计及温度条件下的微穿孔板结构优化设计

微穿孔板吸声体是由穿孔直径在1 mm以下的薄板和板后空腔组成的共振吸声结构,其结构通常可利用经典的微穿孔板理论来设计。但在温度变化条件下,经典的微穿孔板理论已经不足以设计出满足要求的微穿孔板结构。文中在设计微穿孔板吸声结构时,不仅考虑了结构参数孔径d、板厚t、孔间距b及空腔深度D对微穿孔板吸声特性的影响,又计入了温度T这一参数。拟采用改进的粒子群优化算法,分别对一定温度下的单层和双层微穿孔板吸声体的结构参数进行优化设计,搜索得到最优的参数组合,使其在给定的频带范围内平均吸声系数最高。优化结果表明:利用改进的粒子群算法设计出的微穿孔板吸声结构在给定频率范围内吸声系数较大,且符合给定温度的要求。     

双层微穿孔板吸声结构设计中的共振和反共振频率计算

双层微穿孔板吸声结构设计中的共振和反共振频率计算张宗茂，顾熙棠（宁波大学机械工程系）一、引言对微穿孔板吸声结构的吸声机理已有较系统的研究’‘Ｉ“””。单层做穿孔板吸声结构的共振频率可用穿孔板共振吸声结构的共振频率计算公式求得，但双层微穿孔板吸声结构的...     

双层串联微穿孔板吸声体吸声特性研究

单层微穿孔板的吸声频带较窄,采用双层串联微穿孔板结构可进一步拓宽其吸声频带,但由于双层串联微穿孔板结构的吸声曲线中两个波峰之间有很大的下降趋势致使整体吸声系数有所降低,故采用传递函数法建立双层串联微穿孔板吸声体理论模型,分析两层穿孔板的穿孔参数和板后空腔改变时结构整体吸声系数的变化,并通过与COMSOL中所建模型的计算结果相对比进行验证,比选确定合适的结构参数,使其在拓宽吸声频带的同时保持其在吸声频带内的吸声系数均较大,得到较优的吸声效果。     

蜂窝微穿孔吸声体的宽频吸声性能优化设计

针对蜂窝微穿孔吸声体结构,利用粒子群优化(Particle Swarm Optimization,PSO)算法优化吸声体结构的吸声性能.以三蜂窝芯的蜂窝微穿孔吸声体结构中微穿孔板的孔径、穿孔率和背腔深度为优化设计变量,以吸声体的吸声系数和吸声频带为优化目标,得到吸声体宽频范围吸声时的优化结构参数.将三参数优化、两参数优...     

变截面背腔结构的微穿孔板吸声器的设计与研究

如何实现微穿孔板吸声结构的宽频吸声是近年来的研究热点之一。针对微穿孔板吸声结构的宽频吸声问题,本文设计了一种不规则背腔结构,并将其应用到单层和双层微穿孔板的吸声器上,对其吸声性能进行了研究。利用声电类比模型获得吸声器各部分的阻抗关系,然后通过理论计算得到吸声结构的阻抗和吸声系数。理论、仿真和实验结果表明：在不增加结构厚度的情况下,通过内层变截面隔板对背腔进行不等体积分割,可拓宽微穿孔板吸声带宽,且结构相对简单。该研究为微穿孔板吸声器的宽带低频吸声及其应用提供了新的设计思路。     

微穿孔板在抽油烟机噪声控制中的应用

目的:针对抽油烟机的噪声控制问题,采用进气通道吸声的方式对抽油烟机的噪声进行控制。方法:根据抽油烟机的噪声特性分别设计了单层和双层微穿孔板共振吸声结构并进行了噪声和空气性能测试。结果:变空腔微穿孔共振吸声结构降噪效果显著,采用单、双层微穿孔板共振吸声结构降噪的平均降噪量分别能达到1.7 dBA、2.8 dBA,而空气性能改变量不超过5%。结论:变空腔微穿孔共振吸声结构具有较好的宽频吸声特性,双层微穿孔板共振吸声结构比单层结构吸声频带更宽。     

