Ignacio García-Fernández

Interactive terrain simulation and force distribution models in sand piles

This paper presents an application of Cellular Automata in the field of dry Granular Systems modelling While the study of granular systems is not a recent field, no efficient models exist, from a computational point of view, in classical methodologies Some previous works showed that the use of Cellular Automata is suitable for the development of models that can be used in real time applications This paper extends the existing Cellular Automata models in order to make them interactive A model for the reaction to external forces and a pressure distribution model are presented and analyzed, with numerical examples and simulations.

Serious Games for Health and Safety Training

EUROSTAT figures show that 5720 people die in the European Union every year as a consequence of work-related accidents. Training in Health and Safety is indeed a key aspect to reduce this figure, and serious games constitute an effective method to provide this training. However, the development of this type of computer applications is a complex issue, requiring cross discipline knowledge on different areas, including instructional design, psychology, sociology, law, and computer graphics. Beyond the challenges already present in the development of non-educational computer games, serious games for health and safety are instructional tools. Therefore, they require an instructional design to cover specific educational issues, and knowledge on the health and safety regulations which are applicable in each particular context. In addition, these games have as their ultimate goal to increase the worker’s awareness about safety regulations and reduce the number and seriousness of accidents. Thus, the evaluation of this type of applications must be rather different from the evaluation of other games with a focus on entertainment. In this chapter we provide a description of existing serious games in the health and safety area, and describe major instructional and technological aspects related to the development of this type of training tools. Although technological developments will indeed increase the advantages of serious games as a means to deliver instruction in health and safety, we believe that the most challenging issues remain at the instructional side, and further research is still needed to maximize the effectiveness of this kind of training.

Physically-Based Interactive Sand Simulation

The interactive simulation of 3D terrains has been approached from sever al perspectives. Due to the complexity of the system involved, most of the models proposed focus on a visually realis tic animation of the scene, rather than on a physically-based accurate simulation of a granular system. Those m lack generality when interacting with the environment; in most cases, no reaction forces are computed, co nsidering only soil deformation. This limitation reduces their usability in applications such as driving simulators. We pr opose the use of a theoretical discrete model that considers normal forces for 3D real-time simulation of granular systems. We also extend this model to consider horizontal forces, allowing a wider range of interaction s. Several numerical tests have been implemented and detailed results have been analyzed which show a good mo del performance.

Elevation cable modeling for interactive simulation of cranes

In this paper, the way to simulate hoisting cables in real time is addressed. We overcome instability in such simulation by considering a two-layered model: a model for the dynamics of a cable passing through a set of pulleys and an oscillation model based on the classical one-dimensional wave equation. The first layer considers the interaction between the cable and pulleys with the elevation equipment, while the second layer simulates cable oscillation. Numerical instability is avoided by suspending the oscillation layer when required. Due to the system properties, this can be carried out in such a way that does not cause significant loss in the system quality. It considers the oscillation of the cable between every pair of pulleys, collision detection and the variation of the cable length very efficiently. Rendering issues are discussed, with remarks on how to prevent aliasing artifacts in the cable. Efficiency is analyzed, including performance tests which show that the model can be run very efficiently. The paper also covers how to integrate the model in a complex multibody simulation with a high degree of interactivity.

Crane collision modelling using a neural network approach

Abstract The objective of the present work is to find a Collision Detection algorithm to be used in the Virtual Reality crane simulator (UVSim®), developed by the Robotics Institute of the University of Valencia for the Port of Valencia. The method is applicable to box-shaped objects and is based on the relationship between the colliding object positions and their impact points. The tool chosen to solve the problem is a neural network, the multilayer perceptron, which adapts to the characteristics of the problem, namely, non-linearity, a large amount of data, and no a priori knowledge. The results achieved by the neural network are very satisfactory for the case of box-shaped objects. Furthermore, the computational burden is independent from the object positions and how the surfaces are modelled; hence, it is suitable for the real-time requirements of the application and outperforms the computational burden of other classical methods. The model proposed is currently being used and validated in the UVSim Gantry Crane simulator.

Conformation constraints for efficient viscoelastic fluid simulation

The simulation of high viscoelasticity poses important computational challenges. One is the difficulty to robustly measure strain and its derivatives in a medium without permanent structure. Another is the high stiffness of the governing differential equations. Solutions that tackle these challenges exist, but they are computationally slow. We propose a constraint-based model of viscoelasticity that enables efficient simulation of highly viscous and viscoelastic phenomena. Our model reformulates, in a constraint-based fashion, a constitutive model of viscoelasticity for polymeric fluids, which defines simple governing equations for a conformation tensor. The model can represent a diverse palette of materials, spanning elastoplastic, highly viscous, and inviscid liquid behaviors. In addition, we have designed a constrained dynamics solver that extends the position-based dynamics method to handle efficiently both position-based and velocity-based constraints. We show results that range from interactive simulation of viscoelastic effects to large-scale simulation of high viscosity with competitive performance.

