Showing papers in "International Journal of Modelling and Simulation in 2001"
TL;DR: In order to improve the generalization capabilities, which are critical for the specific diagnostic problem, a new multinet architecture is developed, based on the idea of 'majority rule' decision, which is characterized by higher generalized capabilities and robustness.
Abstract: In this paper artificial neural networks are used with promising results in a critical, and at the same time, very difficult problem concerning the diagnosis of gas turbine blading faults. Neural network-based fault diagnosis is treated as a pattern recognition problem, based on measurements and feature selection. Emphasis is given to the design of the appropriate neural network architecture and the selection of the appropriate measuring instruments, which are of critical importance for achieving good performance (high success rates and generalization capabilities). Initially the performance of the classical neural network architectures, namely MultiLayer Perceptron (MLP), Learning Vector Quantization (LVQ), Modular MultiLayer Perceptron and Radial Basis Function (RBF), are investigated for this problem. The implemented neural network structures are trained to classify faulty and healthy patterns coming from twelve different measuring instruments. The performance of the above neural network structures is investigated, and the diagnostic capabilities of the measuring instruments are examined. Next, in order to improve the generalization capabilities, which are critical for the specific diagnostic problem, a new multinet architecture is developed, based on the idea of majority rule' decision. Compared with the classical architectures, this new multinet architecture is characterized by higher generalization capabilities and robustness. A first approach to the design of the appropriate multinet architecture and the selection of the appropriate measuring instruments, in order to provide the basis of a high-performance automated diagnostic system, is proposed. The conclusions derived are of general interest and applicability.
17 citations
TL;DR: In this paper, the authors proposed a new multivariate process capability index that is directly related to the proportion of nonconforming items and calculated in a nonparametric setting; hence, it does not rely on a particular distribution.
Abstract: For the multivariate manufacturing processes, tremendous difficulties are often encountered when one attempts to measure the process capability by directly extending the univariate approach, that is, comparing the specification limits (tolerance zones) with the actual process spread. In fact, the existing multivariate process capability indices developed along the same line are very complicated to apply even under the normality assumption. The authors of this paper propose a new multivariate process capability index that is directly related to the proportion of nonconforming items. Moreover, the new index is calculated in a nonparametric setting; hence, it does not rely on a particular distribution. The estimation methods of the new index are studied in detail. Simulations for the elliptical and rectangular tolerance zones under different bivariate distributions are carried out to illustrate the new approach. The applications of the new index to real-life examples are also presented.
14 citations
TL;DR: In this paper, a modelling framework for the uniform manipulation of network entities with minimum time overhead is presented, which extends to both primitive and composite entities such as communication protocols and nodes, and ensures that composite network entity models are preconstructed.
Abstract: Recent work indicates simulation of dynamic network behaviour may be used as an efiective tool for predicting network performance, for the near future. Conclusions from such simulation, when applied to network performance, can greatly enhance network management. To accomplish this, such simulation must be performed in real time, with the consequent efiect of drastically reducing both modelling and experimentation requirements. This article introduces a modelling framework for the uniform manipulation of network entities with minimum time overhead. This framework, which is based on modular and hierarchical modelling, extends to both primitive and composite entities such as communication protocols and nodes, and ensures that composite network entity models are preconstructed. The framework thus enables the model to reliably depict variable network structure and operation parameters. Sample measurements are presented to illustrate the type of dynamic network behaviour that such simulation techniques have to deal with. The measurements also illustrate the adaptability of the model, including reduced time overhead for simulation experiments.
11 citations
TL;DR: In this paper, a semi-active retuning methodology was proposed to improve the vibration suppression performance of a single-input single-out (SISO) V2V system, which is a common occurrence in industry and brings sub-par performance.
Abstract: Detuning is a common occurrence, which is widely seen in industry and brings sub par vibration suppression performance. This study introduces a semi-active retuning methodology that imparts optimum...
