An assessment of the performance of impedance tube method

The impedance tube method is widely used for measuring sound absorption (or reflection) coefficients of acoustic materials as a function of frequency. However, the sound absorption coefficients obtained using the impedance tube method may have some variations due to the dimensions (limits) of an impedance tube, sample preparation and sample mounting. This paper assesses the performance of the two-microphone impedance tube method as a function of frequency for different tube dimensions and materials and presents suggestions for increasing the reliability and repeatability of impedance tube measurements. First, after summarizing a systematic way for measuring acoustic transfer functions, sound absorption coefficients of a variety of materials ranging from conventional absorbing acoustic materials to samples with thin films are measured using two tubes with different tube diameter and microphone spacing. Uncertainty of sound absorption coefficients for various materials is discussed, and the frequency limits of impedance tubes are assessed. Then, a method for minimizing uncertainty due to sample mounting is proposed and the main findings are discussed.WOS:000346127200009Scopus - Affiliation ID: 60105072Science Citation Index ExpandedQ4ArticleUluslararası işbirliği ile yapılmayan - HAYIRTemmuz2014YÖK - 2013-1

Quantification and minimization of sensor effects on modal parameters of lightweight structures

This paper aims to quantify the adverse effects of contact type sensors on modal parameters of lightweight structures and to present a practical way for identification of modal parameters of structures with minimal sensor effects. The adverse effects of a contact type sensor on natural frequencies, damping levels and mode shapes are explored using the theoretical model of a typical beam-like sample carrying a sensor and a controlled experimental study based on measurement of frequency response functions using non-contact excitation and response sensors. The half-power and circle fit modal identification methods are used to extract modal parameter from measured data. The experimental and theoretical modal analysis results are evaluated, and a practical methodology based on classical acoustic and vibration frequency response functions is suggested to identify modal loss factors and natural frequencies of lightweight structures with minimal sensor effects.WOS:000338129200031Scopus - Affiliation ID: 60105072Science Citation Index ExpandedQ4ArticleUluslararası işbirliği ile yapılmayan - HAYIRHaziran2014YÖK - 2013-1

Assessment of the measurement and prediction Methods for the acoustic properties of natural fiber samples and evaluation of their properties

Although some studies have been conducted to show how natural fibers can replace synthetic materials, the use of many natural fibers is still limited. On the other hand, the use of natural fibers can become very common in many applications once their performance is fully understood. This paper aims to present a critical assessment of the acoustic properties of natural fiber samples. First, the methods commonly used for the measurement and prediction of the acoustic properties of natural fiber samples are determined. Second, the common techniques for measuring sound absorption coefficients (SACs) and sound transmission losses (STLs) are presented, and their advantages and limitations are evaluated. After that, the models commonly used for the prediction of acoustic properties are presented. Then, the SACs of many natural fiber samples are presented along with the thickness, bulk density and flow resistivity of the samples. Furthermore, the SACs of the samples are normalized using sample thickness and bulk density, and the sound absorption performance of the fiber samples is evaluated. Based on the results of many natural fiber samples, an empirical model for estimating the SACs of natural fiber samples is presented. Finally, the STLs of some porous natural fiber samples are presented.TUBITAK (The Scientific and Technological Research Council of Turkey) under Grant 119M115WOS:000641808000001Scopus - Affiliation ID: 6010507Science Citation Index ExpandedQ1Review; Early AccessUluslararası işbirliği ile yapılmayan - HAYIRNisan2021YÖK - 2020-2

Development of an improved mathematical model for the dynamic response of a sphere located at a viscoelastic medium interface

A comprehensive investigation on the static and dynamic responses of a sphere located at elastic and viscoelastic medium interfaces is performed in this study. First, the mathematical models commonly used for predicting the static displacement of a sphere located at an elastic medium interface are presented and their performances are compared. After that, based on the finite element analyses, an accurate mathematical model to predict the static displacement of a sphere located at an elastic medium interface valid for different Poisson's ratios of the medium and small and large sphere displacements is proposed. Then, an improved mathematical model for the dynamic response of a sphere located at a viscoelastic medium interface is developed. In addition to the Young's modulus of the medium and the radius of the sphere, the model takes into account the density, Poisson's ratio and viscosity of the medium, the mass of the sphere and the radiation damping. The effects of the radiation damping, the Young's modulus, density and viscosity of the medium and the density of the sphere on the dynamic response of the sphere located at a viscoelastic medium interface are explored. The developed model can be used to understand the dynamic responses of spherical objects located at viscoelastic medium interfaces in practical applications. Furthermore, the proposed model is a significant tool for graduate students and researchers in the fields of engineering, materials science and physics to gain insight into the dynamic responses of spheres located at viscoelastic medium interfaces.WOS:000741130700001Scopus - Affiliation ID: 60105072Science Citation Index ExpandedQ4ArticleUluslararası işbirliği ile yapılmayan - HAYIRMart2022YÖK - 2021-22Aralı

Assessment of the models for predicting the responses of spherical objects in viscoelastic mediums and at viscoelastic interfaces

