Showing papers in "Simulation in 1982"
TL;DR: A tradeoff analysis can be made to help the modeler decide on a data collection method and budget, the number of observations to collect, and suitable model builder's and user's risk levels for testing the validity under a given set of experimental conditions.
Abstract: A procedure is given for using Hotelling's two-sample T2 test to test the validity with respect to the mean behavior of a multivariate response simulation model that represents an observable system. A tradeoff analysis can be made to help the modeler decide on a data collection method and budget, the number of observations to collect, and suitable model builder's and user's risk levels for testing the validity under a given set of experimental conditions. A model of an M/M/1 queuing system with two performance measures serves as an example for the validation procedure.
51 citations
TL;DR: In this paper, a simulation model of the flow of activities comprising Shuttle turn around processing is developed to assess the feasibility of proposed launch schedules for the Space Shuttle, and the results of an extensive sensitivity analysis indicate that the currently projected schedules are optimistic and that the turnaround time will substan tially exceed the current goal of 28 days.
Abstract: To assess the feasibility of proposed launch schedules for the Space Shuttle, we have developed a simulation model of the flow of activities comprising Shuttle turn around processing. Considering queueing delays caused by the limited capacity of ground facilities, the model estimates flight starting dates needed to meet a given launch schedule with a specified level of confi dence. The results of an extensive sensitivity analysis indicate that the currently projected schedules are optimistic and that the turnaround time will substan tially exceed the current goal of 28 days.
40 citations
TL;DR: This paper reviews and discusses the major classes of factor screening designs and pays attention to two strategies that are useful when there are more factors than available runs, including group-screening and random balance.
Abstract: In many simulation models, only a few input variables have a significant effect on the output. By identi fying those variables in some reasonable way, we could undoubtedly make the model simpler, m...
35 citations
TL;DR: The U.S. Office of Technology Assessment (OTA) recently sent a report brief to this office that presents yet another instance in which the importance of computer modeling is being recognized.
Abstract: The U.S. Office of Technology Assessment (OTA) recently sent a report brief to this office that I would like to share with our readers. It presents yet another instance in which the importance of computer modeling is being recognized. Because the brief is only part of a full report, * / have chosen to reproduce it in its entirety rather than to "excerpt the excerpt."
31 citations
TL;DR: Percentiles are convenient measures of the entire range of values of simulation outputs that are useful in establishing reasonable capacities for facil ities, comparing the overall performance of alternative de signs, or establishing minimum standards.
Abstract: Percentiles are convenient measures of the entire range of values of simulation outputs. Analysts find percentiles partic ularly useful in establishing reasonable capacities for facil ities, comparing the overall performance of alternative de signs, or establishing minimum standards. Unfortunately, per centiles are not easy to estimate in most discrete simulations, since the observations are not independent or normally distrib uted.Several methods are available for estimating percentiles in re generative simulations. Moore's method, which uses a com plex assignment of observations to subsamples, has the best statistical properties but requires a relatively large amount of computer time and storage. Methods that use grids or divide the observations into batches do not perform as well statisti cally but are more efficient computationally. For nonregener ative simulations, an approach is recommended which dis cards the transient period and divides the remaining observa tions into batches.
31 citations
TL;DR: A hardware-in-the-loop simulation has been developed to evaluate the performance of active missiles from prelaunch to inter cept and initial comparisons with flight results support the credibility of the facility.
Abstract: A hardware-in-the-loop simulation has been developed to eval uate the performance of active missiles from prelaunch to inter cept. The facility is used for system integration, design verifica tion,...
26 citations
TL;DR: 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.
Abstract: 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.
18 citations
TL;DR: This model includes risk explicitly through the introduction of Monte Carlo techniques into a traditional corporate model and produces both standard financial reports and the associated probabilities of occurrence, confidence intervals, and standard deviations.
