1,721,068 research outputs found
Progetto e realizzazione di un dispositivo destinato all'equilibratura attiva dei rotori
No full textInvestigation on the noise emission mechanism of PC keyboards
No full textThe noise emitted from information technology (IT) machines is one of the main annoying sound sources in office environments. Although recent research has aimed at reducing the noise emitted by personal computers (PCs) no major effort has been invested with the study of the characteristic and reduction of the noise emitted by PC keyboards.This paper studies the noise emitted by PC keyboards in order to give indications and provide strategies in order to reduce such noise. The main objectives of the research are: 1) suggesting an experimental repeatable way to measure the noise emitted from a keyboard; 2) characterising keyboard noise; 3) identifying possible sources of noise in order to understand the ways of possible intervention.A test rig has been built in order to generate repeatable tapping of the keys which resembles human tapping. Force, acceleration of the key and noise have been recorded and analysed. Noise emitted by different keys and different keyboards have been also compared.The designed test rig has proved to be a reliable tool to measure and study the noise emitted by IT keyboards. The spectral investigation showed that the maximum noise contribution is due to the impact of the key with the base of the keyboard, and to the free oscillation when the key is released. It is also shown that the keyboard structure contributes to the noise radiation
A novel method for the remote condition assessment of buried pipelines using low-frequency axisymmetric waves
No full text“Mapping the Underworld” is a large multi-disciplinary, multi-university research programme taking place in the UK, which aims to revolutionize the way we undertake streetworks. Within this programme, a number of vibration-based techniques for remotely detecting and locating buried pipes have been developed. Relying either on the direct excitation of a pipe as it comes up to the surface or excitation of the ground in the vicinity of a buried pipe, mapping the ground surface vibration response allows information to be gathered concerning the pipe’s exact position. However, contained within this surface response is often information which could, if utilized appropriately, provide insights into the condition of the pipe as well as its location. Furthermore, critical information regarding the condition of the ground in which a pipe is buried could, in some circumstances, be gleaned. In this paper, how this additional information might be extracted, used and eventually exploited is explored. Providing the basis for work currently being undertaken in a new programme, “Assessing the Underworld”, example results are presented which demonstrate the immense potential of the proposed methods
Dynamics of rotating machinery: analysis, identification and control [Dinamica degli organi rotanti: analisi, identificazione e controllo]
No full textThe performance requirements that modern rotating machines must satisfy have introduced a trend toward higher speeds and more stringent vibration levels. The basic tools to fulfil the reduction of vibrations are the analysis and the identification of rotor systems to design proper rotating elements, and the use of control devices. Supports, which are important rotor elements, are characterized with difficulty. The modulating functions identification method was applied to identify the parameters of hydrodynamic bearings. They were identified, both numerically and experimentally, with encouraging results. Moreover, the design of a magneto-rheological squeeze film damper is presented and discussed. A numerical simulation and an experimental campaign were carried out. Since the damping characteristics can be varied continuously by controlling the magnetic field, it is possible to set the optimum conditions for each operating condition. An automatic semi-active control algorithm was devised by means of fuzzy logic and genetic algorithm. Finally, the vibrations of flexible rotating disks in the presence of dry friction were studied. This is a crucial problem, common to many industrial fields. The results of an experimental investigation, carried out on a commercial paper cutting machine and on a test rig, are presented and discussed. The investigation has shown the influence of some operating and design parameters on the system dynamic behaviour.Sommario: Gli organi rotanti di macchinari moderni sono soggetti a velocit`asempre pi`u elevate e limiti vibratori sempre pi`u ristretti. Gli strumenti per ridurretali vibrazioni sono l’analisi e l’identificazione dei sistemi per un opportuno dimensionamento delle parti rotanti, e l’utilizzo di appropriati smorzatori. Elementi importanti nella dinamica dei rotori ma di difficile caratterizzazione sono i supporti. Il metodo identificativo delle funzioni modulanti `e stato