三弹性圆柱壳体多重耦合声辐射计算方法

为研究多圆柱壳组合结构的声辐射特性,采用模态叠加法建立了3个并排无限长弹性圆柱壳的振动声散射耦合物理模型,充分考虑了三圆柱壳的表面振动与散射声场的耦合,其中散射声场可分解为各圆柱壳刚性散射声场和弹性辐射声场的叠加,数学上将各壳间的声场耦合关系通过柱函数加法公式描述。利用该物理模型,分析了多重散射对稳态声场求解结果的影响,比较了三圆柱壳耦合系统与单个圆柱壳系统的辐射声场指向性、声压级及辐射声功率级的差异及其产生机理,结果表明:结构弹性耦合声辐射不仅在低频对总声场有显著影响,在高频范围也不可忽略;另外,针对本文设定参数的组合圆柱壳,在150 Hz以上频段,两旁圆柱壳对中间圆柱壳在正横方位产生了声辐射遮蔽效应,垂直方位则体现声泄漏作用。本文建立的方法可推广到三维空间任意多壳结构的声振耦合建模。     

水下三弹性柱壳耦合声散射特性研究

为研究3个并排无限长弹性圆柱壳受垂直于柱轴方向的平面声波作用的声散射特性,采用Fourier级数展开法建立了圆柱壳声散射数学物理模型,考虑了三圆柱壳弹性振动声辐射和刚性声散射,建立了3个壳体辐射声场和刚性散射声场的耦合作用关系,比对了等效散射强度的刚性散射分量与弹性散射分量,并分析了三壳体等效散射强度特性。计算结果表明:当ka₂>40,在频率f=3000 Hz以上频段,弹性分量对等效散射强度变化趋势的贡献可以忽略。当ka₂>30,在频率f=2400 Hz以上频段,弹性散射分量对等效散射强度影响不超过3 dB;三壳与单壳的等效散射强度在0°入射角方位相当,其它方位三壳体等效散射强度明显大于单壳体。本文的理论公式可推广到任意数量阻抗柱的声透射和声反射问题。      

声场匹配波叠加法的水下结构声辐射预报

提出了一种适用于典型结构声辐射预报的声场匹配波叠加方法。该方法利用少量的参考点声压,通过声场匹配搜索等效源分布,得到最小二乘意义下的最优等效源位置。并研究了表面振动测点位置、数目及振动分布的离散性对声场预报精度的影响。最后在半空间消声水池中,对两端带帽圆柱壳的声辐射预报进行了试验验证。结果表明:等效源最佳位置一经确定,即可利用结构的表面振速,对不同激励下的该结构进行声辐射预报。该方法在较宽频段内对不同的振动分布有较好的适应性。     

水下双层圆柱壳体结构辐射噪声实时预报方法研究

根据Sommerfeld辐射条件和统计能量假设定义了具有方向性特征的声辐射系数,再结合声辐射效率特性定义了新的参数声辐射因子。在外壳体表面速度实时重构理论基础上提出了用声辐射因子实现水下双层圆柱壳体结构辐射噪声实时预报的方法,还提出了有限长水下圆柱壳体结构声辐射因子的试验测量方法。水下声学试验研究表明该方法预报的辐射声压与实测值吻合较好,能满足水下噪声预报的实时性、远场指向性和工况适应性等计算要求。     

基于联合波叠加法的浅海信道下圆柱壳声辐射研究

针对浅海信道下弹性结构声辐射预报尚无高效可靠的研究方法,提出了一种浅海信道下弹性结构声辐射快速预报的联合波叠加法.该方法结合了浅海信道传输函数、多物理场耦合数值计算法和波叠加法理论,运用该方法可对浅海信道下弹性结构辐射声场进行快速预报.经数值法和解析解法验证后,从信道下辐射源、环境影响和辐射声场测量的角度研究分析了浅海信道下弹性圆柱壳的声辐射特性,阐释了进行浅海信道下结构声辐射研究的必要性.研究结果表明,仅在低频浅海信道下弹性结构可近似等效为点源,信道上下边界对声场产生显著的耦合影响,高频段的空间声场指向性分布尤为明显,垂直线列阵进行信道下结构辐射声功率测量时,测量结果受到信道环境边界和潜深的影响较大.     

