We continue the study of the bifurcations and the
structural stability of planar bimodal linear dynamical systems
(that is, systems consisting of two linear dynamics acting on each
side of a straight line, assuming continuity along the separating
line). Here we determine the tangency-saddle singularities in the
saddle/spiral case, the only where they can appear.
We address the problem of robust and efficient treatment of element collapse and inversion in corotational FEM simulations of deformable objects in two and three dimensions, and show that existing degeneration treatment methods have previously unreported flaws that seriously threaten robustness and physical plausibility in interactive applications. We propose a new method that avoids such flaws, yields faster and smoother degeneration recovery and extends the range of well-behaved degenerate configurations without adding significant complexity or computational cost to standard explicit and quasi-implicit solvers.
Structural stability ensures that the qualitative behavior of a system is preserved under small perturbations. We study it for planar bimodal linear dynamical systems, that is, systems consisting of two linear dynamics acting on each side of a given hyperplane and assuming continuity along the separating hyperplane. We describe which one of these systems is structurally stable when (real) spiral does not appear and when it does we give necessary and sufficient conditions concerning finite periodic orbits and saddle connections. In particular, we study the finite periodic orbits and the homoclinic orbits in the saddle/spiral case.
We present a new approach for the simulation of surfacebased fluids based in a hybrid formulation of Lattice Boltzmann Method for Shallow Waters and particle systems. The modified LBM can handle arbitrary underlying terrain conditions and arbitrary fluid depth. It also introduces a novel method for tracking dry-wet regions and moving boundaries. Dynamic rigid bodies are also included in our simulations using a two-way coupling. Certain features of the simulation that the LBM can not handle because of its heightfield nature, as breaking waves, are detected and automatically turned into splash particles. Here we use a ballistic particle system, but our hybrid method can handle more complex systems as SPH. Both the LBM and particle systems are implemented in CUDA, although dynamic rigid bodies are simulated in CPU. We show the effectiveness of our method with various examples which achieve real-time on consumer-level hardware.
Ferrer, J.; Peña, M.; Susin, A. International Conference on Numerical Analysis and Applied Mathematics p. 2205-2208 DOI: 10.1063/1.4825976 Presentation's date: 2013-09 Presentation of work at congresses
We consider bimodal linear dynamical systems consisting of two linear dynamics acting on each side of a given hyperplane, assuming continuity along the separating hyperplane. Focusing in the planar case, we describe which of these systems are structurally stable
We consider bimodal linear dynamical systems consisting of two linear dynamics acting on each side of a given
hyperplane, assuming continuity along the separating hyperplane. Focusing in the planar case, we describe which of these
systems are structurally stable.
Avui dia hi ha una gran demanda per les simulacions realistes en el camp de la computació gràfica. Animacions amb base física s'utilitzen comunament, i un dels problemes més complexos en aquest camp és la simulació de fluids, tant més si aplicacions en temps real són l'objectiu. Els videojocs, en particular, recórren a diferents tècniques que, amb la finalitat de representar els fluids, simplement simulen la conseqüència i no la causa, fent servir mètodes procedurals o paramètrics i, sovint, discriminen la solució física.Aquesta necessitat és la que motiva aquesta tesi, la simulació interactiva dels fluids amb superfície lliure, en general líquids, que són la característica d'interès en la majoria de les aplicacions comunes. A causa de la complexitat de la simulació de fluids, amb la finalitat d'aconseguir una taxa de fotogrames en temps real, s'ha recorregut a utilitzar l'alt paral·lelisme proporcionat per les GPUs de consum actuals. L'algorisme de simulació, el Mètode Lattice Boltzmann (LBM), ha estat triat, per tant, per la seva eficiència i l'assimilació gairebé directa a l'arquitectura de maquinari gràcies a la natura local de les seves operacions.Hem creat dos simulacions de superfície lliure a la GPU: una completament en 3D i una altra restringida només a la superfície superior d'un volum gran de fluid, la qual cosa limita el domini de simulació a 2D. Hem estès aquest últim model per tal de poder rastrejar regions seques, on el fluid no ha arribat, i també l'hem acoblat amb els objectes dinàmics d'una manera independent de la geometria. Com està restringit a 2D, la simulació perd algunes característiques a causa de la impossibilitat de simular la separació vertical del fluid. Per solventar aquesta limitació, s'ha acoblat la simulació de superfície amb un sistema de partícules genèric amb condicions de detecció del trencament de les onades, així les simulacions són totalment independents i només l'acoblament uneix el LBM amb el sistema de partícules escollit.A més, la visualització d'ambdós sistemes també es fa d'una manera realista dins de les taxes de refresc interactives; s'empren tècniques de raycasting per tal de proporcionar els esperats efectes relacionats amb la llum com refraccions, reflexions i càustiques. També s'han aplicat altres tècniques que milloren el detall general com ones de detall de baix nivell i l'escuma de la superfície.
