Simulation of running attitude and speed of a semi-planing craft using database of three-component hydrodynamic forces

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Proc. of Krea-Japan Joint Workshop on Hydrodynamics

in Ship Qesign, Seoul, June 1991 L-

f

SIMULATION OF RUNNING ATTITUDE AND SPEED OF A SEMI-PLANING CRAFT USING DATABASE OF

THREE-coMPONENT HYDRODYNAM I C FORCES

_{TECHNISCHE UNIVEnsjrjr}

1) 2)

Labomij-,.

Yoshiho IKEDA and Koji YOKOMIZO

_{SCheePshydroiiieJij}

MoIce1weg _Deift

SUMMARY

-In the. present study a simulation method to predict the attitude and the

speed of a high-speed semi-planing cr.aft using a- database of the three component -hydrodynamic forces (drag, lift, and moment) which is obtained

experiments. The simulated results are confirmed to be in good agreement with the results of the conventional resistance test.

As examples, the simulated results to predict the effect of initial trim and a fin attached under the bottom on the attitude and the speed of a high-speed craft are shown.

1. INTRODUCTION

To make the- power prediction of a high-speed semi-planing craft a conventional resistance test Is usually carried out. The resistance of such

a craft, however, is very sensitive to load condition, longitudinal location

of center of gravity (CG) which causes initial trim at zero forward- speed,

shaft angle, and appendages as well as the hull form. Therefore the result of the resistance test may be available for only the condition which is chosen

in the experiment, If some changes are made in the design stages the result

would not be -useful fOr the design any more. To overcome the problem systematic tests a-re needed. Moreover it can be said in the exact sense that

the result-s can --used for on-I-y the model ¡f the scale effect causes

significant change of the runnln attitude of the full scale ship. As

mentioned above reasonable experimental procedures to predict the performance of a high speed semi-planing craft have not been established ye-t.

The purpose of the resistance test may be to get the hydrodynamic forces which is difficult to predict. The steady hydrodynamic forces would be determined for a given speed If the sinkage and the trim in running- condition

are given. The effect of the location of CG and the shaft angle on the

resistance can be predicted if the relationship between the hydrodynarnic

forces and the sinkage-/trim in running condition is given.

The author carried out a résistance test using a ship model fixed to a

loadcell on a carriage, whose sinkage and trim are systematically changed and did a simulation of the attitude and the speed for a given thrust force using the hydrodynamic forces (drag, lift and moment) obtained, by the experiments (1] .

In the present study a computer program to simulate the attitude and the

speed of a hi9h-speed semi-planing-c-raft using thedatabase of the measured three-component hydrodynamic forces acting-on the hull -is developed.

Using - the program a designer can make the sensitivity analysis of the

location of the center of gravity, the shaft angle, the initial trim and the sinkage to the resistance and the attitude for required speed.

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- SIMULATION PROGRAM

the hydrostatic forces, the hydrodynamic forces

àVjt'forces should be balanced as followstl).

fØTb1(tIjcos( a + ß )

(horizontal balance.) (I)

e!(b1AFy+Ft-sin( a + ß )+FbW (vertical balance) (2)

ceasMr.4FEt?t+Mb=O

(moment balance about CG) (3)

are the hydrodynamic drag and lift forces and moment, Fb

and Mb the hydrostatic. force and momente a denotes the running trim angle, ß

the shaft angle, W the wéight of the ship, Ft the thrust force -and Lt the

moment lever of the. thrust force about CG. Interaction. effect between the

thrust and the. hull resistance is igñored for sirnpl ification. The value A is

defined asfollows . .

-A=(Fx-Ftcos( a + ß )}2 .

