1,721,053 research outputs found
Trustworthiness in Modeling Unreinforced and Reinforced T-Joints with Finite Elements
Full text linkAs required by regulations, Finite Element Analyses (FEA) can be used to investigate the behavior of joints which might be complex to design due to the presence of geometrical and material discontinuities. The static behavior of such problems is mesh dependent, thus these results must be calibrated by using laboratory tests or reference data. Once the Finite Element (FE) model is correctly setup, the same settings can be used to study joints for which no reference is available. The present work analyzes the static strength of reinforced T-joints and sheds light on the following aspects: shell elements are a valid alternative to solid modeling; the best combination of element type and mesh density for several configurations is shown; the ultimate static strength of joints can be predicted, as well as when mechanical properties are roughly introduced for some FE topologies. The increase in strength of 12 unreinforced and reinforced (with collar or doubler plate) T-joints subjected to axial brace loading is studied. The present studies are compared with the literature and practical remarks are given in the conclusion section
Hermite finite elements for the vibrations and buckling of strain gradient nano plates in hygro-thermal environment
No full textNano structural components have been widely spreading recently due to their novel applications in several engineering fields. Such components have a nonlocal mechanical behavior that might force to employ generalized or higher-order elasticity theories to take into consideration effects on the nano scale. In this context, nonlocal strain gradient theory has been utilized for investigating the linear vibrations and buckling phenomena of nano plates where orthotropic mechanical properties are functionalized through the plate thickness. Reinforcing fibers of such orthotropic layers can be modelled by assuming a non-uniform distribution along each ply thickness. The homogenization of the orthotropic layers is performed by following the Halpin–Tsai approach starting from the two main constituents (fiber and matrix). Through-the-thickness functions are introduced to describe the variation of their volume fraction. As an evidence from industrial applications nano plate behavior depends on external stimuli such as hygro-thermal effects. For this reason, these effects have been included into the formulation in order to study their influence in the dynamic and linear buckling phenomena. The governing partial differential equations are solved via a finite element model where Hermitian shape functions are introduced due to the higher-order nature of the nonlocal theory selected which involved both in-plane and out-of-plane displacement parameters. Numerical applications are provided in order to show hygro-thermal effects on the vibration and buckling problems of nano plates, in particular, the effect of the fiber distribution along the ply thickness is underlined
Vibrations and Buckling of nonlocal laminated nanoplates solved by Finite Element Method
No full textThis work presents a novel finite element (FE) based formulation for analysing the linear buckling and free vibration problems of plates governed by strain gradient theory. The present model is able to deal with general lamination schemes and arbitrary boundary conditions and its validity is tested against semi-analytical results as well as other solutions available in the existing literature. The constitutive relationship deals with stress components at each layer as a function of the nonlocal strains, according to the principles of the aforementioned strain gradient theory. The present FE formulation is based on the weak form of the governing motion equations derived via Hamilton’s Principle. Such principle allows the identification of primary variables which are constitute by classical thin plate displacements as well as their first and higher-order derivatives. Therefore, membrane and bending degrees of freedom must be all approximated by means of Hermite interpolating functions. In particular, Conforming (C) and nonconforming (NC) approaches are consequently developed and compared in the present study in order to test their performances in terms of numerical computations. Validation and novel applications are provided for further studies within the present research topic
XEN Tube: a new surgical device for micro-invasive subconjunctival drainage. Prospective evaluation of the XENTM gel implant: initial 1 year follow-up
No full textDamping capability of lattice structures: a numerical study
No full textLattices are recognized as ultra-lightweight materials with high specific stiffness and high specific strength. The applications of this architectural material range from the aerospace and automotive industry up to the biomedical one.
In the literature, most of the studies address the mechanical responses of lattice structures under static, dynamic (impact) and fatigue loading conditions while only few works deal with the damping capabilities of such structures.
This study focuses on the damping capability of classical lattice configurations whose architecture is made of struts (i.e. CC, CBCC, ACC, Octet, Rhombic dodecahedron). The influence of three aspects has been investigated: the geometrical parameters defining the structure of the lattice cell, the introduction of a compressive pre-stress field within the cell and the plastic constitutive behaviour of the material used for the struts. A broad sensitivity campaign has been performed in order to evaluate the amount of dissipated energy for the different cell architectures according to the variation of the strut diameter and to the presence of local instabilities (post-buckling behaviour of the struts).
In order to perform the sensitivity analyses, two general modelling strategies have been developed. The first one is intended for a linear elastic material behaviour. In this case, the strategy comprises four phases: 1) an eigenvalue buckling analysis, 2) a non-linear buckling analysis, 3) a pre-stress modal analysis and 4) an harmonic analysis.
The second modelling strategy has been developed when a non-linear plastic behaviour is assigned to the struts material. The phases of the numerical strategy change into: 1) an eigenvalue buckling analysis, 2) a non-linear buckling analysis and 3) a non-linear transient analysis with pre-stress.
The numerical results highlight how the damping capability of the considered cell, for the same loading condition, is strongly related to the topology of the cell and to its relative density. By smartly tailoring these parameters, the damping capability without pre-stress can be increased up to 32% and, if the pre-stress is introduced within the cell, the damping effects can intensified up to 60%
Dynamic actuation model for vibration reduction in offshore cranes
No full textThe handling of offshore payloads is a critical operation that presents numerous challenges, in particular related to the required precision in controlling their oscillations in a safely and accurate manner. This study presents a preliminary approach to an anti-sway control conceived to mitigate such problems and possibly to automate some of the operations concerning the payload sway control that are currently done manually. In particular, a system consisting of a translating trolley actuated through a PID controller is taken into consideration to mitigate the oscillations induced by the vessel’s rolling motion onto a simplified two-dimensional and 4 degrees of freedom double-pendulum model representing the hanging payload. A three-dimensional double-pendulum model is also taken into account, in order to have a more representative case with respect to the two-dimensional one
Optimization procedure of an overboarding chute with standards, mechanical and numerical considerations
No full textNowadays, in order to be competitive on the market, it is fundamental to design optimized devices. This is especially true in the Offshore sector where the product’s weight has a material influence on all operations. Reducing this parameter implies a significant decrease in the project’s cost. This paper proposes the study of the kinematic rotation of a prototype machine required to lay down an umbilical system, needed to provide the vital supply (electricity and fiber optic) from platforms or topside vessel to subsea oil and gas furniture.
In this paper, it will be proposed a solution for the delivery of a 600 mm external diameter umbilical product. In the studied case, the Client asked to have a cable that partially floats once it reaches the sea water showing incredible benefits such as the possibility to be replaced and small umbilical deflections due to a catenary effect reduction. Due to this singular request, the proposed prototype machine – characterized by the rotation of an articulated parallelogram, activated by two main pistons – ensures safety operation and integrity of the laid umbilical.
Starting from an accurate structural analysis, a reliable model has been created and a first solution of the forces distribution along the chute elements has been found, highlighting some significant points (static configurations during a dynamic evolution). During the piston design phase, some limitations of current DNV standards (when dealing with offshore technologies) have been highlighted. To investigate this peculiar phenomenon several results obtained by different numerical approaches are proposed.
The present machine could be even applied in the renewable energy field, for connecting wind turbines in the wind farm’s hub and then to carry the produced energy on shore. This analysis results in a 15% machine weight reduction with respect to the initial design. Such simulation provided a practical design tool for the Offshore market
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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