Showing papers on "Modeling and simulation published in 1994"

Modeling and Simulation

Abstract: From the Publisher: This book provides an introduction and comprehensive reference to modeling and simulation techniques using computers. It emphasizes applications in economics and the environmental sciences and contains a disk with simulation software (SIMPAS) and 50 system models.

Modeling and simulation of pedestrian traffic flow

Abstract: Questions about the efficiency and safety of pedestrian traffic systems are of major importance in the planning and design of such systems. As the use of functional—or performance-based—requirements becomes more popular, there is also an increasing need for methods and tools which can be used to evaluate if these functional requirements are met. This article presents a stochastic model based on the following assumptions: Any pedestrian facility can be modeled as a network of walkway sections. Pedestrian flow in this network can be modeled as a queueing network process, where each pedestrian is treated as a separate flow object, interacting with the other objects. Such a microscopic model is useful because it makes detailed modeling of human behavior possible. This article also presents a simulation tool, of which the main objective is to estimate the relevant performance measures of the pedestrian traffic system. The article includes two examples.

A qualitative simulation approach for fuzzy dynamical models

Abstract: This article deals with simulation of approximate models of dynamic systems. We propose an approach that is appropriate when the uncertainty intrinsic in some models cannot be reduced by traditional identification techniques, due to the impossibility of gathering experimental data about the system itself. The article presents a methodology for qualitative modeling and simulation of approximately known systems. The proposed solution is based on the Fuzzy Sets theory, extending the power of traditional numerical-logical methods. We have implemented a fuzzy simulator that integrates a fuzzy, qualitative approach and traditional, quantitative methods.

Simulation of cable-stayed bridges using disco

Abstract: Cable-stayed bridges are ideal for spanning natural barriers such as wide rivers, deep valleys or ravines, and for pedestrian bridges crossing wide interstate highways. The modern construction of cable-stayed bridges makes use of segmental balanced cantilever techniques and involves many repetitive cycles of placing the concrete segments and stay cables. Due to this repetition, it provides a fertile area for the application of computer simulation techniques. The paper employs a graphically-based construction simulation system, DISCO (Dynamic Interface for Simulation of Construction Operations), for the modeling and simulation of the construction of the Pasco-Kennewick Intercity Bridge in the state of Washington. The DISCO system provides a graphical environment in which modeling and simulation of construction operations can be conducted in an interactive fashion. The model developed for the bridge construction and the results of the simulation are presented.

Objects for simulation: Smalltalk and Ecology

Abstract: The object-oriented programming environment Smalltalk is used to implement a tool for modeling and simulation of ecological systems. This PC-based tool makes it possible, and easy, to represent individuals explicitly in the simulation, and to integrate the individual-based approach with a traditional population/concentration-based approach. Object-oriented programming is used to allow for an efficient development of models. The properties of Smalltalk are exploited to make testing and investigation of the models occur interactively, supported by a user-friendly interface. In the paper, modeling and simulation concepts and elements of object- oriented programming as they relate to an individual-based approach, are introduced. The simulation extension in question (EcoTalk) is described. Two applications that make use of EcoTalk are presented, both related to population-dynamics. The discussion centers on practical implications of the approach, e.g. the system characteristics that can be expressed in EcoTalk...

Magnetic hysteresis modeling and simulation using the Preisach theory and TLM technique

Abstract: This paper describes the Preisach theory of hysteresis models using a graphical approach. A new simple mathematical function which can relate the Preisach diagrams and the B-H limiting loop is developed and presented. With this new function, the Preisach hysteresis model can be implemented easily without the use of any statistical functions. The model is implemented using the transmission line modeling method and is tested using a practical example. Good agreement is obtained between measurements and simulations. >

Distributed simulation of DEVS-based multiformalism models

Abstract: In this paper we introduce a new approach for parallel, distributed simulation of modular, hierarchical DEVS and DEVS-based combined discrete/continuous multiformalism models The algorithm combines conservative and optimistic distributed simulation strategies and is able to optimally exploit lookahead capabilities of the model The object oriented implementation in C++ is intended to serve as a powerful simulator in the STIMS modeling and simulation environment >

OmSim/spl minus/an integrated interactive environment for object-oriented modeling and simulation

Abstract: The new integrated and interactive environment OmSim, for modeling and simulation of dynamical systems, is introduced. OmSim uses the object-oriented modeling language Omola. The use of OmSim is illustrated by a practical example. The architecture of OmSim is presented and related to a reference model for open architectures for computer aided control engineering. >

Modeling and velocity stabilization of constrained mechanical systems

Abstract: An application of some one- and multistep methods for the numerical integration ofconstrained mechanical systems with and without stabilization is demonstrated to compare their efficiency. In particular, the use of (high order) multistep methods is considered. Choosingsupernumerary coordinates, constrained mechanical systems are formulated in descriptor form (DAE). For 2D systems at least, an assembling technique methodically different from, but equivalent to, the Lagrange formalism is presented for the computer generation of the equations of motion with constant mass matrix and quadratic constraints. This modeling, which can be generalized to 3D multibody systems, is applied on two non-stiff test problems. An example of the automatic modeling and simulation is given by a seven body mechanism. Computer programs are presented. By index reduction, the DAE model is transferred to an equivalent ODE representation whose unstable numerical solution is stabilized byprojection onto the constraint manifold. A perturbation analysis shows thatvelocity stabilization is the most efficient projection with regard to improvement of the numerical integration. How frequently the numerical solution of the transferred ODE should be stabilized is discussed. For a class of multistep methods, a strategy of stabilizing at certain time steps and performing a much less demandingquasi-stabilization at the others is suggested, especially for high order methods. With these high order methods, stabilization is not even necessary for the second test problem.

