Visual interactive simulation: A methodological perspective

The ideas and methods of Visual Interactive Simulation (VIS) are nearly fifteen years old, yet are still often misunderstood or misrepresented. It is argued that VIS is primarily a methodology, a way of solving problems with simulation modeling, not necessarily a way of building simulation models. Two distinct methodologies are identified, namely active and passive VIS. It is shown that simulation languages and packages tend to implicitly employ a particular methodology, and that each approach requires a different problem-solving life cycle. Present research, and necessary future research, are reviewed from our methodological perspective.     

Visual interactive modelling and manpower planning

Following some years extensive use of a Staff Simulation Model by the Personnel Department of Barclays Bank to demonstrate the effect of different staffing policies, it was felt that there was a need to improve the model, both technically and from the point of view of the presentation of the results. It was decided to use Visual Interactive Modelling Systems as in this way, the changes in the assumption could be seen in a colour, pictorial form on a screen. The results could also be shown diagrammatically either on the screen or as a screen print-out. The pictorial output had an immediate impact, and was felt to be a vast improvement on the large number of sheets of numerical computer print-outs previously produced.     

A microcomputer system for simulation modelling

Microcomputers are now widely used for discrete-event simulation work in Operational Research. An inexpensive microcomputer system for simulation modelling is presented. Based on an Apple II, it allows the programmer to develop three-phase activity based interactive models in Ucsd Pascal. Use is made of disc emulation for the provision of simultaneously available pictorial displays and the extension of fast access on-line memory for the development of large simulations.Use of a microcomputer speeds development time and gives the user a transportable computer dedicated to the simulation. Pascal facilitates the development of readable portable simulations.The simulation of a conveyer belt system demonstrates the simplicity and flexibility of the pictorial display. A practical study in the Health Service (modelling the treatment of chronic renal failure) illustrates that the package may be used to simulate a real and complex system.     

An interactive visual simulation system for industrial management

This paper describes a discrete event interactive simulation system which allows a user to watch the progress of a simulation model on a visual display terminal. The user may interact with the model in a flexible manner, in order to explore the consequence of alternative decisions or strategies. Output from the simulation may be directed, in an animated form, to a refresh display computer graphics screen, a black and white visual display unit or an intelligent colour visual display divice. The interactive system has been specifically designed to assist in decision making processes associated with industrial management problem situations.     

Power system modelling for emergency state simulation

A physically based mathematical model for an electric power system is developed to provide an adequate test bed for the testing and evaluation of slow speed dynamics emergency state control strategies. This model incorporates all the major components of the system, includes explicit representations for all the major physical variables and control, and is capable of simulating a wide variety of emergency contingencies. The dependence of the overall power system's behavior on the response characteristics of mechanical prime movers and the limitations placed on the overall system's response by absolute power and power rate capability constraints of the prime movers are described. Certain stochastic aspects of the system's behavior as well as the mechanisms governing cascading failures, which have characterized many major power system collapses in recent years, are introduced; and problems concerning the control of electric power systems under emergency state operating conditions are identified. Simulations are presented to demonstrate the behavior of the system under normal and emergency operating conditions and to show the importance of tie-line interconnection, especially to a region that is importing power from the rest of the system, as well as the effects of governor control action, initial pressure limiter and generation schedule prior to disturbances.     

Visual latency-based interactive visualization for digital forensics

In this paper, we present an interactive visualization and clustering algorithm for real-time multi-attribute digital forensic data such as network anomalous events. In the model, glyphs are defined with multiple network attributes and clustered with the recursive optimization algorithm for dimensional reduction. The user's visual latency time is incorporated into the recursive process so that it updates the display and the optimization model according to the human factor and maximizes the capacity of real-time computation. The interactive search interface is developed to enable the display of similar data points according to their similarity of attributes. Finally, typical network anomalous events are analyzed and visualized such as password guessing, etc. This technology is expected to have an impact on real-time visual data mining for network security, sensor networks and many other multivariable real-time monitoring systems. Our usability study shows a decent accuracy of context-independent glyph identification (89.37%) with a high precision for anomaly detection (94.36%). The results indicate that, without any context, users tend to classify unknown patterns as possibly harmful. On the other hand, in the dynamic clustering (context-dependent) experiment, clusters of very extremely unusual glyphs normally contain fewer packets. In this case, the packet identification accuracy is remarkably high (99.42%).     

