基于独立分量分析及小波变换的内燃机辐射噪声盲源分离和识别

为了分离和识别内燃机噪声源,结合独立分量分析和小波变换技术对内燃机辐射噪声信号进行了盲源分离和声源识别的研究.根据独立分量分析的基本原理,采用基于负熵极大的FastICA算法对4缸柴油机的辐射噪声信号进行了盲源分离,将噪声信号分解成一系列独立分量.采用快速傅里叶变换和小波变换技术对各个独立分量进行了分析,结合时频分析的结果和内燃机各噪声源信号的频谱结构,确定了分离得到的各独立分量与内燃机不同噪声源的对应关系.研究结果表明:这些独立分量分别对应着柴油机的燃烧噪声、活塞敲击噪声、正时齿轮噪声及排气辐射噪声等噪声源.     

变电站噪声特性及降噪控制措施

目前变电站噪声对周边环境的影响愈发明显,并已成为亟待解决的环境问题。通过对厦门站噪声特性的测试分析,确定了噪声的主要传播途径,通过针对性降噪措施的实施,利用开发的声全息技术可以快速准确地识别配电站、变配电设备的噪声源。通过对噪声源及传播路径的改善,可有效降低变配电设备的噪声量级。     

4缸柴油机怠速噪声及声品质优化研究

针对高压共轨4缸柴油机进行了怠速噪声测试、噪声源识别、降噪以及声品质优化研究工作.通过改变转速、预喷油量、预喷间隔角、轨压和主喷正时,研究了这些参数对怠速噪声的影响,并确定最佳值.通过燃烧噪声分析和噪声源识别,采取怠速噪声降噪措施.对怠速噪声优化前后的结果进行声品质比较,采取的电控标定优化和屏蔽措施能有效改善怠速声品质.研究结果表明:该4缸柴油机经过电控优化标定后的主要怠速噪声源为机械噪声,通过对齿轮室罩盖、气缸盖罩盖等薄壁件采取屏蔽措施,能有效降低怠速噪声,改善声品质.     

基于独立分量分析技术的内燃机噪声源识别

为降低内燃机的噪声,需要有效地识别内燃机的众多噪声源。采用一种新的独立分量分析技术对采集到的内燃机混叠噪声信号进行分离,并结合噪声产生机理辨别出单个噪声分量对应于内燃机的相应噪声源,从而有效地识别内燃机噪声源。实践证明,该技术可以有效识别内燃机的混叠噪声。最后就噪声控制提出了建议。     

内燃机传动噪声识别的小波分析方法

为了降低内燃机噪声必须确定其噪声源。基于内燃机噪声信号非平稳和周期性的特点,用模拟数据说明了将小波分析应用于内燃机噪声信号分析的合理性,并利用连续小渡变换对一台车用发动机前、后端的噪声源进行了识别诊断,确定了发动机的噪声源,证明了小渡分析是内燃机噪声源识别的一种有效方法。     

结合多种方法进行六缸柴油机噪声源识别研究

针对六缸柴油机进行了噪声源识别和降噪研究工作.通过单缸熄火法进行燃烧噪声和机械噪声的分离,以及表面振动法和声学照相法,结合振动和噪声信号的频谱分析法,对发动机表面辐射噪声进行了识别;针对表面噪声辐射的主要噪声源采取了屏蔽措施.研究结果表明:六缸柴油机的主要噪声源为机械噪声,通过对齿轮室罩盖、气缸盖罩盖、充电电机外壳和喷油泵等薄壁件采取屏蔽措施,或者进行结构优化,能有效降低整机噪声.     

阶次分析在发动机进气噪声研究中的应用

进气噪声是发动机主要噪声源之一.为研究发动机转速对进气噪声的影响,采用阶次分析方法对一台车用四缸发动机的进气噪声进行了试验研究,首先分析进气口总声压级随转速的变化关系,并根据进气噪声阶次分析的特征分量分布,初步识别了其主要频率成分及相应噪声源,以及最大噪声产生时的发动机运行工况,分析结果可为发动机进气系统优化设计及噪声控制提供一定的参考依据.     

天然气联合循环电厂的噪声控制

天然气联合循环电厂环保节能,大多安装在经济发达、人口稠密的大、中城市附近,但厂界噪声和周围声环境(主要是居民敏感点)的达标却成了极其突出的问题.本文介绍了厂界噪声和周围声环境的国家标准,以及用户如何对设备制造厂提出设备的噪声限值要求.并以浙江半山天然气联合循环发电工程为例,介绍了在联合循环发电工程建设中对主要噪声源的分析和治理措施,以及工程竣工验收后取得的噪声治理效果.     

