An experimental study of the parameters affecting the drag of barges in current and waves

V

University of Techuciogy

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LorarJ

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Mekeiweg 2 2628 CD Deft

The Nethertar%dS

Ptone.31 1578G73Fax:31 1578183e

n experimental study of the parameters affecting the drag of barqes in current and waves.

A.T. Ractlif f e, P.J. Fisher and G.H.G. Mitchell, School of Marine Technology,

University of Newcastle upon Tyne.

Results are reported of a systematic series of towing-tank tests to establish the drag farces

involved in towing and mooring ocean-going barges.

The odeis were essentially rectangular and buLlO

um in modular fotn so that the effect of varying length/bean r5tios and different tow and stern

shares could be enmined. Water dooth/droit ratios

;sre also varied o eXamine the effect of bottom clearance, and the transverse drag and yaw moments measured fo: towing angles other than longitudinal. TeSts were also conducted on the effect of wave length and height on the added resistance when towed in a seaway of regular and irregiilar waves.

The results are presented in the fo of non-dimensional graphs showing the effect of

para-metric variations.

It is found that the still

water resi000nce, particularly transverse drag, rises significantly when the water depth/d:ít ratio

falls below about 2.5 , the added resistance in

a seaway j5 aggroximately proorticnal to speed

for a given sea-state and shape of barge

INTRO DUCT ICt

The cgerator of ocean going barges is

interested in hull resistance from the point of

view of towing and tooting and this mager ea-mines aSpects of these areas which have not p:ev.cusly been investigated fully, namely; drag

for various angles of drift, the effect of shallow

water, and the effect of waves on the mean drag.

Offshore bercn dtffer from shims in two resPects:

tney are not self-propelled, and their shame is

cenerally fuller, baaisier and ohailower. Compared with ships, small changes in renistance oro not so significant to designer or cperator. On the

other hand, unlike a ship's propulsion which is

dctcomjned once and for all, the approPriate tug power for a barrje cay be varied for any given tow. This charges barre or.eratorz with an undarstandinn of the factors 3ovornir.q huLl, resistance, a

re'suiretsnr, rat nerraji'.' dcconded of shin o:,crstmrs.

15i"renccs ano iltuutrsticn' at end of p.:er.

Copyright 1981 Offshore Technology Conference

This paper was presented at the 13th Annual OTC ri Houston, TX., May 4.7, 1931. The material is sublect to

correction by the author. Permission to copy is restricted to an abstract of not more than 300 ';Ord5.

Fl-'/

a,_'\,

Some inforration is available in the litera-ture on the still-water resistance of barges and other bluff bodies of simple geometry (Ref. i-4).

Useful data has been presented in chart foom by Blight (Ref. 5) who also proposed a method to allow for variations in shape parameters. In this

method, after makir.g corrections for wind,, fouling,

and a fairly arbitrar', allowance for the added resistance due t wa'.'es, the tug power reguired

cari be obtoined directly.

Infoomatiori ort the effoct of shallow water is

more scanty but may be important when towing or

ooring in coastal waters. Ref. 6 and 7 provide

some experimental data on the fprward resistance of scow barges with L/a = 6.2 and B/d = 3.7 in

varIous water depths, both singly arid in flortillas.

Problems of drag also arise when moorìng, arid the

effect of current direction may become important during say a module loadcut on to a barge end-on

lying across a tidal stream, Cr the dynamic

res-ponse of barge type vessel moored to a single point mooring (Ref. 11) . In a transverse current

the drag may be estimated f'om the drag coeffi-cients measured for va.rìou bodies of simple geometry eq. Refs 3 and 9. comprehensive study

of the drag on tankers at aLl drift angles and

varying water depth has been published b', OCII4F (Ref. 10) - Althoush barges are shallower vessels

with generally lows: transverse dreg coefficien:, the trends are relevant.

