| Porous medium acoustic materials,also named as sound-absorbing materials,are widely used in engineering due to its excellent acoustic properties.In most time,the engineer cannot ignore the influence of porous medium acoustic materials in the sound filed design.Describing the propagation process of acoustic waves in the sound-absorbing material,and refraction reflection behaviours of acoustic waves at discontinuous material property surface is a difficult problem.To this end,this paper analyzes the deficiencies and limitations of the existing methods,and develop a numerical simulation program of acoustics in porous media based on the Cell-Vertex Finite Volume Method(CV-FVM),also known as Vertex-Centered Finite Volume Method.Nowadays,the existing porous media acoustic simulation software-with relatively complicated calculation procedure-often based on the frequency domain method.It is impossible to use such software to simulate the acoustic pulse propagation process and get a relatively intuitive result.Though there are local reaction models can simplify the calculation by mapping the acoustic properties of the porous medium to the boundary surface in the time domain.But this treatment cannot solve complex structures and anisotropic medium.Therefore,this paper deduces and simplifies the linear acoustics and porous media acoustic control equations to univariate forms to improve computational efficiency.Uses a unified form to describe the porous media acoustics and linear acoustic control equations to reduce the duplicated code rate.In the field of linear acoustics: This paper base on the basic assumptions of fluid dynamics derives nonlinear acoustic governing equations and introduces linear acoustic assumptions to derive linear acoustic governing equations.In the field of porous acoustics: Due to the complex internal structure of porous materials,it is impossible to simulate the sound wave propagation in it directly.Therefore,the theoretical model has often based on frequency domain multi-scale renormalization phenomenological or semiphenomenological theory.The existing porous medium acoustic model is classified into three categories,total of seven models in this paper.And comprehensively analyses and discusses has been done for the theoretical models to make sure it applies to the existing numerical simulation software development platforms.On the discontinuous material property surface: Drawing on aeroacoustics related theories,we derived the boundary conditions of the interface then develop a discrete simulation implementation scheme for it in CV-FVM scheme.Based on the existing developing resources,we use Fortran95 to program and implement the acoustic time-domain simulation module of porous media.While ensuring the full-featured and standard interface of the module,integrated it into the acoustic solver of the General Transport Equation Analysis(GTEA)platform developed by Harbin Engineering University.Numerical verification is carried out for the classical case in the relevant references,such as phononic crystal,porous sound barrier and impedance composite muffler.We found that the simulation result of CV-FVM porous acoustic solver agrees well with the simulation results of other numerical simulation methods like FDTD in most of the test examples.It shows that the simplified scheme and the treatment method of discontinuous material property surface in this paper are valid and reliable.However,the low-frequency part of the simulation results of some three-dimensional examples did not meet expectations.After analysis,it is considered that the simplified scheme adopted in this paper is not suitable for acoustic materials with high porosity and high flow resistance.It is necessary to improve and introduce new schemes to improve the compatibility of the current program. |
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