柴油机表面噪声源识别技术研究

通过测量柴油机表面振动速度的方法对其进行了表面噪声源识别的研究.首先确定了柴油机各主要噪声辐射部件,并分别测量了其表面振动速度,分析了各部件的振动特性,通过表面振动速度计算了各主要噪声辐射部件辐射的声功率和它们对总噪声的贡献量,得到了各主要噪声源的大小排序,从而识别出了该柴油机的主要表面噪声源,最后提出了为改善柴油机整体噪声辐射水平应采取的降噪措施.     

瓦斯发电厂降噪措施研究

煤矿瓦斯发电已成为煤矿瓦斯综合利用最为经济、有效的方法,但其瓦斯发电机组运行时产生的噪声污染,是煤矿在环境保护方面必须应对的问题.分析了噪声源、传播特征、吸声原理和结构,提出了煤矿瓦斯电厂噪声治理措施.     

A TECHNIQUE TO CIRCUMVENT A SINGULARITY AT A RADIAL CENTER WITH APPLICATION FOR A THREE-DIMENSIONAL CYLINDRICAL SYSTEM

A technique was invented to circumvent computational singularity at a radial center of cylindrical and spherical coordinate systems. The idea is as follows. The radial velocity at a center is given by the average of adjacent circumferential directional velocity components located at ± 0.5π rod. Sample computations are presented for natural convection in a vertical cylinder with two different thermal boundary conditions. Those velocity profiles through a cylinder center are smoothly represented.     

A NONLINEAR INDIRECT MEASUREMENT PROBLEM FOR A MULTITHERMOCOUPLE PROBE IMMERSED IN A LIQUID

The problem described herein concerns the processing of the time-dependent, internal temperatures within a multithermocouple probe. These are used to compute the temperature of the surrounding fluid, as part of an inverse heat conduction problem (IHCP). The novel achievement in this work is that the exchange coefficients do not have to be supplied a priori, but instead are an additional solution output. Consequently the IHCP is nonlinear and requires significant stabilization. Four methods are applied successively, until a satisfactory solution is found: the parameterization of spatial variations in fluid temperatures and exchange coefficients; a functional specification method (using future time data) to address the noncausal nature of the solution; a lower bound on the exchange coefficient; and a maximum number of iterations at each time step (in accordance with the discrepancy principle).     

A solar-assisted biogas system: A new approach

In order to increase the production of biogas, particularly in the winter months of northern India, a new design of a collection-cum-storage water heater integrated with the dome of conventional Indian (KVIC) biogas units has been proposed and studied theoretically. During sunshine hours, the biogas system is exposed to solar radiation to increase the slurry temperature, and is covered with movable insulation to avoid night heat losses from the top as well as the sides of the dome. Some interesting conclusions have been drawn.     

A NUMERICAL STUDY OF JETS IN A REACTING CROSSFLOW

This article is concerned with computational modeling of the mixing of circumferentially placed round jets with a crossflow in a circular duct. This flow is relevant to many engineering applications including gas turbines and steel melting furnaces. Both nonreacting and reacting flows are considered. The fundamental characteristics that govern the mixing of the air and fuel streams are investigated. Further, the applicability of a laminar flamelet model for prediction of the combustion process is assessed through comparison of code predictions to experimental data.     

A contribution for thermoeconomic modelling: A methodology proposal

This work presents a thermoeconomic optimization methodology for the analysis and design of energy systems. This methodology involves economic aspects related to the exergy conception, in order to develop a tool to assist the equipment selection, operation mode choice as well as to optimize the thermal plants design. It also presents the concepts related to exergy in a general scope and in thermoeconomics which combines the thermal sciences principles (thermodynamics, heat transfer, and fluid mechanics) and the economic engineering in order to rationalize energy systems investment decisions, development and operation. Even in this paper, it develops a thermoeconomic methodology through the use of a simple mathematical model, involving thermodynamics parameters and costs evaluation, also defining the objective function as the exergetic production cost. The optimization problem evaluation is developed for two energy systems. First is applied to a steam compression refrigeration system and then to a cogeneration system using backpressure steam turbine.