Spherical objects, such as bubbles and spheres, embedded in mediums and at viscoelastic interfaces are encountered in many applications, including the determination of material properties. This paper assesses the models for predicting the responses of spherical objects in viscoelastic mediums and at viscoelastic interfaces used in various applications. The models are presented very compactly, and evaluations are performed based on the analyses of the models for the spherical objects in viscoelastic mediums and at viscoelastic interfaces. First, the models for predicting the static displacements of spherical objects are presented and assessed. After that, the models for predicting the dynamic responses of spherical objects are presented and their dynamic behaviours are compared. Then, the models for the deformation of the medium around spherical objects and stress distribution are presented and evaluated. The models and evaluations presented in this study can be exploited in various applications, including biomedical applications

Development of a model for predicting dynamic response of a sphere at viscoelastic interface: A dynamic Hertz model

A model for predicting the dynamic response of a sphere at viscoelastic interface is presented. The model is based on Hertz contact model and the model for a sphere in a medium. In addition to the elastic properties of medium and the size of sphere, the model considers the density of sphere, the density and viscosity of medium, and damping of oscillations of sphere due to radiation of shear waves. The model can predict not only the effects of the mechanical properties of medium, the physical properties of sphere, and the amplitude of excitation force on sphere displacement, but also the effects of these parameters on shift of resonance frequency. The proposed model can be used to identify the elastic and damping properties of materials, and to understand the dynamic responses of spherical objects at viscoelastic interfaces in practical applications.Science Citation Index Expanded - Conference Proceedings Citation Index- Scienc

Identification of crack noises in household refrigerators

The crack noises propagating from a refrigerator disturb residents in a household; however, the reasons behind the mechanisms of such noises have not been identified yet. In this study, the crack noises in modern household refrigerators are identified and their root causes are explored. The appropriate parameters for overall and Fourier analyses are first determined and the noise characteristics of typical household refrigerators under various conditions are presented. Then, a special test rig providing remote control of the subcomponents including the compressor, fan and heater is designed and structural acceleration and sound pressure measurements inside and outside the test rig in a quiet room are performed. The acoustic and vibration measurements are conducted under various conditions by separately controlling each subcomponent. The crack noises in typical household refrigerators are identified and their root causes are explored by using the results of the overall and Fourier analyses. Some solutions to minimize the crack noises in household refrigerators are also summarized.WOS:000346546300025Scopus - Affiliation ID: 60105072Science Citation Index ExpandedQ2ArticleUluslararası işbirliği ile yapılmayan - HAYIRMart2015YÖK - 2014-1

Investigation of the vibro-acoustic behaviors of luffa bio composites and assessment of their use for practical applications

New materials as alternatives to petroleum-based composite materials are needed due to adverse effects of chemical materials on nature. On the other hand, there is a need to characterize and evaluate new alternative materials to be effectively used in practical applications. The vibro-acoustic behaviors including damping and elastic properties, sound absorption and transmission loss levels of luffa bio-composites are investigated and their use for practical applications is evaluated in this study. First, the procedure for manufacturing luffa composites is summarized and materials and methods are presented. After that, the acoustic absorption and transmission loss levels of sample luffa composites are explored by using the impedance tube method. The damping and elastic properties of sample luffa composites are determined by using experimental and theoretical modal data. Furthermore, the interface properties of the luffa fibers and matrix are examined by using Scanning Electron Microscope. All the results are evaluated and the potential of the use of luffa composites in practical applications is assessed.WOS:000388480400073Scopus - Affiliation ID: 60105072Conference Proceedings Citation Index- ScienceProceedings PaperTemmuz2016YÖK - 2015-1

Investigation of the acoustic properties of bio luffa fiber and composite materials

Körük, Hasan (MEF Author)Considering the adverse effects of petroleum-based materials on nature, finding and developing new materials as alternatives to these chemical materials become a necessity in practice. On the other hand, these new materials need characterization to be considered and effectively used in practical applications. The acoustic properties of luffa bio fiber and composite materials are investigated in this study. First, the preparation of various luffa test samples and the method for acoustic characterization of the luffa samples is presented. Then, the acoustic absorption properties of both luffa fiber and composite materials are identified using the impedance tube method. After that, the transmission loss levels of the same luffa samples are determined. All the results are evaluated and the acoustic performances of luffa materials are highlighted.WOS:000358973500043Scopus - Affiliation ID: 60105072Science Citation Index ExpandedQ2ArticleUluslararası işbirliği ile yapılmayan - HAYIREkim2015YÖK - 2015-1

A new triangular composite shell element with damping capability

This paper presents a new triangular composite shell element with damping capability. Formulation of the composite triangular shell element is based on stacking individual homogeneous triangular shell ele- ments on top of each other. The homogeneous shell element is an assembly of a triangular membrane element with drilling degrees of freedoms and a plate element. Damping capability is provided by means of complex element stiffness matrix of individual flat layers of the composite element. These elements with damping capability allow modelling general structures with damping treatments. A few test cases are modelled using triangular finite element developed here and the results of the complex eigenvalue analyses are compared with those of the quadrilateral shell elements proposed recently. The results obtained using the presented triangular and previous quadrilateral composite elements are also com- pared with those based on modal strain energy method and experimental results. Comparisons of the experimental and the theoretical results confirm that the modal properties including modal damping lev- els of structures with damping treatments can be predicted with high accuracy using the proposed finite element.WOS:000343838900033Scopus - Affiliation ID: 60105072Science Citation Index ExpandedQ1ArticleUluslararası işbirliği ile yapılmayan - HAYIRAralık2014YÖK - 2014-1