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1
Content available Porous material effect on gearbox vibration and acoustic behavior
Letaief M. R., Walha L., Taktak M., Chaari F., Haddar M.
Journal of Theoretical and Applied Mechanics
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2017
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Vol. 55 nr 4
1381--1395
EN
In this paper, we define a resolution method to study the effect of a porous material on vibro-acoustic behavior of a geared transmission. A porous plate is coupled with the gearbox housing cover. The developed model depends on the gearbox characteristic and poroelastic parameters of the porous material. To study the acoustic effect of the housing cover, the acoustic transmission loss is computed by simulating numerically the elastic-porous coupled plate model, and the numerical implementation is performed by directly programming the mixed displacement-pressure formulation. To study the vibration effect, the bearing displacement is computed using a two-stage gear system dynamical model and used as the gearbox cover excitation. Numerical implementation is performed by direct programming of the Leclaire formulation.
2
Content available Modal analysis of gearbox transmission system in bucket wheel excavator
Karray M., Feki N., Khabou M. T., Chaari F., Haddar M.
Journal of Theoretical and Applied Mechanics
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2017
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Vol. 55 nr 1
253--264
EN
Planetary gears are widely used in modern machines as ones of the most effective forms of power transmission. In this paper, a special configuration of a gearbox composed of one stage spiral bevel gear and a two stage helical planetary gear used in a bucket wheel excavator gearbox is presented to investigate its modal properties. A lumped-parameter model is formulated to obtain equations of motion and the eigenvalue problem is solved. The modes are presented in low-frequency and high-frequency bands. Distributions of modal kinetic and strain energies are studied.
3
Content available Modal analysis of back-to-back planetary gear: experiments and correlation against lumped-parameter model
Hammami A., Rincon A. F. del, Rueda F. V., Chaari F., Haddar M.
Journal of Theoretical and Applied Mechanics
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2015
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Vol. 53 nr 1
125--138
EN
In order to characterize the dynamic behaviour of a back-to-back planetary gear, experimental and numerical modal analysis techniques are achieved. Rotational and translational modal deflections are highlighted. Natural frequencies are compared to the results from the lumped-parameter model. The modes are presented in the numerical studies in low-frequency and high-frequency bands. Distributions of modal kinetic and strain energies are studied.
4
Content available Closed form solution for the collapse of polygonal thin-walled columns in the axial crushing case
Maalej Y, Chaari F., Zouari B., Markiewicz E.
Journal of Theoretical and Applied Mechanics
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2014
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Vol. 52 nr 3
707--718
EN
The main objective of this paper is to propose a new closed form solution, useful in the pre-design stage, that allows one to calculate the mean load in the case of post-collapse of polygonal thin-walled columns in the axial crushing case. This model gives a rapid and accurate evolution of the normalized mean load as function of the corner element angle as well as the ratio between the corner length and the column thickness. To identify the parameters of this model, numerical simulations with an explicit finite element software have been carried out and then compared to experimental results reported in the literature. Finally, all these results combined with the findings based on the known generalized mixed model developed by other researchers working on this topic enabled one to establish the closed form solution. This is a unified and continuous closed form solution, which is suitable for different columns shapes, even non-conventional shapes obtained thanks to the development of extrusion techniques.
5
Content available Effect of camshaft eccentricity and follower backlash on the dynamic behaviour flexible cam mechanism
Tounsi M., Chaari F., Abbes M. S., Fakhfakh A. T., Haddar M.
Diagnostyka
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2010
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nr 2(54)
3-9
EN
A cam follower system is modelled in this work. The equation of motion and the eigenfrequencies are recovered. The computation of the dynamic response is made by mean of combined implicit Newmark-Newton Raphson algorithm. Moreover, dynamic behaviour of the follower train is analysed in presence of an eccentricity in the camshaft and backlash between the follower rods and its guide.
6
Content available remote Analytical Computation of the Mechanical Efficiency of Compound Mechanical Systems
Kantchev K., Baccar W., Chaari F., Haddar M.
Machine Dynamics Problems
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2009
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Vol. 33, No. 1
55-75
EN
In this paper, the mechanical efficiency of mechanical systems is discussed. The influence of the arrangement of the different components of the mechanism and the power distribution over the different modules on the efficiency is investigated. Revolute, slider and contoured joints are studied. Sliding and rolling frictions are taken into account in order to determine their mechanical efficiency. Two numerical examples of a crank-connecting rod mechanism and a cam follower system are presented and the evolution of their mechanical efficiencies over a cycle are computed.
7
Content available A New Design of a Robot Prototype for Intelligent Navigation and Parallel Parking
Abdelmoula Ch., Chaari F., Masmoudi M.