Abstract: Today's financial environment is a broad arena with many uncertain economic, political, and operational factors. Because of this widespread uncertainty, corporations of all sizes are turning to financial forecasting models. For the most part, however, these models are deterministic and do not consider the riskiness, or likelihood, of the projections fed to them. Our model includes risk explicitly through the introduction of Monte Carlo techniques into a traditional corporate model. The resulting model produces both standard financial reports and the associated probabilities of occurrence, confidence intervals, and standard deviations. The model, which has been validated by historical comparisons, allows the planner to test many scenarios and deter mine the likelihood of satisfactory financial performance.
15 citations
TL;DR: Two new simula tion executives allow both the modeler and the user ready access to the facilities of the computer and the simulation, while preventing the user from making unreasonable or impossible changes.
Abstract: The Apple II microcomputer provides powerful facili ties for the writing and execution of both discrete and continuous simulations. Interactive BASIC allows rapid development of new models, while color graphics provides results that are easy to analyze. Came paddles can allow the user to change parameters and control the simulation as it runs. Two new simula tion executives allow both the modeler and the user ready access to the facilities of the computer and the simulation, while preventing the user from making unreasonable or impossible changes. Despite its limited language facilities and relatively low speed, the microcomputer has obvious advantages in user inter action, model development, optimization, and analysis and presentation of results. Many of the microcom puter's limitations, furthermore, will soon disappear as more powerful languages and faster processors become available.
15 citations
TL;DR: This work provides a design for a package in Ada that allows the construction of powerful, process-oriented, discrete-system simulation packages in Ada.
Abstract: Ada, the new Department of Defense standard language, contains many features designed to facilitate the construction of software for embedded computer systems Two par ticularly important features are tasks (independent threads of execution in a program) and packages (collections of routines and data structures that can be compiled separately and in cluded as a unit in other programs) These features allow the construction of powerful, process-oriented, discrete-system simulation packages in Ada We provide a design for such a package and illustrate its use
10 citations
TL;DR: JORN A. GOTTWALD's current interests include all aspects of modelinq and simulating biological and chemical reactions with simultaneous adsorption and diffusion processes.
Abstract: BJORN A. GOTTWALD received his university education at the University of Bonn (diploma in physics, 1962) and at the Technical University of Hannover (doctoral degree in physical chemistry, 1965). Upon completion of his graduate work he pursued his research interests in the physical chemistry of gas-surface interactions emphasizing the kinetics of heterogeneous chemical reactions with simultaneous adsorption and diffusion processes. Since 1973 he has been an associate professor in the Faculty for Bioloqy, University of Freiburg. His current interests include all aspects of modelinq and simulating biological and chemical
TL;DR: In this article, a system dynamics model of retirement policies in the U.S. Department of Defense explicitly represents how military personnel respond to changes and how reductions in retire ment benefits affect accession and maintenance pay pol icies.
Abstract: A system dynamics model of retirement policies in the U.S. Department of Defense explicitly represents how military personnel respond to changes. Analysts can, for example, use the model to study how reductions in retire ment benefits affect accession and maintenance pay pol icies. In a case study, these interactions dramatically af fected cost estimates for proposed changes. The feedback effects in the system dynamics model showed important, unanticipated consequences from reducing retired pay. In teractions between different policy areas (such as retire ment, recruitment, and force maintenance) seldom show up in current models because of the complexity of representing them and because most modeling teams are assigned to a single policy area.
TL;DR: A new, floating-point equation- language simulation system for Digital Equipment (DEC) PDP-11 and LSI-11 minicomputers that needs no external compiler or linker and executes directly on a RUN command at a speed 1.3 to 4 times faster than DEC RT-11 FORTRAN.
Abstract: EARLY DESIRE is a new, floating-point equation- language simulation system for Digital Equipment (DEC) PDP-11 and LSI-11 minicomputers. It combines(1) An interpreted job-control language for inter ...
TL;DR: A formal procedure is employed to validate models at the input-output level by comparing them to simple lumped models for a given experimental frame in a generalized network simulator to investigate the performance of computer networks at a variety of levels.
