Mass Transfer During Osmotic Dehydration Using Acoustic Cavitation

An experimental study on intensifying osmotic dehydration was carried out in a state of nature and with acoustic cavitation of different cavitating intensity (0.5A, 0.TA and 0.9A) respectively, in which the material is apple slice of 5 mm thickness. The result showed that acoustic cavitation remarkably enhanced the osmotic dehydration, and the water loss was accelerated with the increase of cavitating intensity. The water diffusivity coefficients ranged from 1.8 × 10^-10 m^2.s^-1 at 0.5A to 2.6 × 10^-10 m^2.s^-1 at 0.9A, and solute diffusivity coefficients ranged from 3.5×10^-11 m^2.s^-1 at 0.5A to 4.6×10^-11 m^2.s^-1 at 0.9A. On the basis of experiments, a mathematical model was established about mass transfer during osmotic dehydration, and the numerical simulation was carried out. The calculated results agree well with experimental data, and represent the rule of mass transfer during osmotic dehydration intensified by acoustic cavitation.

Boiling Heat Transfer in an Acoustic Cavitation Field

An experimental study has been carried out to investigate systematically the effects of acoustic cavitation parameters and fluid subcooling on boiling of acetone around a horizontal circular tube. The experimentalresults show that acoustic cavitation enhanced remarkably the boiling heat transfer and decreased the incipientboiling superheat and that cavitation bubbles effect on boiling heat transfer reduced with cavitation distance. Forboiling curves in a form of h-q″, elevated cavitation distance shift nucleate boiling curves to the right of the corresponding ordinary pool boiling curve. The associated mechanism of heat transfer enhancement is analyzed withthe consideration of cavitation bubble influence on vapor embryo.

Strain transfer mechanism of passive wireless surface acoustic wave torque sensors using shear lag theory

A shear-lag theory was developed to investigate the strain transfer from the metal substrate to the surface acoustic wave （SAW） resonator through a bonding layer. A three-layer model of host structure-adhesive layer-resonator layer was established. The strain transfer was theoretically analyzed, and the main factors impacting the SAW sensor measurement were studied. The relationship between the sensor response and the individual effect of all these factors under static loads was discussed. Results showed that better accuracy could be achieved with increase in the adhesive stiffness or resonator length, or decrease in the adhesive thickness. The values of the strain transfer rate calculated from the analytical model agreed well with that from the available experiment data.

Prediction of a V-8 diesel engine's structural radiated noise and research of important parameters' effects on the engine's acoustic behaviors

Based on the coupled boundary element method-finite element method （BEM-FEM） method and the acoustic transfer vector （ATV） technology, BEM/FEM model is proposed for a Vtype eight cylinders engine acoustic radiation simulating analysis under semi-anechoic condition. Acoustic radiation power, field points sound pressure level and panel contributions are calculated by acoustic radiation response analysis. Additionally, based on the engine acoustic performance, different acoustic behaviors of engine are studied by changing engine materials, oil pan structures as well as geometry parameters. The acoustic performance of this engine is predicted and the influence of material, structural and geometry parameters on engine radiated noise are generalized. The principle will guide the design and optimization of the engine prototype in further work.

A NOVEL SEMI-ANALYTICAL METHOD FOR SOLVING ACOUSTIC RADIATION FROM LONGITUDINALLY STIFFENED INFINITE NON-CIRCULAR CYLINDRICAL SHELLS IN WATER

Based on the extended homogeneous capacity high precision integration method and the spectrum method of virtual boundary with a complex radius vector, a novel semi-analytical method, which has satisfactory computation efectiveness and precision, is presented for solving the acoustic radiation from a submerged infnite non-circular cylindrical shell stifened by longitudinal ribs by means of the Fourier integral transformation and stationary phase method. In this work, besides the normal interacting force, which is commonly adopted by some researchers, the other interacting forces and moments between the longitudinal ribs and the non-circular cylindrical shell are considered at the same time. The efects of the number and the size of the cross-section of longitudinal ribs on the characteristics of acoustic radiation are investigated. Numerical results show that the method proposed is more efcient than the existing mixed FE-BE method.

Structural and Acoustic Response of A Finite Stiffened Submarine Hull

After borrowing the idea of precise integration method, a precise integration transfer matrix method （PITMM） is proposed by modifying traditional transfer matrix method. The submarine hull can be modeled as joined conical- cylindrical-spherical shells. By considering the effect of the ring-stiffeners, the field transfer matrixes of shells of revolution are obtained accurately by PITMM. After assembling the field transfer matrixes into an entire matrix, the dynamic model is established to solve the dynamic responses of the joined shell. By describing the sound pressure in fluid by modified wave superposition method （MWSM） and collocating points along the meridian line of the joined shell, finally the structural and acoustic responses of a finite stiffened submarine hull can be predicted by coupled PITMM and MWSM. The effectiveness of the present method has been verified by comparing the structural and acoustic responses of the spherical shell with existing results. Furthermore, the effects of the model truncation, stiffness and thickness on the structural and acoustic responses of the submarine hull are studied.

