局域共振型空腔覆盖层的低频吸声机理及调控规律研究

声学覆盖层的低频吸声特性对潜艇声隐身性能具有重要影响。综合考虑空腔型覆盖层结构和局域共振型薄膜材料的低频吸声性能，建立局域共振型空腔覆盖层的有限元模型，研究复合结构在10 Hz～2 000 Hz频段内的吸声特性，并采用局域共振理论和模态分析揭示复合结构的吸声机理，进一步得到复合结构低频吸声性能的调控规律。研究结果表明：(1)在10 Hz～2 000 Hz频率范围内，相比空腔型覆盖层，复合结构的平均吸声系数提高到0.497；(2)复合结构的低频吸声机理为：通过下半部分空腔变形实现纵波向横波的转化，通过局域共振结构的反共振消耗声能，二者共同作用，提高吸声系数；(3)耦合产生的吸声峰峰值主要随覆盖层损耗因子的增大而增大，峰值频率主要随薄膜面积的增大而向高频移动。研究结果可为声学覆盖层的低频吸声特性设计提供理论指导。     

局域共振型空腔覆盖层的低频吸声机理及调控规律研究

声学覆盖层的低频吸声特性对潜艇声隐身性能具有重要影响.综合考虑空腔型覆盖层结构和局域共振型薄膜材料的低频吸声性能,建立局域共振型空腔覆盖层的有限元模型,研究复合结构在10 Hz～2000 Hz频段内的吸声特性,并采用局域共振理论和模态分析揭示复合结构的吸声机理,进一步得到复合结构低频吸声性能的调控规律.研究结果表明:(...     

吸声侧壁对微穿孔共振结构声学性能的影响

在微穿孔共振结构的空腔侧壁铺设吸声层将增大空腔的声顺,引进空腔的声阻,从而明显改进结构的吸声特性。与对应的刚性壁面空腔结构相比较,吸声壁面结构的吸声系数共振峰频率降低,频响曲线平坦,峰-谷起伏减小。其特性与填满吸声材料的空腔结构基本相同。相应的理论公式得到实例的有力支持。与三维理论相比较,一维理论比较简洁,仅需引入材料的垂直入射吸声系数。其预测的共振结构吸声系数幅值能够满足工程设计的要求,但是没能充分反映吸声材料对共振峰频率的影响,预测的共振峰频率偏高。     

薄膜材料吸声性能数值模拟

为了研究薄膜材料的吸声性能,对带空腔的单层薄膜、双层薄膜及未带空腔的双层薄膜的吸声性能进行了数值模拟。在其它参数保持不变时,随着薄膜材料的质量密度和空腔深度的增加,共振频率逐渐向低频方向移动。带空腔的双层薄膜吸声结构的吸声带宽明显高于单层薄膜的吸声带宽;未带空腔的双层薄膜吸声结构在频率低于一定值时,吸声系数可以保持常数不变。     

局域共振型腔体结构吸声瓦的斜入射吸声特性研究EI北大核心CSCD

吸声瓦的吸声特性对于水下航行器的声隐身性能具有重要影响。综合考虑空腔覆盖层的结构和局域共振型薄膜材料的低频吸声性能,利用COMSOL软件建立了局域共振型腔体结构的吸声瓦的有限元模型,研究了其在10~2000 Hz内对斜入射声波的吸声性能,采用振动位移云图揭示其吸声机理,通过位移矢量图和动能密度分布图分析入射角度影响吸声性能的原因。研究结果表明:该吸声瓦的吸声系数随频率的增大、斜入射角度的增大而增大;吸声机理为上下空腔的收缩与扩张引起纵波向损耗因子较大的横波转化,以及局域共振结构的反共振消耗声能,二者共同作用提高吸声瓦的吸声性能;斜入射声波使得吸声瓦横向位移增大,转化成的剪切波增多;斜入射角度越大,吸声瓦的动能密度越高,消耗声能越多,因此吸声性能增强。研究结果可为吸声瓦的低频吸声特性设计提供理论指导。     