Journal of Automation Mobile Robotics and Intelligent Systems
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2009
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Vol. 3, No. 2
47-58
EN
Nowadays, the design of industrial vehicles and movable cars is based on the automation of their different tasks, which are currently handled by humans. These tasks, such as maneuvering robots in complex environments, require high level of precision that cannot be guaranteed by humans. Manual operations are likely to produce errors of computation and optimization of navigation and manoeuvre (left, right, veering…). In this paper, a novel prototype of a well-structured robot for intelligent navigation and parallel parking applications is presented. The robot have two axels, the front one is composed of two wheels that are manoeuvred by a stepper motor, and a pinion rack system for controlling the rotation of the wheels, and also the orientation of the robot. The driving wheels are mounted in the rear axle of the robot and are commanded by two DC motors. The design allows modification of the robot structural components whenever required. In addition to the mechanical components, the prototype is equipped with a DC power supply, three infra-red sensors, one ultrasound sensor, and control modules composed of an FPGA card, microcontroller card and two cards which are responsible for commanding actuators. The parameters of the mechanical and electronics components are optimised to perform multiple tasks for training and instruction applications. A mathematical model that describes the dynamics of the robot prototype is also developed. Simulation, experimental and theoretical investigations were carried out consisting in navigation and parallel parking manoeuvres. It was confirmed that the experimental and theoretical results agree well in both applications.
8
Content available remote Dynamical Behaviour of a Multi-Stage Epicyclic Gear Train
Siala W., Chaari F., Fakhfakh T., Haddar M.
Machine Dynamics Problems
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2007
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Vol. 31, No. 1
82-100
EN
For many years ago, much works were interested in the study of the dynamic behaviour of a simple epicyclical gear stages. But, in our knowledge there are very few or practically unexisting works dealing with the dynamic behaviour of multi stages epicyclical gear systems. This work is directed towards the study of the dynamic behaviour of an epicyclical double stages gear system without defects, by taking account of its essential components (gears, bearing...). Compared to the trains with parallel axes, these epicyclical gears have the characteristic to transmit an important torque with both small overall dimensions and relatively reduced level of vibration and noise. In this work, we present initially a plane model of the epicyclical double stages gear system while taking account of the bearings flexibility. Then, the error of transmission which is the main source of excitation of the train is evaluated. Finally, we develop the equation of total motion of the train to establish the vibratory and dynamic behaviour of the system studied.
9
Content available remote Influence of Eccentricity, Profile Error and Tooth Pitting on Helical Planetary Gear Vibration
Hbaieb R., Chaari F., Fakhfakh T., Haddar M.
Machine Dynamics Problems
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2005
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Vol. 29, No. 3
5--32
EN
Planetary helical gears are widely used in various transmissions such as helicopters, automobiles and heavy industry due to their substantial particularities of compactness, large torque-to-weight ratio and weak bearing loads. Their efficiency is affected by manufacturing errors and tooth faults. To scrutinize the effect of these defects, a three dimensional helical planetary gear model was developed. The energetic Lagrange formulation was used to recover the equations of motion and the modal characteristics of the system. The dynamic response was computed by an iterative spectral method. Eccentricity, profile error and tooth pitting occurring during running were modelled. The effects of these defects on the dynamic response of the planetary gear were discussed in order to extract their features.
10
Content available remote Squeeze flow of concentrated suspensions of spheres in Newtonian or shear-thinning fluids
Collomb J., Chaari F., Chaouche M.
International Journal of Applied Mechanics and Engineering
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2003
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Vol. 8, no spec.
219-224
EN
The squeeze flow behaviour of concentrated suspensions of spheres in both Newtonian and shear thinning fluids is investigated experimentally. Analysing the evolution of the squeeze force as a function of time for different controlled velocities, the suspension is found to present two main flow regimes. The first regime is characterized by the situation in which the force decreases when the velocity decreases, which is expected and corresponds to a power-law fluid flow of the suspension. In the second regime the force increases when the velocity decreases which is an indication of solvent filtration through the particle skeleton that behaves then as a quasi-rigid porous media. It is found that the transition between the two regimes is a result of a competition between the viscous shear forces due the flow of the suspension and the damping force caused by the filtration of the fluid through the porous media made up by the particles. It is shown that the addition of a small amount (1000ppm) of a polymer (Xanthan) to the solvent significantly decreases the squeeze velocity for which we have fluid filtration.
11
Content available remote Rheo-optical characterisation of linear low density polyethylene crystallization under shear
Chaari F., Chaouche M., Benyahia l., Tassin J. F.
International Journal of Applied Mechanics and Engineering
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2003
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Vol. 8, no spec.
213-218
EN
Metallocene linear low density polyethylene (mLLDPE) crystallization under shear flow at controlled shear rates and above its crystallization temperature was investigated experimentally. The evolution of the material optical properties (turbidity, birefringence and dichroism) was monitored following a temperature jump from the melting point to a final crystallization temperature . These properties are discussed in terms of the evolution of the polymer semi-crystalline microstructure. In light of the optical properties evolution, the crystallization process can be split into three regimes (i) incubation phase in which small (compared to the light wavelength) crystalline nuclei spread over the medium, (ii) isotropic crystallite growth phase and (iii) anisotropic crystallite growth phase.
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