bluuebunny/crossref_metadata_2025 huggingface dataset:
Stochastic analysis of process-control models
Authors: Tanthapanichakoon Wiwut , Himmelblau David M.
Published: March 2008

Most conventional methods of process design ignore the stochastic nature of the process and its param eters ; only deterministic models are employed, and the solutions obtained are at best only approxima tions. To allow for the uncertainty of designs based on such a procedure, gross safety factors must be added to the design variables based on the deterministic models.

An alternative approach is to introduce stochastic variability directly into the process model and to use stochastic simulation to estimate the process outputs and design parameters. By using stochastic simulations which incorporate random inputs and ran dom parameters, one can obtain sample estimates of the expected values and expected variances of the output variables. From these and the characteristics of the probability distributions of the output vari ables, one can show when the expected values of the outputs of stochastic process models differ from those of deterministic models in which the random variables are replaced by their expected values and what safety factors are necessary for a satisfactory design.

As an example, we have developed a stochastic dynamic mathematical model for a wastewater treatment plant. The output of the plant was simulated for a period of several days under different random input conditions and different probability distributions of parameters. Differences between the deterministic and stochastic responses of the model are described, as is the effect of frequency of fluctuations of the stochastic inputs on responses of the model and on their variances.

Of particular interest is the use of the results of the simulations, stochastic and deterministic, to estimate safety (overdesign) factors that should be used in designs based on deterministic models. The validity of the propagation-of-variance formula- i.e., the relation used to compute the sample vari ances of the outputs of a nonlinear stochastic model in the unsteady state from the sample variances of the inputs and parameters - is demonstrated. With the aid of this relation, overdesign factors can be esti mated from the magnitudes of the standard deviations of the outputs.

Although stochastic analysis cannot reduce the uncer tainty in design, it can provide a more quantitative assessment of the uncertainty than can deterministic design and so can lead to better designs of process plants.
DISCO- a SIMULA-based language for continuous combined and discrete simulation
Authors: Helsgaun Keld
Published: March 2008

DISCO is a SIMULA-based language for the simulation of systems which contain both continuous and discrete- event processes. It is a true extension of SIMULA's concepts for discrete-event simulation and is capable of representing and analyzing models including both types of processes. With the addition of few new con cepts, a general yet simple simulation language has been achieved.

This paper describes the basic concepts of DISCO and demonstrates through examples the descriptive power of the language. DISCO is described mainly from the user's point of view; its implementation is only sketched.
Using simulation in cardiovascular disease control
Authors: Ravindran A. , Sadagopan S. , Petersen Clifford C. , Hatsell Charles P.
Published: March 2008

The United States Air force is planning a comprehen sive program to reduce the incidence of cardiovascular disease among Air Force personnel. The program will use a risk profile based on the Framingham study to identify high-risk personnel for selective treatment. A risk-reduction program will then provide medication and education for those selected for therapy.

To assist the Air Force in designing a cost-effective risk-reduction program, we developed a comprehensive computer simulation model called P-HEART (Purdue Heart Evaluation and Risk Tabulation). P-HEART simu- Zates the USAF population and the processes of identi fying high-risk individuals and selecting appropriate therapies for them. It also calculates the costs and benefits of the cardiovascular disease control pro gram for different risk-reduction policies. This paper describes the simulation model, its validation, and its results.
Hybrid simulation of reactor kinetics in CANDU reactors using a modal approach
Authors: Monaghan Brian M. , McDonnell Frank N. , Hinds H.W.
Published: March 2008

A hybrid computer model for simulating the behaviour of large CANDU (Canada Deuterium Uranium) reactor cores is presented. The main dynamic variables are expressed in terms of weighted sums of a base set of spatial natural-mode functions with time-varying co efficients. This technique, known as the modal or synthesis approach, permits good three-dimensional representation of reactor dynamics and is well suited to hybrid simulation. The hybrid model provides improved'man-machine interaction and real-time capability.

We have used the model in two applications. The first studies the transient that follows a loss of primary coolant and reactor shutdown ; the second is a simulation of the dynamics of xenon, a fission product which has a high absorption cross-section for neutrons and thus has an important effect on reactor behaviour. Comparison of the results of the hybrid computer simulation with those of an all-digital one is good, within 1% to 2%.
Simulation of an oil-pumping ring seal for a Stirling engine
Authors: Smith P.J. , Keith Theo G.
Published: March 2008

Potentially, the Stirling engine is a more efficient, less polluting replacement for the internal combus tion engine in automobiles, trucks, and buses. However, a critical design problem for this engine is the seal between the working fluid and the lubricat ing fluid. The current approach to solving this problem is to use rolling diaphragm seals to perfect ly separate the working fluid (hydrogen under high pressure) from the lubricating fluid (oil at atmo spheric pressure). The large pressure difference across these rolling diaphragm seals leads to fatigue and failure.

