腔壁弹性对水下小型圆柱形亥姆霍兹共振器共振频率的影响

理论和实验研究了腔壁弹性对水下小型圆柱形亥姆霍兹共振器共振频率的影响.基于电-声类比理论,建立了小型共振器的简化模型,利用电路分析方法得到了便于计算的共振频率一般表达式.分别仿真分析了共振器壁面厚度和材料对共振频率的影响,得到了不同尺寸的小型共振器的近似刚性条件.在充水驻波罐中对不同壁厚、不同材料的小型圆柱形亥姆霍兹共振器的共振频率进行了测量,实验结果较好地验证了理论分析和近似刚性条件的正确性.所得结果对小型圆柱形亥姆霍兹共振器的设计和水下应用具有较好的参考价值. 关键词： 亥姆霍兹共振器 共振频率 传递函数 辐射阻抗     

腔壁弹性对充水亥姆霍兹共振器声学特性的影响:圆柱形腔等效集中参数模型

研究了充水亥姆霍兹共振器的弹性壁对其声学特性的影响。建立了考虑壁面弹性的圆柱形共振器的等效集中参数理论模型,并在静水管路上进行了实验验证。从共振器的共振频率、激励声压与腔内声压的传递函数以及共振器的传递损失等方面阐述了弹性壁的影响,并对刚性壁假设和弹性壁结果进行了比较。理论和实验都证明了腔壁弹性对亥姆霍兹共振器的声学特性有很大的影响。     

具有流动和侧向Helmholtz共振器的驻波管内声场研究Ⅱ.实验验证及结果讨论

利用建立的具有流动和侧向Helmholtz共振器的驻波管的实验装置,成功地证实了作者所作的理论分析,包括有流动驻波管和Helmholtz共振器连接处的间断条件、驻波管末端的反射条件、切向流时Helmholtz共振器声阻抗,并实验确定了末端修正系数和等效半径系数。接着,应用理论分析和实验得到的结果讨论了流动对Helmholtz共振器性能和驻波管声场的影响,结果表明,流动会降低一些消声效果,但在具有流动的驻波管中采用Helmholtz共振器仍然是一种降噪的有效方法。     

具有流动和侧向Helmholtz共振器的驻波管内声场研究——Ⅰ.理论分析

对于无流动的驻波管,侧向加入Helmholtz共振器已经被证实是降低火箭或涡轮发动机燃烧室燃烧噪声的一种好的新方法。但实际情况在燃烧室内是有低速流动的,本文对这种侧向具有Helmholtz共振器又有流动驻波管内的声场进行理论分析,建立相应的数学物理问题,并进行求解,包括:(1)建立有流动驻波管和Helmholtz共振器连接处的间断条件。(2)提出同时计及流动、共振器喉部粘性和多孔影响的Helmholtz共振器声阻抗计算公式。(3)建立驻波管末端反射条件。上述理论工作已得到实验证实。     

水下材料声学性能宽频段测量方法

本文根据脉冲法和传递函数法的测试原理,建立水下声学材料吸声性能宽频段测量方法,在同一水声声管,相同状态下,对橡胶材料吸声性能进行测试分析。分析表明:常压及加压环境下,采用传递函数法和脉冲法测量材料的吸声性能,在重合频段(4 kHz～5.5 kHz)测试结果基本一致,测试偏差小于5%,从而验证了不同测量原理,测试材料水下声学性能的通用性。因此,采用传递函数法和脉冲法,可以实现水下材料声学性能宽频带测试。     

吸声材料对水下小平台上矢量传感器声学特性的影响研究

本文围绕粘贴黏弹性吸声材料方法对水下小平台上安装矢量传感器的指向性和测向的影响展开理论分析和实验研究.首先建立了吸声材料和平台结构组成的复合层结构的数学模型,对声波经过复合层结构的声学特性进行了分析,在此基础上利用有限元耦合边界元法对粘贴吸声材料前后的水下小平台上的矢量传感器的声学特性进行研究.通过理论计算和数值分析研究了吸声材料对矢量传感器的各通道的指向性的影响,并计算了覆盖吸声材料前后矢量传感器的测向精度.水池实验验证了分析结果的正确性.     

