The object of this thesis is to determine the directional stability of a tricycle-geared aircraft during the landing roll. The motion of the aircraft is simulated by a computer program based on the appropriate equations of motion. Empirical aircraft and tire data are utilized in order to improve the simulation process. The stability of the aircraft is obtained by analyzing the motion of the vehicle after an initial disturbance about the vertical axis of the aircraft. The influence of the aircraft's velocity and other parameters on the stability is then determined. For the single-engine Cessna, the results show that a steady-state yaw angle is obtained after an initial disturbance. The results are presented graphically to show the effect of various parameters on the aircraft's stability. / Master of Science

The research described in this thesis is divided conveniently into three components: (1) the credibility assessment of a simulation model for the investigation of dynamically reconfigurable computer network architectures, (2) a comparative study of the standardized time series method of simulation output analysis, and (3) an experimental comparison of the effects of dynamic reconfigurability on message transmission delays and network throughput. The credibility assessment relies almost completely on verification procedures applied to both communicative and program representations of the model. In the absence of an extant system, validation consists of extensive, program traces to assure that model behavior matches expectations and reflects no inconsistencies. Application of a standardized time series technique produces the advantages reported by other researchers with regard to sampling efficiency (information derived per sample unit) when dynamic reconfigurability is precluded. The inherent non-stationarity induced by reconfiguration reveals the sensitivity of standardized time series and the consequent adjustment to preserve coverage. A compromise between coverage and sampling efficiency prompts the choice of the batch means method for experimental comparison. Experimental comparison shows that under high traffic variability reconfigurability / Master of Science

The highway related revenues for the Commonwealth of Virginia from three major tax sources; fuel tax, registration fee, and sales and use tax are estimated under three scenarios. Each scenario assumes different economic conditions for the future. The base case expects normal or moderate situations for future economy, where the optimistic case expects lower inflation rates and the pessimistic case assumes higher inflation rates. Two modeling approaches have been used in forecasting the fuel tax revenue. One is based on travel, and the other is based on gasoline demand. The sales and use tax revenue has also been forecasted using two different approaches. One method depends on the demand for vehicle, and the other on the historical amount of revenues generated. Registration fee revenue for five types of vehicles are forecasted using number of registered vehicles and the average registration fees. A comparison of the developed model with other existing state revenue forecasting models are also presented. / Master of Science

A stochastic computer model was constructed to simulate cow reproductive performance. Parameters for single-service conception rate and days from calving to first service (postpartum interval) were developed from the literature. Estimates of the heritability and repeatability (h², t) of each of these traits in four simulated data sets were RUN1 (.20, .20), RUN2 (.15, .20), RUN3 (.10, .10), RUN4 (.05, .10). Binomial conception rate parameters were normalized to simulate assumed normal underlying genetic and environmental distributions. Postpartum interval has a non-normal phenotypic distribution that was produced by combining an assumed normal genetic distribution with a Pearson III gamma distribution of environmental effects. The breeding season was 63 d. Simulation outputs included annual conception rate (BCR), first service conception rate (FSCR), date of first service (FS), number of services (NS), conception-calving date (CD), postpartum interval (PPI), actual weaning weight (ACTWW) and adjusted 205-d weaning weight (ADJWW). Realized heritabilities and repeatabilities for these outputs were estimated from half-sib intraclass correlations based on 5 yr of records on 100 herds of 50 cows each. Realized heritabilities (RUN1-RUN4) for BCR, FSCR, FS, NS, CD, PPI, ACTWW and ADJWW ranged from .165-.028, .187-.055, .023-.010, .227-.071, .071-.032, .158-.022, .148-.176 and .156-.203, respectively. Repeatability estimates (RUN1- RUN4) for BCR, FSCR, FS, NS, CD, PPI, ACTWW and ADJWW ranged from .178-.059, .212-.108, .125-.101, .244-.118, .187-.155, .207-.116, .266-.263 and .280-.286, respectively. / Master of Science

