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Structural decoupling problem, i.e. predicting dynamic behavior of a particular substructure from the knowledge of the dynamics of the coupled structure and the other substructure, has been well investigated for three decades and ...
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Structural decoupling problem, i.e. predicting dynamic behavior of a particular substructure from the knowledge of the dynamics of the coupled structure and the other substructure, has been well investigated for three decades and led to several decoupling methods. In spite of the inherent nonlinearities in a structural system in various forms such as clearances, friction and nonlinear stiffness, all decoupling studies are for linear systems. In this study, decoupling problem for nonlinear systems is addressed for the first time. A method, named as FRF Decoupling Method for Nonlinear Systems (FDM-NS), is proposed for calculating FRFs of a substructure decoupled from a coupled nonlinear structure where nonlinearity can be modeled as a single nonlinear element. Depending on where nonlinear element is, i.e., either in the known or unknown subsystem, or at the connection point, the formulation differs. The method requires relative displacement information between two end points of the nonlinear element, in addition to point and transfer FRFs at some points of the known subsystem. However, it is not necessary to excite the system from the unknown subsystem even when the nonlinear element is in that subsystem. The validation of FDM-NS is demonstrated with two different case studies using nonlinear lumped parameter systems. Finally, a nonlinear experimental test structure is used in order to show the real-life application and accuracy of FDM-NS.
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In the present paper, an unknown input multiobserver (UIMO) is designed for the state estimation of uncertain non-linear systems. A discrete decoupled state multimodel is exploited to describe the behavior of non-linear systems. A...
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In the present paper, an unknown input multiobserver (UIMO) is designed for the state estimation of uncertain non-linear systems. A discrete decoupled state multimodel is exploited to describe the behavior of non-linear systems. A particular transformation of uncertainties to unknown inputs is considered. The LMI approach is used to establish the convergence conditions of the state estimation error. The efficiency of the proposed strategy is emphasized through an illustrative example and a real time application on a semi-batch reactor that lead to good performance in terms of robustness, convergence speed and precision. (C) 2019 ISA. Published by Elsevier Ltd. All rights reserved.
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Coupled second-order nonlinear differential equations are of fundamental importance in dynamics. In this part of our study on the integrability and linearization of nonlinear ordinary differential equations (ODEs), we focus our at...
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Coupled second-order nonlinear differential equations are of fundamental importance in dynamics. In this part of our study on the integrability and linearization of nonlinear ordinary differential equations (ODEs), we focus our attention on the method of deriving a general solution for two coupled second-order nonlinear ODEs through the extended Prelle-Singer procedure. We describe a procedure to obtain integrating factors and the required number of integrals of motion so that the general solution follows straightforwardly from these integrals. Our method tackles both isotropic and non-isotropic cases in a systematic way. In addition to the above-mentioned method, we introduce a new method of transforming coupled second-order nonlinear ODEs into uncoupled ones. We illustrate the theory with potentially important examples.
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In this work, a simple, stable, non-iterative, uncoupled formulation is proposed for nonlinear pore-dynamic analyses. Here, each phase of the coupled problem is treated separately, uncoupling the governing equations of the porous ...
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In this work, a simple, stable, non-iterative, uncoupled formulation is proposed for nonlinear pore-dynamic analyses. Here, each phase of the coupled problem is treated separately, uncoupling the governing equations of the porous model. Thus, simpler, smaller and better conditioned systems of equations are obtained, providing a more efficient numerical approach. In addition, in the proposed technique, solution is carried out without considering any iterative computation, even when nonlinear models are regarded, further improving the effectiveness of the method. Incompressible and impermeable media may also be directly analysed by the new formulation, without requiring any special discretization procedure, as it is the case in standard analyses. At the end of the paper, numerical examples are presented, illustrating the effectiveness and potentialities of the new technique. (C) 2019 Elsevier B.V. All rights reserved.
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Generalized hydrodynamic equations were originally proposed to describe the rarefied non-equilibrium flows beyond the Navier–Stokes–Fourier (NSF) equations by constructing a non-equilibrium canonical distribution function for th...
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Generalized hydrodynamic equations were originally proposed to describe the rarefied non-equilibrium flows beyond the Navier–Stokes–Fourier (NSF) equations by constructing a non-equilibrium canonical distribution function for the mesoscopic Boltzmann equation. Subsequently, nonlinear coupled constitutive relations (NCCR) were developed under the adiabatic assumption, the Eu’s closure, and Myong’s simplification. NCCR+ was also proposed to include the omitted terms in Myong’s simplification. The goal of this paper is to assess the improvements in the accuracy due to NCCR+ and the influence of the bulk viscosity in one-dimensional steady shock wave structure for monatomic and diatomic gases. In order to solve NCCR+ equations, a coupled solution process based on the time-independent method for non-conserved variables is employed, which is different from the previous uncoupled solution process used for the NCCR equations. Shock structures in argon and nitrogen are calculated up to Mach 50, where the shock profile, inverse shock thickness, asymmetry parameter, and temperature–density separation distance are validated by DSMC and available experimental measurements. The results show that NCCR+ could not provide much improvement in accuracy compared to NCCR but adds to the computational cost, suggesting that Myong’s simplification used in NCCR is satisfactory. Both NCCR and NCCR+ perform better than NSF in computing the one-dimensional shock wave structure at high Mach numbers. It is also shown that the bulk viscosity has significant influence on the accuracy of prediction of the shock wave structure in a diatomic gas using both NSF and NCCR. Stokes’ hypothesis in conventional NSF is valid only for flows in a monatomic gas and for very low Mach number flows in a diatomic gas. Additionally, it is also found that the viscosity exponent s?=?0.81 in variable-hard-sphere model provides a good fit with the experimental data for shock wave in argon using NCCR.
