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TEC:HNISCHE HOGESCHOOL DELFT
AFDELING DER MARITIEME TECHNIEK
LABORATORIUM VOOR SCHEEPSHYDROMECHANICA
Forced oscillation experiments
with a segmented model in shallow
water.
Prof.ir.J. Gerritsffla and
Ing.W. Beuke]iman
Reportflr. 513-P
August 1981
16th i.T.T.C. - Leningrad.
Delft University ofTechnology Ship Hydromechanics Laboratory Mekelweg2
2628 CD DELFT The Netherlands Phone 015 -786882
16th INTERNATIONAL
TOWING ThNK CONFERENCE
LENINGRAD
31 AUGUST 9 SEPTEMBER,
1981PROCEEDiNGS
VOLUME 2
IttC[Ji
References
I.Barr, R.A., Ankudinov V. "Ship rolling. Its prediction and reduction using roil stabilization". Marine Technology Vol. 14 No. I Jan. 1977.
2.Zdybek, T. "The use of bench test re-sults for calculating roll response of the tank stabilized ship". International Shipbuilding Progress Vol. 27, Apr. 1980 No. 308.
3."A methodology of the roll calculations of tank stabilized ships" (in Russian)-Report of the USSR part in the frame-work of technical collaboration between
Shipbuilding Industries if the USSR and Poland. Leningrad 1978.
J. GERRITSMA, W. BEUKELMAN - Delft Uni-versity of Technology, Delft,
theNethel-lands
FORCED OSCILLATION EXPERIMENTS WIT!! A SEGMEN1'ED MODEL IN SHALLOW WATER
Forced oscillation experiments for hea-ving, pitching, swaying and yawing mo-tions have been carried out with a seg-mented model in various water depths.
The Series Sixty, block .70 model was di-vided in seven segments with a total length
of 2.26 meters and has been tested with-out rudder and propeller. /1/
The experiments have been carried out at the following waterdepthB bIT = 2.4, 1.8, 1.5, 1.2 and 1.15 at two forward speeds: Fn = 0.10 and 0.20. For the forced
heav-ing and pitchheav-ing motions three amplitudes
of displacement have,..befl UBOd at
frequenc-ies ranging from
w4..
1.9 to 5.8 and a similar teatprogra1 has been used forsway and yaw.
To allow extrapolation. to very low fre-quencies, which are of interest for the analysis of steering and manoeuvring of shipB, the forced sway and yaw experiments
119
have been extended to include a frequency range of = 0.12 to 0.36 in additiOn
to static drift angle tests.
For vertical motions the tet results indicate an increasing added mass and damping for decreasing waterdeptita, in particular for4.I.5. 3ome non-line-arity with amplitude of motion has been observed at the lowest considered water-depth, see Figure I. The diBtribUtiOfl of the hydrodynamic mass and dmping for the heaving motion -along the length of the model is owüin.PigU1'e 2 for two
water-depths. The distribution of the hydrody-nainic mass, normalized with the total by-drodynamic mass, is not greatly influenced by the waterdepth, but for the
distribu-tion of dwnpirig a significant shift of larger damping values toward the fore body of the shipmodel with decreasing wa-terdepth is obaerved. For sway decreasing hydrodynamiC mass and damping with decrea-sing waterdepth are shown in Figure 3, but for very low frequencies the added masses increased considerably at
decrea-sing waterdepth. A similar trend is found for the mway damping, but for very low frequencies the sway damping increases very strongly.
The normalized distribution of the hydro-dynamic mass and damping of the swaying motion.both show also a tendency of a
shift towards larger values at the fore body of the ship model(FigUDe 4). In the very low frequency range the influence of waterdepth on mass and damping is important
for waterdepthe smaller than bIT 1.5
(for sway smaller than h/T 1.8).
In the static drift angle experiments strong non-linearities have been observed in the measured hydrodynaaiC forces on a base of the driftángle for decreasing Waterdepths.
carri-1'zo
ad' out to compare with the experimental sectional valuei of mass and damping
aM
the total values for the whole model. For heave see fig. I and' 2, for awáy aeefig.3and4.
Theae calculation. are based on eii'e method adapted for a restrIcted water-depth /2/..
It appears that strip method shows
ma-sonable results even for the lowest Wa-terde.pth conaidered.The underestimation of damping of the vertical motion at high-er frequencies and lowhigh-er wathigh-erdepthe may be due to viscous effects. Two calcula-. ted versions with different speed influ-ence are shown in the figures.
The first version contains speed terms with the derivative of the added mass in
longitudinal direction only. The aecond vers±on a]so includes terms with the de-rivative of the damping coefficient in
the longitudinal, direction. in this re-spect for the formulation see /3/. The used expressions are also presented here in appendix I.
I... J.Gerri.tsma, W.Beukelman,
The distribution of the hydrodynam±c forces on a heaving and pitching ship model in still water,
5th ONR Symposium 1964, Bergen,Norway. 2. H.Keil,
The hydrodynamjc foroes'at a periodic motion of a two-dimensional body in the still water surface.(Die
hydrody-namiache Krftebei der periodiechen Bewegung-zwei_dimenajone 'KBrper an dar 0berfiohe flacher Waèaer),
Institut für Schiffbau, Baricht Wr.
Appendix I.
The following exprossiona aroused fcs
Hydrodynamic Coefficients for vertical
'motions.,
,.
Dry
a','aZ.-m.1-)--
7i
v' a'm'. r v
i,i'l
-J
Hydrodynarni'c coefficients for horizontal motions. _ffh,[
.ij]
I,. - I pp&,.K
v V , Vdm"
.1 V
IK'7
K2]ff#i---
ir w1
%--K'x.2n7'V. ,,
Lm'1. [4..
in which: .!ttC[i
sectional added zero speed sectional aamping J forward speed Wp frequency of encounter = sectional added mass5'
sectional damping - sectional mass couplingcoefficient at speed sectional
dampingcoupl-ing coefficient 305, February 1974.
3.J.Gerritsma, W.Beukelman, C.C. Glansdorp, The effect of beam on the
hydrodyna-r
g 2-longitudinal
heave
directionmic characteristics of ship hulls, 10th OflR Symposium 1974', BostOn, USA.
o
p
apitch syaw
VSI0N I-Terms witht
{ )
VSI0N. 2-Terms with
if 22 50 0 10 l5.__._!0 ,.001m SWM FIGURE 3 FIGURE 4 o 15PI
