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RCÌiiF
Written contribution to ITTC seakeeping
Hogoschool
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Scheepbouwkinde
-1-Comparison of Roll Damping between Prediction and Measurement
University of Osaka Prefecture (Japan) Department of Naval Architecture
Nono Tanaka
, Dr., ProfessorYoji Himeno , Dr., Associate Professor Yoshiho Ikeda,Dr., Research Assistant
The authors have recently proposed a method for predicting roll damping of an ordinary ship form 1) to 4)
The roll damping of a ship is assumed to consist of five components , i.e., friction , wave , eddy and lift components of a naked hull, and the damping due to bilge keels. The total roll damping can be obtained by summing up the predicted values for these components , which are briefly described in the following.
Outline of Prediction Method of Roll Damping
The friction component is estimated by Kato-Tamiya's formula , which has been
theoretically and experimentally re-examined fora two-dimensional cylinder and an
axisymmetric ellipsoid by the authors 1),5) Although this component occupies only several percents of the total roll damping for an actual ship , it can not be negle-cted on a small model because of the scale effect.
The wave component can be calculated by use of the strip method at zero advance
speed , although it is not so dominant in roll damping.
A modification factor for the wave damping at advance speed is given by the authors in a simple formula which
has a theoretically-drived form and experimentally-determined coefficients 4).
The eddy component is defined as the non-linear damping of a naked hull. From
the experimental results of the forced-roll test on many two-dimensional cylinders
an empirical formula for the eddy damping is given 3.
The lift damping is the most dominant and important component in the roll damping at forward speed. A simple formula for this component is also obtained by the authors 4), modifying the Yumuro's original form 6) which expresses the roll moment due to the lifting force on the rolling hull at forward speed.
The bilge keel component consists of the normal force of bilge keels and the hull-pressure change created by bilge keels , both of which depend on the roll amplitude or K-C number being analogous to the case of an oscillating flat plate.
A prediction formula of the bilge keel component
2)
without advance speed isdeduced on the basis of the experiments for two-dimensional models. The advance-speed effect on the component and the bilge-keel wave damping are neglected.
Comparison with Experiments
The comparisons of roll damping between the predicted by the present method and the measured are shown in Figs.l thru 18. Figs.l thru 7 are for ordinary cargo ship
models at zero forward speed , and Figs.8 thru 13 represent the case of forward speed.
The agreement between the prediction and the measurement seems good on the whole
showing that the present method will predict a rough value for the roll damping of an
ordinary cargo-ship form in full-load condition.
In Figs.14 thru 16 , a comparison is made for the case of mathematical models
measured by Takaishi et al )
. The agreement also seems good , except for the model
A' and B in the regions of high frequency and high speed. The disagreement is probably
due to the inaccuracy of the wave-component prediction which is based on the model
experiment for ordinary cargo-ship forms in full-load condition.
Finally we must mention about the limitation of the present method. The method is based on many experimental results of ordinary cargo-ship models , so that it may 'not be applied to an extra-ordinary ship form , i.e. , the case of shallow draft
with large skeg , or with other appendages. Fig.l7 shows an example for ballast
condition. The predicted value is slightly larger than the experimental one. For an extreme case , Fig.18 shows the comparison of an escort tugboat with wide beam and huge bilge keels. It is interesting that there appears no bilge-keel effect in the
measued value. The reason is found that the wave due to bilge keels reduces the total wave damping since the wave phase created by bilge keels differs greatly from that of naked hull for such a shallow draft ship-form. The prediction over-estimates the roll damping with bilge keels because of the neglection of the wave damping due to bilge keels.
Ref ere ces
Y.Ikeda, Y.Himeno and N.Tanaka On Roll Damping Force of Ship - Effect of
Friction of Hull and Normal Force of Bilge Keels - , Jour. of The Kansai
Soc. of Naval Arch. Japan , No.161 (1976)
Y.Ikeda, K.Komatsu, Y.Himeno and N.Tanaka : On Roll Damping Force of Ship
- Effect of Hull Surface Pressure Created by Bilge Keels - , Jour. of The
Kansai Soc. of Naval Arch. Japan , No.165 (1977)
Y.Ikeda, Y.Himeno and N.Tanaka On Eddy Making Component of Roll Damping Force on Naked Hull , Jour. Soc. of Naval Arch. of Japan , Vol.142 (1977)'
Y.Ikeda, Y.Himeno and N.Tanaka Components of Roll Damping of Ship at Forwaed
Speed , Jour. Soc. Naval Arch. of Japan , Vol.143 (1978)
Y.Ikeda, T.Fujiwara, Y.Himeno and N.Tanaka : Velocity Field around Ship Hull in Roll Motion , Jour. of The Kansai Soc. of Naval Arch. Japan , No.171 (1978)
A.Yumuro and I.Mizutani A Study on Anti-Rolling Fins (2) , IHI Engineering
Review , Vol.10 , No.2 (1970)
Japan Ship Research Association , SR161 Committee, Report No.310 (1979)
* All references are written in Japanese. For references (1) thru (5), English translations are available.
