挖掘机驾驶室低频结构噪声分析与优化*

针对某小型液压挖掘机驾驶室低频噪声过大问题,对驾驶室结构振动特性进行分析。基于有限元模型计算各工况下驾驶室噪声传递函数,运用统计学方法确定主要噪声峰值频率及相应工况;通过模态声学贡献度计算,确定危险工况下噪声贡献量较大的模态阶数,参照模态振型确定驾驶室振动变形最大的车身板件;并对该板件进行形貌优化处理,提高其一阶固有频率,进而降低驾驶室内噪声。优化结果表明,驾驶室噪声传递函数在危险频率下的峰值下降了2~4 dB。     

基于Timoshenko梁模型的周期充液管路弯曲振动带隙特性和传输特性

充液管路的固液耦合振动广泛存在于各种工程领域中,对其弯曲振动控制进行研究具有重要意义.将声子晶体的周期性思想引入到管路结构设计中,将管壁设计成沿轴向交替排列的周期性复合结构.基于Timoshenko梁模型,采用传递矩阵法计算了固液耦合条件下周期管路结构的弯曲振动能带结构及其传输特性,同时分析了材料阻尼系数、周期和非周期支撑对带隙特性的影响.充液周期管路结构的弯曲振动带隙特性为管路的振动控制提供了一条新的技术途径. 关键词： 声子晶体 充液管路 振动带隙     

基于混合有限元-统计能量分析的箱梁结构噪声特性分析

为了探讨箱梁的结构噪声辐射规律,提高计算精度及效率,基于混合有限元-统计能量分析理论,建立1/10箱梁有限元-统计能量分析计算模型,并进行模态实验与声学实验验证.在此基础上进行声贡献量以及振动传递规律分析,并与相关文献进行比较.研究结果表明:混合有限元-统计能量分析模型不仅适用于箱梁结构噪声分析,而且在保证计算精度的同...     

数控裁剪机切割刀壳体振动噪声预测分析

高频往复式切割刀是柔性材料数控裁剪机的核心部件.该文对切割刀壳体的振动噪声改进措施进行研究.首先对切割刀进行刚体动力学分析,获取其所受动载荷情况,并通过数值计算验证了切割刀刚体动力学模型的可靠性.其次,基于有限元法获取切割刀壳体模态特性,并通过锤击激振实验验证了有限元模型的准确性.然后基于模态仿真结果进行谐响应分析,将...     

SE-MCNN-CTC的中文语音识别声学模型

针对国内外缺少对振动轮噪声预估的问题,以某型振动轮为研究对象,首先基于动力学有限元理论对振动轮进行频率响应分析,其次采用声学边界元技术对振动轮辐射噪声进行了数值模拟,并通过实验验证了仿真结果的准确性,然后比较了垂直振动与圆周振动两种不同激振形式对辐射噪声的影响,得出垂直振动辐射噪声低的结论,最后对驾驶室声腔模态进行了仿真,与振动轮激振频率相近发生共振。通过调整激振频率,降低了司机耳旁噪声。所得研究成果可为振动轮辐射噪声的预估与改进提供一种切实可行的参考依据。     

次级源和误差传感器布放对带弹性障板的充液直管声振复合有源控制的影响*

针对充液管路系统噪声有源控制问题,研究了次级源和误差传感器布放对带弹性障板的充液直管管路系统有源消声与有源消振复合控制效果的影响。基于声固耦合方法建立了带弹性障板的充液直管管路系统的有限元模型,在声激励下对比了次级声源布放对系统有源消声性能的影响,并在组合激励下分析了次级力源、次级声源和误差传感器布放对系统复合有源控制的影响。结果表明,非对称分布的次级声源容易激起管壁振动,进而带动障板振动,导致有源消声效果不佳;采用对称分布的次级声源可使低频段的降噪量提高10 dB以上。复合有源控制可进一步提升全频段的控制效果。通过增加振动误差传感器数量,可使绝大多数频点的降噪量提高1~20 dB不等。此外,在管壁上布放的两圈次级力源的间距小于管壁振动波长的1/4,且都不位于管壁振动节点附近时控制效果更好。     

基于流固耦合的油底壳振动噪声预测分析

为了对油底壳的改进方案进行噪声预测,首先建立油底壳的流固耦合有限元模型,进行耦合模态计算,获得其固有频率和振型,通过模态试验验证了耦合有限元模型的准确性;其次,在发动机工作过程中,通过试验测得油底壳各螺栓固定处的振动加速度;再次,基于模态结果,在油底壳各螺栓固定处施加测试的振动加速度,采用有限元的分析方法对油底壳进行了强迫振动计算和辐射噪声计算,并进行了试验对比,结果表明该方法可用于发动机开发试验确认阶段,对油底壳改进方案进行振动噪声的预测,减小开发风险;最后,对含油量多少对辐射噪声的影响进行了对比分析。     