Complexity of a modelling exercise: A discussion of the role of computer simulation in complex system science

Shifting the emphasis from a model to a modeling task, which involves both a computer model and a modeler, we ask what makes a problem complex. We propose that a modeling task can be seen as a set of questions‐and‐answers, nested at multiple levels. The role of the modeler then lies in posing the questions and choosing the best procedure to answer them, while the role of the model lies in answering the questions, via algorithmic, thus logically simple, procedures. Within this framework, complexity is broadly related to the number of question‐answer levels involved in the process and the nature of the questions posed. Addressing this complexity depends crucially on the ingenuity and creativity of the modeler. This may lead to a view of complexity, which is no more observer‐independent, but rather accounts for both historical and cultural development, that is the context of the problem at hand. © 2008 Wiley Periodicals, Inc. Complexity, 2008.     

Conceptual modelling for simulation Part II: a framework for conceptual modelling

Following on from the definition of a conceptual model and its requirements laid out in a previous paper, a framework for conceptual modelling is described. The framework consists of five iterative activities: understanding the problem situation, determining the modelling and general project objectives, identifying the model outputs, identify the model inputs, and determining the model content. The framework is demonstrated with a modelling application at a Ford Motor Company engine assembly plant. The paper concludes with a discussion on identifying data requirements from the conceptual model and the assessment of the conceptual model.     

Theo: An interactive proof development system

This paper presents an interactive, tactic-driven, proof development system, a Theorem Prover calledTheo. Both the meta and the object levels of our theorem prover are logics presented in Typol. Typol is the programming language that implements Natural Semantics, a semantics developed at Inria and pioneered by G. Plotkin under the name Structural Operational Semantics. So Theo is written in Typol and helps the user to build proofs in an object logic also written in Typol. Tactics and tacticals are written in Typol. Other important features of Theo are the form chosen for representing proofs, and the way proofs are performed. The internal form of the proofs is very compact, expressed with combinators, that can be related to the -calculus used in Automath and its descendants. Meanwhile, Theo performs proofs by a pure calculus on proofs, using a resolution rule. Proofs may be incomplete and may contain logical variables. Theo is developed under the Centaur system, as well as Typol. This system provides a modern graphic man-machine interface that Theo uses, for the user's advantage.     

An algorithm for systems welfare interactive goal programming modelling

Every human system is faced with the problem of choosing between alternative options, and methods of interactive programming have been suggested as the best way to lead decision makers reach decisions that are consistent with their preferences. However, even though a large number of interactive algorithms have been proposed for multiobjective decision making (MODM), there is yet no truly interactive goal programming (GP) algorithm, despite the preference of GP over other MODM methodologies. The current paper presents an algorithm for interactive GP modelling called SWIGP (systems welfare interactive GP) which ensures that the overall welfare of the system under consideration is adequately taken into account in the interactive process. To achieve this, this paper distinguishes between technical, allocative and economic efficiencies and combines an economic efficiency index with interactive GP process. Besides being of wide applicability, the algorithm exerts little cognitive burden on the decision maker (DM). Indeed, even if the DM is assumed to operate under conditions of complete ignorance, SWIGP provides the direction for searching the “best” compromise solution. Moreover, the algorithm converges very fast because of the economic efficiency index that complements the interactive process in aiding the DM arrive at a most preferred solution.     

A simulation of monsoonal cross-equatorial airflow by Lagrangian modelling

The Australian monsoonal cross-equatorial airflow is simulated in an attempt to bridge a highly simplified, while theoretically interesting model to the realities of the actual tropical meteorology. Two factors are found to be essential in the successful simulation of the monsoonal cross-equatorial flow with that model:

• 1.1) the existence of a properly-positioned quasi-elliptic monsoon depression;
• 2.2) sufficient friction to force the decay of anticyclonic inertial oscillations and hence to allow a more ‘balanced’ type of cyclonic flow around that depression.

     

An interactive fuzzy programming system

An interactive system is introduced which supports a decision maker in solving programming models with crisp or fuzzy constraints and crisp or fuzzy goals. One part of the system is the determination of membership functions representing goals. To this purpose fuzzy extreme solutions are computed and are presented to the decision maker. These and each of the proposed compromise solutions are fuzzy-efficient.     