11 citations
TL;DR: In this paper, the authors deal with the development of the crystal growth rate model according to a novel modelling strategy, which combines an artificial neural network (ANN) as an approximator of the grow rate.
Abstract: This paper deals with the development of the crystal growth rate model according to a novel modelling strategy. The method combines an artificial neural network (ANN) as an approximator of the grow...
8 citations
TL;DR: In this article, a new simulation method for switched systems which provides the discrete-time response of the one-cycle average value of any signal in the system is reported, compared to the more traditional simulation methods with respect to accuracy and speed through a numerical simulation example of boost converter.
Abstract: A new simulation method for switched systems which provides the discrete-time response of the one-cycle-average value of any signal in the system is reported. It is compared to the more traditional simulation methods with respect to accuracy and speed through a numerical simulation example of boost converter. This method is shown to be both fast and to give exact average values at switching instants.
7 citations
TL;DR: In this article, a tool-breakage detector was proposed to evaluate the impacts between the cutting edges and the workpieces, and the proposed TBD identified tool breakage in all of the test cases without giving any false alarms when the cutting started and when the tool left.
Abstract: In micro-machining operations, a small amount of material is removed and minute cutting forces are created. Micro-end mills with less than a 2mm diameter have a short and unpredictable tool life. When these tools fail, their shafts are broken. An operator cannot detect tool breakage from the sound or by a visual inspection during the machining operation. In this paper, the tool-breakage mechanism of micro-end mills, wear-induced stress (WIS), is explained by evaluating the thrust direction cutting force characteristics, using scanning electron microscope (SEM) images to inspect tool tips and acoustic emission activity. The experimental data indicate that the tension between the tool and the workpiece suddenly releases when these tools break. A tool-breakage detector (TBD) is proposed to evaluate the impacts between the cutting edges and the workpieces. The proposed TBD identified tool breakage in all of the test cases without giving any false alarms when the cutting started and when the tool left ...
7 citations
TL;DR: In this article, a mathematical model describing the evolution of this diffusion coefficient for disperses dyes as a function of time, initial dye concentration, and the nature of the dyebath (finite or infinite) is proposed.
Abstract: A common goal of all dyers is to achieve the correct shade as early as the first dyeing. But the disperse dyeing process is very complex, being characterized by the diffusion-controlled sorption of dyes that depends on several physicochemical parameters such as dye concentration and temperature of application. Wilson and Hill developed equations describing the uptake of disperse dyes by cylindrical fibres as a function of the diffusion coefficient and the nature of the dyebath. This coefficient is a physical term that permits comparison between different dyeing experiments. However, the literature reveals no equation that expresses the influence of experimental parameters on the diffusion coefficient value. Thus, this work proposes a mathematical model describing the evolution of this diffusion coefficient for disperses dyes as a function of time, initial dye concentration, and the nature of the dyebath (finite or infinite).
6 citations
TL;DR: In this paper, the authors considered the general theory associated with modeling and interpretation of nonstationary ARMA processes driven by symmetric α stable inputs (or infinite variance signals) and provided a set of suitable AR and MA regularity conditions to ensure the existence and uniqueness of regular solutions.
Abstract: This article considers the general theory associated with modelling and interpretation of some nonstationary ARMA processes driven by symmetric α stable inputs (or infinite variance signals). A set of suitable AR and MA regularity conditions is given to ensure the existence and uniqueness of regular solutions. Some explicit prediction results are also reported, as they are very useful in many practical problems that arise in science, engineering and business.
6 citations
TL;DR: The proposed approach for user mobility provides a more realistic mobility model and study the probability distributions of cell sojourn time (CST) and channel holding time (CHT) considering random user mobility.
Abstract: The authors suggest a mathematical formulation to describe the random mobility of users in microcellular systems. Variable user mobility is characterized with an analytical model where users are assumed to change their moving speed and direction randomly. The study on user mobility enables us to improve the accuracy of performance analyses for channel utilization. Utilizing the proposed approach for user mobility, we provide a more realistic mobility model and study the probability distributions of cell sojourn time (CST) and channel holding time (CHT) considering random user mobility.
