| With the development of industrialization,sound absorption and noise reduction have become an important issue in many fields as well as one of the main criteria for people's high-quality of life.In whole-band range,noise in middle and low frequency field is more universal.Due to the strong penetrability,traditional sound absorption structures for this kind of noise take up a lot of space,and the sound absorption bandwidth is relatively narrow,which make it more difficult to get sound well absorbed.In recent years,how to effectively absorb and attenuate the middle-low frequency noise in limited space has been becoming the research emphases of many acoustic technicians.To meet this challenge,this paper attempts to design a channel-type sound absorbing structure,which not only analyses the sound absorption characteristics for middle-low frequency field,but studies the influence of structural parameters and combination methods on the characteristics.Firstly,a channel-type sound-absorbing structure is designed in this paper,of which three-dimensional model is constructed in UG NX.Based on the structural-acoustic coupling method,the sound absorption characteristics and acoustic mode analysis of this original structure are performed.The results show that this sound-absorbing original structure has a middle-low frequency sound absorption capability,and the peaks of the sound absorption coefficient-frequency curve are generated near the natural frequencies of the coupled model.Secondly,the effects of single structural parameters on the sound absorption characteristics and acoustic mode are investigated,including the axial height of the acoustic channel H ,the upper hole diameter of the conical body d ,the width of the acoustic channel a and the groove thickness of the acoustic channel t .The results show that different structural parameters have a great influence on the sound absorption characteristics of the structure.The increase of the axial height of the acoustic channel H can significantly increase the maximum value of the sound absorption coefficient and expand the sound absorption bandwidth(the width of the frequency intervals with the sound absorption coefficient higher than 0.5),with the movement to a lower frequency filed of the sound absorption coefficient-frequency curve.The increase of the width of acoustic channel a can expand the sound absorption bandwidth.The increase of either the upper hole diameter of the conical body d or the groove thickness of the acoustic channel t can make it true that the sound absorption coefficient-frequency curves move to a lower frequency field.Theresults of acoustic modal analysis show that the variation of the natural frequencies with different parameters is consistent with the trends of the curve's movement under different sizes,which proves the relationship between the sound absorption characteristics and the acoustic modes.Moreover,from radial period(the number of sound wave propagation channels in radial direction)and axial period(the number of axial arrays of the acoustic channel),the influence of periodicity on the sound absorption performance of the structure is analyzed.The results show that the broader sound absorption bandwidth can be more accessible by periodicity of the structure.At the same time,the smaller radial period and the larger axial period are,the better sound absorption performance can be more likely to be gotten in middle-low frequency field.Finally,the sound channels of different radial periods are combined to analyze the sound absorption characteristics of the combined structure.Compared with the single radial periodic structures,the combined structures can improve the sound absorption performance on the condition with a high sound absorption coefficient,which has a broader sound absorption bandwidth in middle-low frequency field.And the distribution of sound absorption band is more uniform to get a better structural adaptability. |
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