bluuebunny/crossref_metadata_2025_split huggingface dataset:
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.
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.
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.
Digital computation of inverse Laplace transforms
Authors: Olsen Charles F. 
Published: March 2008

This note describes an algorithm for the digital computation of the inverse Laplace transform of a function containing multiple real or complex poles and discusses its advantages and disadvantages. The algorithm utilizes a well-known, simple mathemat ical technique to evaluate a polynomial and its derivatives at a root of the polynomial. This method allows the nvmerator and denominator polynomials of the function to be treated separately by dividing each repeatedly by a first-order term. Synthetic division of a first-order term into a polynomial when both contain complex coefficients is particularly suited to digital computation. Execution times for Pottle's algorithm and the algorithm proposed in this paper are compared. The paper concludes with a BASIC program which implements the latter algorithm.
Variance reduction for a replacement process
Authors: George Laurence L. 
Published: March 2008

Prediction of replacement requirements for components (such as manufacturing equipment or engines) requires analysis of a replacement process. Unfortunately, unless component lives are exponentially distributed, that analysis requires transform methods, approxima tions, or simulation. Only simulation or approxima tion may be used for prediction of replacement re quirements when the replacement process is complicat ed, when it is subdivided into several periods of time, when replacements are not all new, or when several identical components that operate simulta neously are supplied from the same stock of spares. This paper shows that in a simulation the use of complementary antithetic random variates in the generation of component lifetimes reduces the vari ance of the sample mean number of replacements in a multiple-component multiple-period replacement process in which the components may be either new or used. Reducing the variance results in more accurate predictions for fixed simulation runtimes or, alter natively, allows shorter runtimes (and hence lower costs) to achieve specified accuracy.
A real-time simulation of a hierarchical computer network for process control
Authors: Engelberg George P. , Howard James A. , Mellichamp Duncan A. 
Published: March 2008

Hierarchical computer networks are useful in process control because they decentralize processing and thereby result in easier system development and greater fault tolerance. This type of network can be characterized by the flow of jobs to and from a single node computer. In this work a three-level hierarchy with a single node computer has been simu lated using a dual minicomputer system. One of the machines is used to simulate the node computer, the other machine to represent the low-level computers and the overall master computer. The simulation allows the user to maintain control over all key network parameters and to adjust them dynamically if desired. The output data permits the detailed monitoring of the performance of the net work. Some typical operating results are presented which illustrate the use of the approach to evaluate alternate job-scheduling strategies or to optimize a single scheduling algorithm.
A View On the Simulation of Systems
Authors: Dekker L. 
Published: March 2008

From its beginning about three decades ago, the simu lation of dynamic systems has made fast progress, but it can be expected that, like data processing, the maximum rate of advancement has already passed. In the past, computer hardware has severely limited both data-processing power and the development of sys tems simulation. Recent advances in hardware have re moved hardware as a limiting factor in data processing; hereafter the limitations on the design of simulators will arise from the methodology rather than from the hard ware. Future data-processing systems will combine parallel and serial computation in a hierarchical structure in time (serial) and space (parallel). This architecture will allow a strong one-to-one analogy between the computer model and the mathematical or conceptual model of the system under study. Such one-to-one analogies require develop ment of appropriate data-processing and simulation algo- ri thms. The improved methodology for systems simulation will have beneficial consequences in the teaching of applied sciences by making it convenient to conduct meaningful experiments by simulation. A few decades hence systems simulation will become a saturated art limited by human capabilities.
The method of lines and the advective equation
Authors: Carver Michael B. , Hinds H.W. 
Published: March 2008

The linear advective equation is simple in form and yet it is one of the most difficult equations to solve accurately by numerical means. Because its be havior is similar to that of the conservation equa tions of compressible one- or two-phase flow, the advective equation is extremely useful for testing numerical schemes. This paper summarizes techniques for solving the ad vective equation using, the method of lines on a digi tal or hybrid computer, and assesses how suitable they are for incorporation into large simulations. Some of the dangers of using artificial dissipation terms are described, and a weighted-residual tech nique is shown to be very effective.
Evaluation of startup policies in simulation experiments
Authors: Wilson James R. , Pritsker A. Alan B. 
Published: March 2008

