Acoustic characterization of additive manufactured perforated panel backed by honeycomb structure with circular and non-circular perforations

This paper studies the acoustic properties of an additive manufactured micro-perforated panel backed by a periodic honeycomb structure. Extrusion-based Fused Filament Fabrication (FFF) technique of Additive Manufacturing (AM) is used to fabricate the integrated honeycomb structures with a perforated face sheet. Normal absorption coefficient of the fabricated structure is measured in impedance tube using two microphone transfer function method. A generalized analytical formulation based on unit section analysis applicable to various cross sections of perforations has been proposed to predict the absorption coefficient, where shape dependent viscous effects in the perforation are incorporated by deriving effective complex density of the medium. To study the effect of perforation shape, three geometries viz., circular, triangular and square perforations are considered for analysis where triangular shape found to have more absorption coefficient and lower frequency of peak absorption. In addition, broadband absorption coefficient of proposed structure has been demonstrated by deploying hexagonal cells of different lengths in a unit section. The analytical results are compared with experimental results and a good agreement is observed between them. A parametric study is conducted to understand effect of perforated hole size and cell length on the absorption coefficient and peak frequency. Results show that the proposed structures can be tuned to desired frequency range by altering geometric parameters like cell length, shape and size of perforation hole. Technique and methodology presented in the current study gives an alternative way to design and fabricate honeycomb structures with perforations for acoustic applications such as aircraft cabins, ship structures and building acoustics

Acoustic characterization of additive manufactured micro-perforated panel backed by honeycomb structure

This paper studies the acoustic properties of an additive manufactured micro-perforated panel backed by a periodic honeycomb structure. Extrusion-based Fused Filament Fabrication (FFF) technique of Additive Manufacturing (AM) is used. Absorption coefficient of the proposed structure is measured using an Impedance tube. An analytical model is developed to predict the acoustic absorption coefficient. The analytical results are compared with the experimental results and a good agreement is observed between them. A parametric study is conducted to understand the effect of perforated hole size on the absorption coefficient and peak frequency

Acoustic properties of additive manufactured narrow tube periodic structures

Quarter tube periodic resonators are used to attenuate the acoustic energy of discrete frequencies wherein their sizes can vary from narrow to large. This paper reports acoustical properties of additive manufactured, narrow tube, single and multi-periodic structures, both, theoretically and experimentally. Herein, multi-periodic structures are defined as periodically arranged unit sections of tubes, where each section is composed of periodically repeated unit cells of different sizes and shapes. Structures with hexagonal narrow tubes and octagonal narrow tubes with interfacial gaps are considered for the study, and normal absorption coefficients of these samples are measured by using impedance tube. the theoretical absorption coefficient of these structures is predicted using unit section analysis method and narrow tube theory, where shape dependent viscous and thermal losses are incorporated. Estimated theoretical absorption coefficients are in good agreement with measured results. The result shows that the frequency and amplitude of maximum absorption can be varied by altering the aperture ratio and/or the length of periodic structure. The proposed theoretical method gives an alternative approach for designing and manufacturing periodic narrow tubes for different applications such as absorbing panels, acoustic transducers, and engine filter elements

Implementation of Two-cavity Method for Measuring the Flow Resistivity of Acoustic Material

Acoustic materials are characterized according to their macroscopic and microscopic properties. The sound absorption co-efficient and the air-flow resistivity are of paramount importance among those used to describe the acoustic behaviour of materials. There are several methods developed for measuring the air-flow resistivity of acoustic material. The aim of this paper is to study the existing static flow resistivity measurement methods and then accordingly implement a suitable indirect method based on standard impedance tube. The flow resistivity measurements are carried out for additive manufactured ABS (Acrylonitrile butadiene styrene) sample, foam and glass fibre using the two-cavity method. There are certain similarities observed in their results. Further analysis of the raw impedance data is carried out and conclusions are drawn pertaining to the performance and feasibility of the implemented method

Acoustic measurement of additive manufactured concentric tube reverse flow resonators

This study investigates acoustic properties of additive manufactured (AM) concentric tube reverse flow (RF) resonators where acoustic attenuation with smaller sample length is achieved by increasing effective travel length of acoustic waves within a structure. The theoretical modeling based on narrow tube theory has been proposed to predict absorption coefficient, while numerical estimation of absorption coefficient is carried out using finite element method (FEM). The predicted theoretical and numerical results are found to be in good agreement with measured results in impedance tube, thus demonstrating its potential in achieving low frequency attenuation with compact size structures

