铸造式和焊接式主轴箱体的动态特性对比分析

利用有限元法和试验模态法对立式加工中心的铸造式和焊接式两种结构的主轴箱体进行了模态分析,分别获得了其前六阶固有频率和振型。通过对比两种方法获得的结果,验证了有限元分析模型的有效性。研究表明,两种主轴箱体的阻尼比接近,但焊接式主轴箱体的各阶固有频率均要高于铸造式主轴箱体的各阶固有频率。并且铸造式主轴箱体的固有频率更接近于机床主轴的常用工作频率,焊接式主轴箱体的则远离此频率。因此对于常用主轴转速而言,焊接式主轴箱体的动态性能要优于铸造式主轴箱体的动态性能。     

An experimental and analytical investigation of the dynamic characteristics of a flexible sandwich plate filled with electrorheological fluid

This paper investigates the dynamic characteristics of a sandwich plate embedded with an electrorheological (ER) fluid. A laser holographic interference experiment and modal testing were conducted to identify natural frequencies, modal damping and shapes of the composite structure, under different electric fields applied to the fluid domain. Moreover, the influence of the ER effect on the structural dynamic responses were recorded. It was found that both of the damping and natural frequencies of the sandwich plate increase monotonously with an increasing electric field; while, at the same time, the resonant peaks of the frequency response and the amplitudes of dynamic responses decrease. Furthermore, based on the special properties of the ER fluid, a discrete dynamic model of the sandwich plate containing ER fluids was developed and validated. The numerical simulation verifies the effect of the ER material on the structure, and the calculated dynamic parameters show the coincident changes with the experimental results.     

A quadratic polynomial signal model and fuzzy adaptive filter for frequency and parameter estimation of nonstationary power signals

Accurate estimation of amplitude, phase and frequency of a sinusoid in the presence of harmonics/inter harmonics and noise plays an important role in a wide variety of power system applications, like protection, control and state monitoring. With this objective, the paper presents a novel hybrid approach for the accurate estimation of dynamic power system frequency, phasor and in addition to suppressing the effect of harmonics/interharmonics and noise in the voltage and current signals. The algorithm assumes that the current during a fault occurring on a power system consists of a decaying dc component, and time variant fundamental and harmonic phasors. For accurate estimation of fundamental frequency, phasor, decaying dc and ac components in the fault current or voltage signal, the algorithm uses a quadratic polynomial signal model and a fuzzy adaptive ADALINE filter with a modified Gauss–Newton algorithm. Extensive study has been carried out to demonstrate the performance analysis and fast convergence characteristic of the proposed algorithm. The proposed method can also be implemented for accurate estimation of dynamic variations in the amplitude and phase angles of the harmonics and inter harmonics mixed with high noise conditions.     

Effect of transmission error on the dynamic behaviour of gearbox housing

The dynamic response of gearbox remains a paramount concern because of noise generation. This work is concerned with numerical simulation of the overall dynamic behaviour of a parallel helical gear transmission. A dynamic sub-structuring method using different types of substructure (carrying and slave) is made to determine the natural frequencies and the corresponding mode shapes. The structure to be investigated is subdivided into components or sub-structures, which are then analyzed independently for natural frequencies and mode shapes. A numerical model taking into account the elastic coupling between the various components of a gearbox was developed. It allows studying and analyzing the dynamic behaviour of elastic housing in the presence of gear process. The static transmission error is introduced as a vibratory excitation source and it is represented by time-varying mesh stiffness. The discretization of the housing deformation energy and the kinetic energy expressions using plate finite elements leads to constructions of the stiffness and the mass matrixes. In dynamic analyses, time-discretization based on the Newmark method is used. The different equations governing movement of gearbox are established in a truncated modal base deduced from the average characteristics of the structure. A gearbox example is presented, and analyzed. A presentation and discussion of the numerical results was emphasized. The numerical results allow us to conclude on the dominant phenomena of the overall dynamic behaviour of the gear transmission.     

