Sadok Sassi
Qatar University, Mechanical and Industrial Engineering, Faculty Member
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Previous works made possible to partially achieve the detection and the severity of degradation for a defective bearing, using an appropriate neural network, but only for a restricted number of localized defects. To avoid this limitation,... more
Previous works made possible to partially achieve the detection and the severity of degradation for a defective bearing, using an appropriate neural network, but only for a restricted number of localized defects. To avoid this limitation, a new technique has been developed for a better characterization and recognition without restriction of bearings defects number. This technique, called the shocks extractor, consists in associating the neural network to an advanced technique of signal processing. The method, using the time waveform, consists to recognize, the pattern of each defect, to extract and treat it separately of the original signal. Thus, the effect of each defect in the vibratory signal can be treated independently of the others that make possible to localize the default and to recognize its severity of degradation.
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Drillstring–borehole interaction can produce severely damaging vibrations. An example is stick–slip vibration, which negatively affects drilling performance, tool integrity and completion time, and costs. Attempts to mitigate stick–slip... more
Drillstring–borehole interaction can produce severely damaging vibrations. An example is stick–slip vibration, which negatively affects drilling performance, tool integrity and completion time, and costs. Attempts to mitigate stick–slip vibration typically use passive means and/or change the operation parameters, such as weight on bit and rotational speed. Automating the latter approach, by means of feedback control, holds the promise of quicker and more effective mitigation. The present work presents three separate fractional-order controllers for mitigating drillstring slip–stick vibrations. For the sake of illustration, the drillstring is represented by a torsional vibration lumped parameter model with four degrees of freedom, including parameter uncertainty. The robustness of these fractional-order controllers is compared with traditional proportional-integral-derivative controllers under variation of the weight on bit and the drill bit’s desired rotary speed. The results confir...
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Gear failure is considered the main alarming and undesirable event in gearboxes. Usually, cracks happen by fatigue caused due to cyclic loading. Fatigue stress is focused on the teeth root because of the small tooth fillet radius. This... more
Gear failure is considered the main alarming and undesirable event in gearboxes. Usually, cracks happen by fatigue caused due to cyclic loading. Fatigue stress is focused on the teeth root because of the small tooth fillet radius. This causes progressive damage to gear teeth which causes teeth failure, and hence, a damaged gear. This work shows a numerical framework to identify and quantify cracks' existence at the teeth root of spur gears. The problem is numerically analysed through finite element-based simulation with ANSYS by conducting a modal analysis. There are nine cases of gears with different cracks on their tooth; these cracks are varied by their number (single or multiple), Crack Length Percentage (CLP %), and location. The FEA is used to simulate all nine cases to predict the bending natural frequency of teeth and to investigate the effects of the variation of the crack by looking at the natural frequency of the teeth bending as well as the deformation level. Results...
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Purpose To monitor the progression of diseases such as Parkinson’s disease (PD) or essential tremor (ET), there is a growing interest in understanding their side effects and continuously monitoring the deterioration or progress of... more
Purpose To monitor the progression of diseases such as Parkinson’s disease (PD) or essential tremor (ET), there is a growing interest in understanding their side effects and continuously monitoring the deterioration or progress of patients’ health conditions. The objective of this study was to investigate the feasibility of a wearable monitoring device constructed from compact MEMS for robust tremor detection in the upper limb using three different storage and monitoring techniques. Method Four subjects (2 PD and 2 ET) with varying stages of disease and treatment willingly provided offline, online, and live modes of tremor data using a low-cost, miniaturized accelerometer and microelectromechanical device. Results The results demonstrated differences in voluntary and non-voluntary characteristics of various activities and the distinct separation between them in the vibration spectrum at the limit of 2 Hz. Online and live monitoring provided the best alternatives to continuous in-hom...
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The risk of vibration-induced fatigue in process pipework is usually assessed through vibration measurements. For small-bore pipework, integrity personnel would measure the vibration of the pipework and refer to widely used charts to... more
The risk of vibration-induced fatigue in process pipework is usually assessed through vibration measurements. For small-bore pipework, integrity personnel would measure the vibration of the pipework and refer to widely used charts to quantify the risk of vibration-induced fatigue. If the vibration levels are classified as OK, no action is required on behalf of the operators. However, if it is a CONCERN or PROBLEM vibration level, strain measurements are required to adequately quantify the risk through a fatigue life assessment. In this paper, we examine the suitability of a widely used vibration acceptance criteria through finite element models. A total of 4,800 models are used to study the suitability of this vibration acceptance criteria by monitoring both the vibration and dynamic stress. The model comprises a small-bore pipe (2″ SCH 40) that is fitted on a mainline size 5″ SCH 40 using a weldolet; the length of the mainline takes three values resulting in three models. The mainl...
