João Milho

Information-governing dynamics of attacker–defender interactions in youth rugby union

Abstract Previous work on dynamics of interpersonal interactions in 1 vs. 1 sub-phases of basketball has identified changes in interpersonal distance between an attacker and defender as a potential control parameter for influencing organizational states of attacker–defender dyads. Other studies have reported the constraining effect of relative velocity between an attacker and defender in 1 vs. 1 dyads. To evaluate the relationship between these candidate control parameters, we compared the impact of both interpersonal distance and relative velocity on the pattern-forming dynamics of attacker–defender dyads in the sport of rugby union. Results revealed that when interpersonal distance achieved a critical value of less than 4 m, and relative velocity values increased or were maintained above 1 m · s−1, a successful outcome (i.e. clean attempt) for an attacker was predicted. Alternatively, when values of relative velocity suddenly decreased below this threshold, at the same critical value of interpersonal distance, a successful outcome for the defender was predicted. Data demonstrated how the coupling of these two potential, nested control parameters moved the dyadic system to phase transitions, characterized as a try or a tackle. Observations suggested that relative velocity increased its influence on the organization of attacker–defender dyads in rugby union over time as spatial proximity to the try line increased.

Interpersonal Pattern Dynamics and Adaptive Behavior in Multiagent Neurobiological Systems: Conceptual Model and Data

ABSTRACT Ecological dynamics characterizes adaptive behavior as an emergent, self-organizing property of interpersonal interactions in complex social systems. The authors conceptualize and investigate constraints on dynamics of decisions and actions in the multiagent system of team sports. They studied coadaptive interpersonal dynamics in rugby union to model potential control parameter and collective variable relations in attacker–defender dyads. A videogrammetry analysis revealed how some agents generated fluctuations by adapting displacement velocity to create phase transitions and destabilize dyadic subsystems near the try line. Agent interpersonal dynamics exhibited characteristics of chaotic attractors and informational constraints of rugby union boxed dyadic systems into a low dimensional attractor. Data suggests that decisions and actions of agents in sports teams may be characterized as emergent, self-organizing properties, governed by laws of dynamical systems at the ecological scale. Further research needs to generalize this conceptual model of adaptive behavior in performance to other multiagent populations.

Interpersonal Distance Regulates Functional Grouping Tendencies of Agents in Team Sports

Abstract The authors examined whether, similar to collective agent behaviors in complex, biological systems (e.g., schools of fish and colonies of ants), performers in team sports displayed functional coordination tendencies, based on local interaction rules during performance. To investigate this issue, they used videogrammetry and digitizing procedures to observe interpersonal interactions in common 4 versus 2 + 2 subphases of the team sport of rugby union, involving 16 participants aged between 16 and 17 years of age. They observed pattern-forming dynamics in attacking subunits (n = 4 players) attempting to penetrate 2 defensive lines (n = 2 players in each). Data showed that within each attacking subunit, the 4 players displayed emergent functional grouping tendencies that differed between the 2 defensive lines. Results confirmed that grouping tendencies in attacking subunits of team games are sensitive to different task constraints, such as relative positioning to nearest defenders. It was concluded that running correlations were particularly useful for measuring the level of interpersonal coordination in functional grouping tendencies within attacking subunits.

