1,721,001 research outputs found
Direct modeling approach to improve virtual prototyping and FEM analyses of bicycle frames
Full text linkMain target of this paper is to analyse the advantages in the use of the Direct Modeling in the Virtual Prototyping processes and in the multiphysics analyses with the help of Reverse Engineering procedures. It is a recent CAD technique that allows the creation and/or modification of models that don’t need parameters and constraints, as on the contrary happens in the Feature Based Modeling. So, it is possible to change the shapes and the dimensions of the original prototypes very easily. Hence, in this paper a methodology devised to acquire and modify a “reconstructed” (non-parametric) model to improve and then to submit it to FEM analysis is presented. Furthermore, it is realized and doesn’t even need the Feature Recognition phase of a typical Reverse Engineering process. In particular, this methodology was applied to a frame of a bicycle used as case study. Its shape was acquired by means of a laser scanner and its virtual prototype was “reconstructed”. In addition, starting from it, two alternative frames were obtained and then easily modified by means of the Direct Modeling techniques. Then, they were submitted to FEM analyses to get different solutions with less weight but similar mechanical performances. Afterwards, the ergonomics of the modified configurations was tested by means of different percentile virtual manikins to plan the physical prototyping of a new improved bicycle
New Surface Fitting Approach in Reverse Engineering of Sheet Metal Parts
No full textThe paper is focused on surface reconstruction techniques, developed to enhance the capability of a measurement system set up for analysing sheet-metal parts.
It presents an alternative technique to get accurate results in shape reconstruction in terms of deviation and smoothing. The matrix-like structured data, output of the measure, allows to reconstruct the surfaces following two approaches: Fit curves to sets of aligned points and then blend a surface onto them; fit surfaces on the whole point data set. The first approach is easier to perform because of the wide diffusion, also in the CAD systems, of many robust routines for 2D-curve fitting. The second approach requires a more complex algorithm to surface the 3D point cloud directly but allows to take into account a smoothing factor on the whole data set, that is very useful when more noise is expected on the point cloud
A statistical approach to simulate instances of archeological findings fragments
No full textFirst aim of this paper is to describe a methodology developed to create virtual fragments of archeological archetypes in CAD (Computer Aided Design) environment. A simple Reverse Engineering (RE) technique was adopted to reconstruct the shape of vases allowing the archeologists, and so the CAD inexpert personnel, to use it. Moreover, another relevant aspect is the definition of
a procedure to simulate shape errors on the virtual prototypes to make more realistic the results. The characteristics of the fragments to be reproduced were selected by means of Design of Experiment (DOE) techniques. So, an algorithm was implemented to simulate the shape error, related to the working operations, that represents the typical noise for the feature recognition of archeological findings. Furthermore, this algorithm can make more complex the hypotheses related to the Gaussian model of simulation of the error and can adapt the value of the shape error (i.e. increasing it) according to the data gathered in archaeological excavation. The case study was based on the definition of a catalogue of archetypes of the black Campanian vases studied and classified by the archeologist J.P. Morel. The procedure conceived was applied to five (among one hundred) vases of the
virtual catalogue obtaining forty instances of fragments affected by errors and so creating virtual mock-ups of typical pieces which may be found in the archeological site considered for the case study
Cheap Photogrammetry Versus Expensive Reverse Engineering Techinques in 3D Model Acquisition and Shape Reconstruction
No full text
Tropical deforestation modelling: comparative analysis of different predictive approaches. The case study of Peten, Guatemala
No full textThe frequent use of predictive models for analyzing of complex, natural or artificial phenomena is changing the traditional approaches to environmental and hazard problems. The continuous improvement of computer performance allows for more detailed numerical methods, based on space-time discretisation, to be developed and run for a predictive modelling of complex real systems, reproducing the way their spatial patterns evolve and pointing out the degree of simulation accuracy. In this contribution we present an application of several methods (Geomatics, Neural Networks, Land Cover Modeler and Dinamica EGO) in the tropical training area of Peten, Guatemala. During the last few decades this region, included in the Biosphere Maya reserve, has seen a fast demographic raise and a subsequent uncontrolled pressure on its own geo-resources. The test area can be divided into several sub-regions characterized by different land use dy-
namics. Understanding and quantifying these differences permits a better approximation of a real system; moreover we have to consider all the physical, socio-economic parameters, which will be of use for representing the complex and sometimes random human impact. Because of the absence of detailed data from our test area, nearly all the information was derived from the image processing of 11 ETM+, TM and SPOT scenes; we studied the past environmental dynamics and we built the input layers for the predictive models. The data from 1998 and 2000 were used during the calibration to simulate the land cover changes in 2003, selected as reference date for the validation. The basic statistics permit to highlight the qualities or the weaknesses for each model on the different sub-regions
Integrating remote sensing, GIS and prediction models to monitor the deforestation and erosion in peten reserve, Guatemala
No full textThis contribution provides a strategy for studying and modelling the deforestation and soil deterioration in the natural forest reserve of Peten, Guatemala, using a poor spatial database. A Multispectral Image Processing of Spot and TM Landsat data permits to understand the behaviour of the past land cover dynamics; a multi-temporal analysis of Normalized Difference Vegetation and Hydric Stress index, most informative RGB (according to statistical criteria) and Principal Components, points out the importance and the direction of environmental impacts. We gain from the Remote Sensing images new environmental criteria (distance from roads, oil pipe-line, DEM, etc.) which influence the spatial allocation of predicted land cover probabilities. We are comparing the results of different prospective approaches (Markov Chains, Multi Criteria Evaluation and Cellular Automata; Neural Networks) analysing the residues for improving the final model of future deforestation risk
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
- …
