The Experts below are selected from a list of 9213 Experts worldwide ranked by ideXlab platform

Othman Ben Mekki - One of the best experts on this subject based on the ideXlab platform.

  • Control of Bridge Structures with Semi-active Tuned Mass Damper
    Mechanics Models and Methods in Civil Engineering, 2012
    Co-Authors: Othman Ben Mekki, Frédéric Bourquin, Franco Maceri
    Abstract:

    Tuned mass dampers (TMDs) are widely used in civil engineering. the performance of this Device depends on their state parameters and therefore the evolution of the bridge may pull down the efficiency of this kind of Device. Active tuned mass damper (ATMD) have been explored widely for applications in damping response control of bridges under construction. This paper presents a new semi-active control based on an Electromechanical Device. This semi-active tool consists of a pendulum coupled to an alternator. The alternator converts the mechanical energy of the oscillating pendulum into electric energy to be dissipated through an exterior resistor via Joule effect. In order to damp the torsional mode of a bridge during successive construction phases, the Electromechanical actuator was connected to the bridge and its parameters were changed in real time by using a new semi-active control law. This control law, once applied to the resistor, permits to modify in real time the damping coefficients and the stiffness of the TMD with the aim of obtaining an optimal configuration for the actuator at each construction phase. Numerical and experimental validations on a small-scale bridge dynamical behaviour confirm the interest of the approach.

  • Performance evaluation of semi-active variable stiffness and damping Tuned Mass Damper
    2007
    Co-Authors: Frédéric Bourquin, Othman Ben Mekki
    Abstract:

    The performance of tuned mass dampers (TMDs), widely used in civil engineering, depends on their state parameters. Therefore the evolution of the controlled structure and the evolution of the type of excitation may pull down the efficiency of this kind of Device. Active tuned mass dampers (ATMDs) have been widely explored for damping the dynamic response of bridges under construction and submitted to various types of external excitations such as wind. However in view of permanent control of bridges under operation, active Devices suffer from several drawbacks such as the necessity of an important source of external energy that must always be available. In this paper a new type of semi-active control system based on an Electromechanical Device is presented. This semi-active tool consists of a pendulum coupled to an alternator. The alternator converts the mechanical energy of the oscillating pendulum into electrical energy to be dissipated through an exterior resistor via Joule effect. Given an optimal design of a reference pendulum TMD for the structure in its current configuration, the semi-active control consists in changing the resistor in real-time in such a way to lock the apparent stiffness and damping of the real TMD at their desired optimal values at each construction step and for each type of external excitation. Detailed experimental studies on a small-scale bridge mock-up show the effectiveness of this semi-active control Device and validates the capability of the semi-active control law to make the performance of the actuator independent of the structural evolution and of type of the external excitation.

  • Amortissement semi-actif des structures flexibles
    2006
    Co-Authors: Othman Ben Mekki
    Abstract:

    Tuned mass dampers (TMDs) have obtained an important success in civil engineering. Since their performance depends on the choice of its parameters and evolutions of the structure to be controlled may pull down the efficiency of this kind of Device. In this work we achieved a semi-active version based on Electromechanical Device. This semiactive version consists in a pendulum coupled at an alternator. When pendulum begins to oscillate, the alternator converts the mechanical energy into electric energy to be dissipated through an exterior resistor via Joule effect. Four points have been mainly developed in this work. ² The first point is devoted to obtaining an optimal design of a passive actuator using an optimization criteria. This criteria is based on the maximization of the exponential time decay rate by means of the pole placement technique. Numerical simulations have shown the actuator efficiency and the importance of their optimal parameters in absorbing the torsional mode of small-scale bridge under construction when it is in free vibration or also in harmonic vibration. ² The second point studies the multimodal vibration damping of the demonstrator bridge equipped with multiple actuators. In particular, three actuators have been used for control the first vertical mode, the torsional mode, the third mode and the sixth mode of vibrations of the demonstrator bridge. ² The third point consisted in developing the semi-active control law that permits to adapt the actuator parameters in real-time when the structure evolves. This semi-active control law consists in changing the resistor in real-time in such a way to lock the apparent stiffness of the real TMD at its desired optimal value and to vary the damping coefficient. ² The last point deals with the experimental study of the passive control and the semi active control on a small-scale bridge. In passive control, the theory of optimal design of the actuator parameters has been validated and the efficiency of the Electromechanical actuator has been confirmed. In semi-active control, only the advantage of the actuator in such a way to make its performance independent of the structural evolution has been validated.

