降低通风机噪声的试验研究

本文介绍了在通风机内部结构上采取降低噪声的两种措施及试验研究结果.一种是对风机叶片的进、出气边作锯齿形处理,另一种是对风机叶片的出气边作仿生学处理.试验结果表明,锯齿形处理可降低A声级噪声2—5％,尤以齿距z=0.1b齿高h=0.1b的锯齿形处理为佳,试验结果还表明,“风机叶片的仿生学处理可以降低A声级噪声,降噪幅度在风量一定的条件下主要取决于仿生学处理的叶片相对长度。ΔL/L.上述方法是值得推广的降低通风机噪声的有效措施.     

表面催化反应模型中关联噪声诱导非平衡相变

建立含有关联噪声的双分子-单分子(DM)表面催化反应延迟反馈模型,该模型能同时显示一级和二级非平衡动力学相变,即在一级和二级非平衡动力学相变之间的反应窗口展现.讨论双分子在DM延迟反馈模型中两种吸附机制,即局域和随机吸附模型.研究结果表明:1)外部噪声及两噪声关联性致使反应窗口的宽度收缩;2)内部噪声对非平衡动力学相变行为的影响依赖两噪声关联性,即当两噪声负关联,内部噪声致使反应窗口的宽度变宽;而当两噪声正关联时,内部噪声致使反应窗口的宽度收缩;3)关联噪声致使反应窗口变化对DM模型中一级和二级非平衡动力学相变研究具有重要的科学意义.     

喷流噪声预测中小尺度湍流声源模型

本文在Tam & Auriault提出的喷流噪声预测方法的基础上,导得计算轴对称喷管伴随格林函数的方程以及声源谱、伴随格林函数与噪声谱密度函数之间的关系,比较了几种典型的声源模型,并且采用了一种随频率变化的长度尺度.验证结果表明,TA预测模型中随频率变化长度尺度与Harper-Bourne提出的声源模型的结合能给出更好的预测结果.     

考虑噪声烦恼度的机场飞机噪声收费模型和应用研究

随着我国民航运输业的飞速发展,机场噪声影响问题日趋严重。通过向航空公司或旅客收取噪声费来进行治理,是民航发达国家的普遍做法,也是我国未来的发展方向。该文在国外机场飞机噪声收费模型的基础上,提出了基于飞机噪声特性、噪声烦恼度、噪声治理投入费用和资金回收周期等因素的机场噪声收费模型。模型将机场噪声治理费用通过合理的回收周期按一定比例分配到各年度,再根据飞机噪声特性、噪声烦恼度将每年噪声收费分配到每架次飞机(或每位旅客)。飞机噪声特性根据ACI的机场噪声分级R1～R8来确定,噪声烦恼度借助Mamdani模型构建。应用表明,该收费模型关键因素考虑全面,计算方法先进简洁,费率合理。对于噪声较高飞机,夜间起飞收费为1219.06元/架次,客均收费10.16元;对于噪声很低的飞机,昼间着陆收费为66.10元/架次,客均收费仅0.15元。费率确定符合国际民航组织倡导的以支定收原则,有助于形成航空公司/旅客减噪激励机制同时又不致抑制机场航空业务增长。     

水下对转桨无空化噪声调制理论分析与试验研究

水下对转桨无空化噪声由流场-桨叶相互作用引起,调制特性是水下对转桨无空化噪声的重要特征,本文研究了水下对转桨无空化辐射噪声调制机理。首先利用广义声类比方法得到了无空化条件下水下对转桨的远场声压谱,建立了水下对转桨无空化噪声的调制模型,然后数值仿真了模型对转桨无空化噪声的功率谱和调制谱,最后在空泡水筒中进行了模型对转桨的无空化噪声测量试验,数值仿真结果和试验验证了调制模型的准确性。该模型对于水下对转桨无空化噪声调制特性预报及目标识别具有重要价值.     

