共查询到18条相似文献,搜索用时 140 毫秒
1.
针对工程中普遍存在的薄板结构振动噪声问题,提出了一种对加强筋位置分布进行拓扑优化的控制方法。通过有限元动力学分析结构的速度响应,代入由声辐射模态推导的声功率求解方程中得到声功率。建立以加强筋位置作为设计变量的拓扑优化数学模型,寻找声功率最小的加筋分布。算法中以声辐射模态灵敏度为指导,确定拓扑优化加筋的起始点和搜索过程。通过仿真计算结果表明,优化得到的加筋布局能有效地将声功率降低7.38dB,并讨论了收敛准则和不同频率对加筋布局的影响,在第一阶固有频率内都可用此种算法优化。 相似文献
2.
3.
4.
通过对薄板的振动及近场声场的测量探讨不同开裂特征对薄板结构的振动特性及近场声场响应的影响。首先对具有不同开裂形状、尺寸、位置的薄板结构进行了模态仿真计算,得到理论模态振型。然后通过激光测振仪进行振动实验,实验分析开裂薄板的结构模态,同时布置传声器列阵测量近场声压,通过近场声全息理论重构薄板表面声压分布。最后对比开裂薄板理论模态形状与实验测量结果,分析开裂特征对薄板结构的振动特性及近场声场响应的影响。分析结果表明开裂特征对薄板结构的固有频率和振型有明显影响,同时薄板的声响应跟薄板的振型密切相关。 相似文献
5.
提出了扬声器的声信噪比问题及其测量方法,指出扬声器的声信噪比是评价扬声器音质的重要指标。介绍了现代扬声器的设计方法——模态控制技术及采用模态控制技术设计的龙骨振膜扬声器。在提高振膜的信噪比、音质和有效传递驱动力方面.采用模态控制技术设计的扬声器龙骨振膜结构优于现有的其他结构。 相似文献
6.
7.
8.
利用激光三角测量原理的技术可以实现对扬声器锥体振动的光学测量(扫描振动测量法),这项技术与多谱勒干涉测量法相比更为经济高效。三角测量原理的传感器主要得到的是位移数据,因此,要测量最高可达20 kHz时的振动盆的分裂振动模式,就需要进行足够高信噪比的高级信号处理。除了可以提供辐射图形的闪频动画显示,也将提出新的针对测量数据实现可视化的分解技术。可以把总的振动分解成径向模态的振动与周向模态的振动;也可以分解成辐射振动分量和非辐射振动分量。这种后处理方法揭示出了扬声器锥体极其重要的振动模式,也简化了对于声辐射(振动)的解读,并给出了进一步改善的方向。 相似文献
9.
10.
弯曲振动型薄板扬声器的工作原理 总被引:3,自引:0,他引:3
首先求得矩形薄板弯曲振动偏微分方程的解,分析了薄板弯曲振动的简正频率和它的振型,最后讨论了弯曲振动型薄板扬声器的性能并给出NXT扬声器的相应技术特性,其应用前景广阔。 相似文献
11.
The radiation from electromagnetic sources in an unbounded, isotropic plasma is treated. Using a two-fluid magnetohydrodynamic approach, the problem is formulated in terms of three orthogonal modes, namely, i) the electromagnetic mode, ii) the electron plasma mode and iii) the ion plasma mode. When formulated in this manner, the radiation from simple electromagnetic sources are obtained easily. Three specific sources are treated, namely, i) a point source of electric current, ii) a uniformly moving charge and iii) a short filament with prescribed current distribution. For the case of the electric dipole and the current filament, the total power radiated in each of the three modes are obtained. A point charge moving uniformly with the velocity of sound, for example, is found to excite only the ion plasma mode. The frequency and the angular spectrum of the emitted radiation are obtained. It is found that at frequencies less than a critical frequency which is approximately equal tosqrt{2} times the ion plasma frequency, the radiation has the character of a simple sound wave. 相似文献
12.
