In order to predict the ultimate load capacity and failure modes of a glued-laminated timer dome, two dome models are analyzed by two finite element methods. I-DEAS is utilized to generate shell elements and to compute nodal forces for the dome model. Wind load requirements are studied, and the effect of wind loads is investigated. At first, linear and nonlinear analyses of a space frame are carried out for four load combinations of dead load and snow load. The results are applied as a basis for the modeling of flexible joints and bracings. Then, the 3-D, 3-noded, curved, isoparametric beam element in the first model is replaced by a 3D, 2-noded, straight beam element for the second model. Purlins consist of truss elements. Flexible joints are modeled by adding connector elements to the ends of each beam. A bracing of truss element is applied to simulate the contribution of the decking. The dome is analyzed for two load conditions. The buckling pressures, buckling modes and the material behavior prior to buckling are examined. Finally, conclusions are made and several topics are recommended for future studies. / Master of Science

In this thesis we studied a BIST PLA generator (BPG) which generates BIST PLA layouts from the personality matrix of PLAs. We studied various BIST PLA designs and selected the design proposed by Treur, Fujiwara and Agarwal to be employed by BPG. The BIST PLA design is known to be effective in area and fault coverage. We modified the original design (which is presented for nMOS PLAs) for CMOS PLAs and added the control circuit. Implementation of BPG was based on MPLA, a PLA generator. Tiles necessary for BIST PLAs were created and added to the existing PLA tiles. The source code of MPLA was modified in order to place proper tiles and generate layouts of BIST PLAs. A circuit was extracted from a BIST PLA generated by BPG and simulated to verify the correctness of BPG. The performance of BIST PLAs generated by BPG was measured in three categories: area overhead, time overhead and fault coverage. / Master of Science

Rotor dynamic analysis of liquid ring seals depends upon the correct specification of seal dynamic stiffness and damping characteristics. These are in turn dependent upon several parameters, including the friction holding force between the sealing face and the mating retaining ring. Designers currently assume a value for effective friction coefficient in order to utilize methods for prediction of response and stability. This thesis presents the results of testing on twelve actual seal rings of varying configuration at pressures of 689, 1378, 2068, and 2757 kPa in a static seal test rig to experimentally determine values of effective friction coefficient. The results are presented in graphical form as average effective friction coefficient versus eccentricity ratio for forward and backward motion of the rings. / Master of Science

Long-term CREAMS and GLEAMS model simulations were used to assess significant differences in potential pesticide and nitrate movement to groundwater as affected by several combinations of tillage, cropping, and nutrient and pesticide management practices. The study area is in Richmond County in the Coastal Plain region of Virginia. Alternative management scenarios were based on crop management systems common to the area. Average annual loads from 35-year simulations were used in the analysis. Friedman's distribution-free analysis of variance and sign tests were found to be appropriate statistical procedures to assess significant differences between effects of management practices. Commercial nitrogen split-applied at recommended rates leached less than equivalently applied N from a single pre-plant poultry litter application. Leaching increased, but differences were less, when split-applied commercial N and pre-plant poultry litter applications were increased, with both sources apparently supplying N in excess of crop uptake potential. A 3-way instead of a 2-way split commercial N application reduced nitrate leaching minimally. Though tillage-cropping practices did affect percolation volumes, this did not result in high variability in leaching between practices. Leaching was most sensitive to crop-available N inputs regardless of tillage-cropping practices or the methods of N application. Pesticides with lower soil-adsorptivity, such as atrazine, had greater leaching losses especially on rotations with higher infiltration. However, a relatively high surface- application rate of atrazine for no-till corn did not produce higher leaching losses because additional losses were mostly by volatilization. Surface losses of highly adsorbed chemicals, such as gramoxone, were substantially reduced from no-till fields where runoff and erosion were reduced. Percent reductions in pesticide application rates resulted in equal or greater percent reductions in loading in surface runoff and percolation. / Master of Science

The task of determining which of many available color-difference formulae is appropriate for any give application can be arduous. Researchers and practitioners alike are faced with the selection of one formula which best describes perceived color differences under conditions in which the equation is to be employed. The idea that one equation can be formulated which takes into consideration all factors affecting perceived color difference has yet to be realized, and perhaps never will. As a result, an “every man for himself” approach has developed. Yet, color-difference equations are continually being applied to conditions without empirical evidence to support their use. While the 1976 CIELAB Color Difference Equation has been applied for some time in the photographic industry, its use in describing the perceived magnitude of large color differences in photographic prints has not been validated. Furthermore, a good deal of research has suggested that the CIELAB equation is not applicable under numerous conditions of color-difference assessment. Nonetheless, the results of the study reported here support the use of CIELAB over four other formulae (CIELUV, CMC (1:1), Richter, and Yu’v’) for describing perceived color differences in photographic prints. CIELAB produced moderate correlations for both experienced and non-experienced color judges over the range of color space examined. The results of this work support the use of the 1976 CIELAB Color Difference Equation for describing the perceived magnitude of moderate and large color differences in photographic prints. / Master of Science

