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National Advisory Committee for Aeronautics, Report - Theory and Procedure for Determining Loads and Motions in Chine-Immersed Hydrodynamic Impacts of Prismatic Bodies

A theoretical method is derived for the determination of the
motions and loads during chine-immersed water landings of
prismatic bodies. This method makes use of a variation of
two-dimensional deflected water mass over the complete range
of immersion, modified by a correction for three-dimensional
flow. Equations are simplified through omission of the term
proportional to the acceleration of the deflected mass for use in
calculation of loads on hulls having moderate and heavy beam
loading. The ejects of water rise at the heel are included in
these equations. In order to make a direct comparison of
theory with experiment, a modification of the equations was
made to include the efiect of finite test-carriage mass. A simple
method of computation which can be applied without reading
the body of this report is presented as an appendix, along with
the required theoretical plots for determination of loads and
motions in chine-immersed landings.

Comparisons of theory with experiment are presented as plots
of impact lift coeflicient— and maximum draft-beam ratio against
flight-path angle and as time histories of loads and motions.
These comparisons cover angles of dead rise of 0° and 30°,
trims up to 45°, flight-path angles up to 90°, and beam-loading
coefiicients from 1 to 36.5. Fair agreement is seen to exist over
these ranges. The comparisons show in general that the con-
cept involving the twodimmwiorml deflected mass and a three-
dimensional—flow correction can be used to predict accurately
the loads and motions in landings of prismatic bodiesincolving
immersion of the chines.

This report is concerned with the derivation of a method
for calculating impact loads and motions during water land-
ings of narrow, heavily loaded, prismatic bodies. The prob-
lem of non—chine-immersed impacts of wide, lightly loaded,
prismatic hulls has been treated in reference 1. Comparisons
of the theoretical results of this reference with experimental
data have been made in references 1 to 4, where reasonable
agreement has been demonstrated. Although these reports
are devoted largely to the non—chine—immersed case, refer-
ences 2 and 3 extend the theory to cover impacts during
which a small amount of chine immersion is experienced.