Mathematical Modeling and Simulation for Carding

Abstract: The purpose of this work is to increase the understanding of carding system dynamics based on mathematical tools that will ultimately lead to the development of on-line real-time controllers for ca...

Simulating electrical circuits with an electronic spreadsheet

Abstract: This paper describes ideas on how a spreadsheet can be an effective modeling and simulation tool for studying electrical circuits. An overview of the user interface is presented, and detailed explanations are given so that any teacher can implement different spreadsheet models for simulation. The didactical interest of such a simulation tool is discussed, and a pilot in-field experiment is referred to. The teacher role is emphasized. Some aspects that characterize the computer as a special instrument are highlighted.

Variable DEVS-variable structure modeling formalism: an adaptive computer architecture application

Abstract: Conventional modeling theory gives support only for representing model behavior, providing little aid for describing changes in model structure. Some models are better represented by changes in their structure. Instead of forcing this changes to be represented at the simple behavioral level, a strong theoretical support is needed to allow the representation of structural changes in a natural way. We present a modeling methodology for representing variable structure systems. Examples of such systems include adaptive computer architectures, ecological systems, fault tolerating computers. We describe an application of this methodology to the modeling and simulation of an adaptive computer architecture. >

Modeling and simulation methodology for digital optical computing systems

Abstract: A modeling and simulation methodology for digital optical computing systems is introduced in this paper. The methodology predicts maximum performance of a given optical computing architecture and evaluates its feasibility. As an application example, we apply this methodology to evaluate the feasibility and performance of the optical content-addressable parallel processor proposed in Appl. Opt. 31, 3241 (1992). The approach consists of two major phases. The first phase involves analytical studies of the effects of design parameters such as cross talk, diffraction-limited beam spot diameter, and pitch on system performance parameters such as signal packing density and skew time. In the second phase, a simulation model and a simulator are introduced by the use of glad (General Laser Analysis and Design, an optical software package developed by Applied Optics Research) to evaluate the combined effects of bit-error rate, bit rate, optical power efficiency, available source power, and signal contrast on the performance parameters such as signal packing density, misalignment tolerance, and distance between devices. The methodology presented here investigates the model, not on a component-by-component basis, but as a whole, which produces a more realistic representation of the actual laboratory prototype. The proposed methodology is intended to reduce the optical computing system design time as well as the design risk associated with building a prototype system.

Vector Fields: an Interactive Tool for Animation, Modeling and Simulation with Physically Based 3D Particle Systems and Soft Objects

Abstract: Vectorfields have traditionally been used in computer graphics as a means of visualizing models over time. This paper presents a system which extends the use of vector fields as an interactive tool for physically based three dimensional particle systems and soft objects. The techniques implemented in the system provide the user with new flexibility in animation, modeling and simulation. This paper describes bounded interactive vectorfields and how they can be used to manipulate particle systems and a class of soft objects. Applications to animation, modeling and simulation are also presented.

A methodology for design, test, and evaluation of real-time systems

Abstract: This article presents a methodology that is suitable for use as part of either a prototyping approach or a component-reuse approach. This methodology integrates modeling and simulation as well as developmental and operational testing over the life cycle. The type of systems or components we address operate in real time. Designing and testing real-time systems involves the use of multiple processors and communication links. The real-time system itself can run on a single processor or multiple processors. Even when the system runs on a single processor, the test and evaluation environment uses multiple processors. If the evaluation environment were hosted on the system processor, system performance would be affected. For ease of exposition, we focus on sensor systems; the methodology described is widely applicable to other kinds of systems. We use two examples (a space-borne navigation system and an interferometer system) to describe the methodology and show how it can be used. This methodology can reduce project costs and shorten schedules because it requires performance evaluation and integration testing early, when problems are generally easier and less costly to correct. >

An intelligent robotics simulator

Abstract: An intelligent robotics simulation system is described. The purpose of the robot simulator is to act either as an interactive robot modeling and simulation tool, or as an execution environment for robotics task plans generated by higher-level planners. It provides features for modeling of manipulators, environment configuration, manipulator control, and status reporting. The execution of the plans is performed in a graphics simulation environment and after successful completion the commands can be transmitted to physical robot hardware. The system provides an interactive simulation environment where every command entered by the user is immediately executed and the results are displayed on a graphics screen. From this interactive environment users can change the simulation scenario and operate the robot manipulator models in the system. Advanced features of the simulator that are described include: composite objects supporting the linking of separate objects into a composite object which can be operated on as a unit while presenting the separate accessibility of its components; configuration management with the provision of an automatic configuration selection mechanism based on a set of heuristic rules; collision detection which provides a way to check for collisions during a simulation run; collision avoidance where the simulator provides a heuristic path planning algorithm which is capable of recovering from collision situations to provide collision-free path plans, and interface to control physical robots with the capability of generating command sequences for real robot controllers. >

Modeling and Simulation Requirements for IPng

Abstract: This white paper summarizes the Distributed Interactive Simulation environment that is under development, with regard to its real-time nature, scope and magnitude of networking requirements. This memo provides information for the Internet community. This memo does not specify an Internet standard of any kind.

