流体加载下加肋板结构的声辐射特性研究

本文采用有限元和边界元方法对加肋板结构的声辐射进行了计算分析,研究分析了加肋板结构的板厚、板面积、板边长比、肋骨惯性矩和间距、边界条件以及板材和流体介质等对结构辐射声功率的影响,得到了一些有意义的结论,从而为揭示加板结构声辐射规律,降低结构的声辐射提供了一定的依据。     

板厚对无障薄板声辐射特性影响的分析

分析无障薄板的声辐射特性时通常忽略板厚对格林函数的影响而采用双层势计算.本文考虑板厚引起的声辐射阻抗,采用混合势计算结构表面声压与振速,并分析板厚对声辐射参数的影响。根据交界相容性条件,采用边界积分方程分别表示平板上下表面的声压和振速,并合并同类项.进一步将结构的动力方程代入混合势形式的振速方程中,离散声压差值和板的位移为振动模态叠加的形式,获得二重积分形式的声辐射阻抗,从而求解振动模态系数,确定声辐射特性参数.以水下简支矩形板为例计算对比了声辐射参数,并讨论了其对板厚的敏感性。结果表明:板厚引起的声辐射阻抗对声辐射参数的大小影响较小,但随着频率的增加致使共振频率发生较大偏移;在相同阶数的共振频率范围内,板厚度越大,采用双层势计算的误差越大。      

覆黏弹层加肋双层板的声反射

为评估覆盖层的吸声性能,研究黏弹层在无限大周期加肋双层板背衬下的声反射。首先通过弯曲波与Lamb波的比较,揭示了板近似理论不适用于黏弹性板的原因。为此采用(黏)弹性理论处理(黏)弹性板,而肋板的处理则采用板近似理论,并用Hull提出的方法解决肋板和平板的耦合问题,得到反射声场的解。与板近似理论计算加肋双层板声反射的结果进行比较验证了本文方法的正确性,对反射系数进行计算分析了背衬对声反射的影响,定义平均反射系数比较了不同覆盖层的性能。结果表明,频率较低时覆盖层无法有效抑制背衬的影响,板间流体层与双层板的耦合作用引起共振散射,肋板与双层板的耦合作用降低声反射。      

炉内管阵列中声源辐射特性数值研究

炉内换热器结构类似于声子晶体,基于声子晶体理论,采用数值计算与软件模拟得到管阵列中声源不同方向的声传播特性,并将两种方法所得结果进行对比分析,研究声源在管阵列中不同位置处的辐射特性.结果表明：声指向性特性与声源通过管排数量,声源频率是否处在声波禁带有关.     

海洋波导中目标声辐射场的计算方法

针对海洋波导中目标声辐射场的计算问题,提出了一种基于波叠加法并在近、远场采用不同水声传播模型的建模方法,可以将近、远场作为一个统一的系统进行高效地分析。该方法通过给定的已知表面振动速度的结构计算出目标内部虚拟点声源的源强,再配合在相应的水声环境中点声源传播模型的Green函数计算出结构外的声辐射场。以Green函数为纽带,在求源强和计算近场声辐射场时采用镜像虚源法,而在计算远场声辐射场时采用简正波法。通过该方法得到的有限水深波导中声速剖面为正梯度、负梯度、负跃层的3种情况下的脉动球、刚体摆动球的声辐射场计算结果与COMSOL的有限元计算结果进行对比,结果表明了该方法在提高计算效率的同时保证了计算精度。      

水中有限长加肋圆柱壳体振动和声辐射近似解析解

加肋圆柱壳体是水下航行器的主要结构形式。将肋骨对壳体的作用简化为只有法向力,本文导出了水中有限长加肋圆柱壳体的振动和声辐射的近似解析解。其中肋骨的作用表现为在无肋的耦合振动方程中增加附加阻抗,因此壳体的振动和声辐射由壳体的机械阻抗、流体的辐射声阻抗和肋骨的附加阻抗所决定。数值计算例子表明,在低频情况下,加肋对辐射声功率影响不大,但将降低表面平均振速,从而增加声辐射效率。     

