A grid-switching strategy for computing high-frequency, high wave number motions embedded in geophysical flows (2006)

by Daniel Botelho, Jorg Imberger, Chris Dallimore, and Ben R. Hodges

Citation: Botelho, D., J. Imberger, C. Dallimore, and B.R. Hodges (2006), “A grid-switching strategy for computing high-frequency, high wave number motions embedded in geophysical flows,” submitted to International Journal for Numerical Methods in Fluids (February, 2006).

Abstract

Hydrostatic and non-hydrostatic models were used to simulate the generation of internal surges and associated soliton-like trailing waves from the non-linear steepening of low- frequency basin-scale waves. Results confirmed that the process cannot be modelled using the hydrostatic approximation, however the computational cost of the non-hydrostatic model was much larger than the hydrostatic. A grid switching strategy was developed to reduce the simulation run time of the non-hydrostatic model. In the strategy, a low-resolution grid using a hydrostatic computation of the flow field is dynamically switched to a high-resolution grid in the region of propagation of the leading internal surge, using a non-hydrostatic computation of the flow field. The strategy takes advantage of the small time scale required for non-hydrostatic effects to become important such that a high-resolution grid is invoked only when and where the non-hydrostatic effects become large. Run time reduction, conservation of the interpolation scheme involved in the grid switching and strategies for field scale studies were addressed. The grid switching strategy was shown to be able to predict the phase speed and the amplitude of the leading internal surge with greater agreement with laboratory experiments than the uniform-grid models however; the trailing soliton-like waves lost their signature due to smoothing effects of the interpolation scheme. All non-hydrostatic models predicted the essential features of the energy flux path between low and high-frequency waves showing that the grid switching strategy can be a viable alternative to simulate non-hydrostatic flows where computational power poses a limitation.

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©2006 Ben R. Hodges	• last updated April 19, 2006	• UT • College of Engineering • Dept of Civil Engineering • CRWR • EFM Home •