自适应声学结构中基于声辐射模态的有源控制策略

研究了结构振动模态和声辐射模态之间的对应关系,并利用该关系建立了一种新的自适应声学结构有源控制策略,即引入单个或多个次级结构抵消初级结构振动模态对应的主导声辐射模态,使得主导辐射模态的声功率最小,从而控制总辐射声功率。研究结果表明:利用该控制策略,只需引入4个次级板同时抵消结构前4阶辐射模态的声功率,即可控制结构所有振动模态的声辐射,在宽频带范围内取得满意的控制效果。     

结构声辐射模态分析

从结构振动模态理论的角度论述了结构振动与声辐射之间的基本耦合关系，提出了结构声辐射模态的有关理论。推证了振动结构声幅射模态参数：声辐射模态频率，声辐射模态振型，模态辐射声功率以及模态声辐射系数的表达式；讨论了结构的物理声辐射量（辐射声压，辐射声功率和声辐射系数）与结构的声辐射模态参数之间的关系，指出结构的声辐射模态可用来表征结构本身的固有声辐射特性。并将该理论应用于柴油机缸体的声幅射模态特性计算。     

通过辐射模态研究封闭空间结构声辐射及其有源控制

通过辐射模态研究了封闭空间的结构声辐射及其有源控制问题.分析了辐射模态的数学和物理意义并揭示了辐射模态与声腔模态之间的内在耦合关系,并通过声辐射模态建立了弹性封闭空间结构声辐射有源控制模型.针对辐射模态在有源控制中的应用实现问题,给出了一种新的控制策略,即将辐射模态按对应辐射效率或耦合强度从大到小排列,使前k阶声辐射模态声势能最小化.采用压电陶瓷作动器作为控制力源进行了封闭空间结构声辐射有源控制数值计算与分析研究.结果表明,辐射模态与声腔模态的耦合具有严格的选择性,各阶辐射模态的形状和与相耦合的主导声模态在耦合面上的形状非常相似;在低频范围内,一般只需最小化前三阶辐射模态声势能,在更低频或声模态频率附近,只需最小化前一阶最有效辐射模态声势能,便能和总声势能最小化策略控制效果基本一样.     

有限长圆柱壳体声辐射特性影响因素研究

以水下简支薄壳为研究对象，对外力激励下有限长圆柱壳体声辐射特性的影响因素进行了研究.考虑有限长圆柱壳体与声场之间的互耦合，并讨论它们之间的互辐射阻抗对壳体的辐射声压级和表面振动均方速度级的影响，着重分析了壳体的纵横比以及材质对圆柱壳体声辐射特性的影响.数值计算结果表明,结构与声场之间的互辐射阻抗对壳体的辐射声压级有一定的影响，但是对表面振动均方速度级的影响很小；壳体厚度对声辐射特性的影响比长度对声辐射特性的影响更为明显；材质对声辐射特性的影响是不可忽略的因素.     

PVDF声辐射模态传感器设计中的关键问题研究

利用分布式位移传感材料PVDF薄膜设计声辐射模态传感器,通过检测低阶辐射模态的幅度以获得结构近似的辐射声功率。基于声辐射模态理论和PVDF传感模型,推导了PVDF形状系数理论公式,对设计中的关键问题进行了研究,得出PVDF的形状系数和结构振动模态选取的通用准则,提出分频段设计法解决了形状系数和结构振动模态之间在选取上的矛盾,在此基础上对PVDF传感器进行了优化设计并给出了PVDF对的中心线取值的一般规律,利用声辐射模态的嵌套特性使得输出电荷的放大倍数与频率呈线性关系,并通过实例仿真验证了文中结论。     

利用输入力有源控制水下弹性板辐射声场的分析

本文把利用输入力有源控制弹性板辐射声场的方法推广到水下情况.模型为两边简支弹性板上接受到一列平面波产生再辐射,利用输入力进行控制,并用二次型优化计算最佳控制力向量,使目标函数或辐射声功率最小.结果表明利用两个或三个控制力就能获得低频范围内辐射声级的全空间衰减,并且,控制方案的有效性与板的模态响应和辐射场之间的耦合特性有关.     

冰箱压缩机壳体噪声辐射数值分析

为了降低冰箱压缩机的噪声，并进一步优化壳体的声学特性，利用数值模拟方法，对壳体的振动特性和噪声辐射的影响因素进行了研究.在壳体模态分析的基础上，分析了泵体支撑方式、壳体形状、厚度和阻尼等不同壳体参数对壳体噪声辐射的影响，结果表明，泵体与壳体采用底部支撑方式联接、上壳体采用大的圆角半径、增大壳体壁厚、增大阻尼等均能降低壳体的噪声辐射.运用流固耦合有限元方法，计算了在不同润滑油量下壳体的耦合模态，以及壳体在单点激励下的远场辐射，结果表明，第5阶和第10阶固有频率随着油面高度的增加呈下降趋势；壳体在1 000～2 000 Hz的噪声辐射其峰值随着油面高度的升高逐渐增大，并逐渐向高频移动，实验结果与理论分析相一致.     

