bluuebunny/crossref_metadata_2025 huggingface dataset:
Parameter identification in models of hydrologic systems using the digital simulation language PDEL
Authors: Tam Wing Cheung , Karplus Walter J.
Published: March 2008

Hydrologic systems, like most environmental systems, are usually characterized by partial differential equations. In order to develop a suitable mathe matical model for the analysis of such systems, it, is first necessary to make use of observed data in order to identify or estimate the system parameters. The digital simulation language PDEL has been ex tended so as to facilitate this type of parameter identification. The extended version of the lan guage has been named PDEL-ID. In this paper, two hydrologic modeling problems taken from recent water-resource studies are used as examples to illustrate the parameter identification facilities of PDEL. The solution of these two problems demon strates that little programming effort and virtually no knowledge of optimization techniques are required.
Simulation as an Aid To Understanding Cognitive Processes
Authors: Newsted Peter R.
Published: March 2008

Computer simulation of cognitive processes requires con structing an explicit model of human thinking behavior in the form of a computer program. Such a program cannot avoid being explicit and unambiguous. Thus it serves as a hypothesis to be tested against the corresponding human behavior. Models that don't "work" suggest questions to ask.

Recent work in simulating cognition suggests that the basic elements in cognitive processes are attention, conscious ness, and memory. In this paper, a hypothesis is presented describing probable interactions among these elements for a simple cognitive process. To facilitate simulation a paradigm is presented which characterizes experimenter subject interactions in such a way as to allow an investiga tor to more easily attempt a simulation. A sample simu lation of concept identification behavior is included to illustrate the use. of this paradigm.
Diode circuits for 10V digitally-set analogue computers
Authors: Charlesworth Alan S.
Published: March 2008

It does not seem widely known that there exists a number of diode circuits which do not exhibit 1/2-volt errors but do contain pots whose settings can be precalculated. This paper gives eleven such circuits which are admirably suited for the simula tion of nonlinearities on 10-volt analogue computers that have digitally set pots.
A general - purpose hybrid interface for a minicomputer
Authors: Jarvis R.A.
Published: March 2008

This paper describes a multichannel general-purpose hybrid interface for a minicomputer and illustrates its use in a number of on-line experiments. The in terface was designed with emphasis on simplicity, economy, and the possibility of convenient logical reconfiguration as dictated by the requirements of usage.
The course of French society (1955-73) — a simulation
Authors: Rastogi P.N.
Published: March 2008

This paper analyzes the course of French society in terms of the time path of a set of variables: exoge nous politico-military pressure, economic growth, unemployment, price rise, population growth, ethnic tension, public unrest, administrative effectiveness, expectations of socii, and an overall measure of societal viability termed Government Stability (Z or GS). The variables reflect the performance of interacting societal institutions that together constitute a complex adaptive total-society system. Government operates as the regulatory subsystem of society.

The values of the variables during a given period represent the state of the system. They are ob tained through a simulation algorithm which simu- Zates a societal flow graph representing the pattern of internal system dynamics. The extension of simulation to past and future periods permits retrodictive confirmation and predictive inference. The correspondence and consistency of the generated results with the reported and available data makes possible the validation of the analysis. The simu lation algorithm, which is applicable to all socie tal systems, is here applied to chart the course of French society for the two decades from 1955 to 1973. Values of economic growth, price rise, unemployment, and change of government generated by simulation are directly confirmable from known empirical facts. The confirmation of qualitative variables like ethnic tension, administrative effectiveness, and expectations of socii as gener ated by the model is, however, based on inference. They conform to the broad empirical pattern as outlined in the secondary sources of data.
Similarity between computer control systems and community planning
Authors: Light Richard A. , Johnson R. Curtis
Published: March 2008

The planning of a community's development and opera tions, whether for a small town or an international project, requires the allocation of resources to various areas of endeavor. These resources can best be allocated if a reasonably accurate estimate is made of the needs for corrective action and the effectiveness of it as a function of the type and amount of expenditure. For example, an estimate may be made of the amount of pollution and social conflict which may develop and of the effectiveness of various physical and human countermeasures (sewage disposal facilities, air pollution control, police, hospitals, etc.); on this basis a reasonable allocation may be made. Such a procedure forces one to establish value systems in order to assess social costs on a basis compatible with real costs. This is difficult. Few planners understand the philosophical and long- term implications of their actions.

