Selfexcited Vibrations of the Tire

In this paper a mechanical work of external forces and torques, acting on the tire has been considered. A theory has been developed for the prediction of necessary conditions for selfexciting vibrations. The theory establishes, that the mechanical work of external forces and torques must be positive, or, what is equivalent, that the tire has to transmit energy from external environment to vehicle. The work of forces and torques has been considered as a convolution of functions, which next has been submitted to Laplace transformation. The condition of selfexcitation of vibrations, obtained from above in the frequency domain, establishes, that the imaginary part of all eigenvalues of frequency response matrix must be negative. As an example, the ranges of selfexcited vibrations of the tire have been calculated. The tire has been treated as a stretched circular string. Four different models have been considered. Three of them have been massles (kinematic), namely Pacejka's model, Von Schlippe's model and single-point model. As fourth model the dynamic Pacejka's model has been considered. The influences of longitudinal deflections on the shimmy tendency have been studied for all models

Frequency response characteristics have been numerically computed and compared for all models. A critical speed and a critical reduced frequency of first and second kind have been defined. Admissible, negative, imaginary parts of the eigenvalues of frequency response matrix have been established. These admissible values of imaginary parts of eigenvalues assure, that the energy absorbing does not excite shimmy vibrations.     

高墩大跨度连续刚构桥空间动力特性分析

连续刚构桥动力特性是桥梁结构动力分析的前提和基础。以一高墩大跨度连续刚构桥为研究对象,运用有限元软件ANSYS建立其有限元模型,分析其结构参数对动力特性的影响。分析表明：1）主梁刚度增大,各阶振型频率也随之增大,且侧弯和竖弯振型的频率变化较为明显,对纵飘振型影响较小;2）桥墩刚度的变化对侧弯和纵飘频率影响较大,而对竖弯频率影响相对较小;3）纵向约束弹簧刚度对竖向和横向各阶频率无任何影响,但是可以显著增加纵向频率。     

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。     

空间缆索自锚式悬索桥动力特性及刚度影响规律

空间缆索自锚式悬索桥的主缆直接锚固在加劲梁上,同时由于主缆的空间特性,与地锚式悬索桥及传统平面索相比,其动力性能存在很大的差异.针对青岛海湾大桥大沽河航道桥建立非线性空间有限元模型,对其动力特性及结构刚度影响规律进行了分析.结果表明,该桥振型基本合理,具有密布的频谱;作为自锚式悬索桥其整体刚度较低,固有周期较长;单柱式桥塔的横向刚度较弱,横向振动出现较早;另外,由于缆索横向间距较小,刚度较小,前10阶振型中有5阶索振.各振型受结构刚度的影响不同,主缆刚度主要影响悬索桥的1阶竖弯及扭转,加劲梁竖向刚度对加劲梁1阶竖弯及加劲梁扭转振型影响较大,横向刚度主要影响悬索桥的加劲梁横向振型,扭转刚度主要影响悬索桥的1阶扭转振型;主塔纵向刚度主要影响悬索桥的纵飘振型;横向刚度主要影响索塔的1阶横向振型.     

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.     

Damping of roll vibrations of vehicle suspension

Small forced vibrations of an axle model of independent suspensions having four degrees of freedom are studied. The exact analytical solution of the generalised Lagrange equation enables one to produce 3D plots of the normalised amplitudes of forced vibrations versus frequency and excitation ratio or phase difference of the road inputs. The analysis of these plots exhibits some deficiency in damping of roll vibrations of conventional vehicle suspensions. The possibilities of improvement are discussed.     

Time Domain Model of the Vertical Dynamics of a Railway Track up to 5 kHz

The modelling of the vertical dynamics of a track at high frequencies requires rather complex approaches to take into account section deformations. Validation is usually made by comparing computed frequency responses with measured ones. In this study an experimental model of a railway track is proposed based on the analysis of recorded time histories of impact excitations and the corresponding vibrations of the rail with auloregressive (AR) techniques. Measurements are used not only as a convergence parameter that the model must approach, but are also entirely used to describe the dynamic behaviour of the rail in the frequency range 150 / 5000 Hz. Frequency response functions are reconstructed with a very high fidelity but the model obtained is not general, as it is applicable only to the measured track section under the hypothesis of linearity. The measurement details, the construction and the validation of the model are shown in this paper.     