A three-dimensional coupled numerical model of nonlinear waves in a harbor

A 3-D time-domain numerical coupled model for nonlinear waves acting on a ship in a harbor has been developed in the present study. The whole domain is divided into the inner domain and the outer domain. The inner domain is the area around the ship, where the flow is expressed by the Laplace equation and numerically solved by the finite element method. The other area is the outer domain, where the flow is described by the higher-order Boussinesq equations and numerically solved by the finite difference method. The matching conditions on the interfaces between the inner domain and the outer domain, the procedure of coupled solution, the length of common domain and the mesh generation in the inner domain are discussed in detail. The other coupled model with the flow in the inner domain governed by the simplified linear Euler equations and relevant physical experiment are adopted to validate the present coupled model, and it is shown that the numerical results of the present model agree with the experimental data, so the present model can be used for the study on the effect of nonlinear waves acting on a fixed ship in a large area and provide a reference for the time-domain simulation of nonlinear wave forces on an arbitrary object in a large harbor and the 3-D district computation in the future. Supported by the National Natural Science Foundation of China (Grant Nos. 59979002, 50809008), the Hong Kong Research Grants Council (Grant No. HKU 7171/06E), the China Postdoctoral Science Foundation (Grant No. 20060400972), the Project of the Educational Department of Liaoning Province (Grant No. 2005058) and the Dalian Science and Technology Foundation (Grant No. 2007J23JH027)     

Thermal-dynamical properties and pressure dependence of phonon spectrum of ordered Si<Subscript>50</Subscript>Ge<Subscript>50</Subscript> alloy based on <Emphasis Type="Italic">ab initio</Emphasis> methods

The phonon spectrum of ordered zincblende Si₅₀Ge₅₀ alloy is calculated by ab initio method. The energy band structure at zero pressure and the pressure dependence of phonon dispersion curves are shown up to 20 GPa. The calculation finds a pressure-induced softening of the transverse acoustic phonon mode and the mode frequency reaching zero at about 14 GPa, which indicate breaking of the symmetry and formation of a new phase under high pressure. Supported by the National Natural Science Foundation of China (Grant No. 50771090), the State Key Program for Basic Research of China (Grant No. 2005CB724404) and the Program for Changjiang Scholars and Innovative Team (Grant No. IRT0650)     

Framework and development of digital China

High energy electron is a kind of sources to be detected in the geospace environment. Generally, the particle telescope with much thick semiconductor detector is used as the sensor for energetic electrons because they can penetrate deeply into the detector. The more energy of the electrons is, the deeper they can penetrate into, so that the geometric factor varies with energy of the incident electrons. We discuss the geometric factor of particle radiation detector (PRD), which is a payload on ZY-1 (CBERS-1 and CBERS-2) satellites to monitor the high energy particle radiation inside the satellites. According to the NASA’s AE8 model, the geometric factors of electrons for the low energy bin (0.5–1.0 MeV) and the high energy bin (> 2.0 MeV) are 2.468 and 1.736 cm²·sr, respectively. These results are much different from the traditional calculation of the geometric factor that is 1.18 cm²·sr. The angle-response function of the telescope is also derived, which can be useful for design of the telescope and analysis of the directional distribution. Supported by the National Natural Science Foundation of China (Grant No. 40674097) and Co-constructing Foundation of Beijing Municipal Commission of Education (Grant No. XK100010404)     

A robust technique to reconstruct sound field for all wave-numbers

Near-field acoustic holography (NAH) originated at the beginning of the 1980s, which overcomes the wave-length limitation of the conventional acoustic holography, and thus it became one of the most powerful tools for identifying noise sources and visualizing sound field[1—15]. In this technique, the acoustic quantities such as sound pressure, sound intensity and the far-field directivity can be reconstructed by the sound pressures measured at a finite number of field points and a certain part…     

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 V-type 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.     

二维多频声辐射问题的频域边界元分析方法

针对含有复杂频率成分声源的辐射问题,首先采用傅里叶变换将时域声源传播的控制波动方程转化为频域的Helmholtz方程;其次,选取多个等间隔的频率点作为采样频率,应用边界单元法求解各特征频率的Helmholtz方程,获得不同位置在各采样频率下的声压;最后,采用离散傅里叶反变换将频域声压幅值和相位转化为时域声压.边界元方法...     