圆柱形水下爆炸实验容器壁部强度设计研究

 基于薄壁壳理论和水下爆炸理论,对圆柱形水下爆炸实验容器在爆炸冲击波作用下弹性范围内的壁部应变进行了理论分析和实验研究。导出了圆柱形水下爆炸实验容器在爆炸冲击波作用下壁部弹性应变与容器直径、壁厚及内部爆炸药量之间的关系,并对计算结果进行了实验验证。实验表明公式求解结果与实验结果具有较好的一致性。     

封闭腔体噪声控制中亥姆霍兹共振器的优化设计方法

提出用亥姆霍兹共振器控制声腔内噪声时计算共振器最优阻尼比和最优工作带宽的理论公式,并进行实验验证。首先,建立共振器与待控腔体的声学耦合方程,以最小化腔体内目标声压幅值为参考,对共振器的阻尼比和工作带宽进行理论分析,求出最优阻尼比和最优工作带宽的计算公式。接着,提出在声腔噪声控制中使用最优亥姆霍兹共振器的实施步骤。最后,以一维声学腔体内的噪声为控制对象,通过对比控制前后的理论结果与实测数据,验证最优阻尼比和最优工作带宽的理论公式。结果表明,本文开发的亥姆霍兹共振器优化设计方法能准确地预报共振器的最优阻尼比与最优工作带宽,在声腔中低频噪声控制中有广泛的应用前景。      

四阶声低通滤波光纤水听器的声压灵敏度频响特性

对四阶声低通滤波光纤水听器的声压灵敏度频响特性进行了详细的理论和实验研究.在已有的低频集中参量模型中引入了一个机械声阻,用于描述系统的机械损耗,从而得到了改进的声学等效电路.相位频响特性对于光纤水听器的阵列应用非常重要,关系到阵列的波束形成效果,进而影响系统定位、识别与跟踪目标的能力,因此在分析幅度频响特性的同时研究了相位频响特性.仿真分析了各主要参量对声压传递函数的影响,得到了一些对声低通滤波光纤水听器设计具有重要指导意义的结论.实测声压灵敏度频响曲线与仿真结果基本一致,较好地验证了理论分析的正确性.四 关键词： 光纤传感器 光纤水听器 声压灵敏度 低通滤波器     

水下材料吸隔声性能测试近场长脉冲传递函数法

为消除有限空间壁面反射对大样水下材料声学性能测试的影响,利用传递函数法和脉冲法测试原理,建立声波垂直入射情况下水下材料吸隔声性能测试近场长脉冲传递函数法,10mm均匀钢板模型声学性能试验表明,压力环境下钢板反射及隔声性能测试值与理论值基本一致,反射系数测试偏差小于0.1,隔声量测试偏差小于1dB,可以采用近场长脉冲传递函数法测量声波垂直入射情况下材料声学性能,可有效克服边界反射对测试的影响。     

Helmholtz水声换能器弹性壁液腔谐振频率研究

针对传统Helmholtz水声换能器设计中刚性壁假设的局限性,将Helmholtz腔体的弹性计入到液腔谐振频率计算中,实现低频弹性Helmholtz水声换能器液腔谐振频率精确设计.基于细长圆柱壳腔体的低频集中参数模型,导出了腔体弹性引入的附加声阻抗表达式,得到了弹性壁条件下Helmholtz水声换能器等效电路图,给出了考虑了末端修正的弹性壁Helmholtz共振腔液腔谐振频率计算公式.利用ANSYS软件建立了算例模型,仿真分析了不同材质、半径、长度时的Helmholtz共振腔液腔谐振频率.结果对比表明弹性理论值与仿真值符合得很好,相比起传统的刚性壁理论计算结果,本文的弹性壁理论得出的液腔谐振频率值有所降低,与真实情况更加接近.本文的结论可以为精确设计低频弹性Helmholtz水声换能器提供理论支持.     

The impact of the neck material on the sound absorption performance of Helmholtz resonators

Helmholtz resonators with sound absorption materials filling the neck may have an improved sound absorption capacity. In this work, parallel perforated ceramics with different perforation diameters were installed into the neck of a Helmholtz resonator to improve its acoustic impedance to simultaneously achieve a better acoustic absorption coefficient and a wider absorption bandwidth. An experimental system was built to investigate the effect of the perforation diameters on the sound absorption performance of the resonator. It is found that nonlinear effects near the resonance frequency affect the resonator?s neck mouth impedance and further its sound absorption performance significantly. For frequency range 50–500 Hz, a model of the neck mouth impedance is developed based on a revised Forchheimer relationship. The experimental results are in good agreement with the theoretical model.     

弯曲圆盘驱动的双Helmholtz共振腔换能器

使用双面同相振动的弯曲圆盘换能器驱动双Helmholtz共振腔,既放大了弯曲圆盘换能器弯曲共振频率以下频段的声输出,又利用两个Helmholtz共振腔的同相声源辐射模型实现了在Helmholtz共振频率处的"∞"字形垂直指向性,实现了低频指向性声发射。阐述了换能器实现"∞"字形低频指向性发射的机理,研究了腔体长度、金属圆片厚度及弯曲圆盘边缘简支厚度等关键结构参数对Helmholtz共振频率的影响,求解了换能器的发送电压响应、指向性等参数。依据仿真结果制作了实验样机,在消声水池中进行了电声性能测试。测试结果显示,指向性形状及液腔共振频率与仿真结果基本相符。这种由弯曲圆盘驱动的双Helmholtz共振腔水声换能器为实现水声换能器小尺寸、低频指向性发射提供了一种技术手段。      

