Browsing by Subject "numerical modeling"
Now showing 1 - 5 of 5
Results Per Page
Sort Options
Item A Numerical Study of the Mid-field River Plume(2014-04-02) Cole, Kelly LynneIdealized and realistic simulations of the Merrimack River plume on the east coast of the U.S. are performed using the Regional Ocean Modeling System (ROMS). The effect of discharge, tides and rotation on the evolution of the tidal plume are examined. Experiments investigating the deceleration of the plume body through mixing and the relaxation of the tidal plume front are performed. Three primary findings result from this research. First, more ambient water interacts with the tidal plume front than source water. Because it takes several hours for source water to translate the plume and it is strongly diluted in the plume interior, only a small fraction of source water reaches the front. Therefore, the front is responsible for a small portion of mixing of the total ebb discharge. Second, the mouth and the tidal plume front communicate on an advective time scale. When the ebb discharge is stopped at the estuary mouth, the inertia of the discharge is enough to keep previously released source water necessary to sustain frontal propagation moving frontward. The front begins to slow when the withheld estuarine discharge is not supplied to the front. Third, the net plume mixing, defined as the total mixing of a parcel of source water before it enters the far-field, is altered by rotation. As discharge increases, an irrotational plume will exhibit an increasing trend in net mixing, while a rotational plume will exhibit a decreasing trend. These experiments bridge engineering and geophysical scale plume studies and provide a framework for understanding results reported in literature.Item Engineering, Financial and Net Energy Performance, and Risk Analysis for Parabolic Trough Solar Power Plants(2014-08-08) Luo, JunAn investigation was conducted to determine how technology innovations, potential risks, plant configuration and size, operating strategy, and financial incentives affect the electricity output, financial payback, and net energy performance of a concentrating solar power plant. A set of engineering performance, financial and net energy models were developed as tools to predict a plant?s engineering performance, cost and energy payback. The models were validated by comparing the predicted results to operational data from an actual solar power plant. The models were used to analyze the effect of several combinations of design and operating parameters on the amount and cost of electrical output. In addition, they were used to assess the risk of particular component failures and their effect on plant engineering and financial performance, and to conduct an analysis to predict energy payback. The results show some fundamental conclusions. First, the electricity production could be improved by adjusting plant configuration, increase the storage system size and increase the scale of plant. Second, the cost of electricity generated from a CSP plant will be higher (as much as 400%) than that of fossil fuel based power plants. Several methods could be used to lower the cost, such as constructing large plants, adopting new material and innovation components. However, the cost reduction will not be enough. Survival and future development of CSP plants may rely on external support, which might include incentives or supportive policies. Third, generally a CSP plant will have a positive net energy with an energy payback of approximately 5 years. Last, flex hoses are the most vulnerable components in the solar field. Performming regular maintenance work should be necessary to maintain the solar field?s performance level.Item Fractional Diffusion Modeling of Electromagnetic Induction in Fractured Rocks(2014-08-11) Ge, JianchaoThe controlled-source electromagnetic (CSEM) technique is well-established for non-invasive geophysical survey. Due to the strong attenuation of earth materials to electromagnetic signals, the effective depth of most CSEM surveys is restricted to 1-2 km, a zone where pores and fractures over various length scales are highly complicated. Spatial confinement of fluid or electric charge transport by the fractal geometry gives rise to interesting dynamic processes within the pore space and fractures, such as anomalous diffusion. Conventionally, CSEM data are interpreted in terms of a 1-D, 2-D or 3-D piecewise constant geological structure with uniform conductivity and thickness of each cell. A very fine grid, and hence a lot of computation time, are needed to build and evaluate a model that can explain the Earths actual 3D CSEM response. Good accuracy may not be captured, using the conventional approach, in the presence of multi-scale hierarchical geoelectrical structure. Alternatively, the CSEM response of such structures are easily evaluated if the physics of anomalous diffusion of electromagnetic eddy currents is recognized and cast, for example, in terms of a continuous time random walk. Such a re-formulation leads to a generalization of Maxwell equations containing a fractional order time derivative. The fractional order of the derivative is equivalent to a roughening of the