FL-26风洞模型支撑系统动态仿真分析

研制具有良好力学特性的大迎角模型支撑系统,是解决先进、高机动飞行器大迎角气动力问题的关键技术之一。阐述了FL-26风洞大迎角模型支撑系统结构形式,对系统的动态特性和动力响应进行了有限元分析,获得了大迎角模型支撑系统自由振动时的模态频率和模态振型,以及试验段气动噪声作用下的加速度响应和动应力。仿真结果表明:大迎角模型支撑系统动态特性较好,不同方向的动力响应主频及均方根值分布较为离散且数量级相差较大,未出现共振现象。     

Alternative method for identification of the dynamic properties of bolted joints

Bolted joints often have a significant effect on the dynamical behavior of assembled mechanical structures. An accurate model of an assembled structure depends on correctly determining and identifying the dynamic parameters of bolted joints. This paper presents an alternative method for identifying these dynamic parameters using structure??s natural frequency and damping. A novel experiment is designed with a test piece consisting of only bolted joints, with the governing equations of the test piece established using the analytical method. The relationships between the equivalent dynamic parameters of the bolted joints and the natural frequencies and damping ratios of the test piece are determined for both the normal and tangential directions. The parameter identification problem for bolted joints is thus transformed into a test of the natural frequency and the damping ratio of the test piece. In order to check the accuracy of the proposed identification method, the test piece and bolted joints are modeled using the finite element method (FEM) and the dynamic properties of the test piece are analyzed. The maximum error between the natural frequencies of the FEM result and the experimental values in the normal and tangential models are 4.73% and 0.34%, respectively. The result indicates that the proposed method is valid for the dynamic parameter identification of bolted joints.     

基于振动噪声的柴油机油底壳结构优化研究

基于模态参数的动态特性,针对某型柴油机振动噪声超标问题,利用有限元软件ABAQUS的模态分析功能对主要噪声源油底壳的自由模态进行计算,从固有频率方面着手优化其结构。优化后的其固有频率大幅提高,经整机振动噪声测试,减振降噪效果明显,解决了振动噪声超标问题。     

Noise floor and dynamic range analysis of a microwave attenuation measurement receiver from 50 MHz to 26.5 GHz

The noise floor and dynamic range of a proposed voltage-ratio based microwave attenuation measurement receiver are analysed. The thermal noise and phase noise effect on attenuation measurement is studied. For frequencies higher than 1 GHz, the receiver employs a lock-in amplifier with a coherent frequency reference to minimize the phase noise effect and achieve very wide dynamic range of attenuation measurement. The equivalent noise floor at the receiver mixer output port is found to be around −172 dBm. The dynamic range of the receiver is 181-175 dB from 50 MHz to 26.5 GHz. Measurement results of a 0-170 dB synthesized step attenuator at 26 GHz is given to verify the performance of the proposed receiver.     

利用动态靶标谐波特性评价光电经纬仪的跟踪性能

提出了一种利用动态靶标实现光电经纬仪跟踪性能等效正弦评价的新方法。分析了动态靶标目标及相应跟踪误差的幅度谱和功率谱特性,提出将动态靶标看作由有限项基频谐波和整数倍基频高次谐波的加权和组成的谐波源。根据被检光电经纬仪跟踪性能设计等效正弦信号,利用动态靶标产生与等效正弦信号同频率的谐波信号完成光电经纬仪跟踪误差系统在该频率下幅频特性函数值的测试。等效正弦的幅值和测得的幅频特性值乘积即为跟踪等效正弦信号的跟踪误差最大值,从而实现了跟踪性能评价。利用该方法测得方位方向的最大跟踪误差为0.65′,远小于4′的指标要求,而利用动态靶标直接检测的值为4.7′。实验表明该方法准确、可行,同时避免了直接利用动态靶标检测时可能使跟踪伺服系统出现过度校正的问题。     

基于LHS冷却塔敏感性分析及频率估算

现有冷却塔结构自振频率主要基于有限元分析手段,缺乏简单有效的冷却塔自振频率估算公式。为解决该问题,以国内某179m高的大型冷却塔为基准塔,首先,通过改变结构典型参数(塔高、喉部高度、喉部直径、进风口高度和支柱截面积)获得基准塔的38个模型并进行动力特性分析,同时提炼出基频和倾覆频率随结构参数的变化规律;然后,用扰动法和拉丁超立方抽样(Latin hypercube sampling,简称LHS)两种方法进行结构自振频率参数的敏感性分析,获取了不同阶数下各参数的敏感因子,在此基础上,创新性地拟合提出考虑敏感因子权重值的多参数基频和倾覆频率的实用估算公式;最后,验证自振频率估算公式的精度,选择课题组已有研究的冷却塔进行了误差分析。揭示结构参数对大型冷却塔自振频率的敏感性具有重要意义,可为冷却塔结构抗风抗震设计、动力特性优化设计等提供指导。     