Acoustic properties of additive manufactured narrow tube periodic structures

Quarter tube periodic resonators are used to attenuate the acoustic energy of discrete frequencies wherein their sizes can vary from narrow to large. This paper reports acoustical properties of additive manufactured, narrow tube, single and multi-periodic structures, both, theoretically and experimentally. Herein, multi-periodic structures are defined as periodically arranged unit sections of tubes, where each section is composed of periodically repeated unit cells of different sizes and shapes. Structures with hexagonal narrow tubes and octagonal narrow tubes with interfacial gaps are considered for the study, and normal absorption coefficients of these samples are measured by using impedance tube. the theoretical absorption coefficient of these structures is predicted using unit section analysis method and narrow tube theory, where shape dependent viscous and thermal losses are incorporated. Estimated theoretical absorption coefficients are in good agreement with measured results. The result shows that the frequency and amplitude of maximum absorption can be varied by altering the aperture ratio and/or the length of periodic structure. The proposed theoretical method gives an alternative approach for designing and manufacturing periodic narrow tubes for different applications such as absorbing panels, acoustic transducers, and engine filter elements

Acoustic characterization of additive manufactured perforated panel backed by honeycomb structure with circular and non-circular perforations

This paper studies the acoustic properties of an additive manufactured micro-perforated panel backed by a periodic honeycomb structure. Extrusion-based Fused Filament Fabrication (FFF) technique of Additive Manufacturing (AM) is used to fabricate the integrated honeycomb structures with a perforated face sheet. Normal absorption coefficient of the fabricated structure is measured in impedance tube using two microphone transfer function method. A generalized analytical formulation based on unit section analysis applicable to various cross sections of perforations has been proposed to predict the absorption coefficient, where shape dependent viscous effects in the perforation are incorporated by deriving effective complex density of the medium. To study the effect of perforation shape, three geometries viz., circular, triangular and square perforations are considered for analysis where triangular shape found to have more absorption coefficient and lower frequency of peak absorption. In addition, broadband absorption coefficient of proposed structure has been demonstrated by deploying hexagonal cells of different lengths in a unit section. The analytical results are compared with experimental results and a good agreement is observed between them. A parametric study is conducted to understand effect of perforated hole size and cell length on the absorption coefficient and peak frequency. Results show that the proposed structures can be tuned to desired frequency range by altering geometric parameters like cell length, shape and size of perforation hole. Technique and methodology presented in the current study gives an alternative way to design and fabricate honeycomb structures with perforations for acoustic applications such as aircraft cabins, ship structures and building acoustics

Acoustic measurement of additive manufactured concentric tube reverse flow resonators

This study investigates acoustic properties of additive manufactured (AM) concentric tube reverse flow (RF) resonators where acoustic attenuation with smaller sample length is achieved by increasing effective travel length of acoustic waves within a structure. The theoretical modeling based on narrow tube theory has been proposed to predict absorption coefficient, while numerical estimation of absorption coefficient is carried out using finite element method (FEM). The predicted theoretical and numerical results are found to be in good agreement with measured results in impedance tube, thus demonstrating its potential in achieving low frequency attenuation with compact size structures

Acoustic properties of additive manufactured porous material

Acoustic porous materials are extensively used in many engineering applications like building, automobile, aviation, and marine. The health risk factor and environmental claims, associated with traditional materials such as glass wool, mineral fibers, and polymer foams demand for the alternative porous acoustic absorbing materials. Advances in additive manufacturing (AM) allow to manufacture complex structures and give an alternative method to produce porous materials. This study investigates the acoustic properties of porous sound-absorbing material produced by using additive manufacturing (AM) technique and explores the feasibility of AM to manufacture acoustic absorptive materials. For study, three samples with different aperture ratios were fabricated by AM technique, and their sound absorption coefficients were measured experimentally by using the impedance tube. The theoretical formulation for predicting normal sound absorption coefficient of sample with and without air gap was developed and compared with experimental results. The predicted absorption coefficient agrees well with measured results. The measured results indicate that the absorption coefficient of the structures fabricated through AM can be altered by varying aperture ratio and air gap behind the sample. This study reinforces the capability of AM for producing complex acoustic structures with better acoustic properties

Vibration Measurement of Flexible Narrow Tube Under Acoustic Excitation

 Flexible narrow tubes are used in periodic structures to develop mechanical vibration filters. These structures have very thin walls and measuring modal parameters is quite challenge using electromagnetic excitation methods. This study discusses the acoustic source as vibration excitation to a flexible tube. A test setup is developed by modifying impedance tube and measured vibration response using laser vibrometer