The effect of waves on tho mean drag of bargas is poorly doci-cer,ted although much effort has been directed in rocent years to the germane prcblenz of wove drift at zero Frouds :m. and the added

resistance of fir.e ship forms. By virtue cf their

lower speed and shallower form, the added

rosis-tance of offshore barges due to waves is a creattr

proportion of the total resistance than it is for

chips. c-erritsrsa (qef. 12) has demonstrated

ex-perimentally that the added resistance for shios is

largely independent of opeed and ropertional to

the wave height s-uared. l.1ilo L-oth thce

ooser-vataono supPmrt y.s:'.tr's widoly ncccptcd linorisect

theor'.' of adnd r:uistar.co (Pef. 1)) , they are

t

'rarisrico with tho suthora measurements of

barq-.5tance which suggest that the added resistance .::eaSe5 with speed and a power of wave heryht

s than tuo.

:: ''- ASR,\NGSMENTS

tc models were constructed in modular form

-n that different

lengths could be built up by additIon of different bow and stern sections. :oensions were chosen to be approprIate at about

:/4Cth full-scale. The transverse section was

.ctangular, a uniform breadth of 0.75 with no

ng at the bilge. In the results presented

sre, only three barge shapes were employed a

::rictly rectangular box (denoted rectangular a scow barge rectangular in plan with .fentical bow and stern rakes of 300 to the .orizcntal. and a rectangular box with the same

bow but ro Stern shape. The ballast and its z±strjbution could be varied. The natural mariod of pitch was damped too heavily to be measured

acrurately without forced excitation, being in ali caseS 6-7 seconds full-scale.

The towing tank is 37m long, 3.7m wide and

-as a normal water depth of about l.2o. Because of the relative size of model and tank the

block-ao effect on resistance is significant,

tarticularly when towing the models at an angle of drift and even rmre so ir. shallow water. Must

attempts to correct for blockage have been

in-tetded fr ship models at relatively high Froude

has. (when wave-making resistance beccmes

sIgnificant) and when ao accurate but small

correction is reguired (Ref. 15) . Previous work

by the authors (Rif. 9) suggested that a simple mean velocity correction factor of the form 1/(1-kin)

could be justified on the basis of the drag mf different sizes of similar shames of bluff z-fies. Ir. this expression, ra the blockage factor

the ratio between the projected area of the hull normal to the direction of flow and the

cross-secticral area of the tank, while k is an arbitrary

constant. At high blockage factors it would appear reasonable to take k 1, but k probably

rises to a value of 2 or more for low blockage

factors.

For the present series of still water

tests k was taken as

k - 1 + exp (-1Cm) (1)

Thus the actual speed of the model was corrected

by dividing it by (l-) and the measured

resistance assumed to correspond to thiz higher

smed in omen water. Both corrected and

un-cc:recred results are presented so that the reader can apply his own correction if preferred.

A single tow-line was used for all the longitudinal towing tests, allowir.q the borge all

six degrees of freedcm. Snstch was minLoisod

ith the h5lp of judicious elisticity in the

tOw-li.r.e. Barges towed at an angle of drft (defined as the aigle the longitudinal cer.tre-line makes with the directcn of flow, clockwise

asit',e) had to be held irr rooition by means of three lines in order to balance the combination

cf transverse drag (or lift)

r.d yaw 000ent.

Tuw-line forcus were recorded ustnq a PD?-Ll based data socussirjon system. The anjie of

drift was photographed during each model test, and the three drag components resolved accordingly.

The still-water towing speeds at various

drift ongles corresponded to a full-scale speed of

2.2 knots while the shallow water tests were con-ducted at corresponding speeds ranging from 2 to 6

knots. Skin friction was calculated on the basis

of the 1957 ii'rc formula, no allowance being made

for hull fouling. The total full-scale drag coefficient therefore includes an allowance for skIn friction.

Investigation of the effect of waves was

con-fined to the longitudinal resistance only. Full-scale equivalent towing speeds ranged fm O to B knots. Both regular and irregular wave trains

were ernoloyed, the latter approximating a fully developed Pierson-!oskovitz spectrum (Ref. 14) Four irregular sea-states were used having

significant wave heights equivalent to l.0, 2.1=,

2.9m and 3.2o, while the regular waves were all about 3ra high (crest to trough)-. The models were

allowed to surge freely by virtue of elasticity in

the tow-line, and the mean resistance measured. A fixed wave probe was used to monitor the waves,

while a second wave probe mounted on the bow of the barge provided a sreasure of bow immersion.

