186,861 research outputs found
Experimental study of thin film sensor networks for wind turbine blade damage detection
No full textDamage detection of wind turbine blades is difficult due to their complex geometry and large size, for which large deployment of sensing systems is typically not economical. A solution is to develop and deploy dedicated sensor networks fabricated from inexpensive materials and electronics. The authors have recently developed a novel skin-type strain gauge for measuring strain over very large surfaces. The skin, a type of large-area electronics, is constituted from a network of soft elastomeric capacitors. The sensing system is analogous to a biological skin, where local strain can be monitored over a global area. In this paper, we propose the utilization of a dense network of soft elastomeric capacitors to detect, localize, and quantify damage on wind turbine blades. We also leverage mature off the shelf technologies, in particular resistive strain gauges, to augment such dense sensor network with high accuracy data at key locations, therefore constituting a hybrid dense sensor network. The proposed hybrid dense sensor network is installed inside a wind turbine blade 1:25 scale model, and tested in a wind tunnel to simulate an operational environment. Results demonstrate the ability of the hybrid dense sensor network to detect, localize, and quantify damage.</p
A posteriori error estimation in finite element analysis of plate structures
No full textA posteriori error estimation is an important tool in finite element software development, since it allows to verify and validate the finite element simulations. An efficient and practical way to derive a posteriori error estimators is offered by recovery procedures, which estimate the error by comparing the original finite element solution with the recovered one. The major steps forward in using recovery procedures were made with the Superconvergent Patch Recovery
(SPR) and the Recovery by Equilibrium in Patches (REP) procedures [1,2], both successfully applied to plate problems in [3]. Recently, a new superconvergent procedure called Recovery by Compatibility in Patches (RCP) has been proposed by one of the authors [4] and shown to provide an excellent basis for error estimation in 2D problems [5].
Within this context, the present paper aims at presenting an extension of the RCP-based error estimation to Reissner-Mindlin plates finite element analysis. The basic idea is to recover stress
resultants by enforcing compatibility over patches of elements. Displacements computed by the finite element analysis are prescribed on the boundary of the patch, and improved stress
resultants are computed by minimizing the complementary energy of such a sub-model. The resulting procedure is simple, efficient, numerically stable and does not need any knowledge of superconvergent points. Some numerical examples are given.
References:
1. O.C. Zienkiewicz, J.Z. Zhu, “The superconvergent patch recovery and a posteriori error estimates. Part I: The recovery technique”, International Journal for Numerical Methods in Engineering, v. 33, p. 1331-1364, 1992.
2. B. Boroomand, O.C. Zienkiewicz, “An improved REP recovery and the effectivity robustness test”, International Journal for Numerical Methods in Engineering, v. 40, p. 3247-3277, 1997.
3. B. Boroomand, M. Ghaffarian, O.C. Zienkiewicz, “On application of two superconvergent recovery procedures to plate problems”, International Journal for Numerical Methods in Engineering, v. 61, p. 1644-1673, 2004.
4. F. Ubertini, “Patch recovery based on complementary energy”, International Journal for Numerical Methods in Engineering, v. 59, p. 1501-1538, 2004.
5. A. Benedetti, S. de Miranda, F. Ubertini, “A posteriori error estimation based on the superconvergent Recovery by Compatibility in Patches”, International Journal for Numerical
Methods in Engineering, in press
Bacino campione Foso degli Impiccati - Primi risultati sulla valutazione dell'umidità naturale del terreno per migliorare la stima di un modello di previsione dei deflussi
No full text
Discontinuous Galerkin approach for mechanically driven mass diffusion in elastic solids
No full textMechanically driven mass diffusion is characterized by a two-way interaction between mechanical and diffusive quantities: changes in mass concentration induce volumetric strain in the solid (swelling effect) and, vice versa, volumetric strain induces mass fluxes
(piezo-diffusive effect). In the standard finite element setting, the presence of strain gradients in the piezo-diffusive coupling term demands C1 continuous displacement interpolation. Various techniques can be used to avoid C1 continuous shape functions. In
the literature, the most used strategies for the solution of the problem are: a mixed approach, where the volumetric strain is interpolated as an independent variable (early explored in [1]), and a staggered solution strategy in conjunction with a smoothing L2
projection in the entire domain [2].
In this paper, a new formulation, which requires standard C0 interpolation for both displacement and concentration, is presented, basing on a discontinuous Galerkin approach. Recently, these approaches have been successfully used for strain gradient
models [3]. The new formulation is discussed and compared with a mixed one and with a staggered solution strategy used employing a smoothing superconvergent patch-based recovery procedure, proposed in [4]. An error analysis is carried out to show the convergence rate. The discontinuous formulation exhibits convergence properties comparable to those of the mixed formulation, but allows to drastically reduce the computational cost with respect the other approaches. Some benchmarks are proposed to validate the formulation.
References:
1. S. P. Girrens, F. W. Smith, "Finite element analysis of coupled constituent diffusion in thermoelastic solids", Computer Methods in Applied Mechanics in Engineering, v. 62, p. 209-223, 1987.
2. K. Garikipati, L. Bassman, M. Deal, "A lattice-based micromechanical continuum formulation for stress-driven mass transport in polycrystalline solids", Journal of the Mechanics and Physics of Solids, v. 49, p. 1209-1237, 2001.
3. L. Molari, G. N. Wells, K. Garikipati, F. Ubertini, "A Discontinuous Galerkin method for a strain gradient-dependent damage: Study of interpolations, convergence", Computer Methods in Applied Mechanics in Engineering, v.195, p. 1480-1498, 2006.
4. F. Ubertini, "Patch recovery based on complementary energy", International Journal for Numerical Methods in Engineering, v. 59, p. 1501-1538, 2004
Significato del minimo deflusso vitale e sua determinazione per un corso d'acqua dell'Italia Centrale
No full textDynamic monitoring of compliant bodies impacting the water surface through local strain measurements
No full textThe understanding and the experimental characterization of the evolution of impulsive loading is crucial in several fields in structural, mechanical and ocean engineering, naval architecture and aerospace. In this regards, we developed an experimental methodology to reconstruct the deformed shape of compliant bodies subjected to impulsive loadings, as those encountered in water entry events, starting from a finite number of local strain measurements performed through Fiber Bragg Gratings. The paper discusses the potential applications of the proposed methodology for: i) real-Time damage detection and structural health monitoring, ii) fatigue assessment and iii) impulsive load estimation
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