This paper reports an investigation of the use of a pumping ring to maintain an oil reservoir on the low-pressure side of the seal. The operation of a pumping ring is simulated, taking into account the axially symmetric unsteady flow in the fluid domain coupled with the elastic distortion of the solid ring. The computer program for solving the mathematical model uses finite differences in the fluid domain and finite-element methods in the solid (pumping ring) domain. The validity of the simulation was checked by comparing its results with analytical solutions for limiting cases.

We used the model to investigate the effects of changing various parameters of the ring, such as its geometry, material, rod size and speed, O-ring loca tion, crown spring, and interference fit. Our findings are reported.
The simulation of aircraft electrical power systems
Authors: Fanthome Alan , Kettleborough Gordon
Published: March 2008

This paper describes the digital modelling and simu lation of aircraft electrical power systems. Models of the main power generators, automatic voltage regulators, and a polyphase transformer-rectifier unit typical of ac-to-dc power conversion equipment are described. The main generator is the most com plex component in the system to model, and its per formance with a radar load and two generators in parallel is described. These two examples indicate how individual models may be made to interact and how the tensor approach may be used to eventually form a complete system.
Bond-graphs for some classic dynamic systems
Authors: Margolis Donald L.
Published: March 2008

Bond graphs are developed for several nonlinear dy namic systems which are often used in dynamics courses to demonstrate conservation principles and equation development via Newton's law or Lagrange's equation. The purpose here is to show the use of bond graphs in obtaining nonlinear differential equations of motion for general nonlinear systems. Bond-graph models can also be expanded easily to include energetic interactions with all types of dynamic systems including hydraulic, electrical, thermal, and others. Numerical solutions for one example system are included.
The ETH multiprocessor project: parallel simulation of continuous systems
Authors: Halin Hans J. , Bührer Richard , Halg Walter
Published: March 2008

A new multiprocessor system is currently under con struction at ETH (Swiss Federal Institute of Technol ogy). This multiple-instruction-stream multiple-data stream (MIMD) computer exploits the advantages of low-cost large-scale integrated components. A first model of the ETH multiprocessor featuring a modular expansible architecture will consist of a PDP 11/40 and 16 LS-T-11S. After its completion in 1980 the multiprocessor will be applied mainly to the simula tion of continuous systems.

Evaluations of integration schemes for MIMD systems showed the method of power series expansions to be most appropriate. Starting from a FORTRAN-like source code, the differential equations are automatically decomposed into smaller problems. The higher deriva tives of all variables are computed using analytical recursion formulas. Usually many formulas can be evaluated simultaneously, each by a master cooperating with a number of slaves, using the inherent parallel ism in many of these formulas.

The time behaviour of the multiprocessor is character ized by dynamically changing hierarchies. To imple ment algorithms efficiently, several principal prob lems of parallel computing were solved in hardware rather than in software. Thus the system features provisions for instantaneous data exchange between processors, protection of data, handling of deadlocks, and performance of operating system tasks. As a result, the ETH multiprocessor simplifies the solu tion of problems from different fields.
Study of large power systems after severe disturbances
Authors: Gelopulos Demosthenes P.
Published: March 2008

Several types of power-system simulations are de scribed in this paper. Long-term simulations, transient stability studies, and electrical transient and subsynchronous resonance studies are singled out as especially important classes of power-system simulations.

The mathematical requirements for carrying out sim plified transient stability simulations of power systems are described in detail. Full-scale simula tions require the simultaneous solution of an elaborate set of differential and transcendental algebraic equations. At present such simulations are time-consuming and costly. This paper discusses several techniques for improving the efficiency of digital programs for this kind of simulation.

Further increases in efficiency are still required. Current research in this area is outlined. A large number of related subjects are touched upon, and a list of references is included to help the interested reader.
PASSIM: a discrete-event simulation package for PASCAL
Authors: Uyeno Dean H. , Vaessen Willem
Published: March 2008

This paper describes a set of procedures that can be used to construct discrete-event simulation models in PASCAL. The set of procedures is called PASSIM for PASCAL-based SIMulation The approach combines scheduler and entity concepts from GPSS with pointer- based data structures and control structures from PASCAL. The procedures employ only standard PASCAL statements to ensure portability.
Estimating confidence intervals for simulations of computer systems
Authors: Mamrak Sandra A. , Amer Paul D.
Published: March 2008

In simulation studies, means, percentiles, or pro portions are often used to summarize measurements of system performance. We describe procedures for estimating confidence intervals for each of these three statistics. We conclude that proportions are generally best suited to computer simulation studies. We present empirical data that clarifies the proce dures and justifies the recommendation of proportions.
Using simulation to assign police patrol zones
Authors: Carroll John M. , Laurin Pierre G.
Published: March 2008

The defining of police patrol zones is a complex problem that can be handled by computer simulation. Typical criteria for establishing zone boundaries are average response time and amount of time avail able for actual patrol duties. Typical constraints include the number of patrol cars and a desired minimum response time. In our application, the criterion was to maximize the amount of time avail able for patrol duties (i.e., repressive patrol); the constraints were the current average time to respond to a call and a limit on the number of patrol cars. We developed a multiple linear regres sion model to forecast calls and a simulator to pre dict performance. The results were reasonable and indicated that, possibly, a small increase in patrol time could be achieved by redefining zone boundaries and that the work load in the zones could be made considerably more uniform.

