bluuebunny/crossref_metadata_2025 huggingface dataset:
Knowledge-based simulation model specification
Authors: Murray Karen J. , Sheppard Sallie V.
Published: March 2008

A Knowledge-Based Model Construction (KBMC) system has been developed to automate the model construction phase of the simulation life cycle. The system's underlying rule base in corporates several types of knowledge. This includes domain knowledge that facilitates a structured interactive dialog for the acquisition of a complete model specification from a user. An executable discrete simulation model in SIMAN is automatically constructed by the system from this specification, utilizing model ing knowledge and SIMAN knowledge. We present an overview of the KBMC system and focus on the knowledge-based specifica tion method used in the KBMC system.
Simulation investigation on message based CSMA/CD priority protocols
Authors: Chang Yih-Long , Shen Sheldon
Published: March 2008

In this paper, we develop a simulation model to analyze three different protocols for prioritized messages in CSMA/CD environ ment. Using SLAM // simulation language, the different phases of message transmission are represented as discrete events. Traf fic loads and priority ratios of messages are included in the model. Performance measures such as throughput, average waiting time, and average number of collisions are collected during the simula tion runs. Analysis of variance (ANOVA) is performed on the out puts and indicates statistically significant differences in perfor mance for the three protocols tested. This simulation modeling approach and subsequent analysis can be easily extended to in clude more factors and protocols in CSMA/CD systems.
Ada™ simulation technology- methods and metrics
Authors: Melde John E. , Gage Philip G.
Published: March 2008

This paper describes the impact of the Ada programming lan guage on the development and use of simulation models. Based upon the development in Ada of a discrete-event simulation package (A*SIM), Ada is shown to provide numerous language features and methodologies that are ideally suited for modeling and simulation. Productivity and performance metrics collected during development and extensive use of A*SIM are also pre sented to provide quantitative comparisons of Ada-based model ing and simulation with previous approaches.
A simplified mathematical model for an onboard maneuvering simulator
Authors: Biancardi C.G.
Published: March 2008

This paper suggests the development of an onboard maneuver ing simulator for ship control. The simulator employs a simplified mathematical model and a set of realistic expectations of ship behavior drawn from seagoing expertise and full scale tests. It predicts the result of imminent maneuvers. The onboard simu lator gives ship's officers a chance for self training in real-time conditions, steering the ship. For instance, high-speed prediction of ship motion in a channel, displayed in a suitable form, includ ing pertinent advices such as rules of the road, is expected to help operators anticipate the results of maneuvering decisions and prevent wrong decisions. The suggested model for an onboard simulator makes use of sensors for continuous updating of real- time input, and also includes an on-line system-identification processor by which the mathematical model would be succes sively adjusted to a changing environment. A simplified mathe matical model of the simulator is presented. The block diagrams and the research efforts presented are the research guidelines of the Instituto Universitario Navale at Naples, Italy, for design ing an onboard maneuvering simulator for ship control.
Simulation of insect disease dynamics: an application of SERB to a rangeland ecosystem
Authors: Carruthers Raymond I. , Larkin Timothy S. , Soper Richard S.
Published: March 2008

An object-oriented simulation program, SERB (Simulation En vironment for Research Biologists), has been used to simulate insect disease dynamics in a rangeland ecosystem. SERB was used to construct a mechanistic simulation model of a fungal pathogen of grasshoppers by synthesizing experimentally derived compo nents. Emphasis is placed on how SERB was used to construct and evaluate the model both in a piece-wise and combined manner to aid in understanding population interactions and dynamics. The interactive nature of SERB in the ZetaLisp environ ment was found to be highly conducive to model construction, manipulation and evaluation. Detailed examples from several phases of this process are presented from the perspective of a population bioligist. The orientation of SERB allows the research er to focus on a problem in an intuitive and systematic manner, in biological terms, unconstrained by details of an unfamiliar programming environment.
Collision-free path-planning in a dynamic environment: semantic control approach
Authors: Rodin E.Y. , Ghosh B.K. , Golenko F. , Weil R.
Published: March 2008

There are many large scale control problems in which classical control methods are no longer applicable. In this paper we explore as an example the problem of collision-free path-planning in a dynamic environment. Our new semantic control paradigm, pro posed in this paper, is shown to be able to handle problems that cannot otherwise be handled by classical methods.
A Simulation Of A Hospital Emergency Call System Using SLAMII
Authors: Liu Mu-Shieung , Lee Jui-Tine
Published: March 2008

