Theoretical Analysis and Experimental Research of the Absorption Property of a Variable Cross-Section Diffsorber

2013 ◽  
Vol 838-841 ◽  
pp. 2262-2266
Author(s):  
Lin Qiang Gu
Keyword(s):  
Theoretical Analysis ◽  
Absorption Coefficient ◽  
Cross Section ◽  
Variable Cross Section ◽  
Internal Resistance ◽  
Variable Cross ◽  
Absorption Property ◽  
Radiation Impedance ◽  
Testing Sample ◽  
Internal Impedance

The internal impedance and radiation impedance of a variable cross-section diffsorber were calculated, when adding bandage to the nozzles of tubes of diffsorber, or using non-linear sound resistance to provide appropriate additional internal resistance, the diffsorber will become an excellent sound absorber. Without bandage, the absorption coefficient of the testing sample is larger than 0.7 during 100Hz-2000Hz, and exceed 1 during 500Hz-800Hz; with bandage, the absorption coefficient of the testing samples is no less than 0.8 during 250Hz-4000Hz, and is above 1 during 250Hz-2000Hz. The performance of absorption begins to reduce from 5000Hz to higher frequency due to the mismatch of internal impedance and radiation impedance.

The Experimental Research on the Sound Absorption Coefficient of Several Different Mytilaria Laosensis Veneering Boards

2011 ◽  
Vol 486 ◽  
pp. 95-98
Author(s):  
Chu Wang Su ◽  
Quan Ping Yuan ◽  
Jing Da Huang ◽  
Kang Yang
Keyword(s):  
Absorption Coefficient ◽  
Cross Section ◽  
Sound Absorption ◽  
Medium Density Fiberboard ◽  
Base Material ◽  
Variable Cross Section ◽  
Sound Absorption Coefficient ◽  
Variable Cross ◽  
Section Structure ◽  
Mytilaria Laosensis

The composite acoustics board with pore-tank structure and variable cross section structure are made of Medium Density Fiberboard(MDF) as base material, Mytilaria laosensis sheet as veneer board, and sound absorption mat as the substructure material with the micro-perforation interlayer structure. The test was carried out to compare the absorption coefficient of Mytilaria laosensis sheet and nine samples by standing wave tube The test result shows that Mytilaria laosensis sheet has a low sound-absorbing performance itself, and its sound-absorption coefficient in all frequency ranges less than 0.3 and cannot be used as the sound-absorption board alone; The variable cross section structure sound-absorption board has a better performance than the pore-tank structure; When using the micro-perforation layer structure, the sound absorption board performs better and the sound absorption coefficient improves markedly in middle and low frequency scope.

Transmission Loss of Variable Cross Section Apertures

2014 ◽  
Vol 136 (4) ◽  
Author(s):  
J. Li ◽  
L. Zhou ◽  
X. Hua ◽  
D. W. Herrin
Keyword(s):  
Finite Element ◽  
Cross Section ◽  
Sound Propagation ◽  
Transmission Loss ◽  
Element Model ◽  
Variable Cross Section ◽  
Variable Cross ◽  
Cross Sectional ◽  
Radiation Impedance ◽  
The Cross

Openings in enclosures or walls are frequently the dominant path for sound propagation. In the current work, a transfer matrix method is used to predict the transmission loss of apertures assuming that the cross-sectional dimensions are small compared with an acoustic wavelength. Results are compared with good agreement to an acoustic finite element approach in which the loading on the source side of the finite element model (FEM) is a diffuse acoustic field applied by determining the cross-spectral force matrix of the excitation. The radiation impedance for both the source and termination is determined using a wavelet algorithm. Both approaches can be applied to leaks of any shape and special consideration is given to apertures with varying cross section. Specifically, cones and abrupt area changes are considered, and it is shown that the transmission loss can be increased by greater than 10 dB at many frequencies.

Modified Formula of Estimating Fundamental Frequency of Girder Bridge with Variable Cross-Section

2013 ◽  
Vol 540 ◽  
pp. 99-106 ◽  
Author(s):  
Qing Fei Gao ◽  
Zong Lin Wang ◽  
Bin Qiang Guo
Keyword(s):  
Numerical Simulation ◽  
Theoretical Analysis ◽  
Fundamental Frequency ◽  
Cross Section ◽  
Variable Cross Section ◽  
Variable Cross ◽  
Design Code ◽  
Height Ratio ◽  
Girder Bridge ◽  
Modified Formula

Based on present research, there is a big difference between the estimation of the fundamental frequency of Girder Bridge obtained by the design code of bridge, issued by ministry of transport of the P.R. China in 2004, and the theoretical value in some cases. To overcome above issue, theoretical analysis combined with numerical simulation was applied to estimate the fundamental frequency of Girder Bridge with variable cross-section. The effect of the height ratio between mid-span cross-section and support cross-section on the fundamental frequency was discussed in detail. Finally, an improved formula was proposed to estimate the fundamental frequency of Girder Bridge, and the effectiveness of the proposed formula was verified.

Boundary element method in numerical study of three-dimensional Stokes flows in channels of arbitrary shape

2012 ◽  
Vol 9 (1) ◽  
pp. 94-97
Author(s):  
Yu.A. Itkulova
Keyword(s):  
Boundary Element Method ◽  
Boundary Element ◽  
Cross Section ◽  
Numerical Study ◽  
Three Dimensional ◽  
Cylindrical Tube ◽  
Variable Cross Section ◽  
Variable Cross ◽  
Periodic Flows ◽  
Element Method

In the present work creeping three-dimensional flows of a viscous liquid in a cylindrical tube and a channel of variable cross-section are studied. A qualitative triangulation of the surface of a cylindrical tube, a smoothed and experimental channel of a variable cross section is constructed. The problem is solved numerically using boundary element method in several modifications for a periodic and non-periodic flows. The obtained numerical results are compared with the analytical solution for the Poiseuille flow.

Longitudinal oscillation of a rod with a variable cross section

2019 ◽  
Vol 14 (2) ◽  
pp. 138-141
Author(s):  
I.M. Utyashev
Keyword(s):  
Cross Section ◽  
Natural Frequencies ◽  
Liouville Problem ◽  
Variable Cross Section ◽  
Variable Cross ◽  
Longitudinal Vibrations ◽  
Cross Sectional ◽  
Independent Functions ◽  
The Cross ◽  
The Right

Variable cross-section rods are used in many parts and mechanisms. For example, conical rods are widely used in percussion mechanisms. The strength of such parts directly depends on the natural frequencies of longitudinal vibrations. The paper presents a method that allows numerically finding the natural frequencies of longitudinal vibrations of an elastic rod with a variable cross section. This method is based on representing the cross-sectional area as an exponential function of a polynomial of degree n. Based on this idea, it was possible to formulate the Sturm-Liouville problem with boundary conditions of the third kind. The linearly independent functions of the general solution have the form of a power series in the variables x and λ, as a result of which the order of the characteristic equation depends on the choice of the number of terms in the series. The presented approach differs from the works of other authors both in the formulation and in the solution method. In the work, a rod with a rigidly fixed left end is considered, fixing on the right end can be either free, or elastic or rigid. The first three natural frequencies for various cross-sectional profiles are given. From the analysis of the numerical results it follows that in a rigidly fixed rod with thinning in the middle part, the first natural frequency is noticeably higher than that of a conical rod. It is shown that with an increase in the rigidity of fixation at the right end, the natural frequencies increase for all cross section profiles. The results of the study can be used to solve inverse problems of restoring the cross-sectional profile from a finite set of natural frequencies.

Sign in / Sign up

Export Citation Format

Share Document