Developing a software toolkit for urban traffic modeling

ATLAS is a modeling language that permits a static view of a city section to be defined for simulating traffic in closed areas. We propose a methodology that is focused on the user while being able to improve the software development activities. The models are formally specified, avoiding a high number of errors in the application, thus reducing the problem solving time. Streets are characterized by their traffic direction, number of lanes, etc. Once the urban section is outlined, the traffic flow is automatically set up. Specialized behavior is included to model traffic lights, trucks, traffic signs, railways, etc. The basic idea is to provide a mapping into DEVS and Cell‐DEVS models that can be easily executed with a simulation tool. As the modelers can focus on the problem to solve, development times for the simulators can be dramatically reduced. A front‐end system allows the user to draw city sections (and then parse the drawing to create a valid ATLAS file), and an output subsystem permitting cars to be shown with realistic 3D graphics. Copyright © 2007 John Wiley & Sons, Ltd.     

Model Continuity to Support Software Development for Distributed Robotic Systems: A Team Formation Example

Modeling, design and testing of the software underlying distributed robotic systems is a challenging task, especially when a large number of mobile robots and task coordination are involved. Model continuity, the ability to use the same model of a system throughout its design phases, provides an effective way to manage this development complexity and maintain consistency of the software. In this paper, we describe the design and implementation of a team-formation multi-robot system. This is used as an example to demonstrate how a modeling and simulation environment, based on the DEVS formalism, can support model continuity in the design of distributed robotic systems. This example shows how the intelligent control models of the robots are first designed and tested via simulation and, when verified mapped to physical robots with DEVS-on-a-chip brains for execution.     

Hybrid system modeling using the SIMANLib and ARENALib Modelica libraries

The ARENALib and SIMANLib Modelica libraries replicate the basic functionality of the Arena simulation environment and the SIMAN language. These libraries facilitate describing discrete-event models using the Arena modeling methodology. ARENALib and SIMANLib models can be combined with other Modelica models in order to describe complex hybrid systems (i.e., combined continuous-time and discrete-event systems). The implementation and design of SIMANLib and ARENALib is discussed. The ARENALib components have been built in a modular fashion using SIMANLib. The SIMANLib components have been described as Parallel DEVS models and implemented using DEVSLib, a Modelica library previously developed by the authors to support the Parallel DEVS formalism. The use of Parallel DEVS as underlying mathematical formalism has facilitated the development and maintenance of SIMANLib. The modeling of two hybrid systems is discussed to illustrate the features and use of SIMANLib and ARENALib: firstly, a soaking-pit furnace; secondly, the malaria spread and an emergency hospital. DEVSLib, SIMANLib and ARENALib can be freely downloaded from http://www.euclides.dia.uned.es/.     

Extending the DEVS formalism for massively parallel simulation

The use of multiprocessors for discrete event simulation is an active research area where work has focused on strategies for model execution with little regard for the underlying formalism in which models may be expressed. However, a formalism-based approach offers several advantages including the ability to migrate models from sequential to parallel platforms and the ability to calibrate simulation architectures to model structural properties. In this article, we extend the DEVS (discrete event system specification) formalism, originally developed for sequential simulation, to accommodate the full potential of parallel processing. The extension facilitates exploitation of both internal and external event parallelism manifested in hierarchical, modular DEVS models. After developing a mapping of the extended formalism to parallel architectures, we describe an implementation of the approach on a massively parallel architecture, the Connection Machine. Execution results are discussed for a class of models exhibiting high external and internal event parallelism, the so-called broadcast models. These verify the tenets of the underlying theory and demonstrate that significant reduction in execution time is possible compared to the same model executed in serial simulation.     