变频循环泵振动噪声特性试验研究

为了较为系统地理解变频循环泵的振动噪声特性,以一台比转速为200和最高转速为5600r/min的变频循环泵为研究对象,在背景噪声小于16dB的半消音室和固有频率小于10Hz的振动试验台的试验条件下,对不同流量和转速下的船用循环泵振动噪声特性进行深入的试验研究。试验结果表明:循环泵的总体噪声水平低于66 dB(A),水力诱导的空气传递噪声小于3dB(A);噪声的主要激励频率为工频及谐波,总体结构振动烈度低于1.1mm/s,振动烈度与转速具有良好线性函数关系;结构振动烈度的大小排序为电机、法兰、电机座和泵体.     

Modal identification of spindle-tool unit in high-speed machining

The accurate knowledge of high-speed motorised spindle dynamic behaviour during machining is important in order to ensure the reliability of machine tools in service and the quality of machined parts. More specifically, the prediction of stable cutting regions, which is a critical requirement for high-speed milling operations, requires the accurate estimation of tool/holder/spindle set dynamic modal parameters. These estimations are generally obtained through Frequency Response Function (FRF) measurements of the non-rotating spindle. However, significant changes in modal parameters are expected to occur during operation, due to high-speed spindle rotation.The spindle's modal variations are highlighted through an integrated finite element model of the dynamic high-speed spindle-bearing system, taking into account rotor dynamics effects. The dependency of dynamic behaviour on speed range is then investigated and determined with accuracy. The objective of the proposed paper is to validate these numerical results through an experiment-based approach. Hence, an experimental setup is elaborated to measure rotating tool vibration during the machining operation in order to determine the spindle's modal frequency variation with respect to spindle speed in an industrial environment. The identification of natural frequencies of the spindle under rotating conditions is challenging, due to the low number of sensors and the presence of many harmonics in the measured signals. In order to overcome these issues and to extract the characteristics of the system, the spindle modes are determined through a 3-step procedure. First, spindle modes are highlighted using the Frequency Domain Decomposition (FDD) technique, with a new formulation at the considered rotating speed. These extracted modes are then analysed through the value of their respective damping ratios in order to separate the harmonics component from structural spindle natural frequencies. Finally, the stochastic properties of the modes are also investigated by considering the probability density of the retained modes. Results show a good correlation between numerical and experiment-based identified frequencies. The identified spindle-tool modal properties during machining allow the numerical model to be considered as representative of the real dynamic properties of the system.     

Effect of a dynamic absorber on friction-induced vibration of a rectangular plate

When a plate-like object is rubbed by rubber, friction-induced vibration is generated. To reduce the friction-induced vibration, we experimentally investigate the characteristics of the vibration of a rectangular glass plate. The results show that the frequency of the friction-induced vibration is almost the same as the natural frequency of a glass plate. The vibration is generated when the natural frequency of a rubbing system is close to that of a glass plate. We then examine the effect of a dynamic absorber mounted on the glass plate. The results demonstrate that the damping of a dynamic absorber is effective for suppressing the friction-induced vibration. Numerical simulation is also performed using a simplified analytical model. The calculated results agree qualitatively with the experimental ones.     

Ambient vibration test of building base slab for different ground conditions

It is very important to know the dynamic behavior of base slabs of buildings in earthquake prone areas. The slabs are generally assumed as a rigid diaphragm in structural analysis and design. But their response is considerably affected from ground condition. In this study, the dynamic characteristics of a scaled base slab are determined for different ground conditions. The dimensions of the base slab model are 150 cm long, 100 cm wide and 5 cm thick. This model is designed to be smaller than 20 times from an actual building base. The base slab model is tested for the ground conditions of sand, gravel and clay–silt mixture by ambient vibration test. The dynamic characteristics, such as natural frequencies, modal damping ratios, mode shapes, are identified from collected signals by Operational Modal Analysis method. The first five modes are taken into consideration to compare the effect of ground conditions on the dynamic characteristics. It is observed that the natural frequencies, mode shapes and modal damping ratios are considerably affected from ground conditions. The highest natural frequency is obtained for the gravel ground case. The lowest natural frequency is identified for the clay–silt mixture ground case. The mode shapes changed randomly in each case. But the main modal behaviors are vertical mode and bending modes.     

