Identifying the frequency dependent material property of a hydraulic engine mount through an iterative procedure using 3D finite element modeling

Achieving very restricted noise, vibration and harshness targets in modern vehicles, makes using the hydraulic engine mount crucial. Hydraulic engine mounts have both solid and fluid media in their structures that make their dynamic behavior complex to figure out. We present a three-dimensional model of HEM with using finite element method that encompasses elastomeric material’s nonlinearity and fluid-structure-interaction. Dynamic equivalent modulus of elasticity for elastomeric material is identified through iterative model updating procedure. To do model updating, the results (here, namely, natural frequencies and frequency response function graphs) are compared with real hydraulic engine mount behavior that derived from modal tests. The results showed that the dynamic characteristic of elastomeric material is frequency dependent and can be divided into two distinct regions: below 30 Hz (low frequency) and above 30 Hz (high frequency) with different trends.     

High frequency testing of rubber mounts

Rubber and fluid-filled rubber engine mounts are commonly used in automotive and aerospace applications to provide reduced cabin noise and vibration, and/or motion accommodations. In certain applications, the rubber mount may operate at frequencies as high as 5000 Hz. Therefore, dynamic stiffness of the mount needs to be known in this frequency range. Commercial high frequency test machines are practically nonexistent, and the best high frequency test machine on the market is only capable of frequencies as high as 1000 Hz. In this paper, a high frequency test machine is described that allows test engineers to study the high frequency performance of rubber mounts at frequencies up to 5000 Hz.     

High-precision modeling and simulation of the taper leaf spring of tandem suspension of commercial vehicles

The taper leaf spring of tandem suspension of commercial vehicle is different from the traditional taper leaf spring. Thus, the professional software MSC.ADAMS/CHASSIS leaf spring, which is specially applied in traditional leaf spring, does not reliably develop the computational model of the taper leaf spring of tandem suspension. The multi-body dynamic model of the taper leaf spring of tandem suspension, which is developed in this paper, is a secondary development model that is based on the leaf spring model built by MSC.ADAMS/CHASSIS leaf spring. End contact and friction in the modified model are redefined to exhibit the hysteretic characteristics of the taper leaf spring of tandem suspension. The test of the taper leaf spring of tandem suspension is conducted to validate the reliability of the modified model. The tests in this paper are divided into two groups. The first group started at an unloaded state at an excitation frequency of 1/30 Hz and amplitude of 70 mm to acquire quasi-static behavior. The second group is conducted at various frequencies (2, 3 and 4 Hz) and various amplitudes (±1, ±3 and ±10 mm) in a loaded state to acquire dynamic behavior. A formula to calculate dynamic spring rate for leaf spring is proposed, and details about the formula are presented. The simulations are conducted under the same conditions as the test. The hysteretic characteristics and the relative error of dynamic spring rate from the test are compared with the ones from the simulations for the validation of the reliability of the modified model.     

Parameter optimization of time-varying stiffness method for chatter suppression based on magnetorheological fluid-controlled boring bar

An innovative chatter suppression method based on a magnetorheological (MR) fluid-controlled boring bar for chatter suppression is developed. The MR fluid, which can change stiffness consecutively by varying the strength of the applied magnetic field, was applied to adjust the stiffness of the boring bar and suppress chatter. The cutting dynamic stability under different natural frequencies of the structure was analyzed by an energy method, which shows that cutting dynamic stability depends on both the natural frequency of the structure and the spindle speed. The chatter suppression mechanism with varying natural frequency is analyzed for further parameter optimization. Furthermore, both theoretical analyses and numerical simulations indicate that a square wave exciting current with a large amplitude and a moderate frequency has a better effect on regenerative chatter suppression. Experiments utilizing a MR fluid-controlled boring bar under an exciting current with different waveforms and frequencies were conducted. The experimental results show that the chatter can be significantly suppressed using MR fluid-controlled boring bar under a square wave exciting current with a frequency of 4–6 Hz and an amplitude of 0–2 A.     

