bluuebunny/crossref_metadata_2025 huggingface dataset:
Scattering of energetic ions by solids — a simulation
Authors: Pearce John G. , Shaar Zak , Crosbie Roy E.
Published: March 2008

This paper describes a digital computer simulation of an experiment which measures the energy-intensity distribution of noble gas ions scattered by crystal line solids. The discussion emphasises the simula tion techniques employed (in particular, the choice of integration method), the methods of relating com puter input data to the experimental variables, and the transformation of computer results into a form directly comparable to experimental data.
Briefly Speaking
Authors: Farrand William A.
Published: March 2008

Bill Farrand became involved in simulation in 1943 when he was with Beckman Instruments and in 1945 when he helped set up the vannever Bush Mechanical Differential Analyzer (a wonderful device to behold, now in the Smithsonian) at UCLA. Bill has also worked for Lockheed Aircraft, where he was project engineer for a Total Aircraft Simulator (a flight trainer) and for Telecomputing, as chief engineer. He has been with North American Aviation since 1950, where he is now a staff engineer.
Verbatim and Whole !
Authors: Korn Granino A.
Published: March 2008

Although I had heard of his prowess with analog com puters and their use for simulation when he was still with Lockheed Aircraft in Burbank, California, I didn't meet Granino Korn until 1956-probably because he had been holed up in a trailer with his wife Terry coauthoring that Bible of early simula tionists, Electronic Analog Computers. After finish ing that book Granino joined the faculty of the University of Arizona as professor of electrical engineering, where he has educated and indoctrinated many fine simulationists. No one, they say, is so fervently dedicated as a convert, and Granino illus trates the point. Some of the most notable contri butions to the use of digital computers for simula tion have been made by that old analog hand with his DARE (Digital Analog REplacement) series of hardware/ software systems. Granino continues to write travel, and lecture internationally - and thus influ ence, for the better I am convinced, the lives and fortunes (?) of all us simulationists.
Another View
Authors: Evert Carl F.
Published: March 2008

Carl Evert became interested in simulation in the late fifties through the good influence of another of our contributors, Vince Rideout. When he then went to the University of Cincinnati as associate professor of electrical engineering, he purchased a Donner analog system and subsequently interfaced it via telephone lines for remote computation from a medical research lab! This led to an NSF grant to start a hybrid lab with an AD-4/IBM 1130 system circa 1968. Carl has taught courses in analog, digital, and hybrid systems and has been a consultant in several areas, notably to the drug industry, where he has done discrete modeling of leukemia dynamics.
A Steel Man Reminisces
Authors: Keener Everett L.
Published: March 2008

Ev Keener was introduced to simulation via an EAI 231-R analog computer at the U.S. Steel Research Laboratory in 1960. His simulation experience with that organization since then has been so extensive that I have had to delete the long list of projects he sent with the following writeup.
Shakespeare as Simulationist
Authors: Baker Dennis W.
Published: March 2008

Dennis Baker first became involved with simulation in 1965 when he was at what is now the David W. Taylor Naval Ship Research and Development Center in Annapolis. There, as a co-op student from Drexel University, he met a TR-48 and spent his entire final work period teaching himself analog programming and developing a simple model of ship motion.

Though Dennis was not one of the "thrice-filtered friends" I originally solicited, when he told me on the now-famous SCS Silver Anniversary "Crooze" of his research which led to the following contribution I thought it too important an historical note to be left out of this historical issue.
Peripheral processors for high - speed simulation
Authors: Karplus Walter J.
Published: March 2008

This paper describes some of the results of a study directed to the specification and procurement of a new cockpit simulator for an advanced class of heli copters. A part of the study was the definition of a challenging benchmark problem, and detailed analy ses of it were made to assess the suitability of a variety of simulation techniques. The analyses showed that a particularly cost-effective approach to the attainment of adequate speed for this extremely de manding application is to employ a large minicomputer acting as host and controller for a special-purpose digital peripheral processor. Various realizations of such peripheral processors, all employing state- of-the-art electronic circuitry and a high degree of parallelism and pipezining., are available or under development. The types of peripheral processors- array processors, simulation-oriented processors, and arrays of processing elements - are analyzed and com pared. They are particularly promising approaches which should be suitable for high-speed simulations of all kinds, the cockpit simulator being a case in point.
Simulating the impact of regulatory changes on electric utilities
Authors: Ford Andrew
Published: March 2008

This paper illustrates the use of a computer simula tion model of the electric utility industry by examining the model's behavior under different regu latory conditions. The paper describes the model's structure, behavior, and limitations, and examines several ongoing efforts to deal with the limitations.
A practical cross-power spectral analyser
Authors: Murthy D.N.P. , Smith T.C.
Published: March 2008

In this paper we propose a method for obtaining the cross-spectra of stationary signals. The method is ideally suited for implementation on an analog com puter and we present typical results obtained from such an implementation to illustrate the usefulness of the method.
Using simulation in hospital planning
Authors: Alessandra Anthony J. , Grazman Ted E.
Published: March 2008

A perplexing problem today in many hospital clinics is how to manage patient flow effectively. An example of poor management was found in the family planning clinic of a large Southeastern hospital. Employee workloads and patient service times both varied greatly, with periods of overwork and over crowding followed by periods of virtual inactivity.