PREDENTATION ANO DSCUSS ICN 0F RESULTS

The still-water drag coefficients were formulated on the basis of projected area rather

than the wetted surface area which is more usually employed by naval architects. The reason for this

is that whereas skin friction is graater than form drag for a ship, the reverse is true for rectanguLir

barges. Thus while length Is an important

determinant of resistance for ships, still-water barge resistance is insensitive to length (and

hence wetted surface area). The longitudinal drag

coefficient is obtained from the

relation:-(2)

where V is the relative speed of the barge to the current and the value of C varies with the angle

of drIft 5.

R is the coumonerm of drag force

acting in the longitudinal direction of the barge.

The transverse drag and yaw moment may be similarly expressed:

--

LdC,V2 (3)

Rx .r2d5CVl (4)

Figs 1 and 2 show the variation of these three dra7 coefLciencs with drift angle for a scow barge

and a rectangular pontoon Thee values are valid for dcp water, bu: in shallow water the drag is greeter owing to the constriction of flow under

the bottera. In deep wotar the wavemaking

resistance is small in the speed range of interest and therefore the drag coefficient is not

sensi-tive to t'roudc No. In rhallow water the speed of surface waves (being proportonaJ, to the square root of unter depth) is much reduced, and therefore wuvernaking resistance becomes significant.

in Fig. 3 on a baais of speed, using A

rather than length Proude No. These curves the Increased deperudence of drag

co-on speed in shiLow water.

The effect of incident waves on the forward

:i5t

is shown Fig. 4 The added

rosis-s, u5t be added to the still-water

..-tance to obtain the total hull resistance.

:ne o5t surorising result to ernerge froo this

res of testa is that the added resistance is

l.r:er approxioated by a linear function of wave

hht than by wave height squared as predicted by

:rzt order drift theory.

in; to the lisited

of wave heights and periods investigated, it

s not possible to state whether this unexpected

:cìationship is pore generally valid until further

zests have been cooplted. The added resistance

wsr.oniensionalised by

eans of the factors

gflaodpg52H for regular'and irregular waves respectively. Fig. 4 indIcates in ny cases a ruarly linear dependence of added resistance on zDeed which implies that a correction factor as a

fed proportion of still-water resistance will

rend to underestisate the added resistance at Iwer speeds for any given sea-state. The added

:eeistance aDpears to be greatest in waves which

predinantly slightly longer than the length

of the barge. Resonance does not appear to be a

sionificant factor since this occurs at a wave-length rather Less than the barge wave-length.

The bow wetness (not shown) was calculated

es the ratio of signifIcant anpittude of bow frseboard variation to significant wave height. Its value increasd by only about 20% fros zero to full speed for any given sea-state; and at cero speed lay within the range 0.5 to 0.7. The

ocrrelation of this paraneter with added

resis-tance is positive, but the one cannot be estited

directly froo the other.

NCLATUR bean

C longitudinal drag coefficient

=

2

C. transverse drag coefficient R/t.doV

C yaw tent coefficier.t RxyRL2dpv2

f draft

r

Fraude

- V/gt

Ç gravitational acceleration wave heigrzt (regular)

significant wave height (irregular)

h water depth

L length of barge at half draft

t

ratio hull section to tank

cross-section

ocan added resistance attributable to

incident waves alone

)t., longitudinal cponent of drag force

yaw ocoent. positive clockwise in plan view

V velocity of borgo through water (any direction) f angle of current to barge centreline.

clock-wise negative

A wavelength (regular waves)

X wavelength at sodal frequency

2sg/J

o density of water

a spectral sedal frequency (rad/s)

AC;C;iLEDGEMENTS

The authors gratefully acknowledge the suoporo of this work by the Science Research Council.

R tO' ERENC ES

}ay, A.ID. : 'Effects of varying one end of

barge foros with single geooetrically-shaed

ends, " Prznceton University Report (1549).

