三波谐波齿轮传动拍频现象的理论研究

为探讨三波谐波齿轮传动的拍频现象,分析了三波谐波齿轮传动的运动误差源及其频率特性,指出了三波谐波齿轮传动拍频现象产生的机理,从而为三波谐波齿轮传动动态性能的深入研究提供理论依据．     

精密步进谐波系统谐波参数与步进电机匹配问题的研究

 提出了一种高精度的精密步进系统,指出要获得高精度的步进谐波传动系统必须充分考虑谐波传动的啮合性能、加工精度、系统的动态性能和电机的矩频特性及其控制技术的机电性能匹配问题。     

深部地层地应力水平与爆破振动频率特征的相关性

不同的地应力水平对深部岩体爆破振动的频率和能量分布具有重要影响。通过对不同地应力水平的深埋隧洞爆破开挖过程中实测围岩振动信号进行快速傅里叶变换,采用功率谱分析方法研究振动信号在不同频带上的能量分布。研究表明,实测爆破振动的低频振动(50 Hz)能量占总振动能量的百分比随应力水平的提高而增加;爆破振动在其频域中除了有一个主振频率外,还存在多个子频带,且各子频带振动的能量与主频带振动能量的差距随应力水平的提高而减小;伴随爆破破岩过程而发生的应变能瞬态释放效应诱发围岩振动的主频一般比爆炸荷载诱发振动的主频低;在50 MPa或更高应力水平下,应变能释放诱发的振动能量与爆炸荷载诱发振动能量大致相当。     

深部地层地应力水平与爆破振动频率特征的相关性

不同的地应力水平对深部岩体爆破振动的频率和能量分布具有重要影响。通过对不同地应力水平的深埋隧洞爆破开挖过程中实测围岩振动信号进行快速傅里叶变换,采用功率谱分析方法研究振动信号在不同频带上的能量分布。研究表明,实测爆破振动的低频振动(<50 Hz)能量占总振动能量的百分比随应力水平的提高而增加;爆破振动在其频域中除了有一个主振频率外,还存在多个子频带,且各子频带振动的能量与主频带振动能量的差距随应力水平的提高而减小;伴随爆破破岩过程而发生的应变能瞬态释放效应诱发围岩振动的主频一般比爆炸荷载诱发振动的主频低;在50 MPa或更高应力水平下,应变能释放诱发的振动能量与爆炸荷载诱发振动能量大致相当。     

机电集成压电谐波电机传动系统非线性自由振动分析

设计集压电驱动、谐波传动及活齿传动为一体的机电集成压电谐波电机,并分析其工作机理。借鉴行星齿轮传动理论,建立传动系统动力学模型。利用Linz Ted-Poincaré法推导传动系统非线性频率特性方程及位移响应方程,分析传动系统的非线性频率变化规律及时域响应特点;通过ANSYS有限元软件对频率进行验证。结果表明,传动系统非线性由啮合齿数变化引起,啮合齿数越少系统非线性越显著;系统位移响应受非线性影响最明显、微弱的分别为波发生器x及u向;利用有限元仿真验证动力学模型的正确性。     

永磁交流伺服精密驱动系统机电耦合振动特性分析

为了研究永磁交流伺服精密驱动系统中存在的多物理过程、多参量复杂耦合关系,提出了对该系统进行机电耦合振动特性分析的观点。从全局机电耦合的角度,对永磁交流伺服精密驱动系统进行了机电耦合分析,将该系统归纳为三质量两轴系统,建立了三质量两轴系统的机电耦合振动数学模型和仿真模型,仿真分析了由于电流调节器参数、阻尼、谐波扰动、间隙以及负载扰动等因素引起的系统机电耦合振动动态过程,并通过实验验证了机电耦合振动仿真模型的正确性。该机电耦合振动特性分析对提高系统的动态性能具有重要的意义。     

照明用大功率无桥LED驱动电路输入电流谐波分析

对作者介绍的照明用大功率无桥LED驱动电路的输入交流工频电流波形在设定电路条件后的频谱和谐波含量进行了分析和计算,其结果是,在电路最低工作频率以下的频率范围内基本不存在谐波成分,电路输入电流的总谐波含量THD随最小输入电流脉冲宽度T₀(min) 增大而上升,随电路的输出直流电压与输入交流电压有效值的比U_o/U_i的增大而下降.并指出在电路的输入端需要一个滤波电路,分析了滤波电路的滤波效果,给出了滤波电路的设计方法.     