The hospital administrators wanted to correct the problem without disrupting personnel or patients and without spending money on capital improvements. (The entire clinic was soon to be relocated.)

A computer model was developed to study how changes in staffing policies would affect the observed bottle necks. Current operating procedures along with seven alternatives were examined. Simulation allowed the study of these approaches without large capital expenditures or disturbances in normal operations.

This study not only shows the solution to a particular problem in patient flow but also shows how sophisticat ed analytical techniques can be used in the rapidly expanding health delivery field.
A model of residential energy use
Authors: Hirst Eric
Published: March 2008

A model of residential energy use was developed to simulate the period from 1970 to 2000. The model predicts annual energy use by fuel, end use, and type of housing, and also estimates annual equipment installations and ownership, equipment energy re quirements, structural heat retention, fuel expendi tures, equipment costs, and costs for improving heat retention in new and existing housing units. Thus the model provides considerable detail on residential energy uses and associated costs. These details are useful for evaluating the effects of alternative energy conservation policies, programs, and tech nologies during the next quarter century.

The present version of the model handles four fuels, eight end uses, and three types of housing. Each of these 96 components of total energy use is calculated each year as a function of stocks of occupied housing units and new construction, equipment ownership by fuel and end use, heat retention of housing units, average unit energy requirements for each type of equipment, and usage factors that depend on household behavior.

Simulation of energy use from 1960 to 1975 shows that the model accurately predicts historical data on aggregate energy use, energy use by fuel, energy use by end use, and market shares of ownership of equipment.
Reports From Down Under
Authors: McLeod John , McLeod Suzette , Benyon Peter R.
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 75ç per copy.
The efficient solution of linear constant-coefficient systems of differential equations
Authors: Enright W.H.
Published: March 2008

Most numerical techniques that have been proposed for the solution of constant-coefficient linear prob- Zems involve -either directly or indirectly-approxi mating a matrix exponential. For large systems these techniques can be very expensive to implement on digital computers. In this paper we describe how standard stiff ordinary differential equation (ODE) methods can be modified to take advantage of linear ity and thereby efficiently solve large linear prob lems. Methods based on backward differentiation formulas or second derivative formulas are particular ly suitable for this purpose. The implementation of these methods is discussed and numerical results are presented.
Accurate simulation of control systems with positional limits
Authors: Cox C.S. , Wright F.W. , Brown G.L.
Published: March 2008

This paper reports an analogue-logical simulation study of the performance of a hydraulic servo posi tion-control system. The system has positional limits at which the velocity of the servo output becomes zero. Pairs of logic-controlled integrators are used to simulate these limits without generating a velocity transient. Minimised logic expressions control the integrators. Test results provide examples of system performance.
Using sensitivity analysis to simplify ecosystem models: a case study
Authors: Rose Michael R. , Harmsen R.
Published: March 2008

Theoretical ecology requires simulation because real istic ecosystem models are too complex for mathemati cal analysis. In this paper we propose a way of moving from a complex simulation model based on the "mechanics" of an ecosystem to a much simpler model that exhibits behaviour similar to that of the origi nal model in its major features. The tool used to isolate the key characteristics of the original model is sensitivity analysis. It enables the investigator to identify the variables and parameters that deter mine the essential behaviour of the original model and to formulate a clear picture of that behaviour. With this information in hand, the investigator can devise a simplified model that exhibits the same essential behaviour.

