B.O. Al-Bedoor

Bio: B.O. Al-Bedoor is an academic researcher from University of Jordan. The author has contributed to research in topics: Vibration & Torsional vibration. The author has an hindex of 17, co-authored 34 publications receiving 715 citations. Previous affiliations of B.O. Al-Bedoor include King Fahd University of Petroleum and Minerals.

Wavelet analysis of vibration signals of an overhang rotor with a propagating transverse crack

Abstract: This paper presents an experimental study of the dynamic response of an overhang rotor with a propagating transverse crack using the discrete wavelet transform (DWT)—a joint time frequency analysis technique. Start-up and steady state vibration signatures are analyzed using Daubechies (Db6) mother wavelet and the results are presented in the form of scalograms and space-scale energy distribution graphs. The start-up results showed that crack reduces the critical speed of the rotor system. The steady state results showed that propagating crack produces changes in vibration amplitudes of frequency scale levels corresponding to 1 X , 2 X and 4 X harmonics. The vibration amplitude of frequency scale level corresponding to 1 X may increase or decrease depending on the location of the crack and side load. However, the amplitude of frequency scale level corresponding to 2 X increases continuously as the crack propagates.

Transient torsional and lateral vibrations of unbalanced rotors with rotor-to-stator rubbing

Abstract: This paper presents a model for the coupled torsional and lateral vibrations of unbalanced rotors that accounts for the rotor-to-stator rubbing. The system degrees of freedom, obtained using Lagrangian dynamics, are the rotor rigid-body rotation, the rotor torsional deformation and two orthogonal lateral deflections of the rotor. The rubbing condition is modelled using the elastic impact-contact idealization, which consists of normal and tangential forces at the rotor-to-stator contact point. The model is solved using a predictive-corrective numerical integration algorithm. The system response orbits show clearly the rotor-to-stator impact contact in the start-up period. The inclusion of rotor torsional flexibility has introduced irregular rubbing orbits. Rotor response anisotropy is observed in the rubbing responses for both lateral and lateral-torsional models. Furthermore, a split in resonance is observed due to the rubbing condition when the rotor torsional flexibility is considered. Finally, numerical simulations for rotors with non-zero fluid-film bearing cross-coupling terms have mainly shown a reduction in the split in resonance due to rubbing effects.

Modeling the coupled torsional and lateral vibrations of unbalanced rotors

Abstract: A model for the coupled torsional and lateral vibrations of an unbalanced rotor is developed. The equations of motion, obtained using Lagrangian dynamics, showed inertial coupling and nonlinear interaction between the rotor torsional and lateral vibrations. A softening effect of the rotor torsional stiffness has appeared. This effect and some of the nonlinear interaction effects have appeared, for the first time in this model, due to treating the torsional angle as an individual motion. Simulation results showed energetic interaction between the rotor lateral and torsional vibrations. Responses at 1 X and 3 X in the torsional vibration signal and 1 X and 2 X in the lateral vibration signals have appeared.

An Approximate Analytical Solution of Beam Vibrations during Axial Motion

Abstract: An approximate analytical solution for the transverse vibrations of a beam during axial deployment is derived. The approach relies on removing the time dependency from the boundary conditions, and transferring it to the differential equation. The resulting partial differential equation with time-dependent coefficients is solved by employing the classical method of separation of variables and the method of multiple scales. The approximate analytical solution is obtained for axially moving beams with different end conditions, at constant deployment rates. Except for those assumptions associated with slow axial movement and Euler's beam theory, no further assumptions were necessary. To verify to validity of the approximate analytical solution, comparisons with available numerical solutions are presented. Some numerical results were presented for axially moving beams with moving end supports.

Dynamics of flexible-link and flexible-joint manipulator carrying a payload with rotary inertia

Abstract: A dynamic model of a flexible-arm and flexible-joint manipulator carrying a payload with rotary inertia is presented. The Lagrangian approach in conjunction with the finite element method is employed in deriving the equations of motion, within the assumption of a small deformation theory. All the dynamic coupling terms between the system reference rotational motion, joint torsional deformations and arm bending deformations are accounted for. The dynamics of a payload with rotary inertia are incorporated in the model in a consistent manner. Furthermore, the effects of axial shortening due to beam and bending deformations and motions induced inertial forces as well as the effects of gravity are included in the model. The resulting model and simulation results have shown that the joint flexibility has a pronounced effect on the dynamic behavior of rotating flexible arms that should not be simply neglected. The effect is shown to be due to the nonlinear dynamic interaction between the joint torsional deformations, the arm bending deformations and the system reference rotational motion. Simulation results of the nonlinear and the linearized models are compared and the results are discussed. The effects of the payload are shown to be increasing the elastic deformations’ amplitudes and reducing the frequency of oscillations. Due to the model nonlinearity, different combinations of system parameters are expected to develop different effects. This makes the proposed model valid in the design process as well as in the performance evaluation.

