Parametric variational analysis of compliant sheet metal assemblies with shell elements

One of most demanding tasks in the manufacturing field is controlling the variability of parts as it may affect strongly the deliverability of key characteristics defined at the final (product) assembly level. Current CAT systems offer a good solution to the tolerance analysis/synthesis task, but to handle flexible objects with shape errors more effort is needed to include methods able to capture the elastic behaviour of parts that adds more variability on the final assembly. Usually, sheet metal assemblies require dedicated fixtures and clamps layout to control the gap between parts in the specific location where a join must be placed. Due to the variability of parts the position of clamps can also be varied. The paper describes a FEM-based method able take into account part flexibility and shape error to parametrically analyse sheet metal assemblies by acting on some key parameters to look for the optimal clamp layout that guarantee the gap between parts to be under control after joining parts together. This method offers, with respect to commercial solutions, the ability to model fixtures, clamps and different joint types with no matter on the mesh nodes’ position. Locations of such elements are based on the shape functions defined at element (shell) mesh level and modelled as local constraints. So the user can generate a mesh without a previous knowledge of the exact positions of clamps, for example. This allows to conduit a faster parametric analysis without remeshing the surfaces and with no need to physically model the clamps. An aeronautic case study is described with a four-part assembly riveted on a quite complex fixture by using several clamps

Geoids in General Relativity: Geoid Quasilocal Frames

We develop, in the context of general relativity, the notion of a geoid -- a surface of constant "gravitational potential". In particular, we show how this idea naturally emerges as a specific choice of a previously proposed, more general and operationally useful construction called a quasilocal frame -- that is, a choice of a two-parameter family of timelike worldlines comprising the worldtube boundary of the history of a finite spatial volume. We study the geometric properties of these geoid quasilocal frames, and construct solutions for them in some simple spacetimes. We then compare these results -- focusing on the computationally tractable scenario of a non-rotating body with a quadrupole perturbation -- against their counterparts in Newtonian gravity (the setting for current applications of the geoid), and we compute general-relativistic corrections to some measurable geometric quantities.Comment: 24 pages, 8 figures; v2: reference added; v3: introduction clarified, reference adde

Nuclear Superconductivity in Compact Stars: BCS Theory and Beyond

This chapter provides a review of microscopic theories of pairing in nuclear systems and neutron stars. Special attention is given to the mean-field BCS theory and its extensions to include effects of polarization of the medium and retardation of the interactions. Superfluidity in nuclear systems that exhibit isospin asymmetry is studied. We further address the crossover from the weak-coupling BCS description to the strong-coupling BEC limit in dilute nuclear systems. Finally, within the observational context of rotational anomalies of pulsars, we discuss models of the vortex state in superfluid neutron stars and of the mutual friction between superfluid and normal components, along with the possibility of type-I superconductivity of the proton subsystem.Comment: 41 pages, 16 figures. Chapter contributed to "Pairing in Fermionic Systems: Basic Concepts and Modern Applications", World Scientifi

Structural Response Analyses of Piezoelectric Composites using NURBS

Variational method deduced on the basis of the minimum potential energy is an efficient method to find solutions for complex engineering problems. In structural mechanics, the potential energy comprises strain energy, kinetic energy and the work done by external actions. To obtain these, the displacement are required as a priori. This research is concerned with the development of a numerical method based on variational principles to analyze piezoelectric composite plates and solids. A Non-Uniform Rational B-Spline (NURBS) function is used for describing both the geometry and electromechanical displacement fields. Two dimensional plate models are formulated according to the first order shear deformable plate theory for mechanical displacement. The electric potential varies non-linearly through the thickness, this variation is modelled by a discrete layer-wise linear variation. The matrix equations of motion are reported for piezoelectric sensors, actuator, and power harvester. Normal mode summation technique is applied to study the frequency response of displacement, voltage and the power output. A full three dimensional model is also developed to study the dynamics of piezoelectric sandwich structures. Simulations are provided for thick plates using plate theory and three dimensional models to verify the applicability of those theories in their regime. Newmark’s direct integration technique and a fourth order Runge-Kutta method were used to study the transient vibration. The variational method developed in this thesis can be applied to other structural mechanics problem

A new methodological approach for shoe sole design and validation

Shoe soles are extremely complex to design and manufacture due to their organically shaped but technically precise nature and their manufacturing constraints. Consequently, there is a need for the increased design process flexibility offered by the use of specific CAD methodologies and techniques, to facilitate the work of expert designers and permit effective construction of the three-dimensional elements comprising the complete structure. Recent advances in additive manufacturing systems have extended the possibilities of shoe sole design. These systems can be used to create the final mould and to incorporate dynamic elements that are of particular value in sports footwear. In this article, we present a new methodology for the design and validation of shoe soles. The methodology assists designers in the design concept process and in transfer of the design to manufacturing. The model incorporates both a structural and a functional approach. To this end, a set of specific tools have been developed that can be used to quantify design quality. For example, the model calculates the coefficient of friction or slip resistance, necessary to comply with international standards concerning safety footwear.The financial support of this study comes from IVACE (Instituto Valenciano de Competitividad Empresarial) project: DIHUCA—complex tread designs for footwear soles (IMDEEA/2015/4)