While the simplified model behaves like the original model, its inner workings only generally parallel those of the original. Its simplicity allows the investigator to test his intuitive ideas directly, clarifying understanding of the ecosystem originally modelled. Further, the investigator may be able to adapt the simplified model to other similar ecosystems. The methods outlined in this paper are illustrated by a case study of a forest infested by tent caterpillars.
Hideous functions
Authors: Bark Maurice J. , Woolsey Richard
Published: March 2008

This paper describes a new simulation tool that the authors (seriously) have named the Hideous Function. An application required a function that had certain erratic properties which are inherent in operating machinery. The problem was to generate a random- Zooking function that was actually a predictable single-valued function of time. Since the function would be evaluated in a digital computer, polynomials were used as the primary building blocks. Hideous Functions have proved useful in training simulators because they require less memory and lower processing speed than other approaches. The particular applica tion treated in this paper is the generation of pseu dosonar signals for use in antisubmarine warfare (ASW) trainers.
Modeling heat and moisture flow in soils
Authors: Schroeder Charles , DeMichele Don W. , Pooch Udo W. , Teague William Ray
Published: March 2008

This paper describes a new model of the simultaneous flow of heat and moisture in soils. The model is a user-oriented experimental tool specifically designed for use in research. Computer optimization techni ques, numerical methods, and soil physics were used in developing the model. The model has been used in simulating the two-dimensional transfer of heat and moisture. It includes the effects of the environment and of subsurface sources and sinks.
Tradeoffs in the Use of Wide-Area Telephone Service (WATS)
Authors: Parker A.J. , Silbey Val , Duncan John
Published: March 2008

This paper describes the use of a simple simulation model to evaluate policies for WA TS usage in an organization that has a programmable telephone exchange or PBX. The simulation results indicate that for a small increase in cost, both waiting time and the number of persons who wait can be decreased substantially in a marginal case.
Digital simulation using Fermat number transforms
Authors: Pimentel Juan R. , McVey Eugene S.
Published: March 2008

This paper discusses the use of number transforms in the simulation of dynamic systems. The structure of these transforms is discussed, and the Fermat number transform is selected as the most promising for simulation. The advantages of this approach are in creased speed and the elimination of multiplications and roundoff error. An example of a simulation using Fermat number transforms is presented and this tech nique is compared with standard techniques in terms of error and execution time.
A simulator for multilevel distribution systems
Authors: Blank Leland
Published: March 2008

This article describes the use of simulation to de sign a multilevel distribution system which is supplied by one manufacturing plant and several local suppliers. The program is written in SIMSCRIPT.

Each regional warehouse is assumed to obtain most of its product from one distribution center, which is in turn supplied by the manufacturer. The model generates forecasts at each level based on demand data which is randomized in accordance with empirical distributions.

If the manufacturing capacities, which in the simula tion are user-specified, are too small to meet the demand, the model adjusts the distribution schedule. Each warehouse is provided the opportunity to pur chase some fraction of its demand for any item from a local independent supplier on a routine basis and on an extra-purchase basis when the manufacturer can not supply the item through his distribution centers.

The article discusses model validation and an appli cation of the simulator to determine the optimum number and the locations of storage facilities and to improve inventory control.
Simulation of a shell-and-tube condenser
Authors: Saraf G.R. , Dhar P.L.
Published: March 2008

This paper presents the computer simulation of a shell-and-tube condenser with a subcooler. It con siders the variation of the coefficient of condensa tion heat transfer along the tube in the condenser and the effects of the subcooler. A general computer program for the simulation of such condensers has been developed.

The simulation has been validated by comparing the simulated performance of a typical industrial con denser with the condenser's rated performance as cited by the manufacturer. Close correspondence has been found between the two.
Load management strategies for electric utilities: a production cost simulation
Authors: Blair Peter D.
Published: March 2008

This paper deals with the development and application of a simulation model for analyzing strategies for managing the residential loads of electric utilitities. The basic components of the model are (1) a produc tion-cost model, which simulates daily operation of an electric power system, (2) a load model, which disaggregates system loads into appliance loads and other loads, and (3) a comparison model, which com pares the production costs and energy consumption needed to meet a particular load profile to the cor responding costs and energy consumption required for another load profile. The profiles in each pair define alternative ways of meeting the same demand.

A method for disaggregating load profiles into appliance components is discussed and several alter native strategies for residential load management for a typical northeastern electric utility are formulated. The method is based on an analysis of the composition of electric loads for a number of classes of residen tial customers in the model utility system. The effect of alternative load management strategies on the entire residential loadcurve is determined by predicting the effects of these strategies on the specific appliance components of the loadcurve.