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A new class of drill-strings is proposed for attenuating undesirable vibrations to ensure effective operation. The drill-string is provided with passive periodic inserts, which are integrated with sources of local resonance (LR). The... more
A new class of drill-strings is proposed for attenuating undesirable vibrations to ensure effective operation. The drill-string is provided with passive periodic inserts, which are integrated with sources of local resonance (LR). The inserts make the drill-string act as a low frequency pass mechanical filter for the transmission of vibration along the drill-string. Proper design of the periodic inserts with sources of LR tend to shift these stop bands towards zones of lower frequencies to enable confining the dominant modes of vibration of the drill-string within these bands. In this manner, propagation of the vibration along the drill-string can be completely blocked. A finite element model (FEM) is developed using ANSYS to investigate the bandgap characteristics of the proposed drill-string with sources of LR. The developed FEM accounts for bending, torsional, and axial vibrations of the drill-string in order to demonstrate the effectiveness of the periodic inserts with LR in simu...
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Active Noise Control (ANC) is used in controlling low frequency noise where passive control is ineffective. This paper presents the main results obtained from the development of an active noise control earplug for use in industry. A... more
Active Noise Control (ANC) is used in controlling low frequency noise where passive control is ineffective. This paper presents the main results obtained from the development of an active noise control earplug for use in industry. A simple analogue feedback control system is used to demonstrate the potential of the system. Experimental results show that with existing miniature microphones and loudspeakers characteristics, adequate active noise reduction occurs in the frequency range between 100 Hz to 1000 Hz. The peak noise attenuation of about 15 dB occurs around 400 Hz. A model of the electroacoustic control system is provided and used to predict the performance. Simulation results show that the system secondary path frequency response dictates the closed-loop performance. The response in turn depends mainly on the frequency responses of the microphone and loudspeaker. The controller is used to maximize the noise reduction and its bandwidth. If lower frequency noise reduction is d...
Computational Fluid Dynamics (CFD) analysis is conducted on mono-tube vehicle MRF damper investigated experimentally in a previous study. In this study, the fluid of the type MRF-132DG was inserted inside a damper of a car rear suspension... more
Computational Fluid Dynamics (CFD) analysis is conducted on mono-tube vehicle MRF damper investigated experimentally in a previous study. In this study, the fluid of the type MRF-132DG was inserted inside a damper of a car rear suspension system. The CFD analysis describes the fluid flow through the internal orifices between the compression and the rebound chambers. Averaged Navier–Stokes equations were solved by the SIMPLE method, and the RNG k-ε was used to model the turbulence at the fluid crossing through the orifices. All the CFD model boundary conditions’ values were set to the same values reported in the previous experimental study, except for the viscosity values. When varying the applied magnetic field density, the changes of MRF’s viscosity values were assessed by using a viscosity meter. Results showed a viscosity increase of 70% when the magnetic field excitation current was elevated from 0 A to 5 A. The damping forced and damping values were calculated using the rebound...
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This main purpose of this work is to investigate, through a finite-element simulation, the effect of tire blowout on the collision of a light pickup truck with a guardrail, at a speed of 100 km/h. The finite-element model was calibrated... more
This main purpose of this work is to investigate, through a finite-element simulation, the effect of tire blowout on the collision of a light pickup truck with a guardrail, at a speed of 100 km/h. The finite-element model was calibrated against a dynamic test carried out by the Texas Transportation Institute. Four cases of individual tire blowout were considered. Among these, the case of the left front tire was found to be the most critical one, resulting in a pitch angle of 24°, a roll angle of 12°, and a yaw angle of 30°. For this critical case, the results showed that the deflated tire trapped in the guardrail, which created more interaction between the vehicle and the guardrail beam. These challenging crash conditions were found to be more crucial for the stability of the pickup compared with the fully inflated tire scenario.
