Twenty-Fourth Symposium on Naval Hydrodynamics (2003) / Chapter Skim
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Bow Waves on a Free-Running, Heaving, and/or Pitching Destroyer
Bow Waves on a Free-Running, Heaving, and/or Pitching Destroyer
Pages 211-223
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From page 211... ...
. There is not, at present, a computer code that could predict the response of a destroyer in a random sea, the ship resistance, the bow waves, bow sheet separation, jet/spray formation, subsequent aeration, and the extent of the white water region in the wake of the ship in a viscous fluid with or without surfactants.
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From page 212... ...
In general, the ship Froude number, the shape of the ship (particularly the bow geometry) , the sea state, and the type of motion of the ship determine the characteristics of the bow waves and spray generation and, hence, most of the wave resistance.
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From page 213... ...
Consequently, the delineation of the excursions of a given bow-wave above or below the maximum or minimum of the basic bow wave may be very important in assessing the operational resistance and total hydrodynamic performance of a ship and the spray generation as a function of the bow and sonar geometry. This fact has been effectively used by Cusanelli (1998)
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From page 214... ...
This was done partly to assess the overall accuracy of the data and partly to account for the aforementioned, relatively small, free-surface oscillations. RESULTS AND DISCUSSION The results will be described in the following order: the basic bow wave; the independent as well as combined effects of heave and pitch on the model; the surge phenomena (i.e., the differences between the basic bow wave and mean heave as well as mean pitch at Frs = 0.26~; the case of a higher Froude number (only in the free running case)
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From page 215... ...
However, the most important feature of Figure 7 is that it points out the establishment of the basic bow wave shape in the subcritical Froude number regime and the point of inception of the supercritical regime (X/L > 0.04~. Heave Motions Figure 8a is the average heave profile (the mean of the maximum and minimum of the elevations)
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From page 216... ...
The time of the maximum wave height lags the maximum downward excursion of the model by 2/45 seconds. In other words, if the model reaches its maximum excursion at time 't-1', then the maximum wave height occurs at time 't-3', as noted earlier.
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From page 217... ...
. Pitch Motions Figures lea through lOc show the comparison of the average pitch motion with steady runs for a given frequency and three different amplitudes (measured in degrees)
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From page 218... ...
. Combined Heave and Pitch Motions The data obtained for a heave-pitch combination using a frequency of 1.5 Hz, a heave amplitude of 0.32 cm, a pitch amplitude of 2.5 degrees, and a phase angle of 120 degrees (between the pitch and heave)
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From page 219... ...
Figure 2 was obtained in the supercritical jet facility and shows that one must utilize the supercritical values of the controlling parameters (Froude, Reynolds and Weber numbers) to accurately model sheet separation and subsequent spray on any model smaller than the ship.
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From page 220... ...
Thus, the shear-free freesurface condition and the no-slip condition are incompatible. The consequences of surface tension reduction may manifest themselves in various ways under a variety of circumstances in both supercritical and subcritical flows.
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From page 221... ...
Representative frequency distribution of the vertical component of the normalized tip velocity of the filaments in a supercritical wall jet. 0.19 0.18 0.17 ~ 0.15 _ ~ 0.14 r r _ 0.12 0.11 0.09 0.0 0.1 0.2 0.3 0.4 Frequency Figure 18.
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From page 222... ...
Experiments with non-dissolving surfactants have shown dramatic decreases in the size and ejection velocity of the filaments from supercritical jets. Detailed processing of data from experiments with grid generated turbulence in subcritical channel flows, with and without dissolving and non-dissolving surfactants, will shed considerable light on the decay of the turbulent kinetic energy of the wake and thereby on the decay of short waves.
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From page 223... ...
469-502. Rhee, S.H., and Stern, F., "Unsteady RANS Method for Surface Ship Boundary Layer and Wake and Wake Field," International Journal for Numerical Methods in Fluids, Vol.
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