基于散射矩阵法的飞机壁板声学优化设计

采用散射矩阵法分析夹层板结构声学特性,并对典型的夹层板结构即飞机壁板进行声学优化,预计飞机壁板隔声特性,获得蒙皮、隔声隔热层、内饰板及它们的组合结构的声学性能。针对尾吊飞机客舱后部噪声过大问题,通过增加铺设隔热隔声层以及部分区域优化安装阻尼层等一系列被动降噪处理方法,对主要传递路径的飞机壁板结构进行优化,降低客舱后部噪声水平,并进行试验验证。试验结果表明:散射矩阵法可快速准确获得夹层结构的隔声性能,并与混响室法测试结果吻合较好;在厚度不变的前提下,改变隔热隔声层的铺设方式和材料密度对壁板隔声性能影响较小,但在蒙皮内侧粘贴阻尼层能在一定频段范围提高壁板隔声性能;将优化的壁板构型应用到飞机后舱段侧壁板,舱内噪声水平可降低约3 dB。     

高声压级时多孔金属板的吸声特性研究

针对高声压级下有限厚度多孔金属板在线性阻抗背衬条件下(背衬表面声压与声质点速度为线性关系)的吸声问题,提出了一个描述不同声压级下材料层法向吸声性能的一维模型,并给出求解材料层内部声质点速度的线化与差分方法,以预测多孔金属板在高声压级下的非线性吸声特性。在阻抗管中对两块多孔金属板进行了声学测试,得到了材料层法向表面阻抗和吸声系数随入射声压级变化的实验结果。研究表明:实验与理论预测符合良好,验证了模型与数值方法的正确性。本文所提原理和方法,可用于一般硬质多孔材料。      

转速对弯掠轴流风机气动噪声的影响分析

针对弯掠轴流风机气动噪声问题,采用大涡模拟(LES)和基于Lighthill声类比的FW-H模型相结合的方法进行非定常计算,通过快速Fourier转换(FFT),得到风机远场气动噪声声压级分布。对比研究了三种转速下旋转区内声压级分布规律、时域及频域特性,结果表明:旋转区域内声压级随转速增加而增大,前缘分离涡在某一转速时影响区域和强度最大;在一个旋转周期内,声压脉动呈现出6个波峰与波谷,验证了叶片转动频率是风机内部气动噪声的主要激励频率.     

机体表面湍流边界层噪声特性及预测方法研究

湍流边界层噪声是飞机巡航过程中的主要外部噪声源,对舱内噪声水平的影响尤为重要。因此,对飞机机体表面湍流边界层噪声的研究具有重要意义。本文通过试验获得了某型民机巡航过程中的湍流边界层噪声,试飞工况为3500ft/0.78、3500ft/0.7、2500ft/0.67、1500ft/0.66。对实测数据进行分析,发现湍流边界层噪声与动压、边界层厚度等参数有关。同时,利用计算流体力学的方法得到了飞机机体表面的压力分布,并分析了压力梯度对湍流边界层噪声的影响。最后,基于工程预测方法对湍流边界层噪声进行了预测,对于不存在逆压梯度的区域,预测结果与试验结果吻合较好,仅部分频段存在一定偏差。通过对模型的参数进行优化,改善了预测结果。     

叶片出口角对离心泵流动诱导噪声的影响研究

文采用CFD与声学求解器耦合计算的方法,对一离心泵在不同叶片出口角下的内部流场及其外辐射声场进行了数值计算.通过对比不同出口角下离心泵模型的水力特性、流场内特性及压力脉动来分析叶片出口角对离心泵流场及流动诱导噪声的影响。流场计算结果表明,出口角从18°增加到39°,扬程升高6.48%而效率下降10.89%;出口角增加,导致基频处压力脉动强度降低而二阶谐频处脉动强度增加,脉动总强度增加。蜗壳外表面在二阶谐频处振速明显高于其它频率下的振速.外声场声压级的指向性曲线显示,出口角增大,声压级增大,出口角为39°时声压级比出口角为18°时声压级高出约8.6 dB.     

