矩形梁式前副车架车型车内轰鸣的优化

针对某矩形梁式前副车架车型匀速和加速行驶时的车内轰鸣问题进行了分析和优化。对激励源和传递路径的测试和分析结果表明,动力总成的激励通过悬置传递到副车架上,而副车架的模态与车内空腔模态耦合导致了车内严重轰鸣。通过优化动力总成悬置系统减小动力总成对副车架的激励,以及在副车架上安装动力吸振器的两种方案能有效减小车内轰鸣,改善车内噪声水平。     

低速开式空腔自激反馈流场结构与流致噪声的风洞试验研究

本文主要针对低速开式空腔流动自激振荡产生噪声问题,在0.55 m×0.4 m航空声学风洞开展了不同低马赫数(0.1/0.15/0.2/0.25)条件下长深比为2的空腔腔内流场结构和噪声特性风洞试验研究。通过利用高频粒子图像测速技术捕捉腔内流场结构,分析了腔内声波传递路径;完成空腔远场噪声和壁面压力测试,分析了噪声自激振荡模态和简正波模态,并对空腔壁面脉动压力和远场噪声进行压/声相关性研究。结果表明:空腔内部除主涡外,在腔口前缘处剪切涡与腔口后缘处碰撞涡明显存在;在875 Hz,1288 Hz,1875 Hz,2050 Hz四个频率附近出现了由声腔共振所致的单频噪声;壁面压力与远场噪声密切相关,在壁面压力主频位置有明显单频噪声出现。      

32级模块化Marx发生器机芯模态分析

模态分析可以获得结构的动特性参数。对32级模块化Marx发生器机芯进行了力学特性仿真分析和模态试验,用以评估Marx发生器的力学环境适应性。首先,建立了模块化Marx机芯的有限元模型,获得了初步振型;其次,在自由边界条件下分别开展了Marx机芯整体模态试验、局部模态试验和传递特性试验,得到了整体和局部结构的模态参数。研究表明,模块化Marx机芯在23.58 Hz处出现整体一阶扭转;机芯局部结构固有频率较高;机芯在x,y,z三个方向的振动传递率的范围分别为5～15,6～10和10～35,为后续工程中Marx发生器机芯的针对性设计提供了参考。     

基于流固耦合的油底壳振动噪声预测分析

为了对油底壳的改进方案进行噪声预测,首先建立油底壳的流固耦合有限元模型,进行耦合模态计算,获得其固有频率和振型,通过模态试验验证了耦合有限元模型的准确性;其次,在发动机工作过程中,通过试验测得油底壳各螺栓固定处的振动加速度;再次,基于模态结果,在油底壳各螺栓固定处施加测试的振动加速度,采用有限元的分析方法对油底壳进行了强迫振动计算和辐射噪声计算,并进行了试验对比,结果表明该方法可用于发动机开发试验确认阶段,对油底壳改进方案进行振动噪声的预测,减小开发风险;最后,对含油量多少对辐射噪声的影响进行了对比分析。     

高速列车商务舱内降噪方案研究

轨道交通工具的噪声问题越来越受到人们的关注,本文针对某高铁商务舱内噪声过大的问题应用统计能量模型结合实验进行问题诊断,发现内装地板的振动是车内噪声的主要来源,进而分析结构传递路径是导致内装地板振动过大的原因。结合主要的能量贡献路径提出了应用分布式吸振器、地板吸音板以及改变地板连接结构的方式来降低车内噪声。通过实验验证发现优化后主要的噪声峰值频率100-300Hz之间有明显改善,商务舱内的噪声由75.1dBA下降至71.3dBA,达到了降噪目标。     

新型高频消音器对Whoosh噪声的优化

为了诊断匹配涡轮增压器的汽油车型急加速过程中产生的Whoosh噪声,并分析噪声产生的原理,确定噪声的频率特性以及噪声产生的工况,本文通过对Whoosh噪声在进气系统中贡献量的分析,按照"源-路径-响应"原则,设计出频率相应的高频穿孔消音器并将其插入到进气系统中,从噪声传递路径上进行优化与控制。通过整车道路客观数据分析和主观驾评,确定该方案切实可行,可推广至多款增压车型上应用。     

