A. Menéndez-Díaz

Hexahedral mesh smoothing using a direct method

This paper develops a generalisation of the mesh smoothing direct method proposed by Balendran, to three dimensions by applying its methodology to smoothed hexahedral meshes. A geometric criteria is used where irregular quadrilaterals are converted to regular quadrilaterals on each face of the hexahedron using a local stiffness matrix. This matrix is then converted to a spatial stiffness matrix with reference to absolute coordinates in order to assemble the geometrical stiffness matrix as a global stiffness matrix. The fixing of boundary conditions is analysed and results obtained in a series of hexahedral meshes, used in finite difference method analysis, are illustrated. To evaluate the quality of the obtained results, a degree of uniformity is calculated and a comparative study of the improvement obtained in each zone of the hexahedral mesh is conducted. The proposed method permits the marking out of the portions of mesh in which a Laplacian smoothening fails to improve the mesh quality, therefore, requiring the use of other methods in which inserted mesh points are taken into account.

A Graphical Method to Assist Quality Decisions throughout the Product Development Process

ABSTRACT In product development processes and in the engineering world in general, many situations arise in which a decision must be taken to choose the best alternative or concept from among several already existing ones. Among the most used methods in situations like these are those that use two-dimensional decision matrices, where the concepts or alternatives are compared by evaluating them according to the degree of compliance for preestablished quality criteria. The finally adopted decision is not only conditioned by the decision makers assessment of each alternative but also by the weightings initially assigned to the criteria. This means that variation in the assessment of any alternative or in the weighting of a criterion can lead to a distinct alternative being selected. In this article, we propose a graphical method that makes it simpler to view the margin for variation, for both the assessments of the alternatives and the weightings for the quality criteria, that does not affect the finally adopted decision. In this way, the decision-making team can analyze in greater depth the more critical assessments and weightings that, although consisting of small changes, could affect the decision. Finally, the applicability of the proposed method is demonstrated in a case study involving an electrical switch design.

Stability analysis of a tunnel using LIDAR data and the keyblock method

We describe a stability study for a tunnel excavated in a fractured rock mass. The proposed methodology uses automatic and semi-automatic algorithms to extract joint sets from a LIDAR point cloud. Using that information and considering a model of ubiquitous joints, pyramidal and non-pyramidal unstable blocks were identified using the keyblock method. The algorithms used for the stability analysis were implemented in BLOFOR software, which represented the possible location of the blocks in the tunnel in three dimensions and provided information on tunnel stability, including a safety factor for each block.

A novel geometric approach for 3-D geological modelling

This paper presents a graphics system called the prism network and its boundary (PNB) aimed at representing the stratified solids that are formed in the subsurface terrain. It allows full 3D modelling of these types of spaces formed by superimposed layers bounded by stratification surfaces. A set of boreholes in the ground is used to generate a network of prisms that models the solid space and serves as the basis for creating two secondary networks, one of triangles and another of quadrilaterals, which define the model boundaries. This graphics system has been implemented in C++, using the standard OpenGL graphics API. The paper first defines and implements a model in the PNB data structure, the process by means of which it is generated is then described, and, finally, a range of applications to specific cases is presented and graphically illustrated.RésuméCet article présente un système graphique appelé PNB (sigles en anglais de Réseau de Prismes et sa Frontière) qui vise à représenter les solides stratifiés qui sont formés dans le sous-sol. Il permet la modélisation 3D complète de ces types d’espaces formés par des couches superposées délimitées par des surfaces de stratification. À partir d’un ensemble de forages dans le terrain est généré un réseau de prismes qui modélise l’espace solide et sert de base pour la création de deux réseaux secondaires, l’un de triangles et l’autre de quadrilatères, qui définissent les frontières du modèle. Ce système graphique a été implémenté en C++, en utilisant l’API standard graphique OpenGL. Le article définit d’abord le modèle et le met en œuvre dans la structure de données PNB, puis décrit le processus de leur génération, et enfin, présente et illustre graphiquement une gamme d’applications à des cas particuliers.

Room Design for Underground Slate Workings: Analysis of Safety Factors for Keyblocks

Rock mass is a crucial element that influences operations throughout the life of a mine from its initial design, development and operation to its closure and environmental restoration. Most excavations are carried out in rock masses with very variable geological and geotechnical conditions resulting from the action of water, seismic effects, earth pressures or the dynamics of the mine itself (Prasad et al. 2013). Excavating a mining cavity in the rock mass generates risks for workers and equipment from possible rock falls caused by the effects of gravity or seismic activity. In this sense, we studied possible block instability in a slate mine in Quiroga (north-western Spain). Spain is currently a leading roofing-slate producer worldwide, and the slate mines are located in the Truchas syncline (between Ourense and Leon). Most of the existing workings are open-cast, with the slate layer being accessed by 5-m-high descending benches and large-scale removal of overburden. The continuity of these open-pit mines could be ensured by taking operations underground, as richer areas of the deposit could be mined without incurring the costs of land clearing and preparation (Alejano et al. 2011). Moreover, underground workings would mitigate the significant visual impact of this open-pit mine and would reduce the cost of landscape restoration. This study aims to: (a) determine the optimal advance direction for the underground excavation (b) develop crown support that ensures stability against rock detachment (c) calculate the maximum height for the rooms while maintaining the drift walls stable.

Automatic road edge detection from Mobile Laser Scanning (MLS)

In this article we present an algorithm for automatic road edge detection from MLS (Mobile Laser Scanning) data. The method takes advantage of linear structures derived from MLS point clouds. These lines are extracted from the point cloud and grouped following geometric restrictions. Then, the outlines of the groups are extracted as road edges. Finally, a moving window filter is applied to those points in order to remove outliers and delineate the road edge. The method was tested on an 800m stretch of road, and the results were checked through visual inspection. Correctness and completeness were 99.1% and 97.5%, respectively.