H.E. Dillon, A.F. Emery^†, A.M. Mescher, O. Sprenger, S.R. Edwards

Frontiers in Heat and Mass Transfer, Vol.2, No.2, pp. 1-14, 2011, DOI:10.5098/hmt.v2.2.3002

Abstract The stability of free convection in an annulus is governed by the boundary conditions on the inner and outer walls of the annulus and the upper and lower boundaries. This paper explores the effect of free convection on the inner surface of the annulus, where the boundary conditions for the outer wall and the upper and lower boundaries are controlled. The temperature is measured in the center of the air cavity and just below the surface of the inner annular boundary. Experimental results are shown for a radius ratio of 0.40, aspect ratio of 20.7. More >

S.J. Zhu, Q.H Zeng, J.J Lou, Q.W He

The International Conference on Computational & Experimental Engineering and Sciences, Vol.18, No.2, pp. 43-44, 2011, DOI:10.3970/icces.2011.018.043

Abstract Line spectra are the most visible signs of the ships' radiated noise spectrum. The potential of chaotifying vibration isolation systems to reduce line spectra and improve its capability of concealment have been recently reported. Basically, as the existing isolation system design is based on linear theory, it is difficult to produce the nonlinear chaotic motion; and if the vibration isolation system(VIS) is designed directly using the nonlinear theory, it is also difficult to produce the chaotic motion because of the difficulties in accurate calculation of vibration isolation device parameters. In this paper, a controller design More >

J.L. Sereno¹, J.C.F. Pereira¹

CMES-Computer Modeling in Engineering & Sciences, Vol.73, No.1, pp. 23-44, 2011, DOI:10.3970/cmes.2011.073.023

Abstract The evolution of a two-dimensional vortex pair in ground effect was studied under the influence of random initial inputs comprising vortex strength (circulation) or initial vortex position. The paper addresses the questions of how do variations and uncertainties of initial conditions translate to the variability of vortex pair evolution. The stochastic solutions were obtained recurring to the Polynomial Chaos Expansion method of random processes applied to the Navier-Stokes equations for a laminar flow. The method quantifies the extent, dependence and propagation of uncertainty through the model system and, in particular, a methodology for the calculation More >

Veturia Chiroiu¹, Ligia Munteanu², Ioan Ursu³

CMES-Computer Modeling in Engineering & Sciences, Vol.72, No.3, pp. 229-246, 2011, DOI:10.3970/cmes.2011.072.229

Abstract Chaotic behavior of uncertain nonlinear systems offers a rich variety of orbits, which can be controlled by bounding the signals involved in closed-loop systems. In this paper, systems with nonlinear uncertainties with no prior knowledge of their bounds, unmodeled dynamic law and rapidly varying disturbances are analyzed in order to propose a stabilization controller of the chaotic behavior via the fuzzy logic systems. More >

G.J.A. Loeven^1,2, H. Bijl³

CMES-Computer Modeling in Engineering & Sciences, Vol.36, No.3, pp. 193-212, 2008, DOI:10.3970/cmes.2008.036.193

Abstract In this paper a Two-Step approach is presented for uncertainty quantification for expensive problems with multiple uncertain parameters. Both steps are performed using the Probabilistic Collocation method. The first step consists of a sensitivity analysis to identify the most important parameters of the problem. The sensitivity derivatives are obtained using a first or second order Probabilistic Collocation approximation. For the most important parameters the probability distribution functions are propagated using the Probabilistic Collocation method using higher order approximations. The Two-Step approach is demonstrated for flow around a NACA0012 airfoil with eight uncertain parameters in the More >

L. Parussini¹, V. Pediroda²

CMES-Computer Modeling in Engineering & Sciences, Vol.23, No.1, pp. 29-52, 2008, DOI:10.3970/cmes.2008.023.029

Abstract In this paper different Polynomial Chaos methods coupled to Fictitious Domain approach have been applied to one- and two- dimensional elliptic problems with multi uncertain variables in order to compare the accuracy and convergence of the methodologies. Both intrusive and non-intrusive methods have been considered, with particular attention to their employment for quantification of geometric uncertainties. A Fictitious Domain approach with Least-Squares Spectral Element approximation has been employed for the analysis of differential problems with uncertain boundary domains. Its main advantage lies in the fact that only a Cartesian mesh, that represents the enclosure, needs More >

L. Parussini¹, V. Pediroda²

CMES-Computer Modeling in Engineering & Sciences, Vol.22, No.1, pp. 41-64, 2007, DOI:10.3970/cmes.2007.022.041

Abstract In this paper the Non-Intrusive Polynomial Chaos Method coupled to a Fictitious Domain approach has been applied to one- and two-dimensional elliptic problems with geometric uncertainties, in order to demonstrate the accuracy and convergence of the methodology. The main advantage of non-intrusive formulation is that existing deterministic solvers can be used. A new Least-Squares Spectral Element method has been employed for the analysis of deterministic differential problems obtained by Non-Intrusive Polynomial Chaos. This algorithm employs a Fictitious Domain approach and for this reason its main advantage lies in the fact that only a Cartesian mesh More >

G.Ananthakrishna¹

CMES-Computer Modeling in Engineering & Sciences, Vol.7, No.3, pp. 233-240, 2005, DOI:10.3970/cmes.2005.007.233

Abstract We show that the extended Ananthakrishna's model exhibits all the features of the Portevin - Le Chatelier effect including the three types of bands. The model reproduces the recently observed crossover from a low dimensional chaotic state at low and medium strain rates to a high dimensional power law state of stress drops at high strain rates. The dynamics of crossover is elucidated through a study of the Lyapunov spectrum. More >