充液管路系统流体声与结构声的复合有源控制

采用基于谐频自适应控制算法的有源消声与消振系统对充液管路系统突出的低频线谱噪声进行有源控制实验研究.建立了泵水循环管路实验系统,在管路中安装有源消声器对流体声进行控制,在管路出口障板上采用8×8通道有源消振系统控制结构声辐射。开展的低频线谱噪声与振动有源控制实验结果表明,在50~200 Hz频带内,通过结合有源噪声与振动控制可在多数频点取得10 dB以上的降噪效果。针对该实验系统,通过分别控制流体声和结构声分析了两者的贡献.实验结果验证了有源消声与消振系统具有较好的降噪性能,各频点处流体声与结构声占比情况不同,需要综合控制流体声与结构声才可以取得显著的降噪效果。      

混凝土箱梁相似模型结构噪声对比分析*

为探讨混凝土箱梁噪声的时变特性,以京沪高铁32 m混凝土简支箱梁为原型,制作了1:10的缩尺模型,通过模态试验的方法验证箱梁模型与原型的相似关系,通过声学试验验证箱梁声学计算模型的正确性。然后,建立了箱梁缩尺模型与原型两种计算模型,利用有限元和边界元法求出两种模型的瞬态结构噪声。研究发现,箱梁缩尺模型与箱梁原型的材料参数满足一定关系,模型试验的方法能够验证箱梁模型与箱梁原型之间符合相似关系,箱梁模型的振动噪声测试结果能真实反映原型振动噪声水平。两种模型的结构噪声在时域内声压级及对应场点的声压存在一定相似关系。该研究可为箱梁缩尺模型结构噪声反演至箱梁原型提供依据,所采用的方法和得到的结果对桥梁结构振动与声辐射实验研究具有参考作用。     

暗声学超材料型充液管道的低频消声特性

充液管道低频声的有效吸收和消减一直是一个颇具挑战性的难题.受声学超材料理论启发,本文设计了一种沿管道轴向方向等距布置小体积声学短管的充液周期管道系统.该管道系统可以诱发声波传播超宽低频带隙的产生,使得声波在带隙频率范围内传播将被显著衰减,乃至无法透射,近乎被完全吸收,称为暗声学超材料型充液管道.进一步,揭示了暗声学超材料型充液管道中声传播带隙的产生机理、参数影响规律,研究了该波导管对低频噪声的降噪特性,初步探讨了工程实际可实现的暗声学超材料型充液管道的结构实现形式.研究成果有望为管道低频噪声控制提供一条新的技术途径.     

Assessment of Traffic Noise Pollution in Burla Town,India; An Inclusive Annoyance Study

Noise pollution is one of the major public health problems in urban areas throughout the world. Noise is unwanted sound which produces undesirable problems in day to day life of human being (e.g., physiological and psychological problems). Rapid increase of the industrialization, urbanization, infrastructure, volume of motor vehicles, and increase in the road networks brought noise pollution to the highest level of disaster in a current situation. In urban areas, road traffic noise plays commanding role among all noise sources and affects the exposed inhabitants. The present work is done to evaluate and assess the traffic noise and its effects in Burla town. Burla, Vidyanagari of Odisha, is an emerging town in India, as it hosts national level of teaching and research institutions like IIM Sambalpur, a medical college- cum-hospital (VIMSAR), a technical university (VSSUT) and Sambalpur University. In last two decade, the road traffic volume has been increased and is facing severe noise pollution to its inhabitants. Noise pollution assessment was made at different locations of the town. This study unveiled the dismal state of noise pollution in the town. Noise contour maps were drawn to visualize the noise level at the traffic and its surroundings. The numbers of hearing impaired patients in different hospitals of the locality are increasing. That shows grim picture of the situation. Regression equations were established taking noise levels with percentage of highly annoyed people during study indicates strong correlation.     

New vehicle noise emission for French traffic noise prediction

Traffic noise prediction models in France are based on vehicle noise emission values defined by the French Guide du Bruit des Transports Terrestres (Noise Guide for Ground Transport - Noise levels prediction). These emission values are suited for models addressing the noise assessments of road infrastructures and the dimensioning of acoustic protections, needing traffic noise estimations in terms of ?_Aeq over a long period of time (an hour or more).The values, obtained from measurements collected in the 70s, are updated in the publication of a new guide (Methodological Guide, Vehicle noise emissions, to be published), which addresses the road surface influence on tyre/road noise. The emission values are now expressed through the contributions of a power unit component, function of traffic speed, traffic flow type and road declivity, and of a rolling noise component, function of traffic speed and road pavement.The paper outlines the procedures followed to determine the components, gives their numerical values, and illustrates some vehicle noise emissions.     

Identification of noise sources on a residential split-system air-conditioner using sound intensity measurements

This paper presents the results of experimental studies of the noise of a residential split-system air-conditioner unit. The compressor and condenser and associated fans were removed from the unit and did not form part of the studies. Care was taken with the unit to separate the inlet and exhaust noise from the noise radiated from the cabinet. The measurements were made with a two-microphone sound intensity probe and these resulted in sound power level data. The sound power levels produced by radiation from the inlet, exhaust and cabinet were obtained for five different volume flow rates. The effect on the sound power generated by removing the coil was investigated. Measurements and subjective studies show that the low frequency sound is predominantly radiated from the exhaust and inlet. At high frequency, the cabinet noise dominates.     

