An alternative to the displacement finite element method, the hybrid stress model, is applied to problems in geomechanics. A two-dimensional finite element procedure based on the hybrid stress model is developed for simulation of construction sequences including underground and surface excavations. In this procedure, an eight-node isoparametric element is employed. In the analysis, the effect of soil-structure interaction is incorporated by using a special interface element for behavior at the contact between two different materials. In the elastic-plastic analysis, the Drucker-Prager model is used as a constitutive law. In order to verify the computer program and to examine the accuracy of the hybrid stress model, several problems such as a beam, a plate with circular hole, and footings are analyzed, and the results are compared with those from the displacement method and closed-form solutions. The proposed procedure for simulation of excavation is verified by performing an excavation in linear elastic material. Finally, two field cases of excavation are solved and the results are compared with the displacement method and the field observations. It is believed that the proposed (stress) hybrid method can have significant potential of application for various problems in geomechanics, and it can be particularly appropriate for a situation where computation of stresses is important. / Ph. D.

To achieve the non-proliferation objectives of the United States, the reprocessing of spent nuclear fuel was discontinued in 1977. Since current at-reactor storage capacity is based upon a nuclear fuel cycle which includes reprocessing, this halt in reprocessing is causing large quantities of non-storable spent fuel. Permanent nuclear waste storage repositories will not be available until the end of the century. Present Department of Energy policy calls for sufficient interim Away-Prom-Reactor (AFR) Storage capacity to insure tilat no commercial reactor has to shut down due to inadequate storage space for discharged spent fuel. A descriptive simulation model is developed which includes all aspects of nuclear waste disposition. The model is comprised of two systems, the second system orchestrated by GASP IV. A spent fuel generation prediction module is interfaced with the AFR Program Management Information System and a repository scheduling information module. The user is permitted a wide range of options with which to tailor the simulation to any desired storage scenario. The model projects storage requirements through the year 2020. The outputs are evaluations of the impact that alternative decision policies and milestone date changes have on the demand for, the availability of, and the utilization of spent fuel storage capacities. Both graphs and detailed listings are available. These outputs give a comprehensive view of the particular scenario under observation, including the tracking, by year, discharge from every reactor. Included within the work is a review of the status of spent fuel disposition based on input data accurate as of August 1980. The results indicate that some temporary storage techniques (e.g., transshipment of fuel and/or additional at-reactor storage pools) must be utilized to prevent reactor shutdowns. These techniques will be required until the 1990’s when several AFR facilities, and possibly one repository, can become operational. / Ph. D.

A simulation model is developed in SLAM II to study and analyze conveyor systems.. The adequacy of the model is tested by applying it to a conveyor layout as well as some variant designs. 1he problem of modeling large systems is reduced by decomposing the system into smaller segments (subsystems). Different types of conveyors are considered. Programming modules are prepared for feasible conveyor types and segments. These simulation modules are integrated into a system. / Master of Science

The Model Generator, one of the automated tools of the Model Development Environment, supports the process of discrete event simulation model development by guiding a modeler through model definition and model specification. This research focuses on the specification process within the Model Generator. A design is proposed and requirements are established for extending an existing generator prototype to incorporate model specification. The specification is obtained interactively by engaging a modeler in a series of dialogues. The modeler's responses are stored in a database that is structured to represent a model specification in the notation prescribed by Condition Specifications. The dialogue has been designed to solicit the specific information required for a Condition Specification. Furthermore, the dialogue has been organized according to levels with each dialogue at a given level responsible for completing the database elements prescribed for that level. The results of initial experimentation with an implementation of the design are positive. The prototype appears capable of producing a Condition Specification while offering broader support to the modeling task in concert with utilization and enforcement of the underlying philosophy imparted by the Conical Methodology. / Master of Science

The problem of systems' optimization through simulation was investigated. An external modular optimization procedure applicable to the simulation model of a multiple-variable, single-response, system whose overall performance is defined in terms of cost or profit in designed. The procedure consists of four modules: The simulation model, A sequential search technique, A "Sampling Routine", and A "Control Module". The first two modules were treated as "black-boxes" and were assumed to be given. The third module controls the sampling process. This module offers dynamic adjustments. of the necessary sample size at any point in the course of the search for an optimal system's design. The fourth module controls the optimization process. This module utilizes a statistical inferential technique in determining the duration of the optimization process, such as to maximize the net return from its application. The procedure offers the possibility of utilizing various sequential search techniques, requires no modifications of the simulation model, and can be applied to a reasonably broad class of optimization problems. Descriptions of the procedure's modules, as well as illustrative examples of their implementation are included. / Master of Science