悬链线型斜拉索风雨激振模型及特性分析

斜拉索长度随斜拉桥跨度增大而增长,以抛物线型近似代替实际状态下拉索线型的误差也越来越大。考虑水线与拉索表面之间存在库仑阻尼力和黏滞线性阻尼力,建立了基于悬链线型考虑面内-外耦合振动的运动水线连续弹性拉索风雨激振理论模型,并推导出以各阶模态为坐标的拉索振动微分方程。以不同参数拉索为例,对拉索与水线的耦合运动微分方程组进行数值求解,并将计算结果与基于抛物线型的拉索风雨激振理论模型进行了比较。结果表明：在某些情况下,拉索采用悬链线型与抛物线型的计算结果在拉索振幅、参振模态、空间振动形态、振动频率、拉索与水线相位差以及水线的振动频率上有很大差异;垂度影响系数对拉索低阶模态有较大影响,抛物线型垂度影响系数大约是悬链线型的一半;采用悬链线型建立的拉索风雨激振理论模型得到的拉索各阶模态的自振频率比采用抛物线型模型的计算结果要高,模态阶数越低,自振频率差距越明显。     

路面特性对车辆振动影响规律研究

对软路面上车辆的扭转、垂直和纵向振动进行了研究,首先对振动车辆进行单因素(路面不平度、胎压、路面抗压强度和牵引负荷)分析,找出对车辆振动影响显著的因素及影响规律,在此基础上对影响振动的多因素进行正交试验,分析交互作用对车辆振动的影响规律。同时,对不同路面条件下振动进行研究分析。随着路面波形频率、路面抗压能力、轮胎气压和牵引负荷的增加,车辆扭转、垂直和纵向振动增加。对于垂直振动、扭振和纵向振动,其主要影响因素各不相同。     

Discomfort of vertical whole-body shock-type vibration in the frequency range of 0.5 to 16 Hz

Shock-type vibrations are frequently experienced in vehicles excited by impulsive input, such as bumps in the road, and cause discomfort. Current national and international standard weightings were primarily developed for assessing exposure to sinusoidal or random vibrations and not impulsive excitations or shocks. In this experimental study, various shock signals were systematically produced using the response of a one degree-of-freedom vibration model to hanning-windowed half-sine force input. The fundamental frequency of the shock was varied from 0.5 to 16 Hz at a step of 1/3 of an octave. The magnitude estimation method was used for fifteen subjects to compare the discomfort of shocks with various unweighted vibration dose values between 0.35 ms^−1.75 and 2.89 ms^−1.75 at each frequency. The equivalent comfort magnitude of shock showed greater sensitivity at frequencies less than 0.63 Hz and at the resonance frequency of the human body between 5.0 Hz and 6.3 Hz. The frequency weighting constructed by using both the equivalent comfort magnitude and the growth rate of discomfort obtained in this study was compared with the current standard weightings, W_b of BS 6841 and W_k of ISO 2631. The derived weightings for shock were applied to the acceleration of the shocks, and an enhanced correlation was proved between the magnitude estimations and the weighted physical magnitude of shock.     

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.     

由路面引起的汽车振动能量耗散特性频域分析

针对行驶过程中由路面引起的汽车振动能量耗散问题，提出了基于汽车振动二自由度单轮模型的能量耗散特性频域分析方法。采用汽车振动二自由度单轮模型推导了模型的频率响应，确定了能量耗散振动响应量及其频率响应。将路面激励功率谱密度与振动响应量的功率谱密度和均方根值相结合，建立了能量耗散振动响应量统计特性和振动能量耗散平均功率的表示。采用Matlab开发了汽车振动二自由度单轮模型的能量耗散特性频域分析仿真程序，通过3种分析方案研究了由路面引起的汽车振动能量耗散特性。结果表明，汽车振动能量耗散平均功率与速度和路面等级相关，受到路面等级的影响较大；在以B级路面为主的国内城市行驶工况下，由路面引起的汽车振动能量耗散平均功率比较低。     

早期振动对混凝土抗拉性能影响

对处于初、终凝前后混凝土材料选取了6个不同时间点作为振动的起振点,分别施加4种不同频率和振幅组合的振动,通过劈裂拉伸强度试验,判断受振动混凝土1、3、28d抗拉性能变化情况.试验中得到76组劈裂拉伸强度结果,有29个结果是强度降低的.这些强度降低的数据均在10%以内,其中强度降低在7%以内的占了76%.试验结果表明:对...     

