Exponential Stabilization of a Class of Nonlinear Neutral Type Time-Delay Systems, an Oilwell Drilling Model Example

International audienceThis paper deals with exponential stabilization of the class of nonlinear neutral type time-delay systems that can be transformed into a multi-model system. The approach is based on Lyapunov-Krasovskii techniques and uses a descriptor representation. The exponential stability properties are proved using an appropriate change of variables associated with a polytopic representation. The results are given in terms of LMIs. As an application example, we determine an e ective stabilizing controller for an oilwell drilling system

Applied Radiation and Isotopes Monte Carlo Verification of Output Correction Factors for a TrueBeam STx linac

The recent publication of the new code of practice IEAA/AAPM TRS-483 introduces the use of output correction factors to correct the changes in detector response in relative dosimetry of small photon beams. In TRS-483, average correction factors are reported for several detectors at 6 and 10 MV with and without attening. These correction factors were determined by Monte Carlo simulation or experimental measurements using several linacs of di erent brands and vendors. The goal of this work was to validate the output correction factors reported in TRS-483 for a 6 MV (with and without attening lter) of a TrueBeam STx® linac with Monte Carlo simulation for four radiation detectors employed in the dosimetry of small photon beams and whose output correction factors were determined using di erent radiation source than TrueBeam STx®: PTW®31010, PTW®31016, IBA®CC-01, and IBA®SFD. The results show that Monte Carlo calculated output factors, and those reported in the code of practice TRS-483 fully agree within 1%. The use of generic correction factors for a TrueBeam STx® and the detectors studied in this work is adequate for small dosimetry static beams within the uncertainties of Monte Carlo calculations and output correction factors reported in TRS-483. Key words: TRS-483, Monte Carlo simulation, output correction factors, detector model, Phase Space File, Latent Varianc

Bounds on the response of a drilling pipe model

The drill pipe model described by the wave equation with boundary conditions is reduced through the d'Alembert transformation to a difference equation model. Assuming that the boundary condition at the bottom is perturbed by bounded additive noise, an ultimate bound for the velocity at the bottom of the pipe is obtained. The proposal of a Lyapunov functional for the distributed model allows to provide an ultimate bound for a measure of the distributed variables describing the system in terms of linear matrix inequality conditions. The two approaches are compared through an illustrative example

Exponential Stabilization of a Class of Nonlinear Neutral Type Time-Delay Systems, an Oilwell Drilling Model Example

International audienceThis paper deals with exponential stabilization of the class of nonlinear neutral type time-delay systems that can be transformed into a multi-model system. The approach is based on Lyapunov-Krasovskii techniques and uses a descriptor representation. The exponential stability properties are proved using an appropriate change of variables associated with a polytopic representation. The results are given in terms of LMIs. As an application example, we determine an e ective stabilizing controller for an oilwell drilling system

The control of drilling vibrations: A coupled PDE-ODE modeling approach

The main purpose of this contribution is the control of both torsional and axial vibrations occurring along a rotary oilwell drilling system. The model considered consists of a wave equation coupled to an ordinary differential equation (ODE) through a nonlinear function describing the rock-bit interaction. We propose a systematic method to design feedback controllers guaranteeing ultimate boundedness of the system trajectories and leading consequently to the suppression of harmful dynamics. The proposal of a Lyapunov-Krasovskii functional provides stability conditions stated in terms of the solution of a set of linear and bilinear matrix inequalities (LMIs, BMIs). Numerical simulations illustrate the efficiency of the obtained control laws

Suppressing Axial-Torsional Coupled Vibrations in Drillstrings

International audienceIn drilling operation, a wide variety of oscillations causing failures often arise. Torsional vibrations (stick-slip) are originated by the cutting device (bit) motion, these vibrations in turn excite axial oscillations causing a phenomenon known as bit-bouncing. This paper addresses two important challenges: the modeling of the coupled axial and torsional dynamics in a vertical oilwell drilling system and the design of an effective controller to reduce undesirable behaviors. Through the D'Alembert transformation, the distributed parameter model of the drillstring is reduced to a neutral-type time-delay equation which effectively describes the oscillatory behavior of the system. The Lyapunov theory allows to develop an efficient strategy for the control synthesis guaranteeing the elimination of the stick-slip and bit-bounce. This approach leads the " practical " stabilization of the closed loop system. All results can be easily generalized to any time-delay system subject to bounded disturbances. The effectiveness of the strategy is validated through simulations

Self-Discharge of a Proton Exchange Membrane Electrolyzer: Investigation for Modeling Purposes