Research on Simulation and Prediction of Internal Combustion Engine Structural Acoustic Radiation

With the purpose of efficiently predicting structural radiated noise of internal combustion engine（I.C.E.）,a new simulation technique is introduced,which is an approach based on boundary element method （BEM）,acoustic transfer vector（ATV） technique and coupled boundary element model and finite element model （BEM-FEM） approach.Analyses of vibration exciting loads,computing structural dynamic characteristics and dynamic responses have led to theoretical results,which are tested on an L6 diesel engine to validate this proposed technique in engineering practice.

Merging phononic crystals and acoustic black holes

Phononic crystals(PCs) have recently been developed as effective components for vibration suppression and sound absorption. As a typical design of PCs, wave attenuation occurs in the so-called stop-band. However, the structural response is still significantly large in the pass-band. In this paper, we combine PCs and acoustic black holes(ABHs) in a unique device, achieving a versatile device that can attenuate vibration in the stop-band, while suppress vibration in the pass-band. This approach provides a versatile platform for controlling vibration in a multiband with a simple design.

Analytical model of an acoustic diode comprising a superlattice and a nonlinear medium

We give an analytical analysis to the acoustic propagation in an acoustic diode （AD） model formed by coupling a superlattice （SL） with a nonlinear medium. Analytical solutions of the acoustic transmission are obtained by studying the propagations in the SL and the nonlinear medium separately with the conventional transfer-matrix method and a perturba- tion technique. Compared with the previous numerical method, the proposed approach contributes a better physical insight into the intrinsic mechanism of acoustic rectification and helps us to predict the performance of an AD within the effective rectifying bands in a simple way. This is potentially significant for the practical design and fabrication of AD devices.

High-temperature acoustic properties of porous titanium fiber metal materials

The high-temperature acoustic absorption performance of porous titanium fiber material was investigated in terms of sample thickness, porosity, temperature, air-cavity thickness and double-layer structure arrangement. The effects on absorption coefficient were systematically assessed. The results show that the sound absorption performance is improved by increasing the sample porosity and/or thickness, and/or increasing the air-cavity thickness. Meanwhile, increasing the temperature gives better acoustic absorption performance in the low frequency range but also lowers the performance in the high frequency range, while double-layer structure enables better acoustic absorption performance.

压电复合材料梯度分布声学特性研究

目前,压电复合材料在吸声降噪领域应用广泛,但其低频吸声性能并不理想。为解决此问题,以0-3型压电复合材料为研究对象,提出使压电陶瓷体积含量呈梯度分布以提高其低频吸声系数的方法。首先,基于声电类比法和传递矩阵法,推导多梯度分布的理论公式,并通过文献构型对其进行验证;其次,将均匀分布与梯度分布的吸声系数进行比较,发现梯度分布会改变材料的声阻抗,从而改变吸声系数。最后,进行梯度分布压电复合材料数值分析,结果表明,同等条件下,当压电陶瓷体积含量呈梯度递减,且梯度差和第一梯度的厚度增加时,可明显提高低频吸声系数。

基于声电类比的低频消音结构优化设计

基于声电类比,设计了与电滤波器性能相似的低频消音结构,并结合传递矩阵法和模拟退火法,构造了声学结构的优化设计策略。首先,采用归一化方法,以四阶切比雪夫高通电滤波器为基准,设计了电学带阻滤波器;然后,基于声电类比,将电路中的电感电容转换为声学结构中的细管和圆柱腔,构造了消音结构原型,并利用传递矩阵法,建立其数学模型,推导声波传递损失表达式;最后,结合声学结构的数学模型和模拟退火法,以有效衰减带宽最大为目标,以消音结构的尺寸参数为变量,对原型结构进行优化设计。结果表明:基于声电类比,能获得合理的消音结构原型,克服了仅依靠经典消音结构进行设计的局限;结合推导的传递损失数学模型和模拟退火法,对消音结构原型进行参数优化,能显著提高其消音效果,表现在传递损失超过20 dB的带宽拓宽至410~2 165 Hz,是优化前带宽的202%,特别是优化后的结构克服了原型结构在466~537 Hz频率内不能实现有效消音的缺陷,获得了连续的大跨度有效带宽,且传递损失曲线平均增幅达22.8%。

航空发动机风扇管道径向声模态模拟与识别技术

针对航空发动机风扇管道径向声模态模拟与测试问题,研究了径向声模态模拟技术以及径向声模态识别技术。采用基于径向排布的声源阵列形式,调节阵列预设的各扬声器幅值及相位实现径向模态声源模拟。建立声源管道下游多圈环形阵列,根据阵列位置信息构造求解模态的传递函数矩阵,运用Tikhonov正则化方法减小传递函数矩阵的条件数,从而实现径向声模态识别能力。通过理论推导和数值计算,设计风扇管道径向声模态试验装置,并在消声室进行试验验证。通过试验验证了该系统具备周向4阶以内,径向2阶以内的径向声模态模拟与识别能力。