纳米器件电流噪声的散射理论统一模型研究

传统散射理论在研究器件噪声特性时,并没有考虑非相干输运和库仑作用对散粒噪声的抑制,而在实际纳米器件中这两种效应不可忽略.本文基于散射区等效接触端模型推导了考虑上述两种效应的电流噪声散射理论统一模型,该模型适用于从相干输运到非相干输运的整个输运区,并同时考虑了泡利不相容原理和库仑作用对散粒噪声的抑制.本文也提出了一种基于统一模型的电流噪声数值模拟方法,该方法所得散射区特性与散射区等效接触端模型特性一致. 关键词： 电流噪声 散射理论 统一模型     

确定峰度非高斯海洋环境噪声模型研究

针对非高斯海洋环境噪声仿真问题,利用对衰减正弦信号均匀采样方法,产生了具有特定谱特性同时具有特定峰度值的非高斯海洋环境噪声序列。在理论仿真条件下,通过对低峰度值和高峰度值的分别讨论发现,当峰度值高于3.0时总可以仿真得到较好的结果,而当峰度值低于3.0时,需通过降采样或降阶的方法解决不能仿真的问题。4种海上试验条件下的仿真结果表明,在安静环境、单一航船干扰环境、气枪声源干扰环境以及冲击性干扰环境下,都可以产生与目标谱特性、统计特性几乎相同的非高斯海洋环境噪声序列。     

基于物理机制模型的民机机体噪声预测

为实现民机总体方案快速评估与优化迭代设计,文章对民机增升装置前缘缝翼及后缘襟翼分别建立了基于民机噪声物理机制的预测模型,在此基础上搭建了机体噪声预测体系,开发了相应的预测工具UNICRAFT.为评估预测工具UNICRAFT的计算精度和效率,文章分别针对翼吊式布局,前缘缝翼/Fowler式襟翼形式,以及尾吊式布局,前缘缝...     

双带紧束缚模型中噪声对超晶格中电子输运性质的影响

运用直交流电场驱动下的双带紧束缚模型,研究了噪声对超晶格中电子输运性质的影响.数值结果表明,外部噪声能够破坏瞬时电流的周期性并且能够削减长时平均电流的峰值.随着噪声强度的增加,平均电流峰的高度降低,宽度增加;当增大噪声的衰减常数时,平均电流峰会有类似上述变化.     

热核表面能的Thomas–Fermi统计模型理论

用Seyler-Blanchard动量相关非定域相互作用的含温Thomas-Fermi统计理论,对半无穷大核物质模型计算了核物质表面能系数σ(T,δ)随温度T和不对称度δ的变化,发现在低温T≤5MeV和不对称度δ≤0.2时,可以近似写成σ(T,δ)=σ₀(T)[1+K(T)δ²],其中σ₀(T)和K(T)可以拟合成温度T的二次函数.     

Broadband shock noise reduction in turbulent jets by water injection

The concept of effective jet properties introduced by the author (Kandula M. Prediction of turbulent jet mixing noise reduction by water injection. AIAA J 2008;46(11):2714-22) has been extended to the estimation of broadband shock noise reduction by water injection in supersonic jets. Comparison of the predictions with the test data for cold and hot underexpanded supersonic nozzles shows a satisfactory agreement. The results also reveal the range of water mass flow rates over which saturation of mixing noise reduction and existence of parasitic noise are manifest.     

高层住宅阳台降噪量的计算分析

高层住宅中的阳台不仅具有居住及建筑上的功能,对道路交通噪声也有衰减作用。本文通过建立噪声传播模型计算高层住宅阳台的插入损失,并探讨了影响阳台降噪量的一些因素。同时对阳台内部吸声处理的效果进行了理论预测。     

A study of noise reduction by acoustic shock waves

I.IntroductionAcousticshockwavcs(ASW)isanimportantphcnomcnoninnonlinearacoustics.Experimentalrcsultshavcshownthatwhenanaircraftcngincinletopcratesneartheson-iccondition,vcrystrongnoisegcncratedbythcfanscanbcreduccdgreat1yowingtothcformationofASWatthcthroatofthcin1etll].ASWisadiscontinuityofacousticvaria-bles,whichisdifTcrcntfromthcshockwavesoccurringinhighspcedsteadyflowinducts.Theformer'sintensityismuch1cssthanthelattcr's.Furthcrmorc,thepositionandintensityofASWisalwayschangedwithtime.l…     

金属烧结丝网在内场消声中的应用

利用试验手段研究暂冲式风洞稳定段内安装不同规格烧结金属丝网对风洞上游控制阀后气流噪声和湍流度抑制作用。试验结果表明:多层金属烧结丝网可在全频段内大幅度降低上游气流的噪声,最大可达21 dB;消声量与金属烧结丝网无量纲的压力损失系数成正比,压力降与金属烧结丝网层数呈现出非线性叠加的结果。另外发现烧结金属烧结丝网对气流速度脉动亦具有突出的抑制效果。例如,试验段马赫数Ma=1.5时,120目26层+160目26层组合烧结金属丝网出口气流速压脉动幅值减小为入口来流的18%,湍流度由11.7%降至3%。因此金属烧结丝网适合于暂冲式风洞的内场降噪。     

