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Nwoye I.,Federal University of Technology Owerri | Ogbonna A.I.,Federal University of Technology Owerri | Nwoye C.C.,Modelling and Simulation Unit | Umana R.A.,Federal University of Technology Owerri | And 2 more authors.
Journal of Engineering Science and Technology | Year: 2010

Model for calculating the concentration of dissolved iron during leaching of iron oxide ore in nitric acid solution has been derived. The model was found to be dependent on the value of the weight-input of iron oxide ore and final solution pH measured during the leaching process. It was observed that the validity of the model is rooted on the expression where both sides of the relationship are correspondingly approximately almost equal. The maximum deviation of the model-predicted dissolved %Fe values from the corresponding experimental values was found to be 28% which is quite within the acceptable range of deviation limit of experimental results. Dissolved iron concentration per unit mass of iron oxide ore input evaluated from experimental and model-predicted results are 0.0010%/g and 0.0011%/g respectively, indicating proximate agreement. © School of Engineering, Taylor's University College.

Nagy-Kiss A.M.,Modelling and Simulation Unit | Schutz G.,Modelling and Simulation Unit | Ragot J.,University of Lorraine
2014 European Control Conference, ECC 2014 | Year: 2014

The paper addresses a systematic procedure to deal with the state, unknown input and parameter uncertainty estimation for nonlinear time-varying systems. This is realized by designing a robust observer for dynamic nonlinear systems using a Takagi-Sugeno (T-S) multi-model (MM) approach with nonlinear outputs. The method applies the technique of descriptor systems by considering unknown inputs and parameter uncertainty as auxiliary state variables. This approach allows to apply the tools of the linear automatic to dynamic nonlinear systems by using the Linear Matrix Inequalities (LMI) optimization. The observer estimates the previous mentioned variables and minimizes the effect of external disturbances on the estimation error. The model uncertainties are included in the model in a polynomial way which allows to consider the model uncertainty estimation as a fault detection problem. The residual sensitivity to faults while maintaining robustness according to a noise signal is handled by H∞/H- approach.

Giunta G.,Modelling and Simulation Unit | Biscani F.,Modelling and Simulation Unit | Biscani F.,Polytechnic University of Turin | Belouettar S.,Modelling and Simulation Unit | And 2 more authors.
Composites Part B: Engineering | Year: 2013

This paper presents a free-vibration analysis of simply supported, cross-ply beams via several higher-order as well as classical theories. The three-dimensional displacement field is approximated along the beam cross-section in a compact form as a generic N-order polynomial expansion. Several higher-order displacements-based theories accounting for non-classical effects can be, therefore, formulated straightforwardly. Classical beam models, such as Euler-Bernoulli's and Timoshenko's, are obtained as particular cases. The governing differential equations and the boundary conditions are derived by variationally imposing the equilibrium via the principle of virtual displacements. Thanks to the compact form of the displacement field approximation, governing equations are written in terms of a fundamental nucleo that does not depend upon the approximation order. A Navier-type, closed form solution is adopted in order to derive the governing algebraic equations. Besides the fundamental natural frequency, natural frequencies associated to higher modes (such as torsional, axial, shear and mixed ones) are investigated. A half waves number equal to one is considered. The effect of the length-to-thickness ratio, lamination, aspect ratio and material properties on: (1) the accuracy of the proposed theories and (2) the natural frequencies and modes is presented and discussed. For the latter case, the modes change in order of appearance (modes swapping) and in shape (modes mutation) is investigated. Results are assessed towards three-dimensional FEM solutions. Numerical results show that, upon the choice of the appropriate approximation order, very accurate results can be obtained for all the considered modes. © 2012 Published by Elsevier Ltd.

Giunta G.,Modelling and Simulation Unit | Metla N.,Modelling and Simulation Unit | Koutsawa Y.,Modelling and Simulation Unit | Belouettar S.,Modelling and Simulation Unit
Composites Part B: Engineering | Year: 2013

This paper presents a free vibration and a stability analysis of three-dimensional sandwich beams. Several higher-order displacements-based theories as well as classical models (Euler-Bernoulli's and Timoshenko's ones) are derived assuming a unified formulation by a priori approximating the displacement field along the cross-section in a compact form. The governing differential equations and the boundary conditions are derived in a nucleal form that corresponds to a generic term in the displacement field approximation. The resulting fundamental nucleo does not depend upon the approximation order N that is a free parameter of the formulation. A Navier-type, closed form solution is used. Simply supported beams are, therefore, investigated. Slender up to very short beams are considered. As far as free vibrations are concerned, the fundamental natural frequency as well as natural frequencies associated to torsional and higher modes such as sheet face bending and twisting (typical of sandwich structures) are investigated. The stability analysis is carried out in terms of critical buckling stress in the framework of a linearised elastic approach. Results are assessed towards three-dimensional FEM solutions. It is shown that upon an appropriate choice of the approximation order, the proposed models are able to match the three-dimensional reference solutions. © 2012 Elsevier Ltd. All rights reserved.

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