动力总成异常振动的固有特性识别研究

针对某SUV车柴油机动力总成在常用工作转速条件下产生异常振动的实际问题,给出改进脉冲激振法与有限元计算模态分析法相结合的方法进行不同条件下柴油机动力总成的固有特性识别研究。通过整车道路试验,发现柴油机工作转速的二阶激励激起动力总成系统共振,采用基于变时基技术的改进脉冲激振法进行整车和台架条件下动力总成的振动模态试验,结合有限元模型仿真计算,识别动力总成的固有频率和振型参数,发现飞轮壳结构是导致动力总成弯曲固有频率偏低引起系统共振的薄弱环节。根据识别结果,进行改进设计飞轮壳薄弱结构,提高动力总成系统的固有频率,消除异振。     

新型聚焦反共振式主减隔振系统性能分析

为降低直升机向机体传递的旋翼动载荷,提出了一种新型聚焦反共振式主减隔振装置。通过建立聚焦反共振式主减隔振系统参数模型,分析了聚焦反共振式主减隔振系统的载荷传递特性,讨论了弹簧板刚度、惯性质量等关键参数对主减模态频率以及隔振效率的影响;为了验证该模型及后续进一步研究,按照某型机主减接口加工了一套聚焦反共振式主减隔振装置同时进行了地面试验,计算结果与试验结果吻合。经试验结果表明,加装聚焦反共振式主减隔振装置对垂向、航向和侧向三向激励的隔振效率均达到了80%,为新研直升机以及现役直升机减隔振需求提供一条新的途径。     

几种含惯容元件吸振器动力学特性比较研究

在吸振器振子与主系统之间引入惯容器,与阻尼、弹簧元件并联或串联,采用阻抗导纳法可以对吸振系统传递率进行计算,从而获得系统传递特性曲线,分析各参数(惯容器惯容量,阻尼系数,弹簧刚度)对吸振效果的影响。对比三种模型分析惯容器惯容量对系统影响,结果表明惯容器并联时,惯容值变化会影响反共振峰位置,但只能向低频偏移;惯容器与阻尼串联时,惯容值变化对系统的影响与阻尼类似,增大惯容值会使共振峰和反共振峰响应减小,但是反共振峰位置不会偏移;惯容器与弹簧串联时反共振峰可以向两侧偏移。三种基本模型中惯容量的影响各不相同,可以为复杂含惯容元件的吸振器模型提供参考和借鉴。     

混流式水轮发电机组主轴系统组合共振分析

以混流式水轮发电机组主轴系统为研究对象,用有限单元法建立系统的非线性全局耦合动态方程,并在此动态方程的基础上分析该系统在电磁力、自激惯性力共同作用下的组合共振特性,揭示了组合共振特性与系统的水力参数、电磁参数和结构参数的关系.最后通过一实例进行了仿真分析,得到了系统的组合共振特性.     

反共振双层隔振系统分析

提出以反共振隔振方法进行双层隔振系统设计,在不降低隔振区传递率衰减速率的条件下,抑制共振峰值改善双层隔振性能。针对三型单惯容反共振隔振器(anti-resonant vibration isolator, AVI),进行了结构选型分析,优选了二级串联型三元件反共振隔振器用于双层隔振系统;基于传递曲线存在与阻尼无关的固定点性质,建立了反共振双层隔振系统的调谐优化方法;考虑了反共振隔振器作为上层和下层隔振装置两种情形,根据所建立的优化方法分别得到了两种情形下刚度比和阻尼比的优化数值解,分析了调谐状态下共振峰值关于质量比的变化规律,最后讨论了传统隔振器(conventional vibration isolator, CVI)阻尼的影响。结果表明：反共振隔振器在共振区有效抑制共振峰值,在隔振区保持双层隔振传递率衰减速率;共振峰值与质量比成负相关性;传统隔振器阻尼对反共振隔振效果不产生实质影响,但改变隔振区传递率衰减速率。     

考虑物料质量随机波动的反共振振动机动力学分析

考虑了物料质量均值的不固定性和物料质量的随机波动性，研究了反共振振动机工作体和下质体在随机参数条件下的动力响应特性，分析了系统参数与反共振振动机随机响应成分之间的关系。研究得出了下质体不同参数组合与系统的随机响应成分之间的关系，揭示了物料质量均值的波动对工作体和下质体振幅的稳定性影响较大，需对激振频率进行控制。     

模糊动态AHP导弹识别算法

针对导弹预警卫星系统中的真假弹头识别问题,提出了一种在决策系统中对弹头目标识别的新算法,该算法提出用弹头的温度变化率、热容差异、辐射强度、灰度特性、红外运动特性等红外特征作为弹头目标识别特征量,运用多属性决策中的AHP方法进行信息融合,并对属性重要性判断矩阵采用模糊动态法进行构建,有效地解决了属性权重随时间变化的问题.最后根据融合结果排序,识别真弹头.通过仿真实验证明了该算法的有效性.     