Nowadays there is great demand for realistic simulations in the computer graphics field. Physically-based animations are commonly used, and one of the more complex problems in this field is fluid simulation, more so if real-time applications are the goal. Videogames, in particular, resort to different techniques that, in order to represent fluids, just simulate the consequence and not the cause, using procedural or parametric methods and often discriminating the physical solution.
This need motivates the present thesis, the interactive simulation of free-surface flows, usually liquids, which are the feature of interest in most common applications. Due to the complexity of fluid simulation, in order to achieve real-time framerates, we have resorted to use the high parallelism provided by actual consumer-level GPUs. The simulation algorithm, the
Lattice Boltzmann Method, has been chosen accordingly due to its efficiency and the direct mapping to the hardware architecture because of its local operations.
We have created two free-surface simulations in the GPU: one fully in 3D and another restricted only to the upper surface of a big bulk of fluid, limiting the simulation domain to 2D. We have extended the latter to track dry regions and is also coupled with obstacles in a geometry-independent fashion. As it is restricted to 2D, the simulation loses some features due to the impossibility of simulating vertical separation of the fluid. To account for this we have coupled the surface simulation to a generic particle system with breaking wave conditions; the simulations are totally independent and only the coupling binds the LBM with the chosen particle system.
Furthermore, the visualization of both systems is also done in a realistic way within the interactive framerates; raycasting techniques are used to provide the expected light-related effects as refractions, reflections and caustics. Other techniques that improve the overall detail are also applied as low-level detail ripples and surface foam.
Ojeda, Jesús; Susin, A. Annual Conference of the European Association for Computer Graphics p. 25-28 DOI: 10.2312/conf/EG2013/short/025-028 Presentation's date: 2013-05 Presentation of work at congresses
We present a novel approach at simulating fluids in real-time by coupling the Lattice Boltzmann Method for
Shallow Waters (LBMSW) with particle systems. The LBM can handle arbitrary underlying terrain and arbitrary
fluid depth, which, in turn, allows us to extend it to track dry regions. The LBM is also two-way coupled with rigid
bodies. The particle system adds more detail to the LBM; breaking waves are detected from the surface simulation
and particles are generated to provide the effect, taking effectively certain amounts of fluid and reintegrating it
back once they fall over again. Both the LBM and the particle simulation are implemented in CUDA, although
rigid bodies are simulated in CPU. Finally, we show the effectiveness of the method on commodity hardware.
We introduce a hybrid approach for the simulation of fluids based in the Lattice Boltzmann Method for Shallow Waters and particle systems. Our modified LBM Shallow Waters can handle arbitrary underlying terrain and arbitrary fluid depth. It also introduces a novel and simplified method of tracking dry-wet regions. Dynamic rigid bodies are also included in our simulations using a two-way coupling. Certain features of the simulation that the LBM can not handle, as breaking waves, are detected and automatically turned into splash particles. Albeit we use a simple ballistic particle system, our hybrid method can handle more complex systems as SPH. Both the LBM and particle systems are implemented in CUDA, yet dynamic rigid bodies are simulated in CPU. We show the effectiveness of our method with various examples which achieve real-time on commodity hardware
Fernández-Baena, A.; Susin, A.; Lligadas, X. IEEE International Conference on Intelligent Networking and Collaborative Systems p. 656-661 DOI: 10.1109/iNCoS.2012.66 Presentation's date: 2012-09 Presentation of work at congresses
ew and powerful hardware like Kinect introduces
the possibility of changing biomechanics paradigm,
usually based on expensive and complex equipment. Kinect is
a markerless and cheap technology recently introduced from
videogame industry. In this work we conduct a comparison
study of the precision in the computation of joint angles
between Kinect and an optical motion capture professional
system. We obtain a range of disparity that guaranties enough
precision for most of the clinical rehabilitation treatments
prescribed nowadays for patients. This way, an easy and cheap
validation of these treatments can be obtained automatically,
ensuring a better quality control process for the patient’s
Fortuny, G.; López-Cano, M.; Susin, A.; Herrera, B. Computer methods in biomechanics and biomedical engineering Vol. 15, num. 2, p. 195-201 DOI: 10.1080/10255842.2010.522182 Date of publication: 2011-05 Journal article
We are interested in studying the genesis of a very common pathology: the human inguinal hernia. How the human inguinal
hernia appears is not definitively clear, but it is accepted that it is caused by a combination of mechanical and biochemical
alterations, and that muscular simulation plays an important role in this. This study proposes a model to explain how some
physical parameters affect the ability to simulate the region dynamically and how these parameters are involved in
generating inguinal hernias. We are particularly interested in understanding the mechanical alterations in the inguinal region
because little is known about them or how they behave dynamically. Our model corroborates the most important theories
regarding the generation of inguinal hernias and is an initial approach to numerically evaluating this affection.
