Browsing by Subject "hybrid"
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Item Boussinesq-equation and rans hybrid wave model(2009-05-15) Sitanggang, Khairil IrfanThis dissertation presents the development of a novel hybrid wave model, comprised of the irrotational, 1-D horizontal Boussinesq and 2-D vertical turbulence-closed Reynolds Averaged Navier-Stokes (RANS) wave models. The two constituents are two-way coupled with the interface placed at a location where turbulence is relatively small. Boundary conditions on the interfacing side of each model is provided by its counterpart model through data exchange, requiring certain transformation due to the difference in physical variables employed in both models. The model is intended for large-scale wave simulation, accurate in both the nonbreaking and breaking zones with relatively coarser grid in the former and finer in latter, and yet efficient. Hybrid model tests against idealized solitary and standing wave motions and wave-overtopping on structure exhibit satisfactory to very good agreement. Compared with pure RANS simulations, the hybrid model saves computational time by a factor proportional to the reduction in the size of the RANS domain. Also, a large-scale tsunami simulation is provided for a numerical setup that is practically unapproachable using RANS alone; not only does the hybrid model offer more rapid simulation of relatively small-scale problems, it provides an opportunity to examine very large total domains with the fine resolution typical of RANS simulations. To allow for implementation on even larger domain with affordable CPU time, the hybrid model is parallelized to run on distributed memory machine. This is done by parallelizing the RANS model while leaving the Boussinesq model serial. One of the processors is responsible for both the sub-RANS and Boussinesq calculations. ICCG(0) for solving the pressure equation is parallelized using the nonoverlappingdecomposition technique, requiring more iterations than the serial one. Standing wave and hypothetical tsunami simulations with 960?66 and 1000?100 grids, and using 8 processors confirm model validity and computational efficiency of 82% and 65%. Finally, the 2-D Boussinesq model is parallelized using domain decomposition technique. The solution to the tridiagonal system arising in the model is calculated as the sum of the homogeneous and particular solutions. Parallel model tests using up to 32 processors exhibit model accuracy and efficiency of 80% for simulation with 500?500?2000?2000 grids.Item Design of a Control Strategy for a Fuel Cell/Battery Hybrid Power Supply(2010-01-14) Smith, Richard C.The purpose of this thesis is to design hardware and a control strategy for a fuel cell/battery hybrid power supply. Modern fuel cell/battery hybrid power supplies can have 2 DC/DC converters: one converter for the battery and one for the fuel cell. The hardware for the power supply proposed in this thesis consists of a single DC/DC buck converter at the output terminals of the fuel cell. The battery does not have a DC/DC converter, and it is therefore passive in the system. The use of one single converter is attractive, because it reduces the cost of this power supply. This thesis proposes a method of controlling the fuel cell's DC/DC buck converter to act as a current source instead of a voltage source. This thesis will explain why using the fuel cell's buck converter to act as a current source is most appropriate. The proposed design techniques for the buck converter are also based on stiff systems theory. Combining a fuel cell and a battery in one power supply allows exploitation of the advantages of both devices and undermines their disadvantages. The fuel cell has a slow dynamic response time, and the battery has a fast dynamic response time to fluctuations in a load. A fuel cell has high energy density, and a battery has high power density. And the performance of the hybrid power supply exploits these advantages of the fuel cell and the battery. The controller designed in this thesis allows the fuel cell to operate in its most efficient region: even under dynamic load conditions. The passive battery inherits all load dynamic behavior, and it is therefore used for peaking power delivery, while the fuel cell delivers base or average power. Simulations will be provided using MATLAB/Simulink based models. And the results conclude that one can successfully control a hybrid fuel cell/battery power supply that decouples fluctuations in a load from the fuel cell with extremely limited hardware. The results also show that one can successfully control