Table 1 Particulars of models
SR1O8 container ship Series 60 CB=O.6 Series 60 CB=O.7 Series 60 CB=O.8 ballast cond. cargo-ship model I escort tugboat mathematical model A A' B 4 3 2 BODY PLAN WATER UNES L (m) XB (m) Xd (m) 1. 75X0.254x0.095 1. 80x0. 237X0.096 l.80X0.257X0.103 1 .80X0.277x0.1ll l.80X0.277x0.0684 2.00XO. 319X0.130 1.675x0.41x0.13 4. 50X0. 45X0 . 24 4. 50X0.45x0.34 3. 00X0 . 42x0. 16 V(m3) 0.0241 0. 0247 0.0331 0.0439 0.0264 0. 0592 0. 04455 0.2886 0.4236 0.1195 CB 0.572 0.60 0.70 0.80 0.7748 0.7119 0.499 0.594 0.615 0.593 CM 0.97 0.977 0.986 0.994 0.990 0.991 0.780 0.889 0.889 0.889 B.K. (m) 0.0045X0.44 0.0054X0.63 O . 0054X0. 63 0.0054X0.63 0. 0054x0 .63 0. 005x0. 5 0.0175X0.5 OG/d o O O O -0.276 0.108 O O O O F P escort tugboat TOP OF 0 000CL Lt
piiJi1PiI1I
w
s 'W
i
'1NL1UIi
1i4Î4IJ
LVAS1PiW1I
VAi s.0.006
E.
0 006 0.004 0.002 0.0 0.0 Fig. I 0.004 0.002 0.0 0.0 0.009 0.006 0.004 0.002 00 0.1 0.2 0.3 0.4 0.5 0.6 lrad)Roll damping coefficient Ê for
container ship model
Series 60 ,C50.8 without O.K. o
-3
0.01 0.0 0.004 0.002 0.02 0.0 0.004 00 o Series 60 ,C0 0.7 9,0.l7Srad estimated O measured O measured with O.K. 9-05deg' O 8,.10deg Oi 9 Sdeg without O.K. L 9.-Isdeg 4.-lOdeg i 9,- OJeg_ est i te ted with 9.0.) 9.l0de O-l0deg 0, Sdeg 0.0 0.5 1.0Fig. 5
Components of roll damping coefficientÊ:, for ship hull (Series 60 C8=O.7)
measured by
Tasas and Takagj.
-K,.lSdr.j
t estietsted(wjthout 8.0
0.0 0.5 1.0
Fig. 7
Roll damping coefficient Ê4 forFig. 4
Components of roll damping coefficient cargo ship model (CB=0.7119)for ship hull (Series 60 CR000. 6)
0.0 0.1 0.2 B,(rsd) 0.3
Fig.3 Roll damping coefficient Ê for
ship hull (Series 60 CB=O. 8)
0.0 0.1 1.0
Fig. 6
Components of roll damping coefficientÊ:4 for ship hull (Series 60 C=0. 8)
0.002 o Series 60 ,c 0.8 00=O.l7Srad B» O 0.006 Fig. 2 0.1 0.2 90(rad) 0.3
Roll damping coefficient Ê4 for
ship hull (Series 60 CmO. 6)
o o o estimated o measured .622 0.0 0.5 1.0 0 1.5 0.008 0.006
0.015 S44 0.010 0.005 00 0.0 0.1 0.2 0.3 F0
Fig. 8 Roll damping coefficient Ê:4 for ship
model at forward speed
4 .1 0.015 0.010 0.005 O .0 (L 02 0.0 Series 60, C50.6 roll axis O 0,0. l7lrad 2 0.6 Series 60, C5=O.8
roll axis
O 0=0. l7Srad 0 =0.533 estimated (with 8.0 2.01 estjniated (without B.K.) A o oN
0.01 es t i nia ted o (without B.K.) meas ured A r with BK. O r without O.K. estimated(wtth B.K.( ereasured A r with B.X. O r without B.K. 0.01 0.02 844 00 844 0.01 0.005 0.0 0.0 0.005cargo ship model (C5-0.7119(
roll axis r O
0.-0. llSrad 2 -0.50 A r with B.C.
O r withOut 8.11.
cargo ship model (C80.7119)
roll axis r G (OC/d=0.108
0,0. lS7rad F50 .15 meas ured Ar with B.C. Or without B.C. £ o
cargo ship nrodel (C8=0.7119)
roll axis r G (OG/d5.108(
O.'0.lS7rad F00.2 measured A r with B.C. A O r without O.K. A estimated (with 8.0.1 o estimated (rutirOut B.C.) o 0.0 0.5 1.0 2
Fig. 13 Roll damping coefficient Ê4 for cargo ship model at F5=O.2
44
o
0.0 0.1 0.2 F0 0.3
Fig. (j Roll damping coefficient Ê4 for cargo
ship model at forward speed
0.0 0.1 0.2 0.3 F0
Fig. 4 Roll damping coefficient Ê for ship model at forward speed
0.0 0.5 1.0 2(-wJ
Fig. 12 Roll damping coefficient Ê:4 for cargo
ship model at F0sr0. 15
Fig. 10 Roll damping coefficient B4 for ship model at forward speed
g44
O02
0.01
0.0
Fig.14 0011 damping coefficient of model A.
measured by Takaishi O r 0.447 O =0.387 0.316
5-0.04 0.0 Series 60. CBO.O mea sured 0.0 Os,.
LS 1.0 1Fig.)? Roll darping coefficient B4 for
Series 60. C00. 8 (ballast rond.) at zero forward speed.
O Or with 9.0. without RK. F5 0.0 - 10.Odeg estimated O 844 (with O.K.) o O 0.01 O estimated (without BK.) 0.0 0.1 0.2 F5 0.3
Fsg.lS Roll damping coefficient of model A. Fig.lR Roll damping coefficrert of escort tugboat.
0.0 0.1 0.2 Fm 0.3
Fiq.16 Roll damping coefficient of model R.
0.0 0.1 0.2
escort tugboat OG/d = 0.0 e, = l0deg
estimated (with O.K.)
measured Or with O.K. O without O.K. S "estimated (without R. O 0.0 0.5 1.0