The approach adopted in this paper bears great similarity to optimal process control by computer, but it cannot solve problems unless suitable value systems can be established. Even when values cannot be adequately established, however, this approach to examining community problems allows decision- makers to better understand the implications of their actions. This approach helps educators to better plan programs which differ from the tradi tionally narrow engineering curricula and to intro duce the concept that technical tools and techniques have important applications in politics and philosophy.
A new single-step implicit integration algorithm with A-stability and improved accuracy
Authors: Brandon Daniel M.
Published: March 2008

This report describes and illustrates a new nonlinear single-step implicit method for the numerical integra tion of general differential systems. The method is A-stable, operates with fixed or variable step size, is computationally fast, and has accuracy comparable to or better than that of other widely used methods. This paper reports computational experiments using this new method and compares the results with those obtained using other integration algorithms, includ ing high-order methods. The comparisons are generally favorable to the new method. The method is applicable to both "stiff" and "nonstiff" systems. On stiff systems the new method was much more accurate than any of the other algorithms tested.
A generalized model for simulating lake ecosystems
Authors: Park Richard A.
Published: March 2008

CLEAN, a generalized lake-ecosystem model with strong ecological realism, has been developed in response to one aspect of the growing need for models suitable for helping man to manage his environment. The model currently consists of twenty-eight ordinary differ ential equations which represent approximately six teen compartments, including attached aquatic plants, phytoplankton, zooplankton, bottom-dwelling aquatic insects, fish, suspended organic matter, decomposers, sediments, and nutrients. These equations can be linked in any meaningful combination to simulate a given point in a lake (a separate model for lake cir culation is available to represent spatial variations and to couple simulations of different regions of the lake). Subprogram functions exist for each principal physiological and ecological process, and a submodel for lake water balance is presently being implemented. The program is written in FORTRAN for UNIVAC and IBM time-sharing systems.

The model has provided intuitionally realistic simu lations and has given us insight into the effects of nutrient enrichment on the functioning of the lake ecosystem as a whole. Sensitivity analysis has in dicated priorities for further studies to obtain more precise estimates of parameters. Also, evalua tion of the logic and organization of the model by experimenting with it are providing information to use in planning new experimental approaches. CLEAN is presently being tested using data from Lake George, New York, and Lake Wingra. Wisconsin.
Gasp IV urban model of cadmium flow
Authors: Talavage Joseph J. , Triplett Mark
Published: March 2008

The 60-square-mile region of extreme northwest Indiana, which includes the cities of Gary and East Chicago, is a highly urbanized and industrialized area. Pollution data over the region show high levels of cadmium, a toxic metal. There are several hundred sources of cadmium in the area, and the impact of each type of source is unclear. An accurate representation of the flow of cadmium would make it possible to structure a reasonable and efficient policy for controlling cadmium pollution. This paper describes a GASP IV computer model for that flow.

The basic model is an aggregate continuous model which displays the time behavior of cadmium levels in each of nineteen compartments over a two-year period. This aggregate model raises several ques tions regarding the effects of discrete events such as rainfall. Since the GASP IV language is capable of combined continuous-discrete simulation, these new factors are easily incorporated into the model. Results of the simulation show the relative impact of the various types of sources and provide some insight into control policies.

A continuous model was first constructed. Then modifications based on real-world data were implemented as discrete events. The successive forms of the model proved useful for studying at least two of the characteristics of cadmium flow in an urban ecosystem.
Insurge transients from a surge tank using CSMP
Authors: Cheng S.C. , Kulkarni K. , Birta L.G.
Published: March 2008

The Continuous System Modeling Program (CSMP) has become a widely used tool in simulation studies of engineering systems. This paper discusses one such application which involves the study of insurge transients from the surge tank of a nuclear reactor. The handling of the problem requires the simultaneous solution of the Fourier heat conduction equation together with an ordinary differential equation which describes the pressure variations in the surge tank. The results from this study are in good agreement with available experimental data.
Diogenes revisited -the search for a valid model
Authors: House Peter W.
Published: March 2008

PETER W. HOUSE has, since November of 1971, been with the U.S. Environmental Protection Agency where he is assistant director of the Washington Environ mental Research Center in the office of Research and Development. He is the former president of Envirometrics, Inc. During his four and one-half years at the Washington Center for Metropolitan Studies and Envirometrics (April 1967-October 1971) he directed the development of three urban operation al simulation models, including the CITY models and the RIVER BASIN MODEL.

Dr. House received his master's degree in economics from Clark University and thereafter went to work for the U.S. Department of Agriculture as a research economist in the Economic Research Service (ERS). During his tenure at ERS (February 1960-March 1967) he performed a number of studies concerning suburban/ farmland and preferential tax assessment, and was selected to attend Cornell University to complete work on his doctorate.