A framework for hybrid modeling/simulation of discrete event systems

Abstract: This paper presents a hybrid modeling/simulation framework within which both accuracy in models and speed in simulation experimentations are obtained. Based on the Zeigler's DEVS formalism and associated system theory, the framework is based on the transformation of selected DEVS model into equivalent analytic ones to simulate both analytic and simulation models within a single environment. For high-speed hybrid simulation, the authors extended DEVSim++ which is a realization of the DEVS formalism in C++. To exemplify the proposed approach, the authors demonstrate performance modeling and simulation of a simple communication network. >

Non-linear transformer modeling and simulation

Abstract: Transformers models for simulation with Pspice and Analogy's Saber are being developed using experimental B-H Loop and network analyzer measurements. The models are evaluated for accuracy and convergence using several test circuits. Results are presented which demonstrate the effects on circuit performance from magnetic core losses, eddy currents, and mechanical stress on the magnetic cores.

Mathematic-physical engine: parallel processing for modeling and simulation of physical phenomena

Abstract: Mathematical modeling of various physical phenomena, ranging from fluid flow to electromagnetic field dynamics, from thermal patterns inside a semiconductor wafer to thermal patterns on a geophysical scale, and from combustion inside an automotive cylinder to ion transport across a biological membrane, is a challenge for the 1990s and beyond. These processes share in common a basic underlying structure in that they are described by systems of partial differential equations. This paper proposes parallel processing concepts for the real time simulation of such physical phenomena. Specifically we present a mathematic-physical engine (MPE) to solve in real time, and to display three-dimensionally, the solution of sets of ordinary or partial differential equations. In fact, different versions of the MPE are discussed ranging from a single commercial parallel machine, to networked supercomputers, to a stacked-wafer dedicated machine to suit the needs of scientists/engineers around the world. High speed networking is proposed for remote usage of an expensive MPE facility. Such a capability can enhance the ability of scientists and engineers to accelerate basic research on the one hand, and product development on the other. >

A modular approach in the simulation of high speed networks

Abstract: The advent of high speed networks such as ATM networks has led to an important role for simulation, since exact analysis is difficult in most cases. This paper describes a modular approach in the modeling and simulation of ATM networks and with other networks such as FDDI networks. The OPNET graphics simulation tool is used as the underlying platform of the ATM simulator. The various protocol layers of the ATM network and any control functions that need to be studied are simulated in well defined modules. The main benefit of this approach is that performance issues can be studied independently, and a large number of scenarios constructed and analyzed easily. The detailed simulation model for an ATM network using OPNET is presented, together with a brief/summary of some initial results. >

Hierarchical simulation of high speed digital interconnects using a packaging simulator

Abstract: A hierarchical strategy is presented which permits the tradeoff of modeling and simulation accuracy with simulation speed in the simulation of high speed signals on interconnects in multichip modules and printed circuit boards. Using a point modeling paradigm for discontinuities and impulse response thresholding a smooth transition is achieved between delay modeling and full circuit simulation. >

Modeling and simulation of Space Station Laboratory Module Electric Power System

Abstract: This paper describes modeling and simulation of International Space Station Laboratory Module (US LAB) Secondary Electric Power System (SEPS). The US LAB SEPS consists of multiple levels of switching DCIDC converters with negative resistance characteristics. Subsystems that contain these DCIDC converters may interact with each other which may result in poor power quality and in extreme cases system instability. In this paper LAB SEPS is modeled using EASY5x software. Capabilities of EASYSx in modeling and analysis of large power systems are described. The concept of modularized modeling of power systems is described. Examples of modeling DCIDC converters using averaging techniques that are easily implemented in EASY5x are presented. Subsystem interaction and methods of analysis of distributed power systems are discussed. Results of small signal stability analysis of the power system

Modeling and simulation of solid-state transducers: the thermal and electrical energy domain

Abstract: This paper deals with a basic strategy towards the (efficient) numerical modeling of semiconductor micro-structures in which electric, thermal and thermoelectric effects are important. In particular, we discuss a very efficient method of O(n) for solving the nonlinear semiconductor thermoelectric model equations, where n is the total number of elements in the grid. The method is based on the multigrid method in combination with the mixed finite element discretization method and a nonlinear Vanka-type relaxation method. For a simple, but representative test problem we demonstrate the feasibility of this approach by showing that (nearly) mesh-size independent convergence rates can be obtained.