# Grid-Induced Errors in Depth-Averaged Flow Fields

*by*R. E. Heath, US Army Engineer Waterways, Experiment Station, Vicksburg, United States,

B. H. Johnson, US Army Engineer Waterways, Experiment Station, Vicksburg, United States,

K. W. Kim, US Army Engineer Waterways, Experiment Station, Vicksburg, United States,

**Document Type:**Proceeding Paper

**Part of:**Hydraulic Engineering

**Abstract:**

A computer code called CH2D (Curvilinear Hydrodynamics in Two Dimensions) for computing depth-averaged free-surface flow fields has been used to assess the impact of the rate of change of grid spacing and grid skewness on numerically generated solutions. The impacts of these two grid characteristics are assessed for both linear and nonlinear solutions by computing depth-averaged flow in a simple tidally forced basin closed at one end. Results show that a rate of change in grid spacing of less than 1.5 and grid skewness of less than 30 deg result in very little difference from the solution computed on a uniform rectangular grid. Nonuniformity in the grid appears to impact the computed velocity more than the water-surface elevation, whereas grid skewness appears to impact the computation for the water surface more than for the flow velocity. Results are similar for both linear and nonlinear solutions.

**Subject Headings:**Skewness | Tides | Computing in civil engineering | Spacing | Linear functions | Nonuniform flow | Fluid velocity | Free flow

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