基于迭代更新近似模型的车内噪声优化

基于声固耦合分析与迭代更新近似模型对车身板件进行了优化。首先通过板件声学贡献量分析,确定影响车内噪声的关键板件,将其厚度作为设计变量,在减少计算量的同时去除了无关变量的干扰。然后建立不同激励下驾驶员右耳处最大声压与关键板件厚度之间的组合近似模型,对其进行多目标优化并采用序列二次规划和K均值聚类算法对近似模型进行更新,使得采样样本逐渐靠近Pareto前沿,从而提高近似模型在Pareto前沿上的精度。优化结果表明,迭代更新近似模型能够有效优化车身结构,在保证轻量化的同时,降低了车内噪声。     

蜂窝层芯夹层板结构振动与传声特性研究

蜂窝层芯夹层板应用于飞行器、高速列车等交通工具的主体及底板结构时需要考虑其振动及隔声特性. 针对声压激励下的四边简支蜂窝层芯夹层板结构,应用基于Reissner夹层板理论的结构振动方程建立了的声振耦合理论模型(声压以简支模态双级数的形式引入振动控制方程),结合流固耦合条件求解了声振耦合系统控制方程,应用有限元模拟对理论预测进行了验证. 基于理论模型的数值计算结果,系统研究了蜂窝层芯夹层板结构的振动特性和传声特性,刻画了层芯厚度、蜂窝壁厚、夹层板面内尺寸和声压入射角度等关键系统参数对夹层板振动和传声特性的影响,为此类结构的工程优化设计提供了必要的理论参考.     

铁路客车室内噪声预测与控制技术研究

为探索铁路客车室内低频噪声预测分析与控制的可行办法,提高车室内噪声品质,本文基于有限元和边界元结合的方法给出了铁路客车结构-声场耦合系统振动分析模型的建模方法;通过对比分析结构振动模态、车室内空腔声学模态以及结构-声场耦合系统模态的相关性,澄清车室内噪声形成机理;对客车结构-声场耦合系统在0 Hz～200Hz频率范围内进行谐响应分析之后,确定了室内噪声观测平面及测试点在不同频率下的声压级,通过对客车车身面板声学贡献度的分析,确定主要噪声源和对内部声场影响较大的面板,为降低噪声而试图对客车结构进行修改提供了理论依据.     

内部声激励下加筋圆柱壳的声辐射特性分析

从Flügge薄壳理论和Helmholtz波动方程出发,根据模态叠加原理推导了有限长加筋圆柱壳受机械力和内部声源简谐激励下的"内部声腔-加筋柱壳-外部声场"耦合方程.比较了点力和点声源作用时圆柱壳的声辐射特性以及传递损失.结果表明:在讨论的频率范围内,点声源对内场均方声压起主要作用;点声源作用下外场辐射声压分布较均匀,其传递损失较点力作用下的大,但壳体的外场声辐射效率较点声源作用下的高.分析结果对圆柱壳体结构的声学设计具有一定的参考价值.     

高速磁浮列车近场气动特性及其诱导噪声的数值仿真研究

磁浮列车具有高速性和非接触性，其噪声水平主要依赖于近场气动特性.本文中针对某型号三编组高速磁浮列车，基于Lighthill声学理论，应用大涡模拟法(LES)和FW-H声学模型，仿真分析了1:10列车缩比模型在600 km/h明线工况下的稳态气动特性及瞬态气动噪声激励源特性.结果表明：高速磁浮列车车头与车尾鼻尖位置呈现等压线密集、压力梯度大现象，且车头鼻尖处压力值明显高于车尾鼻尖；列车表面声功率级最高可达155 dB，主要噪声源产生在车头鼻尖区域、表面曲率发生较大变化位置；低频段下列车车头与车尾表面对应位置监测点的声压级分布规律相同，且车头鼻尖位置监测点声压级高于车尾鼻尖，车头与车尾向车身过渡位置两监测点声压级在低频段有明显波动.文中所得研究成果，可为高速磁浮列车车内噪声计算以及为后续低频噪声优化提供一定的科学依据和指导，实现乘客对乘坐舒适性要求.     

