Abstract:
This thesis concerns the control of wave transmission through one-dimensional structural members, such as beams, using tunable inserts. These inserts act to absorb vibrational energy or reflect it away from vibration sensitive regions. Tunable inserts are constructed from a length of tunable fluid filled beam that comprises two elastic layers between which is sandwiched a layer of a tunable fluid such as Electro-Rheological (ER) or Magneto-Rheological (MR) fluid. The tunable insert is inserted into an otherwise uniform to affect transmission there. As the tunable insert forms a discontinuity in the main waveguide then propagating waves incident upon the insert are reflected and transmitted. A wave solution for free vibrations of a tunable fluid filled beam is presented. The wavenumbers in the beam depend on the field applied to the tunable fluid. Expressions are derived for reflection coefficients for waves incident on a boundary of a tunable fluid filled beam. These are also depend on the applied field. Further, expressions are derived for the reflection and transmission coefficients at the junction between an Euler-Bernoulli beam and a tunable beam and these too depend on the applied field. The net transmission through a section of tunable fluid filled beam inserted into an otherwise uniform wave guide is found. It is seen that this can provide isolation. The transmission characteristics depend on the applied field and hence the structure is tunable. Experimental verification of the theoretical results for an ER fluid filled beam insert is given.