1,721,268 research outputs found
JONES R.W., International trade : essays in theory
No full textMucchielli Jean-Louis. JONES R.W., International trade : essays in theory. In: Revue d'économie industrielle, vol. 14, 4e trimestre 1980. Vers une nouvelle division internationale du travail. p. 246
Wave propagation, reflection and transmission in tunable fluid-filled beams
No full textThis paper concerns wave motion in tunable fluid-filled beams. The beams comprise two elastic faceplates with a central core of tunable fluid such as electro-rheological or magneto-rheological fluid. Free wave propagation is considered and three wave modes are seen to exist. The corresponding wavenumbers depend on the viscoelastic properties of the tunable fluid, which in turn depend on the field applied to the fluid. Consequently, the wavenumbers can be controlled. A systematic technique for describing wave transmission and reflection in one-dimensional waveguides is described. This involves transformations between wave amplitudes and waveguide displacements and internal forces. Expressions are derived which describe wave reflection at a boundary, reflection and transmission at a change in section and reflection and transmission at an attachment. Numerical results are presented for electro-rheological fluid-filled beams and the junction between such a beam and an Euler–Bernoulli beam. The reflection and transmission coefficients also depend on the applied field so that the transmission characteristics are tunable
A tubular dielectric elastomer actuator: fabrication, characterisation and active vibration isolation
No full text
Wave transmission through structural inserts
No full textThe transmission of waves through two discontinuities in a one-dimensional waveguide system is considered. Attention is focused on transmission through a structural insert, which is defined here to be a waveguide segment which is inserted into an otherwise continuous structural member with different properties. A general expression for the net transmission through the insert is found. It has bandpass/stop characteristics and its frequency average is somewhat greater than that normally assumed due to the coherent interaction of the waves in the insert. The particular case is then considered where the insert comprises a three-layer composite beam inserted in a thin beam which vibrates in bending. The composite beam comprises two elastic faceplates and a core filled with a tunable electro- or magneto-rheological fluid. The net transmission and the stop bands depend on the properties of the insert. Since these properties are tunable by adjusting the field to which the tunable fluid is exposed, then so too are the transmission characteristics of the insert
Comparison of convergence characteristics of adaptive IIR and FIR filters for active noise control in a duct
No full textThere are perceived drawbacks to using adaptive IIR filters, as opposed to adaptive FIR filters, for active noise control (ANC). These include stability issues, the possible convergence of estimated parameters to biased and/or local minimum solutions and relatively slow rate of convergence. Stability issues can generally be resolved easily using well-established methods. In this Technical Note convergence rates are compared with particular reference to the active control of noise in a duct, for which the dynamics of the cancellation path are important. The characteristics of this application of ANC set it apart from usual signal processing applications of adaptive IIR filters and this has implications for the convergence properties. Various control approaches are considered: IIR least mean squares (IIR-LMS), IIR recursive least squares (IIR-RLS) with FASPIS (Fast Algorithm Secondary Path Integration Scheme) and FIR-LMS. Numerical examples are presented. It is seen that the cancellation path dynamics generally have the effect of changing the performance surface of the estimated IIR filter from bimodal to unimodal, which has consequences for improving the convergence rate of adaptive IIR filters. It is also seen that IIR-RLS has a comparable rate of convergence to FIR-LMS, with the steady-state performance being as good or better
Adaptive-passive control of vibration transmission in beams using electro/magnetorheological fluid filled inserts
No full textA method for the control of the transmission of bending vibrations in beams is described. A composite beam (a structural insert) is inserted into a part of the structure to affect the transmission there. The insert comprises two elastic face plates and a central core of tunable fluid such as an electrorheological (ER) or magnetorheological (MR) fluid. By adjusting the applied electric or magnetic field the theological properties of the fluid can be controlled and so can the vibration transmission properties of the insert. Theoretical results concerning the transmission of vibrations in beam-like structures are reviewed. Numerical results are presented for the transmission through ER and MR fluid filled inserts, with experimental results for an ER case. The transmission is seen to show a pass/stopband structure with the stopbands being tunabl
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