Dynamic character animation is a technique
used to create character movements based on
physics laws. Proportional derivative (PD)
controllers are one of the preferred techniques
in real time character simulations for driving
the state of the character from its current state
to a new target-state. In this paper is presented
an alternative approach named velocity
based controllers that are able to introduce
into the dynamical system desired limbs relative
velocities as constraints. As a result, the
presented technique takes into account all the
dynamical system to calculate the forces that
transform our character from its current state
to the target-state. This technique allows realtime
simulation, uses a straightforward parameterization
for the character muscle force capabilities
and it is robust to disturbances. The
paper shows the controllers capabilities for the
case of human gait animation.
In the animation process of a human-like 3D model, a skeleton must be specified to define the model’s surface deformation of its
limbs. Nowadays the skeleton specification is hand made and very time consuming task. In this paper we propose a novel semi-automatic method for rigging a 3D model in an arbitrary pose using a skeleton defined in an animation datafile with no specific initial pose. First a skeleton is
extracted from the voxelizated model, this skeleton is refined and transformed into a tree-data structure. Because the 3D model can be in an arbitrary pose, user interaction is required to select the five limbs correspondence (head, hands and feet), and finally a skeleton taken from an animation data file or a external source is adjusted to the geometric skeleton.
Simulating the muscular system has many applications in biomechanics, biomedicine and the study of
movement in general. We are interested in studying the genesis of a very common pathology: human
inguinal hernia. We study the effects that some biomechanical parameters have on the dynamic
simulation of the region, and their involvement in the genesis of inguinal hernias. We use the finite element method(FEM) and current models for the muscular contraction to determine the deformed fascia transversalis for the estimation of the maximum strain. We analysed the effect of muscular tissue
density,Young’smodulus, Poisson’s coefficient and calcium concentration in the genesis of human inguinal hernia. The results are the estimated maximum strain in our simulations,has a close correlation with experimental data and the accepted commonly models by the medical community.Our
model is the first study of the effect of various biological parameters with repercussions on the genesis of heinguinal hernias.
Fortuny, G.; Rodriguez-Navarro, J.; Susin, A.; Armengol-Carrasco, M.; Lopez-Cano, M. Computers in biology and medicine Vol. 39, num. 9, p. 794-799 DOI: 10.1016/j.compbiomed.2009.06.007 Date of publication: 2009-09 Journal article
In this paper we present a 3D facial animation system named FACe! It is able to generate different expressions of the face throughout punctual and combined activation of Action Units, defined by Facial Acting Coding System(FACS). This system is implemented on a 3D human head controlled by bones, riggers and skinning to deform the
geometry. The bone system is implemented in order to move single or combined Action Units, so that they can implement superior layers such as expressions, phonemes, words, emotions and the synchronization of all them
In the animation, the process of rigging a character is an
elaborated and time consuming task. The rig is developed for a specific
character, and it can not be reused in other meshes. In this paper we
present a method to automatically adjust a human-like character rig to
an arbitrary human-like 3D mesh, using a extracted skeleton obtained
from the input mesh. Our method is based on the selection and extraction
of feature points, to find an equivalence between an extracted skeleton
and the animation rig.
Fortuny, G.; Susin, A.; Lopez, M.; Marcé-Nogué, J. International Symposium on Biomechanics in Vascular Biolgy and Cardiovascular Disease p. 28 Presentation's date: 2008-04-24 Presentation of work at congresses
López-Cano, M.; Fortuny, G.; Rodríguez-Navarro, J.; Armengol, M.; Susin, A. Hernia: the journal of hernias and abdominal wall sugery Vol. 12, num. 3, p. 331 DOI: 10.1007/s10029-008-0347-3 Date of publication: 2008 Journal article
Carta a l'editor de la revista "Hernia" en referència a l'article publicat amb el títol: "Arthur Keith, the anatomist who evisioned herniosis"
We would like to add a comment on another important contribution of Arthur Keith
to the Weld of herniology, that is, the original and accurate
description of the inguinal “shutter” mechanism, a remarkable
anatomic action against development of an inguinal hernia. [...] Today, virtual reality surgical
simulation models allowing three-dimensional (3D) visualization
of the human inguinal anatomy can be used as a complementary tool to assess dynamics of the inguinal area. In fact, using simulations with the Wnite element
method we have recently confirmed the physiological “shutter” mechanism already described almost 100 years ago. These virtual reality Wndings are our present
tribute to the outstanding anatomic descriptions of Arthur
We introduce a facial deformation system that allows artists to define and customize a facial rig and later apply the same rig to different face models. The method uses a set of landmarks that define specific facial features and deforms the rig anthropometrically. We find the correspondence of the main attributes of a source rig, transfer them to different three-demensional (3D) face models and automatically generate a sophisticated facial rig. The method is general and can be used with any type of rig configuration. We show how the landmarks, combined with other deformation methods, can adapt different influence objects (NURBS surfaces, polygon surfaces, lattice) and skeletons from a source rig to individual face models, allowing high quality geometric or physically-based animations. We describe how it is possible to deform the source facial rig, apply the same deformation parameters to different face models and obtain unique expressions. We enable reusing of existing animation scripts and show how shapes nicely mix one with the other in different face models. We describe how our method can easily be integrated in an animation pipeline. We end with the results of tests done with major film and game companies to show the strength of our proposal.
