Discrete layer finite element modeling of anisotropic laminated shells based on a refined semi - inverse mixed displacement field formulation

This paper concerns the finite element (FE) modeling of anisotropic laminated shells. A discretelayer approach is employed in this work and a single layer is first considered and isolatedfrom the multilayer shell structure. The weak form of the governing equations of theanisotropic single layer of the multilayer shell is derived with Hamiltons principle using amixed (stresses/displacements) definition of the displacement field, which is obtained througha semi-inverse (stresses/strains-displacements) approach. Results from 3-D elasticity solutionsare used to postulate adequate definitions of the out-of-plane shear stress components, which,in conjunction with the Reissner-Mindlin theory (or first order shear deformation theory) de-finitions of the shell in-plane stresses, are utilized to derive the mixed displacement field.Afterward, the single layer shell FE is regenerated to a 3-D form, which allows interlayerdisplacements and out-of-plane stresses continuity between adjacent interfaces of different layersto be imposed, and a multilayer shell FE is obtained by assembling, at an elemental FElevel, all the regenerated single layer FE contributions. A fully refined shell theory, wheredisplacement and full out-of-plane stresses continuity and homogeneous stress conditions onthe top and bottom surfaces are assured, is conceptually proposed, and a partially refined shelltheory, where the out-of-plane normal stress continuity is relaxed and a plane stress state is considered,is developed and used to derive a FE solution for segmented multilayer doubly-curvedanisotropic shells

Experiment K-6-16. Morphological examination of rat testes. The effect of Cosmos 1887 flight on spermatogonial population and testosterone level in rat testes

Testes from rats flown on Cosmos 1887 for twelve and a half days were compared to basal control, synchronous control and vivarium maintained rats. When the mean weights of flight testes, normalized for weight/100 gms, were compared to the vivarium controls they were 6.7 percent lighter. Although the flight testes were lighter than the synchronous, the difference is not significant. Counts of spermatogonial cells from 5 animals in each group revealed a 4 percent decrease in flight compared to vivarium controls. In both cases the t-Test significance was less than 0.02. The serum testosterone levels of all animals (flight, synchronous and vivarium) were significantly below the basal controls

Controlo activo de vibrações de vigas com sensores e actuadores piezoeléctricos: modelação e experimentação

Neste trabalho apresentam-se e caracterizam-se as principais fases envolvidas naconcepção de um sistema de controlo activo de vibrações de estruturas adaptativas:modelação numérica (modelo estrutural, modelo de controlo e simulação) e experimentação(montagem dos sensores e actuadores, implementação do controlador e análise dosresultados experimentais). Para isso, um caso de estudo específico de uma viga adaptativa éapresentado, demonstrando a necessidade e a capacidade do modelo na antevisão depotenciais instabilidades do sistema de controlo. O modelo espacial é caracterizado,apresentando-se o modelo de elementos finitos de viga adaptativa de três camadas, assentenuma formulação layerwise parcial dos deslocamentos e numa teoria com acoplamentoelectromecânico total. No modelo de controlo, o sistema dinâmico é representado na basemodal do espaço de estados. No caso de estudo apresentado, um sistema de controlo porfeedback, com base nas medições da velocidade efectuadas por um transdutor laser, éavaliado por via numérica e experimental na capacidade de amortecer as vibrações numaviga adaptativa em regime forçado harmónico. Da análise dos resultados numéricos eexperimentais demonstra-se, por um lado, a robustez e representatividade do modelo deelementos finitos e, por outro, a aplicabilidade e funcionalidade do sistema de controloactivo de vibrações apresentado

On the performance of hybrid active-passive damping treatments mechanisms for vibration control of beams using adaptive feedforward strategies

This paper concerns the adaptive feedforward control of vibration of a freely supported beamwith two distinct surface mounted hybrid active-passive damping treatments. The first configurationconcerns the use of an Active Constrained Layer Damping (ACLD) patch alone, wherethe piezoelectric constraining layer is actively utilized to increase the shear deformation of thesandwiched passive viscoelastic layer and at the same time to apply forces and moments intothe structure, which will balance the power flows into the structure, and is denoted by ACLDconfiguration. The second configuration regards the use, as an active element in the control,of a piezoelectric patch alone, denoted by Active Damping (AD), and since the constraininglayer of the ACLD treatment also bonded on the other side of beam is not actively utilized,a Passive Constrained Layer Damping (PCLD) treatment is utilized in combination with AD,and an AD/PCLD configuration is considered. A finite element (FE) model of the beam withthe damping treatments is used for the simulation of the adaptive feedforward controller whichis also tested in real-time. The aims are to compare the predicted and measured damping performancesof the two treatments, in terms of vibration reduction, control effort, stability androbustness when a filtered-reference LMS algorithm is used to cancel the effects of a broadbandvoltage disturbance applied into a third surface mounted piezoelectric patch which is used toexcite the beam

Shells with hybrid active-passive damping treatments: modeling and vibration control

