guide for power prediction.doc

8/17/2019 Guide for power prediction.doc

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TMR7 Experimental Methods in Marine Hydrodynamics

Guide to scaling of resistance and prediction of full scale power

Ship data are found later in this document. Values of some coefficients used in the resistanceand power prediction are given here. There is also an enclosure with formulas used in the

resistance and power prediction. hat you find here is a guide on how to use those formulas.

!n this analysis it is recommended to use Excel or a similar tool.

"or all speeds tested do as follows#

$alculate total resistance coefficient C Tm$alculate residual resistance coefficient C R% using C BDm&'% ()k o&(.'*++% νm&(.'7,-('* m/0s

$alculate full scale total resistance coefficient C Ts% using C A&'.//1E'2. C BDs&'% νs&(.(17-('

* m/0s

$alculate full scale resistance RTs 3 now you are done calculating full scale resistance4

The open water test has 5een given to you as part of the model data. 6ou will need to

interpolate in the open water diagram as part of the analysis of the propulsion test. This can 5e

done manually on a printed diagram% or it can 5e done 5y in a spreadsheet or Matla5.

description of how to do this in Excel follows.

!mport the open water curve into Excel 8or similar9. $reate thirdorder polynomials of J as

function of K T % and K Q as function of J . 6ou can do this 5y creating a graph with the curve%

add a trend line% select polynomial as type of trend line% and select :display e;uation on

graph


2/11

/

TOWING TESTS

SHIP RESISTANCE

ENCL. >>E@A!B (

REPORT *'(*//.''.'(

DATE /''2'C('

REF M/27,D

The hull model is towed 5y the carriage at which the total resistance is measured at different speeds.

The hull model is e;uipped with a rudder and a tripwire at station + 8(+9. The conversion from hull

model 8m9 into ship 8s9 is made 5y using the form factor method. !n this method it is assumed that the

total resistance can 5e divided into two parts% represented 5y the viscous resistance and the residuary

8due to vorticity% wave ma=ing and wave 5rea=ing9 resistance 8$R 9. The viscous resistance is

determined 5y multiplying the frictional resistance 8$"9 with a constant form factor 8= o9% which is

identical for model and ship. "urther% it is assumed that the residuary resistance 8$R 9 is identical for

model and ship.

MODEL (m):

Total resistance coefficient# BDm AAm Rmo Fm

mm

m

Tm

Tm C C C k C

S V

RC ++++⋅=

⋅⋅

= 9(8

/

/ ρ

"rictional resistance coefficient# /9/8log

'7,.'

−=

nm

Fm R

C 8!TT$ 3 ,7 correlation line9

Residuary resistance coefficient# BDm AAm FmoTm Rm C C C k C C −−⋅+−= 9(8

SHIP (s):

Total resistance coefficient# BDs AAs Ao F Fs RmTs C C C k C C C C ++++⋅∆++= 9(898

"rictional resistance coefficient# /9/8log

'7,.'

−=

ns

Fs R

C

Total resistance# s s s

TsTs S V C R ⋅⋅⋅= /

/

ρ

Effective power#('''

sTs E

V R P

⋅=

"orm factor# 2'.* 7,ok ϕ ϕ = + where BT T

L

C FP AP

L

B⋅+= 98ϕ

ir resistance coefficient#S AC AA

T''(.' ⋅=

Transom stern resistance coefficient#/0(

/02

98

908'/+.'

F

B BD

C

S S C

⋅=

Roughness allowance# [ ] //(.' 22.C'2982(.((' Fs s F C V ! C ⋅−⋅⋅=∆

here H & hull surface roughness in µ8('2 mm9. H&(,' µ.

and Vs & ship speed in m0s

Fnly ∆$" values G ' are used


3/11

PROPULSION TESTS

ENCL. >>E@A!B /

REPORT *'(*//.''.'(

DATE /''2'C('

REF M/27,D

The hull model is supplied with a propelling machinery and a driving propeller. The rate of

revolution is regulated until the model is free relatively to the attached towing carriage. !n order too5tain tur5ulent flow around the model% a trip wire is placed at station + 8(+9. To compensate the

difference 5etween the frictional resistance of the model and the frictional resistance of the ship%

converted to model scale% the model is unloaded with a towing force in the direction of motion.