the fuel cell to operate in its most efficient region.Item Detection of bacterial endospores by means of ultrafast coherent raman spectroscopy(Texas A&M University, 2008-10-10) Pestov, Dmitry SergeyevichThis work is devoted to formulation and development of a laser spectroscopic technique for rapid detection of biohazards, such as Bacillus anthracis spores. Coherent anti-Stokes Raman scattering (CARS) is used as an underlying process for active retrieval of species-specific characteristics of an analyte. Vibrational modes of constituent molecules are Raman-excited by a pair of ultrashort, femtosecond laser pulses, and then probed through inelastic scattering of a third, time-delayed laser field. We first employ the already known time-resolved CARS technique. We apply it to the spectroscopy of easy-to-handle methanol-water mixtures, and then continue building our expertise on solutions of dipicolinic acid (DPA) and its salts, which happen to be marker molecules for bacterial spores. Various acquisition schemes are evaluated, and the preference is given to multi-channel frequency-resolved detection, when the whole CARS spectrum is recorded as a function of the probe pulse delay. We demonstrate a simple detection algorithm that manages to differentiate DPA solution from common interferents. We investigate experimentally the advantages and disadvantages of near-resonant probing of the excited molecular coherence, and finally observe the indicative backscattered CARS signal from DPA and NaDPA powders. The possibility of selective Raman excitation via pulse shaping of the preparation pulses is also demonstrated. The analysis of time-resolved CARS experiments on powders and B. subtilis spores, a harmless surrogate for B. anthracis, facilitates the formulation of a new approach, where we take full advantage of the multi-channel frequency-resolved acquisition and spectrally discriminate the Raman-resonant CARS signal from the background due to other instantaneous four-wave mixing (FWM) processes. Using narrowband probing, we decrease the magnitude of the nonresonant FWM, which is further suppressed by the timing of the laser pulses. The devised technique, referred to as hybrid CARS, leads to a single-shot detection of as few as 104 bacterial spores, bringing CARS spectroscopy to the forefront of potential candidates for real-time biohazard detection. It also gives promise to many other applications of CARS, hindered so far by the presence of the overwhelming nonresonant FWM background, mentioned above.Item Experimental analysis of the extension to shear fracture transition in Berea Sandstone(Texas A&M University, 2005-11-01) Bobich, Jennifer KayTo characterize low-pressure, brittle deformation in porous, granular rock, notchcut cylinders (30 mm neck diameter) of Berea Sandstone were extended in a triaxial apparatus from 10 to 160 MPa confining pressure at strain rates of 10-4 s-1 and 10-5 s-1. Acoustic emission counts were monitored when extending samples at a slow strain rate. Stress at fracture is characterized by the least compressive principal stress, ??3, and maximum compressive principal stress, ??1 (??1 = Pc). A change in strength dependence on pressure at Pc = 50 MPa corresponds to a change from pure macroscopic extension fracture to mixed-mode opening and shear fracture, and likely reflects the increase in mean stress that suppresses the propagation of extension fractures and the interaction between closely-spaced stepped cracks. Within the extension fracture regime (Pc < 50 MPa), ??3 at failure becomes slightly more tensile with an increase in Pc. At Pc > 50 MPa, ??3 at failure becomes more compressive with an increase in Pc and follows Coulomb behavior; however, the angle between the fracture surface and ??1 increases continuously with Pc. Fracture surfaces characteristic of the extension to shear fracture transition appear as linked, stepped extension fractures; the length of extensional segments decreases with increasing pressure. The onset of acoustic emissions and inelastic strain at fracture occurs at earlier points in the strain history with pressure, consistent with the Griffith prediction of the beginning of fracture growth.Item Kinetics and dynamics study on the allosteric pathway of phosphofructokinase from Escherichia coli(Texas A&M University, 2008-10-10) Tie, CuijuanPhosphofructokinase from Escherichia coli (EcPFK) is allosterically regulated by MgADP and phosphoenolpyruvate (PEP), which act to activate or inhibit, respectively, by changing the substrate (Fru-6-P) affinity of the enzyme. Both ligands bind to the same allosteric site in EcPFK. Therefore, the