Application of the wavelet transform in machine condition monitoring and fault diagnostics: a review with bibliography

Abstract: The application of the wavelet transform for machine fault diagnostics has been developed for last 10 years at a very rapid rate. A review on all of the literature is certainly not possible. The purpose of this review is to present a summary about the application of the wavelet in machine fault diagnostics, including the following main aspects: the time–frequency analysis of signals, the fault feature extraction, the singularity detection for signals, the denoising and extraction of the weak signals, the compression of vibration signals and the system identification. Some other applications are introduced briefly as well, such as the wavelet networks, the wavelet-based frequency response function, etc. In addition, some problems in using the wavelet for machine fault diagnostics are analysed. The prospects of the wavelet analysis in solving non-linear problems are discussed.

Recent advances in time–frequency analysis methods for machinery fault diagnosis: A review with application examples

Abstract: Nonstationary signal analysis is one of the main topics in the field of machinery fault diagnosis. Time–frequency analysis can identify the signal frequency components, reveals their time variant features, and is an effective tool to extract machinery health information contained in nonstationary signals. Various time–frequency analysis methods have been proposed and applied to machinery fault diagnosis. These include linear and bilinear time–frequency representations (e.g., wavelet transform, Cohen and affine class distributions), adaptive parametric time–frequency analysis (based on atomic decomposition and time–frequency auto-regressive moving average models), adaptive non-parametric time–frequency analysis (e.g., Hilbert–Huang transform, local mean decomposition, and energy separation), and time varying higher order spectra. This paper presents a systematic review of over 20 major such methods reported in more than 100 representative articles published since 1990. Their fundamental principles, advantages and disadvantages, and applications to fault diagnosis of machinery have been examined. Some examples have also been provided to illustrate their performance.

Dynamics of rotating machines

Abstract: This book equips the reader to understand every important aspect of the dynamics of rotating machines. Will the vibration be large? What influences machine stability? How can the vibration be reduced? Which sorts of rotor vibration are the worst? The book develops this understanding initially using extremely simple models for each phenomenon, in which (at most) four equations capture the behavior. More detailed models are then developed based on finite element analysis, to enable the accurate simulation of the relevant phenomena for real machines. Analysis software (in MATLAB) is associated with this book, and novices to rotordynamics can expect to make good predictions of critical speeds and rotating mode shapes within days. The book is structured more as a learning guide than as a reference tome and provides readers with more than 100 worked examples and more than 100 problems and solutions.

Computational strategies for flexible multibody systems

Abstract: The status and some recent developments in computational modeling of flexible multibody systems are summarized. Discussion focuses on a number of aspects of flexible multibody dynamics including: modeling of the flexible components, constraint modeling, solution techniques, control strategies, coupled problems, design, and experimental studies. The characteristics of the three types of reference frames used in modeling flexible multibody systems, namely, floating frame, corotational frame, and inertial frame, are compared. Future directions of research are identified. These include new applications such as micro- and nano-mechanical systems; techniques and strategies for increasing the fidelity and computational efficiency of the models; and tools that can improve the design process of flexible multibody systems. This review article cites 877 references. @DOI: 10.1115/1.1590354#

Vibration analysis of rotating machinery using time-frequency analysis and wavelet techniques

Abstract: Time–frequency analysis, including the wavelet transform, is one of the new and powerful tools in the important field of structural health monitoring, using vibration analysis. Commonly-used signal analysis techniques, based on spectral approaches such as the fast Fourier transform, are powerful in diagnosing a variety of vibration-related problems in rotating machinery. Although these techniques provide powerful diagnostic tools in stationary conditions, they fail to do so in several practical cases involving non-stationary data, which could result either from fast operational conditions, such as the fast start-up of an electrical motor, or from the presence of a fault causing a discontinuity in the vibration signal being monitored. Although the short-time Fourier transform compensates well for the loss of time information incurred by the fast Fourier transform, it fails to successfully resolve fast-changing signals (such as transient signals) resulting from non-stationary environments. To mitigate this situation, wavelet transform tools are considered in this paper as they are superior to both the fast and short-time Fourier transforms in effectively analyzing non-stationary signals. These wavelet tools are applied here, with a suitable choice of a mother wavelet function, to a vibration monitoring system to accurately detect and localize faults occurring in this system. Two cases producing non-stationary signals are considered: stator-to-blade rubbing, and fast start-up and coast-down of a rotor. Two powerful wavelet techniques, namely the continuous wavelet and wavelet packet transforms, are used for the analysis of the monitored vibration signals. In addition, a novel algorithm is proposed and implemented here, which combines these two techniques and the idea of windowing a signal into a number of shaft revolutions to localize faults.