This thesis presents elastic finite difference simulations of two dimensional wavefield propagation for line-9, recorded during the 1993 part of the multi-institutional, multi-year Mendocino Triple Junction (MTJ) Seismic Experiment. Line-9 is a high-resolution, large-aperture seismic profile oriented in north-south direction, extending from the subduction regime north of the MTJ to the transform regime south of the MTJ. Snapshots of the wavefield are recorded during the simulation to create a movie which assists with the analysis of the synthetic seismograms. The simulations are computed on a 64 processor CM-5 parallel supercomputer. First a velocity model obtained by the Mendocino Working Group is examined. The model is based on information from depth-migrated single-fold reflection profiles and tomographic inversion of first arrivals. The synthetic seismic sections show acceptable first arrival traveltime fit but fail to correctly model secondary arrivals and amplitude variations of the wavefield. Based on the shortcomings of the initial model an alternative model for the north-south line is proposed. The new model introduces several distinct structures, like a subducted Gorda plate, a slabless window, and a wedge shaped low velocity zone between Franciscan material and Gorda plate. The big difference between the two models is that the initial model is too smooth to contain any discontinuities and cannot account for any reflection arrivals. In addition all structures in the lower crust of the alternative models are located about 4 km deeper than the equivalent velocities in the initial model. The seismic sections of the alternative model show much improved traveltime and amplitude fit. Also, some characteristics of the wavefield observed in the field data (e.g. traveltime oscillations, amplitude variations, and discontinuous arrivals) are also observed in the synthetic seismograms.. The position of the southern end of the Gorda plate (SEDGE) is at 80 km in the model (39.7°N). Because of the limited resolution it is not possible to resolve whether the Gorda plate just north of the SEDGE is fragmented or continuous. To add attenuation by scattering or coda waves generation to the model, the effects of a stochastic velocity description for Franciscan rocks on the wavefield are explored. The best velocity contrast between sandstones and melange units in a bimodal, seifaffine, sinuous connected model is determined as 0.5 km/s. Stochastic models of this kind successfully model background noise and coda waves and to some degree discontinuous phases, amplitude variations, and traveltime oscillations. They cannot, however, account for the full range of characteristics observed in the field data. For this, additional large scale velocity variations must be added to the model. For the final model, the (deterministic) alternative model and the statistical description of Franciscan rocks are combined. The resulting wavefield shows good amplitude and traveltime fit and the observed wavefield characteristics are similar to the characteristics of the field data. / Graduation date: 1997 / Best scan available for figures.

A computational model for a resonantly coupled alpha free-piston Stirling cooler is presented. The cooler consists of two isothermal working spaces for compression and expansion connected by a regenerator consisting of a stack of narrow parallel channels. The regenerator is assumed to have a linear temperature distribution along its axial direction and the working fluid is taken as an ideal gas. Control volume analysis is adapted in this model, in which each of the components of the cooler is considered a separate control volume. The compression piston is given a predetermined motion to provide the work needed by the cooler. The expansion piston and the gas trapped between the piston and the walls of the expansion cylinder are modeled as a mass, spring, and damper system. The motion of the compression piston generates a pressure difference across the cooler, and forces the working fluid to pass through the regenerator. The expansion piston responds to the pressure in its space according to Newton's second law of motion. The motion of the expansion piston is governed by the forces originating from the pressure and the cold side gas spring and dash-pot. In this way the dynamics of the moving pistons are coupled to the thermodynamics of the cooler system. A definition for the coefficient of performance (COP) that considers the heat transfer by conduction through the material making up the regenerator is introduced. This definition of the COP reflects the dependence of the cooler's performance on the length of the regenerator. From a systematic variation of this regenerator length, an optimal value can be found for a given set of operating parameters. Conservation laws of mass, momentum and energy along with ideal gas relations are used to form a set of equations fully describing the motion of the pistons and the thermal state of the cooler. A marching-in-time technique with a Runge-Kutta scheme of the fourth order is adapted to integrate the equation of motion. The plots of the motion of the pistons, the pressure-volume diagrams of the workspaces and the COP plots are provided to describe the cooler behavior. / Graduation date: 1999

