130,478 research outputs found
Electro-mechanical problems in superconductiong coils
No full textThis paper presents the most recent research activity performed by the authors in the field of contact problems in superconducting coils. The research is related to the development of the coils for the experimental nuclear fusion machine “ITER”. The results here summarized are related to the inter-strand electromechanical behavior and its dependence on the electromechanical contact resistance. The effects related to the distribution of the superconducting zones within the wire, and of the mechanical properties of the materials are presented. Moreover a microscopical formulation for a more accurate treatment of the contact resistance is formulated. The adopted strategy is based on the statistical characterization of the surface roughness and the electro-mechanical behavior of the contacting asperities. In such a way the contact resistance is build up starting from a physical background
Extensions of the large penetration strategy for contact problems with large load steps
No full textThe so-called large penetration strategy, proposed by the authors in previous investigations, has proved very e↵ective to deal with frictionless contact problems involving large load steps. The strategy is based on a sub- division of the solution process into two stages: in the first one, performed when the field of the unknowns is still far from the solution point, a predefined pressure limit is enforced and a simplified tangent sti↵ness with the exclusion of the geometric term is adopted in Netwon’s iterations; in the second stage, limited to the neighbourhood of the solution point, the standard consistent lin- earization is used, which guarantees in this phase an asymptotically quadratic convergence rate. Thus far, the e↵ectiveness and robustness of the strategy have been demonstrated in combination with the node-to-segment algorithm for linear finite elements
Contact with friction between beams in 3-D Space
No full textIn this paper a formulation to deal with friction between straight beams undergoing large displacements in 3-D space is proposed. The detection of the contact point and the computation of the amount of sliding are carried out using a completely symmetric treatment between the two contacting beams. Starting from the virtual work equation the consistent linearization of the frictional contact contribution is computed and the complete equation set is arranged in matrix form suitable for FE implementation. Some numerical examples are added to show the eectiveness of the method
A microscopical model for electric-mechanical contact
No full textIn this paper a model to deal with electric-mechanical contact problems in the framework of the FEM is presented. On the basis of some micro-mechanical studies, a new approach is developed to define the non-linear constitutive law that governs the normal force-displacement behaviour and the electric resistance of the contacting surfaces
A numerical formulation for electric-mechanical contacts based on microscopic interface laws
No full textThis work is devoted to the development of a new constitutive model for electric–mechanical contacts, based on a micro-macro approach to describe the contact behaviour.
In order to model properly the physical aspect of the problem the surface microrugosity must be considered. In the proposed contact element a macroscopic formulation, based on microscopic evidences, is set up and implemented in the contact formulation.
Some thermo-mechanical macroscopic models, based on microscopic characterizations, have already been developed to compute the normal and tangential contact stiffness and the thermal contact resistance. On the basis of such macroscopic models, a similar model, suitable for the electric-mechanical field, is developed. With reference to the thermal constriction resistance the electric contact resistance is studied, assuming a flux tube around each contacting asperity, and choosing a suitable geometry for its narrowing at the contact zone.
Finally these selected microscopic laws are adapted to the macroscopic numerical necessities to obtain a constitutive law for the electric-mechanical contact element.
Consistent linearization is developed in order to improve the computational speed, within the framework of the implicit methods
Combined mechanical and electrical analysis of super conducting cables, EURATOM/ENEA Contr. EFDA/00-521 – Final Report, Padova, Italy, 2002.
No full textRapporto di ricerca applicat
A generalized formulation for contact between beams
No full textThe currently available formulations for contact between beams are based on the identification of the minimal distance points along the beam axes, followed by some tuning in case of non-circular beam cross-sections. Up to now a suitable implementation within the framework of the Finite Element Method is available both for the frictionless and for the frictional case. The procedure requires the explicit computation of the virtual work contribution due to the contacts. In such a context for solving the problem with implicit schemes, the formulation has also to be consistently linearized. With this respect both the frictionless and the frictional formulation present severe problems. To overcome all the cited problems a generalized formulation is proposed, which deals with contact between circular beams. It has to be remarked that the contact problem is treated first in a completely generic framework, and only in a second step the results are particularized to the FE formulation. For such purpose the centroids of the beams in the 3-D space are considered as parametric functions. The framework for the consistent linearization is developed in a very rigorous and systematic way, providing evidence of the symmetry of the operators. The procedure is quite cumbersome, hence here only the most heavy part, related to the computation of all the fundamental geometrical terms involved, is presented
A formulation for electric-mechanical contact and its numerical solution
No full textThe progress in advanced technology fields requires more and more sophisticated formulations to consider contact problems properly. This paper is devoted to the development of a new constitutive model for electrostatic–mechanical contacts, based on a micro-macro approach to describe the contact behaviour. The electric-mechanical contact constitutive law is obtained considering the real microscopic shape of the contacting surfaces, the microscopic behaviour of force transmission and current flow. Some thermo-mechanical macroscopic models based on microscopic characterizations have already been developed to compute the normal and tangential contact stiffness and the thermal contact resistance. On the basis of such macroscopic models, a similar model, suitable for the electric-mechanical field, is developed. With reference to the thermal constriction resistance the electric contact resistance is studied, assuming a flux tube around each contacting asperity, and choosing a suitable geometry for its narrowing at the contact zone. The contact element geometry is based on well known theoretical and experimental micro-mechanical laws, suitably adapted for the FEM formulation. The macroscopic stiffness matrix is calculated on the basis of the microscopic laws and it is continuously updated as a function of the changes in the mechanical and electric significant parameters. A consistent linearization of the set of equations is developed to improve the computational speed, within the framework of implicit methods
A coupled electric-mechanical approach for contact problems
No full textThe progress in advanced technology fields requires more and more sophisticated formulations to consider contact problems properly. In this paper an approach is proposed to deal with electric-mechanical contact within the framework of the Finite Element techniques.
The electric-mechanical contact constitutive law is obtained considering the real microscopic shape of the contacting surfaces, the microscopic behaviour of force transmission and current flow. The contact element geometry is based on well known theoretical and experimental micro-mechanical laws, suitably adapted for the FEM formulation.
The macroscopic stiffness matrix is calculated on the basis of the microscopic laws and it is continuously updated as a function of the changes in the mechanical and electrical significant parameters. A consistent linearization of the set of equations is developed in order to achieve a good level of computational efficiency within the Newton Raphson iterative scheme
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