The simulation, however, was undertaken primarily as a training exercise and did not represent the com plete problem. As a result of factors outside of the scope of the work reported here, the findings were not applied. Even so, it can be argued that the study produced benefits that justified its cost.
Planning and policy-making for tenure
Authors: Hill Robert R. , Wolf Edwin M.
Published: March 2008

Universities have not traditionally analyzed the temporal effects of the tenure decision on the university or on its faculty. The consequences of a tenure policy on the financial and academic health of a university are substantial and long-lasting. This paper describes a program that allows university administrators to build a model of any proposed tenure policy, to operate the model, and to project the effects of the policy on the university. The models formulated use Markov chains to represent the various policies being analyzed along with macro forecasts of the size and composition of the university.
An interactive simulator for the KIM-1 microcomputer
Authors: Nagata Wesley M. , Miller Donald S.
Published: March 2008

The KIM-1 simulator is a development tool for the MOS Technology 6502 microprocessor and the KIM-1 microcomputer. It is written in the C programming language and runs under the UNIX operating system on a DEC PDP-11/60. The input to the simulator is ob ject code produced by a cross-assembler. The simu lator helps in debugging 6502 programs by providing the user with the ability to interactively load and display memory and registers, dynamically set and clear breakpoints, handle interrupts, and trace pro gram execution.

The simulator is user-oriented; it supplies prompts, English diagnostics, and instructions on usage. Its execution speed and core requirements allow truly interactive debugging.

The KIM-1 simulator, in conjunction with the cross- assembler and the actual KIM-1 microcomputers, has been an excellent educational tool for an introduc tory course in computer organization and assembly- language programming. In addition, it has helped researchers using the 6502 microprocessor in appli cations.
Simulating urban obstructions
Authors: Frank Randall S. , Gerding R. Bruce , O'Rourke Patricia A. , Terjung Werner H.
Published: March 2008

A problem that urban planners have to deal with is the obstruction of sunlight by buildings which may shade streets adjacent to them as well as other near by buildings, thus strongly affecting (1) the need for summer cooling and winter heating at particular sites, and (2) the suitability of sites for particular uses. This problem becomes very complicated when buildings are irregularly shaped and are located in an irregular pattern, and when street widths vary. Doing the necessary calculations by hand is extremely tedious, highly error-prone, and costly.

A generalized computer model of great flexibility has been developed to overcome the drawbacks of hand caZ culations of solar shadowing. The program, which is called OBSTRUCT, is modular and is written in FORTRAN IV to run on an IBM 3033 computer. The pro gram is available at no charge. Sample runs for two illustrative cases are included in this report.
A generator program for models of discrete-event systems
Authors: Subrahmanian Eswaran , Cannon Robert L.
Published: March 2008

Researchers in simulation methodology have been attempting to develop both theories of modelling and software tools to assist in applying those theories. Using results from system theory and automata theory, Oren and Zeigler have demonstrated the need for the design and development of software for modular con struction of models; manipulation, documentation, validation, and generation of simulation programs; and automatic verification of algorithms. We have implemented a software system based on their propo sals. The user describes the structure of the model in a well-defined language. At this time, our system supports only discrete-event models using a next- event strategy; a typical example is a queuing model of service at a bank. However, this simple system demonstrates the feasibility of a more complex system.
Microanalytic simulation models as tools for legislative planning
Authors: Bungers Dieter
Published: March 2008

Microanalytic simulation models (or micromodels) are useful tools for analyzing and forecasting the social and budgetary effects of government tax and transfer programs. A micromodel actually models the individ ual units passing through the system, rather than dealing with aggregated statistics. The micromodel derives the overall effects of the system by summing its effects on a representative sample of individual units. This type of model is necessary because the complicated interaction of legal regulations and the socioeconomic structure of the population must be modeled in detail if the simulation is to describe all the significant effects of programs.