Identification of Journal Bearing Force Coefficients under High Dynamic Loading Centered Static Operation

Lightly damped rotor bearing systems experience large amplitudes of vibration when traversing critical speeds. Bearing linearized force coefficients, strictly valid for minute motions about an equilibrium position, may not be reliable for design or troubleshooting in rotordynamics predictive analyses. Experiments assessing the dynamic forced response of a plain journal bearing undergoing large orbital motions due to single-frequency excitation forces were conducted in a test rig. The short test bearing of slenderness ratio L/D = 0.25 has a nominal radial clearance of 0.127 mm (5 mils). Tests were conducted at three rotor speeds (900, 1800, and 2700 rpm), three feed pressures (1, 3, and 6 psig), and three excitation frequencies (15, 30, and 45 Hz). Baseline bearing motions due to shaft runout are recorded and subtracted in the parameter identification procedure. The forces exerted on the bearing induce large orbital motions with peak amplitudes exceeding 50% of the nominal bearing clearance. Identified cross-coupled stiffness and direct damping coefficients fall within value bands predicted by the π and 2π models of the fluid film, even for the largest amplitudes of motion. The bearing whirl frequency ratio approaches the typical 50% value at the highest speed tested. Excitation frequency has a marked influence of the test direct dynamic stiffness coefficients with added mass coefficients at least twice as large as predicted values.     

A vibration-control platform on the basis of magnetorheological elastomers

The design of a vibration-control platform on the basis of magnetorheological (MR) elastomers is described. The platform is designed for protecting precision equipment and instruments against external vibrations at frequencies of up to 200 Hz and amplitudes of up to 100 µm. The platform contains four active dampers on the basis of MR elastomers and four elastic-support units with a mass corrector using which the platform is adjusted to a required equipment mass and a required resonance frequency. The proposed platform provides passive vibration isolation at a level of ～10 dB at frequencies of from 0.5 to 30 Hz and vibration amplitudes of up to 500 µm. The results of experimental studies of transient processes (the minimum transient-process time is 30 ms), the transfer coefficient of the vibration-displacement amplitude, and the mechanical hysteresis are presented.     

Physics based modelling and analysis of IPMC vibration energy harvester

Advancement in smart materials and decrease in power requirement of electronic devices motivates researchers to use smart materials for energy harvesting applications. In this study, a physics-based modelling approach by considering the effect of convective transport on cation migration and the effect of local deformation on anion concentration is used to model IPMC based vibration energy harvester and solved with the help of COMSOL Multiphysics 5.5 finite element method. The present harvester model voltage and power output under fixed load resistance, and power output under variable load resistance for both excitation frequencies (2 Hz and 5 Hz) and both excitation amplitudes (3 mm and 5 mm) are analysed by both FEM and experimental results. At 5 Hz and 5 mm excitation amplitude and frequency, the peak voltage is 171.9 mV, and the peak power is 60.48 nW for 2 Hz excitation and 5 mm amplitude of mechanical vibration. According to the findings, physics-based modelling can be utilized to develop and analyse IPMC vibration energy harvesters. It will also be useful for analyzing IPMC-based sensors and actuators.

     

Optimal design of nonlinear hydraulic engine mount

This paper shows that the performance of a nonlinear fluid engine mount can be improved by an optimal design process The property of a hydraulic mount with inertia track and decouplen differs according to the disturbance frequency range. Since the excitation amplitude is large at low excitation frequency range and is small at high excitation frequency range, mathematical model of the mount can be divided into two linear models One is a low frequency model and the other is a high frequency model The combination of the two models is very useful in the analysis of the mount and is used for the first time in the optimization of an engine mount in this paper Normally, the design of a fluid mount is based on a trial and error approach in industry because there are many design parameters In this study, a nonlinear mount was optimized to minimize the transmissibilities of the mount at the notch and the resonance frequencies for low and high-frequency models by a popular optimization technique of sequential quadratic programming (SQP) supported by MATLAB^(r) subroutine. The results show that the performance of the mount can be greatly improved for the low and high frequencies ranges by the optimization method     

磁流变液悬置用于发动机隔振模糊控制

设计了一种基于圆盘挤压模式磁流变悬置,利用试验方法得出了不同激励频率条件下磁流变悬置的循环耗散功与励磁电流的关系.利用磁流变悬置,建立了发动机振动半主动控制的研究模型.提出了一种模糊控制方法,利用转速、加速度和动态拉压力传感器,借助美国国家仪器公司的数据采集和实时控制器,构建了发动机隔振模糊控制试验系统,并开展了怠速和常用工况条件下的发动机振动隔离控制试验研究.研究结果表明,与橡胶悬置相比,基于磁流变悬置的模糊控制系统,能够降低发动机动态激振力传递到支承,并且低转速条件下的振动隔离效果优于高转速条件下的.     

