基于正交试验的进气消声元件优化设计

论文分析了进气噪声的产生机理,针对原机各阶次噪声出现的噪声尖点,找出了对应的振动频率。利用正交试验对空滤器的扩张比(容积恒定)、Helmholtz谐振腔和1/4波长管消声元件的结构参数进行综合优化设计,最大限度降低进气噪声。结果表明:基于正交试验得到的消声元件组合方案的进气插入损失最大(61.45d B),各阶次噪声均在阶次噪声限值以下,提升了进气消声系统的开发效率。     

抗性消声结构声腔模态对其消声特性的影响研究

为分析抗性消声结构声腔模态对消声器消声性能的影响,以典型3种抗性消声结构为对象,基于有限元法计算了其传声损失及扩张腔室的声模态,分析了扩张腔室声模态和进出口管位置对传声损失的影响规律。研究结果表明:扩张腔室的声模态和进出口管布置对抗性消声结构传声损失的影响非常显著。只有在极低的低频范围内,抗性消声结构的传声损失与基于一维平面波理论模型的传声损失结果才相吻合,进出口管布置位置对传声损失的影响才较小。消声器的进出口管布置位置对腔室的高阶声模态抑制和激发有重要影响,将进出口管布置在扩张腔室声模态节点区域能显著改善消声器中高频消声性能。对某汽车消声器进行改进设计,改进后平均传声损失提高了15.8dB。     

先进的排气消声技术

主动和半主动消声技术可使采用变排量或变功率发动机的汽车的排气系统实现标准化.     

分流气体对冲消声结构的消声性能与压力损失

从排气气流角度出发,利用发动机排气气流自身分流并发生对冲的思路,设计了一种新型消声结构一一分流气体对冲消声结构.排气气流分流对冲可有效降低消声器内排气气流速度,减少消声器内湍流噪声的产生,在兼具消声性能的前提下,有效降低了消声器的排气背压,提升了发动机的输出功率.从传统消声结构和分流气体对冲消声结构的数值模拟和试验验证...     

发动机排气噪声自适应有源消声系统的设计与试验研究

针对发动机排气噪声的特点,选取与噪声基频相关的振动和点火信号作为控制器参考信号,以Filtered—X LMS算法作为调节自适应滤波器各权系数的基本依据,并采用外加抖动信号的次级通道在线自适应建模方式,建造并实现了相应的试验系统。在所设计的有源消声试验台架上,对SUZUKI AX-100摩托车发动机排气噪声进行了有源消声试验,在400Hz以下取得了30dB以上的降噪效果。     

柴油机排气噪声有源消声系统的设计与实现

为解决柴油机排气低频噪声问题,基于噪声有源消声技术理论,选用与排气噪声相关的转速信号作为数字信号处理控制器的参考信号,以自适应陷波滤波算法为基础,采用次级通路离线自适应建模方式,设计了单通道有源噪声前馈控制系统,并在Matlab平台上进行仿真分析,最终选取迭代步长μ为0.003.在某柴油机排气管路上进行了排气噪声有源消...     

基于剪齿轮的齿轮噪声优化研究

齿轮噪声是内燃机主要噪声源之一。本文简要阐述了齿轮噪声的产生机理和控制措施,描述了齿侧间隙对齿轮噪声的影响以及剪齿轮的降噪原理。并对某型柴油机机油泵驱动齿轮采用剪齿轮方案进行噪声实测,结果表明剪齿轮可明显降低齿轮的阶次噪声。由此为解决工程应用中的齿轮噪声问题提供了一定的参考。     

内燃机燃烧压力振荡对燃烧过程影响的模拟研究

结合可视化发动机、高速摄影和激光剪切干涉测量设备拍摄的燃烧过程照片和获得的燃烧二维温度场,建立了燃烧室空腔模型,并将空腔声学模型划分为未燃区和已燃区,通过空腔声模态和瞬态响应研究,获得了燃烧室空腔在多点激励下的声场变化情况,结果表明,燃烧室空腔在多点激励下在未燃区产生局部压力集中现象,燃烧压力振荡可能是引起燃烧过程未燃区出现局部自燃现象的根本原因。     

二次光学元件侧面溢胶对聚光光伏组件光学效率的影响

基于全反射原理,该文理论研究二次光学元件在使用光学胶贴装过程中,二次光学元件底部侧面溢胶对接收器组件光学效率的影响。模拟分析3种不同二次光学元件的侧面溢胶高度对光学效率、接收角和温度变化的影响。结果表明,对于球透镜二次光学元件,光线在其传输过程中以折射为主,可有效减小侧面溢胶产生的光损失。对于平顶四棱锥镜,为减小侧面溢胶对光线的损失,在封装工艺过程中应严格控制侧面溢胶的高度,或优化设计侧面的倾斜角度。     