We used the microanalytic approach to develop a planning system for the German Federal Student Aid Program (BAFPLAN). This project required the solu tion of several important methodological problems. These included: (1) the construction of a data file representative of the initial population, (2) the arti ficial aging of the data file, and (3) the modeling of changes in human behavior. Future research will ex tend the use of micromodels in legislative planning and will deal with the problem of access to the requir ed data.
Simulating space requirements and scheduling policies in a hospital surgical suite
Authors: Kuzdrall Paul J. , Kwak N.K. , Schmitz Homer H.
Published: March 2008

Simulation provides a useful tool for capacity plan ning and facilities management in the hospital envi ronment where experimentation is usually impractical. A typical example is the determination of the number of operating rooms and recovery-room beds required to handle an increased patient load. Simulation not only showed how large a facility was needed but also allowed experimentation with different policies for admitting patients to the surgical suite. Two strategies were simulated; one allowed a random in put, while the other gave priority to patients re quiring the longest surgery. The results of the GPSS model showed the importance of scheduling policy as the priority technique allowed a 25% reduction in the surgical workday, thus providing a large savings in manpower costs.
Worldwide growth in simulation and SCS
Authors: Schlesinger Stewart
Published: March 2008

A major consideration before the Society for Computer Simulation has been the potential expansion of our activities throughout the world. As one of the key- note speakers at the United Kingdom Simulation Coun cil's 1981 Conference, I discussed this topic in a talk entitled Worldwide Growth in Simulation and SCS. Since this subject is of interest to the entire mem bership, the presentation is included in this extended President's Message.
Methods for Solving Stiff Differential Equations
Authors: Crosbie R.E. , Javey S.
Published: March 2008

In the conclusion of the paper "Solving Stiff Differen tial Equations in the Simulation of Physical Systems (Simulation, Aug. 1981) T.D. Bui states, "The results ... show that LSTIFF is much more effective and reliable than the well-known GEAR program." This statement could be misleading to readers who are not familiar with stiff integration methods, and the main purpose of this note is to clarify this point.
Simulation in the Service of Society
Authors: McLeod John , McLeod Suzette
Published: March 2008

This Newsletter was published independently from January 1971 through August 1976. Back issues are available from SITSOS, 8484 La Jolla Shores Drive, La Jolla, CA 92037, for 75C per copy.
Reduction of time delays in Runge-Kutta integration methods
Authors: Nowack Stefan , Feil Georg
Published: March 2008

Numerical (digital) integration in a real-time simulation is often performed using explicit Runge-Kutta methods. Real-time system simulation places high demands on computers and integration routines, if data must be sampled from input signals and incor porated into the numerical integration algorithm in order to evaluate the derivatives of the state variables.

A modified fourth-order Runge-Kutta (RK4) method, which meets these requirements particularly well is proposed. As an example the routine is applied to a complex flight simulation problem. The results of the modified routine and of the RK4 standard are compared and the specific advantages of the new routine demonstrated.
An expert system framework based on a simulation generator
Authors: Haddock Jorge
Published: March 2008

Expert Systems (ES) implementations automatically perform tasks for which specially trained or talented people have been re quired. Fifth generation simulation systems integrate the tools developed in the fourth generation and capture the knowledge of the expert programmer as well as that of the simulation model ing expert. Haddock has programmed a user- oriented simula tion generator for the design and control of flexible manufac turing systems (FMS). The development of an ES based on the generator is described in this paper.

The system to be described solely requires knowledge of the system to be simulated from the user. FORTRAN written sub routines, incorporated within the software structure of SIMAN, interpret the results of experimental runs and make statistical inferences about the performance measure.

Simulation generators can assist simulationists in model develop ment and update, as well as in the analysis of alternative sce narios. A very desirable feature of Intelligent Front Ends (IFEs) is to have the capabilities of analyzing their output. These capa bilities not only reduce the total time required to perform the simulation, but also prevent its misuse.
A mathematical model of the orbital maneuvering vehicle
Authors: Walls Justin , Greene Michael , Teoh William
Published: March 2008

A mathematical model was designed and developed of the Or bital Maneuvering Vehicle (OMV), a critical part of the OMV man-in-the-loop simulation at Marshall Space Flight Center, Huntsville, Alabama. The OMV evaluator is a full-scale, six- degree-of-freedom simulator that can replicate the motion of the actual OMV spacecraft in orbit. Translational and rotational equa tions of motion that model the OMV are presented. Simulation results that verify the correctness of the model are also given. This high-fidelity simulator is valuable for crew training, develop ing and testing new teleoperated equipment, and verification of the OMV final design. The evaluator also serves as an impor tant test ground for determining the capabilities of the OMV in performing orbital operations.
Comments on "Linear systems revisited"
Authors: Hundal Tejpal S. , Gottfried Byron S.
Published: March 2008

Conley (1985) uses a modified Monte Carlo method to solve sys tems of simultaneous linear algebraic equations and linear pro gramming problems. We have used Conley's two sample prob lems to compare his proposed method with the classical methods of Gauss-Jordan elimination and the revised simplex algorithm. The classical methods are about three orders of magnitude faster; therefore, Conley's proposed method does not warrant serious consideration as a viable solution procedure.
A hybrid paradigm for modeling of complex systems
Authors: Ruiz-Mier Sergio , Talavage Joseph
Published: March 2008

The network modeling approach to simulation provides the mo deler with simple and powerful concepts which can be used to capture the significant aspects of the system to be modeled. Yet the most advanced network modeling environments lack ex plicit concepts for the representation of complex behavior such as decision-making. Artificial intelligence research, because of its emphasis on knowledge representation, provides several meth odologies which can be successfully applied to the modeling of decision-making behavior.