Influence of Er:YAG laser frequency on dentin caries removal capacity

The purposes of this study were to evaluate in vitro the influence of different frequencies of Er:YAG laser on the human dentin caries removal capacity. Thirty fragments obtained from third molars were randomly assigned into three groups (n = 10) according to the laser frequency used: 4, 6, and 10 Hz. The caries lesion (±1 mm deep) was induced before the irradiation by S.mutans cultures for 6 weeks. The specimens of all groups were irradiated with 200 mJ of energy in noncontact and focused mode under constant refrigeration (water flow: 2.5 mL/min). Quantitative analysis of the caries removal was performed by DIAGNOdent^TM and the Axion Vision^TM software. Qualitative analysis was performed by Scanning electron microscope (SEM) and light microscope (LM). Data were analyzed by ANOVA and Fishers' tests. The DIAGNOdent^TM revealed that the caries removal was similar with 4 and 6 Hz and was superior with 10 Hz (P < 0.05). The analysis with Axion Vision^TM software revealed that the caries removal was similar with 6 and 10 Hz and the 4 Hz group promoted the lowest caries removal. Through SEM morphologic analysis, some specimens irradiated with 4 Hz presented, under the demineralized dentin, a disorganized collagenous matrix. The LM images revealed that all frequencies used promoted irregular caries removal, being observed over preparations with 6 and 10 Hz. It can be concluded that the increase of Er:YAG laser frequency provided a higher dentin caries removal without selectivity to the disorganized dentin. Microsc. Res. Tech., 2010. © 2010 Wiley‐Liss, Inc.     

The effect of gas inclusions on the parameters of hydraulic vibration mounts

Problems of improving damping characteristics of hydraulic vibration mounts are considered. It is shown that, when there are nondissolved air bubbles present in a working fluid, damping characteristics are not weakened but improved significantly in a number of cases. Testing of a hydraulic vibration mount was carried out at a vibration test stand within a frequency range from 20 to 55 Hz. The vibration frequency of the vibration test stand platform was measured discretely with a step of 5 Hz. As soon as the stand’s input vibration signal was not a purely harmonic one, harmonic components from 0.5 to 100 Hz were present in its spectrum. This frequency range was exposed to spectral and cepstral processing. It was determined that efficient vibration suppression with presence of gas cavities with a total volume of 5 mL occurs in the whole range of harmonic change.     

空气弹簧液压悬置动特性及隔振特性研究

研究了具有可变刚度阻尼的发动机空气弹簧液压悬置的动特性和隔振特性。针对影响发动机空气弹簧液压悬置动特性的关键参数上液室等效体积刚度,采用理论和试验方法研究了上液室等效体积刚度的等效值,基于该等效值建立了空气弹簧液压悬置的理论模型,对空气腔开闭两种工况进行了空气弹簧液压悬置动特性的仿真和试验研究。搭建了发动机空气弹簧液压悬置系统试验台架,研究了台架各种激励频率下的空气弹簧液压悬置的隔振特性。结果表明:本研究采用的上液室等效体积刚度进行空气弹簧进行建模是正确、可行的,提高了空气弹簧建模效率和准确性;空气弹簧液压悬置在空气腔开启和关闭两种状态下,峰值动刚度增大幅值达78.5%,峰值阻尼角增大幅值达250%。台架试验表明:当台架激励频率小于25Hz时,悬置采用大刚度大阻尼;当台架激励频率大于等于25 Hz时,悬置采用小刚度小阻尼;悬置隔振率提升明显,不同频率下提升幅值达10%～67%。     

