NUMERICAL ASSESSMENT OF REVERSE-FLOW MUFFLERS USING A SIMULATED ANNEALING METHOD

It has been noted that the application of high performance, compact mufflers is the future for modern factories where place is at a premium. However, as research on mufflers equipped with extended tubes has been exhausted, and frankly at the juncture, shown to be inadequate (unsuitable), attention has turned to mufflers conjugated with perforated intruding tubes which can dramatically increase acoustical performance. Therefore, the focus of this paper is not only to analyze the sound transmission loss (STL) of a one-chamber open-ended perforated muffler but also to optimize the best design shape within a limited space. In this paper, the four-pole system matrix for evaluating the acoustic performance ― sound transmission loss (STL) ― is derived by using a decoupled numerical method. Additionally, a simulated annealing (SA), a robust scheme used to search for the global optimum by imitating the metal's heating process, has been used during the optimization process. Before dealing with a broadband noise, the STL's maximization with respect to a one-tone noise is introduced for a reliability check on the SA method. Also, an accuracy check on the mathematical model is performed. To appreciate the acoustical ability of the new mufflers, traditional mufflers, including a simple expansion muffler as well as a non-perforated intruding-tube muffler, have been assessed. Results reveal that the maximal STL is precisely located at the desired targeted tone. In addition, the acoustical performance of mufflers conjugated with perforated intruding tubes is found to be superior to the traditional mufflers. Consequently, the approach used for the optimal design of the noise elimination proposed in this study is quite effective.

Recently, research on new techniques of single-chamber mufflers equipped with a non-perforated intruding tube has been addressed; however, the research work on multi-chamber mufflers conjugated with open-ended perforated intruding inlet-tubes which may dramatically increase the acoustical performance has been neglected. Therefore, the main purpose of this paper is not only to analyze the sound transmission loss (STL) of a multi-chamber open-ended perforated inlet-tube muffler but also to optimize the best design shape within a limited space. In this paper, the four-pole system matrix for evaluating the acoustic performance - sound transmission loss (STL) - is derived by using a decoupled numerical method. Moreover, a genetic algorithm (GA), a robust scheme used to search for the global optimum by imitating a genetic evolutionary process, has been used during the optimization process. Results reveal that the maximal STL is precisely located at the desired tone. In addition, it has been shown that the acoustic performance for both pure tone and broadband noise will increase if the muffler has more chambers.

Noise control is essential in an enclosed machine room where the noise level has to comply with the occupational safety and health act. In order to overcome a pure tone noise with a high peak value that is harmful to human hearing, a traditional reactive muffler has been used. However, the traditional method for designing a reactive muffler has proven to be time-consuming and insufficient. In order to efficiently reduce the peak noise level, interest in shape optimization of a Helmholtz muffler is coming to the forefront. Helmholtz mufflers that deal with a pure tone have been adequately researched. However, the shape optimization of multi-chamber Helmholtz mufflers that deal with a broadband noise hybridized with multiple tones within a constrained space has been mostly ignored. Therefore, this study analyzes the sound transmission loss (STL) and the best optimized design for a hybrid Helmholtz muffler under a space- constrained situation. On the basis of the plane wave theory, the four-pole system matrix used to evaluate the acoustic performance of a multi-tone hybrid Helmholtz muffler is presented. Two numerical cases for eliminating one/two tone noises emitted from a machine room using six kinds of mufflers (muffler A~F) is also introduced. To find the best acoustical performance of a space-constrained muffler, a numerical assessment using a simulated annealing (SA) method is adopted. Before the SA operation can be carried out, the accuracy of the mathematical model has been checked using the experimental data. Eliminating a broadband noise hybridized with a pure tone (130 Hz) in Case I reveals that muffler C composed of a one- chamber Helmholtz Resonator and a one-chamber dissipative element has a noise reduction of 54.9 (dB). Moreover, as indicated in Case II, muffler F, a two-chamber Helmholtz Resonator and a one-chamber dissipative element, has a noise reduction of 69.7 (dB). Obviously, the peak values of the pure tones in Case I and Case II are efficiently reduced after the muffler is added. Consequently, a successful approach in eliminating a broadband noise hybridized with multiple tones using optimally shaped hybrid Helmholtz mufflers and a simulated annealing method within a constrained space is demonstrated.

