触刚度和接触阻尼是直接影响界面振动水平的两个重要动力学参数。本文介绍了一种测试机械连接界面接触刚度和接触阻尼的实验装置和方法,并针对用两种不同加工方法(激光加工及线切割)加工出的具有不同尺寸织构的试样与光滑平面相接触的界面进行了测量,初步探索了平面接触刚度和接触阻尼的表面织构效应,并得出结论：织构及润滑对接触刚度会产生一定影响,而实验中均未观察到这两者对接触阻尼有明显影响。     

Correlation between Functionated Structure and Nanomechanical Property Profiles of Silsesquioxane Films and Bulks

Three silsesquioxane (SSO) building blocks based on [3-(methacryloxy)propyl]trimethoxysilane (MPMS), [(3-glycidoxy)propyl] trimethoxysilane (GPMS), (vinyl)trimethoxysilane (VMS) and modified with 15 wt-% tetraethoxysilane (TEOS) were prepared using hydrolytic condensation. The hardness, elastic modulus and harmonic contact stiffness for three films [f-MTSSO (film-MPMS-TEOS-SSO), f-GTSSO and f-VTSSO] and bulks (b-MTSSO, b-GTSSO and b-VTSSO) derived from the three SSOs were tested by instrument-indentation testing. Different profiles of nanomechanical properties of the films can be attributed to a different functionality and the functionated structure of the different SSOs. The f-MTSSO shows better mechanical properties which are higher than the other two films containing more OH or OCH₃ groups. For the f-GTSSO with a bulky organic substituent, the unsatisfactory properties resulting from ring opening during hydrolytic condensation and an incomplete crosslinking network are discussed. However, the nanomechanical properties of the three bulks are very different from the corresponding nanomechanical properties of their films: b-VTSSO possesses the best nanomechanical properties (note: not b-MTSSO) among three bulks due to the differences in reaction conditions and chain less flexibility which are also discussed.