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Vessel Movement

The hydrodynamic effects of a vessel moving through a flow field significantly affect a navigation channel. The waves produced by moving vessels increase the rate of shoreline erosion and affect other vessels moving through the channel. Vessel movement induces shear stresses on the channel bed, which alters sediment transport and deposition patterns. Successful modeling of such effects provides a valuable tool for predicting the impact vessels have on the channel and other vessels.

Quantifying the effects of vessels sailing along a waterway is a complex problem because the flow is unsteady and the river bathymetry is nonuniform. These effects include: drawdown of the water surface, return cur-rents around the vessel, and increased bed shear stresses and pressures that act to re-suspend the bed material and perhaps erode banks. Historically, studies to capture vessel effects required that the flow first be modeled, then the bed effects were computed, and finally, the fate of the bed material that is re-suspended was determined. A seamless modeling system would allow the hydraulic engineer conducting the study to focus more on model results and remediation than on the modeling process.

The current study addresses these issues using the Adaptive Hydraulics (AdH) flow solver. The shallow-water module of AdH solves the depth-averaged two-dimensional (2D) flows using serial or parallel processing. However, one of the most beneficial attributes of AdH is the adaptive mesh technique, which gives it the capability of refining or coarsening the mesh based on error estimates during flow calculations. The vessel effects are modeled in AdH by moving a pressure field through the flow. Due to mesh adaption abilities, the code is able to improve upon the previous technique by reducing computational times. Mesh refinement can be limited to the vessel vicinity even though the position changes with time. As a vessel approaches a region within the channel, the mesh in that region is refined for the calculations in the more complex flow. As the vessel continues past that point, the mesh is then coarsened. This automated mesh adaption reduces the cost of studying the impact vessels have in confined waterways. Because the refinement indicator is determined by the flow variables, AdH will adapt any region in which the flow is strongly disturbed. Generally this will be in the area near the vessel. However, if the vessel- induced waves are still significant at some distance away, AdH will recognize this and adapt. More information can be obtained in ERDC/CHL TR-08-7.