Calculation and Analysis of Acoustic Characteristics of Straight-Through Perforated Pipe Muffler Based on Multilayer Sound Absorbing Material

Using the multi-physical field simulation software COMSOL,the acoustic characteristics of the multilayer sound absorbing material straight-through perforated pipe muffler are studied by the finite element method.The results show that the finite element calculation of the multilayer sound absorbing material straight-through the perforated pipe muffler agrees well with the experimental measurement results.The reliability of the finite element method for studying the acoustic performance of the straight-through perforated pipe muffler with multilayer sound absorbing materials is shown.Furthermore,the influence of some structural parameters of porous sound absorbing material and micro-perforated plate on the acoustic performance of the multilayer sound absorbing material straight-through perforated pipe muffler is analyzed.The muffler based on multilayer sound absorbing material is different from the traditional muffler.After applying the multilayer sound absorbing material to the straight-through perforated pipe muffler,the transmission loss value greatly increases,which provides new ideas and directions for future research on the muffler.

Theoretical Calculation and Analysis of Muffler Based on Multilayer Sound Absorbing Material

The multilayer impedance composite sound absorption structure of the new muffler is proposed by combining the microporous plate structure with the resonant sound absorption structure of the porous material.Firstly,the acoustic impedance and acoustic absorption coefficient of the new muffler structure are calculated by acoustic electric analogy method,and then the noise attenuation is calculated.When the new muffler structure parameters change,the relationship among the noise frequency,the sound absorption coefficient and the noise attenuation is calculated by using MATLAB.Finally,the calculated results are compared with the experimental data to verify the correctness of the theoretical calculation.The variation of resonance peak,resonance frequency and attenuation band width of each structural parameter is analyzed by the relation curve.The conclusion shows that it is feasible to use multilayer sound absorbing materials as the body structure of the new muffler.And the influence relationship between the change of various parameters of the sound absorption structure with the sound absorption coefficient and noise attenuation is obtained.

A Combined Shape and Topology Optimization Based on Isogeometric Boundary Element Method for 3D Acoustics

A combined shape and topology optimization algorithm based on isogeometric boundary element method for 3D acoustics is developed in this study.The key treatment involves using adjoint variable method in shape sensitivity analysis with respect to non-uniform rational basis splines control points,and in topology sensitivity analysis with respect to the artificial densities of sound absorption material.OpenMP tool in Fortran code is adopted to improve the efficiency of analysis.To consider the features and efficiencies of the two types of optimization methods,this study adopts a combined iteration scheme for the optimization process to investigate the simultaneous change of geometry shape and distribution of material to achieve better noise control.Numerical examples,such as sound barrier,simple tank,and BeTSSi submarine,are performed to validate the advantage of combined optimization in noise reduction,and to demonstrate the potential of the proposed method for engineering problems.

The admittance feature representation and impact sound feature extraction in the material identification of ribbed plates

The admittance features representing the physical attributes are used as the in termediates to extract the materialattributesrelated impact sound features of ribbed plates. Firstly, the admittance feature representations of metal ribbed plates attributes are obtained and the relationship between the admittance features and the impact sound features are established via correlation analysis method. Then, materialattributesrelated impact sound features are obtained indirectly. Finally, the performances of different sound features for the material recognition of ribbedmetal plates are verified through the Support Vector Machine classifier. The results indicate that the obtained four sets of features can effectively identify the materials of the metal ribbed plates, while the accuracy of a single feature depends on the separable degree of the corresponding material attribute. And the features extracted based on admittance functions have higher average accuracy than that of timbre features. Therefore, the proposed sound feature extraction method based on admittance features is valid, and the extracted sound features can effectively reflect the physical attributes.

Research on sound velocity measurement in a laboratory for large elastic materials

A measurement scheme carried out in a tank is designed to obtain the compressionaland shear-wave velocities of a large elastic material.A hydrophone is used to receive the high frequency acoustic signals which penetrate the tested material,in order to determine the transmission time from the source to the hydrophone,the transmission time is also calculated according to the ray acoustic theory in layered media.A cost function is built based on the measured and the calculated transmission time,then the compressional- and shear-wave velocities can be obtained using the optimization algorithm.Compared with the traditional measurement scheme,this approach can not only get the 2 kinds of sound velocities in the tested material at the same time,but also keep the integrality of the tested material.With the proposed measurement system,the uncertainty of measurement results is less than 3.5%.

Improving operation lifetime of OLED by using thermally activated delayed fluorescence as host

We fabricated organic light-emitting diodes （OLEDs） with the thermally activated delayed fluorescence （TADF） mate- rial of 4CzlPN, Which show better stability compared with the 4,4＇-Bis（carbazol-9-yl）biphenyl （CBP） based devices. The half lifetime of the device using 4CzlPN as host material has doubled, and a slower voltage rise compared with that of CBP-based devices has been achieved, which indicates the improvement of stability. We attribute the better sta- bility to the good film morphology and difficult crystallization property of 4CzlPN. Our results suggest that employing the 4CzlPN as host material can be a promising way of fabricating OLEDs with longer operation lifetime.