水下复杂壳体结构在多源激励下的振动及声辐射特性研究

为了综合评估水下复杂壳体结构在多源激励下的振动与声辐射特性,专门设计了一个多舱段复杂壳体模型,分别进行了单台设备激励、多台设备激励的壳体振动与声辐射试验.试验结果表明,多源激励下的结构响应和辐射声场可以近似为单源激励下结构响应和辐射声场的非相干叠加.通过对激励源与结构响应、辐射声场之间传递关系的理论分析,讨论了以单源激励响应非相干叠加合成得到多源激励响应的合理性和误差.研究结果对复杂壳体结构在实际激励下的振动与噪声预报具有重要价值.     

环筋对水下平底圆柱壳的声振特性影响

本文建立了计算两端带平底板的有限长圆柱壳水中声辐射的FEM／BEM三维模型，探索了加筋的高度、宽度、数目对平底圆柱壳的辐射功率、辐射效率、法向声强、声场指向性的影响规律。计算方法是在有限元软件ANSYS中做加筋平底圆柱壳建模、模态分析基础上，将有关数据（网格、模态）导入边界元软件SYSNOISE中计算流体结构耦合状态下的辐射声场特性。结果表明：（1）随着环筋高度、宽度增大，激励点声压峰和法向声强峰在0-400Hz频率范围内数目减少且峰向高频方向移动，同时辐射声功率在减小（除个别模态峰值外），而辐射效率随筋高增大而增大。（2）环筋数目的增加使激励点辐射声压和法向声强峰数目明显减少，使辐射声功率明显低于无筋圆柱壳的辐射声功率，辐射效率随环筋数目增大而增大。（3）环筋宽度变化对声场指向性影响不大；圆柱壳声场指向性随环筋高度和数目增加出现较大变化，尤其是在研究的频段内的f=51Hz和f=301Hz上。这对于水下结构辐射噪声预报以及噪声抑制具有重要意义。     

复杂双层壳体声辐射性能分析

研究了加肋的环板双层壳体的振动和声辐射性能,采用经典Flugge微分算子描述壳体的运动,通过将加强构件等效为反力和反力矩加在内外壳体的表面上而引入壳体振动方程,并利用Helmholtz波动方程和壳体表面的位移连续条件来解位于内层壳和外层壳之间的环形流场,最终建立和求解了双壳体声-流体-结构耦合方程,详细讨论了双壳体参数和双壳间连接型式的变化对其声辐射性能的影响。得出了以下结论:双层壳体内外壳间距减小,内外壳的耦合作用就越强,壳体辐射声功率和表面振动均方速度级升高,外壳的“屏蔽”作用就越不明显;内外壳厚度的改变对壳体振动速度级有较大的作用,对声辐射的影响不是很明显,厚度越大,振动速度级就越低。     

外部加环肋有限长圆柱壳体声散射

为了深入理解双层加肋圆柱壳体的声散射机理,专门研究了两层壳体之间环肋的声散射。仅考虑模型的刚性散射,采用Kirchhoff近似推导了单个环肋的反向散射声场的解析解,并推广到等间距的环肋散射,结合圆柱壳刚性散射得到外部加周期性环肋的圆柱壳体的散射声场近似解。同时,利用图形声学方法(GRACO)对模型的目标强度进行数值计算。理论与实验的结果表明,刚性散射在反向散射声场中起主要作用,周期性环肋引起的Bragg散射对散射声场有重要贡献,同时遮挡效应在实际情况下有较大作用。     

