离心风机整机三维数值仿真方法及分析

离心风机的性能特征与其内部流场结构是密切关联的,某些简化模型下对风机内某个部件或某个流道做的数值仿真并不能准确反映蜗壳与叶轮之间的相互作用.为了解其性能变化的根本原因,达到优化风机性能改善系统特性,需要对整机进行详细的流场结构分析.在软件Numeca的Fine/ Turbo模块上,采用壁面函数法,对某离心风机在设计转速下不同工况点进行了数值仿真,与已有的试验数据对比,吻合较好,并准确反映了蜗壳与叶轮之间的相互作用,为风机的设计和性能优化提供了可信的理论依据.     

高速列车集电部气动噪声数值模拟

针对铁路提速后高速列车集电部气动噪声过大的问题,在集电部引入导流罩,应用FLUENT对不合导流罩及含导流罩集电部的外流场和气动噪声分别进行数值模拟和分析．流场计算采用稳态雷诺平均纳维斯托克斯（Reynolds Averaged Navier—Stokes,RANS）方法,声学模型选择边界层噪声模型．计算结果表明导流罩的设计至关重要,合理的设计能使得导流罩较好地引导气流,起到降低集电部气动噪声的作用．     

TLT离心风机的产品模型分析及数学模型建立

本文介绍了TLT离心风机的产品模型分析，及数学模型建立的基本方法。通过对TLT离心风机的产品特点进行分析，建立由各部件组成的层次模型，以及各部件相应的数学几何模型，并产生相应的几何和工程的约束控制关系。     

动车组司机室空调蒸发器气动噪声数值仿真

为研究动车组司机室空调蒸发器的噪声响应,建立某型司机室分体式空调蒸发器的计算流体动力学模型,采用FLUENT中的大涡模拟（large eddy simulation, LES）计算瞬态气动流场。对瞬态流场数据进行傅里叶变换,得到空气流场的频域数据。基于流场频域数据,采用Virtual.Lab的边界元法计算蒸发器的气动噪声,采用声压法计算蒸发器的辐射声功率,并与测试结果进行对比分析。结果表明：蒸发器出口位置气动噪声最高,最大声压级高于56 dB;最大声功率级出现在125~400 Hz的低频段;声功率级随着频率的增加逐渐降低,但在5 000 Hz的高频辐射中声功率级仍然超过55 dB,这表明空调蒸发器气动噪声属于宽频噪声;计算结果与测试结果吻合良好,验证声压法计算空调蒸发器气动声功率可行。     

基于混合数值算法的锯齿形喷管气动噪声仿真

为了预测航空发动机喷流噪声远场声压级,满足未来的航空器噪声适航要求,采用计算流体力学(CFD)和计算航空声学(CAA)混合数值算法,对安装Chevron型锯齿的喷管进行气动噪声仿真计算.使用大涡模拟(LES)计算喷管的瞬态喷流流场.在流场计算的基础上使用Ligthill声类比进行声源提取,结合有限元/无限元方法对喷流噪...     

Helmholtz共振腔气动噪声数值仿真

为探究出一套完整、准确的气动噪声仿真方法,用FLUENT和Actran仿真Helmholtz共振腔旁接管道系统模型.针对流场仿真,采用六面体网格建模,分析选择合适的网格密度,明确网格及边界条件的影响,以获得准确的声源信息;运用Lighthill声类比方法对声场进行仿真,采用数值计算、传声损失仿真和气动噪声仿真计算等3种方法提取管道内部场点声压级频谱曲线,分析曲线峰值频率特征,包括共振频率分析和声模态分析等.采用CFD软件与声学仿真软件相结合的方法,可以有效进行流场和声场的仿真.     

管道泄漏噪声的数值仿真分析

在管道运输的研究中,针对实时监控问题,目前管道泄漏噪声的获得主要是采用实验的方法,易受模型尺寸、测量精度等因素限制.以广义莱特希尔(Lighthill)理论为基础,利用商业软件fluent对输流管道泄漏的流场进行数值仿真.据实际情况设置边界条件,分析了流速的变化.接着运用基于LES大涡仿真法和FW-H方程相匹配的技术,对管道泄漏噪声进行了CAA数值仿真,通过快速傅立叶变换对泄漏点处及测量点处的压力进行了频谱分析,对比了不同点声压的特点.通过仿真实验,结果表明,为噪声研究提供了参考,对实际的管道泄漏声场分析和监测有较大的参考价值.     

