机械阻抗板复合微穿孔板结构的低频吸声技术研究

发布时间：2018-10-17 22:08

【摘要】：微穿孔板结构具有清洁、环保、无污染等优点,在工程中有着广泛的应用,但其在低频段吸声效果不佳,限制了该结构的适用范围,因此如何提高微穿孔板结构的低频吸声性能成为众学者研究的主要方向。单层机械阻抗板复合微穿孔板结构在低频段出现吸声峰值,在一定程度上改善低频吸声效果,但仍存在吸声峰值单一及吸声频带较窄等问题。针对这一问题,本文进一步开展工作,从增加吸声峰值数目和拓宽吸声频带这两条途径研究提高复合结构的低频吸声性能。首先总结微穿孔板及机械阻抗板的吸声机理的基础知识,在此基础之上提出在单层机械阻抗板的背面并联机械阻抗,与微穿孔板结合,构成一种复合吸声结构,研究思路是通过并联机械阻抗形成多个共振峰来起到提高吸声性能作用。对提出的复合结构开展计算研究:复合吸声结构由机械阻抗和微穿孔板两部分组成,对机械阻抗部分采用集总参数的方法进行分析,由并联机械阻抗系统的特征,获得整个机械阻抗部分的等效电路,将机械阻抗转换成声阻抗,推导出这部分的声学传递矩阵,与微穿孔板和空腔部分的传递矩阵串联,完成复合吸声结构声阻抗的理论分析,获得整个复合结构的吸声系数计算表达式。运用前面的理论分析,选择合适的结构参数,将机械阻抗部分的频率设定在低频,开展试验研究,使用驻波管测量复合结构的吸声系数。试验显示:试验结果与理论计算基本吻合,说明建立的计算模型合理;与单层机械阻抗板只有一个吸声峰相比,复合结构在低频出现三个吸声峰值,明显提高了低频吸声性能。分析机械阻抗板的品质因子,提高机械阻抗板结构的阻尼能够降低品质因子,拓宽吸声频带。机械阻抗板的粘弹性性能一般采用密实性材料提供,在低频吸声需要降低材料的弹性系数,而弹性系数降低的同时阻尼也降低,吸声频带变窄。本文提出用橡胶管代替密实材料,橡胶管的弹性系数比密实材料的弹性系数低,能够在低频吸声,并且在橡胶管上加工小孔,形成多孔弹性管,为机械阻抗板提供粘弹性。对提出的结构开展试验研究,仔细观察试验结果,采用多孔弹性管和采用未加工小孔的弹性管的吸声性能对比,共振频率稍微向低频移动,分析原因是因为加工小孔以后弹性管的弹性系数降低所导致;试验结果还显示,采用多孔橡胶管吸声系数有提高,吸声频带拓宽,分析机理,声音入射到机械阻抗板时,机械阻抗板带动多孔弹性管共同振动,多孔弹性管振动过程中压缩内腔空气,空气流过弹性管侧壁小孔,产生阻尼,耗散振动能量,从而拓宽了吸声频带,提高了吸声性能。
[Abstract]:The microperforated plate structure has many advantages such as clean, environmental protection, no pollution and so on. It is widely used in engineering, but its sound absorption effect in low frequency band is not good, which limits the application range of the structure. Therefore, how to improve the low-frequency sound absorption of micro-perforated plate structure has become the main research direction of scholars. The single-layer mechanical impedance plate composite microperforated plate structure has the peak sound absorption in low frequency band, which can improve the low frequency sound absorption effect to some extent, but there are still some problems such as single peak sound absorption peak and narrow sound absorption band. In order to solve this problem, this paper further studies how to improve the low frequency sound absorption performance of the composite structure by increasing the number of absorption peaks and widening the sound absorption band. Firstly, the basic knowledge of the sound absorption mechanism of the microperforated plate and the mechanical impedance plate is summarized. On this basis, the mechanical impedance parallel on the back of the single-layer mechanical impedance plate is proposed, which is combined with the micro-perforated plate to form a compound sound absorption structure. The research idea is to improve the sound absorption performance by forming multiple resonance peaks in parallel mechanical impedance. The composite structure is composed of two parts: mechanical impedance and microperforated plate. The mechanical impedance is analyzed by lumped parameter method, and the characteristics of parallel mechanical impedance system are analyzed. The equivalent circuit of the whole mechanical impedance part is obtained, the mechanical impedance is converted into acoustic impedance, the acoustic transfer matrix of this part is deduced, and the acoustic impedance of the composite acoustic absorption structure is analyzed in series with the transfer matrix of the microperforated plate and the cavity part. The expression of the sound absorption coefficient of the composite structure is obtained. The frequency of the mechanical impedance is set at low frequency and the sound absorption coefficient of the composite structure is measured by standing wave tube. The experimental results show that the experimental results are in good agreement with the theoretical calculation, which indicates that the proposed model is reasonable, and compared with the single layer mechanical impedance plate with only one absorption peak, the composite structure has three peak sound absorption peaks at low frequency, which obviously improves the low frequency sound absorption performance. By analyzing the quality factor of the mechanical impedance plate and increasing the damping of the mechanical impedance plate structure, the quality factor can be reduced and the sound absorption band can be widened. The viscoelastic properties of mechanical impedance plates are generally provided by dense materials. In low frequency sound absorption, the elastic coefficient of materials is reduced, while the damping coefficient is also reduced, and the band of sound absorption is narrowed. In this paper, the rubber tube is used to replace the dense material. The elastic coefficient of the rubber tube is lower than that of the dense material. The rubber tube can absorb sound at low frequency, and it can process holes in the rubber tube to form a porous elastic tube, which provides viscoelasticity for the mechanical impedance plate. The experimental study of the proposed structure was carried out, and the experimental results were carefully observed. The resonance frequency shifted slightly to the low frequency by comparing the sound absorption performance of the elastic tube with the porous elastic tube and the elastic tube with a small unmachined hole. The reason is that the elastic coefficient of the elastic tube decreases after the small hole is processed. The experimental results also show that the sound absorption coefficient of the porous rubber tube is improved, the sound absorption band is widened, the mechanism is analyzed, and the sound is incident to the mechanical impedance plate. The mechanical impedance plate drives the joint vibration of the porous elastic tube. During the vibration process of the porous elastic tube, the air flows through the small hole of the lateral wall of the elastic tube, resulting in damping and dissipation of vibration energy, thus widening the frequency band of sound absorption and improving the sound absorption performance.
【学位授予单位】：江苏大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TB535.1

【参考文献】