某轻客低速轰鸣分析与改进*

某轻客车型在1100-1500rpm加速工况下存在明显车内轰鸣,严重影响乘坐舒适性。本文通过对激励源、悬挂结构传递路径和车身响应详细诊断和分析,分析主要原因为传动系扭振激励过大、激励前悬挂系统模态导致振动传递到车身零件与声腔模态耦合引起轰鸣。最终通过在前风窗下横梁和尾门增加CBS、前围板加强和前转向节增加动力吸振器解决了轰鸣问题。该优化思路为类似问题的优化控制提供重要的参考价值。     

非对称阻抗插入管消声器的Chebyshev-变分法建模与求解

针对非对称阻抗插入管消声器三维理论建模与求解问题,提出了一种半解析变分建模和求解方法,试验及有限元结果验证了理论模型和求解结果的正确性,开展了模态频率、声压响应及传递损失等声场特性的预测分析。首先构建插入管消声器内部子声场拉格朗日泛函,基于声压与质点振速连续性条件,得到插入管消声器三维理论模型。随后,将子声场声压展开为切比雪夫-傅里叶级数组合形式,按里兹法求得消声器三维声场模态信息。搭建了消声器传递损失试验平台,进行了刚性壁面和阻抗壁面消声器传递损失测试试验,对理论模型和计算结果进行了验证。通过算例分析了壁面阻抗的大小、阻抗面积和分布形式以及插入管偏置对消声器消声性能的影响。结果表明,提出的变分建模求解方法是有效的,对消声器壁面阻抗位置和形式的合理设置可有效降低输出声压。      

时域传递路径分析在路噪声品质开发中的应用

基于某SUV在30～40 Hz频段的路噪声品质问题,采用时域传递路径分析方法进行了问题的研究,并通过传递路径分析分解确定主要贡献来自于后副车架安装点的Z向。采用CAE方法完成了主路径噪声传递函数的优化,通过尾门的结构优化降低噪声传递函数,使得30～40 Hz的路噪降低了约4 dB。采用声音回放技术完成了CAE优化方案的主观评价,评价通过后再进行实车验证,提高开发效率。     

湍流边界层激励下腔体内水动力自噪声预报与测量

循环水槽中试验测量了腔体内水动力自噪声,并与模态法建立的湍流脉动压力引起腔体自噪声预报进行比较验证。透声窗振动以简支边界为条件,腔体内部声波以刚性边界为条件模态展开,通过辐射边界条件建立模态耦合振动方程。在随机湍流脉动压力作用下,推导了模态振动方程在随机力激励下的自噪声功率谱响应。对循环水槽中5 m/s和8 m/s两种流速工况下的腔体水动力自噪声和湍流脉动压力进行了测试,结合测量的脉动压力预报方法可以计算腔体水动力自噪声量值,理论预报与试验测量结果大致吻合,趋势一致,为声呐罩材料选取及声学环境控制提供了一种分析方法。     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Measurement of nonlinear coefficient of optical fiber based on small chirped soliton transmission

We measure the waveform and phase curves of short optical pulses before and after transmission over different lengths of fibers by use of the pulse analyzer with the frequency-resolved optical gating (FROG),and numerically simulate pulse evolution under the experimental conditions.The nonlinear coefficient of the fiber is given by comparing the experimental results with the numerical ones.Difference between the experiment and numerical simulation is analyzed.     