The towing force 8"A9 is calculated 5y the formula#

mm

m

S D S V C F ⋅⋅⋅= /

/

ρ

[ ] 989(898 BDs BDm Ao F Fs Fm s C C C k C C C C −+−+⋅∆+−=

Auring the tests% the following parameters are recorded#

>ropeller thrust T

>ropeller tor;ue

Rate of revolution n

Model speed V

Thrust and tor;ue measured during propulsion and open water tests are expressed non

dimensionally as#

C/ Dn

T K T

⋅⋅=

ρ and ,/ Dn

Q K Q

⋅⋅=

ρ

!n the open water diagram I T and I are presented as functions of the advance coefficient 8D9. Jy

entering the open water diagram with the thrust coefficient 8I T9 measured during the propulsion

test% corresponding DF and I Fvalues are o5tained which are used to estimate wa=e fraction%

relative rotative efficiency% hull efficiency and ;uasipropulsive coefficient.

a=e fraction#

Dn

V

J w "

⋅

−= (

Relative rotative efficiency#Q

Q"

R K

K =η

Hull efficiency#w

t !

−

−=(

(η

uasipropulsive coefficient# R ! " D η η η η ⋅⋅= 8ηF & propeller efficiency in open water9

Thrust deduction fraction#T

F Rt DT

−−= ( 8note# T is total thrust 3 sum of all props.9


4/11

OPEN WATER TESTS

ENCL. >>E@A!B 2

REPORT *'(*//.''.'(

DATE /''2'C('

REF M/27,D

The propeller model is driven 5y a dynamometer at which thrust% tor;ue and rate of revolution arerecorded. The immersion of the propeller shaft is ≥ propeller diameter.

Test procedure#

The rate of revolution is =ept constant and 5y varying the speed% we get the variation of the

advance coefficient 8D9. t each advance coefficient exact rate of revolution% 8n9% propeller thrust%

8T9% and tor;ue% 89% are recorded. The results are presented dimensionless as#

Dn

V

J A

⋅=

% advance coefficient

C/ Dn

T K T

⋅⋅=

ρ % thrust coefficient

,/ Dn

Q K Q

⋅⋅=

ρ % tor;ue coefficient

π η

/⋅

⋅=

Q

T

" K

J K % propeller efficiency in open water


5/11

PERFORMANCE PREDICTION

ENCL. >>E@A!B C

REPORT *'(*//.''.'(

DATE /''2'C('

REF M/27,D

The performance prediction is 5ased on the assumption that the thrust deduction fraction% t% the

wa=e fraction w and the relative rotative efficiency% ηR % are free from scale effects.

"rom the total resistance of the ship% RTs% and the thrust deduction fraction% t% the following relation

is esta5lished#

/ / / /8( 9 8( 9TsT

s s

R K

J nprop t D V w ρ =

× × − × × × − 8nprop is num5er of propellers9

"or each speed% the intersection point of the I T 3 D/ curve given a5ove with the open water

diagram is found. The advance coefficient DK at this point gives the rate of revolution#

K

9(8*'

J

V

D

w RP#

s s⋅

−⋅

=

The corresponding tor;ue coefficient I % and the relative rotative efficiency% ηR % gives the

delivered power#

, 2/8 9 8 9(''' *'

Q

D R

K RP# P k nprop D

π ρ

η = × × × × ×

The calculation is repeated for different speeds giving the speed0power curve for the actual pitch

ratio. n extrapolation of the open water diagram gives speed0power curves for different pitch

ratios. The final pitch ratio and speed0power curve is found 5y interpolation for the actual R>M

and power.

"inally the 5ra=e power and merit coefficient are calculated#

#

D B

P k P

η =98

B

s

AD# P

V C

220/⋅∇

= 8VS in m0sec.9


6/11

LIST OF SYMBOLS

ENCL. >>E@A!B ,

REPORT *'(*//.''.'(

DATE /''2'C('

REF M/27,D

Sym5ol Title Aimensions

AEFTB

c

$$$AM$AB

$J$JA$A$"

