1,721,065 research outputs found
Modal parameters estimation in the Z-domain
Full text linkThis paper aims to explain in a clear, plain and detailed way a modal parameter estimation method in the frequency domain, or similarly in the Z-domain, valid for multi degrees-of-freedom systems. The technique is based on the rational fraction polynomials (RFP) representation of the frequency-response function (FRF) of a single input single output (SISO) system but is simply extended to multi input multi output (MIMO) and output only problems. A least-squares approach is adopted to take into account the information of all the FRFs but, when large data sets are used, the solution of the resulting system of algebraic linear equations can be a long and difficult task. A procedure to drastically reduce the problem dimensions is then adopted and fully explained; some practical hints are also given in order to achieve well-conditioned matrices. The method is validated through numerical and experimental examples
Rayleigh-Ritz analysis of sandwich beams
No full textThe paper discusses the possibility of predicting the dynamic behaviour, in terms of modal frequencies and loss factors, of sandwichbeams with a constrained viscoelastic layer configuration. The problem is approached by the Rayleigh-Ritz method so that virtually any boundary condition can be dealt with by applying a single procedure. Simple polynomials are used as admissible functions and evidence of their good performance is given. The method is also suitable for the analysis of those arrangements where not only the viscoelastic material but also the external layers of the sandwich are damped
A vibration absorber for motorcycle handles
Full text linkThis paper describes the application of a vibration absorber to ameliorate the comfort of motorcycle handles. The concept of dynamical absorber is briefly summarised and a frequency response function is expressed as the ratio of vibration amplitudes (transmissibility).
Some practical hints on the tuning strategy are also suggested in order to correctly define the absorber and then achieve the most effective vibration reduction. A specifically designed item is presented, with the peculiar characteristic of taking advantage of the damping properties of viscoelastic material undergoing shear deformations. An experimental verification of the good performances of the absorber is eventually given on the basis of both a modal analysis of a motorbike and the testing of its handle on an electrodynamical shaker
Identification of linear mechanical systems by deconvolution techniques
No full textThis paper describes how the impulse response function of a linear and time invariant dynamic system can be computed numerically by deconvolution techniques, starting from its input and output time histories. The integral equation governing the problem is transformed into a severely ill-conditioned set of linear equations whose approximate solution is obtained through regularisation methods. A proposal, with the aim of taking into account the possible non-null initial conditions of the physical system, is suggested together with an algorithm that allows the definition of long impulse responses with limited computing effort. The implementation developed can deal with single input single output, single input multiple output and multiple input multiple output systems and has been tested both numerically and on two simple real structures. The advantages and disadvantages of these time domain techniques are discussed in comparison with the widely used frequency methods
Progress in pyroshock simulation for qualification tests: A systematic literature review
Full text linkpacecraft and their onboard equipment are subjected to significant dynamic loads, particularly when the activation of pyrotechnic devices induces intense high-frequency shocks, known as pyroshocks, which propagate throughout the entire structure and can cause critical damages. Qualification tests are needed to ensure aerospace equipment can withstand impulsive loads and therefore test rigs and simulation models are designed to replicate real-world pyroshocks while pursuing repeatability, accuracy, and safety.
This paper systematically categorizes and analyzes existing research papers on pyroshock simulation techniques, examining both experimental and numerical approaches. Scientific databases were queried but only a selection of the most relevant papers is presented and labeled, according the publication year, the purpose, the physical domain, the numerical method, the kind of fixture, and the excitation method. Additionally, a shorter review on contact mechanics is included to offer complementary insights, considering its relevance to pyroshock simulations
Acustica - Fondamenti e applicazioni
No full textAcustica, curato da Renato Spagnolo, anche grazie al contributo dei più apprezzati esperti della disciplina è la più completa ed esaustiva opera mai pubblicata sull'acustica. Non solo, tutto il libro è ricco di puntuali e sistematici richiami alle norme tecniche, alle prescrizioni di legge, alle modalità e prassi operative della specifica situazione italiana. Per questo è uno strumento irrinunciabile per i professionisti, oltreché per i ricercatori, i docenti e gli studenti. Guardando all'autorevole fonte Physics and Astronomy Classification Scheme (PACS) dell'American Institute of Physics (AIP), l'acustica risulta ordinata in dodici aree, che vanno, per citare solo le più note, dall'acustica generale lineare a quella non lineare, all'acustica musicale e alla bioacustica, passando per l'acustica subacquea, gli ultrasuoni e i loro effetti fisici e biologici, le misurazioni acustiche e la strumentazione, l'acustica strutturale e le vibrazioni, gli effetti e il controllo del rumore, l'acustica architettonica, la psicoacustica. In questo libro tutti questi campi sono esplorati e analizzati approfonditamente: dalla propagazione lineare e non lineare delle onde fino ai temi più specialistici come le tecniche di misura e di analisi numerica del segnale, dall'acustica subacquea alla bioacustica, dalla funzione uditiva alla voce, fino alle applicazioni degli ultrasuoni in campo medico e alle complesse problematiche del rumore e delle vibrazioni nei luoghi di lavoro e di vit
An Experimental Rig For Damage Detection Of Rolling Bearings
No full textThis paper describes the design of a rig devoted to testing rolling bearings. In order to control the signal-to-noise ratio of the measures, a potentially very silent test rig has been designed and assembled, with the possibility of simply changing the bearing under investigation as well as its load level and rotating speed. Acceleration data have then been examined by means of envelope, wavelet transform and cyclostationarity analyses, showing that the testing machine fulfils its task
Identification of nonlinear vibrating structures by polynomial expansion in the z-domain
Full text linkA new method in the frequency domain for the identification of nonlinear vibrating structures is described, by adopting the perspective of nonlinearities as internal feedback forces. The technique is based on a polynomial expansion representation of the frequency response function of the underlying linear system, relying on a z-domain formulation. A least squares approach is adopted to take into account the information of all the frequency response functions but, when large data sets are used, the solution of the resulting system of algebraic linear equations can be a difficult task. A procedure to drastically reduce the matrix dimensions and consequently the computational cost - which largely depends on the number of spectral lines - is adopted, leading to a compact and well conditioned problem. The robustness and numerical performances of the method are demonstrated by its implementation on simulated data from single and two degree of freedom systems with typical nonlinear characteristics
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