机械阻抗与声阻抗结合提高微穿孔板低频吸声性能

提出了在微穿孔板后部引入机械阻抗形成组合结构来解决微穿孔板低频吸声性能差的问题。由机械阻抗板两侧质点速度相同得出机械阻抗单元的传递矩阵,采用传递矩阵法将其与空腔、微穿孔板单元串接,建立组合结构理论计算模型;通过分析品质因子获得带宽与机械阻抗板质量成反比;试验得出组合结构在400 Hz附近有系数为0.8以上的吸声峰值,试验结果与理论计算吻合。在传统微穿孔板共振吸声机制的基础上加入机械共振,能够实现在不增加结构厚度的前提下提高低频吸声性能;降低机械阻抗板质量并且适当控制边界阻尼系数可以实现吸声频带的拓宽。     

变厚度圆板、环板振动分析的传递矩阵法*

变厚度圆板和环板是在工程设计中经常遇到的一类构件,与等厚度板相比,通过适当的沿径向厚度的变化,这种变厚度板在振动、失稳、弯曲等方面能起到更好的效果。将沿径向任意变厚度圆板、环板划分为一系列等厚度环板单元,基于Mindlin中厚板理论采用逆向推导的方式推导了其传递矩阵,建立起变厚度圆板、环板的频率方程。通过计算线性变厚度环板自由振动时的频率,并与ANSYS模态分析结果相比较,验证了计算模型的精确性。逆向推导法避免了高阶数传递矩阵推导复杂的问题,是对传递矩阵法的很好推广。     

多层微穿孔板结构声学性能计算方法对比分析

计算多层微穿孔板结构声学特性方法传统主要用声电类比法,目前出现阻抗转移法和传递矩阵法,对比分析这三种计算方法,同时进行相应的实验验证。结果表明:阻抗转移法和传递矩阵法实质上是相同的,这两种方法计算结果与实验结果吻合良好。声电类比法在空腔较大时计算结果偏离实验值,原因是声电类比法采用集总参数分析,计算多层结构时,空腔单元只考虑声顺,忽略声质量,导致误差。阻抗转移法和传递矩阵法不存在这一误差,计算准确。     

微孔板结合化学发光法快速测定覆盆子中总糖蛋白的抗氧化活性

在碱性条件下,覆盆子总糖蛋白对鲁米诺-过氢化氢、鲁米诺-邻苯三酚-氢氧化钠和鲁米诺-硫酸铜-过氧化氢化学发光体系具有明显的抑制作用。基于这一特点,本文将微孔板与化学发光法结合,在优化条件下,建立了覆盆子总糖蛋白清除H2O2、O2-和.OH自由基能力的快速检测方法,结果表明该方法具有样品用量少、操作简单、检测速度快等优点,适用于药物中有效成分的活性检测及筛选。     

加工误差对马氏理论关于超微孔微穿孔板吸声结构适用性的影响

从理论和实验上探讨了加工误差对马氏理论关于超微孔微穿孔板(micro-perforated panel,MPP)吸声结构适用性的影响。建立了计及加工误差的MPP理论分析模型,并应用MEMS工艺制作了超微孔MPP,由于工艺本身存在一定的加工误差,造成实际孔径与设计孔径10%-20%的偏差,在阻抗管中测量得到其垂直入射吸声系数。将实验结果和计及加工误差的理论预测值与马氏理论预测值进行对比发现,差别均较小,最大误差仍在6%以内,说明马氏理论在计及加工误差的情况下仍然适用。此外,对马氏理论关于加工误差的适用极限进行了仿真计算,结果表明,适用极限的大小具体依赖于超微孔MPP的孔径大小。     

微孔板荧光法对土壤糖酶活性的测定研究

应用荧光共轭物质作为底物,将96微孔板和荧光检测法结合进行稻-麦轮作系统CO₂倍增条件(FACE)下土壤两种糖酶(木聚糖酶和纤维素酶)活性的测定,探讨了微孔板结合荧光法测定糖酶活性的可行性。结果表明,此种方法可以灵敏的检测到土壤稀释液中的糖酶活性,测定结果重现性较好(变异系数最大为4.879%)。与传统的分光光度法相比,是一种准确、快速、简便的土壤糖酶活性测定方法。CO₂倍增条件下土壤木聚糖酶活性高于自然条件,且在小麦的拔节期,抽穗期和成熟期及水稻的抽穗期和成熟期显著高于对照(P<0.05),CO₂浓度升高提高作物的生长代谢水平,进而影响微生物活性造成土壤木聚糖酶活性提高。纤维素酶活性在CO₂倍增条件下未发生显著变化,说明土壤纤维素酶在短时期内对CO₂增加的响应不显著。     

