Thesis (Ph. D.)--University of Wisconsin--Madison, 1983. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 150-164).

M.Ing. / In the drilling process, the majority of hole inaccuracies can be corrected with the use of secondary hole operations. Hole location errors cannot be corrected as their magnitude is determined at the beginning of penetration of the drill point into the material. This thesis investigates the influence of the drill bending stiffness on the hole location error when drilling with ordinary twist drills. Infrared sensors were developed for the drill point location measurements, the initial wandering of the drill and the final hole location error. Also investigations were made into the on-line monitoring of the drilling process using acoustic emission in the audio range. The acoustic signal was transformed to the frequency domain and related to the torque and the thrust magnitudes. The relationships in the acoustic emission, torque and thrust and chip formation between drilling low carbon steel and aluminium were determined.

Stiffness identification of an impacted constraint is the main issue discussed in this thesis. Primarily, a change of stability (bifurcation) is used to determine the dynamical stiffness of an impacted beam for a piecewise-linear impact oscillator. Detailed one- and two-parameter bifurcation analyses of this impacting system are carried out by means of experiments and numerical methods. Particularly, the two-parameter numerical continuation of the obtained codimension-one bifurcation (period-doubling bifurcation, or fold bifurcation) indicates a strong monotonic correlation between the stiffness of the impacted beam and the frequency at which this bifurcation appears. In addition to the bifurcation techniques, another method for stiffness identification is analysis of impact duration. To accurately detect impact durations from numerical or experimental signals, nonlinear time series methods are utilised. Two impacting systems, including the piecewise-linear impact oscillator and a drillbit-rock vibro-impact system, are studied to demonstrate this proposed method. For either system, the impact duration is relatively constant when the response of oscillator is a period-one one-impact motion, and it is approximated as a half of the natural period of the oscillator-constraint system. When the mass of oscillator is constant, for an impacted constraint with a certain stiffness, the higher the stiffness, the lower the impact duration. This monotonic correlation provides another mechanism to estimate the stiffness of the impacted constraint. Based on the developed two dynamical methods for stiffness identification, a control algorithm for parameter adjustment of the axial vibration for rotary-percussive drilling applications is designed. This control algorithm aims to maintain the optimal drilling state under the varying formations. By this way, the efficiency of rotary-percussive drilling is expected to be promoted.

In laser percussion drilling, a series of laser pulses with specified energies and durations irradiate the workpiece surface to gradually heat, melt, and vaporise material until a hole with-required depth-and-diameter-is-achieved. Despite being the quickest technique for producing small diameter holes, laser percussion drilling regularly suffers from difficulties in controlling the hole quality such as hole circularity, hole taper and recast layer. Therefore, in order to produce holes to a specific requirement at minimum cost and time, it is crucial to fully understand the effects of each parameter on hole quality. In this research, a new mathematical model for multiple pulsed laser drilling is developed to predict the hole depth, hole taper, and recast layer thickness, and to investigate the effects of key laser parameters on hole dimensions. The new model accounts for recoil pressure, melt ejection, O2 assist gas effects, as well as solidification of the melt. The development of-the new model is divided into two stages; pulse on stage where interaction between laser beam-material takes place, and pulse off stage where solidification of the melt is modelled. Governing equations are established from heat conduction, energy, and mass equations at the solid-liquid and liquid-vapour interfaces with appropriate boundary and initial conditions. Analytical solutions are derived by using Mathematica 7 software as a tool to solve the system of non-linear equations. To validate the model, experimental work has been conducted and the measured results are compared to those calculated from the model. It is shown that the new model gives a good prediction of the hole depth and acceptable prediction of the recast layer thickness. Laser peak power and pulse width are shown to have a significant influence over the drilled hole quality whereas the changes due to pulse frequency are less pronounced.

This thesis has been motivated by the need to construct reliable, experimentally callibrated models of the drill-string assembly, that capture important phenomena associated with the drilling process, such as torsional oscillations, stick-slip and whirling. This can be achieved using a continuous finite element model, as well as low-dimensional torsional pendulum models in limited cases. The importance of this work lies in the fact, that the experimental rig utilizes real industrial drillbits and rock samples, which after careful identification of TOB speed curves, allows to use an equivalent friction model to accommodate for both frictional and cutting components of the bit-rock interactions. As a first step, a preliminary calibration of the FE model for a straight configuration of the drill-string is carried out, that allows to utilize the low-dimensional model to replicate behaviour of the system. In both of these cases, the agreement between experiments and modelling is achieved. Based on these preliminary studies, it is possible to verify the model in a prebuckled drill-string configuration, for which case a qualitative as well as quantitative agreement with the experiment is obtained. This allows to identify regions where the most dangerous phenomenon of stick-slip is present in parameter space of WOB and top angular speed. Next, the analysis is focused on the whirling phenomenon and calibration of the reduced order rotor model to replicate the motion of the BHA in the bore-hole. A qualitative agreement with the experiments is obtained. An interesting phenomenon of co-existing forward and backward periodic whirling solutions are observed both experimentally and numerically. The influence of the initial conditions and the friction between the BHA and the borehole are investigated, what revealed that there is a threshold value of friction coefficient for which the whirling direction changes from forward to backward.

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