The results of using the model to analyze alternative strategies for residential load management suggest that load management strategies in the residential sector, if adopted by utilities whose operating and load characteristics are similar to those of the sys tem modeled here, must take into account a wide variety of appliances to achieve significant changes in the total load profile. Moreover, the results also suggest that it is not easy to reduce costs significantly through new strategies for managing residential loads only and that, to be worthwhile, cost-reducing strategies will have to encompass many kinds of appliances,
Compensator design using the frequency - domain approach
Authors: Olsen Charles F.
Published: March 2008

This paper presents an analytical technique for com pensating a system in the frequency domain to meet phase margin and static-error coefficient require ments at a specified gain-crossover frequency. The paper describes a BASIC program that implements the techniaue.
Improvements in a single-step integration algorithm
Authors: Babcock Paul D. , Stutzman Leroy F. , Brandon Daniel M.
Published: March 2008

THis paper describes and illustrates extensions and iimprovements to a particularly efficient numerical integration method which was first presented in the July 1974 issue of Simulation.5 The algorithm is a single-step A-stabZe implicit method. The recent improvements provide better control over error in both integration and roundoff and greater computa tional efficiency than current methods for both linear and nonlinear systems. The results of apply ing the new algorithm to seven benchmark problems are reported and are compared with results obtained in solving the same problems by Gear's method.
A computer simulation of oil spills
Authors: Capehart Barney L. , Welsh Leonard W.
Published: March 2008

The discovery and development of oil resources in the Northern Florida Gulf Outer Continental Shelf will ultimately cause oil spills in this area. This study estimates the percentage of the spills that will reach the Florida coast. A computer simulation model incorporating data for seasonal winds, weathering of oil on the sea, and develop ment and transportation of crude oil is presented. Investigations show the effects of both the original location of the spill and the seasonal winds on the frequency with which oil spills reach the coast.
Validation, statistical testing, and the decision to model
Authors: Greig Ian D.
Published: March 2008

This paper outlines a decision-theory approach to the validation of simulation models. This approach in volves trading off the chances of incurring the cost of using an invalid model against the costs of additional modelling to increase the Z2-keZihood that the model will fulfill its intended purpose. Importantly, the decision-theory approach provides a conceptual base that has hitherto been lacking for the use of statistical testing in validation. Further, by explicitly relating validation to the decision of whether or not to model in the first place, more soundly based estimates of the costs and probabilities can be obtained than would otherwise be possible. Notwithstanding the formal decision approaches, more subjective methods such as Turing type tests are recommended as also being necessary for a balanced approach to the validation of simulation models.
SLAM: simulation language for alternative modeling
Authors: Pegden Claude Dennis , Alan A. , Pritsker B.
Published: March 2008

This paper introduces the new simulation language SLAM, which has the features of network-oriented, discrete-event, and continuous simulation languages. Emphasis is given to the use of networks and the combination of network models with discrete-event and continuous models. This paper discusses how models are developed using these different approaches and how they can be used in combination through the use of interfaces built into SLAM.
Using simulation in implementing property-tax reform
Authors: Shannon Patrick , Gallup V. Lyman , Merz C. Mike , Maxson Emerson
Published: March 2008

In November 1978 Idaho voters passed an initiative which limited real and personal property taxes to 1 percent of market value. This paper reports on a joint effort by the Idaho State Tax Commission and researchers at Boise State University to develop a computer model which could be used to evaluate alter native implementations of the initiative within the framework of Idaho's constitution. This model esti mated the fiscal impact of the initiative on all tax ing districts in Idaho. The Idaho Legislature used outputs from the model during their budget delibera tions.
Simulation of a supercritical once-through boiler
Authors: Suzuki Yutaka , Sik Pyong , Uchida Yoshihisa
Published: March 2008

The problem addressed is that of improving the control system of an existing supercritical once-through boiler. To do this, it was necessary to construct a dynamic mathematical model of it. This paper describes the model that was developed; it is based on the nonlinear partial differential equations which describe the physical phenomena in the boiler. These equations involve transfer functions that cannot be obtained directly; they were found by linearizing the equations and estimating the values of unknown parameters from the boiler's input-output operational records. The model includes both forward and back ward causalities in determining the water and steam flow. Simulation results indicate that the model is valid and that the control system requires modifica tion.

The investigated boiler has a capacity of 450 MW and is presently operating at Kainan Thermal Power Station of Kansai Electric Power Company.
The simulation of Coulomb friction in mechanical systems
Authors: Bernard James E.
Published: March 2008

Coulomb or dry friction occurs in mechanical systems when nonlubricated surfaces come into sliding contact. The force resulting from Coulomb friction has a magnitude dependent on the contact force and a direc tion opposite to the relative velocity. If the re lative velocity is zero, the Coulomb friction assumes the value, within bounds, to maintain zero velocity. This, of course, presents the opportunity for a variety of equilibrium configurations.

