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Aerodynamic admittance functions (AAFs) of twin-box decks are particularly complex due to the presence of a central gap, so require the performance of dedicated studies to determine them. Two main approaches are available for this purpose, which consist of studying the aerodynamic forces produced by the section when impinged by sinusoidal gusts or continuous turbulence, respectively. However, owing to the difficulty in the generation of large-scale turbulence in traditional wind tunnel tests, the two aforementioned approaches often provide remarkably different results. To address this problem, this study aims to systematically investigate the admittance function of twin-box decks by comparing three approaches: active wind tunnel tests, and large eddy simulations (LESs) using both sinusoidal gusts and continuous synthetic turbulence. In particular, wind tunnel tests equipped with an active gust generator are conducted to generate a series of single-frequency vertical sinusoidal gusts. The effects of gust amplitudes and gap widths on the AAFs are experimentally investigated. In addition, LESs are performed aiming to provide valuable insights regarding the discrepancy between AAFs obtained in the two inflow conditions. Results obtained adopting all the aforementioned methodologies are compared, showing good agreement among the three approaches and values sometimes higher than the Sears function. It is also shown that buffeting forces are mainly produced by the upstream deck, so explaining the good agreement obtained between sinusoidal gust and continuous turbulent inflows. [ABSTRACT FROM AUTHOR]

While in the atmosphere nitrogen is abundant, this element plays a limited role as nutrient for plants. Cereal crops, as an example, are uncapable to directly use freely available nitrogen gas. As a consequence, their optimal growing and, in general, the productivity of such crops relies mainly on the use of chemical fertilizers, which, under the European Green Deal and the Farm to Fork Strategy are under scrutiny with plans of reduction of their use. As increasing crop production is a vital target for agriculture and food systems, the role of nitrogen fixers could play a fundamental role to match the targets of increasing the food production by decreasing the use of chemical fertilizers. Also, such approach is very appropriate from the perspective of sustainable production and conservative agriculture. The present work has the objective to examine the role of nitrogen fixers on the maize yield, respectively the productivity in harvested maize crop treated with Azotobacter chrococcum, Azotobacter vinelandii and Bacillus megaterium, three different nitrogen-fixing bacteria. The investigations were based on field tests. Thus, there at the beginning the seeds were inoculated before seeding; and during the vegetation the crops were treated with the three bacteria species. The fields experiment was organized in four variants (one non-treated variant and three with the bacteria Azotobacter chrococcum, Azotobacter vinelandii and Bacillus megaterium) and three replicates. The examination of collected samples revealed a general increase in productivity in the variants treated with Azotobacter vinelandii. [ABSTRACT FROM AUTHOR]

In this paper, a first-order virtual element method for Reissner–Mindlin plates is presented. A standard displacement-based variational formulation is employed, assuming transverse displacement and rotations as independent variables. In the framework of the first-order virtual element, a piecewise linear approximation is assumed for both displacement and rotations on the boundary of the element. The consistent term of the stiffness matrix is determined assuming uncoupled polynomial approximations for the generalized strains, with different polynomial degrees for bending and shear parts. In order to mitigate shear locking in the thin-plate limit while keeping the element formulation as simple as possible, a selective scheme for the stabilization term of the stiffness matrix is introduced, to indirectly enrich the approximation of the transverse displacement with respect to that of the rotations. Element performance is tested on various numerical examples involving both thin and thick plates and different polygonal meshes. [ABSTRACT FROM AUTHOR]

Summary: Within the framework of the displacement‐based virtual element method (VEM), namely, for plane elasticity, an important topic is the development of optimal techniques for the evaluation of the stress field. In fact, in the classical VEM formulation, the same projection operator used to approximate the strain field (and then evaluate the stiffness matrix) is employed to recover, via constitutive law, the stress field. Considering a first‐order formulation, strains are locally mapped onto constant functions, and stresses are piecewise constant. However, the virtual displacements might engender more complex strain fields for polygons, which are not triangles. This leads to an undesirable loss of information with respect to the underlying virtual stress field. The recovery by compatibility in patches, originally proposed for finite element schemes, is here extended to VEM, aiming at mitigating such an effect. Stresses are recovered by minimizing the complementary energy of patches of elements over an assumed set of equilibrated stress modes. The procedure is simple, efficient, and can be readily implemented in existing codes. Numerical tests confirm the good performance of the proposed technique in terms of accuracy and indicate an increase of convergence rate with respect to the classical approach in many cases. [ABSTRACT FROM AUTHOR]

