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The purpose of this research paper was to translate a Computer Model (SIGART), capable of simulating a progressive traffic signal lights system, from Burroughs B5500 FORTRAN II to the IBM 360 FORTRAN IV computer language, to outline the program algorithm, to set up detailed program documentation and to validate this model by applying practical system data. Expansion of the SIGART program by addition of an option to produce a time space plot of the output data utilizing a Calcomp plotter was also to be considered.

The purpose of this research report is to compare two simulation languages; GASP and GPSS. An economical comparison was performed by simulating the same system in each language and examine parameters such as run time, core size, program time, and debug time. A statistical comparison of the results of the system simulation was also performed using a 90% confidence level testing procedure. The system simulated was the proposed Orlando Police Department Automatic Vehicle Locator (AVL) Operational System.

Simulation is one of the most important tools for system performance evaluation in communication networks as well as many other areas. However, simulation is computationally intensive. A traditional sequential simulation of a complex model or a rare-event system may require days or even weeks of computer execution time. Therefore, simulation often becomes a bottleneck of a performance study. With the growing availability of multiprocessor computing systems (e.g., tightly-coupled parallel computers or distributed networks of workstations), parallel simulation, which parallelizes a simulation program for execution on multiple processors, becomes an attractive means to reduce simulation execution time. With few exceptions, existing parallel simulation algorithms can be broadly classified into four methods: multiple replication, time-parallel, parallel regenerative, and space-parallel. Each method is associated with some advantages and limitations. We study these methods and propose a number of parallel simulation algorithms for a class of communication network systems modeled by queueing systems. In multiple replication simulation, each processor simulates a replication of the target simulation model independently. Due to the lack of a prior: knowledge about the steady state conditions, an arbitrarily selected initial state is often used for each simulation run. This can result in significant bias in the simulation outcome. To reduce this initial transient bias, we propose a polling initialization technique, in which a pilot simulation is used to find 'good' initial states that are representative of the steady-state conditions. Time-parallel simulation obtains parallelism by partitioning the time domain of the simulation model into a number of batches. Each batch is computed by a processor independently. Time-parallel simulation has not been fully explored by the research community partly because finding the exact initial states for the batches is often challenging and problem dependent. We develop two approximation time-parallel simulation algorithms for acyclic networks of loss G/G/1/K and G/D/1/K queues. These algorithms exploit unbounded parallelism and can achieve near-linear speedup when the number of arrivals is large. Two other time-parallel approaches are also proposed for Markov chains. For more general simulation models, an approximation approach that uses a substate matching technique is presented. Parallel regenerative simulation exploits parallels in by partitioning the simulation trajectory into a number of regeneration cycles. The amount of parallelism relies on the regeneration frequency of the model. In practice a regeneration state that has a short expected regeneration cycle length often does not exist in the target simulation model. As a result, a sufficient number of observations can not be obtained in a finite simulation interval. To overcome this constraint, we propose a partial regeneration algorithm that uses a substate matching technique to increase the number of observations. When the memory requirement of the target simulation models exceeds the storage capacity of a single processor, space-parallel simulation is an appropriate method. In space-parallel simulation, the target simulation model is decomposed into a number of components such that each component contains a disjoint subset of the model state variables. Each component is mapped into a logical process which is responsible for computing the trajectory corresponding to the component over the simulation time interval. An important class of space-parallel simulation is the conservative simulation, in which each logical process can proceed processing an event only if the process ensures that no event. will arrive later with a smaller timestamp. A number of previous experimental studies have suggested that lookahead, a capability that allows a simulation to look into the simulation time future, plays an important role in the performance of the conservative simulation. Although the performance of conservative simulation has been the interest in many previous studies, there has been a lack of formal arguments to quantify the impact of lookahead to conservative simulation performance. To address this question, we develop stochastic models to study the relationship between the amount of lookahead and the simulation performance with respect to different model topologies. We show that for closed simulation models, the simulation execution time is proportional to the amount of lookahead. For open models, on the other hand, lookahead is effectively useless when the simulation length is long. / Ph. D.

The mining of coal within 110 feet below a previously mined seam creates interaction effects which can be detrimental to work in the lower seam. These interaction effects are characterized by zones of very high stress and result in floor and roof instability and pillar crushing. Recent developments in the field of ground control make it possible to determine with a certain degree of confidence the location of these zones and estimate the degree to which the interaction will affect the lower seam. This information has been incorporated into a software package for microcomputers which will predict lower seam problems and suggest design criteria for minimizing the difficulties which will be encountered. / M.S.

A computer simulation program was developed to simulate the Virginia Tech low pressure steam heating system. Based on the total heat available to the buildings and the buildings' relative transmission heat losses, this program will determine the distribution of the heat produced by the steam plant and determine the conditions of the steam at the buildings and along the pipeline. The above distribution of heat consists of heat lost from the pipeline and heat delivered to the buildings. This program was used to perform a preliminary performance evaluation of the steam heating system during the 1983-84 heating season, and for the coldest day (12/24/83) and day of maximum steam load (2/29/84) in particular. During this heating season 2.397 x 10¹¹ Btu was delivered by the steam plant to the buildings. Also, about 3% of the total heat delivered by the steam plant was lost through the pipeline. To enhance the usefulness of this program two actions were recommended. First, the steam pipeline and the buildings should be instrumented to allow for verification of the program results. Second, in order to produce more accurate results the program's data should be based on more accurate measurements of the pipeline characteristics and the building heating loads. / Master of Science

A hydrostatic drive test stand was constructed to aid in the instruction of the characteristics of hydrostatic transmissions and to develop a time-varying load in a shaft to compare torque transducers. A mathematical model of the device was derived using the bond graph approach and was implemented using the Advanced Continuous Simulation Language (ACSL). The test stand was used to obtain experimental data to try to refine the model parameters. To facilitate the measurement of system flows, a microprocessor-based digital flow indicator was developed. Steady-state tests were performed at various constant pump swashplate angles; for the dynamic tests, the pump swashplate angle was cycled from zero degrees to 6.5 degrees. / Master of Science / incomplete_metadata

This paper presents a hierarchical modeling method that can be used to simulate a Flexible Manufacturing System (FMS) at all levels of detail. The method was developed specifically to aid the software development needed for the hierarchy of computers that are present in an FMS. The method was developed by modeling an existing FMS. The models developed of the existing FMS are described in detail to provide an example of how to model other FMSs. The basic building blocks needed for designing other FMSs with this modeling method are provided. The models were written in the SIMAN simulation language. SIMAN was found to be an easy language to use for the hierarchical modeling of FMSs. / M.S.

The purpose of the thesis was to investigate the influence communication architecture decisions have on the performance of a simulation system with distributed components. In particular, the objective was to assess the relative importance of factors affecting reliability and variability of an external data interface to the performance of the simulation, as compared to factor within the simulation itself.

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