applicato all’identificazione dei coefficienti dinamici di cuscinetti idrodinamici. Sono statiottenuti risultati incoraggianti sia dalle analisi numeriche che sperimentali. Inoltre `e presentato il progetto di uno smorzatore magnetoreologico a “squeezefilm”. Sono stati condotti sia una analisi numerica che una campagna sperimentale. Poich`e il coefficiente smorzante del cuscinetto pu`o essere variato con continuit`a `estato possibile impostare le condizioni di funzionamento ottimo per ogni condizione operativa. Un controllore automatico `e stato progettato con l’uso di logica Fuzzye algoritmi genetici. Infine sono state studiate le vibrazioni di dischi sottili rotanti in presenza diattrito secco, problema molto complesso e molto sentito in vari ambiti industriali. Sono quindi presentati e discussi i risultati di un’indagine sperimentale condotta siasu un macchinario commerciale di una cartiera che su una attrezzatura sperimentale.`Estata mostrata l’influeza di alcuni parametri sull’insorgere delle vibrazioni
Novel methods for the condition assessment of buried pipelines using low-frequency axisymmetric waves
No full textZero Leakage 2050, the UK’s strategic research initiative for the water industry: acoustic and vibrational methods for acoustic leak detection
No full textShape of a spectral excitation matrix for a linear road/tyre interaction numerical analysis
No full textTyre/road interaction is recognised as the main source of interior and exteriornoise in vehicles at velocities over 40 km/h. Previously, the authors proposeda linear stochastic approach to predict the tyre vibrations due to the road/tyreinteraction. A mechanical model of the tyre was connected to the road througha series of parallel springs (Winkler model) assumed to be in contact with theroad at all the time. Such a linear model is only strictly valid for smooth roadand soft tyres. In this paper, the range of validity of the linearity assumptionis investigated and, a modified shape of the excitation matrix, that takes intoaccount the contact nonlinearity, is proposed. The investigation is based on a2D numerical nonlinear model of the tyre/road contact so that the displacementsof the contact springs can be used to evaluate the nonlinear excitationmatrix. An approximated nonlinear excitation spectrum has been proposedand his validity has been checked on a 2D linear tyre model
Dynamic response of a nonlinear parametrically excited system subject to harmonic base excitation
No full textA Nonlinear Parametrically Excited (NPE) system subjected to a harmonic base excitation is presented. Parametric amplification, which is the process of amplifying the system’s response with a parametric excitation, has been observed in mechanical and electrical systems. This paper includes an introduction to the equation of motion of interest, a brief analysis of the equations nonlinear response, and numerical results. The present work describes the effect of cubic stiffness nonlinearity, cubic parametric nonlinearity, and the relative phase between the base excitation and parametric excitation under parametric amplification. The nonlinearities investigated in this paper are generated by an electromagnetic system. These nonlinearities were found both experimentally and analytically in previous work [1]; however, their effect on a base excited NPE is demonstrated in the scope of this paper. This work has application in parametric amplification for systems, which are affected by strong stiffness nonlinearities and excited by harmonic motion. A careful selection of system parameters, such as relative phase and cubic parametric nonlinearity can result in significant parametric amplification, and prevent the jump from upper stable solutions to the lower stable solutions
A unified approach to optimal conditions of power harvesting using electromagnetic and piezoelectric transducers
No full textPower harvesting systems generate electric power from mechanical vibration using electromechanical transducers. To assess the practical performance of these systems, it is important to be able to estimate the maximum power that could be harvested from a specific structure and to derive the optimal conditions for the harvesting. We introduce a two-port network model which can fully describe the electromechanical coupled dynamics of the transducer, including the interaction between the structure and the electrical load in a unified manner. Electromagnetic and piezoelectric transducers are then considered as special cases of this general treatment. The power harvested by both types of transducer on a simply supported beam is derived and the optimal matching conditions and the maximum harvested power are obtained theoretically. In this numerical example, a piezoelectric transducer would have higher potential than an electromagnetic device of equal mass for the harvesting, but only when the transducer parameters are tuned optimally
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