乘性二次噪声驱动的线性过阻尼振子的随机共振

针对乘性二次噪声和加性周期调制噪声联合驱动的线性过阻尼振子, 利用随机平均法推导了系统响应的一阶、 二阶稳态矩以及稳态响应振幅和方差的解析表达式. 理论分析和仿真实验均表明这类系统具有比传统的由线性噪声驱动的线性系统更丰富的动力学特性; 当二次噪声的系数满足一定条件时, 系统稳态响应的振幅及方差均存在广义随机共振现象.     

不同光照条件下CCD相机时间噪声和空间噪声的研究

在用CCD相机进行目标探测时,多数情况下目标的背景具有一定的照度,这个照度会对探测结果产生影响。为了了解背景对探测结果的影响,通过建立CCD相机三维噪声模型及其测试系统,在不同光照条件下对CCD相机的时间噪声和空间噪声进行了测量与分析。给出了测试系统的结构框图和部分测试结果,得到了对CCD输出质量产生主要影响的噪声以及时间噪声和空间噪声随光照度变化的规律。测试结果表明：随着CCD相机光敏面光照度的提高,空间噪声和时间噪声均升高,符合CCD相机的实际性能。     

Noise impact assessment by utilizing noise map and GIS: A case study in the city of Chungju, Republic of Korea

In this study, a scheme to develop a noise map and noise impact assessment method using GIS has been suggested. After developing a road-traffic noise map for the city of Chungju, Republic of Korea, noise impact assessment was performed through analyzing the map. A 3-dimensional terrain model was generated using digital maps and building models were prepared using the information from draft and digital maps. To develop a noise evaluation model, a noise-source map for each road was generated. The noise levels at 25 locations close to roads were measured and compared with the expected noise levels to verify the developed noise map. An excess noise map was generated by comparing the road-traffic noise map with a noise-standard map. Using the excess noise map, the areas exceeding environmental noise standards were effectively evaluated through a GIS space analysis. The 3-dimensional facade noise map was generated to calculate the number of people exposed to a certain noise level.     

热像仪空间NETD测量技术

凝视阵列型热像仪的空间噪声制约着热像仪对远距离目标的探测、分辨、跟踪性能。为解决热像仪空间噪声实际测量问题,分析了热像仪的空间噪声测量原理,给出了热像仪基于信号传递函数的空间噪声测量数学模型,介绍了热像仪某一组、某一区域或全部像素如何剔除时间域NETD,再通过统计计算得到其空间NETD的数学模型。对制冷型MCT320256凝视列阵热像仪的SiTF和空间NETD进行测量,当背景黑体温度为5 ℃时,FOV区域中心信号传递函数（SiTF）为27.29 mV/℃,NETD为0.128 ℃,20 ℃时FOV区域中心SiTF为29.03 ℃,NETD为0.121 ℃。测量结果表明:该方法可评估空间噪声对热像仪性能的影响。     

Design and experimental tests of active control barriers for low-frequency stationary noise reduction in urban outdoor environment

Active noise control (ANC) techniques are based on the emission of an antiphase signal in order to cancel the noise produced by a primary source. ANC has been successfully applied especially for reducing noise in confined environments, such as headphones and ducts. In this study, we present an application of ANC concepts to the design of an anti-noise barrier for an outdoor environment and its experimental testing. Even though passive techniques are effective in noise reduction at middle-high frequencies, they become less efficient at low frequencies (below 300 Hz) due to the limited dimensions of commonly deployable barriers. In this paper, we analyze the properties of a low-cost active noise system able to efficiently operate on stationary, almost pure-tone, low-frequency noise, such as that produced by electrical transformers and reactors in power and transformation plants. A prototype has been implemented and on-the-field experimental tests have been carried out. The results (confirmed also by numerical simulations) demonstrate a remarkable efficiency in the far field, with a reduction up to 15 dB with respect to the absence of the ANC system.     

基于功率谱收敛的低压电力载波信道中的噪声检测与建模

在低压电力线载波信道中,复杂的噪声特性是阻碍低电压电力线载波通信广泛应用的主要原因之一。因此,准确的噪声模型对于设计和优化电力线通信系统具有重要意义。为了得到更加准确噪声模型,给出一种等效背景噪声和功率谱收敛算法。通过对多组拟合参数的求解,并以归一化理论和噪声特性为基础,实现功率谱收敛算法对准确噪声模型的搭建。通过低压电力线信道噪声分析,验证了功率谱收敛算法在噪声模型中应用的可行性。     

CCD噪声标定及其在边缘定位中的应用

成像过程中的CCD噪声将给图像测量结果带来误差,因此能否有效地抑制这些噪声是提高测量精度的关键。分析了CCD暗电流噪声和随机噪声的特性,并针对各自特性提出了相应的噪声标定技术以及抑制方法。结合精密图像测量任务,分别研究了暗电流噪声和随机噪声对一维边缘定位、结构光相移法相位提取的影响。通过仿真和实验,比较了噪声抑制前后的测量结果,结果表明,噪声抑制后边缘定位精度有很大的提高,证实了该CCD噪声标定技术和抑制方法的有效性和必要性。