4 citations
TL;DR: In this paper, the authors present a high-fidelity, event-driven model for performance analysis of various applications on Myrinet system area networks (SANs), designed for the Block-Oriented Network Simulator (BONeS) commercial CAD environment for discrete-event simulation.
Abstract: This paper presents a high-fidelity, event-driven model for performance analysis of various applications on Myrinet system area networks (SANs). The model, designed for the Block-Oriented Network Simulator (BONeS) commercial CAD environment for discrete-event simulation, is accurate down to the Myrinet character level, and supports a wide variety of topologies and parameter permutations. An analytical model is also presented by which the simulation model is verified, and validation of the simulation model is achieved through comparisons with experimental testbed results on both networking and parallel computing tests. In addition, a case study on performance analysis of Myrinet-based networks and clustered computers is included. This case study examines the impact of Myrinet data rate and buffer size on communication and computing performance, further demonstrating the flexibility and versatility of the new simulation model.
TL;DR: An eight-state Markov model of voice activity in conversational speech has been used in order to assess the adequacy of an Internet audio mechanism that dynamically sets the playout delay value of packet audio in Internet voice-based connections.
Abstract: Proposed new control mechanisms for the transmission of packetized voice across the Internet utilize the presence of silent intervals in conversational speech in order to dynamically adapt the behaviour of the audio application to the network fluctuating traffic conditions so as to minimize the effect of packet loss and varying delays on the quality of audio delivered to the destinations. An accurate model of the on-off characteristics of the conversational speech is thus necessary to analyze the performance of those audio communication systems. In this paper, an eight-state Markov model of voice activity in conversational speech has been used in order to assess the adequacy of an Internet audio mechanism that dynamically sets the playout delay value of packet audio in Internet voice-based connections. Based on this model, several simulation experiments have been carried out that show that a sufficient number of silence periods (of sufficiently long duration) occur in a typical human conversation that permit an adequate application of the proposed audio mechanism. In addition, a number of simulative/experimental trials are reported that show that the proposed Internet audio mechanism strikes a favourable balance between the average playout delay and the packet loss percentage experienced during audio conversations over the Internet.
TL;DR: In this paper, the authors present a knowledge representation scheme for the symbolic reasoning mechanisms in object-oriented programming environments, which can be expressed in terms of a collection of bond graph elements, which are then mapped directly into a qualitative equation and a symbolic mathematical equation.
Abstract: directly onto a symbolic mathematical model, a qualitative model, and a numerical simulation model if necessary. An object-oriented programming environment can easily be built in terms of a collection of bond graph elements. These elements are then mapped directly into a qualitative equation and a symbolic mathematical equation. This capability results in a powerful approach to integrating various symbolic reasoning methods with standard numerical techniques. As there is a direct association between the bond graph element and the mathematical relationships, this knowledge representation scheme allows for a systematic approach to creating the models required for the symbolic reasoning mechanisms. For qualitative reasoning, each relation maps directly into a qualitative representation.
TL;DR: A new probabilistic predicate transition net model is proposed for efficiency of reasoning in expert systems in the presence of imprecision and inconsistency of the database and uncertainty in the knowledge base, which also may include self-references.
Abstract: A new probabilistic predicate transition net model is proposed in this paper for efficiency of reasoning in expert systems in the presence of imprecision and inconsistency of the database and uncertainty in the knowledge base, which also may include self-references. The dynamic behaviour of the model has been analyzed in detail to determine the condition for stability and existence of limit cycles in the reasoning system. The scope of inconsistency management has also been discussed for models with stable dynamic behaviour. The concepts presented in the paper have been illustrated with reference to a self-referential expert system, designed for scene interpretation.
TL;DR: In this paper, a method of constructing cutter-swept surfaces (CSS) for use in NC machining simulation and verification using NURBS interpolation is described, where a general cutter path curve along with the cutter geometry in the form of critical curves are taken into account to derive a cutterswept surface.
