Articles you may be interested inFourier transform infrared and tunable diode laser spectra of the 13C12CH6 ν12 torsion-vibration-rotation band: Frequencies, intensities, and barriers to internal rotation Diode laser spectra of most of the Q branches of the v 9 band of ethane from R Q s j Q 15 have been recorded. The Q branches RQo_RQ 4 were deconvoluted to yield an effective resolution of (0.5-1.0) X IO~J cm~ 1 FWHM. Torsional spliuings were observed for most lines. In contrast to predictions based on first order theory, the spliUings which range from (2-53) X 1O~3 cm ~ 1, have a marked J and K dependence. A second order theory of torsion-vibration-rotation interaction between v 9 and 3v 4 is developed, which fits the spliuings with an rms error of 0.

A novel idea to control the rotary speed incorporates the torque signal, in addition to the speed signal, to produce a more uniform motion of the drillstring. This produce a more uniform motion of the drillstring. This method is easily incorporated into existing equipment used to control the rotary speed. We have tested this control system on a full-scale research drilling rig and have demonstrated that such a system can stop slip-stick motion and prevent it from starting. As an additional benefit, such a control system leads to smoother rotation of the bit which can lead to a reduction in axial and lateral vibrations of the drillstring. In this paper we present the theoretical basis behind such a system and give an example of the experimental results. Introduction Torsional drillstring vibrations, in particular slip-stick oscillations, have been studied intensively in the last few years. Frequency analysis of the driving torque has shown that a large number of peaks in the torque spectrum can be identified as torsional drillstring resonances. The sharpness of the resonance features indicates that there is little damping of such vibrations. Slip-stick motion of the bottom hole assembly can be regarded as extreme, self-sustained oscillations of the lowest torsional mode, called the pendulum mode. Such a motion is characterized by finite time intervals during which the bit is non-rotating and the drillpipe section is twisted by the rotary table. When the drillstring torque reaches a certain level (determined by the static friction resistance of the bottom hole assembly), the bottom hole assembly breaks free and speeds up to more than twice the nominal speed before it slows down and again comes to a complete stop. It is obvious that such motion represents a large cyclic stress in the drillpipe that can lead to fatigue problems. In addition, the high bit speed level in the problems. In addition, the high bit speed level in the slip phase can induce severe axial and lateral vibrations in the bottom hole assembly which can be damaging to the connections. Finally, it is likely that drilling with slip-stick motion leads to excessive bit wear and also a reduction in the penetration rate. It is therefore desirable to cure, or at least to reduce, the torsional vibrations in the drillstring. P. 277

This paper deals with torsional oscillations caused by slip/stick motion of the drill-collar section. This phenomenon is associated with a large-amplitude, saw-tooth-like variation in the applied torque. "Slip/stick motion" refers to the belief that the amplitude of the torsional oscillations becomes so large that the drill-collar section periodically comes to a complete stop and does not come free until enough torque is built up in the drillstring to overcome the static friction.A mathematical model of slip/stick motion is presented. This model includes parameters describing downhole friction effects and a simplified description of the drillstring. The effects of damping, finite rotary-table inertia, and the rotary-speed control system are discussed. Theoretical predictions are compared with measured torque signals recorded during field drilling.This kind of drilling performance is likely to be less effective than normal drilling and may also lead to fatigue problems. This paper discusses ways to avoid severe torsional oscillations by using a more sophisticated feedback system to control the rotary speed.

Several groups have reported emission from the v 9 band of ethane at 12 ¡im in the spectra of Jupiter, Saturn, Neptune, and Titan. This paper reports the results of a laboratory study of v 9 using both high-resolution Fourier transform and diode laser absorption spectroscopy. Approximately 2000 transitions in this band have been subjected to an analysis that includes the normal rovibrational terms as well as the higher order effects of /-doubling, /-resonance, internal rotation, and a Coriolis resonance with the 3v 4 state. A model for this band capable of reproducing observed v 9 features to better than 0.001 cm" 1 is presented. High-precision values of the primary ground-state constants have also been determined: B 0 = 0-6630279(24) cm" 1 , Do 7 = 1.0324(23) x 10" 6 cm" 1 and D 0 JK = 2.651(88) x 10" 6 cm" 1 . A list of v 9 transitions occurring near 14 C02 laser lines that are good candidates for laser heterodyne searches has been compiled. An atlas is available from the authors that includes (1) plots of the observed and simulated v 9 spectra between 750 and 900 cm" 1 and (2) a list of over 8500 calculated transitions and intensities. Subject headings: line identifications -laboratory spectra -molecular processes 1984ApJ. . .280 . . 92ID 922DAUNT ET AL. Vol. 280

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