船用三通调节阀流-固耦合噪声数值模拟

针对船用PN10DN32三通调节阀噪声声压频谱、声指向性等声学特性规律不明确,噪声声压级是否满足使用要求的问题,基于流-固耦合理论,同时考虑流-固耦合面及流体域内的脉动声学激励源,开展阀门噪声数值模拟研究。分别对三通调节阀在80%及60%开度阀外1 m处的噪声进行数值模拟,分析研究噪声声压频谱特性及声指向性规律。结果表明：80%及60%开度下的噪声声压级分别为49.14 dB(A)、50.79 dB(A),均小于60 d B(A)的噪声限制,满足使用要求。该文为船用三通调节阀噪声数值模拟提供了理论及方法参考。     

基于光子相关光谱分析的声压量值复现方法

寻求不依赖于实验室标准传声器的灵敏度而直接溯源至国际单位制基本单位的声压量值复现技术是声学计量的长期目标,对声压量值摆脱实物基准具有重要意义,激光多普勒测速技术是实现这一目标的有效途径.以行波管内平面波声场为测量对象,建立无固定频移的激光多普勒测速系统,采用光子相关光谱分析法解调多普勒信号,获得声管内示踪粒子的振动速度,根据平面波声压与质点振动速度的线性关系,复现声管测量点处的声压.以工作标准传声器的测量结果为参考,评估测量方案的可行性和测量结果的准确性,分析影响测量准确性的主要因素.测量结果表明,声波频率为315Hz,声压级在100dB~110dB范围内间隔1dB变化时,测量偏差小于0.5dB;声压级为105dB,声波频率为315,400,500,800Hz时测量偏差小于0.3dB.     

氧化铟锡薄膜的磁感应热声分析

基于优良导体在磁场下的涡流效应理论和固体的热声效应理论,建立了氧化铟锡(ITO)导电薄膜磁-热-声效应的理论模型,推导了导电薄膜热致发声的温度振荡和输出声压表达式。对有基底的ITO导电膜进行了磁场下的热声理论计算和实验测试,结果表明：薄膜的温度振荡值随频率呈上升趋势,与电-热-声模型相比趋势相反;薄膜声压的理论值与实验值在频域内的变化趋势基本吻合,验证了理论模型的正确性。进而,根据磁-热-声的理论模型,分析了线圈相关参数对薄膜声压级的影响,结果表明：薄膜声压级随着线圈匝数的增加而增大,随着薄膜与线圈中心距离的增加而减小,随着线圈半径的增加而减小。文中的研究结果拓展了导电薄膜在扬声器等领域的应用。     

基于多聚合过程神经元的A380客舱内温度预测

对A380在机坪泊位期间客舱内部环境变化情况进行研究,分析影响A380舱内的热环境的主要因子并建立因子模型,采集大量A380机舱内的温度数据,通过分析建立了机舱内热环境预测模型。并在此模型基础上,采用多聚合过程神经元的BP神经网络,对机舱内热环境算子和历史数据进行非线性聚合、分析和学习,最终实现对机舱内的温度的变化进行准确预测,此模型将为舱内热环境控制算法的研究提供一个良好的平台。     

大空间人群声学模型

经典扩散声场理论难以适用于大空间建筑。为了探究大空间建筑中人群分布对声场的影响,本文用模拟与实测相结合的方法,提出了一种适用于大空间的人群声学模型,得到了确定等效声源和人群声源的简化方法,以及人群密度与声压级之间、人群总数与发声人数之间的关系。用实测数据对该人群声学模型进行了验证。     

Empirical method for the prediction of business executive jet cabin noise levels

As a result of flight noise measurements made at various locations in the cabin of the standard lined/no interior Westwind model 1124 business executive jet, it was possible to develop an empirical method for predicting the overall sound pressure level (OASPL) at any required location in the cabin. The cabin overall sound level in decibels (linear) may be found from nomographs related to aircraft altitude, mach number or velocity. The noise spectrum at any location may be found from a reference spectrum shape corrected for local parameters. The accuracy of the prediction method, verified by additional tests, was found to be ± 1 dB.     

A hybrid SEA/modal technique for modeling structural-acoustic interior noise in rotorcraft

This paper describes a hybrid technique that combines Statistical Energy Analysis (SEA) predictions for structural vibration with acoustic modal summation techniques to predict interior noise levels in rotorcraft. The method was applied for predicting the sound field inside a mock-up of the interior panel system of the Sikorsky S-92 helicopter. The vibration amplitudes of the frame and panel systems were predicted using a detailed SEA model and these were used as inputs to the model of the interior acoustic space. The spatial distribution of the vibration field on individual panels, and their coupling to the acoustic space were modeled using stochastic techniques. Leakage and nonresonant transmission components were accounted for using space-averaged values obtained from a SEA model of the complete structural-acoustic system. Since the cabin geometry was quite simple, the modeling of the interior acoustic space was performed using a standard modal summation technique. Sound pressure levels predicted by this approach at specific microphone locations were compared with measured data. Agreement within 3 dB in one-third octave bands above 40 Hz was observed. A large discrepancy in the one-third octave band in which the first acoustic mode is resonant (31.5 Hz) was observed. Reasons for such a discrepancy are discussed in the paper. The developed technique provides a method for modeling helicopter cabin interior noise in the frequency mid-range where neither FEA nor SEA is individually effective or accurate.     