This paper describes a procedure for evaluating pro posed startup policies that define the initial condi tions and the truncation point in a simulation ex periment. The evaluation procedure involves the tabulation of bias, variance, and mean square error of the sample mean over a fixed range of truncation points and initial conditions. For each policy, the tabulated values are averaged with respect to an empirical truncation-point distribution based on independent model runs. These results are used to construct confidence intervals for the steady-state mean with the same average length for all policies; the corresponding average confidence interval cover age can then be used to compare policies. To illustrate the procedure, several well-known policies are evaluated for two finite-state Markovian queueing systems—α single-server queue with a capac ity of 15 and a machine-repair system with 3 repair- men and 14 machines. The results for both systems indicate that the best initial condition is the most frequently observed value (the mode) of the steady- state distribution of the number-in-system process, and that the judicious selection of an initial condi tion is more effective than truncation in improving the performance of the sample mean as an estimator of the steady-state mean.
Dynamic modeling and simulation of a relief valve
Authors: Ray Asok 
Published: March 2008

A nonlinear dynamic model of a relief valve is for mulated in state-space form from fundamental princi ples of rigid-body motion and fluid dynamics. Model parameters are calculated from steady-state character istics and the physical dimensions of the valve. The transient response of the nonlinear model (as well as system eigenvalues and the frequency response of a linearized model) is obtained by digital simulation. Results indicate that the opening time of the valve is linearly related to the dimensionless parameter given by the ratio of orifice length to its radius. The analysis provides design information and perform ance evaluation for fluid systems incorporating relief valves. It is particularly suitable for relief valves for liquids and it can be adapted for other applications.
Computed temperature-time excursions at succeeding locations in an industrial reactor
Authors: Franks Roger G. E. , Miller Donald N. 
Published: March 2008

Traveling thermal transients have been observed in deep-bed catalytic reactors. With certain combina tions of parameters and stimuli, these transients can increase in amplitude with increasing axial distance into the bed. The resulting peak temperatures can exceed structural equipment limitations and cause catalyst deactivation or physical deterioration. Reaction systems in which abrupt changes in operating parameters can occur are particularly susceptible. An understanding of the causes of such transients is important not only for design but also in operations where optimization of output and product quality is essential. This paper describes a numerical procedure that effi ciently simulates thermal transients on a digital computer. Results are shown for a generalized reactior, scheme that includes the effects of reaction rate, activation energy, absorption, heat of reaction, heat capacities of gas and solids, and catalyst bed depth. Also covered is initiation through various stimuli such as feed rate, composition and temperature dis continuities, pressure variations, and abrupt activity changes. The transients travel because the solid fixed-bed heat capacity causes temperature to lag concentration re sponses with step changes in operating conditions. An interesting result is that temperatures in the bed move in the direction opposite to the initiating stimulus. A decrease in feed temperature, for example, produces a positive peak wave temperature. A computer simulation of the phenomenon can aid in developing effective control strategies and operating procedures.
Simulating modular microcomputers
Authors: Langley Frank J. , Sheehan Joan , LaGro Gerald 
Published: March 2008

Detailed logic design followed by breakboarding of microprocessor-based systems makes development costly. This paper reports on the use of a high-order language for designing simulation models of microcomputer functional elements ("macromodules") at the register level and for verifying the timing and interface requirements for a family of microcomputer configura tions. The definitions of these microcomputer macro modules (i.e., microprocessors, memories, and input/ output interface modules) was derived in previous system analyses and simulation work reported in References 1 through 5, which were sponsored by the Office of Naval Research. Of the several simulation or emulation methods avail able for studying the design of computer architecture, the technique adopted here provides the level of simulation required to verify timing, interface logic, and data flow within and between macromodules in the family for subsequent simulations of system performance. Furthermore, module-level simulation using discrete logic forms the necessary link between system design and the ultimate description of hardware for a low cost, step-by-step design process. Writing and executing the module simulation programs provides a disciplined approach to hardware design, since the components have to be modeled in detail to follow the flow of data and timing in a microcomputer. The modeling was done in a register-transfer language called Computer Design Language, which is very con venient for this kind of simulation model. Examples of programs in CDL are included.
Improving ecological simulation through sensitivity analysis
Authors: Thornton Kent W. , Lessem Allan S. , Ford Dennis E. , Stirgus Connie A. 
Published: March 2008

Ecosystem models require extensive data for initial ization and calibration. Since data collection is expensive and time-consuming, it should be guided by knowledge of the model's sensitivity to initial con ditions, coefficients, and update intervals. These factors were studied using an ecological model of a reservoir. For this model, it was found that (a) biological and chemical variables need to be considered in addition to temperature during calibra tion, (b) changes in the effective diffusion coeffi cients produce the greatest changes in the model's responses, (c) nutrient update intervals of less than one week yield results similar to those for one week but dissimilar to those for two weeks or one month, and (d) nutrient concentrations strongly affect the model's sensitivity to small changes in a number of coefficients.
Simulation of the nonlinear behavior of an electrohydraulic exciter
Authors: Lebrun Michel , Scavarda Serge 
Published: March 2008