一种空间润滑装置的流固耦合振动

面向空间润滑中常采用的被动润滑不及时的问题,提出一种主动润滑方法。为了达到主动润滑的目的,提出了一种结构简单易于加工的压电微喷润滑装置。压电微喷装置的固有频率和振型对液滴形成和喷射效果具有重要作用。首先建立考虑压电-流固耦合和压力波传播效应的等效模型。进而利用有限元法对整个装置的固有频率和相应的振型进行分析。最后利用激光测振仪对整个机构实际的振型和固有频率进行测量。通过结果对比验证此流固耦合模型的有效性和方法的实用性。     

On the forced vibration analysis of Timoshenko nanobeams based on the surface stress elasticity theory

This paper aims to present nonlinear forced vibration characteristics of nanobeams including surface stress effect. By considering the local geometrical nonlinearity based on von Karman relation, a new formulation of the Timoshenko beam model is developed through the Gurtin–Murdoch elasticity theory in which the effect of surface stress is incorporated. By using a variational approach on the basis of Hamilton’s principle, the size-dependent equations of motion and associated boundary conditions are obtained. The generalized differential quadrature (GDQ) method is employed to discretize the non-classical governing differential equations over the spatial domain by using the shifted Chebyshev–Gauss–Lobatto grid points. Subsequently, a Galerkin-based numerical approach is put to use in order to reduce the set of nonlinear equations into a time-varying set of ordinary differential equations of Duffing-type. In the next step, the time domain is discretized via spectral differentiation matrix operators which are defined based on the derivatives of a periodic base function. Finally, the pseudo arc-length method is employed to solve the resulting nonlinear parameterized algebraic equations. The frequency–response curves for forced vibration behavior of nanobeams including the effect of surface stress are predicted corresponding to various values of beam thickness, length to thickness ratio and surface elastic constants. It is revealed that by incorporating the surface stress effect, the maximum amplitude occurs at lower excitation frequencies and the wide of region of the response tends to decrease.     

大型空分设备冷箱的钢结构应力计算分析

介绍了48000m3/h空分设备冷箱所受主要载荷:珠光砂、风载荷和地震载荷的计算,分析了冷箱钢结构中的关键部位在组合应力作用下的受力情况及取材。     

传动轴扭矩测量装置的结构设计及实验分析

为解决传动轴扭矩难以实现长期监测的问题,设计一种新型传动轴扭矩测量装置.在传动轴表面焊接一底座,用紧固螺栓把扭矩测量装置固定在上面,通过测量敏感梁的应变测出所受扭矩.对自制的实验扭矩测量装置利用ANSYS Workbench进行静力学分析,同时进行静态特性和动态响应实验,得出特性指标和响应曲线,实验结果证明:该扭矩测量装置可行有效,对解决传动轴扭矩的监测具有实际指导意义.     

Modeling of hybrid vibration control for multilayer structures using solid-shell finite elements

A self-control method of vibrations is presented in this paper. This method combines the passive damping capabilities afforded by viscoelastic materials with the active control properties associated with piezoelectric materials. Active control is introduced, using the piezoelectric properties, in order to improve the reduction in vibration amplitudes that can be obtained by viscoelastic passive damping alone. To this end, a filter has been mounted between the sensors and the actuators. The resulting nonlinear problem is discretized using the recently developed solid-shell finite element SHB20E, due to the advantages it offers in terms of accuracy and efficiency as compared to standard finite elements with the same geometry and kinematics. In order to solve the discretized problem, a resolution method using DIAMANT approach is developed. A set of selective and representative numerical tests are performed on multilayer plates to demonstrate the interest of the proposed damping model.     