This paper presents an overview of the common tech niques for the digital simulation of Coulomb fric tion. All these techniques use the relative velocity to determine the friction force and are therefore flawed since they cannot predict multiple equilibrium positions. By means of an example, this paper shows that modeling Coulomb friction as a function of posi tion rather than of velocity allows multiple equili bria and offers features that are useful in modeling high-friction, low-mass systems.
Analysis of continuous linear systems on an IBM 5100
Authors: Meyer C.R. , Michel J.M.
Published: March 2008

This article describes a set of computer programs for anazyzing, synthetizing, and identifying the parameters of continuous linear control systems. The programs are written in APL, with the algorithms chosen for rapid solution and ease of programming on the IBM 5100 portable minicomputer. After describ ing the organisation of the program, we discuss the algorithms in detail and present an example of their use.
Using a computer model to evaluate business operating plans
Authors: Duersch Ralph R. , Meenan Peter M. , Shu Frank
Published: March 2008

This paper describes a simulation model that can be used to examine plans for marketing, manufacturing, and distributing the products of an assembly line. The manufacturing plants are flow-oriented and use assembly lines to integrate subassemblies and pur chased parts into products. The simulation permits an economic evaluation of alternative allocations of manufacturing, marketing, and financial resources to select a best response to changes in customer demands. As an illustration, we compare the effects of two production schedules on inventory levels.
Dynamo
Authors: Shaffer William A.
Published: March 2008

DYNAMO is a continuous-system simulation language with features useful in teaching simulation at levels ranging from secondary schools through advanced graduate and professional training. These features include:
Using simulation to calculate floating-point quantization errors
Authors: Phillips Charles L.
Published: March 2008

This paper considers digital controllers using floating-point arithmetic. An error analysis tech nique is developed and is implemented by a computer program that is based on a simulation of the system. The outputs of the program include the form required to minimize quantization errors and the output errors for a given bit configuration. The program can be integrated into system simulations.
Manufacturing resource planning: an integrated decision-support system
Authors: Cox James F. , Adams Fred P.
Published: March 2008

A manufacturing resource planning system provides a vertically and horizontally integrated set of plans for each level of management and for each of the supporting areas of the organization. Computer simulations are used to generate these coordinated plans. Thus, a total system model is available for simulating alternative actions and evaluating the effects of each strategy of the business enterprise. The input requirements, benefits, and problems associated with such a planning and control system are also discussed.
Simulation of a queueing problem with balking
Authors: van Tits Martien , van der Veeken Henk
Published: March 2008

Queueing systems become complicated if balking occurs, that is, if impatient customers refuse to join the queue. Analytical results for expected queue length and waiting time have been obtained for the standard queueing problem (M/M/1) with balking. This report describes an investigation into the general validity of these formulas.

Since an analytical approach to the general queueing problem is not feasible, we used simulation. An efficient simulation model was constructed and ana lysed using regenerative properties, a technique for handling correlated observations. The results extend standard queueing theory and indicate areas for further theoretical investigation.
Improving the throughput of a chemical plant
Authors: Miner Robin J. , Wortman David B. , Cascio Danis
Published: March 2008

This paper describes a modular GASP IV model of a chemical plant and its use in analyzing the operation of the plant. The model represents multiple stages and products and was developed to evaluate methods for increasing throughput. The plant manufactures six products, each going through a series of steps; different products can be in production at the same time. These products differ in chemical treatment, production rate, and demand. Production must be scheduled to meet demands and to maintain minimum inventories, and it must operate within the con straints on processing space and in-process storage. This paper also includes the data-collection proce dures and the evaluation of several alternatives pro posed to increase the throughput of the plant by as much as 100%.
Analysis of production facilities- a network simulation approach
Authors: Maani Kambiz E.
Published: March 2008

The existing analytic and heuristic techniques for the assembly-line problem are generally limited in scope and applicability. The restricted and often unrealistic assumptions of these procedures handicap them as a practical tool for modern manufacturing problems. This article presents a comprehensive model for the design and analysis of production-line facilities. The Generalized Network Simulator (GNS), a network-based simulation model, integrates the handling of time, queue, resource, and cost character istics of realistic situations in a single package and offers a "total system" tool for systems analysis and research. A companion Assembly Line Information System (ALIS) facilitates both the construction of the data base through interactive data input entry and the specification of desired statistical outputs. An example illustrates the application of the model in a fictitious manufacturing environment involving the cost and resource features of the GNS/ALIS programs.
Across My Desk
Authors: Pratt Charles A.
Published: March 2008

Many of us were delighted to hear of the award of the 1980 Nobel Prize in economics to Dr. Lawrence Klein of the University of Pennsylvania. He was presented this award as ''the leading research worker within the field of the economic science which deals with the construction and analysis of empirical models of business fluctuations." Since Dr. Klein is a long-time simulationist, I thought we should hear from him and contacted him by phone for the following interview.
Determining the optimum size of a coal silo
Authors: Chu Jean , Ermolowich Hichael
Published: March 2008

We have used computer simulation to help determine the optimum size of a silo for coal produced from the McInnes Mine in Pike County, Kentucky. The silo is used to store coal that is waiting to be cleaned. Previous experience suggested a silo capacity of 6000 tons. However, because of the complexity of the operation, we undertook a further study to evaluate the proposed size.