This paper presents a computer simulation of the non linear behavior of an electrohydraulic exciter. The experimental results and the simulated results are compared. The model used takes into account the nonlinearities of the two-stage servovalve and the jack. Major nonlinearities included in the simulation are torque- motor hysteresis, flow forces acting on the servovalve spool, the pressure-flow relationships in the orifices (particularly near the null region), compressibility of the hydraulic fluid, clearance of the mechanical feedback link, fluid leakages, sticking forces, and variations of dead volumes.
A model of the temperature-dependent operation of a MOSFET
Authors: Akers Lex A. 
Published: March 2008

Nonuniform temperature distributions can greatly affect the operation of semiconductor devices. At present, computer programs using numerical methods can be used to simulate the steady-state or transient response of one- or two-dimensional models of semi conductor devices operating at constant temperature. Recently developed programs allow the steady-state analysis of semiconductor devices under nonisothermal conditions. The transient response, the mode of operation for most high-power semiconductor devices, has not been analyzed for a MOSFET. This paper presents a one-dimensional mathematical model for predicting the nonisothermal behavior of a MOSFET under pulse excitation. Both the transient electrical and temperature responses are shown. Redistribution of voltages and carriers resulting from the differences in the electrical and tempera ture time constants is discussed.
A nonlinear model of the U.S. economy
Authors: Niedercorn John H. , Kalaba Robert , Kandoole Benson F. 
Published: March 2008

According to orthodox Keynesian economic theory, sig nificant unemployment and inflation should not occur simultaneously (i.e., "stagflation" should not exist) in a highly developed modern economy. However, both have occurred simultaneously in the United States since 1973. This paper describes an economic model being developed to investigate the causes of stagflation; this model includes nonlinearities and discontinuities not in corporated in other macroeconomic models. In its present form the model does not include all the var iables necessary to achieve its purpose, and its parameters and initial conditions have been set at arbitrary "reasonable" values. Much work remains to be done before it can simulate stagflation in the economy of the United States. The responses of the present model to initial conditions leading to stag nation, moderate growth, and high-pressure growth situations are reported and analyzed in this paper. The results obtained by experiments conducted on the model reflect the behavior of an idealized competi tive capitalistic economy with implicitly flexible prices and explicitly flexible interest rates. The model eventually produces full employment and steady growth regardless of the initial conditions used. This behavior implies that the simultaneous occur rence of unemployment and inflation should not exist very long in such an economy.
Stochastic analysis of process-control models
Authors: Tanthapanichakoon Wiwut , Himmelblau David M. 
Published: March 2008

Most conventional methods of process design ignore the stochastic nature of the process and its param eters ; only deterministic models are employed, and the solutions obtained are at best only approxima tions. To allow for the uncertainty of designs based on such a procedure, gross safety factors must be added to the design variables based on the deterministic models. An alternative approach is to introduce stochastic variability directly into the process model and to use stochastic simulation to estimate the process outputs and design parameters. By using stochastic simulations which incorporate random inputs and ran dom parameters, one can obtain sample estimates of the expected values and expected variances of the output variables. From these and the characteristics of the probability distributions of the output vari ables, one can show when the expected values of the outputs of stochastic process models differ from those of deterministic models in which the random variables are replaced by their expected values and what safety factors are necessary for a satisfactory design. As an example, we have developed a stochastic dynamic mathematical model for a wastewater treatment plant. The output of the plant was simulated for a period of several days under different random input conditions and different probability distributions of parameters. Differences between the deterministic and stochastic responses of the model are described, as is the effect of frequency of fluctuations of the stochastic inputs on responses of the model and on their variances. Of particular interest is the use of the results of the simulations, stochastic and deterministic, to estimate safety (overdesign) factors that should be used in designs based on deterministic models. The validity of the propagation-of-variance formula- i.e., the relation used to compute the sample vari ances of the outputs of a nonlinear stochastic model in the unsteady state from the sample variances of the inputs and parameters - is demonstrated. With the aid of this relation, overdesign factors can be esti mated from the magnitudes of the standard deviations of the outputs. Although stochastic analysis cannot reduce the uncer tainty in design, it can provide a more quantitative assessment of the uncertainty than can deterministic design and so can lead to better designs of process plants.
DISCO- a SIMULA-based language for continuous combined and discrete simulation
Authors: Helsgaun Keld 
Published: March 2008

DISCO is a SIMULA-based language for the simulation of systems which contain both continuous and discrete- event processes. It is a true extension of SIMULA's concepts for discrete-event simulation and is capable of representing and analyzing models including both types of processes. With the addition of few new con cepts, a general yet simple simulation language has been achieved. This paper describes the basic concepts of DISCO and demonstrates through examples the descriptive power of the language. DISCO is described mainly from the user's point of view; its implementation is only sketched.