Currently, at EPA, Dr. House and his staff conduct studies and develop forecasts which can move EPA to a position of being able not only to enhance the environment but also to provide for long-term preven tion of pollutants. He is project leader of the team responsible for development of the Strategic Environmental Assessment System (SEAS).

Two books under his authorship have recently been published: The Urban Environmental System: Modeling for Research, Policy-Making and Education, published by Sage Publications: and, with Edward R. Williams, The State of the System (SOS) Model, published by EPA.
CHINA 1: a model of growth for the People's Republic of China
Authors: Brinton William , Rosenberg Gerald H. , Wolfe John
Published: March 2008

This paper describes a simulation model of population growth in the People's Republic of China from 1953 to 2103. Our model, CHINA1, is based on the WORLD3 model of D. L. Meadows et al., and thus it analyses population growth in the context of a large, inter related economic and environmental system. It assumes that China will continue her present policy of material self-sufficiency. Model simulation runs based on current trends in China show continued population growth well into the twenty-first century, despite a falling birth rate. A precipitous decline in population then ensues due to resource depletion, collapse of the industrial sector, and mass starva tion. Policies designed to avert such an outcome are tested in the model. The simulation indicates that a successful policy must include all of the following:

1. The family size norm declining to two children by 1985

2. Industrial output per capita stabilizing at the level projected for 1990

3. Dependency on nonrenewable resources lessening over the long-run.
Ecosystem simulation through use of models of subsystem response structures
Authors: Maguire Bassett
Published: March 2008

Every system has specific kinds and levels of re sponses to conditions as they exist and change in the environment in which the system is immersed. Each response can be expressed quantitatively by a structure in N- dimensional space, where N refers to the number of different environmental factors which operate together to determine the level of that response, and each dimension represents one of the determinative environmental factors. Examination via this response structure of the relationship between environmental factor levels and the system's response permits analysis and modeling of the system's dynamics and allows accurate evaluation of its relationships to other systems. This paper in cludes examples of use of this approach in the modeling of the ecological processes of population growth, competition, predation, and evolution, and it presents a model of a simple hierarchical eco system. Suggestions are made concerning the utiliza tion of this analytical and heueristic approach to examine other, very different systems; brief examples from economics, public health, and social psychology are given.
A composite approach to generating autocorrelated sequences
Authors: Fraker John R. , Rippy Douglas V.
Published: March 2008

In this paper a procedure is developed for internally generating autocorrelated sequences of variates for use in simulation of systems such as production- inventory systems, queueing systems, and economic systems. The procedure is based on the composite method, or method of mixtures. The procedure permits specification of the mean and variance of the dis tribution of variates, the magnitude and direction (positive or negative) of the lag-1 autocorrelation of the sequence, and the general form of the distrib ution. In general, the procedure does not permit specification of higher-order moments or higher-order lagged correlations. An illustrative example is included. A flow chart for the procedure is given, and a GPSS program is available.
Correlated simulation experiments
Authors: Fishman George S.
Published: March 2008

This paper studies the effects of using correlated random-number streams in replications of a simula tion experiment in which output is to be related to input by linear or quadratic response surfaces. For the linear case, it is shown that either positively or negatively correlated streams produce a smaller generalized variance for the least-squares estimates than occur when the streams are independent. Al though the prediction variance is small with nega tively correlated streams, positively correlated streams produce a smaller variance for the estimated slope.

In the quadratic case it is shown that of twenty- seven possible input correlation designs only six guarantee a smaller generalized variance. Only one of these produces a smaller prediction variance. However, no plan will guarantee a smaller slope variance. In the quadratic case one often wants the slope variance to be as small as possible since the objective of the study may be to determine where the maximum or minimum response occurs in terms of the input.
Simulation program generators
Authors: Mathewson Stephen C.
Published: March 2008

This paper introduces the concept of a general inter face between simulation models and simulation pro gramming languages. The interface is a program generator. The simulation model is represented in a symbolic form through an entity-cycle diagram. Three program generators are cited, and examples of two are given. The advantages of the technique are discussed.
Exploration of a Menstrual Cycle Model
Authors: Best Eric N.
Published: March 2008

This paper reports on the exploration and use of a sim ulation of the human menstrual cycle published in the July 1972 (Vol. 35, No. 1) issue of The Journal of Clinical Endo crinology & Metabolism by R. J. Bogumil, M. Ferin, J. Rootenberg, L. Speroff, and R. L. Vande Wiele. The simula tion appears to duplicate well the cyclic hormonal fluc tuations of a normally ovulating woman. But when asked to duplicate the results of giving a woman exogenous es tradiol, the simulation produces results which are in dis agreement with other published research data. Extrapo lation from the reported simulation beyond the normal undisturbed cycle produced results that do not agree with published physiological data, suggesting that the model needs further refinement. However, simulations run using the model indicate the possibility of stopping the menstrual cycle by a properly timed application of the hor mone estradiol (E2).
Analysis of Harvesting, Loading, and Transportation of Farm Grains
Authors: Baker C.H. , Horrocks R.D. , Braaten M.
Published: March 2008