+{Fy+Ftsin( a + ß )+Fb-W}2

+{Mg+F'tLt+Mb}2 . (4)

and the point where A is zero for a given speed Vs is searched by systematically changing the sinkage (upward direction ¡s defined plus ) H and

the trim angle a. The hydrostatic calculation program Is used to get Fb and Mb. and the database of the hydrodynamic forces is used to get Fx, Fv and Mg. In the present simulation program, Eq.(1) is- solved using the experimental data of the drag force at fast at a given forward speed to get.

Ft for given H and a values which are systematically changed. After then the

value Of A defined as

A=iFy+F'tsi'n( a + ß )+b_W)2+{Mg+FtLtfMb}'2 . (5) are calculated to find zerO value pints.

-MEASUREMENTS OF HYDRODYNAMIC FORCES

the three-component hydrodynamic forces acting on the model of a

high-speed passenger craft were measured at the towing tank of University of Osaka Prefecture (70m X 30m X1.6m). Söhematic' view of the experiment is shown in. Flg.1. The principal particulars of the model are shown in Table i and the body plan is shown in Fig.2, which was the ship used in cooperative resistance tests in Japan [2].

The hydrodynamic' forces acting on the model of: a high-speed passenger

craft fixed b a load cell oñ a towing carriage áre systematically measured for various t-rim angle, sinkage, and forward speed. The measured hydrodynamic forçes are shown in Figs.'3-1L

The hydrodynamic moments about a load cèli shown in Figs.3-5 demonstrate

that it increaseswith forward speèd, reaches the pèak valUe around Froude

number of O.5-0.6 and then decreases with the spéed.

The lift forces shoWn in Figs.6-8 demonstrate that t low forward speed the downward force is' large and that at high speed the upward force which lifts up the craft occurs. The Froude number where the lift force becomes to be plus values is significantly affected by the trim angle'. lt is noted that

the lift forces at high speed do not depend on the sinka'ge as shown the

figure for trim angle of 4 degree (Fig.8);

The thrust forces acting on the model shown in Figs.9-i1 demonstrate that it increases with forward speed,' decreases with' increás'in.g sinkage, and

increases with running trim. SIMULATION RESULTS

We can usually get a solution where A defined b Eq.(5) is zero for a

given speed, but there are some cases where several solutions exist as shown

in Fig.12. From this figure several solutions where A is zero can be seen in the region of a=I.O-2.O and l-I=-2.O-O.O. The thrust force using Eq.(l)

2

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corresponding for each combination of a and H are obtained as -shown in Fig.13. Since the craft must run in the condition of minimum thrust force, we

can get a final solution of a, H and Ft by finding the minimum thrust point in Fig.13 for a given Fròúde number. lt is noted, however that there i-s a

possibility to exist sevral solutions or the balahce e4uatio. Tha means the craft cañ ruñ in different attitude and thrust force at the same forward speed. This situation may occur when the solUtions exist in separate point.

Then the craft ¡s traed in the attitude where the thrust is not minimum,

and the craft neéds larger thiust.

In Figs.14 and 15 the comparison of the- rnning trim and the sinkage

between experimental results and the simulation are shown. The models used in experiments and simulatioñ are in the same scale1 but the model uséd in the experiment has appendages. We can safely say that the simulation give us reasonable results although the simulated sinkage is slightly smaller than

experimental ones. In Fig.16 the simulated thrust force is compared with

measured one. It ¡s found that the simulation give slightly smaller thrust force in high speed region. This discrepancy may be caused by the reasons why hydrodynamic forces in this region are extrapolated from measured results because of lack of dat-a.

Using the simUlation met-hod we can get various information on the performance of a high speed craft. Some examples will be shown as follows.

In Figs.17-19 the effect of thé initial trim on the- running attitude and

the thrust force is shown. As the initial trim increases the running trim and the sinkage increase. Although the effect of the initial trim on the thrust -force ¡s not so significant, we can see that the thrus-t decreases with increasing initial trim because of high lift force due to larger running tr-im ang le

Next example ¡s the prediction of the effect of a fin on the attit-ude and the resistance. In Figs.20-22 the effect of a fin which is attached under the bottom on the running atti-tude and thrust force are shown. Due to the fin

the sinkage increases in high speed although the running trim is not

affected. As the craft is lifted up, the thrust force decreases at high speed area as shown in Fig.22.