Abstract: This article describes a method of constructing cutter-swept surfaces (CSS) for use in NC machining simulation and verification using NURBS interpolation. Most methods of CSS surface construction and evaluation today rely on linear cutter path curves, thus introducing error in the process of converting curved cutter paths to line segments. Our method takes a general cutter path curve in NURBS form along with the cutter geometry in the form of critical curves to derive a cutter-swept surface in NURBS form. This surface can then be intersected with the surface being cut to form an intermediate surface that can be evaluated for cutting error, volume removal calculations, and more.
TL;DR: It is shown that the use of Simulink S-functions and Bondsim tools will simplify the modelling and simulation of dynamic systems and notions of Fakri transformation, such as owner bonds of junctions, internal and external bonds, and constitutive blocks and connection with Bondsim elements are introduced.
Abstract: This article presents methods for transforming bond graph models into their representation by block diagrams. The authors show that the use of Simulink S-functions and Bondsim tools will simplify the modelling and simulation of dynamic systems. The application of Bondsim elements is based on Fakri transformation of bond graphs into block diagrams. This article introduces notions of Fakri transformation, such as owner bonds of junctions, internal and external bonds, owner blocks of junctions, and constitutive blocks and connection with Bondsim elements. The efficiency of the proposed approach for modelling dynamic systems is illustrated using an example.
TL;DR: The results obtained with a tool used to model and simulate discrete event systems, based on Discrete Event systems Specification (DEVS) formalism, are presented and its use shown through application examples.
Abstract: This paper presents the results obtained with a tool used to model and simulate discrete event systems, based on Discrete Event systems Specification (DEVS) formalism. Its main features are presented and its use shown through application examples. The use of this formal approach allowed development of safe and cost-effective simulations. A simulated processor was built to study the different levels of a computer system. The goal was to help the full comprehension of the computer behaviour used in computer organization courses. The environment helped the students understand these complex systems and also allowed them to make empirical comparisons and performance studies for educational purposes.
TL;DR: In this paper, a correlation between the crosswind and vertical concentrations in the Gaussian atmospheric dispersion model is examined for various downwind positions for each Pasqui-quasi position.
Abstract: A correlation between the crosswind and vertical concentrations in the Gaussian atmospheric dispersion model is examined. This correlation is analyzed for various downwind positions for each Pasqui...
TL;DR: There is a good built-in margin of safety in the ETA ring components as indicated by high PMS values, and it further includes the existing results for membrane and grid forces of ETARing after incorporating the uncertainty of these variables based on the existing data in the literature and past experience at NASA.
Abstract: This work deals with performance analysis of an external tank attach ring of a space shuttle. The shuttle consists of the orbiter and the main engines along with the solid rocket boosters, external tank (ET), and external tank attachment (ETA) ring. The study discussed in this paper is restricted solely to the ETA. Performance analysis in the traditional deterministic sense involves calculation of margin of safety values for yield and ultimate allowable stresses. Performance analysis using probabilistic principles uses probabilistic margins of safety (PMS). These values are determined for various parts of ETA ring cross-sections and a comparison is made between the two sets of results. This study also indicates that there is a good built-in margin of safety in the ETA ring components as indicated by high PMS values, and it further includes the existing results for membrane and grid forces of ETA ring after incorporating the uncertainty of these variables based on the existing data in the literature and past experience at NASA.
TL;DR: In this paper, a simple finite difference beam propagation method (FDBPM) involving the fourth-order Runge-Kutta algorithm (RKBPM) is proposed to analyze 2-D and 3-D optical waveguides.
Abstract: In this paper, a simple finite difference beam propagation method (FDBPM) involving the fourth-order Runge-Kutta algorithm (RKBPM) is proposed to analyze 2-D and 3-D optical waveguides. We compare the accuracy and computational efficiency with those of the conventional FDBPM employing the Crank-Nicholson method (CNBPM). The simulation results have demonstrated that the RKBPM is a superior technique to the CNBPM and complicated patterns of photonic circuits, based on bent waveguides, can be designed by the RKBPM.
