Abdullah Seçgin

The Effects of Composite Plate Design Parameters on Linear Vibrations by Discrete Singular Convolution Method

This study is devoted to some specific free vibration analysis of thin composite plates based on discrete singular convolution (DSC) approach. As the first analysis, a parametric study is performed on the basis of number of lamination, boundary condition, and orientation angle of symmetrically laminated composite plates. As the second, the effects of material type, boundary condition, and stacking sequence on the modal characteristics of laminated plates made of E-glass/epoxy, Kevlar/epoxy, and carbon/epoxy are investigated. Thirdly, linear modal characteristics of fiber metal laminates are specifically analyzed due to their common use in aircraft design. Hopefully, the results presented in the article may be practically of interest for engineers and designers. This study displays the applicability of the DSC method for real-life problems.

An Efficient Sound Source Localization Technique via Boundary Element Method

The boundary element method (BEM) is a widely used technique in vibro-acoustics. This method is effective not only in the determination of exterior and interior sound fields but also for the sound source localization of complex systems. In this chapter, the Helmholtz integral equation formulation and its boundary element discretization are presented. Half-space algorithm and half-space-contact version of this algorithm feasible for most machine locations are introduced. Some theoretical examples, for a dilating sphere in half-space, are presented. The chapter continues with a case study: Sound source identification and characterization of a refrigerator, via a cost-effective and easy-to-use technique, based on surface velocity measurements and BEM computation of surface and field acoustic pressures.

A modal impedance-based statistical energy analysis for vibro-acoustic analysis of complex systems having structural uncertainty

A modal impedance-based statistical energy analysis for point, line, and area connected complex structural-acoustic systems is introduced. The proposed methodology is applied to perform mid- and high-frequency vibro-acoustic analysis of a cabinet model. The cabinet is composed of several composite plates with local mass variability simulating structural uncertainty, isotropic beams, and an acoustic enclosure. The method uses point mobilities, which are determined using modal parameters obtained by finite element method, to define line and area mobilities via dimension reducing principle. The methodology presented here is successfully verified by several numerical and experimental Monte Carlo computations. With this study, conventional statistical energy analysis is improved for mid-frequency vibro-acoustic analysis of complex systems.

Vibration bounding of uncertain thin beams by using an extreme value model based on statistical moments

The paper introduces an extreme value model based on statistical moments to predict modal and vibration response bounds for stochastic structures. The approach is applied to a thin beam having two input uncertain parameters: elasticity modulus and specific volume (inverse of the mass density). The input parameters are controllably generated with random shifted normal distributions that have positive statistics. Then the first two statistical moments, mean and standard deviation of natural frequency, and bending vibration displacement are predicted by solving stochastic differential equation of bending vibration of thin beams. Here, the differential equation is solved by utilizing a powerful numerical technique, discrete singular convolution. The accuracies of the discrete singular convolution method and the statistical moment approach are separately ensured with analytical comparisons and experimental and numerical Monte Carlo simulations. These statistical moments are then processed by an extreme value model to predict uncertainty bounds for modal and vibration displacement responses. Predicted bounds are compared with random responses obtained by numerical Monte Carlo simulations. The proposed approach estimates very accurate results with less computation memory and time compared to Monte Carlo solutions. Therefore, the approach proves its efficiency in the use of uncertainty propagation problems governed by partial differential equations.

Monte-Carlo simülasyonsuz-Uç Değer Modelleme ile Kompozit Bir Plakanın Belirsiz Titreşim Sınırlarının Belirlenmesi

Belirsizlige sahip titresim sistemlerinde, cevap olasiliksal veya olasiliksal olmayan bazi simulasyon yontemleri ile hesaplanabilmektedir. Monte Carlo simulasyonu bu amacla en cok kullanilan olasiliksal yontemlerden biridir. Ancak bu yontem ile istenilen belirsiz cevap fonksiyonunun eldesi yuksek ornekleme sayisi ve buna bagli olarak uzun hesaplama sureleri gerektirmektedir. parametrelerine sahip simetrik katmanli bir kompozit plakanin serbest ve zorlanmis titresim cevabinin sinirlari bir Monte-Carlo simulasyonsuz-uc deger model kurularak elde edilmistir. Kurulan model kompozit yapinin diferansiyel denkleminin istatistiki cozumune dayanmaktadir. Denklem cozucu olarak ayrik tekil konvolusyon yontemi basari ile kullanilmistir. Elde edilen sonuclar Monte Carlo simulasyonlari ile sinanarak, sunulan metodolojinin dogruluk ve cozum suresi baglamindaki verimi acikca ortaya konmustur

Sound radiation in a half space with impedance surface

This study deals with sound radiation of a vibrating body in a half space. Half space may be formed by a rigid, anechoic or specifically by an impedance surface. The practical application of the impedance surface may be the sound field determination of a machine sitting on a floor, coated with an isolation material, for passive noise control. The study is based on the solution of Helmholtz integral equation by the boundary element method (BEM). A BEM code developed for general vibro-acoustic applications is used for numerical solutions. Examples include sound sources taken from theory and daily life. Some benchmark studies and real life applications are involved.