对汽车平顺性评价方法的探讨与建议

首先分析了现行国家标准GB4970-1996<汽车平顺性随机输入行驶试验方法>与国际上通行的人体振动评价标准ISO2631-1997的区别.通过道路试验测量了驾驶员坐垫、靠背和脚部的平移振动以及坐垫的旋转振动共lO个方向的振动.分析发现汽车中人体振动的峰值因子一般小于9;而按照GB4970和ISO2631的试验数据对比表明,GB4970在一定程度上低估了人体振动.分析各方向振动所占的比例发现,坐垫垂向振动、靠背前后振动和坐垫侧倾振动影响最大.最后提出了对汽车平顺性评价方法的建议.     

Assessment of wheel loader vibration on the riding comfort according to ISO standards

Vibration accelerations were measured on a compact wheel loader during 11 operations with two drivers and with/without the activated boom suspension system (BSS). Two standards, ISO 2631-1 (1985) and ISO 2631-1 (1997), were used to assess the effect of wheel loader vibration on comfort. The assessment results of ISO 2631-1 (1985) showed that vibration in the frequency range from 4 to 20 Hz in the vertical direction and in the frequency range from 1.6 to 3.15 Hz in the vertical and driving directions plays an important role in comfort assessment. The overall total values of vibration measured on the wheel loader in all operations exceeded the ‘uncomfortable’ boundary specified in ISO 2631-1 (1997). The speed had a larger influence on the vibration intensity than the bucket load, the BSS or the driver biodynamic response during driving. During driving and V-cycle, the difference of vibration intensity with two drivers in the z-direction is larger than that in the x- and y-direction.     

Subjective absolute discomfort threshold due to idle vibration in passenger vehicles according to sitting posture

Idle vibration, occurring when a vehicle comes to a stop while the engine is on, is known to be a main cause of discomfort for passengers, and the customer effect has been recently growing. The frequency of idle vibration is determined by the engine type. To lower the vibration, various technologies have been applied to optimize the engine mount and vehicle body structure. In addition to the technological developments, research on human response with a consideration of idle vibration is needed to effectively reduce the level of discomfort experienced by passengers. Seats aimed at enhancing static comfort influence the sitting posture of passengers; sitting posture is a factor affecting human body characteristics that response to idle vibration. This study examined the absolute discomfort threshold of idle vibration according to the sitting postures of 13 taxi drivers. The four sitting postures of subjects on a rigid-body seat without a backrest were variables in the determination of absolute discomfort threshold of idle vibration. The absolute discomfort threshold curves obtained in this experiment were less sensitive to frequency changes than the frequency weighting function of ISO 2631-1.     

Noise,vibration, harshness model of a rotating tyre

ABSTRACT

The tyre plays a fundamental role in the generation of acoustically perceptible driving noise and vibrations inside the vehicle. An essential part of these vibrations is induced by the road excitation and transferred via the tyre into the vehicle. There are two basic ways to study noise, vibration, harshness (NVH) behaviour: Simulations in time and frequency domains. Modelling the tyre transfer behaviour in frequency domain requires special attention to the rotation of the tyre. This paper shows the approach taken by the authors to include the transfer behaviour in the frequency range up to 250?Hz from geometric road excitations to resulting spindle forces in frequency domain. This paper validates the derived NVH tyre model by comparison with appropriate transient simulations of the base transient model.     

An Analytical and Experimental Investigation of the Driver-Seat-Suspension System

SUMMARY

Vertical seat-suspension systems are characterized by a generalized two- degree-of-freedom model incorporating nonlinearities due to shock absorber damping, linkage friction and bump stops. The analytical model is validated using the results obtained from laboratory tests performed under sinusoidal excitations in the 0.5-8.0 Hz frequency range. Human body models of varying complexities, derived from the mechanical impedance data, are discussed and integrated to the nonlinear seat-suspension model to derive a coupled driver- seat-suspension model. Nonlinear analytical models are expressed by their linear equivalent models using a local equivalent linearization technique based on energy similarity. The vibration attenuation performance characteristics of the seat-suspension and driver-seat-suspension models are investigated for deterministic and random cab floor excitations. The results of the study revealed that the seated human body contributes considerably to the overall ride performance.     

