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Simon X Yang - One of the best experts on this subject based on the ideXlab platform.

  • a Discrete optimal control method for a flexible cantilever beam with time delay
    Journal of Vibration and Control, 2006
    Co-Authors: Guoping Cai, Simon X Yang
    Abstract:

    Time delay inevitably exists in active control systems. It may cause unsynchronized control forces that can not only degrade the perFormance of the control systems, but also induce instability of the dynamic systems. In this paper, an active vibration controller (with time delay) for a flexible cantilever beam is studied and a method for treating the time delay is proposed. The dynamic equation of the controlled mode with time delay is first presented using the independent modal space control, and is then discretized and transFormed into a standard Discrete Form with no explicit time delay by augmenting the state variables. The continuous perFormance index is also transFormed into a Discrete Form. Then, a Discrete optimal control algorithm is designed based on the augmented state system. Since time delay effect is incorporated in the mathematical model of the dynamic system throughout the control design and no approximations and assumptions are made in the control algorithm derivation, system stability is...

Véronique Duprat - One of the best experts on this subject based on the ideXlab platform.

  • Long-Time Stability Analysis of Acoustic Absorbing Boundary Conditions for Regular-Shaped Surfaces
    Mathematical Models and Methods in Applied Sciences, 2013
    Co-Authors: Hélène Barucq, Julien Diaz, Véronique Duprat
    Abstract:

    This work deals with the stability analysis of a one-parameter family of Absorbing Boundary Conditions (ABC) that have been derived for the acoustic wave equation. We tackle the problem of long-term stability of the wave field both at the continuous and the numerical levels. We first define a function of energy and we show that it is decreasing in time. Its Discrete Form is also decreasing under a Courant-Friedrichs-Lewy (CFL) condition that does not depend on the ABC. Moreover, the decay rate of the continuous energy can be determined: it is exponential if the computational domain is star-shaped and this property can be illustrated numerically.

Guoping Cai - One of the best experts on this subject based on the ideXlab platform.

  • a Discrete optimal control method for a flexible cantilever beam with time delay
    Journal of Vibration and Control, 2006
    Co-Authors: Guoping Cai, Simon X Yang
    Abstract:

    Time delay inevitably exists in active control systems. It may cause unsynchronized control forces that can not only degrade the perFormance of the control systems, but also induce instability of the dynamic systems. In this paper, an active vibration controller (with time delay) for a flexible cantilever beam is studied and a method for treating the time delay is proposed. The dynamic equation of the controlled mode with time delay is first presented using the independent modal space control, and is then discretized and transFormed into a standard Discrete Form with no explicit time delay by augmenting the state variables. The continuous perFormance index is also transFormed into a Discrete Form. Then, a Discrete optimal control algorithm is designed based on the augmented state system. Since time delay effect is incorporated in the mathematical model of the dynamic system throughout the control design and no approximations and assumptions are made in the control algorithm derivation, system stability is...

Vincenzo Tibullo - One of the best experts on this subject based on the ideXlab platform.

  • Seismic oscillations of an elastic rectangular structure protected by a viscoelastic stratum: in-plane problem
    Meccanica, 2014
    Co-Authors: Michele Ciarletta, Mezhlum A. Sumbatyan, Vincenzo Tibullo
    Abstract:

    We study the problem of seismic protection of a rectangular elastic construction by mean of a viscoelastic stratum made of material of Kelvin–Voigt type. In particular we consider the in-plane problem. By using the standard boundary integral equations method (BIEs), the dynamic problem is reduced to a system of BIEs over the set of boundary lines. In order to reduce the dimension of the problem in its Discrete Form, for wave processes in the stratum and in the half-space foundation we use a special Green’s function satisfying the stress-free boundary conditions over the boundary of the half-space. A numerical algorithm is used to solve the problem after discretization and finally we discuss the physical meaning of the results and the efficiency of the seismic protection by the viscoelastic stratum.

Hongbing Fang - One of the best experts on this subject based on the ideXlab platform.

  • a deFormation gradient tensor and strain tensors for atomistic simulations
    Modelling and Simulation in Materials Science and Engineering, 2008
    Co-Authors: Phillip M. Gullett, Mark F. Horstemeyer, Michael I. Baskes, Hongbing Fang
    Abstract:

    A kinematical algorithm is proposed for the construction of strain tensors from atomistic simulation data. Local strain tensors such as the Almansi and Green strain tensors suitable for use in large deFormation molecular dynamics/statics simulations are computed directly from a Discrete Form of the deFormation gradient. The Discrete, incremental Form of the deFormation gradient emerges from a weighted least squares minimization that includes a length scale relating the distance from the atom in question with a particular radius. This region defines the nonlocal domain of the strain at that atom. The local atomic strain tensors are then computed using continuum definitions in terms of the deFormation gradient. The results of molecular dynamics simulations are presented that compare the Almansi and Green strain tensors under inhomogeneous deFormation and indicate that the small-strain approximation should not be used to determine large atomic strains.