Selecting harvesting equipment for greatest capacity is often a compromise between excess capacity for some years and too limited capacity for others. We expected that the harvester capacity producing the highest long-run profit would also produce a higher year-to-year variability of profit than would a larger-capacity machine which would also produce a lower long-run profit. To balance the long-run profit against the higher risk, the decision- maker needs a measure of the risk involved.

Simulating production systems is an effective way to develop decision-making information. Trans forming observations of the behavior of real-world systems into the kind of information which can form a basis for decisions is a challenging task in agri cultural-production systems. This paper discusses a harvesting and transportation system simulator that can help the decision-maker to determine the size and amount of machinery needed to complete a har vesting operation in a given amount of time.

Inputs to the model include the size and number of fields and their distance from a farm elevator, elevator and storage-bin sizes, combine and truck sizes, and certain timeliness factors such as dryer time and trips per day to market. The simulator was tested and found to be logically correct.
Evaluating analog-to-digital converters
Authors: Polge R.J. , Bhagavan B.K. , Callas L.
Published: March 2008

Dynamic performance of an A/D converter cannot be assessed by conventional tests since they employ slowly varying inputs. In this paper, a digital computer procedure is developed to determine the presence and extent of errors due to time jitter, nonlinearity, gain, quantization, and locked bits. The procedure is based on discrete power-spectrum analysis of recorded outputs of the A/D converter using a weighted or nonweighted sine wave input. In the latter case, a discrete weighting of the recorded output must be performed before power-spectrum analysis. Outside of the narrow band containing the signal spectrum, the power spectrum corresponds to the errors in the A/D converter.

Error models are suggested and implemented in a simulation program which is executed to show the power spectra for various combinations of errors. On this basis an A/D converter evaluation procedure is proposed and illustrated by an example.
Generation of forcing functions for evaluating performance at the man-machine interface
Authors: Sherwood Arthur M. , Sengupta Debasis
Published: March 2008

The evaluation of the performance of individuals or devices at the man-machine interface can, in most instances, be accomplished through the simulation of typical dynamic tasks. This paper describes a simple, flexible technique for the generation of waveforms for use as forcing functions in such situations. The technique uses an analog computer under the control of external digital logic. A one-dimensional tracking problem illus trates the use of the technique. Diagrams and all relevant parameters for this problem are given. The simulation system creates a straight-line- segment graph to control the target. The system includes an automated scoring feature with digital printou t.
Simulation of secondary autogenic succession in the shortgrass prairie ecosystem
Authors: Gutierrez Luis T. , Fey Willard R.
Published: March 2008

Ecological succession is the process that dominates the dynamic behavior of ecosystems as they proceed from immaturity to a stage in which the living com munity achieves equilibrium with its physical envi ronment. Secondary succession refers to the tran sients that arise in response to a perturbation of a mature ecosystem. The growth-then-saturation dynamic pattern associated with this process is well known, but not well understood. The research reported in this paper formulates a dynamic model embodying a hypothesis to explain successional modes of behavior as they arise from the internal feedback structure of the ecosystem, and tests it by means of simulation experiments. The general structure of the model is based on Odum's tabular model of ecological succession;16 it traces the mutual causalities between energy, living and non- living matter, and the diversity of species as they interact in time and space to produce succession. The equations are derived from grassland observations and research, biological theory, and logical neces sity. Simulation results are shown for secondary succession in a shortgrass prairie ecosystem. The simulated patterns exhibit consistency with the over all successional patterns observed in nature. Pro spective generalizations of the model to account for successional dynamics in grasslands and other eco systems are pointed out.
Corporate simulation models: a survey
Authors: Naylor Thomas H. , Jeffress Charles
Published: March 2008

Within a period of less than five years, computer- simulation techniques have penetrated corporations in the United States, Canada, and Europe at the highest possible level. This paper summarizes the results of a survey of 346 corporations, most of which are either using, developing, or planning to develop some form of corporate simulation model. Among the questions addressed by the survey for which empirical answers have been sought are: Who is actually using corporate simulation models? Why are they being used? What resources are required to develop them? What techniques are employed? How much do they cost? What are the benefits to be derived from their use?