A Mixed Model for Real‐Time, Interactive Simulation of a Cable Passing Through Several Pulleys

A model of a cable and pulleys is presented that can be used in Real Time Computer Graphics applications. The model is formulated by the coupling of a damped spring and a variable coefficient wave equation, and can be integrated in more complex mechanical models of lift systems, such as cranes, elevators, etc. with a high degree of interactivity.

Atrial Fibrosis Hampers Non-invasive Localization of Atrial Ectopic Foci From Multi-Electrode Signals: A 3D Simulation Study

Introduction: Focal atrial tachycardia is commonly treated by radio frequency ablation with an acceptable long-term success. Although the location of ectopic foci tends to appear in specific hot-spots, they can be located virtually in any atrial region. Multi-electrode surface ECG systems allow acquiring dense body surface potential maps (BSPM) for non-invasive therapy planning of cardiac arrhythmia. However, the activation of the atria could be affected by fibrosis and therefore biomarkers based on BSPM need to take these effects into account. We aim to analyze the effect of fibrosis on a BSPM derived index, and its potential application to predict the location of ectopic foci in the atria. Methodology: We have developed a 3D atrial model that includes 5 distributions of patchy fibrosis in the left atrium at 5 different stages. Each stage corresponds to a different amount of fibrosis that ranges from 2 to 40%. The 25 resulting 3D models were used for simulation of Focal Atrial Tachycardia (FAT), triggered from 19 different locations described in clinical studies. BSPM were obtained for all simulations, and the body surface potential integral maps (BSPiM) were calculated to describe atrial activations. A machine learning (ML) pipeline using a supervised learning model and support vector machine was developed to learn the BSPM patterns of each of the 475 activation sequences and relate them to the origin of the FAT source. Results: Activation maps for stages with more than 15% of fibrosis were greatly affected, producing conduction blocks and delays in propagation. BSPiMs did not always cluster into non-overlapped groups since BSPiMs were highly altered by the conduction blocks. From stage 3 (15% fibrosis) the BSPiMs showed differences for ectopic beats placed around the area of the pulmonary veins. Classification results were mostly above 84% for all the configurations studied when a large enough number of electrodes were used to map the torso. However, the presence of fibrosis increases the area of the ectopic focus location and therefore decreases the utility for the electrophysiologist. Conclusions: The results indicate that the proposed ML pipeline is a promising methodology for non-invasive ectopic foci localization from BSPM signal even when fibrosis is present.

Modeling, Evaluation, and Scale on Artificial Pedestrians: A Literature Review

Modeling pedestrian dynamics and their implementation in a computer are challenging and important issues in the knowledge areas of transportation and computer simulation. The aim of this article is to provide a bibliographic outlook so that the reader may have quick access to the most relevant works related to this problem. We have used three main axes to organize the article’s contents: pedestrian models, validation techniques, and multiscale approaches. The backbone of this work is the classification of existing pedestrian models; we have organized the works in the literature under five categories, according to the techniques used for implementing the operational level in each pedestrian model. Then the main existing validation methods, oriented to evaluate the behavioral quality of the simulation systems, are reviewed. Furthermore, we review the key issues that arise when facing multiscale pedestrian modeling, where we first focus on the behavioral scale (combinations of micro and macro pedestrian models) and second on the scale size (from individuals to crowds). The article begins by introducing the main characteristics of walking dynamics and its analysis tools and concludes with a discussion about the contributions that different knowledge fields can make in the near future to this exciting area.

Real-time Inextensible Hair with Volume and Shape

Hair simulation is a common topic extensively studied in computer graphics. One of the many challenges in this field is simulating realistic hair in a real-time environment. In this paper, we propose a unified simulation scheme to consider three of the key features in hair simulation; inextensibility, shape preservation and hair-hair interaction. We use an extension to the Dynamic Follow the Leader (DFTL) method to include shape preservation. Our implementation is also coupled with a Lagrangian approach to address the hair-hair interaction dynamics. A GPU-friendly scheme is proposed that is able to exploit the massive parallelism these devices offer, being able to simulate thousands of strands in real-time. The method has been integrated in a game development platform with a shading model for rendering and several test applications have been developed using this implementation.