TLT离心风机CAD系统的升级优化

介绍了计算机辅助设计软件AutoCAD的二次开发技术,然后以上海鼓风机厂TLT离心机CAD系统的升级优化为例,详细阐述了如何把利用AutoCAD二次开发技术进行开发设计的有关CAD设计的第三方专业软件由ADS开发版本升级到ObjectARX开发版本,以期提高CAD设计第三方专业软件的运行速度,最终达到系统升级的目的。     

洗扫车用吸尘盘气动噪声的优化

吸尘盘作为洗扫车的关键组成部件,降低吸尘盘的气动噪声可极大提升产品性能.基于FLUENT软件和FW-H声比拟模型,对吸尘盘的气动噪声强度进行了计算,设计了一种带有肩部结构和倾斜壁面的新型吸尘盘结构,重点研究了肩部夹角和上壁面倾角对吸尘盘气动噪声产生的综合影响,基于MATLAB软件,采用多项式拟合方法分别建立了两参数与吸尘盘全压以及总声压级之间的函数关系,并结合多目标优化遗传算法对目标函数进行了优化分析.数值结果表明：肩部夹角对气动噪声的影响较为显著,在0°~20°范围内,夹角每增加1°,噪声可以降低0.4dB;合理地增大肩部夹角,可以在降低能量损失的同时有效降低吸尘盘的气动噪声,最大降幅为6.2dB.     

一种新型气动蠕动机器人的机理研究

本文提出了一种新型气动蠕动机器人,分析了它的驱动机理和动态特性,这种蠕动机器人有一个基于气动驱动器的新颖驱动机构和四个吸附足,它结构简单,制造成本低,易于小型化,仿真表明本文的控制策略可行,响应快速,控制可靠,因而这种新型机器人在很多领域有着广泛的应用潜力。     

大型车辆发动机冷却风扇流场的数值仿真方法

给出了发动机冷却风扇的数值仿真的建模方法和求解技术。以大型车辆发动机冷却风扇为研究对象,采用分区域划分网格的方法,运用滑移网格技术,对大型车辆冷却风扇三维流场进行了数值模拟和气动性能、气动噪声的研究。流场稳态模拟采用了基于雷诺平均的RNGκ-ε湍流模型,流场瞬态模拟采用了大涡模拟方法。给出了风扇流场的压力分析和速度分析,讨论了对风扇流量和气动噪声的影响因素。     

An efficient solution to improve the spectral noise suppression rules

Typical spectral noise suppression rules employ a multiplicative gain function in the frequency domain. In this paper, we propose a modified gain function to improve the speech enhancement. The general principle is based on a theoretical development of the classical gain function in order to derive an efficient estimator for the noise reduction system. The idea combines the performances of spectral subtraction method and statistical model estimator. The obtained combination involves two parameters. These parameters control the rate of noise reduction and speech distortion. Performances of the idea were evaluated using a number of tests in various environments through speech distortion measurement. Experimental evaluations show that the modified gain function yields better results as compared to the conventional gain functions.     

Authenticating corrupted photo images based on noise parameter estimation

Photo image authentication is an interesting and demanding field in the computer vision and image processing community. This research is motivated by its wide range of applications, which include smart card authentication systems, biometric passport systems, etc. In this paper, we propose a method of authenticating corrupted photo images based on noise parameter estimation. The proposed method first generates corrupted images by adjusting the noise parameters in the initial training phase. This set of corrupted images and the noise parameters can be represented by a linear combination of the prototypes of the corrupted images and the noise parameters. In the testing phase, the noise parameters of the corrupted photo image can be estimated with a corrupted image and an original image. Finally, we can make a synthesized photo image from the original photo image using the estimated noise parameters and verify it with the corrupted photo image. The experimental results show that the proposed method can estimate the noise parameters accurately and improve the performance of photo image authentication.     

Estimating aerodynamic resistance of rough surfaces using angular reflectance

Current wind erosion and dust emission models neglect the heterogeneous nature of surface roughness and its geometric anisotropic effect on aerodynamic resistance, and over-estimate the erodible area by assuming it is not covered by roughness elements. We address these shortfalls with a new model which estimates aerodynamic roughness length (z₀) using angular reflectance of a rough surface. The new model is proportional to the frontal area index, directional, and represents the geometric anisotropy of z₀. The model explained most of the variation in two sets of wind tunnel measurements of aerodynamic roughness lengths (z₀). Field estimates of z₀ for varying wind directions were similar to predictions made by the new model. The model was used to estimate the erodible area exposed to abrasion by saltating particles. Vertically integrated horizontal flux (F_h) was calculated using the area not covered by non-erodible hemispheres; the approach embodied in dust emission models. Under the same model conditions, F_h estimated using the new model was up to 85% smaller than that using the conventional area not covered. These F_h simulations imply that wind erosion and dust emission models without geometric anisotropic sheltering of the surface, may considerably over-estimate F_h and hence the amount of dust emission. The new model provides a straightforward method to estimate aerodynamic resistance with the potential to improve the accuracy of wind erosion and dust emission models, a measure that can be retrieved using bi-directional reflectance models from angular satellite sensors, and an alternative to notoriously unreliable field estimates of z₀ and their extrapolations across landform scales.     

