敷设阻尼材料的双层圆柱壳声辐射性能分析

研究了外层壳上敷设粘弹性阻尼材料的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,敷设粘弹性阻尼材料的双层壳体的粘弹性阻尼层的运动用三维Navier方程描述,将阻尼沿厚度方向的位移用泰勒展开表示,利用位移和应力的连续性边界条件建立振动方程。详细讨论了阻尼层厚度、弹性模量、损耗因子及静水压缩因子等参数对双层壳体振动和声辐射的影响,表明阻尼材料的弹性模量越高,阻尼层越薄,损耗因子越小,壳体的辐射声功率越高;对于较高频率的激励,必需考虑阻尼层质量的影响,选择密度低的阻尼材料对减振降噪有利。     

阻尼材料敷设方式对双层壳体声辐射性能的影响

研究了内、外壳体敷设粘弹性阻尼材料的有限长加肋双层圆柱壳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,运用Helmholtz波动方程和壳体表面的边界条件来求解位于内、外层壳之间的环形流场,并利用傅氏变换,可以求出声压的表达式,粘弹性阻尼层的运动用三维Navier方程描述,将阻尼沿厚度方向的位移用泰勒展开表示,利用不同的位移和应力的连续性边界条件分别建立了无阻尼以及三种阻尼材料敷设方式的振动方程,并用数值计算讨论了光壳和三种阻尼材料敷设方式对三种壳间连接形的双层壳体振动和声辐射的影响,结果表明敷设阻尼材料能降低壳体的辐射噪声,并且内壳敷设阻尼比外壳敷设阻尼的减振降噪效果好,内外壳均敷设阻尼材料的减振降噪效果最好。     

The modeling of the radiation and response green's function of a fluid-loaded cylindrical shell with an external compliant layer

Scattering and radiation of acoustic waves from a fluid-loaded cylindrical shell with an external compliant layer are of interest. The compliant layer can be modeled by a normally reacting impedance layer, which has the advantage that complex compliant layer geometries, such as partial compliant layers, can be considered. A question may, however, arise as to the accuracy of this approach. A more rigorous approach is to model the elastic shell and compliant layer using a multilayer shell theory, which has the disadvantage that it cannot be extended to consider partial layers. In this paper scattering results from the normally reacting compliant layer model are compared to those from the multilayer shell model to show that the two approaches produce similar results, except for thickness resonances of the compliant layer. Having established the consistency between the two approaches, results for the far-field acoustic radiation as a function of frequency and radiation angle for a fluid-loaded shell with an external compliant layer excited by an internal ring force are obtained using the normally reacting impedance layer model. These results clearly show the reduction in the far field radiation due to the presence of the compliant layer.     

Parametric study on sound radiation from an infinite fluid-filled/semi-submerged cylindrical shell

This work presents the parametric study on the far-field sound pressure radiated from an infinite fluid-filled/semi-submerged cylindrical shell excited by a radial point load. Here, the exterior fluid is non-viscous, isotropic and irrotational coaxial flow. The formula of the radial velocity of the shell in wave-number domain is developed by using the wave-number domain approach (WDA). Then, the analytic expressions are derived for the far-field sound pressure radiating from the shell by using the same method presented in Salaün [Journal of the Acoustical Society of America 90 (1991) 2173]. The influences of parameters such as fluid velocity, structural damping, position of the force, and structural thickness on the far-field sound pressure are investigated. The sound pressure is shown to be very different from the one in the case of a fluid-filled/full-submerged cylindrical shell. Furthermore, it is shown that the pressure and the resonance frequency would increase with the fluid velocity increasing for downstream propagation. The reverse is true for upstream propagation. Moreover, the far-field sound pressure is related to the position and frequency of the excited force. In addition, the influences of structural damping and thickness are shown to be very important.     

Acoustic scattering from a submerged cylindrical shell coated with locally resonant acoustic metamaterials

Using the multilayered cylinder model, we study acoustic scattering from a submerged cylindrical shell coated with locally resonant acoustic metamaterials, which exhibit locally negative effective mass densities. A spring model is introduced to replace the traditional transfer matrix, which may be singular in the negative mass region. The backscattering form function and the scattering cross section are calculated to discuss the acoustic properties of the coated submerged cylindrical shell.     

Study on sound transmission characteristics of a cylindrical shell using analytical and experimental models

A circular cylindrical cavity enclosed by a thin elastic shell is found in many practical devices such as expansion volume mufflers, hermetic compressors and aircraft cabins. Analytical and experimental studies are conducted in this work to understand the characteristics of sound transmission through the cylindrical wall of such a system. Using an infinitely long circular cylindrical shell subjected to a plane incident wave, an exact solution is obtained by solving the classical shell vibration equations and the acoustic wave equations simultaneously. Transmission losses obtained from the solution are compared to the transmission losses that are measured for a cylindrical shell of finite length and the same cross-sectional dimensions. The comparison suggests that the theoretical model can be used as an effective design tool despite considerable simplifications involved.     

Structural, Raman, and photoluminescence characteristics of ZnO nanowires coated with Al-doped ZnO shell layers

Al-doped ZnO (AZO) shell layers were coated on core ZnO nanowires to fabricate ZnO/AZO core–shell nanowires. The energy-dispersive X-ray spectra confirmed the presence of Al element in the shell layers, and the lattice resolved transmission electron microscopy image revealed that these layers corresponded to the hexagonal ZnO structure. The X-ray diffraction pattern exhibited a shift of the ZnO peaks, suggesting the substitutive incorporation of Al into the ZnO lattice. The A₁(LO) mode line in the Raman spectra was enhanced by the AZO coating. In the photoluminescence measurements, the AZO coating enhanced the intensity ratio of the UV to green emission.     

Effects of cavity resonances on sound transmission into a thin cylindrical shell

In the context of the transmission of airborne noise into an aircraft fuselage, a mathematical model is presented for the effects of internal cavity resonances on sound transmission into a thin cylindrical shell. The “noise reduction” of the cylinder is defined and computed, with and without including the effects of internal cavity resonances. As would be expected, the noise reduction in the absence of cavity resonances follows the same qualitative pattern as does transmission loss. Numerical results show that cavity resonances lead to wide fluctuations and a general decrease of noise reduction, especially at cavity resonances. Modest internal absorption is shown to greatly reduce the effect of cavity resonances. The effects of external airflow, internal cabin pressurization, and different acoustical properties inside and outside the cylinder are also included and briefly examined.     

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。     

水中弹性圆柱壳的共振声辐射

研究了在内壁简谐法向线力激励下的水中弹性圆柱壳的振动和声辐射问题,这有助于深入认识水中结构的声辐射机理,验证水下结构共振声辐射理论。本文从经典Rayleigh简正级数解出发导出共振声辐射公式,然后分别用经典公式和共振声辐射公式计算钢圆柱壳的辐射声功率及壳体表面声压曲线。计算结果表明两者符合良好。