IRIS - UNIRSM (Univ. degli Studi della Repubblica di San Marino)
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Un papiro onora un museo. Vicissitudini di un papiro diplomatico dal Castello del Catajo a Vienna, attraverso documenti inediti
No full textInvestigation on the Structural Response of Plates and Shells with Variable Mechanical Properties: Modeling of the Damage
No full textThe structural response of plates and shells in terms of static and dynamic behavior is highly affected by the variability of the mechanical properties within the reference domain. It should be noted that in the literature several approaches have been introduced to define variable mechanical properties. For instance, the class of graded materials and of laminated composites reinforced by curvilinear fibers can be taken as a reference. In the current work, an innovative way to describe the variability of the mechanical properties is presented. A proper mathematical formulation is developed to define linear, sine-wave, and exponential variations of the elastic constants of the composites. In particular, two-dimensional laws, such as the Gaussian and the elliptic functions, are taken into account to model the damage of plates and shells. In other words, the damage of a structure can be seen as a rapid and concentrated variation of the mechanical properties of the elastic medium. Several parametric investigations are performed to analyze the effect of the damage parameters (intensity and size) on the structural response. The solution is achieved numerically by means of the Generalized Differential Quadrature (GDQ) method. The structural model is developed in the framework of a Unified Formulation which allows to consider in an efficient manner several higher-order theories. Finally, it should be pointed out that the description of the doubly-curved geometries with variable radii of curvature is obtained by using the well-known differential geometry
Chemotherapy extravasation management. 21-Year experience
No full textChemotherapy extravasation may result in serious damage to patients, with irreversible local injures and disability. Evidence-based standardization on extravasation management is lacking and many institutions do not practice adequate procedures to prevent the severer damages. Our aim was to explore the prevention and treatment of extravasation injuries, proposing a standard therapeutic protocol together with a review of the literature. From January 1994 to December 2015, 545 cases were reviewed (age range, 5-87 years; 282 men and 263 women). Our therapeutic protocol consisted of local infiltration of saline solution and topical occlusive applications of corticosteroids. The infiltrations were administrated 3 to 6 times a week depending on damage severity. Our protocol allowed us to prevent ulceration in 373 cases. Only 27 patients required surgery (escarectomy, skin graft, regional, and free flap). Numerous treatments have been proposed in literature. The antidotes have been discussed controversially and are not considered standard methods for treatment, especially when polychemotherapy is administrated and the identification of the responsible drug is not possible. We proposed the use of saline solution injection to dilute rapidly the drug, thus reducing its local toxic effects. This method is easy to use and always reproducible even when the drug is not known or when it is administrated in combination with other drugs. It is possible to perform it in ambulatory regimen, and, overall, it represents a standard method
Isogeometric Analysis of Arbitrarily Shaped Structures: A Numerical Approach Based on the Strong Formulation
No full textA numerical solution is sought for many engineering applications since it is not always possible to achieve analytical results. This statement is even more truthful when the reference domain of the problem under consideration is characterized by an irregular or arbitrary shape. For this purpose, several numerical approaches have been developed in the last decades to deal with these kinds of problems. Let us consider the mechanical analysis of some structural elements, such as membranes, plates, and shells. In this regards, the most common numerical scheme to obtain a solution is given by the Finite Element (FE) method. Its basic aspect is the domain decomposition in many elements, in which the unknown field is approximated through low order polynomials. The weak form of the governing equations is typically solved. In addition, the so-called mapping technique is used to deal with arbitrarily shaped subdomains. The main aim of this research is to present a new numerical approach which implements higher-order approximating polynomials within each discrete element. Unlike classic schemes, the present methodology is developed to solve the strong form of the fundamental equations [1]. Thus, the mathematical problem is approximated numerically by means of the Differential Quadrature (DQ) method. Arbitrarily shaped domains are accurately described using a nonlinear mapping based on NURBS curves. The employment of peculiar blending functions allows to reduce the number of elements required to approximate accurately any irregular domain [2-4]. Therefore, this approach is part of the well-known framework of Isogeometric Analysis (IGA). Due to its features, the methodology at issue is named Strong Formulation Isogeometric Analysis (SFIGA). Several numerical applications are investigated to prove the accuracy, reliability, and stability features of the technique. In particular, this research is focused on the study of the mechanical behavior of membrane, as well as laminated composite plates and shells. This approach is validated by means of the comparison with the results available in the literature or obtained through a FE model realized by commercial codes