Couch, R.5. and

oss, 3L. :

"Notas on sea-going barge hydrodynaoics, " Gulf Section

of SN;d4.E, New Orleans, April 1964.

Fisher. P.A. r "The effect of variatIon of

hull gocsnetric paraneters of towed

ocean-going barges, Gulf Section of SN?M, April

1977.

Lattore, R. and Ashcroft, F. : "Recent

develo-paente in barge design, towing and pushing. Great takes/Great RIvers SectIon,

Jan. 1963.

Blight, G.J. and Dai, R.Y.T. : "Resistance of offohore barges and required tug horsepower,

OTC paoer 3320 (1976(

"Model E:perioents with 3arges and Towsoats

In Various Towing Fostions and in soveral Depths of Water,' 3SP_; Report No. 9 (ulv

1947)

¡7.

;Lian, J.F. and Walker, W.?.: "Reststar.ce of barges in deep and shallow water," Trans.

RINA Vol. 90 (1943) os. 154-167.

0. Ohasi, S. and Ikebuchi, Y.: "Res.otance tests

on floating boxes," PaWers of the Snotuilang

Research Centre of Jacan, Vol. 1 (1977).

P.actliffe, A.T. and Mttchell, G.N.G.: "The drag and wave drift of basic shapes of

floating structures," Trans. NEC Inst.Eng.Sh.

Vol. 93 (1976) pp. 15-17.

"The predIction of wind and current loads on

VLCC's," Cil Conpanies InternatIonal Marine Foru'n Report (1976)

RactIlfIe A.T. and Clarke. D., "Develoonertt

of a coeprenensive zisula:on co3el of an 5PM syoten," Trans. RINA. '.'ol. 122 (1930) p. 33-44.

12 Gerritsoc et.aL. r "Prooulston in regular and

Irregular waves," International ShipbuiLing Progress. Val. 8 (1061) op. 235-247.

13. Maruo, . , "The excess resistance of a si

in rough teas," tnternatonal Shpbu1dir.g

Progress, Vol. 4 (1557).

'14. Ochi ,M.., and Sotos, S.L. "Effect of

various spectral foru1tions in predicting

responses of sanno vehiclas and ocean

structures," TC Pnoer 2743 (1977).

15. SCott, J.R. r 'On blockage correction and

extrapolation to 50.00th ship resstance,"

H E

0.1

P

Q3 LONGITUDINAL DRAG

: COEFFICIENT C

(corrected for blockage)

0.2-3RIFT ANGLE fi

r

L/B=2.5

B/d=18

o

L/B=2.6

B/d.= 9

o

L/E=2.7

_B/d=

6

Rectangular PonLoon L/B2A r B/d=18

o B/d= 9

o

_B/cI

₆

'LONGITUDINAL DRAG

0.3

_{COEFFICiENT Cx}

=

(corrected for blockage)

0.2

0.1

DR[F1T ANGLE

30

50

₇₀

i (b'). J -t

-J H 1

itO

50

0.9

0.8

0.7

I

0.6

0.5

0.4

0.2

0.1

0.7

0.6

0.4

0.1

nrJ

uu

-O2

Ir

300 Scow ends

V

0.6

F

o L/B=2.7

B/d.= 6

0.5

TRANSVERSE DRAG

COEFFICIENT Cy

(corrected for

blockage)

0.3

TRANSVERSE DRAG

0.5

COEFFICIENT Cy

(corrected. for

blockage)

DRIFT ANGLE

Rectangular PonLoon

L/B=2.4

DRIFT ANGLE ¡

10

50

r I 1 -4 J

i

70

90

io

30

50

70

90

0.07

0.06

0.05

0.04

0.03

0.02

0.01

0.04

rr

_'j

r /

0.02

Y

0.0.1

300 Scow ends

E

L/B=2.5

B/d=18

L/B=2.6

B/d= 9

= O

L/E=2.7

B/d= 6

-YAW MOMENT DRAG

=

C0EFFICENT Cçy

(corrected for b1ocage)

0.07

_{YAW MOMENT DRAG}

E

COEFFiCIENT C

0.06 F(correctec.

for 'blockage)

DRI.VtI' AC.i::

i

Dfl

lU

JU

-

r----._.