航天器噪声试验中结构振动响应预示方法研究

航天器在随运载火箭发射过程中要承受严酷的噪声环境,需通过噪声试验来检验航天器承受噪声环境并能正常工作的能力.航天器噪声试验中结构振动的响应特性是结构强度设计应该考虑的因素之一,更是制定器上组件随机振动试验条件的重要依据,因此有必要在航天器研制初期对噪声载荷作用下的结构振动进行响应预示.文章应用商用有限元分析软件MSC.Patran和MSC.Nastran建立了某型号航天器结构舱板的有限元模型,将噪声载荷声压谱转换为脉动压力功率谱密度,进而采用模态法分析结构在噪声载荷作用下的随机振动响应,并将仿真预示结果与试验结果进行对比研究,在仿真分析中考虑阻尼参数模型和流场附加质量效应等因素的影响;通过研究表明:采用阻尼比随频率提高而减小的经验阻尼参数模型可以较好地反映中高频响应特性、得到较为准确的总均方根响应分析结果,进一步采用虚拟质量法考虑流场附加质量效应可以得到较为准确的功率谱密度响应分析结果.文章提出的仿真分析方法建模简便、计算成本低,适用于在航天器研制初期对航天器噪声试验中的结构振动进行响应预示.      

固定界面动态子结构方法研究车内噪声问题

随着社会的发展，降低车内噪声越来越受到人们的重视。由于整车结构复杂，本文采用包括软子结构的动态子结构方法，把整车模型划分为多个子结构，包括动力总成子结构、副车架子结构、车身与车内声场耦合子结构、非簧载质量子结构及多个线性和非线性软子结构等。采用固定界面模态综合法，建立整车结构车内声场流固耦合动力学模型。对于车身与车内声场耦合子结构，由于其总质量和刚度矩阵为非对称矩阵，传统的模态叠加法不能应用到耦合系统中，本文引入了左特征向量的概念，用左特征向量左乘原方程，使耦合系统微分方程得到解耦。在已建立的总系统动力学模型基础上，在时域内对前后轴分别激励时汽车振动和车内噪声特性进行仿真模拟，并通过台架试验对仿真结构进行验证。     

MEMS系统中微平板结构声振耦合性能研究

微机电系统(micro-electro-mechanical system,MEMS) 是指内部微结构尺寸在微米甚至纳米量级的微电子机械装置,是一个独立的智能系统. 长宽厚均处于微米量级的微平板为MEMS 中的典型结构,其声学和力学特性直接影响MEMS 的性能. 针对同时受声压激励和气膜力(通过考虑相同尺寸微平板振动引入) 作用的四边简支微平板结构,应用Cosserat 理论和Hamilton 原理,建立了考虑微尺度效应(本征长度和Knudsen 数)影响的声振耦合理论模型,并通过多重Fourier 展开法求解了耦合方程,得到了系统的传声损失结果. 通过频域分析,考虑微平板的不同振动频率、振动幅度和板间距,系统研究了不同尺度效应下微结构中气体薄膜所产生的阻尼力对微平板结构传声特性的影响. 研究发现尺度效应对于微结构的声振特性影响巨大,振动行为对微结构的传声特性也有很大影响,控制并减小微平板的振动幅度以及增大微平板的间距都能够提高微平板的声振性能. 研究结果为MEMS 中微平板的稳定性优化设计提供了理论参考.      

基于发动机主轴轴承异常油膜噪声特征的模拟试验研究

由发动机主轴轴承油膜空穴造成的不规则打字机敲击噪声一直是汽车领域未解决的难题. 为了探究发动机主轴轴承动态载荷性能耦合作用下产生的异常空穴噪声，本文作者利用自行设计的平行板挤压油膜试验机进行模拟噪声试验并探究空穴噪声的特征. 该试验机可同时采集振动、位移、声压、力和空穴图像等五种信号，通过试验探究了不同激励信号、挤压振幅、挤压频率、润滑油黏度等因素对空穴噪声的影响，结果表明在方波、大振幅、使用高黏度润滑剂以及挤压频率为12 Hz的状况下容易产生空穴噪声.      

一类非线性系统的随机振动频率响应分析研究

Volterra级数是研究非线性系统的一种重要数学工具, 它可看作线性系统理论中的卷积运算在非线性系统分析中的推广. 基于Volterra级数, 给出了受高斯白噪声激励下的非线性系统输出功率谱的计算公式. 公式表明, 该系统输出功率谱可用激励强度的多项式函数来表示, 其结果为研究激励强度对非线性系统输出功率谱的影响提供了有效途径.      