轻轨桥架声屏障降噪效果的测量与分析

在轻轨桥架两侧设置声屏障是控制轨道交通噪声的主要措施之一，对上海轻轨明珠线桥架两侧设置不同高度声屏障实际降噪效果的测量与分析，对声屏障的实用设计有重要的参考价值。     

The effect of a suppressor to environmental noise – A case study

The purpose of the study is to describe the effect of a suppressor to environmental noise with a typical Finnish rifle shooting range that has a shooting shelter and some noise berms. The noise measurements were carried out at Kyronpelto shooting range situated near Mikkeli in Finland. The range is equipped with wooden shooting shelter, the shooting distance is 150 m, and it has berms on sides and at the impact end. The terrain is relatively flat in the area. The best noise area reduction caused by a suppressor could be seen at angles of 315–45° from the shooting direction. The projectile noise dominates at angles 45–70°, and the effect of the suppressor is very small. To the side and back the shooting shelter has already gained significant noise attenuation, and therefore the suppressor cannot reduce the noise area much more. When there was a relatively tight shooting shelter to the side and back, the suppressor did not reduce the environmental noise area significantly any more. It can be calculated that the noise area of 65 dB (L_AImax) is reduced from 95 ha to 50 ha (0.95 km²–0.50 km²) with the help of a suppressor. However, most of the area is situated to the shooting sector and it has to be unoccupied for safety reasons.     

Experimental study on the noise reduction of an industrial forward-curved blades centrifugal fan

Many previous researches have concentrated on the noise of backward-curved (BC) blades and forward-curved (FC) multi-blade centrifugal fans. In this paper, an experimental study has been carried out to study the noise reduction of an industrial FC blades centrifugal fan. First of all, the performance and noise characteristics of the FC centrifugal fan were tested to compare the similarities and differences from those of BC blades and FC multi-blade centrifugal fans. And then, some different volute geometric configurations were carried out in order to study the effects of inclined volute tongue, impeller blade-tongue clearance, hub-volute clearance and their coupling effect to the performance and noise of the FC blades centrifugal fan. The aim of many different experimental tests is to validate whether the effects of different modifications to fan performance and noise are additive and to find a good impeller-volute matching to reduce the centrifugal fan noise without reducing performance. The experimental results show that a good coupled modification not only could reduce the fan noise but also could advance the fan performance and extend the operating range.     

Minimum noise temperature of a practical SIS quantum mixer

Noise temperature of a SIS quantum mixer has been calculated as function of local oscillator voltage and signal source conductance on the basis of a measured I–V characteristic. Applying Tucker's quantum theory of mixing /1/, it is shown that the SIS mixer is quantum noise limited. Using cryogenic intermediate frequency amplifier, receiver noise temperature of 20 K seems to be possible at mm wavelength.     

光伏电站电力听诊系统降噪方法*

在光伏电站电力听诊系统中,为降低光伏电站采集声音的噪声,对光伏电站常见的各种噪声进行时频谱分析,基于各类噪声特点和经典的U型网络结构设计了降噪网络,为提升降噪效果,将能量信息加入到复数卷积网络中,同时融合基于Transformer的专家子系统进一步提升效果。最后,通过构建数据集和多组对比实验证明了所设计网络对常见混叠信号可以大幅提高声音信号的信噪比,最高可达6.14dB。另外,通过多组烧蚀实验证明了文章中所述各项优化点的有效性。     

A study of noise in CNG driven modes of transport in Delhi

Measurements of noise and its spectral characteristics were made inside various types of transport running on Compressed Natural Gas (CNG) fuel in Delhi. Noise indices L₁₀, L₅₀, L₉₀ and L_eq were estimated from the measured noise levels for vehicles in neutral gear, slow speed (speed ?20 km/h) and under free flow (speed ?30 km/h) conditions. It is found that background levels, when averaged over all speeds, are maximum in Rural Transport Vehicles (RTV) followed by Buses, Auto-rickshaws and Taxis. With increase in the speed, noise levels are appreciably enhanced except in the case of auto-rickshaws where the increase is moderate. The spectral distributions of noise inside vehicles obtained at 1-octave band frequencies, show a rather similar nature. The study reveals significantly lower noise levels inside CNG driven public modes of transport compared to those found in an earlier survey inside diesel and petrol driven vehicles.