1,721,055 research outputs found
Non-linear modelling of rotor dynamic systems with squeeze film dampers: an efficient integrated approach
No full textSqueeze film dampers used in rotor assemblies such as aero-engines introduce non-linear damping forces into an otherwise linear rotor dynamic system. The steady state periodic response of such rotor dynamic systems to rotating out-of-balance excitation can be efficiently determined by using periodic solution techniques. Such techniques are essentially faster than time marching techniques. However, the computed periodic solutions need to be tested for stability and recourse to time marching is necessary if no periodic attractor exists. Hence, an efficient integrated approach, as presented in this paper, is necessary. Various techniques have been put forward in order to determine the periodic solutions, each with its own advantages and disadvantages. In this paper, a receptance harmonic balance method is proposed for such a purpose. In this method, the receptance functions of the rotating linear part of the system are used in the non-linear analysis of the complete system. The advantages of this method over current periodic solution techniques are two-fold: it results in a compact model, and the receptance formulation gives the designer the widest possible choice of modelling techniques for the linear part. Stability of these periodic solutions is efficiently tested by applying Floquet Theory to the modal equations of the system and time marching carried out on these equations, when necessary. The application of this integrated approach is illustrated with simulations and an experiment on a test rig. Excellent correlation was achieved between the periodic solution approach and time marching. Good correlation was also achieved with the experiment
The prediction of the non-linear dynamics of a squeeze-film damped aero-engine rotor housed in a flexible support structure
No full textThis paper shows how the non-linear dynamics of a rotor running in unsupported squeeze-film dampers (SFDs) housed in a flexible support structure can be efficiently modelled using an integrated analytical technique and a standard model for the SFDs. A test rig that reproduces, to a limited extent, the essential dynamic features of an aero-engine gas turbine is considered and the aim of the analysis is to assess the ability to predict and interpret the observed non-linear vibrations as indicated by amplitude–speed plots, frequency spectra, orbital motion plots and Poincaré maps. The solution process starts with the application of a fast harmonic balance method that uses receptance functions to determine periodic solutions. A modal-based approach is then used for the analysis of the stability and bifurcation of these solutions, as well as the analysis of aperiodic motion. The simulation correctly predicts the overall performance, including subharmonic motion, combination frequencies and subcritical superharmonic resonances
Symbiotic fungi associated with Ips acuminatus (Coleoptera Curculionidae) in the Italian Alps.
No full textTesting phenotypic trade-offs in the chemical defence strategy of Scots pine under growth-limiting field conditions.
No full textInduced responses of Pinus sylvestris to fungi associated with Ips acuminatus (Coleoptera Scolytinae).
No full textRisposte del pino silvestre alla colonizzazione da parte di Ips acuminatus (Coleoptera, Curculionidae, Scolytinae) e funghi associati.
No full textModelling the non-linear dynamics of an aero-engine low pressure rotor mounted on squeeze film bearings
No full textThe design of an adaptive tuned vibration absorber with a variable shape stiffness element
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