The main purpose of this system is to develop a simulation model as well as to perform an analysis of hospital resources including sick beds, ambulances, and ambulances of Police Rescue Centers called by 119, the emergency telephone number Here, the key items we are going to analyze include the number of sick beds and ambulances, the rate of use of sick beds andambulances, time of each ambulance on duty, and delay time (from calling ambulances to the arrival at hospitals) for an emergency call. With this system, we can assist the related personnel in making a complete program ming such that all resources can be employed both efficiently and sufficiently. By using SLAM II, we can obtain the minimum number of sick beds andambulances required to sustain the indispensable requirements under the existing and abnormal conditions. At the same time, we can observe the delay time for an emergency call and the rate of use of sick beds and ambulances within the limited availability of sick beds and ambulances.
Flight simulation for museums
Authors: Stewart Stephen J.
Published: March 2008

A generalized microcomputer based flight simulator has been developed, one part of this simulator is a numerical solution of the equations of flight. For accurate solution, a simple numerical scheme would demand a very small timestep: A modified scheme is therefore developed which allows a much larger timestep to be used by introducing certain scaling factors. These factors are themselves functions of the timestep and of the characteristic response time of the equations being solved. The modified numerical scheme is shown to be adequate when applied to simultaneous solutions of all the components of an aircraft motion. Within limits, the simulation is independent of the aircraft being simulated. Relevant performance and control parameters are entered before the commencement of solution.
A Study of Terminology and Issues in Qualitative Simulation
Authors: Fishwick Paul A.
Published: March 2008

Much of the recent AI research related conceptually to simula tion may be found under the heading "qualitative simulation and reasoning." This paper will present terminology used within AI and critically analyze the terminology with respect to current simulation literature. By discussing terminology, we will help to bridge the gaps between work in qualitative simulation and traditional simulation and provide the foundation for future discussions on the relationships between these two areas.
An integrated simulation approach to design of flexible manufacturing systems
Authors: Kiran Ali S. , Schloffer Albert , Hawkins Duane
Published: March 2008

Simulation has been used in the design of manufacturing cells at General Dynamics-Pomona Division. At the preliminary design stage, mean value analysis has been used to define basic system characteristics and to develop design alternatives. Siman simula tion language and a specifically designed user interface have been utilized in evaluating alternative designs. The performance of the final designs has been analyzed using statistical techniques.
Information structures for simulation modeling of manufacturing systems
Authors: Ketcham Michael G. , Shannon Robert E. , Hogg Gary L.
Published: March 2008

This paper presents an information-based approach to simula tion modeling and an information-based simulation environment called IBIS. IBIS uses information relationships to structure simulation models and to coordinate multiple models at different levels of hierarchical development. Because of its database orien tation, IBIS models do not exist as programming code but exist in the form of information links stored in a simulation database. The paper describes a sample manufacturing problem and the IBIS formulation for this problem. The information relationships defined in IBIS allow for hierarchical modeling of stations and entities, flexible product routing, multiple product assembly re quirements, and "push" and "pull" drivers for parts flow.
RSIM: A circuit simulation program for VLSI interconnect networks
Authors: Massengill Lloyd W. , Bengtson Neal
Published: March 2008

This paper describes RSIM, a circuit simulation tool for the analysis and design of power supply routing in VLSI digital cir cuits. A review of existing VLSI solution techniques is make to show the development of RSIM. The program simulates the distributed power supply voltages and currents,and the resulting noise margins and operational reliability environments. The in put structure of RSIM allows for easy entry of circuit design and facilitates parameter changes. Examples show a speed improve ment of more than 500% over that of the widely used SPICE program. RSIM can handle much larger circuits than SPICE. RSIM output has proven to give accurate results in the analysis of power supply noise margins in large circuits.
Matrix environments for continuous system modeling and simulation
Authors: Cellier François E. , Rimvall C. Magnus
Published: March 2008

In any future standard for continuous system simulation lan guages, it is of primary importance that the data and program structures are made sufficiently general and flexible. In this paper, the use of matrix structures in modeling and simulation, and the impact of matrix environments on the design of simulation languages and their experimental frames will be discussed.
An improved simulation model for cannibalization policy performance comparisons in a complex maintenance system
Authors: Fisher Warren W.
Published: March 2008

A model of a two-echelon (bases and a depot), two-indenture (machines have components which may have modules) maintenance system with spares, repair, cannibalization, preven tive maintenance, and two classes of manpower constraints is presented. A base is modeled with a SLAM II combined net work and discrete event simulation, while other bases and a depot are incorporated analytically. Although designed primarily for the study of cannibalization decisions, the model is also suitable for testing the performance of repair, spares, and other maintenance policies in complex systems, including those main taining fleets of aircraft. Applicability of the model and its new features are demonstrated by showing how previously-reported results change under different assumptions.
Throughput analysis in an automated material handling system
Authors: Pulat P. Simin , Pulat B. Mustafa
Published: March 2008

Throughput analysis in an automated material handling system, such as an Automated Storage and Retrieval System(AS/RS), may be a complex problem. In the past, several approaches have been used for such an analysis. This paperpresents a combinatorial ap proach to evaluating the throughput performance of a mini-load system, with simulation as the primary method of investigation.
Simulation as a cure process design tool for aerospace materials
Authors: Chiao Leroy , Darfler Stephen C. , Borris Peter W.
Published: March 2008

Composite aerospace materials, known for their good mechanical properties and low weight, present interesting cure process design problems to the engineer. It is shown that computer simulation can be used as a powerful tool in solving these problems.

