This thesis examines those aspects of simulation with digital computers which concern the use of conceptual frameworks (CFs) for the design and implementation of a model. A literature review of CFs which are in common use is conducted. These CFs are applied to a complex modeling problem, a traffic intersection system. A comparative review of the CFs is given based upon the lessons learned from the above applications, and a taxonomy is developed. The research clarifies the differences that exist among the myriad of CFs in use today. In particular, the comparative review highlights the significant CF features that are necessary for successful model representation of discrete-event systems. The taxonomy provides a useful and meaningful classification of CFs and produces insights in to the conceptual relationships that exist among them. The characteristics of CFs that are desired to enable the development of model specifications that are analyzable, domain independent, and fully translatable are identified. The roles of CFs are better understood and specific potential directions for future research are pinpointed. / Master of Science

A mathematical simulation model based on the theories of transport phenomena and thermodynamics was developed to predict the storage behavior in a bed of corn. Coupled heat and mass transfer equations for a porous-capillary hygroscopic body were utilized in this study. The boundary conditions of heat and moisture were determined using the law of conservation, the law of heat and mass diffusion, and the law of convective heat and mass transfer. The system was solved using the implicit finite difference method with matrix inversion for an axisymmetric body with 36 annular elements. The bulk moisture diffusivities were determined using five mixing models(parallel, series, equivalent-resistor, modified Maxwell, and geometric mean). Five phase conversion factors(0.0, 0.25, 0.50, 0.75, and 1.0) were utilized to evaluate the five mixing models. Three laboratory storage bins, and eight grain sample columns were designed and constructed. Three experiments were conducted to enable the determinations of temperature and moisture content within the interior of the storage bin. The simulation model was verified by comparing the predicted results with the experimental values. Results indicate that the geometric mean model with a phase conversion factor of zero was the best selection. A postulated path for internal moisture flow was suggested. / Master of Science

A deterministic beef cattle computer simulation was used to estimate effect of genetic change in mature size (WMA), maximum daily milk production (PMA) and 60-d conception rate (CP) on costs per 100 kg slaughter weight (COST) and costs per 100 kg weaned weight (WNCOST) both adjusted for cull cow sales. Genetic inputs were defined as peak values for mature cows in an unrestricted environment and ranged from 400 to 800 kg WMA, 6 to 30 kg/d for PMA and 75 to 95% for CP. Two planes of nutrition for wintering cows, high and low and two economic schemes, high. versus low cow herd costs, were simulated. In all four systems, WMA and CP had quadratic effects (R² > .99) on cost over the range simulated. PMA effects were also curvilinear but could not be described by a simple quadratic curve (R² < .63). PMA appears to have a feasible range within which COST and WNCOST are little changed by changes in PMA. PMA levels below the lower end of the range were associated with increased costs due to increased calf death losses. Levels above the upper limit increased costs due to increased lactational stress and lower reproductive rates. The width of this range was reduced by lowering the plane of nutrition for wintering cows. The phenotypic manifestations of these three traits were also investigated, weaning rate (WRATE), weaning weight of an average 7 mos old steer (W117) and mature size (WMA). The results for these traits are similar to the genetic variables. The worth of a phenotypic standard deviation change in each trait (ah²) predict that a change in PMA or W117 is worth the most when outside the feasible range, followed by WMA and then CP or WRATE when COST is the measure. When WNCOST is the economic measure, PMA or W117 is again the most important of the traits but is now followed by CP or WRATE and then WMA. / M.S.

A comparative simulation study was performed to investigate the effect of uncertainty or unreliability in job processing times on designing schedules in a pure job shop environment. Five performance measures were employed in an effort to examine the effect of variations between estimated and actual processing times. These variations are common in job shop systems where estimations are used to set processing times. It was hypothesized that a variation has an effect on relative system performance. In addition, three priority rules, namely, FIFO, SOT and EDD, were studied to determine the best rule for controlling the shop in situations of unreliable processing times data. The percentage variation in processing times was clearly the dominant variable for most of the performance measures. A 60% variation in estimated processing times appeared to be the maximum level under which the mean flowtime, mean tardiness and percent of late jobs performance measures were insensitive. The simulation results indicated that the makespan and average shop utilization performance measures were insensitive to reliability of input information about processing times for up to a 100%. The performance of FIFO and EDD priority rules suffered drastically while SOT was the least sensitive to the reliability of processing times information. / M.S.

M.S.