微穿孔板-聚合物层状结构材料的制备和吸声性能

以微穿孔板(MPP)、聚氨酯泡沫(PU)、丁腈橡胶(NBR)和空腔(AG)为原料,根据不同的结构顺序分别制备出MPP-AG共振结构、MPP-PUFM层状结构、MPP-AG-NBR-PUFM多层结构材料和NBR-PUFM-MPP-AG多层结构材料,研究了MMP穿孔率、PUFM厚度、泡沫层孔径、泡沫厚度和结构交替顺序对复合材料吸声性能的影响。结果表明：在频率较低的条件下MPP穿孔率越低或在较高频率条件下MPP穿孔率越高,层状结构材料的吸声系数越高;随着PUFM厚度的增大层状结构材料的共振峰值频率向低频方向移动。与MPP-PUFM层状结构材料相比,MPP-AG-NBR-PUFM在500~1600Hz频率范围的平均吸声系数由0.58提高到0.66;NBR-PUFM-MPP-AG多层结构材料具有优异的中低频吸声性能,频率为400 Hz时最大吸声系数达到0.94,频率为2700 Hz时吸声系数达到0.85。     

椭圆柱空腔吸声覆盖层的声学特性

采用波导有限元方法（WFEM）分析了共振腔型吸声覆盖层内轴向波的传播和损耗特性,以椭圆柱空腔吸声层为例,在保持穿孔系数不变的前提下,分别从轴向波传播和波型转换的角度分析了空腔形状改变吸声覆盖层声学特性的机理。在此基础上,结合波导有限元方法和传递矩阵（TM）建立了变截面空腔吸声覆盖层的分析模型,以圆台空腔吸声层为例,与二维解析方法对比验证了WFEM-TM方法的正确性,并讨论了椭圆台空腔吸声层的声学特性。     

基材含微粒的空腔结构吸声器吸声性能预报的研究

采用一种近似方法计算含球形微粒和空腔结构吸声器的吸声系数,即首先用自洽理论,计算掺入微粒的复合材料的等效力学参数,再用求空腔结构吸声器的等效力学参数方法,计算这种复合材料具有空腔结构的该参数,最后用声波在分层吸收媒质中传播模型来计算能量吸收系数。所得数值模拟结果表明:基材掺入微粒形成的复合材料其吸声性能有不同程度的变化,性能的提高与否与基材和微粒的种类、孔隙率及粒子分布概率密度等因素有关;对于某些含微粒的复合材料若开空腔则可进一步提高吸声器的低频吸声性能。总之,基材含微粒的空腔结构吸声器的吸声系数是以不同程度的灵敏度受控于表征微粒的参数以及空腔结构。     

局域共振型腔体结构吸声瓦的斜入射吸声特性研究

吸声瓦的吸声特性对于水下航行器的声隐身性能具有重要影响.综合考虑空腔覆盖层的结构和局域共振型薄膜材料的低频吸声性能,利用COMSOL软件建立了局域共振型腔体结构的吸声瓦的有限元模型,研究了其在10～2 000 Hz内对斜入射声波的吸声性能,采用振动位移云图揭示其吸声机理,通过位移矢量图和动能密度分布图分析入射角度影响吸...     

多层材料椭球形空腔吸声覆盖层的吸声特性分析

针对椭球形空腔吸声覆盖层低频吸声性能比较差的问题,建立了多层材料椭球形空腔结构覆盖层的Comsol有限元模型,采用传递矩阵法验证有限元模型并对其进行吸声特性数值仿真分析。结果表明:理论计算与数值仿真的曲线趋势大致吻合,证明该有限元模型是有效的;相同穿孔率下多层材料吸声覆盖层低频吸声特性明显优于单层材料吸声覆盖层,并且根据穿孔率、表层厚度、损耗因子、杨氏模量等参数的变化分析了各种参数对吸声系数曲线的影响,为下一步声学优化提供具体指导。     