A computer simulation model written in PL/I of the flowering phenology of C. thoermeri and the seasonal population dynamics of R. conicus was constructed based on a synthesis of the literature, and on laboratory experiments which determined developmental periods, mortality for immature stages and the ovipositional pattern of R. conicus. The model successfully simulated the ovipositional pattern of R. conicus and the flowering phenology of C. thoermeri. Larval population dynamics of R. conicus, in the model however, did not fit the validation data. Though the model was temporally synchronized with the field data, the model results were one degree of magnitude less. The poor fit was attributed to sampling errors in the validation data. Studies of the overwintering mortalities of both organisms were performed. R. conicus was found to overwinter with lowest mortality on musk thistle rosettes; mortality was 73.6% in 1981, higher than previously reported but possibly more representative of field conditions. No overwintering mortality was observed for established rosettes of C. thoermeri. Studies of seed dispersal of C. thoermeri were performed to determine the percentage of seeds removed from the vicinity of the plant where they originated. Seed dispersal observed for different wind velocities demonstrated that less than 1% of seeds are blown further than 100m and most seeds are deposited within 50m of the release site. A Gaussian model of seed dispersal based on experimentally determined parameters and literature values corroborated these results. / Master of Science

A model is developed for use by logistics planners in determining period by period maintenance requirements for repairable item populations. The model generates maintenance requirements with respect to manpower and facility requirements and spare parts requirements. The model is capable of capturing nonsteady-state failure behavior of populations of repairable items. Each item within the population is broken down into one or more families of components and subcomponents that can have different failure/repair characteristics. Probability of component failure may be generally distributed. A specific data requirement for the model is established. The model is structured to allow the user to conduct various"what if gaming" through an iterative procedure on a personal computer. This research document includes a literature review that establishes a history of logistics modeling. The literature review provides impetus to the proposed research by defining a need for a transient state model for maintenance requirements planning. The model is validated by a case study involving the generation of maintenance requirements for a case population. / Master of Science

To reduce the variance of metamodel coefficients, simulation analysts often advocate the use of correlation induction strategies. Under certain conditions, these strategies have been shown to reduce the variance of metamodel coefficients without producing significant bias in the coefficient estimates. Although these procedures are very useful for estimating metamodels, the application of many statistical analysis techniques is inappropriate unless the analyst is assured that a pure error component is present in the response. Crenshaw and Tew have demonstrated the absence of pure error in experiments in which all random number streams are used to induce correlations. Mihram argues that a pure error component can be maintained by selecting the seeds for at least one random component randomly and non-repetitively for all design points and replications. In this thesis, random components for which seeds are randomly and non-repetitively selected are referred to as pure error generators. This thesis examines the selection of pure error generators in the context of univariate response, replicated simulation experiments. To assess the impact of pure error generator selection, we give the results of an extensive series of Monte-Carlo experiments in which the Schruben-Margolin strategy is applied for each possible pure error generator in each of two simulation models. To determine causes for the differences in pure error generator performance, four pure error generator selection methods are outlined, tested, and compared to the results of the Monte-Carlo experiments. The results strongly suggest the importance of careful pure error generator selection and indicate that the primary difference in their performance is related to their ability to maintain the prescribed correlation structures of the correlation induction strategy. / Master of Science

This thesis presents a simulation and performance evaluation of the Vector Sum Excited Linear Prediction Coder (VSELP). Recently there has been an incredible demand for personal communication services. To meet this demand various technologies have been developed. The U. S. digital cellular standard uses the 8 kbps VSELP speech coder to accommodate more users in the same bandwidth. This standard is currently being introduced in several markets. Performance evaluation of the speech coder in terms of speech quality is done for different channel conditions using the BERSIM simulation tool. Simulations for realistic channel conditions were performed using the SIRCIM simulation tool. Quantitative results in the form of mean squared error and qualitative results in the form of speech quality are presented. / Master of Science

A real time generation station simulator which is to be used as an operator trainer is developed. The software developed simulates a Y-wound generator connected to an infinite bus through a Δ/Y step up transformer and two parallel lines. The operation of the generator is simulated under normal or abnormal conditions of the power system or the generator itself. The system is simulated in two microcomputers and interaction between the simulator and the operator is provided through the computer's screen and keyboard. Different screen representations show the behavior of the generator at any moment and based on these the operator can take any action through the generator controls provided in his keyboard. / Master of Science