Browsing by Author "Vdovina, Tetyana"

Now showing 1 - 3 of 3
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    Getting It Right Without Knowing the Answer: Quality Control in a Large Seismic Modeling Project
    (2009-04) Symes, William W.; Terentyev, Igor S.; Vdovina, Tetyana
    Phase I of the SEAM Project will produce a variable-density acoustic synthetic survey over a 3D geological model simulating a deepwater subsalt exploration target. Due to the intended use of the data, the project places a premium on accuracy. Commercially produced Phase I synthetics will be spot-checked against benchmark simulations to assure quality. Thus the accuracy of the benchmark simulator required careful assessment. The authors designed and implemented the benchmark simulator used in this program, subjected it to verification tests, and assisted in the qualification phase of the Phase I project. The key lessons that we have learned so far from this assessment are that (1) the few verification tools available to us - a few analytic solutions and Richardson extrapolation - seem to be adequate, at least in a rough way, and (2) the standard approach to this type of simulation - finite difference methods on regular grids - requires surprisingly fine grid steps to produce small relative RMS errors for models of the type defined by this project.
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    Interface Error Analysis for Numerical Wave Propagation
    (2008-10) Symes, William W.; Vdovina, Tetyana
    The numerical error associated with finite-difference simulation of wave propagation in discontinuous media consists of two components. The first component is a higher order error that leads to grid dispersion; it can be controlled by higher-order methods. The second component results from misalignment between numerical grids and material interfaces. We provide an explicit estimate of the interface misalignment error for the second order in time and space staggered finite-difference scheme applied to the acoustic wave equation. Our analysis, confirmed by numerical experiments, demonstrates that the interface error results in a first-order time shift proportional to the distance between the interface and computational grids. A two-dimensional experiment shows that the interface error cannot be suppressed by higher-order methods and indicates that our one-dimensional analysis gives a good prediction about the behavior of the numerical solution in higher dimensions.
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    The Acoustic Radiation Solution
    (2008-10) Symes, William W.; Vdovina, Tetyana
    The well-known radiation solution of the acoustic wave equation may also be viewed as the pressure field in the solution of the first-order system of linear acoustics, in two different ways. The first version casts in the source term as a defect in the acoustic constitutive law, the second presents it as an equivalent body source. The second form requires the addition of a parasitic stationary singular pressure field.