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NB-EGM-RPI-abstract_09_V060909.doc
An Analysis of Skimboard Hydrodynamics
N. D. Barnett1 and E. Gutierrez-Miravete*2
1
General Dynamics-Electric Boat, 2Rensselaer at Hartford
*Corresponding author: 275 Windsor Street, Hartford, CT 06120, [email protected]
Introduction
A skimboard is a device approximately 1-2 m in length and 1m diameter that is used to plane along the
shoreline for a short distance (10 m max). The boards are usually employed in less than 2 inches (50mm) of
water. The flow is similar to the flow underneath a surfboard, or powerboat, except the flow is bounded by
very shallow water. This project simulates the flow under a skimboard using CFD in COMSOL
Multiphysics, and validates the analysis by comparison to results obtained in previous works. Future work
resulting from this project includes the possibility of expanding the techniques learned to other types of
skimming hulls, such as surfboards, jet skis, and small power boats.
Figure 1 shows a schematic representation of a skimboard sliding over a thin water layer from right to left.
The skimming effect is obtained from the relative motion of the tilted board over the water surface. The
upward directed jet at the bow of the board is the result of the mass flow imbalance underneath. The goal of
this project was to investigate the hydrodynamic performance of a simple skimboard as a function of the
various parameters illustrated in the figure.
Figure 1: Schematic representation of a skimboard
Use of COMSOL Multiphysics
The Steady State Fluid Dynamics module in COMSOL Multiphysics was used to create a two-dimensional
model of the skimboard-water layer system based on the schematic representation of Fig. 1. Regarding
boundary conditions, no-slip, non-moving walls boundary conditions are designated as u = 0. Free surfaces
are assumed to be symmetry boundaries, and are defined by having no shear, as in
. For moving
walls, the nodes on the boundary are given the velocity of that boundary (u= u w). For sliding walls, the
nodes are given the tangential velocity entered and it is assumed to have no-slip. Localized mesh
refinement was used to resolve the flow in selected areas of the system and mesh independent results were
obtained by using ~ 1500 elements.
Expected Results (Optional)
The COMSOL model was used to test many different scenarios in order to determine the set of parameter
values and boundary conditions that produced the best agreement with the results of prior studies and with
physical intuition. Figure 2 shows a typical FE mesh used in our calculations and Figure 3 shows the
computed pressure distribution underneath the skimboard. It is interesting to note that the resulting
pressure hill yields enough force to withstand the weight of a 65 kg person traveling on top of the board.
Figure 2. Finite Element Mesh
Figure 3. Computed Pressure (Pa) underneath
the skimboard
Conclusion
Useful information about the flow underneath a planning skimboard can be obtained from simple CFD
models. Use of an appropriate set of boundary conditions resulted in a computed lift similar to that noted in
previous theoretical studies and consistent with physical observation. For future consideration many other
cases can be studied. For example, the flow along the bottom of a jet ski (hull and the jet) could be
visualized quickly and compared to the models of previous successful and failed.
Reference
1. Tuck, E.O. Dixon, A. Surf skimmer hydrodynamics. Journal of Fluid Mechanics. 205, 581-592, 1
February 1989.
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