VALIDATED MULTIBODY MODEL FOR TRAIN CRASH ANALYSIS

The development of numerical simulation tools for train crashworthiness design requires their validation with reference crash scenarios similar, in nature, to the eventual collision conditions in which the new train designs have to be used. The modeling assumptions and the suitability of these tools can be verified using data feedback from experimental testing. In this work, a validated multibody-based model is presented for the design of train crashworthy components. In the proposed methodology, the moving components of a vehicle are described as sets of rigid bodies, with their relative motion constrained by kinematic joints. Rigid bodies connected by nonlinear force elements, which represent the lumped flexibility of the structural components, model the sub-structures that deform as a result of the train collisions. The characteristics of these nonlinear force elements represent the force-deformation curves of individual car-bodies extremities, couplers between car-bodies and stiffness of the suspensions springs. The wheel-rail contact is also represented by a model in which the normal and friction forces are present. The friction forces are described by Coulomb friction, which includes their dependency on static and dynamic friction coefficients. The contact forces between the end extremities of the colliding car-bodies, that model the longitudinal impact, include the action of anti-climber devices, which are designed to prevent sliding between the contacting buffers. The validated model is applied to the collision of two different trains, which have distinct specifications for the nonlinear force elements that represent the end extremities of the colliding car-bodies and their couplers. These two force-deformation curves correspond to the design specifications and to the experimental data acquired in a crash test. The validation of the model is discussed considering the deviations between the results of the test and the numerical tool with both design and experimental specifications. It is shown that the simulation of the model with the design specifications, characterized by elastic-perfectly plastic deformation curves for the structural elements, leads to results similar to those observed in the experimental test. When the force-deformation curves obtained experimentally are used to represent the structural elements the correlation between simulation and experimental test results increases significantly.

Design of train crash experimental tests by optimization procedures

Abstract Advanced train crashworthiness design requires not only numerical simulation tools capable of describing the dynamic response of train sets during general crash scenarios, but also, optimization procedures that can be used efficiently in the earlier design stages. A multibody dynamics based methodology that combines optimization with efficient analysis techniques is proposed in this work, for the design of train crashworthy components. In this methodology, the components of the trains are described as rigid bodies that have their relative motion constrained by kinematic joints and among which there are nonlinear spring-damper type elements that represent the structures of the trains that deform under normal operating conditions or during the train crash. Interaction between the colliding trains components are described by contact detection and contact force models. A planar dynamics formulation is used to access out-of-direction dynamics of the train cars. Through the use of an optimization algorithm, a general design framework is developed for single objective optimization problems, applied to the design of train crashworthy components. The selection of any optimization function is allowed, particularly, the ones related with train crashworthiness such as train car accelerations, deformations of train car structures or energy absorbed during train impact. Design variables related to the characteristics of the train car structures or components are used, such as train car mass or material behavior of train car structures defined by force-displacement curves. This methodology is applied to optimize the characteristics of complete train sets to design full-scale experimental crash tests. The results are compared with those obtained in simplified unidimensional multibody train models, using optimization algorithms that do not use analytical sensitivity information.

A multibody methodology for the design of anti-climber devices for train crashworthiness simulation

Abstract The impact of train sets is characterized by a very high potential for the longitudinal instability of the train resulting in overriding of the individual car-bodies. Consequently, the end-underframe structural mechanisms for crash energy management are not loaded and the train kinetic energy has to be dissipated by structural components not designed for that purpose. In this work, a multibody-based methodology is presented for the study of train crashworthiness including the anti-climber devices. The simulation of train impact requires models for the structures of the individual train car-bodies, contact forces between train components, systems and mechanisms responsible for the connections between vehicles. The most important motions of the train set are developed in the vertical plane, therefore, the methodology now developed uses a planar dynamics formulation. The vehicles are described by a set of rigid bodies with their relative motions constrained by kinematic joints. The forces that develop during contact, except for the joint reactions are modelled by nonlinear deformable elements. The mechanical characteristics of such elements represent the force-deformation structural response of each train car-body end, obtained by experimental testing or through detailed finite element models. The nonlinear characteristics of the suspension systems, the structural behaviour of the couplers and the friction forces between wheel-sets and rail arc also represented in these models. The anti-climber mechanical devices are modelled using the description of the contact between the train car-bodies ends. This is represented by a continuous contact force model, which accounts for the relative geometry between the car-body ends and material characteristics of the structural devices. The formulation is finally applied to train impacts in various crash scenarios, which are characterized by the collision of complete train sets with different velocities against stopped trains. The modelling assumptions and the suitability of the numerical tools developed are discussed in the framework of their application to the design of train crashworthy components.