大跨度人行斜拉桥TMD减振分析

为避免人行桥发生共振,以新金牛(岛型)公园C、D地块人行斜拉桥为例,通过数值仿真和脉动试验得到了人行斜拉桥的一阶自振频率。进一步地,选取人行激励荷载,确定舒适度评价标准。最后,数值分析了原桥的振动响应,并根据原桥动力分析结果设计了调谐质量阻尼器(TMD)减振方案。研究结果表明：本桥端跨的一阶竖弯频率为2.73 Hz,跨中频率为1.51 Hz；安装TMD后,端跨和跨中的加速度峰值符合舒适度标准,TMD减振效果最大可达到60%。     

板式无砟轨道交通引起的环境振动数值分析

利用已研究出的高速铁路动荷载,采用粘弹性边界,运用有限元法建立轨道-路基-大地二维动力分析模型,分析板式无砟轨道交通引起的振动在大地中的传播特性。计算分析表明:地表的振动强度随着离轨道中心线的距离增加而逐渐衰减。离轨道中心线近处,地表振动较强,而且加速度主要频段在20 Hz以上;离轨道中心线较远处,振动较小,加速度主要频段在10 Hz以下。随着离轨道中心距离的增加,加速度幅值随之减小,而且地表20 Hz以上的振动衰减得较快,10 Hz以下的振动衰减得较慢。     

Driver recognition of a run-over accident

If a driver passes over a pedestrian lying on the road and flees, it is considered a crime. In several cases, even if the driver fled and was arrested, he/she often asserts that they did not know that the victim was a human being. However, the investigation agency often believes that a driver can certainly recognize when he/she passes over a person. Accordingly, such cases frequently lead to disputes due to the lack of criteria for recognizing when a driver was involved in run-over accidents. In this study, tests were conducted both to identify if drivers can recognize whether their vehicles passed over a person and to examine how they feel at the time. A silicon dummy, which was manufactured to have the same characteristic as the human chest, was used in this study. According to the method specified in ISO2631, the vibration delivered to the driver was measured, and eighteen participants drove a vehicle over the silicon dummy to experience how the vibrations felt. When the passenger car for the test ran over the dummy at speeds ranging from 10 km/h to 60 km/h, all participants recognized the delivered vibration, and the VDV that was delivered to the participants ranged from 1.81 m/s ^1.75 to 2.38 m/s ^1.75. The participants thought that the object they drove over was a stone or a piece of wood. This indicates that the driver certainly can recognize the vibrations generated from passing over a human chest even though it feels like a solid object.     

Development of an experimental methodology to evaluate the influence of a bamboo frame on the bicycle ride comfort

In the current environment of increased emphasis on sustainable transport, there is manifold increase in the use of bicycles for urban transport. One concern which might restrict the use is the ride comfort and fatigue. There has been limited research in addressing the difficulty in bicycle ride comfort quantification. The current study aims to develop a methodology to quantify bicycle discomfort so that performance of bicycles constructed from bamboo and aluminium alloy can be compared. Experimentally obtained frequency response functions are used to establish a relation between the road input and the seat and rider response. A bicycle track input profile based on standard road profiles is created so as to estimate the acceleration responses. The whole-body-vibration frequency weighting is applied to quantify the perception of vibration intensity so that eventual discomfort ranking can be obtained. The measured frequency response functions provide an insight into the effect of frame dynamics on the overall resonant behaviour of the bicycles. The beneficial effect of frame compliance and damping on lower modes of vibration is very clear in the case of bamboo frame, in turn affecting seat and rider response. In the bamboo frame, because of multiple resonances, the frequency response of the handlebar is smaller at higher frequencies suggesting effective isolation. Further improvements may have come from the joints made from natural composites. Overall, based on the comparative analysis and the methodology developed, bamboo frame shows significant improvement in ride comfort performance compared with the aluminium frame.     