弱耦合封闭声腔的声辐射模态理论与计算

有源结构声控制是耦合封闭声腔的声辐射控制的有效方法。在此前的研究中有学者提出了"耦合封闭声腔的声辐射模态"概念,但其在概念和应用上均存在不便之处:其定义实质上是结构模态幅值的一组基函数,这与自由空间内声辐射模态是结构表面法向振速或声压的一组基函数的物理意义并不一致;另一方面,在计算和利用其进行控制时仍然需要用到结构模态,而在实际中辐射结构有用的结构模态信息难以准确、方便地得到。为了解决这些问题,类比自由空间声辐射模态理论,将声势能直接表示为结构表面法向振速的二次型形式,提出了新的结构向耦合封闭声腔的声辐射模态计算方法,并从理论上证明了当耦合面均匀离散时,在一定的条件下,可以简单地利用声腔模态投影向量代替耦合封闭声腔的声辐射模态,从而有效地节约计算资源。通过理论研究,形成了与自由空间内相统一、便于应用的耦合封闭声腔声辐射模态理论,数值计算案例表明,所提出的理论方法可以极大方便耦合封闭声腔的声辐射计算及其有源结构声控制。     

双层周期加肋有限长圆柱壳声散射精细特征研究

研究了双层周期性加肋有限长圆柱壳在水中的声散射特性. 壳体振动用薄壳理论的Donnell 方程描述,环肋振动用相互独立的薄板纯弯曲振动和平面应力状态下的振动方程描述,忽略弦间流体对环肋轴向力的作用. 数值计算给出远场收发合置情况下的周向目标强度和角度-频率谱图,并据此进行机理分析. 计算结果表明远场散射声场中除壳体弹性贡献外,弦间流体以及环肋与内外壳的相互作用对散射声场的贡献也是很重要的,并且在角度-频率谱中出现了舷间流体引起的流体附加波以及周期环肋引起的Bragg散射等回波精细特征,其中流体附加波是双层加肋圆柱壳声散射最重要的散射精细特征,是以往单层圆柱壳声散射所不具有的现象. 最后通过实验对理论推导进行了验证,实验与理论基本符合. 关键词： 声散射 圆柱壳 环肋 流体附加波     

稀疏网格条件下的水下航行体低频水动力噪声计算

利用结构有限元结合声学有限元方法以及无反射边界条件,构建了复杂结构受湍流边界层脉动压力激励的声振响应计算模型,通过引入网格虚拟细化实现非相关流激载荷的修正,解决了有限元模型网格尺寸与湍流边界层脉动压力空间相关性尺度的不兼容问题,在满足声振响应要求的稀疏网格条件下实现了航行体低频水动力噪声计算。以典型回转体模型为例,计算了其低频水动力辐射噪声,与循环水槽试验结果和离散子单元法计算结果进行了比较,三者趋势基本吻合,重合频段偏差小于3 dB。该方法兼顾了计算精度和计算效率,具有良好的适用性。     

充液管路系统流体声与结构声的复合有源控制

采用基于谐频自适应控制算法的有源消声与消振系统对充液管路系统突出的低频线谱噪声进行有源控制实验研究.建立了泵水循环管路实验系统,在管路中安装有源消声器对流体声进行控制,在管路出口障板上采用8×8通道有源消振系统控制结构声辐射。开展的低频线谱噪声与振动有源控制实验结果表明,在50~200 Hz频带内,通过结合有源噪声与振动控制可在多数频点取得10 dB以上的降噪效果。针对该实验系统,通过分别控制流体声和结构声分析了两者的贡献.实验结果验证了有源消声与消振系统具有较好的降噪性能,各频点处流体声与结构声占比情况不同,需要综合控制流体声与结构声才可以取得显著的降噪效果。      