微穿孔板传递矩阵计算方法的改进及实验

传统的声电类比法对双层微穿孔板吸声结构进行计算时,忽略了空腔声质量的影响,对于空腔距离比较短,频率比较低时是适用的,但是当空腔距离比较大或频率比较高时,则存在误差。用传递矩阵法对微穿孔板吸声结构进行分析：解决了空腔声阻抗的近似计算带来的误差;对于微孔部分传递矩阵中的声阻抗计算仍然采用马大猷教授的理论,不需要引入修正参数δx。通过上述工作,进行了微穿孔板吸声结构的吸声系数的计算和相应的实验验证,理论计算结果与实验数据吻合良好。     

脉冲爆震发动机微穿孔消声喷管研究

针对脉冲爆震发动机的噪声辐射特性,计算分析微穿孔板孔径、板厚、穿孔率、前后腔厚度等设计参数对单／双层微穿孔板吸声体共振频率、吸声系数的影响。设计并加工一组微穿孔消声喷管。实验研究发现：影双层微穿孔消声喷管对脉冲爆震发动机噪声辐射的降低都有一定的作用,双层结构优于单层结构;消声喷管越长,消声效果越好;发动机工作频率为20Hz时,300mm长双层微穿孔消声喷管可使噪声辐射峰值声压级降低2dB左右,脉冲声压级和声功率级降低4dB左右,声功率从1377．2W下降至542W。     

封闭式背腔微穿孔板吸声结构

为提高微穿孔板吸声体的吸声性能,提出一种宽频带封闭式背腔微穿孔板吸声结构.使用薄膜封闭背腔中的特定气体,改变背腔声抗,配合参数合理的微穿孔板,能够提升低频吸声性能并有效拓宽吸声频带.基于声电类比法推导该吸声体的吸声系数计算方法,通过有限元仿真以及阻抗管实验对理论计算结果进行验证,最后探究背腔气体、微穿孔板振动和薄膜厚度...     

前向型叶片高压离心风机噪声控制的治理研究

微穿孔板吸声结构及其吸声系数高,吸收频带宽,无需填充特等优点,广泛应用于噪声控制的各个领域。本文采用微穿孔板吸声结构,并应用于南通风机厂生产的9.26No6.3高压离心风机,运用优化设计的方法设计了双层微穿孔板蜗舌共振器,并用计算法与经验法相结合设计了风机双层微穿孔板进出口消声器,分别取得降噪3.5dB(A)与17dB(A)的效果。     

Omnidirectional broadband absorption enhancement in laterally assembled quadrangle silicon nanowire solar cells

In this paper, effects of geometry and spatial placement of quadrangle silicon nanowires (NWs) on the performance of laterally assembled NW solar cells are investigated. Two different approaches are proposed to reach the broadband absorption enhancement in these types of solar cells. In the first method, a semi-periodic array is used to have a better utilization of the optical antenna effect. The current density can be enhanced as a result of a compromise between the diffraction and optical antenna effects. In the second approach, multiple NWs with different geometries are employed to use the cavity modes of the various NWs. The best current density is achieved for the combination of both of these methods. The different parameters in each structure are selected using the optimization algorithm. Finally, a multilayer structure with the optimized dimensions is proposed to obtain the maximum achievable current density in ultrathin solar cells. The broadband absorption enhancement in the proposed structure is preserved for a wide range of incident angles. Using the multilayer NW arrays, it is possible to improve the absorption enhancement of solar cells without introducing more absorbing material.     

爆破优化的神经网络模型

文章在简要阐述了前馈多层神经网络及其反传算法一般原理的基础上，建立了露天矿爆破效果预测的人工神经网络模型，进而提出了基于神经网络的爆破参数分段优化模型。     

爆破优化的神经网络模型

文章在简要阐述了前馈多层神经网络及其反传算法一般原理的基础上,建立了露天矿爆破效果预测的人工神经网络模型,进而提出了基于神经网络的爆破参数分段优化模型。     

基于仿生观念的多层薄壁结构承载热防护一体化分析设计

受仿生观念启发,通过对力学与传热性能的表征和优化分析,研究了多层薄壁结构的承载和热防护的一体化设计问题。以生活在印度洋底的蜗牛壳结构为原型,构造了分层薄壁结构受力和传热的概念性模型,开展了热防护和承载性能的表征与分析。通过三维气动加热算例和基于遗传算法的优化设计,验证了仿生结构具有最佳的材料参数的排布,是综合热防护和承载性能于一体的优越结构形式。     