A computer simulation program, Controlled Atmosphere Simulation (CAS), was written in Microsoft Visual Basic 3.0, Professional Edition to evaluate energy use by three type of atmosphere generators used in fruit storage warehouses. The program consists of pulldown time and energy use models for a membrane air separator, an ammonia fractionating burner, and a catalytic oxygen burner. Predicted results subsequently became input to an interactive computer program, Fruit Storage Refrigeration Energy Simulation (FruSTRES), which was developed to simulate energy use by cold storage ammonia refrigeration systems. The resulting model package was then used to predict overall annual energy use in fruit storages, based on number and size of rooms, building construction, equipment operation (both refrigeration and CA), commodity stored, storage period(s), and weather conditions. The CAS accurately predicted the pulldown time of each type of equipment under normal operation. The resulting model package (CAS and FruSTRES), will be an invaluable tool in design and analyses of ammonia refrigeration and atmosphere generation systems used in common and controlled atmosphere fruit storages. / Graduation date: 1998

The principal objective of this study was to investigate process simulation and optimization of an existing offshore natural gas process which needed profitability improvements. Optimization was done using two alternative approaches: a global approach (response surface methodology) or a local approach (successive quadratic programming). The global approach was characterized by process performance at selected case study points throughout the feasible operating region and made use of global information, while the local approach was characterized by numerical iterative computation driven by local information in the neighborhood of a single point in the design space. A Box-Behnken design was used as a second-order response surface design for the estimation of correlation between process simulator design variables and an economic objective function, and the estimation model was then optimized. In the local approach, a process simulator (ASPEN PLUS) with optimization capabilities was used. From the investigation, three major design variables were identified that had significant effects on the objective function of maximum product sales value. The three variables were: the compression ratio of the Production Compressor, the heat duty of the Gas/Gas Exchanger, and the compression ratio of the Expander. The results indicated that profitability of the offshore natural gas process could be improved by greatly (about 60%) increasing the production of raw condensate, even though this meant slightly lower (about 4%) sales of natural gas as a main product. The improvement found, however, was only 7% when the design variables were limited by currently installed equipment. The global approach was found to converge more consistently because once the global quadratic model was calculated, convergence to its unique optimum was simple. On the other hand the local approach had non-unique termination points due to the small effects of some design variables. The global approach provided better engineering insight since the effects of each design variable could be easily calculated from the quadratic model. However, the global approach was less efficient in terms of engineering manpower because of the time required to identify the quadratic model. / Graduation date: 1995

One of the commonly used simulation approaches is process orientation. This is based on the use of nodes (or blocks) that perform functions in series. In spite of the compactness and ease of learning that characterize process-based simulation, many languages are somewhat complex, primarily the result of the large number of nodes that users have to deal with and the considerable gulf between a user's abstract notion of the model and the details required to implement it. This paper describes a process-based simulation system that integrates object-oriented programming, visual interactive simulation and graphical model specification. Object-oriented programming techniques and simulation seem to be a natural match. The process classes are represented as network blocks or network nodes, and the process as a network diagram or directed graph. Arcs connect the nodes and specify the next step in the process. Each block type has its own icon. Developing an application model requires selecting a set of nodes, connecting them, and specifying the parameters (such as activity durations and random number streams) of the nodes through dialog boxes or inspection panels. Nodes have been designed to accomplish the major requirements in simulation modeling, including creation and termination of entities, attribute assignment, branching, queues and resources, activity specification and statistics collection and display. Additional system features include: statistics manipulation for steady state results, execution trace utilities, and limited animation capabilities. The system has been implemented for the NeXT programming environment using Objective-C. The NeXT includes an extensive object-oriented user interface library, relatively powerful hardware, and a modern multi-tasking and virtual memory operating system. Objective-C allows object-oriented concepts such as inheritance and subclassing while adding only a few constructs to that of the C language. The system modeling environment developed in this research enhances the applicability and usability of high level modeling tools. The program also provides a platform for further work on the distribution of the modeling process over several cooperating, communicating applications. / Graduation date: 1992

