Strategies for using cellular automata to locate constrained layer damping on vibrating structures

It is often hard to optimise constrained layer damping (CLD) for structures more complicated than simple beams and plates as its performance depends on its location, the shape of the applied patch, the mode shapes of the structure and the material properties. This paper considers the use of cellular automata (CA) in conjunction with finite element analysis to obtain an efficient coverage of CLD on structures. The effectiveness of several different sets of local rules governing the CA are compared against each other for a structure with known optimum coverage-namely a plate. The algorithm which attempts to replicate most closely known optimal configurations is considered the most successful. This algorithm is then used to generate an efficient CLD treatment that targets several modes of a curved composite panel. To validate the modelling approaches used, results are also presented of a comparison between theoretical and experimentally obtained modal properties of the damped curved panel

Damping of double wall panels including a viscothermal air layer

This paper deals with the dynamic behaviour of double wall panels, with emphasis on damping and sound radiation. It will be shown that a narrow air layer separating the two plates of a panel significantly alters the mentioned quantities by its viscothermal properties. Numerical and experimental results will be presented for a double wall panel excited with a point force. Numerical results are obtained using a fully coupled vibro-acoustic finite element model. The air between the plates is modelled by special viscothermal elements. A very efficient frequency response method is used to determine the structural response to harmonic excitations. The radiated power is calculated with the help of socalled radiation modes. Experimental results are obtained using a special designed set-up. An electrodynamic shaker excites one panel and the excitation power is measured. The radiated sound power is measured with a sound intensity meter. The dissipated energy is determined by considering an energy balance. Typical parameters such as the distance between the plates and the ratio of plate thicknesses are varied. Numerical and experimental results agree fairly well. From the results it can be concluded that for narrow air layers, i.e. when the so called ’shear wave number’ is low, a large amount of energy is dissipated by viscothermal effects in the air layer

Modelo de vibrações de vigas de reforço utilizadas em plataformas ofshore

Tese (doutorado) - Universidade Federal de Santa Catarina, Centro Tecnológico. Programa de Pós-Graduação em Engenharia MecânicaPlacas reforçadas por vigas são os principais componentes de estruturas de plataformas offshore, usadas na prospecção e produção de petróleo. As vibrações geradas pelas máquinas propagam-se através da estrutura gerando altos níveis de ruído nos alojamentos. Para determinar com precisão o fluxo de potência através de placas reforçadas por vigas, um modelo que inclua o efeito das ressonâncias próprias da alma e aba da viga e as ondas no plano deve ser considerado, sendo o efeito das ondas no plano importante principalmente nas altas freqüências. Este trabalho apresenta um modelo para determinar a resposta de placas reforçadas por vigas utilizando uma abordagem analítica. Os modelos incluem vigas L e T e uma placa reforçada por uma viga L submetida a um carregamento distribuído. Este modelo pode ser usado para a determinação dos fatores de acoplamento de estruturas a serem utilizadas em uma análise de Análise Estatística Energética (SEA). Este método é útil devido ao baixo tempo de processamento comparado aos outros métodos existentes e a precisão é consideravelmente boa especialmente nas altas freqüências. Os resultados obtidos são validados comparando-se com o Método de Elementos Finitos. Outros métodos para a determinação da mobilidade de estruturas tipo placa reforçada por vigas também são apresentados neste trabalho. Um destes métodos é o Método de Imagens, que envolve a distribuição de fontes e imagens de vibrações de forma que obedeça as condições de contorno da estrutura. Este método é aplicável principalmente para estruturas de grandes dimensões e alto amortecimento estrutural

Evolution of constrained layer damping using a cellular automaton algorithm

Constrained layer damping (CLD) is a highly effective passive vibration control strategy if optimized adequately. Factors controlling CLD performance are well documented for the flexural modes of beams but not for more complicated mode shapes or structures. The current paper introduces an approach that is suitable for locating CLD on any type of structure. It follows the cellular automaton (CA) principle and relies on the use of finite element models to describe the vibration properties of the structure. The ability of the algorithm to reach the best solution is demonstrated by applying it to the bending and torsion modes of a plate. Configurations that give the most weight-efficient coverage for each type of mode are first obtained by adapting the existing 'optimum length' principle used for treated beams. Next, a CA algorithm is developed, which grows CLD patches one at a time on the surface of the plate according to a simple set of rules. The effectiveness of the algorithm is then assessed by comparing the generated configurations with the known optimum ones