Shape optimization of multi-chamber cross-flow mufflers by SA optimization

Numerical analysis of circular straight mufflers equipped with three chambers at high-order-modes

Research on new techniques of multi-chamber mufflers equipped with a side inlet and an internal non-perforated tube has been well addressed and developed; however, the research work of multi-chamber mufflers in conjunction with side inlet and internal perforated tubes which may efficiently increase the acoustical performance is rare. Therefore, the main purpose of this paper is to not only analyze the sound transmission loss (STL) of three-chamber side mufflers with a perforated tube but also to optimize their best design shape under a limited space. In this paper, both the generalized decoupling technique and plane wave theory in solving the coupled acoustical problem are used. The four-pole system matrix in evaluating the acoustic performance is also deduced in conjunction with a simulated algorithm (SA). To verify the liability of the SA technique, the noise minimization of muffles at a targeted frequency is exemplified first. To appreciate the acoustical performance of various multi-chamber mufflers with/without inner perforated tube, three kinds of multi-chamber mufflers ― a one-chamber side muffler, a two-chamber side muffler hybridized with a non-perforated tube, and a three-chamber side muffler hybridized with a perforated tube are introduced and assessed. In eliminating the broadband exhausted noise emitted from an air compressor’s inlet. Before the SA operation can be carried out, the accuracies of the mathematical models have to be checked by experimental data. The result reveals a three-chamber side muffler hybridized with a perforated tube exhibits an excellent acoustical ability beyond the other mufflers. Consequently, the approach used seeking the optimal design of the STL proposed in this study is indeed easy, economical and quite effective.

In order to enhance the acoustical performance of gun mufflers, a multi-chamber muffler internally inserting with expansion cones and perforated tubes ducts is presented. Because of the complicated geometry of gun muffler, traditional analytic method used in predicting a muffler’s acoustical performance is difficult; therefore, a finite element method using the COMSOL software is adopted to predict the gun muffler’s sound transmission loss. Moreover, because an objective function (or fitness function) is needed during the optimization process, a simplified mathematical model using Artificial Neural Network (ANN) is used. Here, a polynomial objective function is established by inputting the muffler’s geometric design parameters and the related simulated Sound Transmission Loss (STL) (run on the COMSOL) via the Artificial Neural Network. Furthermore, Genetic Algorithm (GA), an optimizer, is linked to the simplified mathematical model to maximize the gun muffler’s acoustical performance. To pursue a maximal STL at the targeted tones, the geometric parameters of cone’s horizontal length (L1) and first cone’s span (L2) is optimally adjusted. Results demonstrates the STL of gun muffler at the specified frequencies of 1000, 2000, and 4000 Hz can be improved from 15.8 dB, 72.6 dB, 184.8 dB to 18.2 dB, 112.6 dB, and 416.3 dB, respectively. The paper aims to provide an optimal design method of gun muffler using Finite Element Method (FEM), Artificial Neural Network, and Genetic Algorithm. Consequently, the simulated results reveal that the optimally shaped gun muffler can efficiently depress the gun’s shooting noise.

Re-entrant auxetic designs, known for their superior mechanical properties, are increasingly explored in various industrial applications. This study aims to enhance the multifunctionality of such designs by preserving their mechanical characteristics while improving their acoustic performance. A multi-layer hybrid structure integrating microperforated panels with auxetic geometry was proposed. This design enabled each auxetic cavity to function as a Helmholtz resonator. Sample fabrication was performed with fused deposition modeling (FDM), an Additive Manufacturing technique, using PLA as build material. The perforations and minimum structural features were designed to maintain structural integrity and mechanical properties while facilitating ease of manufacturing. A computational modeling approach was verified and validated using numerical and experimental results from the literature. Impedance tube testing techniques were employed to validate the numerical model for sound transmission loss (STL) and sound absorption coefficient (SAC), ensuring precise measurement of acoustic properties and confirming the accuracy of the simulations. A total of 18 variants of proposed design were numerically examined in the low to mid-frequency range (50–1800 Hz). The effects of various geometric and material parameters on acoustic performance were recorded. Results indicate substantial enhancement in SAC as well as STL from baseline design of the same dimensions. SAC above 0.5 was achieved for a broad frequency range of 1180 Hz with an average STL of 55 dB. This research advances the development of multifunctional subwavelength metamaterials by presenting a structure that exhibits exceptional STL and SAC—a combination not previously documented in recent literature.