The paper concludes with a series of specific recom mendations for improving the effectiveness of cor porate simulation models. First, corporate models should be made more user-oriented. Second, more attention needs to be given to the production acti vities of firms. Third, the possibility of inte grating optimization models into corporate models needs to be explored further. Fourth, financial, marketing, and production models should be linked together. Fifth, the use of models to simulate the global environment of corporations should be con sidered. Sixth, greater emphasis should be placed on the "politics" of corporate model building.
An introduction to bond-graph techniques for biomedical system modeling
Authors: Margolis Donald L.
Published: March 2008

Since engineers need to have reasonable competence in mathematics but practioners of the medical profes sions need not, the two groups often find it hard to work together in biomedical research. A key area in which such cooperation is essential is the building of models. This paper shows how the bond-graph technique may be used to develop linear dynamic models of biomedical systems that can be implemented on a digital computer. This technique requires vir tually no knowledge of mathematics, numerical methods, or computers, thus removing a communications barrier between the two groups. The technique is illustrated by applying it to a case taken from the biomedical literature. The result is a "whole-body model" which is useful in determining comfort factors which affect the design of suspension systems for passenger vehi cles. This paper shows how the physical model was represented by a bond graph and how this representa tion could be converted into a digital-computer model yielding engineering design data for a comfortable suspension system.
A simulation model for studying the needs for correctional institutions
Authors: Bateman Barry L. , Doescher Allen L.
Published: March 2008

A digital-computer simulation model of the incar ceration rates and characteristics of criminal offenders was developed and used to study the needs for developing new correctional institutions. The model gives insight into the snarls and pitfalls of the system and allows alternate plans to be studied prior to actual implementation. The data from an actual multicourt system are presented in detail.
TACL - a timeshared hybrid system for control laboratories
Authors: Volz Richard A. , Aravena Jorge
Published: March 2008

A generalized control-system model encompassing a wide variety of systems has been programmed on the analog portion of a hybrid computation system. Five terminals with storage oscilloscopes are con nected to the hybrid computer and are serviced on a round-robin basis. The generalized system can be configured in milliseconds to a specific problem by setting the values of the digital coefficient units and switches of the analog system. A library of specific problems is kept on the system's digital disk. Students use the system by referencing a problem in the library and entering parameter values to define the problem from their terminals. The per-solution time varies with the time scale seZect ed, but averages around a few hundred milliseconds. A user-oriented compiler helps the instructor define new problems to be added.

Digital values are assigned by the student to select ed parameters of specific problems, and families of curves representing system performance as a function of control settings may be displayed on the student's terminal. The terminals also display digital data and alphanumerical information.
A model for prediction of world food production and allocation
Authors: DeWitt Calvin B.
Published: March 2008

This report presents and documents a computer model of world food production and allocation whose purpose is to serve as an organizational framework, a heur istic tool, and a basis for development of future models in the study of the world climate/food system. The assumptions upon which this model is based are not fully realistic since they do not take into account the constraints of data availability; nor do they adequately deal with the yet-but-little-under stood components and linkages of the climate/food system. Yet this model provides a basis upon which successively better models will be built. It pro vides the starting point for the evolution of a series of models toward one whose response to the various climatic, technological, and human inputs is sufficiently similar to the response of the real system to make it useful as a predictive and heuris tic policy tool.
Simulation of cell-cycle kinetics based on a multicompartmental model
Authors: Jansson Birger
Published: March 2008

Biological cells, healthy or malignant, perform in most respects similar activities:

(a) They proliferate by growing and maturing and, after reaching a certain level of maturation, they divide into daughter cells.

(b) They differentiate by changing irreversibly to new types of cells.

(c) They compete by participating in ecological struggles with other cells that share the same ecological niche. Through the principle of com petitive exclusion, slower-dividing cells may be eradicated from a mixture of cells.

This paper presents a mathematical model of the above processes and describes a computer simulation which includes the effects of chemotherapy or radiation therapy on a system consisting of healthy and malig nant cells. The simulation develops qualitatively and quantitively the kinetic properties during treat ment of the mixture of the two types of cells in tissues and shows how the favorable protocols for treatment can be found. Such knowledge can, among other things, be used to devise good strategies for the treatment of cancer by radiation or chemotherapy and to increase the efficiency of research in their use.

The example described is a simplified one in which only two types of cells are considered, but the simu lation model can be applied to much more complex and realistic situations.
Digital computation of frequency response
Authors: Mitchell E. Eugene , Olsen Charles F.
Published: March 2008

This paper describes three algorithms for the digital computation of the frequency response of linear sys tems and discusses their advantages and disadvantages.