Abstract The accurate evaluation of wind loads on high-rise buildings represents a key point in their design process. Traditionally, atmospheric boundary layer wind tunnel tests, conceived in order to be representative of the wind conditions expected on site, are used for this purpose. Recently, owing to the increase in computational power, Computational Fluid Dynamics (CFD) techniques have gained interest as a complementary tool to wind tunnel testing. Unfortunately, wind flow around bluff bodies is often very complex and substantial research efforts are still needed in order to assess the accuracy and reliability of CFD results. In this paper, Large Eddy Simulations (LES) are performed aimed at evaluating the wind loads on an isolated high-rise building. In order to assess the capabilities of LES for adoption as a design tool, the results are analysed in terms of both pressure distributions and internal forces on the structural elements. It is found that the accuracy of LES in reproducing the fluctuating pressure field is not necessarily maintained when internal forces are taken into account. Nevertheless, the design values predicted by LES can be still considered satisfactory, in particular when maximum and minimum values over different angles of attack are considered. Highlights • LES are performed to evaluate wind loading effects in the structural elements of a high-rise building. • The inflow turbulence is generated using the MDSRFG method and compared to experimental measurements. • LES results in terms of pressure distributions statistics are compared to wind tunnel data. • Finally, numerical and experimental results are compared in terms of internal forces in the structural elements. [ABSTRACT FROM AUTHOR]

The characterization of the structural response to the wind action is usually obtained by means of dynamic analyses based on the unsteady pressure distributions recorded in wind tunnel tests. In order to simplify the design operations, equivalent static wind loads (ESWLs) can be extracted so allowing to reproduce the extreme effects recorded in a series of dynamic analyses by enveloping a few, statically applied, load conditions. Recently, a new efficient technique for the extraction of ESWLs has been proposed, where the sharp maximum/minimum operator, typical of envelope evaluation procedures, has been smoothed, so allowing to adopt efficient gradient-based optimization techniques in order to individuate the ESWLs. In the present paper, such technique is analyzed from a numerical perspective highlighting the fundamental role played by the applied smoothing operation in the correct individuation of the optimal load conditions. Similarities between the proposed technique for the extraction of ESWLs and well known procedures used in linear classification are highlighted and the proposed smoothing operation is framed in the context of graduated optimization techniques. Numerical results confirm the soundness of the proposed approach. [ABSTRACT FROM AUTHOR]

The incompressible high Reynolds number flow around the rectangular cylinder with aspect ratio 5 : 1 has been extensively studied in the recent literature and became a standard benchmark in the field of bluff bodies aerodynamics. The majority of the proposed contributions focus on the simulation of the flow when a smooth inlet condition is adopted. Nevertheless, even when nominally smooth conditions are reproduced in wind tunnel tests, a low turbulence intensity is present together with environmental disturbances and model imperfections. Additionally, many turbulence models are known to be excessively dissipative in laminar-to-turbulent transition zones, generally leading to overestimation of the reattachment length. In this paper, Large Eddy Simulations are performed on a 5 : 1 rectangular cylinder at non-null-attack angle aiming at studying the sensitivity of such flow to a low level of incoming disturbances and compare the performance of standard Smagorinsky-Lilly and Kinetic Energy Transport turbulence models. [ABSTRACT FROM AUTHOR]

In this paper, an enhanced Virtual Element Method (VEM) formulation is proposed for plane elasticity. It is based on the improvement of the strain representation within the element, without altering the degree of the displacement interpolating functions on the element boundary. The idea is to fully exploit polygonal elements with a high number of sides, a peculiar VEM feature, characterized by many displacement degrees of freedom on the element boundary, even if a low interpolation order is assumed over each side. The proposed approach is framed within a generalization of the classic VEM formulation, obtained by introducing an energy norm in the projection operator definition. Although such generalization may mainly appear to have a formal value, it allows to effectively point out the mechanical meaning of the quantities involved in the projection operator definition and to drive the selection of the enhanced representations. Various enhancements are proposed and tested through several numerical examples. Numerical results successfully show the capability of the enhanced VEM formulation to (i) considerably increase accuracy (with respect to standard VEM) while keeping the optimal convergence rate, (ii) bypass the need of stabilization terms in many practical cases, (iii) obtain natural serendipity elements in many practical cases, and (vi) effectively treat also nearly incompressible materials. • An enhanced VEM formulation with improved strain is proposed for plane elasticity. • Approximation capabilities of polygonal elements with many sides are fully exploited. • An energy norm is introduced in the projection operator definition. • Various enhancements are proposed and tested. • Highly accurate, self-stabilized, serendipity elements can be obtained. [ABSTRACT FROM AUTHOR]