Using physical principles, simple mathematical models are constructed which describe observed phenomena. With the advent of high-speed microcompu ters and desktop workstations, the simulations can be run at low cost. It is shown that with a properly validated model, the process engineer can use simulation to efficiently optimize cure cycles, as well as map undesirable operating regions.

Examples are presented, which show that "standard" cure cycles for these materials can be modified to shorten processing times. Also, conditions which could cause reaction runaway are exposed.
An intelligent simulation model generator
Authors: Hitz Martin , Werthner Hannes , Guariso Giorgio
Published: March 2008

The conceptual design and a prototype implementation of a knowledge based interactive genera tor of simulation models is pre sented. The system administrates several components, among them a model base, a knowledge-base, and a data base. Emphasis is laid on the integration of the model and the knowledge base. This connection of numeric and knowledge representa tion components is one of the main advantages of the system. A frame based approach has been chosen for the semantic representation of the simulated models. The prototype has been implemented on a XEROX 1186 workstation and takes advan tage of the presence of two proces sors : a LISP processor managing the logical description, selection, and maintenance of models as well as the overall control of the system, and an 8088 processor to run the simulation programs that are written in classical programming languages like FORTRAN. The system is designed to free the scien tific expert from details about computer science and to let him concentrate on the actual simulation problems.
Automated decision support systems for hurricane mitigation planning
Authors: Berke Philip , Stubbs Norris
Published: March 2008

The risks posed by hurricanes are significant and rising. Recent advances in computer technology have stimulated interest in the potential applica tion of automated decision support systems to hurricane mitigation planning. This article discusses why computer technology should be used in hurricane mitigation planning. Reviews of the several different, though often interrelated, lines of advance in automated decision support systems and hurricane risk assessment modeling are presented. Recent research on organizational concerns that should be ac counted for in the design of such systems is also reviewed. Guide lines are then provided showing how future research might be directed to effectively design and implement decision support systems.
Simulation analysis of dynamics and decentralized control of robot manipulators
Authors: Tarokh M.
Published: March 2008

The dynamic equations of robot manipulators which include the effect of payload are simulated using Runge-Kutta and Adams- Bashforth methods. A decen tralized scheme is developed for independent joint control of robot manipulators and a simple algorithm is presented for simulating the decentralized control laws. Responses of the robot to joint torques are ob tained to show the basic characteristics of the robot dy namics. Closed-loop system consisting of the robot and the decentralized controller is simu lated to demonstrate the capabilities of the control scheme.
Dynamic Nuclear Power Plant Simulations Using Single-Board Peripheral Array Processors
Authors: Hsing Chien Yeh  , Kastenberg William E. , Karplus Walter J.
Published: March 2008

The application of a host/ coprocessor system, consisting of an IBM PC/AT and a Marinco peripheral array proc essor, to the simulation of nuclear power plant transients is described. The simulation algorithm employs a multistep, multirate integration method. Rapidly varying transients were implemented on the array processor, while the slow components of the system dynamics were handled by the host computer. The generation of nonlinear functions of dependent variables using table lookup techniques was also implemented on the array processor. A simplified model of a pressurized water reactor was employed as a benchmark. Flow rate and power transients using a variety of integration formulas are presented along with data showing the speed up achieved through the use of the peripheral processor.
Simulation analysis of some basic hypotheses about the spread of AIDS
Authors: Virkkunen Juhani , Hämäläinen Raimo P.
Published: March 2008

The basic dynamics of the AIDS epidemic in an homogeneous population is studied from three different points of view using simple mathematical models. The first model assumes a constant transmission probability per sexual intercourse and a constant frequency of sexual intercourses. Then the probabil ity for HIV infection strongly increases with increasing number of partners only if the infection probability per intercourse is relatively high.

Second, the assumption that each carrier transmits the infection a constant number of times with a constant time interval between transmissions is shown to result in an exponential rise in the number of infected. Taking the saturation effect into account the number of new infections per year and the actual proportion of infected are studied in populations of different sizes.

