Twenty-Fourth Symposium on Naval Hydrodynamics (2003) / Chapter Skim
Currently Skimming:
Viscous Roll Predictions of a Circular Cylinder with Bilge Keels
Viscous Roll Predictions of a Circular Cylinder with Bilge Keels
Pages 682-697
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 682... ...
Bilge keels will significantly increase the damping of roll motions as well as generate a lift force if any forward motion of the ship is present. The prediction of ship roll motions has been difficult because of its nonlinear nature as well as the strong dependence on forward speed.
|
From page 683... ...
The current effort demonstrates some RANS calculations to simulate roll motions of a 3-D cylinder with bilge keels. Measurement data from experiments performed at Naval Surface Warfare Center, Carderock Division (NSWCCD)
|
From page 684... ...
i_,_ 0.2 r 0.15 ~ 0.1 Oh C 0.05 Ct o ~5 4, ~ -0.05 00 0 4) 1 -0.15 -1 RMS Error / Amplitude = 20.8% L2EO-A3F1~132 A, Measured , Sinusoid Van ', I, I · 1 1.2 1.4 1.6 1.8 2 22 2.4 2 6 2.8 3 Oscillation Cycles (12.5 see period Figure 4 Slow Roll rate RMS Error/Amplitude = 6.1% Oscillation Cycles (3.12 see periods Figure 5 Faster Roll Rate The two dimensional, flow field near the port bilge keel is measured using Particle Image Velocimetry (PIV)
|
From page 685... ...
The large cylinder was tested under 70 different conditions. Figure 7 PIV Image showing bilge keel interaction with free surface Governing Equations and Numerical Implementation Math Mode/ and UNCLE To compute the viscous flow field the incompressible Reynolds Averaged Navier-Stokes equations are solved using the Mississippi State University code UNCLE, (Taylor et al 1991, 1995~.
|
From page 686... ...
The cylindrical emerged body has been extended downstream to the outflow boundary because of difficulties with the free surface boundary conditions for the actual flat back of the cylinder. Flow region - volume grids Structured grids are used for the present calculations.
|
From page 687... ...
The one period of measured angular velocity,—, is dt used for input to the RANS solver for all time and the Figure 9 Grid rotation for the emerged body same one period of measured flow results is used for validating the RANS solver solutions. Force comparisons are made of the measured normal force on the individual bilge keels with the RANS force for one period of roll.
|
From page 688... ...
immersed Body Comparisons Figures 10-13 show comparisons for the immersed body. Each figure shows the calculated and measured normal force on the bilge keels versus time for one period of roll motion.
|
From page 689... ...
, Immersed Figure 14 shows a comparison of the calculated velocity vectors with the velocities obtained from PIV data, looking aft at the port bilge keel, for the zero forward speed case where the roll motion amplitude is approximately 15° and its frequency is .32 Hz. The calculated velocity was interpolated to the PIV point locations.
|
From page 690... ...
Experiment _ _ _ _ _ ~~ItIJIt~ fIll ~ J ~ I ~ ~ I I J I dlJItlIIIJI l I I I I ~ I ~ ~ ~ I I I 1 1 1 1 1 1 1 ~ 1 1 1 ~ ~ ~ t ~ I ~ I I I I I ~ \~\ t I ~ l l I l l I ~ ~~~\ _-~\ ~1' -;;~.~; , ''''',/1 7 '''/~y 1 'l,/~/~t 'IJI/lI33~!
|
From page 691... ...
The linearized free surface boundary condition is used in these calculations. For the O forward speed case there is a significant difference between the measured port and starboard bilge keel forces.
|
From page 692... ...
Once convinced of the good performance of the RANS code for predicting bilge keel forces for forced roll body tests, the solutions are used to compare differences in force data due to varying roll test parameters. These tests use an ideal sinusoidal roll motion, resulting in smooth force results.
|
From page 693... ...
. The Fourier decomposition of the force histories shown in Figure 20, shows that the first harmonic sin and cos terms have about equal contributions at a particular speed, but reduce as the forward speed increases.
|
From page 694... ...
t/T = 0.0 / (d) t/T = 0.250 Figure 21 RANS Vorticity: Ideal Roll Motion f = .32 Hz., A = 15°, U = 0.0 m/s (a)
|
From page 695... ...
axial Velocity 1 o.9o Q.8O i o.7o ; 0.60 0.50 OAO 0.30 0.20 ~ O1D Figure 24 RANS: f = .32 Hz., A = 15°, U = 2.0 m/s (4 kts.) , t/T = 0.25 This indicates an influence on the port bilge keel force due the starboard bilge keel and vice versa.
|
From page 696... ...
Calculations performed using an ideal sinusoidal roll motion allowed trends to be investigated by enforcing the same roll motion for a number of forward speeds and simplified (somewhat) the harmonic content of the total bilge keel force.
|
From page 697... ...
L., "Oscillating Flow About Two and Three-Dimensional Bilge Keels," Journal of Offshore Mech. Arctic Eng., Vol.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.