Jesus Felez

Real-Time Traffic Simulation With a Microscopic Model

This paper describes a microscopic model that is able to simulate traffic situations in an urban environment in real time for use in driving simulators. Two types of vehicles are considered in the simulation, namely the user-driven vehicle at the center of the simulation model and the other vehicles that interact with it and its surroundings, which configure the developed traffic model. Simulation is performed in a reduced zone, called the control zone, surrounding the user-driven vehicle. This control zone is a mobile zone centered on the user-driven vehicle. The size of the control zone depends on the maximum number of vehicles involved simultaneously, the traffic density, and the drivers limit of visibility. The other vehicles involved in the traffic simulation are created or destroyed within the limits of the control zone. The general behavior of the traffic model is based on the following theory. Vehicles have an associated driver model that establishes several control functions for them to follow the path, while the steering, acceleration, and braking maneuvers follow certain models of behavior. A traffic light regulation is also included but only in the control area. The possibility of introducing anomalous traffic situations into the simulation is also considered, such as the presence of obstacles, abnormal maneuvers, etc. The developed model is immediately applicable to large-scale driving simulators for driver training, traffic control studies, and safety studies

Deriving simulation models from bond graphs with algebraic loops.: The extension to multibond graph systems

Abstract The first part of this paper makes an introduction to the causal problems raised in some bond graph models when implementing causality. As a consequence, zero-order causal paths (ZCPs) provided of algebraic loops appear. Variables involved in these loops are related themselves by means of algebraic assignments. An algorithm to detect and open all the zero-order causal paths existing in any bond graph model is described. Opening of topological loops will be the employed method. Break variables will be the key to open the loops. The algorithm selects in an optimized way the number of variables necessary to open all the topological loops corresponding to the ZCPs existing in the model. The result is a set of differential-algebraic equations solved using a backward-differential formulae numerical method. How to solve multibond graph systems including zero-order causal paths is the subject of the second part of this paper. The constitutive relationships of multibond resistors, transformers and gyrators give way to a new class of zero-order causal paths whose most important characteristic is that their associated topological loops involve more than one direction. In medium–large models these relationships produce a combinatory explosion of causal paths only treatable via software. The same presented algorithms will be able to analyze and optimally choose the appropriate break variables to open all the zero-order causal paths.

BOND GRAPH ASSISTED MODELS FOR HYDRO-PNEUMATIC SUSPENSIONS IN CRANE VEHICLES

SUMMARY The high weight and critical conditions of wheel load distribution shown by crane vehicle supported on a special chassis, suggest hydro-pneumatic suspensions as most suitable so that they should replace the conventional mechanical types. The Instituto Tecnologico de Aragon, Zaragoza (Spain) in the collaboration with Industrias Luna S.A., Huesca (Spain) has been working on the analysis of hydro-pneumatic suspensions using bond graph techniques, different alternatives to their use being presented in this paper.

Experiences in education innovation: developing tools in support of active learning

The paper focuses on educational projects developed in the ETSII (Escuela Técnica Superior de Ingenieros Industriales) of the Polytechnic University of Madrid during the past few years. These projects were developed as new tools for enhancing the active role of students, for improving practical teaching, especially by means of virtual laboratories and different sets of problems and exercises, and for promoting self-learning. The paper analyses the use of ICT in teaching, with the case of a developed e-learning platform as a tracking system for subjects. The paper concludes by discussing the new educational trends in the Centre, devoted to develop an active role of students by activities such as peer mentoring and laboratory monitors programs, and competitions for achieving multidisciplinary engineering challenges.

A constraint solver to define correctly dimensioned and overdimensioned parts

Creating mechanical parts through conceptual design implies the use of constraints. When developing conceptual design-based CAD programs, two independent modules must be created: on the one hand, the sketcher module, which must define the models geometrical constraints and interpret the users intention through a system of rules. On the other, the calculation module which must resolve the final geometry and eventually dimension the mechanical part. This paper presents a new approach to the constraint-based solvers. The proposed approach establishes the complete two-dimensional geometry and constraints of a sketch and relates it with the complete dimensioning of the sketch. The developed methodology gives as result a complete and consistent dimensioning of the sketch following the rules established by a standard like ISO, determining also if the system is over-constrained and detecting the redundant dimensions. The methodology establishes the most suitable dimensioning but, it is also possible to obtain other alternatives of full sets of dimensions. First, the geometric constraints considered are described, and the use of each one justified, together with the numerical methods used to resolve the set of non-linear constraints obtained. A procedure has also been developed for choosing the set of independent constraints of the system, by introducing the priority factor concept, which lets the overriding constraints in the system be decided, and then the algorithms developed for automatically assigning the constraints are presented. Also described are the criteria followed that lead to an automatic generation of dimensions, as well as to equivalent and alternative dimensioning. Finally, a series of examples are presented to show the possibilities of the developed methodology.