含损伤黏弹性阻尼加筋层合板声功率和指向性变异*

该文旨在研究损伤位置和程度对自由阻尼加筋层合板声辐射功率和指向性的影响。基于Mindlin和Timoshenko梁理论,建立了自由阻尼层合板-梁组合结构有限元模型。数值求解四边简支边界条件自由阻尼加筋层合板振动响应,继而通过Rayleigh积分计算加筋层合板辐射声功率和指向性。将计算得到的前4阶模态固有频率、声辐射功率与指向性与已有文献进行了对比基本一致,验证了数值模型的正确性。最后,详细讨论了损伤位置和程度对自由阻尼加筋层合板固有频率、振型、声辐射功率和指向性的影响,结果表明：随着结构损伤程度的增大,声辐射功率峰值向低频移动,在更多角度上出现明显的指向性;声辐射功率和指向性对损伤位置比损伤程度更加敏感。     

Acoustic radiation from the submerged circular cylindrical shell treated with active constrained layer damping

Based on the transfer matrix method of exploring the circular cylindrical shell treated with active constrained layer damping(i.e., ACLD), combined with the analytical solution of the Helmholtz equation for a point source, a multi-point multipole virtual source simulation method is for the first time proposed for solving the acoustic radiation problem of a submerged ACLD shell. This approach, wherein some virtual point sources are assumed to be evenly distributed on the axial line of the cylindrical shell, and the sound pressure could be written in the form of the sum of the wave functions series with the undetermined coefficients, is demonstrated to be accurate to achieve the radiation acoustic pressure of the pulsating and oscillating spheres respectively. Meanwhile, this approach is proved to be accurate to obtain the radiation acoustic pressure for a stiffened cylindrical shell. Then, the chosen number of the virtual distributed point sources and truncated number of the wave functions series are discussed to achieve the approximate radiation acoustic pressure of an ACLD cylindrical shell. Applying this method, different radiation acoustic pressures of a submerged ACLD cylindrical shell with different boundary conditions, different thickness values of viscoelastic and piezoelectric layer, different feedback gains for the piezoelectric layer and coverage of ACLD are discussed in detail. Results show that a thicker thickness and larger velocity gain for the piezoelectric layer and larger coverage of the ACLD layer can obtain a better damping effect for the whole structure in general. Whereas, laying a thicker viscoelastic layer is not always a better treatment to achieve a better acoustic characteristic.     

Estimation of broadband acoustic power radiated from a turbulent boundary layer-driven reinforced finite plate section due to rib and boundary forces

Previous papers considered an infinite fluid-loaded plate with parallel line attachments, driven by a wave-number-white pressure excitation invariant in the direction of an attachment, and established the conditions and procedure for estimating the broadband radiated power by assuming the ribs to radiate independently. This paper applies those results to a finite rectangular ribbed plate, and extends the methodology to include the contribution of the plate's boundary support forces to the radiation and the consideration of excitation that varies in the direction parallel to the ribs. The approach is relevant to problems of sound radiation by underwater stiffened steel plates driven by turbulent boundary layer (TBL) pressures, and is also applicable to stiffened circular cylindrical shells when the response is dominated by bending. Comparisons of sample calculations with results of rigorous models validate the approximation.     

一种分析周期加筋板声辐射的高效方法

为了研究周期加筋板的声辐射特性,建立了一种计算水中周期加筋板在简谐点力作用下的远场辐射声压的高效方法。该方法借助于傅里叶变换法只要先将耦合系统的声振方程,加强筋的弯曲和扭转运动方程,声学波动方程和耦合边界条件转换到波数域中,联合求解得到一组关于平板横向位移的无限大耦合代数方程组,再将该方程组截断成有限大小由数值方法求出波数域中的位移响应,便可结合稳相法得到远场辐射声压。与现有方法给出的结果对比发现二者完全吻合,验证了本文方法的有效性;通过数值方法研究了激励力位置、板厚,加强筋间距和宽度对周期加筋板声辐射特性的影响,得到了具有实际意义的结论。      

ANALYSIS OF SOUND TRANSMISSION THROUGH PERIODICALLY STIFFENED PANELS BY SPACE-HARMONIC EXPANSION METHOD

An analysis method is developed to study sound transmission characteristics of a thin plate stiffened by equally spaced line stiffeners. The dynamic equation that describes the vibro-acoustic response of the system is derived by expanding the structural and acoustic responses in terms of the space harmonics and by using the virtual energy method. The series solution can be considered as the exact solution because the structural and acoustic-structural coupling effects in the system are fully considered and the solution converges. Parameter studies are conducted for major design parameters to understand the characteristics of the system.     