The third model assumes an exponen tial rise in the number of infected and a randomly distributed incubation time of AIDS. This results in stochastic simula tion of the rise in AIDS cases. With repeated simulation runs the stochastic dispersion of the rise is shown to be quite large obscuring the so-called transient phenomenon in the initial phase of the epidemic.
Numerical simulation of a casting furnace
Authors: Ouellet R. , Bui R.T. , Perron J.
Published: March 2008

Industrial furnaces constitute a complex, nonlinear, distributed- parameter thermal system. The usual way to model them is to write the equations describing the physical phenomena. The analytic model thus obtained is often too complex to be useful for control and optimization purposes.

We propose to build a linear model by running the analytic model to obtain the simulated data, then apply the least square approximation to those data to obtain the linearizing coefficients. This statistical approach is simple to implement and yields linear models with good representativity. The annoying aspect is that some of the coefficients thus obtained may not lend themselves to a direct interpre tation of the physical process. But with proper consideration, this is no obstacle to the use of the model.
The role of modeling and simulation in operational test and evaluation
Authors: Goodin Jim Riley , Bomber Thomas M.
Published: March 2008

Modeling and Simulation play a significant role in the De partment of Defense's Operation Test and Evaluation activities. However, it is extremely important to understand the capabilities and limitations of modeling. The test members should agree to the role model ing will play in each test, as well as what particular parts of the test activity will be affected by the model. If carefully designed and executed, models can be used to provide highly credible results that cannot be feasibly achieved by any other means.
NEMS: A database support environment for numerical experimentation
Authors: Birta Louis G. , So Maria
Published: March 2008

Simulation and computer based experimentation in general, are activities that can rapidly generate large amounts of data. The usefulness of this data depends very much on the convenience with which it can be examined, summa rized and/or tabulated. In this paper, we outline the design of a generalized Numerical Experiments Management System (NEMS) that provides a framework for managing the large amount of relevant data that are typically associated with numerical studies. This includes the management of both the parameter values that are used in the experiments and the results that are produced. The work is based on a model of the problem solving envi ronment which consists of three types of entities called solution engines, problem instances and ex periments. The system environ ment for NEMS consists of a personal computer which runs NEMS and provides the database function, and a mainframe computer which carries out the ex periments. The necessary intercon necting mechanism is assumed to be available. The organization of NEMS and its functional capabili ties are described.
Fast subdivision of Bezier surfaces
Authors: Harrand Vincent J. , Ziebarth John P. , Choudry Amar
Published: March 2008

In this paper the classical subdivision method for paramet rically defined surfaces by Lane and Riesenfeld is reformulated for Bezier surfaces. The new algorithm is based on matrix multiplications, which results in a very concise and elegant formulation. In addition, for geometry modeling this formula tion allows very fast implemen tations. Three implementations are described along with some test results.
Job shop configuration optimization at Tinker Air Force Base
Authors: Leemis L. , Badiru A. , Foote B.L. , Ravindran A. , Williams Larry
Published: March 2008

This paper discusses a large simulation model that was developed to aid the reconstruc tion efforts after a disastrous fire at Tinker Air Force Base. The model, developed in SLAM, facilitated the analysis and efficient design of the functional layout that replaced the previous machine-based layout in the appropriate number of machines to place within a modular repair center (MRC), stacker capacity for in-process inventory, location of elevators for sending parts to the conveyor, and the optimal design and routing scheme for overhead conveyor system. The new layout, as predicted by the simulation model, has proven to be quite effective compared with the pre fire layout. Improvements that have been achieved include a 50 to 80% decrease in material handling, substantive decrease in flow times, better manage ment control of part transfers, $4.3 million savings from the elimination of excess capacity, and $1.8 million savings resulting from higher direct labor efficiency.
PASSIM - A Pascal discrete event simulation program generator
Authors: Shearn D.C.S.
Published: March 2008

Most simulation program generators expect the simulator to amend the generated program whenever complex requirements are met. This can be extremely time consuming and tedious if the original model specification has to be modified since all the edits are likely to have to be repeated. The Pascal based generator described in this article was developed alongside the main simulation program so that all complex requirements can be specified by including embedded code in the model specification. The system operates at differing levels of complexity so that for straight forward simulations it behaves as a standard generator, and as complications are needed they can be included in a natural way. The system has been found to be very effective both in a teaching environment and in solving practical problems.
Simulation of distributed algorithms using OCCAM
Authors: Love Andrew E. , Aburdene Maurice F.
Published: March 2008

