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

Manufacturing and testing of 3D-printed polymer isogrid lattice cylindrical shell structures

This article focuses on the use of fused deposition modeling (FDM) technology to manufacture and test polymer isogrid lattice cylindrical shell (LCS) structures with equilateral triangular unit-cells using non-professional and conventional 3D printing software and hardware. A parametric and automated 3D model for these structures is created in SolidWorks using the Visual Basic (VBA) programming language. Different configurations of the isogrid LCS structure are modeled, manufactured, and tested in order to determine the compressive structural strength and stiffness, as well as to investigate structural instability. The experimental results are used to deduce the inherent limitations of 3D printing, including the inhomogeneities, imperfections, and non-isotropic nature of FDM, as well as the effect of the configurations on local buckling behavior. The results suggest that coupling between local and global buckling has an impact on the compressive stiffness and strength of LCS structures, reducing the accuracy of structural designs neglecting these effects.F71E-503E-DE74 | AD?LIO MANUEL DE SOUSA CAVADASN/

A 3D-printed continuously variable transmission for an electric vehicle prototype

This paper aims to present the design of a new 3D-printed continuously variable transmission (CVT) developed for an electric vehicle prototype competing in Shell Eco-marathon electric battery category, a world-wide energy efficiency competition sponsored by Shell. The proposed system is composed of a polymeric conic geared friction wheel assembled in the motor axle and directly coupled to the rear tire of the vehicle. The conical shape allows to implement a continuous variation of the geared friction wheel diameter in contact with the tire. The motor with the geared friction wheel was mounted over a board with linear bearings, allowing the speed ratio to change by moving the board laterally. A computational simulation model of a prototype electric vehicle with the proposed 3D-printed CVT was created in Matlab/Simulink environment to obtain the traction force in the geared friction wheel and also to analyze the vehicle performance. The simulation results demonstrated possibilities of increasing vehicle speed range output and available torque in the rear traction wheel. Also, it is shown with the simulated model that the designed CVT consumes 10.46% less energy than a fixed transmission ratio, demonstrating the CVT concept?s potential for battery consumption reduction. Lastly, a 3D-printing slicing software with an optimization algorithm plug-in was used to determine the best printing parameters for the conic geared friction wheel based on the tangential force, maximum displacement and safety factor. When compared to the original part with a 100% infill density, the optimized solution reduced the component mass by about 12% while maintaining safe mechanical resistance and stiffness.2314-4B69-C2B9 | C?sar Miguel de Almeida VasquesN/

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

Effects of intervention programs on child and adolescent BMI: a meta-analysis study

This meta-analysis study aims to assess the efficacy of school-based and after-school intervention programs on the BMIs of child and adolescents, addressing the correlation between some moderating variables. Methods: We analyzed 52 studies (N = 28,236) published between 2000-2011. Results: The overall effect size was 0.068 (P < .001), school (r = .069) and after-school intervention (r = .065). Programs conducted with children aged between 15-19 years were the most effective (r = .133). Interventions programs with boys and girls show better effect sizes (r = .110) than programs that included just girls (r = .073). There were no significant differences between the programs implemented in school and after-school (P = .770). The effect size was higher in interventions lasting 1 year (r = .095), with physical activity and nutritional education (r = .148), and that included 3-5 sessions of physical activity per week (r = .080). The effect size also increased as the level of parental involvement increased. Conclusions: Although of low magnitude (r = .068), the intervention programs had a positive effect in prevention and decreasing obesity in children. This effect seems to be higher in older children's, involving interventions with physical activity and nutritional education combined, with parent's participation and with 1-year duration. School or after-school interventions had a similar effect

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