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数值模拟不等距叶片对贯流风机的影响 总被引:3,自引:0,他引:3
贯流风机的通过频率(BPF)是其重要的噪声频率.降低BPF噪声可以降低基频处的声压级,其中一种方法是采用不等距叶片.本文采用3种叶片距分布形式,采用realizable k-ε两方程和大涡模拟(LES)湍流模型模拟了风机的内流场,计算线性欧拉方程(LEE)中声源项得到声源位置及强度,采用基于Lighthill声类比的FW-H积分方程获得了叶轮和蜗舌处偶极子型的离散噪声频谱.比较了不同叶片距对风机性能,噪声特别是BPF噪声的影响.计算结果表明在对性能影响较小的情况下,不等距叶轮可降低BPF噪声和总A声级噪声. 相似文献
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本文提出了一种具有简单微带线/共面波导谐振器结构的新型超宽带带通滤波器,滤波器在通带的两侧具有两个传输零点。滤波器的输入、输出微带(开路)线之间具有耦合电容效应,该电容可以用来调整低端传输零点。微带(开路)线各自与共面波导谐振器可以形成两个串联电容,同时共面波导谐振器的一条短路枝节线形成了一个并联电感。微带开路线上的延伸微带枝节尺寸可以用来调整滤波器的上端传输零点。利用HFSS对该滤波器进行了仿真设计,详细的设计过程也一并给出。仿真表明滤波器的3dB带宽可以覆盖UWB的整个波段。 相似文献
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In this paper, a Slotted Stepped-Impedance Resonator (SSIR) is proposed. Due to the slots in the low-impedance section of the conventional SIR, the new resonator has a lower fundamental resonance f0 and can provide a potential finite transmission zero fz close to f0. Based on the proposed SSIR, a fourth-order Chebychev BandPass Filter (BPF) is designed at f0=1 GHz. The measured results show that a better than –65 dB rejection is achieved on both the lower and the upper stopband. Moreover, the new filter has a wide –30 dB rejection upper stopband from 1.13f0 to 6.52f0. The fab-ricated filter exhibits a size of The new filter has a planar topology and is easily integrated with modern portable communication systems. 相似文献
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Jiajia Yang Yun Li Jincheng Wang Xiaoli Sun Syed Mazhar Shah Rong Cao Jiping Chen 《Analytica chimica acta》2015
Bisphenol A (BPA) imprinted sponge mesoporous silica was synthesized using a combination of semi-covalent molecular imprinting and simple self-assembly process. The molecularly imprinted sponge mesoporous silica (MISMS) material obtained was characterized by FT-IR, scanning electron microscopy, transmission electron microscopy, and nitrogen adsorption–desorption measurements. The results show that the MISMS possessed a large specific surface area (850.55 m2 g−1) and a highly interconnected 3-D porous network. As a result, the MISMS demonstrated a superior specific adsorption capacity of 169.22 μmol g−1 and fast adsorption kinetics (reaching equilibrium within 3 min) for BPA. Good class selectivity for BPA and its analogues (bisphenol F, bisphenol B, bisphenol E and bisphenol AF) was also demonstrated by the sorption experiment. The MISMS as solid-phase extraction (SPE) material was then evaluated for isolation and clean-up of these bisphenols (BPs) from sediment samples. An accurate and sensitive analytical method based on the MISMS–SPE coupled with HPLC–DAD has been successfully established for simultaneous determination of five BPs in river sediments with detection limits of 0.43–0.71 ng g−1 dry weight (dw). The recoveries of BPs for lyophilizated sediment samples at two spiking levels (50 and 500 ng g−1 dw for each BP) were in the range of 75.5–105.5% with RSD values below 7.5%. 相似文献
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Compact multi‐band bandpass filters using quad‐mode stub‐loaded resonators are proposed in this letter. Firstly, a novel approach about the mode‐splitting characteristics of the quadruple‐mode resonator is investigated, which can provide dual‐band behavior. Secondly, a quad‐band filter is proposed and designed by cascading two quadruple‐mode resonators; the upper one operates at 1.8/2.4 GHz (GSM‐ and WiMax‐band) and the lower one at 1.57/2.1 GHz (GPS‐ and WCDMA‐band). Finally, the proposed filters have been fabricated. Respectable agreement between simulation and measurement verifies the validity of this design methodology. 相似文献
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Herein, we present a compact transversal bandpass filter (BPF) with an extremely wide upper stopband and multiple transmission zeros (TZ). Three signal transmission paths with shorted stubs and open-coupled lines allow signal transmission from input port to output port. Two resonant modes can be excited simultaneously and managed easily for bandpass response. Eleven TZs are achieved via transmission path cancelation; an extremely wide upper stopband with an attenuation level better than –12 dB is achieved up to 11.7 f0, where f0 is the center frequency (CF). In addition, bandwidth and CF can be controlled by adjusting electrical lengths. For proof of concept, a wideband BPF centered at 1.04 GHz with 3 dB fractional bandwidths of 49.2% was designed, fabricated, and evaluated. The overall circuit measures 0.045λg × 0.117λg; good agreement was observed between the measured and simulated results. 相似文献
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Zhiyao Zhang Xiaojun Zhou Rui Liang Zujun Qin Yong Liu 《Optics Communications》2009,282(15):3163-3167
In this paper, a novel all-optical bit-error indicating scheme is numerically studied. The bit-error indicating function is achieved by two all-optical processing stages. Firstly, the amplified original bit stream propagates through a high-nonlinear fiber and experiences self-phase modulation which causes intensity-dependent spectrum broadening and split. And then, the bit stream output from the high-nonlinear fiber is filtered by a band-pass filter with the same central wavelength as the original bit stream to generate an error bit indicating signal. The error bit indicating signal, in which only the “Error” bits have the highest peak power, is synchronous with the delayed original bit stream. Therefore, the position of the “Error” bits in the original bit stream can be identified by setting only one judge threshold in the error bit indicating signal. The scheme is demonstrated for an 80 Gb/s bit stream with return-to-zero format by simulation. The results show that the scheme can be used for the all-optical bit-error indicating of the super high bit-rate systems using the return-to-zero format which is favored in the optical time division multiplexing transmission systems. 相似文献
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