Improving low-frequency sound absorption of micro-perforated panel absorbers by using mechanical impedance plate combined with Helmholtz resonators

The traditional Micro-perforated plate (MPP) is a kind of clean and non-polluting absorption structure in the middle and high frequency and has been widely used in the field of noise control. However, the sound absorption performance is dissatisfied at low frequencies when the air-cavity depth is restricted. In this paper, a mechanical impedance plate (MIP) is introduced into the traditional MPP structure and a Helmholtz resonator is attached to the MIP. Mechanical impedance plate (MIP) provides a good absorption at low frequency by using mechanism of mechanical resonance and the acoustic energy is dissipated in the form of heat with viscoelastic material. Helmholtz resonator can fill in the defect of the poor absorption effect between the Micro-perforated plate (MPP) and the mechanical impedance plate (MIP). The acoustic impedance of the proposed sound absorber is investigated by using acoustic electric analogy method and impedance transfer method. The influence of the tube’s length of Helmholtz resonator and the number of Helmholtz resonator on the sound absorption is studied. The corresponding results are in agreement with the theoretical calculation and prove that the composite structure has the characteristics of improving the low frequency sound absorption property.     

A study on the multi-freedom broadband impedance model for time-domain simulations

The purpose of this paper is to construct a general broadband impedance model, which is suited for predicting acoustic propagation problems in time domain.A multi-freedom broadband impedance model for sound propagation over impedance surfaces is proposed and the corresponding time domain impedance boundary condition is presented.Basing on the extended Helmholtz resonator,the multi-freedom impedance model is constructed through combing with a sum of rational functions in the form of general complex-conjugate pole-residue pairs and it is proved that the impedance model is well posed.The impedance boundary condition can be implemented into a computational aeroacoustics solver by a recursive convolution technique, which results in a fast and computationally efficient algorithm.The two dimensional and three dimensional benchmark problems are selected to validate the accuracy of the proposed impedance model and time domain simulations.The numerical results are in good agreement with the reference solutions.It is demonstrated that the proposed impedance model can be used to describe the broadband characteristics of acoustic liners,and the corresponding time domain impedance boundary condition is viable and accurate for the prediction of sound propagation over broadband impedance surfaces.     

谐振管内非线性驻波的有限体积数值算法

为了扩展谐振管内非线性驻波在工程中的应用, 以及克服现有数值计算方法仅局限于求解直圆柱形和指数形谐振管内非线性驻波的问题. 根据变截面的非稳态可压缩热黏性流体Navier-Stokes方程和空间守恒方程, 并基于求解压力速度耦合方程的半隐式算法和交错网格技术, 构建一种能够计算任意形状轴对称谐振管受活塞驱动时内部非线性驻波的有限体积算法. 分别对圆柱形、指数形和圆锥形谐振管内的非线性驻波进行仿真计算. 通过与现有试验结果以及数值仿真结果的对比, 验证了该方法的正确性.并获得除驻波声压之外的另外一些新的物理结果, 包括速度、密度、温度的瞬时变化.在直圆柱形谐振管内产生冲击声压波, 速度波形中出现钉状结构.而在指数形和圆锥形谐振管内产生高声压幅值的驻波, 没有出现冲击波, 速度波形中均未发现钉状结构. 计算结果表明谐振管内非线性驻波的物理属性与谐振管形状之间有密切关系.     

Suppression of Helmholtz resonance using inside acoustic liner

When a Helmholtz resonator is exposed to grazing flow, an unstable shear layer at the opening can cause the occurrence of acoustic resonance under appropriate conditions. In this paper, in order to suppress the flow-induced resonance, the effects of inside acoustic liners placed on the side wall or the bottom of a Helmholtz resonator are investigated. Based on the one-dimensional sound propagation theory, the time domain impedance model of a Helmholtz resonator with inside acoustic liner is derived, and then combined with a discrete vortex model the resonant behavior of the resonator under grazing flow is simulated. Besides, an experiment is conducted to validate the present model, showing significant reduction of the peak sound pressure level achieved by the use of the side-wall liners. And the simulation results match reasonably well with the experimental data. The present results reveal that the inside acoustic liner can not only absorb the resonant sound pressure, but also suppress the fluctuation motion of the shear layer over the opening of the resonator. In all, the impact of the acoustic liners is to dampen the instability of the flow-acoustic coupled system. This demonstrates that it is a convenient and effective method for suppressing Helmholtz resonance by using inside acoustic liner.     

A theoretical model to predict the low-frequency sound absorption of a helmholtz resonator array

A theoretical method based on mutual radiation impedance is proposed to compute the sound absorption performance of a Helmholtz resonator array in the low-frequency range. Any configuration of resonator arrangement can be allowed in the method, while all the resonators may or may not be identical. Comparisons of the theoretical predictions with those done by the past studies or experiments show that the present method can accurately predict the absorption performance in more general cases.