We used computer simulation to model the system and estimate the amount of lost coal production for different silo capacities. Based on the simulation results, we recommended a silo capacity of 7 500 tons to eliminate a potential bottleneck which could cause a loss of production.

The total study took two weeks, including model development and preparation of the report for model uses. The cost, including man-hour charges and computer charges, was approximately three thousand dollars.

We expect this study to provide savings of 1.5 million dollars, the difference in total life-cycle costs (including the cost of lost production and the initial investment) between the two proposed silo sizes. This cost/benefit ratio demonstrates the usefulness of computer simulation as a tool to solve real problems.
General Equation Modeling Systems (GEMS)- a mathematical simulation language
Authors: Babcock Paul D. , Stutzman Leroy F. , Koup Thomas G.
Published: March 2008

This paper describes extensions of and improvements to an efficient numerical integration method, the Implicit Modeling Package (IMP), which was presented in the July 1974 issue of SIMULATION and subsequent ly in the July 1979 issue of SIMULATION. The exten sion described here is a simulation language, General Equation Modeling System (GEMS), for the solution of systems of algebraic and differential equations. GEMS provides a simple and convenient way to formulate complex mathematical models for simulation using the IMP algorithms. GEMS is well suited for the solution of sets of stiff, nonlinear algebraic and differential equations. The GEMS package is compared to ACSL (Advanced Continuous Simulation Language) using a set of nine benchmark problems.
The FORTRAN synthetic program
Authors: Rucks Andrew C.
Published: March 2008

The FORTRAN Synthetic Program (FSP) facilitates simu lation of a computer workload by providing control of processing time, memory usage, and instruction mix. The FSP features modular design, parameterized control, and internal defaults that enhance flexib ility. The FSP offers the advantages of system independence, ease of use, high flexibility, and the ability to produce verifiable, predictable, and repeatable experiments.
Converting a batch simulation program to an interactive program with graphics
Authors: Kaufman Arie , Hanani Michael Z.
Published: March 2008

Interactive, menu-driven graphics and animation can make a minicomputer-based simulation more informative and more useful than an equivalent simulation running in batch mode on a large computer. Converting a large batch program to interactive operation with graphics is, however, a difficult problem. A top- down, modular approach is essential. As an example, we discuss a program that simulates vehicle motion and driver behavior at a signal-free intersection. We converted the original batch version into an inter active program. The final product, which runs inter actively with animated graphics on a PDP-11 mini computer, is a highly convenient tool for studying intersection design and traffic control.
What If
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.
Using bond graphs in nonlinear simulation problems
Authors: Karnopp Dean
Published: March 2008

A unique feature of bond-graph techniques is that they provide the modeler with a graphical representa tion of the causality (i.e., the input-output rela tionships) in the underlying system. An understand ing of causality makes the modeler aware of algebraic loops and implicit differential equations at an early stage in the solution process. It also clarifies the effects of adding or deleting features of the model. The modeler can use causal information to create simulation programs for nonlinear systems even when some variables cannot readily be expressed in equation form. The resulting program is equivalent to a set of state equations but contains subroutines instead of algebraic expressions. For many complex systems, using vector bond graphs to represent causal interactions among large subsystems can help the modeler write programs using sets of variables rather than individual variables.
The simulation of gasoline queuing
Authors: Huss William R. , Cooper Ralph E.
Published: March 2008

Lines at gasoline service stations have become a fre quent phenomenon in many countries. When lines occur, drivers demand immediate action but government and oil company officials are uncertain about what steps to take. The Battelle event-structured simulation model GASQUE is designed to show which policies are most effective in reducing the length of lines and the amount of time spent in lines.

GASQUE simulates the interaction of 1 500 automobiles and three stations. Many parameters of the model are selected from distributions over time of day, day of week, or the 1 500 automobiles. Such parameters in clude purchase decision levels, consumption rates, driver availabilities, tank sizes, and station hours. The model also permits the simulation of end-user allocation plans such as assigning purchase days by automobile license number (e.g., the so-called odd- even plans). Output from the model includes statis tics such as average line length and average number of hours spent in line per week.

The application of GASQUE requires the use of compara tive analysis, that is, the examination of changes from standard or base-case simulations. In one series of simulations, studying the joint effects of tank-topping (buying a small amount of gasoline sim ply to keep the tank full) and reductions in station hours shows that either may cause lines to form. Imposing a maximum purchase limitation causes longer lines, especially when combined with reduced hours.