The approach to modeling complex behavior, outlined in this paper, is based on a hybrid methodology unifying the concepts of Object-Oriented programming, Logic Programming and the discrete event approach to systems modeling. We present SIM YON, an experimental network simulation environment which provides explicit constructs for the representation of complex behavior of real-world systems. SIMYON is implemented by de fining a library of logic objects in the Object-Oriented, Logic Programming environment CAYENE. These objects, which are analogous to the "nodes" of network simulation languages, are the building blocks for modeling.

Examples are given in SIMYON to model a job scheduler in a manufacturing situation and an adaptive material handling dis patch mechanism for flexible manufacturing systems.
A forest canopy height surface model for scene simulation
Authors: Balick Lee K.
Published: March 2008

A model of forest canopy heights can support realistic remote sensing scene simulation. The final pixel (x, y) array of canopy heights results from merging structural and statistical sub-models. The structural model considers tree crowns to be structural primitives and permits explicit specification of forest structural characteristics (crown forms and spacing). The statistical model allows the inclusion of smaller scale effects (clumping or rough ness), and nonstationary effects can be introduced by merging the structural and statistical model results with spatially varying weights. The model supports several tasks in realistic scene simu lation (e.g., for use with algorithms which use surface geometry to determine pixel brightness). It also helps define realistic forest- top geometry classes or types so that simulations do not require high-level user expertise or detailed specification. The model also provides controlled test-bed data for canopy measurement and analysis technique development. By retaining tree shape and spacing information in a height surface, the model partially fills the gap between stochastic texture modeling and three- dimensional tree (object) models in scene synthesis.
Parallelization of an event driven simulator for computer systems simulation
Authors: Wilson Andrew
Published: March 2008

The technological revolution fueled by the microprocessor has produced commercial multiprocessors. Using basic parallel pro gramming constructs, an existing multiprocessor system simulator is modified to execute in parallel on a shared memory multi processor. Several key techniques used to maximize parallelism are discussed. The simulation speedups achieved while simulating a proposed large scale multiprocessor architecture are reported. Finally, the techniques used in this research are compared with those that have been used by other parallelized simulators.
Procedural animation blocks in discrete simulation
Authors: Magnenat-Thalmann Nadia , Thalmann Daniel
Published: March 2008

A way of integrating discrete-event simulation and animation is proposed using procedural animation blocks. This approach allows the use of complex animation software for displaying results of simulation and is illustrated by a simulation of freeway tolls.
Interactive graphics in GPSS/PC™
Authors: Cox Springer
Published: March 2008

GPSS/PC is a recent implementation of the discrete event simula tion language GPSS, the General Purpose Simulation System. With the introduction of Version 2, GPSS/PC has added interac tive graphics and animation to its simulation environment. Its graphics windows are truly interactive, allowing manipulation via an optional pointing device, and assertion of all simulation primitives. All windows are online, providing for a visualization of model dynamics, and one of the windows allows animations of the simulation to be played out in an essentially unbounded virtual screen.

In addition, a CAD-based animation postprocessor is scheduled for release in late 1987. It can lend considerable realism to pre viously recorded animations. In accordance with the design goals of the interactive graphics of GPSS/PC, the animation postpro cessor is designed to run with minimal hardware requirements, if necessary.

This paper discusses the design alternatives leading to the im plementation of the interactive graphics in GPSS/PC, and the use and limitations of animated simulations.
Polishing the analysis of the statistical output of comparative simulation experiments
Authors: Balmer David William
Published: March 2008

Statistical tests have always played an important role in the analy sis of comparative simulation experiments. This paper argues for a shift of emphasis toward a more exploratory approach to the analysis of such data and, in particular, the wider use of Tukey's median polish.
Hierarchical, modular discrete-event modelling in an object-oriented environment
Authors: Zeigler Bernard P.
Published: March 2008

Hierarchical, modular specification of discrete-event models of fers a basis for reusable model bases and hence for enhanced simulation of truly varied design alternatives. We describe an envi ronment which realizes the DEVS formalism developed in Zeigler (1984) for hierarchical, modular models. It is implemented in PC-Scheme, a powerful Lisp dialect for microcomputers contain ing an object-oriented programming subsystem. Since both the implementation and the underlying language are accessible to the user, the result is a capable medium for combining simula tion modelling and artificial intelligence techniques. The envi ronment is developed in an object-oriented manner which lends itself to model base organization using the entity structure knowl edge representation. It also serves as a medium for developing hierarchical distributed simulation models and architectures.
A fire-spread simulation model developed as an extension of a dynamic percolation process model
Authors: Hirabayashi Fusako , Kasahara Yutaka
Published: March 2008

A stochastic model of a fire-spreading process has been devel oped to simulate pertinent time-dependent changes. This model has been obtained by extending an existing stochastic model in which the fire-spreading process is described as a percolation process. The extended model considers the time period from ignition to the point at which flames have spread to an unburnt unit. In this model, the above two quantities (the time required for ignition and that required for reading an unburnt unit) are treated as continuous random variables dependent upon the respective probabilities of blaze up and fire spread.