Resonance scattering of canonical elastic shells in absorbing fluid medium

Resonance scattering of elastic spherical shell and cylindrical shell while the surrounding fluid medium has absorption is studied. The normal mode solution derived using exact elastic theory and the separation of variables is still applicable. However, the scattering form function has to be modified for the absorbing medium, otherwise the unreasonable result would be obtained. The backscattering form function in the absorbing medium is redefined, and the form function of elastic spherical and cylindrical shell with vacuum or solid matter filled is calculated in various absorption conditions. The results show that the absorption of surrounding fluid leads to notable attenuation of the coincidence resonances in the mid-frequency, but it has a little influence on the low-frequency resonance scattering induced by the filler inside the shell.     

Single-beam self-referenced phase-sensitive surface plasmon resonance sensor with high detection resolution

A versatile and low-cost single-beam self-referenced phase-sensitive surface plasmon resonance(SPR)sensing system with ultra-high resolution performance is presented.The system exhibits a root-mean-square phase fluctuation of ±0.0028.over a period of 45 min.i.e.a resolution of±5.2×10-9 refractive index units.The enhanced performance has been achieved through the incorporation of three design elements:a true single-beam configuration enabling complete self-referencing so that only the phase change associated with SPR gets detected,a differential measurement scheme to eliminate spurious signals not related to the sensor response,and the elimination of retardation drifts by incorporating temperature stabilization in the liquid crystal phase modulato .Our design should bring the detection sensitivity of non-labeling SPR biosensing closer to that achievable by conventional fluorescence-based techniques.     

Influences of SiO2 protective layers and annealing on the laser-induced damage threshold of Ta2O5 films

Ta2O5 films are prepared on BK7 substrates with conventional electron beam evaporation deposition.The effects of SiO2 protective layers and annealing on the laser-induced damage threshold (LIDT) of the films are investigated.The results show that SiO2 protective layers exert little influence on the electric field intensity(EFI)distribution,microstructure and microdefect density but increase the absorption slightly.Annealing iS effective on decreasing the microdefect density and the absorption of the films.Both SiO2 protective layers and annealing are beneficial to the damage resistance of the films and the latter is more effective to improve the LIDT.Moreover,the maximal LIDT of Ta2O5 films is achieved by the combination of SiO2 protective layers and annealing.     

A stereo matching algorithm using multi-peak candidate matches and geometric constraints

Gray cross correlation matching technique is adopted to extract candidate matches with gray cross correla- tion coefficients less than some certain range of maximal correlation coefficient called multi-peak candidate matches. Multi-peak candidates are extracted corresponding to three closest feature points at first. The corresponding multi-peak candidate matches are used to construct the model polygon. Correspondence is determined based on the local geometric relations between the three feature points and the multi-peak candidates. The disparity test and the global consistency checkout are applied to eliminate the remaining ambiguous matches that are not removed by the local geometric relational test. Experimental results show that the proposed algorithm is feasible and accurate.     

Fiber Modal Index Measurements Based on Fiber Gratings

A novel method based on fiber gratings for measuring the effective indices of fiber modes is proposed. The effective index difference between the core mode and a cladding mode was obtained by analyzing the interference fringe of a pair of cascaded long-period fiber gratings. In order to extract the core mode index from the measured index difference, an index matching oil immersion method is proposed. By analyzing the interaction between the cladding mode and the oil applied on the cladding surface, the mode order and the effective index of the involved cladding mode might be calculated. Experimental results about the interference fringe shifts induced by the oil index and the oil-applied length are also presented.     

Optical Pulse Compression Schemes That Use Nonlinear Bragg Gratings

Nonlinear optical pulse compression of picosecond pulses typically requires long lengths of optical fiber and multiple components. Periodic structures, such as fiber Bragg gratings, are highly dispersive at wavelengths outside of the photonic bandgap. This implies that such gratings can be used as very short all-fiber compressors. In this paper a number of such compression schemes are reviewed involving uniform and nonuniform fiber Bragg gratings, relying on both soliton and nonsoliton compression principles. Experimental results supporting the corresponding underlying theory are also presented. Finally, an extension of one of the compression schemes is shown, which allows the generation of adjustable high-repetition rate soliton trains.