模态试验分析对解决汽车振动问题的应用

针对某车辆在行驶试验时,在车速57 km/h时出现低频5.4 Hz的驾驶室异常振动的现象,振动形式为俯仰振动,人体乘坐舒适性主观感觉很差。先后采用多种常规振动分析试验方法对该车进行振动分析,也未能分析出引起驾驶室异常振动的原因。最后对该车的车架和驾驶室进行模态试验分析,分析判断得出该车在行驶时驾驶室异常振动的频率与车架整体一阶弯曲时的接近,由此判断该车驾驶室异常振动是由车架整体-阶弯曲引起的。根据试验分析结果,文章最后对某车问题的改进方案综合评价后提出了合理的改进方案。     

无锡地铁运行引起上马墩站振动的现场试验研究

高频次的地铁运营引发的超量振动对于周边生活和工作造成了明显的负面影响,为了获取地铁诱发振动的传播规律,在无锡地区进行从车站到上盖物业的现场振动实测。在上马墩站搭建整套加速度信号振动测试系统,获取各测点3个方向时域加速度信号,分析结构在时域和频域的基本特征,对地铁运行造成上马墩站振动影响进行评价。研究发现： 1）垂向振动在通常情况下明显占优,横向、纵向振动相当; 2）上盖物业振动主要集中为25~50 Hz; 3）车站的Z振级接近规范规定白天限值,超出了夜间限值,有必要采取结构优化或减振措施对地铁运行引起的振动进行控制。     

Field measurements of the evolution of wheel wear and vehicle dynamics for high-speed trains

This investigation demonstrates the wheel wear evolution and related vehicle dynamics of high-speed trains with an operating distance (OD) of around two million kilometres. A long-term experimental test lasting two years was conducted to record the wheel profiles and structural vibrations of various trainsets. The wheel wear, namely the profile shape, worn distribution and wheelset conicity, is investigated for several continuous reprofiling cycles. Typical results are illustrated for the stability analysis, and the ride quality is examined with increasing OD. In addition, the vibration transition characteristics between suspensions are investigated in both the time and frequency domains. The experiments show that the dominant wear concentrates on the nominal rolling radius, and the wear rate increases with OD because of the surface softening resulting from the loss of wheel material. The vibration of structural components is aggravated by the increase of the equivalent conicity of the wheelset, which rises approximately linearly with the wheel wear and OD. High-frequency vibrations arise in the bogie and car body related to the track arrangement and wheel out-of-roundness, causing the ride comfort to worsen significantly. Additionally, the system vibration characteristics are strongly dependent on the atmospheric temperature. Summaries and conclusions are obtained regarding the wheel wear and related vehicle dynamics of high-speed trains over long operating times and distances.     

悬索桥吊索高阶涡激振动及摆锤式MTMD减振技术研究

为了解大跨度悬索桥吊索出现的大幅高频振动现象,并进行减振,以国内某主跨1688 m的悬索桥为背景(最长吊索长184.6 m),基于理论方法和施工期吊索大幅高频振动实测结果,分析吊索的振动类型及参数(频率、阻尼比);提出一种摆锤式多重调谐质量阻尼器(MTMD,其由一定形状的锤头提供质量参数,由钢绞线提供刚度及阻尼参数),采用有限元和室内试验的方法,分析其振动特性,并进行实桥验证。结果表明:该桥吊索振动频率范围为5~25 Hz,阻尼比低,单个吊点的多根吊索易发生同相位的高阶涡激振动;摆锤式MTMD单个锤头具有2个控制主频,自身阻尼比约10%,具有位移放大作用,对高频振动的响应灵敏,在很宽的频率范围内具有很好的减振性能;摆锤式MTMD可有效增加吊索自身阻尼比,控制吊索高阶涡激振动,实测减振效果达到90%以上,具有很好的实用性。     