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Abstract The propagation of waves in helical rods has been studied extensively. However, studying the wave propagation in double helical rods have received less attention although this can be useful in multiple fields of science and... more
Abstract The propagation of waves in helical rods has been studied extensively. However, studying the wave propagation in double helical rods have received less attention although this can be useful in multiple fields of science and engineering. Obtaining an analytical model for a double helical rod is challenging since the curvature and tortuosity are not constant. Thus, resolving the wave behaviour analytically is nearly impossible. In this paper, wave propagation in a double helical rod will be studied using the wave and finite element method which is a technique that can be used to model homogeneous and periodic one and two dimensional structures based on the periodic structure theory. For modelling a double helical rod, the finite element model of a single turn is processed using Bloch waves. The dispersion curves and wavemodes are obtained and the similarities and differences of waves in helical and double helical rods are highlighted.
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ABSTRACT Since the performance of the guardrail system depends in part on the compatibility of vehicle-to-roadside hardware, it is important to improve the interaction of the vehicle with the guardrail system by adding more compliance to... more
ABSTRACT Since the performance of the guardrail system depends in part on the compatibility of vehicle-to-roadside hardware, it is important to improve the interaction of the vehicle with the guardrail system by adding more compliance to the guardrail system. In this paper, a finite-element baseline model of a guardrail system consisting of a light truck (2000 kg) travelling at 100 km/h and striking a guardrail was developed in accordance with the NCHRP Report 350 guidelines for Test Level 3 safety performance. The model was validated through comparison to a full-scale test conducted by the Texas Transportation Institute. In order for the guardrail system to absorb more energy and offer better stability to the vehicle, a rigid wooden blockout was replaced by a new crushable blockout design that was evaluated at the component level. The new blockout was formed by three crash cans and triggered at the corner, then was implemented in the full-scale model. The results of the analysis indicate that the both models satisfy the requirements of NCHRP Report 350 for the Test 3-11 conditions and show that the crushable blockout offers better vehicle stability in terms of roll angle and vehicle deceleration.
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In this paper, the dynamic behaviour of a vehicle having one of its tyres burst is examined through a model-based analysis. The model considered in this study is a classical one, considering only straight line motion in Z-direction. In... more
In this paper, the dynamic behaviour of a vehicle having one of its tyres burst is examined through a model-based analysis. The model considered in this study is a classical one, considering only straight line motion in Z-direction. In total, nine degrees of freedom are analysed: four translations of the un-sprung masses, one translation of the centre of gravity, two rotations of the body and two translations of the seat and its support. When a tyre blows out (for example in the front-left side), several changes are observed to occur. These changes affect the vehicle stability and geometry, the operating conditions and the tyre-road interaction. The numerical simulation of the effects of tyre deflations on vehicle behaviour was achieved by using MATLAB/Simulink. It is concluded that the blast coming from the tyre blowout generates enough energy to excite the wheel structure resonances but has relatively little effect on the comfort of the driver. The main effect is observed to be on the safety of the vehicle which, under the action of a lateral push, is deviated from its trajectory towards the side of the deflated tyre.
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Research Interests: Engineering, Electronic Engineering, Mechanical Engineering, Civil Engineering, Aerospace Engineering, and 15 moreDesign, Structural Engineering, Vibrations, Structural Dynamics, Electronics, Digital Signal Processing, Fault Detection, Numerical Analysis, Structural Health Monitoring, Damage detection, Mechanical Vibrations, Rolling element bearings, Bearings, Electronics Engineering, and Civil/Structural Engineering
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Previous works made possible to partially achieve the detection and the severity of degradation for a defective bearing, using an appropriate neural network, but only for a restricted number of localized defects. To avoid this limitation,... more
Previous works made possible to partially achieve the detection and the severity of degradation for a defective bearing, using an appropriate neural network, but only for a restricted number of localized defects. To avoid this limitation, a new technique has been developed for a better characterization and recognition without restriction of bearings defects number. This technique, called the shocks extractor, consists in associating the neural network to an advanced technique of signal processing. The method, using the time waveform, consists to recognize, the pattern of each defect, to extract and treat it separately of the original signal. Thus, the effect of each defect in the vibratory signal can be treated independently of the others that make possible to localize the default and to recognize its severity of degradation.
