Contact and HiL interaction in multibody based machinery simulators

[Abstract] Multibody simulators allow to predict and evaluate the motion of machines and mechanisms under the action of the user and the interaction with the simulated environment. Interactive simulators guided by a human or a piece of hardware must be efficient enough to compute the state of the system in real time. ?erefore, employing fast and sufficiently accurate techniques is a must. In this work, generic tools for the implementation of this kind of simulators are provided. Efficient multibody formulations are reviewed for implementing real-time simulators. ?e index-3 Augmented Lagrange formulation with projections of velocities and accelerations is selected, due to its efficiency and stability. ?e integration of the equations of motion follows the Generalized-a method, which provides high-frequency dissipation, and can be unconditionally stable and secondorder accurate if suitable integrator parameters are chosen. Contact modeling and detection is essential for computing the interaction among the mechanisms and the simulated environment. Normal and tangential contact force models are presented. For the normal contact, a Hertz-type Hunt- Crossley model is chosen. ?e tangential force model is based on Coulomb’s law, and includes stiction and viscous friction effects. Both models were compared with the output of the Bowden-Leben stick-slip experiment. A real-time, simplified terrain model featuring digging forces for excavator simulators is also discussed. Several techniques are shown for detecting colliding bodies at run-time. ?e collision detection process is divided into two stages. ?e first one is a broad range and coarse grained process, where potentially colliding pairs of objects are discovered. Spatial and hierarchical division techniques as Octrees, BSP-trees and Directed Acyclic Graphs are presented for this purpose. In the second stage, fine-detailed contact properties are computed from each pair of bodies. Several models are presented for testing object enclosing volumes or more complex surfaces discretized as triangular meshes. State-of-the-art, Commercial Off ?e Shelf hardware devices are presented as the physical foundation of a simulator. Industrial-quality controllers, projection screens and audio devices are reviewed for this purpose. ?e implementation details for the use of those devices are also considered. Network communication procedures between the simulator and monitoring nodes are discussed, too. Finally, a particular implementation of all the techniques described in previous chapters is presented in the form of an interactive excavator simulator, which features all the degrees of freedom of the machine, and is able to perform earthmoving operations in a realistic environment. Monitoring capabilities are also available, and any training session can be defined by user scripts. ?e techniques described in this document constitute a generic and efficient compendium of algorithms that are well-fi?ed for medium or low-end computational systems, as desktop or even laptop computers

Real-time Simulation of Cable Pay-Out and Reel-In with Towed Fishing Gears

[Abstract] Achieving real-time simulation of fast cable pay-out and reel-in manoeuvres with towed fishing gears is a challenging task. This work presents two new simulation methods based on simplified cable models for this kind of application. First, three numerical techniques are proposed to enhance a classical spring-based cable model, increasing its computational efficiency in manoeuvres that involve reeling the cable around a winch drum. Second, the development of an efficient multibody modelling approach based on natural coordinates is reported. The performance of these methods was assessed with two realistic examples. The numerical experiments involved different values of cable axial stiffness and spatial discretization levels, since these parameters were found to have a major impact on computational efficiency. The proposed methods achieved real-time performance in the simulation of systems modelled with up to a few thousand variables. Each modelling approach has advantages and limitations that must be considered when addressing a given application.MINECO; JCI-2012-1237

Direct Sensitivity Analysis of Multibody Systems With Holonomic and Nonholonomic Constraints via an Index-3 Augmented Lagrangian Formulation With Projections

This is a post-peer-review, pre-copyedit version of an article published in Nonlinear Dynamics. The final authenticated version is available online at: http://dx.doi.org/10.1007/s11071-018-4306-y[Abstract] Optimizing the dynamic response of mechanical systems is often a necessary step during the early stages of product development cycle. This is a complex problem that requires to carry out the sensitivity analysis of the system dynamics equations if gradient-based optimization tools are used. These dynamics equations are often expressed as a highly nonlinear system of Ordinary Differential Equations (ODEs) or Differential-Algebraic Equations (DAEs), if a dependent set of generalized coordinates with its corresponding kinematic constraints is used to describe the motion. Two main techniques are currently available to perform the sensitivity analysis of a multibody system, namely the direct differentiation and the adjoint variable methods. In this paper, we derive the equations that correspond to the direct sensitivity analysis of the index-3 augmented Lagrangian formulation with velocity and acceleration projections. Mechanical systems with both holonomic and nonholonomic constraints are considered. The evaluation of the system sensitivities requires the solution of a Tangent Linear Model (TLM) that corresponds to the Newton-Raphson iterative solution of the dynamics at configuration level, plus two additional nonlinear systems of equations for the velocity and acceleration projections. The method was validated in the sensitivity analysis of a set of examples, including a five-bar linkage with spring elements, which had been used in the literature as benchmark problem for similar multibody dynamics formulations, a point-mass system subjected to nonholonomic constraints, and a full-scale vehicle model.Ministerio de Economía y Competitividad (MINECO); DPI2016-81005-PXunta de Galicia; ED431B2016/03