Modeling discrete event scalable network systems

Scalability in simulation tools is one of the most important traits to measure performance of software. The reason is that today’s Internet is the main instance of a large-scale and highly complex system. Simulation of Internet-scale network systems has to be supported by any simulation tool. Despite this fact, many network simulators lacks support for building large models. In this work, in order to propose a new approach for scalability issue in network simulation tools, a network simulator is developed based on behavior of honeybees and high performance DEVS, modular and hierarchical system theoretic approach. A biologically-inspired discrete event modeling approach is described for studying networks’ scalability and performance traits. Since natural systems can offer important concepts for modeling network systems, key adaptive and emergent attributes of honeybees and their societal properties are incorporated into a set of simulation models that are developed using the discrete event system specification approach. Large-scale network models are simulated and evaluated to show the benefits of nature-inspired network models.     

Discrete-event modelling of fire spreading

We deal here with the application of discrete-event System Specification (DEVS) formalism to implement a semi-physical fire spread model. Currently, models from physics finely representing forest fires are not efficient and still under development. If current softwares are devoted to the simulation of simple models of fire spread, nowadays there is no environment allowing us to model and simulate complex physical models of fire spread. Simulation models of such a type of models require being easily designed, modified and efficient in terms of execution time. DEVS formalism can be used to deal with these problems. This formalism enables the association of object-oriented hierarchical modelling with discrete-event techniques. Object-oriented hierarchical programming facilitates construction, maintenance and reusability of the simulation model. Discrete-events reduce the calculation domain to the active cells of the propagation domain (the heated ones).     

Modeling physical systems using finite element Cell-DEVS

We propose a method to analyze complex physical systems using two-dimensional Cell-DEVS models. These problems are usually modeled with one or more Partial Differential Equations and solved using numerical methods. Our goal is to improve the definition of such problems by mapping them into the Cell-DEVS formalism, which permits easy integration with models defined with other formalisms, and its definition using advanced modeling and simulation tools. To show this, we used two methods for solving PDEs, and deduced the updating rules for their mapping to Cell-DEVS. As our simulation results show, the accuracy of the Cell-DEVS solution is the same of these previous methods, showing that we can use Cell-DEVS as a tool to obtain numerical solution for systems of PDEs. Simultaneously, this method provides us with a simpler mechanism for model definition, automated parallelism, and faster execution.     

Hierarchical model-based diagnosis for high autonomy systems

Deep reasoning diagnostic procedures are model-based, inferring single or multiple faults from the knowledge of faulty behavior of component models and their causal structure. The overall goal of this paper is to develop a hierarchical diagnostic system that exploit knowledge of structure and behavior. To do this, we use a hierarchical architecture including local and global diagnosers. Such a diagnostic system for high autonomy systems has been implemented and tested on several examples in the domain of robot-managed fluid-handling laboratory.Research supported by NASA-Ames Co-operative Agreement No. NCC 2-525, A Simulation Environment for Laboratory Management by Robot Organization.     

Distributed simulation platform to design advanced RFID based freight transportation systems

RFID systems, known to improve supply chains performances, are little implemented so far in industry, particularly in the field of transport, due to the high economic investment it requests in comparison to other existing solutions. However, their benefits may be theoretically proved by using a distributed simulation platform to support the design and test of any technical solution and organizational approach devoted to optimize RFID-based logistics systems. This paper deals with the development of this simulation platform, based on Generalized Discrete Event Specification (G-DEVS) models and HLA (High Level Architecture) standard. The different partner's components of the networked logistics enterprise are described. The proposed solution is applied to a freight transportation system and emulates the behaviour of the various components (RFID coupled to geolocation and mobile technology) required to optimize the products routing. The behaviour of the main components is G-DEVS formalized including the logistics supplier server, the smart product and the vehicle onboard device to interface the products with a centralized server. Delivery scenarios are then elaborated and simulated to check the behaviour and the intensity of communication network use between distributed G-DEVS models and other simulation components. The strength of the approach lies in the interoperability of the platform to simulate scenarios including discrete event models, real software and hardware devices all linked via an HLA connection. From these results, a discussion is given to validate or reject the conceptual choices about logistics components behaviour and their network bandwidth requirement regarding GSM, GPRS, Bluetooth and RFID networks theoretical capacities.     