Distributed algorithms often cannot be analyzed to give an accurate estimate of performance. ELECTOR, a program written in OCCAM™(a parallel pro gramming language) has been developed to simulate a class of distributed algo rithms, election algorithms. This simula tor and a description of the methods used to design a distributed system simulator are presented. A description of the design of an equivalent simulator on a SIMD machine (the Connection Machine) is then presented. Simulation results from ELECTOR for the performance of three election algorithms are presented. These results show that the performance of election algorithms with similar upper bounds on average number of messages transmitted can be better evaluated by simulation. Results from the second simulator for one of these algorithms confirm the validity of the first results.
Spreadsheet risk analysis using simulation
Authors: Seila Andrew F. , Banks Jerry
Published: March 2008

For many financial models implemented in electronic spreadsheets, input data values frequently are random variables because they are actually estimates of unknown quantities. As a result, the bottom-line performance measure of the model is a random variable, and risk is associated with decisions based upon it due to the uncer tainty in its value. We describe in detail how to evaluate this risk using simulation in a spreadsheet and illustrate the procedure with an example. Formulas for generating random variates from many common distributions using LOTUS 1-2-3 are given, and data analysis considerations are also discussed.
A comparative simulation study of the performance of single-bus and two-bus multiprocessors
Authors: Obaidat M.S. , Radaideh M.A.
Published: March 2008

This paper presents a comparative simulation modeling of the performance of the uniprocessor, single-bus multiprocessor, and two-bus multipro cessor computer systems. The performance indexes of the single-bus and two-bus multiprocessor systems compared to the uniprocessor system, that are used in the modeling, are processor speedup factors SP1 and SP2 respectively. A third perfor mance index, Bus-speedup factor, SB, is derived to compare the performance of the two-bus and single- bus systems. The first two indexes provide measures of the processing speedup improvement of both multiprocessors with respect to the uniprocessor system, while the third index provides a measure of the performance improvement resulting from adding an extra bus to the single- bus multiprocessor system. Three data transfer protocols are considered in this work: First Come First Served (FCFS), Token Ring (TR), and the Priority (PR) Policy. Simulation experiments show that increasing the number of processors in the considered multiprocessor architectures does not necessarily improve the overall performance. Moreover, adding an extra bus to the single- bus architecture provides some speedup improvement that depends on the nature of the task program and the data transfer protocol. Simulation results show that FCFS and TR scheduling policies provide better performance than the PR policy. However, FCFS requires relatively less hardware and software complexity than the TR.
PKDEMO - A Pharmacokinetic Demonstration simulation program
Authors: Pearce Bruce A. , Young John F.
Published: March 2008

A demonstration simulation program was developed on an IBM AT personal com puter to aid students in understanding the effects of altering rate constants on simple one and two compartment pharmacokinetic models. This menu driven system graphi cally presents specific sets of simulated curves illustrating how all components of a model interact. The student selects one of the five models and also determines which portion of the model is to be altered. The aim of the program is to teach the user to anticipate the outcome of the model alteration and interactions. The program was developed with the use of PC Storyboard, a demonstration software package, which provided the tools necessary for an elegant program presentation. This interactive presentation graphic program illustrates a viable means of conveying simulation models to a novice audience.
Bootstrap confidence intervals for estimating audit value from skewed populations and small samples
Authors: Muralidhar Krishnamurty , Ames Gary Adna , Sarathy Rathindra
Published: March 2008

Classical estimation procedures that are often used in estimating the population audit value rely on the assumption of normality. Empirical evidence suggests however, that this may not be a valid assumption. Consequently, the use of normal theory methods may lead to errone ous or misleading conclusions. The boot strap method is an effective alternative in many cases where the classical assumptions are in question. The bootstrap method replaces complex analytical techniques by computer intensive, simulation based, empirical analysis. This study illustrates the use of the bootstrap method in estimating the audit value from skewed populations and small samples. The results of Monte-Carlo simulations indicate that the bootstrap is more effective and efficient than the normal theory method.
The design of simulation languages for systems with multiple modularities
Authors: Rowley Steve , Rocklandt Charles
Published: March 2008

Biological systems exhibit several characteristics that are not shared by human-engineered systems: there are often no clear module boundaries (or there are several module boundaries, depending on the question being asked); individual parts often serve multiple roles, depending on the behavior being studied; and system characteristics often vary from individual to individual.

Conventional simulation languages, however, do not cope well with this non-modularity. We have developed a theory of the design of simulation languages for such systems, and partially verified it in one case study. We separate the notion of "structure" S of a system from the "behavior" B of its parts. We allow multiple versions of both the structure (S1, S2, ...) and the corresponding behavior (B1,[Si], B2 [Si], ...) of each part Si. The different structures or behaviors might be alternative theories, or abstractions of each other, for example.

We also have theories of how to interpret the simulations produced by (Si' B i [Si]) pairs. One goal is to extract "design" information, i.e., explain how the system solves problems. Another is to test the effects of alternative models of behavior B1 [Si], B2 [Si], ... for the same structure, or the effects on behavior due to alterations in structure. A third is to judge the relative degree of consistency between various (Si , Bi [Si]) pairs.