车辆发动机悬架系统现状与进展

理想的发动机悬架系统应隔离发动机工作转速范围内由发动机干扰力所引起的发动机振动，并阻止由冲击而激起的发动机弹跳，这意味着发动机悬架的动态刚度和阻尼是与频率和振幅有关的，改善依赖于频率和振幅特性的动态刚度与阻尼是发动机悬架系统发展的关键所在。传统的弹性悬架不能满足所有的要求，它仅能在静偏转和隔振之间进行折衷，特别在低频域，被动的液压悬架能比弹性悬架提供更好的特性，通常半主动技术，由于其可调性而被用来进一步改善液压悬架的特性，为了隔振、低频时主动发动机悬架系统非常硬，而在高频域内被调整的非常软，主动的发动机悬架已被认为是发动机悬架的新一代，发动机悬架系统的优化是相当可取的，但发动机悬架的优化工作出现一些局限性，文中综述国内，外发动机悬架技术的现状与进展。     

飞轮组件微振动对高分辨率光学卫星光轴的影响

为了研究高分辨率光学卫星星上飞轮的微振动对卫星成像质量的影响,分别建立了飞轮扰动模型和整星结构动力学模型。首先,对飞轮组件系统进行了地面扰动测试,对实测扰动数据的分析表明,飞轮组件在与转速相关的一阶频率50Hz处产生一次谐波,在190Hz与280Hz左右存在与转速无关的一系列峰值。然后,对整星进行了单位正弦激励,获得了光轴角位移响应,并对其与飞轮实测扰动数据进行了集成分析。分析结果表明:整星在50~80 Hz和230~280Hz的角位移响应有较多的谐振响应频率成分,沿光轴方向和垂直光轴方向整星光轴的角位移最大谐振响应幅值分别为2.718″、2.739″,在245Hz左右存在较多幅值为0.5″量级的谐波。分析显示飞轮组件微振动对高分辨率光学卫星成像质量影响较大,得到的结果可为整星系统的优化设计和隔振补偿措施提供参考依据。     

Decoupling analysis for a powertrain mounting system with a combination of hydraulic mounts

The existing torque roll axis(TRA) decoupling theories for a powertrain mounting system assume that the stiffness and viscous damping properties are constant. However, real-life mounts exhibit considerable spectrally varying stiffness and damping characteristics, and the influence of the spectrally-varying properties of the hydraulic mounts on the powertrain system cannot be ignored. To overcome the deficiency, an analytical quasi-linear model of the hydraulic mount and the coupled properties of the powertrain and hydraulic mounts system are formulated. The influence of the hydraulic mounts on the TRA decoupling of a powertrain system is analytically examined in terms of eigensolutions, frequency, and impulse responses, and then a new analytical axiom is proposed based on the TRA decoupling indices. With the experimental setup of a fixed decoupler hydraulic mount in the context of non-resonant dynamic stiffness testing procedure, the quasi-linear model of the hydraulic mount is verified by comparing the predictions with the measurement. And the quasi-linear formulation of the coupled system is also verified by comparing the frequency responses with the numerical results obtained by the direct inversion method. Finally, the mounting system with a combination of hydraulic mounts is redesigned in terms of the stiffness, damping and mount locations by satisfying the new axiom. The frequency and time domain results of the redesigned system demonstrate that the torque roll axis of the redesigned powertrain mounting system is indeed decoupled in the presence of hydraulic mounts (given oscillating torque or impulsive torque excitation). The proposed research provides an important basis and method for the research on a powertrain system with spectrally-varying mount properties, especially for the TRA decoupling.     

复杂机械系统多维耦合振动传递矩阵分析

以特性传递矩阵描述复杂机械系统中子结构输入、输出力与速度矢量关系,提出了复杂振源激励、多弹性支承与基础板结构三维耦合隔振系统传递矩阵力学模型。考虑隔振支承多维波动效应,推证了弹性支承耦合振动传递矩阵,为复杂系统功率流特性及隔振器多维驻波效应研究确立了有效途经。数值模拟计算表明,基础板结构的前两阶弯曲共振模态是高频域系统功率流提高的主要原因。振源力矩或垂向激振力诱发的隔振器纵向谐振使系统功率流明显提高:增大基础板厚度,驻波共振峰值提高。     

Study of fluid damping effects on resonant frequency of an electromagnetically actuated valveless micropump