To evaluate this model, a Monte Carlo simulation system has been developed. Experiments on hypothetical and real city layouts show that this model is a useful simulation tool in studies con cerned with firefighting.
Turbo-simulation: A technical note
Authors: Korn Granino A.
Published: March 2008

Many reported computer execution-speed benchmarks involve artificial programs exploring the fixed- and floating-point instruc tion sets. Instead, we report results from two actual dynamic- system simulation problems long used as benchmarks by the simulation community. PHYSBE (Korn and Wait 1978) is a blood- circulation model used in physiological studies, and the Hidinger benchmark (Hidinger 1982) is a practical three-dimensional flight simulation (really a torpedo/ autopilot simulation) developed at the Naval Ocean Systems Center. Such programs can give realistic indications of practical results obtainable with different machines.

Specifically, we report on a study of measured and predicted simulation speeds of personal computers with speeded-up clocks and of new 32-bit personal computers. This is a glimpse into a new, bright world of very cost-effective simulation; an 80386/ 387-based PC clone outruns a timeshared VAX 11/780 in the flight-simulation benchmark.
Simulation in corporate decision making: Then and now
Authors: Ford F. Nelson , Bradbard David A. , Cox James F. , Ledbetter William N.
Published: March 2008

We present the results of a 1985 study, which replicates a 1975 study by Cox, Ledbetter, and Smith (1977), and attempt to mea sure the use of simulation modeling to support decision-making in major U.S corporations. Specifically, the purposes of the paper are to (1) measure the development and use of simulation models at all levels of decision-making (operational, tactical, and stra tegic) ; (2) examine the use of simulation within each functional area; (3) identify specific application areas within each functional area where simulation is being used; and (4) compare this study's results with those from the Cox, Ledbetter, and Smith (1977) study.
HeartLab: A multi-mode simulation for teaching cardiac auscultation
Authors: Bergeron Bryan P.
Published: March 2008

A threaded interpretive language (TIL), Forth, was utilized to im plement HeartLab, a simulation-based program designed to teach medical students the essentials of the auscultatory cardiac exam. The simulation output, high-resolution bit-mapped graphics cou pled with realistic, computer-generated heart sounds, makes full use of the Apple Macintosh sound and graphics capabilities. Multimode simulation of this type and construction of an ap propriate patient model create a number of design challenges for which this approach proved to be particularly well suited.
POSE: a Process-Oriented Simulation Environment embedded in SCHEME
Authors: Stairmand Malcolm C. , Kreutzer Wolfgang
Published: March 2008

POSE is part of a research program to explore potential benefits of new software technologies for various modelling paradigms. It is a SCHEME-based queueing network simulator, whose discus sion serves to demonstrate the suitability of symbolic languages and exploratory programming styles for system simulation.

After justifying the use of symbolic languages and an object- oriented approach to model design, basic features of POSE are presented, using a simple example. This is followed by a brief description of the simulator's architecture. A final chapter sum marizes and reflects on our experiences, suggesting that object- oriented simulation environments hosted on powerful personal workstations may well offer major breakthroughs in terms of ef fectiveness and user acceptance. Computational efficiency, while a lesser concern to "investigative simulation," remains unsatisfac tory in simulations used for quantitative predictions. This prob lem may hopefully be overcome through future advances in soft ware and hardware technologies.
Modeling and simulation of an Analog Charge-Pump Phase Locked Loop
Authors: Can Sumer , Sahinkaya Yilmaz E.
Published: March 2008

We describe a nonlinear computer simulation model of an Ana log Charge-Pump Phase Locked Loop (ACP-PLL). Offsets of the Phase Detector and Analog Charge-Pump are modeled as dis turbances to simulate their effects on the steady-state phase error of the loop.

