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Browsing by Author "Zachmann, David W., committee member"

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    An implicit method for water wave problems
    (Colorado State University. Libraries, 1983) Aston, Martha B., author; Thomas, J. W. (James William), 1941-, advisor; Zachmann, David W., committee member; Schubert, Wayne H., committee member
    This paper presents an implicit scheme for numerically simulating fluid flow in the presence of a free surface. The scheme couples numerical generation of a boundary-fitted coordinate system with an efficient solution of the finite difference equations. The method solves the two dimensional Navier-Stokes equations by applying an implicit backward in time difference scheme which is linearized by Taylor series expansion about the known time level to produce a system of linear difference equations. The difference equations are solved by an Alternating-Direction-Implicit procedure which defines a sequence of one dimensional block tridiagonal matrix equations. A standard block elimination scheme solves the one dimensional equations. For each time step, solutions for all equations are calculated simultaneously and noniteratively. Preliminary solutions of free surface fluid flow in an open channel are presented. These solutions are examined to define initial stability criteria for the numerical scheme.
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    Network multiple frame assignment architectures
    (Colorado State University. Libraries, 2001) Lu, Suihua, author; Poore, Aubrey, advisor; Kirby, Michael J., committee member; Zachmann, David W., committee member; Miranda, Rick, 1953-, committee member
    Multiple target tracking methods divide into two broad classes, namely single frame and multiple frame methods. The most successful of the multiple frame methods are multiple hypothesis tracking (MHT) and multiple frame assignments (MFA). In dense tracking environments the performance improvements of multiple frame methods over single frame methods is very significant, making it the preferred solution for many tracking problems. Thus, in addition to the availability single frame processing, multiple frame data association methods are an essential class of methods for almost all tracking needs. The application of multiple frame tracking methods must consider an architecture in which the sensors are distributed across multiple platforms. Such geometric and sensor diversity has the potential to significantly enhance tracking and discrimination accuracy. A centralized architecture in which all measurements are sent to one location and processed with tracks being transmitted back to the different platforms is a simple one that is probably optimal in that it is capable of producing the best track quality (e.g., purity and accuracy) and a consistent air picture. The centralized tracker is, however, unacceptable for several reasons, notably the communication overloads and single-point-failure. Thus, one must turn to a distributed architecture for both estimation/fusion and data association. One of the simplest network-centric architectures is that of placing a centralized tracker on each platform. The architecture is called Network MFA Centralized, which removes the problem of single-point-failure. However, due to communication delays in the network, the order the measurements arrive at different platforms varies. Each composite tracker is making its own tracking decisions based on the data it receives, regardless of decisions of other platforms. Therefore, a consistent air picture may not be achieved across the network. Thus, the objective of this thesis is the development of two near-optimal Network-Centric MFA architectures, namely Network MFA on Local Data and Network Tracks and Network MFA on All data and Network Tracks, that preserve the quality of a centralized tracker across a network of platforms while managing communication loading and achieving a consistent air picture. One technique that has proved useful for achieving SlAP is to require that each platform be in charge of assigning its own measurements to the network tracks. In the architecture of Network MFA on Local Data and Network Tracks, only local data are used in the sliding windows and track initiations are based on local data only. In the architecture of Network MFA on All Data and Network Tracks, all data (remote and local) are used in the sliding window. Communication loading is only addressed by the architectures in that track states and their error covariances are not required to be transmitted back to the various platforms. The results of extensive computations are presented to validate the differences in four tracking architectures.
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    Optical performance of cylindrical absorber collectors with and without reflectors
    (Colorado State University. Libraries, 1994) Menon, Arun B., author; Duff, William, advisor; Burns, Patrick J., committee member; Zachmann, David W., committee member
    The optical efficiency of a solar collector, which depends on the collector geometry and material properties (i.e., geometry and radiative properties of the cover, absorber and any reflector), contributes significantly towards its overall performance. This optical efficiency is directly proportional to the transmittance-absorptance or τα product for all possible angles of incidence. A 3-D Monte Carlo ray tracing technique is used to determine this τα product for evacuated tubular collectors (ETCs) with cylindrical absorbers in an effort to identify the most efficient optical design parameters. These collectors are asymmetric with respect to the incident solar radiation and their optical efficiencies are therefore difficult to estimate using any other method. The collector geometry is modeled using constructive solid geometry (CSG). CSG allows the generation of complex collector shapes by combining simple primitive objects. The ray tracing algorithm tracks individual photons through the collector geometry to provide a means of obtaining the absorbed fraction for a particular angle of radiation incident on the collector plane. Incidence angle modifiers (IAMs), the ratio of the τα product at a particular set of longitudinal and transverse radiation incidence angles to the τα product at normal incidence are thereby obtained. IAMs are calculated for variations in five different design parameters to determine the most advantageous geometries. It is found that diffusely reflecting back planes significantly enhance optical performance of tubular collectors. Verification of the ray trace calculations is made by comparing with experimental results from the indoor solar simulator at CSU. TRNSYS predicted values of τα are within 1% of the ray trace results for normal incidence tests and within 7% for off-normal tests. Inaccuracies resulting from the use of a multiplicative technique wherein off-axis IAMs are obtained by a multiplicative combination of the biaxial IAMs are also addressed. The multiplicative approach is found to be very inaccurate for angles of incidence greater than 40°. To further assess the relative advantages of tubular collectors over flat plate collectors and whether a reflective back plane is really necessary, the two types of collectors are modeled in a simple fashion and the amount of radiation that is available for collection by each is determined. Calculations show that reflectors would probably not be required for collector slopes in excess of 50°. However, for slope angles less than 50°, a reflector placed behind the tubes is beneficial.