Mesh relationship modeling and dynamic characteristic analysis of external spur gears with gear wear

Gear wear is one of the most common gear failures, which changes the mesh relationship of normal gear. A new mesh relationship caused by gear wear affects meshing excitations, such as mesh stiffness and transmission error, and further increases vibration and noise level. This paper aims to establish the model of mesh relationship and reveal the vibration characteristics of external spur gears with gear wear. A geometric model for a new mesh relationship with gear wear is proposed, which is utilized to evaluate the influence of gear wear on mesh stiffness and unloaded static transmission error (USTE). Based on the mesh stiffness and USTE considering gear wear, a gear dynamic model is established, and the vibration characteristics of gear wear are numerically studied. Comparison with the experimental results verifies the proposed dynamic model based on the new mesh relationship. The numerical and experimental results indicate that gear wear does not change the structure of the spectrum, but it alters the amplitude of the meshing frequencies and their sidebands. Several condition indicators, such as root-mean-square, kurtosis, and first-order meshing frequency amplitude, can be regarded as important bases for judging gear wear state.     

基于ANSYS的轴承-转子系统动力特性研究

在ANSYS中建立了轴承-转子系统的实体模型,采用Solid185和Solid95单元进行了网格划分,得出了转子系统的固有频率和振型,通过改变油膜刚度获得了转子系统固有频率随油膜刚度的变化规律。结果表明支承刚度对转子系统的动力特性有很大的影响,在进行高速旋转机械动力学设计时,轴承与转子设计必须一起协调进行,轴承刚度的动态特性不容忽视。     

Response selection and dynamic damper application to improve the identification of multiple input forces of narrow frequency band

In identifying input forces by using FRF matrices and response measurements, improper selection of the response measurement position and the excitation frequency, if it coincides with the natural frequencies of the structure, may cause doubtful accuracy and effectiveness. This paper presents two methods to improve force identification. The first is by improving the conditioning of the system FRF matrix by a proper selection of the measurement positions. An expression for the covariance matrix representing the uncertainty on the force estimate is defined. Then the response selection algorithm, which is both systematic and effective, is derived. The basic strategy in selecting the response positions is to let the smallest singular value be as large as possible. The second method is to modify the structure by attaching a dynamic damper at a suitable location to minimise the ill-conditional nature of the FRF matrix especially near a resonance frequency. The methods suggested are tested numerically and experimentally in two examples: a beam structure and a rectangular plate structure. The test results show that the response selection and the addition of a dynamic damper are very effective in solving ill-conditioning problems, especially when the structure has a large degree of freedom and when the excitation frequencies are near one of the structure's natural frequencies.     

超静定结构振动筛的设计与动态特性分析

运用有限元法分析了超静定结构振动筛的固有频率、固有振型及动力响应,通过分析得出超静定结构增加了振动筛的强度,提高了弯扭变形的固有频率,并有效避开工作频率,避免了共振的发生.     

Analytical solution for dynamic behavior of multiwall carbon nanotubes subjected to mechanical shock loading

Dynamic behavior and frequency analysis of multiwall carbon nanotubes (MWCNTs) with finite length are investigated using an analytical method. By applying multiple elastic shells and a linearized model of van der Waals forces, a comprehensive continuum dynamic model of MWCNTs is developed. Also, by utilizing Laplace transform, time histories of MWCNTs subjected to shock lading are obtained. Then by using the fast Fourier transform (FFT), the time responses are transferred to the frequency domain and natural frequencies are found. The accuracy of results is verified by comparing the results of sudden loading with those obtained by numerical methods. Furthermore, an abrupt unloading after ramp loading is simulated, and the dependency of diameter and length on the axial and radial natural frequencies of MWCNTs is examined. Also, by characterizing the longitudinal displacement, the wave propagation velocities are obtained and an explicit expression is found for the axial natural frequencies of MWCNTs subjected to shock loading.     

基于DRNN动态整定PMSM的SVPWM控制

为解决传统的永磁同步电机控制系统中存在的低速转矩脉动大以及由此引起的高频噪声、动态响应慢等问题,提出了一种基于对角神经网络动态自整定的永磁同步电机矢量控制系统的实施方案.给出了基于对角递归神经网络的PID动态自整定控制器的结构,以及PID参数动态自整定的学习控制算法,并将这种综合控制策略引入永磁同步电机空间电压矢量PWM控制中.仿真结果表明,系统低速性能好,转矩脉动小,谐波含量少,当电机参数改变或者受到外部扰动时,系统具有良好的动态特性.