A second series of simulations studied the effects of end-user allocation plans. In general, lines are made shorter by requiring minimum purchases and re quiring stations to remain open on weekends. Odd- even plans result in longer lines. A comparison of these findings with reports from various sections of the United States suggests that the simulation results agree with the 1979 experience with gasoline queues.
Using computer simulation to develop optimal inventory policies
Authors: Gaither Norman
Published: March 2008

A method is presented for simultaneously determining order points and order quantities for materials stocked to meet an uncertain and independent demand. A computer simulation procedure minimizes total annual costs (carrying, ordering, incoming transportation, acquisition, safety stock carrying, and expected stockout) for individual stock keeping units. This method allows for the interdependence of order points and order quantities, a comprehensive range of costs as deci sion criteria, discontinuous cost functions, and optimal solu tions for discrete units. Flowcharts document the procedure, and cost tables of actual applications demonstrate the results of the model.
1ST FIRST PLACE WINNER Axe: A language for the simulation of digital hardware
Authors: Van den Bout David E.
Published: March 2008

Axe is a new simulation language built upon the foundations of C language. It allows a designer to hierarchically describe and simulate a digital system at the procedural level, gate level, or switch level. The Axe compiler and the simulation code it gen erates require minimal computer system resources and execute in an efficient manner. This results from the use of the module concept as the central modeling device and by employing a stan dard C compiler as the "backend" of the Axe compiler. In con junction with the C compiler, Axe allows the user to have access to a full-fledged general-purpose programming language which also supports the simulation of digital systems. This flexibility allows Axe to generate simulations which can be used and modi fied to meet several needs. In addition, Axe allows modification of the timing parameters of system components in order to gauge the effects upon system performance. A complete example ofthe use of Axe is given, and several larger simulations are described.
3RD THIRD PLACE WINNER Simulation of the signalized intersection
Authors: Jacobs Larry W.
Published: March 2008

Simulation is commonly used to model vehicular behavior at intersections in urban grid networks. In recent years traffic volume in suburban areas has increased to the point where it rivals urban congestion. This shift in traffic concentrations has placed increased emphasis on the need for understanding traf fic flows at non-grid or isolated intersections. A computer simula tion model of a prototypical isolated intersection was developed. The model was used to test preliminary hypothesis regarding ef ficient isolated intersection design and signal operation policy.
Validation of simulation models using decision theory
Authors: Velayas James M. , Levary Reuven R.
Published: March 2008

To determine the necessary resources for sufficient validation of a simulation model is an extremely difficult and subjective task. There are two potential trouble spots for individuals validating the project. First, they may overvalidate a model and conse quently waste resources. Second, they may insufficiently validate a model; consequently, the results of the model may be in error. In this paper, the validation process is divided into two separate phases. Within each phase, techniques using decision theory con cepts are presented to aid in the validation process.
A new software technique for sub-model invocation
Authors: Korn Granino A.
Published: March 2008

Direct-executing ENHANCED DESIRE simulation on PC/XT/AT and compatible personal computers employs a new method for declaring and invoking sub-model macros and user-defined functions in the DYNAMIC program segment representing the simulation model. Submodel and function invocations are not true macros but compiler procedures; like all of the DYNAMIC segment, they compile into fast in-line code, and no extra translator pass is needed.
A prototype knowledge-based simulation support system
Authors: Hill Timothy R. , Roberts Stephen D.
Published: March 2008

As a preliminary step toward the goal of an intelligent automated system for simulation modeling support, we explore the feasibility of the overall concept by generating and testing a prototypical framework. A prototype knowledge-based computer system was developed to support a senior level course in industrial engineer ing so that the overall feasibility of an expert simulation support system could be studied in a controlled and observable setting. The system behavior mimics the diagnostic (intelligent) process performed by the course instructor and teaching assistants, find ing logical errors in INSIGHT simulation models and recom mending appropriate corrective measures. The system was pro grammed in a non-procedural language (PROLOG) and designed to run interactively with students working on course homework and projects. The knowledge-based structure supports intelligent behavior, providing its users with access to an evolving accumula tion of expert diagnostic knowledge. The non-procedural ap proach facilitates the maintenance of the system and helps merge the roles of expert and knowledge engineer by allowing new knowledge to be easily incorporated without regard to the ex isting flow of control. The background, features and design of the system are described and preliminary results are reported. Initial success is judged to demonstrate the utility of the reported approach and support the ultimate goal of an intelligent model ing system which can support simulation modelers outside the classroom environment. Finally, future extensions are suggested.
Process planning simulation: An FMS modeling tool for engineers
Authors: Mellichamp Joseph M. , Wahab Ahmed F. A.
Published: March 2008