混合型空腔结构覆盖层吸声性能研究及其优化设计

基于有限元法研究了以空气为背衬的混合型空腔结构覆盖层的吸声特性。建立了具有混合型空腔结构的覆盖层有限元模型,对其进行吸声特性数值仿真分析。结果表明,该空腔结构的吸声特性明显优于相同穿孔率的单腔结构。通过优化设计,进一步提升了混合型空腔结构覆盖层在全频段的吸声性能,并得到了若干覆盖层结构参数影响其吸声性能的规律。     

A spectral alternating method for elastostatic problems with multiple spherical cavities

The problem of an infinite elastic solid containing an arbitrary number of non-overlapping spherical cavities of arbitrary sizes and locations and with arbitrary boundary tractions is considered. The numerical procedure to solve this boundary value problem is based on a spectral method in which the boundary displacements and tractions are represented by truncated series of surface spherical harmonics. By using an alternating method, the problem containing multiple spherical cavities is replaced by a sequence of problems for a single spherical cavity with the boundary conditions adjusted iteratively to account for the cavity interactions. A least squares approximation is used to determine the unknown coefficients of surface spherical harmonics representing these cavity interactions. Several examples are given to illustrate the approach. An erratum to this article can be found at     

Singular stresses in an infinite solid with a flat annular crack around a spherical cavity under tension

The problem of singular stresses in an infinite elastic solid containing a spherical cavity and a flat annular crack subjected to axial tension is considered. By application of an integral transform method and the theory of triple integral equations the problem is reduced to that of solving a singular integral equation of the first kind. The singular integral equation is solved numerically, and the influence of the spherical cavity upon the stress intensity factor and the influence of the annular crack upon the maximum stress at the surface of the spherical cavity are shown graphically in detail.     

Scattering of a pulsed wave by a sphere with an eccentric spherical inclusion

A dielectric sphere with an eccentric spherical dielectric inclusion and an incident amplitude-modulated plane electromagnetic wave constitute an exterior radiation problem, which is solved in this paper. A solution is obtained by combined use of the Fourier transform and the indirect-mode-matching method. The analysis yields a set of linear equations for the wave amplitudes of the frequency-domain expansion of the electric-field intensity within and outside the externally spherical inhomogeneous body; that set is solved by truncation and matrix inversion. The shape of the backscattered pulse in the time domain is determined by application of the inverse fast Fourier transform. Numerical results are shown for a pulse backscattered by an acrylic sphere that contains an eccentric spherical cavity. The effects of cavity position and size on pulse spreading and delay are discussed.     

Ideal-Gas Heat Capacity for 2,3,3,3-Tetrafluoropropene (HFO-1234yf) Determined from Speed-of-Sound Measurements

The isobaric ideal-gas heat capacity for HFO-1234yf, which is expected to be one of the best alternative refrigerants for HFC-134a, was determined on the basis of speed-of-sound measurements in the gaseous phase. The speed of sound was measured by means of the acoustic resonance method using a spherical cavity. The resonance frequency in the spherical cavity containing the sample gas was measured to determine the speed of sound. After correcting for some effects such as the thermal boundary layer and deformation of the cavity on the resonance frequency, the speed of sound was obtained with a relative uncertainty of 0.01 %. Using the measured speed-of-sound data, the acoustic-virial equation was formulated and the isobaric ideal-gas heat capacity was determined with a relative uncertainty of 0.1 %. A temperature correlation function of the isobaric ideal-gas heat capacity for HFO-1234yf was also developed.     

Stokes resistance of a porous spherical particle in a spherical cavity

The boundary effect on the asymmetrical motion of a porous spherical particle in an eccentricspherical cavity is investigated in the quasi-steady limit under creeping flow conditions. The porous particletranslates and rotates in the viscous fluid, located within the spherical cavity, normal to the line connectingtheir centers. The fluid inside the porous particle is governed by the Brinkman equation. A tangential stressjump condition at the interface between the fluid and the porous particle is applied. A semi-analytical approachbased on a collocation technique is used. Due to the linearity of the present problem, the flow variables for theclear fluid region are constructed by superposing basic solutions of two problems: the first one is the regularsolution inside the cavity region in the absence of the porous particle where a first system of coordinates has itsorigin at the center of the cavity, while the second problem is the regular solution in the infinite region outsidethe spherical porous particle where a second coordinate system with its origin at the center of the porousparticle is used. Numerical results displaying the resistance coefficients acting on the particle are obtainedwith good convergence for various values of the physical parameters of the problem. The results are tabulatedand represented graphically. The findings demonstrate that the collocation results of the resistance coefficientsare in good agreement with the corresponding results for the impermeable solid particle.     