This paper concerns the mathematical modeling and finite element (FE) solution of general anisotropic shells with hybrid active-passive damping treatments. A fully-coupled piezo-visco-elastic mathematical model of the shell (host structure) and segmented arbitrarily stacked layers of damping treatments is considered. A discrete layer approach is employed in this work, and the weak form of the governing equations is derived for a single generic layer of the multilayer shell using Hamilton's principle and a mixed (displacement/stresses) definition of the displacement field. First, a fully refined deformation theory of the generic layer, based on postulated out-of-plane shear stress definitions and in the in-plane stresses obtained with a Reissner-Mindlin type shell theory, is outlined. A semi-inverse procedure is used to derive the layer mixed non-linear displacement field, in terms of a blend of the generalized displacements of the Love-Kirchhoff and Reissner-Mindlin theories and of the stress components at the generic layer interfaces. No assumptions regarding the thinness of the shell are considered. Regarding the definition of the electric potential, the direct piezoelectric effects are condensed into the model through effective stiffness and strains definitions, and the converse counterpart is considered by the action of prescribed electric potential differences in each piezoelectric layer. Then, the weak forms of a partially refined theory, where only the zero-order term of the non-linear fully refined transverse displacement is retained, are derived for an orthotropic doubly-curved piezo-elastic generic shell layer. Based on the weak forms a FE solution is initially developed for the single layer. The degrees of freedom (DoFs) of the resultant four-noded generic piezo-elastic single layer FE are then "regenerated" into an equivalent eight-node 3-D formulation in order to allow through-the-thickness assemblage of displacements and stresses, yielding a partially refined multilayer FE assuring displacement and shear stress interlayer continuity and homogeneous shear stress conditions at the outer surfaces. The shear stresses DoFs are dynamically condensed and the FE is reduced to a displacement-based form. The viscoelastic damping behavior is considered at the global FE model level by means of a Laplace transformed ADF model. The active control of vibration is shortly discussed and a set of indices to quantify the damping performance and the individual contributions of the different mechanisms are proposed

Classical and optimal active vibration control of smart piezoelectric beams

In this paper a numerical study concerning the active vibration control of smartpiezoelectric beams is presented. A comparison between the classical control strategies,constant gain and amplitude velocity feedback, and optimal control strategies,linear quadratic regulator (LQR) and linear quadratic Gaussian (LQG) controller, isperformed in order to investigate their effectiveness to suppress vibrations in beamswith piezoelectric patches with sensing and actuating capabilities.As a mathematical model, a one-dimensional finite element of a three-layered smartbeam with two piezoelectric surface layers and metallic core is utilized and brieflypresented. The mathematical model considers a partial layerwise theory, with threediscrete-layers, and a fully coupled electro-mechanical theory. The finite elementmodel equations of motion and electric charge equilibrium are presented and recastinto a state variable representation in terms of the physical modes of the beam.The analyzed case studies concern the vibration reduction of a cantilever aluminumbeam with a pair of collocated piezoelectric patches mounted on the surface. The displacementtime history, for an initial displacement field and white noise force disturbance,and point receptance at the free end are evaluated with the open- and closedloopclassical and optimal control systems. The case studies allow to compare theirperformances and demonstrate their advantages and disadvantages

Identifying and correcting oblique striping in the topodata digital elevation model.

The Topodata digital elevation model (DEM) is the best DEM available for digital soil mapping (DSM) in Brazil. However, it is not ready to use. We show that the kriging interpolator used to downscale the SRTM DEM from 3 arc-seconds to 1 arc-second spatial resolution increased the double oblique striping (15º and 60º) so common to SRTM DEMs. This is because kriging is quite sensitive to outliers. Besides, the Gaussian model of spatial covariance used in the downscaling enhanced the sensitivity of kriging to outliers, thus enhancing the striping. 2D Fast Fourier Transform can be used to identify whether a destriping procedure need to be employed. The bilinear or cubic resampling methods should be used to warp Topodata DEMs because they are insensitive to the double oblique striping

Experimental identification of GHM and ADF parameters for viscoelastic damping modeling

The implementation of the Golla-Hughes-McTavish (GHM) and Anelastic DisplacementFields (ADF) models in a general finite element (FE) model with viscoelastic dampingis presented and discussed in this paper. Additionally, a direct frequency analysis (DFA) isalso described and employed. A methodology to identify the complex shear modulus of theviscoelastic materials is described. The identified complex shear modulus of the viscoelasticmaterial 3M ISD112 is curve-fitted in order to obtain the modeling parameters of the GHMand ADF models. A sandwich plate with a viscoelastic core and elastic skins is analyzed. Measuredand predicted frequency response functions (FRFs) are compared with the purpose ofassessing the performance of the presented damping models. The analysis allows to asses thevalidity of the methodology to determine the frequency dependent complex modulus, the GHMand ADF parameters identification and the outcomes and drawbacks of the DFA, GHM andADF viscoelastic damping modeling strategies