1000MW机组发电机密封油管道安装位置对氢气泄漏的影响分析

介绍了对某1 000MW电厂发电机氢气泄漏严重问题的检查情况,通过对发电机密封油及氢气系统的研究,发现了由于密封油系统油氢差压阀的两根信号取样管(氢汽压力和密封油压力信号取样管)的安装位置问题而导致取样管内油静压无法合理消除和补偿情况,导致了发电机氢气泄漏量大,并提出了改进措施。     

柴油电站的降噪方案分析

对柴油机组的降噪方法、降噪结构及其效果进行了分析；分析了降噪特性曲线对消音器参数选择的指导作用。     

Aero—Acoustics of Modern Transonic Fans—Fan Noise Reduction from Its Sources

The noise of aerodynamics nature from modern transonic fan is examined from its sources with the perspective of noise reduction through aero-acoustics design using advanced Computational Fluid Dynamics (CFD) tools. In particular the problems associated with the forward propagating noise in the front is addressed. It is identified that the shock wave spillage from the leading edge near the fan tip is the main source of the tone noise. Two different approaches have been studied to reduce the forward arc tone noise and two state-of-art transonic fans are designed using the strategies developed. The following rig tests show that while the fans exhibit other noise problems, the primary goals of noise reduction have been achieved through both fans and the novel noise reduction concept vindicated.     

基于声学超材料的齿轮减速器箱体减振方法研究

齿轮减速器振动噪声性能直接影响了船舶的舒适性和安全性,但目前普遍采用的减振降噪手段已进入瓶颈期。针对这一问题对声学超材料在齿轮减速器箱体上的减振方法进行了研究,分析了齿轮减速器箱体在不同激励下的振动特性,设计了超材料单体结构和具有类似振动特征的箱体缩比模型,系统分析了超材料的质量比、阻尼比和单体结构数量等对减振效果的影响。针对缩比模型设计了超材料减振方案1（单体结构固有频率分别为2 690,2 790和2 970 Hz）和超材料减振方案2（相比于方案1增加单体结构,固有频率为4 000 Hz）。经分析得到,在缩比模型主要峰值频率处方案1的减振效果不小于7 dB。并通过试验对该计算结果进行验证,减振频带误差小于4.0%,减振幅值误差不超过10.3%,证明了超材料方案的有效性。     

The Effect of Spherical Surface on Noise Suppression of a Supersonic Jet

Experiments were carried out to eliminate the screech tone generated from a supersonic jet. Compressed air was passed through a circular convergent nozzle preceded by a straight tube of same diameter. In order to reduce the jet screech a spherical reflector was used and placed at the nozzle exit. The placement of the spherical reflector at the nozzle exit controlled the location of the image source as well as minimized the sound pressure at the nozzle exit. The weak sound pressure did not excite the unstable disturbance at the exit. Thus the loop of the feedback mechanism could not be accomplished and the jet screech was eliminated. The technique of screech reduction with a flat plate was also examined and compared with the present method. A good and effective performance in canceling the screech component by the new method was found by the investigation. Experimental results indicate that the new system suppresses not only the screech tones but also the broadband noise components and reduces the overal     

The influence of the structural properties of carbon on the oxygen reduction reaction of nitrogen modified carbon based catalysts

Nitrogen modified carbon based catalysts for the oxygen reduction reaction (ORR) were synthesized using three different types of carbon, carbon black (CB), carbon nanotube (CNT) and platelet carbon nanofiber (P-CNF) with nitrogen containing organic precursors. The relationship between the ORR activity and the carbon nanostructure was explored using various electrochemical and physical characterization methods. It was found that the ORR activity was affected by the type and content of the nitrogen functional group instead of the carbon surface area. The formation of nitrogen functional group, in turn, strongly depends on the carbon nanostructure. Unlike the basal plane, the edge plane exposure provides the appropriate geometry for the nitrogen incorporation into carbon structure, resulting in high nitrogen content and high pyridinic-N and graphitic-N content, providing an active site for ORR. Therefore, the P-CNF based catalyst with the highest edge plane exposure has the highest ORR activity despite having the smallest surface area.     