不同声强宽带噪声激励下结构参数对穿孔板消声器吸声特性影响的实验研究

高声压级激励下,由于非线性效应的存在,穿孔板消声器的吸声特性将发生改变,而改变量的大小与穿孔板的结构参数(穿孔率,孔径,板厚)密切相关。本文设计搭建了实验平台来研究结构参数的变化对穿孔板消声器的吸声特性的影响。根据实验结果发现:随着声压级的升高,由于穿孔板结构的非线性加剧,其声阻抗将发生变化,导致穿孔板消声器的吸收峰值降低,但吸收频带却拓宽了;在穿孔率一定的情况下,孔径越小的穿孔板消声器更适合低声压级环境工作;在孔径一定的情况下,穿孔率越低的穿孔板消声器也更适合低声压级环境工作。     

基于传递矩阵法的热声发动机频率设计计算

介绍利用传递矩阵法计算热声发动机的工作频率的思路和方法。理论分析表明该方法是切实可行的 ,和其他方法得到了相互的印证。利用该方法的计算结果和已发表的试验结果进行了对比分析。研究结果表明 ,相比已有的计算方法而言 ,传递矩阵法更加简单直观 ,方便于采用计算机编程计算复杂结构的热声系统的工作频率。     

计算二维声腔传递矩阵的正方形线声源模型

在比较现有二维矩形声腔的声源计算模型特点的基础上,提出了一种新的正方形线声源计算模型,用于计算基于模态级数叠加法的压力响应函数.分析表明,此模型不仅可以克服点声源模型的奇异性,而且在合理选择模型的几何尺寸的前提下能得到比面源模型更为均匀的压力分布,提高了传递函数计算的准确率.数值试验考察了此模型的实际应用效果,表明新的线声源数学模型较圆形线声源更为简便,可以提高计算效率. 关键词： 传递矩阵 正方形线声源模型 二维声腔 模态级数叠加法     

环状气囊水消声器声学性能的预测与分析

水消声器作为一种有效的噪声控制装置被广泛应用于水管路系统,本文分别使用模态匹配法和有限元法对环状气囊水消声器的声学性能进行仿真计算,分析气囊水消声器声学特性的原理,并研究气囊水消声器不同媒介间的特性声阻抗大小关系对消声性能的影响规律。计算结果表明：由于阻抗失配关系,在气囊水消声器中气体对声波的传递起主要反射作用。随着橡胶的特性阻抗增大,橡胶会对从水中传递过来的声波起到一定的阻碍作用。当气体体积被压缩时,气体对声波的反射衰减效果会逐渐减弱,从而使得气囊水消声器的传递损失曲线整体幅值下降,消声性能减弱。     

A pilot study on improving the absorptivity of a thick microperforated panel absorber

Microperforated panel (MPP) absorbers are promising as a basis for the next-generation of sound absorbing materials. MPPs are typically made of a thin metal or plastic panel. However, thin limp panels are generally not suitable as an interior finish of room walls because they do not have sufficient strength, which prevents practical application of MPPs as an interior finish of room walls. In order to overcome the lack of appropriate strength required for room walls, it is possible to make an MPP out of a thick panel. However, thick MPPs are usually not efficient because the resistance and/or reactance become too high. In this study, trial production of thick MPPs and measurement of their normal absorption coefficients were carried out. Results show that efficient absorption can be given with a thick MPP by using a tapered perforation.     

A note on the relationship between the sound absorption by microperforated panels and panel/membrane-type absorbers

The sound absorption mechanism of microperforated panel (MPP) absorbers and panel/membrane-type absorbers is both based on a certain resonance system and utilising its resonance effect. However, the relationship between the absorption mechanisms of MPPs and panel/membrane-type absorbers has not been discussed: it is not clarified whether they can occur simultaneously, or how they interfere each other. On the other hand, in a previous study there is an attempt to cause both absorption mechanisms simultaneously. In this paper, using an electro-acoustical equivalent circuit model, their sound absorption mechanisms and their relationship are discussed. In this study, three cases are considered: (1) the case in which only the mass reactance of the MPP is considered, (2) the case in which the losses of the panel is considered, and (3) the case in which the sound absorption of the back wall surface is considered. The results suggest that the microperforated panel absorption, which is Helmhotz-type resonance, and the panel/membrane-type absorption can be regarded as phenomena of the same kind which can be smoothly transformed into each other by changing a parameter, and can be consistently modelled and comprehensively discussed.     

Experimental study on sound absorption performance of microperforated panel with membrane cell

Microperforated panel (MPP) absorbers have been widely used in noise reduction and are regarded as a promising alternative to the traditional porous materials. However, the absorption bandwidth of a single-layer MPP is insufficient to compete with the porous materials. In order to improve the sound absorption ability of the single-layer MPP, a composite MPP sound absorber with membrane cells (MPPM) is introduced. Sound absorption properties of the MPPM are studied by the impedance tube experiment. Results show that the membranes have a significant influence on the sound impedance. The sound absorption performance of MPPM gradually increases with the increase of the membrane area. The single-layer MPP with some small area membrane cells may have the same effect and single large area membranes. By adjusting the size of the membrane cells, one can implement a sound absorber with a wider absorption bandwidth and higher absorption peaks than the single-layer MPP.     

