On the dependence of acoustic performance on pavement characteristics

Acoustic-based mix design is still far from achieving a clear and accepted rationale. The three main dominions (generation, absorption, propagation) which affect pavement acoustic performance involve a number of acoustic parameters. Their relationship with pavement properties is scarcely or insufficiently known. In more detail, the parameters that define the acoustic coupling between the two phases that comprise a porous material are: porosity, resistivity, tortuosity, and viscous and thermal factors. Consequently, the spectrum of a pavement absorption coefficient depends, in particular, on tortuosity, whose relationship with HMA (hot mix asphalt) bulk properties is still an issue.Given that, the study described in this paper aimed at: (i) assessing the effect of the tortuosity on the absorption coefficient of a pavement layer; (ii) assessing the dependence of tortuosity on mix design parameters and/or mix properties; (iii) deriving a straightforward algorithm to estimate the effect of tortuosity-related properties on the absorption coefficient.Based on the above issues, an experimental plan was designed and carried out in order to study these relationships and set out a tentative theoretical and practical framework. The relationships between acoustic and traditional bulk properties of pavement mixtures were analysed. Acoustic models and hydraulic analogies were considered and, based on them, relationships were formalised and submitted to experimental validations. A simple relationship to derive tortuosity from nominal maximum aggregate size and thickness was derived. This relationship was used to derive the frequency of the first peak of the absorption spectrum, based on HMA properties. Nominal maximum aggregate size and lift thickness emerged as key factors in patterning peak frequency.Future research will address a number of issues among which the following can be listed: synergetic assessment of the influence of HMA properties on the absorption coefficient over the entire spectrum, synergetic consideration of generation and absorption factors. Practical benefits and outcomes are expected for both practitioners and researchers.     

城市地铁车站钻孔桩旋挖施工噪音对周边环境的影响分析

以北京地铁6号线一期工程南锣鼓巷站为背景,研究了夜间进行钻孔灌注桩旋挖施工对周边房屋所产生的噪音影响。通过对实际检测结果的对比分析得出了夜间进行旋挖施工对周边环境的噪音影响很小,可以正常组织施工,为类似工程提供借鉴经验。     

喷水推进技术在水面舰船声隐身方面的应用研究

阐述了喷水推进技术在水面舰船声隐身方面的优势及应用现状,并对喷水推进装置噪声的机理进行分析,对降低喷水推进装置噪声的一些措施进行了研究。     

灰色GM(0,N)法在轨道交通噪声预测中的应用

以实测样本数据为基础,根据灰色系统理论对列车车速、距轨道中心的距离两个因素进行灰色关联度分析,发现前者对线路侧方噪声级的影响要强于后者;分别建立线性回归模型和GM(0,N)模型,将预测值和实测值进行比较,发现灰色GM(0,N)模型的预测方法性能良好,是一种优秀的噪声预测方法.研究成果对轨道交通噪声影响因素的主次识别、降...     

街道峡谷型道路交叉口交通噪声动态模拟

应用几何声学理论分析了声波在建筑群间传播过程中的直射、反射和绕射3种传播路径,并以此建立了街道峡谷型十字道路交叉口交通噪声动态计算模型.以实测的交通量、车型比例等参数作为输入,结合该计算模型和微观交通仿真对街道峡谷型十字道路交叉口交通噪声进行了动态模拟,并用实测的交通噪声数据与模拟结果进行了比较.结果表明:各出口车道附...     

峭度分析法在发动机噪声信号故障特征提取中的应用

将峭度分析法引入发动机噪声信号故障特征提取中。基于连续小波变换对信号时间-尺度特征的细致刻画功能,提出了噪声信号中瞬时特性的峭度敏感特征参数计算方法,对不同转速不同工况下的发动机噪声信号进行了基于尺度-峭度的特征提取。研究结果表明,峭度结合连续小波变换能够很好地提取发动机噪声信号的故障特征。利用连续小波变换的尺度-峭度分析,能够有效提取噪声信号不同转速不同工况下的故障特征,为发动机的状态监测与故障诊断提供了重要的理论和现实依据。     

电控柴油机噪声的评估和试验优化

对一台已经完成了性能排放标定的电控共轨柴油机的噪声水平进行了评估,并在不影响性能排放的原则下对噪声进行了研究和优化。研究和优化的内容主要是对预喷、轨压和喷油正时的小范围调整。研究表明:是否开启预喷对电控共轨发动机的噪声有明显影响。     

关于一种新型消声器的研究与设计

在机动车辆的行驶中,发动机的排气噪音和排放污染是非常高的,为降低噪音和减少排放污染,在机动车辆上都设置有消声装置。但目前常见的各种原理的消声器效果都不太理想,而且经过消声处理的气体中还含有大量的粒状物、絮状物、油水混合物以及一氧化碳等有害物质,这些物质直接危害着生态环境。本文目的是提供一种新型的消声器设计方案,从而提高现有消声器性能,降低其噪音污染并减少排放的有害物质量。     

国内外客车车内噪声限值及降噪措施

介绍了国内外客车车内噪声值的要求及对地板、侧墙等车体主要构件所采取的降噪措施。     

加装前置导翼降低叶轮入口处流体噪声

对离心泵叶轮入口处液体的流动状态进行了分析,提出了采用固装式前置导翼改善叶轮叶片入口处液体的流动状态,以在降低流体噪声的同时,提高泵的效率,改善汽蚀性能.