Effect of boundary layer trip on reduction of jet noise in over-expanded nozzle flow

A flow resonance accompanied by the emission of acoustic tones occurs in an over-expanded convergent-divergent (C-D) nozzle when operated at comparatively low pressure ratios.This phenomenon is distinguished from conventional screech tones and is referred to as “transonic tones”.In contrast to screech tones,the peak resonant frequency for transonic tones increases with pressure ratio;the peak sound pressure level exceeds 110 dB.In this study,we investigated the basic characteristics of transonic resonance and tones using a circular C-D nozzle in an anechoic room.The effects of the boundary layer trip were also evaluated using a tripping wire for the suppressing transonic resonance and tones.The results of acoustic measurements show that several predominant peaks correspond to transonic tones.However,the boundary layer trip inside the nozzle effectively eliminated these tones and suppressed the unsteadiness of the flow inside the nozzle.     

基于支持向量机的垃圾焚烧炉SNCR系统优化控制

针对目前垃圾焚烧厂选择性非催化还原(SNCR)系统工程应用中的问题,提出了SNCR控制系统优化方案。引入声波测温系统测量炉膛二维温度场,实现了SNCR系统分区精准喷射还原剂。采用支持向量机建立的SNCR系统模型预测烟气氮氧化物排放浓度的准确率达98.82%。设计了SNCR系统的PLC控制逻辑,可实现对各种工况下还原剂喷入量的精确控制。该优化方案针对性地解决了SNCR系统的工程问题,提高了脱硝效率。     

The influence of carbon nanofiber support properties on the oxygen reduction behavior in proton conducting electrolyte-based direct methanol fuel cells

Platinum nanoparticles supported on fishbone carbon nanofibers (CNFs) were synthesized and studied for the oxygen reduction reaction (ORR). The crystalline and textural properties of the CNFs were modified by synthesizing them at different temperatures, allowing the comparison of supports with either improved graphitization degree or improved porosity. A carbon black (Vulcan XC-72R) was used for comparison. Half-cell studies determined that the ORR activity is enhanced when using a CNF with improved graphitization, in contrast with CNFs with better textural properties such as surface area or pore volume. The catalysts were tested at the cathode of a direct methanol fuel cell corroborating the suitability of using highly graphitic CNFs, and a similar behavior was found in comparison with the state of the art carbon black used in this field.     

The effect of oxygen reduction on activated carbon electrodes loaded with manganese dioxide catalyst

The statistical design-of-experiment method was used to identify the significant factors for making a manganese oxide-loaded activated carbon matrix. The carbon matrixes, which were made by reacting KMnO₄ with carbon material, were tested as gas-diffusion electrodes for oxygen reduction. Three factors—KMnO₄ concentration, reaction temperature, and reaction duration were tested in a two-level full-factorial design-of-experiment. The modification of carbon morphology and its effect on the performance of oxygen reduction are discussed. Temperature, KMnO₄ concentration, and the interaction between temperature and reaction time were found to have a significant influence on the catalytic activity of the manganese oxide-loaded carbon electrode.     

Kinetic effect of the ionomer on the oxygen reduction in carbon-supported Pt electrocatalysts

The mechanism of the oxygen reduction reaction (ORR) on nanoparticulated Pt/C-Nafion electrodes prepared in one step has been studied to simulate the reaction in the cathode of a Polymer Electrolyte Fuel Cell (PEFC). The kinetic parameters have been obtained by hydrodynamic polarization in O₂-saturated 0.01–1.00 M H₂SO₄ and temperatures in the range 25.0–50.0 °C. The ORR current density was maximum and practically independent of the ionomer fraction in the rage 10–55 wt% Nafion. The poorer proton conductivity for lower Nafion fractions and the formation of catalyst areas completely surrounded by Nafion together with adsorption of Pt sites by sulfonate groups for higher Nafion fractions, explain the minor ORR activity in these conditions. The ionomer influence on the O₂ diffusion at high overpotentials for Pt/C-Nafion was negligible when the Nafion content was smaller than 20 wt%. The higher kinetic current density for Pt/C-Nafion (100 mA cm⁻²) with respect to smooth Pt-Nafion (40 mA cm⁻²), together with the smaller activation energy of the former (25 ± 4 kJ mol⁻¹) with respect to the latter (42 ± 5 kJ mol⁻¹) highlighted the better properties attained by the nanosize effect. A remarkable novel result is that the reaction order of H⁺ in HClO₄ is close to unity, whereas in sulfuric acid it is significantly smaller and changes with potential, what has been related to the sulfate adsorption. The anomalous dependence of the charge transfer coefficient with temperature was then explained by the thermal change of the double layer structure and the variation of the coverage of adsorbed species on Pt. The more sensitive effect for Pt/C-Nafion than for smooth Pt-Nafion was ascribed to the stronger interaction between the components when the nanoparticles are involved.