An extensive computer simulation study is carried out for the design of an example Analog CP-PLL using the proposed non linear model and comparing it to the conventional linear model. Results demonstrate the linear model is not sufficient to fully analyze and predict the behaviour of the Analog CP-PLL.
On simulating dynamic behaviour of three phase induction machines with squirrel cage rotor
Authors: Ghani Sayeed Nurul
Published: March 2008

A new time domain static network model of a three phase in duction motor with squirrel cage rotor is presented. Simulation of the dynamic behaviour of a machine fed through static power control equipment containing switching devices of one kind or another can be conveniently achieved using this model. The pro cedure is simple and can be applied, with considerable flexibility, to any system containing one or more induction machines. The model is inherently capable to account for iron losses as well. It is also suited for simulation of machine dynamics with un balance introduced in the stator electrical circuits by a fault, pro vided the structure of the windings remains unaltered. A similar network model can be derived to represent a machine with an asymmetrical internal fault which splits one or more stator phases into multiple sections with or without interconnections. A pre viously published model of a triac has been improved (Ghani 1981).
A new analytic technique for the study of deterrence, escalation control, and war termination
Authors: Davis Paul K.
Published: March 2008

The paper describes work of the RAND Strategy Assessment Center on knowledge-based models of strategic decisionmak ing. The models are more realistic than those focusing exclusively on quantitative calculations and they can provide a mechanism for focusing debate on policy issues where qualitative and quan titative measures must be used conjunctively. Debating the merits of formal rule-based models encourages the participants to con verge on the relative value of alternative variables, details of con text, and definitions.
GASP/S: A GASP IV version with a stiff-ODE integrator
Authors: Havlik Ivo , Votruba Jaroslav
Published: March 2008

We present a simulation language GASP/S, an extension of a well- known FORTRAN-based simulation language GASP IV. GASP IV language has been extended using an integration package for solving models of continuous and combined systems described by a set of stiff ordinary differential equations. The V Runge-Kutta- England integration procedure employed in standard GASP IV is unsuitable for problems of this nature. The integration package STIFFSOLVER-81 used in GASP/S has been developed primarily for use in the field of microbial engineering and chemical kinetics.
Process hierarchy and inheritance in PASION
Authors: Raczynski Stanislaw
Published: March 2008

Process hierarchy and inheritance make it possible to add new properties to existing objects of simulation models. Thus, the user can construct complex models using a code developed earlier. This feature is discussed and its implementation in the language PASION is pointed out. Examples are given.
Exchange rate system simulation by means of vector processing
Authors: Amman Hans M. , Jager Henk
Published: March 2008

This paper presents optimal control simulations in order to evaluate the major types of exchange rate systems for a small open economy. This is done by using a macroeconometric model of the Dutch economy. The econometric models relevant for ex change rate policy evaluation contain a large number of equa tions. In applying optimal control techniques to such models, computational difficulties are encountered. However, these pro blems can be overcome if the algorithm of the control problem is reformulated to be effectively utilized on a computer with vec tor processing capabilities.
Evaluating multiprocessor performance: an exercise in metamodeling
Authors: Ghosh Jay B.
Published: March 2008

This paper points to the viability of metamodels in performance evaluation. A metamodel, in the sense it is used here, is a simple mathematical expression that describes a performance measure in terms of the system parameters, and is derived from experi ments with a simulation model of the system. The system con sidered is a bus-sufficient multiprocessor, and the performance measure under focus is its processing efficiency. The process of metamodel development is illustrated to show that a reliable metamodel can be derived with relative ease. It is also argued that with sufficient care taken in selecting the form of the meta model, it may be justifiable to use the metamodel beyond the experimental domain over which it is developed. Specifically, a metamodel is proposed for the processing efficiency of a multi processor system. It is shown to be a reasonably good approxima tion to the simulation model, and by extension, to the original system.
Simulation and object-oriented programming: the development of SERB
Authors: Larkin Timothy S. , Carruthers Raymond I. , Soper Richard S.
Published: March 2008

An object-oriented programming language (OOPL), Flavors, was used to implement a modeling language and ancillary simula tion tools designed specifically to meet the needs of research biologists. A biological system is typically considered as a set of interacting entities, an abstraction which closely matches the pro gramming paradigm of Flavors. Some of the important charac teristics of Flavor programming are presented. Then SERB (the Simulation Environment for Research Biologists) is described. SERB uses Flavor objects to represent biological entities, resulting in a high degree of transparency between model and simuland. The simulationist creates model components from a library of component types and defines a model as some interacting set of these components. These models can then be used in simula tions or by higher level functions, such as sensitivity analysis. Flavors was found to be an ideal language for implementing modeling and simulation software for this domain.
A simulation model for mechanized log harvesting systems
Authors: Wiese Christoph , Olsen Eldon D. , Randhawa Sabah U.
Published: March 2008

The design, evaluation and control of mechanized harvesting systems is a problem of considerable importance in the forest products industry. However, due to the complexity and diversity of such systems, mathematical analysis of these systems is not computationally feasible. Although the simulation approach to model the harvesting problem has received considerable atten tion, the simulation models developed to date have primarily concentrated on modeling specific components of the system. Furthermore, the simulation models developed for log harvesting have seen little use. This is because the model input requires the user to be familiar with the simulation language, and the simulation results are difficult to interpret in terms of system costs and productivity.