The impact of damping on the sound transmission loss of locally resonant metamaterial plates

Recently, research on new mufflers equipped with connected curved tubes using phase cancellation techniques has been addressed in the industrial field. On the basis of the transfer matrix method and the stiffness matrix method, researchers have explored noise reduction effects within a constrained space. However, the attenuation bands are too narrow and the overall acoustical performance in dealing with broadband noise is thus insufficient. Therefore, in order to broaden the spectrum of the acoustical performance curves at various targeted tones (250, 500, and 900 Hz), a wool optimally lined within the ducts of HQ mufflers is proposed. In this paper, five kinds of HQ mufflers with rectangular sections (muffler A: a double-connected curved tube muffler; muffler B: a double-connected abrupt tube muffler; muffler C: a one-sided triple-connected curved tube muffler; muffler D: a two-sided tripleconnected curved tube muffler; muffler E: a one-sided triple-connected abrupt tube muffler) within a fixed length are assessed. In order to facilitate the assessment of optimal mufflers, a boundary element model (BEM) is adopted as the mathematical objective function. To assess the optimal mufflers, a genetic algorithm (GA) is linked with the BEM. Before the GA operation can be carried out, the accuracy of the mathematical models must be checked using the experimental data. Optimal results reveal that the maximum value of the sound transmission loss (STL) can be optimally improved at the targeted frequencies. Consequently, the optimum algorithm proposed in this study provides an efficient way to find a better silencer for industry.

Recently, sandwich structures have been widely used in different fields because of their good mechanical properties, but these structures are weak in acoustic performance. In this paper, by combining pyramidal truss core sandwich structure with frame, a new structure is proposed with both good mechanical properties and excellent acoustic performance at low frequency. An analytical model of the pyramidal truss core sandwich structure with frame is developed to investigate the sound transmission loss (STL) performance. Finite element method (FEM) is also used to investigate the STL performance at low frequency. The effects of the incident wave angle and the geometrical parameters on the STL of the structure are discussed.

Periodic sound reduction at some frequencies and high pressure loss could be considered as the disadvantages of simple expansion silencers. Generally, reactive elements are applied in silencers to optimize their acoustic and aerodynamic performance. In this paper, we were going to investigate the combined and independent effects of reactive elements, baffle and extended tubes at the inlet and outlet of simple expansion silencer, on the acoustic performance and pressure loss of simple expansion silencer. Firstly, simple expansion silencer dimensions were determined based on theoretical calculations to attenuate the noise by 10 dB. Secondly, the simulation was performed using COMSOL acoustical module software based on finite element method to predict silencer sound transmission loss and pressure loss, respectively, before and after adding reactive elements. Then, according to ISO7235, ISO3744 and ISO3746 standards noise insertion loss of various silencers under study was measured in a free field and in the following that silencers pressure loss evaluated. Finally, the predicted results with the software were compared with the experimental ones. The addition of the extended tubes increased the transmission loss and insertion loss at low and medium frequencies and mitigated the pressure loss of the silencer compared to the simple expansion silencer. The baffle increased the transmission loss curve in the medium frequencies compared to the simple expansion silencer. The combination of baffle and extended tube elements caused an extraordinary increase in insertion loss and transmission loss at the medium frequencies and a decrease in pressure loss. It could be concluded from the present study that using extended tube might be probably the best choice to reduce pressure loss and increase the acoustic performance of simple expansion silencer at low and medium frequencies and what's more is that the best acoustic performance in medium frequencies can be achieved by using a combination of baffle and extended tube.