Progress Towards an Acoustic/Microwave Determination of the Boltzmann Constant at LNE-INM/CNAM

The Boltzmann constant k will be re-determined by using the simple, exact connection between the speed of sound in noble gases (extrapolated to zero pressure) and the thermodynamic temperature T, the molar mass of the gas M, and the universal gas constant R. The speed of sound will be determined in a spherical cavity of known volume V by measuring the acoustic resonance frequencies. This acoustic method led to the CODATA-recommended value of k; however, the CODATA value of k came from measurements using an almost perfectly spherical, stainless-steel-walled cavity filled with stagnant argon. The steel cavity’s volume was determined by weighing the mercury of well-known density required to fill it. In contrast, a copper-walled, quasi-spherical cavity (intentionally slightly deformed from a sphere), filled with helium gas that is continuously refreshed by a small helium flow that will mitigate the effects of outgassing, will be used. The volume of the copper cavity will be determined by measuring the microwave resonance frequencies and/or by three-dimensional coordinate measurements. If the microwave method is satisfactory, the measurement of k will be based on the ratio of the speed of sound in helium—obtained by acoustic resonance measurements—to the speed of light, obtained by microwave resonance measurements. This method exploits the theorem that the frequency ratios are independent of the details of the shape of the quasi-spherical cavity. Here, progress at LNE-INM/CNAM towards a better mechanical design and better understanding of the excess of the half-widths of the acoustic and microwave measurements are reported.     

电场仪球形传感器涂覆方案研究

电场仪涂层的均匀性是影响其电场测量精度的重要因素,手工喷涂方案难以满足涂层的均匀性需求,且工艺不稳定.为解决电场仪球形传感器涂层喷涂的均匀性问题,提出了一种新的喷涂方案,采用机械臂带动喷枪运动,在喷枪与球形传感器之间增加带开口的挡板,通过改变开口的形状控制喷涂到球形传感器上的涂料量,从而实现涂层的均匀性.初步实验得到的结果看,涂层的均匀性较好,而且提高了涂层质量,因此该方案能够最终解决电场仪球形传感器的涂覆问题.     

Centrally symmetric quasistatic problem of thermoelasticity for a temperature sensitive body

The perturbation method is used to construct the general solution of a centrally symmetric quasistatic problem of elasticity under the assumption that all thermomechanical characteristics of a body are functions of temperature. As special cases, we obtain the solutions of the corresponding problems of thermoelasticity for hollow and continuous balls and a space containing a spherical cavity. We also perform the numerical analysis of the temperature field and the stress-strain state induced by this field in the space with spherical cavity free of external loads. Note that the process of convective heat exchange with an ambient medium of constant temperature is realized through this cavity.Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 40, No. 3, pp. 62–68, May–June, 2004.     

Point force excitation of a thick-walled elastic infinite pipe with an embedded inhomogeneity

The propagation of elastic waves in thick-walled pipe with an embedded inhomogeneity is considered. The pipe is excited by a point force applied on its surface and the time harmonic problem is solved using the null field approach, a method whose main characteristics are surface integral representations and expansions in spherical and cylindrical vector wave functions. Entering in the expression for the scattered field are the transition matrix for the cavity, the reflection matrices for the inner and outer surfaces of the pipe, the transformation functions between the spherical and cylindrical vector wave functions and also the translation for the cylindrical waves. Numerical examples, both in the frequency and time domain, are presented for a spherical cavity and an open circular crack.