TL;DR: In this article, model estimation and prediction using nonlinear identification techniques are presented for a water treatment system using NARMAX model (Nonlinear Autoregressive Moving Average model with eXogenuous inputs).
Abstract: In this paper, model estimation and prediction using nonlinear identification techniques are presented for a water treatment system. The dynamics of the system relating rainfall, river level, and influent flow are modelled using a NARMAX model (Nonlinear Autoregressive Moving Average model with eXogenuous inputs). The parameters of the model are estimated using an orthogonal least squares algorithm with intelligent structure detection. The identification of both linear and nonlinear difference equation models are described to represent the relationship between rainfall and river level (inputs) and influent flow (output) for a waste water treatment plant in Greenville, North Carolina.
TL;DR: The authors attempt to convert the DSA to a function approximation problem, which is well-suited to be tackled by multilayer feedforward neural networks, and it has been shown that the tcr can be estimated by the trained network in a few milliseconds.
Abstract: This article presents a new artificial neural network (ANN)—based approach for online power system dynamic security assessment (DSA). The authors represent an application of feedforward neural networks in estimating the critical clearing time (tcr) for transient stability analysis. Knowing that for a particular fault scenario, the tcr is a function of only pre-fault system operating point, the main objective of the article is to show how one may develop an ANN-based method for estimating the tcr by considering the smallest set of directly monitorable variables characterizing this operating point adequately. The proposed technique does not require any supplementary tools such as load-flow and⁄or transient stability software for input determination of the ANN. The authors attempt to convert the DSA to a function approximation problem, which is well-suited to be tackled by multilayer feedforward neural networks. The technique has the following two main advantages: (1) The tcr is estimated as fast as ...
TL;DR: A system for integrating several overlapping images and then projecting them onto a 3-D developable composite surface has potential applications in automated inspection of the interior and exterior of developable surfaces in poor visibility and difficult-to-reach environments such as pipes and tanks.
Abstract: This article describes a system for integrating several overlapping images and then projecting them onto a 3-D developable composite surface. Such a system has potential applications in automated inspection of the interior and exterior of developable surfaces in poor visibility and difficult-to-reach environments such as pipes and tanks. The system consists of two parts. The first is image patching, in which a sequence of overlapping images grabbed through a moving camera are put together in one big image. The second part involves the mapping of this resulting patched image onto a 3-D developable surface. Simulation results are presented, validating the algorithms developed.
TL;DR: In this article, a computer simulation model is built and used to study the frequency response of two GHz harmonic filters using unidirectional transducers, which provides moderate insertion loss.
Abstract: The fabrication of surface acoustic wave (SAW) filters employing the conventional interdigital transducer (IDT) involves significant loss in the transmitted signals. An inherent problem in IDT is that the minimum insertion loss is 6 dB (1) owing to bidirectionality and strong passband ripple from triple-transit echo and secondary effects. To avoid these flaws and gain a simple structure of the filter, two-phase unidirectional transducers were chosen in this study. The fabrication of devices for frequencies above 1.5 GHz is still difficult and hence expensive. In this paper, a computer simulation model is built and used to study the frequency response of two GHz harmonic filters using unidirectional transducers. The proposed design provides moderate insertion loss. A simple model to find the input impedance of the proposed transducer is discussed.
TL;DR: In this paper, the thermal performance of a horizontal-spiral, two-phase flow with low heat flux and mass velocity is modelled and a set of first-order differential equations are integrated using a fourth-order Runge-Kutta algorithm, with a local, root-bisection iteration method for determining the local density gradient.