Acoustic impedance of perforated panels covered by membranes

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夹心式压电超声换能器串并联传输矩阵设计法

将压电环片等效为一有源六端网络,考虑预应力螺栓对系统建模的影响,并将其等效为一机械四端网络,基于串并联传输矩阵法,建立了Langevin换能器的总体网络模型,导出其总传输矩阵,进而推算出换能器的共振频率。结果显示该方法比普遍采用的Langevin换能器传输矩阵设计法有更高的参量计算精度。此方法也为分析换能器其它电学参数提供了方便。     

A theoretical study on the effect of a permeable membrane in the air cavity of a double-leaf microperforated panel space sound absorber

A double-leaf microperforated panel absorber (DLMPP) is composed of a two microperforated panel (MPP) with a air cavity in-between, and without any backing structure. It shows a Helmholtz-type resonance peak absorption and additional low frequency absorption, therefore it can be used as a wideband space sound absorber. In this study, a theoretical study is made to examine the effect of a permeable membrane inside the air-cavity. Permeable membranes are studied in our previous studies and proved to be effective to improve the sound absorption performance of various type MPP sound absorbers. We investigate the absorption characteristics of a DLMPP with a permeable membrane in the cavity through numerical examples, and also studied the effect of honeycomb in the cavity of the same sound absorption structure.     

Comparison of 1D transfer matrix method and finite element method with tests for acoustic performance of multi-chamber perforated resonator

Multi-chamber perforated resonator (MCPR) is a kind of typical silencer element which can both attenuate broadband noise and satisfy specific installation requirements. The one-dimensional transfer matrix method (TMM) and finite element method (FEM) are widely used to predict the transmission loss of the resonators. This paper mainly focuses on the comparison between 1D TMM and FEM in which detailed perforation modeling is applied for the acoustic modeling of MCPRs. Five resonators with different acoustic attenuation frequency ranges are built for simulation and test. In order to verify the results of the above methods, a transmission loss test facility is designed based on two-load method. Through adjusting the distance between microphones, the facility’s effective measurement frequency can be changed. The results show that despite of the complex modeling and calculation, FEM with detailed perforation modeling shows good consistency with test results in both frequency and amplitude within entire frequency range. In comparison, TMM is limited by the cut-off frequency when calculating transmission losses. Besides, accuracy of TMM in low frequency range is also affected by perforation conditions. However, TMM is time-saving in calculation and structure optimization. In MCPRs’ development process, TMM can be used to quickly design and optimize structure parameters while FEM can be used to verify the acoustic performance before prototyping.     

Coupling transfer matrix method to finite element method for analyzing the acoustics of complex hollow body networks

This paper exposes a procedure to couple multiport transfer matrices to finite elements for analyzing the acoustics of automotive hollow body networks with a minimum of memory requirements and computational time. Generally, hollow body networks are made up from a series of elongated fluid partitions similar to ducts or waveguides. These fluid partitions generally contain complex elements: junctions, noise control elements, and cavities. The location and type of these elements in the network, mainly the noise control elements (e.g., sealing parts), may impact the noise inside a car. In the proposed hybrid method, the elongated fluid partitions are modeled with fluid finite elements. All complexities are modeled with two-port or multiport transfer matrices. The coupling of these matrices to finite elements is naturally done at the weak integral formulation stage of the acoustical problem. The coupling does not add any degrees of freedom to, nor modify, the original finite element matrix system. Consequently, changing locations and types of noise control elements in the hollow body network is fast and does not require rebuilding the finite element system. This enables optimizing the acoustics of a complex network on a desktop computer. The hybrid method is compared to experimental results on a tee-shaped hollow body networks. Good correlations are obtained.     

利用转移矩阵方法求解一维散射问题

利用转移矩阵方法,求解粒子通过任意势垒的透射系数及反射系数,并给出粒子的概率密度分布曲线.     

Preproduction prediction of the optical normalized reflectance transient of MOVPE-grown AlGaAs films using transfer matrix method

This paper reported on the prediction and analysis of the optical normalized reflectance (NR) transient of AlGaAs multi layers and Distributed Bragg Reflector (DBR) using transfer matrix method (TMM). The simulation result correlated well with the measured NR transient of grown samples. Deviations of Al_xGa_1?xAs composition between the expected and real grown sample were predicted successfully. Smaller optical oscillation amplitude in the first DBR layer was predicted and could be used as an indication of Al composition. Special characteristics of NR transient within the first three pairs of DBR were also clarified using the calculated transmissivity changing with the growth thickness. TMM simulation of NR transient was thus shown to be a convenient and reliable pre-production technique, also not restricted to the AlGaAs material.