基于波数域直接求解法的正交加筋板声辐射研究

为了研究正交加筋板的声辐射问题,基于波数域直接求解法,建立了研究正交加筋板声辐射特性的理论模型。先利用傅里叶变换法求解周期结构的声振理论模型,得到波数域中关于结构响应的无限大耦合代数方程组,采用数值方法将其截断成有限项求解,结合稳相法便可快速获得远场辐射声压。该方法对单向和正交加筋板的预测结果与现有文献中的理论结果取得了良好的吻合,验证了理论模型的准确性和可靠性;并进一步通过数值算例研究了作用点位置,加强筋间距及平板厚度对结构声辐射特性的影响。      

Acoustic radiation from a simple structure in supersonic flow

It is well established that fluid flow can have significant effects on structural acoustic behavior, as is the fact that induced coupling between discrete modes of vibration becomes significant as flow velocity increases. To date, work in this area has been confined to subsonic flows, with the effects on sound radiation efficiency and sound power radiation quantified and compared for various subsonic flow speeds. The purpose of this work is to study the effects that supersonic flow has on these structural acoustic phenomena, along with an investigation of the uncoupled behavior of single modes in the transonic region. Theoretical development of the equations governing the vibration of a simply supported plate in an infinite baffle and an aerodynamic system that models a semi infinite flowing medium along with the method for coupling these systems is included. Computational results are presented illustrating the behavior of the uncoupled modes in the transonic region and the uncoupled and coupled effects on the structural response and sound power radiation as well as a study of the radiation efficiency of the coupled system.     

板结构的声辐射模态分析及其高分辨率法向振动速度重建

提出了一种基于声辐射模态的速度基向量构建方法,该速度基向量不受网格划分的影响,可用于高分辨率的板结构法向振动速度重建。首先对板表面稀疏网格的声辐射模态进行计算,再以声辐射模态和模态系数构建板法向振动速度分布的基向量,然后由声场测量声压求解基向量系数,最后由该系数和加密网格的速度基向量重建高分辨率的板法向振动速度分布。以简支板声源进行仿真计算,当测量声压信噪比为30 dB时,低频的法向振动速度重建误差最低可达3.7%;以固支板声源在消声室中进行实验验证,131.5 Hz振动频率下的重建误差低于7%。该方法实现了只需要少量声压测量点即可精确重建板声源更高分辨率的法向振动速度分布。      

A unified approach for predicting sound radiation from baffled rectangular plates with arbitrary boundary conditions

This paper discusses sound radiation from a baffled rectangular plate with each of its edges arbitrarily supported in the form of elastic restraints. The plate displacement function is universally expressed as a 2-D Fourier cosine series supplemented by several 1-D series. The unknown Fourier expansion coefficients are then determined by using the Rayleigh-Ritz procedure. Once the vibration field is solved, the displacement function is further simplified to a single standard 2-D Fourier cosine series in the subsequent acoustic analysis. Thus, the sound radiation from a rectangular plate can always be obtained from the radiation resistance matrix for an invariant set of cosine functions, regardless of its actual dimensions and boundary conditions. Further, this radiation resistance matrix, unlike the traditional ones for modal functions, only needs to be calculated once for all plates with the same aspect ratio. In order to determine the radiation resistance matrix effectively, an analytical formula is derived in the form of a power series of the non-dimensional acoustic wavenumber; the formula is mathematically valid and accurate for any wavenumber. Several numerical examples are presented to validate the formulations and show the effect of the boundary conditions on the radiation behavior of planar sources.