P. Benkart - One of the best experts on this subject based on the ideXlab platform.

  • Analytical and numerical modelling of AlGaNnext term/previous termGaNnext term/previous termAlNnext term heterostructure based cantilevers for mechanical sensing in harsh environments
    Sensors and Actuators A: Physical, 2011
    Co-Authors: S. Vittoz, L. Rufer, G.p. Rehder, U. Heinle, P. Benkart
    Abstract:

    Some industrial areas as oil, automotive and aerospace industries, require Electromechanical systems working in harsh environments. An elegant solution is to use III-V materials alloys having semiconductor, piezoelectric and pyroelectric properties. These materials, particularly nitrides such as previous termGaNnext term or previous termAlNnext term, enable design of advanced Devices suitable for harsh environment. A cantilever structure based on previous termAlGaNnext term/previous termGaNnext term/previous termAlN heterostructures coupled with a High Electron Mobility Transistor (HEMT) can act as an Electromechanical Device suited for sensing applications. In this article, we present the mechanical modelling of such a structure. An analytical and a numerical model have been developed to obtain the electrical charge distribution in the structure in response to mechanical stress. A theoretical Electromechanical sensitivity of 3.5 μC m−2 was achieved for the cantilever free end displacement of several hundreds of nanometres. Both models show good agreement, presenting less than 5% deviation in almost the whole structure. The differences between the two models that are pronounced near the clamped area can be explained by particular boundary conditions of the numerical model. The topological characterization and numerical modelling allowed the estimation of the equivalent intrinsic residual stress in the structure and the stress distribution within each layer. Finally, the dynamic mechanical characterization of fabricated cantilevers using laser interferometry is presented and compared to numerical modal analysis with less than 10% deviation between theoretical and experimental resonant frequencies. The obtained results enable the use of the analytical model for further study of the Electromechanical coupling with the HEMT structure.

Samuel Bowong - One of the best experts on this subject based on the ideXlab platform.

  • Dynamics and chaos control of the self-sustained Electromechanical Device with and without discontinuity
    Communications in Nonlinear Science and Numerical Simulation, 2006
    Co-Authors: R. Yamapi, Samuel Bowong
    Abstract:

    Abstract In this paper, we consider the dynamics and chaos control of the self-sustained Electromechanical Device with and without discontinuity. The amplitude equations are derived in the general case using the harmonic balance method. The model without discontinuity is first considered. The effects of the amplitude of the parametric modulation and some particular coefficients are found in the response curves. The transition to chaotic behavior is found using numerical simulations of the equations of motion. We find that chaos appears in the model between the quasi-periodic and periodic orbits when the amplitude of the external excitation E 0 vary. An adaptive Lyapunov control strategy enables us to drive the system from the chaotic states to a targeting periodic orbit. The effects of elasticity and damping on the dynamics of the self-sustained Electromechanical system are also derived.