The self-discharge phenomenon results in a decrease of the open-circuit voltage (OCV), which occurs when an electrochemical device is disconnected from the power source. Although the self-discharge phenomenon has widely been investigated for energy storage devices such as batteries and supercapacitors, no previous works have been reported in the literature about this phenomenon for electrolyzers. For this reason, this work is mainly focused on investigating the self-discharge voltage that occurs in a proton exchange membrane (PEM) electrolyzer. To investigate this voltage drop for modeling purposes, experiments have been performed on a commercial PEM electrolyzer to analyze the decrease in the OCV. One model was developed based on different tests carried out on a commercial-400 W PEM electrolyzer for the self-discharge voltage. The proposed model has been compared with the experimental data to assess its effectiveness in modeling the self-discharge phenomenon. Thus, by taking into account this voltage drop in the modeling, simulations with a higher degree of reliability were obtained when predicting the behavior of PEM electrolyzers

Analysis and Control of Oilwell Drilling Vibrations: A Time-Delay Systems Approach

International audience-Develops a comprehensive model of coupled torsional-axial vibrations to show the practicing engineer how to reduce the most damaging forms of drillstring vibration.-Uses partial differential equations to show the researcher how a distributed-parameter model can be transformed into a neutral-type time-delay system or simplified analysis and simulation.-Various methods of modeling and control analysed comparatively so that the reader can choose the most appropriateSelf-contained treatment introduces the student to mathematical background and existing models before developing novel techniques and results.This book reports the results of exhaustive research work on modeling and control of vertical oilwell drilling systems. It is focused on the analysis of the system-dynamic response and the elimination of the most damaging drillstring vibration modes affecting overall perforation performance: stick-slip (torsional vibration) and bit-bounce (axial vibration). The text is organized in three parts.The first part, Modeling, presents lumped- and distributed-parameter models that allow the dynamic behavior of the drillstring to be characterized; a comprehensive mathematical model taking into account mechanical and electric components of the overall drilling system is also provided. The distributed nature of the system is accommodated by considering a system of wave equations subject to nonlinear boundary conditions; this model is transformed into a pair of neutral-type time-delay equations which can overcome the complexity involved in the analysis and simulation of the partial differential equation model.The second part, Analysis, is devoted to the study of the response of the system described by the time-delay model; important properties useful for analyzing system stability are investigated and frequency- and time-domain techniques are reviewed.Part III, Control, concerns the design of stabilizing control laws aimed at eliminating undesirable drilling vibrations; diverse control techniques based on infinite--dimensional system representations are designed and evaluated. The control proposals are shown to be effective in suppressing stick-slip and bit-bounce so that a considerable improvement of the overall drilling performance can be achieved.This self-contained book provides operational guidelines to avoid drilling vibrations. Furthermore, since the modeling and control techniques presented here can be generalized to treat diverse engineering problems, it constitutes a useful resource to researchers working on control and its engineering application in oilwell drilling

An SVM-Based Neural Adaptive Variable Structure Observer for Fault Diagnosis and Fault-Tolerant Control of a Robot Manipulator

A robot manipulator is a multi-degree-of-freedom and nonlinear system that is used in various applications, including the medical area and automotive industries. Uncertain conditions in which a robot manipulator operates, as well as its nonlinearities, represent challenges for fault diagnosis and fault-tolerant control (FDC) that are addressed through the proposed FDC technique. A machine-learning-based neural adaptive, high-order, variable structure observer for fault diagnosis (FD) and adaptive, modern, fuzzy, backstepping, variable structure control for use in a fault-tolerant control (FC) algorithm, are proposed in this paper. In the first stage, a variable structure observer is proposed as an FD technique for the robot manipulator. The chattering phenomenon associated with the variable structure observer(VSO) is solved using a high-order variable structure observer. Then, the dynamic behavior estimation performance in the high-order variable structure observer is improved by incorporating a neural network algorithm in the FD pipeline. This adaptive technique is also effective in improving the robustness of the fault signal estimation. Moreover, support vector machines (SVMs) that can derive adaptive threshold values are used to categorize faults. To design an effective fault-tolerant controller (FC), an adaptive modern fuzzy backstepping variable structure controller is used in this study. First, a new variable structure controller is designed. Next, to increase robustness and reduce high-frequency oscillations in uncertain conditions, a backstepping algorithm is used in parallel with the variable structure controller to design the backstepping variable structure controller. To design an effective hybrid controller, a fuzzy algorithm is integrated into the backstepping variable structure controller to create a fuzzy backstepping variable structure controller. Then, to improve the robustness and reliability of the FC, a neural adaptive. high-order. variable structure observer is applied to the fuzzy backstepping variable structure controller to design a modern fuzzy backstepping variable structure controller. An adaptive algorithm is used to fine-tune the variable structure coefficients and reduce the effect of faults on the robot manipulator. The effectiveness of the selected algorithm is validated using a PUMA robot manipulator. The neural adaptive. high-order variable structure observer improves the average performance for the identification of various faults by about 27% and 29.2%, compared with the neural high-order variable structure observer and variable structure observer, respectively