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The primary purpose of this work is to experimentally investigate the damping coefficient of a viscous damper, intended to be used in railway applications to reduce noise emission. The viscous shock absorber used in this study is a... more
The primary purpose of this work is to experimentally investigate the damping coefficient of a viscous damper, intended to be used in railway applications to reduce noise emission. The viscous shock absorber used in this study is a commercial vehicle damper to which minor modifications were added. This investigation was focused on detecting the variation in the damping coefficient value over a wide range of frequencies. The experimental setup tends to simulate the railway vibration represented by a strong steel metal sheet structure attached to a shaker from its lower side. The shaker itself is connected to the damper rod through a dual acceleration-force sensor. A sinusoidal load with wide range of frequencies was applied by the shaker to the top of the damper’s rod. Both acceleration and force time-responses were collected, stored and analyzed to extract the Force-Displacement and the Force-Velocity graphs. Based on the damping coefficients obtained for the different values of exc...
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One of the least investigated approaches in passive vibration control is the possibility of combining different types of dampers that use different damping principles. Such a combination process, if wisely designed and implemented, has... more
One of the least investigated approaches in passive vibration control is the possibility of combining different types of dampers that use different damping principles. Such a combination process, if wisely designed and implemented, has the potential to increase the damping performance and extend the damper’s application. The primary purpose of this work is to experimentally and numerically investigate the damping behavior of a novel Fluid-Impact Hybrid Damper. This damper combines a conventional Viscous Fluid Damper with a Particle-Impact Damper. The Fluid-Impact Hybrid Damper comprises a 3D-printed plastic box attached to the Viscous Fluid Damper’s moving rod and filled with stainless steel balls. An experimental setup was designed to drive the Viscous Fluid Damper’s rod into harmonic oscillations at different frequencies (1, 2, 4, 6, and 8 Hz). The number of balls was changed three times (5, 10, and 15) to assess the effect of this parameter on the damping performance of the Fluid...
This paper presents a novel real-time rotating machinery damage monitoring system. The system detects, quantifies, and localizes damage in ball bearings in a fast and accurate way using one-dimensional convolutional neural networks... more
This paper presents a novel real-time rotating machinery damage monitoring system. The system detects, quantifies, and localizes damage in ball bearings in a fast and accurate way using one-dimensional convolutional neural networks (1D-CNNs). The proposed method has been validated with experimental work not only for single damage but also for multiple damage cases introduced onto ball bearings in laboratory environment. The two 1D-CNNs (one set for the interior bearing ring and another set for the exterior bearing ring) were trained and tested under the same conditions for torque and speed. It is observed that the proposed system showed excellent performance even with the severe additive noise. The proposed method can be implemented in practical use for online defect detection, monitoring, and condition assessment of ball bearings and other rotatory machine elements.
The knowledge of wave scattering and power flow in waveguide structures is important for many engineering applications. In this paper, power flow and scattering in a straight-helical-straight waveguide structure are investigated using the... more
The knowledge of wave scattering and power flow in waveguide structures is important for many engineering applications. In this paper, power flow and scattering in a straight-helical-straight waveguide structure are investigated using the wave and finite element (WFE) method. For simple (straight or helical) waveguides, wave scattering (and subsequently the power flow and scattering) can be resolved analytically. This is not the case for complex waveguides such as laminated or sandwiched waveguides or waveguides with noncanonical cross-sections. In such cases, the WFE method is used to model the wave behavior in each waveguide in the structure. The power flow is then studied by considering how waves reflect and transmit at the boundaries that join the straight waveguides with the helical waveguide. We present three numerical examples but analytical solutions can be obtained for the first example only; for the second and third examples, the WFE is used in earnest since the wave behav...
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Page 1. An innovative magnetorheological damper for automotive suspension: from design to experimental characterization This article has been downloaded from IOPscience. Please scroll down to see the full text article. 2005 Smart Mater.... more
Page 1. An innovative magnetorheological damper for automotive suspension: from design to experimental characterization This article has been downloaded from IOPscience. Please scroll down to see the full text article. 2005 Smart Mater. Struct. 14 811 ...