R. Yamapi - One of the best experts on this subject based on the ideXlab platform.

  • Dynamics and chaos control of the self-sustained Electromechanical Device with and without discontinuity
    Communications in Nonlinear Science and Numerical Simulation, 2006
    Co-Authors: R. Yamapi, Samuel Bowong
    Abstract:

    Abstract In this paper, we consider the dynamics and chaos control of the self-sustained Electromechanical Device with and without discontinuity. The amplitude equations are derived in the general case using the harmonic balance method. The model without discontinuity is first considered. The effects of the amplitude of the parametric modulation and some particular coefficients are found in the response curves. The transition to chaotic behavior is found using numerical simulations of the equations of motion. We find that chaos appears in the model between the quasi-periodic and periodic orbits when the amplitude of the external excitation E 0 vary. An adaptive Lyapunov control strategy enables us to drive the system from the chaotic states to a targeting periodic orbit. The effects of elasticity and damping on the dynamics of the self-sustained Electromechanical system are also derived.

  • Dynamics and synchronization of coupled self-sustained Electromechanical Devices
    Journal of Sound and Vibration, 2004
    Co-Authors: R. Yamapi, Paul Woafo
    Abstract:

    Abstract The dynamics and synchronization of two coupled self-excited Devices are considered. The stability and duration of the synchronization process between two coupled self-sustained electrical oscillators described by the Rayleigh–Duffing oscillator are first analyzed. The properties of the Hill equation and the Whittaker method are used to derive the stability conditions of the synchronization process. Secondly, the averaging method is used to find the amplitudes of the oscillatory states of the self-sustained Electromechanical Device, consisting of an electrical Rayleigh–Duffing oscillator coupled magnetically to a linear mechanical oscillator. The synchronization of two such coupled Devices is discussed and the stability boundaries of the synchronization process are derived using the Floquet theory and the Hill's determinant. Good agreement is obtained between the analytical and numerical results.

C. Vallee - One of the best experts on this subject based on the ideXlab platform.

  • Selective electromyography of dorsal neck muscles in humans
    Experimental Brain Research, 1997
    Co-Authors: M. A. Mayoux-benhamou, Marie Revel, C. Vallee
    Abstract:

    The patterns of activation of splenius capitis, semispinalis capitis, transversospinalis, and levator scapulae muscles were studied during various head-neck positions, movements, and isometric tests in 19 healthy human subjects. Myoelectric activities were recorded with intramuscular bipolar wire electrodes. Cervical computerized tomography of each subject was performed before the electromyography session in order to guide electrode insertion. Head motion was recorded using an Electromechanical Device. This report demonstrates that head motion results from a complex interaction of active muscular forces, passive ligamentous forces, and gravity. Splenius capitis has two main functions, i.e., cervical extension and ipsilateral rotation. Semi spinalis capitis and the transversospinalis are mainly extensors, and levator scapilae acts primarily on the shoulder girdle. Splenius capitis, semispinalis capitis, and transversospinalis play a subordinate part in ipsilateral tilting. In addition, most subjects' semispinalis capitis were gradually recruited during ipsilateral rotation. No signal was detected from the transversospinalis during rotation tests.

  • Surface electrodes are not appropriate to record selective myoelectric activity of splenius capitis muscle in humans
    Experimental Brain Research, 1990
    Co-Authors: M. A. Mayoux Benhamou, Marie Revel, C. Vallee
    Abstract:

    Splenius capitis (SPL) electromyograms were recorded using conventional surface and intramuscular wire electrodes simultaneously during various head-neck movements and isometric tasks to test the selectivity of surface electrodes for SPL myoelectric signals. The insertion of bipolar wire electrodes was aided by a computerized tomographical study of each subject's neck. Surface electrodes were placed over the superficial SPL area. Head motion was recorded with an Electromechanical Device. The selective SPL wire recordings confirmed that SPL has two main functions: ipsilateral rotation and extension. It also plays a subordinate role in ipsilateral tilting of the head. Intramuscular and surface recording results were contradictory mainly for flexion and contralateral rotation. These discrepancies appeared to be due to ‘cross-talk’ from adjacent muscles, particularly from the sternocleidomastoid muscle. We conclude the validity of electrode recordings is questionable for SPL and most dorsal neck muscles, especially during isometric tests.