Wyniki wyszukiwania - BazTech

1

Active vibroacoustic control of plate structures with arbitrary boundary conditions

Nowak Ł., Zieliński T. G., Meissner M.

IPPT Reports on Fundamental Technological Research

|

2013

|

nr 4

5--9

EN

The paper describes briefly some main aspects of the active feedback control system that has been developed and constructed for reduction of vibroacoustic emission of vibrating plate structures with arbitrary boundary conditions. Relations between the forms and frequency of the vibrations induced by an external harmonic excitation and the distribution of the generated acoustic pressure field are investigated using the developed numerical model based on indirect variational boundary element method. The aim of the control system is to minimize the sound pressure level in a given point of the ambient space. The system uses small, rectangle-shaped piezoelectric transducers as both sensors and actuators. The transducers are connected in a number of independent feedback loops, and the feedback gains are the control parameters which are optimized using the developed optimal control algorithm. The constructed active system has been tested for the stability and control performance during experimental research performed in an anechoic chamber. Results of experiments are presented in the paper, proving a high level of noise reduction and a good agreement with numerical predictions.

2

Acoustic absorption of a new class of alumina foams with various high-porosity levels

Zieliński T. G., Potoczek M., Śliwa R. E., Nowak Ł. J.

Archives of Acoustics

|

2013

|

Vol. 38, No. 4

495--502

EN

Recently, a new class of ceramic foams with porosity levels up to 90% has been developed as a result of the association of the gelcasting process and aeration of the ceramic suspension. This paper presents and discusses original results advertising sound absorbing capabilities of such foams. The authors man- ufactured three types of alumina foams in order to investigate three porosity levels, namely: 72, 88, and 90%. The microstructure of foams was examined and typical dimensions and average sizes of cells (pores) and cell-linking windows were found for each porosity case. Then, the acoustic absorption coefficient was measured in a wide frequency range for several samples of various thickness cut out from the foams. The results were discussed and compared with the acoustic absorption of typical polyurethane foams proving that the alumina foams with high porosity of 88-90% have excellent sound absorbing properties competitive with the quality of sound absorbing PU foams of higher porosity.

3

Acoustic radiation of vibrating plate structures submerged in water

Nowak Ł., Zieliński T. G.

Hydroacoustics

|

2012

|

Vol. 15

163-170

EN

The paper presents results of the theoretical and numerical investigation on acoustic radiation of vibrating plate structures submerged in water. The current state of the art on the considered issues is briefly reviewed. Then, the method for determining eigenmode shape functions and eigenfrequencies of plate vibrating in water that has been used in presented study is introduced. The constitutive equations for solid domain and the pressure acoustic equation for liquid domain are coupled via boundary conditions and solved numerically using the finite element method. Structural mode shapes and eigenfrequencies computed for plate submerged in water are compared to analogous results obtained for air and for the in vacuo case. It is assumed, that the plate is rectangle shaped and that it is placed in an infinite rigid baffle. Three-dimensional near- and far-field acoustic radiation characteristics for the plate vibrating in water are introduced. Possibilities of implementation of the active control system for reduction of the hydroacoustic emission are briefly discussed.

4

Fundamentals of multiphysics modelling of piezo-poro-elastic structures

Zieliński T. G.

Archives of Mechanics

|

2010

|

Vol. 62, nr 5

343-378

EN

The paper discusses theoretical fundamentals necessary for accurate vibroacoustical modeling of structures or composites made up of poroelastic, elastic, and (active) piezoelectric materials, immersed in an acoustic medium (e.g. air). An accuratemodeling of such hybrid active-passive vibroacoustic attenuators (absorbers or insulators) requires a multiphysics approach involving the finite element method to cope with complex geometries. Such fully-coupled, multiphysics model is given in this paper. To this end, first, the accurate PDE-based models of all the involved single-physics problems are recalled and, since a mutual interaction of these various problems is of the uttermost importance, the relevant couplings are thoroughly investigated and taken into account in the modeling. Eventually, the Galerkin finite element model is developed. This model should serve to develop designs of active composite vibroacoustic attenuators made up of porous foams with passive and active solid implants, or hybrid liners and panels made up of a core or layers of porous materials fixed to elastic faceplates with piezoelectric actuators, and coupled to air-gaps. A widespread design of such smart mufflers is still an open topic and should be addressed with accurate predictive tools based on the model proposed in the present paper. The model is accurate in the framework of kinematical and constitutive (material) linearity of behaviour. This is, however, the very case of the vibroacoustic application of elasto-poroelastic panels or composites, where the structural vibrations are induced by acoustic waves. The developed fully-coupled FE model is finally used to solve a generic two-dimensional example and some issues concerning finite element approximation and convergence are also discussed.

5

Metoda Impulsowych Dystorsji Wirtualnych z zastosowaniem do modelowania i identyfikacji defektów w konstrukcjach

Zieliński T. G.

Prace Instytutu Podstawowych Problemów Techniki PAN

|

2004

|

nr 4

3-160

PL

Głównym celem rozprawy jest zaprezentowanie oryginalnej koncepcji zastosowania idei tzw. dystorsji wirtualnych do problemów dynamiki konstrukcji. Do tej pory podejście dystorsyjne stosowano z powodzeniem w zagadnieniach statyki konstrukcji w postaci twz. Metody Dystorsji Wirtualnych (MDW). Fundamentem dla wszelkich obliczeń dokonywanych w ramach tej metody jest tzw. macierz wpływu. Taką statyczną macierz wpływu starano się również w specyficzny sposób wykorzystywać w celu rozwiązania pewnych problemów dynamicznych. W niniejszej pracy zostanie przedstawiona Metoda Impulsowych Dystorsji Wirtualnych (MIDW) pozwalająca na w pełni konsekwentne wykorzystanie podejścia dystorsyjnego dla zagadnień dynamiki konstrukcji. Ten uwidoczniony w tytule cel nie jest jednak jedynym zadaniem niniejszej rozprawy. Pośrednim, choć również istotnym zamierzeniem autora było przedstawienie ogólnej meotdologii realizacji idei dystorsji wirtualnych w konstrukcjach składających się z dowolnych elementów skończonych. Praca, a zwłaszcza zawarte w niej obliczenia i przykłady numeryczne bazują na zrealizowanym przez autora obiektowym programie dotyczącym Metody Elementów Skończonych (MES) dla mechaniki konstrukcji, w którym po raz pierwszy zaprojektowano i zrealizowano obiektowe ujęcie metod dystorsyjnych (zarówno dla statyki jak i dynamiki). Obiektowa realizacja oprogramowania stanowiła z punktu widzenia autora kolejny, bardzo ważny cel pracy. Praca prezentuje sposób wykorzystania dystorsji wirtualnyc do pisu wrażliwości konstrukcji obciążonej dynamicznie na modyfikację parametrów, związanych z jej cechami sztywnościowymi. Kolejnym zamierzeniem było więc opracowanie algorytmu opartego na MIDW, pozwalającego dokładnie obliczać gradienty tzw. funkcji przejścia opisujących propagację fali sprężystej wzbudzonej w konstrukcji. Końcowym zadaniem niniejszej rozprawy jest zastosowanie podejścia dystorsyjnego do problemu modelowania i identyfikacji defektów w konstrukcjach, m.in. w celu niebanalnej weryfikacji opracowanych metod i algorytmów.