The direct boundary element method: 2D site effects assessment on laterally varying layered media (methodology)

The Direct Boundary Element Method (DBEM) is presented to solve the elastodynamic field equations in 2D, and a complete comprehensive implementation is given. The DBEM is a useful approach to obtain reliable numerical estimates of site effects on seismic ground motion due to irregular geological configurations, both of layering and topography. The method is based on the discretization of the classical Somigliana's elastodynamic representation equation which stems from the reciprocity theorem. This equation is given in terms of the Green's function which is the full-space harmonic steady-state fundamental solution. The formulation permits the treatment of viscoelastic media, therefore site models with intrinsic attenuation can be examined. By means of this approach, the calculation of 2D scattering of seismic waves, due to the incidence of P and SV waves on irregular topographical profiles is performed. Sites such as, canyons, mountains and valleys in irregular multilayered media are computed to test the technique. The obtained transfer functions show excellent agreement with already published results.

Use and abuse of audivisual media in the college classroom. Slides show and web pages

The multimedia development that has taken place within the university classrooms in recent years has caused a revolution at psychological level within the collectivity of students and teachers inside and outside the classrooms. The slide show applications have become a key supporting element for university professors, who, in many cases, rely blindly in the use of them for teaching. Additionally, ill-conceived slides, poorly structured and with a vast amount of multimedia content, can be the basis of a faulty communication between teacher and student, which is overwhelmed by the appearance and presentation, neglecting their content. The same applies to web pages. This paper focuses on the study and analysis of the impact caused in the process of teaching and learning by the slide show presentations and web pages, and its positive and negative influence on the student’s learning process, paying particular attention to the consequences on the level of attention within the classroom, and on the study outside the classroom. The study is performed by means of a qualitative analysis of student surveys conducted during the last 8 school Civil Engineering School at the Polytechnic University of Madrid. It presents some of the weaknesses of multimedia material, including the difficulties for students to study them, because of the many distractions they face and the need for incentives web pages offer, or the insignificant content and shallowness of the studies due to wrongly formulated presentations.

Statistical mechanics approaches to granular media: between micromechanics and macromechanics

The mechanical behavior of granular materials has been traditionally approached through two theoretical and computational frameworks: macromechanics and micromechanics. Macromechanics focuses on continuum based models. In consequence it is assumed that the matter in the granular material is homogeneous and continuously distributed over its volume so that the smallest element cut from the body possesses the same physical properties as the body. In particular, it has some equivalent mechanical properties, represented by complex and non-linear constitutive relationships. Engineering problems are usually solved using computational methods such as FEM or FDM. On the other hand, micromechanics is the analysis of heterogeneous materials on the level of their individual constituents. In granular materials, if the properties of particles are known, a micromechanical approach can lead to a predictive response of the whole heterogeneous material. Two classes of numerical techniques can be differentiated: computational micromechanics, which consists on applying continuum mechanics on each of the phases of a representative volume element and then solving numerically the equations, and atomistic methods (DEM), which consist on applying rigid body dynamics together with interaction potentials to the particles. Statistical mechanics approaches arise between micro and macromechanics. It tries to state which the expected macroscopic properties of a granular system are, by starting from a micromechanical analysis of the features of the particles and the interactions. The main objective of this paper is to introduce this approach.

Letters to the editor [An implementation of the Boundary Element Method for zoned media with stress discontinuities, T.J. Rudolphi, 1983]

En esta carta al editor, el profesor D. Enrique Alarcón Álvarez comenta el artículo de Thomas J. Rudolphi "An implementation of the Boundary Element Method for zoned media with stress discontinuities" publicado en la revista "International Journal for Numerical Methods in Engineering" Vol. 19, Nº 1, pags. 1–15, enero 1983.