基于信息熵改进的粒子群算法在桁架结构

提出了信息熵改进的粒子群优化算法用于解决有应力约束、位移约束的桁架结构杆件截面尺寸优化设计问题.首先介绍了信息熵基本理论和基本粒子群优化算法理论,然后对粒子群优化算法作了合理的参数设置,并将信息熵引入粒子群优化算法的适应函数和停机判别准则中.最后对2个经典的优化问题进行求解并与其他算法进行了比较.数据结果表明信息熵改进后的粒子群优化算法在桁架结构优化设计中优于其他同类算法.     

Characterization of a multilayer highly reflecting mirror by spectroscopic phase-modulated ellipsometry

The characterization of optical multilayer coatings has been a challenging task for thin-film scientists and engineers because of the various complex, interdependent layer parameters that exist in the system. Spectroscopic phase-modulated ellipsometry has some advantages in the postanalysis of the layer parameters of such multilayer coatings because it suitably models the layer structure with respect to the ellipsometric measurements. An algorithm to characterize multilayer optical coatings with large numbers of layers has been described by spectroscopic ellipsometry by use of a discrete spectral zone fitting approach. A 23-layer multilayer highly reflecting mirror has been characterized by this technique in the wavelength range 280-1000 nm. The ellipsometric spectra (? and D versus wavelength) have been fitted separately in three wavelength regimes. Fitting the ellipsometric spectra in the wavelength regime of 700-1000 nm permitted the sample structure to be determined. The data were then fitted in the wavelength range 280-340 nm, i.e., near the fundamental absorption edge of TiO(2), to yield the dispersion relation for the optical constants of TiO(2). Finally, the data were fitted in the wavelength range 340-700 nm, and the true dispersion of the refractive index of TiO(2), along with the best-fitting sample structure, was obtained.     

Development of two-phase neural network-genetic algorithm hybrid model in modeling damage evolution in roll forming of aluminum sheet

In this paper a two-phase artificial neural network-genetic algorithm (ANN-GA) hybrid model has been developed for the modeling and prediction of the damage evolution in the roll forming (RF) process of aluminum sheet metal, as a function of process parameters. The multilayer perceptron is used to build the network while the genetic algorithm (GA) is employed to optimize the network structure in the modeling phase. In detail, the number of hidden layer, hidden neurons, weights and biases of the network are optimized by GA to minimize the error between predicted values and actual results. After the modeling phase the optimization of parameters is carried out in the optimization phase to minimize the damage in the aluminum sheet during the forming process. In this work the experimental data used for training and verifying the network is obtained automatically by the integration between CAD-CAE. As a result, the predicted results are validated with the actual values and a good agreement is observed. Moreover, the parametric study also is performed to find the relative influences of process parameters on the damage evolution. It is proven that the hybrid model is the powerful tool for modeling and predicting such a highly nonlinear problem as the damage evolution in RF process. The developed two-phase ANN – GA hybrid model is a new approach that can bring benefits to the forming industry by predicting and preventing the failure at the design stage, as well as improving efficiently the product's quality by optimizing the process parameters.     

多层 U 形A瓦楞结构材料的共面力学性能

目的在不同冲击速度的共面载荷条件下,获取多层U形A瓦楞结构材料动态力学性能参数。方法建立有限元分析模型,并简化能量吸收模型,来评估其能量吸收性能。结果随着冲击速度的不断增大,均匀变形、过渡变形和动态变形等模式随之呈现。结论最佳单位体积的能量吸收主要由动态峰应力决定。在结构参数一定的条件下,共面动态峰应力取决于多层U形A瓦楞结构材料所受到的冲击速度。通过对数值结果的物理分析和讨论,提出了动态峰应力关于冲击速度的经验关系式。     

变密度多层绝热的理论分析

讨论了一种新型的多层绝热结构,针对径向内外侧不同层间辐射阻断的强弱比例特征、材料重量、以及结构强度,对多层材料的布置进行了优化设计.主要分析多层绝热的绝热性能随层密度分布的变化规律,寻找特定条件下最优化层密度的分布方式,并研究了最优化层密度分布方式与绝热系统各参数之间的关系.