共查询到14条相似文献,搜索用时 0 毫秒
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A predictive method is proposed to determine the transmission loss of reactive silencers using the three-dimensional (3-D) time-domain computational fluid dynamics (CFD) approach and the plane wave decomposition technique. Firstly, a steady flow computation is performed with a mass-flow-inlet boundary condition, which provides an initial condition for the following two unsteady flow computations. The first unsteady flow computation is conducted by imposing an impulse (acoustic excitation) superimposed on the constant mass flow at the inlet of the model and then adding the non-reflecting boundary condition (NRBC) when the impulse completely propagates into the silencer. The second unsteady flow computation is conducted for the case without acoustic excitation at the inlet. The time histories of pressure and velocity at the upstream monitoring point as well as history of pressure at the downstream monitoring point are recorded during the two transient computations. The differences between the two unsteady flow computational results are the corresponding acoustic quantities. Therefore, the incident sound pressure signal is obtained by using plane wave decomposition at upstream, while the transmitted sound pressure signal is just the sound pressure at downstream. Finally, those two sound pressure signals in the time-domain are transformed into the frequency-domain by Fast Fourier Transform (FFT) and then the transmission loss (TL) of silencer is determined. For the straight-through perforated tube silencers with and without flow, the numerical results agree well with the published measurements. 相似文献
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Comparison and implementation of the various numerical methods used for calculating transmission loss in silencer systems 总被引:2,自引:0,他引:2
S. Bilawchuk 《Applied Acoustics》2003,64(9):903-916
Issues concerning the design and use of large-scale silencers are more prevalent today then ever before. With the increased use of large industrial machinery (such as gas turbines) and the increase in public awareness and concern for noise control, the desire to be able to properly design silencers for specific applications is increasing. Even today, most silencer design is performed by simply modifying existing designs without full confidence of the new performance characteristics. Due to the size and expense of these silencers, it would be beneficial to have means to predict the insertion loss (IL) or transmission loss (TL) characteristics at the design stage. To properly accomplish this, many factors such as geometry, absorptive material properties, flow effects, break out noise, and self-generated noise must be considered. The use of the finite element method (FEM) and the boundary element method (BEM) can aid in the prediction and design. This paper examines three of the different methods used in calculation of TL values; namely the “traditional” laboratory method, the 4-pole transfer matrix method and the 3-point method. A comparison of these methods based on such criteria as accuracy, computation time, and ease of use was conducted. In addition, the idiosyncrasies and problems encountered during implementation are presented. The conclusions were that the FEM is better suited for this kind of application and that the 3-point method was the fastest method and was easier to use than the 4-pole method. 相似文献
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I.Mathematicalmodelofacousticfie1dByapplyingtheSommerfeldradiationcondihonThus,anacousticfic1disdescribcdbyHelmholtzformula.Byconsideringaficldpointinthearea,Helmholtzformulaisgivenbythefollowingthreeintegra1equations:(1)Theexternalintcgra1fOrmu1a'(2)Thcintcrnalintegralformu1af(3)Thesurfaceintegralformu1afwhcreP.isthesoundpressureonthcSsurface;rthedistancefrompointqtothee1ementsurfacedSiqtheficldpoint,tuthefrcqucncyoftheacousticradiation;pthedensityofthesurroundingmedium,vsthenormalvibrati… 相似文献
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Rohollah Fallah Madvari Mohammad Reza Monazzam Mohsen Niknam Sharak Mohsen Mosa Farkhani 《声与振动》2020,54(2):127-137
Honeycomb structures have recently, replaced with conventional homogeneous materials. Given the fact that sandwich panels containing a honeycomb
core are able to adjust geometric parameters, including internal angles, they are
suitable for acoustic control applications. The main objective of this study was
to obtain a transmission loss curve in a specific honeycomb frequency range along
with same overall dimensions and weight. In this study, a finite element model
(FEM) in ABAQUS software was used to simulate honeycomb panels, evaluate
resonant frequencies, and for acoustic analysis. This model was used to obtain
acoustic pressure and then to calculate the sound transmission loss (STL) in
MATLAB software. Vibration and acoustic analysis of panels were performed
in the frequency range of 1 to 1000 Hz. The models analyzed in this design
includes 14-single row-honeycomb designs with angles of −45°, −30°, −15°,
0°, +15°, +30°, +45°. The results showed that a-single row and −45°cell angle
honeycomb panel in the frequency range of 1 to 1000 Hz had the highest STL
as well as the highest number of frequency modes (90 mods). Furthermore, the
panel had the highest STL regarding the area under the STL curve (dB∙Hz).
The panels containing more frequency mods, have a higher transmission loss.