Simulation framework for small scale engagement

Developing future weapons systems has become increasingly complicated and costly. The armed forces of major nations use modeling and simulation techniques for new weapons systems from the conceptual stage to design, production, deployment and training stages to shorten the development cycle and guarantee their effectiveness. Failure in the development cycle carries too much loss in time and money. Therefore, computer-based modeling and simulation techniques are applied from the conceptual stage to gauge the efficacy of new weapons systems. The objective of this study is to develop a modeling and simulation methodology for small scale engagement using the DEVS formalism. The entities required for modeling and simulation are divided into three categories: combat, logical, and environmental entities. Combat entities represent the military hardware or combatants; logical entities represent the judgment and decision entities for the interaction between various entities; and environmental entities emulate the constituents of real combat environment. The combat entities are further modeled into Shell and Core Parts to maximize their reusability under various combat scenarios. The proposed framework is verified using a one-on-one combat engagement simulation (written in C++) between two submarines.     

An efficient approach to human motion modeling for the verification of human-centric product design and manufacturing in virtual environments

The efficient and reliable human-integrated design of products and processes is a major goal of the manufacturing industry. Thus, numerous human-related product functionality and manufacturability aspects need to be verified, using simulation, in the context of the product development procedures. The natural representation of human motions in virtual environments is crucial for the reliability of the simulation results. In this context, the paper presents an efficient approach to human motion analysis and modeling with respect to the anthropometric parameters, based on real motion data. Statistical methods employed for the analysis of the data and additive motion models are derived. The models are capable of predicting human motion and driving digital humans in product and worker simulation environments. A specific test case is presented to demonstrate the application of the suggested methodology on a real industrial problem.     

Activity-based simulation using DEVS: increasing performance by an activity model in parallel DEVS simulation

Improving simulation performance using activity tracking has attracted attention in the modeling field in recent years. The reference to activity has been successfully used to predict and promote the simulation performance. Tracking activity, how- ever, uses only the inherent performance information contained in the models. To extend activity prediction in modeling, we propose the activity enhanced modeling with an activity meta-model at the meta-level. The meta-model provides a set of interfaces to model activity in a specific domain. The activity model transformation in subsequence is devised to deal with the simulation difference due to the heterogeneous activity model. Finally, the resource-aware simulation framework is implemented to integrate the activity models in activity-based simulation. The case study shows the improvement brought on by activity-based simulation using discrete event system specification （DEVS）.     

Explicit dynamics of space free-flyers with multiple manipulators via SPACEMAPLE

This paper focuses on the dynamics of a multiple manipulator space free-flying robot (SFFR) with rigid links and issues relevant to the development of appropriate control algorithms. To develop an explicit dynamics model of such complex systems, the Lagrangian formulation is applied. First, the system kinetic energy is derived based on a developed kinematics approach. Then, through vigorous mathematical analyses, three formats are obtained which describe the contribution of each term of kinetic energy to the equations of motion. Next, explicit derivations of a system's mass matrix, and of the vectors of non-linear velocity terms and generalized forces are introduced for the first time. The obtained dynamics model is very useful for dynamics analyses, design and development of control algorithms for such complex systems. The explicit SFFR dynamics can be implemented either numerically or symbolically. Following the latter approach, the developed symbolic code for dynamics modeling, i.e. SPACEMAPLE, and its verification procedure are described, and issues relevant to the development and computation of dynamics models in control algorithms are briefly discussed. Specific dynamic characteristics of SFFRs compared to fixed-base manipulators are pointed out.     

DEVS methodology for evaluating time-constrained message routing policies

Due to its ability to support temporal issues of systems, discrete event simulation is widely applicable to real-time system design. This paper presents a methodology for the modeling and simulation of time-constrained message routing policies for hypercube interconnected real-time systems. The methodology is based on a framework called the DEVS (discrete event systems specification) formalism which supports modular and hierarchical specification of discrete event models. Within the methodology, we first develop DEVS specification for models for hypercube computers and experimental frames to measure the performance of alternative message routing policies. We then implement such specification in DEVSIM++, a C++-based modeling/simulation environment that implements the DEVS formalism. Simulations of various message routing policies are performed, and the performances of such policies are compared.     

