Browsing by Subject "Transient analysis"
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Item Envelope tracking integral equation based hybrid electromagnetic circuit simulators(2016-12) Subramanian, Vivek, Ph. D.; Yilmaz, Ali E.; Neikirk, Dean; Ling, Hao; Alu, Andrea; Chakraborty, SwagatoThis dissertation presents envelope-tracking hybrid field-circuit simulator for efficiently analyzing narrowband scattering from distributed structures loaded with nonlinear devices. The simulator models the interactions of fields with distributed structures and lumped elements by coupling and simultaneously solving the electric field integral equation and Kirchhoff’s equations, respectively. The coupled nonlinear system of equations is iteratively solved by a time marching scheme that represents the fields, voltages, and currents of interest (signals) as a truncated series of harmonic sinusoids (carriers) multiplied with complex-valued time-varying coefficients (envelopes). Unlike time-domain simulators, which sample the signals at a rate proportional to their maximum frequency content, the proposed envelope-tracking simulator samples the envelopes at a rate proportional to their maximum bandwidth; thus, it requires significantly fewer time steps when solving narrowband problems. Moreover, the envelope-tracking simulator is generally more accurate than its time-domain counterpart because of smaller integration and interpolation errors. Numerical results demonstrate that the proposed simulator improves the tradeoff between accuracy and computational cost, especially when analyzing distributed structures excited by narrowband signals or/and loaded with weakly nonlinear devices. Although the Fourier envelope simulator uses smaller number of time steps, there are other issues relating to the Fourier envelope simulator which are addressed in this thesis: (i) lumped element models that relate voltage envelopes and current envelopes for nonlinear elements are generally unavailable and the approximations used in the simulator to find them are inaccurate for broader band excitations. Higher order interpolation schemes were used in this dissertation to improve the accuracy of these approximations. Numerical results that demonstrate the ability to solve for problems with broader bandwidth of excitation are presented. (ii) As in its timedomain counterpart, adaptive integral method is used to reduce the computational cost of the simulator thus enabling the simulation of larger problems and (iii) Sparse preconditioners are used to improve the convergence of the solution algorithms. Finally, the Fourier envelope method is extended to the analysis of infinitely periodic arrays containing lumped nonlinear loads. Numerical results are presented to highlight the .features of this algorithm.Item Optimizing fluid cleanup efficiency using mud-filtrate contamination transient analysis and the reciprocal contamination derivative method(2020-12-02) Gelvez Gonzalez, Camilo Andrés; Torres-Verdín, CarlosSuccessful in situ fluid cleanup and sampling operations are commonly driven by a fast and reliable analysis of pressure, rate, and contamination measurements. Techniques such as pressure transient analysis (PTA) and rate transient analysis (RTA) currently provide important information to quantify reservoir complexity, while fluid contamination measurements are commonly overlooked for reservoir characterization purposes. I introduce a new interpretation technique to relate fluid contamination measurements with reservoir properties by identifying early- and late-time flow regimes in the derivative plots of reciprocal fluid contamination. Contamination transient analysis (CTA) evaluates transient measurements acquired during cleanup of mud-filtrate invasion to infer important reservoir geological and flow conditions. This thesis project presents the application of derivative methods to the reciprocal of the time evolution of fluid contamination to identify flow regimes, and an evaluation of the performance of several probe configurations under equivalent reservoir conditions to quantify and optimize filtrate cleanup efficiency. The study is carried out using a compositional simulator for a water-bearing reservoir invaded with blue-dye tracer included in water-base mud (WBM) filtrate. Complex tracer dynamics are accurately and expediently modeled using a flexible numerical algorithm to account for different probe types and tool configurations. Numerical simulations compare the fluid cleanup efficiency for various commercial formation-testing probes together with innovative probe designs that could potentially lead to a new tool or probe development. In addition, seven reservoir cases of WBM invading either water-or hydrocarbon-saturated formations are simulated to obtain contamination data: (1) homogeneous isotropic reservoir, (2) formation thickness, (3) laminated formations, (4) geological faults, (5) mud-filtrate invasion, (6) reservoir properties, and (7) permeability anisotropy. Reservoir limits and reservoir features are identified in the flow regimes detected with derivative plots of the reciprocal of the contamination. Moreover, field case studies are analyzed to highlight the value of the reciprocal contamination derivative (RCD) in real-time operations. The new approach of the RCD is an alternative to optimize fluid cleanup efficiency and to quantify the spatial complexity of the reservoir during real-time operations