Moreover, the sound transmission loss is more sensitive to the cell angle variable
(θ). In other studies, the STL was more sensitive to the number of honeycomb
cells in the horizontal and vertical directions, as well as the angle of cells. 相似文献
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Jiu-sheng Li 《Optik》2008,119(1):19-22
A novel optical modulator using SiO2 waveguides on a silicon substrate is proposed. The modulator is analyzed and designed with the finite element method. The numerical results have shown that an optimally designed modulator can give a broad bandwidth, good impedance match, and low cost. The proposed modulator can be fabricated easily using Si-based very large-scale integrated technology, and it is very suitable for opto-electronic integrated circuits. 相似文献
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The radio interference (RI) from HVDC transmission lines can block communication systems. In this paper the RI of a HVDC transmission line has been analyzed by the superposition of the electromagnetic field generated by the corona current based on phase-model transformation, where the corona current can be solved by the flux-corrected transport and finite difference method combining the upstream finite element method for bipolar conductor model instead of corona cage or excitation function. Our calculated values for 0.5 MHz RI from the proposed method compare well with measured values from a 800 kV HVDC test line established in China. With this validation, we find that RI should increase with temperature, increase with altitude, and vary in a complex way with relative humidity. Therefore, the proposed method can be adopted in transmission lines design and electromagnetic environment evaluation. 相似文献
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Gain/loss effect on bright solitary wave in a cigar-shaped attractive condensate in the presence of expulsive parabolic potential 下载免费PDF全文
<正>Taking into account both gain/loss and time-dependent atomic scattering length,this paper analytically derives an exact bright solitary wave in a cigar-shaped attractive condensate in the presence of an expulsive parabolic potential. Due to the balance of the scattering length and gain/loss,the bright solitary wave is shown to have constant amplitude. Especially,it is found that the bright solitary wave is accelerated by expulsive force,whose velocity can be modulated by changing the axial and transverse angular frequencies.The results are in good agreement with the experimental observations by Khaykovich et al(2002 Science 296 1290). 相似文献
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Jijun Wang Zhonghua Shen Xiaowu Ni Baiqiang Xu Jianfei Guan Jian Lu 《Optics & Laser Technology》2007,39(1):21-28
The optimum finite element model in the system consisting of a transparent coating and an opaque substrate is established based on the analysis of two important parameters: meshing size and time step, and the stability of solution. Taking into account the temperature dependence of material properties, the transient temperature and temperature gradient field are obtained. According to the thermoelastic theory, this temperature gradient field can be taken as a buried bulk source to generate ultrasonic wave. The surface acoustic waves (SAWs) are obtained. The influence of the coating thickness on the SAWs is analyzed. The model provides a useful tool for the determination of modes which are generated by a laser source in transparent coating on opaque substrate. The surface skimming longitudinal wave exists for the multiple oscillations and it charges from unipolar waveforms to dipolar. 相似文献
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Xueling FanWeixu Zhang Tiejun WangGuiwu Liu Jinghua Zhang 《Applied Surface Science》2011,257(15):6718-6724
Multiple cracking behavior in a thin elastic film bonded to a thick elastic substrate is investigated by the extended finite element method. Stress and stress intensity factor are obtained using a periodic finite element model for the cracked film/substrate system. The influences of various parameters including crack length, film thickness, periodic crack spacing, and relative stiffness of the substrate on the stress and stress intensity factor are discussed in detail. It is demonstrated that the effects of geometric parameters are more sensitive than that of material property. In particular, the crack spacing has a saturation value due to interactions of neighboring cracks and relief of tensile stress in the film. The film/substrate couple with multiple periodic cracks can exhibit a positive potential in improving the durability of the film/substrate system. 相似文献
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Bochong WangJianqiang Wei Liang QiaoTao Wang Fashen Li 《Journal of magnetism and magnetic materials》2012,324(5):761-765
In this work, the influence of interface reflections on the microwave reflection loss (RL) for carbonyl iron/paraffin composite backed by a perfect conduction plate with 30 vol% concentration at various thicknesses was investigated in the 0.1-18 GHz. Using a vector network analyzer, the scattering parameters (S11 and S21) were measured in two different ways. Based on the quarter-wavelength matching model, the results of measurement were analyzed. The experiment shows that there are many minimum values (dips) in RL at various thicknesses when the reflective wave, which is reflected from the absorbing layer and the emerging wave, which is reflected from the backed metal plate are out of phase by 180°, and the peak intensity of the RL is directly affected by the intensity of the reflective wave and the emerging wave. Furthermore, the experiment and numerical calculation demonstrates that the modulus of the normalized input impedance |Zin/Z0| equals approximately 1, but the ratio between the modulus of permittivity and permeability |ε/μ| is far from unity at the minimal reflection point. 相似文献