Abstract: A generalized network simulator has been constructed to help investigate the performance of computer networks at a variety of levels. The simulator accounts for user-host, host-node (a node is a communications interface unit), and node-node interactions. The program is highly modular so that the user can change one level without affecting the others; this structure allows for innovation and efficient experimentation.Model validation has been a major consideration in the develop ment of the simulator. We have employed a formal procedure to validate models at the input-output level by comparing them to simple lumped models for a given experimental frame.The simulator can handle a variety of network structures and protocols. A particular network is described in terms of a schedul ing function, a grouping function, and a distance control matrix. Several network topologies and protocols have been simulated successfully.One problem with the modular approach is that it may lead to inefficient programs. Our simul...
TL;DR: An analog model of human microvascular exchange of fluids and plasma proteins has been programmed and tested and the results agree well with clinical observations but less well with indirectly calculated terms.
Abstract: An analog model of human microvascular exchange of fluids and plasma proteins has been programmed and tested. The results agree well with clinical observations but less well with indirectly calculated terms. Examples show the model used to predict the dynamic response of the microvascular exchange system to body changes. These changes include a simulated heart attack and an allergic reaction.
TL;DR: CUSUM charts as discussed by the authors are a practical approach to establishing standards and determining compliance for autoregressive data, and they can be used as inputs in simulation models to determine whether a change is permanent or not.
Abstract: The use of moving averages is gaining acceptance in environmental standards and regulations. Indexes based on moving averages are useful because they summarize a fixed number of the immediately preceding observations. If calendar-based monthly averages, for example, are used rather than moving averages of the last 30 days, data from industrial sources would not have a uniform time base. Only four observations would be averaged from a source inspected on the 4th of the month, while 28 would be averaged for a source inspected on the 28th. Many problems occur in implementing a standard based on moving averages: (1) Most environmental data are autocorrelated because they are averages of successive measurements. Autocorrelation changes the variance of the statistical distribution and, therefore, the probability of detecting a violation. (2) When continuous monitors are installed, a suitable averaging time must be determined. (3) Time-averaging affects the variance of the statistical distribution. This effect must be incorporated into simulation studies. (4) The relationships between exceedances (probable violations), transient changes, and long-term trends should be specified and used as inputs in simulation models. In environmental monitoring, a statistical decision about whether a change is permanent may result in substantial penalties. Cumulative sum (CUSUM) chartsmore » are a practical approach to establishing standards and determining compliance for autoregressive data. An example of an air-quality monitor illustrates the procedure. 16 references, 8 figures, 5 tables.« less
TL;DR: Theil's Inequality Coefficient (TIC) is presented as a basis for model validation in specific applications and an example illustrates the special utility of TIC for simulation model validation.
Abstract: Many simulation applications require the generation of a set of sample functions to characterize the physical system being modeled. Probability modeling using minimal data bases are reviewed and model credibility issues examined. Modeling methods include the Box-Jenkins time series, the fixed- memory and the α-β filters, the generalized expand ing memory filter, the Kalman filter, the Bayes filter, and the square-root filter. Such methods are particularly suitable in situations involving limited data, for instance, where the physical sys tem observations may be limited by cost or by the physical experiment. Theil's Inequality Coefficient (TIC) is presented as a basis for model validation in specific applications. An example illustrates the special utility of TIC for simulation model validation.
TL;DR: GPSS/Hl, a new version of GPSS, not only increases the execution speed of models but also removes many of the language’s minor restrictions, allowing the analyst to design and implement GPSS models that can be run by users who have no knowledge of the underlying language.
Abstract: GPSS3 is a long-established, widely-used discreteevent simulation language. Recent observers have suggested that GPSS is obsolete, slow, and definitely unfashionable. However, GPSS still has many advocates who particularly stress the small amount of effort required to model a complex system. GPSS/Hl, a new version of GPSS, not only increases the execution speed of models but also removes many of the language’s minor restrictions. Furthermore, GPSS/H operates interactively in a time-sharing environment. These improvements allow the analyst to design and implement GPSS models that can be run by users who have no knowledge of the underlying language.
TL;DR: Examples show bar charts, snap shots, dot plots, bit density plots, and contour plots of simulation results generated using an Atari 800 micro computer, a color television, and an Epson MX-80 printer with graphics capability.