S3 (Softwood Sawmill Simulator) is a sawmill simulation system for modeling the operations of Pacific Northwest softwood lumber mills. S3 consists of three main parts. The first part is the framework for construction of the sawmill layout. The second part focuses on individual machine centers, their process and down times, and their interconnections. The third part consists of databases for raw material and final products. S3 inputs process logic from external data files. All parts are integrated in an object-oriented framework. The system was developed using the object-oriented environment, Actor. All data input and output are through database files in dBASE IV format. S3 can model a sawmill represented by the machine center and connection types defined in S3. The size of the model is controlled by the Actor programming environment. The construction of a sawmill model is demonstrated. / Graduation date: 1993

The ion implantation process is a very precise, controllable, and reproducible method used to enhance material properties of finished components such as ball bearings. Essentially, the target material is bombarded by accelerated ions to form a thin alloyed layer in the substrate. As the ions deposit their kinetic energy in the target it begins to heat up. To prevent thermal distortion in the finished pieces the ion implantation is performed at dose levels (dependent on the ion fluence and time duration of implantation) to insure that the target pieces stay at relatively low temperatures. Consequently, the low temperature requirement for many applications limits the economic, and probably, the physical success of ion implantation. The purpose of this study was to show the applicability of using a two-dimensional computer code developed to model plasma disruptions and subsequent energy deposition on a fusion reactor first wall to calculate surface and bulk temperature information during ion implantation. In turn the code may assist researchers pursuing development of adequate cooling for target materials in an attempt to overcome the low temperature constraint. All data supported the hypotheses that the two-dimensional code previously developed for fusion reactor applications was adequate to model the ion implantation process. / Graduation date: 1992

Land application of industrial wastewater with high levels of nitrogen requires adequate management practices to prevent groundwater pollution by nitrates. In this study a predictive computerized model was developed for nitrate leachate concentrations resulting from land application of wastewater onto crop systems including poplars. The study included a literature review, development of a computer program that could serve this purpose, and a field investigation to test the validity of the computed predictions. The literature review focused on poplar water and nitrogen uptakes, and suggested that mature poplars could uptake up to 400 lb of nitrogen /acre/year and 2 3 million gallons of water per acre per year. The computer model, based on 10-day water and nutrient balances, takes into account a number of parameters such as wastewater quality, evapotranspiration and precipitation data, irrigation volumes, soil water holding capacities, fertilization, crop nutrient uptakes and crop coefficients. This study involves a number of assumptions selected to give conservative (i.e., worst case approach) model predictions. Attempts to validate the model were conducted through soil and groundwater sampling along with precipitation data collection in four distinct fields in Brooks, Oregon, from October 1996 to April 1997. The variations in nitrogen soil profiles from October to April helped determine the amount of nitrogen leaving the soil, and groundwater samples from 5 feet deep wells gave nitrate concentrations in groundwater below the root zone. A sensitivity analysis of the program demonstrated how important nitrogen and water uptakes values were to the model predictions. An increase of 1% in nitrogen uptake or of 0.4% in crop coefficients generated 1% decrease in nitrogen concentration of the leachate. These results are important to consider when adopting highly uncertain literature values for crop uptakes -especially with poplars. The field validation of the model showed promising results in terms of estimating average yearly leachate concentrations in nitrogen resulting from land application of wastewater, but also suggested that more groundwater wells were needed to obtain a statistically significant validation of the model. These preliminary field results indicate that the model can provide an indication of groundwater nitrogen concentration trends but needs to further verified to be used confidently as a predictive tool. / Graduation date: 1998

This document contains a proposal for the creation of a simulator that can accurately model the interaction of electromagnetic (EM) and semiconductor effects for modern wireless devices including nonlinear and/or active devices. The proposed simulator couples the balanced semiconductor equations (charge, momentum, kinetic energy) with a FDTD full-wave Yee-based electromagnetic (EM) simulator. The resultant CAD tool is able to model the response of one semiconductor device to both small signal and DC bias based on the process parameters (material, charge distribution and doping) without any a-priori knowledge of the device performance characteristics, thus making it extremely useful in modeling and integrating novel devices in RF and Wireless topologies. As a proof of concept an n+--i--n+ diode will be simulated. In the future, more complicated structures, such as MODFETs, will be modeled as well.

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