We exhibit how these ideas apply to the motor nervous system of the nematodes C. elegans and Ascaris suum. We also provide arguments that this kind of simulation methodology is also applicable to engineered artifacts, such as systems where parts must serve multiple roles.
A design of expert system architecture for communications engineering simulation
Authors: Tsang Chit-Sang
Published: March 2008

Simulation expert system architecture for communications simulation including the features of common data structure, top- down information driven technique, optimization, and expert system approach is addressed. The concepts can be combined to implement a very user-friendly simulation system for either a novice or experienced user. The architecture block diagram of the simulator is discussed to highlight the important functions. Complete or partial features addressed can be adopted in any simulator design.
Conditions for computer simulation of thought processes to become actual thought
Authors: Wojcik Vladimir
Published: March 2008

This paper is intended to break the current research impasse on issues of mechanized thought. It bypasses the untractable recursive question: Is the human brain powerful enough to understand its own working? focusing on a more tractable:

Can we model, and maybe induce the process of thought? Given that this modeling effort is a particular thought process, this second question is also recur sive in nature and more general: it permits us not to consider the limitations of our brains due to their biological implementa tion.

In this article I model the concepts of complexity, error, surprise, intuition, thought and insight. I also analyze the concepts of consciousness and feelings. I describe the features any thinking system must have. It appears that humans might be able to create such systems in future.
An interactive robotic simulation package
Authors: Parkin Robert E.
Published: March 2008

Described is a graphics package called RobSim intended for the real-time simula tion of the kinematics of automated workcells containing one or more robots with any configuration and up to six degrees of freedom. The user can enter information with joint or position teachboxes, or with joint or position spreadsheets. All trajecto ries are velocity controlled. The graphics illustrates each robot so its joint configura tion and position are evident. The scene can be viewed from any or all of the three projections onto the major planes and/or from one or more camera images taken from user defined positions. The software runs on any Macintosh computer from Mac Plus upwards.
Real-time berthing simulator for space station and space shuttle
Authors: Veerasamy Sam , Hubbard Joseph
Published: March 2008

A real-time pilot-in-the-loop berthing simulator is being developed at NASA/JSC (National Aeronauticsand Space Administration/Lyndon B. Johnson Space Center) to conduct a berthing study and to measure forces during contact conditions of the actual docking hardware mechanisms or ports for the Space Station Freedom (SSF) and the Space Shuttle (shuttle). In berthing, the docking ports of the SSF and the shuttle are brought together using the shuttle Remote Manipulator System (RMS) to control the relative motion of the vehicles. The berthing simulator consists ofa dynamic docking test system (DDTS), computer system, simulator software, and RMS workstation. During the real-time berthing simulation, the docking ports of the SSFand the shuttle, mounted on a six- degree-of-freedom (6 DOF) table of the DDTS and a fixed platform above the table, are brought together by a computer simulated 6 DOF shuttle RMS. Load cells are used on the fixed platform to measure forces during contact conditions of the docking ports. The point of resolution (POR) of the shuttle RMS is selected as the SSF docking port. The dynamic initialization, developed to synchronize the POR with the 6 DOF table, the data structure, and the real-time sequence of the berthing simulation are briefly described in this paper. The berthing test can be extended for any two orbiting vehicles, using a simulated RMS.
Man Overboard Rescue
Authors: Jensen Mary C. , Hines J. Matt , Foale C. Michael
Published: March 2008

The purpose of this paper is to examine the Manned Maneuvering Unit (MMU) Rescue Study that is being conducted in the Systems Engineering Simulator (SES) at the Johnson Space Center, Houston, Texas. The study explores the possibility of rescuing a man-overboard from the Space Station Freedom (SSF) using the MMU. The details of the study as well as some of the interesting problems that arise are discussed and a mathematical development of the equations that govern the behavior of two orbiting bodies is included.
Dynamics of Spacecraft and Manipulators
Authors: Thomas Segun
Published: March 2008

The status and some recent developments of dynamic analysis and simulation of spacecraft and manipulators are summa rized. Discussion focuses on a number of aspects: common methods for the rigid body analyses of spacecraft and manipulations; how one of these methods could be extended to include constrained systems and flexible bodies; the trend in multi-body analysis from the hand-derived, purpose-built algorithms to generic algorithms and finally to symbolic code generators; research directions in structural flexibility, coupling dynamics, order-n algorithms and other areas such as contact dynamics. Also, different approaches for generating dynami cal equations are illustrated and compari sons made between them. How dynamical equations could be developed for constrained systems is demonstrated. Lastly, effect and consequences of using the Euler-Bernoulli theory to represent a beam is discussed and an illustration of how a more rigorous beam theory could be incorporated into the dynamical equations is given.
A simulation of satellite motion for the study of cross-link pointing, acquistion, and tracking
Authors: Konkle Daniel , Greene Michael
Published: March 2008