Lopez-Cano, M.; Rodriguez-Navarro, J.; Rodriguez-Baeza, A.; Armengol-Carrasco, M.; Susin, A. Computers in biology and medicine Vol. 37, num. 9, p. 1321-1326 DOI: 10.1016/j.compbiomed.2006.12.006 Date of publication: 2007-09 Journal article
Reproducing the subtleties of a face through animation requires developing a sophisticated character rig. But, creating by hand the inner structure and controls of each character is a very labor-intensive and time-consuming task. We developed an application that is 90--99% faster than traditional manual rigging. The application automatically transfers the rig and animations from the source to a target model. Unlike prior work related to morphing and re-targeting  that focus on transferring animations, we transfer the complete facial setup in addition to animations. Our method is general, so artists can define their own rig and then quickly apply it to different models, even with disparate proportions and appearance (human, cartoon or fantastic). This gives artists complete freedom to manipulate the characters: they can create new animations and not be limited by pre-generated ones.
We use our adapted versions of the two most used methods in Computer Fluid Animation, Marker and Cell and Smoothed Particle Hydrodynamics, to develop a new method taking advantage of the calculation speed of the first and the great level of detail and controllability of the second. Such a method is very useful in animations with a great volume of fluid where the events needing high-level detail take place on the surface.
Finally, we present some simulation examples made with this new method.
We present a facial deformation system that adapts a generic fa-
cial rig into di®erent face models. The deformation is based on labels
and allows transferring speci¯c facial features between the generic rig
and face models. High quality physics-based animation is achieved
by combining di®erent deformation methods with our labeling system,
which adapts muscles and skeletons from a generic rig to individual
face models. We describe how to ¯nd the correspondence of the main
attributes of the generic rig, transfer them to di®erent 3D face models
and generate a sophisticated facial rig based on human anatomy. We
show how to apply the same deformation parameters to di®erent face
models and obtain unique expressions. Our goal is to ease the char-
acter setup process and provide digital artists with a tool that allows
manipulating models as if they were using a puppet. We end with
di®erent examples that show the strength of our proposal.
We introduce a facial deformation system that helps the character setup process and gives artists the possibility to manipulate models as if they were using a puppet. The method uses a set of labels that define specific facial features and deforms the rig anthropometrically. We find the correspondence of the main attributes of a generic rig, transfer them to different 3D face models and automatically generate a sophisticated facial rig based on an
anatomical structure. We show how the labels, combined with other deformation methods, can adapt muscles and skeletons from a generic rig to individual face models, allowing high quality physics-based animations. We describe how it is possible to deform the generic facial rig, apply the same deformation parameters to different
face models and obtain unique expressions. We show how our method can easily be integrated in an animation pipeline. We end with different examples that show the strength of our proposal.
A new hybrid approach for deformable models is presented here and carried out in a virtual reality environment, achieving real time performance with haptic interactions. Our implementation consists in using two approaches for the deformable model. The deformation is modelled using simultaneously a Finite Element Method and a Mesh Free Method.
With this Mesh Free method, particles are used to simulate large deformations in the volume region near the surface of the object. The remaining internal volume of the object can be modelled employing a coarse mesh using the Finite Element Method.
We present a Finite Element Method (FEM) implementation for cloth simulation on the GPU. The advantages of FEM are twofold: the realism of cloth simulations using this method is improved compared with other methods like the widely used mass-spring one, and it has a wider application rank because it can be used for general triangulated cloth meshes.
We are able to detect collisions between cloth and other objects (solids or deformables) and also we deal with self cloth collisions. This is also done in the GPU using image-based collision methods. We have also improved a GPU-Gradient Conjugate method for solving the linear equation systems involved in the FEM solution. Two more methods are also implemented in the GPU to compare with the FEM method: a mass-spring model (based on rectangular meshes) and a constraint method (based on triangular meshes).