본 논문은 고속열차 객실 내 유리창의 차음 성능을 향상시키기 위한 기반연구로, 접합유리에 사용되는 고분자 필름의 물성과 음향학적 특성을 분석하여 그 상관관계를 살펴보고자 하였다. 기존에 사용되고 있는 PVB(polyvinyl butyal) 필름 및 다른 단량체 비율을 가지는 PVB 유도체, 그리고 유리 사이 차음재로 사용가능 한 PC(polycarbonate)의 동적기계적 특성을 분석(DMA)하였다. DMA 분석을 통해 상온에 가까운 온도범위에서 유리전이온도(<TEX>$T_g$</TEX>)를 가지며 tan <TEX>${\delta}$</TEX>(loss tangent) 값이 큰 것으로 나타난 PVB-HEMU 시편의 댐핑(damping) 성능이 가장 우수할 것으로 예측하고, 이를 고속철도 차량의 접합유리창과 동일한 구조에서의 투과손실 시험과 해석을 통해 검증하고자 하였다. 접합필름의 종류에 따른 유리창 투과손실 값을 투과손실 측정(인텐시티법)과 FE 해석을 이용해 도출하고, 고분자 필름의 물성과 음향성능 간 상관관계 분석을 위한 기초자료를 구축하였다. To improve the sound insulation performance of laminated glass in high speed trains, it is beneficial to study the relationship between the characteristics of interlayer films and the acoustical performance. In addition to those of conventional PVB (polyvinyl butyral), the dynamic mechanical properties of PVB derivatives and PC (polycarbonate), which are candidates for interlayer films, were analyzed. We assumed that PVB-HEMU, which has a glass transition temperature (<TEX>$T_g$</TEX>) around room temperature and a large tan <TEX>${\delta}$</TEX> (loss tangent) value, can be made to damp efficiently. The damping capability was tested utilizing sound transmission loss measurement and simulation under the identical structure of laminated glass in high speed trains. We also built a database for analysis of relations between interlayer film characteristics and acoustical performance; this was followed by the determination of sound transmission loss using the intensity technique and FEA.

In this study Laminated Veneer Lumber (LVL)-widely used in structural wood applications-was manufactured from seven poplar veneers bonded with polyurethane (PU) adhesive and reinforced with either one sheet of glass fiber or carbon fiber fabrics. In order to determine the effects of the fiber fabrics incorporated into the structure of the produced LVLs on their thermal and acoustic insulation performance in structural applications, the thermal conductivity coefficient (λ), thermal transmittance (U), sound absorption coefficient (α), and sound transmission loss (dB) values were determined. The experimental results indicated that the thermal conductivity coefficient of the glass fiber-reinforced LVL was lower than that of both the control group and the carbon fiber-reinforced LVL. The thermal transmittance coefficient, an important indicator of thermal insulation performance in buildings, followed a similar trend. Regarding the sound absorption coefficients, the fiber fabric-reinforced LVL samples demonstrated lower coefficients compared to the control group. For sound transmission loss, no significant differences were observed among the groups, and the sound transmission loss was found to increase with frequency. Results indicate that glass fiber-reinforced LVL composites can be used as replacement of other wood-based insulating materials in green buildings which exhibit worse sound insulation or thermal insulation and which are significantly more affected by changes in relative humidity of surrounding air.

Polyurethane foam is commonly used in the automobile industry due to its favorable acoustic performances. In this study, a new tung oil-based polyurethane composite foam (TOPUF) was prepared by a one-step method. Different forms and contents of miscanthus lutarioriparius (ML) were used in TOPUF for improving acoustic performance. Polyurethane foams were characterized by means of Fourier transform infrared and SEM. The acoustic properties and mechanical properties of TOPUF, obtained with ML, were determined and compared with pure petroleum-based polyurethane foam. The results illustrate that the modification of TOPUF with the ML has a positive effect on the acoustic and mechanical properties in comparison to the unmodified foam. TOPUF obtained with ML powders has better acoustic performance than that obtained with ML strips. The optimum acoustic performance is achieved at the filler content of 0.3 wt%. The average sound absorption coefficient and transmission loss can reach 0.518, and 19.05 dB, respectively.