'-S

70

1 (f

_5/'

0.05

II! II1

RecLan,gLJa: PonLoon L,/B-2.4

E Bdl8

r-(>

B/d= g

= O

B/cl= 6

0.4

0.2

0.1

0.9

0.7

0.5

0.3

- LONGITU3INAL DRAG

COEFFICIENT Cx

(no b1ocage correction)

0.1

10

DRIFT ANGLE

O.5

LONGITLIDINAL DRAG

0.3

L

_{COEFFiCIENT Cx}

E

(no blockage correcLon)

0.2L

50

DRIFT ANGLE

_fi

'i'

,

30° Scov ends

o L/B=2.5

B/d=18

L/B=2.6

B/d=

9

o L/B=2.7

B/d= 6

70

Rectangular Pontoon L/B2.4o

B/d=18

0.51

B/d9

H

o B/d=6

50

70

F-0.6

O.5

TRANSVERSE DRAG

COEFFICIENT Cy

(no blockage

correcLion)

0.2

0.1

300 Scow ends

L/ß=2.5

B/d.=iB

L/Th2.6

B/d.= 9

L/B=2.7

B/d.= 6

Recbangular Pontoon L/B=2.4

0.6

t-E

TRANSVERSE 3RAG

0.5

COEFFICIENT Cy

(no blockage

correction)

0.4

L

neil

U.-3 E

o

_ß/d.=18

o

_F3/d

₉

o

_E/d=

DR1FT ANGLE lE?

...

10

30

50

70

90

2 (d

50

30

10

70

90

2(c)

0.07

0.06

0.05

0.04

0.03

0.02

0.01

0.04:

n nr'

-

YAW MOMENT DRAG

-

COEFFICIENT Cxy

-

(no blockage correction)

300 Scow ends

E

_L/B=2.5

_B/d=18

L/ß=2.6

B/d= 9

o

_L/B=2.7

B/d= 6

10

/ D

O

: .... r'" r'

(u

2(f

. D Rl PF YO ¡ [

I

10

30

.50

70

90

2(e.

0.08

E

Rectangutar Pontoon L/B2.4

E

B/d=18

oo

Ö

_E/d=

°

I

YAW MOMENT

DRAG

B/d= 6

COEFFICIENT C:

I j

300 Scow end

s

LONGITUDINAL DRAG

-

COEFFICIENT C

I

(ccrrecbecl for blockage)

i.0I

LONGITUDINAL DRAG

COEFFICIENT C

L(corrected for blockage)

t-V/gd

0.1

0.2

L/B=2.7B/d=6

A

h/d

-

1.2

V

h/d

-

1.4'+ h/d 1.?

-xh/d 2.0=

Eh/cl 2.5-

_{hd -}

3.0-oh d b.0

_{h/c 9.ö}

flO

fiA

_Lì.-r

L

-D1

B/'d

6

0.5

A

h/d

-

1.2

V

h/cl

-

1.4

xh/d-2.0

h/cl

-

3.0

oh/d-5.O

h/d

-

9.5

V/ Vg d

0.5

0.6

3 ( a.

J

0.6

3 (.

0.5

1.5

O.5

I I i_' -L_J__b. L i

0.1

0.2

0.3

O.1

2.0=

L

-

TRANS\IRSE DRAG

COEFFICIENT Cy

(corected for

blockage)

B/d= 6

=

h/d - 1.2

y h/d - 1.4

± h/d 17

-xh/d 2.01

h/d

-

3.O

oh/d

V/Vgd

0.1

0.2

0.3

O.

Rectangular Pontoon L/B=2

TRANSVERSE DRAG

COEFF.ICNT Cy

(corrected for

blockage)

1.0

_T

f'

I I T t T $ I I i i i T TI

B/d= 6

Ah/d

vh/d

±h/d

x h/c

h'/d

o h/cl

I _i...L..i r I

0.3

1.2

1

'

1i

2.0

Ç)

u.