questions we want to address are how these two molecules regulate EcPFK and how the allosteric signal is propagated throughout the enzyme. EcPFK has 28 potential site-site interactions. These interactions in turn derive from multiple copies of 6 potentially unique homotropic interactions and 4 potentially unique heterotropic interactions. Making hybrid tetramer of EcPFK is used to isolate a single heterotropic interaction. To improve the yield of the 1:3 hybrid, the in vivo hybrid formation method was developed. Four heterotropic interactions were isolated by this manner and re-evaluated. The same kinetics characteristics were obtained for each 1:3 hybrid from both the in vivo and in vitro method. To address the question of how the allosteric signal is transmitted throughout EcPFK, we identified residues (G184, Asp59 and S157) that are important for the allosteric regulation for both PEP inhibition and MgADP activation. The impact of each mutation on individual interaction is unique and also suggests that the structural basis for PEP inhibition is different from that for MgADP activation. Most importantly, since the sum of each heterotropic interaction with a modification in only one subunit is equal to the total heterotropic interaction with a modification in all four subunits, this result indicates that the heterotropic allosteric signal transmission is realized in a single subunit. The 23? heterotropic interaction, which contributes the most to the PEP inhibition, was chosen to study the dynamic properties. Fluorescence was used to study the dynamic perturbations of the 23? interaction upon ligand binding. Taking advantage of the hybrid formation strategy and the tryptophan-shift mutagenesis method, a tryptophan residue can be placed at different individual locations throughout the native subunit containing the 23? heterotropic interaction. The steady-state anisotropy and lifetime measurement at each tryptophan position indicate that the 23? allosteric interaction involves the perturbation of side-chain dynamics both near and quite far away from the respective ligand binding sites.Item The Limits of Fire Support: American Finances and Firepower Restraint during the Vietnam War(2013-07-12) Hawkins, John MichaelExcessive unobserved firepower expenditures by Allied forces during the Vietnam War defied the traditional counterinsurgency principle that population protection should be valued more than destruction of the enemy. Many historians have pointed to this discontinuity in their arguments, but none have examined the available firepower records in detail. This study compiles and analyzes available, artillery-related U.S. and Allied archival records to test historical assertions about the balance between conventional and counterinsurgent military strategy as it changed over time. It finds that, between 1965 and 1970, the commanders of the U.S. Military Assistance Command, Vietnam (MACV), Generals William Westmoreland and Creighton Abrams, shared significant continuity of strategic and tactical thought. Both commanders tolerated U.S. Army, Marine Corps, and Allied unobserved firepower at levels inappropriate for counterinsurgency and both reduced Army harassment and interdiction fire (H&I) as a response to increasing budgetary pressure. Before 1968, the Army expended nearly 40 percent of artillery ammunition as H&I ? a form of unobserved fire that sought merely to hinder enemy movement and to lower enemy morale, rather than to inflict any appreciable enemy casualties. To save money, Westmoreland reduced H&I, or ?interdiction? after a semantic name change in February 1968, to just over 29 percent of ammunition expended in July 1968, the first full month of Abrams? command. Abrams likewise pursued dollar savings with his ?Five-by-Five Plan? of August 1968 that reduced Army artillery interdiction expenditures to nearly ten percent of ammunition by January 1969. Yet Abrams allowed Army interdiction to stabilize near this level until early 1970, when recurring financial pressure prompted him to virtually eliminate the practice. Meanwhile, Marines fired H&I at historically high rates into the final months of 1970 and Australian ?Harassing Fire? surpassed Army and Marine Corps totals during the same period. South Vietnamese artillery also fired high rates of H&I, but Filipino and Thai artillery eschewed H&I in quiet areas of operation and Republic of Korea [ROK] forces abandoned H&I in late 1968 as a direct response to MACV?s budgetary pressure. Financial pressure, rather than strategic change, drove MACV?s unobserved firepower reductions during the Vietnam War.