A simulation for analyzing the orbits and crosslink parameters of any arbitrary combination of satellites is developed and presented. Primary consideration is given to the extraction of parameters critical to the pointing, acquistion, and tracking between satellites. This simulation is general in configuration and allows for arbitrary orbital parameters for the satellites. In addition, a computationally attractive method of determining when any two arbitary satellites are visible to each other is developed.
Simulation Network News
Authors: Fishwick Paul
Published: March 2008

This column focuses on a single topic within the field of computer simulation. All the material comes directly from the electronic news group (bulletin board) called Simulation Digest. The Digest can be obtained over INTERNET by accessing the news group 'comp.simulation' or by sending e-mail to: simulation-request@bikini.cis.ufl.edu'
Decimal pseudo-random number generator
Authors: Komo John J. , Park William J.
Published: March 2008

A pseudo-random generatar for decimal numbers (biquinary pairs) based on a combination of a binary and a quinary maximal-length sequence is presented. With an appropriate vector mapping of the combined maximal-length sequences the autocorrelation function is shown to be tri- level with approximate values of 1, 0.5, and 0. This effectively renders the numbers uncorrelated except at values equal to the lengths of the individual maximal-length sequences, where this autocorrelation is 0.5. The first peak value of the autocorrelation function occurs at a value equal to the length of the shorter of the component sequences.
A simulation approach to PERT network analysis
Authors: Badiru Adedeji B.
Published: March 2008

This paper presents simulation as a useful analytical tool for project network analysis. Simulation is a powerful tool for evaluating many of the decision parameters involved in project management. A computer program, named STARC, is used to illustrate the effectiveness of computer simulation for project planning. STATGRAPHICS software is used to illustrate some of the post-simulation statistical analyses that can be conducted.
Simulating a JIT/kanban production system using GEMS
Authors: Swinehart Kerry D. , Blackstone John H.
Published: March 2008

Just-in-time refers to the movement of material at the necessary place at the necessary time. The implication is that each operation is closely synchronized with the subsequent ones to make that possible.

A method of just-in-time production which uses standard containers with a single card attached to each. It is a pull system in which work centers signal with a card that they wish to withdraw parts from feeding operations or vendors. Kanban, in Japanese, loosely translated means, "card ", literally "billboard" or "sign ". The term is often used synonymously for the specific scheduling developed and used by Toyota Corporation in Japan.
Time series forecasting using neural networks vs. Box- Jenkins methodology
Authors: Zaiyong Tang  , de Almeida Chrys , Fishwick Paul A.
Published: March 2008

We discuss the results of a comparative study of the performance of neural networks and conventional methods in forecasting time series. Our work was initially inspired by previously published works that yielded inconsistent results about comparative performance. We have experimented with three time series of different complexity using different feed forward, backpropagation neural network models and the standard Box-Jenkins model. Our experiments demonstrate that for time series with long memory, both methods produced comparable results. However, for series with short memory, neural networks outper formed the Box-Jenkins model. We note that some of the comparable results arise since the neural network and time series model appear to be functionally similar models. We have found that for time series of different complexities there are optimal neural network topologies and parameters that enable them to learn more efficiently. Our initial conclusions are that neural networks are robust and provide good long-term forecasting. They are also parsimonious in their data requirements. Neural networks represent a promising alternative for forecasting, but there are problems deter mining the optimal topology and parameters for efficient learning.
Analytical computer simulation of a complete battlefield environment
Authors: Smith Roger D.
Published: March 2008

This paper discusses the necessity of studying new weapons systems with a comprehensive battlefield simulation. In the past, evaluations have been done with single event operations research models. These are useful, but today's systems are more interdependent than ever before. It is necessary to consider a system's contribu tion to the outcome of the battle and the availability of its support systems in carrying out its mission. A weapon may perform its designated function flawlessly but contribute little toward winning the war. A simulation which reproduces the entire environment in which a system will operate is a useful tool for answering complex questions about the utility of that system.
COSMOS: A simulation language for continuous, discrete and combined models
Authors: Kettenis Dirk L.
Published: March 2008

COSMOS is a new simulation language for description of continuous, discrete or combined continuous/discrete models. For continuous models, the COSMOS language definition constitutes a superset of CSSL with many additional structuring elements being incorporated, e.g. for convenient modelling of piecewise continuous models and variable structure systems. Discrete models are coded according to the process interaction world view.