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An effective medium approximation and a refined Monte Carlo simulation procedure for solving the stochastic groundwater flow problem are presented. The effective medium approximation permits one to solve the stochastic groundwater flow problem in a single run to generate the expected pressure head field. The proposed effective hydraulic conductivity expression for the effective medium is of the same form as the local Gardner’s equation and is easy to use. The refined Monte Carlo simulation procedure uses analytical means to estimate the sample size by controlling the error incurred in using the sample average in place of its population mean at a chosen confidence level. This estimator consistently performs well. Also, a variance reducing estimator which is different from the simple average for pressure head is developed. This estimator takes advantage of the correlation between the saturated conductivity and the pressure head distribution to reduce the output variance and is unbiased. This reduced variance results in a smaller width of uncertainty about the predicted pressure head. Both the effective medium approximation and the Monte Carlo approaches perform well when applied to several problems. / Ph. D.

A thesis submitted to the faculty of Engineering, University of the Witwatersrand, Johannesburg , in fulfillment of the requirements for the degree of Doctor of Philosophy. Johannesburg, November 1994 / Organ function is often characterised using imaging techniques. In particular a tracer is often used which does not react with tissue, is low in concentration, follows body fluid flows and is distinguishable from the observed system and thus measurable. These requirements ensure linear characteristics of the tracer. In this thesis, these linear characteristics are used to develop a generalised mathematical theory to determine organ function from imaged tracer experiments. The theory is based on anatomical and physiological information for single and multiple input organs. [Abbreviated Abstract. Open document to view full version] / MT2018

Recent water scarcities across the southwestern U.S. with severe effects on the living environment inspire the development of new methodologies to achieve reliable drought forecasting in seasonal scale. Reliable forecast of hydrologic variables, in general, is a preliminary requirement for appropriate planning of water resources and developing effective allocation policies. This study aims at developing new techniques with specific probabilistic features to improve the reliability of hydrologic forecasts, particularly the drought forecasts. The drought status in the future is determined by certain hydrologic variables that are basically estimated by the hydrologic models with rather simple to complex structures. Since the predictions of hydrologic models are prone to different sources of uncertainties, there have been several techniques examined during past several years which generally attempt to combine the predictions of single (multiple) hydrologic models to generate an ensemble of hydrologic forecasts addressing the inherent uncertainties. However, the imperfect structure of hydrologic models usually lead to systematic bias of hydrologic predictions that further appears in the forecast ensembles. This study proposes a post-processing method that is applied to the raw forecast of hydrologic variables and can develop the entire distribution of forecast around the initial single-value prediction. To establish the probability density function (PDF) of the forecast, a group of multivariate distribution functions, the so-called copula functions, are incorporated in the post-processing procedure. The performance of the new post-processing technique is tested on 2500 hypothetical case studies and the streamflow forecast of Sprague River Basin in southern Oregon. Verified by some deterministic and probabilistic verification measures, the method of Quantile Mapping as a traditional post-processing technique cannot generate the qualified forecasts as comparing with the copula-based method. The post-processing technique is then expanded to exclusively study the drought forecasts across the different spatial and temporal scales. In the proposed drought forecasting model, the drought status in the future is evaluated based on the drought status of the past seasons while the correlations between the drought variables of consecutive seasons are preserved by copula functions. The main benefit of the new forecast model is its probabilistic features in analyzing future droughts. It develops conditional probability of drought status in the forecast season and generates the PDF and cumulative distribution function (CDF) of future droughts given the past status. The conditional PDF can return the highest probable drought in the future along with an assessment of the uncertainty around that value. Using the conditional CDF for forecast season, the model can generate the maps of drought status across the basin with particular chance of occurrence in the future. In a different analysis of the conditional CDF developed for the forecast season, the chance of a particular drought in the forecast period can be approximated given the drought status of earlier seasons. The forecast methodology developed in this study shows promising results in hydrologic forecasts and its particular probabilistic features are inspiring for future studies.

To provide a basis for the development of interaction curves for tubular beam-columns of annular cross section, a general purpose beam-column computer program is developed, and used to determine ultimate load capacities. The paper presents the analytical model and the computer method. The analytical results are compared with published test data as well as experimental data obtained as part of this project.