The study dealt with developing methodologies for predicting basal area distributions and individual tree basal areas. Data for the study was from the Hill Farm Experiment Station at Homer, Louisiana. Five height-diameter (basal area) curves were examined to determine which was most appropriate for the data set utilized. The model H = a + b log(BA), where H denotes height and BA denotes basal area, was chosen as best, based on several fit and prediction oriented statistics. A stochastic basal area distribution model, called the parameter distribution model, was developed. The model was based on the Chapman-Richards growth curve. This curve was fit to all stems on approximately 3/4 of the data set. Two parameters of the curve were fixed a priori, leaving two parameters to be estimated. A sampling distribution was fit to the estimates of the rate parameter, k. Models were developed to predict the parameters of this distribution from stand variables. A model was then derived to predict m, the shape parameter of the C-R curve, from k and stand variables. Finally, an existing survival function was modified. The overall model was implemented as follows: first, the number of surviving stems was predicted. Then k and m values were predicted for each predicted stem. Substitution of these two values into the C-R curve yielded a predicted basal area for each stem. The previously mentioned height diameter curve was employed to predict a height for each predicted basal area. Stochastic elements were built into the prediction model for m and the height-diameter curve. Predicted basal area and height distributions were compared to observed on the remaining 1/4 of the data set. Although the two--sample K-S test was statistically significant, the observed and predicted distributions did appear to be close, in general, from a practical standpoint. This approach appears promising as a stochastic method of predicting size distributions. The Chapman-Richards curve was also modified for use as an individual tree basal area growth model. Two parameters of the curve were fixed, and the remaining two were modelled as functions of tree- and stand-level variables. The modified growth function fit the data well, but on an independent data set, a simpler linear model of basal area growth performed better in terms of mean difference and mean absolute difference between observed and predicted basal areas. Thus, the only anticipated use of the modified C-R model is in situations where extrapolation beyond the range of observed data is required, since this model has desirable long-term characteristics, whereas the linear model does not. / Ph. D.

Intermodal traffic has been steadily increasing on the nation's railroads since the mid 1950's. Intermodal flatcar activity is now second only to coal in terms of total car loadings throughout the industry. The intermodal segment of the nation's transportation system is expected to play an ever increasing role in the future. Intermodal managers faced with increasing demands on their systems, have expressed a need for methods to aid in the development of new management techniques, economic costing models, and management information systems. The computer simulation intermodal model that is presented in this paper is designed to aid managers with the analysis of their current terminal systems and to plan for future growth in intermodal activity. The intermodal terminal model employs discrete, next event, simulation techniques. The Q-GERT simulation language, developed by A. Allen B. Pritsker, provides the vehicle necessary to approximate the required activities and associated flow of transactions through the terminal system. Three specific types of containers and flatcars are provided for, in addition to provisions for over-the-road container pick up and delivery. Thus, the model is adaptable to complex terminal systems, including sea ports where highly specialized containers are commonly encountered with rail, truck and ship interfaces. It is possible to simulate terminal activities for any period of time required for a specific analysis. The model's simulation output can also be modified, with little difficulty, to provide estimates of specific variables of interest for a particular terminal. Provisions for the operating environment of a terminal are also included in the model. These include week-end work rules, switching rules, container consignee notification rules, types of handling equipment employed and the standard working hours for a terminal. The primary applications of the model are viewed to be in the areas of planning and analysis for intermodal terminal current operations and future design concepts. The graphical network orientation of the model, however, could provide managers with a communications tool to apprise upper level decision makers of new concepts. Current problems, with recommended solutions, could also be visually illustrated. / Ph. D.

Analysis and evaluation of the simultaneous growth and yield equations presented by Beck and Della-Bianca (1972) for predicting basal area growth and cubic-foot volume growth and yield in yellow-poplar stands after a single thinning indicated that a separate set of coefficients was required for stands thinned twice. A joint loss function involving both volume and basal area was used to estimate the coefficients in the system of equations. The estimates obtained were analytically compatible, invariant for projection length, and numerically equivalent with alternative applications of the equations. Given estimates of basal area and cubic-foot volume from these equations, board-foot volumes can also be calculated. As an adjunct to the stand level equations, compatible stand tables were derived by solving for the parameters of the Weibull distribution from attributes predicted with the stand-level equations. This procedure for estimating the parameters of the diameter distributions of the stands before thinning gave reasonable estimates of number of trees, basal area, and cubic-foot volume per acre by diameter class. The thinning algorithm removes a proportion of the basal area from each diameter class and produces stand and stock tables after thinning from below that are consistent with those generated before thinning. Finally, volume ratio equations were fitted to provide estimates of merchantable volume, i.b. or o.b., to either a specified diameter or height limit, where volume between any two diameter or height limits can be obtained through subtraction. Through rearrangement of the ratio equations, implicit taper functions were specified to predict height at a given diameter and diameter at a given height. / Master of Science

Forty-eight licensed pilots flew three cross-country flights in which certain aspects of perceptual workload were varied by altering the rate and number of instrument-displayed incipient danger conditions. A moving-base simulation of a single-engine general aviation aircraft was used. The sensitivity of eight mental workload estimation techniques investigated to changes in perceptual workload was within a univariate factorial design. Concurrently, the differential intrusion of the eight techniques on four primary task measures was investigated using multivariate analysis. Of the eight techniques, six displayed statistically-significant sensitivity to load level. These included two opinion rating scales, secondary task measures of time estimation standard deviation and tapping regularity, respiration rate, and a primary task measure of danger condition detection/identification time. No intrusion effect was found. Recommendations for applying the various techniques, based on the relative sensitivity of those showing significance, are discussed. / Ph. D.

The Monte Carlo method has been utilized to determine a procedure for the simulation of π° production near threshold. A number of computer programs have been written to perform as well as test the simulation process. The method consists of generating the pion angles in the center of mass frame and subsequently its decay gammas in the lab frame of the reaction. The gamma distribution generated is fitted via the method of maximum likelihood, and the angular distribution parameters are compared to those utilized in the generation process. Due to an ambiguity in the normalization of the parameters, the ratios of the parameters are considered instead of their absolute magnitude. The fitted parameters are found to agree with the parameters used in the generation program within the limits expected from statistical theory. / Master of Science