As mentioned above the present simulation procedure can offer various

useful information for designing a high speed craft, although the experiment

of measuring the hydrodynamic forces in systematic way is of course more time consuming one than a conventional resistance test.

5. CONCLUSIONS

In the present study a computer program to simulate the attitude and the

speed of -a semi-planing craft using a database of the three-component

hydrodynamic forces acting on the hull is developed. We c-an s-afely say that

the simulation give us reasonable re-suIts. Using the program a designer can mak-e the sensitivity analysis of the location of the center of gravity, the shaft angle, the initia.l trim and the displacement to the resistance -and the attitude for a required speed. In addition the effect of appendages on the

attitude and the speed can be pred-icted if the forces induced by them are considered in the equation. We have a plan to make a database of the hydrodynamic forces acting on ship models whose hull forms are systematically

changed. Using the database we will be able to predict the performance of

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Reference

Y. lkeda et. al." Hydrodynamic Forces Acting on.A High-Speed Craft Moving in Calm Water and Head Waves ,Jour of the Kansai Society of Naval

Architects, Japan1 No 210, September 1988 (In Japanese)

(English version of a part of the paper is available in RESEARCH MEMORANDUM

TUB-1 by Y. .tkeda, August 14, 1990)

The report cl the high-speed mariné vehcles committee1 Proc of 19th ITTC, Vol 1, Madrid1 September 1990

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FLOCHART OF THE SIMULATION PROGRAM

OFFSET DATA

INPUT I DISPLACEMENT

CG LOCATION KG

INITIAL TRIM Tm

INPUT 2 : SHAFT ANGLE a

MOMENT LEVER Lt DO

VsVmn TO Viiiax

DO HH

TO Huax

i

'1' '1 gr DO a=-2 TO 6 degree 'lt CALCULATION

OF Fb

AND Mb

FOR GIVEN H AND a

HYDRODYNAMIC FORCES

F, F9, M

FOR GIVEN H, a ,V 1' NEXT a NEXT H NEXT V5 CALCULATION OF A SEARCHING _{OF MINIMUM} A

HYDROSTAfIt CALCULAT ION

PROGRAM DATABASE OF HYDRODYNAMIC COEFFICIENTS

F, F9,

M ¿t'-CALCULATION OF Mg OBTAINED a

I

OUTPUT Ft-V5 CURVE (THRUST)

a-V5

CURVE (RUNNING TRIM)

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CRC FO&CE

LIFT IOtCt

Flg.l Schegatic vlea of experfient

Flg.2 Body p1a of iode! ship

6

.1OZT4D taocnr or aooa

TRIM ItftT

TRIM IICLE:

Table I

Principal partIculars of iodet ship

Length (o.a) 0.8534 .

Length (pip) 0.75 g

Breadth 0.168! i

Depth

0.0776.

Draft

00281i

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Fig_3

easared hydrodáuIô móieüt acting on

odeÍ Te-I.

3n.l.

2Cd.o) (k.t*=) .06 .04 02 o - .02 o -o

£ £

£ -O o o £ O - A .15

000

3 .45 .6 .75 .9 1.05 1.2 Slàlcsç.

o :-3()

£ OCá)

a :

3(..)-Fn .15 .3 .45 .T5 - :9

i.os

*2

fa

Fjg4 MeasUred hydrodynamic moment acting on model

o

40

L £

a

₄o

o

U. .n t TC. anelq Ø(d.ã)

Siakf.

(kefsá)

_{O :-3()}

o .08 .06 .04 .02 o -.02 O o

a

(8)

a

s

Tri. gnu. 0(d.o)

.15 .3 .45 - ;6 -.75 .9 l.O5 1.2 2 o

o0

O

sp

o 5

A-00

o --3(..)