声学结构单元传递函数的建立方法及应用

基于三维有限元的时域仿真法,探讨了建立声学结构单元传递函数模型的一般方法。所建立的声学单元传递函数由结构参数高精度表达,能简化一般声学结构设计问题的流程。首先,建立了两种声学结构单元,仿真其幅频特性,并结合试验测量,验证幅频特性曲线的准确性,而后基于幅频特性曲线拟合传递函数,选择精度最高的零极点匹配方案,确定拟合传递函数的最优型式。结果表明,匹配7个极点和无零点来拟合膨胀腔单元的传递函数,匹配2个极点和2个零点来拟合亥姆霍兹共振腔单元的传递函数,拟合精度最高。然后,分析声学单元的结构参数对幅频特性的影响,并基于拟合传递函数的最优型式,通过数值仿真和拟合计算,建立由结构参数表达的声学结构单元传递函数模型。最后,构造了由膨胀腔和亥姆霍兹共振腔构成的复合声学结构,通过单元传递函数的组合计算,获得声学结构的总传递函数,并与COMSOL仿真结果比较,验证所建立声学单元传递函数模型的正确性,它能准确描述声学结构的传递损失特性。

高阶声学相对传递函数的参数化辨识

针对声学相对传递函数的模型阶次高以及辨识数据信噪比低的问题,文章运用频域系统辨识方法,建立了一种相对传递函数的高精度参数化辨识方法。首先建立变量带误差辨识框架,采用周期扫频信号作为声源激励,给出声学相对传递函数的极大似然算法。然后使用正交福赛斯(Forsythe)多项式解决高阶系统带来的雅克比矩阵条件数过高的数值问题,并建立了极大似然方法所需初始值的生成策略。最后通过仿真算例和实验测试,验证文中方法在混响声场下辨识声学相对传递函数的有效性。

一种基于VGGish神经网络的水声目标识别方法

水声目标智能识别是水声装备智能化的重要组成部分,深度学习则是实现水声目标智能识别的重要技术手段之一。当前水声目标智能识别经常面临数据集较小带来的训练样本量不足的情况,针对小数据集识别中存在的因过拟合导致模型泛化能力不足,以及输入的水声信号二维谱图样式不统一的问题,文章提出了一种基于VGGish神经网络模型的水声目标识别方法。该方法以VGGish网络作为特征提取器,并在VGGish网络前部加入了信号预处理模块,同时设计了一种基于传统机器学习算法的联合分类器,通过以上措施解决了过拟合问题和二维谱图样式不统一问题。实验结果显示,该方法应用在ShipsEar数据集上得到了94.397%的识别准确率,高于传统预训练-微调法得到的最高90.977%的准确率,并且在相同条件下该方法的模型训练耗时仅为传统预训练-微调方法的0.5%左右,有效提高了识别准确率和模型训练速度。

高温升燃烧室热声耦合特性研究

为建立燃烧室热声不稳定性预测和分析方法,以某高温升单管燃烧室试验件为研究对象,构建了试验系统低阶热声网络(LOTAN)模型。基于试验数据,利用优化的方法获得了各工况下的火焰传递函数(FTF),并利用Kriging模型拟合出了增益与迟滞时间对工况参数的响应模型。利用拟合出的FTF响应模型分析了油气比和进气速度对燃烧室热声稳定性的影响。研究结果表明:通过优化得到的FTF能够较准确反映各工况下的非稳态热释放特性,导入LOTAN中计算得到的结果与试验结果吻合较好,最大误差约3.32%;油气比的改变会引起不稳定模态的转变,油气比或进气速度升高时,系统特征频率也随之升高。

改进声发射信号的桥梁焊缝裂纹识别仿真研究

针对因环境中存在过多噪声,导致桥梁焊缝裂纹识别精准度低的问题,提出基于声发射信号的桥梁焊缝裂纹识别方法。利用传感器提取桥梁周围的实时信号,通过信号在周期序列上的幅值变化,判定噪声信号,采用小波变换算法对噪声信号实施重构变换,建立硬阈值和软阈值函数,约束噪声信号。采用神经元传递函数计算原始信号序列中隐含层神经元的具体特征表现参数,得到信号的特征类间平均值,通过类间参数求得特征量。以带有声发射信号提取技术的传感器作为识别载体,将特征参数输入到识别传感器中,针对不同的桥梁测试点,建立焊缝裂纹识别通道,完成有效识别。实验结果证明,所提方法的识别精准度较高,无论是以持续频率还是持续时间信号作为测试指标,均能实现高效识别。

超声波声速测量及悬浮传送装置设计

阐述基于单片机和外围电路的超声波声速测量及悬浮传送装置设计,该装置可以实现测量声速、悬浮平面、无接触传送的功能。

基于传递矩阵法的声学覆盖层透射系数预报研究

针对含周期单元声学覆盖层的透射系数计算方法展开研究,提出一种数值加解析的联合方法用于改善计算效率,首先以声阻抗管三水听器双负载法测试原理为基础,建立有限元模型并获取覆盖层的等效传递矩阵,结合多层均匀介质声透射解析理论计算覆盖层透射系数。为验证算法的准确性,将有限元直接计算结果与该算法计算结果对比,结果显示采用该算法在大部分频率范围内能准确预报透射系数。该方法可为有效优化声学覆盖层降噪性能提供理论支撑与方法指导。