General harmonic balance solution of a cracked rotor-bearing-disk system for harmonic and sub-harmonic analysis: Analytical and experimental approach

The effect of crack depth of a rotor-bearing-disk system on vibration amplitudes and whirl orbit shapes is investigated through a general harmonic balance technique and experimental verification. Two models of the crack, which are the breathing and the open crack models, are considered. Finite element models and general harmonic balance solutions are derived for breathing and open cracks which are valid for damped and undamped rotor systems. It is found via waterfall plots of the system with a breathing crack that there are large vibration amplitudes at critical values of crack depth and rotor speed for a slight unbalance in the system. The high vibration amplitudes at the backward whirl appear at earlier crack depths than those of the forward whirl for both crack models. Resonance peaks at the second, third and fourth subcritical speeds emerge as the crack depth increases. It is shown that the unique signature of orbits for the breathing crack model which have been verified experimentally can be used as an indication of a breathing crack in the shaft. In addition, the veering in the critical frequencies has been noticed in the open crack case.     

Dynamical responses for a vertical vibration model of a four-roller cold rolling mill under combined stochastic and harmonic excitations

Considering that random fluctuations can affect the rolling process of cold rolling mills, leading to abnormal cold mill performance and defects in the rolled product. Therefore, it is crucial to study the influence of random fluctuations on the system of cold rolling mills. In this paper, taking a model of the vertical vibration of a four-roller cold rolling mill under harmonic excitation as a prototype class for a real system, the effects of random fluctuations on the system response are analyzed. Firstly, based on the deterministic vertical vibration model of a four-roller cold rolling mill under harmonic excitation, a stochastic vertical vibration model of a four-roller cold rolling mill with random fluctuation as Gaussian white noise is introduced. Subsequently, the vertical vibration model of a four-roller rolling mill is theoretically analyzed by the averaging method and the stochastic averaging method, respectively. The effectiveness of the proposed theoretical method is verified by numerical simulation results, and the influences of harmonic excitation and random excitation on the system response are also investigated in detail. Finally, the results show that the noise induces the occurrence of stochastic transitions and bifurcations, and the steady-state probability density function and time history diagrams are given to further explain the existence of these dynamic phenomena. The related research can provide theoretical guidance for the realization of vibration control and reliability design in the four-roller cold rolling mill system.     

大口径望远镜水平轴系的模态分析

根据某大口径望远镜水平轴系的结构设计方案，利用结构分析软件I—DEAS，建立了结构分析模型。求得了水平轴系前几阶固有频率和振型图。分析结果显示出了水平轴各部分结构振动的强弱分布，为结构的动力学优化设计提供了可靠的依据。提出了次镜支撑的偏置十字型中心结构，该结构具有较高的谐振频率，因此可以用于大口径望远镜中。     

大马力拖拉机驱动桥有限元分析及试验研究

驱动桥作为拖拉机的传动和承载部件,受力较大且使用频繁,通过对桥壳模型的有限元分析,可以验证设计的安全性并可以通过分析结果来改进设计。首先采用Pro/E对拖拉机驱动桥壳、转向节、半轴进行三维建模并导入Hypermesh中进行有限元分析的前处理工作,然后将导出的文件输入ANSYS中进行有限元分析。最后通过桥壳的刚度试验和疲劳试验验证了此驱动桥的安全性,并给出了改进意见。     

The analysis of residual stress in glass-to-metal seals for solar receiver tube

The solar receiver tube is a key component in the parabolic trough solar thermal power system. Breakage of glass-to-metal sealing is main cause for damages of receivers in existing power plants. The residual stresses that are generated during the cooling process of the seal can decrease the seal strength and induce the breakage of the glass-to-metal sealing. Residual stresses were simulated by finite element software ANSYS and measured experimentally by photoelastic techniques. In order to lower the seal failure probability, the effects of the component dimensions were analyzed using finite element method. The simulation results agreed with the measurement results. The dangerous tensile stresses occur not only at the glass–metal interface but also on the outer surface of glass tube near the sealing area. When the depth of metal embedded into glass increases, the magnitude of residual stress decreases and the sealing strength will increase. The results of this study have important implications on the optimization of seal configuration in the solar receiver tubes.     

