R. Dufour

Dynamic Behavior of a Drill-String: Experimental Investigation of Lateral Instabilities

This paper focuses on laboratory tests concerned with the lateral behavior of a rod representative of part of drill-string in the area of rotary oil drilling. The original experimental set-up takes into account the curvature of the rod, mud, stabilizers and rotation speed. The lateral behavior of the drill-string subjected to the axial excitations of the bit is governed by time varying parameter equations due to torsionlateral and longitudinal-lateral couplings. The experimental results highlight the different kinds of lateral instabilities and they are compared either with existing experimental, or theoretical results. The experimental investigation described in this paper is included in a wide ranging study which also involves theory and the development ofa computer code, both briefly presented here.

Optimization procedure for identifying constitutive properties of high speed induction motor

In order to predict the rotordynamics of a high speed induction motor in bending, an optimization procedure is proposed for identifying the constitutive properties especially those of the magnetic core made of lamination stack, tie rods, short-circuiting rods, etc. Modal parameters predicted by a finite element model based mainly on beam elements, and measured on an induction motor are included in modal error functions contained in a functional. The minimization of this functional by using the Levenberg-Marquardt algorithm permits extracting the constitutive properties along the magnetic core.

Metric Damping of MDOF Systems in High Transient Motion

This paper deals with damping due to transient motion in the case of multi-degree-of-freedom (MDOF) system. The main aim of this research is to make the method presented by the authors in a previous paper available for MDOF systems. An method based on relativity concepts is developed in order to identify and evaluate a metric damping due to time-varying forcing frequency. An additional dimension for each degree of freedom (DOF) is introduced. The variational problem of the metric of a Riemannian space gives the geodesic equations, i.e., equations of motion that, after time integration carried out with several types of numerical schemes, permit one to predict the forced transient response of a 3-DOF system. The proposed metric approach makes the experimental results correspond with the simulated results.

A Self-Deployment Hexapod Model for a Space Application

This paper presents an efficient simulation tool for predicting a self deployment of an on-board deployable hexapod based on the release of stored strain energies provided by six tape-spring actuators. Six restoring force models describe their hysteretic behavior. A formulation of a direct dynamic model developed with a Lagrangian approach is achieved. Furthermore, tensor representation is used to condense and simplify the calculation of Lagrangian partial derivatives. Results are compared with a numerical model that performs the recursive Newton-Euler technique. Finally, the impact of the excitation of the base on the deployment performances is evaluated taking advantage of the proposed restoring force models.Copyright

Damping in High Transient Motion

An original method for evaluating the dissipative effect in SDOF systems due to the transient phenomenon was presented in a previous article. This method based on the use of an additional dimension, and the general relativity concept was validated experimentally. However, the function of the forcing frequency required to establish the metric of the space was identified using an experimental transfer function. In the present paper the main objective is to solve the geodesic equations in order to avoid the experimental identification of the function contained in the metric. The variational problem of the metric of Riemannian space gives three geodesic equations for the SDOF system studied. Solving these equations gives in particular the transient forced response which, when compared with experimental results, permits validating the proposed method and therefore proving that the transient motion bends the space-time.