1,720,976 research outputs found
On cross-constraints method and physical contact laws
No full textOne of the crucial problems arising during iterative solution of contact problems is related to the unstable behaviour of the contact elements. Standard formulations do not permit oscillation of the solution path from one side to the other of the constraint limits. If a recursive change of state occurs the solution may not be reached. This fact is mainly due to the discontinuity which takes place moving from the status of gap closed to the status of gap open. A new method has recently been proposed to overcome such limitations. It permits the solution to take place on both sides of the constraint limit. Change of contact status in this case is smooth, hence a more stable solution path can be obtained. The basic formulation of the cross-constraints method adopts analytical functions to represent the non-linear behaviour of the contact. Both traditional penalty and barrier methods can be obtained as limit case of the proposed technique.
In this paper we extend the method by replacing the analytical functions with constitutive laws based on micro- scopic characterisation of contact surfaces. The formulation permits problems where high precision and physical insight are required, to be dealt with. Many high-tech problems can be analysed by using the proposed method; the present work is a preliminary step for the thermomechanical analysis of cable in conduit superconductors
Cavitation modelling in saturated geomaterials with application to dynamic strain localization
Full text linkA model to simulate cavitation phenomena in the pores of saturated porous media is developed. Such phenomena appear in connection with pore water traction, which may be observed during strain localization in dense sand samples or in dynamic fluid-structure interaction problems where the structure is made of geomaterials. The model makes use of an isothermal two-phase flow approach. Numerical examples relating to strain localization are shown
A method for solving contact problems
No full textIn this paper a further method is presented to solve problems involving contact mechanics. The basic idea is related to a special modification of the unconstrained functional to include inequality constraints. The modification is constructed in such a way that minimal point of the unconstrained potential can be exactly shifted to the constraint limit. Moreover, the functional remains smooth and the admissible range of the solution is not restricted. The solution search process with iterative techniques takes advantage from these features. In fact, due to a better control of gap status changes, a more stable solution path with respect to other methods is usually obtained.
The characteristics of the method are evidenced and compared to other classical techniques, like penalty and barrier methods. The finite element discretization of the proposed method is included and some numerical applications are shown
A fast error check for structural analysis using the virtual force principle
No full textAn fast and effective error check for the FE stresses, based on the unit load theorem is proposed. The relative stress error is estimated by the relative error between displacements obtained by the unit load theorem and by the FE method. Analytical examples and numerical applications are presented
Thermo-hydro-chemical couplings considered in safety assessment of shallow tunnels subjected to fire load
No full textFire loading of concrete tunnel linings is characterized by various physical, chemical, and mechanical processes, resulting in spalling of near-surface concrete layers and degradation of strength and stiffness of the remaining tunnel lining. In this paper, the governing transport processes taking place in concrete at elevated temperatures are considered within a recently published fire-safety assessment tool [Savov K, Lackner R, Mang HA. Stability assessment of shallow tunnels subjected to fire load. Fire Safety J 2005; 40: 745-763] for underground structures. In contrast to consideration of heat transport only [Savov et al.], a coupled thermo-hydro-chemical analysis, simulating the heat and mass transport in concrete under fire loading, is performed, giving access to more realistic temperature distributions as well as gas-pressure distributions within the tunnel lining. These data serve as input for the structural safety assessment tool considering, in addition to the temperature dependence of mechanical properties, the effect of the gas pressure on the strength properties of the heated lining concrete. The combination of the two analysis tools (coupled analysis of governing transport processes and structural safety assessment) is illustrated by the fire-safety assessment of a cross-section of the Lainzer tunnel (Austria) characterized by low overburden (shallow tunnel)
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