Low-frequency vibration control of floating slab tracks using dynamic vibration absorbers

This study aims to effectively and robustly suppress the low-frequency vibrations of floating slab tracks (FSTs) using dynamic vibration absorbers (DVAs). First, the optimal locations where the DVAs are attached are determined by modal analysis with a finite element model of the FST. Further, by identifying the equivalent mass of the concerned modes, the optimal stiffness and damping coefficient of each DVA are obtained to minimise the resonant vibration amplitudes based on fixed-point theory. Finally, a three-dimensional coupled dynamic model of a metro vehicle and the FST with the DVAs is developed based on the nonlinear Hertzian contact theory and the modified Kalker linear creep theory. The track irregularities are included and generated by means of a time–frequency transformation technique. The effect of the DVAs on the vibration absorption of the FST subjected to the vehicle dynamic loads is evaluated with the help of the insertion loss in one-third octave frequency bands. The sensitivities of the mass ratio of DVAs and the damping ratio of steel-springs under the floating slab are discussed as well, which provided engineers with the DVA's adjustable room for vibration mitigation. The numerical results show that the proposed DVAs could effectively suppress low-frequency vibrations of the FST when tuned correctly and attached properly. The insertion loss due to the attachment of DVAs increases as the mass ratio increases, whereas it decreases with the increase in the damping ratio of steel-springs.     

Fuzzy adaptive sliding mode controller for an air spring active suspension

A fuzzy adaptive sliding mode controller for an air spring active suspension system is developed. Due to nonlinearity, preload-dependent spring force and parameter uncertainty in the air spring, it is difficult to control the suspension system. To achieve the desired performance, a fuzzy adaptive sliding mode controller (FASMC) is designed to improve the passenger comfort and the manipulability of the vehicle. The fuzzy adaptive system handles the nonlinearity and uncertainty of the air suspension. A normal linear suspension model with an optimal state feedback control is designed as the reference model. The simulation results show that this control scheme more effectively and robustly isolates vibrations of the vehicle body than the conventional sliding mode controller (CSMC).     

Wheel Vibrations and Transient Tire Forces

This paper presents a survey of the state-of-the-art in predicting the wheel vibrations in a complex dynamic vehicle suspension system and their influence on the forces transduced in a high frequency area from the tire to the vehicle's body. Secondly it presents also the transient evolution of tire models used for prediction and understanding high frequency movements in the tire's contact area, producing the guiding forces and torques during vehicle handling.     

Study on influence of walking experience on traffic safety attitudes and values among foreign residents in Japan

The most vulnerable user in road space is still an ordinary pedestrian even though the top fatalities by traffic mode differ in countries. Thus, prioritizing/protecting vulnerable road users is essential to improve road safety. People's safety perceptions toward vulnerable users are strongly associated with surrounding elements and their own experiences, especially as pedestrians. Therefore the attitude and values toward vulnerable users would vary due to culture and customs related to walking in each country. This study examines how a walking experience change reflects people with diverse backgrounds' traffic safety attitudes by conducting an online questionnaire survey for foreigners living in Japan for five years or less. As a result, 75% of respondents walk more frequently due to increased public transportation usage. For all the respondents, the increase in the walking frequency also drives the shift in the attitude toward vulnerable users and the values regarding travel safety and comfort indirectly intermediated by the shift in attitudes toward walkability, applying structural equation modeling. To focus on the structure of the shift according to nationality, people from Southeast/South Asia, where motorcyclists are the top fatalities in the road space and somehow regarded as vulnerable road users, the increased walking experience contributes significantly to the improvement of awareness of vulnerable road users and to the formation of safety and comfort values. Regarding people from Europe/North America, although their walking frequency increases after coming to Japan, there is a static causal relationship that does not influence their attitude toward walkability or safety and comfort values. Additionally, they already have an attitude of protecting/prioritizing pedestrians and placing more importance on safety and comfort. At the same time, people from Southeast/South lacks the attitude toward pedestrians due to much less frequency of walking in daily life. It suggests that establishing safe and having comfortable pedestrian spaces and public transport in developing countries where traffic infrastructure is at the development stage will encourage people to walk and likely help foster an attitude of placing importance on safety.     

车辆振动对公路路基健康检测面波法的影响分析

面波法在建设前和建设期间的公路路基勘测技术早已成熟,但用此技术对正在运行的公路路基进行健康检测的研究尚无先例。交通车辆的振动噪音阻碍了人们对公路路基定期进行无损检测的尝试,从而不能对潜在问题采取预警措施。通过一系列实测数据,经对比有无车辆时的面波记录,并分析两种状态下面波记录组成频率的不同,总结正常运行状态下公路路基健康检测的面波法经验与建议。通过有无车辆时面波法所得路基土层力学特性的对比进一步证明了本文所给经验和建议。     

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.