∆CF$L$M$>$R $S$T$T$Vd

A

"A"ng

D

I 'I

I TI TAI T>LFL>>LLn

nprop

>

>J>A

>E>S

Expanded blade area

Disc area

Transverse projected area of ship/model above the waterline

Breadth moulded

Chord length

Empirical correlation coefficient determined from trial analyses

Air resistance coefficient

Merit coefficient

Admirality coefficient

Block coefficient

Transom stern resistance coefficient

Drag coefficient

Frictional resistance coefficient

Roughness allowance

Lift coefficient

Midship section coefficient

Prismatic coefficient

Residuary resistance coefficient

Towing force coefficient

Total resistance coefficientAppendage resistance coefficient

Viscous resistance coefficient

Hub diameter

Propeller diameter

Towing force

Froude number

Acceleration due to gravity

Advance coefficient

Form factor

Torque coefficientThrust coefficient

Duct thrust coefficient

Propeller thrust coefficient

Length overall

Length between perpendiculars

Length of waterline

Rate of revolution

Number of propellers

Propeller pitch

Brake power

Delivered power at propeller

Effective power

Shaft power

L/

L/

L/

L

L

L

L

LMT/

-

LT/

-

-

-

--

-

L

L

L

REVS.T-1

-

L

L2MT-3

L2MT-3

L2MT-3

L2MT-3


7/11

7


8/11

LIST OF SYMBOLS

ENCL. >>. , cont.

REPORT *'(*//.''.'(

DATE /''2'C('

REF M/27,D

Sym5ol Title Aimensions

R

R nR TS

SJt

t

T

TTAT>V

Vw

α

ηA

Torque

Propeller radius

Reynolds number

Total resistance

Wetted surface

Area of transom stern below the waterline

Max. thickness of a propeller section

Thrust deduction fraction

Draught moulded

Thrust

Duct thrust

Propeller thrust

Speed of ship or model

Speed of advance of propeller

Wake fraction

Number of blades of a propeller

Angle of attack

Propulsive efficiency or quasi-propulsive coefficient

L2MT-2

L

-

LMT-2

L2

L2

L

-

L

LMT-2

LMT-2

LMT-2

LT-1

LT-1

-

-

-

-

ηH Hull efficiency -

ηM Mechanical efficiency -η' Propeller efficiency in open water -

ηR Relative rotative efficiency -

λ

ν

ρ

∇

∆

Linear scale ratio

Kinematic viscosity

Mass density of water

Displacement volume

Displacement mass

-

L2T-1

ML-3

L3

M


9/11

PRINCIPAL HULL DATA

ENCL.

REPORT 1C*''(./'.'(

DATE /''C'*/(

REF M/27,D

HULL MODEL NO.: M2375J Model Scale: 25.676Loading condition: Design WL

Draught AP/FP: 6.500 / 6.500 !"Setu#: !2$75%0s&0

S'!(ol )nit SHIP MODEL ************************************************************** Length o+erall L,A !" &-0.0& 5.-5$Length on designed aterline LWL !" &$-.600 5.2-2Length (et. #er#. LPP !" &$&.$00 5.&&-readth !oulded !" 22.700 0.11-readth aterline WL !" 22.700 0.11-De#th to &st dec D !" 26.002 &.0&$Draught at LPP/2 3 !" 6.500 0.25$Draught at FP 3FP !" 6.500 0.25$Draught at AP 3AP !" 6.500 0.25$3ri! 4#os. at t !" 0.000 0.000ae o eel !" 0.000 0.000ise o loor !" 0.000 0.000ilge radius !" $.000 0.&&7

************************************************************** Water densit' ρs g/!$" &025.17 1.62Shell #lating thicness !!" 0.00 0Shell #lating in 8 o dis#l. 8" 0.50 0.00

**************************************************************

9olu!e dis#lace!ent ∇ !$" &&0-.$ 0.655Dis#lace!ent ∆ t" &&-$1.2 0.655Pris!atic coeicient ;P


10/11

OPEN WATER TEST

ENCL.

REPORT 1C*''(./'.'(

DATE /'(*'C2'

REF M/27,D

PROPELLER MODEL No.: P1284 Model Scale: 25.676

S'!(ol )nit SHIP MODEL ************************************************************** Pro#eller dia!eter D !!" -500 &75.26Pitch ratio at r/ ? 0.7 P/D0.7


11/11

OPEN WATER DIAGRAM

ENCL.

REPORT 1C*''(./'.'(

DATE /'(*'C2'

REF M/27,D

0.0

0.1

0.2

0.#

0."

0.5

0.&

0.%

0.

0.

1.0

0.0 0.1 0.2 0.# 0." 0.5 0.& 0.% 0. 0. 1.0 1.1 1.2

* + ' 1 0 , * - ' . o

/

PROPELLER MODEL No.: P128

NO SCALING APPLIED

Pi+h r+io 1.220

Se+3p$ p12"s1

3hrust coeicient Gt < data#oints

3orHue coeicient &0EGH < data#oints

,#en Water @icienc' Io < data#oints

ShipX (RepGen version 2.0.1&) Sep 2&' 2005 #$"%$" P

guide for power prediction.doc

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