基于ADAMS的全断面硬岩隧道掘进机主机耦合振动分析

为明确不同工况下TBM主机振动耦合规律，基于Adams软件,依据其结构装配关系和力传递关系，对TBM主机节点进行重新划分，引入非线性弹簧元件对油缸、轴承和齿轮啮合进行非线性等效，建立TBM主机非线性耦合动力学模型，并详细计算结构本身的刚度和结构间的非线性连接刚度。根据掘进地质条件，定义了全推力、上软下硬和转弯3种典型刀盘载荷，并对3种载荷下的振动进行分析。结果表明： 1)在全推力工况下，主机关键部件的振动最大，为低频的受迫振动；机头架的振动横向和纵向受到齿轮的耦合作用，在150 Hz左右的频率上存在耦合振动。 2)刀盘轴向最大加速度幅值为2.5g，从刀盘到主梁，机头架的振动衰减了约25%，主梁前段振动衰减了约55%，与已有全推力工况下实测结果相接近，证实了仿真计算的正确性。3）根据对上软下硬和转弯纠偏2种典型工况的振动规律分析，刀盘的轴向力和速度分别减少约40%和80%。     

Chatter vibrations of high-performance motorcycles

Motorcycle racing teams occasionally experience speed-limiting vibrations of around 25 Hz frequency in mid-corner. The nature of the vibrations has not been closely defined yet and the mechanics are currently not properly understood. Conventional motorcycle-dynamics models are shown here to reveal the existence of a vibration mode that aligns with the experience being referred to, suggesting some explanations. Root loci for variations in speed or cornering vigour, demonstrating modal characteristics for small perturbations from trim states, are employed to indicate how the mode responds to changes in operation and design. Modal participation is examined for a lightly damped case. Influences on the natural frequency and damping of the mode are found and a way of stabilising the mode is suggested.     

Investigating the influence of rail grinding on stability,vibration, and ride comfort of high-speed EMUs using multi-body dynamics modelling

ABSTRACT

High-speed electric multiple units (EMUs) have been popularised rapidly all around the world and have become a major transportation method. Increases in running velocity and wheel-rail deterioration lead to excessive vibration and reduced ride comfort, which are common issues encountered in the operation of high-speed EMUs. While built-in sensors on a car body are able to detect abnormal vibrations in the car body itself, they cannot effectively reflect the ride comfort of passengers. Wheel-rail profile matching can improve the wheel-rail interaction, and rail grinding has thus been introduced as a practical solution to alleviating the aforementioned problems. Nonetheless, the working mechanism of rail grinding has not been investigated theoretically. This study develops flexible car body and human body models based on the rigid-flexible coupled method to systematically study the effects of wheel-rail wear and rail grinding on passenger ride comfort. Case studies show that the proposed models can predict the ride comfort of passengers accurately. It is also demonstrated that rail grinding can significantly alleviate excessive vibration and improve passenger ride comfort in the long term. A long-term investigation reveals that rail grinding can improve the smoothness of the rail surface and reduce the damage to the rail.     

Nonlinearity in the vertical transmissibility of seating: the role of the human body apparent mass and seat dynamic stiffness

The efficiency of a seat in reducing vibration depends on the characteristics of the vibration, the dynamic characteristics of the seat, and the dynamic characteristics of the person sitting on the seat. However, it is not known whether seat cushions influence the dynamic response of the human body, whether the human body influences the dynamic response of seat cushions, or the relative importance of human body nonlinearity and seat nonlinearity in causing nonlinearity in measures of seat transmissibility. This study was designed to investigate the nonlinearity of the coupled seat and human body systems and to compare the apparent mass of the human body supported on rigid and foam seats. A frequency domain model was used to identify the dynamic parameters of seat foams and investigate their dependence on the subject-sitting weight and hip breadth. With 15 subjects, the force and acceleration at the seat base and acceleration at the subject interface were measured during random vertical vibration excitation (0.25–25 Hz) at each of five vibration magnitudes, (0.25–1.6 ms^?2 r.m.s.) with four seating conditions (rigid flat seat and three foam cushions). The measurements are presented in terms of the subject's apparent mass on the rigid and foam seat surfaces, and the transmissibility and dynamic stiffness of each of the foam cushions. Both the human body and the foams showed nonlinear softening behaviour, which resulted in nonlinear cushion transmissibility. The apparent masses of subjects sitting on the rigid seat and on foam cushions were similar, but with an apparent increase in damping when sitting on the foams. The foam dynamic stiffness showed complex correlations with characteristics of the human body, which differed between foams. The nonlinearities in cushion transmissibilities, expressed in terms of changes in resonance frequencies and moduli, were more dependent on human body nonlinearity than on cushion nonlinearity.     