大功率船用齿轮箱试验模态分析*

由于大功率船用齿轮箱的特殊使用工况,其性能要求远远高于其他齿轮箱。论文对某大功率船用齿轮箱结构和传动原理进行分析,根据试验模态分析的基本原理和方法,利用最小二乘法对频响函数进行优化,并利用单模态识别法对大功率船用齿轮箱进行模态参数识别,得出系统的前20阶固有频率和阻尼,结果表明该船用齿轮箱系统的转频、啮合频率远离固有频率,系统不存在共振现象。但考虑齿轮箱实际工作的复杂性,在系统转速变化达到临界转速时存在较为剧烈的共振现象。试验结果可为进一步系统研究动态特性提供分析依据。     

X射线检测中散射模型的理论分析

目的　研究 X射线检测中的散射特征 ,并消除散射的影响 .方法　用高斯模型对散射分布进行合理逼近 .结果　从理论上对散射模型进行了分析和推导 .结论　得到了在散射场中散射分布的定量描述     

多失效模式下多状态伺服转塔刀架系统频率可靠性分析EI北大核心CSCD

根据频率响应函数特性曲线的连续性,传统频率可靠性分析中仅将共振区与非共振区二分化值得商榷。提出了多失效模式下多状态频率可靠性分析方法,综合考虑影响系统固有频率各结构参数的随机性、激励频率的随机性,应用Monte Carlo仿真估计出系统频率可用度,并根据相关性分析识别各结构随机参数对系统频率可靠性的影响。将该方法用于基于多体系统传递矩阵法所建立的伺服转塔刀架系统动力学模型中,研究了其频率可用度以及与系统状态最为相关的结构参数,所得分析结果为系统优化设计提供了依据。     

Effect of electric load impedances on the performance of sandwich piezoelectric transducers

Based on the electromechanical equivalent circuit, the sandwich piezoelectric transducer with adjustable resonance frequency is studied. The underlying theory of frequency adjustment is its piezoelectric effect. In this paper, the influence of electric load impedance (including electric resistance, electric inductance, and electric capacitance) on the resonance frequency, the antiresonance frequency, and the effective electromechanical coupling coefficient is analyzed theoretically and experimentally. It is demonstrated that the electric load impedance can change the resonance frequency, the antiresonance frequency, and the effective electromechanical coupling coefficient. When the electric load resistance is increased, the resonance frequency and the antiresonance frequency are increased; the effective electromechanical coupling coefficient has a maximum value when the electric load resistance changes. When the electric load resistance becomes large, the effect of the electric load resistance on the effective electromechanical coupling coefficient is negligible. When the electric load inductance is increased, the resonance frequency and the antiresonance frequency are decreased, whereas the effective electromechanical coupling coefficient is increased. When the electric load capacitance is increased, the resonance frequency, the antiresonance frequency, and the effective electromechanical coupling coefficient are all decreased. It should be noted that when the electric load impedance becomes large, the effect of the electric load impedance on the resonance frequency, the antiresonance frequency, and the effective electromechanical coupling coefficient of a sandwich piezoelectric transducer becomes negligible.     

Resonance and antiresonance of symmetric and asymmetric cantilevered piezoelectric flexors

The resonances of dynamically excited symmetric piezoelectric bimorphs have been determined from the equations of state. Under the effect of sinusoidal stimuli: a moment exerted at the tip M, a force exerted perpendicular to the plane of the bimorph also applied at the tip F, a uniformly applied pressure p, and an electrode voltage V, they respond with a sinusoidal tip rotation alpha, tip deflection delta, volume displacement nu, and electrode charge Q. All of the former are related to all of the latter through a dynamic admittance matrix B. The antiresonance frequency of the capacitance C have been found while also antiresonance in off-diagonal elements have been determined. The latter indicate that at these frequencies the bimorph does not work as an actuator or sensor in the particular domain of the off-diagonal. The mode shape at these antiresonance frequencies has been determined. The antiresonance of b(14) determines that for this frequency the tip has deflection but no rotation, while the antiresonance of b(24 ) indicates that the tip has rotation but no deflection. No antiresonance in the volume displacement is found, indicating that the bimorph is a pressure converter (microphone) at all frequencies. Micromachined piezoelectric heterogeneous bimorphs have been fabricated using the techniques of I.C. fabrication. Their deflections have been measured as a function of frequency and applied voltage, while these have been compared with the theoretical predictions. An anomalously large quadratic deflection has been found, superimposed on the linear piezoelectric behavior. The agreement between the linear part of the experimental deflection and the theory was quite good.     

NMR Study of Disordered Inclusions in the Quenched Solid Helium

With the help of the Green function technique and the equation of motion approach, we study the thermoelectric efficiency (characterized by the figure of merit) in parallel-coupled double quantum dots (QDs) system. It is found that the configurations of the dot-lead coupling strengths exert a significant impact on the figure of merit through the Fano effect, due to which electrons experience an abrupt change from resonant to antiresonant tunneling. The absolute value of the thermopower is increased by the Fano resonance and antiresonance, while the electrical conductance is separately enhanced and suppressed, leading to the enhancement of the thermal efficiency of the device.     

