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A recent key challenge in noise engineering is the development of structures or materials that achieve desirable acoustic performance in practical settings. Combinations of porous layers and perforated plates offer potential composite absorbers for various acoustic applications. The present work conducts experimental characterizations of sound absorption performance of absorbers based on membrane foams combined with perforated plates. Membrane foams with the well-controlled cell size and porosity are fabricated by milli-fluidic tools, whereas perforated plates are made within a tuned perforation ratio. The three-microphone method is used to perform the acoustic measurements. The results obtained from ten combination samples reveal that the sound absorption behavior of the foam-based layers can be successfully tailored and improved by a thin perforated plate within a reasonable hole diameter and spacing while maintaining the total thickness of the composite absorber.

The diffuse sound absorption was investigated theoretically and experimentally for a periodically arranged sound absorber composed of perforated plates with extended tubes (PPETs) and porous materials. The calculation formulae related to the boundary condition are derived for the periodic absorbers, and then the equations are solved numerically. The influences of the incidence and azimuthal angle, and the period of absorber arrangement are investigated on the sound absorption. The sound-absorption coefficients are tested in a standard reverberation room for a periodic absorber composed of units of three parallel-arranged PPETs and porous material. The measured 1/3-octave band sound-absorption coefficients agree well with the theoretical prediction. Both theoretical and measured results suggest that the periodic PPET absorbers have good sound-absorption performance in the low- to mid-frequency range in diffuse field.

As an important component of inlet and exhaust mufflers, the acoustic characteristics of perforated components are inevitably affected by the flow of air. Therefore, obtaining the acoustic impedance of the perforated element under airflow conditions is a prerequisite for accurate calculation of the muffler’s muffling performance. In this work, the frequency domain linear Navier–Stokes (L-NS) method is used to extract the acoustic impedance of perforated plates under grazing flow. The predicted perforated acoustic impedance is consistent with the calculation results of published acoustic impedance expression, and the impedance boundary condition is defined to calculate the transmission loss (TL) of the perforated muffler, which agrees well with the experimental results and verifies the accuracy of the method. The effect of perforation angles on the transmission loss of mufflers in different Mach numbers (Ma) and aperture plate thickness ratio (dh/tp) is analyzed by the frequency domain L-NS method. The results show that when 1≤dh/tp<2 and Ma≤2, the effect of perforation angles on the muffler performance is obvious, and the angle tilted upstream shifts the resonant frequency to a lower frequency while its corresponding peak value is also increased. As an engineering application, it has certain significance for the prediction of muffler muffling performance and the regulation of the muffling frequency band.

In this study, practical formulas for the critical buckling loads of simply supported square circular perforated steel plates with different hole ratios and slenderness ratios subjected to uniaxial and biaxial load conditions are developed. Database is composed with the help of the commercial software package ANSYS that uses the finite element method for calculations and the formula was developed by using gene expression programming. A total of 847 datasets were generated, and they used to establish and validate the formula. The effect of perforation size and slenderness ratio on the buckling strength of the perforated plates is investigated with this study. The buckling coefficients of uniaxially and biaxially loaded simply supported perforated square steel plates can be easily calculated quickly and accurately by using the empirical formulas developed in this study. One of the novelty of this research study is unique buckling coefficients can be calculated for each slenderness ratio. After the evaluation, it has seen that the results from the formulas are much more acceptable out of the results of the available literatures.

This study proposes a novel open-type rectangular breakwater combined with horizontal perforated plates on both sides to enhance the sheltering effect of the rectangular box-type breakwaters against longer waves. The hydrodynamic characteristics of this breakwater are analyzed through analytical potential solutions and experimental tests. The quadratic pressure drop conditions are exerted on the horizontal perforated plates to facilitate assessing the effect of wave height on the dissipated wave energy of breakwater through the analytical solution. The hydrodynamic quantities of the breakwater, including the reflection, transmission, and energy-loss coefficients, together with vertical and horizontal wave forces, are calculated using the velocity potential decomposition method as well as an iterative algorithm. Furthermore, the reflection and transmission coefficients of the breakwater are measured by conducting experimental tests at various wave periods, wave heights, and both porosities and widths of the horizontal perforated plates. The analytical predicted results demonstrate good agreement with the iterative boundary element method solution and measured data. The influences of variable incident waves and structure parameters on the hydrodynamic characteristics of the breakwater are investigated through further calculations based on analytical solutions. Results indicate that horizontal perforated plates placed on the water surface for both sides of the rectangular breakwater can enhance the wave dissipation ability of the breakwater while effectively decreasing the transmission and reflection coefficients.

