Abstract

Dynamic vibration absorbers and dampers are used to reduce the vibration responses of mechanical systems. A dynamic vibration absorber reduces vibrations of a primary system over a desired frequency range by absorbing the energy through responding with opposite phase to that of the force acting on the primary system. A damper, on the other hand, is a device used for reducing the magnitude of a shock or vibration by energy dissipation methods. The latter is extensively used in automotive engines to reduce torsional oscillations and in aircraft landing gears to damp out shimmy oscillations. This thesis aims to study and understand an optimally tuned viscous torsional vibration damper which is a combination of a dynamic vibration absorber and damper. The primary system whose vibration is to be suppressed, along with the optimally tuned viscous torsional vibration damper, will form a two-degree-of-freedom system which will be studied for its dynamic behaviour. The analytical model includes parameters such as primary inertia, damping and stiffness and secondary inertia, damping and stiffness. Numerical determination of optimum damping and stiffness for a secondary system is carried out and simulated results are presented and discussed. Validation of some aspects of the analytical studies is carried out with experimental investigation for the optimally tuned viscous torsional vibration damper and viscous damper. The test results of the two damping devices and the analytical investigations are compared. In addition, the study is extended, applying the optimally tuned viscous torsional vibration damper to a seven-degree-of-freedom torsional system namely to a four-stroke six-in-line cylinder internal combustion engine. This numerical study compares the engine response with and without damping. For both cases same excitation torque per cylinder was applied. The optimally tuned viscous damper reduces the vibrations.