有限元-统计能量分析法的拖拉机驾驶室噪声研究*

对某拖拉机驾驶室内中频噪声进行预测,建立了拖拉机驾驶室FE-SEA(有限元统计能量分析)混合模型,通过理论计算和试验方法获取驾驶室结构内损耗因子等数据；加载振动和噪声激励后进行有限元-统计能量分析联合仿真,将仿真获取的驾驶室声压级与实测数据进行对比,分析对比表明该模型在中频段利用FE-SEA混合法分析所得结果与试验测试值拟合程度较高,分析各子系统对驾驶室声腔的能量贡献度,确定对驾驶室噪声贡献较大的子系统,针对性对驾驶室声学包进行整改,获得一定降噪效果。     

On sound transmission into a thin cylindrical shell under “flight conditions”

In the context of the transmission of airborne noise into an aircraft fuselage, a mathematical model for sound transmission into a thin cylindrical shell is used to study sound transmission under “flight conditions”: i.e., under conditions of external air flow past a pressurized cylinder at flight altitude. Numerical results for different incidence angles are presented for a typical narrow-bodied jet in cruising flight at 10 660 m (35 000 ft) with interior pressure at 2440 m (8000 ft). A comparison is made between no-flow sound transmission at standard conditions on the ground to sound transmission under flight conditions. It is shown that at M = 0, the cylinder transmission loss has dips at f_R (cylinder ring frequency) and f_c (critical frequency for a flat panel of same material and thickness as shell). Below f_R cylinder resonances affect TL. Between f_R and f_c, cylinder TL follows a masslaw behavior. Flow provides a modest increase in TL in the mass-law region, and strongly interacts with the cylinder resonances below f_R. For normally-incident waves, TL is unaffected by flow.     

VIRTUAL REALITY OF SOUND GENERATED FROM VIBRATING STRUCTURES

The advancement of virtual reality (VR) technology in cyberspace is amazing, but its development is mainly concentrated on the visual part. In this paper, the development of VR technology to produce sound based on the exact physics is studied. Our main concern is on the sound generated from vibrating structures. This may be useful, for example, in apprehending sound field characteristics of an aircraft cabin in design stage.To calculate sound pressure from curved surface of a structure, a new integration scheme is developed in boundary element method. Several example problems are solved to confirm our integration scheme. The pressure distributions on a uniformly driven sphere and cylinders are computed and compared with analytic solutions, and radiation efficiency of a vibrating plate under one-dimensional flow is also calculated. Also, to realize sound through computer simulation, two concepts, “structure-oriented analysis” and “human-oriented analysis”, are proposed. Using these concepts, virtual sound field of an aircraft cabin is created.     

Prediction of jet noise in flight from static tests

The sound intensity of jet noise from aircraft in flight is derived in a co-ordinate system fixed to the jet engine. For this reason a convected form of the Lighthill equation is solved, with special care taken of jet temperature effects. Under certain assumptions and approximations, the in-flight and static sound intensities are related in a simple manner. Thus the directivity of jet noise in flight can be predicted. The theoretical result is checked with measurements. The agreement is remarkably good.     

On the sensitivity of sound power radiated by aircraft panels to turbulent boundary layer parameters

The objective of the present study is to investigate and quantify how sensitive the response of an aircraft panel is to the change of the turbulent flow parameters. Several empirical models currently exist that provide the turbulent boundary layer wall pressure cross spectrum. These wall pressure cross spectrum models are usually dependent on four parameters: the reference power spectrum, the flow convective velocity, and the coherence lengths in streamwise and spanwise directions. All the proposed models provide different predictions for the wall pressure cross spectrum. Also, real flow conditions over aircraft do not conform to the ideal behavior of the turbulent boundary layer pressure predicted by the models. In this context, the questions that this work aims to explore are “What is the impact of different wall pressure estimates in the radiated sound power?” and “What is the effect of the range of possible flow conditions on the radiated sound power?”. For that objective, data from flight tests and estimates provided by the empirical models are used to predict radiated sound power, and the results are compared. A sensitivity analysis is performed and the relative contribution of each boundary layer parameter to the radiated sound power is obtained.