No description available.

No description available.

The finite element process is now used almost routinely as a tool of engineering analysis. From early days, a significant effort has been devoted to developing simple, cost effective elements which adequately fulfill accuracy requirements. In this thesis we describe the development and application of one of the simplest elements available for the statics and dynamics of axisymmetric shells . A semi analytic truncated cone stiffness element has been formulated and implemented in a computer code: it has two nodes with five degrees of freedom at each node, circumferential variations in displacement field are described in terms of trigonometric series, transverse shear is accommodated by means of a penalty function and rotary inertia is allowed for. The element has been tested in a variety of applications in the statics and dynamics of axisymmetric shells subjected to a variety of boundary conditions. Good results have been obtained for thin and thick shell cases .

A method is presented for generating shaped command inputs which significantly reduce or eliminate endpoint vibration. Desired system inputs are altered so that the system completes the requested move without residual vibration. A short move time penalty is incurred (on the order of one period of the first mode of vibration). The preshaping technique is robust under system parameter uncertainty and may be applied to both open and closed loop systems. The Draper Laboratory's Space Shuttle Remote Manipulator System simulator (DRS) is used to evaluate the method. Results show a factor of 25 reduction in endpoint residual vibration for typical moves of the DRS.

No description available.

No description available.

The purpose of this work is to present a methodology to predict vibrations of drilllstrings for oil recovery service. The work extends a previous model of the drill collar between two stabilizers in the literature to include drill collar flexibility utilizing a modal coordinate condensed, finite element approach. The stiffness due to the gravitational forces along the drillstring axis is included. The model also includes the nonlinear effects of drillstring-wellbore contact, friction and quadratic damping. Bifurcation diagrams are presented to illustrate the effects of speed, friction at wellbore, stabilizer clearance and drill collar length on chaotic vibration response. Their effects shifts resonance peaks away from the linear natural frequency values and influences the onset speed for chaos. A study is conducted on factors for improving the accuracy of Lyapunov Exponents to predict the presence of chaos. This study considers the length of time to steady state, the number and duration of linearization sub-intervals, the presence of rigid body modes and the number of finite elements and modal coordinates. The Poincare map and frequency spectrum are utilized to confirm the prediction of Lyapunov exponent analysis. The results may be helpful for computing Lyapunov exponents of other types of nonlinear vibrating systems with many degrees of freedom. Vibration response predictions may assist drilling rig operators in changing a variety of controlled parameters to improve operation procedures and/or equipment.

Thèse de doctorat : Acoustique : Villeurbanne, INSA : 2002. / Titre provenant de l'écran-titre. Bibliogr. p.165-169.

Thèse doctorat : Acoustique : INSA LYON : 2003. / Titre provenant de l'écran-titre. Bibliogr. p. 193-204.

Reproduction de : Thèse de doctorat : Acoustique : Le Mans : 2006. / Titre provenant de l'écran-titre. Bibliogr. p. 171-178.