Mechanical Engineering
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Item INVESTIGATIONS INTO THE EFFECTS OF SECONDARY-FREQUENCY ADDITIONS ON SLENDER ROTATING STRUCTURES(2014) Meyer, Gregory William; Balachandran, Balakumar; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Drill strings are slender structures used extensively in drilling and mining operations. In this thesis work, secondary-frequency input additions to the drive speed input are considered and the resulting influence on system dynamics is examined. Experimental studies are conducted with a laboratory scale drill-string arrangement, and high-frequency and low-frequency additions are considered for cases in which the drive speed frequency is close to either a bending mode or torsion mode natural frequency. It is found that carefully chosen secondary-frequency additions can be used to attenuate undesirable system dynamics, especially, for rotary systems. To complement the experiments, numerical studies are conducted with a reduced-order model of the drill-string system. The obtained numerical results are found to be in reasonable agreement with the experimental results. Preliminary numerical results obtained in the presence of rotor-stator interactions are also included. In addition, areas in which the model construction will need further development are also discussed. The findings of this work can be useful for considering secondary-frequency addition based schemes for controlling bending and torsional motions of drill-string systems.Item Traveling Wave Thermoacoustic-Piezoelectric Energy Harvester: Theory and Experiment(2011) Roshwalb, Andrew Zvi; Baz, Amr; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This thesis presents a theoretical and experimental investigation of a piezoelec- tric energy harvester coupled to a traveling wave thermoacoustic engine (TWTAE). By simplifying the engine using a lumped-parameter model, the performance pa- rameters such as pressure oscillation frequency and amplitude, regenerator hot end temperature, and piezoelectric output voltage are predicted. Also, an axisymmetric finite element model of the piezoelectric energy harvester is developed, resulting in a two-part reduced-order model of the electromechanical impedance of the harvester. The predictions of the finite element model are compared with those of ANSYS finite element analysis and validated experimentally. The two-part model is utilized in a numerical analysis of the TWTAE using DeltaEC (Design Environment for Low- Amplitude ThermoAcoustic Energy Conversion). Results from pressure transducers and the piezoelectric disc attached to a physical realization of the TWTAE are com- pared with theoretical predictions of the lumped-parameter models and DeltaEC analysis. The developed theoretical techniques and experimental validation provide invaluable tools for effective design of the thermoacoustic-piezoelectric harvester.