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Self-healing materials have recently become more popular due to their capability to autonomously and auto-genously repair the damage in concrete material. A simple damage healing law is proposed in this paper. The proposed damage ...
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Self-healing materials have recently become more popular due to their capability to autonomously and auto-genously repair the damage in concrete material. A simple damage healing law is proposed in this paper. The proposed damage healing law is based on a time-dependent healing variable which represents the opposite of the damage variable. The damage-healing model is applied on an isotropic concrete material at the macroscale under tensile load. The coupled and un-coupled self-healing mechanisms are studied using the proposed model and new healing variables are defined for each self-healing mechanism. Both healing mechanisms represent the capability of the material to autonomously and autogenously heal the cracks in concrete material. In addition, the so-called nonlinear healing theory is applied on both coupled and uncoupled self-healing mechanisms, and compared to the classical self-healing theory. The objective of the present work is to describe the capability of the proposed damage-healing model to describe the behavior of the partially and fully healed concrete material after it has been damaged in both coupled and uncoupled self-healing mechanisms using both linear and nonlinear self-helaing theories. The results show that the damage-healing model is capable to simulate both coupled and uncoupled healing mechanisms, and the nonlinear healing theory underestimates the healing efficiency in both coupled and uncoupled healing mechanisms comparing to the classical healing theory.
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The present paper deals with the design of sliding mode multiobserver for nonlinear systems with delayed measurements. The discrete uncoupled state multimodel is exploited to describe the global behavior of nonlinear systems. Ther...
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The present paper deals with the design of sliding mode multiobserver for nonlinear systems with delayed measurements. The discrete uncoupled state multimodel is exploited to describe the global behavior of nonlinear systems. Therefore, the complexity of the latter can be reduced by its decomposition into a finite number of partial models. The proposed sliding mode multiobserver is designed based on this uncoupled multimodel approach. Sufficient conditions are formulated in terms of linear matrix inequalities in order to ensure the asymptotic stability of the designed multiobserver. Illustrative examples are included to show the effectiveness of the proposed strategy.
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The identification and the design of an accurate control are still an active researches of nonlinear systems subject to harmonic disturbances. In this paper, we propose two techniques to deal with nonlinear system identification a...
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The identification and the design of an accurate control are still an active researches of nonlinear systems subject to harmonic disturbances. In this paper, we propose two techniques to deal with nonlinear system identification and control problems. First, a new identification scheme based only on input/output measurements is proposed. In this scheme, an adaptive filter is used to extract the periodic disturbance and the non-perturbed system dynamics from the real output. Then, a multimodel approach is adopted to obtain the models base of the real non-perturbed system. Secondly,the models base is used to develop a multi-model sliding mode control (MM-SMC). Thereafter, the structure of plug-in repetitive control is incorporated into the MM-SMC to ensure good closed loop performances in terms of harmonic disturbance rejection and tracking in the case of nonlinear systems. Simulation results of two numerical examples shows the effectiveness of the proposed identification and control strategies in spite the presence of nonlinearities and harmonic disturbances.
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The bottom slamming of a Very Large Floating Structure (VLFS) has been studied with theoretical and numerical tools. The strategies adopted are: (i) a linear analysis for modeling the global motions of the platform, followed by (i...
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The bottom slamming of a Very Large Floating Structure (VLFS) has been studied with theoretical and numerical tools. The strategies adopted are: (i) a linear analysis for modeling the global motions of the platform, followed by (ii) a fully nonlinear description for the bottom-slamming occurrence. Model (i) is used to examine the global behavior of a VLFS at model and full scales, and model (ii) is applied to investigate the bottom-slamming features in terms of flow evolution and induced pressure and stresses on the platform bottom. Excitation of hydroelastic coupling and occurrence of air cushion are also discussed together with the challenges connected with scaling effects.
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The objective of this paper is to present comparative and parametric studies employing uncoupled and hybrid methodologies for the motion analysis of floating platforms and their consequences for the fatigue damage of the risers. T...
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The objective of this paper is to present comparative and parametric studies employing uncoupled and hybrid methodologies for the motion analysis of floating platforms and their consequences for the fatigue damage of the risers. The studies are performed using a model of the P18 platform, located at Campos Basin, Brazil, that comprises the first Steel Catenary Riser (SCR) installed by Petrobras. The structural/fatigue analysis of this SCR was used for the comparison of both methodologies. Some typical results of motions are compared separately in wave and low frequency ranges.
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