水下双层加肋圆柱壳全空间收发分置散射声场快速预报方法

针对水下双层加肋圆柱壳的全空间收发分置散射声场求解,提出了一种快速预报方法。该方法将散射声场表示为声散射传递函数与声源密度函数的乘积,以目标表面网格信息、少量的仿真或测试多基地散射声压数据作为已知信息,借助数值积分、矩阵理论、最小二乘法对其他收发分置散射声场进行预报。分别以有限元仿真和试验测试的散射声压数据作为输入,对水下双层加肋圆柱壳的多基地散射声场进行了计算,并与完全采用有限元方法的计算结果进行了对比。结果表明:该方法在目标表面结构和部分散射声场数据已知条件下能对目标的全空间收发分置散射声场进行预报;已知散射声压数据量越多,计算频率越低,预报精度越高。     

Estimation of the far-field directivity of broadband aeroengine fan noise using an in-duct axial microphone array

This paper presents a measurement technique for estimating the far-field directivity of the sound radiated from a duct using measurements of acoustic pressure made inside the duct. The technique is restricted to broadband, multi-mode sound fields whose directivity patterns are axi-symmetric, and whose modes are mutually uncorrelated. The technique uses a transfer function to relate the output from an in-duct axial beamformer to measurements of the far-field polar directivity. A transfer function for a hollow cylindrical duct with no flow is derived, and investigated in detail. Transfer functions for practical cases concerning aeroengine exhausts are also presented. The transfer function is shown to be insensitive to the mode-amplitude distribution inside the duct, and hence can be used to predict the directivity in practice where the noise source distribution is unknown. The technique is then validated using a no-flow facility, and is shown to be able to predict variations in the far-field directivity pattern and also estimate the far-field sound pressure levels to within 2 dB. It is suggested that the proposed technique will be especially useful for fan rig experiments, where direct measurement of directivity, for example by use of an anechoic chamber, is impossible.     

三维浅海下弹性结构声辐射预报的有限元-抛物方程法

利用多物理场耦合有限元法对结构和流体适应性强、抛物方程声场计算高效准确的特点,提出了三维浅海波导下弹性结构声振特性研究的有限元-抛物方程法.该方法采用多物理场耦合有限元理论建立浅海下结构近场声辐射模型,计算局域波导下结构声振信息,并提取深度方向上复声压值作为抛物方程初始值;然后采用隐式差分法求解抛物方程以步进计算结构辐射声场.重点介绍了该方法对浅海下结构声辐射计算的准确性、高效性以及快速收敛性后,对Pekeris波导中有限长弹性圆柱壳的声振特性进行了分析.研究得出,当圆柱壳靠近海面(海底)时,其耦合频率比自由场下的要高(低),当潜深达到一定范围时,与自由场耦合频率基本趋于一致;在低频远场,结构辐射场与同强度点源声场具有一定的等效性,且等效距离随着频率增加而增加;由于辐射声场受结构振动模态、几何尺寸和简正波模式影响,结构辐射场传播的衰减规律按近场声影响区、球面波衰减区、介于球面波和柱面波衰减区、柱面波衰减区四个扩展区依次进行.     

A compound secondary source for active noise radiation control

Based on the analysis of active noise control system with multi-channel monopole secondary sources, a kind of compound secondary source is proposed in this paper. The proposed compound secondary source consists of two closely located monopole sources with their distance much smaller than a wavelength. The characteristics of the compound source are analyzed, and the performances of the active noise control system with the compound secondary sources on the monopole primary sound field and sound radiated by a plate are investigated both numerically and experimentally. It has been found that the proposed compound secondary sources control system can provide higher noise reduction for free field noise radiation control with the same number of control channels. It is shown that the better performance in noise reduction of the compound secondary sources control system is mainly due to the directivity of the secondary sources where the energy radiation pattern of the compound sources is similar to that of the primary sources.     

