Locking-free two-layer Timoshenko beam element with interlayer slip

A new locking-free strain-based finite element formulation for the numerical treatment of linear static analysis of two-layer planar composite beams with interlayer slip is proposed. In this formulation, the modified principle of virtual work is introduced as a basis for the finite element discretization. The linear kinematic equations are included into the principle by the procedure, similar to that of Lagrangian multipliers. A strain field vector remains the only unknown function to be interpolated in the finite element implementation of the principle. In contrast with some of the displacement-based and mixed finite element formulations of the composite beams with interlayer slip, the present formulation is completely locking-free. Hence, there are no shear and slip locking, poor convergence and stress oscillations in these finite elements. The generalization of the composite beam theory with the consideration of the Timoshenko beam theory for the individual component of a composite beam represents a substantial contribution in the field of analysis of non-slender composite beams with an interlayer slip. An extension of the present formulation to the non-linear material problems is straightforward. As only a few finite elements are needed to describe a composite beam with great precision, the new finite element formulations is perfectly suited for practical calculations. (c) 2007 Elsevier B.V. All rights reserved

Estimate of turbulent fluxes with eddy-covariance technique in a complex topography: A case study in the Italian Alps

A sensitivity analysis to different eddy—covariance data processing algorithms is presented for a dataset collected in an Alpine environment with complex topography. In Summer 2012 a micrometeorological station was installed at Cividate Camuno (274 m a.s.l., Oglio river basin, Central Italian Alps), in a flat and rectangular grass-covered lawn. The grass was 0.6 m tall during most of the field campaign. The station is equipped with traditional devices, four multiplexed TDR probes, and an eddy--covariance apparatus sampling at 20 Hz (Gill WindMaster Sonic Anemometer and Licor Li7500 Gas Analyzer), at about 3 m above the ground. The local winds regime is strongly affected by the morphology of the valley, and the topography is complex also due to the heterogeneity of the surrounding-areas land—cover. Using EddyPro software, the sensitivity of the turbulent fluxes estimate was assessed addressing three major issues of the data processing procedure, i.e. the choice of the computational averaging period, of the axis rotation method and of the data detrending criterion. Once identified three test periods of consecutive days without rainfall, the fluxes of momentum, sensible heat and latent heat were computed at the averaging period of 30, 60 and 120 min respectively. At each averaging period, both the triple rotation method, the double rotation method and the planar fit method were applied. Particularly the latter was applied both fitting a unique plane for all the wind directions and fitting multiple planes, one for each sector of the wind rose. Regarding the detrending criteria, data were processed with a block average and a linear detrend, the latter with time constant of 5, 30, 60 and 120 min respectively. Therefore, for each test period about 50 estimates of the fluxes were provided. As a result the obtained fluxes were compared. Even if with different flux quality, their pattern is quite stable with regard to the applied estimate procedures, but with sensitively different average values

Exact slip-buckling analysis of two-layer composite columns

A mathematical model for slip-buckling has been proposed and its analytical solution has been found for the analysis of layered and geometrically perfect composite columns with inter-layer slip between the layers. The analytical study has been carried out to evaluate exact critical forces and to compare them to those in the literature. Particular emphasis has been placed on the influence of interface compliance on decreasing the bifurcation loads. For this purpose, a preliminary parametric study has been performed by which the influence of various material and geometric parameters on buckling forces have been investigated. (C) 2009 Elsevier Ltd. All rights reserved

Failure Probability Analysis of Levees Affected by Mammal Bioerosion

Mammal bioerosion is an emergent threat to the functionality of levees. In the present paper, the problem of assessing the failure probability of levees affected by mammal bioerosion is addressed. A fully bivariate description of peak flow discharge and flood duration is combined with a deterministic unsteady seepage flow model to obtain a suitable model of variably disturbed levee response to the observed natural variability of floods. Monte Carlo analysis is also implemented to evaluate the epistemic uncertainty connected to the description of the river system. The obtained model is tested with respect to a real-world levee located along the Secchia River in northern Italy, which underwent a disastrous failure caused by mammal bioerosion in 2014. The convex linear combination of two Archimedean copulas is found to fit the empirical dependence structure between peak flow discharge and flood duration. The reliability of the unsteady seepage flow model is tested against detailed numerical simulations of the seepage occurring through the levee body. A limit state function is obtained by comparing the maximum extent of the seepage front to the distance between the den end and the riverside levee slope, and the corresponding levee safety and failure regions are delimited. Results obtained from the developed model reveal a significant impact of mammal dens located near the levee crest in terms of failure probability and related return period. This impact is consistent with failures observed in the study area

Association between Asthma Control and Exposure to Greenness and Other Outdoor and Indoor Environmental Factors: A Longitudinal Study on a Cohort of Asthmatic Children

Achieving and maintaining asthma control (AC) is the main goal of asthma management. Indoor and outdoor environmental factors may play an important role on AC. The aim of this longitudinal study was to evaluate the association between AC and exposure to greenness and other outdoor or indoor environmental factors in a cohort of asthmatic children. This study involved 179 asthmatic children (5–16 years). Parents were interviewed through a modified version of the SIDRIA questionnaire. AC was assessed at each visit. Exposure to greenness was measured using the normalized difference vegetation index (NDVI). A logistic regression model was applied for assessing risk factors for uncontrolled asthma (UA). Low NDVI exposure was a risk factor for UA (OR: 2.662, 95% CI (1.043–6.799)); children exposed to passive smoke during pregnancy had a higher risk of UA than those non-exposed to passive smoke during pregnancy (OR: 3.816, 95% CI (1.114–13.064)); and a unit increase in the crowding index was associated with an increased risk of UA (OR: 3.376, 95% CI (1.294–8.808)). In conclusion, the current study provided a comprehensive assessment of urban-related environmental exposures on asthma control in children, using multiple indicators of greenness and other outdoor or indoor environmental factors

Fire analysis of timber composite beams with interlayer slip

The purpose of this paper is to model the behaviour of timber composite beams with interlayer slip, when simultaneously exposed to static loading and fire. A transient moisture-thermal state of a timber beam is analysed by the Luikov equations, and mechanical behaviour of timber composite beam is modelled by Reissner's kinematic equations. The model can handle layers of different materials. Material properties are functions of temperature. The thermal model is validated against the experimental data presented in the literature. Generally, the model provides excellent agreement with the experimental data. It is shown that the material properties of timber play an important role in the fire resistance analysis of timber structures when exposed to fire

Upstream Operations in the Oil Industry: Rigorous Modeling of an Electrostatic Coalescer

This paper deals with a first-principle mathematical model that describes the electrostatic coalescer units devoted to the separation of water from oil in water-in-oil emulsions, which are typical of the upstream operations in oil fields. The main phenomena governing the behavior of the electrostatic coalescer are described, starting from fundamental laws. In addition, the gradual coalescence of the emulsion droplets is considered in the mathematical modeling in a dynamic fashion, as the phenomenon is identified as a key step in the overall yield of the unit operation. The resulting differential system with boundary conditions is then integrated via performing numerical libraries, and the simulation results confirm the available literature and the industrial data. A sensitivity analysis is provided with respect to the main parameters. The mathematical model results in a flexible tool that is useful for the purposes of design, unit behavior prediction, performance monitoring, and optimization