The third method presented is a novel one which applies the standard polynominal quadratic synthetic division algorithm in a unique way to the problem. The method allows the forward and feedback-path transfer functions to be inputted in any form; it computes the open-loop and closed-loop frequency responses in one pass; and, most importantly, it does not require numerical factoring at any point. The method is easy to use and appears to run effi ciently, particularly for high-order systems. The paper concludes with FORTRAN and BASIC programs which implement the algorithm of Method Three.
Synthesis and simulation of systems possessing ferromagnetic hysteresis
Authors: Davis Artice M.
Published: March 2008

Ferromagnetic hysteretic behavior is a particularly complex phenomenon; it can actually be construed as the response of a large-scale system consisting of interacting magnetic domains. The problem of simula tion of systems containing one or more ferromagnetic devices is correspondingly very difficult. Classical modeling attempts have suffered on the one hand from complex mathematics unsuited for practical implemen tation and on the other from simplistic models that retain no connection with underlying physical processes. The model developed in this paper is of a phenomenological nature; yet it bears rather close correspondence on an energy-exchange level with the physics of ferromagnetism. The basic mathematical model has the nature of a mechanical analog that possesses the same qualitative features as ferro magnetic material. It is a planar representation on which a systems-theoretic state-space analysis is performed. A method for estimation of the model parameters is outlined, and simulation results are compared with experimental data for an iron-core toroid.
HAPS, a Handy Analog Programming System
Authors: Højberg K. Søe
Published: March 2008

HAPS (Hybrid Analog Programming System) is an analog compiler that can be run on a minicomputer in an interactive mode. Essentially HAPS is written in FORTRAN. The equations to be programmed for an ana log computer are read in by using a FORTRAN-like notation. The input must contain maximum and minimum values for the variables. The output file includes potentiometer coefficients and static-test 'measuring values.' The file format is fitted to an automatic potentiometer-setting and static-test program. Patch instructions are printed by HAPS.

The article describes the principles of HAPS and emphasizes the limitations HAPS puts on equation structure, types of computing circuit, scaling, and static testing.
Dynamic simulation of ferromagnetic hysteretic behaviour by digital computer
Authors: Hay John L. , Chaplin Robert I.
Published: March 2008

A model is presented which produces the locus on the B-H plane of a ferromagnetic specimen subject to dynamic operating conditions. The model accurately represents the magnetisation curve and the saturation Zoop as well as exhibiting the correct inner loop behaviour. The concept of a primitive magnetic eZe ment is introduced, and the paper illustrates how a finite number of these elements may be combined and their characteristics chosen so as to represent the hysteretic behaviour of a ferromagnetic device. Validation is achieved by comparing experimental and computed results for both symmetrical and asymmetri caZ inner Zoop behaviour. The incremental inductance of an electro-magnetic device may be readily calculat ed from the proposed model which is presented in a form suitable for either digital or analog computer simulation.
Practical and ethical issues of development in traditional societies
Authors: Picardi Anthony C.
Published: March 2008

The results of a system dynamics model of pastoralism in the sahel region of West Africa are presented and analyzed, and the conclusion is drawn that not all the desired objectives for developing the region can be attained simultaneously. The fact that practical tradeoffs exist leads to a consideration of some ethical issues which may enter into the choice of alternative development policies.

The principal data source for this study is the sahel and subdesert region of Niger north of Tahoua, where herdsmen practice traditional animal husbandry, seeking pastures in the north during the rainy sea son and descending south toward the agricultural zones in the dry season. The probable effects of aid efforts in the past were analyzed, with the con clusion that if they had any effect at all, it was to increase the severity of the drought disaster in both ecological and human terms.

A set of seven desirable long-term objectives is defined and policies to achieve them are simulated. The simulation results indicate definite tradeoffs among the desired objectives. The existence of mutually exclusive attainable objectives leads to a consideration of the ethical issues involved in the choice of alternate development policies.

This case study serves as an example of how system dynamics may be used to reduce complex social prob- Zems to a set of relevant ethical questions.
Hybrid simulation- key to successful flight-test program
Authors: Driscoll Thomas R. , Eckenroth Howard F.
Published: March 2008

The purpose of this paper is to focus on the applica tion of modern analog- and hybrid-computer analysis techniques for both the planning of control test vehicle (CTV) flights, which was instrumental to the success of the flights, and the verification of the design of the missile. The hybrid simulation had features generally not available in existing programs and reflected major advancements in simulation and modeling technology. It permitted tolerances to be analyzed by use of either the individual parameter variation or the Monte Carlo approach. Error sources were modeled as they existed in the actual hardware.