Experimental Estimation of the Emission Directivity of a Moving Surface Vessel in Shallow Water

The possibility of constructing an acoustic model of a surface ship’s noise emission in the far field using monopole-type emitters uniformly distributed along the hull is investigated. Experimental data obtained in shallow water are used to calculate the characteristics of equivalent monopole emission sources that form a total sound field similar to the sound field from a moving surface ship. The powers of each monopole and the cross-correlations between them are calculated. For the selected discrete components and linear model of an extended source, the directivity patterns are constructed, reduced to the free space. In the experiments and calculations, technical tools and algorithms were used that ensure high-precision positioning of the vessel with respect to the receiving elements of the array. An equivalent model of the waveguide transfer function in the operations area was preliminarily obtained by acoustic waveguide calibration using specially developed equipment, experimental techniques, and processing algorithms. This made it possible to use adequate seafloor models and the waveguide transfer function when calculating the equivalent sound field and directivity pattern. Good agreement is shown between the calculated and experimental data, both of the directivity pattern and field distribution along the transit characteristics. Practical recommendations are given for developing methods to measure the noise fields of surface vessels.

     

有限波束作用下掩埋球体的散射声场计算

计算并分析了海底掩埋物体的三维散射声场。采用“等效垂直线列阵”方法来进行有限波束的建模,并将浅海波导中点声源散射声场的波数积分计算方法,推广到有限波束作用下海底掩埋物体的散射场计算,本文导出了物体位于沉积层中的散射声场计算公式。计算结果表明,在波导中垂直面内的散射声场,与沉积层中点源形成的声场非常相似;当距离较远时,散射声波呈柱面波衰减。文章还分析利用海面反射以提高散射能量的可能性,表明波束指向性及波束宽度对散射声场有较大影响。     

Numerical study on reduction of the elevated structure noise by surface absorption on plate girders

With the aim to propose a reasonable and effective countermeasure for the elevated structure noise, the sound field radiated by a steel plate girder, which is the main source of the elevated structure noise, have been theoretically analysed. In the present study, steel plate girders are modelled as infinitely long elastic plate strips placed in parallel and numerical examples on the sound field radiated by the steel plate girders are shown. In the analysis of the radiated sound field, the equivalent source method is employed. Effect of the surface absorption on the sound field radiated by the girders is discussed through numerical examples. The results show that the surface absorption is effective for reduction of the radiated sound field, especially in the area that increase of sound pressure due to reflection by adjacent plate girders is observed. Furthermore, to design for reasonable countermeasure, variation of the noise reduction effect due to changing the pattern of surface absorption area on plate girders is classified.     

Recovery of the free field in noisy environment by using the spherical wave superposition method

To remove the scattering effect of the disturbing sound on the target source when implementing nearfield acoustic holography in a non-free field, a free field recovery technique based on the spherical wave superposition method is proposed. In the method, the sound field separation technique based on the spherical wave superposition method is first used to separate the incoming and outgoing fields, and a further step for separating the radiated and scattered fields is performed by utilizing the surface admittance of the target source as the boundary condition. The technique makes it possible to correctly identify noise sources in a non-free sound field. The basic principle of the technique is described firstly, a method for choosing the optimal number of spherical wave expansion terms is given, and two numerical simulations are used to demonstrate the validity of this technique. It is shown that, for the lower frequency, the scattering effect can be neglected, and the radiated field of the target source can be obtained by the sound field separation technique, however, as the increasing of the frequency, the scattering effect cannot be neglected, and the free field recovery technique has to be used to obtain the radiated field of the target source.     

跑道线圈换能器在铁路重载货车探伤中的应用*

针对在线车轮超声探伤系统的工程应用,研究了跑道线圈电磁超声换能器由洛伦兹力换能机制在钢中产生的辐射声场。根据外磁场和线圈配置,将表面力源近似为非均匀的水平剪切力源,数值计算得到了此力源的辐射声场指向性图,并与实验结果进行比对,结果表明辐射的水平偏振横波具有中间强两侧弱的指向性,对理解跑道形电磁线圈超声换能器的辐射声场和在重载货车车轮辋裂缺陷探伤中的工程应用具有一定的指导意义。