Experimental identification of multiple faults in rotating machines

Mahfoud, Jarir,Breneur, Claire Techno-Press 2008 Smart Structures and Systems, An International Jou Vol.4 No.4

The aim of this paper is to define the required measurements and processing tools necessary for developing a maintenance approach applied to rotating machines in the presence of multiple faults. The system responses measured were accelerations and transmission errors. Acceleration measurements provide most of the information on bearing conditions, while transmission error measurements provide pertinent information on gear conditions. The measurements were carried out for several operating conditions (loads and speeds). System responses were processed in several analyzing domains (Time, Spectrum, and Cepstrum domains). The approach developed enables the detection and identification of combined faults and it can be applied to other types of rotating machines once the critical elements and their associated faults have been defined.

Investigations on critical speed suppressing by using electromagnetic actuators

Mahfoud, Jarir,Der Hagopian, Johan Techno-Press 2012 Smart Structures and Systems, An International Jou Vol.9 No.4

The possibility of suppressing critical speeds by using electromagnetic actuators (EMAs) is assessed experimentally in this paper. The system studied is composed of a horizontal flexible shaft supported by two ball bearings at one end and one roller bearing that is located in a squirrel cage at the other end. Four identical EMAs supplied with constant current are utilized. The EMAs associated to the squirrel cage constitutes the hybrid bearing. Results obtained, show that the constant current, when applied to the EMAs, produces a shift of the first critical speed toward lower values. Moreover, the application of constant current for a speed interval around the critical speed enables a smooth run-up or run-down without crossing any resonance.

Free vibration of FGM plates with porosity by a shear deformation theory with four variables

Mahfoud Yousfi,Hassen Ait Atmane,Mustapha Meradjah,Abdelouahed Tounsi,Riadh Bennai 국제구조공학회 2018 Structural Engineering and Mechanics, An Int'l Jou Vol.66 No.3

In this work, a high order hyperbolic shear deformation theory with four variables is presented to study the vibratory behavior of functionally graduated plates. The field of displacement of the theory used in this work is introduced indeterminate integral variables. In addition, the effect of porosity is studied. It is assumed that the material characteristics of the porous FGM plate, varies continuously in the direction of thickness as a function of the power law model in terms of volume fractions of constituents taken into account the homogeneous distribution of porosity. The equations of motion are obtained using the principle of virtual work. An analytical solution of the Navier type for free vibration analysis is obtained for a FGM plate for simply supported boundary conditions. A comparison of the results obtained with those of the literature is made to verify the accuracy and efficiency of the present theory. It can be concluded from his results that the current theory is not only accurate but also simple for the presentation of the response of free vibration and the effect of porosity on the latter.

Free vibration of FGM plates with porosity by a shear deformation theory with four variables

Yousfi, Mahfoud,Atmane, Hassen Ait,Meradjah, Mustapha,Tounsi, Abdelouahed,Bennai, Riadh Techno-Press 2018 Structural Engineering and Mechanics, An Int'l Jou Vol.66 No.3

In this work, a high order hyperbolic shear deformation theory with four variables is presented to study the vibratory behavior of functionally graduated plates. The field of displacement of the theory used in this work is introduced indeterminate integral variables. In addition, the effect of porosity is studied. It is assumed that the material characteristics of the porous FGM plate, varies continuously in the direction of thickness as a function of the power law model in terms of volume fractions of constituents taken into account the homogeneous distribution of porosity. The equations of motion are obtained using the principle of virtual work. An analytical solution of the Navier type for free vibration analysis is obtained for a FGM plate for simply supported boundary conditions. A comparison of the results obtained with those of the literature is made to verify the accuracy and efficiency of the present theory. It can be concluded from his results that the current theory is not only accurate but also simple for the presentation of the response of free vibration and the effect of porosity on the latter.

Investigations on critical speed suppressing by using electromagnetic actuators

Jarir Mahfoud,Johan Der Hagopian 국제구조공학회 2012 Smart Structures and Systems, An International Jou Vol.9 No.4

The possibility of suppressing critical speeds by using electromagnetic actuators (EMAs) is assessed experimentally in this paper. The system studied is composed of a horizontal flexible shaft supported by two ball bearings at one end and one roller bearing that is located in a squirrel cage at the other end. Four identical EMAs supplied with constant current are utilized. The EMAs associated to the squirrel cage constitutes the hybrid bearing. Results obtained, show that the constant current, when applied to the EMAs, produces a shift of the first critical speed toward lower values. Moreover, the application of constant current for a speed interval around the critical speed enables a smooth run-up or run-down without crossing any resonance.

