1,721,187 research outputs found
Correlation between Preload and Geometric Characterisation of metal meshes for space antenna reflectors
No full textContact management in knitted metal mesh through an adaptive node placing
No full textThe structural analysis of metal knitted meshes needs important computational resources due to non-linear behavior. The structures made of several filiform elements interlaced together often show large displacements and several contacts among yarns, so that they require advanced methods to predict their response. In this work, a contact-search algorithm between thin curved beams is presented. The contact recognition is based on the intersections between single elements to evaluate possible contact and its location. The method allows simplifying the 3D problem of contacts among wires into a 2D structure, easy to manage and model with a reduced computational cost. The filiform elements are modeled through a Wire Element, whose characteristic is to decouple its structural behavior – based on ending nodes – to its geometrical internal shape that is used for contact management. The Wire Element considers thin wires with circular sections. Its shape is entrusted to intrinsic geometry using a cubic polynomial function whose independent variable is the angle of the tangent to the curve. This approach is useful when analyzing complex structures such as meshes in which several loops are intertwined and subjected to contact activation during loading. Some examples to explain the method and its potential are shown
The importance of mechanistic studies in the development of cold plasma-based degradation of persistent organic pollutants in water
Full text linkAn overview is given of major recent advancements in cold plasma-based water treatment, with specific focus on the degradation mechanisms of organic pollutants. Mechanistic insight is indeed a powerful tool for process optimization considering the treatment duration, its products, and energy costs as it provides guidelines for the design of optimized reactors and the selection of best experimental conditions. The cases considered emphasize the importance of matching the plasma composition in terms of reactive species with the reactivity of the target pollutant(s), and of identifying and understanding the reciprocal effects of different pollutants as well as those of complex aqueous matrices. Harnessing the chemistry activated by the plasma to achieve the desired goal is the key to treatment success. A general strategy is outlined for designing the best plasma experimental set-up and for predicting possible byproducts
Analytical Stiffness Matrix for Curved Metal Wires
Full text linkThe paper presents an analytic stiffness matrix for curved thin metal wires, derived by the application of the second Castigliano’s Theorem. The matrix accounts both bending and axial stiffness contributions in plane. The beam geometry is described by a cubic polynomial function of the curvature radius with a monotonical attitude angle as the independent variable. The solution proposed if fully analytical although a consistent number of adding factors appear. Some test cases are discussed and compared with Finite Element solutions, formed by a plentiful assembly of straight beams
Structural Modelling of Knitted Meshes Through an Original Wire Finite Element
No full textThe knitted metal mesh is the fundamental component of a Deployable Reflector (DR). The Radio Frequency performance of a DR is profoundly affected by the mesh’s void/filled ratio that change according to the its tensioning. Simulate its behaviour is challenging, inasmuch some nonlinear phenomenon manifest during its loading; just to name a few: the considerable shape change, the huge number of contacts between the wires and the sliding between them. This paper focuses on the geometric nonlinearity. The most used strategies to deal with this type of nonlinearity are discussed, including the analytical and numerical approaches. Finite Element Analysis (FEA) is debated in details, comparing the classic isoparametric approach with a new Wires Finite Element proposed by the authors. This new Element allows to model the mesh with long curvilinear elements, obtaining a considerable gain regarding the required elements number (i.e. less computational effort). The presented numerical comparisons between the proposed Wire Element and the isoparametric ones show similar results regarding the convergence rate, but the proposed element involve many fewer degrees of freedom, i.e. a considerable gain about of absolute time required for the simulation
Contact Modelling among Wires in the Mechanical Characterization of Mesh Reflectors
No full textLarge Deployable Reflectors have become crucial for earth observation, scientific missions, and space communications. Reflector meshes are made of metal wires, forming a repetitive pattern of numerous loops in reciprocal contact. During the operational transmission/reception of electromagnetic waves, unwanted intermodulation products affect the signal-to-noise ratio due to uncertainties in electrical contacts. The mesh has an almost planar shape, but the physical contacts among the wires would require 3D modelling. The direct approach with 3D FEM models, even if implemented through one-dimensional elements (the wires), often leads to simulations presenting convergence difficulties already with very small mesh portions. Possible alternative strategies consist of a 2D approach to the problem and appropriate tricks to make the convergence easier, such as using contacts activated through fictitious point elements placed between wires in contact, allowing the sliding between them. This paper presents a new 2D technique for modelling wires adopting a simplified although effective contact algorithm. The wires are subdivided into portions using original curvilinear one-dimensional elements (named Wire elements). The structural modelling of the curvilinear wires is developed in the middle mesh plan. The 2D recognition of the contacts is entrusted on the intersections of the wires to monitor the appearance of contacts. This technique reduces the overall number of DOFs and deals with the sliding among wires simply and automatically. Contact constraints enter into the solver through the method of Lagrange multipliers
Modelling of structures made of filiform beams: Development of a curved finite element for wires
No full textThis paper presents a finite element formulation of curved thin beams, useful for modelling structures made of filiform elements. The proposed element is intended to model structures formed by several wires, subjected to very large bending displacements so that their final shapes can be completely different from the original ones. The model is based on the description of the planar wire geometry through the integration of the radius of curvature, which is approximated by means of a cubic polynomial. The solution of an overdetermined system is necessary to compute the coefficients of the polynomial. This approach allows determining the stiffness matrix of the curved wire in closed form, through the application of Castigliano's Theorem. A technique for automatic remeshing during large deformations, based on the curvature change, is also discussed in the paper. To validate the model refined finite element analyses and an experimental test have been carried out. The solution is performed analytically, and it allows to identify the actual stiffness matrix of a curved wire, considering only the degrees of freedom at the ends
Optical Method to measure mesh tensioning, Procedia Structural Integrity
No full textThe present paper presents a method to estimate the tensional status of a knitted mesh. To reach this result, the relationship between the frequencies of vibration, recorded by a high-sampling camera and analysed through image processing, and different tensioning on the mesh itself, has been investigated.
After having conducted several tests, all the collected pairs frequency-tensional status have been used to extrapolate an optimal (in a least-squares sense) correlation between frequency of vibration and tension of the mesh
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