Joint tracking and classification based on aerodynamic model and radar cross section

We present interacting multiple model regularized particle filter for the X-band active surveillance radar to jointly track and classify air threaten targets. The actual aerodynamic equations for flight are used as motion model, and automatic target classification is made possible by the inclusion of radar cross section in the measurement vector. Thus, tracking and classification are closely coupled, giving full play to the advantages of joint tracking and classification. The proposed methodologies show good performance according to simulations.     

A new adaptive filtering subband algorithm for two-channel acoustic noise reduction and speech enhancement

This paper addresses the problem of acoustic noise reduction and speech enhancement by adaptive filtering algorithms. Most speech enhancement methods and algorithms which use adaptive filtering structure are generally expressed in fullband form. One of these widespread structures is the Forward Blind Source Separation Structure (FBSS). This FBSS structure is often used to separate speech form noise and therefore enhance the speech signal at the processing output. In this paper, we propose a new subband implementation of this FBSS structure. In order to give more robustness to the proposed structure, we adapt then we apply to this subband structure a new combination of criteria based on the system mismatch and the smoothing filtering errors minimizations. The combination between this proposed subband structure with this optimal criteria allows to obtain a new two-channel subband forward (2CSF) algorithm that improves the convergence speed of the cross adaptive filters which are used to separate speech from noise. Objective tests under various environments are presented showing the good behavior of the proposed 2CSF algorithm.     

A fuzzy logic-based model for noise control at industrial workplaces

Ergonomics is a broad science encompassing the wide variety of working conditions that can affect worker comfort and health, including factors such as lighting, noise, temperature, vibration, workstation design, tool design, machine design, etc. This paper describes noise-human response and a fuzzy logic model developed by comprehensive field studies on noise measurements (including atmospheric parameters) and control measures. The model has two subsystems constructed on noise reduction quantity in dB. The first subsystem of the fuzzy model depending on 549 linguistic rules comprises acoustical features of all materials used in any workplace. Totally 984 patterns were used, 503 patterns for model development and the rest 481 patterns for testing the model. The second subsystem deals with atmospheric parameter interactions with noise and has 52 linguistic rules. Similarly, 94 field patterns were obtained; 68 patterns were used for training stage of the model and the rest 26 patterns for testing the model. These rules were determined by taking into consideration formal standards, experiences of specialists and the measurements patterns. The results of the model were compared with various statistics (correlation coefficients, max-min, standard deviation, average and coefficient of skewness) and error modes (root mean square error and relative error). The correlation coefficients were significantly high, error modes were quite low and the other statistics were very close to the data. This statement indicates the validity of the model. Therefore, the model can be used for noise control in any workplace and helpful to the designer in planning stage of a workplace.     

现代数字图像噪声滤除技术及其评价

图像噪声滤除是数字图像处理领域中一项重要的方法技术。首先在对图像噪声模型及其特征介绍的基础上,对去除图像噪声的传统线性滤波和非线性滤波技术,以及针对脉冲噪声、高斯噪声等的新颖滤波理论技术进行了分析与综述,最后对图像噪声滤除的质量评价、现状与发展做了探讨与展望。     

Numerical sensitivity analysis for aerodynamic optimization: A survey of approaches

The calculation of the derivatives of output quantities of aerodynamic flow codes, commonly known as numerical sensitivity analysis, has recently become of increased importance for a variety of applications in flow analysis, but the original motivation came from the field of aerodynamic shape optimization. There the large numbers of design variables needed to parameterize surfaces in 3D necessitates the use of gradient-based optimization algorithms, and hence efficient and accurate evaluation of gradients. In this context over the last 20 years a variety of approaches have been developed to supply these gradients, raising particular challenges that have required novel algorithms. In this paper, we examine the historical development of these approaches, describe in some detail the theoretical background of each major method and the associated numerical techniques required to make them practical in an engineering setting. We give examples from our own experience and describe what we consider to be the state-of-the-art in these methods, including their application to optimization of complex 3D aircraft configurations.     

A numerical simulation of the greenhouse microclimate

A numerical one-dimensional model was designed to simulate the diurnal changes of the greenhouse environment. The model takes into consideration a soil layer, a vegetation layer, an air layer and a cover. The thermal radiative, sensible, latent and conductive heat fluxes were modeled in each layer in terms of its unknown temperature and vapor pressure. The model was applied to the coastal region of Israel during the winter and summer seasons in order to assess the heating/cooling requirements of glass and polyethylene covered greenhouses.