Approximate Entropy Normalized Measures for Analyzing Social Neurobiological Systems

ABSTRACT When considering time series data of variables describing agent interactions in social neurobiological systems, measures of regularity can provide a global understanding of such system behaviors. Approximate entropy (ApEn) was introduced as a nonlinear measure to assess the complexity of a system behavior by quantifying the regularity of the generated time series. However, ApEn is not reliable when assessing and comparing the regularity of data series with short or inconsistent lengths, which often occur in studies of social neurobiological systems, particularly in dyadic human movement systems. Here, the authors present two normalized, nonmodified measures of regularity derived from the original ApEn, which are less dependent on time series length. The validity of the suggested measures was tested in well-established series (random and sine) prior to their empirical application, describing the dyadic behavior of athletes in team games. The authors consider one of the ApEn normalized measures to generate the 95th percentile envelopes that can be used to test whether a particular social neurobiological system is highly complex (i.e., generates highly unpredictable time series). Results demonstrated that suggested measures may be considered as valid instruments for measuring and comparing complexity in systems that produce time series with inconsistent lengths.

Implications of the inline seating layout on the protection of occupants of railway coach interiors

The aim of this work is to present a systematic approach to the improvement in the passive safety in railway interiors. During the primary collision, the vehicle is subjected to an abrupt deceleration, causing the unrestrained occupants to continue their original motion. The occupants are then projected through the vehicle until the secondary collision occurs, i.e., until they come in contact with some part of the interior of the vehicle or with other occupants. Due to its importance, in terms of railway vehicle interiors, the inline seating is investigated with the objective of identifying the potential sources of injury for railway occupants and suggesting directions for the improvement in interior arrangements. The numerical model of this layout is developed using a multibody description for the dummies and a finite element approach for the seats and structural features of the vehicle interior. The crash scenario is studied using the MADYMO code, for which models of the dummies are already validated and which has all features necessary to handle finite element and multibody models in a common simulation environment. The crash pulse used for the virtual testing corresponds to that accepted by the industry and operators as being representative of the most relevant accidents. Of particular importance is the identification of the relevant injuries for this type of scenario and their variability with occupant size and seating position. It is shown here that depending on the type of fixing of the seat to the railway coach, the position of the occupant can play a role in his/her exposure to injury. Furthermore, it is shown that the injuries in the neck region occur in those occupants who exhibit higher risks. Femoral injuries, not being as severe as neck injuries, also have a high potential to develop for the scenarios considered.

Quantifying synergies in two-versus-one situations in team sports: An example from Rugby Union

Collective behaviors in team sports result in players forming interpersonal synergies that contribute to performance goals. Because of the huge amount of variables that continuously constrain players’ behavior during a game, the way that these synergies are formed remain unclear. Our aim was to quantify interpersonal synergies in the team sport of Rugby Union. For that purpose we used the Uncontrolled Manifold Hypothesis (UCM) to identify interpersonal synergies that are formed between ball carrier and support player in two-versus-one situations in Rugby Union. The inter-player angle close to the moment of the pass was used as a performance variable and players running lines velocities as task-relevant elements. Interpersonal synergies (UCM values above 1) were found in 19 out of 55 trials under analysis, which means that on 34% of the trials, the players’ running line velocities contribute to stabilizing the inter-player angle close the moment of the pass. The strength of the synergy fluctuates over time indicating the existence of a location effect during attack phases in Rugby Union. UCM analysis shows considerable promise as a performance analysis tool in team sports to discriminate between skilled sub-groups of players.

Rigid Multibody Systems: The Plastic Hinge Approach

Multibody systems are generally complex arrangements of structural and mechanical subsystems with different design purposes and mechanical behavior. Depending on the type of applications, operating speeds, external or internal loading of the components, the multibody system may experience small or large deformations that lead to a change of the system performance. This is well known in aerospace mechanisms where slender elements are present. Other cases include vehicle components under extreme conditions or machine rods operating at high speeds. The structures, on the other hand, may behave as multibody systems due to their large rotations or because they develop well defined mechanisms of deformation, as in crashworthiness applications.