Past research at Virginia Tech (VPI) explored the aerodynamic loss of the transonic VPI turbine blade, which 1s based on the pitchline profile of a high pressure turbine blade for a large commercial aircraft gas turbine. The current experiment explores the loss of the VPI blade for different axial solidity ratios near the design point. Ten percent changes in the solidity ratio were accomplished by varying the blade pitch and changing the blade stagger to maintain a constant throat to spacing ratio. Reaction, exit angle and exit Mach number were kept constant with this method. Cascades with three different solidities were tested in VPI’s transonic blowdown wind tunnel. Downstream total pressure loss and static pressure measurements were obtained. In addition, inviscid calculations were made for each case. Static pressure contours and Mach number profiles from the calculations were compared with the experimental results. A ten percent decrease in solidity caused no cascade loss penalty as compared to the Baseline solidity for a wide range of Mach numbers. Calculated blade Mach number profiles agreed well with experimental profiles except on the suction side near the throat and downstream of the shock/boundary layer interaction. Predicted downstream static pressure values agreed well with experimental values, except that the inviscid code tended to over-predict the pressure rise across the suction side shocks. / Master of Science

This report will describe the process of transport delay measurement along several points in the signal path for piloted flight simulators. Measurements were made in both the frequency and time domain. A new method for collecting data from video transitions was designed and tested. The accuracy and ease of use of the new method was compared to the previous data collection method. The transport delays for individual pieces of equipment were determined as well as the delays associated with the computational flow of two vehicle math models. Hardware and software was then modified to significantly improve the overall transport delay characteristics of the simulation. / Master of Science

The characteristics of a given stream or river are linked to the material that makes up its channel bed. Usually, a vertical stratification by particle size can be recognized. The presence a coarser surface layer is considered to be one of the most important features of a gravel bed stream. Since this surface layer consists of a distinct population of material, it is necessary to be able to separate it from the underlying material and quantify it distinctly. This is done through surface sampling. Two of the most common adhesive areal sampling techniques, and the subject of the present work, are known as clay and wax sampling. If the material obtained in an areal sample is analyzed as a frequency distribution by weight, it has been shown that the size distribution is biased in favor of the larger particles when compared to the results of a bulk sample. The present research shows that this bias is dependent not only upon the sampling method used to remove the material but also upon the size distribution of the sample itself. Not only are the raw results of areal samples not comparable with volumetric samples, but they are not comparable with other areal samples. Before any comparisons are made among areal samples, it is recommended that the size distribution of each areal sample be first converted into the size distribution that would have resulted from an equivalent volumetric sample. The features and limitations of the gravel simulation model that is used to obtain the necessary conversion formula is also the subject of the present work. In addition, the conversion of both matrix and framework supported gravel mixtures that has been areally sampled with either clay or wax, is addressed. Finally, criteria for approximating the minimum depth required for a volumetric sample is presented. / Master of Science

This thesis describes the development of a Model Analyzer prototype for the Simulation Model Development Environment that analyzes the specifications of a discrete-event simulation model. The Model Analyzer provides early feedback by operating on model specifications instead of waiting until an executable version is produced. Analysis of model specifications allows the modeler to detect errors early in the life-cycle and provides information about the model that may prove helpful in the verification, validation, and eventual translation of the model. With the help of a graphical user interface, the Model Analyzer provides automated and semi-automated support to the modeler. The Condition Specification, a world-view independent specification, of a model is parsed and stored in a relational database. Using graph-based diagnostic techniques, the Model Analyzer presents graphical representations of the model and performs analytical, comparative, and informative diagnosis. Also, an expert system is developed that uses generic simulation knowledge to simplify one graphical representation of the model. Based on the accomplishment of the design objectives, an evaluation of the Model Analyzer is conducted. Results from the expert system and Model Analyzer are provided that indicate the Model Analyzer and the expert system are helpful analysis tools. / Master of Science

The ever increasing demand on the air transportation system is causing a lot of congestion and delays, leading to large monetary losses and passenger inconvenience. This has prompted the development of many analysis tools to help the understanding of the airport system where some improvements could be performed to enhance the capacity of the airports. The Center for Transportation Research at Virginia Tech, in line with the FAA’s Capacity Enhancements Plan, is developing strategies to alleviate the airport congestion problem by developing a model (REDIM) to design and optimally locate high-speed exit taxiways. The objective of this research is to develop a computer simulation model to predict the airport capacity enhancements due to the above mentioned high-speed exit taxiways and as well as due to other changes in operational procedures, aircraft characteristics, airport environmental conditions, etc. RUNSIM (RUNway Simulation Model), a discrete event simulation model was developed using SIMSCRIPT 11.5 language. This model simulates dual operations on a single runway, with capabilities of simulating FAA standard and REDIM designed high-speed exits, variable intrail separations, different aircraft mixes, and weights, arrival rates and patterns, etc. Currently it has a 30 aircraft data base to perform the simulation. Its output includes such global statistics as total arrival and departure delays, weighted average ROT and its standard deviation, aircraft exit assignment table, arrival and departure event lists. It has the capability to perform multiple iterations on a single application, which helps in performing statistical analyses on the results for better inference. / Master of Science