Simulation methods are effectively used to investigate design issues of a proposed flexible manufacturing system (FMS). Un fortunately, process design engineers rarely have the necessary expertise to take full advantage of simulation methodology. Pro cess Planning Simulation (PPS) is a software package which allows engineers with virtually no simulation expertise to define FMS designs and generate the simulation code necessary to model designs of interest. PPS uses SIMAN to model process elements of an FMS, and IFPS to model the financial aspects of the system.
An expert manufacturing simulation system
Authors: Ford Donnie R. , Schroer Bernard J.
Published: March 2008

An expert simulation system for an electronics manufacturing plant has been developed with emphasis on the natural language interface. This includes the transformer and the understander, the simulation writer, the simulation analyzer, and the simula tion language.
Generic error control coding modules
Authors: Robinson John P. , Wade William D. , Leong Peter K. , Mortara Mary E.
Published: March 2008

The design and test of error control encoding and decoding mod ules for simulating data communications systems is described. Generic application library modules for the Interactive Commu nications Systems Simulation Module (ICSSM) were developed for block and convolutional codes using the programming lan guage FORTRAN. The end user specifies a system for simulation study by linking various communications, signal processing and error control modules.

In developing the encoding and decoding modules, a top-down approach resulted in a heirarchy of subroutines and function calls. This approach simplified the validation task and allowed easier upgrades and maintenance. Some of the design trade-offs for both the block code and convolutional code modules are viewed. It was found that modest use of storage can be traded for execution time. Various computations and operations can be efficiently accomplished with table look-up when using a high-level language such as FORTRAN.

A simple communication system using these modules was studied. The error behavior was as expected. The key problems identified in this development were systems issues; primarily, module initialization and synchronization.
Performance of various computers using standard linear equations software in a Fortran environment
Authors: Dongarra Jack J.
Published: March 2008

This note compares the performance of different computer systems while solving dense systems of linear equations using the LINPACK software in a Fortran environment. About 100 com puters, ranging from a CRAY X-MP to the 68000-based systems such as the Apollo and SUN Workstations to IBM PC's, are compared.
Visual Interactive Simulation — History, recent developments, and major issues
Authors: Bell Peter C. , O'Keefe Robert M.
Published: March 2008

Visual Interactive Simulation (VIS) has dominated discrete-event simulation in the United Kingdom throughout the eighties. Con ceived and initially implemented by Hurrion (1976), who also coined the phrase, VIS first gained widespread exposure through the package SEE-WHY The ideas behind VIS are fundamentally different from what is referred to in the United States as anima tion, since the prime motivator is user interaction with the run ning simulation, rather than just portrayal of the simulation.

After presenting a short history of VIS, we will discuss some of the research and development that has been undertaken in the United Kingdom and North America. Following presentation of an example, the state of VIS and a number of generally accepted guidelines for doing VIS are discussed.

A number of recent developments, many of them also relevant to animation, and four major issues in the research and prac tice of VIS are presen ted.
Expanding the domain of systems analysis
Authors: Brannen J.P. , Hiebert-Dodd Kathie L.
Published: March 2008

Systems often contain a human component. The human reacts, interprets, errs, ..., succeeds or fails. However, usual analyses of such systems omit the human component, concentrating instead on the, more easily analyzed, software and hardware subsystems. A technique has been developed for including human decision processes by the use of an expert system in a systems analysis. This technique is applied to a surveillance system consisting of sensors which respond to stimuli and the interpretation of these responses by humans. The analysis is carried out via simulations of hardware responses to stimuli, simulations of human inter pretations of those hardware responses, and a measure of the performance of the total system. While the technique was ap plied to a particular system, the inclusion of simulations of human decision processes is essentially independent of the application.
Parallel continuous system simulation using the Transputer
Authors: Hamblen James O.
Published: March 2008

Parallel processing methods can be used to decrease the solu tion time of simulation models. Techniques are shown for the parallel solution of a continuous system simulation using digital hardware. Using a new VLSI single chip computer, the TRANS puter, a simple parallel digital computer system is constructed and its performance is evaluated on two example problems.
On spacecraft attitude display
Authors: Mukundan R.
Published: March 2008

A calculation minimised procedure for the graphics display of spacecraft attitude changes is presented. Based on the attitude errors, the body orientations with respect to two fundamental reference frames are computed and plotted using multiple view ports. The display is continuously updated with the help of dou ble buffering techniques on a bitplane-oriented screen. As an alternate scheme, the use of segment definitions is considered. Computation time as well as device overhead are effectively reduced by appropriate choice of the mathematical model and related hidden surface algorithm. Also discussed is the extension of the procedure for complex surface geometries and under pro jections along arbitrary directions.