geological medium, introducing multi-scale variations of fractures and heterogeneities in a compact manner. This theory renders CSEM modeling and inversion much more efficient, as only a few model parameters are now required to be fit. However the EM fractional diffusion theory is far from perfect, e.g. the correlation between the roughness of a fracture model with its fracture properties. In this research, I use numerical modeling tool to answer this question and explore if classical piece-wise constant conductivity model can generate a fractional type response. In this thesis, I will review the fundamental theory of traditional CSEM survey technique and the continuous time random walk approach, and review the derivation of the generalized Maxwell equation. More importantly, I propose the finite difference method to discrete the generalized Maxwell equation in 2D and 3D. I explore a classical fractured model response created from the von Karman random media approach. I will show that the von Karman fractured model generates a classical type response which is inconsistent with the fractional diffusion response. It is difficult to generate a classical model numerically that is comparable with the rough natural model.Item Numerical modeling of alongshore sediment transport and shoreline change along the Galveston coast(Texas A&M University, 2005-02-17) Sitanggang, Khairil IrfanAn alongshore sediment transport and shoreline change analysis on Galveston Island in the period of 1990-2001 is conducted in this study using the Generalized Model for Simulating Shoreline Change (GENESIS). The study is divided into three main parts: 1. Assessment of the numerical accuracy of GENESIS, 2. Assessment of the alongshore sediment transport and shoreline change on the Galveston coast in the period of 1990-2001, and 3. Assessment of several erosion control practices on the Galveston coast for the period of 2001-2011. The first assessment shows that GENESIS has a numerical error which tends to be large for low energy wave (small breaking wave height) and large breaking wave angle. This numerical inaccuracy cannot be neglected and needs to be compensated for. This can be done, for instance, by adjusting the transport parameter K1. In the second assessment, good agreement between the calculated and measured transport/shoreline is achieved, particularly on the West Beach. Comparison between the potential alongshore sediment transport and sediment budget-inferred alongshore transport provides a systematic way of selecting the proper wave data set for the alongshore and shoreline change calculation. The third assessment proves that beach nourishment is the best alternative to overcome/reduce the erosion problem on the Galveston coast. Constructing coastal structure (groins, offshore breakwater) on the West Beach does not resolve the problem of erosion, but instead shifts it further west.Item Numerical Modeling of Fracture Permeability Change in Naturally Fractured Reservoirs Using a Fully Coupled Displacement Discontinuity Method.(2010-07-14) Tao, QingfengFractures are the main flow channels in naturally fractured reservoirs. Therefore the fracture permeability is a critical parameter to production optimization and reservoir management. Fluid pressure reduction caused by production induces an increase in effective stress in naturally fractured reservoirs. The change of effective stress induces fracture deformation and changes fracture aperture and permeability, which in turn influences the production. Coupled interactions exist in the fractured reservoir: (i) fluid pressure change induces matrix deformation and stress change; (ii) matrix deformation induces fluid volume change and fluid pressure change; (iii) fracture deformation induces the change of pore pressure and stress in the whole field (the influence disappears at infinity); (iv) the change of pore pressure and stress at any point has an influence on the fracture and induces fracture deformation. To model accurately the influence of pressure reduction on the fracture permeability change in naturally fractured reservoirs, all of these coupled processes need to be considered. Therefore, in this dissertation a fully coupled approach is developed to model the influence of production on fracture aperture and permeability by combining a finite difference method to solve the fluid flow in fractures, a fully coupled displacement discontinuity method to build the global relation of fracture deformation, and the Barton-Bandis model of fracture deformation to build the local relation of fracture deformation. The fully coupled approach is applied to simulate the fracture permeability change in naturally fracture reservoir under isotropic in situ stress conditions and high anisotropic in situ stress conditions, respectively. Under isotropic stress conditions, the fracture aperture and permeability decrease with pressure reduction caused by production, and the magnitude of the decrease is dependent on the initial effective in situ stress. Under highly anisotropic stress, the fracture permeability can be enhanced by production because of shear dilation. The enhancement of fracture permeability will benefit to the production of oil and gas.