An experimental investigation on the large deflection of perforated composite plates is performed in this study. The fabrics of the composite plates are considered as unidirectional and woven. The effects of the variations in diameter, number and location of hole on plates are examined. The effects of the fabrics are also examined. One short edge of the composite plate is clamped, and a constant weight is hanged from the other short edge of the composite plate during the experiments. In order to prove the accuracy of the study done in the experiment, the large deflection analysis of the perforated plates is also made by the SolidWorks simulation program. SolidWorks simulation program is capable of performing large deflection analysis based on finite elements. When the results are examined, the large deflection is less in the woven type fabric and the large deflection value in the multi-hole specimens is higher than the single-hole ones. It is also determined that the increase in the distance of the hole position from the clamped end of the plate reduces the large deflection. As a result of the comparison of linear and nonlinear calculations, it is seen that nonlinear calculation should be preferred especially if the applied force is large. When the experimental and the numerical results are compared, it is seen that the obtained results are compatible.

Based on the analysis of existing collective shockwave protection methods worldwide, this paper addresses the mitigation of shock waves by means of passive methods, namely the use of perforated plates. Employing specialized software for numerical analysis, such as ANSYS-AUTODYN 2022R1®, the interaction of shock waves with a protection structure has been studied. By using this cost-free approach, several configurations with different opening ratios were investigated, pointing out the peculiarities of the real phenomenon. The FEM-based numerical model was calibrated by employing live explosive tests. The experimental assessments were performed for two configurations, with and without a perforated plate. The numerical results were expressed in terms of force acting on an armor plate placed behind a perforated plate at a relevant distance for ballistic protection in engineering applications. By investigating the force/impulse acting on a witness plate instead of the pressure measured at a single point, a realistic scenario can be considered. For the total impulse attenuation factor, the numerical results suggest a power law dependence, with the opening ratio as a variable.

The reduction of fan noise in ducts is a challenging task for acoustic engineers. Usually, the confined space where an absorber can be integrated is small. In addition, one has to consider the influence of the absorber on the flow field and the attenuation of noise should be as great as possible. In this contribution, we investigate the application of a micro-perforated absorber (MPA) in the direct vicinity of a low-pressure axial fan operating at low Mach number conditions. The micro-perforated plates (MPP) are modeled using the Johnson–Champoux–Allard–Lafarge (JCAL) model for porous materials. The entire geometrical setup of duct, fan and MPA is then simulated with the Finite Element (FE) method; the pre-processing effort is reduced by using non-conforming grids to discretize the different regions. The influence of the cavity length and the positioning of the fan are analyzed. The results are then applied to the construction of a full-sized MPA duct component that takes the limited space into consideration. Simulation results and overall functionality are compared to experimental results obtained in an axial-fan test rig. The Finite Element framework proved to be robust in predicting overall sound pressure level reduction in the higher volume flow rates. It is also shown that the MPP increases sound reduction in the low-frequency regime and at two resonant frequencies of the MPA setup. However, its main benefit lies in maintaining the efficiency of the fan. The location of the fan downstream or within the MPA has a significant effect on both the simulated and measured sound reduction.

Duct silencers provide effective noise reduction for heating, ventilation and air conditioning systems. These silencers can achieve an excellent sound attenuation through the attributes of their design. The reactive silencer works on the principle of high reflection of sound waves at low frequencies. On the other hand, the dissipative silencer works on the principle of sound absorption, which is very effective at high-frequencies. Combining these two kinds of silencers allowed covering the whole frequency range. In this paper, the effect of liner characteristics composed of a perforated plate backed by a porous material and geometry discontinuities on the acoustic power attenuation of lined ducts is evaluated. This objective is achieved by using a numerical model to compute the multimodal scattering matrix, thus allowing deducing the acoustic power attenuation. The numerical results are obtained for six configurations, including cases of narrowing and widening of a radius duct with sudden or progressive discontinuities. Numerical acoustic power attenuation shows the relative influence of the variation in the values of each parameter of the liner, and of each type of radius discontinuities of ducts.

This study presents an examination of the transmission properties of multilayered partitions made up of multiple micro-perforated plates (MPPs) coupled to acoustic enclosures with general impedance boundaries. Multi-layered MPPs can lower the transmission while minimizing reflection in the source and receiving enclosure. Previous research has mainly focused on the double MPPs or triple MPPs partition itself. However, it is vital to analyze the in-situ sound transmission loss of the multi-layered MPP and their efficiency in a complex vibro-acoustic environment. The case when the multilayered MPPs are coupled to a receiving enclosure or coupled to both a source and receiving enclosure is investigated. The objective is to provide an analytical method to evaluate the transmission properties of multilayered MPPs coupled to acoustic enclosures while being computationally more efficient than the finite element method (FEM). Using the modified Fourier series for the acoustic pressure, a variational form for the acoustic and structure medium yields a completely coupled vibroacoustic system. A comparison between the sound transmission loss of the double MPPs, when mounted on an impedance tube and coupled to acoustics enclosures, shows the modal effect of the enclosures. The effect of enclosure shape, impedance boundary, perforation ratio, air gap thickness on the sound transmission properties of the double MPPs structure is examined for both cases. Finally, in both situations, the performance of triple MPP structure insulation is evaluated.