Vibrating soap films: An analog for quantum chaos on billiards

We present an experimental setup based on the normal modes of vibrating soap films which shows quantum features of integrable and chaotic billiards. In particular, we obtain the so-called scars -narrow linear regions with high probability along classical periodic orbits- for the classically chaotic billiards. We show that these scars are also visible at low frequencies. Finally, we suggest some applications of our experimental setup in other related two-dimensional wave phenomena.Comment: 5 pages, 7 figures. Better Postscript figures available on reques

High speed thin plate fatigue crack monitor

A device and method are provided which non-destructively detect crack length and crack geometry in thin metallic plates. A non-contacting vibration apparatus produces resonant vibrations without introducing extraneous noise. Resulting resonant vibration shifts in cracked plates are correlated to known crack length in plates with similar resonant vibration shifts. In addition, acoustic emissions of cracks at resonance frequencies are correlated to acoustic emissions from known crack geometries

Piezo-electromechanical smart materials with distributed arrays of piezoelectric transducers: Current and upcoming applications

This review paper intends to gather and organize a series of works which discuss the possibility of exploiting the mechanical properties of distributed arrays of piezoelectric transducers. The concept can be described as follows: on every structural member one can uniformly distribute an array of piezoelectric transducers whose electric terminals are to be connected to a suitably optimized electric waveguide. If the aim of such a modification is identified to be the suppression of mechanical vibrations then the optimal electric waveguide is identified to be the 'electric analog' of the considered structural member. The obtained electromechanical systems were called PEM (PiezoElectroMechanical) structures. The authors especially focus on the role played by Lagrange methods in the design of these analog circuits and in the study of PEM structures and we suggest some possible research developments in the conception of new devices, in their study and in their technological application. Other potential uses of PEMs, such as Structural Health Monitoring and Energy Harvesting, are described as well. PEM structures can be regarded as a particular kind of smart materials, i.e. materials especially designed and engineered to show a specific andwell-defined response to external excitations: for this reason, the authors try to find connection between PEM beams and plates and some micromorphic materials whose properties as carriers of waves have been studied recently. Finally, this paper aims to establish some links among some concepts which are used in different cultural groups, as smart structure, metamaterial and functional structural modifications, showing how appropriate would be to avoid the use of different names for similar concepts. © 2015 - IOS Press and the authors

A finite element model using a unified formulation for the analysis of viscoelastic sandwich laminates

In this paper we present a layerwise finite element model for the analysis of sandwich laminated plates with a viscoelastic core and laminated anisotropic face layers. The stiffness and mass matrices of the element are obtained by Carrera's Unified Formulation (CUF). The dynamic problem is solved in the frequency domain with viscoelastic frequency-dependent material properties for the core. The dynamic behaviour of the model is compared with solutions found in the literature, including experimental data

Growth of nanostructured zinc oxide on flexible conductive substrate: a review

In this paper, a review on the structural and morphological of nanostructured zinc oxide (ZnO) fabricated on flexible conductive substrate, mainly indium tin oxide coated on polyethylene terephthalate (ITO/PET) via various fabrication method is reported. Besides fabrication method, the effect of fabrication condition such as immersion time of ZnO-ITO/PET via hydrothermal method, concentration of modification material of precursor solution via sol-gel method, value of applied cathodic voltage and value of current densities via electrochemical deposition are also discussed. XRD analysis showed that the growth of ZnO-ITO/PET are preferred on (002) or (101) planes. SEM analysis revealed various type of nanostructured ZnO when prepared by sol-gel, spin coating, HWT and hydrothermal method, highlighting ZnO nanorods as the main morphology of ZnO�ITO/PET. The diameter of ZnO nanorods ranges from 10 nm to 830 nm