5.0

J

0.5

3(d).

¡ T T r T

L B-2.7

¡ T

300 Sco\v ends

0.4

0.5

2.0

1.0

3.0

L

LONGITUDINAL DAC

COEFFICIENT Cx

(no blockage correction)

300 Scow ends

L/B=2.7

B/d

6

-vh/d

+h/d

xh/d

-E

h/d

-h"d

ohd

?Eh/d

-V

V/Vgd

i I r X H

1.2

1

1.4

1.?

-2.01

2.5-'-D

u-5.0

9.51

i I I r

Rectangular Pontoon L

B/d=

9 5

F- LONGITUDINAL

DRAG

COEFFICIENT Cx

(no blockage

correction)

2.0

0.1

0.2

r,'

.0

-

c____:/

-0.1

0.3

0.4

Ç) 4

h/cl

1.2

6

V h/d - 1.4

X h/d - 2.0

h/d

-

3.0

O fl/d -

5.0

h/d

-

9.5 -

_-I /

---,ç____

-,

0.5

3 (e)

-1 -r H -1 -i -4 -4

'I

_L

Z

L

0.2

O:.

0.4

0.5

3/.

1.0

0.5

_1 L -4

r

r

-4

1.5

-r

6.0

o

2.0

4.0:

2.O

Ï ¡ T I I

300 Scow ends

TRANSVERSE DRAG

COEFFICiENT Cy

-

(no blockage

correo

Lion)

L/B=2.7

B/d= 6

-A h/d

1.2:

V h/d

1.4:

-

1.7:

xh/d 2.0-

_{h/d _3.O}

o h/d -

5.0:

V/Vgd

0.1

0.2

6.0

I I I

Rectangular Ponboon L/B2.4

B1/d= 6

È TRANSVERSE 3RAG

COEFFICIENT Cy

(no blockage

correction)

0----

-0--I t I ¡

A h/d

y h,/d

X fl//d

h/d

oh/d

-3(g).

0.4

1.2

1.4

i.7

2.03

3.0

5.0

I

-4 -4

0.1

0.2

0.3

0.4

3 (.

Vg d

¡ L i

LJL_

i

0.02: RA

È pgB2H

0.01

0.04

0.03

L

0.02-

RA

E pgB2H

0.01 H

t. I * I

300 Scow ends

L/B = 3.2

B/d

= 9

Regular waves

=

AVL=0.88

0.03

-=

0.02

0.02

0.04

0.06

0.08

0.10

0.12

A X/L = 0.90

0.04

0.06

Regular waves

n no

U U -1 T

OJO

0.1.2 41

=

1.15

+

= 1.56

X

=

1.84

E

=

2.93

y

±

<

E

X/L

X/L

X/L

=

1.12

1.51

1.79

=,2.84

30° Bow only

L/B = 3.1

B/

=9

RecLangular

rr

0.04-

_{y X/L =}

-0.03

L

0.02

0.01

(\(CJ

0.02

0.01

/

0.02

0.04

0.06

(T T /i 'T) 'T)

- U.0

0.02

0.01

Pcnoon

L/B = 3.0

B/d

0.93

Regular waves

1.19

1.61

1.90

3.02

0.08

B/d= 9

Irregular waves

9:

H F11:

0.10

0.12

4 (c.

0.06

0.08

0.04

E

30° Scow encs

:

A

_Xm/L

0.62

=

y Xrn/L = 0.90

+

X/L

1.15

=

x Xm/L = 1.5

I I I I ci

¡ ï

i

OQO

_{Scow ends}

_L/B

_{= 2.6}

_B/d

= 9

=

Irregular waves

A Xm/L = 0.78

0.03

y

m/L = 1.13

+ Xm/L= 1.44

X X/L = 1.82

0.02

0.01

pgEFi

0.02

30° Bow only

L/B = 3.2

B/d =

9

004E

A Xm/L = 0.64

y

= 0.93

0.03

± Xm/L

1.19

X X/L = 1.50

Irregular waves

0.02

4(e.

0.04

0.06

-.

0.08

0.02

0.04

0.06

0.08