Online Collaborative Learning. Pedagogical Design in the Mediational Artifacts
No full textThe idea to apply collaborative learning strategies widely experimented in face-toface educational setting, lead researchers to think a possible transposition mutatis mutandis also in online social environment (Delfino et al, 2006). Looking at some of the existing pedagogical planners none of them are specifically intended to support the design of online collaborative learning activities (Pozzi, Persico, 2006). In this paper we present a pedagogical reflection between two educational experiences of Online Role Play (ORP) carried out in the university context through the use of different mediational tools. In the first experience, the teacher has a specific software that manages the online cooperative learning, a “management” software ad hoc created to guide the teacher in the development of Online Collaborative Learning Path. In second experience the teacher has a plurality of tools by which he/she can (potentially) put on online cooperative learning activities
Paese che vai Pinocchio che trovi
No full textTradotto in oltre duecento lingue il romanzo di Collodi rappresenta uno dei "biglietti da visita" più eloquenti della rappresentazione della nostra nazione fuori dai confini dell'Italia. Pinocchio come personaggio esemplare dei vizi e delle virtù dell'Italia è certamente uno dei personaggi che meglio interpretano i nostri caratteri nazionali
A Numerical Approach Based on the GDQ Method for the Linear Static Analysis of Laminated Composite Shells Subjected to Point and Line Loads
No full textThe numerical analysis of laminated composite doubly-curved shells represents a challenging topic in the computational mechanics field due to the difficulties related to the description of their peculiar geometries. Those issues are even more evident when concentrated forces, such as point and line loads, are applied on the external surfaces of the shells. For the sake of clarity, examples of these configurations are shown in Figure 1. It is well-known that concentrated forces represent strong mechanical discontinuities which can negatively affect the static solution when a numerical approach is employed, as highlighted by many researchers in the pertinent literature. The present study aims to investigate the linear static response in terms of displacements, stresses and strains along the shell thickness. For this purpose, a recovery procedure based on the three-dimensional equilibrium equations is developed by the authors. As far as the theoretical framework is concerned, a two-dimensional structural theory able to deal with several Higher-order Shear Deformation Theories (HSDTs) in a unified manner is considered. These refined models could provide more accurate results especially when particular mechanical configurations, such as lamination schemes with inner soft-core, are taken into account. The numerical solutions are obtained by means of the Generalized Differential Quadrature (GDQ) method, due to their outstanding features to solve this kind of structural problem [1]. Since the present technique is able to approximate the partial differential derivatives, which appear in the governing equations, the strong formulation of the fundamental system of equations obtained through the Hamilton’s variational principle is solved. In the present research, the concentrated loads are modeled by means of the well-known Dirac-delta function applied to a two-dimensional domain, due to its property to assume a zero value everywhere in the domain except in the application point of the force. Alternatively, the Gaussian function could be used for the same aim. As highlighted in the papers [2, 3], an integral statement is solved in the point (or along the line) in which these forces are applied. For this purpose, the Generalized Integral Quadrature (GIQ) method is employed for the numerical implementation of these concentrated loads. For the sake of completeness, it should be noted that these concentrated forces can be described by variable orientations; analogously, they can be combined to obtain cross loads or different load cases. The validity of the current approach is tested by means of the comparison with several examples of laminated shell structures subjected to point and line loads and with the semi-analytical solutions for composite plates as well. These validation procedures are carried out in terms of both displacements and through-the-thickness stress profiles. New findings are shown for doubly-curved shells with more complex geometries, by varying boundary conditions, lamination schemes and applied loads. Finally, the present research can be considered as the proof that the GDQ method can deal accurately with these structural problems by solving the strong form of the governing equations