-

OC..)

3(.)

En

Fig.6 _Measured _{hydrodyaaijc lift}

_force

_actingon

_iodel

-g

a .15 3 .4S

₀₆

.60 5 .9 lO5 1.2

0000

_£ ₆ 0

O LaO

00

Fig.7 Measured hydrodynamic lift

_force

_{acting on iodes}

Tri. angi.. 4(d.g) 2 o

(:úpward)

En Sink....

o :,3(ái)

A : OC..) o 3Cm.) ÇA

Fig8 )easured hydrodynajc lift

_törce

acting on iodel

I5 '3

45o6

.75 .9 1.05 I.2

o

Os

8°

Lift Tri. àn.i. 2(d..) _S1uk...

(kàf

_à

.8 _{£ :} _OCa.) o 3C..) .2 o -.4 .4 .2

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Orso

(ka?)

.5

.2

g

Trim snot. OCd.)

Q _o2 o A o .3 45 6 .75 9 1.05 1.2 Fn

Fig.9 _{Kèasùred bydrodynaijc drag torce acting oü iode!}

Trio anal. 2(d.ä) o o L O o .15 .3 .45 .6 .75 9

1.05 I2

Fjg.1O _{Measured hydrodyna.jc drag. förce acting on iodel}

Slnks. o :-3(ms) A : O(a.) o : 3(u)

o -3(o.)

L iO(sii) S1nkog. o a o : 3(...) (+ upward) Orsi Tlà anal. (ka ) 4(d.g) .5 .4 o QL .3 o o a .2 o a

.2 o

Ao o o .2 _o a A a 2 o o A o A

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I.

0.5 lo

« Fn

7 »

Trim

_angle(deg)

o:-2.O

0:-LO

: 0.0

:

1.0 : 2.0

Q

3.0 y: 4.0

O: 5.0

X: 6.0

-5..O

_5.0

_{lo_o}

Sinkage H(m)

Flg..I2 Expte of the calcuieted value of A

-5.0

0.0

50.

10.0

Sinkage

H(mm)

Fjg.13 Exauple of thrust force. for each coibjnatjo _{of « and H}

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-4

Fig.15 Coiparisor* betweeg experliental and siiulated _sinkage

of iode! ship -o measured -A o o .2 ¶4 6 8 1 1.2 Fn

Fig.14 Coaparison between expert iental and sfLulated _{running trii}

of iode! ship

o A e

£ A

_oO

.0

_A

.0

0A

o A .6.

.81

_:1.2 Fn .4 6 FA .2

-2

O o o o A A o Trim _o _meásured anUle _{A :} _shiulated

(deg) 3

Sinkage (ma)

Q:

leisured 6 A : shuttLed 2

_ÇA

fit

(kg f) .32 .24 .16 .08

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Rt (kaf). .24 2 .06 3 a o .2 8 a O a a

00

. - .6 .8 I

Fig.17 Effect of the initial trim on the running trim

simulated by preat method

.6 0 .8

Flg.18 Effect of the Initial trim on the sinkage

shunted by present method

V a o o L o o

L.A.

a

o

8 i

L2

Fn

Fig.lS Effect

of the

initial trim on the thrust force simulated by present method

.12 a o o 1.2 CC location

a :

(a)

o :

C0.Ö882(a) Initial trilt 0.01488(m) -0.00189(m) 0.01111(m)

cc ition Initial trim

a :00 (ii)

-0.01488()

o :l0.044j(*)

0.0189(a)

o :G-0.0882(m)

Ö.0l1i1(m)

SI kaa.

(s-)

6 a o cc

location

C=0.Q

(i)

Initial trim

-0.01488(a)

-0.00189(i)

4 a a o o _G0.ß882(i) _O.O1111(m)

.0

o o a L

000

o

000

+:backvard) z o o -2 -4