Abstract: It is difficult to relate the output of a simulation model to the physical system it describes. Graphic representa tions of results can make simulations more credible and more interesting. On most large computers, how ever, there are software and hardware barriers between the user and graphical output. Microcomputers, on the other hand, are easy to use, and simple graphics are easy to produce without help from a programmer or systems specialist. Examples show bar charts, snap shots, dot plots, bit density plots, and contour plots of simulation results generated using an Atari 800 micro computer, a color television, and an Epson MX-80 printer (costing about $600) with graphics capability. All the user must do to obtain such plots is write short programs (less than 100 statements) in BASIC.
TL;DR: In this article, an EAI 681 analog computer allowed the operator to examine quickly the effects of engine capacity, fly wheel size, battery voltage, gear ratios, and mode of operation.
Abstract: Hybrid vehicles using both internal combustion en gines and electric motors represent one way to reduce fuel consumption. Our demonstration project envi sioned more than halving the fuel consumption of a passenger vehicle by reducing greatly the capacity of its engine and adding regenerative braking and an all-electric range. We also envisaged maintaining the same performance as current passenger vehicles. A 0–6 000 rpm gasoline-driven internal combustion engine, two 0–7800 rpm electric motors, a 0–7800 rpm flywheel, and lead-acid batteries are the major com ponents assembled using a mechanical epicyclic gear box. An EAI 681 analog computer allowed us to examine quickly the effects of engine capacity, fly wheel size, battery voltage, gear ratios, and mode of operation. An external potentiometer control on the computer allowed the operator to drive the vehicle through any acceleration cycle on level ground. We have shown that a 1.3 litre gasoline engine, two 13 kW separately excited direct current electric motors, a 38 kg flywheel, and a 48-volt battery pack will provide the same maximum performance as a conventional 4.1 litre internal combustion engine with automatic transmission at vehicle speeds below 60 km/h, and lower but satisfactory highway performance up to a top speed of 130 km/h. The transmission has under gone laboratory tests; it is to be road-tested in the first half of 1982.
TL;DR: First-order explicit integration as mentioned in this paper is an economical means of solving differential equations numerically, it is easy to implement and requires less computation time than Runge-Kutta integration for stiff equations.
Abstract: A first-order explicit integration technique can be an economical means of solving differential equations numerically. It is easy to implement and requires less computation time than Runge-Kutta integration for stiff equations. Error estimates can be derived and the method converges if the coefficient function is always positive and if it and the forcing function exist every where.
TL;DR: The optimal method for solving parabolic partial differential equations uses the method of lines to discretize the spatial variables and a finite-difference scheme to discrete time and minimizes the global error caused by discretization of time.
Abstract: Many direct and inverse problems in hydrology re quire the efficient solution of parabolic partial differential equations which are characterized by stiffness and numerical dispersion. An optimal method for solving such equations uses the method of lines to discretize the spatial variables and a finite-difference scheme to discretize time. This method is asymptotically stable and minimizes the global error caused by discretization of time. The numerical performance of the method has been evaluat ed on test problems that realistically simulate aquifers.
TL;DR: In this article, the results show that LSTIFF is much more effective and reliable than the well-known GEAR program, and this statement could be misleading to readers who are not familiar with stiff integration methods.
Abstract: In the conclusion of the paper "Solving Stiff Differen tial Equations in the Simulation of Physical Systems (Simulation, Aug. 1981) T.D. Bui states, "The results ... show that LSTIFF is much more effective and reliable than the well-known GEAR program." This statement could be misleading to readers who are not familiar with stiff integration methods, and the main purpose of this note is to clarify this point.
TL;DR: In this paper, an analog computer has been used to simulate a high-gain adaptive control method for regulating the speed of an internal combustion engine, where an on-off relay main tains the high gain in the forward loop that is necessary to produce a one-to-one relationship between input and output.
Abstract: An analog computer has been used to simulate a high-gain adaptive control method for regulating the speed of an internal combustion engine. A nonlinear element (an on-off relay) main tains the high gain in the forward loop that is necessary to produce a one-to-one relationship between input and output. Such high gain leads to limit-cycle behaviour in the model. A high-frequency dither at the relay input acts as a stabilizing signal to deal with this problem.