As fluid flow effects on the actuation and dynamic response of a vibrating membrane are crucial to micropump design in drug delivery, this paper presents both a mathematical and finite-element analysis (FEA) validation of a solution to fluid damping of a valveless micropump model. To further understand the behavior of the micropump, effects of geometrical dimensions and properties of fluid on the resonant frequency are analyzed to optimize the design of the proposed micropump. The analytical and numerical solutions show that the resonant frequency decreases with the slenderness ratio of the diffuser and increases with the opening angle, high aspect ratio, and thickness ratio between the membrane and the fluid chamber depth. A specific valveless micropump model with a 6-mm diameter and 65-μm thickness polydimethylsiloxane (PDMS) composite elastic membrane was studied and analyzed when subjected to different fluids conditions. The resonant frequency of a clamped circular membrane is found to be 138.11 Hz, neglecting the fluid. For a gas fluid load, the frequency is attenuated by slightly shifting to 104.76 Hz and it is significantly reduced to 5.53 Hz when the liquid fluid is loaded. Resonant frequency remarkably shifts the flow rate of the pump; hence, frequency-dependent characteristics of both single-chamber and dual-chamber configuration micropumps were investigated. It was observed that, although the fluid capacity is doubled for the latter, the maximum flow rate was found to be around 27.73 μl/min under 0.4-A input current with an excitation frequency of 3 Hz. This is less than twice the flow rate of a single chamber of 19.61 μl/min tested under the same current but with an excitation frequency of 4.36 Hz. The proposed double-chamber model analytical solution combined with the optimization of the nozzle/diffuser design and assuming the effects of damping proved to be an effective tool in predicting micropump performance and flow rate delivery.     

简易压电晶片式液压发电装置的设计及试验

为实现低频率,高强度的振动能量回收和利用,提出一种基于压电流体耦合作用的压电晶片式液压发电装置。通过理论分析设计结构,采用直径60mm,厚度1.6mm的压电晶片以及直径16mm,高度50mm的液压缸制作样机,用水作为工作介质,测试了装置在不同激励频率、激励电压、系统背压及加载质量等条件下的电压输出情况。试验结果表明:当激励频率(工作频率)在27Hz左右时,该压电晶片式液压发电装置的输出电压达到最大,且在一定的范围内,发电装置输出电压随着激励电压、系统背压及加载质量的增加而增加,验证了液压-压电发电的可行性。     

Development of frequency weighting function for Asian (Korean) people in vertical whole-body vibration; in comparison with ISO 2631-1

In the field of ‘human vibration’, until now most frequency weighting functions have been derived from particular experiments whose subjects were only Western people. However, because of inherent differences (e.g., characteristic and shape of body parts, muscular and cellular tissue) between Western people and Asian people, frequency weighting function based on Asian people is required. An experiment was carried out to develop a frequency weighting function for the Korean people in vertical whole-body vibration, and to verify whether this weighting is acceptable in practical applications in comparison with ISO 2631-1. Ten male subjects of mean weight and height were tested for a posture similar to sitting in a passenger seat (footrest, upright and placement of the palms of hands on thighs, etc.) of a car. This experiment was performed using sinusoidal excitation in the range from 2 to 250 Hz, which was a combination of one-half and one-third octave bands at eight determined amplitudes. To guarantee the reliability and accuracy of the test, non-parametric statistics was adopted to resolve the fact that there was not enough of the sample. Furthermore, two methods were considered to make the frequency weighting function and equal sensation curves. The first method changes the amplitude at every fixed frequency, and the other assigns weighting values. Korean people showed the most sensitivity to vertical whole-body vibration at 6.3 Hz excitation, so much higher weighting factors than weighting factors of other frequencies must be assigned near that frequency.     

Low-frequency inertial-type pressure-gradient receivers for oceanological investigations

Technical solutions for the construction of inertial-type pressure-gradient receivers were developed. The manufactured laboratory prototypes with dimensions of 110 × ?32 mm and 112 × ?80 mm have acoustic-pressure sensitivities of 70–80 and 500 μV/Pa, respectively, in a plane wave at a frequency of 100 Hz. The performance characteristics of the hydroacoustic pressure-gradient receivers, which are used in oceanological investigations at frequencies that are substantially lower than 1 kHz, were improved.