Free vibration and stability of functionally graded plates according to a 2-D higher-order deformation theory

Natural frequencies and buckling stresses of plates made of functionally graded materials (FGMs) are analyzed by taking into account the effects of transverse shear and normal deformations and rotatory inertia. The modulus of elasticity of the plates is assumed to vary according to a power-law distribution in terms of the volume fractions of the constituents. By using the method of power series expansion of displacement components, a set of fundamental dynamic equations of a two-dimensional (2-D) higher-order theory for rectangular functionally graded (FG) plates is derived through Hamilton’s principle. Several sets of truncated approximate theories are applied to solve the eigenvalue problems of FG plates with simply supported edges. In order to assure the accuracy of the present theory, convergence properties of the fundamental natural frequency are examined in detail. Critical buckling stresses of FG plates subjected to in-plane stresses are also obtained and a relation between the buckling stress and natural frequency of simply supported FG plates without in-plane stresses is presented. The distributions of modal displacements and modal stresses in the thickness direction are obtained accurately by satisfying the surface boundary conditions of a plate. The modal transverse stresses have been obtained by integrating the three-dimensional equations of motion in the thickness direction starting from the top or bottom surface of a plate. The present numerical results are also verified by satisfying the energy balance of external and internal works are considered to be sufficient with respect to the accuracy of solutions. It is noticed that the present 2-D higher-order approximate theories can predict accurately the natural frequencies and buckling stresses of simply supported FG plates.     

A study of the vibration of delaminated beams using a nonlinear anti-interpenetration constraint model

In this paper, the vibration of a beam with an embedded delamination is studied within the formalism of Timoshenko beam theory. As the free-body model results in dramatic interpenetration of the delaminated sublaminates that is physically impossible, a novel nonlinear constraint model is introduced to prevent the interpenetration. Unlike the previous model in the literature, the present constraint model automatically produces the zero or a proper contact traction following any given contact law without specifying whether the sublaminates are in contact or not before solving the problem. The resulted nonlinear partial differential equations are solved numerically. It is found that the predicted vibration of the beam with the constraint model is remarkably different from that without it. Moreover, the vibration mode of the beam depends upon the type of the contact function.     

超材料混凝土单胞骨料的有阻尼自由振动特性研究

超材料概念的提出激发了功能混凝土的研究热潮,超材料混凝土的振动研究也成为热点之一。基于one-dimensional spring-mass system模型,建立了单胞骨料有阻尼自由振动的三维振动模型,模型中软涂层和砂浆均用弹簧等效代替,并计算了等效长度、等效刚度和等效阻尼。以单胞骨料为研究对象,用达朗贝尔原理导出有阻尼自由振动的非线性控制方程,获得系统的固有频率和振动解。用MATLAB软件编程进行算例分析,讨论初始条件、骨料内部尺寸及软涂层弹性模量等参数对固有频率和振动特性的影响。算例分析表明：非线性振动与线性振动中的无阻尼固有频率和有阻尼固有频率间的关系并不一致;阻尼对非线性振动固有频率的影响比线性振动的大;初速度对初相位的影响(非线性)比初始位移的大(“类线性”),初始条件既影响振幅,又影响固有频率,也会影响超材料混凝土抗冲击能力。减幅系数η随初始速度、软涂层弹性模量的增大而减小,随软涂层厚度的增大而增大,这可通过减小初始速度、增大软涂层弹性模量、增加重核的大小等方式降低减幅系数对超材料混凝土结构的影响。这对超材料混凝土抵抗高频荷载和冲击荷载的研究有工程指导价值。