TL;DR: FIST (Flexible Integrated Simulation Tool), a program for the design and evaluation of flexible integrated manufacturing systems, became available in February 1982.
Abstract: Factory automation is a large and growing field that is rapidly becoming more complex. Simulation is an important tool used by planners in that field as an aid in designing factory processes, work areas, equipment installations, and assembly lines. There are several software packages available to perform this type of simulation. One of the newest of these is FIST (Flexible Integrated Simulation Tool), a program for the design and evaluation of flexible integrated manufacturing systems. This program became available in February 1982.
TL;DR: In this paper, a linear, energy-equivalent damping model is proposed for room windows to estimate the maximum response as a function of the duration of the sonic boom, based on a one-dimensional lumped parameter model.
Abstract: Sonic booms can cause considerable annoyance and damage. Studying the response of a room with an open win dow can be useful in design and acoustic treatment. In most cases, a one-dimensional lumped parameter model can be used for the acoustics of the room-window system. A linear, energy-equivalent damping model is adequate for shock response calculations at off-resonance conditions. A shock response spectrum showing the maximum response as a function of shock duration is a convenient way to present results for design purposes. Output from a CSMP program suggests that a little damping is usually sufficient when the natural period of the room and window is well above the duration of the sonic boom; heavy damping is necessary when this is not true.
TL;DR: In this article, a quasi-linearization method for solving the identification problem associated with a set of parabolic differential equa tions is described, and the computational aspects of the method are discussed, pay ing special attention to the case in which the para bolic equations have widely varying coefficients.
Abstract: Identification problems are fundamental to science, engineering, and medicine. In such problems the characteristics of a system must be determined from observations. For example, in managing water re sources, we must determine the transmissivity of an aquifer from measurements of the underground water level at a number of wells.In this paper we describe the quasi-linearization method for solving the identification problem associated with a set of parabolic differential equa tions. For problems in two spatial dimensions, we discuss the computational aspects of the method, pay ing special attention to the case in which the para bolic equations have widely varying coefficients (i.e., they exhibit numerical dispersion). We apply this method to the problem of identifying transmis sivity for an underground water reservoir. This parameter identification problem is improperly posed. Finally, we present the results of numerical experi ments performed on some test problems.
TL;DR: In this paper, a simulation model of an integrated energy system can help a consumer decide whether to purchase a new system for generating electricity, and what the size of its components should be.
Abstract: A simulation model of an integrated energy system can help a consumer decide whether to purchase a new sys tem for generating electricity, and what the size of its components should be. In the present study, the system consists of a liquid-metal magnetohydrodynamic (LMMHD) converter, parabolic sun collectors, and a heat storage unit. The system is in the final stages of development at the Ben-Gurion University of the Negev. The consumer in this study is a typical Israeli col lective farm (kibbutz). The consumer's aim is to reduce the expected discounted unit cost of electricity.
TL;DR: An equation of the form y = f(x), x ∈ [a,b] defines a geometrical curve, and a microcomputer can draw the curve on its television display.
Abstract: An equation of the form y = f(x), x ∈ [a,b] defines a geometrical curve. A microcomputer can draw the curve on its television display. The problems are selecting the proper coordinate system, translating points into the chosen coordinates, and scaling the curve so that it is as large as possible without running off the screen. Simple BASIC programs and an adaptive coordinate system result in a variety of useful, attractive figures.
TL;DR: The author of a recent book on microcomputers and physiological simulation, his interests have turned to the development and promotion of teaching simulations as a method of communicating a quantitative view of body functions.
Abstract: a graduate degree in physiology and biophysics from Ohio State. Since then his teaching has emphasized the physical mechanisms which underlie living processes. His research has concentrated upon the application of enqineerinq analytical methods in the study of physiological systems. Laboratory computers have been important tools in these studies. With the advent of inexpensive microcomputers, his interests have turned to the development and promotion of teaching simulations as a method of communicating a quantitative view of body functions. He is the author of a recent book on microcomputers and physiological simulation.