The research reported in this paper developed a simulation model for analyzing the entire logging operation (tree-to-mill) in the forest products industry. Using this system, the user is able to define on-line, in an interactive session the configuration of the timber harvesting system the user would like to analyze. A network-based simulation model then performs the simulation and reports the results in an easy to analyze and readable form.
A Comparative study of finite difference and multiquadric schemes for the Euler equations
Authors: Kansa E.J.
Published: March 2008

We present a true scattered-data, grid free spatial approximation scheme called multiquadrics (MQ) first developed by Hardy. We have modified the original MQ scheme and demonstrated that it is exceptionally accurate for not only surface approximations, but also partial derivative estimates. Unlike familiar polynomial ap proximations, MQ is excellent for moderate to steep gradient regions, but rather poor in relatively flat regions. For that reason, we advocate a hybrid scheme which uses MQ in moderate to steep regions, but switches to the familiar polynomial methods in relatively flat regions.

In this paper, we compare the accuracy and operation counts of finite differences and MQ schemes for the solution of time depen dent nonlinear set of hyperbolic partial differential equations. We have demonstrated both from an operations count and accuracy that MQ is superior to the familiar finite difference scheme.
Analytic performance estimation for complex maintenance systems
Authors: Fisher Warren W.
Published: March 2008

Earlier models are extended and combined to provide an analytic means of estimating the average number of inoperative machines in a two-echelon (bases and a depot), two-indenture (machines have components which may have modules) maintenance system with spares and repair. Separate expressions are developed for the no cannibalization and complete, instantaneous cannibaliza tion cases. The expressions are suitable for verification of aircraft maintenance system simulation models as well as for estima tion of system performance and the maximum benefit of cannibalization.
A prototype implementation of GPSS in SAS
Authors: Jones Gretchen K. , Greene Michael A.
Published: March 2008

This paper describes a program written in the SAS language which allows constructing a simulation with a subset of the GPSS language. A discrete event model is encoded and then run in the SAS environment. The advantage of this approach is the ability to use the statistical and graphics procedures in SAS for monitoring of the simulation during the run and/or for post-simulation analysis. Examples of the interaction of the GPSS blocks and the SAS pro cedures are provided.
On modelling and differential/algebraic systems
Authors: Mattsson Sven Erik
Published: March 2008

It is of a vital interest that software for model development and simulation supports models given as differential/algebraic equa tions (DAE), since many models for physical systems are naturally given as sets of ordinary differential and algebraic equations and since, as motivated in the report, the equation form is the only reasonable for model libraries. Unfortunately, most simulation packages of today do not allow models given as DAE systems, but require assignment statements for derivatives and algebraic variables.

There are numerical solvers for DAE systems, but they are not as reliable and robust as numerical solvers for ordinary differential equations on state space form. Unfortunately, DAE systems may exhibit bad properties, which make them difficult to solve numerically today. The purpose of the paper is to give an over view of important properties of DAE systems, indicate possible ways to handle difficulties and to motivate others to do research in this area.

By means of examples it is illustrated that even small, simple DAE systems can exhibit bad properties. The examples are by no means pathological. They arise naturally during model development.

There are many open questions to answer. The questions cover a broad range from theoretical to practical problems. To en courage research in this area, interesting issues are listed.
Qualitative methodology in simulation model engineering*
Authors: Fishwick Paul A.
Published: March 2008

Qualitative methodology in simulation requires high level model ing constructs such as causal graphs, bond graphs, or natural language. Even though there exists a virtual continuum between qualitative and quantitative simulation methods, it is important to discuss qualitative methods since they relate to notions of pro cess abstraction and discovery during model evolution. We will refer to the evolutionary process as simulation model engineer ing. We define the basic notions of qualitative simulation, give specific examples for a pendulum system, and finally discuss various issues and directions for future work.
Testing for initialization bias in simulation output
Authors: Vassilacopoulos G.
Published: March 2008

A test is presented for detecting the presence of initialization bias in the mean of a simulation output process. The test is based on a standardized sequence of linear combinations of the ranks of the simulation observations. The validity and power of the test are illustrated by applying it to a large number of in dependently seeded experiments on the M/M/s queue with s=1 and s= 4.
Comparison of the RK4M4, RK4LIN and RK4M1 methods for systems with time-delays
Authors: Metzger Mieczyslaw
Published: March 2008

The higher-order Runge-Kutta methods can be used in three different ways when the time- delays occur. The RK4M4, RK4LIN and RK4M1 methods are an application of the most popular fourth-order Runge- Kutta method for time-delays. The RK4M4 method requires a storage of four variables, so it is hardly ever used. Based on the discussion and experimental testing it has been shown that the RK4M4 method nevertheless provides the most significant economy of memory and shortest computing time.