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This work aims to develop the theoretical fundamentals and numerical details of new software, dedicated to the simulation of the dynamic behavior of rotating ball bearings in the presence of localized surface defects. In this article, the... more
This work aims to develop the theoretical fundamentals and numerical details of new software, dedicated to the simulation of the dynamic behavior of rotating ball bearings in the presence of localized surface defects. In this article, the generation of vibration by a point defect in a rolling element bearing is modeled as a function of the rotation of the bearing, of the distribution of the load in the bearing, of the bearing structure elasticity, of the oil film characteristics, and of the transfer path between the bearing and the transducer. The numerical model is developed with the assumption that the dynamic behavior of the bearing can be represented by a coupled three-degree-of-freedom system, after which the governing equations of the simulation model are solved using computer simulation techniques. A new application, called BEAT (BEAring Toolbox), was developed in order to simulate bearings' vibratory response to the excitations produced by localized defects. By adding a noisy response due to the sliding friction occurring between the moving parts to the impulsive response caused by localized defects, the BEAT software is able to provide realistic results, similar to those produced by a sensor during experimental measurements.
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The prediction of the response of waveguides to time-harmonic base excitations has many applications in mechanical, aerospace and civil engineering. The response to base excitations can be obtained analytically for simple waveguides only.... more
The prediction of the response of waveguides to time-harmonic base excitations has many applications in mechanical, aerospace and civil engineering. The response to base excitations can be obtained analytically for simple waveguides only. For general waveguides, the response to time-harmonic base excitations can be obtained using the finite element method. In this study, we present a wave and finite element approach to calculate the response of waveguides to time-harmonic base excitations. The wave and finite element method is used to model free wave propagation in the waveguide, and these characteristics are then used to find the amplitude of excited waves in the waveguide. Reflection matrices at the boundaries of the waveguide are then used to find the amplitude of the travelling waves in the waveguide and subsequently the response of the waveguide. This includes the displacement and stress frequency response transfer functions. Numerical examples are presented to demonstrate the ...
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During the drilling process in oil and gas fields, slender drill strings often experience a multitude of complex and simultaneous vibrational phenomena. Drill string vibrations hinder the drilling process and can cause premature wear and... more
During the drilling process in oil and gas fields, slender drill strings often experience a multitude of complex and simultaneous vibrational phenomena. Drill string vibrations hinder the drilling process and can cause premature wear and damage to the drilling equipment. Here, the suppression of drill string vibrations during drilling operations is experimentally investigated using a novel drill string design, based on the use of innovative periodic inserts that control the vibration transmissibility in different directions. These inserts are equipped with viscoelastic rings that act as sources of local resonances, surrounding piezoelectric actuators that generate internal axial loading when electrically excited. An experimental prototype that combined all these details was constructed and tested to demonstrate the periodic drill string's feasibility and effectiveness in minimizing undesirable vibrations. The obtained results indicate that the periodic inserts' careful desig...
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In rotating machinery, the second most common fault after imbalance is misalignment. Misalignment can have a severe impact on equipment and may reduce the machine’s lifetime considerably. In this paper, the simultaneous effect of... more
In rotating machinery, the second most common fault after imbalance is misalignment. Misalignment can have a severe impact on equipment and may reduce the machine’s lifetime considerably. In this paper, the simultaneous effect of imbalance and misalignment (parallel or angular) on the vibration spectra of rotating machinery will be discussed. A numerical model is developed and used to obtain the time and frequency responses of the rotor-coupling-bearing system to the simultaneous effect of these faults. The numerical model shows that the imbalance was mainly related to the peak located around 1X, whereas misalignment was linked to the peak around 2X. In addition, the parallel misalignment fault magnifies the 2X amplitude of the displacement response, whereas the response of angular misalignment is captured at the 2X and 4X amplitudes. This study also examines the effects of changing the model’s rotational speed, misalignment level, and coupling type for angular and parallel misalign...
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This research aims to analyze the vibration response of damaged rolling element bearings experimentally and to assess their degree of degradation by examining parameters extracted from the time domain. This task was accomplished in three... more
This research aims to analyze the vibration response of damaged rolling element bearings experimentally and to assess their degree of degradation by examining parameters extracted from the time domain. This task was accomplished in three phases. In the first phase, a test rig was carefully designed and precisely manufactured. In particular, an innovative solution for rapidly mounting and dismounting bearings on the supporting shaft was tested and used successfully. In the second phase, a specific technique of seeding defects inside the ball bearings was developed. In the last phase, damaged bearings (and healthy ones serving as a reference) were installed on the test rig, and different vibration measurements were taken. The results obtained from this work show that different parameters could be extracted from the time domain. In addition to the six common indicators (peak, root mean square, crest factor, kurtosis value, impulse factor, and shape factor), four hybrid new ones have be...