ERDC/CHL CHETN- IX-7
December 2001
Additional work is ongoing in several areas to improve this data set. First, we will examine the
error inherent in comparing field hWA,CG at a point that does not correspond exactly to the ship
CG. This small variation in the location of the field average hWA,CG might explain some of the
observed variation between laboratory and field. Second, response amplitude operators (RAO)
are being calculated for each transit that will show the vessel response as a function of the wave
conditions. These RAO's can then be used to predict the ship's six DOF motions for different
wave conditions and spectral shapes. Third, the effect of wave directionality needs to be
quantified. The laboratory waves were simulated with a unidirectional wavemaker, even though
the field waves did exhibit some spreading. Additional testing with multidirectional waves would
be required. Finally, we are working to analyze the laboratory data in a probabilistic sense that
will make it more useful for predicting hWA for other wave conditions and ship types. The
random nature of waves can be incorporated in the prediction algorithm to include some
uncertainty.
Squat is an integral part of the underkeel clearance. Unfortunately, it is not possible to measure
it in the laboratory with the MOTAN system. Upgrades to our existing set of infrared Charged
Coupled Device (CCD) cameras would be required to provide the extreme level of accuracy
required to measure squat. These cameras have the added advantage that they can show ship
tracks in the channel during transits. The combination of these two systems would provide a
state-of-the-art capability for measuring ship motions in the laboratory.
The goal of this research is to develop data to support improvements to the ERDC ship simulator
and provide an empirical approach to aid in coastal entrance channel design. This will minimize
project and maintenance dredging costs and allow quick assessment of proposed changes in
channel design. Field measurements are preferred, but are expensive to obtain and have the risks
inherent in field data collection. A verified physical model is less expensive and provides a more
controlled environment for generating empirical data for a range of channel, ship, and wave
conditions. These results give us confidence that laboratory models can be used as an effective
tool in optimizing entrance channel depths, as well as developing empirical data sets needed to
support other research and development needs.
ADDITIONAL INFORMATION: For additional information, contact Dr. Michael J. Briggs
(Voice: (601) 634-2005, e-mail: ) or Dr. Zeki Demirbilek
(Voice: (601) 634-2834, e-mail: ). This Technical Note
should be cited as follows:
Briggs, M., Melito, I., Demirbilek, Z., and Sargent, F. (2001). "Deep-draft
entrance channels: Preliminary comparisons between field and laboratory
measurements," Coastal and Hydraulics Engineering Technical Note CHETN-IX-
7, U.S. Army Engineer Research and Development Center, Vicksburg, MS.
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