The design of the language constructs makes it possible to write simulation programs in accordance with modem software engineering methodology. The model and experiment description, for example, are totally separated. In addition, models can be separated into submodels.
Simulation of single tether systems
Authors: Theron Carter J. , Greene Michael
Published: March 2008

A simulation of an orbiting single tether system composed of two subsatellites and a connecting tether is developed. The dynamics of the tethered system is modelled using a series of mass beads interconnected by springs and dash pots. The bead model allows the tether to become slack (no tension) and to deform to an arbitrary shape. Simulation results are presented and discussed for two types of motion: (1) tether vibrations and (2) end mass retrieval.
Extendible simulation software for dynamic systems
Authors: Rosenberg Ronald C. , Whitesell Joseph , Reid John
Published: March 2008

Simulation of dynamic physical system models is an integral part of the engineering design process. The software used to perform simulations and the language used to develop that software are, in themselves, important issues to the simulation commu nity. Some significant characteristics of simulation software are: robustness, solution efficiency, ease of learning, ease of regular use, range of modeling features, maintain ability, and extendibility. This work investigates the extendibility properties of the relatively new software methodology- object oriented programming - in a simula tion context. The reason is that many existing softwares seem to have reached an effective limit with respect to enhancing their capabilities within their original design framework. Object oriented programming, on the other hand, promises to provide good extendibility features by the very nature of its basic concepts. Our investigation, which involved the development of a pilot simula tion program in a series of planned stages, shows that this promise is soundly based for dynamic physical system simulation software.
A note on Wild and Pignatiello's experimental design strategy
Authors: Kleijnen Jack P. C.
Published: March 2008

In the December 1991 issue of this journal, Wild and Pignatiello proposed an experimental design strategy for designing robust systems using discrete-event simulation; their strategy used Taguchi's method for improving product and process quality in manufacturing. Now I propose two alternative techniques. One technique requires fewer observa tions than Taguchi's technique does. The second technique requires many more observations, but pays off since it quantifies the risk caused by uncontrollable environmental conditions.
Techniques for sensitivity analysis of simulation models: A case study of the CO2 greenhouse effect
Authors: Kleijnen Jack P. C. , van Ham Greet , Rotmans Jan
Published: March 2008

Sensitivity analysis is needed for valida tion, what-if analysis, and optimization of complicated simulation models. One set of techniques for sensitivity analysis consists of least squares curve fitting, regression analysis, and statistical designs such as factorial designs. In this case study these techniques are applied to several modules of a large integrated assessment model for the greenhouse effect, developed in The Nether lands. The regression models turn out to be valid approximations to the simulation models. Some estimated effects are quite surprising for the simulation users.
A multicompartmental model which simulates the Thallium-201 exercise stress test
Authors: Charkes N. David , Siegel Jeffrey A. , Maurer Alan H. , Hansen Christopher , Bove Alfred A.
Published: March 2008

Thallium-201 exercise stress testing is a standard method of identifiying ischemia of coronary artery disease, but no model exists for simulating the test. We have developed such a model using compartmental analysis methods. Blood samples were obtained from resting dogs following IV Tl-201 adminis tration, and fitted by a sum of four exponentials, indicative of a four compart ment system. The intercompartmental rate constants were estimated from fitting blood, heart and urinary excretion data using a table top computer; a best fit was obtained by non-linear least squares regression. By partitioning the heart into normal flow and ischemic zones, the effects of varying blood flow during treadmill exercise could be simulated, by summing resting flow and increased flow whose duration was varied by a damping circuit and delay line. Progressively decreasing flow in the perturbed model reproduced the abnormal Tl-201 distribution seen clinically by scanning, and experimentally. This model appears to be a useful simulation of the Tl- 201 exercise stress test.
Simulation of hemodynamics and regulatory mechanisms in the cardiovascular system based on a nonlinear and time-varying model
Authors: Ying Sun  , Chiaramida Salvatore
Published: March 2008

Software is developed to simulate pressure- flow relationships and regulatory mecha nisms in the cardiovascular system. The core of the software is a set of state equations that characterizes the cardiovascular dynamics based on an analog electrical model. The state is propagated forward in time by numerical integration with a time step of 1 ms. Nonlinear and time-varying elements are treated in the simulation by updating the state equations every 5 ms. Hemodynamic waveforms from each cardiac cycle are averaged and used as input to several models of circulatory regulation. The regulatory mechanisms under investigation include the systemic autoregulation, the carotid baroreflex, and the effect of intramyocardial accumulation of calcium ions on left ventricular contractility. It is shown that the simulation accurately represents several observations of the cardiovascular dynamics and physiology. The software should be valuable for develop ing hypotheses and protocols of in vivo studies, for integrating and interpreting experimental results, and as a tool of computer aided instruction.