An efficient dynamic point algorithm for line‐based collision detection in real time virtual environments involving haptics

In real time computer graphics, “interactivity” is limited to a display rate of 30 frames per second. However, in multimodal virtual environments involving haptic interactions, a much higher update rate of about 1 kHz is necessary to ensure continuous interactions and smooth transitions. The simplest and most efficient interaction paradigm in such environments is to represent the haptic cursor as a point. However, in many situations, such as those in the development of real time medical simulations involving the interactions of long slender surgical tools with soft deformable organs, such a paradigm is nonrealistic and at least a line‐based interaction is desirable. While such paradigms exist, the main impediment to their widespread use is the associated computational complexity. In this paper, we introduce, for the first time, an efficient algorithm for computing the interaction of a line‐shaped haptic cursor and polygonal surface models which has a near constant complexity. The algorithm relies on space‐time coherence, topological information, and the properties of lines in 3D space to maintain proximity information between a line segment and triangle meshes. For interaction with convex objects, the line is represented by its end points and a dynamic point, which is the closest point on the line to any potentially colliding triangle. To deal with multiple contacts and non‐convexities, the line is decomposed into segments and a dynamic point is used for each segment. The algorithm may be used to compute collision detection and response with rigid as well as deformable objects with no performance penalty. Realistic examples are presented to demonstrate the effectiveness of our approach. Copyright © 2008 John Wiley & Sons, Ltd.     

Coordinated Control Architecture for Motion Management in ADAS Systems

Advanced driver assistance systems (ADAS) seek to provide drivers and passengers of automotive vehicles increased safety and comfort. Original equipment manufacturers are integrating and developing systems for distance keeping, lane keeping and changing and other functionalities. The modern automobile is a complex system of systems. How the functionalities of advanced driver assistance are implemented and coordinated across the systems of the vehicle is generally not made available to the wider research community by the developers and manufactures. This paper seeks to begin filling this gap by assembling open source physics models of the vehicle dynamics and ADAS command models. Additionally, in order to facilitate ADAS development and testing without having access to the details of ADAS, a coordinated control architecture for motion management is also proposed for distributing ADAS motion control commands over vehicle systems. The architecture is demonstrated in a case study where motion is coordinated between the steering and the braking systems, which are typically used only for a single functionality. The integrated vehicle and system dynamics using the coordinated control architecture are simulated for various driving tasks. It is seen that improved trajectory following can be achieved by the proposed coordinated control architecture. The models, simulations and control architecture are made available for open access.      

Statistical shape modeling in virtual assembly using PCA-technique

The use of virtual assembly tools is one way to understand and improve the geometric product tolerance setting and the conditions for successful manufacturing. Recent developments enable consideration to be given to the deformability of parts (single components or subassemblies) when joined. In order to produce reliable results, the geometric deviations of the mating surfaces must be correctly assumed. In this paper, statistical shape models built on the Principal Component Analysis-technique (PCA) are proposed to be used to describe the part variation. A generalized model is presented and the underlying intentions and implications are discussed. It is demonstrated how the PCA-technique can be applied on bigger structures. The method is exemplified using the software RD&T. In the presented case, a non-rigid sheet metal assembly is modeled and distorted to create a set of sample shapes from which a statistical model is built. In the result, the statistic representation bears a good resemblance to the distorted nominal model when the two are compared.     

一种DEVS原子模型向UML状态图映射方法研究

离散事件仿真规范DEVS形式化的一个重要不足在于它缺乏一种标准的、图形化的描述形式。该文研究提出了一种将DEVS的原子模型与复合模型分别映射到UML的状态图和组件图的方法,并用形式化的数学方法对DEVS原子模型向UML状态图的映射过程进行了描述与构造。这种映射将DEVS规范融入到了UML的描述形式当中,将DEVS的抽象化描述与UML的表示能力、计算机处理能力结合起来,为两种建模形式的统一提供了一个可行的思路。该文研究的成果在C^4ISR系统总体方案规范化建模中得到了逐步的应用。