Modeling for temperature compensation and temperature characterizations of BAW resonators at GHz frequencies

This paper deals with the temperature dependence of electrical and physical features of various kinds of solidly mounted resonators (SMR). The presented bulk acoustic wave (BAW) devices are designed for the 2 GHz application. The temperature coefficient of frequency (TCF) is determined from measurements well above the temperature range defined for wireless telecommunication system specifications. Therefore, evolution of electromechanical coupling factors and quality factors at resonance and antiresonance are also monitored. Results of characterizations show the trend for a subsequent theoretical temperature compensation study by using analytical modeling. To improve accuracy of modeling, an attempt to extract temperature dependence of dielectric permittivity epsilon(33) and piezoelectric coefficient e(33) is made. Finally, a well-known analytical model is modified to take into account the temperature dependence of length, density, stiffness coefficient, dielectric permittivity, and piezoelectric coefficient. Modeling highlights the need to deposit a material with positive temperature coefficient of stiffness on the top electrode. Realistic thickness of such a layer is determined. At the same time, it is necessary to adjust piezoelectric and electrode thin film thicknesses for simultaneously keeping a constant antiresonance frequency, reaching a zero temperature coefficient of frequency for antiresonance, and minimizing the decrease in the coupling factor because of the mass-loading deposition.     

质量弹簧串联系统发生原点反共振时子系统的响应特性

本文利用机械阻抗方法,对无阻尼质量弹簧串联系统进行了动力学分析,发现该系统在发生反共振时,子结构各质量的振幅之比总是等于该子结构模态向量各元素之比,从而可以方便地求得系统在简谐激振力下的响应.     

Efficiency of excitation of piezoceramic transducers at antiresonance frequency

The efficiency of piezoceramic transducers excited at both the resonance and antiresonance frequency was investigated. Losses in piezoceramics are phenomenologically considered to have three coupled mechanisms: dielectric, mechanical, and piezoelectric losses. Expressions for the resonance and antiresonance quality factors, which ultimately determine transducer efficiency, have been received on the basis of complex material constants for both stiffened and unstiffened vibration modes. Comparison of electric and mechanical fields, thermal and electrical losses of power supply, and their distribution in the transducer volume have been made. For a given constant mechanical displacement of the transducer top, the required electric voltage applied to the transducer at the antiresonance frequency is proportional to the resonance quality factor, but the changes in the intrinsic electric and mechanical field characteristics in the common case are not too essential. The requirements on the piezoceramic parameters, types of transducer vibration, and especially on the factor of piezoelectric losses in a range of physically valid values were established to provide maximal quality factors at the antiresonance frequency.     

Reducing vibration of sandwich structures using antiresonance frequencies

A method for reducing vibration of a sandwich structure using the antiresonance technique is presented. It is found that with appropriate resonators, the motion of the sandwich structure due to disturbances with certain frequencies can be effectively suppressed. A simple two-degree-of-freedom system consisting of an absorbing mass connected by springs to a drive mass is introduced and used to interpret the vibration behavior of the sandwich structure with resonators.     

发泡聚乙烯隔振性能研究

为研究发泡聚乙烯的隔振性能,测试了质量块和振动台的加速度信号;运用最小二乘原理,消除了实验数据的趋势项;建立了发泡聚乙烯多项式动力学模型,识别出了一个工况下的衬垫的参数;运用Runge-Kutta法和重构恢复力-位移曲线,证明了模型的正确性;最后,运用相同的方法,得出了其它工况下的参数识别结果。研究的结果可直接为防震包装提供理论依据。     

吊挂机构对力标准机工作准确度的影响与应对措施

静重式力标准机的加载系统是通过吊挂将砝码施加到被检测力仪上的.为保证工作平稳性和工作效率,吊挂必须附加一些复杂的机构.分析了1MN静重式力标准机的吊挂系统对力值检测计量精度的影响,建立了加载系统力学模型,从理论上分析了杠杆平衡装置、吊挂、防摆机构与系统测量准确度的关系,提出了误差计算方法和公式.结果表明,复杂的吊挂机构对系统的力值检测计量精度确是有影响的,但可以通过保证设备的机械结构装配精度来减小联结点的摩擦力,并同时保证位移控制精度来减小以至消除这种影响.     

二维分布动载荷识别的频域方法

运用频域法在广义正交域中识别二维分布动载荷。基于数学拟合理论，二维动态载荷在广义正交域中可分解为二维正交函数的级数形式，未知的二维分布动载荷就可以表示为各阶正交基函数线性叠加，这时未知的复杂分布动载荷的识别就可以转化为简单的正交拟合系数的识别。根据线性系统的叠加原理，将待识别载荷的分解基函数看成已知分布动载荷作用于结构时，结构的响应与待识别载荷作用下结构的响应成线性关系。只要结构实测的响应点数大于待识别的系数，就能求出各系数，因而就可以识别分布动载荷。通过计算机仿真验证该方法能有效识别二维分布动载荷，且能与有限元方法结合，识别复杂结构上的分布动载荷。该方法具有很好的通用性，能简单方便运用于工程结构，能很好地抑制噪声的干扰。仿真试验说明该方法具有很好的识别精度。进一步的试验验证了该方法工程适用性。