Soil-structure interaction effects in single bridge piers founded on inclined pile groups
No full textThis paper investigates the seismic response of bridge piers founded on inclined pile groups in different soil
deposits, evaluating effects of soil-structure interaction induced by different pile group geometries and piles
inclinations. Analyses are performed in the frequency domain by means of the direct approach taking advantage
of a numerical model developed by the authors for the analysis of inclined pile groups. Both the superstructure
and piles are modelled with beam elements and the soil is schematized as a visco-elastic medium constituted by
independent infinite horizontal layers. The soil-pile and the pile-soil-pile interaction are captured in the
frequency domain by means of elastodynamic Green's functions that also allow including the hysteretic and
radiation damping. The significance of kinematic stress resultants in piles, the foundation filtering effect and the
rotational component of the input motion due to the coupled roto-translational behaviour of the soil-foundation
system are also investigated; to this purpose kinematic interaction analyses are performed. These analyses
revealed essential for the understanding of the general phenomena governing the dynamic response of the
whole soil-foundation-superstructure systems. Results of numerical investigations highlight that conventional
design approaches suggested by codes do not provide reliable predictions of the superstructure displacements
and stress resultants
Composite Structures of Arbitrary Shape by Using Nonlinear Isogeometric Mapping
No full textComposite structures have been widely used in several engineering applications nowadays. Their use is mainly in advanced components at all scales from small to large, such as in bio medical engineering and civil and aerospace engineering. In the former body parts are involved in the design process, whereas in the latter large roof and fuselages are studied for industrial applications. Since the 1950s several numerical methods have been introduced to study such structures, most of these techniques were related to weak form finite element methods wherein the variational form of the governing equation is analyzed. Unfortunately, such numerical schemes might have numerical issues due to geometry approximation and convergence behavior. For solving such problems strong form numerical approaches were introduced in order to have higher accuracy trends and “almost exact” geometry approximation since such scheme is based on collocation points. Among all the recent developed strong form techniques the Differential Quadrature (DQ) method has been deeply investigated in the last years. However, the DQ method can only be applied to geometries of regular shape such as domains in Cartesian, polar or orthogonal curvilinear coordinates. In order to be able to generalize such approach the mapping technique and the domain decomposition method must be introduced. The authors developed a strong form finite element technique which considers Not Uniform Rational B-Splines (NURBS) to described geometrically the edges of the elements within the given mesh. Such curves are taken from CAD software so that the resulting geometric approximation of the physical structure is more accurate and flexible than other classic mapping approaches
Interpretation of Boundary Conditions in the Analytical and Numerical Shell Solutions for Mode Analysis of Multilayered Structures
No full textThe paper proposes the first 18 vibration modes for plates, and the first 14 vibration modes for cylinders and cylindrical shells. All the edges of these structures are simply supported and the free frequencies are calculated using an exact three-dimensional shell model. A comparison is proposed using two different numerical models such as a classical two-dimensional finite element model and a refined two-dimensional generalized differential quadrature model. The 3D exact model gives all types of vibration modes, when the four edges are simply supported, changing the imposed half-wave numbers m and n in the two in-plane directions α and β. Some of these modes have one of the two half-wave numbers equals zero. When this condition is simultaneously combined with the condition of transverse displacement different from zero, the resulting vibration mode is defined as cylindrical bending mode. The cylindrical bending case has all the derivatives made in the direction where m=0 or n=0 equal zero. This feature means that the vibrational behavior does not change along this particular direction. The numerical models with the simply supported boundary conditions for all the edges do not achieve these results. These cylindrical bending numerical results are obtained modifying the boundary conditions. Proposed results will demonstrate the validity of this idea and how to modify the mathematical models in order to obtain and improve the cylindrical bending solutions