熨平板振动分析与找平支架隔振设计

通过对某熨平板进行动力学分析,获得扰动力和扰动力矩的频率、大小及作用方向,由此确定了找平支架隔振系统的固有频率为16 Hz,并设计、计算了弹性支撑元件的力学参数和形状尺寸。最后通过测试验证了隔振效果,结果显示:在低频区域,加速度放大了20%~50%,但从25 Hz左右开始,加速度幅值开始低于输入信号幅值,达到了预期效果。     

Improvements in Dynamic Characteristics of Automobile Suspension Systems Part 1. Two-Mass Systems

In a previous paper, [3] the random vibrations of simple linear models of automobile suspension were solved with respect to seat elasticity and human sensitivity to vibrations. The present study uses more realistic linear models taking into account the unsprung mass.

Two configurations of masses are investigated: a two-mass system consisting of a sprung mass and an unsprung mass, and a three-mass system having an additional mass which acts as a vibration absorber. The gain in comfort obtained by lowering the natural frequency of the sprung mass is calculated for various two-mass and three-mass models along with other characteristics such as the dynamic tyre load, spring and damper forces and relative motion of the masses.     

High-frequency random vibration analysis of a high-speed vehicle–track system with the frequency-dependent dynamic properties of rail pads using a hybrid SEM–SM method

A hybrid Spectral Element Method (SEM)–Symplectic Method(SM) method for high-efficiency computation of the high-frequency random vibrations of a high-speed vehicle–track system with the frequency-dependent dynamic properties of rail pads is presented. First, the Williams-Landel-Ferry (WLF) formula and Fractional Derivative Zener (FDZ) model were, respectively, applied for prediction and representation of the frequency-dependent dynamic properties of Vossloh 300 rail pads frequently used in China's high-speed railway. Then, the proposed hybrid SEM–SM method was used to investigate the influence of the frequency-dependent dynamic performance of Vossloh 300 rail pads on the high-frequency random vibrations of high-speed vehicle–track systems at various train speeds or different levels of rail surface roughness. The experimental results indicate that the storage stiffness and loss factors of Vossloh 300 rail pad increase with the decrease in dynamic loads or the increase in preloads within 0.1–10,000?Hz at 20°C, and basically linearly increase with frequency in a logarithmic coordinate system. The results computed by the hybrid SEM–SM method demonstrate that the frequency-dependent viscous damping of Vossloh 300 rail pads, compared with its constant viscous damping and frequency-dependent stiffness, has a much more conspicuous influence on the medium-frequency (i.e. 20–63?Hz) random vibrations of car bodies and rail fasteners, and on the mid- (i.e. 20–63?Hz) and high-frequency (i.e. 630–1250?Hz) random vibrations of bogies, wheels and rails, especially with the increase in train speeds or the deterioration of rail surface roughness. The two sensitive frequency bands can also be validated by frequency response function (FRF) analysis of the proposed infinite rail–fastener model. The mid and high frequencies influenced by the frequency-dependent viscous damping of rail pads are exactly the dominant frequencies of ground vibration acceleration and wheel rolling noise caused by high-speed railways, respectively. Even though the existing time-domain (or frequency-domain) finite track models associated with the time-domain (or frequency-domain) fractional derivative viscoelastic (FDV) models of rail pads can also be used to reach the same conclusions, the hybrid SEM–SM method in which only one element is required to compute the high-order vibration modes of infinite rail is more appropriate for high-efficiency analysis of the high-frequency random vibrations of high-speed vehicle–track systems.