Motivation

The dynamics of slender continua has been under intense investigation for a long time in mechanical engineering. As a result of the distinctively small diameter-to-length ratio, such structures are normally very sensitive to torsional vibrations. Examples of such structures are long bridges, driveshafts of large container ships or drill-strings. Due to the complexity of external forces (e. g. nonlinear friction, impulse-like breakaway phenomena from the borehole wall), especially drill-strings exhibit a broad variety of dynamic behavior, including steady-state behavior, but also self-excited stick-slip limit cycles. In general, controlling such structures under the influence of unknown, time varying disturbances is very challenging.

Approach

The system behaviour of a drill-string is simulated numerically with the use of different models. Additionally, two small-scale setups are available for experimental testing. In order to actively damp torsional vibrations, a wave-based control approach is used, which has been developed at the Institute of Mechanics and Ocean Engineering. It is implemented in a theoretical model at the computer as well as in the experimental setups and is continually improved. The effectiveness of this technology and its robustness against discontinuities along a real drill-string are of particular interest. These discontinuities arise from the screw connections of the individual drill-pipes and manifest themselves in joint damping as well as mass and stiffness changes. Besides that, the control approach is compared to other existing technologies.

Student Theses

This topic covers a wide range of mechanics and control theory and offers much space for student works. Please contact us, if you are interested to contribute to this topic within the scope of a project work or a Bachelor-/Master-/Diplomathesis.