Abstract: The thermal performance of a horizontal-spiral, two-phase flow with low heat flux and mass velocity is modelled. Refrigerant flows helically in a single plane where the axis of the spiral is horizontal. The focus of this paper is to predict the heat transfer and pressure drop of the refrigerant. The refrigerant two-phase flow is modelled as homogeneous and one-dimensional. Empirical correlations for straight, two-phase flow as well as single-phase, helical flow are used. An equation set of continuity, momentum, energy, and refrigerant's equation of state are presented. The set of first-order differential equations are integrated using a fourth-order Runge-Kutta algorithm, with a local, root-bisection iteration method for determining the local density gradient. Numerical results of the spatial variation of enthalpy, density, velocity, pressure, and temperature are presented, and comparisons are made to show the effect of the curved-tube on the solution In addition a second law analysis of the flow is made in order to quantify and compare individual losses. It is found that the heat transfer performance at high quality is improved by the helical flow by five percent. Corresponding pressure drop losses also increase by eight percent.
TL;DR: This paper uses the level crossing technique to evaluate the outage probability in continuous channels with memory by means of the exponential and Rayleigh distributions.
Abstract: The level crossing technique was initially used to asymptotically analyze the duration of fades in radio communications. It has also been used to study the minimum duration outage. In this paper, we use this technique to evaluate the outage probability in continuous channels with memory. Outage probability approximations are made by means of the exponential and Rayleigh distributions. The former takes into account level crossings when the threshold level is high. The latter accounts for medium and low threshold levels.
TL;DR: In this article, the effects of the interactions between the subsystems are considered as uncertainty for the large-scale system and a bound on the high-gain factor is computed to nullify the effect of the interaction and also to ensure the overall closed-loop stability.
Abstract: In this article a high-gain decentralized controller is designed for a large-scale system. The effects of the interactions between the subsystems are considered as uncertainty for the large-scale system. A bound on the high-gain factor is computed to nullify the effects of the interactions and also to ensure the overall closed-loop stability. In order to avoid saturation, the anti-windup integrator method is used in designing high-gain controller. Due to high-gain feedback, the closed-loop system is robust with respect to output disturbances and uncertainties.
TL;DR: An interactive multimedia bomb threat training simulator is developed for land transportation facilities to mitigate the operational disruption that can be caused by bombs and bomb threats targeted towards these types of transportation facilities.
Abstract: The large numbers of passengers in close proximity in land transportation facilities present attractive targets for terrorist attacks. Land transportation facilities are also particularly susceptible to operational disruption, as problems in one node can affect an entire transportation network. This paper describes an effort to mitigate the operational disruption that can be caused by bombs and bomb threats targeted towards these types of transportation facilities. The authors develop an interactive multimedia bomb threat training simulator for land transportation facilities. With the simulator, land transportation facility personnel can receive simulated bomb threats, gather information, and decide whether to ignore the threat, conduct a search for suspect devices, or evacuate the facility. Because this training is simulated, users can receive realistic bomb threat training that might not otherwise be possible due to time, cost, or operational considerations. Quantitative training validation analysis indicates improved bomb threat response skills as a result of training with the simulator.
TL;DR: In this article, the results of a simulation model of the surface produced by milling with end-ball cutting tools, as well as determining the resulting surface roughness, are presented.
Abstract: This article presents the results of a simulation model of the surface produced by milling with end-ball cutting tools, as well as determining the resulting surface roughness. This model simulates the kinematics of the tool and determines the geometrical contribution to roughness, considering the possible tool contact angle with respect to the feed direction. These results can be utilized for the choice of optimum cutting conditions in multi-axis milling.
TL;DR: The authors define the modelling environment concept and show the architecture, structure, and components of a new one called HOMME, which establishes a new approach to the construction and maintenance of models using a modelling environment.
Abstract: This article focuses on the modelling of complex industrial systems. Primarily, it establishes a new approach to the construction and maintenance of models using a modelling environment. The authors define the modelling environment concept and show the architecture, structure, and components of a new one called HOMME. The main components of the environment are the language, the structures that support the construction of the models, and the object-oriented database that allows the manipulation of complex models in order to retrieve the piece of information that is needed. An example of this is presented along with a description of the modelling environment, demonstrating the availability of a single model that can be used for multiple purposes or applications.