Efficient simulation of mechanism kinematics using bond graphs

Abstract This paper presents a methodology for obtaining the equations corresponding to a mechanism that are necessary for carrying out a kinematic simulation. A simulation of this kind means obtaining the coordinates dependent on the system according to the movements imposed by the degrees of freedom. Unlike a dynamic simulation, where the set of elements moves according to the different external forces existing, in kinematic simulation the movement of the whole set depends exclusively on imposing movement on one or more of the bodies according to the degrees of freedom initially possessed by the mechanism. After presenting an analysis of how to obtain the necessary equations for several simple systems, this methodology is applied to the particular case of a front-loader, where in order to move and tilt the bucket, various closed mechanisms are integrated.

A Full Driving Simulator of Urban Traffic including Traffic Accidents

This paper describes a model for traffic simulation of an urban environment and its implementation in a driving simulator. The simulator is also able to reproduce realistic traffic accidents. In order to attain real-time simulation, the simulation environment has been partitioned considering the city as divided into segments of road, junctions, and sectors that minimize the interaction between the cars involved in the traffic simulation and the traffic simulation is considered only in a control zone centered on the driven vehicle. Simplified dynamic vehicle models have also been used when vehicles are not involved in the accident, allowing for a sufficiently realistic behavior. A traffic light regulation only in the area next to the driven vehicle is also included. A complex model for the vehicles involved in traffic accidents has been developed, including multibody components and different collision models. The developed model is then immediately applicable to large scale driving simulators.

Sensitivity analysis to assess the influence of the inertial properties of railway vehicle bodies on the vehicle's dynamic behaviour

A sensitivity analysis has been performed to assess the influence of the inertial properties of railway vehicles on their dynamic behaviour. To do this, 216 dynamic simulations were performed modifying, one at a time, the masses, moments of inertia and heights of the centre of gravity of the carbody, the bogie and the wheelset. Three values were assigned to each parameter, corresponding to the percentiles 10, 50 and 90 of a data set stored in a database of railway vehicles. After processing the results of these simulations, the analysed parameters were sorted by increasing influence. It was also found which of these parameters could be estimated with a lesser degree of accuracy for future simulations without appreciably affecting the simulation results. In general terms, it was concluded that the most sensitive inertial properties are the mass and the vertical moment of inertia, and the least sensitive ones the longitudinal and lateral moments of inertia.

Influence of the track quality and of the properties of the wheel–rail rolling contact on vehicle dynamics

This work describes an analytical approach to determine what degree of accuracy is required in the definition of the rail vehicle models used for dynamic simulations. This way it would be possible to know in advance how the results of simulations may be altered due to the existence of errors in the creation of rolling stock models, whilst also identifying their critical parameters. This would make it possible to maximise the time available to enhance dynamic analysis and focus efforts on factors that are strictly necessary. In particular, the parameters related both to the track quality and to the rolling contact were considered in this study. With this aim, a sensitivity analysis was performed to assess their influence on the vehicle dynamic behaviour. To do this, 72 dynamic simulations were performed modifying, one at a time, the track quality, the wheel–rail friction coefficient and the equivalent conicity of both new and worn wheels. Three values were assigned to each parameter, and two wear states were considered for each type of wheel, one for new wheels and another one for reprofiled wheels. After processing the results of these simulations, it was concluded that all the parameters considered show very high influence, though the friction coefficient shows the highest influence. Therefore, it is recommended to undertake any future simulation job with measured track geometry and track irregularities, measured wheel profiles and normative values of the wheel–rail friction coefficient.

Kinematic Analysis Of Mechanism By Using Bond-Graph Language

This paper presents a methodology for obtaining the equations corresponding to a mechanism that are necessary for carrying out a kinematic simulation. A simulation of this kind means obtaining the co-ordinates dependent on the system according to the movements imposed by the degrees of freedom. Unlike a dynamic simulation, where the set of elements moves according to the different external forces existing, in kinematic simulation the movement of the whole set depends exclusively on imposing movement on one or more of the bodies according to the degrees of freedom initially possessed by the mechanism. After presenting an analysis of how to obtain the necessary equations for several simple systems, this methodology is applied to the particular case of a wheel loader, where in order to move and tilt the bucket, various closed mechanisms are integrated.