某调距导管桨系泊工况水力性能和流激直发声预报

采用经验证的计算流体力学方法,对某艏辅推调距导管桨设计螺距和系泊工况螺距的水动力性能进行了有效预报,并对系泊工况装船桨流激噪声进行了分析。系泊工况下,由于导管桨的抽吸作用在导管外壁近壁面区域存在与导管内部流动方向相反的逆向流动,且导管桨尾流场速度梯度分布不均匀、流动紊乱,此时桨叶与导管的推力之比约为1.2∶1。系泊工况船+桨的瞬态流场脉动信息表明,导管桨各部件噪声源强度均表现出从1倍到4倍叶频依次下降的规律,最强幅值集中在桨叶导边和导管内壁;在远场声源级频谱曲线中轴向测点线谱较高峰值位置体现出导管桨进流流场的流动特性。对比分析该艏辅推整体和各部件宽带声源级指向性,可知旋转部件(桨叶、桨榖)对总噪声级的贡献较大,静止部件是径向测点噪声的主要贡献源。     

Surface integral analogy approaches for predicting noise from 3D high-lift low-noise wings

Three surface integral approaches of the acoustic analogies are studied to predict the noise from three concep- tual configurations of three-dimensional high-lift low-noise wings. The approaches refer to the Kirchhoff method, the Ffowcs Williams and Hawkings （FW-H） method of the permeable integral surface and the Curle method that is known as a special case of the FW-H method. The first two approaches are used to compute the noise generated by the core flow region where the energetic structures exist. The last approach is adopted to predict the noise specially from the pressure perturbation on the wall. A new way to con- struct the integral surface that encloses the core region is proposed for the first two methods. Considering the local properties of the flow around the complex object-the actual wing with high-lift devices-the integral surface based on the vorticity is constructed to follow the flow structures. The surface location is discussed for the Kirchhoff method and the FW-H method because a common surface is used for them. The noise from the core flow region is studied on the basis of the dependent integral quantities, which are indicated by the Kirchhoff formulation and by the FW-H formulation. The role of each wall component on noise contribution is analyzed using the Curle formulation. Effects of the volume integral terms of Lighthill＇s stress tensors on the noise pre-diction are then evaluated by comparing the results of the Curle method with the other two methods.     

Vibro-acoustic modeling and validation using viscoelastic material

In aerospace industries, on-board electronics are carried during flight, and such equipment must be qualified to withstand the loads to which they are exposed. In this fashion, the knowledge of the different dynamic aspects of excitations and the behavior of structures, components and/or acoustic enclosures are crucial to have controlled and performing space systems. Passive control techniques using viscoelastic materials (VEM) are widely applied and their effects on space systems must be studied aiming to obtain adequate operational environments. The effect of damping insertion on the dynamic behavior of a vibro-acoustic system is assessed in this work. A coupled structural–acoustic system, composed by a VEM coated aluminum panel and an acoustic box, is modeled by Finite Element Method (FEM). On the other side, tests are preformed using the KU Leuven facilities to validate the FEM model. Numerical vs. experimental comparisons were done and acceptable agreement was obtained. On the other side, it was found that sound inside the box reduces due to the smaller sound radiation generated by the treated panel.     

Stochastic sensitivity analysis of coupled acoustic-structural systems under non-stationary random excitations

This paper presents a new sensitivity analysis method for coupled acoustic–structural systems subjected to non-stationary random excitations. The integral of the response power spectrum density (PSD) of the coupled system is taken as the objective function. The thickness of each structural element is used as a design variable. A time-domain algorithm integrating the pseudo excitation method (PEM), direct differentiation method (DDM) and high precision direct (HPD) integration method is proposed for the sensitivity analysis of the objective function with respect to design variables. Firstly, the PEM is adopted to transform the sensitivity analysis under non-stationary random excitations into the sensitivity analysis under pseudo transient excitations. Then, the sensitivity analysis equation of the coupled system under pseudo transient excitations is derived based on the DDM. Moreover, the HPD integration method is used to efficiently solve the sensitivity analysis equation under pseudo transient excitations in a reduced-order modal space. Numerical examples are presented to demonstrate the validity of the proposed method.     

