Volume 2 Issue 1
Authors: E.M.M. Fonseca
Abstract: This work presents a numerical model for thermal analysis of steel hollow tubular sections under high temperatures. Curved and straight pipes are structural tubular elements of essential application in the fluids transport, chemical processes or energy generation plants, eventually subjected at mechanical and thermal loading conditions. Hollow tubular sections may have internal voids filled with air (hollow columns, profile sections thermally insulated or steel pipes). The internal temperature should be calculated with some simplified formulas obtained from heat transfer equations. The results obtained in this work, using the internal void formulation, were compared with the thermal response from finite element formulation, for heat conduction with internal insulation and with corresponding results obtained using the simplified heat conduction equation, according Eurocode 3. For small values of the pipe thickness, the thermal behaviour may be determined with high accuracy using one-dimensional mesh approach, with axisymmetric boundary thermal conditions across section.
Keywords: Hollow Tubular Section; Pipe; Internal Void
Authors: Ioannis G. Raftoyiannis
Abstract: A simplified nonlinear stability analysis for moderately large rotations and small strains is performed on a rectangular two-bar frame subjected to a concentrated eccentrically applied joint load. Such a simplification consisting of adopting linear kinematic relations leads to very reliable results for the initial postbuckling path in the vicinity of the critical point of the above imperfect frame. The existence of an asymmetric bifurcation point is thoroughly discussed and a direct evaluation of the bifurcational load is readily obtained. Using this technique the effect of imperfection sensitivity is also addressed. A qualitative analysis associated with the physical phenomenon yields a substantial reduction of the computational work. The efficiency and reliability of this approximate nonlinear stability analysis proposed herein is illustrated by means of several examples for which a lot of numerical results based on a more accurate nonlinear analysis are available.
Keywords: Nonlinear Stability; Imperfect Frame; Eccentric Load
Authors: Gonzalo Alduncin
Abstract: Macro-hybrid primal mixed variational formulations of evolution filtration problems, with seawater intrusion, are studied. This is an evolution version of our previous paper on steady macro-hybrid penalized variational problems (G. Alduncin, “Steady filtration problems with seawater intrusion: macro-hybrid primal mixed variational analysis,” Appl. Anal., vol. 88, pp. 921-936, 2009). Well-posedness analysis is performed at the continuous level via duality principles and penalization. For parallel computing, macro-hybrid primal mixed spatial decompositions are formulated and analyzed, with transmission conditions variationally dualized. In this manner, penalized pressure-velocity mixed variational formulations are considered on the basis of nonoverlapping domain decompositions, with vertical interfaces, of sections of coastal aquifers.
Keywords: Evolution- Mixed Variational Filtration; Open Flow in Porous Media; Seawater Intrusion; Slightly Compressible Filtration Problem; Evolution Two-Free Boundary Problem; Hybrid Domain Decomposition
Authors: Jean-Robert Clermont; Amine Ammar
Abstract: In this paper, we present a variational approach that allows the Stream-Tube Method (STM) to be considered with discretized finite elements, in order to solve solid strain and fluid flow problems. The analysis concerns a reference domain, used as computational domain, related to the physical domain by an unknown transformation function to be determined numerically, using the concepts of streamlines and stream tubes. The variational approach leads to eliminate the pressure in fluid flow problems and avoids developing a mixed displacement-pressure method in the case of incompressible solids. Applications are provided for fluid flow problems and also in the bending problem, in elasticity.
Keywords: Domain Transformation; Stream Tubes; Variational Formulation; Finite Elements; Elasticity; Fluid Flow