No abstract

No abstract

This article presents a three-dimensional formulation for the analysis of acoustic barriers over an impedance plane as infinitely thin structures. The barriers are therefore modeled as simple surfaces rather than volumetric structures. Using this approach, the problems caused by near-singular integrations and near-degenerate systems of equations are averted, and mesh generation is made easier. A dual-boundary-element method is used in the analysis, involving the simultaneous solution of standard and hypersingular boundary integral equations. An optimization procedure is used to speed up the assembling of the system of equations, increasing the applicability of the method to a wider range of frequencies.

SUMMARYAn axisymmetric hypersingular boundary integral formulation for elasticity problems is presented in this paper. The hypersingular and strong-singular fundamental solutions are derived and their singular behaviour is discussed in detail for di erent locations of the source point. Several free terms arise from the limiting process when generating hypersingular boundary integral equations, including an extra one speciÿc to the axisymmetric formulation which does not appear in two and three dimensional cases. The singularity subtraction technique is used to regularize all strong-singular and hypersingular integrals, and their evaluation procedure is explained. Finally, the developed formulation is assessed through simple numerical tests.

This paper presents a new boundary integral formulation for two-dimensional acoustic radiation in a uniform subsonic flow in which the Green’s function automatically incorporates the convective effect. The integral equation representation is derived in detail, and shown to incorporate the Sommerfeld radiation condition at infinity. The order of singularities in the integrals is also analyzed. The resulting integral equation involves the derivative of the velocity potential in the flow direction; thus an approximation is necessary to express this extra variable in terms of the potential and its normal derivative. Numerical results are included to verify the formulation.

No abstract

No abstract

The alkali-aggregate reaction (AAR) is a chemical reaction that provokes a heterogeneous expansion of concrete and reduces important properties such as Young's modulus, leading to a reduction in the structure's useful life. In this study, a parametric model is employed to determine the spatial distribution of the concrete expansion, combining normalized factors that influence the reaction through an AAR expansion law. Optimization techniques were employed to adjust the numerical results and observations in a real structure. A three-dimensional version of the model has been implemented in a finite element commercial package (ANSYS F ) and verified in the analysis of an accelerated mortar test. Comparisons were made between two AAR mathematical descriptions for the mechanical phenomenon, using the same methodology, and an expansion curve obtained from experiment. Some parametric studies are also presented. The numerical results compared very well with the experimental data validating the proposed method.