The SAM-D hybrid simulation program was designed to use automatic data-reduction techniques to provide the analyst with detailed technical data on both nominal and toleranced flight performance. Special routines allowed statistical predictions to be made on all important parameters within the system to en sure that all requirements were met under toleranced conditions. The use of a detailed hybrid simulation, including nominal and comprehensive tolerance models, and of automatic data-reduction techniques, provided a high degree of confidence in a successful flight under all possible military flight conditions.

The simulation program described herein was supported by a comprehensive wind-tunnel test program and other subsystem ground tests to provide input data of high quality compatible with the extent of the detailed simulation. The value of this approach to modern flight-vehicle design was confirmed by the close agreement between predicted and flight-test data. Thus the simulation not only enhanced the success of the flight tests, but also enabled the simulation to be used for evaluating system performance under conditions not covered by flight tests.
Simulation of a multistage domestic heating system
Authors: Eltimsahy A.H. , Woeller J.W.
Published: March 2008

This study compares the performance of a single gas- fired conventional domestic space heater with that of the same conventional heater in combination with a smaller auxiliary heater. The auxiliary heater could be a solar heater or could obtain its energy from more conventional sources. The auxiliary heater is presumed to have a shorter time constant than the main furnace. As room temperature falls below the present temperature, the auxiliary heater turns on before the main furnace, but turns off when the main furnace comes on. In the study the following param eters were varied:

Hysteresis of the main furnace's thermostat Hysteresis of the auxiliary heater's thermostat

Time constants of the controller, main furnace, and auxiliary heater

The size (heat output capacity) of the auxiliary heater as a percentage of the size of the main furnace.

The outputs recorded were temperatures variations of the room air and the cycling time of the system. In each case results are plotted as a function of the relative size of the auxiliary heater for 3 values of one of the time constants, the other two time con stants and the hystereses of the thermostats being held constant. Operating conditions were a set point temperature 70°F (21°C) for room air and an outdoors air temperature of 0°F (-18°C). In all cases examined the system with the auxiliary heater produced more uniform room temperatures. Shortening the time constants of the controller and the auxiliary heater reduced variations in room temperature.
Finding quadratic factors by an analog minimization procedure
Authors: Tang I.
Published: March 2008

A method is developed for the analog computer using a minimization process to find quadratic factors of a polynomial.
On-line simulation of solar systems heating
Authors: Eltimsahy A.H. , Copass C.H.
Published: March 2008

This paper deals with the programming of a minicom puter system which is connected to a small solar heating system to create a model of a larger solar heating system. The program enables the computer to serve as an on-line control and real-time data col lection system. The small solar heating system is heavily instrumented to provide dynamic input data to the computer. The output of the computer program simulates the operation of a much larger solar heat ing system. This combination of software with the hardware has proven to be a broadly useful research tool for solar-heating investigations. This paper describes both aspects of the simulation model.
Program- generation system for modern hybrid computers
Authors: Landauer J. Paul
Published: March 2008

This paper describes the use of a new integrated hybrid programming system which provides equation- oriented specification of continuous-system simula tion models. The programming system also provides automated setup, checkout, and operation of the hybrid computer. It is based upon the APSE compiler originally developed through the National Computing Center in England and the HYTRAN ® Operations Interpreter (HOI) implemented on EAI hybrid computers. The new program-generation system uses analog and digital processors that have been enhanced in order to enrich the programming languages used and to pro vide compatible analog and digital file-processing. This enables the computer to automatically generate a complete HYTRAN object program file which is processed on-line by the hybrid system for setup, checkout, and operation of the analog processor. The benefits of automatic program generation over the manual process include significant reduction of programming difficulty, time, and cost, error-free program setup and operation, and increased producti vity for both all-analog and hybrid simulations.
Data enrichment for simulation
Authors: Kaplan Alan , Orr Donald A.
Published: March 2008

Data enrichment in the present context is concerned with the creation of a stochastic time series whose parameters are consistent with a prior data base and whose cumulative values over a given period satisfy constraints dictated by the prior data base. The specific problem is to generate statistical data for shorter time intervals than the raw data provides. The need for this type of enrichment arises, for example, when historical data gives total demand in each quarter over a multiyear period but the output of a simulation is sensitive to the manner in which demand is distributed over each quarter.

The method utilizes a random fraction to select re cursively a portion of the remaining demand in a quarter. Formulae for the mean and variance of the random fraction are derived. This random fraction can be computer generated with a single random number using hybrid spike-uniform distributions with given means and variances. The properties of such dis tributions are derived, and may have applications in other contexts.
An interface to link dynamic system models
Authors: Miller James H. , Brosilow Coleman B.
Published: March 2008

An interface is developed to link general-purpose simulation processors such as MIMIC and CSMP to sub system computer models containing their own integra tion routines.* Implementing the interface requires no modification of CSMP and only simple additions to MIMIC.