Effects of leaky-wave propagation in metamaterial grounded slabs excited by a dipole source 总被引:2,自引:0,他引:2
Baccarelli P. Burghignoli P. Frezza F. Galli A. Lampariello P. Lovat G. Paulotto S. 《Microwave Theory and Techniques》2005,53(1):32-44
In this paper, dispersive propagation and radiation properties of leaky waves on metamaterial grounded slabs are investigated. The proper or improper nature of leaky modes supported by such structures is shown to be related to the metamaterial being /spl epsi/-negative, /spl mu/-negative, or double-negative, and to field polarization, giving rise to backward or forward radiation depending on the frequency range of operation. These spectral features and the associated frequency scan of the radiated beam are illustrated by considering the field excited by a dipole source in the presence of an infinite metamaterial grounded slab. The possibility to achieve nearly equal values for the phase constants of a TE and a TM leaky mode on a large frequency range is shown; this allows us to obtain a conical radiation pattern and, also, for suitable values of the attenuation constants, the radiation of a pencil beam at broadside. Conditions for achieving maximum power density at broadside are derived, when one constitutive parameter is much smaller than the other. In order to illustrate these novel features, numerical results based on experimentally tested dispersion models for permittivity and permeability of the metamaterial media are provided, concerning leaky-wave modal properties and near and far fields excited by a dipole source. 相似文献
13.
The far-field radiation pattern of a diagonal horn has been calculated by aperture integration. The radiation patterns for a 4×4 diagonal horn array, measured at 100 GHz, agree very well with theoretical predictions. The aperture electric field was also expanded into Gauss-Hermite modes. The results indicate that the fraction of the power radiated into the fundamental Gaussian mode is about 84%. About 10% of the power is radiated in the cross-polarized component 相似文献
14.
提出近场辐射电磁干扰模态测试方法,设计近场模态检验测试系统,采用近场电磁场头对待测设备进行扫描式测量,获得待测设备的近场电磁场分布情况,并根据测得电磁场强度大小可分析得到待测设备的辐射EMI模态。实验结果表明,该方法可对电子电路的近场辐射EMI模态进行有效识别和检验,分别得到近场辐射共模噪声和差模噪声EMI模态,为辐射电磁干扰噪声的抑制提供有益参考。 相似文献
15.
《Microwave Theory and Techniques》1963,11(1):39-50
The radiation characteristics of a line source of magnetic current embedded in a homogeneous electron plasma of infinite extent are investigated for the case in which a uniform magnetic field is impressed externally throughout the medium in the direction of the source. The single-fluid theory of magnetohydrodynamics is employed. A very simple model is assumed for the plasma. Under this assumption, it is found that there are two modes of propagation of waves of small amplitude. By examining the behavior of these modes in the limiting cases of vanishing external magnetic field or infinite source frequency, they are identifiable as the modified forms of the usual plasma and optical modes which exist in an isotropic electron plasma. The dispersion relations for these two modes are discussed. The power radiated in each of the two modes is also evaluated. It is found that the power radiated in the optical mode is always lower than that due to the line source in free space, whereas the power radiated in the plasma mode is higher than that value for certain ranges of the source frequency. 相似文献
16.
17.
The radiation characteristics of a line source of magnetic current embedded in an unbounded plasma are investigated for the case in which a uniform magnetic field is impressed externally throughout the medium in the direction of the source. The plasma is assumed to be a homogeneous and macroscopically neutral mixture of compressible gas of electrons and ions. A two-fluid continuum theory of plasma dynamics is employed. It is shown that it is possible to define three suitable wave functions which satisfy separately simple wave equations whose solutions are written down by inspection. These wave functions specify the three possible modes which are identified, respectively, to be the modified forms of the electromagnetic, the electron plasma and the ion plasma modes. The limiting behavior of these modes are discussed for the following two cases: 1) infinite source frequency and 2) vanishing external magnetic field. The dispersion relations for the three modes are examined in detail for the general case using a perturbation procedure. It is shown that the modified ion plasma (MIP) mode propagates for all frequencies whereas both the modified electron plasma (MEP) mode and the modified electromagnetic (MEM) mode have a low-frequency cutoff. Explicit expressions for the cutoff frequencies are obtained. The power radiated in each of the three modes is also evaluated. It is found that the power radiated in the MEM mode is always lower than that due to the line source in free space, whereas the power radiated in the two plasma modes is higher than that value for certain ranges of frequency. 相似文献
18.
《Electronics letters》1969,5(12):271-272
The effect on mode propagation of small (with respect to wave-length) irregularities or imperfections in a dielectric waveguide is analysed. Asymptotically, for large frequencies, the power which is scattered in the form of radiation (not guided) has an ?2 behaviour, and that scattered into the modes obeys a 1/?2 relationship. At the frequency of paramount interest for optical communication (cutoff for TM01 mode), the radiated power is 22dB larger than the power scattered into the HE11 mode. 相似文献