应力参数对圆柱壳声辐射影响的初探

对加筋圆柱壳由于肋骨数目改变所引起的结构应力参数变化对辐射噪声的影响进行了探索．运用Ansys软件建立不同结构参数的加筋圆柱壳有限元模型，计算了模型在激振力作用下的耦合振动响应，提取结构表面的位移，在Sysnoise软件中计算各种声学物理量．得到了各工况下模型在水下受激振动时的结构表面速度、水中辐射声压和辐射声功率等分布规律．找出了肋骨数目改变引起的结构应力参数与加筋圆柱壳振动和结构声辐射之间的关系，对舱段结构振动与噪声的控制有重要的参考意义．     

Seismic damage-cracking analysis of arch dams using different earthquake input mechanisms

In this study, a nonlinear model is presented for analysis of damage-cracking behavior in arch dams during strong earthquakes using different seismic input mechanisms. The nonlinear system includes a plastic-damage model for cyclic loading of concrete considering strain softening and a contact boundary model of contraction joint opening. Two different earthquake input mechanisms are used for comparison, including massless foundation input model and viscous-spring boundary model considering radiation damping due to infinite canyon. The results demonstrate that effects of seismic input mechanism and radiation damping on nonlinear response and damage-cracking of the dam are significant. Compared with the results of using massless foundation input model, the damage-cracking region and contraction joint opening are substantially reduced when using viscous-spring boundary model to take into account radiation damping. However, if the damping ratio of the dam is artificially increased to about 10%―15% for massless foundation input model, the joint opening and damage-cracking of the dam are comparable to the results obtained from the viscous-spring boundary model.     

Filterbank implementation for multi-channel sampling in fractional Fourier domain

Reconstruction of a continuous time signal from its periodic nonuniform samples and multi-channel samples is fundamental for multi-channel parallel A/D and MIMO systems. In this paper, with a filterbank interpretation of sampling schemes, the efficient interpolation and reconstruction methods for periodic nonuniform sampling and multi-channel sampling in the fractional Fourier domain are presented. Firstly, the interpolation and sampling identities in the fractional Fourier domain are derived by the properties of the fractional Fourier transform. Then, the particularly efficient filterbank implementations for the periodic nonuniform sampling and the multi-channel sampling in the fractional Fourier domain are introduced. At last, the relationship between the multi-channel sampling and the filterbank in the fractional Fourier domain is investigated, which shows that any perfect reconstruction filterbank can lead to new sampling and reconstruction strategies. Supported by the National Natural Science Foundation of China for Distinguished Young Scholars (Grant No. 60625104), the National Natural Science Foundation of China (Grant Nos. 60890072, 60572094) and the National Key Basic Research Program Founded by MOST (Grant No. 2009CB724003)     

Study on pure silica core optical fibers

An optimal refractive index profile of pure silica core optical fiber (PSCF) was designed, in combination with the characters of the modified chemical vapor deposition (MCVD) process. Techniques of preform fabrication by a new furnace round heating MCVD process and fiber drawing process were reviewed. Difficulties in doping fluorine in silica, widening the depressed-index cladding and maintaining the index of fiber core were discussed. Methods used to overcome these difficulties were given at the same time. Additionally, the optimal refractive index profiles of PSCF were presented. Supported by the Hi-Tech Research and Development Program of China (Grant No. 2002AA312190), National Natural Science Foundation of China (Grant No. 60477017), Program for the New Century Excellent Talents in University (Grant No. NCET-06-0076), Beijing Natural Science Foundation (Grant No. 4052023) and the Beijing Jiaotong University Foundation (Grant No. 2006XM003)     

Compensation for time-delayed feedback bang-bang control of quasi-integrable Hamiltonian systems

The stochastic averaging method for quasi-integrable Hamiltonian systems with time-delayed feedback bang-bang control is first introduced. Then, two time delay compensation methods, namely the method of changing control force amplitude (CFA) and the method of changing control delay time (CDT), are proposed. The conditions applicable to each compensation method are discussed. Finally, an example is worked out in detail to illustrate the application and effectiveness of the proposed methods and the two compensation methods in combination. Supported by the National Natural Science Foundation of China (Grant No. 10772159), the Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20060335125), Zhejiang Natural Science Foundation (Grant No. Y7080070), and Fujian Provincial Science and Technology Project (Grant No. 2005YZ1021)     

High performance 1.3 μm InGaAsN superluminescent diodes

High performance 1.3 μm InGaAsN superluminescent diodes (SLDs) were fabricated with Schottky contact. The structure was grown by metal organic chemical vapor deposition (MOCVD). Output power of 3 mW was obtained in continuous wave (CW) mode at room temperature. The full width at half maximum (FWHM) of the emission spectrum was 30 nm. The devices operated up to 100℃.     

Novel approach for evaluation of service reliability for electricity customers

Understanding reliability value for electricity customer is important to market-based reliability management. This paper proposes a novel approach to evaluate the reliability for electricity customers by using indifference curve between economic compensation for power interruption and service reliability of electricity. Indifference curve is formed by calculating different planning schemes of network expansion for different reliability requirements of customers, which reveals the information about economic values for different reliability levels for electricity customers, so that the reliability based on market supply demand mechanism can be established and economic signals can be provided for reliability management and enhancement. Supported by the Program for New Century Excellent Talents in University (Grant No. NCET-07-0484), the National Natural Science Foundation of China (Grant No. 50777031) and the Fok Ying-Tong Education Foundation (Grant No. 104020)