Tests using the interface to link subsystem models with CSMP and MIMIC programs showed substantial increases in computing efficiency over carrying out the same simulation with only a general-purpose pro cessor. The test cases consisted of stiff systems surrounded by control loops. The control loops were modeled using the general-purpose simulation languages, while the stiff systems were modeled with FORTRAN subroutines incorporating appropriate integration algorithms.
Using common random numbers in simulation experiments — an approach to statistical analysis
Authors: Heikes Russell G. , Montgomery Douglas C. , Rardin Ronald L.
Published: March 2008

A widely applied method of experimental design in stochastic simulation is to use the same pseudo random-number stream for each of the systems or alternatives to be compared. If there are only two alternatives, there is a well-known simple method of statistical analysis. This paper presents Graybill's3 extension of that analysis technique to the case of several systems or alternatives and points out its applicability in the simulation environment. The technique is illustrated using a stochastic simula tion model of a small inventory system. An empirical comparison with other methods of design and analysis is included.
Optimum shuttle scheduling — a GPSS simulation
Authors: Ragazzini John F. , Tapiero Charles S.
Published: March 2008

This paper studies the operating policies of a two- station shuttle system consisting of a fleet of finite size and vehicles of finite capacity which transport passengers between two terminals (each terminal having dispatching control). Passengers arrive at either station according to independent negative exponential processes, and dispatching deci sions are made on the basis of fixed-time intervals or queue lengths (greater than zero). The objective is minimization of a total opportunity cost function defined by passenger waiting time, nonutilization of vehicles, and unused passenger seats. The travel time is probabilistic with known distribution and mean. This paper shows by GPSS simulation techniques that optimal values for any or all of the three variable parameters (fleet size, vehicle capacity, dispatching interval) can be empirically determined through sensitivity analysis. The simulation model constructed is flexible and can be adapted to a wide variety of other problems of the shuttle-system genre.
On the information content of a discrete-event simulation model
Authors: Davies N.R.
Published: March 2008

Programming systems such as DRAFT1 and ECSL2 generate a discrete-event simulation program from the user's response to a man-computer dialogue or questionnaire about a life-cycle diagram. This paper examines the function of a program generator in the light of in formation with which it must be supplied. This in formation is classified into information which is fundamental to the structure of the model and that which is dependent on a particular simulation program ming language or the details of a particular program run. The language-independent information is summar ised in an activity-based descriptive unit. An inter active program generating system10 is described in which a file of descriptive units forms a link between two on-line questionnaires. The first asks the user to define the underlying structure of his model, while the second asks for information which is pecu liar to the simulation programming language in which a program is to be generated and for information about a particular run.

The system differs from others in offering the user a choice between three questionnaires, each of which incorporates the terminology of a different model ling scheme. They enable the user to define his model in terms of (a) event routines appropriate to a two-phase event-oriented simulation programming language such as SIMSCRIPT,5 (b) bound and conditional events as for a three-phase language like SIMON,6 and (c) life-cycle diagrams.4 The system can easily be extended to generate programs in any simulation pro gramming language for which a compiler becomes available.
Signal flow graphs for electroacoustic transducers (or modeling made easy)
Authors: Ashley J. Robert , Ciletti Michael D. , Wiatrowski Claude A.
Published: March 2008

The simulation of an electroacoustic transducer such as a loudspeaker system requires a mathematical model that can serve as the basis for building a computer model. We have three kinds of elements in a loud speaker : electrical, mechanical, and acoustical. Understanding the model and the results of the simu lation suggests that we not follow the traditional path of converting the mechanical and acoustical eZe ments to equivalent electrical elements to form an electrical network as the model to study. Instead, we have found it easier to follow a scheme originally suggested by Larrowe1,3 and form a model based on stating all physical laws in an integral formulation. In modern notation, this is simply accomplished by drawing a signal flow graph as a mathematical model of the system. The resulting signal flow graph (if we use the "right" technique) has an optimum set of state variables in the sense that all quantities are of clear physical significance in the system. For a loudspeaker system, the state variables turn out to be voice-coiz current, voice-coil velocity, voice- coil displacement, cabinet pressure, and volume velocity at the vent. Once this signal flow graph has been drawn, an analog computer model can be formed by proper insertion of minus signs and scale factors. The state-variable differential equation read from the signal flow graph can be converted to a phasor equation and then solved by complex matrix inversion. A time-shared computer terminal or a minicomputer programmed in BASIC is a convenient way to implement a digital simulation of an electro acoustic transducer.