Brief note: thoughts about the essentials of simulation modelling

During the past few years, I have been involved, in one way or another, with developing courses on simulation methods, simulation methodology, and applications of simulation techniques to real world problems. In the course of developing and teaching such courses, a reasonable step-by-step approach to the simulation of real world systems has evolved. This paper represents an attempt to present a “kernel” on the subject and it is not offered as a definitive treatment of the subject, but rather, it is offered in the hopes of stimulating further thinking and refinement.     

Conceptual modelling for simulation Part I: definition and requirements

Conceptual modelling is probably the most important aspect of a simulation study. It is also the most difficult and least understood. Over 40 years of simulation research and practice have provided only limited information on how to go about designing a simulation conceptual model. This paper, the first of two, discusses the meaning of conceptual modelling and the requirements of a conceptual model. Founded on existing literature, a definition of a conceptual model is provided. Four requirements of a conceptual model are described: validity, credibility, utility and feasibility. The need to develop the simplest model possible is also discussed. Owing to a paucity of advice on how to design a conceptual model, the need for a conceptual modelling framework is proposed. Built on the foundations laid in this paper, a conceptual modelling framework is described in the paper that follows.     

A switched system approach to dynamic race modelling

The paper presents and analyses some nonlinear continuous-time dynamic models of social systems whose members, groups or individuals, may change partners and/or opponents at any time, according to a greedy criterion. The main structural properties of these models, which belong to the class of positive switching systems, are investigated with particular regard to the existence of solutions, their positivity, boundedness and asymptotic behaviour. Simulations show how the cooperative or hostile attitudes of the participants affect their yield.     

Controlling the precision of estimated means in interactive simulation

The computing power of modern workstations has made it possible to simulate many queueing systems interactively. Recent development in simulation software has mainly concentrated on interactive facilities. Unfortunately the precision of estimates has widely been overlooked in interactive simulation. In this paper we propose a method for controlling the precision of estimated means during an interactive simulation run. Since in a typical situation of interactive simulation the user is simultaneously interested in several means, we consider both the simultaneous precision and individual precisions of the estimated means. The method is based on the existing methods for estimating standard errors and on the Bonferroni inequality. The Bonferroni inequality is used to obtain a lower bound for the simultaneous precision.     

Evaluating alternative system configurations using simulation: A nonparametric approach

The real utility of simulation lies in comparing different alternatives that might represent competing system designs. Conventional statistical techniques are not directly applicable to the analysis of simulation output data in the evaluation of competing alternatives since the usual assumptions of normality and common variance are difficult to justify in simulation experiments. This paper revisits a known nonparametric test whose application has recently become feasible due to considerable increases in computing power:randomization tests assess the significance of the observed value of the test statistic by evaluating different permutations of the data. The procedure only requires invariance of the data under all permutations.     

The interactive system “PARACHUTE”

The structure and uses of an interactive system are described. The results of computations of the resistance and inflatibility of corrugated parachute canopies are presented.Translated fromDinamicheskie Sistemy, No. 6, 1987, pp. 30–35.     

A framework for an interactive project scheduling system under limited resources

In this paper, we propose a framework for an interactive project scheduling system under limited resources. The framework includes a modelling module (model) and a scheduling module (scheduler). The modelling module model allows the Decision Maker (DM) to develop his/her own model with features such as alternative operating modes for activities; renewable, nonrenewable and/or doubly-constrained resource constraints; general cash flow patterns, related to the realization of activities or events; and progress payments distributed over the project span. The performance criteria include the maximization of Net Present Value (NPV), and either the minimization of maximum tardiness (when a project due date exists) or the minimization of the project duration (when there is no project due date). The scheduler is developed on a constraint-based scheduling algorithm, which is called Local Constraint Based Analysis (lcba) and which has previously been tested and shown to produce near-optimal results with respect to the criterion of minimizing project duration. The decisions taken in the scheduler consist of determining the start times of activities and the specific operating modes in which they are to be realized. The decisions are taken by activating relevant essential conditions in lcba and in cases where resource conflicts are not resolved, the DM reaches a final decision by testing the alternatives proposed by lcba through a what-if routine. The scheduler represents a realistic scheduling system which is useful not only in the planning phase of a project but can also be employed during the progress of a project for updating the project plan, if necessary. An important feature is that the project plan can be updated by performing the least modification of future commitments. It is possible to freeze the activities already scheduled in the near future while admitting the changes in the activity/network information.