Experimental measurements of non-Newtonian fluid flow through a stenotic tube

Trea Imane,Mahfoud Mohamed,Haddad Fadila 한국유변학회 2022 Korea-Australia rheology journal Vol.34 No.4

This paper presents an experimental study of the laminar flow of a non-Newtonian fluid through 75% (by area reduction) stenotic tubes. The fluid behaviour was described by the Herschel Bulkey non-Newtonian model. The non-Newtonian fluids were aqueous solutions of 0.1% Carbopol 940. Upstream flow conditions were steady and spanned a range of generalized Reynolds numbers Reg from 0.20 to 13.66. The velocity profiles were measured with a Laser Doppler Anemometry (LDA). This study allows us to see locally the influence of the geometry and the non-Newtonian character of the fluid on the velocity profiles, the pressure drops and flow resistance. From the experimental data, the frictional resistance decreases with increasing generalized Reynolds number Reg and resistance gave a weak value in a stenotic tube as compared to the flow in a simple tube. At the level of stenosis, a correlation relating of the Euler number to the generalized Reynolds number is developed. To compare the upstream and downstream parts of the stenosis, it is preferable to represent the pressure drops by the friction factor f. This factor f in upstream and downstream decreases linearly with the generalized Reynolds number Reg.

Adaptive balancing of highly flexible rotors by using artificial neural networks

Saldarriaga, M. Villafane,Mahfoud, J.,Steffen, V. Jr.,Der Hagopian, J. Techno-Press 2009 Smart Structures and Systems, An International Jou Vol.5 No.5

The present work is an alternative methodology in order to balance a nonlinear highly flexible rotor by using neural networks. This procedure was developed aiming at improving the performance of classical balancing methods, which are developed in the context of linearity between acting forces and resulting displacements and are not well adapted to these situations. In this paper a fully experimental procedure using neural networks is implemented for dealing with the adaptive balancing of nonlinear rotors. The nonlinearity results from the large displacements measured due to the high flexibility of the foundation. A neural network based meta-model was developed to represent the system. The initialization of the learning procedure of the network is performed by using the influence coefficient method and the adaptive balancing strategy is prone to converge rapidly to a satisfactory solution. The methodology is tested successfully experimentally.

Electromagnetic actuator design for the control of light structures

Der Hagopian, Johan,Mahfoud, Jarir Techno-Press 2010 Smart Structures and Systems, An International Jou Vol.6 No.1

An ElectroMagnetic Actuator (EMA) is designed and assessed numerically and experimentally. The EMA has the advantage to be without contact with the structure so it could be applied to light and small mechanism. Nevertheless, the open-loop instability and the nonlinear dynamic behavior with respect to the excitation frequency could limit its application field. The EMA is designed and dimensioned as a function of the experimental structure to be controlled. An inverse model of the EMA is proposed in order to implement a linear action block for the used frequency range. The control strategy is a fuzzy controller with displacements and velocities as inputs. A fuzzy controller of Takagi-Sugeno type is used. The air gap is estimated by using a modal approximation of the displacements issued from all measurements. Several configurations of control are assessed by using numerical simulations. The block diagram used for numerical simulations is implemented under Dspace$^{(R)}$ environment. The implemented controller was tested experimentally in the context of impact perturbations. The results obtained show the effectiveness of the developed procedures and the robustness of the implemented control.

Adaptive balancing of highly flexible rotors by using artificial neural networks

M. Villafañe Saldarriaga,J. Mahfoud,V. Steffen Jr.,J. Der Hagopian 국제구조공학회 2009 Smart Structures and Systems, An International Jou Vol.5 No.5

The present work is an alternative methodology in order to balance a nonlinear highly flexible rotor by using neural networks. This procedure was developed aiming at improving the performance of classical balancing methods, which are developed in the context of linearity between acting forces and resulting displacements and are not well adapted to these situations. In this paper a fully experimental procedure using neural networks is implemented for dealing with the adaptive balancing of nonlinear rotors. The nonlinearity results from the large displacements measured due to the high flexibility of the foundation. A neural network based meta-model was developed to represent the system. The initialization of the learning procedure of the network is performed by using the influence coefficient method and the adaptive balancing strategy is prone to converge rapidly to a satisfactory solution. The methodology is tested successfully experimentally.

Electromagnetic actuator design for the control of light structures

Johan Der Hagopian,Jarir Mahfoud 국제구조공학회 2010 Smart Structures and Systems, An International Jou Vol.6 No.1

An ElectroMagnetic Actuator (EMA) is designed and assessed numerically and experimentally. The EMA has the advantage to be without contact with the structure so it could be applied to light and small mechanism. Nevertheless, the open-loop instability and the nonlinear dynamic behavior with respect to the excitation frequency could limit its application field. The EMA is designed and dimensioned as a function of the experimental structure to be controlled. An inverse model of the EMA is proposed in order to implement a linear action block for the used frequency range. The control strategy is a fuzzy controller with displacements and velocities as inputs. A fuzzy controller of Takagi-Sugeno type is used. The air gap is estimated by using a modal approximation of the displacements issued from all measurements. Several configurations of control are assessed by using numerical simulations. The block diagram used for numerical simulations is implemented under Dspace?environment. The implemented controller was tested experimentally in the context of impact perturbations. The results obtained show the effectiveness of the developed procedures and the robustness of the implemented control.