Low frequency acoustic properties of bilayer membrane acoustic metamaterial with magnetic oscillator

A bilayer membrane acoustic metamaterial was proposed to overcome the influence of the mass law on traditional acoustic materials and obtain a lightweight thin-layer structure that can effectively isolate low frequency noise. The finite element analysis(FEA) results agree well with the experimental results.It is proved that the sound transmission losses(STLs) of the proposed structures are higher than those of same surface density acoustic materials. The introduction of the magnetic mass block is different from the traditional design method, in which only a passive mass block is fixed on the membrane. The magnetic force will cause tension in the membrane, increase membrane prestress, and improve overall structural stiffness. The effects of the geometry size on the STLs are discussed in detail. The kind of method presented in this paper can provide a new means for engineering noise control.     

On aerodynamic noises radiated by the pantograph system of high-speed trains

Pantograph system of high-speed trains become significant source of aerodynamic noise when travelling speed exceeds 300 km/h. In this paper, a hybrid method of non-linear acoustic solver （NLAS） and Ffowcs Williams-Hawkings （FW-H） acoustic analogy is used to predict the aerodynamic noise of pantograph system in this speed range. When the simulation method is validated by a benchmark problem of flows around a cylinder of finite span, we calculate the near flow field and far acoustic field surrounding the pantograph system. And then, the frequency spectra and acoustic attenuation with distance are analyzed, showing that the pantograph system noise is a typical broadband one with most acoustic power restricted in the medium-high frequency range from 200 Hz to 5 kHz. The aerodynamic noise of pantograph systems radiates outwards in the form of spherical waves in the far field. Analysis of the overall sound pressure level （OASPL） at different speeds exhibits that the acoustic power grows approximately as the 4th power of train speed. The comparison of noise reduction effects for four types of pantograph covers demonstrates that only case 1 can lessen the total noise by about 3 dB as baffles on both sides can shield sound wave in the spanwise direction. The covers produce additional aerodynamic noise themselves in the other three cases and lead to the rise of OASPLs.     

Turbulent travel speeds in nonlinear vehicle dynamics

Quarter car models of vehicles rolling on wavy roads lead to limit cycles of travel speed and acceleration with period doublings and bifurcation effects for appropriate driving force parameters. In case of narrow-banded road excitations, speed jumps occur, additionally. This has the consequence that the driving speed becomes turbulent. Bifurcation and jump effects vanish with growing vehicle damping. The same happens for increasing bandwidth of road excitations when, e.g., on flat highways there are no big road waves but only small noisy slope processes generated by rough road surfaces. The paper derives a new stability condition in mean. Numerical time integrations are stabilized by means of polar coordinates. Equivalently, Fourier series expansions are introduced in the angle domain. Phase portraits of travel speed and acceleration show new period-doublings of limit cycles when speed gets stuck before resonance. The paper extends these investigations to the stochastic case that road surfaces are random generated by filtered white noise. By means of Gaussian closure, a nonlinear mean speed equation is derived which includes the extreme cases of wavy roads and road noise.

     

RESEARCH ON IMPROVEMENTS OF LRN TURBULENCE MODEL BASED ON FLOW AROUND AUTOMOBILE BODY 1)

本文将汽车绕流模块化为各典型局部流动,通过常用湍流模型对各典型局部流动进行数值模拟,结果验证了湍流模型对转捩的捕捉能力是准确模拟汽车绕流的关键. 在分析汽车绕流分离及转捩机理的基础上,优化了稳态和瞬态求解方法,改进了湍流模型对转捩的预测能力,进而提高了湍流模型在汽车流场模拟上的精度. 针对汽车绕流的稳态问题,将流线曲率因子及 响应阈值引入 LRN $k$-$\varepsilon $ (low Reynolds number $k$-$\varepsilon $) 模型,获得了一种能够更准确预 测转捩的改进低雷诺数湍流模型 (modified LRN $k$-$\varepsilon $),改善了原模型对湍流耗散率的过强依赖性及全应力发展预测不足等问题;针对汽车绕流瞬态求解,通过分析 RANS/LES 混合湍流模型的构造思想及特点,引入约束大涡模拟方法,结合本文提出的改进的 LRN $k$-$\varepsilon $ 湍流模型,提出了一种能准确捕捉转捩现象 的转捩 LRN CLES 模型. 分别将改进的模型用于某实车外流场和风振噪声仿真中,通过 Ansys Fluent 求解器计算,并将计算结果与常用湍流模型的仿真结果、HD-2 风洞试验结果和实车道路实验结果进行对比,表明改进后的湍流模型能够更准确模拟复杂实车的稳态和瞬态特性,为汽车气动特性的研究提供了可靠理论依据及有效数值解决方法.