Roll Angle Estimation of a Motorcycle through Inertial Measurements

Abstract: Currently, the interest in creating autonomous driving vehicles and progressively more sophisticated active safety systems is growing enormously, being a prevailing importance factor for the end user when choosing between either one or another commercial vehicle model. While fourwheelers are ahead in the adoption of these systems, the development for two-wheelers is beginning to gain importance within the sector. This makes sense, since the vulnerability for the driver is much higher in these vehicles compared to traditional four-wheelers. The particular dynamics and stability that govern the behavior of single-track vehicles (STVs) make the task of designing active control systems, such as Anti-lock Braking System (ABS) systems or active or semi-active suspension systems, particularly challenging. The roll angle can achieve high values, which greatly affects the general behavior of the vehicle. Therefore, it is a magnitude of the utmost importance; however, its accurate measurement or estimation is far from trivial. This work is based on a previous paper, in which a roll angle estimator based on the Kalman filter was presented and tested on an instrumented bicycle. In this work, a further refinement of the method is proposed, and it is tested in more challenging situations using the multibody model of a motorcycle. Moreover, an extension of the method is also presented to improve the way noise is modeled within this Kalman filter.Ministerio de Ciencia, Innovación y Universidades; (TRA2017-86488-R)

Using nondeterministic learners to alert on coffee rust disease

Motivated by an agriculture case study, we discuss how to learn functions able to predict whether the value of a continuous target variable will be greater than a given threshold. In the application studied, the aim was to alert on high incidences of coffee rust, the main coffee crop disease in the world. The objective is to use chemical prevention of the disease only when necessary in order to obtain healthier quality products and reductions in costs and environmental impact. In this context, the costs of misclassifications are not symmetrical: false negative predictions may lead to the loss of coffee crops. The baseline approach for this problem is to learn a regressor from the variables that records the factors affecting the appearance and growth of the disease. However, the number of errors is too high to obtain a reliable alarm system. The approaches explored here try to learn hypotheses whose predictions are allowed to return intervals rather than single points. Thus,in addition to alarms and non-alarms, these predictors identify situations with uncertain classification, which we call warnings. We present 3 different implementations: one based on regression, and 2 more based on classifiers. These methods are compared using a framework where the costs of false negatives are higher than that of false positives, and both are higher than the cost of warning prediction

Síndrome inflamatorio multisistémico asociado a COVID-19 en pacientes pediátricos

Introduction: since the first cases of COVID-19 appeared, it has spread around the world dangerously fast. At the beginning, it was thought that it mainly affected adults and the elderly, but in early May 2020, cases of children began to be described, who after being infected, developed a multisystemic inflammatory syndrome, causing death in some cases. Objective: to describe the multisystemic inflammatory syndrome associated with COVID-19 in children, for which a total of 17 bibliographies were consulted. Development: this syndrome is a recent pathology with little incidence, but it evolves in a torpid way. It manifests itself with several symptoms and signs, among the most frequent are the fever and gastrointestinal manifestations.Conclusions: without a proven treatment yet, detecting patients in the early stages of the disease is the key to avoiding future complications.Introducción: desde la aparición de los primeros casos de COVID-19, esta se ha propagado por todo el mundo a una velocidad vertiginosa. En su inicio se pensaba que afectaba mayormente a adultos y ancianos, pero a principios de mayo del 2020 se comienzan a describir casos de niños que luego del contagiado, desarrollaban un síndrome inflamatorio multisistémico, llegando en algunos casos hasta la muerte. Objetivo: describir el síndrome inflamatorio multisistémico asociado a la COVID-19 en niños, para ello se consultó un total de 17 bibliografías. Desarrollo: este síndrome es una patología reciente con poca incidencia, pero que evoluciona de manera tórpida. Se manifiesta con varios síntomas y signos, entre la más frecuente fiebre y manifestaciones gastrointestinales. Conclusiones: sin un tratamiento aún comprobado, el detectar a los pacientes en los primeros estadios de la enfermedad constituye la clave para evitar futuras complicaciones

Multisystemic inflammatory syndrome associated with COVID-19 in pediatric patients

Introduction: since the first cases of COVID-19 appeared, it has spread around the world dangerously fast. At the beginning, it was thought that it mainly affected adults and the elderly, but in early May 2020, cases of children began to be described, who after being infected, developed a multisystemic inflammatory syndrome, causing death in some cases. Objective: to describe the multisystemic inflammatory syndrome associated with COVID-19 in children, for which a total of 17 bibliographies were consulted. Development: this syndrome is a recent pathology with little incidence, but it evolves in a torpid way. It manifests itself with several symptoms and signs, among the most frequent are the fever and gastrointestinal manifestations. Conclusions: without a proven treatment yet, detecting patients in the early stages of the disease is the key to avoiding future complications

M. Petrucidius y los hornos romanos y canteras de extracción de arcilla de La Vereda (Burguillos, Sevilla)

Peer reviewe

Poliembrionía en mamíferos

La mulita, al igual que otros armadillos, gesta durante su preñez crías idénticas que provienen de un único óvulo fecundado. Este fenómeno se conoce como poliembrionía y es el que da lugar a los gemelos univitelinos humanos.Fil: Solari, Alberto Juan. Universidad de Buenos Aires. Facultad de Medicina. Departamento de Biología Celular e Histología. Centro de Investigación en Reproducción; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay; ArgentinaFil: Merani, Maria Susana. Universidad de Buenos Aires. Facultad de Medicina. Laboratorio de Biología Cromosómica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay; ArgentinaFil: Luaces, Juan Pablo. Universidad de Buenos Aires. Facultad de Medicina. Laboratorio de Biología Cromosómica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay; ArgentinaFil: Rossi, Luis Francisco. Universidad de Buenos Aires. Facultad de Medicina. Laboratorio de Biología Cromosómica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay; Argentin